You Have Never Felt Gravity, Only Your Chair

Push down into your chair. That heaviness is real, but it is not gravity. It is the seat pushing up into you.

Gravity pulls on every atom of your body at once, evenly, all the way through. A nerve works by being deformed — something has to press one part of you against another part of you. A pull that acts on every part equally leaves nothing for a nerve to compare, so no nerve you own can sample it. What you actually feel is the contact force: the chair against your back and your thighs, the floor against your soles, your shoes against your feet.

A bathroom scale works the same way. It never measures gravity. It measures how hard it is pushing back at you. That is why a lift accelerating upward makes the number climb exactly as though gravity had strengthened — and why an accelerometer in free fall reads zero while the field around it is still fully present. The measurable quantity is proper acceleration, not gravity. Your inner ear is an accelerometer. It has been reading the chair this whole time.

Take the support away and the pull is unchanged at full strength, but the sensation vanishes completely. That is what the half-second of a jump actually is. It is the only time in your life you have ever been alone with gravity, and it feels like nothing at all.

Einstein got there in 1907 and called it the happiest thought of his life: for an observer falling freely, the gravitational field does not exist. Not weakened — locally unmeasurable.

Which is what the space station really is. At that altitude Earth's gravity is still about 90 percent of what it is at the surface. NASA states that directly, and NASA also says outright that calling it "zero gravity" is misleading. The crew are not floating because the pull has gone. They are falling around the Earth, and the station and everything in it are falling with them, so nothing is pushing on anybody. They are living permanently in the state you occupy for half a second at the top of a jump.

One caveat the 50 seconds had no room for, and it is the honest one. Gravity is not undetectable full stop — it is undetectable *locally*. Across an extended body the field is very slightly non-uniform, and that tidal gradient is real and measurable. Quantified for a person standing on Earth, across a 1.8 m body it comes to roughly 5.5 x 10^-6 m/s2 — about 0.6 millionths of g, around one part in 1.8 million of your body weight. Hundreds of thousands of times below any sensory threshold you own. So the claim is not "gravity cannot be measured." The claim is that nothing in your body can sample it. That one holds.

The pull never changed. Only the pushing did.

Sources:
https://www.nasa.gov/learning-resources/for-kids-and-students/what-is-microgravity-grades-5-8/
https://einstein.stanford.edu/SPACETIME/spacetime2.html
https://aether.lbl.gov/www/classes/p10/gr/Thehappiestthoughtofmylife.html
https://phys.libretexts.org/Bookshelves/Relativity/General_Relativity_(Crowell)/01:_Geometric_Theory_of_Spacetime/1.05:_The_Equivalence_Principle_(Part_1)
https://phys.libretexts.org/Bookshelves/Relativity/Special_Relativity_(Crowell)/05:_Inertia/5.02:__The_Equivalence_Principle
https://en.wikipedia.org/wiki/Equivalence_principle