nickdanger said:
Can you answer a newbee question? I work in quantum mechanics but with the new ideas in cosmology impacting particle physics, it's hard not to get lured into paying attention to some of the astrophysics.
I understand how a supernova and star production can take us back to a view of what was happening a few hundred thousand or hundred million years after the big bang. (Blanchard's comment is that light will never give us a better view than 400,000 years after the big bang.) But how does CMB give us a picture earlier than light data?
And finally, what I am truly interested in: How is it we believe that there are relatively unevolved (chemically) regions of space that give us a view of a few billionths of a second after the big bang? I understand if this were true it would be our particle physics laboratory in space, but how can anything still be giving us data about a high energy event from so long ago? Why do we think these regions haven't evolved?
Hello Nick, welcome
I just saw a post where you mentioned a talk at U. Penn. Dont remember seeing your posts earlier. It is really nice to have your perspective here since you are already working in a related field but just getting interested in cosmology (the newcomer's perspective is often the best and fits in well here at PF)
I will give you my (not necessarily authoritative) take on your questions and others may chime in too.
the CMB is light (stretched out 1100-fold)
and dates from 300,000 to 400,000 years (estimates vary)
when plasma cooled down and formed neutral (mostly H) atoms and
stopped scattering the light
so people talk about the "last scattering" era and the "surface of last scattering" which is where the CMB came from and which goes back to
year circa 300,000
there isn't any older light so in a sense "light can't tell us" about anything before that, like you say.
but there was a time in the first milli or micro second called "nucleosynthesis" when baryons stuck together----so there was H-nuclei and isotopes of some other light elements: He, Li.
Doubtless there are observable regions of space where the original mix still hasnt condensed very much into stars and therefore hasnt been fused into heavier nuclei. So what you say about "unevolved (chemically) regions of space" telling us about the first small fraction of a second. Doesnt Weinbergs book "First 3 Minutes" talk about this?----there must be a lot of good writng about how conditions during the instant of nucleosynthesis can be inferred by measuring abundances of elements and isotopes
You ask how we can look back.
Just to measure relative abundances we don't have to look back to before 300,000.
We just have to look back to, say 500,000 or one billion, a time when the first stars of the first galaxies were forming of of that original mix.
And then measure the abundances. And from that we can INFER back to
one microsecond and estimate the temperature etc, because that was when the relative abundances were established.
Someday there will be telescopes able to see primordial big bang neutrinos which subsequently cooled down so much that presentday instruments can't detect them. People say that this will allow us to see into the earlier conditions. If you are a graduate student or postdoc today then sometime in your career there maybe
primordial neutrino data, showing you a picture of the first microsecond. Maybe, I'm not too sure about this, or the actual time quantity.
But at present we don't get any light older than 300,000
and are still able to infer back earlier than that, from isotope abundances and suchlike.
I'm probably not the only one here who would be delighted if you would keep us posted on U.Penn particle-cosmology colloquia and stuff