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moving finger
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The core of "Mach's Principle" is something like this: the inertia of a body is determined in relation to all other bodies in the universe (in short, "matter there governs inertia here").
Newton was aware of something akin to Mach's principle, and it is said the principle played a central role in Einstein's development of GR.
Imagine a simple gedanken experiment.
We are aboard a space-station in free space, with no significant gravitational masses in the vicinity of the space-station. We can induce a kind of artificial gravity aboard the space station if we set it spinning (recall "2001 - A Space Odyssey" for a perfect example).
Question 1 : What is the space station spinning relative to?
Obviously it is not spinning relative to itself (it is stationary in it's own reference frame). And since we believe there is no "aether" or absolute space, it is not spinning relative to that either.
Mach's principle would suggest it is the fact it is spinning relative to the background stars that allows us to know that it is spinning (and so also must the masses inside the space station "know" it is spinning relative to the background stars, otherwise they would not experience the artificial gravity).
Question 2 : What happens if we could simultaneously remove all of the background stars (remember, this IS a gedanken experiment)? Would the space-station still be spinning? and if "yes", what is it now spinning relative to?
Thanks
MF
Newton was aware of something akin to Mach's principle, and it is said the principle played a central role in Einstein's development of GR.
Imagine a simple gedanken experiment.
We are aboard a space-station in free space, with no significant gravitational masses in the vicinity of the space-station. We can induce a kind of artificial gravity aboard the space station if we set it spinning (recall "2001 - A Space Odyssey" for a perfect example).
Question 1 : What is the space station spinning relative to?
Obviously it is not spinning relative to itself (it is stationary in it's own reference frame). And since we believe there is no "aether" or absolute space, it is not spinning relative to that either.
Mach's principle would suggest it is the fact it is spinning relative to the background stars that allows us to know that it is spinning (and so also must the masses inside the space station "know" it is spinning relative to the background stars, otherwise they would not experience the artificial gravity).
Question 2 : What happens if we could simultaneously remove all of the background stars (remember, this IS a gedanken experiment)? Would the space-station still be spinning? and if "yes", what is it now spinning relative to?
Thanks
MF