Physics for dummies
David Mitchell
Apologies (since this is off-topic), but this is the only science based
newsgroup I subscribe to and I've been impressed by the knowledge
displayed by the posters.
My question is: do you know of an online (or offline, hell, even paper
will do :-) resource that explains some of the more (to me) bizarre
aspects of physics?
I have a strong amateur interest in physics (and, as you will see, a
dangerous amount of knowledge); but I've never read a book that explains
all the actual processes of things.
Things like:
How _do_ atoms absorb and emit photons which have wavelengths thousands
of times greater than their diameter?
How is it possible for the insides of black holes to have _infinite_
density?
How _do_ electrons change from shell to shell in zero time?
These are all, to me, situations where the maths is perfectly clear, and
seemingly correct, but the actual nuts-and-bolts mechanisms of the
processes seem impossible.
Thank you for your time.
--
==========================================================================
David Mitchell ===== A life spent making mistakes is not only
================================ more honourable but more useful than a
da...@edenroad.demon.co.uk ===== life spent doing nothing. - GBS
==========================================================================
Aaron Bergman
>
>These are all, to me, situations where the maths is perfectly clear, and
>seemingly correct, but the actual nuts-and-bolts mechanisms of the
>processes seem impossible.
I would advise you to abandon a mechanistic way of looking at
physics. Your intuition is trained on things very large compared
to the stuff you're talking about -- the physics of the very
small simply doesn't correspond to your intuition.
Aaron
--
Aaron Bergman
<http://www.princeton.edu/~abergman/>
Erik Max Francis
> Things like:
> How _do_ atoms absorb and emit photons which have wavelengths
> thousands
> of times greater than their diameter?
Because that's the way things work at a subatomic level.
> How is it possible for the insides of black holes to have _infinite_
> density?
Actually, this comes from general relativity, which we know breaks down
under extremely strong gravitational fields, where quantum mechanical
effects should dominate. A singularity is most assuredly an example of
this -- it may well be that with a full theory of quantum gravity, there
is no singularity inside a black hole. (But we don't have such a theory
yet.)
> How _do_ electrons change from shell to shell in zero time?
Because that's the way things work at a subatomic level.
> These are all, to me, situations where the maths is perfectly clear,
> and
> seemingly correct, but the actual nuts-and-bolts mechanisms of the
> processes seem impossible.
It sounds like you're using a Newtonian mindset for analyzing quantum
mechanical phenomena. As you're discovering, that rapidly gets you
nowhere.
--
Erik Max Francis | email m...@alcyone.com | icq 16063900
Alcyone Systems | web http://www.alcyone.com/max/ | q3a Product
San Jose, CA | languages en, eo | icbm 37 20 07 N 121 53 38 W
USA | 965.339 Ms p.L. | 314 days left | &tSftDotIotE
__
/ \ Once the people begin to reason, all is lost.
\__/ Voltaire
Chuck Stewart
da...@edenroad.demon.co.uk (David Mitchell) wrote in
<tOFciUA+...@edenroad.demon.co.uk>:
>Hi,
<Snip newtonian plea for help in a non-newtonian world>
Hei,
The sci.physics.* groups FAQ's on physics and relativity are a good
start from your current newton-centric mindset.
Physics FAQ
http://math.ucr.edu/home/baez/physics/faq.html
http://www.public.iastate.edu/~physics/sci.physics/faq/faq.html
http://www.weburbia.com/physics/faq.html
http://www.corepower.com/~relfaq/faq.html
Relativity FAQ
http://math.ucr.edu/home/baez/physics/relativity.html
http://www.public.iastate.edu/~physics/sci.physics/faq/relativity.html
http://www.weburbia.com/physics/relativity.html
http://www.corepower.com/~relfaq/relativity.html
>
>Thank you for your time.
S'okay, I'm just nuking burritos.
--
Chuck Stewart
"Anime-style catgirls: Threat? Menace? Or just studying
algebra?"
David Mitchell
<m...@alcyone.com> writes
>David Mitchell wrote:
>
>> Things like:
>> How _do_ atoms absorb and emit photons which have wavelengths
>> thousands
>> of times greater than their diameter?
>
>Because that's the way things work at a subatomic level.
Yes, but _how_?
I appreciate that I have a Newtonian world-view, (I think that's what
most people start with); but I also think that I'm asking a deeper
question than you're answering.
Whenever I've spoken to people about this, they just tell me that the
only way to "understand" QM is to do the math, ignore common-sense and
just calculate.
Fine.
I can do that (in theory, given a few years of study ;-) but the
question I'm asking is: is the maths describing reality or defining it?
If the maths is describing something more fundamental then what is it
describing, if it isn't then _how does it all work_?
>
>> How _do_ electrons change from shell to shell in zero time?
>
>Because that's the way things work at a subatomic level.
Okay, so I'm reasonably happy to accept that little charged pointy
things aren't whizzing around a charged nuclear thing, but is anything
moving at all? Is the electron just a mathematical abstraction, in
which case is it only information that's moving, and if so how does
_that_ work? How is this information stored?, transferred?, and why?
If it's not just information, then what is it? If it's something
physical then how does _that_ move instantaneously?
David Mitchell
<zapk...@hotmail.com> writes
>(The kitty takes time out to lend a paw...)
>
Many thanks.
Have some fish on me ;-)
Charles R. Capko Jr.
>If the maths is describing something more fundamental then what is it
>describing, if it isn't then _how does it all work_?
