Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Breaking the speed of light - It's been done, twice!

  1. Jul 10, 2010 #1
    On two disparate levels science says that it is possible to exceed the speed of light. The first inkling this was true can be traced back to the big bang theory.

    Background: In 1929 Astronomer Edwin Hubble published a scientific paper that proved celestial bodies are moving away from each other. This means the universe as we know it is expanding. Oddly the objects closest to the center of the universe are moving more slowly than objects that are further out and this acceleration continues in an exponential fashion the further out we look.
     
    Last edited by a moderator: Jul 13, 2010
  2. jcsd
  3. Jul 11, 2010 #2
    There is NO center of the Universe for things there to be moving slower for. If you have 2 objects moving how can one be slower than the other. Even if one speeds up the speed between them changes for both.

    Your application of entangled photons completely ignores the real issues they pose.

    In fact, this looks more like a blog add.
     
  4. Jul 11, 2010 #3

    tom.stoer

    User Avatar
    Science Advisor

    It is true that in general relativity / for cosmological models like an expanding universe one can observe distant objects (galaxies) moving faster than the speed of light. This does not violate GR but is something like an optical illusion.

    The reason is that in GR velocity is well-defined only locally. And locally all observers (defining physicals reference frames) agree that these objects are moving with v<c; the observers may not agree on v, but on v<c.
     
  5. Jul 13, 2010 #4
    Actually there isn't a true center of the universe, but there is in a way... according to the standard theories of cosmology, the universe started with a "Big Bang" about 14 thousand million years ago and has been expanding ever since. Yet there is no centre to the expansion; it is the same everywhere. The Big Bang should not be visualised as an ordinary explosion. The universe is not expanding out from a centre into space; rather, the whole universe is expanding and it is doing so equally at all places, as far as we can tell.

    In 1929 Edwin Hubble announced that he had measured the speed of galaxies at different distances from us, and had discovered that the farther they were, the faster they were receding. This might suggest that we are at the centre of the expanding universe, but in fact if the universe is expanding uniformly according to Hubble's law, then it will appear to do so from any vantage point.

    If we see a galaxy B receding from us at 10,000 km/s, an alien in galaxy B will see our galaxy A receding from it at 10,000 km/s in the opposite direction. Another galaxy C twice as far away in the same direction as B will be seen by us as receding at 20,000 km/s. The alien will see it receding at 10,000 km/s:

    A B C
    From A 0 km/s 10,000 km/s 20,000 km/s
    From B -10,000 km/s 0 km/s 10,000 km/s

    So from the point of view of the alien at B, everything is expanding away from it, whichever direction it looks in, just the same as it does for us.

    In Quantum Mechanics it is possible for the bodies within an expanding universe to in essence move faster than the speed of light but to travel faster than light across the universe is still a problem.

    Hope this helps explain things?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook