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Comment by smartscience | Hacker News Reader

> You'd be hard pressed to go anywhere with an absence of gravity acting in that spot.

Okay I think I've found somewhere, but I'm not sure. What experiment should I perform to test that gravity is really absent?

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Given the size of the universe and the fact that it's not entirely observable makes it... impractical to even consider measuring gravity. Where we can measure it it's done with accelerometers or doppler shift and measuring the orbital perturbation [0]. Objects close to home are studied more intensely.

You can't really conclude there is no gravity acting in some random point across the universe but you can use other methods to determine when it is acting even if you have no chance of putting an instrument there. Like gravitational lensing. [1]

There's definitely not enough space in a comment to discuss general relativity and measuring gravity of an object in free fall. But if you're curious for more and have time to read Wikipedia has one of the most accessible explanations that don't involve a pile of imperfect or misleading analogies. [2]

[0] https://www.youtube.com/watch?v=cMdjAKn_uXw

[1] https://en.wikipedia.org/wiki/Gravitational_lens

[2] https://en.wikipedia.org/wiki/General_relativity

You can't. You can only measure acceleration (with an accelerometer). If you get zero acceleration, you're in an inertial frame of reference and for all intents and purposes in zero gravity. Newtonian physics says you're technically wrong, but general relativity says Newton is wrong so you're okay.

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