I recently wrote a popular science book called “Decoding Reality: The Universe as Quantum Information.” The point I was trying to make is that the fundamental building blocks out of which everything around us is constructed are bits of information (rather than energy and matter, or cheese and crackers, or whatever else).

Quantum physics naturally lends itself to this view, as the way we describe the world within the quantum formalism is already very much information-theoretic. (FQXi’s Caslav Brukner also talks about this relationship in the article, “The End of the Quantum Road.”) First and foremost, we talk about states of a physical system as catalogues of information (a term that Schrödinger himself coined when he invented quantum physics) giving us probabilities with which we should expect experiments to yield different results. The physical evolution of the system is then just a rule telling us how this catalogue of bets on the future states of the system should be updated with time (we call this rule for updating bets the Schrödinger equation).

This is all fine, but, of course, in addition to quantum physics, we have another equally successful physical theory, namely general relativity, that describes gravitational phenomena. And to date quantum physics and general relativity have not be unified. In order to understand the world we seem to need both quantum physics and general relativity. Unifying them is possibly the biggest open problem in physics today. So if I claim that information is fundamental and that quantum physics is naturally a theory of information, what happens with gravity?

The way I dealt with this issue in my book was to invoke a very beautiful paper of FQXi’s Ted Jacobson. In 1995 he published a letter in the Physical Review, where he showed how to derive Einstein’s gravity from thermodynamics! I adopted his logic in my book to suggest, with a tongue in cheek, that gravity can in fact be derived from information theory (albeit with a little bit of help from quantum entanglement).

I understand that Jacobson’s idea was (and still probably is) considered very controversial because it might imply that all those physicists trying to quantize gravity are simply wasting their time (since, according to Jacobson, gravity is not a fundamental force, but merely a kind of thermodynamic quantum noise). This is why I was surprised to see that recently a Dutch physicist Erik Verlinde has been writing to add extra weight to Jacobson’s argument (see arxiv.org/abs/1001.0785).

Having skimmed through his most recent paper, my feeling is that Verlinde has in the end not added much to Jacobson. What he did try to do is perhaps bring it closer to everyday physics, rather than engage the full machinery of Riemannian manifolds (which regrettably is necessary to phrase general relativity properly). Verlinde shows (the word “shows” should be interpreted very loosely – he effectively just performs a dimensional analysis of a kind) how to derive Newton’s “inverse square” law of gravitational attraction. Given that Jacobson has already shown how to derive the full Einstein field equations from thermodynamics, Newton’s law just follows as a special case of Jacobson’s derivation. However, it is likely that Jacobson’s stunning idea has not had as much impact in the wider physics community simply because of its high level of mathematical sophistication. The merit of Verlinde’s publication might then just be to help bring Jacobson to the masses.

Let me now go in medias res. It’s very simple to explain how gravity might arise from entropy. First we acknowledge the fundamental thermodynamical relationship that entropy times temperature equals heat. Heat itself is nothing but a form of energy, which according to Einstein equals mass times speed of light squared. The entropy we assume to be proportional to area (the so called Holographic principle, which you can read about in more detail in the article, “The Black Hole and the Babel Fish”), in other words proportional to radius squared. The temperature is, according to FQXi’s Paul Davies and Bill Unruh, proportional to acceleration, which in turn is force divided by mass (from Newton’s second law). Putting all this together gives us the force equal to the product of masses divided by distance squared, namely Newton’s gravity! And that’s more or less what Verlinde does.

How watertight is this argument? How much of gravity is really just thermodynamics? The derivation involves two crucial relationships we believe to be true, but which, at present, have no experimental evidence to support them. First of all, the relationship between entropy and area – the aforementioned Holographic principle – has never been tested. Initially argued within black hole theomodynamics by Jacob Bekenstein, the relationship has been elevated to a universally-held principle (i.e. the Holographic principle) by Leonard Susskind. Although this principle is supported by a host of other theoretical ideas (including quantum entanglement, that I used in my book to explain why entropy is proportional to area), it has never been experimentally tested. Secondly, the Unruh-Davies beautiful formula linking acceleration to temperature requires accelerations far beyond what can presently be achieved in order to generate enough detectable heat.

However, lack of experimental evidence aside, there are more fundamental objections that might invalidate the whole logic. One is that the entropy and area connection is not exact and requires additional corrections. This realization comes from a number of directions, including my own, in quantum information theory. Secondly, a physicist Danny Terno, from Macquarie University in Sidney, has argued that the geometric entropy (the one related to area) in quantum field theory is not a Lorentz scalar, while the black hole entropy is. His main point in a 2004 Physical Review Letter is that differently observers would each have to introduce a different temperature, preventing any description in terms of a single Davies-Unruh temperature that features in Jacobson’s derivation.