I think you are asking the fundimerntal questions that science has
been trying to answer for mellenia. All we have now is a model that we
think works, but we are liable to find that we are infact completely
wrong, but we keep trying.
You should try to take a physics cource in a community college, I
think you have the mentality and drive that is nessisary to complete
it, or atleast become hopelessly frusterated at the fact that, our
math can define reality, but not often illuminate it for us.
--Calling in from a newtonian universe.--
Chuck.
David McKee
: In article <38B1DD4E...@alcyone.com>, Erik Max Francis
: <m...@alcyone.com> writes
: >David Mitchell wrote:
: >> Things like:
: >> How _do_ atoms absorb and emit photons which have wavelengths
: >> thousands
: >> of times greater than their diameter?
: >Because that's the way things work at a subatomic level.
: Yes, but _how_?
:
: I appreciate that I have a Newtonian world-view, (I think that's what
: most people start with); but I also think that I'm asking a deeper
: question than you're answering.
Well, they just do...the realization (which you talk about later) that we
are not talking about little billard balls with classical trajectories is
crucial here.
: Whenever I've spoken to people about this, they just tell me that the
: only way to "understand" QM is to do the math, ignore common-sense and
: just calculate.
This is the thing to do, but it won't help you peace of mind.
The only cheeply-, and macroscopicly-observeable, quantum behavior
that comes to mind is the polarization of light. Get several (3 or
more) sheets of polarizing material (dissect some cheep sun glasses),
and play with them.
Do the experiment where a third polarizer inserted between crossed
polarizers results in _increased_ transmission. Think about it for
a while.
It won't give you a sudden understanding of quantum mechanics, but it
should shake up you intuition.
At that point you will be more ready to "understand" quantum mechanics by
doing the math.
: Fine.
:
: I can do that (in theory, given a few years of study ;-) but the
: question I'm asking is: is the maths describing reality or defining it?
:
: If the maths is describing something more fundamental then what is it
: describing, if it isn't then _how does it all work_?
I am familiar with the frustration that you seem to feel. The desire to
dig under the abstraction and lay hands on what is _really_ happening--
whats _really_ there. Intrinsic angular momentum (or "spin") has long
been the target of my desire to understand.
The best answer that I can offer (and you're not going to like it) is:
Physics does not deal with what or how things _are_, only with
how things can be sucsefully modeled. Whatever an electron may
_be_ in a philosophical sense, in physics, it is just a
particle with mass about .511 MeV, charge about 1.60e-19 C,
magnetic moment about 1.00116 Bohr magnetons, spin quantum
number 1/2, lepton qunatum number 1, and no observable extent
down to the smallest scales we're every probed.
For what it's worth,
--
-- David McKee
-- dmc...@jlab.org
-- (757) 269-7492 (Office)
Aaron Bergman
>
>Well, they just do...the realization (which you talk about later) that we
>are not talking about little billard balls with classical trajectories is
>crucial here.
I think the best way to illustrate this is with the two slit
experiment. A few preliminaries:
Two slits with waves:
If you shine a wave on a set of two slits and look at the pattern
that appears on a screen, you see a series of alternating peaks
and valleys, ie diffraction.
Two slits with bullets:
If you shoot bullets at different angles at the two slits, we
simply see two peaks, one from each of the slits. Each peak is
made of lots of small points from each bullet.
So, what happens in real life? We shine a very bright light at a
pair of slits, we see a diffraction pattern like the first
example above. Now, as we turn down he light slowly, the pattern
starts getting dimmer. Soon something weird starts happening. If
the light is on very dim, we start to see individual points of
light appearing on the screen, one at a time. However, if we wait
a while and add up all the points, we see that the individual
points start to form the diffraction patter one point at a time.
So, what's really happening? Apparently light is made out of
particles, but somehow each particle knows about the existence of
both slits and thus interferes. What if we try to find out which
slit the photon goes through by putting a detector there?
Suddenly, the diffraction pattern completely disappears and we
just see the two peaks.
Weird, huh? It's stuff like this that made people decide that the
world just won't conform to our intuition. "What's really
happening?" just isn't a phrase that one can make sense of. We
have formulas that can describe the results of experiments.
That's all you can really do in the end. Who's to say that that's
no "what's really happening"?
Brendan Hall
David McKee wrote in message <88uhkq$985$1...@inn.jlab.org>...
>David Mitchell (da...@edenroad.demon.co.uk) wrote:
>: In article <38B1DD4E...@alcyone.com>, Erik Max Francis
>: <m...@alcyone.com> writes
>: >David Mitchell wrote:
>: >> Things like:
>: >> How _do_ atoms absorb and emit photons which have wavelengths
>: >> thousands
>: >> of times greater than their diameter?
>: >Because that's the way things work at a subatomic level.
Actually, this is a wave phenomena, which can be (at least partially)
understood classically. Imagine a cork bobbing on the surface of a pond.
What does it bob on? Waves. The wavelength is the distance from one peak
to the next. This has nothing to do with the size of the cork. If our
ideal cork can absorb the wave, leaving calm water behind it wherever wave
hits the cork, then we have a situation similar to that asked about here.
It doesn't matter how long the distance between the wave peaks, the cork
will still leave a calm water behind it. (Of course, the wave will diffract
around the cork, resulting in a shortened wake which is dependent on
wavelength, however, that too is classical.)
>
>: Whenever I've spoken to people about this, they just tell me that the
>: only way to "understand" QM is to do the math, ignore common-sense and
>: just calculate.
>
>This is the thing to do, but it won't help you peace of mind.
