Gravity?

[Bill]

Here's an interesting tidbit:

https://astronomy.com/news/2018/05/the-case-against-dark-matter

It seems possible that gravity may be an effect of inertia rather than a
fundamental force - maybe.

Bill

[Bob Casanova]

On Tue, 08 Dec 2020 15:42:30 -0600, the following appeared
in talk.origins, posted by Bill <fre...@gmail.com>:

Per GR, gravity isn't a *force" at all, at least in the
sense of a particle-mediated effect like EM.
--

Bob C.

"The most exciting phrase to hear in science,
the one that heralds new discoveries, is not
'Eureka!' but 'That's funny...'"

- Isaac Asimov

[jillery]

The cited article makes no mention of "inertia" or its effects. You're
confused.

The article itself is quite speculative, and provides no evidence that
Erik Verlinde's Entropic Gravity actually answers any questions about
dark matter or dark energy or General Relativity.

--
You're entitled to your own opinions.
You're not entitled to your own facts.

[erik simpson]

Another interesting description of Verlinde's work (not just this
later one) in here:

https://www.quantamagazine.org/erik-verlindes-gravity-minus-dark-matter-20161129/

I am often irritated at references to "popular" articles, and I can only offer the
following excuse; I am ignorant of the formalism of string theory, and have no
hope of following Verlinde's work. Appparently even experts in the field have difficulty
understanding it. If it pans out, it may represent the first useful application of string
theory to the real world. Or not.

[Athel Cornish-Bowden]

On 2020-12-09 01:41:36 +0000, jillery said:

> On Tue, 08 Dec 2020 15:42:30 -0600, Bill <fre...@gmail.com> wrote:
>
>> Here's an interesting tidbit:
>>
>> https://astronomy.com/news/2018/05/the-case-against-dark-matter
>>
>> It seems possible that gravity may be an effect of inertia rather than
>> a>fundamental force - maybe.
>>
>> Bill
>
>
> The cited article makes no mention of "inertia" or its effects. You're
> confused.

What else is new?

>
> The article itself is quite speculative, and provides no evidence that
> Erik Verlinde's Entropic Gravity actually answers any questions about
> dark matter or dark energy or General Relativity.


--

Athel -- British, living in France for 34 years

[jillery]

On Tue, 8 Dec 2020 20:18:44 -0800 (PST), erik simpson
<eastsi...@gmail.com> wrote:

>On Tuesday, December 8, 2020 at 5:45:28 PM UTC-8, jillery wrote:
>> On Tue, 08 Dec 2020 15:42:30 -0600, Bill <fre...@gmail.com> wrote:
>>
>> >Here's an interesting tidbit:
>> >
>> >https://astronomy.com/news/2018/05/the-case-against-dark-matter
>> >
>> >It seems possible that gravity may be an effect of inertia rather than a
>> >fundamental force - maybe.
>> >
>> >Bill
>> The cited article makes no mention of "inertia" or its effects. You're
>> confused.
>>
>> The article itself is quite speculative, and provides no evidence that
>> Erik Verlinde's Entropic Gravity actually answers any questions about
>> dark matter or dark energy or General Relativity.
>>
>

>Another interesting description of Verlinde's work (not just this
>later one) in here:
>
>https://www.quantamagazine.org/erik-verlindes-gravity-minus-dark-matter-20161129/
>
>I am often irritated at references to "popular" articles, and I can only offer the
>following excuse; I am ignorant of the formalism of string theory, and have no
>hope of following Verlinde's work. Appparently even experts in the field have difficulty
>understanding it. If it pans out, it may represent the first useful application of string
>theory to the real world. Or not.

Your cited article is much better, as it discusses all of the evidence
for dark matter, not just stellar velocities within galaxies. Thank
you for citing it.

There are galaxies which appear to not have any dark matter. ISTM
these would be evidence against Verlinde's hypothesis. However, it
may turn out that's not the case:

<https://www.forbes.com/sites/startswithabang/2020/12/01/galaxies-without-dark-matter-really-do-exist-new-study-shows-exactly-how/?sh=2a7ed2755775>

<https://tinyurl.com/y2lnbnfp>

How Verlinde thinks dark energy, which is repulsive, is supposed to
account for dark matter, which is attractive, and how he accounts for
the evidence for dark energy in the first place, as well as how he
eliminates GR's warping of spacetime, are all beyond me. I suffer a
similar problem as you do; almost all of string theory is beyond my
pay grade. The answers to my questions might be hiding within those
tiny loops of quatum energy.

