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Interesting point about gravity I came across in a book recently (The Beginning of Infinity by David Deutsch): > most non-physicists consider it self-evident t
by adriand 15y ago
Interesting point about gravity I came across in a book recently (The Beginning of Infinity by David Deutsch):
> most non-physicists consider it self-evident that when you hold your arm out horizontally you can feel the force of gravity pulling it downwards. But you cannot. The existence of a force of gravity is, astonishingly, denied by Einstein's general theory of relativity. This says that the only force on your arm in that situation is that which you yourself are exerting, upwards, to keep it constantly accelerating away from the straightest possible path in a curved region of spacetime.
I won't pretend to understand all of this (perhaps someone would like to explain it?) but it's interesting nonetheless.
- kmm 15y agoThis is hardly the place to discuss General Relativity but I can give a small explanation. Do you know the metaphor for gravity with a rubber sheet? Masses make dimples in the sheet and when particles pass, they get deflected. Similarly, when something moves past the Sun, it gets deflected and that's the reason we stay in orbit. Of course you could say you're holding your arm still and there's no reason for it to veer of course and suddenly start moving. But it actually is in motion, everything moves through time! It's this movement that gets deflected into spatial directions. We human observers have to move through time, we can't stop to get the big picture and that's why objects in the vicinity of masses suddenly start accelerating. ...Maybe I should write a book.