>
>The only cheeply-, and macroscopicly-observeable, quantum behavior
>that comes to mind is the polarization of light. Get several (3 or
>more) sheets of polarizing material (dissect some cheep sun glasses),
>and play with them.
>
>Do the experiment where a third polarizer inserted between crossed
>polarizers results in _increased_ transmission. Think about it for
>a while.
>
>It won't give you a sudden understanding of quantum mechanics, but it
>should shake up you intuition.
>
Actually, no. Polarisers allow light to pass through by re-emitting it at
the other end. So a polariser of orientation | will pass light with any |
component, for example /, |, or \. It wont pass _ because this has no
component in the | direction. So two cross polarisers will not pass any
light (except circularly polarised) because it cuts out all components, ie.
| and _. A third / placed in the middle of the two will pass the component
in the | direction, then / direction, then _ direction. At each filter, it
will change the direction of the polarisation. So light in the _ direction
wont pass because it hits the | polariser first. Light in the / direction
will loose some intensity going through the | polariser. The resultant
light is now | polarised. Encountering the / filter, it loses some
intensity, and comes out / polarised. Encountering the _ filter, the now /
polarised light will lose further intensity and come out _ polarised.
Classically understood therefore a classical problem.
B.H.
David Mitchell
<aber...@princeton.edu> writes
>In article <88uhkq$985$1...@inn.jlab.org>, David McKee wrote:
>>
>>Well, they just do...the realization (which you talk about later) that we
>>are not talking about little billard balls with classical trajectories is
>>crucial here.
>
>I think the best way to illustrate this is with the two slit
>experiment. A few preliminaries:
>
<experiment snipped>
>
>Weird, huh? It's stuff like this that made people decide that the
>world just won't conform to our intuition. "What's really
>happening?" just isn't a phrase that one can make sense of. We
>have formulas that can describe the results of experiments.
>That's all you can really do in the end. Who's to say that that's
>no "what's really happening"?
>
I don't want to seem hopelessly old-fashioned; but surely there must
_be_ a fundamental level of reality, at which things _actually_ happen,
otherwise why are there "laws" of nature at all? (Now necessarily in
the sense of "laws which fundamental entities consult in order to know
how to behave", but even in the looser, implicit, "laws which appear to
describe behaviour").
In other words, we're back to asking why mathematics works so well.
If you're suggesting that perhaps mathematics is in some way the
fundamental level of reality, then how does _that_ work?
Erik Max Francis
> In other words, we're back to asking why mathematics works so well.
We've always been there.
> If you're suggesting that perhaps mathematics is in some way the
> fundamental level of reality, then how does _that_ work?
The laws of physics are described by mathematics. With quantum
mechanics, however, that mathematics just happens to be a little more
complicated than with, say, Newtonian mechanics.
If you learn the maths of quantum mechanics, then you understand that
theory. Science can only model reality with (mathematical) theories;
what's "really going on" is a question beyond science.
--
Erik Max Francis | email m...@alcyone.com | icq 16063900
Alcyone Systems | web http://www.alcyone.com/max/ | q3a Product
San Jose, CA | languages en, eo | icbm 37 20 07 N 121 53 38 W
USA | 965.455 Ms p.L. | 313 days left | &tSftDotIotE
__
/ \ Death to all fanatics!
\__/ Malaclypse the Younger
Erik Max Francis
> I appreciate that I have a Newtonian world-view, (I think that's what
> most people start with); but I also think that I'm asking a deeper
> question than you're answering.
>
> Whenever I've spoken to people about this, they just tell me that the
> only way to "understand" QM is to do the math, ignore common-sense and
> just calculate.
Pretty much. Quantum mechanics applies (quite well!) to a realm so
beyond our everyday experience that it would be bizarre to _expect_ our
common sense notions to apply.
> I can do that (in theory, given a few years of study ;-) but the
> question I'm asking is: is the maths describing reality or defining
> it?
>
> If the maths is describing something more fundamental then what is it
> describing, if it isn't then _how does it all work_?
I'm still not sure quite what you're asking. It seems that you're
asking a question somewhat like, "No, really, seriously, disregard all
the mathematics and all that stuff, how does it _really_ work?" There
isn't an easy answer for you, and there probably isn't _any_ answer.
Physics is a science. In science, you make mathematical theories. You
compare the predictions of these theories to reality, and use the
results to either refine or reject the theories. What you end up with,
hopefully, is quite a successful theory. These theories don't represent
what's "really" going on, they just represent our theories. Quantum
mechanics is such a theory, and it's extraordinarily successful despite
the fact that it is extremely counterintuitive and downright confusing.
What's really going on? That question is beyond science.
Aaron Bergman
>
>I don't want to seem hopelessly old-fashioned; but surely there must
>_be_ a fundamental level of reality, at which things _actually_ happen,
>otherwise why are there "laws" of nature at all?
There may well be a fundamental level, but there's no way to know
when you've reached it.
> (Now necessarily in
>the sense of "laws which fundamental entities consult in order to know
>how to behave", but even in the looser, implicit, "laws which appear to
>describe behaviour").
Quantum mechanics does describe behavior.
>
>In other words, we're back to asking why mathematics works so well.
That's a "why" question. It's difficult to even formulate what an
acceptable answer to a why question could be. Usually an answer
just introduces a new level to which one can ask why again. For
that reason, physics generally doesn't try to answer why
questions outside of the context of a preexisting theory.
>
>If you're suggesting that perhaps mathematics is in some way the
>fundamental level of reality, then how does _that_ work?
