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Can mass go faster than the speed of light?

  1. Jul 16, 2008 #1
    My original post had a bunch of theorys on the matter, but I know very little about this subject.

    Can matter go faster than c? if so, what changes at this point? anything?

    if not, why cant it?

    personally I dont think it can, and had some reasoning, but Id rather hear what we know before making a bunch of stuff up first :)
     
  2. jcsd
  3. Jul 16, 2008 #2

    Hootenanny

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    Am I correct to assume that you have posted here before, specifically under an different username?
    According to Einstein's Theory of Relativity a massive body cannot travel at or faster than C, however, it may travel at a speed arbitrarily close to C. Relativity also requires than any massless particles travel at C throughout all time and space.
     
  4. Jul 16, 2008 #3
    No, I posted and it was removed because I didnt read the rules :( lol twas my own fault.

    I posted this question in the form of an answer (my own uninformed theories) and I wanted to hear if it was right, partially right, wrong, partially wrong etc.

    ah, I guess thats a cue to read up on that right? :) or would you care to laymanize the reason why massive bodies cannot travel >=c :-D

    as far as massless bodies, are there more than photons? I thought that was it. everything else is just negligible (for our uses) but still has some mass.
     
  5. Jul 16, 2008 #4

    Hootenanny

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    That's okay then, things can get a little confusing if people post with multiple usernames.
    I would certainly recommend reading something about Einstein's theories, a good place to start is Einstein's own book 'Relativity', which was intended for the layman. However, a somewhat mathematical illustration of why massive particle's cannot attain C is shown here. The post is rather brief, so let me know if you need more clarification.
    Gluons and the theorised Gravitions are both also massless particles.
     
  6. Jul 16, 2008 #5
    Im definitely going to get Einstein’s book, but in the meantime, what does Mo stand for? (The extent of my formal physics info is limited to HS :D)
     
  7. Jul 16, 2008 #6

    Hootenanny

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    M0 is the invariant or rest mass of a body and is what one would normally call an object's mass.
     
  8. Jul 16, 2008 #7
    It actually depends a bit on how you look at it. :)

    It is a fact that no two objects of mass can travel at a relative speed of c. I say relative speed since there is of course no such thing as an absolute speed! However take note that a traveler could certainly travel for one year to something 10 light years away. In fact the faster he accelerates the less time it would take him to get there, but he won't be able to get there instantly.
     
  9. Jul 16, 2008 #8

    JesseM

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    Of course, in the frame of an inertial observer who's moving along with him once he's accelerated up to a significant velocity relative to his destination, the distance between his destination and his starting point is a lot less than 10 light years. Meanwhile, in inertial frame where the distance is 10 light years, it will always take more than 10 years for the traveler to reach his destination.
     
  10. Jul 16, 2008 #9
    Yes but think about it practical terms. Sirus B is 8.6 light years away, a space colony could do the trip in one year as long they accelerate hard or long enough.
     
  11. Jul 16, 2008 #10
    I thought c was absolute?

    as far as traveling 10 lightyears in less than 10 years, thats from the point of view of a third party right?
     
  12. Jul 16, 2008 #11
    Nope, it is from the point of view of the traveler.
     
  13. Jul 16, 2008 #12

    JesseM

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    The time is from the point of view of the traveler as MeJennifer says, but the distance is from the point of view of a third party (someone who remains at rest relative to the starting point and the destination). As I said, once the traveler is moving at a significant velocity relative to the destination, in the inertial frame where he's temporarily at rest, the distance will be much smaller.
     
  14. Jul 16, 2008 #13
    so you are saying, if I am moving at .9c, and I emit photons they are going 1.9c?

    I didnt think that was right.
     
  15. Jul 16, 2008 #14
    I am not saying that at all.
     
  16. Jul 16, 2008 #15

    JesseM

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    Well, it's 8.6 light years away in our frame, all spatial distances are relative. And if a space ship wanted to go there and then return to Earth, although the trip could be shorter from their point of view, they would always find that when they returned to Earth more than 17.2 years would have passed here.
     
  17. Jul 16, 2008 #16
    I know time is relative to the stuff around him, but wouldnt he still "experiance" 10 years, where as the rest of the world would have only passed about 1 year or so.
     
  18. Jul 16, 2008 #17
    if its from the point of view of the traveler, then to a third party the light would be going faster than light speed right?
     
  19. Jul 16, 2008 #18

    JesseM

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    "Moving at 0.9c" doesn't mean anything unless you specify what it's relative to. If you're moving at 0.9c relative to Earth and you fire a photon, it will move at 1c relative to you, and also at 1c relative to the Earth, because of the way relativistic velocity addition works.
     
  20. Jul 16, 2008 #19
    Hello all.

    Does no one want to commit themselves to say specifically that nothing can traveller at a speed greater than c ?

    Matheinste.
     
  21. Jul 16, 2008 #20

    Doc Al

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    It just means that he can travel 10 Earth lightyears in less that 10 traveler years, so you are mixing frames a bit (but it makes an important point about high-speed space travel). If the traveler measured the distance he traveled according to his own frame, his speed would of course be less than c.
     
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