Question about cosmological constant

[haushofer]

Mmm, I'm still a bit confused, but I'll take another look at it. I wasn't talking about QG per se; how about a QFT on a (A)dS background? Would Lambda then also receive contributions from renormalization?

 

[strangerep]

I don't want to discuss DeSitter spacetime, b/c doing quantum gravity in that setting is an absolute ill-defined mess. It is relatively easier to discuss quantum gravity in AdS space, where as you know you still have a local Lorentz symmetry, but there will be an asymptotic Anti deSitter group acting on your theory. [...]

Perhaps I misunderstand, but I thought the dS group still has a Lorentz subgroup. (I'm thinking in the context of "de Sitter special relativity", as proposed in, e.g., this paper by Aldrovani et al.)

I think what you have in mind is when you change the *local* symmetry group from the Poincare group to the AdS or dS group. People have played with that, but there are issues with that formalism.

Hmm, not sure what "local" would mean in this context, since dS space, as a Riemannian space, is still locally flat (isn't it?). I'd assumed people meant "dS in the absence of matter".

Certainly there are difficulties with that approach, since the dS energy-momentum generators are no longer mutually-commuting, hence one cannot construct elementary modes as easily as in the Poincare case.

 

[Haelfix]

Haushofer, yes, the paper George Jones linked to in the thread has a technical section about what changes when you properly take into account changes in the background from the flat case (things change a bit, but it still doesn't help you).

Strangerep, Yep, I mean local exactly as in that paper you just mentioned. If you want, the tetrad fields instead of having lorentz Symmetry are now enlarged into a ds group. This is a nonstandard formulation, most attempts at qg always insist on keeping things locally Lorentz. The spacetime itself will be a background and the really important symmetries are those that alter the asymptotic symmetry group (so when people are doing AdS/CFT this is what they have in mind)

The worry one might have with enlarging into the ds group in that formalism, is that a priori there will be new representations where new particles could live, and I'm not sure if people have really succeeded in quantizing this formalism properly.

 

[Stavros Kiri]

... What about string theory versions vs Quantum loop gravity? What do they produce about the cosmological constant?

Correction: Loop Quantum Gravity (LQG). But Haelfix did not reply to that comment ...

 

[Stavros Kiri]

... QF particles ...

QF stands for "Quantum Field" or "Quantum Foam" ? Quantum foam particles are virtual particles (of very high energy). I assume that's what you mean.

 

[Stavros Kiri]

It seems that cosmology, quantum field theory and quantum gravity fail to explain the cosmological constant problem. Furthermore, other unsolved related problems, such as dark energy and dark matter, remain.
An alternative but promising apporoach is that of Serkan Zorba, which has now been modified to deal with the isotropy issue, and dares to explain all 3 problems in one stroke, which cannot be a coincidence:

http://arxiv.org/abs/1210.3021

I attach here the abstract:

"A disk-shaped universe (encompassing the observable universe) rotating
globally with an angular speed equal to the Hubble constant is postulated. It
is shown that dark energy and dark matter are cosmic inertial effects resulting
from such a cosmic rotation, corresponding to centrifugal (dark energy), and a
combination of centrifugal and the Coriolis forces (dark matter), respectively.
The physics and the cosmological and galactic parameters obtained from the
model closely match those attributed to dark energy and dark matter in the
standard Λ-CDM model."

 

[PeterDonis]

An alternative but promising apporoach is that of Serkan Zorba

We have had previous threads on this paper. As was commented in those threads, the model this paper proposes is not isotropic, which already makes it contradict observation. The fact that the model happens to contain inertial effects that can mimic dark matter and dark energy does not mean it must be a viable candidate. A viable candidate has to explain all known observations, not just some of them.

 

[Stavros Kiri]

We have had previous threads on this paper. As was commented in those threads, the model this paper proposes is not isotropic, which already makes it contradict observation. The fact that the model happens to contain inertial effects that can mimic dark matter and dark energy does not mean it must be a viable candidate. A viable candidate has to explain all known observations, not just some of them.

