Ali and Das, "Cosmology from quantum potential"

[Ken G]

I don't know, this seems restrictive. Of course nature tells us how things work, but building a theory, deriving observable consequences, and then constructing the observations seems as good as devising a priori observations without knowing what the results might mean.

I'm not commenting on whether doing those things are good or not, I'm commenting on what conclusions we can, or cannot, draw from having done the exercise. It should never have surprised us that a clever physicist could create a model that started at t=0, and that another could take that same model, and modify it so that it went to t = -infinity, and that both models would equally well match every observation we have ever done. Should we really be surprised both these things are possible to do? What we should be asking ourselves is, what observation can we do which is capable of distinguishing them, because until we have a specific way to distinguish them, it's not obvious that they are even different. For example, I can do a trivial functional remapping of the t parameter in quantum mechanics to some new function f(t), such that df/dt = 1 for the entire observed history of the universe, but f goes to -infinity when t goes to zero. What would it mean to do that? My "theory" makes all the same predictions as quantum mechanics, and has the same beginning as our current concept of time does, but it calls that beginning f=-infinity. So which one is the "real time", t or f(t)? No observation answers that, so the question is moot, yet I can still claim that my f(t) is some kind of "quantum mechanical correction" for any philosophical reason I want. But if I can't give a specific or testable reason why my f(t) is something different from their t, then we should all be dubious that there is any difference that is not angels on a pin.

 

[ftr]

So, are they saying that the matter energy in the universe equals vacuum energy. That is, Einstein did not make a blunder.

 

[Demystifier]

Is that really a correct way to get a Bohmian model of quantum gravity? For comparison, another Bohmian model of early cosmology is http://arxiv.org/abs/1407.8262 Primordial quantum nonequilibrium and large-scale cosmic anomalies by Samuel Colin and Antony Valentini.

Different choices of the wave function (recall that wave equations, including Wheeler-DeWitt, have many different solutions) lead to different predictions, with or without Bohmian trajectories.

 

[JonnyMaddox]

Hi, here some opinion from a blogger:
http://backreaction.blogspot.de/2015/02/black-holes-dont-exist-again-newsflash.html
She says that it's completely bullshit and is based on a wrong and unjustified model of GR called "rainbow gravity" and even stringtheory.

 

[martinbn]

Hi, here some opinion from a blogger:
http://backreaction.blogspot.de/2015/02/black-holes-dont-exist-again-newsflash.html
She says that it's completely bullshit and is based on a wrong and unjustified model of GR called "rainbow gravity" and even stringtheory.

That's unrelated.

 

[ftr]

So, are they saying that the matter energy in the universe equals vacuum energy. That is, Einstein did not make a blunder.

Let me clarify my question. They claim to solve the coincidence problem, what do they exactly mean by that, and How did they do that.

 

[Ken G]

Perhaps I'm wrong, but it looked to me like they "solved" it with pure sleight of hand-- they embedded the current size of our observable universe as if it was a "natural" parameter in their theory, and then the fact that dark energy is just starting to dominate seems "natural" as well, but it's actually still a coincidence. Their main point seemed to be that the term corresponding to a cosmological constant falls out naturally, but it's perhaps not too shocking that a constant term can appear in a quantum "correction."

 

[ChrisVer]

A similar post is in the cosmology section:
https://www.physicsforums.com/threads/quantum-equations-suggest-the-big-bang-never-happened.797073/
although the references there are not so reliable...

 

[bcrowell]

Low and behold, once I ran the search, what popped up on the google search engine was something like "the big bang never happened" and a link the Phys.org article and the Glenn Beck link:

a paper that says that the big bang didn't exist, e.g., http://www.glennbeck.com/2015/02/10/watch-the-big-bang-never-happened/ .

Your quote makes it sound like I said very nearly the opposite of what I said:

Some elements of the popular media seem to be picking up on it and describing it as a paper that says that the big bang didn't exist, e.g., http://www.glennbeck.com/2015/02/10/watch-the-big-bang-never-happened/ .

I would have thought it would be pretty clear from what I wrote that I think this is a silly, ignorant interpretation of the paper.

