Is gravity an emergent phenomenon?

[czes]

The two are inextricable. Neither came first, nor second.

A photon moves in a Vacuum, which is not empty. There are fields of the virtual particles-antiparticles.
The fields of virtual pairs are more fundamental than a photon.
The question is:
What is a relation between a gravitational field and Vacuum (density of the virtual particles-antiparticles) ?

 

[_PJ_]

I think gravity, which really describes a mutual acceleration between energetic* objects, is not so much an emergent phenomena of spacetime or GR, but is something deeper that contributes to, or even forms a foundation for the structure of spacetime even at the quantum level.
Taking a cue from the WardConstruction, if the smallest spacetime curvature (essentially the effect of the instanciation of a single graviton) is evaluated and, by naturally, as gravity does, interacting with spacetime, it therefore causes decoherence in any entangled system, possibly offering insight into a solution to Quantum measurement problem as well as perhaps suggesting why Gravity has no 'charge', - is always attractive.

As to what Gravity "IS", I cannot hope to imagine. I don't think it's as easily explained as a "Force", such as the others. I think it's wholly more exotic.

*(since even bosons can be affected by gravity, distinguishing between mass and energy is impractical, so I take momentum in terms of energy and velocity - since no object is truly at rest this also prevents any issues with objects cited as 0 rest mass.)

 

[baywax]

No. The RHS of the Einstein equation is the energy of matter, which may not be emergent. The LHS is the gravitational field, which may also not be emergent. (Actually the gravitational field is in the RHS too, since the energy of matter cannot be defined without it. However this indicates the mutual interaction of matter and gravity, not the emergence of one from the other.)

However, there are research programmes in which gravity and matter both emerge from more fundamental degrees of freedom (ie. the Einstein equation emerges as a limit of other equations). String theory is an example of such a programme.

The contrasting programme in which gravity is not emergent is called Asymptotic Safety.

In layman's terms what you're saying is that you can't have one without the other when it comes to gravity, matter and energy. So there is no causal relationship here, where phenomena can arise from one microsystem, moreover, these seemingly separate properties are all one and the same since none can exist independently. Is that why it's hard to determine if they are emergent or not?

 

[czes]

The emergent gravity by R.T.Cahill, (2011)
The dynamical theory for this 3-space involves G, which determines the dissipation rate of space by matter, and alpha, which experiments and observation reveal to be the fine structure constant. For the 1st time we have a comprehensive account of space and matter and their interaction - gravity.
http://arxiv.org/abs/1102.3222

 

[baywax]

The emergent gravity by R.T.Cahill, (2011)
The dynamical theory for this 3-space involves G, which determines the dissipation rate of space by matter, and alpha, which experiments and observation reveal to be the fine structure constant. For the 1st time we have a comprehensive account of space and matter and their interaction - gravity.
http://arxiv.org/abs/1102.3222

Pretty interesting. Is anyone subscribed to this site?

 

[baywax]

This looks like the full story, PDF

http://www.ptep-online.com/index_files/2011/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/feature/id/63190/title/A_New_View_of_Gravity

 

[baywax]

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/feature/id/63190/title/A_New_View_of_Gravity

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]

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/

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]

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

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]

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.

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/bre...s-to-test-hypothesis-of-holographic-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]

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/bre...s-to-test-hypothesis-of-holographic-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)

OK, I'll bite.

Are illusions an emergent phenomenon?

 

[atyy]

In layman's terms what you're saying is that you can't have one without the other when it comes to gravity, matter and energy. So there is no causal relationship here, where phenomena can arise from one microsystem, moreover, these seemingly separate properties are all one and the same since none can exist independently. Is that why it's hard to determine if they are emergent or not?

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]

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

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]

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.

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]

How does gravity arise?

Different theories have different answers.

 

[Finbar]

Different theories have different answers.

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]

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 clever 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.

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.

 

[Finbar]

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.

I think the difference between CDT and LQG is that LQG starts at the level of the microscopic description in terms of spin foams which don't yet describe classical general relativity. One needs to some how coarse grain the spin foam in such a way that the classical metric of say de sitter space comes out. CDT starts at the level of a regularised spacetime and then aims to show that there is a good continuum limit.

I'm certainly not saying string and loop are similar. Only that they are both somehow putting in the two dimensionality of spacetime by hand when thy choose the microscopic degrees of freedom which they would like to quantize. CDT and AS only choose the coarse grained degrees of freedom and aim to uncover the microscopic ones.

 

[czes]

Lee Smolin:
"We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime. "
http://arxiv.org/abs/1001.3668

I have not read such article of another LQG authors. Instead of the Holographic Principle there is a Big Bounce of Bojowald and an infinite dense singularity.
Do Rovelli and Ashtekar reject the Holographic Principle in LQG ?

 

[baywax]

Is space-time (re: distance) an emergent property?

 

[atyy]

Is space-time (re: distance) an emergent property?

In general relativity, gravity=spacetime, so that is the same question as the original.

When the gravity=spacetime identification is made, it is assumed that there is matter, or at least test particles, clocks and rulers.

 

[baywax]

In general relativity, gravity=spacetime, so that is the same question as the original.

When the gravity=spacetime identification is made, it is assumed that there is matter, or at least test particles, clocks and rulers.

Ha! Very good, thank you. Is beer an emergent phenomenon?! (or part of the foam?!)

 

[atyy]

Ha! Very good, thank you. Is beer an emergent phenomenon?! (or part of the foam?!)

Beer is fundamental. Foam is emergent.

 

[baywax]

Beer is fundamental. Foam is emergent.

If all we can observe is emergent, what are we missing? Surely mathematical formulas do not thoroughly represent or depict the fundamental source of all that is emergent. Is it like throwing flour into the wind and saying we know what the wind looks like?

 

[alt]

Originally Posted by czes

The emergent gravity by R.T.Cahill, (2011)
The dynamical theory for this 3-space involves G, which determines the dissipation rate of space by matter, and alpha, which experiments and observation reveal to be the fine structure constant. For the 1st time we have a comprehensive account of space and matter and their interaction - gravity.
http://arxiv.org/abs/1102.3222

Pretty interesting. Is anyone subscribed to this site?

Cahill is an interesting Aussie scientist. If you click onto his name at the top of the page of the above link, you get to all his papers, including;

A Quantum Cosmology: No Dark Matter, Dark Energy nor Accelerating Universe

Why, I recall a couple of years ago, emblazoned over the front page of our newspapers, he had defeated the speed of light .. or something .. (most likely in one of his other papers).

Anyway, I clicked onto this thread in the hope of understanding gravity more - but now I understand in less.

 

[zhermes]

Cahill is an interesting Aussie scientist.

Cahill is not a scientist.