I agree. Unless tested and proved nothing is accepted. But even the LUX experiment for detecting dark matter on Earth probably is also failing, although it reached its maximum resolution limit, and the standard Λ-CDM model is also under question. Especially after a possible new discovery that the Hubble constant may be bigger than thought (and the universe is expanding 9℅ faster than thought):

https://www.newscientist.com/articl...-expanding-9-per-cent-faster-than-we-thought/

P.S.(edit): the quoted ref. in my previous comment is a new version of his paper, also addressing isotropy. But I don't plan on insisting on a further discussion on the topic, because I think there is insufficient data to support any of the views in the subject (e.g. observing of rotation vs the also yet undetected WIMPs and MACHOs).

 

[jim meyer]

I have been reading about this stuff for many years and wonder why the constants being used at this time to devise models are never questioned other than the Cosmological Constant. It seems to me there are two basic kinds of constants-those that are observed and those that are calculated in some way. An observed constant like redshift and the speed of light are observed while Planck's Constant is calculated from prior thermal constants. And E=mc^2 is not even a constant although I cannot prove it is not. Using it as a constant has been the law of the land for a century now and it should be looked into and seen as a first approximation- a very good flash of intuition from a great mind for sure and made without a cell phone or a computer. The Hubble Constant is observed and has been assumed to be caused by motion when it just as well can be caused by gravity. These problems have huge influences on current models being kicked around and this has been going on for most of a century always with the same result-isn't that a definition the author of E-mc^2 kicked around?

 

[PeterDonis]

why the constants being used at this time to devise models are never questioned

Assuming that by "questioned" you mean "questioned whether they are really constants", you are wrong to thing that those questions are not being asked. They are, and so far, measurements indicate that they are indeed constant to the accuracy we can measure. See, for example, here:

https://en.wikipedia.org/wiki/Time-variation_of_fundamental_constants

E=mc^2 is not even a constant

That's true, it's not a constant, it's an equation. I don't understand what you are trying to say here.

The Hubble Constant is observed and has been assumed to be caused by motion when it just as well can be caused by gravity.

I don't understand what you are trying to say here either.

I think you need to learn some more about the actual models and experiments.

 

[jim meyer]

OK I'll try to explain. The constants that are observed can be explained some day maybe in the distance future. I have no problem with any of them. The calculated constants are all based on prior art like the laws of thermal events which are very handy tools. Except Newton's Laws, none of these older laws work in areas far from our environment. Thermal laws were developed from observations calibrated from ambient conditions. If all observations could be calibrated from absolute zero rather than some point around ambient and a uniform system of units developed maybe many of the mysterious puzzles that have evolved in physics would vanish and QM would be much clarified. Now as for the Hubble red shift being caused by an expanding universe the effect could be caused by gravity since most of the mass in the universe fills vacuum of space and surely could be why the red shift exists.

 

[Nugatory]

Except Newton's Laws, none of these older laws work in areas far from our environment. Thermal laws were developed from observations calibrated from ambient conditions. If all observations could be calibrated from absolute zero rather than some point around ambient...

That makes no sense. It was more than a century ago that we discovered that the laws of thermodynamics follow directly from Newton's laws by using the methods of statistical mechanics; it's just not true that they depend on observations made around ambient. I'm not sure what you mean by "calibrating from absolute zero", but we've been working with degrees Kelvin before doing our calculations for almost as long, and every serious physics lab has access to a supply of liquid nitrogen just like it has electrical power and running water - many physics experiments are looking for effects that are easiest to see when thermal noise from ambient temperature has been eliminated.

Now as for the Hubble red shift being caused by an expanding universe the effect could be caused by gravity since most of the mass in the universe fills vacuum of space and surely could be why the red shift exists.

Please be mindful of the Physics Forums rule prohibiting posting personal theories and speculations. Unless you can provide a link to a peer-reviewed paper presenting this idea, you are not allowed to present it here. There is much discussion of why we have this policy in various threads in the Feedback section.

 

[Vanadium 50]

most of the mass in the universe fills vacuum of space

There are two ways to read this. One is incorrect and the other is tautological.

 

[Stavros Kiri]

Now as for the Hubble red shift being caused by an expanding universe the effect could be caused by gravity since most of the mass in the universe fills vacuum of space and surely could be why the red shift exists.

There has been a very good discussion here (in PF) about "Gravitational Redshift and Hubble":

https://www.physicsforums.com/threads/gravitational-redshift-and-hubble.745905/

Gravitational redshift is usually much smaller and negligible (etc.)

So, in general, instead of assuming, it is always good to see what already science has found.