Einstein quote, emphasis added

[Alan Grayson]

“Then there occurred to me the 'glucklichste Gedanke meines Lebens,' the happiest thought of my life, in the following form. The gravitational field has only a relative existence in a way similar to the electric field generated by magnetoelectric induction. Because for an observer falling freely from the roof of a house there exists-at least in his immediate surroundings-no gravitational field [his italics]. Indeed, if the observer drops some bodies then these remain relative to him in a state of rest or of uniform motion, independent of their particular chemical or physical nature (in this consideration the air resistance is, of course, ignored). The observer therefore has the right to interpret his state as 'at rest.' Because of this idea, the uncommonly peculiar experimental law that in the gravitational field all bodies fall with the same acceleration attained at once a deep physical meaning. Namely, if there were to exist just one single object that falls in the gravitational field in a way different from all others, then with its help the observer could realize that he is ina gravitational field and is falling in it. If such an object does not exist, however-as experience has shown with great accuracy-then the observer lacks any objective means of perceiving himself as falling in a gravitational field. Rather he has the right to consider his state as one of rest and his environment as field-free relative to gravitation. The experimentally known matter independence of the acceleration of fall is therefore a powerful argument for the fact that the relativity postulate has to be extended to coordinate systems which, relative to each other, are in non-uniform motion.”
― Albert Einstein

What does the sentence emphasized by me, mean? TY, AG

[Cosmin Visan]

The "physical world" itself has only a relative existence to the particular consciousness that observes it. If that consciousness is a male, excitation will exist when a female enters the scene. If that consciousness is a female, this will not exist.

[Alan Grayson]

I'm puzzled by the sentence emphasized because the magnetic field comes into existence due to motion of charged particles, but motion in a gravity field seems to erase the field. So the effects of motion seem opposite. AG 

[John Clark]

On Sat, May 24, 2025 at 3:46 AM Alan Grayson <agrays...@gmail.com> wrote:

 Einstein quote: "The gravitational field has only a relative existence in a way similar to the electric field generated by magnetoelectric induction" 

> What does the sentence emphasized by me, mean? TY, AG

Electric fields and magnetic fields are relative, one man's electric field is another man's magnetic field and vice versa. So in General Relativity there is no such thing as an electric field or a magnetic field, although they can often be useful fictions, there is only an electrodynamic field. In the same way a gravitational field is a useful fiction, it's not fundamental, it's relative. An observer in a rocket without a porthole accelerating at 1G will see a gravitational field, but an observer outside would see no such field, he would just see a rocket accelerating in a way that Isaac Newton would understand.  

 John K Clark    See what's on my new list at  Extropolis

4$b 

[Alan Grayson]

On Saturday, May 24, 2025 at 6:28:25 AM UTC-6 John Clark wrote:

On Sat, May 24, 2025 at 3:46 AM Alan Grayson <agrays...@gmail.com> wrote:

 Einstein quote: "The gravitational field has only a relative existence in a way similar to the electric field generated by magnetoelectric induction" 

> What does the sentence emphasized by me, mean? TY, AG

Electric fields and magnetic fields are relative, one man's electric field is another man's magnetic field and vice versa.

If someone is at rest relative to a current carrying wire, the magnetic field will be measurable, but what about the electric field? AG

 

So in General Relativity there is no such thing as an electric field or a magnetic field, although they can often be useful fictions, there is only an electrodynamic field. In the same way a gravitational field is a useful fiction, it's not fundamental, it's relative.

I disagree. The gravitational field produces an acceleration, and thus, IMO, is real. It also causes a test particle which is spatially at rest, to accelerate. This, I think, is because the time coordinate is embedded in the geodesic equations of motion, so as time increases, the particle's position must change spatially. But this seems to imply a universal clock which every particle has, or can measure. AG

 

An observer in a rocket without a porthole accelerating at 1G will see a gravitational field, but an observer outside would see no such field, he would just see a rocket accelerating in a way that Isaac Newton would understand.

The equivalence principle can not exactly simulate a gravitational field, since it produces no forces toward a center of mass. I forget what that's called. AG 

[John Clark]

On Sat, May 24, 2025 at 10:01 PM Alan Grayson <agrays...@gmail.com> wrote:

>> Electric fields and magnetic fields are relative, one man's electric field is another man's magnetic field and vice versa.

> If someone is at rest relative to a current carrying wire, the magnetic field will be measurable, but what about the electric field? AG

If a test particle is at rest with respect to an uncharged current carrying wire then it is not at rest with respect to the electrons flowing in that wire, and that's what causes the magnetic field. If a negative test particle starts moving in the opposite direction that the electrons in the current are then the relative speed between the test particle and the electrons in the wire will increase, and the distance between the moving electrons will decrease due to relativistic length contraction, so the test particle will observe a stronger negative electrical charge from the part of the wire that is closest to it even though the wire is a whole is not electrically charged. So the test particle will be repelled from the wire because both the test particle and the electrons in the wire have a negative electrical charge.

But If the test charge is moving in the same direction as the electrons in the wire then it will be attracted to the wire for exactly the same reason, relativistic length contraction, although in this case the part of the wire that is closest to it will seem to have a positive electrical charge.

So from the point of view of the test particle there is no need to even mention something called a "magnetic field", BUT from the point of view of someone in the same frame of reference as the stationary wire a magnetic field is a very useful fiction.    

 

 

> So in General Relativity there is no such thing as an electric field or a magnetic field, although they can often be useful fictions, there is only an electrodynamic field. In the same way a gravitational field is a useful fiction, it's not fundamental, it's relative.

> I disagree.

Then you're not disagreeing with me, you're disagreeing with Einstein.  Who do you think a rational person should bet their money on, you or Einstein? 

> The gravitational field produces an acceleration, and thus, IMO, is real.

A man in a sealed rocketship without a porthole steps on a scale and notes that he weighs the same as he did when he was standing on the surface of the Earth but, if you ignore tidal effects which you can for something as small as a human, he would have no way of knowing if his rocketship was resting on the surface of a planet similar to Earth or if he was in intergalactic space in a rocketship that was accelerating at 9.8 meters per second squared a million light years from anything more massive than a grain of sand.

> The equivalence principle can not exactly simulate a gravitational field, since it produces no forces toward a center of mass. I forget what that's called. AG 

It's called tidal effects, the smaller the size the smaller are the tidal effects, at zero size (a point) the tidal effects are also zero. Einstein's field equations of General Relativity can tell you exactly what pressures and tensions those tidal effects will produce in an object of a given size and shape if it moves from point X to point Y in curved 4D spacetime (also called a gravitational field). 

  John K Clark    See what's on my new list at  Extropolis

agf

[Alan Grayson]

On Sunday, May 25, 2025 at 6:08:41 AM UTC-6 John Clark wrote:

On Sat, May 24, 2025 at 10:01 PM Alan Grayson <agrays...@gmail.com> wrote:

>> Electric fields and magnetic fields are relative, one man's electric field is another man's magnetic field and vice versa.

> If someone is at rest relative to a current carrying wire, the magnetic field will be measurable, but what about the electric field? AG

If a test particle is at rest with respect to an uncharged current carrying wire then it is not at rest with respect to the electrons flowing in that wire, and that's what causes the magnetic field. If a negative test particle starts moving in the opposite direction that the electrons in the current are then the relative speed between the test particle and the electrons in the wire will increase, and the distance between the moving electrons will decrease due to relativistic length contraction, so the test particle will observe a stronger negative electrical charge from the part of the wire that is closest to it even though the wire is a whole is not electrically charged. So the test particle will be repelled from the wire because both the test particle and the electrons in the wire have a negative electrical charge.

But If the test charge is moving in the same direction as the electrons in the wire then it will be attracted to the wire for exactly the same reason, relativistic length contraction, although in this case the part of the wire that is closest to it will seem to have a positive electrical charge.

So from the point of view of the test particle there is no need to even mention something called a "magnetic field", BUT from the point of view of someone in the same frame of reference as the stationary wire a magnetic field is a very useful fiction.    

 

 

> So in General Relativity there is no such thing as an electric field or a magnetic field, although they can often be useful fictions, there is only an electrodynamic field. In the same way a gravitational field is a useful fiction, it's not fundamental, it's relative.

> I disagree.

Then you're not disagreeing with me, you're disagreeing with Einstein.  Who do you think a rational person should bet their money on, you or Einstein? 

I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation. With sufficiently sensitive measurements, the reality of a gravitational field, or not, can be determined by internal measurements. AG 

[John Clark]

On Sun, May 25, 2025 at 3:33 PM Alan Grayson <agrays...@gmail.com> wrote:

> I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation.

The Equivalence Principle, which is the foundation of General Relativity, states that at sufficiently small scales there is no way to tell the difference between a gravitational field and a simple acceleration. And it is not an approximation. But is it always correct? That is not certain because General Relativity does not take Quantum Mechanics into account, nevertheless so far at least the Equivalence Principle has easily passed every experimental test put to it.

For fun I asked GPT to do "Deep Research" on the following questions: 

"Have there been any proposed experimental tests to see if Einstein's Equivalence Principle remains true even when quantum mechanics is taken into account? In other words tests to determine if gravity can change the quantum entanglement of two particles, and if not are any such tests planned?" 

SPOILER ALERT: GPT's ultimate conclusion was "So far, all completed tests have found no anomalous effect – entangled states remain intact in different gravitational or accelerated frames, consistent with EEP and standard quantum theory"

GPT put those words in boldface type, not me. Below is GPT's full response: 

========

Tests of the Equivalence Principle with Quantum Entanglement

Einstein’s equivalence principle (EEP) – that all objects fall identically in a gravitational field – is classically tested to extreme precision. Extending EEP to quantum systems, especially entangled ones, poses conceptual challenges (the EEP is classically formulated and its quantum generalization “requires careful considerations”ar5iv.org). Recent proposals and experiments therefore ask: Can gravity alter quantum entanglement? Would any change signal a breakdown of EEP? Below we summarize key efforts, completed or proposed, that probe this question using entangled photons or atoms in varying gravitational or inertial conditions.

Space- and Satellite-Based Experiments

• Micius satellite test (Xu et al. 2019) – An experiment by Pan, Ren, Ralph et al. (China/U.S.) sent one photon of a time-energy–entangled pair to orbit aboard the Micius satellite while keeping the other photon on the groundpub.math.leidenuniv.nl. This setup exposed the two photons to different gravitational potentials. The goal was to test predictions of a speculative “event formalism” model that entanglement would probabilistically decohere when particles traverse different gravity gradients. The result (published in Science) was that no abnormal decoherence was seen: the entanglement correlations matched standard quantum theory, not the model’s decohering predictionpub.math.leidenuniv.nl. In other words, despite the large gravitational potential difference, the quantum entanglement survived intact. (Team: Jian-Wei Pan et al., USTC and collaborators; status: completed 2017/19.)

• Space-QUEST mission concept (Joshi et al. 2017) – A European “Quantum Entanglement Space Test” proposal (ESA/Topical Team) led by Ursin, Ralph, Cacciapuoti et al.. This feasibility study outlined sending entangled photon pairs between ground and the International Space Station (ISS)ar5iv.labs.arxiv.org. One photon would be sent upward while its partner remained on Earth, testing theories (e.g. by Ralph and co-workers) that such a setup could induce decoherence of entanglement if each photon samples a different gravitational field gradientar5iv.labs.arxiv.org. The paper presents a detailed mission design (Space-QUEST) and notes that under standard quantum field theory no decoherence is expected, but some exotic models (the same “event operator” models) predict irrecoverable loss of entanglementar5iv.labs.arxiv.org. (Team: international quantum optics collaboration including Austrian Academy of Sciences, University of Vienna, ESA, etc.; status: proposed/concept study.)

