Before Hydrogen formation : ProtonElectronHydrogen10 9 Photons Photons scatter off the free electrons, so the universe is “ opaque ” Lots of photons have E > 13.6eV Hydrogen can ’ t form… but the Universe is expanding, making photons “ stretch ” … Temp 3000 Kelvin t 380,000 yr.
During Hydrogen formation : ProtonElectronHydrogen10 9 Photons Hydrogen starts to form, so the Universe suddenly gets “ clearer ” … Temp ≈ 3000 Kelvin t ≈ 380,000 yr. During this time, the photons will have their “ last interaction ” with the electrons, and carry away information about their environment…
After Hydrogen formation : ProtonElectronHydrogen10 9 Photons Very few free electrons Universe is “ transparent ” Temp 3000 Kelvin t 380,000 yr. The photons travel freely, only being affected by gravity… and the universe continues to expand.
t = today (13.7 gigayears) matter = 10 9 times less Temp ≈ 3 Kelvin Cosmic Microwave Background (CMB) photons: today ~ 1 mm to 10 cm
13.7 Giga light-years
Gravity Wave 13.7 Giga light-years
Scattering of light by electrons 1. The electric field of a light wave shakes an electron along the direction of polarization.
Scattering of light by electrons 2. Light is not emitted in the direction of shaking! Green = probability of emitting in that direction…
Environment around electrons at t=380,000 years leads to polarization Uniform “ glow ” around electron “ shaking ” in all directions all polarizations emitted equally.
Environment around electrons at t=380,000 years leads to polarization Non-uniform “ glow ” around electron preferential “ shaking ” polarized emission.
Gravity waves stretch space…
… and create variations
Gravity Wave