Happy Accidents Series — Exhibit #2

Pigeons & The Big Bang

In 1964, Arno Penzias and Robert Wilson were calibrating a radio antenna at Bell Labs in New Jersey. They kept detecting an irritating, uniform noise — coming from every direction in the sky. They ruled out every possible source: radar interference, nearby New York City, instrument errors. They even found pigeons nesting inside the antenna and thoroughly cleaned out the droppings. The noise remained.

💬 "We looked for pigeons. We found them and removed them. We cleaned everything. The noise was still there." — Penzias & Wilson, 1964

What they couldn't get rid of was the Cosmic Microwave Background — the thermal afterglow of the Big Bang itself, cooled to just 2.725 Kelvin above absolute zero after 13.8 billion years of cosmic expansion. They won the Nobel Prize in Physics in 1978.

Explore the CMB
Interactive 3D Exhibit — Planck Satellite Data

CMB Temperature Map

False-color map of CMB anisotropy. Temperature variations of ±200 μK around 2.725 K — one part in 100,000. Drag to rotate · Scroll to zoom.

Hot (+200 μK)
Mean (2.725 K)
Cold (−200 μK)
+ΔT 2.725K −ΔT
CMB Temperature
2.725 K
Δ 380,000 yr post-BB
drag · scroll · auto-rotate
🕊️
The Discovery
▾
1948
Alpher & Herman predict the Big Bang should leave a ~5 K thermal relic. Ignored for 15 years.
1964
Penzias & Wilson point the Holmdel Horn Antenna at the sky. Detect 3.5 K of excess noise. Can't explain it.
1965
Princeton group (Dicke, Peebles, Roll, Wilkinson) contacts Bell Labs. Identification: this is the CMB. Two papers published simultaneously.
1978
Nobel Prize in Physics awarded to Penzias & Wilson. Princeton group was not included — a controversial omission.
1992
COBE satellite maps the anisotropy for the first time. Stephen Hawking: "the discovery of the century, if not all time."
"We were looking for noise sources. We found the creation of the universe." — Robert Wilson
⚛
The Physics
▾

At 380,000 years after the Big Bang, the universe cooled enough for protons and electrons to combine into neutral hydrogen. For the first time, photons could travel freely — the universe became transparent.

Those photons have been traveling ever since. As the universe expanded, they were redshifted from ~3000 K visible light down to microwave radiation at 2.725 K.

Release temp.
3,000K
Today's temp.
2.725K
Redshift
z ≈ 1100
Peak frequency
160GHz
Blackbody spectrum
The CMB has the most perfect
blackbody spectrum ever measured.
Deviations < 50 parts per million.
∑
The Mathematics
▾
CMB temperature vs redshift
T(z) = T₀ × (1 + z)
T₀ = 2.725 K, z = 1089
T_emit = 2.725 × 1090 ≈ 2,971 K
Planck blackbody function
B(ν,T) = (2hν³/c²) / (e^(hν/kT) − 1)
h = 6.626×10⁻³⁴ J·s
k = 1.381×10⁻²³ J/K
Wien's displacement law (frequency)
ν_max = 2.821 × kT/h
ν_max(2.725K) ≈ 160 GHz
λ_max ≈ 1.9 mm
CMB power spectrum peak (ℓ ≈ 200)
θ ≈ π/ℓ ≈ 0.9° — the size of
the sound horizon at recombination
≈ 147 Mpc (comoving)
🔭
What It Proves
▾
The Big Bang happened. A homogeneous CMB with a perfect blackbody spectrum is only possible if the early universe was an extremely hot, dense plasma in thermal equilibrium.
The universe is 13.8 billion years old. CMB anisotropy patterns constrain the Hubble constant and universe geometry to ±0.3%.
Dark matter exists. The ratio of acoustic peak heights reveals that 27% of the universe is cold dark matter — invisible but gravitationally present.
Dark energy dominates. The peak positions show the universe is geometrically flat — requiring dark energy (68%) to explain the missing mass-energy.
Normal matter is only 5%. Everything we can see, touch, and measure is a cosmic afterthought.
Interactive Planck Function

The Perfect Blackbody

Drag the slider to any temperature — then snap to 2.725 K to see why this is the most precise blackbody spectrum ever measured. The dots are real FIRAS/COBE data.

Temperature 2.725 K
Perfect blackbody match — Nobel Prize level precision
The CMB spectrum was measured by the FIRAS instrument on the COBE satellite in 1990. The fit to a 2.725 K blackbody is so perfect that the error bars on the data points are smaller than the line thickness in any published plot. This immediately ruled out alternative cosmologies (steady-state theory, plasma cosmology) that predict non-thermal spectra. George Smoot and John Mather won the 2006 Nobel Prize in Physics for this measurement.
Scientific References — CMB Exhibit
CMB Discovery — Penzias & Wilson (1965)
Penzias, A. A. & Wilson, R. W. (1965). A Measurement of Excess Antenna Temperature at 4080 Mc/s. The Astrophysical Journal, 142, 419–421. | Dicke, R. H. et al. (1965). Cosmic Black-Body Radiation. ApJ, 142, 414–419.
CMB Temperature: T₀ = 2.725 K (conventional); 2.7255 ± 0.0006 K (precise)
Fixsen, D. J. (2009). The Temperature of the Cosmic Microwave Background. ApJ, 707, 916–920. | Fixsen, D. J. et al. (1996). The Cosmic Microwave Background Spectrum from the Full COBE FIRAS Data Set. ApJ, 473, 576.
COBE/FIRAS Blackbody Spectrum (1990) — perfect blackbody, deviations < 50 ppm
Mather, J. C. et al. (1990). A Preliminary Measurement of the Cosmic Microwave Background Spectrum by the Cosmic Background Explorer (COBE) Satellite. ApJ Letters, 354, L37–L40. | COBE/FIRAS data archive — NASA LAMBDA. George Smoot & John Mather awarded 2006 Nobel Prize in Physics.
CMB Anisotropy — COBE (1992), WMAP (2003–2012), Planck (2009–2018)
Smoot, G. F. et al. (1992). Structure in the COBE DMR First Year Maps. ApJ Letters, 396, L1–L5. | Planck Collaboration. (2020). Planck 2018 results. VI. Cosmological parameters. A&A, 641, A6. | WMAP Mission — NASA | Planck Mission — ESA
Cosmological Parameters (Planck 2018): Universe age 13.80 Gyr, Ω_Λ = 0.683, Ω_m = 0.317 (dark matter 26.8%, baryonic 4.9%), flat geometry
Planck Collaboration. (2020). Planck 2018 results. VI. Cosmological parameters. A&A, 641, A6. arXiv:1807.06209.
Recombination Epoch: z ≈ 1089, T ≈ 3,000 K, ~380,000 years after Big Bang
Planck Collaboration. (2020). ibid. | Peak frequency ν_max ≈ 160.4 GHz by Wien's displacement law (ν_max = 2.821 kT/h).
Sound Horizon at Recombination: ≈ 147 Mpc (comoving); CMB power spectrum first acoustic peak ℓ ≈ 200 (θ ≈ 1°)
Eisenstein, D. J. & Hu, W. (1998). Baryonic Features in the Matter Transfer Function. ApJ, 496, 605. | Planck Collaboration (2020). ibid.