Horava Gravity

[Bill S]

I’v

I've been looking for “hitch-hiker” level information about Horava gravity. Most of what I have found is way beyond my maths, but I’m wondering about the reasoning of this point from Anathaswamy. (NS. 07.08.10.).

 

“Investigating the properties of graphene was a significant factor in the development of Horava’s ideas.”…..”An odd feature of this material is that its electrons move about on its surface”. their movements are described using QM, and, “…because their motion is at only a small fraction of the speed of light, relativistic effects can be ignored”.

 

When it is cooled to temperatures close to 0K. “… the motions of its electrons speed up to the extent that relativistic effects become important. Lorenz symmetry is now required”…. “Horava noticed that Lorenz symmetry was not always apparent in the motions of these electrons. He wondered if this could be applied to the Universe. If what we observe is a cooled Universe, in which Lorenz symmetry is a well established feature, could it be that this was not the case in the earlier, hotter, stages? In other words, might Lorenz symmetry not be fundamental? Could it be something that emerged as the Universe cooled?”

I run into a problem here. What he seems to be saying is: Lorenz symmetry applies to the motion of the electrons at higher temperatures, but may be absent at very low temperatures. In transferring this idea to the Universe, he seems to be saying that Lorenz symmetry applies, rigidly, to the (cooled) Universe, but might not have applied when the Universe was hotter.

 

Have I misinterpreted this?

[MigL]

Haven't researched Horava gravity, maybe one of the other members ( Mordred ? ) may have heard of it and can add some insight...

 

If the electrons in graphene move slowly such that relativistic effects are negligible, that doesn't mean they are absent. And if they speed up to relativistic speeds these effects become more pronounced such that they can no longer be ignored, but Lorentz symmetry or covariance is in effect in both cases.

 

That being said, the early universe underwent one or more symmetry breaks during the first fraction of a second as it rapidly cooled. During this symmetry break the Higgs mechanism allowed certain particles to modify one of their properties to one we call mass. Previously all particles were massless, and so moved at the speed Lorentz covariance dictates.

But I don't see how the fact, that every particle was massless and moved at c, doesn't require Lorentz covariance.

[Mordred]

I hadn't heard of this particular model but can certainly take some time researching it. I will see what I can find out about it. If the OP has a particular reference it would certainly help.

 

Ok a bit into Horava gravity, so the Graphene example above makes a bit more sense. What is being described is the renormalization aspects of gravity in that under GR, gravity isn't renormalizable in QFT treatment as it leads to a negative value under typical QFT treatments.

 

Horava tempts to address this, the graphene example is probably a heuristic example describing renormalization of a superconductor though without seeing the paper the OP is referring to that is a guess.

 

Edit its referring to the Lifshitz Point in superconductors is the transition point between a feromagnet and a paramagnet. (recall seeing hovering superconductors ?) the Lifchitz point is involved.

 

Horaz is applying a similar point at value z=3. from Condensed matter theory.

 

http://www.google.ca/url?sa=t&source=web&cd=3&ved=0ahUKEwifguX_2srRAhUO0GMKHWPqD4AQFggpMAI&url=https%3A%2F%2Farxiv.org%2Fabs%2F0901.3775&usg=AFQjCNFETtByzSZ7FVIwMZnJWn_uKqhtWA&sig2=CaFIAkp7JHbuNs_y06UYXA

 

Hope that helps brief review of this model is that it leads to a preferred reference frame. Just a side note.

 

If you have further questions I can certainly help step you through it. My apologies though I had started studying this model when you first posted but got distracted by RL and forgot to get back to it.

Edited January 18, 2017 by Mordred

[nsbqft]

Horava gravity is a horrible attempt to solve the divergences of quantum gravity.

 

Basically it tries to introduce a cutoff. This is done at the price of breaking the symmetry between space and time.

 

The associated mathematical framework is ugly and contrasts with the beautiful framework of Einstein's gravity.

 

As a matter of fact, the divergences of quantum gravity can easily be removed using much more elegant frameworks. These do respect the symmetry between space and time, and try to remove divergences either using covariant cutoff, or by other mathematical techniques.

 

If you are interested in relevant theoretical papers, you can search for divergence-free quantum field theory and divergence-free quantum gravity.

[Strange]

Why does searching for that only find results on vi racconto? Why nothing published?

[MigL]

Are you Nazir S Baaklini ?

[nsbqft]

Are you Nazir S Baaklini ?

Is that you Clint Eastwood? Grandpa says Hi ..

Why does searching for that only find results on vi racconto? Why nothing published?

Your search engine isn't good enough..

Edited January 24, 2017 by nsbqft

[Bill S]

Thanks for the info, folks. Sluggish response on my part does not equate to lack of interest, just lack of time. Just need to do some follow up, now.

[Bill S]

The OP arose from Anathaswamy’s article in New Scientist, 07.08.2010, which I found when throwing out some back numbers. The article contained a ref. to Physical Review D, vol 79; which took to material that was beyond me, and seemed not relevant to my problem. The following is an extract from the article:

 

“Something has to give in this tussle between general relativity and quantum mechanics, and the smart money says that it's relativity that will be the loser. So Horava began looking for ways to tweak Einstein's equations. He found inspiration in an unlikely place: the physics of condensed matter, including the material of the moment- pencil lead. Pull apart the soft, grey graphite and you have a flimsy sheet of carbon atoms just one atom thick, called graphene, whose electrons ping around the surface like balls in a pinball machine. Because they are very small particles, their motion can be described using quantum mechanics; and because they are moving at only a small fraction of the speed of light there is no need to take relativistic effects into account. But cool this graphene down to near absolute zero and something extraordinary happens: the electrons speed up dramatically. Now relativistic theories are needed to describe them correctly. it was this change that sparked Horava's imagination. One of the central ideas of relativity is that space-time must have a property called Lorentz symmetry: to keep the speed of light constant for all observers, no matter how fast they move, time slows and distances contract to exactly the same degree. What struck Horava about graphene is that Lorentz symmetry isn't always apparent in it. Could the same thing be true of our universe, he wondered. What we see around us today is a cool cosmos, where space and time appear linked by Lorentz symmetry- a fact that experiments have established to astounding precision. But things were very different in the earliest moments. What if the symmetry that is apparent today is not fundamental to nature, but something that emerged as the universe cooled from the big bang fireball, just as it emerges in graphene when it is cooled?”

 

Having read it again, I think I was wrong first time, and Horava is actually saying that Lorentz symmetry isn't always apparent in the graphene until it is cooled, when it becomes apparent. He then compares this to the Universe, and speculates that Lorentz symmetry might have appeared as the Universe cooled.

 

Could I have solved my own problem?