I'm not a cosmologist but I have interest in it and pretty much thought we had a pretty good handle on what happened back to 10^-43 seconds through the "first 3 minutes." The news of this topic and model's like Penrose's CCC model now make me question to what measure can I trust the reliability of these ostensibly pseudo-exact measurements of the features of the birth of the universe I read in the big bang and chronology of the universe wiki's, say

http://en.wikipedia.org/wiki/Big_Bang
http://en.wikipedia.org/wiki/Chronology_of_the_universe

Neither CCC nor the Ali-Das paper invalidates anything about the accepted picture of the time period you're referring to. (CCC has also been falsified because of its predictions about particle physics, although Penrose, disappointingly, doesn't seem willing to admit that.)

My question is, why am I studying this standard big bang cosmology that the universe was such and such a size at such and such a time, and baryongenesis happened at this microsecond, and the the quark gluon plasma happened at that microsecond, when everyone goes running for the hills when someone comes along and gets an article published in Physics Letters B which says that the big bang never happened and the universe is eternal.

You're misinterpreting and oversimplifying the content of the paper.

 

[plschwartzx]

First I want to address the Glenn Beck issue. Hopefully I am wrong but it almost seems that a few suggest that publishing this paper gave fuel to his arguments and it might have been better not to publish this.. For me mentioning him at all on this forum plays into his rants. In fact he is just like cow patties in a field. Just walk around them.
Second it was enlightening to see a physics strongly influence by Indian physicists. Just as a Big-Bang theory is consonant with the Judeo-Chrtistian creation story, this perhaps Indo-centric physics reflects an eternal universe consonant with Hindu mythology.

 

[DiracPool]

I would have thought it would be pretty clear from what I wrote that I think this is a silly, ignorant interpretation of the paper.

I think it was pretty clear myself, I didn't intend to imply anything otherwise.

Your quote makes it sound like I said very nearly the opposite of what I said:

I don't know how you got that from that post. My intent was to agree with you and say I was alarmed as well when the the popular media (ala Glenn Beck) twisted this instantly into a big bang denial debate. So I think we are of like mind there.

 

[bolbteppa]

I haven't read the paper but it seems like it's no surprise that they began with one theory that has issues with special relativity (bohmian mechanics) to derive results in another theory that has issues with special relativity (loop quantum gravity) to cast doubts on basic results in general relativity...

My (weak) understanding is that Bohmian mechanics assumes an actual true trajectory but says that information about it is inaccessible, contradicting the Heisenberg uncertainty principle as Landau states it: "there is no such concept as the path of a particle". By ignoring standard quantum mechanics so blatantly, any Bohmian claim about paths directly should immediately be suspect, right?

From this perspective it seems like what they do will look consistent. If they start from classical mechanics by talking about geodesic paths, and then attempt to encode but obscure it's information in some potential function that apparently implies we are doing quantum mechanics, then there's no reason why you can't end up with an apparent quantum geodesic equation.

But Heisenberg as Landau states is completely destroys this whole approach. That one claim is the difference between quantum and classical mechanics, and they seem to be making a huge classical assumption that QM completely refutes. Furthermore, given that Bohmian mechanics apparently has huge issues with special relativity, quantum field theory and spin, let alone about Heisenberg actually means, I see no reason to trust any of this. So from my ill-educated perspective it kind of looks like a piece of mathematics only.

I may be wrong, I do not wish to learn too much about a theory that looks so fraught with problems at this moment, later Thoughts?

 

[atyy]

I haven't read the paper but it seems like it's no surprise that they began with one theory that has issues with special relativity (bohmian mechanics) to derive results in another theory that has issues with special relativity (loop quantum gravity) to cast doubts on basic results in general relativity...

I don't know if there is a rigourous proof that Bohmian mechanics is ok for gravity. However, Bohmian Mechanics is generally thought to be ok for non-relativistic quantum mechanics. I think gravity can be put on a lattice, so by this informal argument, Bohmian Mechanics should be ok for gravity.

As far as I can tell, neither the paper in the OP nor Valentini's has anything to do with LQG. LQC was brought up only because there are good arguments that there is a bounce in that theory.

My (weak) understanding is that Bohmian mechanics assumes an actual true trajectory but says that information about it is inaccessible, contradicting the Heisenberg uncertainty principle as Landau states it: "there is no such concept as the path of a particle". By ignoring standard quantum mechanics so blatantly, any Bohmian claim about paths directly should immediately be suspect, right?