[Jonathan]

The key statement in the article you posted is...

"To make his case, Verlinde has adopted a radical perspective
on the origin of gravity that is currently in vogue among
leading theoretical physicists. Einstein defined gravity as
the effect of curves in space-time created by the presence
of matter. According to the new approach, gravity is an
*emergent phenomenon*."



The term 'emergent' has a specific definition now, not just
the ...generic meaning used to describe something new.

The technical definition of emergence means something that
has been created without an apparent cause.

Like a system tendency, the system must exist first, but the
tendency can't possibly be traced back to any specific cause
since it's the result of the entire system and its complex
interactions, non-linear behavior and highly random interactions.

Emergence is an *effect without an identifiable cause*.

Hence the mystery of the source of gravity. It has no
identifiable source, as it's emergent.

Some of the confusion over gravity may the fact that
some 70% of the energy of the universe is repulsive
not attractive, and also is still a complete mystery.
Hence the name, dark energy.

But the following paper introduces an idea for the
emergence of dark energy. An attractor solution
not unlike the analogy of when you compress something
it can get hotter.

When the universe reaches a critical point, dark energy
goes from negligible to dominant. Such as the critical
point of transitioning from a radiation to matter dominated
universe, the dark energy at that point emerges to take over
the future behavior of the universe, a second period of
expansion.

Emergence also addressed the coincidence and fine tuning
problems for the same reasons those are addressed in
Darwinian evolution by emergence. Self organization
creates *its own* ideal conditions, no mystery as
to why the conditions at the start of the universe
were 'just right' to produce the life giving universe
we see today.

And also the fine-tuning problem is addressed as emergence
is an evolutionary process, a problem solving process that
generates the better solution, or fine-tunes the system
as it goes.


From the Director of the Theoretical Physics Dept at Princeton
and a founder of modern inflationary theory.


A Quintessential Introduction into Dark Energy
By Paul J. Steinhardt
Department of Physics


"In this scenario, the coincidence problem is beautifully
addressed. Why did the Universe begin to accelerate just
as humans started to evolve? Cosmic acceleration and human
evolution are both linked to the onset of matter domination.

The k-essence component has the property that it only behaves
as a negative pressure component after matter radiation equality
so that it can only overtake the matter density and induce
cosmic acceleration after the matter has dominated the Universe
for some period, at about the present epoch.

And, of course, human evolution is linked to matter domination
because the formation of planets, stars, galaxies and
large-scale structure only occurs after the beginning of the
matter-dominated epoch."
http://physics.princeton.edu/~steinh/steinhardt.pdf


Evolution is a universal process, biological evolution
merely a special case. Although a higher example.

Everything you wanted to know about emergence is below, in
abstract form so it can be applied universally.

As the concept of emergence, and effect, is responsible for all
visible order, even gravity. Effects drives causes, not the
other way around.

Whether for life, the universe and everything else.


Emergence Taxonomy
https://arxiv.org/ftp/nlin/papers/0506/0506028.pdf





















A Quintessential Introduction to Dark Energy
http://physics.princeton.edu/~steinh/steinhardt.pdf

























--
https://twitter.com/Non_Linear1

[Bill]

I find the whole collection of speculation about the universe to be
fascinating, especially when the proposed answers lead to more questions.
Dark matter is one of those. It was proposed as an explanation for motions
that were otherwise problematic. It's an ad hoc kind of thing. It may exist
of course, but it could also be simple fudging. I certainly don't know but
it appears that no one else does either.

Bill

[Bill]

jillery wrote:

> On Tue, 08 Dec 2020 15:42:30 -0600, Bill <fre...@gmail.com> wrote:
>
>>Here's an interesting tidbit:
>>
>>https://astronomy.com/news/2018/05/the-case-against-dark-matter
>>
>>It seems possible that gravity may be an effect of inertia rather than a
>>fundamental force - maybe.
>>
>>Bill
>
>
> The cited article makes no mention of "inertia" or its effects. You're
> confused.

No need to mention inertia since I offer it as a alternative to a "force" of
gravity. We know things move and we can calculate how with no reference to
other forces. Gravity is how we describe effects, not causes.

[jillery]

My experience is good answers usually lead to more and different

questions.


>Dark matter is one of those. It was proposed as an explanation for motions
>that were otherwise problematic. It's an ad hoc kind of thing.