Laboratory/Accelerated-Frame Experiments

• Acceleration (free-fall/centrifuge) test (Fink et al. 2017) – In Vienna, Fink, Ursin, Scheidl et al. placed a polarization-entangled photon source and detectors on a platform that was dropped 12 m (microgravity) and separately spun in a centrifuge up to 30 g. They measured an entanglement witness for accelerations spanning 0.03 g (near-free-fall) up to 30 gnature.com. The result (Nature Communications) was that entanglement quality showed no significant loss beyond noise limits at any acceleration testednature.com. In effect, even extreme inertial forces (equivalent to gravitational fields by the EP) did not degrade the photon entanglement. The experiment set an upper bound on any acceleration-induced decoherence of the entangled statenature.com. (Affiliation: Vienna Institute of Quantum Optics (IQOQI) and University of Vienna; status: completed 2017.)

• Rotational (Sagnac interferometer) test (Cromb et al. 2023) – At the University of Glasgow, Cromb, Padgett, Faccio et al. placed a Hong–Ou–Mandel interferometer (entangled photons) on a rotating platform (fiber Sagnac loop). They observed that as rotation rate increased, the two-photon interference pattern flipped from the usual HOM dip to a peakjournals.aps.org. This indicates that noninertial (rotating) motion fundamentally altered the symmetry of the entangled state. While not directly a gravity test, this table-top demonstration (Phys. Rev. Research 2023) shows that entangled photons are sensitive to rotational (relativistic) effects and “paves the way” to test entanglement in curved spacetimejournals.aps.org. (Affiliation: University of Glasgow; status: completed 2023.)

Proposed and Future Tests

• Entangled-atom interferometer (Geiger & Trupke 2018) – A theoretical proposal (Phys. Rev. Lett.) by Geiger (Paris Observatory) and Trupke (Vienna) suggests using two entangled atoms of different species in a differential free-fall interferometer. Each atom (e.g. ^85Rb and ^87Rb) forms its own atom interferometer; the two are prepared in an entangled superposition via a heralded photon detection at the input beam splitterhal.science. The interferometers then measure the differential acceleration of the two species. Crucially, because the atoms start entangled, this probes WEP in a regime where “the two particles involved … are not classically independent, but entangled”hal.science. Their proposed setup (high-finesse cavity, Raman processes) predicts sensitivity to Eötvös parameter η below 10^−7hal.science. (Institutions: LNE-SYRTE/Observatoire de Paris, University of Vienna; status: proposed in PRL 2018.)

• Entanglement-witness protocols (Bose et al. 2023) – Sougato Bose and collaborators (UCL, Groningen, Glasgow) have introduced the idea of a “quantum equivalence principle” test using entanglement. They propose creating massive particles in large spatial superposition and using an entanglement entropy witness to detect any WEP violationar5iv.org. In essence, both matter and the gravitational source are treated as quantum; any difference between inertial and gravitational masses in this fully quantum regime would reveal itself through lack of entanglement. Their 2022/23 paper provides a protocol for such experiments and argues it is “unique” for testing the weak equivalence principle in the quantum domainar5iv.org. (This work is theoretical/preprint (Entropy 2023) but outlines concrete tabletop schemes.)

• SUPREME-QG space mission (Shahriar et al. 2023–25) – A NASA-funded concept (NIAC Phase I, 2025) led by Selim Shahriar (Northwestern U.) envisions a spaceborne WEP test using macroscopic entangled atomic statesnasa.gov. The idea is two simultaneous atom interferometers with ^85Rb and ^87Rb, each using a Schrödinger-cat–like state of N≈10^6 entangled atoms generated by cavity spin-squeezingnasa.gov. Such a many-particle entangled state behaves as one massive superposition, boosting sensitivity by √N∼10^3. The goal is to measure differential free-fall with precision η∼10^−20nasa.gov – orders of magnitude beyond current tests. (The proposal outlines technology development for these giant entangled statesnasa.gov. Status: concept study, NIAC-awarded 2025.)

Each of these efforts is explicitly aimed at the intersection of gravity and entanglement. So far, all completed tests have found no anomalous effect – entangled states remain intact in different gravitational or accelerated frames, consistent with EEP and standard quantum theorypub.math.leidenuniv.nlnature.com. Future and proposed experiments (e.g. entangled atoms in free-fall) aim to push these tests into new regimes; any observed entanglement degradation tied to gravity would signal new physics.

Sources: Peer-reviewed articles and official reports as cited abovepub.math.leidenuniv.nl

 

[Brent Meeker]

Very interesting, John.  Thanks for that.

Brent

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[Alan Grayson]

On Monday, May 26, 2025 at 5:57:36 AM UTC-6 John Clark wrote:

On Sun, May 25, 2025 at 3:33 PM Alan Grayson <agrays...@gmail.com> wrote:

> I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation.

The Equivalence Principle, which is the foundation of General Relativity, states that at sufficiently small scales there is no way to tell the difference between a gravitational field and a simple acceleration. And it is not an approximation. But is it always correct? That is not certain because General Relativity does not take Quantum Mechanics into account, nevertheless so far at least the Equivalence Principle has easily passed every experimental test put to it.

Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. That's pretty obvious regardless of contrary opinions, including Einstein's. AG 

[Alan Grayson]

On Monday, May 26, 2025 at 3:51:29 PM UTC-6 Alan Grayson wrote:

On Monday, May 26, 2025 at 5:57:36 AM UTC-6 John Clark wrote:

On Sun, May 25, 2025 at 3:33 PM Alan Grayson <agrays...@gmail.com> wrote:

> I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation.

The Equivalence Principle, which is the foundation of General Relativity, states that at sufficiently small scales there is no way to tell the difference between a gravitational field and a simple acceleration. And it is not an approximation. But is it always correct? That is not certain because General Relativity does not take Quantum Mechanics into account, nevertheless so far at least the Equivalence Principle has easily passed every experimental test put to it.

Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. That's pretty obvious regardless of contrary opinions, including Einstein's. AG 

BTW, in what way is the EP the foundation of GR? Not at all obvious how Einstein actually use the EP to develop GR. AG 

[John Clark]

On Mon, May 26, 2025 at 5:55 PM Alan Grayson <agrays...@gmail.com> wrote:

> Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. 

What the hell?! Name one physical principle on any subject in which measurement accuracy was NOT an important factor in checking its correctness. 

> That's pretty obvious regardless of contrary opinions, including Einstein's. AG 

I would be willing to bet money that there is no true fact about physics that is obvious to you that was not obvious to Albert Einstein. I could say the same thing about me, but unlike you I'm smart enough to know that I'm not smarter than Einstein.  

 John K Clark    See what's on my new list at  Extropolis

3x1

[Alan Grayson]

On Monday, May 26, 2025 at 4:11:37 PM UTC-6 John Clark wrote:

On Mon, May 26, 2025 at 5:55 PM Alan Grayson <agrays...@gmail.com> wrote:

> Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. 

What the hell?! Name one physical principle on any subject in which measurement accuracy was NOT an important factor in checking its correctness. 

While they're generally idealizations which depend on measurements for verification, the EP fails straight out in most cases, with accurate measurements. The EP depends on poor measurements, unlike the other cases. AG 

> That's pretty obvious regardless of contrary opinions, including Einstein's. AG 

I would be willing to bet money that there is no true fact about physics that is obvious to you that was not obvious to Albert Einstein. I could say the same thing about me, but unlike you I'm smart enough to know that I'm not smarter than Einstein.  

Did you know that Einstein believed in the aether -- but what aether was he a believer in? And he didn't believe in QM, and surely not Everett's interpretation, so you must be smarter than him. Moreover, and most important IMO, according to you and the AI, the EP was crucial in the development of GR, but neither have a clue, how. Too funny. AG

[Brent Meeker]

On 5/26/2025 2:51 PM, Alan Grayson wrote:

On Monday, May 26, 2025 at 5:57:36 AM UTC-6 John Clark wrote:

On Sun, May 25, 2025 at 3:33 PM Alan Grayson <agrays...@gmail.com> wrote:

> I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation.

The Equivalence Principle, which is the foundation of General Relativity, states that at sufficiently small scales there is no way to tell the difference between a gravitational field and a simple acceleration. And it is not an approximation. But is it always correct? That is not certain because General Relativity does not take Quantum Mechanics into account, nevertheless so far at least the Equivalence Principle has easily passed every experimental test put to it.

Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. That's pretty obvious regardless of contrary opinions, including Einstein's. AG

It was just an inspiring idea that Einstein had.  It didn't need to have three digit accuracy.

Brent

For fun I asked GPT to do "Deep Research" on the following questions: 

"Have there been any proposed experimental tests to see if Einstein's Equivalence Principle remains true even when quantum mechanics is taken into account? In other words tests to determine if gravity can change the quantum entanglement of two particles, and if not are any such tests planned?" 

SPOILER ALERT: GPT's ultimate conclusion was "So far, all completed tests have found no anomalous effect – entangled states remain intact in different gravitational or accelerated frames, consistent with EEP and standard quantum theory"

GPT put those words in boldface type, not me. Below is GPT's full response: 

========

Tests of the Equivalence Principle with Quantum Entanglement

Einstein’s equivalence principle (EEP) – that all objects fall identically in a gravitational field – is classically tested to extreme precision. Extending EEP to quantum systems, especially entangled ones, poses conceptual challenges (the EEP is classically formulated and its quantum generalization “requires careful considerations”ar5iv.org). Recent proposals and experiments therefore ask: Can gravity alter quantum entanglement? Would any change signal a breakdown of EEP? Below we summarize key efforts, completed or proposed, that probe this question using entangled photons or atoms in varying gravitational or inertial conditions.

Space- and Satellite-Based Experiments

• Micius satellite test (Xu et al. 2019) – An experiment by Pan, Ren, Ralph et al. (China/U.S.) sent one photon of a time-energy–entangled pair to orbit aboard the Micius satellite while keeping the other photon on the groundpub.math.leidenuniv.nl. This setup exposed the two photons to different gravitational potentials. The goal was to test predictions of a speculative “event formalism” model that entanglement would probabilistically decohere when particles traverse different gravity gradients. The result (published in Science) was that no abnormal decoherence was seen: the entanglement correlations matched standard quantum theory, not the model’s decohering predictionpub.math.leidenuniv.nl. In other words, despite the large gravitational potential difference, the quantum entanglement survived intact. (Team: Jian-Wei Pan et al., USTC and collaborators; status: completed 2017/19.)

• Space-QUEST mission concept (Joshi et al. 2017) – A European “Quantum Entanglement Space Test” proposal (ESA/Topical Team) led by Ursin, Ralph, Cacciapuoti et al.. This feasibility study outlined sending entangled photon pairs between ground and the International Space Station (ISS)ar5iv.labs.arxiv.org. One photon would be sent upward while its partner remained on Earth, testing theories (e.g. by Ralph and co-workers) that such a setup could induce decoherence of entanglement if each photon samples a different gravitational field gradientar5iv.labs.arxiv.org. The paper presents a detailed mission design (Space-QUEST) and notes that under standard quantum field theory no decoherence is expected, but some exotic models (the same “event operator” models) predict irrecoverable loss of entanglementar5iv.labs.arxiv.org. (Team: international quantum optics collaboration including Austrian Academy of Sciences, University of Vienna, ESA, etc.; status: proposed/concept study.)

Laboratory/Accelerated-Frame Experiments

• Acceleration (free-fall/centrifuge) test (Fink et al. 2017) – In Vienna, Fink, Ursin, Scheidl et al. placed a polarization-entangled photon source and detectors on a platform that was dropped 12 m (microgravity) and separately spun in a centrifuge up to 30 g. They measured an entanglement witness for accelerations spanning 0.03 g (near-free-fall) up to 30 gnature.com. The result (Nature Communications) was that entanglement quality showed no significant loss beyond noise limits at any acceleration testednature.com. In effect, even extreme inertial forces (equivalent to gravitational fields by the EP) did not degrade the photon entanglement. The experiment set an upper bound on any acceleration-induced decoherence of the entangled statenature.com. (Affiliation: Vienna Institute of Quantum Optics (IQOQI) and University of Vienna; status: completed 2017.)

