PeterDonis's latest activity

Any Lorentzian metric satisfies the EFE for some stress-energy tensor.

The top line of links is good and looks like the previous styling. Just below that top line of links is a "Latest Activity" listing...

Just knowing the spacetime geometry is not enough to assess this. You also need to know the worldlines of the observer (us here on...

Unfortunately I can't stand night mode (or the "dark" as opposed to "light" theme setting), not just for this site, but in general.

Of course not. There are many expanding models that have no cosmological horizon. However, de Sitter spacetime, which is the only...

It's in your user preferences.

I've done the same. One further comment to add to the ones I've already made: to me the new style looks drab. The old one has some...

Well, in that case I think the answer is as given by Bonnor - the redshift is not determined by those constraints because there isn't...

Same comment about individual threads in a forum view: it's hard for me to tell which ones are unread now.

One other comment: it's hard for me to tell now which forums have unread posts. In the old style, there was a color change that made it...

This is clearly false. An obvious counterexample is Newtonian spacetime. It is homogenous and isotropic but is not described by any...

And that references section 8.4 (p. 363) in his GR book (downloadable from this page). That notes that Hoyle worked in a more-or-less GR...

A couple of additional notes - as I understand it, ##ds^2=dt^2-a(t)(\frac{1}{1-kr^2}dr^2+d\Omega^2)## is the most general isotropic and...

My cosmology notes refer to the metric with ##a(t)## unconstrained by the Friedmann equations as the RW metric, and with the additional...

Unfortunately this font is very hard for me to read when surrounded by the other fonts. (I think monospace fonts in general are a bad...