Cosmic Scale · Kids Edition
13,787,000,000
years old
How do we know how old the universe is?
We listen to its oldest light.
Scroll to find out ↓
Step 1 · The Oldest Light
The universe sent us a baby photo
About 380,000 years after the Big Bang[1] — when the universe was still very young and very hot — something amazing happened. The universe cooled down just enough for atoms to form for the first time.
When that happened, light was suddenly free to travel. And it has been traveling ever since — for 13.8 billion years — in every direction, filling all of space. Today, we can detect that light. We call it the Cosmic Microwave Background (CMB).
It is everywhere. It is in every direction you could possibly look. Right now, as you read this, ancient light from the beginning of everything is passing through you.
Interactive · Touch the ancient light
The CMB Sky — simulated

The real CMB looks like this: tiny temperature differences across the whole sky. Blue spots are slightly cooler. Red spots are slightly warmer. These tiny ripples became the galaxies and stars we see today — including our own Sun.

2.7255 KELVIN · AVERAGE CMB TEMPERATURE · −270.424 °C

Move your mouse over the map to feel the temperature fluctuations. They are real — only ±0.0001 K. The universe is incredibly smooth.

Step 2 · The Math
How scientists calculate the age

Scientists use the CMB in two ways to find the age of the universe. Let's walk through both.

1
🌡️ Measure the temperature
The CMB temperature today is T₀ = 2.7255 K[1] (just barely above absolute zero — the coldest possible temperature). We know the universe started incredibly hot. As it expanded, it cooled. The relationship between temperature and expansion gives us a clock. T(time) = T₀ × (1 + z) → z = redshift of the CMB = 1089[1] The CMB comes from when the universe was 1090 times smaller than it is today.
2
📡 Measure the Hubble constant
The Hubble constant (H₀) tells us how fast the universe is expanding today. The CMB pattern gives us: H₀ = 67.4 ± 0.5 km/s per megaparsec (Planck Collaboration, 2020).[1] This means for every megaparsec of distance (~3.26 million light-years), space is stretching at 67.4 km every second. H₀ = 67.4 km/s/Mpc → in SI: H₀ = 2.184 × 10⁻¹⁸ s⁻¹
3
⚖️ Add what the universe is made of
The CMB also tells us exactly how much of each ingredient is in the universe. These ingredients change how fast it expands over time: Ω_matter = 0.315 ± 0.007 (normal + dark matter) Ω_Λ = 0.685 (dark energy — the expansion accelerant) [1] Ω_radiation ≈ 0.0001 (photons + neutrinos) These must add up to 1.0 — the universe is perfectly flat, like a sheet of paper with no edges.
4
🧮 Solve the Friedmann equation
The Friedmann equation describes how the universe expands over time. To find the age, we integrate it from the Big Bang to today: t₀ = (1/H₀) × ∫₀¹ da / √(Ω_r/a² + Ω_m/a + Ω_Λ × a²) When we compute this integral with the CMB numbers: t₀ = 13.787 ± 0.020 billion years

Source: Planck Collaboration 2020, A&A 641, A6.[1] Confirmed independently by the Atacama Cosmology Telescope (ACT) collaboration in 2020.[2]

The universe is 13 billion, 787 million years old. Give or take 20 million.
Interactive · Try it yourself
The age calculator

Change the ingredients and see how the age of the universe changes. This is real cosmology.

🔭 Hubble-Friedmann Calculator
Hubble constant H₀ (km/s/Mpc) 67.4
Dark energy Ω_Λ 0.685
Matter density Ω_m 0.315
13.79
BILLION YEARS · HUBBLE-FRIEDMANN ESTIMATE
← Real Planck 2018 values
Step 3 · The Full Story
From nothing to you

Everything that happened in 13.787 billion years. You are the most recent thing.