• Rotational (Sagnac interferometer) test (Cromb et al. 2023) – At the University of Glasgow, Cromb, Padgett, Faccio et al. placed a Hong–Ou–Mandel interferometer (entangled photons) on a rotating platform (fiber Sagnac loop). They observed that as rotation rate increased, the two-photon interference pattern flipped from the usual HOM dip to a peakjournals.aps.org. This indicates that noninertial (rotating) motion fundamentally altered the symmetry of the entangled state. While not directly a gravity test, this table-top demonstration (Phys. Rev. Research 2023) shows that entangled photons are sensitive to rotational (relativistic) effects and “paves the way” to test entanglement in curved spacetimejournals.aps.org. (Affiliation: University of Glasgow; status: completed 2023.)

Proposed and Future Tests

• Entangled-atom interferometer (Geiger & Trupke 2018) – A theoretical proposal (Phys. Rev. Lett.) by Geiger (Paris Observatory) and Trupke (Vienna) suggests using two entangled atoms of different species in a differential free-fall interferometer. Each atom (e.g. ^85Rb and ^87Rb) forms its own atom interferometer; the two are prepared in an entangled superposition via a heralded photon detection at the input beam splitterhal.science. The interferometers then measure the differential acceleration of the two species. Crucially, because the atoms start entangled, this probes WEP in a regime where “the two particles involved … are not classically independent, but entangled”hal.science. Their proposed setup (high-finesse cavity, Raman processes) predicts sensitivity to Eötvös parameter η below 10^−7hal.science. (Institutions: LNE-SYRTE/Observatoire de Paris, University of Vienna; status: proposed in PRL 2018.)

• Entanglement-witness protocols (Bose et al. 2023) – Sougato Bose and collaborators (UCL, Groningen, Glasgow) have introduced the idea of a “quantum equivalence principle” test using entanglement. They propose creating massive particles in large spatial superposition and using an entanglement entropy witness to detect any WEP violationar5iv.org. In essence, both matter and the gravitational source are treated as quantum; any difference between inertial and gravitational masses in this fully quantum regime would reveal itself through lack of entanglement. Their 2022/23 paper provides a protocol for such experiments and argues it is “unique” for testing the weak equivalence principle in the quantum domainar5iv.org. (This work is theoretical/preprint (Entropy 2023) but outlines concrete tabletop schemes.)

• SUPREME-QG space mission (Shahriar et al. 2023–25) – A NASA-funded concept (NIAC Phase I, 2025) led by Selim Shahriar (Northwestern U.) envisions a spaceborne WEP test using macroscopic entangled atomic statesnasa.gov. The idea is two simultaneous atom interferometers with ^85Rb and ^87Rb, each using a Schrödinger-cat–like state of N≈10^6 entangled atoms generated by cavity spin-squeezingnasa.gov. Such a many-particle entangled state behaves as one massive superposition, boosting sensitivity by √N∼10^3. The goal is to measure differential free-fall with precision η∼10^−20nasa.gov – orders of magnitude beyond current tests. (The proposal outlines technology development for these giant entangled statesnasa.gov. Status: concept study, NIAC-awarded 2025.)

Each of these efforts is explicitly aimed at the intersection of gravity and entanglement. So far, all completed tests have found no anomalous effect – entangled states remain intact in different gravitational or accelerated frames, consistent with EEP and standard quantum theorypub.math.leidenuniv.nlnature.com. Future and proposed experiments (e.g. entangled atoms in free-fall) aim to push these tests into new regimes; any observed entanglement degradation tied to gravity would signal new physics.

Sources: Peer-reviewed articles and official reports as cited abovepub.math.leidenuniv.nl

 

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[Brent Meeker]

On 5/26/2025 2:55 PM, Alan Grayson wrote:

On Monday, May 26, 2025 at 3:51:29 PM UTC-6 Alan Grayson wrote:

On Monday, May 26, 2025 at 5:57:36 AM UTC-6 John Clark wrote:

On Sun, May 25, 2025 at 3:33 PM Alan Grayson <agrays...@gmail.com> wrote:

> I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation.

The Equivalence Principle, which is the foundation of General Relativity, states that at sufficiently small scales there is no way to tell the difference between a gravitational field and a simple acceleration. And it is not an approximation. But is it always correct? That is not certain because General Relativity does not take Quantum Mechanics into account, nevertheless so far at least the Equivalence Principle has easily passed every experimental test put to it.

Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. That's pretty obvious regardless of contrary opinions, including Einstein's. AG 

BTW, in what way is the EP the foundation of GR? Not at all obvious how Einstein actually use the EP to develop GR. AG

Not a "foundation" just a suggestion that acceleration due to a gravitational field could be modeled as force-free, geodesic motion in a curved spacetime.

Brent

For fun I asked GPT to do "Deep Research" on the following questions: 

"Have there been any proposed experimental tests to see if Einstein's Equivalence Principle remains true even when quantum mechanics is taken into account? In other words tests to determine if gravity can change the quantum entanglement of two particles, and if not are any such tests planned?" 

SPOILER ALERT: GPT's ultimate conclusion was "So far, all completed tests have found no anomalous effect – entangled states remain intact in different gravitational or accelerated frames, consistent with EEP and standard quantum theory"

GPT put those words in boldface type, not me. Below is GPT's full response: 

========

Tests of the Equivalence Principle with Quantum Entanglement

Einstein’s equivalence principle (EEP) – that all objects fall identically in a gravitational field – is classically tested to extreme precision. Extending EEP to quantum systems, especially entangled ones, poses conceptual challenges (the EEP is classically formulated and its quantum generalization “requires careful considerations”ar5iv.org). Recent proposals and experiments therefore ask: Can gravity alter quantum entanglement? Would any change signal a breakdown of EEP? Below we summarize key efforts, completed or proposed, that probe this question using entangled photons or atoms in varying gravitational or inertial conditions.

Space- and Satellite-Based Experiments

• Micius satellite test (Xu et al. 2019) – An experiment by Pan, Ren, Ralph et al. (China/U.S.) sent one photon of a time-energy–entangled pair to orbit aboard the Micius satellite while keeping the other photon on the groundpub.math.leidenuniv.nl. This setup exposed the two photons to different gravitational potentials. The goal was to test predictions of a speculative “event formalism” model that entanglement would probabilistically decohere when particles traverse different gravity gradients. The result (published in Science) was that no abnormal decoherence was seen: the entanglement correlations matched standard quantum theory, not the model’s decohering predictionpub.math.leidenuniv.nl. In other words, despite the large gravitational potential difference, the quantum entanglement survived intact. (Team: Jian-Wei Pan et al., USTC and collaborators; status: completed 2017/19.)

• Space-QUEST mission concept (Joshi et al. 2017) – A European “Quantum Entanglement Space Test” proposal (ESA/Topical Team) led by Ursin, Ralph, Cacciapuoti et al.. This feasibility study outlined sending entangled photon pairs between ground and the International Space Station (ISS)ar5iv.labs.arxiv.org. One photon would be sent upward while its partner remained on Earth, testing theories (e.g. by Ralph and co-workers) that such a setup could induce decoherence of entanglement if each photon samples a different gravitational field gradientar5iv.labs.arxiv.org. The paper presents a detailed mission design (Space-QUEST) and notes that under standard quantum field theory no decoherence is expected, but some exotic models (the same “event operator” models) predict irrecoverable loss of entanglementar5iv.labs.arxiv.org. (Team: international quantum optics collaboration including Austrian Academy of Sciences, University of Vienna, ESA, etc.; status: proposed/concept study.)

Laboratory/Accelerated-Frame Experiments

• Acceleration (free-fall/centrifuge) test (Fink et al. 2017) – In Vienna, Fink, Ursin, Scheidl et al. placed a polarization-entangled photon source and detectors on a platform that was dropped 12 m (microgravity) and separately spun in a centrifuge up to 30 g. They measured an entanglement witness for accelerations spanning 0.03 g (near-free-fall) up to 30 gnature.com. The result (Nature Communications) was that entanglement quality showed no significant loss beyond noise limits at any acceleration testednature.com. In effect, even extreme inertial forces (equivalent to gravitational fields by the EP) did not degrade the photon entanglement. The experiment set an upper bound on any acceleration-induced decoherence of the entangled statenature.com. (Affiliation: Vienna Institute of Quantum Optics (IQOQI) and University of Vienna; status: completed 2017.)

• Rotational (Sagnac interferometer) test (Cromb et al. 2023) – At the University of Glasgow, Cromb, Padgett, Faccio et al. placed a Hong–Ou–Mandel interferometer (entangled photons) on a rotating platform (fiber Sagnac loop). They observed that as rotation rate increased, the two-photon interference pattern flipped from the usual HOM dip to a peakjournals.aps.org. This indicates that noninertial (rotating) motion fundamentally altered the symmetry of the entangled state. While not directly a gravity test, this table-top demonstration (Phys. Rev. Research 2023) shows that entangled photons are sensitive to rotational (relativistic) effects and “paves the way” to test entanglement in curved spacetimejournals.aps.org. (Affiliation: University of Glasgow; status: completed 2023.)

Proposed and Future Tests

• Entangled-atom interferometer (Geiger & Trupke 2018) – A theoretical proposal (Phys. Rev. Lett.) by Geiger (Paris Observatory) and Trupke (Vienna) suggests using two entangled atoms of different species in a differential free-fall interferometer. Each atom (e.g. ^85Rb and ^87Rb) forms its own atom interferometer; the two are prepared in an entangled superposition via a heralded photon detection at the input beam splitterhal.science. The interferometers then measure the differential acceleration of the two species. Crucially, because the atoms start entangled, this probes WEP in a regime where “the two particles involved … are not classically independent, but entangled”hal.science. Their proposed setup (high-finesse cavity, Raman processes) predicts sensitivity to Eötvös parameter η below 10^−7hal.science. (Institutions: LNE-SYRTE/Observatoire de Paris, University of Vienna; status: proposed in PRL 2018.)

• Entanglement-witness protocols (Bose et al. 2023) – Sougato Bose and collaborators (UCL, Groningen, Glasgow) have introduced the idea of a “quantum equivalence principle” test using entanglement. They propose creating massive particles in large spatial superposition and using an entanglement entropy witness to detect any WEP violationar5iv.org. In essence, both matter and the gravitational source are treated as quantum; any difference between inertial and gravitational masses in this fully quantum regime would reveal itself through lack of entanglement. Their 2022/23 paper provides a protocol for such experiments and argues it is “unique” for testing the weak equivalence principle in the quantum domainar5iv.org. (This work is theoretical/preprint (Entropy 2023) but outlines concrete tabletop schemes.)

• SUPREME-QG space mission (Shahriar et al. 2023–25) – A NASA-funded concept (NIAC Phase I, 2025) led by Selim Shahriar (Northwestern U.) envisions a spaceborne WEP test using macroscopic entangled atomic statesnasa.gov. The idea is two simultaneous atom interferometers with ^85Rb and ^87Rb, each using a Schrödinger-cat–like state of N≈10^6 entangled atoms generated by cavity spin-squeezingnasa.gov. Such a many-particle entangled state behaves as one massive superposition, boosting sensitivity by √N∼10^3. The goal is to measure differential free-fall with precision η∼10^−20nasa.gov – orders of magnitude beyond current tests. (The proposal outlines technology development for these giant entangled statesnasa.gov. Status: concept study, NIAC-awarded 2025.)

Each of these efforts is explicitly aimed at the intersection of gravity and entanglement. So far, all completed tests have found no anomalous effect – entangled states remain intact in different gravitational or accelerated frames, consistent with EEP and standard quantum theorypub.math.leidenuniv.nlnature.com. Future and proposed experiments (e.g. entangled atoms in free-fall) aim to push these tests into new regimes; any observed entanglement degradation tied to gravity would signal new physics.