There can be a path in non-relativistic quantum mechanics - what is forbidden is a path in which position and momentum (as specified by the canonical commutation relations) simultaneously exist at all times (even that may have some exceptions).

Furthermore, given that Bohmian mechanics apparently has huge issues with special relativity, quantum field theory and spin, let alone about Heisenberg actually means, I see no reason to trust any of this. So from my ill-educated perspective it kind of looks like a piece of mathematics only.

QED itself has problems with special relativity, since it has a Landau pole. So if we believe QED is just formulated on a fine lattice, Bohmian Mechanics can be argued not to have a problem. As far as I know, the major problem with Bohmian Mechanics is whether it can treat chiral fermions interacting with non-Abelian gauge fields. But that problem is also being worked on by lattice gauge theorists (for reasons not related to Bohmian Mechanics), so if lattice gauge theory has a chance, then so does Bohmian Mechanics.

 

[Demystifier]

As far as I know, the major problem with Bohmian Mechanics is whether it can treat chiral fermions interacting with non-Abelian gauge fields.

Why do you think that this is the major problem with Bohmian mechanics? Any reference?

 

[Demystifier]

Furthermore, given that Bohmian mechanics apparently has huge issues with special relativity, quantum field theory and spin,

Bohmian mechanics does have some problems with special relativity and quantum field theory, but it does not have any problems with spin.

 

[Demystifier]

I haven't read the paper but it seems like it's no surprise that they began with one theory that has issues with special relativity (bohmian mechanics) to derive results in another theory that has issues with special relativity (loop quantum gravity) to cast doubts on basic results in general relativity...

I agree that both Bohmian mechanics and loop quantum gravity have some problems with special relativity, but I strongly disagree that Lubos Motl's blog is a good place to read about these problems.

 

[martinbn]

Not to digress but what problems does loop quantum gravity have with special relativity!?

 

[atyy]

Why do you think that this is the major problem with Bohmian mechanics? Any reference?

I'm basing my argument on the idea that Bohmian Mechanics should be able to handle any lattice model. As far as I know, the major obstacle to a lattice standard model is chiral fermions interacting with non-Abelian gauge fields.

http://arxiv.org/abs/1003.5896
"At the moment of writing, a generalization of the proof to general anomaly-free nonabelian chiral gauge theories is not known. Apart from the fermion measure problem, there are other issues with the formulation of lattice chiral gauge theories with Ginsparg-Wilson fermions by the path integral (26):"

http://arxiv.org/abs/0912.2560 "In contrast, there is currently no practical way to regulate general nonabelian chiral gauge theories on the lattice. (There has been a lot of papers in this area, however, in the context of domain wall - overlap - Ginsparg-Wilson fermions; for a necessarily incomplete list of references that gives you a flavor of the work in this direction, see (Kaplan, 1992; Kaplan, 1993; Narayanan and Neuberger, 1993; Narayanan and Neuberger, 1995; Narayanan and Neuberger, 1996; Kaplan and Schmaltz, 1996; Luscher, 1999; Aoyamand Kikukawa, 1999; Luscher, 2000b; Kikukawa and Nakayama, 2001; Kikukawa, 2002; Kadoh and Kikukawa, 2008; Hasenfratz and von Allmen, 2008) ). Thus we lack of a nonperturbative regulator for the Standard Model - but then again, we think perturbation theory suffices for understanding the Standard Model in the real world."

There are proposals, but I believe there is no consensus on their correctness.

http://arxiv.org/abs/0912.3892
"A first objection against our construction of weak gauge fields in section 4.2 is that it presents a lattice regularization for chiral gauge field theory. But to obtain such a regularization is a famous problem of chiral lattice gauge theory [15], and there are various no-go theorems for such regularizations. But the regularization problem of chiral gauge theory is the problem to find a gauge-invariant regularization. Our regularization has no exact gauge invariance on the lattice. Instead, we have only approximate gauge invariance - the generators of the gauge group are associated with nontrivial lattice shifts. Thus, our regularization is not in contradiction with the various no-go theorems for regularizations with exact gauge invariance."

http://arxiv.org/abs/1305.1045
"Defining standard model non-perturbatively is a well=known long standing problem, which is referred generally as chiral-fermion/chiral-gauge problem. There are many previous researches that try to solve this general problem. There are lattice gauge theory approaches, which fail since they cannot reproduce chiral couplings between the gauge field and the fermions."

