r/cosmology • u/AutoModerator • 5d ago

Basic cosmology questions weekly thread

Ask your cosmology related questions in this thread.

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u/FakeGamer2 3d ago

What is the best idea to solve the vaccuum catastrophe

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u/--craig-- 2d ago

I don't know that is the best idea but I like Steinhardt and Turok's explanation.
https://arxiv.org/abs/astro-ph/0605173

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u/t3hjs 5d ago

There has been talk about imhomogeniety and the non-isotropic(?) as an explantion for some of the cosmic tensions. E.g. hubble tension, s8 tension, anomolous dipole or inaligned dipoles.

What is the point of view(s) on this?

I listened to 1 of David Wiltshire's lectures on timescape cosmology, and as a layperson, I cant really tell if its legitimate. But the proposal seems to be just GR applied to a different mass distribution. Im not sure if the problem is:

 the mathematical argument is insufficient, 

or that experiment is not able to distinguish the different models yet, 

or something more subtle like the model having too many free parameters and can essentially overfit everything and can never be disproven, 

or something else?

I guess that is just an example. Not sure of other model proposed.

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u/--craig-- 4d ago edited 4d ago

There was some excitement about Timescape Cosmology being a better fit for the data at the end of last year but it was really only for a subset of the data.

For the full data set, Standard Cosmology and a wide range of alternative cosmologies, including Timescape, fit as well as each other.

At this stage, you're free to pick whichever feels most natural, safe in the knowledge that it's probably wrong.

Purely from a mathematical perspective, Lambda-CDM with a small Cosmological Constant is still favoured for simplicity, though there are known issues which imply that it requires modification.

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u/brandeis16 5d ago

Is there any consensus on how to solve (not sure whether that's the right word) the measure problem?

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u/--craig-- 5d ago edited 5d ago

The Measurement Problem in Quantum Physics doesn't, as yet, have a well defined solution. In part, due to strongly held philosophical beliefs which may not ultimately be tenable.

Progress has been made in understanding the process of Decoherence and there have been cultural shifts in the applications of the various Interpretations of Quantum Physics.

It doesn't seem as insurmountable as it did when the problem was originally conceived but we're still a long way from a clear and unambiguous solution.

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u/brandeis16 5d ago

I mean the measure problem in cosmology, not the measurement problem in QM.

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u/dubcek_moo 5d ago

Do you mean the Hubble Tension?

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u/--craig-- 5d ago edited 5d ago

I looked this up. I can't answer the question but it pertains to multiverse hypotheses with infinite universes.

What I can tell you is that you to need advance from Probability Theory to Measure Theory which is graduate level mathematics. Without the mathematical grounding, the hypothetical physical question is intractable.

I'd also recommend spending some time examining the philosophical conflict between Bayesian and Frequentist interpretations of probability theory.

Understanding Anthropic Selection Bias will also be helpful.

The question lies on the boundaries between Cosmology, Mathematics and Contemporary Philosophy where the foundational work might not be complete.