Sources: Peer-reviewed articles and official reports as cited abovepub.math.leidenuniv.nl

 

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[Alan Grayson]

On Monday, May 26, 2025 at 7:44:59 PM UTC-6 Brent Meeker wrote:

On 5/26/2025 2:51 PM, Alan Grayson wrote:

On Monday, May 26, 2025 at 5:57:36 AM UTC-6 John Clark wrote:

On Sun, May 25, 2025 at 3:33 PM Alan Grayson <agrays...@gmail.com> wrote:

> I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation.

The Equivalence Principle, which is the foundation of General Relativity, states that at sufficiently small scales there is no way to tell the difference between a gravitational field and a simple acceleration. And it is not an approximation. But is it always correct? That is not certain because General Relativity does not take Quantum Mechanics into account, nevertheless so far at least the Equivalence Principle has easily passed every experimental test put to it.

Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. That's pretty obvious regardless of contrary opinions, including Einstein's. AG

It was just an inspiring idea that Einstein had.  It didn't need to have three digit accuracy.

Brent

Sure, but inspiring how, in what way? No one seems able to put some beef on this. AG 

[Brent Meeker]

On 5/26/2025 9:29 PM, Alan Grayson wrote:

On Monday, May 26, 2025 at 7:44:59 PM UTC-6 Brent Meeker wrote:

On 5/26/2025 2:51 PM, Alan Grayson wrote:

On Monday, May 26, 2025 at 5:57:36 AM UTC-6 John Clark wrote:

On Sun, May 25, 2025 at 3:33 PM Alan Grayson <agrays...@gmail.com> wrote:

> I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation.

The Equivalence Principle, which is the foundation of General Relativity, states that at sufficiently small scales there is no way to tell the difference between a gravitational field and a simple acceleration. And it is not an approximation. But is it always correct? That is not certain because General Relativity does not take Quantum Mechanics into account, nevertheless so far at least the Equivalence Principle has easily passed every experimental test put to it.

Since the EP depends on measurement accuracy, it's mischaracterized as some absolute principle. That's pretty obvious regardless of contrary opinions, including Einstein's. AG

It was just an inspiring idea that Einstein had.  It didn't need to have three digit accuracy.

Brent

Sure, but inspiring how, in what way? No one seems able to put some beef on this. AG

He saw that gravity didn't need to be treated as a force, it could be treated as force-free motion in non-flat spacetime.  This explained why all objects, whatever the material, fall with the same acceleration, something already determined experimentally by Baron von Etvos.  It's sometimes referred to as inertial mass = gravitational mass.

Brent

[Alan Grayson]

Interesting, TY, but does GR explain the acceleration? AG 

[John Clark]

On Mon, May 26, 2025 at 8:46 PM Alan Grayson <agrays...@gmail.com> wrote:

>> Name one physical principle on any subject in which measurement accuracy was NOT an important factor in checking its correctness. 

> While they're generally idealizations which depend on measurements for verification, the EP fails straight out in most cases, with accurate measurements. The EP depends on poor measurements, unlike the other cases. AG 

I am unable to make any sense whatsoever out of the above word salad. 

>>> That's pretty obvious regardless of contrary opinions, including Einstein's. AG 

>> I would be willing to bet money that there is no true fact about physics that is obvious to you that was not obvious to Albert Einstein. I could say the same thing about me, but unlike you I'm smart enough to know that I'm not smarter than Einstein.  

> Did you know that Einstein believed in the aether

Einstein is the one who killed the idea of the aether in 1905 with his paper on Special Relativity. And if you'd been around in 1879 when Einstein was born would you have said it's "pretty obvious" the aether didn't exist? I don't think so.

Incidentally 1905 was a very good year for Einstein, in that year he published another paper on the Photoelectric Effect which was what earned him the Nobel Prize. And still in 1905 Einstein wrote a paper that gave the theoretical explanation for Brownian Motion and for the first time allowed someone to calculate the size of atoms, and that finally convinced the last holdouts that atoms were real. 

And in 1917 Einstein used Quantum Mechanics to discover "Stimulated Emission", the fundamental principle that allows the LASER to work, in fact the word is an acronym that stands for Light Amplification by Stimulated Emission of Radiation. Even if Einstein had not said one word about Special or General Relativity he would've still been considered one of the greatest physicists of the 20th century, as it is the only one who made a comparable contribution to physics would be Isaac Newton. They are in a class by themselves. 

 

 > he didn't believe in QM,

Bullshit. Einstein was one of the principal pioneers of Quantum Mechanics, in fact that's what he got his Nobel prize in 1921 for, it was NOT for Relativity. Einstein believed that Quantum Mechanics was true but incomplete, and it may turn out he was right about that, he also thought the Copenhagen interpretation was gibberish, and he was certainly right about that.   

 

> and surely not Everett's interpretation,

True, Einstein didn't believe in the Everett interpretation, but he didn't disbelieve in the Everett interpretation either. That's because Everett didn't come up with his interpretation until 1957. Einstein died in 1955. 

 > according to you and the AI, the EP was crucial in the development of GR,

According to Einstein too, he said he came up with the Equivalence Principle in 1907 and it was the "happiest thought" of his life, although it took him another 8 years of  grueling work to state that simple idea in the language of non-Euclidean 4D tensor calculus.  He worked so hard on it he lost 50 pounds and nearly died.  

 John K Clark    See what's on my new list at  Extropolis

d4c

[Alan Grayson]

On Tuesday, May 27, 2025 at 5:53:18 AM UTC-6 John Clark wrote:

On Mon, May 26, 2025 at 8:46 PM Alan Grayson <agrays...@gmail.com> wrote:

>> Name one physical principle on any subject in which measurement accuracy was NOT an important factor in checking its correctness. 

> While they're generally idealizations which depend on measurements for verification, the EP fails straight out in most cases, with accurate measurements. The EP depends on poor measurements, unlike the other cases. AG 

I am unable to make any sense whatsoever out of the above word salad. 

The meaning is obvious. One requires poor measurements to affirm the EP, whereas, say for other laws, the better the measurements, the more sure we are of those laws. AG 

>>> That's pretty obvious regardless of contrary opinions, including Einstein's. AG 

>> I would be willing to bet money that there is no true fact about physics that is obvious to you that was not obvious to Albert Einstein. I could say the same thing about me, but unlike you I'm smart enough to know that I'm not smarter than Einstein.  

> Did you know that Einstein believed in the aether

Einstein is the one who killed the idea of the aether in 1905 with his paper on Special Relativity. And if you'd been around in 1879 when Einstein was born would you have said it's "pretty obvious" the aether didn't exist? I don't think so. 

Later in his career, Einstein embraced an aether of some type. Look it up and you'll affirm it. AG 

Incidentally 1905 was a very good year for Einstein, in that year he published another paper on the Photoelectric Effect which was what earned him the Nobel Prize. And still in 1905 Einstein wrote a paper that gave the theoretical explanation for Brownian Motion and for the first time allowed someone to calculate the size of atoms, and that finally convinced the last holdouts that atoms were real. 

And in 1917 Einstein used Quantum Mechanics to discover "Stimulated Emission", the fundamental principle that allows the LASER to work, in fact the word is an acronym that stands for Light Amplification by Stimulated Emission of Radiation. Even if Einstein had not said one word about Special or General Relativity he would've still been considered one of the greatest physicists of the 20th century, as it is the only one who made a comparable contribution to physics would be Isaac Newton. They are in a class by themselves. 

 

 > he didn't believe in QM,

Bullshit. Einstein was one of the principal pioneers of Quantum Mechanics, in fact that's what he got his Nobel prize in 1921 for, it was NOT for Relativity. Einstein believed that Quantum Mechanics was true but incomplete, and it may turn out he was right about that, he also thought the Copenhagen interpretation was gibberish, and he was certainly right about that.   

 

> and surely not Everett's interpretation,

True, Einstein didn't believe in the Everett interpretation, but he didn't disbelieve in the Everett interpretation either. That's because Everett didn't come up with his interpretation until 1957. Einstein died in 1955. 

I am aware of those dates, but I seriously doubt Einstein would have accepted Everett's interpretation if he denied the final form of QM, and its general philosophy of indeterminism. AG

[John Clark]

On Tue, May 27, 2025 at 9:22 AM Alan Grayson <agrays...@gmail.com> wrote:

>>> While they're generally idealizations which depend on measurements for verification, the EP fails straight out in most cases, with accurate measurements. The EP depends on poor measurements, unlike the other cases. AG 

>> I am unable to make any sense whatsoever out of the above word salad. 

> The meaning is obvious. One requires poor measurements to affirm the EP, whereas, say for other laws, the better the measurements, the more sure we are of those laws. AG 

I am unable to make any sense whatsoever out of the above word salad. 

 

 >> Einstein didn't believe in the Everett interpretation, but he didn't disbelieve in the Everett interpretation either. That's because Everett didn't come up with his interpretation until 1957. Einstein died in 1955. 

> I am aware of those dates, but I seriously doubt Einstein would have accepted Everett's interpretation

Your "serious doubt" means absolutely nothing. We will never know what Einstein would've thought of Everett's interpretation, or of Bell's inequality which Bell didn't discover until 1964. 

 

> if he denied the final form of QM, and its general philosophy of indeterminism. AG

Then that's reason to believe Einstein might have liked Everett's interpretation because it is deterministic, as deterministic a Schrodinger's equation is. But as I say we will never know for sure. 

 

  John K Clark    See what's on my new list at  Extropolis

eec

[Brent Meeker]

I just wrote, "This explained why all objects, whatever the material, fall with the same acceleration,.."

Brent

[Alan Grayson]

Change in position must occur because (I conjecture) geodesic motion depends on time, which is always incrementing. Doesn't this imply that every test particle has its own clock, or there's a universal clock which every particle can read? And why does acceleration exist; because the velocity vector changes direction due to the curvature of spacetime? TY, AG 

[Brent Meeker]

Right

or there's a universal clock which every particle can read?

One uses a t coordinate which is just to label events, as do x, y, and z  But it's not necessarily anyone's time.

And why does acceleration exist; because the velocity vector changes direction due to the curvature of spacetime? TY, AG

Following a geodesic, force-free motion, is not acceleration in general relativity.  It is an extremal path, one of maximum proper time.  The four-velocity changes both direction and magnitude, due the curvature of spacetime.

Brent

[Alan Grayson]

If t isn't a clock reading, then why would anything move? AG 

[John Clark]

On Tue, May 27, 2025 at 6:21 PM Alan Grayson <agrays...@gmail.com> wrote:

> If t isn't a clock reading, then why would anything move? AG 

What physicists call "Proper Time" is a specific clock reading, it's what you see when you look at your wristwatch.  And if no force has been applied to enhance your motion then the path you are following through 4D spacetime is a geodesic. And the amount of time it took you to travel through space from point A to point B, as determined by your wristwatch, will be longer than the proper time of anybody else, as determined by their wristwatch, who HAS had an external force applied to them and thus are not on a geodesic path through 4D spacetime.

 John K Clark    See what's on my new list at  Extropolis

ge,

[Alan Grayson]

So, if a test particle is spatially at rest, which presumably is non-geodesic motion in spacetime, what causes it to move spatially when the force holding it spatially at rest, is released? AG 

[John Clark]

On Wed, May 28, 2025 at 6:25 AM Alan Grayson <agrays...@gmail.com> wrote:

>>What physicists call "Proper Time" is a specific clock reading, it's what you see when you look at your wristwatch.  And if no force has been applied to enhance your motion then the path you are following through 4D spacetime is a geodesic. And the amount of time it took you to travel through space from point A to point B, as determined by your wristwatch, will be longer than the proper time of anybody else, as determined by their wristwatch, who HAS had an external force applied to them and thus are not on a geodesic path through 4D spacetime.

