this post was submitted on 30 Oct 2024
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Science Memes

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submitted 1 month ago by [email protected] to c/[email protected]
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[–] [email protected] 24 points 1 month ago* (last edited 1 month ago) (2 children)

I don't understand. What's a uniform gravitational field and why does being inside one feels like standing in an accelerating elevator?

[–] [email protected] 28 points 1 month ago (1 children)

This is a joke about Einstein's form of the Equivalence Principle:

https://en.m.wikipedia.org/wiki/Equivalence_principle

[–] [email protected] 9 points 1 month ago* (last edited 1 month ago) (1 children)

Thanks. Let's see:

The weak equivalence principle, also known as the universality of free fall or the Galilean equivalence principle can be stated in many ways.

And

"... in a uniform gravitational field all objects, regardless of their composition, fall with precisely the same acceleration." "The weak equivalence principle implicitly assumes that the falling objects are bound by non-gravitational forces."[11]

I'm just beginning to understand. I'm not there yet.

[–] [email protected] 29 points 1 month ago (1 children)

If you are standing in a closed box, there is no experiment you can make that tells you whether that box is standing on earth, or is on a rocket in space accelerating at 9.81m/s²

This has a bunch of interesting implications about the nature of spacetime

[–] [email protected] 12 points 1 month ago* (last edited 1 month ago) (1 children)

It's just that normal gravity on earth feels exactly like being in an accelerating elevator in space. So you can't tell the difference from the inside. Like in the elevator you can ask them, whether you're still on earth or accelerating in space. Einstein used this thought experiment to develop the general theory of relativity.

Basically Einstein thinking about that weird feeling you get in your gut when an elevator starts upwards led to him concluding that mass bends spacetime making light from distant stars go in curves around the sun, which was confirmed during the next available solar eclipse.

[–] [email protected] 3 points 1 month ago

Aaah. I understand. :)