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Fraser
2016-Nov-16, 11:10 PM
A Dutch theoretical physicist has come up with a new way of seeing gravity that doesn't require the need to invent dark matter.
The post New Theory of Gravity Does Away With Need for Dark Matter (http://www.universetoday.com/131901/new-theory-of-gravity-does-away-with-need-for-dark-matter/) appeared first on Universe Today (http://www.universetoday.com).


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Trebuchet
2016-Nov-17, 01:04 AM
This (my bold)

Entropy is a measure of disorder in a system or put another way, the number of different microscopic states a system can be in. One of the coolest descriptions of entropy I’ve heard has to do with the heat our bodies radiate. As that energy dissipates in the air, it creates a more disordered state around us while at the same time decreasing our own personal entropy to ensure our survival. If we didn’t get rid of body heat, we would eventually become disorganized (overheat!) and die.
sounds quite wrong to me.

moozoo
2016-Nov-17, 02:30 AM
Any experts on here willing to give feedback on the paper (not the article...)
My understanding is that the reaction to his first paper was "thats interesting wonder what it means". i.e. it was seen as an interesting observation. I don't recall any serious attack on it.
Is it a similar situation with his new paper.

Cougar
2016-Nov-17, 02:44 PM
Any experts on here willing to give feedback on the paper (not the article...)....

Before I look at the paper, I note the article says:



I’ll be the first one to say how complex Verlinde’s concept is, wrapped in arcane entanglement entropy, tensor fields and the holographic principal, but the basic idea, that gravity is not a fundamental force, makes for a fascinating new way to look at an old face.



In other words, it sounds unintelligible. I don't find that "fascinating."

cjameshuff
2016-Nov-17, 03:18 PM
"In a word, gravity is a consequence of entropy and not a fundamental force."

This seems falsified by even the earliest measurements of gravity. It's a function of mass-energy, not entropy. The majority of gravity on galactic scales is due to dark matter...it's not some minor correction factor, it's the majority of the mass. If this was actually due to entropy, gravitational mass would be obviously temperature-dependent. Instead, it's precisely identical to inertial mass to the best of our ability to measure. It'd probably also make substantial differences in the behavior of white dwarfs and other compact objects, due to their very low entropy.

And then there's the little issue that galaxy rotation curves are just one of several pieces of evidence for dark matter, and no modified gravity theory can account for all of them...like all the other modified gravity theories, this seems to fall into the trap of solving one tiny corner of the problem and ignoring the fact that the solution does nothing to explain the rest.

Kwalish Kid
2016-Nov-17, 03:27 PM
If this idea can explain and get measurements from 1) the bending of light around galaxies and galaxy clusters, 2) the anisotropy of the background radiation, 3) the clustering of galaxies and galaxy clusters over time, and 4) the Bullet Cluster, then we can begin to think of it as a viable alternative hypothesis to dark matter.

Cougar
2016-Nov-17, 03:32 PM
Any experts on here willing to give feedback on the paper (not the article...)...

I'm surely not an expert, and I'm thinking it would take not just an expert, but a specialist expert to understand that paper.

I do understand the final sentences of the paper, though, where Verlinde himself points out that questions remain, and until those questions are answered, his new gravity theory is, basically, up in the air:



In particular, one should be able to derive the cosmological evolution equations from
emergent gravity. For this one needs to first properly understand the role of quantum
entanglement and the evolution of the total entropy of our universe.
So it is still anopen question if and how the standard cosmological picture is incorporated in a theory
of emergent gravity. How does one interpret the expansion of the universe from this
perspective? Or does inflation still play a role in an emergent cosmological scenario?


All these questions are beyond the scope of the present paper. So we will not make
an attempt to answer all or even a part of these questions. This also means that before
these questions are investigated it is too early to make a judgement on whether our
emergent gravity description of dark matter will also be able to replace the current
particle dark matter paradigm in early cosmological scenarios.