> So, if a test particle is spatially at rest, which presumably is non-geodesic motion in spacetime, what causes it to move spatially when the force holding it spatially at rest, is released? AG 

If you're holding an apple above the ground then that apple is on a non-geodesic path because you must apply a force to prevent it from hitting the ground. From the viewpoint of General Relativity and the equivalence principle you're accelerating the apple upward at about 10 m/s^2, but curved 4D spacetime "wants" the apple to fall downward at the same rate, so the spatial distance between the apple and the ground remains the same. But when you drop the apple the force drops to zero and the apple is then able to follow a geodesic path which leads to the ground.

 John K Clark    See what's on my new list at  Extropolis

w8!

 

--

[Alan Grayson]

Why does it "want" to fall when you cease applying the upward force? AG 

[John Clark]

On Wed, May 28, 2025 at 3:45 PM Alan Grayson <agrays...@gmail.com> wrote:

> Why does it "want" to fall when you cease applying the upward force?

Because if no force is applied the apple wants to take the shortest path possible through 4D space-time; or to put another way, it wants to take the longest possible proper time to get from your hand to the ground.  Remember that unlike the formula for calculating the distance in space, the formula for calculating the spacetime distance between two events contains a minus sign, that's why space is different from time.  

John K Clark    See what's on my new list at  Extropolis

ok@

[Alan Grayson]

On Wednesday, May 28, 2025 at 1:56:51 PM UTC-6 John Clark wrote:

On Wed, May 28, 2025 at 3:45 PM Alan Grayson <agrays...@gmail.com> wrote:

> Why does it "want" to fall when you cease applying the upward force?

Because if no force is applied the apple wants to take the shortest path possible through 4D space-time; or to put another way, it wants to take the longest possible proper time to get from your hand to the ground.  Remember that unlike the formula for calculating the distance in space, the formula for calculating the spacetime distance between two events contains a minus sign, that's why space is different from time.  

But before it starts to move, how does it know which path satisfies the requirement you allege? AG 

[Alan Grayson]

On Wednesday, May 28, 2025 at 2:26:25 PM UTC-6 Alan Grayson wrote:

On Wednesday, May 28, 2025 at 1:56:51 PM UTC-6 John Clark wrote:

On Wed, May 28, 2025 at 3:45 PM Alan Grayson <agrays...@gmail.com> wrote:

> Why does it "want" to fall when you cease applying the upward force?

Because if no force is applied the apple wants to take the shortest path possible through 4D space-time; or to put another way, it wants to take the longest possible proper time to get from your hand to the ground.  Remember that unlike the formula for calculating the distance in space, the formula for calculating the spacetime distance between two events contains a minus sign, that's why space is different from time.  

But before it starts to move, how does it know which path satisfies the requirement you allege? AG 

I don't think it knows or wants anything. And I don't think GR can answer my question. It must be a postulate of GR, that geodesic paths maximize proper time and consequently this is the path a test particle will take in free fall. In other words, we don't actually KNOW why it takes the path it does. AG 

[Brent Meeker]

"Spatially at rest"??  It's called Relativity Theory for a reason.  Everything's at rest in it's own frame.  Force-free motion is geodesic motion.  So when all force goes away the particle follows a geodesic.

Brent

[Alan Grayson]

When sitting on your butt, you're spatially at rest! That force=free motion is geodesic, must be a posulate of GR, not something a particle wants to do, or knows the path to do. AG 

[Brent Meeker]

On 5/28/2025 2:09 PM, Alan Grayson wrote:

On Wednesday, May 28, 2025 at 2:26:25 PM UTC-6 Alan Grayson wrote:

On Wednesday, May 28, 2025 at 1:56:51 PM UTC-6 John Clark wrote:

On Wed, May 28, 2025 at 3:45 PM Alan Grayson <agrays...@gmail.com> wrote:

> Why does it "want" to fall when you cease applying the upward force?

Because if no force is applied the apple wants to take the shortest path possible through 4D space-time; or to put another way, it wants to take the longest possible proper time to get from your hand to the ground.  Remember that unlike the formula for calculating the distance in space, the formula for calculating the spacetime distance between two events contains a minus sign, that's why space is different from time.  

But before it starts to move, how does it know which path satisfies the requirement you allege? AG 

I don't think it knows or wants anything. And I don't think GR can answer my question. It must be a postulate of GR, that geodesic paths maximize proper time and consequently this is the path a test particle will take in free fall. In other words, we don't actually KNOW why it takes the path it does. AG

It's just a definition of "geodesic" that geodesic paths maximize proper time.  Did you KNOW why massive bodies attracted one another in Newtonian physics?  Do you know why like charges repel and opposite charges attract, instead of the other way around?  If I told you it was God's will that test particles fall along geodesics would you then KNOW why? There are never answers to "why" questions at a fundamental level...otherwise they wouldn't be fundamental.

Brent

[Alan Grayson]

On Wednesday, May 28, 2025 at 5:02:16 PM UTC-6 Brent Meeker wrote:

On 5/28/2025 2:09 PM, Alan Grayson wrote:

On Wednesday, May 28, 2025 at 2:26:25 PM UTC-6 Alan Grayson wrote:

On Wednesday, May 28, 2025 at 1:56:51 PM UTC-6 John Clark wrote:

On Wed, May 28, 2025 at 3:45 PM Alan Grayson <agrays...@gmail.com> wrote:

> Why does it "want" to fall when you cease applying the upward force?

Because if no force is applied the apple wants to take the shortest path possible through 4D space-time; or to put another way, it wants to take the longest possible proper time to get from your hand to the ground.  Remember that unlike the formula for calculating the distance in space, the formula for calculating the spacetime distance between two events contains a minus sign, that's why space is different from time.  

But before it starts to move, how does it know which path satisfies the requirement you allege? AG 

I don't think it knows or wants anything. And I don't think GR can answer my question. It must be a postulate of GR, that geodesic paths maximize proper time and consequently this is the path a test particle will take in free fall. In other words, we don't actually KNOW why it takes the path it does. AG

It's just a definition of "geodesic" that geodesic paths maximize proper time.

No, it's not just a defintion. You can calculate proper time along different paths, and find a path which maximizes proper time. But why a particle takes that path, AFAICT, is unknown. It must be a postulate of GR. I was hoping for more. AG

 

  Did you KNOW why massive bodies attracted one another in Newtonian physics?  Do you know why like charges repel and opposite charges attract, instead of the other way around?  If I told you it was God's will that test particles fall along geodesics would you then KNOW why? There are never answers to "why" questions at a fundamental level...otherwise they wouldn't be fundamental.

The "why" questions change as we go down the rabbit hole. Some get answered. Asking such questions motivates deeper theories. It's just that I had higher hopes for GR. AG 

Brent

[Alan Grayson]

Another problem is this; starting from some point in spacetime, we can find the geodesic path to some other point in spacetime. But since the particle doesn't know beforehand, the endpoint of its path, how is the motion determined? AG 

Brent

[Brent Meeker]

Then you have to specify the starting point AND an initial velocity...just like in Newtonian mechanics, which can also be written as an extremal principle.

Brent

[Alan Grayson]

OK. But still, the fact that it takes a path which maximizes proper time, must be a postulate. And how does wrist watch time relate to the path taken? Do test particles carry clocks? AG 

[Brent Meeker]

Go study some classical mechanics.  Do you think particles carry least-action watches?

Brent

[John Clark]

On Wed, May 28, 2025 at 4:26 PM Alan Grayson <agrays...@gmail.com> wrote:

>>> Why does it "want" to fall when you cease applying the upward force?

>> Because if no force is applied the apple wants to take the shortest path possible through 4D space-time; or to put another way, it wants to take the longest possible proper time to get from your hand to the ground.  Remember that unlike the formula for calculating the distance in space, the formula for calculating the spacetime distance between two events contains a minus sign, that's why space is different from time.  

> But before it starts to move, how does it know which path satisfies the requirement you allege? AG 

The fundamental reason is nature is lazy. For example, high energy states are less stable than low energy states. Things that are not experiencing a force move from one event to another through 4D space-time on the shortest path that takes the longest proper time. And then there is the principle of least Action.

I intuitively think of "Action" as a way of keeping score on how much a system wants to move versus how much it's being held back. More formally. Action is defined as the integral of the Lagrangian over time. And the Lagrangian is defined as the kinetic energy MINUS the potential energy of a system. The principle of least Action says that among all possible paths a system could take between two points in spacetime, the one you actually see is the one that makes the action stationary.  All those paths make a contribution but the one that makes the action stationary is the classical limit. In this context "stationary" means a saddle point, which in real world cases is almost always a minimum.

The Lagrangian has units of energy. Action has units of energy × time . Or you could say Action has units of angular momentum since that also has units of energy times time.  Planck's constant h is also expressed in units of energy × time, so you could say that Planck's constant h is an expression of angular momentum, or you could even say h is an expression of Action. 

Paul Dirac made good use of this fact when he developed his famous equation which predicted the existence of antimatter and the fact that electrons have spin. It's possible to do physics without thinking about forces EVER, and in some cases it makes life much easier. Trying to calculate the movements of a double pendulum using Newton's idea of force is possible but it's a nightmare, however if you use the principle of least Action the task becomes much easier.  

I know that your next question will be why is nature inherently lazy? My short answer is I don't know. My slightly longer answer is I suspect that question simply has no answer because it is a brute fact. After all, an iterated sequence of "why" questions either goes on forever or terminates with a brute fact. You may not like either eventuality but one of them must be true. 

 John K Clark    See what's on my new list at  Extropolis

)%c

[Brent Meeker]

On 5/29/2025 6:22 AM, John Clark wrote:

I know that your next question will be why is nature inherently lazy? My short answer is I don't know. My slightly longer answer is I suspect that question simply has no answer because it is a brute fact. After all, an iterated sequence of "why" questions either goes on forever or terminates with a brute fact. You may not like either eventuality but one of them must be true.

One thing that leads to confusion (and endless questions from AG) in popular discourse is that Lagrangians and least-action and differential equations and Hamiltonians, etc, are maps not the territory and, depending on which map you're using, you find the boundary "brute fact" to have different expression.

Brent

[Alan Grayson]

One brute fact worth mentioning, is that unless and until we understand why gravity chooses the extremal path, we can't say we understand it. Another point is about the clock. Test particles have no clocks, so how do they "know", as they traverse an extremal path, that it is in fact extremal? AG 

[Brent Meeker]

You completely missed the point that the exact same problems solved by finding the extremal path can also be solved by half a dozen other methods and they are all mathematically equivalent.  So it make no sense to ask how Nature knows to use this or that method.

Brent

[Alan Grayson]

Fine.  Then accept the fact that you don't really understand gravity, and with that attitude you never will. AG 

[Brent Meeker]

Define "really understand" and give an example of something you really understand.

Brent

[Alan Grayson]

For example, generally what operators are, and specifically that Hermitian operators have real eigenvalues. AG

 

[John Clark]

On Thu, May 29, 2025 at 8:12 PM Alan Grayson <agrays...@gmail.com> wrote:

 > Test particles have no clocks

No. Particles do have internal clocks. Muons are particles and are produced by high energy cosmic rays hitting atoms of air very high up in our atmosphere. The half-life of a muon is only 1.5*10^-6 seconds, that's so short that almost none of them should reach the ground, and yet a significant number of them do. That's because that half-life figure was determined in a lab that was not moving relative to the muon being measured, but the average muon made by cosmic rays is moving at about 99.4% the speed of light, and if you use the formula 1 / √(1 - (v²/c²) for time dilation you find those muons have a half life that is 9.14 times longer than the half-life of muons measured in a lab.

