- #36
MTd2
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CHIKO-2010 said:But what this statement has to do with the holographic sreens and Verlinde's theory?
That in the paper, the neutron initially has no energy whatsoever, so, it doesn`t exist.
CHIKO-2010 said:But what this statement has to do with the holographic sreens and Verlinde's theory?
CHIKO-2010 said:these are the so-called virtual states, they are part of the vacuum, and as such do not create neither entropy nor temperature
MTd2 said:That in the paper, the neutron initially has no energy whatsoever, so, it doesn`t exist.
MTd2 said:They do create entropy, as they all contribute to the actual mass. In fact, if you look how similar the path integral looks like a partition function, that the virtual particles are in fact the microstates of a particle. That also brings a problem, similar to what was raised by Motl, that due a limit bound on information, some virtual particles may be killed, just like interference fringes.
I personally think this is a possible advantage. That is, what if there are "hole" particles and they are responsible for dark matter?
In the paper, a neutron was set with zero entropy. But if you are dealing with calculations inside the theory of verlinde, all entropy must be taken into account, including the one from the mass. So, the neutron cannot possibly be started with a 0 entropy because that would be ignoring the entropy of the mass and given that we are talking about gravity, gravity cannot be forgotten because it is the main part of the problem.CHIKO-2010 said:Could you please be more specific where in the paper you find that "the neutron initially has no energy"?
CHIKO-2010 said:Sorry, but what you have written above does not make any sense! You seems are confused with some basic stuff of quantum field theory.
MTd2 said:In the paper, a neutron was set with zero entropy. But if you are dealing with calculations inside the theory of verlinde, all entropy must be taken into account, including the one from the mass. So, the neutron cannot possibly be started with a 0 entropy because that would be ignoring the entropy of the mass and given that we are talking about gravity, gravity cannot be forgotten because it is the main part of the problem.
MTd2 said:Verlinde`s theory does not look like QFT for me.
CHIKO-2010 said:You commented on virtual particles producing entropy -- if you are talking about thermodynamics, what the virtual particles have to do with it?
MTd2 said:Although there is a typo in the line above eq. 15 (it uses eq. 15 to find eq. 15), I cannot agree with eq. 15. It assumes that the entropy increases to mc, from 0, using eq. 12.
MTd2 said:I checked the origin of eq. 11, that's eq. 3.6 of Verlinde's paper.
Where is the holographic screen, for you? For me, it is of order ~10billion light years away, which is 10^23.The compton length is 10^-15, so the suppression, in 8, factor is about exp(-5*10^-8), that is, 50 parts in one billion.
I guess z in (18) must be between the absorber and the mirror, for z higher than the absorber neutrons are not passing the slit, this is just due to the experimental setup. I do not understand where did you get ~10billion light years (?!) from when you just need to reproduce local gravitational field of Earth
CHIKO-2010 said:So the question in this particular discussion is that whether Motl's objections and the related arguments in the paper indeed show that Verlinde's idea on entropic gravity is false. I tend to think they do
CHIKO-2010 said:gravity is due to the difference in entropy of a particle related with its position. The questions related with detailed physics of holographic screens, observers etc are irrelevant here, in my opinion.
CHIKO-2010 said:I do not understand where did you get ~10billion light years (?!) from when you just need to reproduce local gravitational field of Earth
MTd2 said:Given the cosmological aspect of this theory, we have to look for ways to find what went wrong in the above derivation. We know that the entropy of a particle at the particle horizon is 0. So, there must be a boundary condition for the U operator, otherwise, this problem will look like it was done in a universe a little bit larger than Earth, where the absober is a few micrometers away from the edge of the universe.
czes said:Could we say the pure quantum state is something like a virtual particle ?
When I wrote the massive real particle alone has its environment the gravitational field, the virtual particles-antiparticles. The real massive particle absorbs and emits the virual p-a and therefore it oscillate. The virtual p-a hasn't an entropy and temperature but the massive real particle has. It is in a rest if the absorption=emission. it means the entropy and temperature remains on the same level.
