New Theory of Gravity?

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New Theory of Gravity?

#1  Postby Arnold Layne » Nov 15, 2016 10:08 am

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Re: New Theory of Gravity?

#2  Postby newolder » Nov 15, 2016 10:27 am

It's an updated version of Modified Newtonian Dynamics (aka MOND) theory that has a few problems ("highly incomplete"), according to yer man and blogger Lubos Motl...

ETA from the blog:
...
It seems conceivable to me that some form of MOND is right. And assuming MOND is right, it seems rather likely to me that dark energy and dark matter effects must be explained simultaneously. And those explanations are likely to have something to do with the "spacetime is entanglement" ideas because "the spacetime is entanglement" and this fact must be consistent with everything that the science of gravity may study. In this sense, Erik Verlinde's paper could be a sketch of something that is on the right track. However, I would bet that the bulk of those 51 pages are just wrong and will have to be replaced.
...
Last edited by newolder on Nov 15, 2016 10:35 am, edited 1 time in total.
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Re: New Theory of Gravity?

#3  Postby Arnold Layne » Nov 15, 2016 10:31 am

Thanks!
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Re: New Theory of Gravity?

#4  Postby tuco » Nov 15, 2016 8:35 pm

There is some weird stuff going on here .. I was gonna post Motl!

By the way, if you care, Frank Wilczek has attended a talk by Erik Verlinde and his words were harsher than mine.


That is hard to believe ;)
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Re: New Theory of Gravity?

#5  Postby Scar » Nov 16, 2016 9:32 am

Anyone got an Eli5 or Eli10 for me?
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Re: New Theory of Gravity?

#6  Postby tuco » Nov 16, 2016 4:58 pm

Something like .. space(-time) is like rubber sheet and when you place a bowling ball on such sheet it curves?

Eli10 probably is: Mr Motl is a bit upset that Mr Verlinde got 6.5 millions of euros in some grant ;)
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Re: New Theory of Gravity?

#7  Postby Pulsar » Nov 17, 2016 11:58 am

Sean Carroll talks about Verlinde's paper in a facebook video:
http://www.preposterousuniverse.com/blog/2016/11/11/talking-about-dark-matter-and-dark-energy/

He first talks about the supernova analysis by Nielsen, Guffanti, and Sarkar (on which 5th ape started this thread). As a nitpick, I disagree that the 1998 supernova papers came as a shock. It didn't; by that time there was already compelling indirect evidence for the existence of dark energy, see for example this 1995 paper from Lawrence Krauss.

His opinion on Verlinde's paper starts around 7.5 minutes into the video. I wish he'd talked more about the underlying principle (which alas I don't understand), but I do agree with his main criticism: all the proponents of an alternative form of gravity beyond standard GR always focus on the rotation curves of spiral galaxies, which is by far the weakest evidence for dark matter. The best evidence are the specific temperature fluctuations in the cosmic microwave background, which Carroll explains nicely. If Verlinde or anyone else is able to explain the CMB fluctuations without dark matter and dark energy, then the scientific community will pay attention. Until then, these will remain fringe ideas. Right now, Verlinde has only a toy model; interesting enough to keep an eye on, but he has a lot more work to do if he wants to convince the majority of physicists.

Oh, and the relevant xkcd cartoon:

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A new theory of Gravity

#8  Postby the_5th_ape » Nov 19, 2016 7:12 am

A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by invoking dark matter. Prof. Erik Verlinde, renowned expert in string theory at the University of Amsterdam and the Delta Institute for Theoretical Physics, published a new research paper today in which he expands his groundbreaking views on the nature of gravity.

In 2010, Erik Verlinde surprised the world with a completely new theory of gravity. According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.


Gravity is in dire need of new approaches like the one by Verlinde, since it doesn't combine well with quantum physics. Both theories, crown jewels of 20th century physics, cannot be true at the same time. The problems arise in extreme conditions: near black holes, or during the Big Bang. Verlinde says, "Many theoretical physicists like me are working on a revision of the theory, and some major advancements have been made. We might be standing on the brink of a new scientific revolution that will radically change our views on the very nature of space, time and gravity."

http://phys.org/news/2016-11-theory-gravity-dark.html
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Re: A new theory of Gravity

#9  Postby newolder » Nov 19, 2016 9:37 am

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Re: New Theory of Gravity?

#10  Postby John Platko » Oct 31, 2017 7:01 pm

I've recently become interested in this. Here's Dr. Erik Verlinde explaining what's up.



And this is interesting:

I like to imagine ...
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Re: New Theory of Gravity?

#11  Postby DavidMcC » Nov 01, 2017 12:10 pm

Pulsar wrote:Sean Carroll talks about Verlinde's paper in a facebook video:
http://www.preposterousuniverse.com/blog/2016/11/11/talking-about-dark-matter-and-dark-energy/

He first talks about the supernova analysis by Nielsen, Guffanti, and Sarkar (on which 5th ape started this thread). As a nitpick, I disagree that the 1998 supernova papers came as a shock. It didn't; by that time there was already compelling indirect evidence for the existence of dark energy, see for example this 1995 paper from Lawrence Krauss.

His opinion on Verlinde's paper starts around 7.5 minutes into the video. I wish he'd talked more about the underlying principle (which alas I don't understand), but I do agree with his main criticism: all the proponents of an alternative form of gravity beyond standard GR always focus on the rotation curves of spiral galaxies, which is by far the weakest evidence for dark matter. The best evidence are the specific temperature fluctuations in the cosmic microwave background, which Carroll explains nicely. If Verlinde or anyone else is able to explain the CMB fluctuations without dark matter and dark energy, then the scientific community will pay attention. Until then, these will remain fringe ideas. Right now, Verlinde has only a toy model; interesting enough to keep an eye on, but he has a lot more work to do if he wants to convince the majority of physicists.

...

I thought the strength of the dark matter hypothesis lies not in one particular gap or other that it fills in the application of the theory of gravity, but in the fact that it works for all the gaps at once.
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Re: New Theory of Gravity?

#12  Postby newolder » Mar 29, 2018 12:57 pm

Dark matter probably exists because there's a galaxy without any: https://physicsworld.com/a/galaxy-devoi ... tronomers/
A distant galaxy apparently devoid of dark matter has been discovered by astronomers in the US, Canada and Germany. Paradoxically, they believe their finding could strengthen the case for dark matter as the source of the universe’s “missing mass” – because alternative theories that modify gravity should apply to all galaxies. Other researchers, however, remain unconvinced.
...

The observations are described in Nature.


Lubos Motl also weighs in at his blog The reference frame
...

That's why I still find it much more likely than 50% – and the probability has surely approached a bit closer to 100% today – that dark matter of some kind is the right explanation of all these phenomena. That's why I think that her MOND activities are just another reason to consider Sabine Hossenfelder a crackpot and Erik Verlinde a guy who became a fringe pop-science theorist. That's why I remain unexcited by frequent mails from a David that I am receiving and that claim that a guy named Milgrom is a Copernicus of our century or something like that. Most likely, all these people are just elaborating upon a concept that has been ruled out and that is getting increasingly clearly falsified.

...
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