Is gravity an emergent phenomenon?

baywax

Pretty interesting. Is anyone subscribed to this site?

baywax

This looks like the full story, PDF

http://www.ptep-online.com/index_fil...1/PP-24-05.PDF

czes

So it’s not necessarily crazy, even if still very speculative, to suppose that thermodynamics and information will serve as the bridge for bringing gravity and quantum physics together. Einstein’s equations link energy to matter and matter to gravity, and the new work connects matter and energy to information and entropy. These links imply that Einstein’s equations are more about information than energy, the physicists write. “In other words, information might be a more profound physical entity than matter or field.”
http://www.sciencenews.org/view/feat...iew_of_Gravity

baywax

Yes, however, "information" is an anthropomorphic word for "energy". Don't you agree? Its all in how or even "if" the energy is received, interpreted and/or perceived. And, what does this have to do with my original question about gravity being emergent?

czes

The gravity may be emergent from the vacuum energy disstribution.
The change of refractive index of the vacuum caused by the presence of matter has exactly the same effect on the path of light as the curvature of space in Einstein's General Relativity.
http://arxiv.org/abs/gr-qc/0604009

If a particle absorbs more information from the vacuum than emits, it is accelerating toward the source of the information (“denser vacuum”). The massive object creates the vacuum around due to the Compton wavelength of its rest mass particles. If the emission is faster than the absorption the particle decelerates then (Davies-Unruh effect). So the vacuum is transformed into a real, detectable thing.
http://www.calphysics.org/articles/chown2007.html

The vacuum as a volume is an illusion made of relation between the information on a flat screen.
Also the non-local process of producing a holographic reconstruction is explained purely in terms of interference and diffraction. Thus, someone looking into the hologram "sees" the objects even though they are no longer present. The hologram is not an image, but an encoding system which enables the scattered light field to be reconstructed. Images can then be formed from any point in the reconstructed beam either with a camera or by eye.
May be we are a part of an Holographic Universe ?
http://www.hologram.glt.pl/

baywax

you might want to pursue this in the philosophy forum.

Now that I have asked about emergent phenomena and properties I wonder if there's an answer to this question that's nagging me...

What is the quantum state or "microcosmic world" a product of? Does it all emerge from energy?

czes

There are many evidences that quantum state and energy emerge from the quantum information relation.
Bekenstein's topical overview "A Tale of Two Entropies" describes potentially profound implications of Wheeler's trend in part by noting a previously unexpected connection between the world of information theory and classical physics. Bekenstein summarizes that "Thermodynamic entropy and Shannon entropy are conceptually equivalent: the number of arrangements that are counted by Boltzmann entropy reflects the amount of Shannon information one would need to implement any particular arrangement..." of matter and energy. The only salient difference between the thermodynamic entropy of physics and the Shannon's entropy of information is in the units of measure; the former is expressed in units of energy divided by temperature, the latter in essentially dimensionless "bits" of information, and so the difference is merely a matter of convention.

baywax

Same Bekenstein?

http://www.phys.huji.ac.il/~bekenste/

czes

In 2008, Fermilab particle astrophysicist Craig Hogan made waves with a mind-boggling proposition: The 3D universe in which we appear to live is no more than a hologram.
Now he is building the most precise clock of all time to directly measure whether our reality is an illusion.
http://www.symmetrymagazine.org/brea...phic-universe/

The Compton wave seems to be a fundamental unit of which our Observable Universe is built. The proton's Compton wavelength is a basic lattice and other particles have to correspond with the proton's wavelength. It is a question now.
Hogan wants to measure the quantum states made of the Compton wavelength of the proton (10^-15 m)

baywax

OK, I'll bite.

Are illusions an emergent phenomenon?

atyy

No, I meant that in general relativity, gravity=spacetime is not emergent.

To me, an emergent property is one of which it makes sense to talk about sometimes, but not all the time. For example, when we study resistors and capacitors, it makes sense to talk about resistance, Ohm's law and all that. However, resistance is not a fundamental property. If we blow the resistor up into its individual atoms, then we have to use atomic physics or something other than Ohms law. So Ohmic resistance is emergent.

