Comment by Aseyhe on 20/07/2022 at 19:30 UTC

7 upvotes, 0 direct replies (showing 0)

View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science

For seeing beyond the last scattering surface, here are some of the methods we already use.

Big Bang nucleosynthesis. Based on assumptions about the composition of the early universe and its expansion history during the first few minutes, we can predict the abundance of light elements. We can then compare those predictions to present-day abundances.
Neutrino decoupling (also known as "the effective number of neutrino species"). The energy density of neutrinos is determined by what was going on in the universe at the time of neutrino decoupling, at an age of roughly a second. We don't actually measure the neutrino density directly, but it's imprinted in temperature variations in the CMB and density variations within the observable universe.

Here are some more prospective methods (but this is a bit of a judgement call -- for all of these methods, absence of a detection can already constrain models of the early universe).

CMB spectral distortions[1]. Events somewhat prior to last scattering that disturb the thermal equilibrium can cause the CMB frequency spectrum to not be a perfect blackbody.
Dark matter clustering. If dark matter is capable of clustering at early enough times and small enough scales, then its clustering properties today can tell us about significant events prior to neutrino decoupling.
Primordial black holes. Similar idea to dark matter clustering but with a few differences. PBHs aren't as sensitive to properties of the dark matter (you can make them out of pure radiation), but they are difficult to form with post-inflationary physics and mostly tell us about inflation.
Primordial gravitational waves mostly tell us about inflation.

Replies

There's nothing here!