Is this enough evidence to challenge Jacobson (and Verlinde)? Well, there are, as always, two ways of interpreting the more fundamental objections. Fundamental issues might indeed invalidate the Jacobson claim to entropic gravity altogether. This would simply spell an end to gravity being a consequence of thermodynamics and information theory.

But there is a more optimistic possibility. The fundamental objections could be turned on their head. They might mean that, if Jacobson’s logic is correct in spirit if not in all its details, we need to make corrections to Einstein’s field equations in order to accommodate possible changes to the Holographic principle and the nonexistence of a unique Davies-Unruh temperature. This is obviously exciting. Not only would it confirm that gravity is not a fundamental force, but it would also point to the need to modify Einstein’s equations. Much as one would like to speculate about further consequences of all this, it is for now probably best to exercise the scientific method of suspended judgement. Only time indeed can tell what will turn out to be correct.

“Decoding Reality: The Universe as Quantum Information” is published by Oxford University Press, 2010. Check out more about it here.

this post has been edited by the author since its original submission

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"The point I was trying to make is that the fundamental building blocks out of which everything around us is constructed are bits of information (rather than ... cheese and crackers...)."

Vlatko, haven't you seen A Grand Day Out?

http://en.wikipedia.org/wiki/A_Grand_Day_Out

The fundamental building blocks of nature are definitely cheese.

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"if Jacobson's logic is correct in spirit if not in all its details"

Out of loyalty, I'm driven to emphasize that Ted's argument is rigorous [unlike Verlinde's?]. Meaning, the logical steps of the argument are correct. What is in question is the set of beginning assumptions, specifically the entropy = area law and the identification of the local 'temperature'. Also, the formal definition of the local temperature is precise and unambiguous---what is really in question is the meaning of this 'temperature' in terms of more familiar, non-relativistic senses. I'd say the argument is correct in detail, but maybe not in spirit.

Regarding corrections to the entropy=area law, Ted, Chris Eling, and Raf Guedens worked out an extension of the argument that implies corrections to Einstein's Eqns, and requires a non-equilibrium statmech interp.

Obviosly, lack of testability is the thorn in the side of pretty much any theory that attempts to deal with the energy scales under scrutiny in today's research. What do you do, then? How do you do Physics when experimental verification is out of reach? The best you can do is look for certain patterns or relationships that at least give you the sense that you are headed in a direction that seems to be taking you down the path of least resistence, in the spirit of Occam's Razor.

The interesting part of the thesis is that, in theory, gravity can be formulated as an emergent feature of fundmanetal relationships between dynamical variables. If there is more than one way to skin a cat, then the path of least resistence wopuld imply looking for ways that a phenomeon can be explained as an emergent feature of something simpler.

Good luck. Most research topday is tied up in String Theory and you will get smashed down pretty quickly if you get in the way.

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HI

I like the idea that information bits are the ultimate reality. However since I haven't read your book I wonder if you could answer some of my questions here about the viewpoint?

1. Whose information bits are these? and what these information are about?

2. Are these information bits independent reality? (i.e. independent from observers)

3. Is this viewpoint proven experimentally or only suggested by quantum theory? Is it even possible to prove it experimentally?

4. Even if it is true that gravity is some kind of thermodynamic-like phenomenon, this does not mean that gravity or spacetime is fundamentally information bits. So I think Jacobson's view has not much relevance to your viewpoint.

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If everything is made out of information bits, then does that mean that space-time itself is some kind of a "processor" of information? Perhaps every scattering event has inputs" quantum entanglements, everything that adds or subtracts to the local potential energy; and then the event occurs (is calculated), the dice are rolled.

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It is more likely that curvature is a processor. An elementary way to see this is with the two state system

|ψ> = 1/sqrt{2}(|0> + exp(iθ)|1>)

will evaluate the curvature if the phase angle θ is due to a curvature. Curvature is a deficit angle divided by the area enclosed by a loop R = θ/A. So a flat disk will have zero deficit angle, while a cone has one. Now for a Regge strut passing perpendicular to the disk or cone there is a “flux” which determines the curvature and thus changes the phase in the above 2-state system.

There is also the Bekenstein bound which determines the amount of entropy in a system S = kA/4L_p^2, where L_p = sqrt{Għ/c^3} and k is the Boltzmann constant. So a black hole with area A = NL_p^2 has an entropy. Entropy is related to information through the Shannon-Khinchon formula and the von Neumann formula for entropy entanglement. So for a black hole the area of the event horizon is then a set of fields, or strings, with N units of information that determine the entropy by a form of entanglement in holography.

