Why we've got the cosmological constant all wrong

[Analog]

(PhysOrg.com) -- Some scientists call the cosmological constant the "worst prediction of physics." And when today’s theories give an estimated value that is about 120 orders of magnitude larger than the measured value, it’s hard to argue with that title. In a new study, a team of physicists has taken a different view of the cosmological constant, Λ, which drives the accelerated expansion of the universe. While the cosmological constant is usually interpreted as a vacuum energy, here the physicists provide evidence to support the possibility that the mysterious force instead emerges from a microscopic quantum theory of gravity, which is currently beyond physicists’ reach.

The scientists, Stefano Finazzi, currently of the University of Trento in Povo-Trento, Italy; Stefano Liberati at SISSA, INFN in Trieste, Italy; and Lorenzo Sindoni from the Albert Einstein Institute in Golm, Germany, have published their study in a recent issue of Physical Review Letters.
The authors are far from the first who are dissatisfied with the cosmological constant. Previously, other scientists have suggested that the huge discrepancy between the observed and estimated values is due to the use of semi-classical effective field theory (EFT) calculations for estimating a quantity that can be computed only using a full quantum theory of gravity. Although no one can show what value a quantum theory of gravity would give without having such a theory, physicists have shown that EFT calculations fail at estimating similar values in analogue gravity models.
Here, the physicists consider an analogue gravity model in the form of a Bose-Einstein condensate (BEC), a group of atoms that behave as a single quantum system when cooled to temperatures near absolute zero. While a BEC may seem to have nothing in common with the expanding universe, the physicists showed in a previous paper that a BEC can be described by the same Poisson equation that describes nonrelativistic (Newtonian) gravity. This framework includes a term that is analogous to the cosmological constant; this term describes the part of a BEC’s ground-state energy that corresponds to the condensate’s quantum depletion.
Since BECs are accurately described by other (quantum) equations, the physicists decided to test how well EFT calculations could compute the BEC’s analogous cosmological constant term. They found that EFT calculations do not give the correct result. The finding confirms the earlier studies that showed that EFT calculations produce an incorrect result when used to compute the ground-state energy of other analogue gravity models.

 

[AstroManLuca]

wat

 

[FoBoT]

did you want this in highly technical or were you just trying to make us feel bad

 

[Analog]

did you want this in highly technical or were you just trying to make us feel bad

That's true - somehow having this in the same place a thread on using food color on pubes might be a mismatch... .. :whiste:

 

[SagaLore]

That big A is missing a line.




...could you summarize this into layman's terms please?

 

[NikolaeVarius]

Cliffs

Measured value and theoretical value of the cosmological constant is off by 120 orders of magnitude

This stems from the fact that we don't have a Quantum Theory of gravity which is needed to calculate such a value.

We instead use the EFT, a similar "type" of theory to try and approximate value.

However large discrepancy in these values makes physicists think that EFT is a poor way of doing such calculations, and other experiments have shown EFT is inaccurate for many similar types of experiments.

So in this experiment they used a group of Atoms with a known cosmological constant value and attempt to use the EFT to calculate it again. This failed and the calculated value of the EFT was not correct.

This shows that the EFT value for the cosmological constant is incorrect and needs to be fixed because EFT is a poor way of finding the CC.

Pretty easy.

 

[BurnItDwn]

Fucking Bose-Einstein condensate! Shoulda went with Klipsh-Einstein or perhaps Kef-Einstein condensates.

 

[FoBoT]

and they say science is all based on facts :awe:

 

[Matthiasa]

Hypothetical physics tends to be based a little less on facts and a little more on what they think is probably the case.
Sometimes they end up being right, other times not so much.

 

[Analog]

Hypothetical physics tends to be based a little less on facts and a little more on what they think is probably the case.
Sometimes they end up being right, other times not so much.

by that many orders of magnitude?

 

[destrekor]

and they say science is all based on facts :awe:

. . .

 

[Matthiasa]

by that many orders of magnitude?

Well for quantum physics being in the same order of magnitude as reality is often a feet in and of itself.

People often get PHDs for that.
And why tables are really nice for designing stuff at that level.