To the best of my recollection, everything I have read about dark
matter explicitly identifies the term as a placeholder for phenomena
without an explanation. For all we know, it might not even be matter.
For example, Neil Tyson prefers to use "dark gravity" in order to
avoid that presumption.

>It may exist
>of course, but it could also be simple fudging. I certainly don't know but
>it appears that no one else does either.
>
>Bill

The problem with most MOND hypotheses is, when they are adjusted to
work for stellar velocities in galaxies, they don't fit the data for
even larger distances. Apparently Verlinde's hypothesis overcomes
that problem, but as I said, I have no idea how.

[jillery]

On Wed, 09 Dec 2020 12:11:52 -0600, Bill <fre...@gmail.com> wrote:

>jillery wrote:
>
>> On Tue, 08 Dec 2020 15:42:30 -0600, Bill <fre...@gmail.com> wrote:
>>
>>>Here's an interesting tidbit:
>>>
>>>https://astronomy.com/news/2018/05/the-case-against-dark-matter
>>>
>>>It seems possible that gravity may be an effect of inertia rather than a
>>>fundamental force - maybe.
>>>
>>>Bill
>>
>>
>> The cited article makes no mention of "inertia" or its effects. You're
>> confused.
>
>No need to mention inertia since I offer it as a alternative to a "force" of
>gravity. We know things move and we can calculate how with no reference to
>other forces. Gravity is how we describe effects, not causes.

So you know your comments have nothing to do with your cited article.
It would have helped to have said so in the first place.

>> The article itself is quite speculative, and provides no evidence that
>> Erik Verlinde's Entropic Gravity actually answers any questions about
>> dark matter or dark energy or General Relativity.
>>

[Bill]

Someone mentioned my mention of inertia which I had cited as a possible
conclusion if there is no force of gravity. It's relevant but maybe too
subtle ...

Bill

[jillery]

On Wed, 09 Dec 2020 13:30:24 -0600, Bill <fre...@gmail.com> wrote:

>jillery wrote:
>
>> On Wed, 09 Dec 2020 12:11:52 -0600, Bill <fre...@gmail.com> wrote:
>>
>>>jillery wrote:
>>>
>>>> On Tue, 08 Dec 2020 15:42:30 -0600, Bill <fre...@gmail.com> wrote:
>>>>
>>>>>Here's an interesting tidbit:
>>>>>
>>>>>https://astronomy.com/news/2018/05/the-case-against-dark-matter
>>>>>
>>>>>It seems possible that gravity may be an effect of inertia rather than a
>>>>>fundamental force - maybe.
>>>>>
>>>>>Bill
>>>>
>>>>
>>>> The cited article makes no mention of "inertia" or its effects. You're
>>>> confused.
>>>
>>>No need to mention inertia since I offer it as a alternative to a "force"
>>>of gravity. We know things move and we can calculate how with no reference
>>>to other forces. Gravity is how we describe effects, not causes.
>>
>>
>> So you know your comments have nothing to do with your cited article.
>> It would have helped to have said so in the first place.
>>
>>
>>>> The article itself is quite speculative, and provides no evidence that
>>>> Erik Verlinde's Entropic Gravity actually answers any questions about
>>>> dark matter or dark energy or General Relativity.
>>>>
>>
>
>Someone mentioned my mention of inertia which I had cited

....no you did not...


>as a possible conclusion


....no it is not...

>if there is no force of gravity. It's relevant but maybe too
>subtle ...
>
>Bill

[William Hyde]

For once we agree. It was rather ad hoc. But that's not a bad way to start. When observation contradicts theory we must try to determine why. The first stab is often wrong, sometimes has no truth in it, sometimes it does.

When I first read about "wrong" galactic rotation rates the ad-hoc explanation was a "halo" of dim stars in the halo of every galaxy. Dim matter instead of dark matter, so to speak. This turned out to be wrong, but led to the idea of a specific form of dark matter, massive compact halo objects. Which, as it turns out, also don't exist. At least in enough quantity to solve our problem.

But in addition to messing up galactic rotation *something* is performing more gravitational lensing than it should. And there is lensing where there is no, or very little, baryonic matter. So dark matter is needed for another reason, which makes it a little less ad hoc.

Still, as in the case of the neutrino, there will always be a whiff, more than a whiff, of ad-hocery until we find the stuff. Or prove it doesn't exist. My money is on supersymmetric particles, but they haven't been detected yet either, and may also not exist. Though they do make the math look nice.

Luckily it's someone else's problem. If I live long enough I may learn the solution. Some problems take a long, long, time, though.

William Hyde