Cheers LC

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Rank amateur here, but it seems to me that information and energy are like two sides of the same coin. Energy manifests information and information defines energy.

The assumption seems to be that there are some sort of platonic laws out there, from which everything emerges, but it seems to me that laws are as emergent as the stuff they model. Complex laws emerge from more basic ones, just as complex interactions emerges from more basic interactions. If the vacuum isn't fluctuating, it's just void.

The prejudice is that our minds are the processing of information, yet our brains consist of energy. Without the brain, there is no mind.

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Ok I want delve deep into this interesting post, but lets see if we can first scale the quantum scales to macro scales?..so does anyone object to this analogy statement:The quantum scale communicates information to information in a perticular form, thus in a macro domain if you pick up a coin off a counter and toss it into the air, it will come down either heads or tails with equal probability. On quantum scale, the knowledge of what comes up, heads or tails is known within the system, prior to the event.

If any part of the above statement is flawed please say so, then I will proceed with some interesting, hopefully reletive points .

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Paul,

"is known within the system"

What is "the system?"

Isn't one of the principles of relativity that there is no objective point of view, as every perspective contextualizes information differently, so the possibility of knowing"initial conditions" is practically and theoretically impossible?

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The little example I gave above is a quantum 2-state system or a system of 2states in a q-bits. It is the quantum analogue of the coin toss problem. For two spins A, B in an entangled state the entropy is

S = S(A) + S(B) - S(A|B),

For the two spins in a pure state the total entropy is zero. If there is a decoherence established the mutual of joint entropy S(A|B) is removed (hidden or “destroyed”), so the resulting statistical mixture has entropy S = S(A) + S(B). For each of the two outcomes having probability 1/2 this entropy is



which is easily calculated as S = k log(2) > 0.

In gravity the thing which conceals the S(A|B) are event horizons. This might be seen if we do an EPR pair experiment where Alice and Bob attempt to teleport a quantum state from inside a black hole. The energy of the EPR pair, say some energy E, is reduced to near zero on the horizon or E’ ~ E(L_p^2/A), for A the area of the BH horizon. As a result the detector threshold is passed and the pair can’t be teleported. However, for an ideal setting if the state of the black hole is known completely, say Alice and Bob have a complete entanglement registry of states with everything which composed the BH with idea detectors, then teleportation of states is possible. This can only happen if the exterior observer has a complete description of the stretched horizon of the BH. From a practical consideration this is not possible at all.

Cheers LC

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Vlatko,

Thanks! Having just introduced myself to Verlinde's ideas, I ordered your book immediately. I think it is significant that if gravity is derived from information and if time is identical to information, relativistic quantum field theory follows. Details on the InterJournal archive, or

my site

That time is identical to information is also held by another FQXI contributor, Lev Goldfarb. I also believe the same conclusion follows from Fotini Markopoulou's hypothesis.

Best regards,

Tom

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This statement:"I understand that Jacobson’s idea was(and still probably is) considered very controversial because it might imply that all those physicists trying to quantize gravity are simply wasting their time (since, according to Jacobson, gravity is not a fundamental force, but merely a kind of thermodynamic quantum noise)."

The force of Gravity in extreme/pure thermodynamic systems, behave vastly different from Gravity under normal physical domains. Take a super-cooled BEC, the molocules/liquid can climb up and over the container, defying "gravity". Information within such extreme systems tend to behave as one, thus entanglement is the therml pure extension?

The lowering of the temperature of the system prevents matter structure colliding, on a quantum scale the perfect surface tension created out of near thermal absolute zero, pushes the matter to slide, or better wording is to smear_out.

Take two different atomic structures, if you can lower both to the same temperature, close to absolute zero, then the little information extracted from the system should not be able to diffrientiate which atoms get entangled?..close to absolute zero all energies get merged into one "type" of thermal "information" ?

In the steel making industry, you can pour vast amounts of water onto steel to "qwench", this process on the quantum scale has interesting consequense, for instance:. is anoulous to the system being corrupted by certain impurities?

You cannot pour the other way around?

Information input/output is specific, but can vary depending on the environment on macro scales. But if one constructs a quantum system that has pure channels to relay information, then accordingly so, any input/noise will alter the expectant results, because every single experiment has to relay its information finally into the Macro domain, all observers are macro impurities!

You have to extract gravity out from the quantum, into the macro domain, NOT push and squeeze it down from the macro into the Quantum.

Gravity allready exists in Macro domains, ask any Relative Observer about the noise in everyday life!