Quite well, actually.
In QM, say, we have our fundamental entity, the state vector, we
have equations for how it evolves, and we have equations for what
we can measure. And, most importantly, the answers we get
correspond to what we measure.
Sound pretty good to me.
Geoffrey A. Landis
da...@edenroad.demon.co.uk writes:
>...
>How _do_ electrons change from shell to shell in zero time?
I can answer this one: they don't.
I don't know how this one got into the popular culture, but a transition
(aka a "quantum jump") does *not* take zero time.
It turns out that in quantum mechanics you can learn almost everything
you need to know about the transition by analyzing the initial state and
the final state, and ignoring the details of the transition between them,
including how long it takes. But just because you can do the analysis by
thinking of it as jumping from the one state to the other doesn't mean
that there is no time required for it to do so.
The only place that the transition time really shows up as an important
factor is when you are calculating the spectral line width; the faster
the transition the wider the line (although there are other contributions
to line width, such as the thermal doppler broadening, that usually
obscure this contribution).
--
Geoffrey A. Landis
Scientist and part-time science fiction writer
http://www.sff.net/people/geoffrey.landis
MA Lloyd
>I don't want to seem hopelessly old-fashioned; but surely there must
>_be_ a fundamental level of reality, at which things _actually_ happen,
>otherwise why are there "laws" of nature at all? (Now necessarily in
>the sense of "laws which fundamental entities consult in order to know
>how to behave", but even in the looser, implicit, "laws which appear to
>describe behaviour").
>In other words, we're back to asking why mathematics works so well.
Well in a sense this is hopelessly old fashioned. It's not really a
question of physics at all, but one of philosophy, you are probably
looking for things like the ideal forms or the first cause, or questions
about why it's possible to understand anything at all, which as a rule
science no longer even attempts to address. We're still working on
"what", if you want answers to "why" ask a philosopher or theologian.
--
-- MA Lloyd (mall...@io.com)
David Mitchell
>
>
>> fundamental level of reality, then how does _that_ work?
>
>mechanics, however, that mathematics just happens to be a little more
>complicated than with, say, Newtonian mechanics.
>
>If you learn the maths of quantum mechanics, then you understand that
>theory. Science can only model reality with (mathematical) theories;
>what's "really going on" is a question beyond science.
>
Isn't finding "What's really going on" the _point_ of science?
I'm not trying to be facetious; but to understand your point.
Are you saying that there are fundamental levels of reality which no
science, no matter how advanced, will ever discover?
If so, why do you think that?
MA Lloyd
>The only place that the transition time really shows up as an important
>factor is when you are calculating the spectral line width; the faster
>the transition the wider the line (although there are other contributions
>to line width, such as the thermal doppler broadening, that usually
>obscure this contribution).
Which is related to why you can't ever know exactly how long a transition
took. If you know a transition took place (that is you measure the energy
level difference of the initial and final states, it's actually *impossible*
to measure how long it took. One way to cast the uncertainty principle
is in energy and time, which is also where this spectral line broadening
comes from. People who tell you quantum processes (and tunnelling is probably
far more popular for this than transitions) are "instantaneous" don't know
what they are talking about.
David McKee
: David McKee wrote in message <88uhkq$985$1...@inn.jlab.org>...
: >David Mitchell (da...@edenroad.demon.co.uk) wrote:
[snippage]
: >: Whenever I've spoken to people about this, they just tell me that the
: >: only way to "understand" QM is to do the math, ignore common-sense and
: >: just calculate.
: >This is the thing to do, but it won't help you peace of mind.
: >
: >The only cheeply-, and macroscopicly-observeable, quantum behavior
: >that comes to mind is the polarization of light. Get several (3 or
: >more) sheets of polarizing material (dissect some cheep sun glasses),
: >and play with them.
: >
: >Do the experiment where a third polarizer inserted between crossed
: >polarizers results in _increased_ transmission. Think about it for
: >a while.
: >
: >It won't give you a sudden understanding of quantum mechanics, but it
: >should shake up you intuition.
:
: Actually, no. Polarisers allow light to pass through by re-emitting it at
: the other end. So a polariser of orientation | will pass light with any |
: component, for example /, |, or \. It wont pass _ because this has no
: component in the | direction. So two cross polarisers will not pass any
: light (except circularly polarised) because it cuts out all components, ie.
: | and _. A third / placed in the middle of the two will pass the component
: in the | direction, then / direction, then _ direction. At each filter, it
: will change the direction of the polarisation. So light in the _ direction
: wont pass because it hits the | polariser first. Light in the / direction
: will loose some intensity going through the | polariser. The resultant
: light is now | polarised. Encountering the / filter, it loses some
: intensity, and comes out / polarised. Encountering the _ filter, the now /
: polarised light will lose further intensity and come out _ polarised.
: Classically understood therefore a classical problem.
Hmm...when I choose the basis on which to measure (by choosing the
orientation of the polarizer) I affect not only the degree of
tranmission, but I also set the state of the system after the
observation. I can introduce componets in a direction that were
originally zero. Further, I can do this down to the level of a single
photon[1].
Sounds like a quantum phenomena to me.
You claim that polarizers work by re-emmision in the selected
polarization. But absorption and re-emmision is an explanation at the
photon level (rather than at the classical field level), and I do not
understand how this can fail to be quantum mechanical in nature.
For all this, I am willing to be corrected.
For Mr. Mitchell (even as his eyes glaze over): whether or not
polarization phenomena have a fully classical explanation[2], the
mathematics of polarizing filters take the same counter intuitive form
as those of qunatum mechanics.