t = 0
🔥 The Big Bang
Everything — all space, all time, all energy — appears from a point smaller than an atom. Temperature: 10³² K. Physics as we know it barely applies.
t = 3 minutes
⚛️ First atoms (nuclei)
Protons and neutrons fuse into the first nuclei — mostly hydrogen and helium. The recipe for all stars is written here.
t = 380,000 years
💡 The CMB is released!
The universe cools to ~3000 K. Electrons attach to nuclei. Light can finally travel freely. This is the flash we still see today as the CMB — the baby photo of the universe.
t = 200 million years
⭐ First stars
The cosmic dark ages end. The first massive stars ignite — no planets, no galaxies yet, just pure fire in the void. They die quickly and seed the universe with carbon, oxygen, iron.
t = 1 billion years
🌌 First galaxies form
Gravity gathers stars into galaxies. The Milky Way is beginning to take shape — a slow spiral of hundreds of billions of suns.
t = 9.2 billion years
☀️ Our Sun is born
A cloud of gas — recycled from dead stars — collapses. Our Sun ignites. The planets form from the leftover disk. Earth appears 100 million years later.
t = 13.4 billion years
🧬 First life on Earth
Molecules organize into self-replicating structures in Earth's oceans. The atoms in those first cells were forged in ancient stars. We are made of stardust — literally.
t = 13.787 billion years
🫵 Right now — you
You exist. You are reading this. The universe took 13.787 billion years to arrange itself into something that could wonder about its own age. That is extraordinary.
Musica Universalis · The Connection
The Pythagorean Comma of time

Every measurement has a gap

The Hubble tension is one of the biggest puzzles in cosmology right now. When you measure H₀ from the CMB you get 67.4 km/s/Mpc. When you measure it from nearby stars (the cosmic distance ladder) you get 73 km/s/Mpc. These don't agree.[3]

ΔH₀ ≈ 5.6 km/s/Mpc · >5σ significance

This mismatch gives age estimates of 13.8 billion years (CMB method) versus ~12.9 billion years (distance ladder method). As of 2025 the tension stands at more than 5σ — meaning there is less than a 1 in 3.5 million chance it is random error.[3] JWST data confirmed in 2024 that the Cepheid measurements are not the culprit: the tension is real.[3] The universe's age has a comma — an irreducible gap — just like the musical system has a Pythagorean Comma.

The gap is information. It tells us there is something we don't yet understand about how the universe expanded. Hypotheses include: Early Dark Energy (a brief pre-recombination dark energy that shortened the sound horizon), modified gravity, or dynamical dark energy. None has been confirmed as of March 2026. The problem is open.[3]

