altitude · GR · faster
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THE GROUND / STRATUM / VERIFICATION VENUE · A TOOL
You are a time traveler. Everyone is — quietly, constantly, by fractions of a second nobody can feel. Two effects do it, and they pull against each other: living up high makes you age faster, and moving fast makes you age slower. Enter your life below and watch the real gap open between you and a twin who never left sea level.
engine.js this page and the verifier (29/29) import — from c, μ = GM⊕ and Earth's spin; the hand-drift is exaggerated to be visible, the rates are the readouts. The soundtrack is two clock voices detuned to beat apart — a craft sonification, not a measured tone. Source: research/time-dilation/film.
“Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That's relativity.”— attributed to Albert Einstein (a 1929 paraphrase; the line is real, the physics below is the other kind)
This is not the relativity of feeling. It is the measurable kind: two clocks, started together, that genuinely disagree afterward — and not by a metaphor, by a number you can compute. The number is tiny for a human life, microseconds, far below anything you could notice. But it is real, it is the same physics your phone depends on every second to find you on a map, and it is the reason an astronaut came home from orbit younger than his identical twin. Below, the tool puts your own life into the equations. Then it proves the equations against the world.
Imagine a twin who, the day you were born, stayed at sea level and never left — never climbed, never flew. You went and lived your life. By the rules of relativity your two clocks have drifted apart. Set the dials to your life; the verdict updates live.
Altitude lifts you out of Earth's gravity well a little, where clocks run faster (general relativity). Motion through space costs you ticks, so you run slower (special relativity). For most lives the altitude effect wins and you end up a few hundred microseconds older than your sea-level twin — unless you fly enough, or live low, to swing it. Flights mostly add time: a subsonic jet's altitude beats its speed.
A few hundred microseconds. Real, computable, and yours.
It feels like nothing, and for your body it is nothing. But the very same two terms — gravity's up and motion's down — are not negotiable for any clock that has to agree with another one precisely. Push the clocks far enough apart in altitude and speed and the microseconds become a system that breaks. We have built such a system, and we live on top of it.
Below are three places the world has already measured this. Each number is computed live, here, by the exact same engine that just weighed your life — and printed beside the figure science actually published or measured. Same equations, no special-casing.
The first is not a thought experiment: it is the device in your pocket. A GPS satellite sits high in Earth's gravity well (clock runs fast) and moves at nearly four kilometres a second (clock runs slow). The two don't cancel — they net to about +38 microseconds per day, and a navigation system works by turning clock-time into distance at the speed of light. Leave the relativity out and the error grows at — — your blue dot would wander off the map by mid-morning. GPS receivers carry the correction in firmware; relativity is load-bearing infrastructure.
The second flips the sign. The International Space Station orbits low and fast, so for it the speed term beats the altitude term and its clocks run slow — about —. Over his 340 days aboard, astronaut Scott Kelly aged roughly — less than his identical twin Mark, who stayed on the ground. They are no longer quite the same age. It is the closest any human has come to the twin paradox, and it is in the right direction and the right size.
The third is the experiment that nailed it on a commercial budget. In 1971 Hafele and Keating flew caesium atomic clocks around the world on scheduled airliners — once eastward, once westward — and compared them to a clock left at the U.S. Naval Observatory. Because the planes ride with or against Earth's rotation, the speed term changes sign between the two trips: the eastward clock should lose time, the westward clock should gain it. It did, in both direction and size.
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What is exact here, and what is a model The GPS and ISS figures are computed directly from published constants in the weak-field, low-velocity limit, and they match the engineered and measured values closely. The Hafele–Keating panel is a deliberately simplified model — one altitude, one constant ground speed, a clean equatorial loop — so it reproduces the signs, the east/west asymmetry, and the tens-to-hundreds-of-nanoseconds scale, but not the exact published ±ns, which came from integrating the real flight logs (changing altitude, latitude and speed over the whole journey, with ground stops). Published predicted vs. observed: eastward −40 ± 23 vs −59 ± 10 ns; westward +275 ± 21 vs +273 ± 7 ns (Hafele & Keating 1972). The personal tool uses your speed relative to the ground and omits one small rotation cross-term — which is precisely the term that makes east and west differ, shown on its own above. Everything is the leading-order physics, named where it approximates.
running…
Yes — in the only sense the universe enforces. Not by jumping decades; by drifting microseconds, in a direction you can choose. Climb a mountain and you tip toward the future, faster than the people in the valley. Fly the red-eye and you mostly do the same, a few nanoseconds at a time, because at airline altitude gravity's gift outweighs the speed's tax. To win the other way — to come home younger — you have to go very fast and stay low, which on this planet means orbit. The microseconds are small because we are slow and the well is shallow. The equations don't care about the size. They only care that the clocks, once parted, never fully agree again.
Two clocks, started together, that the universe will not let you reconcile. That is the time travel you do every day.
Kindred ground — The Sphere of You (your place in spacetime, read off the speed of light) · The Farthest Point (a place fact re-derived from defining constants) · the rest of the ground →