John K Clark    See what's on my new list at  Extropolis

8g[

[Alan Grayson]

On Friday, May 30, 2025 at 4:17:37 AM UTC-6 John Clark wrote:

On Thu, May 29, 2025 at 8:12 PM Alan Grayson <agrays...@gmail.com> wrote:

 > Test particles have no clocks

No. Particles do have internal clocks.

They're not pendulums or wrist watches. So how would you describe them? AG

[Brent Meeker]

That's just mathematics.  Mathematics can be understood because we invent it.  We understand the theory of general relativity but it's a map of gravity, not gravity itself.  To understand something in physics generally means explaining it in terms of something more fundamental.  So string theory seemed to explain some things about gravity, e.g. why the graviton was spin 2 and why gravity was so weak.  But it has stalled in other respects.

Brent

 

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[Alan Grayson]

On Friday, May 30, 2025 at 3:34:21 PM UTC-6 Brent Meeker wrote:

On 5/30/2025 3:03 AM, Alan Grayson wrote:

On Friday, May 30, 2025 at 3:13:02 AM UTC-6 Brent Meeker wrote:

On 5/29/2025 11:18 PM, Alan Grayson wrote:

On Thursday, May 29, 2025 at 9:16:02 PM UTC-6 Brent Meeker wrote:

On 5/29/2025 5:12 PM, Alan Grayson wrote:

On Thursday, May 29, 2025 at 3:34:34 PM UTC-6 Brent Meeker wrote:

On 5/29/2025 6:22 AM, John Clark wrote:

I know that your next question will be why is nature inherently lazy? My short answer is I don't know. My slightly longer answer is I suspect that question simply has no answer because it is a brute fact. After all, an iterated sequence of "why" questions either goes on forever or terminates with a brute fact. You may not like either eventuality but one of them must be true.

One thing that leads to confusion (and endless questions from AG) in popular discourse is that Lagrangians and least-action and differential equations and Hamiltonians, etc, are maps not the territory and, depending on which map you're using, you find the boundary "brute fact" to have different expression.

Brent

One brute fact worth mentioning, is that unless and until we understand why gravity chooses the extremal path, we can't say we understand it. Another point is about the clock. Test particles have no clocks, so how do they "know", as they traverse an extremal path, that it is in fact extremal? AG

You completely missed the point that the exact same problems solved by finding the extremal path can also be solved by half a dozen other methods and they are all mathematically equivalent.  So it make no sense to ask how Nature knows to use this or that method.

Brent

Fine.  Then accept the fact that you don't really understand gravity, and with that attitude you never will. AG

Define "really understand" and give an example of something you really understand.

Brent

For example, generally what operators are, and specifically that Hermitian operators have real eigenvalues. AG

That's just mathematics. 

You asked me what I really understand, and I told you. You can't claim that we understand mathematics because we invented it, because the same can be said of physics. I understand some of the conservation laws, such as conservation of charge and energy. What I can say is that you don't understand gravity, and that won't occur until there is a deeper theory which explains why motion in a gravity field obeys extremal principles. AG

[John Clark]

On Fri, May 30, 2025 at 5:59 PM Alan Grayson <agrays...@gmail.com> wrote:

> You asked me what I really understand, and I told you. You can't claim that we understand mathematics because we invented it, because the same can be said of physics. 

We didn't invent the way Mercury orbits the sun, and as early as 1859 observations were good enough for us to know that Newton couldn't explain it, and in general Newton couldn't accurately predict how ANY planet that was close to its star would behave; but in 1915 Einstein could do both. So at the very least would you admit that Einstein understood gravity better than Newton did?

> What I can say is that you don't understand gravity, and that won't occur until there is a deeper theory which explains why motion in a gravity field obeys extremal principles

And if tomorrow somebody comes out with a theory that says matter tells spacetime how to curve and spacetime tells matter how to move because of X then you would still say we don't understand gravity because this new theory doesn't explain why X exists. If that's what it takes to "understand" something then it would be impossible even in principle to understand gravity. In fact it would be impossible to understand ANYTHING because even pure mathematics needs to start with unproven and unprovable axioms. 

If nothing is understandable, absolutely positively nothing, then the very word  "understandable" loses its meaning because meaning needs contrast.  Saying everything has the property X is operationally equivalent to saying nothing has the property X. That's why I have no patience for philosophers who triumphantly tell us that "nothing is real", it's equivalent to saying "everything is real".  

> I understand some of the conservation laws, such as conservation of charge and energy.

Then by all means tell the entire world about this marvelous new understanding you have developed. I'd love to have a deep understanding of exactly how an electron is able to generate a negative charge. I'd love to know what an electron is made of, what makes electron stuff different from non-electron stuff.  But remember if you say energy and electrical charge are conserved because of X then you know what the next question I'm going to ask will be.  

  John K Clark    See what's on my new list at  Extropolis

089

[Alan Grayson]

On Saturday, May 31, 2025 at 5:52:02 AM UTC-6 John Clark wrote:

On Fri, May 30, 2025 at 5:59 PM Alan Grayson <agrays...@gmail.com> wrote:

> You asked me what I really understand, and I told you. You can't claim that we understand mathematics because we invented it, because the same can be said of physics. 

We didn't invent the way Mercury orbits the sun, and as early as 1859 observations were good enough for us to know that Newton couldn't explain it, and in general Newton couldn't accurately predict how ANY planet that was close to its star would behave; but in 1915 Einstein could do both. So at the very least would you admit that Einstein understood gravity better than Newton did?

Yes, for sure. Definitely! I'm just saying that why anything moves in a gravity field seems unknown, even by Einstein. It's probably a postulate of GR, via the application of extremal principles. I'd like to go beyond this, to a deeper view of why there's motion induced or described by "gravity". AG 

> What I can say is that you don't understand gravity, and that won't occur until there is a deeper theory which explains why motion in a gravity field obeys extremal principles

And if tomorrow somebody comes out with a theory that says matter tells spacetime how to curve and spacetime tells matter how to move because of X then you would still say we don't understand gravity because this new theory doesn't explain why X exists.

There will likely always be unanswered questions, but you seem to be affirming the "shut up and calculate" attitude, and prefer to think we've gotten to the end of the road as far as knowledge is concerned. As far as that "quote" by Wheeler is concerned, it really says nothing IMO. How matter tells spacetime how to curve is unknown, although GR tells us how to calculate it. AG 

 

If that's what it takes to "understand" something then it would be impossible even in principle to understand gravity. In fact it would be impossible to understand ANYTHING because even pure mathematics needs to start with unproven and unprovable axioms. 

I am not opposed to postulates. I just want to know more. AG 

If nothing is understandable, absolutely positively nothing, then the very word  "understandable" loses its meaning because meaning needs contrast.  Saying everything has the property X is operationally equivalent to saying nothing has the property X. That's why I have no patience for philosophers who triumphantly tell us that "nothing is real", it's equivalent to saying "everything is real".  

What is likely true, is that there's no underlying material substance in the universe, and it's the apparent solidity and restrictions on motion in certain locations that creates the illusion of an underlying material substance. This, of course, is NOT to claim that nothing is real. AG

> I understand some of the conservation laws, such as conservation of charge and energy.

Then by all means tell the entire world about this marvelous new understanding you have developed.

Well, one thing is clear. Consciousness is fundamental, and some claim that the structure of the human brain is very similar to the structure of the physical universe. What's your opinion on that? But at present nothing can achieved by focusing exclusively on consciousness as Cosmin does. AG

I'd love to have a deep understanding of exactly how an electron is able to generate a negative charge. I'd love to know what an electron is made of, what makes electron stuff different from non-electron stuff.  But remember if you say energy and electrical charge are conserved because of X then you know what the next question I'm going to ask will be.  

You seem stuck in a negative mode of thought. The hierachy of "turtles" might form an infinite regression, but you seem to prefer to give up at the present level despite its obvious shortcomings. Someday we might know much more than we do today. But that will never happen if your attitude prevails. I don't claim to have "the answer". But I see that you don't have it either, and sadly resort to mockery to presumably satisfy some psychological requirements. AG 

[Alan Grayson]

On Friday, May 30, 2025 at 8:05:29 AM UTC-6 Alan Grayson wrote:

On Friday, May 30, 2025 at 4:17:37 AM UTC-6 John Clark wrote:

On Thu, May 29, 2025 at 8:12 PM Alan Grayson <agrays...@gmail.com> wrote:

 > Test particles have no clocks

No. Particles do have internal clocks.

They're not pendulums or wrist watches. So how would you describe them? AG

I await your reply. How do you know particles have internal clocks? What form do they take? AG 

[John Clark]

On Sun, Jun 1, 2025 at 10:27 PM Alan Grayson <agrays...@gmail.com> wrote:

 >>>> Test particles have no clocks

>>>No. Particles do have internal clocks.

>> They're not pendulums or wrist watches. So how would you describe them? AG

> I await your reply.

You did? Sorry, I didn't think I really needed to answer a question that had such an obvious answer, but apparently I was wrong. 

> They're not pendulums or wrist watches.

Both pendulums and wrist watches have something in common, they both change in a constant predictable interval of time. And that's what a clock does.  

> How do you know particles have internal clocks?

Because muons change in a constant predictable interval of time. If you had a bunch of muons you could measure how much time had elapsed by measuring the percentage of them that have decayed. 

Not all particles have internal clocks, photons don't, photons have no rest mass so they move as fast as it's possible for anything to move and thus from their point of view Einstein tells us time comes to a complete halt and everything for them happens at the same instant. And that's why from our point of view photons never change unless something external changes them. 

We once thought neutrinos had zero mass and so moved at the speed of light, but then we discovered neutrinos change over time in a periodic way. We mistakenly believed the electron neutrino, the muon neutrino, and the tau neutrino were 3 different particles, but then we discovered there was only one type of neutrino but it oscillated between those 3 different flavors in a predictable periodic way.  So neutrinos must have a very small rest mass, although we still haven't been able to measure just how small. All we know is that it's greater than zero and smaller than 0.8 electron volts. The electron is the second lightest known particle and it has a rest mass of  511,000 electron volts. 

Although neither would be very practical you could in theory make a clock out of both muons and neutrinos, but you could never make a clock out of photons if you just observed them and never interfered with them. 

John K Clark    See what's on my new list at  Extropolis

jot

[Alan Grayson]

On Monday, June 2, 2025 at 5:44:24 AM UTC-6 John Clark wrote:

On Sun, Jun 1, 2025 at 10:27 PM Alan Grayson <agrays...@gmail.com> wrote:

 >>>> Test particles have no clocks

>>>No. Particles do have internal clocks.

>> They're not pendulums or wrist watches. So how would you describe them? AG

> I await your reply.

You did? Sorry, I didn't think I really needed to answer a question that had such an obvious answer, but apparently I was wrong. 

Yes, you were wrong. I was interested in probing your concept of a clock. You're INFERRING the existence of a muon's clock, but can't describe its FORM. For a muon to know the time, it must be able to read its internal clock, which means it has self-reference, aka CONSCOUSNESS! Do you agree? Or do you claim that a muon has a clock but doesn't read or can't read it? AG 

> They're not pendulums or wrist watches.

Both pendulums and wrist watches have something in common, they both change in a constant predictable interval of time. And that's what a clock does.  

> How do you know particles have internal clocks?

Because muons change in a constant predictable interval of time. If you had a bunch of muons you could measure how much time had elapsed by measuring the percentage of them that have decayed. 

Not all particles have internal clocks, photons don't, photons have no rest mass so they move as fast as it's possible for anything to move and thus from their point of view Einstein tells us time comes to a complete halt and everything for them happens at the same instant. And that's why from our point of view photons never change unless something external changes them. 

We once thought neutrinos had zero mass and so moved at the speed of light, but then we discovered neutrinos change over time in a periodic way. We mistakenly believed the electron neutrino, the muon neutrino, and the tau neutrino were 3 different particles, but then we discovered there was only one type of neutrino but it oscillated between those 3 different flavors in a predictable periodic way.  So neutrinos must have a very small rest mass, although we still haven't been able to measure just how small. All we know is that it's greater than zero and smaller than 0.8 electron volts. The electron is the second lightest known particle and it has a rest mass of  511,000 electron volts. 