Yours,
--
-- David McKee
-- dmc...@jlab.org
-- (757) 269-7492 (Office
[1] I've done this with microwaves and a condutive-bars type polarizer.
[2] Polarization is, of course, well defined in Maxwell's theory, and
there are classical explanations for (at least) some of the interesting
things that happen to polarized light in terms of anisotropic
properties of materials, however many (most? all?) polarizing phenomena
occur down to the level of a single photon.
Andrew Plotkin
> In article <38B3A7A6...@alcyone.com>, Erik Max Francis
> <m...@alcyone.com> writes
>>mechanics, however, that mathematics just happens to be a little more
>>complicated than with, say, Newtonian mechanics.
>>
>>If you learn the maths of quantum mechanics, then you understand that
>>theory. Science can only model reality with (mathematical) theories;
>>what's "really going on" is a question beyond science.
>
> Isn't finding "What's really going on" the _point_ of science?
Well, if you take that point of view, no. The point of science is "How do
things *behave*?"
But it's easy to shorten that to "What's really going on," and mean the
same thing. Especially when you try to pin down the difference. Are there
things which are "real", but which make no difference to how the universe
behaves? Well, you can say yes or no, but *that's* what's outside the
realm of science.
> I'm not trying to be facetious; but to understand your point.
>
> Are you saying that there are fundamental levels of reality which no
> science, no matter how advanced, will ever discover?
That's an ambiguous question.
Einsteinian physics was a layer under Newtonian physics, and we discovered
that. Quantum theory is a layer, well, slightly off to the side, and we
discovered that. If you're imagining some layer underneath quantum physics
and relativity, which is (unlike the others) somehow impenetrable and
opaque to scientific inquiry, then no, of course not. When we see it,
we'll investigate it.
On the other hand, our knowledge is finite, so there will always be
something we don't know. In that sense, there's something science can't
discover -- it's defined as what we'll discover *next*! :-) A moving
target, if you see what I mean.
So we say "Science isn't concerned with what's *really* going on" in that
sense. It's an impossible goal. What we've got are theories, which
all include the principle that a better theory may come along.
--Z
"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the
borogoves..."
Erik Max Francis
> In article <38B3A7A6...@alcyone.com>, Erik Max Francis
> <m...@alcyone.com> writes
>
> >If you learn the maths of quantum mechanics, then you understand that
> >theory. Science can only model reality with (mathematical) theories;
> >what's "really going on" is a question beyond science.
>
> Isn't finding "What's really going on" the _point_ of science?
In some sense, yes, but in other senses, no. Science is about modelling
and describing the Universe. It describes _what_, not _why_. When you
ask a _why_ question in science, they usually interpret you to be asking
how to explain the phenomena in terms of other, generally-accepted
scientific theories. If you ask _why_ in terms of a fundamental theory,
then the question is usually taken at face value and you get a shrug,
followed by, "That is not a question science can answer."
> I'm not trying to be facetious; but to understand your point.
>
> Are you saying that there are fundamental levels of reality which no
> science, no matter how advanced, will ever discover?
>
> If so, why do you think that?
I'm not saying that at all. It may well be true, but obviously we can't
know what's "really" going on. That is to say, if you _do_ have a
fundamental theory, you will have no way of knowing it. Theories can
never be proven; physics is about describing, not explaining. When you
can explain something in terms of more fundamental theories, you're
doing well. But that just leads to another layer of _why_ questions,
and you will _always_ run into a fundamental theory where there is
simply no _why_ that science can answer.
Your questions seemed to want to peel away the models and theories and
get at what's _really_ going on with quantum mechanics. The problem is
that those models and theories _are_ quantum mechanics -- that's what
physics is all about. Peel those away and you've got nothing left at
all.
--
Erik Max Francis | email m...@alcyone.com | icq 16063900
Alcyone Systems | web http://www.alcyone.com/max/ | q3a Product
San Jose, CA | languages en, eo | icbm 37 20 07 N 121 53 38 W
USA | 965.484 Ms p.L. | 313 days left | &tSftDotIotE
__
/ \ I go out with actresses because I'm not apt to marry one.
\__/ Henry Kissinger
David Allsopp
<da...@edenroad.demon.co.uk> writes
>I don't want to seem hopelessly old-fashioned; but surely there must
>_be_ a fundamental level of reality, at which things _actually_ happen,
>otherwise why are there "laws" of nature at all? (Now necessarily in
>the sense of "laws which fundamental entities consult in order to know
>how to behave", but even in the looser, implicit, "laws which appear to
>describe behaviour").
>
>
>fundamental level of reality, then how does _that_ work?
Well, lots of very famous scientists have been just as perplexed by this as you
are. From my Dictionary Of Scientific Quotations:
John von Neumann:
"In mathematics you don't understand things. You just get used to them."
Bertrand Russell]
"Mathematics may be defined as the subject in which we never know what we are
talking about, nor whether what we are saying is true."
Nils Bohr
"When it comes to atoms, language can be used only as in poetry. The poet too,
is not nearly so concerned with describing facts as with creating images"
The strange thing is, the maths works, and there isn't any easy way of
translating the maths into explanations/pictures/whatever that "make sense" to
people.
If you really want some elementary QM stuff explained non-mathematically about
as well as anyone has, go to your library/bookshop and get a copy of "QED: The
Strange Theory Of Light And Matter" by Richard Feynman.
