Microwave radiation {cosmic microwave background}| (CMB) {microwave background} {background radiation, microwave} comes from all universe directions. Cosmic microwave background radiation is same visible-light-frequency radiation that was in hot plasma before plasma cooled enough, to 3000 K, for neutral-charge atoms to form, 300,000 years after universe origin, and comes from 13.72 billion light years away.
temperature
At that distance, recession velocity is near light speed, and redshift divides frequency by 1000, so radiation is now microwaves, with effective temperature 2.7 K.
temperature fluctuations
Cosmic-microwave-background temperature varies over space by less than 1 part in 10000. Temperature variations have Gaussian distribution. Temperature fluctuations arose from early-universe in-phase acoustic waves, density differences, and gravity waves. Gravitational waves cause red-shift and blue-shift. Gravitational-wave handedness causes polarization curls. Gravitational lensing affects CMB.
Largest same-temperature structures have one-degree diameter. Temperature variations depend on in-phase acoustic-wave wavelength, such as the largest spatial distance {first Doppler peak}. The four largest spatial distances have same intensity differences {scale-invariance}.
Gravity affects photon trajectories and energies. About 300,000 years after universe origin, when neutral-charge atoms formed, photons in higher-density regions lost more energy than photons in lower-density regions {Sachs-Wolfe effect}, because they had to overcome more potential energy. Sachs-Wolfe effect cancels gravity-photon effects.
If photons enter higher-energy-density regions and then exit them, universe space-expansion energy makes photons have higher energies than before {integrated Sachs-Wolfe effect}.
Galaxy-cluster plasma scatters cosmic microwave background radiation {Sunyaev-Zel'dovich effect}.
Perhaps, universe is homogeneous because light can go faster than light speed {varying-speed-of-light theory} {varying speed of light} (VSL). Fast light can bring all universe regions into contact, making one closed system (with nothing outside, before, or after), and so make thermal equilibrium, so there was no need for cosmic inflation.
During universe first seconds, subatomic-particle creation made x-rays {background radiation, x-ray} {x-ray background radiation} that still travel through universe.
5-Astronomy-Universe-Cosmology
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Date Modified: 2022.0225