F·01 · The embarrassing pie chart
95% missing
Here is modern cosmology's report card, and it is glorious and humiliating at once: everything ever seen by every telescope — every star, galaxy, planet, and dust cloud — is about five percent of the universe. The rest is two kinds of unknown with placeholder names.
Dark matter — the missing mass
Galaxies spin too fast for their visible mass; clusters bend light more than their stars can explain. Something unseen — about 27% of the cosmic budget — supplies the extra gravity. It clumps, it scaffolds galaxy formation, and gravitational lensing maps it in exquisite detail. What it is remains unknown: decades of underground detectors and collider searches for WIMPs have come back empty, pushing attention to alternatives — axions, primordial black holes, or something stranger. A substance that outweighs everything visible five-to-one, and not one confirmed particle of it.
Dark energy — the accelerator
In 1998 two rival teams timing distant supernovae found the expansion of the universe is speeding up. The label for whatever drives it — some 68% of everything — is dark energy. The simplest guess is a constant energy of empty space, but recent survey results have hinted it may be weakening over time, which would rewrite the universe's forecast. Whether the cosmos ends in cold dilution or something stranger hangs on a number we cannot yet pin down.
F·02 · The argument
The Hubble tension
Ask the early universe how fast space expands and it answers ~67. Ask the nearby universe and it answers ~73. Both measurements are precise. They disagree. That is either a subtle error hiding in beautiful data — or the first crack in the standard model of cosmology.
One number comes from the cosmic microwave background — the Planck satellite's baby picture of the universe — run forward through the standard model. The other comes from the classic distance ladder: Leavitt's Cepheids → calibrating supernovae, measured today. Independent methods keep landing on one side or the other, and JWST's sharper Cepheid photometry has, if anything, hardened the disagreement. If both are right, the model is missing an ingredient — early dark energy, new particle physics, something. Cosmologists are in the rare position of hoping they are wrong.
Planck and the microwave sky — the early universe's side of the argument. ESA/NASA/JPL
F·03 · Too big, too soon
JWST's impossible galaxies
Webb was built to watch the first galaxies assemble. It found them — earlier, brighter, and more mature than the models comfortably allow.
Within its first year, JWST's deep fields turned up candidate galaxies from a few hundred million years after the Big Bang that look surprisingly grown-up — massive, luminous, some already quenched or organized. Each one forces a question: did star formation ignite faster than we thought? Are early black holes juicing the brightness? Is the initial recipe for stars different at cosmic dawn? None of these is heresy, but together they are a running audit of galaxy-formation theory, live, in public, with new data every cycle. The machine doing the auditing →
Webb's first deep field — some of these smudges are the problem. NASA/ESA/CSA/STScI
F·04 · The open ledger
Questions still on the board
A short honest list of what nobody knows — the inheritance of everyone reading this.
| Question | Why it's hard | What might crack it |
|---|---|---|
| What is dark matter? | It interacts by gravity and, apparently, nothing else we've tried | Axion experiments, lensing surveys, Rubin's sky movie |
| What is dark energy — and is it constant? | It only shows up at cosmic scales | DESI & Euclid surveys, next-gen supernova samples |
| Why does the expansion rate disagree with itself? | Two exquisite measurements, one universe | Gravitational-wave "standard sirens" — a third, independent referee |
| Why is there something rather than antimatter? | The Big Bang should have made equal parts; it didn't | Neutrino experiments hunting CP violation |
| Did inflation happen — and what drove it? | The evidence is circumstantial, the first trillionth of a second is fog | Primordial gravitational-wave imprints in the CMB |
| Are we alone? | One data point: us | The census next door → |
The instrumental cousins of these questions — anomalies measured by real hardware, honestly stamped — live in the open file →. Every era of the history page → thought its picture was nearly complete. This table is the current era admitting, in advance, that it isn't.