Arrow of time · Frontiers of knowledge

SIMULATING THE ARROW OF TIME

Run a collision between two particles backwards and no law is broken; a boxful of gas gathering itself back into one corner is something nobody has ever seen. The microscopic equations are very nearly time-symmetric, and the T violation measured in the kaon system is far too small to build everyday directionality out of. The standard account has to add a postulate: the universe began in a state of extremely low entropy, known as the Past Hypothesis. Why the Big Bang had entropy that low is unsolved, so the question has been pushed back rather than answered.

▸ Loading the microscopic laws (time-symmetric, T)…

▸ Building the time axis past → future

▸ Installing the "arrows": thermodynamic · cosmological · radiative · psychological

▸ Setting the initial condition: an EXTREMELY LOW-entropy Big Bang (Past Hypothesis)

▸ ⚠ Note: WHY time has a direction is still an OPEN QUESTION

▸ Ready — Online. ✅

Entropy gauge

⏳ S chỉ TĂNG (định luật 2)

Arrow in focus—

Time direction—

Entropy (illustrative)—

Cosmic expansion—

Question status—

Viewing—

The honest boundary

The microscopic laws are nearly time-symmetric (T-symmetry) — so why does macroscopic time have a clear DIRECTION? Most reduces to the Past Hypothesis (an extremely low-entropy Big Bang). But why the past was low is NOT fully explained — this is an OPEN question.

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Pick a "Scenario" (microscopically reversible / thermodynamic / cosmological / Past Hypothesis / open question) · click Reverse on the micro scene (still valid) & thermo (looks WRONG) · click a concept to see "known / open"

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Entropy over time — rising one way only entropy Stime direction