Entropic Accelerating Universe (Smoot et al)

[marcus]

Ulf Danielsson has joined battle with Easson Frampton Smoot.
http://arxiv.org/abs/1003.0668
Entropic dark energy and sourced Friedmann equations
Ulf H. Danielsson
7 pages
(Submitted on 2 Mar 2010)
"In this paper we show that a recent attempt to derive dark energy as an entropic force suffers from the same problems as earlier attempts motivated by holography. The remedy is again the introduction of source terms."

He says their paper does not change the picture, he deems their proposal equivalent to one already studied!

 

[MTd2]

The s he found, in the smoot paper, as I told above, is just a linear approximation, otherwise Smoot wouldn't attempt a further work on inflation. Denielsson insisted that it is contant otherwise it would violate the second law of thermodynamics. But it isn't the case here because if we are talking about holography, we are talking also about volume, which contains matter content. So it is no surprising that there are source terms when he tries to fix the model by using a constant, because that represents the work done by gravity. After all, we are dealing with a universe with matter! What he did was to use a non linear approximation.

That gives more reasons of why holography just not account for dark energy, but all gravity!

 

[czes]

This entropic/holographic principle brought by Marcus seems very important.
In general holographic principle takes in acount an information only. There isn't a space nor a distance at all. The Universe is a result of the interfering information due to a specific program. (Let's hope, there isn't a virus).

The distance is just a number of the information between the objects. Therefore when you supply an information the distance (potential energy) increases. If the information is absorbed the particle accelerates.
The acceleration needs a supply of the information and it causes increase of the entropy like in a computer.

 

[marcus]

Sabine Hossenfelder has posted some notes commenting on Verlinde's paper.

http://prime-spot.de/Physics/notes6.pdf

She summarized her comments on her blog

http://backreaction.blogspot.com/2010/03/gravity-is-entropy-is-gravity-is.html

===sample excerpts from Bee's blog===
Here is a short summary: With a suitable definition of quantities, describing gravity by a Newtonian potential or describing it as an entropic force in terms of an "entropy," "temperature" and "holographic screens" is equivalent. One can do it back and forth. The direction Verlinde has shown in his paper is the more difficult and more surprising one. That it works both ways relies on the particularly nice properties that harmonic functions have. Formally, one can also do this identification for electrostatics. In this case however one finds that the "temperature" can be negative and that the "entropy" can decrease without having to do work.

Some assumptions made in the paper are actually not necessary. For example,...

The biggest problem is that Verlinde's argument to show ...
... It does not seem entirely impossible to actually do this derivation, but there are some gaps in his argument.

In any case, let us consider for a moment these gaps can be filled in. Then the interesting aspect clearly is not the equivalence. The interesting aspect is to consider the thermodynamical description of gravity would continue to hold where we cannot use classical gravity, that it might provide a bridge to a statistical mechanics description of a possibly underlying more fundamental theory...
==endquote==

 

[MTd2]

Will Erik be able to convince his identical twin brother, Herman, of his ideas?

http://www.physics.princeton.edu/~verlinde/

 

[marcus]

Thanks for spotting today's Easson Frampton Smoot et al followup!

Now they have an explanation for inflation! as well as an alternative to dark energy.

 

[MTd2]

Didn't I tell you they just needed a more accurate approximation to find something better! Now, let's wait for the (bounce at) big rip

 

[marcus]

What is getting the most attention about the entropic force idea is it's application to cosmology---first to explain today's accelerated expansion ("dark energy" effect) and then to explain early universe accelerated expansion ("inflation").

Without needing to imagine either a made-up dark energy field, or an inflaton field.

Now today Modesto and Randono posted a new entropic force paper which has possible relevance both to the problem of TESTING the idea, by predicting corrections to Newton law, and also to cosmology as well. MTd2 spotted this earlier today.

http://arxiv.org/abs/1003.1998
Entropic corrections to Newton's law
Leonardo Modesto, Andrew Randono
7 pages, 2 color figures
(Submitted on 9 Mar 2010)
"It has been known for some time that there is a deep connection between thermodynamics and gravity, with perhaps the most dramatic implication that the Einstein equations can be viewed as a thermodynamic equation of state. Recently Verlinde has proposed a model for gravity with a simple statistical mechanical interpretation that is applicable in the non-relatvistic regime. After critically analyzing the construction, we present a strong consistency check of the model. Specifically, we consider two well-motivated corrections to the area-entropy relation, the log correction and the volume correction, and follow Verlinde's construction to derive corrections to Newton's law of gravitation. We show that the deviations from Newton's law stemming from the log correction have the same form as the lowest order quantum effects of perturbative quantum gravity, and the deviations stemming from the volume correction have the same form as some modified Newtonian gravity models designed to explain the anomalous galactic rotation curves."