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The behavior of superfluids is not a case of gravitation in action. A superfluid in free space, say falling in a frame or in an orbiting spacecraft, will not behave any differently than a hot body. The effect of a superfluid climbing out of a dewer is a quantum fluid case of capillary action.

Cheers LC

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Ive lost some details of my previous posting, cant blame the LHC for that!

What I wanted to highlight was the fact information is quite distinct and diferent, from Macro to Quantum and Quantum to Macro scales?

The environmental experiment setups can never be equal, just creating a near zero "pure" vacuum in order to send "bits" along channels for Quantum scales, has no Macro comparable situation, the nearest would be throwing a particle into a near vacuum space for a similar effect to this

some effect or no effect?

The obvious difference of an actual coin_toss experiment is that there is a conscious observer making decisions and witnessing events in macro scales, the experimenter has a choice to toss coins, not on how she/he would like them to land!

Gravity to a coin_toss observer is paramount to the effect of causing a coin to "fall"? On quantum scales there is no comparable experiment?

So one can understand how Jacobson see's so much gravitational "noise", we are all contributing to the informaton pollution to gravitational systems, up to a point, actually up to a quantum point that is?

All quantum systems have be clinically purged of impurities/noise? so one can ask this, how can a system with zero "noise" be a true system?

If: "gravity was just thermodynamics", then why do hot things explode/expand/repel (or at least appear to leave this as a event signature), and cold things too explode/expand/repel?

opposite attracs

For macro observers Gravity must be the fundemental force, yet if one removes the macro pollutent (observers) from any system, then I can contend that Gravity has no part in making trees fall!

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Thinking about "information".

The mere information, that "information" could be physical, suggests that it is indeed so... because it seems to be an information of very high relevance...

Besides this somewhat tautological statement above, it could be indeed the case that the informational redundance of the holographic principle shows one thing: The unity of the whole creational process and its interdependences. This poses the question if nature is strictly deterministic all the way down to the last bit.

The next information about information comes from QM, saying that there's somewhat a lack of information because of quantization. How can one merge these two lines of reasoning...

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... and what interdependences are there between the randomness and the information...

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On the topic of entropic gravity, I think it comes down to the likelihood of detection of a photon probability wave.

For stars that are millions of light years away, there wave functions are spread out over an area of A = 4piR^2 (where R = several million light years). In practice, you probably can't see them. As a thought experiment, what if the physics community was going to give out a 1 million dollar prize to some lucky astronomer who could detect that one photon from a particular distant star, fifty million light years away. All of the astronomers in the contest would begin to worry about how if somebody else detects their photon, then they won't detect it. They wouldn't win $1 million dollars. What if the photon is wasted on some bird flying by who happens to see this photon, but couldn't care less? Not just birds or other astronomers, but anything that can detect a photon would have a very good chance of collapsing the wave function, and depriving he or she of the million dollar prize.

I know it's a silly example, but all potential absorbers of these photons will have a chance to detect that photon. In fact, the last photon from this very distant star will face more potential absorbers in places where there is a lot of matter, versus empty space, right?

If photons transmit information, and the last photon from a very distant star has a wavefront with a diameter of 50 millions light years, then every potential taker (absorber) of that photon has an equal chance of absorbing that photon. The large dense objects will most like absorb it, as opposed to a thin gas of empty space.

My point is that photon detection of the probability waves of photons, equates to entropic gravity. Does anyone disagree?

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So why is gravity attractive? For the zillions of potential wave collapsers, all huddled together in a very small space (high density), they will have a higher likelihood of detecting the photon. The result is that they reach out and attempt to clutch the photon.

That clutching is called gravity.

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Imagine that a satellite in deep space is putting out spherical wavefront, one photon at a time. Let's further imagine that, at some distance R in the deep vacuum of space, there are 100x more photon absorbers in the North direction then there are in the South direction. Everywhere else, at that radius R, there is nothing around that can absorb a photon.

Wouldn't we expect the large number of detectors in the north to absorb more photons than the smaller number in the south? If so, that would skew the number of photon absorptions, and flow of energy, towards the north. Wouldn't this indirectly cause a skew of energy flow in the northerly direction?

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Dear Eckard,

I'm just an electronics technician with a BS in physics. I use analogies to give me approximate answers to many of these questions. I don't think that my interpretation of entropic gravity is going to payoff. I admit that entropic gravity still doesn't male sense.

I am familiar with phonons form solid state physics. They are just lattice waves. I have entertained the idea that space-time itself acts like a lattice, a lattice that obeys causality; which means that time travel is impossible. So how would a phonon description of a photon that is light years away from its source be able to collapse all of its energy into an absorbing electron, inside of a millisecond? Answer: it's a probability wave, not a real wave. Probability moves at the speed of ...

