Recent content by PeterDonis

Where here "expanding" means "has a positive expansion scalar", which is an invariant property of a congruence.

Why do you think this is "worth drawing a line under"?

Looks ok now, yes.

Testing: ##p = w \rho##.

I'm having a somewhat different problem: whatever is going on in the editor changes my LaTeX to symbols like those from the "insert symbol" dropdown, but only after I hit "Post". It previews as LaTeX but posts as symbols. That is most emphatically not the behavior I want or expect. For one...

It's a theorem about spacetime models using General Relativity. Such models can include stress-energy that has an equation of state that can only be accounted for by some kind of quantum theory, but the quantum theory itself doesn't appear in the spacetime model. In other words, even if we're...

Can you revert to a previous version that is known not to have this problem?

I've already explained that: anything with an equation of state ##p = w \rho## where ##w < −1/3## violates the energy conditions that are one of the assumptions of the singularity theorem. Anything that can cause inflation falls into that category.

Not exactly. ##w## is the ratio of pressure to density. For the simplest model of inflation (which works just like a cosmological constant), ##w = -1##, meaning ##p = - \rho##. So all three pressures (since they all are equal to ##p## in this model) are equal to minus the energy density. Yes...

That shouldn't be possible with a cosmological constant, because the energy density of matter and radiation can only decrease with expansion, so once the universe has expanded to the point where the cosmological constant dominates, it should keep dominating (i.e., expansion should keep...

Who said the superposition had to be equal?

Thanks, that makes it much clearer what experiment you're talking about. Unfortunately, your OP doesn't really give a good description of either the experiment or what your question is about it, so I'm not sure how to respond. But briefly: As the Wikipedia page notes, there is no actual...

Where? Please give a reference.

No worries, post as you can. I hope you feel better soon.

Yes. Not "never". Just not in the last two billion years. Inflation does cause accelerated expansion, yes. In our best current model, that occurred in the very early universe. Yes. In cosmology, we model matter, radiation, dark energy, and the field that causes inflation as fluids with an...