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Thread: At what speed are the celestial bodies moving apart?

  1. #1 At what speed are the celestial bodies moving apart? 
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    I have been unable to find out the speed the celestial bodies are moving apart. It is easy enough to find information they are accelerating their speed but nowhere have I been able to find out the speed of current dispersal.


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  3. #2  
    Veracity Vigilante inow's Avatar
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    Joe - If you are asking about two specific bodies, you'd need to identify which ones... as the speed at which the distance between them increases depends on which two objects you are viewing.

    Second, you would need to define the perspective... and add "speed relative to whom." If you're asking about two specific bodies, your question is akin to asking, "What's the difference between a duck?" There's a critical component missing, and that's "relative to what/whom?"

    On the other hand, I think you may be asking about the expansion of the universe, in which case that too depends on where you are asking about... The speed is proportional to the distance. Locally things are expanding slower than things farther away. The farther away from us, the faster the expansion.

    http://en.wikipedia.org/wiki/Metric_expansion_of_space


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  4. #3 Speed of expansion of the universe 
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    You should have been in politics. I mean that in the nicest way possible. You gave me the most politically correct answer possible. So you managed to guess that I am asking about expansion of the universe. I suspected that the speeds may vary. But let me be a little more explicit. Is the speed over 186000 miles per second? What is the fastest speed of dispersion? What is the slowest speed of dispersion? Is the speed variation due to different mass? If necessary, I will let you pick two bodies and give me an answer relative of those two bodies. I am not looking for an exact answer- just a ball park figure. You apparently have access to some sort of an answer. I have not been able to find a source for answer. sincerely, thanks for your answer.
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    Veracity Vigilante inow's Avatar
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    Thanks for the nice words. I'm actually quite a jerk most of the time, but only toward certain types of people. When an individual is genuinely seeking to learn something and enrich their mind, my kindness shines through. I want to reinforce that experience, and encourage more questions and sincere seeking of answers. I just often lack patience when it comes to people who show up preaching, or who think they know the answers and are unwilling to listen to corrections, or who are trollish. That's not you... not one iota... so, I think we're good. :wink:

    If I were to distill your question down to its essence, I'd say that you are wondering if the expansion of the universe can be faster than the speed of light... and... if so... how that's possible since the speed of light is the fastest speed there is (and no object with mass can achieve it). Yes?

    If I've interpreted your question correctly, then I would respond by sharing with you that the expansion of space is not limited by relativity. Expansion is not a speed of something in space, but is instead a speed of space itself expanding.

    It's somewhat difficult to wrap our meager human minds around the concept, but the expansion of space is not movement, it's just an increase of distances. Other galaxies are not moving through space away from us. Instead, it's somewhat more accurate to think of it as "more space" being added between us and those other galaxies... more distance.

    This space (or distance) being added between objects is independent of any local motion. When local motion is taken into account, the local forces (like gravity or EM) are stronger than the expansion force (there's not really an "expansion force" as far as I know, but I'm not sure how else to say it). Even on the scale of galaxies and galaxy clusters the gravitational attraction between objects is greater than the expansion, so things stay together and they, too, can be considered to be "local."

    However, overall... Yes, the universe can expand faster than the speed of light since it is not about objects in motion, but about increasing distances between those objects.


    These links may be useful:
    http://curious.astro.cornell.edu/que...php?number=575
    http://map.gsfc.nasa.gov/universe/uni_expansion.html

    I'm not sure if I've managed to clear things up for you or if I've only muddied the waters. Either way, thanks for giving me something fun to think about while I wind down from my week.
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  6. #5  
    Moderator Moderator Dishmaster's Avatar
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    This is described by the Hubble constant. The currently established value is around 70 km/s per Mpc of distance. This means that the relative speed of two bodies that are subjected to the universal expansion depends on their distance.

    One Mpc means one Megaparsec. You can look up the definition of a parsec.
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