Cosmic Microwave Background — 2D Sky Map & Blackbody Spectrum

Cosmic Timeline

Cosmic time 30%

Sky Map

Visual exaggeration 20000×

Live Readout

Age of universe

380 thousand yr

Temperature

3000 K

Redshift z

1100

ΔT/T anisotropy

—

Spectrum peak

160.2 GHz

Peak wavelength

1.06 mm

Hot opaque plasma — photons scatter constantly, light cannot travel freely.

How it works

Before recombination (~380,000 years after the Big Bang), the universe was a hot, opaque plasma of free electrons and protons that scattered photons relentlessly, so no light could travel far. Once the plasma cooled to about 3000 K, electrons bound to nuclei to form neutral hydrogen and the universe suddenly became transparent — that flash of light has been streaming freely ever since, redshifting as space expands.

Today that same light arrives as the Cosmic Microwave Background: a near-perfect blackbody spectrum at T ≈ 2.725 K, peaking at radio/microwave frequencies (Wien's law: ν_peak ≈ 2.821·kT/h ≈ 160.2 GHz). Satellites COBE, WMAP and Planck mapped its whole-sky temperature and found it isotropic to an extraordinary degree — anisotropies of only about 1 part in 100,000 (ΔT/T ~ 10⁻⁵, tens of microkelvin). The exaggeration slider multiplies that real amplitude by up to 100,000× purely so the pattern is visible on screen; the readout panel always shows the true, un-exaggerated physics.

Those tiny ripples are not noise — they are density fluctuations frozen in at recombination that gravity later amplified into every galaxy and galaxy cluster in the observable universe.

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