Space is expanding, but....

Discussion in 'Astronomy, Exobiology, & Cosmology' started by LostInThought7, Jun 21, 2010.

  1. LostInThought7 Registered Senior Member

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    We can see galaxies getting further away, which to me means that while space is expanding, the matter is staying the same size. But I don't see my garage getting further from the house.

    Where's the line? I mean, do galaxies get ripped in half from the change in size, or are even they too small to really feel the effects of space expanding?

    I know this is probably pretty elementary, so if someone can just point me to something online that explains it, that'd be cool, too. (some things are hard to ask in a search engine, heh)

    Much thanks, in advance.
     
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  3. James R Just this guy, you know? Staff Member

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    Your house/garage and the ground it sits on are all (a) held down by the Earth's gravity, and (b) held together by strong electromagnetic forces.

    Their local gravity is sufficient to negate the general expansion.
     
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  5. LostInThought7 Registered Senior Member

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    Ah, interesting. So it's slightly as if matter is being "shot out into space" in that gravity negates the expansion. If I'm understanding correctly.
     
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  7. kurros Registered Senior Member

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    Imagine a 2D array of little balls held together by springs, sitting flat on a piece of paper. If you imagine the paper were to uniformly expand (slowly!) for some reason, it would try to pull all the little balls apart from each other, since they want to remain locally stationary with respect to the paper. However, the springs would hold the array together, so instead the little balls would slide with respect to the paper. End result: paper is bigger, but array of little balls stay the same size.

    This is imperfect analogy but I think it contains some important conceptual ingredients. Gravity = springs, Balls = stars etc. in galaxy, paper = spacetime.
     
  8. cosmictraveler Be kind to yourself always. Valued Senior Member

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    Imagine a galaxy is like a solar system. There's enough mass in it to keep the solar system from flying apart and so does the entire galaxy.
     
  9. Skeptical Registered Senior Member

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    The scale of expansion is millions of light years. The Andromeda galaxy is part of the local group of galaxies. It is 2 million light years away and is, in fact, on a collision course towards our own. To measure genuine expansion, you need to be looking at objects separated by a lot more than 2 million light years.
     
  10. Big Chiller Registered Senior Member

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    I thought space independent of the matter or energy in it is what's expanding i.e. empty space around and through the matter and energy is whats expanding, although the matter and energy are being carried strong nuclear forces even gravity are strong enough to keep matter from being torn apart for now.
     
  11. hrebic Registered Senior Member

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    I think that the OP asks a good, basic question. The responses so far seem to be saying that matter stays together by one or more forces, i.e., gravity, nuclear, etc.

    However the complete answer must acknowledge that these forces would be acting to keep things together even as if the universe weren't expanding. Classical mechanics is very successful despite the fact that it does not presume the expansion of space. So there must be more to the explanation.
     
  12. Café Cappuccino Truth can only be half said Registered Senior Member

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    .... for now.

    Bwahahahahahahahahaaaaaaaaa!
    :mufc:
     
  13. Shadow1 Valued Senior Member

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    .

    i'm was going to make a threat about that right now, i think the univerce, will complete expanding, intill it collapse and all get strashed, like you cuted a peace of paper into many parts OR, to reach a point in expanding, when it can't expand more, then, it start to shrink again, intill it collapse on it's self, like, a spring, you can expand it, intill you can't expand it no more, and when you leave it, it will go back as it was in the first place, with a strong crush, when you leave the spring and stop pulling it, it will go back to it's first place strongly, in teh case of univerce, we supoe that the black matter is what causes the expanding, or other causes, after all, we can say, we don't know anything about space, in our own planet, we only know 1 million and 300 000 species, while their is approximtly 13 millions and other nulmbers, species, i readed it somewhere, but who knows, maybe it's wrong, anyway, so, the point is, for the second theoy, that the univerce will expand, intill it reach a point, and start pullign it self back, shrinking, intill it collapse on it's self.
     
  14. Shadow1 Valued Senior Member

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    .

    so as the univerce, well i think;
     
  15. Fraggle Rocker Staff Member

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    But that's the question here, isn't it? At intergalactic distances, is the force of gravity sufficient to counteract the force of the expansion of space? Gravity attenuates as the square of distance, and the distance between galaxies is on the order of magnitude of millions of light-years. Thats hundreds of thousands of times greater than the distance between stars, which means that gravity is billions of times weaker.

    Isn't this where dark matter comes into play?
     
  16. cosmictraveler Be kind to yourself always. Valued Senior Member

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    A new look at the data from one of the telescopes used to establish the existence of this strange stuff is causing some scientists to question whether they really exist at all. Yet other experts are holding firm to the idea that, whether we like it or not, the "dark side" of the universe is here to stay.

    As if that weren't weird enough, scientists think another 74 percent of the mass-energy budget could be made of some strange quantity called dark energy. This force is thought to be responsible for the accelerating pace of the expansion of the universe. (For those keeping track, that would leave only a measly 4 percent of the universe composed of normal matter.)

    http://www.msnbc.msn.com/id/37687623/ns/technology_and_science-space/
     
  17. Shadow1 Valued Senior Member

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    yup,
    so,
    do you think, that,
    one day:
    either the univerce will get strached, or cuted or whatever, when it rach a very large expansion size, where gravity becomes weak
    but i don't beleive in this, because the gravity will always keep pulling back, so i think when the univerce get expanded and expanded and expanded,it will reach a level, where the univerce will start to go smaller and smaller, intill it crash into itself, or just collapse in general, or, when it get smaller too much than normal, the gravity, or maybe the dark mater, will expand it again, and so on, OR, it will finally crash on itself, and just collapse in general
    so what do you think?
     
  18. LostInThought7 Registered Senior Member

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    The thread is old, but I just read the last few posts to it (I don't visit this site as much as I'd like). The thing that gets me that as far as I understand, all space is expanding in all directions. The square inch that my thumb inhabits of space is expanding. However, from what was said here, pure, simple gravity and atomic forces, etc, keep the matter from expanding with it. During the Big Bang, why didn't the singularity of mass and energy just sit in that point, due to all this? Simple answer, the energy of it all was stronger than the previous mentioned forces.
     
  19. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    No, it's not.

    Simpler answer: gravity didn't exist until AFTER the Big Bang.
     
  20. Jim S Registered Senior Member

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    Hey, Lost in Thought - you're probably just not old enough to have noticed the change in distance from the house to the garage. I've lived in my house since 1970 and the distance to the garage seems to be getting greater every year lately.
     
  21. AlexG Like nailing Jello to a tree Valued Senior Member

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    Well, you're asking why it didn't sit at that point. The answer is, it did. But that point, which was the entire universe, has expanded. Driven by the inflaton field, which at the time contained all the energy available in the universe, the spatial and time-like aspects of the universe expanded at an incredible rate. When the initial expansion slowed, due to the inflaton field reaching a non-zero lowest energy state, the energy percipitated out of the field into matter and the three/four basically unified forces, The Strong force, the electroweak force and gravity.
     

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