Centripedal Forces Plus Relativity
I'm not sure if this address is the right one to write to asking a physics question. But I saw a list of questions and answers at the page with this address. Therefore, I would be very grateful if you could forward this question to someone who answers it.
Another question, that I think is related to the first one: How is fastness and acceleration measured in the theory of relativity. As far as I know it says, nothing can travel faster than light. But does this mean, the distance of any two things can't increase or decrease faster than with speed of light? Thanks for answering,
I'm glad to see that we get questions from Switzerland. Thank you very much for your interest.
Your first Question:
If space contained only two things and they would rotate compared to each other, would their mass and distance influence the size of the centripetal forces the two things feel?
For someone looking at the situation from a spaceship, it is clear what really causes the force that prevents the moon from crashing into earth: the rotation. Earth and moon rotate around each other like two spinning ice-skaters, but they don't need to hold hands as they have enough gravitational attraction. (Perhaps think of it as an invisible rubber band.) The person looking on from the outside clearly identifies the centrifugal force as the force to keep the moon from approaching earth.
Your second question:
In general relativity, can the distance of any two things increase or decrease faster than the speed of light?
When our universe was "born" in a Big Bang, something remarkable seems to have happened (at least to our current theory and present experimental observations in astrophysics). Space itself expanded. Physicists call this phase after the Big Bang the period of inflation. Think of it as if the invisible carpet is being stretched and getting longer. Well, there is no speed limit on this expansion of space. And space expanded very fast at early times. Even you and I, just "walking on this invisible carpet," would have been faster than the speed of light.
Astrophysicists have actually made a recent discovery that confirms the inflation theory. Check out the explanation at http://www.sdss.org/news/releases/20000413.qso.q.html
The discovery of the most distant quasar is described at http://www.sdss.org/news/releases/20000413.qso.html
Kurt Riesselmann Fermilab
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