 

[Demystifier]

I'm basing my argument on the idea that Bohmian Mechanics should be able to handle any lattice model. As far as I know, the major obstacle to a lattice standard model is chiral fermions interacting with non-Abelian gauge fields.

But this is a problem irrespective of whether you use Bohmian mechanics or not. So this is not a problem for Bohmian mechanics per se. Besides, lattice models are usually considered to be only approximations, so there is no fundamental reason why Bohmian mechanics should be able to handle lattice models.

I am usually not sarcastic, but in this case sarcasm may be a good tool to convey the message. So let me try with sarcasm: The world peace is a big problem, and nobody knows how to solve it with Bohmian mechanics. Yet, we usually don't say that the world peace is a big problem for Bohmian mechanics.

 

[atyy]

But this is a problem irrespective of whether you use Bohmian mechanics or not. So this is not a problem for Bohmian mechanics per se. Besides, lattice models are usually considered to be only approximations, so there is no fundamental reason why Bohmian mechanics should be able to handle lattice models.

I am usually not sarcastic, but in this case sarcasm may be a good tool to convey the message. So let me try with sarcasm: The world peace is a big problem, and nobody knows how to solve it with Bohmian mechanics. Yet, we usually don't say that the world peace is a big problem for Bohmian mechanics.

What I mean is getting a Bohmian standard model, and Bohmian supersymmetry and Bohmian (post)quantum gravity are the big problems with Bohmian Mechanics, or any attempt to solve the measurement problem. The lattice approach seems to me most promising to getting a Bohmian standard model, which is why I mention the chiral fermion problem. Are there other promising ways to get a Bohmian standard model?

Are lattice models only approximations? Yes! But maybe even AdS/CFT can be an approximation, if the CFT can be put on the lattice :)

 

[Demystifier]

The lattice approach seems to me most promising to getting a Bohmian standard model

Why?

 

[atyy]

Why?

Because a lattice model is non-relativistic quantum mechanics, and Bohmian Mechanics is usually thought to be ok for that.

 

[Demystifier]

Because a lattice model is non-relativistic quantum mechanics, and Bohmian Mechanics is usually thought to be ok for that.

I see your point.

 

[atyy]

I see your point.

I also wonder if this approach can be used to get Bohmian quantum gravity, if the CFT can be put on the lattice. I'm still hoping that some Bohmian professionals* will work on it :) I think there are still problems with supersymmetry on the lattice, but there seems to be more progress than with lattice chiral fermions.

*Maybe the same one who worked on Bohmian string theory :P

 

[Demystifier]

I also wonder if this approach can be used to get Bohmian quantum gravity, if the CFT can be put on the lattice. I'm still hoping that some Bohmian professionals* will work on it :) I think there are still problems with supersymmetry on the lattice, but there seems to be more progress than with lattice chiral fermions.

*Maybe the same one who worked on Bohmian string theory :P

At the moment I am working on something completely different.

 

[Terry M]

Perhaps I'm wrong, but it looked to me like they "solved" it with pure sleight of hand-- they embedded the current size of our observable universe as if it was a "natural" parameter in their theory, and then the fact that dark energy is just starting to dominate seems "natural" as well, but it's actually still a coincidence. Their main point seemed to be that the term corresponding to a cosmological constant falls out naturally, but it's perhaps not too shocking that a constant term can appear in a quantum "correction."

I think it goes something like this. There are bosons (their "condensate") with small masses that supply the dark energy for the observed cosmological constant. These bosons have a wave function which must extend over the observable universe. The macroscopic ground state of that wave function is therefore of this size. So to the degree that the theory is true, their use of the current observable universe size is legitimate.

 

[Ken G]

I think it goes something like this. There are bosons (their "condensate") with small masses that supply the dark energy for the observed cosmological constant. These bosons have a wave function which must extend over the observable universe. The macroscopic ground state of that wave function is therefore of this size. So to the degree that the theory is true, their use of the current observable universe size is legitimate.

