2

If I'm in a room that accelerates through empty space uniformly I won't measure tidal forces. The situation is the same as standing on an infinite massive plane. So I could think, while looking outside, that all stars are actually in free fall to that infinite plane. My acceleration is absolute but my motion is not. I could just as well stand still while all stars gain motion. Or is there a way to tell which is the case? I can't see the infinite plane though, but maybe that's situated far away, say behind the horizon. Maybe all matter in the universe is falling to such a plane at this moment! In a closed universe this would be impossible. But who says this isn't the case if the universe is infinite? We can gauge it away, or can't we?

Qmechanic
  • 201,751
MatterGauge
  • 1
  • Think your question addresses the ´equivalence principle´ https://physics.stackexchange.com/q/9476/332384 – Sam Ginrich Apr 07 '22 at 15:06
  • @SamGinrich The EP is clear to me. I just wondered, because it is said it holds locally only, if that is because we compare it with gravity around a spherically symmetrical source. Can't we say that there is an infinite massive plane causing uniform gravity? (However implausible that might be). – MatterGauge Apr 07 '22 at 16:02
  • ... rethinking your question: What could ´accelerate in empty space´ be, unless by a uniform gravitational field, e.g. a sufficient distant massive object? – Sam Ginrich Apr 07 '22 at 16:43
  • @SamGinrich You could attach rocket thrusters below the room you're in... A few tons of antimatter maybe (though 60 trillion dollars per gram is rather expensive). It would seem that all stars fall freely due to that infinite plane. Maybe all stars fall freely already! – MatterGauge Apr 07 '22 at 17:13
  • Ok, "Rocket-Lady", this is anti-matter impulse drive, no warp-bubble, so we have plain space around the flying room. Inside the room you observe an acceleration, equivalent to a gravitational force against moving direction. And in your idea is, that this can equally be induced by a massive plane? If this is the question, then the answer is YES. – Sam Ginrich Apr 07 '22 at 17:34
  • @SamGinrich But why then the EP is said to hold locally? Because gravity fields of a spherical mass are involved in it? Can we say that all stars are in free fall? – MatterGauge Apr 07 '22 at 18:00
  • Well the observation of forces due to acceleration is locally, from whatever cause. Assume the preservation of impuls still holds globally and you should be able to observe a long term movement in the rocket case, "falling stars", not so in the gravitation case. – Sam Ginrich Apr 07 '22 at 18:23

0 Answers0