Finally, one that caught my eye as I was looking up the other quotes:
Enrico Fermi
"Before I came here I was confused about this subject. Having listened to your
lecture, I am still confused. But on a higher level."
--
David Allsopp Houston, this is Tranquillity Base.
Remove SPAM to email me The Eagle has landed.
Charles R Martin
MA Lloyd wrote:
>
> David Mitchell <da...@edenroad.demon.co.uk> writes:
>
> >I don't want to seem hopelessly old-fashioned; but surely there must
> >_be_ a fundamental level of reality, at which things _actually_ happen,
> >otherwise why are there "laws" of nature at all? (Now necessarily in
> >the sense of "laws which fundamental entities consult in order to know
> >how to behave", but even in the looser, implicit, "laws which appear to
> >describe behaviour").
>
> >In other words, we're back to asking why mathematics works so well.
>
> Well in a sense this is hopelessly old fashioned. It's not really a
> question of physics at all, but one of philosophy, you are probably
> looking for things like the ideal forms or the first cause, or questions
> about why it's possible to understand anything at all, which as a rule
> science no longer even attempts to address. We're still working on
> "what", if you want answers to "why" ask a philosopher or theologian.
Actually, though, it's a really *interesting* question. Consider for example
that differential equations with closed-form solutions apparently occur with
probability zero, while the other kind with prob. 1. How did it happen that
the closed-form ones so often match reality? (In essence, it isn't so much of
a surprise, IMHO, that some parts of the real world are chaotic as it's a
surprise that any of it *isn't* chaotic.)
--
================ Charles R Martin crma...@indra.com =================
"Evil does not naturally dwell in the world, in events, or in people. Evil is
a by-product of forgetfulness, laziness, or distraction: it arises when we
lose
sight of our true aim in life." -- Epictatus
David Mitchell
<geoffre...@grc.nasa.gov> writes
>In article <tOFciUA+...@edenroad.demon.co.uk> David Mitchell,
>da...@edenroad.demon.co.uk writes:
>>...
>>How _do_ electrons change from shell to shell in zero time?
>
>I can answer this one: they don't.
>
Thank you.
!*&$%! popular science books!
David Mitchell
<aber...@princeton.edu> writes
>In article <knZOoDAO...@edenroad.demon.co.uk>, David Mitchell wrote:
>>
>>
>>If you're suggesting that perhaps mathematics is in some way the
>>fundamental level of reality, then how does _that_ work?
>
>
>In QM, say, we have our fundamental entity, the state vector, we
>have equations for how it evolves, and we have equations for what
>we can measure. And, most importantly, the answers we get
>correspond to what we measure.
>
>Sound pretty good to me.
>
I think it's still avoiding the issue. Please excuse my lack of
precision, I'm only a computer programmer ;-) Be gentle with me.
An example of the kind of thing I mean is the pressure exerted by a gas.
This can be described by nice, classical equations; but at heart it's
due to the random bumping of particles against the container walls.
It's only the huge number of them which makes the maths work.
This is the kind of thing I mean, the maths here works because of some
explicable property of the system (large numbers of things); in other
situations it's the 3-D properties of space which make the equations
turn out the way they do.
It seems to me that whenever the maths "works", whatever it's describing
must, at heart, have a "reason" for behaving in ways which maths can
describe (for example, by virtue of being part of a system of very
similar objects, or by virtue of describing an interaction which occurs
in n-dimensional space-time).
Are these fundamental attributes of physics known?
Erik Max Francis
> An example of the kind of thing I mean is the pressure exerted by a
> gas.
>
> This can be described by nice, classical equations; but at heart it's
> due to the random bumping of particles against the container walls.
> It's only the huge number of them which makes the maths work.
>
> This is the kind of thing I mean, the maths here works because of some
> explicable property of the system (large numbers of things); in other
> situations it's the 3-D properties of space which make the equations
> turn out the way they do.
This is a good example, because it's a case of being able to describe a
classical theory in terms of another, more fundamental, classical
theory.
So perhaps some high-level quantum phenomena are describable in terms of
more fundamental theories (I think that it could be said that this is
already the case, with quantum mechanics fitting both bills). But why
would you think that those more fundamental theories would be classical,
or at least any simpler than quantum mechanics itself?
You see what I'm getting at? If some quantum phenomena are explicable
in terms of a more fundamental theory, that more fundamental theory
could be just as, if not more, counterintuitive than quantum mechanics.
--
Erik Max Francis | email m...@alcyone.com | icq 16063900
Alcyone Systems | web http://www.alcyone.com/max/ | q3a Product
San Jose, CA | languages en, eo | icbm 37 20 07 N 121 53 38 W
USA | 965.527 Ms p.L. | 312 days left | &tSftDotIotE
__
/ \ Men and women, women and men. It will never work.
\__/ Erica Jong
Joseph Hertzlinger
<da...@edenroad.demon.co.uk> wrote:
>How _do_ atoms absorb and emit photons which have wavelengths thousands
>of times greater than their diameter?
Radio antennas can absorb and emit radio waves which have wavelengths
thousands of times greater than their diameter.
Frank Palmer
Da> I don't want to seem hopelessly old-fashioned; but surely there must
Da> _be_ a fundamental level of reality, at which things _actually_
Da> happen, otherwise why are there "laws" of nature at all? (Now
Da> necessarily in the sense of "laws which fundamental entities consult in
Da> order to know how to behave", but even in the looser, implicit, "laws
Da> which appear to describe behaviour").
There is.
However, the fundamental level of reality for really-small
objects does not consist of objects like the ones we are used
to.
