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Galaxies moving faster than the speed of light?

  1. May 18, 2012 #1
    I cant post a link so just bing or google the topic.

    I have heard a little bit about this phenomenon and was wondering if anyone knows more about it or can give me a reference.

    If galaxies farther away from the milky-way are moving faster as they get more distant, then should galaxies behind our own move slower? Shouldnt the blue-shift show that the galaxies moving toward us travel slower as they are farther away?

    If it is like raisin bread baking and the raisins getting farther apart, then wouldnt matter and energy be more condensed as we perceive light on the blue-shift side and less dense where we see light on the red-shift side?
  2. jcsd
  3. May 18, 2012 #2
    There's already a thread on this with almost exactly the same title.
  4. May 18, 2012 #3
    Yes their are but i dont think they are asking the same question i am about the subject.
  5. May 18, 2012 #4


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    The expansion of space is taking place in all directions - there is nothing "behind". The speed of light speed limit does not apply to the expansion, so that galaxies far enough away will be going away from us faster than the speed of light.
  6. May 18, 2012 #5
    if the expansion of space is taking place in all directions then what is the blue-shift? i must be misunderstanding what it is.

    Is this phenomenon of galaxies moving faster then the speed of light the reason we beleive space is expanding?
  7. May 19, 2012 #6


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    No. The reason for believing expansion is based on supernova studies.
  8. May 19, 2012 #7


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    In addition to the expansion of space, galaxies have proper motion. Therefore galaxies which are not too far away may be moving toward the Milky Way, leading to blue shift.
  9. May 19, 2012 #8
    for blue shift clarification see this picture http://physics.weber.edu/carroll/expand/Doppler.htm
    it give you a good idea

    edwin hubble http://www.pbs.org/wnet/hawking/cosmostar/assets/auto_generated_images/img_50928008.gif with his telescope measured the red/blue shift of galaxies and found out that the farther away a galaxy was from us, the greater its redshift that means The farther a galaxy is from us, the faster it is moving away from us ..so physicists interpreted it as expansion of space

    my personal opinion is that space is not actually expanding literally like the explanation..but in GR it says space has same dynamics of matter&energy ie empty space is something REAL ..however it is not proven :tongue:

    galaxies are getting farther away farther than where they should be with BB calculation if those galaxies has to be there where they are now they must be going faster than light which is not possible..so physicist conjured up the idea that it is not the galaxy that is moving at light speed but empty FLAT Space between us and those galaxies SELF GRAVITATING COMPACT structures move away from each other

    i say though not a GR genius myself

    either BB theory is wrong or there's lot more to be discovered than what we already know about universe

    matter could be just spreading out into pre existing space ..not necessarily mind boggling expansion of space

    when we open our eyes slowly we see more world around us that doesn't mean as we open eyes world is blossoming around us

    i like your question i had the same doubt ..dont take anything for granted what says in theory

    if you are really curious abt these stuff take astronomy classes learn equations and rediscover the universe by yourself
  10. May 19, 2012 #9


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    Very few galaxies in the universe are blue shifted, and none lay beyond the local group. This is exactly what is expected in an expanding universe. There is no BB calculation that tells us where distant galaxies 'should' be. We know their distance by virtue of redshift and standard candles [i.e., supernova]. Redshift is what tells us the distance to remote galaxies is increasing faster than light. Physicists did not 'conjure up' anything to explain this, they merely accepted the redshift at face value.
  11. May 20, 2012 #10
    Well whether or not space is expanding we do know that galaxies moving away from us move faster than the speed of light relative to where we are in space now. But what if Gravity slows light?

    when we see a blueshift the waves are more frequent and smaller/condensed. Say a car is a lightwave exherting said amount of horsepower to travel at 60 mph, say gravity or an anchor is tied to the car. Its not going to travel as fast allthough it is exerting the same amount of energy.

    what if the shift is from light moving slower as it gets deeper and deeper into the "expanding universe." Expanding from one central point. The first galaxies that formed after the big bang will be emitting light that slows as it comes our way. Where we see the galaxy, isnt where it really is. Gravity, slowing light down; makes us beleive that the galaxy travels faster than light when really gravity slowed light on its way here.

    But what do i know im a highschool dropout contemplating on getting my GED
  12. May 21, 2012 #11
    yes..you cant take redshift blindly and say all gal's are receding .redshift occur for variety of reasons ..unless physicist figure out what dark energy is (which is what universe is all about) all these are best guesses:shy: may be we'll have new theory which make sense
  13. May 21, 2012 #12


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    What 'variety of reasons', aside from crackpot material, do you have in mind?
  14. May 21, 2012 #13


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    What if questions don't help anyone. We have no reason to think that gravity slows light. All current observations point towards the speed of light being invariant. What gravity does do is it alters the path of light (and everything else) by making the shortest distance between two points a curve instead of a straight line.

    There are two reasons that light becomes redshifted. Either an object is moving away from us or light is moving out of a gravity well. Since going into a gravity well and then coming out has no net effect on the light, IE the wavelength is the same before and after, the only remaining source of redshift is recession.

    As for dark energy, no one can claim that dark energy is "what the universe is all about". Our current ideas and theories are exactly what you claimed however, best guesses. Just as ALL theories and models in science are "best guesses".