Dark Energy May Not Be A Constant Force

[zapatos]

Quote

Distant, ancient galaxies are giving scientists more hints that a mysterious force called dark energy may not be what they thought.

...findings published earlier this year by an international research collaboration of more than 900 scientists from around the globe yielded a major surprise. As the scientists analyzed how galaxies move they found that the force pushing or pulling them around did not seem to be constant. And the same group published a new, broader set of analyses Tuesday that yielded a similar answer.

The map they are building would not make sense if dark energy were a constant force, as it is theorized. Instead, the energy appears to be changing or weakening over time.

 

[zapatos]

Sorry, forgot to add the link...

https://apnews.com/article/dark-energy-desi-cosmology-astronomy-7856ae96fab5cb42e6b4a6fd7c3555ec

[swansont]

“If dark energy is constant, the universe will continue to expand, forever getting colder and emptier. If it’s growing in strength, the universe will expand so speedily that it’ll destroy itself in what astronomers call the Big Rip.”

If they’ve considered it might grow in strength, the notion that it was assumed to be constant is overstated.

[exchemist]

7 hours ago, zapatos said:

Sorry, forgot to add the link...

https://apnews.com/article/dark-energy-desi-cosmology-astronomy-7856ae96fab5cb42e6b4a6fd7c3555ec

Would be funny if it turns out to be some very large scale inverse square law. Newton would be cackling in his grave.

[TheVat]

Could energy density vary from one region of space to another?

[TheVat]

This paper considers a field variable over time (not space).

https://arxiv.org/abs/astro-ph/9505060

 

Quote

We explore the cosmological implications of an ultra-light pseudo-Nambu-Goldstone boson. With global spontaneous symmetry breaking scale f≃1018 GeV and explicit breaking scale comparable to MSW neutrino masses, M∼10−3 eV, such a field, which acquires a mass mϕ∼M2/f∼H0, would have become dynamical at recent epochs and currently dominate the energy density of the universe. The field acts as an effective cosmological constant for several expansion times and then relaxes into a condensate of coherent non-relativistic bosons. Such a model can reconcile dynamical estimates of the density parameter, Ωm∼0.2, with a spatially flat universe, and can yield an expansion age H0t0≃1 while remaining consistent with limits from gravitational lens statistics.

 

[Genady]

2 hours ago, TheVat said:

Could energy density vary from one region of space to another?

If it does, the cosmological principle needs to be reconsidered.

[TheVat]

BTW, if the main facility that is generating quintessence theories is called DESI, then they should have a facility that generates rival  vacuum energy theories called LUCY.  

[swansont]

1 minute ago, TheVat said:

BTW, if the main facility that is generating quintessence theories is called DESI, then they should have a facility that generates rival  vacuum energy theories called LUCY.  

They would have some explaining to do 

[TheVat]

8 minutes ago, Genady said:

If it does, the cosmological principle needs to be reconsidered.

So I wondered, if a standard quintessence field alone is not expected to be anisotropic because it is modeled as a homogeneous scalar field across the universe, then are there other theoretical frameworks where a quintessence field could exhibit anisotropic behavior?  I had seen something a while ago where researchers are investigating scenarios where a quintessence field within a compact star (like a neutron star) could contribute to anisotropic pressure due to the star's internal structure, leading to an anisotropic manifestation of the quintessence field within that specific region.

Beyond my understanding of physics, but could there be some anisotropic stress component in the energy-momentum tensor?  Modifying GR?

10 minutes ago, swansont said:

They would have some explaining to do 

Hahaha!

[Genady]

2 minutes ago, TheVat said:

So I wondered, if a standard quintessence field alone is not expected to be anisotropic because it is modeled as a homogeneous scalar field across the universe, then are there other theoretical frameworks where a quintessence field could exhibit anisotropic behavior?  I had seen something a while ago where researchers are investigating scenarios where a quintessence field within a compact star (like a neutron star) could contribute to anisotropic pressure due to the star's internal structure, leading to an anisotropic manifestation of the quintessence field within that specific region.

Beyond my understanding of physics, but could there be some anisotropic stress component in the energy-momentum tensor?  Modifying GR?

Local inhomogeneities and anisotropies do not matter on cosmological scales. The cosmological principle's assumption is that on some large scale, currently about 100+ Mpc AFAIK, the universe is homogeneous and isotropic. All manifestations of the DE so far are on such scales.

[Mordred]

2 hours ago, Genady said:

The cosmological principle's assumption is that on some large scale, currently about 100+ Mpc AFAIK

100 Mpc is the correct currently accepted scale though there was roughly 5 years ago some consideration of using 120 Mpc instead. Never happened as it wasn't really necessary.

Here is a counter paper to the DESI findings and it raises a couple of valid points in so far as DESI uses the Hubble tension as part of its argument however the Hubble tension is largely resolved in so far as the later papers brought forward.

https://arxiv.org/abs/2404.18579

In essence the paper strongly suggests caution as the evidence isn't strong enough yet.

Edited 9 hours ago by Mordred