But my contention is, if you take that as your boson size, then you are building a theory that will automatically have the right cosmological constant. In other words, you either think that we live in a special age that just happens to have the scale of the universe be the scale of the boson rest energies, or you think the boson rest energies dynamically respond to the scale of the universe. Either way, it sounds like a manual inclusion-- a universe that is built to have a cosmological constant like we see. Nothing wrong with putting in the cosmological constant that is needed, but then they seem to say, what a surprise, the cosmological constant just "falls out" of our theory, but rather it seems to be to simply be built into it and then had its tracks covered up. I don't have an objection to building a theory with a cosmological constant in it, I object to the claim that this somehow "explains" the cosmological constant. There are many ways to build gravity to make the universe flat, the question is, why is it built that way?

 

[write4u]

But my contention is, if you take that as your boson size, then you are building a theory that will automatically have the right cosmological constant. In other words, you either think that we live in a special age that just happens to have the scale of the universe be the scale of the boson rest energies, or you think the boson rest energies dynamically respond to the scale of the universe. Either way, it sounds like a manual inclusion-- a universe that is built to have a cosmological constant like we see. Nothing wrong with putting in the cosmological constant that is needed, but then they seem to say, what a surprise, the cosmological constant just "falls out" of our theory, but rather it seems to be to simply be built into it and then had its tracks covered up. I don't have an objection to building a theory with a cosmological constant in it, I object to the claim that this somehow "explains" the cosmological constant. There are many ways to build gravity to make the universe flat, the question is, why is it built that way?

How about inevitability in accordance to available potential, the Implicate. (Bohm)

But even if the universe is flat, how deep is it? IMO, spacetime is 3 dimensional, which would indicate sufficient vertical room to express itself. The 3D sphere of a giant black hole the size of 12,000,000,000 galaxies has been discovered. If the universe is flat, how deep is this flatness or surface?

Why is a fractal consisting of straight lines able to create circular constructs? Could it be an expression of gravity or could it be causal to the existence of gravity?

The fractal dimension of a curve can be explained intuitively thinking of a fractal line as an object too detailed to be one-dimensional, but too simple to be two-dimensional.[6] Therefore its dimension might best be described not by its usual topological dimension of 1 but by its fractal dimension, which in this case is a number between one and two

, and

Fractals are different from other geometric figures because of the way in which they scale. Doubling the edge lengths of a polygon multiplies its area by four, which is two (the ratio of the new to the old side length) raised to the power of two (the dimension of the space the polygon resides in). Likewise, if the radius of a sphere is doubled, its volume scales by eight, which is two (the ratio of the new to the old radius) to the power of three (the dimension that the sphere resides in). But if a fractal's one-dimensional lengths are all doubled, the spatial content of the fractal scales by a power that is not necessarily an integer.[2] This power is called the fractal dimension of the fractal, and it usually exceeds the fractal's topological dimension.[7]

As mathematical equations, fractals are usually nowhere differentiable.[2][5][8] An infinite fractal curve can be conceived of as winding through space differently from an ordinary line, still being a 1-dimensional line yet having a fractal dimension indicating it also resembles a surface

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

CDT (causal dynamical triangulation, Renate Loll) is currently being studied in several areas of physics and cosmology.

The expression, "we live on the surface of spacetime fabric" seems misleading to me.
I like to think of it as, "we live inside the spacetime fabric".

Just a musing.

 

[write4u]

Bohmian mechanics does have some problems with special relativity and quantum field theory, but it does not have any problems with spin.

Question: To my understanding quantum events (QM) occur regardless of GR. However GR is a result of the conditions created by QM. It seems a one-way street.
QM = causality (potential) of future physical events and conditions (Implicate)
GR = apparent results of physical events and conditions depending on the point of the observer (Explicate)

As I understand Bohm, QM and GR were valid aspects (universal laws) of spacetime but addressed specific and separate properties of our universe.
In his "holomovement" Bohm treats them as compatible if seen in a larger framework.

 

[Demystifier]

Question: To my understanding quantum events (QM) occur regardless of GR. However GR is a result of the conditions created by QM. It seems a one-way street.

I don't think so. Gravity (GR) does influence quantum events. See e.g.
http://www.ift.uam.es/oldIFT/paginaspersonales/bellido/cuantica/articulos/PhysRevLett.34.1472.pdf