Within general relativity, it always makes sense to talk about gravity=spacetime, even in extreme circumstances like black holes (let's ignore the singularity for now). So in general relativity, gravity=spacetime is not emergent, although it is curved by matter.

Of course general relativity could be wrong, and perhaps it doesn't make sense to talk about gravity=spacetime under all conditions. The AdS/CFT conjecture is an example of a theory in which gravity is emergent.

czes

There is locality in General Relativity and the particle is defined in the spacetime=gravity.
Therefore there are some problems with singularity, dark matter, dark energy....
In quantum mechanics there isn't locality. The particle is not defined in the spacetime and the gravity is an emergent phenomenon. The particle is non-local and we can't calculate how it curves the spacetime.

baywax

Maldacena duality, this is deep physics. I thought about how gravity=spacetime is potential energy. I wondered if its like a rubber band that sits unused then someone with some energy stretches it and it's potential energy is actualized. Its not a product of energy, necessarily, but can be made to act like/with energy. If matter is emergent perhaps that doesn't mean gravity is automatically emergent as well. Would that be Asymptotic Safety? Gravity is microscopic in nature and therefore easily viewed as non-emergent.

Is there any theory that suggests all energy is a product of space=time?

czes

In General Relativity the particle is localized in the spacetime=gravity. We have the energy then.
On the fundamental quantum level there isn't a locality and therefore there isn't a distance and no spacetime=gravity. There is a quantum information and relation between them. The energy emerges when we compare the frequencies of the information.

It seems that most fundamental is the information (quantum state) which may move toward the increasing entropy which creates the gravity. It is discussed according to
article: Gravity is not entropic force:
http://arxiv.org/abs/1009.5414

dimension10

Different theories have different answers.

Finbar

or do they....?

Nearly all theories of quantum gravity seem to imply that spacetime emerges from an effectively two dimension theory either by starting from two dimensional degrees of freedom, in string theory or LQG, or by predicting that spacetime is two dimensional on small scales e.g. CDT, asymptotic safety or Horava gravity. So two dimensions seems to be an input or an output in all the top theories of quantum gravity. The reason for this is very simple; two dimensions is the dimension in which Newton's constant is dimensionless.


The problem for strings and LQG is to get from the two dimensional degrees of freedom to the standard model. In strings one has to compactify the extra dimensions in a cleaver way whereas LQG faces the problem of recovering classical GR from its highly non-perturbative and non-standard stating point.

CDT and AS are much more conservative and have both already shown that they have classical spacetime as an appropriate limit. The challenge for these theories is to understand the underlying microscopic degrees of freedom that they seem to be uncovering.

marcus

This is intriguing and even inspiring---it may contain an important insight. However it seems to me that LQG could be more in the situation of CDT and AS. That is, according to Modesto's work, 2D emerges at small scales. Steve Carlip's review of QG spontaneous dimensional reduction echoed and cited Modesto on this.
http://arxiv.org/abs/0911.0437
Fractal Space-Time from Spin-Foams
Elena Magliaro, Claudio Perini, Leonardo Modesto
(Submitted on 2 Nov 2009)
"In this paper we perform the calculation of the spectral dimension of spacetime in 4d quantum gravity using the Barrett-Crane (BC) spinfoam model. We realize this considering a very simple decomposition of the 4d spacetime already used in the graviton propagator calculation and we introduce a boundary state which selects a classical geometry on the boundary. We obtain that the spectral dimension of the spacetime runs from approximately 2 to 4..."

So they found the dimensionality (measured by a diffusion process) to be around 2 at very small scale and 4 at macro scale. This is similar to what Loll et al found for CDT, using the same measure of dimensionality.

Also quite a lot of evidence has accumulated that Loop gets ordinary gravity at large scale, but no rigorous proof---the eyes and tees still need to be dotted and crossed on that. Rovelli's February review discusses the current situation:
http://arxiv.org/abs/1102.3660
E.g. starting on page 18 with section D3: "Large distance expansion", and continuing into sections E1 and E2: "n-point functions" and "cosmology".


Opinions can of course differ but offhand I would say the situation with Loop is more comparable with CDT on that score (than you suggest) and less comparable with String.