Particles have "spin." This spin can be tested in any
direction, and for whole classes of particles is either +1/2
(times Planck's constant) or -1/2 in the direction for which
you test. If you get +1/2 for North, you will get -1/2 for
South.
And you will *probably*, although not certainly, get +1/2 for
north-northwest. But you will never get any number between
those values.
___ Blue Wave/QWK v2.12
--
Frank Palmer
flpa...@ripco.com
Aaron Bergman
>
>An example of the kind of thing I mean is the pressure exerted by a gas.
>
>This can be described by nice, classical equations; but at heart it's
>due to the random bumping of particles against the container walls.
>It's only the huge number of them which makes the maths work.
Why do molecules bump into the walls? After all, atoms are mostly
empty space, so why doesn't it just go right through the wall?
>
>This is the kind of thing I mean, the maths here works because of some
>explicable property of the system (large numbers of things); in other
>situations it's the 3-D properties of space which make the equations
>turn out the way they do.
The equations are just simplifications of other equations. It's
true that the thermodynamic equations come from statistical
properties of large numbers of molecules, but we're still applying
statistics to some set of equations. In fact, to get all this to
work, one really needs quantum statistical mechanics -- classical
statistical mechanics just doesn't work (without some fudging --
the Gibbs factor) and can fail quite spectacularly (the blackbody
curve).
>
>It seems to me that whenever the maths "works", whatever it's describing
>must, at heart, have a "reason" for behaving in ways which maths can
>describe (for example, by virtue of being part of a system of very
>similar objects, or by virtue of describing an interaction which occurs
>in n-dimensional space-time).
>
>Are these fundamental attributes of physics known?
Some people think it might be string theory. Right now, the most
fundamental tested theories we have are quantum field theory (more
specifically, the standard model) and general relativity.
We know that these cannot be the most fundamental theories,
howevever, because it turns out that they are incompatible. So,
we're still looking for a most fundamental set of equations.
But it's not going to be little balls colliding.
David Mitchell
<m...@alcyone.com> writes
>David Mitchell wrote:
>
>
>You see what I'm getting at? If some quantum phenomena are explicable
>in terms of a more fundamental theory, that more fundamental theory
>could be just as, if not more, counterintuitive than quantum mechanics.
>
It could well be; but I suspect that whatever is at the heart of physics
will ultimately be simple in operation, if not in consequence.
I have no reason to think this, BTW.
pervect
> Fine.
>
> I can do that (in theory, given a few years of study ;-) but the
> question I'm asking is: is the maths describing reality or defining it?
I'd say that the math describes reality. The current situation is we've
got a couple of mathematical systems which describe reality very well,
each in their own domains, but they aren't fully compatible with each
other. (QM and GR).
It's pretty clear IMO. that math doesn't define reality - one can write
down equations, and they're just equations, they're not reality.
> Okay, so I'm reasonably happy to accept that little charged pointy
> things aren't whizzing around a charged nuclear thing, but is anything
> moving at all? Is the electron just a mathematical abstraction, in
> which case is it only information that's moving, and if so how does
> _that_ work? How is this information stored?, transferred?, and why?
> If it's not just information, then what is it? If it's something
> physical then how does _that_ move instantaneously?
Well, the most useful advice I ever got on the subject is - "it's all
just linear algebra".
Schrodinger's wave equation may not seem like linear algebra, at first.
But it turns out that you can describe functions in term of a vector
space, so that the matrix formulation of quantum mechanics (Heisenberg)
and the approach using functions and differential eq's (Schrodinger) can
be unified in one formalism (vector spaces).
There's a lot of different books out there and probably people better
qualified to give advice on them than I am. Personally I found the
combination of Messiah's book on quantum mechanics, together with an
auxiliary math book (Mathematics of Classical and Quantum Physics I
think) to be the most helpful.
If you want a possibly confusing overview (of non relativistic quantum
mechanics) you can represent the state of a quantum mechanical system in
a "pure state" as a unit vector in a vector space (possibly infinite
dimensional). And one needs probability theory as well, to be able to
represent the states of quantum systems that are not in a "pure state".
Observables also enter the picture, they're what you need to go from the
description of the state of a system to get results that one
"measures". What constitutes "measurement" is an interesting question
as well, one that's usually simple in practice but rather complicated in
theory.....
As to why you do this, the answer is that it works. It's not what you'd
expect. One thing that's particularly different about QM is that the
representation of two particles requires one to use the "tensor product"
of the vector spaces of each individual particle. Taken as a
mathematical abstraction this doesn't sound bad, but it means that the
vector space grows exponentially with the number of particles. If one
has only one particle, it may take, for example, two complex numbers to
describe something simple like it's spin. But it takes 2^n complex
numbers to describe the spins of n particles, i.e. 4 complex numbers for
2 particles, 8 for 3, 16 for 4, etc.
This makes life difficult as far as computation goes from fundamental
principles. It also plays havoc with one's intuition (well, that may
depend on the individual). But it also allows for some interesting
results, such as quantum computing.
This may not really answer your question - I'd say that ultimately there
is no "why" that we currently understand, there are simply things that
work, and things that don't work. You are probably suffering a conflict
between your intuitive models and what QM requires. This is perfectly
normal, and it takes a long time and a lot of effort to begin to get
even the beginning of an intuition for how QM works. Sorry, but that's
the way it is.
As far as "reality" goes, different "interpretations" of quantum
mechanics identify different parts of the math as being "real". Usually
people pick either the wavefunctions (the vectors), or the observables
(things that can actually be measured) as being good candidates for
something that's "real". It's sort of a dead end question, as one can
wind up with a self consistent philosophy in several different ways.
