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> Are gyroscopes entirely local or does the gravity of distant galaxies present a sort of universal reference frame? Or is it something else entirely? Somethin

> Are gyroscopes entirely local or does the gravity of distant galaxies present a sort of universal reference frame? Or is it something else entirely? Something else entirely. You don't need other galaxies or a universal reference frame. Even if the gyroscope were the only thing in the universe, it would be easy to tell if it were spinning: a very tiny person standing on the inside rim would be held down if it were spinning, or free floating if it were not.

fiddlerwoaroof 9y ago
But that doesn't distinguish between the gyroscope spinning and the existence of a sufficiently massive object in the appropriate place, right?
- letlambda 9y ago
  Walk around to the opposite side of the gyro wheel. If the acceleration is due to the rotation of the gyroscope, it still points out radially. If it was due to a mass out beyond the rim, you're falling on your head.
  - apsophus 9y ago
    What if the mass is distributed in a ring surrounding the gyro at a distance? How would you distinguish between spinning versus mass in that case? General Relativity may seem counterintuitive, but experimentally it really does seem to be the way our universe works. Starting out from the position that absolute motion is meaningless has proven remarkably fruitful. It's also something a lot of very smart people have been thinking about for a hundred years. Whether or not you find Mach's arguments plausible, they're fundamental philosphical claims and can't simply be dismissed through a half-baked thought experiment.
    - thaumasiotes 9y ago
      > What if the mass is distributed in a ring surrounding the gyro at a distance? How would you distinguish between spinning versus mass in that case? In that case, it wouldn't be drawing you outward no matter where you were located. So, spinning would be "you feel a gravitational force", and a ring of mass would be "you don't feel a gravitational force".
    - jfhufl 9y ago
      Seems to me the main difference is that all the particles in the gyro are trying to go in a straight line, but can't due to being a part of a rigid structure. You should be able to tell the difference by dropping a ball bearing. It will land "straight down" if it's gravity, but move "to the side" if it's rotating.
monochromatic 9y ago
This is exactly what Mach’s principle disputes.
- phkahler 9y ago
  Then Mach's principle is a straw man, we do not have access to an empty universe.
Neeek 9y ago
which is obvious because a gyro is not rigid and has parts the move relative to each other, but would the entire system feel a force if exerted on it and correct it's orientation? What would it be "pointed" at? If it did, wouldn't that imply an absolute point of reference?
- epistasis 9y ago
  Not an absolute point of reference, but an inertial point of reference: https://en.wikipedia.org/wiki/Inertial_frame_of_reference https://en.wikipedia.org/wiki/Inertial_frame_of_reference
  - Neeek 9y ago
    https://en.wikipedia.org/wiki/Inertial_frame_of_reference#Absolute_space https://en.wikipedia.org/wiki/Inertial_frame_of_reference#Ab... Is what the entire article is about! That our idea of an intertial frame of reference is incomplete.

fiddlerwoaroof 9y ago

But that doesn't distinguish between the gyroscope spinning and the existence of a sufficiently massive object in the appropriate place, right?

letlambda 9y ago
Walk around to the opposite side of the gyro wheel. If the acceleration is due to the rotation of the gyroscope, it still points out radially. If it was due to a mass out beyond the rim, you're falling on your head.
- apsophus 9y ago
  What if the mass is distributed in a ring surrounding the gyro at a distance? How would you distinguish between spinning versus mass in that case? General Relativity may seem counterintuitive, but experimentally it really does seem to be the way our universe works. Starting out from the position that absolute motion is meaningless has proven remarkably fruitful. It's also something a lot of very smart people have been thinking about for a hundred years. Whether or not you find Mach's arguments plausible, they're fundamental philosphical claims and can't simply be dismissed through a half-baked thought experiment.
  - thaumasiotes 9y ago
    > What if the mass is distributed in a ring surrounding the gyro at a distance? How would you distinguish between spinning versus mass in that case? In that case, it wouldn't be drawing you outward no matter where you were located. So, spinning would be "you feel a gravitational force", and a ring of mass would be "you don't feel a gravitational force".
  - jfhufl 9y ago
    Seems to me the main difference is that all the particles in the gyro are trying to go in a straight line, but can't due to being a part of a rigid structure. You should be able to tell the difference by dropping a ball bearing. It will land "straight down" if it's gravity, but move "to the side" if it's rotating.

monochromatic 9y ago

This is exactly what Mach’s principle disputes.

phkahler 9y ago
Then Mach's principle is a straw man, we do not have access to an empty universe.

Neeek 9y ago

which is obvious because a gyro is not rigid and has parts the move relative to each other, but would the entire system feel a force if exerted on it and correct it's orientation? What would it be "pointed" at? If it did, wouldn't that imply an absolute point of reference?

epistasis 9y ago
Not an absolute point of reference, but an inertial point of reference: https://en.wikipedia.org/wiki/Inertial_frame_of_reference https://en.wikipedia.org/wiki/Inertial_frame_of_reference
- Neeek 9y ago
  https://en.wikipedia.org/wiki/Inertial_frame_of_reference#Absolute_space https://en.wikipedia.org/wiki/Inertial_frame_of_reference#Ab... Is what the entire article is about! That our idea of an intertial frame of reference is incomplete.