Thanks. I do often read Wikipedia entries, but figured I understood what the words "hot" and "cold" meant. Seems I didn't in this case. Quoting from their entry on "hot dark matter": "As we shall see below, it is useful to differentiate dark matter into "hot" (HDM) and "cold" (CDM) types–some...
Again, I may be displaying some ignorance here, but ordinary matter can be quite hot and still engage in strong gravitational attraction. Why is dark matter thought necessarily to be cold (at or near zero Kelvin according to one response) in order to do the same, i.e., to fulfill its role in...
I may have to display some ignorance here, as I'm unclear on the functional difference between "cold" matter and "dark" matter. Clearly we can postulate a new type of matter that doesn't interact with photons regardless of its vibrational, rotational, or linear kinetic energy (temperature). (I...
The latter, and also "cold" nucleosynthesis. The redshift/distance relationship can also be explained in a much more visualizable and intuitive way as an inherent redshift of ancient matter's light emissions/absorptions, and that the latter have gradually been getting bluer since then. Also...
Agreed that there wouldn't necessarily be a big hole at the "center," as one can postulate that some matter was essentially stationary early on. (But, the theory is that there was no actual "explosion" anyway, right? Just space being created between clumps of matter at some minimal distance...
It seems to me that a Universe that began as you described would have a very different appearance than our current Universe. For one, it'd have a huge gaping hole at the origin. For two, there'd be a wall of blackness beyond the distance the furthermost galaxies have moved radially outward...
My main question was about the underlying assumptions of the Big Bang Theory. It's not all of the Cosmological Principle, but just the part about the redshift/distance relationship looking the same from anywhere in the Universe, that underlies it. (Along with the Doppler interpretation of the...
So, then, it would be correct to say that the Big Bang Theory does NOT depend---no longer depends---upon our assuming the cosmological principle, because the data (as you say, at large scales) has proven the latter.
I think I read a recent (and not definitive) article about observations from the James Webb Space Telescope, dealing somewhat with the issue (maybe in Nature or Nature Astronomy). I'll see if I can track it down.
Here's a link to a description of the new findings:
https://scitechdaily.com/einstein-vindicated-quasar-clocks-show-universe-was-5x-slower-soon-after-the-big-bang/
I assume the researchers noticed that quasars of a certain type (which have luminosity variations of a certain period) have their luminosity vary 5-fold slower than quasars much closer to us.
Is the theoretical basis for a hot Big Bang simply the combination of the assumedly redshifted CMBR (whose photons were thus thought to be much more energetic long ago), along with the assumed much tighter packing of matter in the initially much smaller space? (The perceived need for such a hot...
Regarding the new "quasar clock" data showing that time ran more slowly (~5-fold) shortly after the Big Bang: is it all based on the periodic variation in luminosity at various wavelengths of some quasars (and presumably explained by the special relativistic time dilation effect from "spatial...
Is the basic idea behind the CDM theory regarding the production of the Universe's large scale structure simply that dark matter, being dark, doesn't interact with photons, and thus was able to coalesce gravitationally soon after the Big Bang, forming the scaffolding toward which regular matter...
Galaxies far away---that evolved soon after the Big Bang---are reported to be closer together than the galaxies we observe near us. This could be due to two distinct reasons. One is that relatively nearby galaxies, over time, tend to merge, and the ones we see from far away haven't had time to...