Although neither would be very practical you could in theory make a clock out of both muons and neutrinos, but you could never make a clock out of photons if you just observed them and never interfered with them. 

John K Clark    See what's on my new list at  Extropolis

[Alan Grayson]

On Monday, June 2, 2025 at 6:01:19 AM UTC-6 Alan Grayson wrote:

On Monday, June 2, 2025 at 5:44:24 AM UTC-6 John Clark wrote:

On Sun, Jun 1, 2025 at 10:27 PM Alan Grayson <agrays...@gmail.com> wrote:

 >>>> Test particles have no clocks

>>>No. Particles do have internal clocks.

>> They're not pendulums or wrist watches. So how would you describe them? AG

> I await your reply.

You did? Sorry, I didn't think I really needed to answer a question that had such an obvious answer, but apparently I was wrong. 

Yes, you were wrong. I was interested in probing your concept of a clock. You're INFERRING the existence of a muon's clock, but can't describe its FORM. For a muon to know the time, it must be able to read its internal clock, which means it has self-reference, aka CONSCIOUSNESS! Do you agree? Or do you claim that a muon has a clock but doesn't read or can't read it? AG 

Oh, one other thing. I get tired of being under-rated, even though I don't claim to be the brightest light in the room. AG 

[John Clark]

On Mon, Jun 2, 2025 at 8:11 AM Alan Grayson <agrays...@gmail.com> wrote:

> For a muon to know the time, it must be able to read its internal clock, which means it has self-reference, aka CONSCIOUSNESS!

So you believe that your alarm clock is conscious. I am skeptical of that claim although I can't prove that you're wrong.   

> Do you agree?

I think you already know the answer to that question. 

 John K Clark    See what's on my new list at  Extropolis

www

[Alan Grayson]

On Monday, June 2, 2025 at 6:53:58 AM UTC-6 John Clark wrote:

On Mon, Jun 2, 2025 at 8:11 AM Alan Grayson <agrays...@gmail.com> wrote:

> For a muon to know the time, it must be able to read its internal clock, which means it has self-reference, aka CONSCIOUSNESS!

So you believe that your alarm clock is conscious. I am skeptical of that claim although I can't prove that you're wrong.   

I am unsure what to believe. I don't believe an alarm clock is conscious. But with muons there's no discernable clock and yet, as you point out, something within seems to know the time, or behave as if it does. I'm pointing out the deep mystery with these muons and more generally with SR.  AG

> Do you agree?

I think you already know the answer to that question. 

I don't think you believe that an alarm clock is conscious, but you seem too comfortable in your inability to explain the time reality of a muon. I suppose you're not immune to just calculate predictions and leave it at that. AG 

[Brent Meeker]

And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

Brent

[Alan Grayson]

On Monday, June 2, 2025 at 7:14:47 PM UTC-6 Brent Meeker wrote:

And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

Brent

You'd be in a much better position to defend Clark if either of you could define the clock inherent in a muon, but you don't seem able to meet that challenge. AG 

[Brent Meeker]

On 6/2/2025 6:48 PM, Alan Grayson wrote:

On Monday, June 2, 2025 at 7:14:47 PM UTC-6 Brent Meeker wrote:

And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

Brent

You'd be in a much better position to defend Clark if either of you could define the clock inherent in a muon, but you don't seem able to meet that challenge. AG

I think John can take care of himself. 

If muon's don't have an inherent clock, how do they know when to decay?

Brent

[Alan Grayson]

You're assuming they have a clock, but avoid describing its form, or how it reads the time, if it reads the time. So many things assumed but no answers in sight. AG 

[Alan Grayson]

I suppose you were referring to the atmosphere producing an anti-inertial effect on the muons, but what's lacking is an explanation, or if you like MODEL, of how that effects the half-life of those particles. There are major mysteries here which haven't been addressed. And Yes, Clark can take care of himself, but so far the only "care" that's discernible, is his silence on this issue. AG 

[John Clark]

On Monday, June 2, 2025 at 7:14:47 PM UTC-6 Brent Meeker wrote:

> And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

On Mon, Jun 2, 2025 at 9:48 PM Alan Grayson <agrays...@gmail.com> wrote:

> You'd be in a much better position to defend Clark if either of you could define the clock inherent in a muon, but you don't seem able to meet that challenge. AG 

Define "define". I'm just kidding, I know you can't do that without tying yourself up into an infinite loop. So instead give me an example so I can understand what's worrying you. Let's start with the first timepiece humans ever invented, what is the clock inherent in a sundial?  

> with muons there's no discernable clock

If there was no discernible clock in a muon then we wouldn't be able to, in theory, use them as a clock, and yet we can thanks to radioactive decay. A muon clock is possible but not practical, however other types of radioactive clocks are very practical. Before scientists learned how to read the clocks inherit in unstable nuclei such as uranium-238, uranium-235, potassium-40, rubidium-87 and of course carbon-14, geologist were able to tell that one layer of rocks was older than another layer of rocks but they didn't know the absolute age of any of them. However now thanks to radioactive clocks we know that the Earth formed 4.54 billion years ago.

And you never answered Brent's question.  Do you understand "the reality of inertia"? Richard Feynman said he had an interesting conversation about inertia with his father when he was about 8 or 9. He ran up to his father and said: 

“Say, Pop, I noticed something: When I pull my wagon the ball rolls to the back of the wagon, and when I’m pulling it along and I suddenly stop, the ball rolls to the front of the wagon. Why is that?”

His father said: 

“Nobody knows. The general principle is that things that are moving try to keep moving and things that are standing still tend to stand still unless you push on them hard. This tendency is called inertia but nobody knows why it’s true. If you look close you’ll find the ball does not rush to the back of the wagon that you’re pulling against the ball; that the ball stands still or as a matter of fact from the friction starts to move forward really and doesn’t move back.”

Feynman said: 

"I realized dad was right! The ball never moved backwards! Relative to the wagon it moved backwards, but relative to the sidewalk it actually moved forward a little bit! It’s just that the wagon caught up with it!”

 John K Clark    See what's on my new list at  Extropolis

edc

[Brent Meeker]

On 6/2/2025 8:50 PM, Alan Grayson wrote:

On Monday, June 2, 2025 at 9:14:49 PM UTC-6 Brent Meeker wrote:

On 6/2/2025 6:48 PM, Alan Grayson wrote:

On Monday, June 2, 2025 at 7:14:47 PM UTC-6 Brent Meeker wrote:

And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

Brent

You'd be in a much better position to defend Clark if either of you could define the clock inherent in a muon, but you don't seem able to meet that challenge. AG

I think John can take care of himself. 

If muon's don't have an inherent clock, how do they know when to decay?

Brent

You're assuming they have a clock,

NO.  I'm inferring they have a clock.  Just as if you had a friend that came to your house ever 44hrs.  You'd infer he had a clock.

but avoid describing its form, or how it reads the time, if it reads the time. So many things assumed but no answers in sight. AG

NOT assumed.  Inferred.  If you don't know the difference consult your dictionary.

Brent

 

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[Alan Grayson]

On Tuesday, June 3, 2025 at 5:59:49 AM UTC-6 John Clark wrote:

On Monday, June 2, 2025 at 7:14:47 PM UTC-6 Brent Meeker wrote:

> And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

On Mon, Jun 2, 2025 at 9:48 PM Alan Grayson <agrays...@gmail.com> wrote:

> You'd be in a much better position to defend Clark if either of you could define the clock inherent in a muon, but you don't seem able to meet that challenge. AG 

Define "define". I'm just kidding, I know you can't do that without tying yourself up into an infinite loop. So instead give me an example so I can understand what's worrying you. Let's start with the first timepiece humans ever invented, what is the clock inherent in a sundial?  

> with muons there's no discernable clock

If there was no discernible clock in a muon then we wouldn't be able to, in theory, use them as a clock, and yet we can thanks to radioactive decay. A muon clock is possible but not practical, however other types of radioactive clocks are very practical. Before scientists learned how to read the clocks inherit in unstable nuclei such as uranium-238, uranium-235, potassium-40, rubidium-87 and of course carbon-14, geologist were able to tell that one layer of rocks was older than another layer of rocks but they didn't know the absolute age of any of them. However now thanks to radioactive clocks we know that the Earth formed 4.54 billion years ago.

And you never answered Brent's question. 

I did, but in a negative way, by referring to external forces effecting a particle's path. Inertia is not hard to understand, so there's no need to repeat its definition. The relevant question is what structure within a muon can act as a clock. Since you're so sure it exists, please describe its structure. Maybe more important is why this "clock" which does not evidence time delay in the frame in which it is alleged to exist, would effect the muon's half-life. AG

[Alan Grayson]

On Tuesday, June 3, 2025 at 1:22:04 PM UTC-6 Brent Meeker wrote:

On 6/2/2025 8:50 PM, Alan Grayson wrote:

On Monday, June 2, 2025 at 9:14:49 PM UTC-6 Brent Meeker wrote:

On 6/2/2025 6:48 PM, Alan Grayson wrote:

On Monday, June 2, 2025 at 7:14:47 PM UTC-6 Brent Meeker wrote:

And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

Brent

You'd be in a much better position to defend Clark if either of you could define the clock inherent in a muon, but you don't seem able to meet that challenge. AG

I think John can take care of himself. 

If muon's don't have an inherent clock, how do they know when to decay?

Brent

You're assuming they have a clock,

NO.  I'm inferring they have a clock.  Just as if you had a friend that came to your house ever 44hrs.  You'd infer he had a clock.

but avoid describing its form, or how it reads the time, if it reads the time. So many things assumed but no answers in sight. AG

NOT assumed.  Inferred.  If you don't know the difference consult your dictionary.

Brent

OK, let's split hairs. If "assumed" means zero evidence for a muon's clock, then "inferred" is better IF you believe a muon has some structure for defining a clock. OTOH, if a muon has no such structure, then it's OK to "assume" the existence of the clock. But instead of splitting hairs, how about a description of the structure of a muon's clock? And if that clock shows no time dilation within the muon's frame of reference, how would that FACT effect its half-life? AG 

[John Clark]

On Tue, Jun 3, 2025 at 6:13 PM Alan Grayson <agrays...@gmail.com> wrote:

> what structure within a muon can act as a clock. 

As far as we know the muon, like the electron, has no internal structure. Nevertheless we know for a fact that a muon can and does change from one moment in time to another. So evidently something doesn't need an internal structure to act as a clock, you may be unhappy with that fact but that doesn't prevent it from being true.  

> Since you're so sure it exists, please describe its structure. 

Please describe how your alarm clock is able to keep time without invoking the idea of "inertia", unless of course you are able to explain the fundamental reason why inertia exists. 

> Maybe more important is why this "clock" which does not evidence time delay in the frame in which it is alleged to exist, would effect the muon's half-life. AG

I am unable to parse the above word salad.

 John K Clark    See what's on my new list at  Extropolis

udz

[Brent Meeker]

On 6/3/2025 2:05 AM, Alan Grayson wrote:

On Monday, June 2, 2025 at 9:50:54 PM UTC-6 Alan Grayson wrote:

On Monday, June 2, 2025 at 9:14:49 PM UTC-6 Brent Meeker wrote:

On 6/2/2025 6:48 PM, Alan Grayson wrote:

On Monday, June 2, 2025 at 7:14:47 PM UTC-6 Brent Meeker wrote:

And you are too susceptible to casually assuming you understand the familiar just because it's familiar.  Your alarm clock measures time by the oscillations of a wheel, which depend on the inertia of the wheel.  Do you understand "the reality of that inertia"?

