4 ms·

Does relativity apply also to rotating reference frames?

by ithkuil 5y ago

WalterBright 5y ago
Of course.
- kadoban 5y ago
  Is which object orbits which actually relative to a reference frame though? Does not seem like it should be. The Sun has a certain mass, the Earth has a certain mass, the center of the point of orbit of both (barycenter? That seems to be the right term) is inside of the Sun no matter what frame you hang out in. What am I missing?
  - WalterBright 5y ago
    You can set up whatever frame of reference works best for a situation. We do it all the time. It's very convenient for us earthers to use a geocentric framing of the universe for our daily life, where the skies revolve around the Earth. We do it every day. Such as the word "sunrise" is very geocentric. We don't even have a word for the heliocentric term for the same thing. We also use geocentric phrases like "jets chasing the Sun" and "sundials track the movement of the Sun", etc.
    - kadoban 5y ago
      You can use whatever frame of reference you want, sure. Does there exist one in which the Sun orbits the Earth though? I don't think so. Those examples sound either metaphorical or about angular position/velocity, not orbit.
      - WalterBright 5y ago
        > Does there exist one in which the Sun orbits the Earth though? Yes. It's what I've been talking about in this thread. You could always, of course, demand that the local TV station change the word "sunrise" to "when the Earth rotates until the Sun shines on the TV station", but I suspect that won't be successful.
        kadoban 5y ago
        That seems a lot like it's relative in the same way as the universe's existence is when I put my hand over my eyes.
- ithkuil 5y ago
  I mean the principle of relativity (not the theory of relativity), i.e. the fact that the laws of physics are exactly the same in any (inertial) frame of reference and you cannot tell at which speed you're moving except relative to something. A rotating reference frame is different. A local experiment can tell you whether you're rotating and how fast you're rotating.
brandmeyer 5y ago
NIST Technical Note 1385 "GPS Receivers and Relativity" by Ashby and Weiss discusses how to solve the GPS positioning equations in a relativistically correct way. It turns out that since the frame of reference (Earth-Centered/Earth-Fixed) is rotating, it is non-inertial and you have to apply some corrections to do the job right.

Does relativity apply also to rotating reference frames?

WalterBright 5y ago

Of course.

kadoban 5y ago
Is which object orbits which actually relative to a reference frame though? Does not seem like it should be. The Sun has a certain mass, the Earth has a certain mass, the center of the point of orbit of both (barycenter? That seems to be the right term) is inside of the Sun no matter what frame you hang out in. What am I missing?
- WalterBright 5y ago
  You can set up whatever frame of reference works best for a situation. We do it all the time. It's very convenient for us earthers to use a geocentric framing of the universe for our daily life, where the skies revolve around the Earth. We do it every day. Such as the word "sunrise" is very geocentric. We don't even have a word for the heliocentric term for the same thing. We also use geocentric phrases like "jets chasing the Sun" and "sundials track the movement of the Sun", etc.
  - kadoban 5y ago
    You can use whatever frame of reference you want, sure. Does there exist one in which the Sun orbits the Earth though? I don't think so. Those examples sound either metaphorical or about angular position/velocity, not orbit.
    - WalterBright 5y ago
      > Does there exist one in which the Sun orbits the Earth though? Yes. It's what I've been talking about in this thread. You could always, of course, demand that the local TV station change the word "sunrise" to "when the Earth rotates until the Sun shines on the TV station", but I suspect that won't be successful.
      - kadoban 5y ago
        That seems a lot like it's relative in the same way as the universe's existence is when I put my hand over my eyes.
ithkuil 5y ago
I mean the principle of relativity (not the theory of relativity), i.e. the fact that the laws of physics are exactly the same in any (inertial) frame of reference and you cannot tell at which speed you're moving except relative to something. A rotating reference frame is different. A local experiment can tell you whether you're rotating and how fast you're rotating.

brandmeyer 5y ago

NIST Technical Note 1385 "GPS Receivers and Relativity" by Ashby and Weiss discusses how to solve the GPS positioning equations in a relativistically correct way. It turns out that since the frame of reference (Earth-Centered/Earth-Fixed) is rotating, it is non-inertial and you have to apply some corrections to do the job right.