For futher clarification: Pure state can describe both virtual and real particles. real massive (quantum-mechanical) particle which is described by pure state has no entropy and no temperature. The classical particle (or field) can be viewed as a incoherent collection of many (statistically large number of) quantum-mechanical states and only that object carries entropy!
The gravitational field could be here as a field of the virtual plasma (virtual particles-antiparticles). The virtual p-a appear and disappear due inversely proportional to the squared distance from the massive particle. Therefore the location is important.
Verlinde's entropy is not like Boltzman's entropy in a gas. The virtual p-a due to Unruh are not real but the calculation is similar.
In certain sense you are right. In field-theoretic approach Newton's law (potential) can be derived as an exchange of virtual gravitons bewteen two gravitating real particles (weak gravity approximation + take non-relativistic limit). however for isolated particle (take the second particle to infinity) the gravitons are essentially on-shell, they are real -- these describe gravitational radiation (waves)
All the above is the very standard view on gravity as well as other interactions, say electromagnetism etc...Verlinde's theory is radically different though. There are NO gravitons there neither virtual nor real
MTd2 said:Given the cosmological aspect of this theory, we have to look for ways to find what went wrong in the above derivation. We know that the entropy of a particle at the particle horizon is 0. So, there must be a boundary condition for the U operator, otherwise, this problem will look like it was done in a universe a little bit larger than Earth, where the absober is a few micrometers away from the edge of the universe.
CHIKO-2010 said:There are no cosmological issues in deriving Newton's law within Verlinde's theory! Newton's force is a local force, which presumes that the Universe is static locally. Newton's law of gravity does not hold on cosmological scales.
Fra said:Ok that point is well taken. You're right that's the specific question here. And I admit that if we define the question as such, it's probably false. But my only point was that I feel that's somehow a too simple question & conclusion.
My point is that, although Verlindes idea seems imperfect, I think it's more interesting to try to discuss how it can be improved, rather than trying to just proove that it's false.
I disagree. I merely question that then notions of entropy is more complex than verlinde admits, but I think the underlying idea is not wrong. It may be wrong because the measures of information and the holographic principle is wrong. Both these things are IMHO related to the careless treatment of the observer, because the observer is also the home of the theory in my view.
So while it seems probably that the specific attempt of verlinde is flawed, there is something about the idea that I think is right. And since ideas in this direction are unfortunately rare, I show my support even though his first attempt is wrong. I see more than a flawed theory here - I see a way of reasoning that can generate theories.
/Fredrik
MTd2 said:Quantum Mechanics is not a local theory so you will have to look for boundary values and sum over all space if you want to do it right. For example,the operator U is expanded linearly as its border conditions at the holographic screen were irrelevant. In reality, U should be written like U=Aexp(...), where A is a function that makes U goes smoothly to 0 at the screen and to the maximum value of entropy at r=0.
What are you talking about? U as it is defined in the paper is the standard operator of translations which is valid in quantum mechanics! acting on a state \psi(z) it transforms the state into a new state \psi(z+\delta z) (\delta z can be counted as infinitesimally small). Again, it is completely irrelevant what are the entropies of these two states \psi(z) and \psi(z+\delta z). what is relevant is an entropy difference. QM is nonlocal theory in ceratin sense but in this particular case we are talking about gravitational potential energy of neutron-Earth system which depends only on local coordinate z.
CHIKO-2010 said:U as it is defined in the paper is the standard operato
MTd2 said:A standard operator that is non unitary...
CHIKO-2010 said:well, you could try to modify quantum mechanics also -- the claim in the paper is only valid if the usual quantum mechanical description of the given problem is correct, of course.
MTd2 said:This is what is done in the paper too, it is set up its own axioms to modify quantum mechanics. There are other ways too, like, I sugested, setting up a kappa modification dependent on space and/or time.