Brent

You'd be in a much better position to defend Clark if either of you could define the clock inherent in a muon, but you don't seem able to meet that challenge. AG

I think John can take care of himself. 

If muon's don't have an inherent clock, how do they know when to decay?

Brent

You're assuming they have a clock, but avoid describing its form, or how it reads the time, if it reads the time. So many things assumed but no answers in sight. AG 

I suppose you were referring to the atmosphere producing an anti-inertial effect on the muons, but what's lacking is an explanation, or if you like MODEL, of how that effects the half-life of those particles.

Do you have a model of how relativistic motion makes a wrist watch run slower?

Brent

[Alan Grayson]

In the frame wherein you allege the wrist watch is running slower, it isn't. In some other frame, moving at constant velocity wrt that wrist watch, it appears to be running slower. Which watch should we pay attention to? AG 

[Brent Meeker]

On 6/3/2025 3:25 PM, Alan Grayson wrote:

OK, let's split hairs. If "assumed" means zero evidence for a muon's clock, then "inferred" is better IF you believe a muon has some structure for defining a clock. OTOH, if a muon has no such structure, then it's OK to "assume" the existence of the clock.

IF you assume a clock requires some internal structure.

But instead of splitting hairs, how about a description of the structure of a muon's clock?

So you want to assume that the muon can't keep time just by moving thru spacetime, but requires some structure.  Do you have a proof or is this mere surmise?

And if that clock shows no time dilation within the muon's frame of reference, how would that FACT effect its half-life? AG

I guess that would show that it wasn't the clock that determines the muon's decay.

Brent

[Alan Grayson]

On Tuesday, June 3, 2025 at 9:42:30 PM UTC-6 Brent Meeker wrote:

On 6/3/2025 3:25 PM, Alan Grayson wrote:

OK, let's split hairs. If "assumed" means zero evidence for a muon's clock, then "inferred" is better IF you believe a muon has some structure for defining a clock. OTOH, if a muon has no such structure, then it's OK to "assume" the existence of the clock.

IF you assume a clock requires some internal structure.

But instead of splitting hairs, how about a description of the structure of a muon's clock?

So you want to assume that the muon can't keep time just by moving thru spacetime, but requires some structure.  Do you have a proof or is this mere surmise?

 

It's a surmise, not a mere surmise, based on clocks I am familiar with. You're the relativity expert. You teach the masses. What's your concept of time keeping by a muon? AG

And if that clock shows no time dilation within the muon's frame of reference, how would that FACT effect its half-life? AG

I guess that would show that it wasn't the clock that determines the muon's decay.

So what clock does it, if any? AG 

Brent

[Brent Meeker]

The one in the frame where the muons run slower.

Brent

[Alan Grayson]

That would have been my guess, but it makes no sense. How would a muon have contact with another frame as the observer, in which its clocks seem to tick at a lower rate? AG 

[Brent Meeker]

I don't know.  But it must that something to do with the mass of the muon, the electron, and neutrino and the coupling of the neutrino, muon, and electron fields since a muon decays into and electron and a anti-neutrino.

Brent

Brent

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[Alan Grayson]

On Tuesday, June 3, 2025 at 10:46:58 PM UTC-6 Brent Meeker wrote:

On 6/3/2025 8:53 PM, Alan Grayson wrote:

On Tuesday, June 3, 2025 at 9:42:30 PM UTC-6 Brent Meeker wrote:

On 6/3/2025 3:25 PM, Alan Grayson wrote:

OK, let's split hairs. If "assumed" means zero evidence for a muon's clock, then "inferred" is better IF you believe a muon has some structure for defining a clock. OTOH, if a muon has no such structure, then it's OK to "assume" the existence of the clock.

IF you assume a clock requires some internal structure.

But instead of splitting hairs, how about a description of the structure of a muon's clock?

So you want to assume that the muon can't keep time just by moving thru spacetime, but requires some structure.  Do you have a proof or is this mere surmise?

 

It's a surmise, not a mere surmise, based on clocks I am familiar with. You're the relativity expert. You teach the masses. What's your concept of time keeping by a muon? AG

And if that clock shows no time dilation within the muon's frame of reference, how would that FACT effect its half-life? AG

I guess that would show that it wasn't the clock that determines the muon's decay.

So what clock does it, if any? AG

I don't know.  But it must that something to do with the mass of the muon, the electron, and neutrino and the coupling of the neutrino, muon, and electron fields since a muon decays into and electron and a anti-neutrino.

Brent

I don't see how those factors would effect the muon's half-life. I appreciate your honesty. I suspect the issue I have raised is unsolved, and this is what troubles me about Relativity. AG

[Brent Meeker]

Why are you troubled by lack of a model.  Inertia is a farm more common phenomenon, but you're untroubled by it.  Why...I suspect because you have lots of experience of inertia.  Well scientists, particularly particle physicists have lots of experience of relativistic time dilation.

Brent

[Brent Meeker]

You seem to have lost the point.  We're not discussing why time dilation occurs.  It's obviously not a matter of "contact" between frames; but it's also beside the point.  The point is that whatever is responsible for muons having a particular half-life when stationary, changes with speed exactly the same way clocks change with speed.  It's a point of evidence for muons having the same physical relation to time as clocks.

Brent

[Alan Grayson]

Why should I be troubled by inertia? It's easily understood. But the change in half-life of muons is hardly understood, and I am not going off on some wrong track here. You think it's OK to shut up and calculate, and sweep the real issue under the proverbial rug. AG

[Alan Grayson]

Pardon me for extending the scope of the discussion. What was it we were discussing? I can't recall. AG

 

It's obviously not a matter of "contact" between frames; but it's also beside the point. 

 

I never claimed anything about "contact", except that the frame observing the decayed muons implies time dilation of those muons, and it's OK IMO to ask how that could happen. AG

 

The point is that whatever is responsible for muons having a particular half-life when stationary, changes with speed exactly the same way clocks change with speed.  It's a point of evidence for muons having the same physical relation to time as clocks.

If you can't see there's something rather deep occurring to produce time dilation in the frame where clocks are at rest, I can't help you. In effect, you're satisfied with "shut up and calculate", and the underlying physical reality is of no interest. You were ahead of the game when you admitted you don't know why the half-life changes. AG

[Brent Meeker]

Then perhaps you can explain why a muon has about 200x the inertia of an electron?  And why inertia and gravity are always proportional?

Brent

But the change in half-life of muons is hardly understood, and I am not going off on some wrong track here. You think it's OK to shut up and calculate, and sweep the real issue under the proverbial rug. AG

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[Alan Grayson]

On Wednesday, June 4, 2025 at 12:17:40 AM UTC-6 Brent Meeker wrote:

On 6/3/2025 11:00 PM, Alan Grayson wrote:

On Tuesday, June 3, 2025 at 11:33:26 PM UTC-6 Brent Meeker wrote:

On 6/3/2025 10:05 PM, Alan Grayson wrote:

On Tuesday, June 3, 2025 at 10:46:58 PM UTC-6 Brent Meeker wrote:

On 6/3/2025 8:53 PM, Alan Grayson wrote:

On Tuesday, June 3, 2025 at 9:42:30 PM UTC-6 Brent Meeker wrote:

On 6/3/2025 3:25 PM, Alan Grayson wrote:

OK, let's split hairs. If "assumed" means zero evidence for a muon's clock, then "inferred" is better IF you believe a muon has some structure for defining a clock. OTOH, if a muon has no such structure, then it's OK to "assume" the existence of the clock.

IF you assume a clock requires some internal structure.

But instead of splitting hairs, how about a description of the structure of a muon's clock?

So you want to assume that the muon can't keep time just by moving thru spacetime, but requires some structure.  Do you have a proof or is this mere surmise?

 

It's a surmise, not a mere surmise, based on clocks I am familiar with. You're the relativity expert. You teach the masses. What's your concept of time keeping by a muon? AG

And if that clock shows no time dilation within the muon's frame of reference, how would that FACT effect its half-life? AG

I guess that would show that it wasn't the clock that determines the muon's decay.

So what clock does it, if any? AG

I don't know.  But it must that something to do with the mass of the muon, the electron, and neutrino and the coupling of the neutrino, muon, and electron fields since a muon decays into and electron and a anti-neutrino.

Brent

I don't see how those factors would effect the muon's half-life. I appreciate your honesty. I suspect the issue I have raised is unsolved, and this is what troubles me about Relativity. AG

Why are you troubled by lack of a model.  Inertia is a farm more common phenomenon, but you're untroubled by it.  Why...I suspect because you have lots of experience of inertia.  Well scientists, particularly particle physicists have lots of experience of relativistic time dilation.

Brent

Why should I be troubled by inertia? It's easily understood.

Then perhaps you can explain why a muon has about 200x the inertia of an electron?  And why inertia and gravity are always proportional?

Brent

It's caused by its larger mass, about 200x, compared to the electron. The statement of Inertia, what it is, is easy to grasp. However, many experimental findings of physics are not physically grounded, that is, understood, so why do you expect me to answer your questions? In physics, there's too much bluster about what is known, and too little is grounded in physical reality. AG 

[Brent Meeker]

I do know why it changes.  Time dilation is just a consequence of spacetime geometry.  But I don't know why a muon has sense of time; and it can't just be a property of the muon because the muon wouldn't decay if it didn't have the electron state to decay into.  It's a probabilistic event, so it doesn't have a definite time to decay, it just has a constant probability of decay per unit time.

Brent

[Brent Meeker]

That's just saying the same thing in different words.  In the context of decay you're demanding a mechanism.  What's the mechanism for resisting acceleration?  Saying it's "mass" is just giving it a name.

The statement of Inertia, what it is, is easy to grasp. However, many experimental findings of physics are not physically grounded, that is, understood, so why do you expect me to answer your questions? In physics, there's too much bluster about what is known, and too little is grounded in physical reality. AG

You're the one who's blustering about what's known.  I'm pointing out that "known" can mean different things.  Physic students soon realize that "known" means we know how to predict its behavior.  Sometimes this is based on the "known" behavior of subsystems.  But this kind of reductionism has to stop at some level where we just know how to predict behavior but not based on some deeper or more general level.

Engineering is even more this way.  What is known about materials is often just tables of empirical data.  If I want to know the yield strength of 17-40 steel I look it up in a table based on testing many samples.  I know it's made of atoms of iron and carbon and nickel and chromium, but it would be foolish to try to calculate the yield strength from that.  So what do you think we "know" about the strength of steel?  Is it unknown?  Am I sweeping an issue under the rug?

Brent

[PGC]

But has this stopped anyone on the list before? I'm sure if Alan ran around screaming it's impossible, unknown, physics is bs, and accused you of sweeping the issue under the rug, you would start determining the lattice parameters of the phases (e.g. Burgers vector) and using density functional theory, calculate elastic constants of 17-4 PH stainless steel alloy's matrix, model solid solution strengthening, compute misfit strain fields caused by atoms of chromiu, nickel, copper on the iron lattice to see to what degree they impede dislocation motion (=> thereby increasing yield strength), model nucleation and growth of the hardening phases (Ni3Cu) for precipitation strengthening, using thermodynamic predctions from molecular dynamics simulations to obtain size, distribution etc. of these prcipitates, model the dislocation-precipitate interactions, grain boundary strengthening (idk, but I'm sure you do) and add all the stuff in all the units that I don't care to look up... without any need to calibrate these calculations against experimental yield strength data. That's for lazy people. 

 

So what do you think we "know" about the strength of steel?  Is it unknown?  Am I sweeping an issue under the rug?

Yes, you are. Because the "real issue" is how the steel knows that these interactions might not be linear. Because when chromium, nickel, and copper have a conversation with the iron lattice, they could conspire to make the engineer with his table fail, and effectively decide to dislocate below the stress level. That's why there are accidents in the oil and gas sectors at times, as everybody knows that those companies are so rich, they would never buy substandard steel. They would never be that cheap as it would impede the greed.