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starfyredragon OP t1_j0ekbul wrote

So motion is relative, but acceleration is not.

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BadBoyJH t1_j0f3tln wrote

Not quite, this isn't about acceleration vs motion, but that motion is relative in an inertial frame of reference.

If you are accelerating, then you're not in an inertial frame of reference, so it's not the same as the distant stars exceeding c.

If something else is accelerating, then that is relative, and can be viewed differently depending on the frame of reference.

As a semi-practical example, a plane taking off on an aircraft carrier. Let's have him take off backwards for the purposes of explanation, even though they wouldn't practically.
Let's say an outside observer is watching the plane take off, going back off a ship travelling forwards at 30kph. To the outside observer the plane accelerating from 30kph, through 0, and then out to -170kph.
But from someone on the ship, the plane has gone from 0 to 200kph.
That acceleration is still relative in both of those frames of reference.
But the pilot in the plane is not in an inertial frame of reference, and so it's not the same as the world accelerating under him (eg he experiences inertial G forces).

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Octolavo t1_j0ez4cj wrote

Mach’s principle states that rotation is absolute with respect to the distant stars and the overall distribution of matter in the universe.

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Game_Minds t1_j0guh1t wrote

And it's a principle because while it's handy and you can use it to make correct assumptions about the universe, it's also sort of fundamentally unprovable

Gödel is one of my all time faves lol

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