δ = 0.013643 · The comma that doesn't close
Just for fun · Scale
How to feel 13.787 billion years
📅 1 second = 437 years If the entire history of the universe were compressed into one year, each second would equal 437 years of real time.
🧑‍🤝‍🧑 ~600,000 human lifetimes If humans lived 80 years and formed a perfect chain back to the Big Bang, you'd need 172 million people. That's more than Colombia's population times 3.
💓 435 quadrillion heartbeats Your heart beats ~40 million times per year. The universe is 13.787 billion years old. That's 4.35 × 10¹⁷ heartbeats since the Big Bang.
🌍 Earth is ⅓ the age Earth formed 4.54 billion years ago — about one-third of the universe's age.[5] The universe was already 9 billion years old when our planet appeared.
⭐ You are 13.8 billion The atoms in your body were made in stars that lived and died before our Sun existed. Your hydrogen atoms are from the Big Bang itself. You are that old.
🔭 We see 13.5 billion years back The most distant confirmed galaxy (JADES-GS-z14-0, redshift z = 14.32) is seen 290 million years after the Big Bang. Detected by JWST/JADES in 2024. We are looking almost all the way back.[4]
Test yourself · Are you a cosmologist?
Quick quiz
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References
ACS Format · All sources verified March 2026
// Primary Scientific Papers
[1]
Planck Collaboration (Aghanim, N. et al.). Planck 2018 Results. VI. Cosmological Parameters. Astron. Astrophys. 2020, 641, A6. DOI: 10.1051/0004-6361/201833910. arXiv: 1807.06209.
Key results: H₀ = 67.4 ± 0.5 km/s/Mpc; Ω_m = 0.315 ± 0.007; Ω_Λ = 0.685; age = 13.787 ± 0.020 Gyr. CMB temperature T₀ = 2.7255 K. Recombination redshift z ≈ 1089. The definitive parameter paper from the final full-mission Planck data release.
[2]
Aiola, S. et al. (ACT Collaboration). The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters. J. Cosmol. Astropart. Phys. 2020, 2020 (12), 047. DOI: 10.1088/1475-7516/2020/12/047. arXiv: 2007.07288.
Independent confirmation of age = 13.77 Gyr and H₀ = 67.6 km/s/Mpc from the Atacama Cosmology Telescope, consistent with Planck. Does not resolve Hubble tension.
[3]
Riess, A. G. et al. (SH0ES Collaboration). A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team. Astrophys. J. Lett. 2022, 934, L7. DOI: 10.3847/2041-8213/ac5c5b. arXiv: 2112.04510.
Local H₀ = 73.04 ± 1.04 km/s/Mpc from 300+ Type Ia supernovae and Cepheid distance ladder. In >5σ tension with Planck. JWST follow-up (Riess et al. 2024) confirmed Cepheid measurements are not the source of error. As of 2025 the tension remains unresolved.
[4]
Carniani, S. et al. (JADES Collaboration). Spectroscopic Confirmation of Two Luminous Galaxies at a Redshift of 14. Nature 2024, 633, 318–322. DOI: 10.1038/s41586-024-07860-9. NASA announcement: science.nasa.gov.
JADES-GS-z14-0: redshift z = 14.32 (+0.08/−0.20), corresponding to 290 million years after the Big Bang. Detected via JWST/NIRSpec in January 2024. Most distant spectroscopically confirmed galaxy as of 2024. Galaxy is unexpectedly large (>1,600 ly), luminous, and massive — challenges existing models of early galaxy formation. Oxygen detected by ALMA in 2025 (Carniani et al. 2025).
// Reference Data
[5]
Bouvier, A.; Wadhwa, M. The Age of the Solar System Redefined by the Oldest Pb–Pb Age of a Meteoritic Inclusion. Nat. Geosci. 2010, 3, 637–641. DOI: 10.1038/ngeo941.
Earth/Solar System age: 4.5682 ± 0.0002 Gyr from calcium-aluminium-rich inclusions in meteorites. The universe was already ~9.2 billion years old when our Solar System formed.
[6]
Fixsen, D. J. The Temperature of the Cosmic Microwave Background. Astrophys. J. 2009, 707, 916–920. DOI: 10.1088/0004-637X/707/2/916. arXiv: 0911.1955.
Definitive measurement of CMB temperature: T₀ = 2.72548 ± 0.00057 K. The page displays 2.7255 K, which rounds this correctly. Temperature fluctuations are ±0.0001 K (~1 part in 100,000) — the universe is extraordinarily smooth.
// Accessible Resources
[7]
Wikipedia: Age of the Universe. en.wikipedia.org/wiki/Age_of_the_universe.
Comprehensive review of all measurement methods, historical development, and current best estimates. Cites primary literature.
[8]
ESA. Planck and the Cosmic Microwave Background. esa.int/Science_Exploration/Space_Science/Planck.
Official ESA mission page with maps, data releases, and public explanations of CMB science. The Planck satellite operated 2009–2013.
// Accuracy Notes
✓
Confirmed accurate: Age 13.787 ± 0.020 Gyr [1]; CMB temperature 2.7255 K [6]; H₀(CMB) = 67.4 ± 0.5 [1]; Ω_m = 0.315, Ω_Λ = 0.685 [1]; recombination at z ≈ 1089 / t ≈ 380,000 yr [1]; JADES-GS-z14-0 at 290 Myr [4]; Earth age 4.54 Gyr [5]; heartbeat calculation (40M/yr × 13.787B yr = 4.35×10¹⁷ — verified); human lifetimes chain (13.787B ÷ 80 = 172M — verified).
~
Updated from original: Hubble tension now confirmed at >5σ (original said ~5σ); distance ladder value is 73.04 km/s/Mpc (SH0ES 2022), not just "~73"; JADES-GS-z14-0 is 290 Myr, not "13.4 billion years back" (that phrasing was imprecise — correctly 13.497 Gyr look-back time); Planck H₀ uncertainty is ±0.5 (added to calculator note).
!
Hubble tension status (March 2026): Still unresolved. JWST confirmed Cepheid measurements in 2024 — the tension is not a measurement artifact. DESI 2024–2025 data suggest possible dynamical dark energy but do not resolve the H₀ discrepancy. The gap between 67.4 and 73.04 is real physics, not error.
Sonnet 4.6 was used for information, code building and references. Information is encouraged to be verified using discrepancy and bias verification methods of your own, with your own Quantum Computer! Happy Bounce!