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Guide · the big picture

How it all fits together

The labs each show one piece. Here is the whole story in eight panels: what acts on what, and what happens next. Every panel follows the same observed arrow.

Things · stuff that is
GasDark matterStarsPlanetsBlack holesLight
Doers · stuff that does
Gravity: pullsFusion: lights starsRadiation: carries energy awayDark energy: stretches space
The rules · every panel obeys them
Time only runs forwardEntropy only rises
1Gravity pulls
Gravityacts onGasDark matter
After the Big Bang, gas and dark matter were spread almost perfectly evenly. Gravity pulls them into clumps, with dark matter as the scaffolding. With gravity, clumping is the likely direction.
Established Entropy box · Add gravity → The Janus point →
2A star lights up
GravityFusionacts onStars
Squeeze a clump hard enough and its core gets hot enough to ignite. Fusion turns a little of the star's mass into energy and builds heavier elements from lighter ones.
Established Stars forge the elements → Cosmic timeline →
3Light carries it away
Radiationacts onLight
The energy leaves as light. Each fusion reaction in a star like the Sun ends up as about 20 million photons of sunlight, streaming into space. They never come back.
Established Entropy box →
4A planet catches some
Radiationacts onPlanets
Earth catches a little sunlight and sends the same energy back out as about twenty times as many infrared photons. Weather, plants and people all run on that difference.
Established Earth's energy budget →
5Big stars die
Gravityacts onStarsGas
Big stars burn fast and die young: they collapse and explode, scattering the elements they made. New stars and planets form from that dust. The iron in your blood was made inside stars that died before the Sun was born.
Established Stars forge the elements →
6Some collapse completely
Gravityacts onBlack holes
The biggest collapse all the way into black holes. They swallow whatever comes too close, and now hold far more entropy than everything else in the universe combined. They hold it, but they can't keep it.
Established The River → Black holes evaporate →
7Meanwhile, space stretches
Dark energyacts onLight
All the while, dark energy stretches space. Galaxy groups drift apart, light stretches redder on its way, and faraway clocks appear to run slow. What dark energy is, nobody knows.
Established Contested Expanding universe → Cosmic horizons →
8The long wait
Radiationacts onBlack holesLight
The stars go out. Over up to 10¹⁰⁰ years even black holes evaporate back into faint light, which carries away more entropy than they held. Dark energy keeps them too far apart to merge into one. Everything ends spread impossibly thin, and the clock has only ever run one way. (Physics we trust, projected far ahead.)
Established Black holes evaporate → Cosmic timeline →
?What we don't know
  • What is dark matter? Its pull built every galaxy; no particle has been found. Contested
  • What is dark energy, and is it changing? Expanding universe → Contested
  • Why did it all start so smooth? The entropy gauge had to start low. Why it did is an open hole. Hole H3 →
  • How do gravity and quantum theory fit together? They disagree about what time is. Hole H1 →

The illustrations are simplified pictures, not simulations Analogy; the gauges are schematic. The captions' claims are tagged as everywhere else, and each links to a lab that runs the real equations.

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