Try them all on, and pick the one you like (you don't even have to pick
the same interpretation all the time, you can pick different ones for
different applications, sometimes one interpretation is more convenient
than another.)
Brendan Hall
David Mitchell wrote in message <$etYmGAa...@edenroad.demon.co.uk>...
>>>
>>>
>>>If you're suggesting that perhaps mathematics is in some way the
>>>fundamental level of reality, then how does _that_ work?
>>
>An example of the kind of thing I mean is the pressure exerted by a gas.
>
>This can be described by nice, classical equations; but at heart it's
>due to the random bumping of particles against the container walls.
>It's only the huge number of them which makes the maths work.
>
>This is the kind of thing I mean, the maths here works because of some
>explicable property of the system (large numbers of things); in other
>situations it's the 3-D properties of space which make the equations
>turn out the way they do.
>
>It seems to me that whenever the maths "works", whatever it's describing
>must, at heart, have a "reason" for behaving in ways which maths can
>describe (for example, by virtue of being part of a system of very
>similar objects, or by virtue of describing an interaction which occurs
>in n-dimensional space-time).
>
>Are these fundamental attributes of physics known?
Some insight may be gleaned from analysing what maths is. Maths is simply a
language. Its stilted, expansive, difficult to learn, but it is precise and
transferrable. Why does maths work so well? Because its precision is
transferrable. Also, there is liberty to invent maths as concepts arise
that don't fit the current inventory.
Other languages are not as precise. However, concepts can go far wider than
those in maths. For instance, how can you put a numeric value on love. Or,
has anyone seen any mathematical humor? (If you have, please send me some.)
Almost by definition, the ambiguity of humor makes it non-mathematical.
On the point of precision, how many people understand the word love in
exactly the same way? Ancient greek was more precise by describing love in
5 different words. These included selfless love, affection, passion, sexual
attraction, and object valuing. In English, we love our children, love our
dog, love a book etc. We would be ready to risk our life to save our child
from harm, but there are few that would do the same for a favorite book.
Thus is the imprecision of English, and most other languages.
Maths IMO is therefore not the fundamental of the universe, it is simply the
language that we have adopted to precisely compile the understanding of many
people. It would be interesting to speculate (as did Catherine Asaro in The
Last Hawk) an alien species (or culture) that is technologically advanced
which uses an entirely different communication means and therefore
understands the universe entirely differently. Also, how has our history of
trade underpinned the development of mathematics? It certainly provided the
most fundamental concept in mathematics, that of equality. Is there a way
of describing without comparisons?
Just some thoughts
Brendan
pervect
>
> In article <tOFciUA+...@edenroad.demon.co.uk> David Mitchell,
> da...@edenroad.demon.co.uk writes:
> >...
> >How _do_ electrons change from shell to shell in zero time?
>
> I can answer this one: they don't.
>
> (aka a "quantum jump") does *not* take zero time.
Didn't this come from non-relativistic quantum theory?
Timothy Little
>
>Actually, though, it's a really *interesting* question. Consider for example
>that differential equations with closed-form solutions apparently occur with
>probability zero, while the other kind with prob. 1. How did it happen that
>the closed-form ones so often match reality? (In essence, it isn't so much of
>a surprise, IMHO, that some parts of the real world are chaotic as it's a
>surprise that any of it *isn't* chaotic.)
That one's pretty easy, really. We make models that we can solve. I
have no doubt that there are an infinite number of models that are
capable of describing observed physical phenomena. Models that give
useful information (e.g. closed-form solutions) are preferentially
selected.
An interesting observation in support of this is that with the advent of
high-speed computational devices, models tend to have uglier solutions.
Besides, any given measure space of differential equations is rather
arbitrary. If you introduce a weighting for simplicity of syntactic
form (to model human preferences), you would no doubt find that the
probability of a closed-form solution is no longer zero. After all,
dx/dt=0 is about the simplest possible differential equation, and it
certainly has a closed-form solution.
One interesting thought I haven't seen elsewhere is that the *true* laws
of nature, when expressed in mathematical form, may form an infinite
irreducible system. Not really a pleasant thought for a scientist...
Considering that infinite formal systems infinitely outnumber finite
systems, you would expect any given system to be infinite.
Not that I really believe this, but it would explain why we haven't got
a Theory of Everything yet. Is there any real reason to believe that
Nature is finite in complexity? If so, why should it be *that* level of
complexity, and no other?
--
Tim Little
Geoffrey A. Landis
perv...@netscape.com writes:
>"Geoffrey A. Landis" wrote:
>> I don't know how this one got into the popular culture, but a transition
>> (aka a "quantum jump") does *not* take zero time.
>
>Didn't this come from non-relativistic quantum theory?
No.
The theory that tells you that a transition from energy level Ee to
energy level Ef releases a photon of energy (Ei-Ef) comes from
non-relativistic quantum theory. However, NOWHERE in this theory is an
assumption that this transition takes zero time.
(there is, however, a result to the effect that no matter how you
measure, you will never measure the energy of the system in the
intermediate state. This doesn't mean that the atom spends zero time in
the intermediate state, however; it just means that if you measure when
the atom is in the intermediate mixed state |i>+|f> the measurement will
either be Ei or Ef.)
--
Geoffrey A. Landis
Watch for _Mars Crossing_, coming from Tor Books, fall 2000
http://www.sff.net/people/geoffrey.landis