3 ms·

> It turns out that is only true if the elevator is sufficiently small. Do you have more context, explanation or source for this? This is the first time I’ve h

> It turns out that is only true if the elevator is sufficiently small. Do you have more context, explanation or source for this? This is the first time I’ve heard of this being the case and would love to learn more about it.

jungturk 2y ago
This video w/ Dr Iva Fuentes, from two weeks ago, spends a few segments on the breakdown of the equivalence principle w/ quantum clocks. https://youtu.be/cUj2TcZSlZc?t=4006&si=Ykt0JDqEKk1ObMp3 https://youtu.be/cUj2TcZSlZc?t=4006&si=Ykt0JDqEKk1ObMp3 Video notes have lots of references to relevant papers (and the video itself surveys a few aspects of these issues).
stavros 2y ago
I assume they mean that, in a gravity well, you get less acceleration as you get away from the well, whereas in an elevator you'll get the same acceleration in all places inside the elevator. Then again, the intent of the thought experiment was that you stay in one place.
patmorgan23 2y ago
Time moves slower at the bottom of an elevator shaft because it is closer to the earth. We have instruments so precise we can measure that difference now.
- moi2388 2y ago
  Yes I’ve always wondered about this. I thought the thought experiment basically dealt with points not regions though
DemocracyFTW2 2y ago
1) what the others said, in a gravity well it depends on height above the floor, but not in an accelerating elevator; this limits the height according to the sensitivity of your instruments 2) additionally, we do not know of any disc-shaped objects of sufficient density and matter distribution to produce a uniformly linear gravity field; only galaxies come close but their gravity is small compared e.g. to that of Earth. Most of the time gravity is caused by spherical objects, meaning the lines of the fields diverge. If you had an elevator with a sufficiently large, completely flat floor, you could tell that you're hovering above a planet by observing that a plumb bob forms different angles with different (perfectly upright) walls of the cabin.

jungturk 2y ago

This video w/ Dr Iva Fuentes, from two weeks ago, spends a few segments on the breakdown of the equivalence principle w/ quantum clocks. https://youtu.be/cUj2TcZSlZc?t=4006&si=Ykt0JDqEKk1ObMp3 https://youtu.be/cUj2TcZSlZc?t=4006&si=Ykt0JDqEKk1ObMp3 Video notes have lots of references to relevant papers (and the video itself surveys a few aspects of these issues).

stavros 2y ago

I assume they mean that, in a gravity well, you get less acceleration as you get away from the well, whereas in an elevator you'll get the same acceleration in all places inside the elevator. Then again, the intent of the thought experiment was that you stay in one place.

patmorgan23 2y ago

Time moves slower at the bottom of an elevator shaft because it is closer to the earth. We have instruments so precise we can measure that difference now.

moi2388 2y ago
Yes I’ve always wondered about this. I thought the thought experiment basically dealt with points not regions though

DemocracyFTW2 2y ago

1) what the others said, in a gravity well it depends on height above the floor, but not in an accelerating elevator; this limits the height according to the sensitivity of your instruments 2) additionally, we do not know of any disc-shaped objects of sufficient density and matter distribution to produce a uniformly linear gravity field; only galaxies come close but their gravity is small compared e.g. to that of Earth. Most of the time gravity is caused by spherical objects, meaning the lines of the fields diverge. If you had an elevator with a sufficiently large, completely flat floor, you could tell that you're hovering above a planet by observing that a plumb bob forms different angles with different (perfectly upright) walls of the cabin.