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A question that has been plaguing me

  1. Sep 10, 2010 #1
    Hey everyone,

    This is my first post. I wanted to ask a pretty random question about speed of light travel that I hope someone can answer. I know enough about physics to know why traveling at the speed of light isn't possible, but for the sake of this theoretical question lets assume that we can.

    So, as you increase your speed up to the speed of light, the relative time that you perceive is slowed down according to how close you are to the limit. So my question is, if you could travel at the speed of light would travel seem instantaneous to you? Since time wouldn't be passing, would you not perceive the approximate 8.3 minutes it would take for you to travel to the sun?

    My apologies if this is an easy question, or if it has been answered somewhere else.

    Second quick question, if the speed of the earth around the sun increased would gravity increase? I think the force we would feel might increase, but I'm not sure that to say gravity would increase would be the right way to look at it. Any elucidation on either of these questions would be greatly appreciated.

  2. jcsd
  3. Sep 10, 2010 #2
    The first question has no real answer. The most commonly given response is that the question itself is pointless because it is not physical. Nothing (except light itself) can ever travel at the speed of light. It will take an infinite amount of energy to accelerate anything with mass to the speed of light. What happens at that speed is unknown and most likely cannot be known.

    As for the second question, if the orbiting speed were to increase for the Earth, either the radius of the orbit would have to change or there would need to be a stronger gravitation attraction for it to stay in orbit. Note that I am not saying that increasing the speed of orbit would actually increase gravitation attraction, but rather that greater attraction is needed for Earth to stay in the same orbit as now.
  4. Sep 10, 2010 #3
    http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html [Broken]
    Last edited by a moderator: May 4, 2017
  5. Sep 12, 2010 #4
    Fortunately the reaction mass is also approaching infinity, which means that the rocket will still have the same subjective acceleration rate regardless of the absolute speed.
  6. Sep 13, 2010 #5
    Length contracts, too, so as long as you were moving towards your destination when you started, as soon as you hit the speed of light, you'd be at top of your destination....

    ... and the place you came from.
  7. Sep 13, 2010 #6
    I partially disagree with saying it's unknowable. It may be argued that provided a photon does not interact with anything else, it will exist forever. I think this may suggest that time does not pass from its point of view, so to speak.

    The bold text is correct. With increased velocity, orbital distance would increase. As it moves away, gravitational influence from the sun would decrease, but I think a proportional increase in centripetal force balances that out if I recall my university physics correctly.
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