Information travels no faster than the speed of light, c; that's a solid yes or no. Maybes travel a lot faster. Quantum mechanics tells us that our universe is wishy-washy. "Yeah, I'll take out the trash,...eventually."

Anything that absorbs a photon, wants to see the money, see the energy, immediately. For a photon from ten light years away, the hv energy has to travel at the speed of light. For the underlying tessellated lattice of uncertainty, the wishy-washy crystal, probabilities distribute instantly.

I'm telling you, we live in a lazy, sluggish universe. The universe knows the Laws of Physics. It's just lazy about getting things done. If the speed of light were faster, the Planck constant would be a lot smaller. The speed of light determines how much energy is necessary to signal, send information. The speed of light tells you how fast information can travel. In a universe with a faster speed of light, decisiveness occurs more quickly.

I know these are funny ways to interpret the physics, but I can explain all of this. Information, yes or no, decisiveness moves at the speed of light. But probability moves faster.

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Jason, I feel the probability explanation possibly to simple. How long is the coherence length of light waves from the sun?

Curious,

Eckard

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Eckard,

Several weeks ago, I had read about astronomers who had observed light from galaxies that were many billions of light years away. Coherence is just the property of waves in that they will engage in interference patterns, such as through the lens of a telescope. I guess what you are really asking is whether or not photons can engage in interference patterns with things that are far away, particularly quantum entanglement. I'm not sure what the range of quantum entanglement is. From what I've read, you only get a few meters before noise gets really bad.

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Jason,

Yes, I asked for concrete values of what is imagined to look like this . Incidentally, an other nice simulation illustrates the double slit experiment.

I merely fear, if calculations are based on assumed plane waves, they might be incorrect. I cannot understand how, for instance Gauss pulses, which extend from minus infinity to plus infinity, react to suddenly changing influences. I guess they are merely approximations. I still maintain my reproach.

Eckard

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The first paragraph on quantum entanglement should ease your mind.

http://en.wikipedia.org/wiki/Quantum_entanglement

Quantu
m entanglement has to do with probability amplitudes. Probability amplitudes are not "information" traveling faster than the speed of light - which, we are told, is impossible.

In order to have any chance to detect a particle, you have to deal with probability density (Psi#)(Psi). That is the only part that is observable to us. It is the product of conjugate Psi with Psi that must obey speed of light restrictions. The wave function Psi is not directly observable to us, but is allowed to be entangled with something that is far away.

Confusion results when we don't understand what information content really is. Information is a definitive yes or no, which cannot exceed the speed of light. An entangled wave function doesn't really transmit "information". I don't think we have a word for what it transfers back and forth. Correlation?

Correlation is not bound by the speed of light.

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You are right in that quantum entanglements do not communicate information. They only correlate quantum bits nonlocally in space or spacetime.

Cheers LC

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PET or Positron Emission Tomography, uses the gamma rays released by decaying nucleotides to look at what's happening inside someone's body. The gamma rays are detected by gamma cameras.

http://www.radiologyinfo.org/en/info.cfm?PG=pet

It would be nice to better understand how quantum entanglement occurs, is achieved.

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"The detection of the gamma ray destroys any entanglement as it is."

That's the big question. Is it destroyed? Or is it subordinated? I guess that is impossible to test for. If it were subordinated, then everything is entangled to everything else, however weakly or non observable. However, if entanglement is destroyed, then there is only one layer of entanglement.

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Vlatko,

My apologies. I finished your book a while ago and meant to check back in here to tell you how much I liked it. Better late than never -- cover to cover, it was an excellent and fascinating survey of a difficult leading-edge subject.

Thanks.

Tom

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How about this answer. Gravity is the imbalance in the inertial field. The inertial field is a range of frequencies of virtual photons; this range is from DC to gamma ray frequencies. When virtual photon frequencies are not balanced on both sides, there is a net force. That net force is gravity.

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Dear Steve,

Ok, I understood that message. My opinion remains the same: I know what mass is. I appreciate you sharing your honest opinion with me.

James

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Is gravitational field a kind of a virtual plasma made of virtual particles-antiparticles ?

We can write (Fg/Fe)alfa = (Lp/Lx)(Lp/Ly)

where Fg=Newton force, Fe=Coulomb force, alfa=fine structure const.

Lp=Planck length, Lx,Ly=Compton wavelength

I found this tautology in 2007 and it shows that each interference between quantum information of the charged particles due to their Compton wave cause Planck length contarction or Planck time dilation.

Therefore the gravity is a secondary efect because the quantum information interference. Holography is just an interference of the information.

http://www.hlawiczes1.webpark.pl/gravastar.html

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