Expansion of space

Discussion in 'The Science Forum' started by Top_Crab, Jan 4, 2012.

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  1. Ok, this Hubble thing has me a bit puzzled, with the galaxies all moving away from each other like currents in a pudding as the mix expands, the further away, the faster they recede.

    I suppose space could be considered the expanding pudding mix, but a small metal ruler in an expanding pudding mix would stay the same length as the pudding mix expands (Ignoring thermal effects on the ruler)

    Now, as a thought experiment, imagine a tape measure tethered to the Earth extending to a distant galaxy which is moving away from us at half the speed of light.

    (1) Does the tape measure stay the same length despite the expanding space it is in & the galaxy travels away from the end of the measure at half the speed of light?

    (2) Does the tape measure expand with the space & keep up with the galaxy? If so, surely the atoms in the tape measure would become separated? What would happen then?

    It might be easier to imagine the effects on a thick steel rod, how is it effected by expanding space? After all, surely there is space between & within the atoms which will expand too?

    Would the atoms lose their grip on each other?

    Any insight into this would be greatly appreciated.
  2. I believe the universe is stretching like a rubber band. Take a rubber band, mark the centre, then stretch it. The end bits will expand with greater expansion going on at the end bits than nearer the centre. I think we're still trying to figure out if there's going to be a big rip or not.

    You may also be interested in this:

    BBC - BBC Radio 4 Programmes - In Our Time, The Vacuum of Space

    Dl here: http://downloads.bbc.co.uk/podcasts/radio4/iots/iots_20020207-0900a.mp3


    BBC - BBC Radio 4 Programmes - In Our Time, The Universe's Shape

    Dl here: http://downloads.bbc.co.uk/podcasts/radio4/iots/iots_20090430-0900b.mp3
  3. seaweed

    seaweed LE Book Reviewer

    My problem is slightly different. The universe is seen to be expanding in all directions and this is presented as if we were in the centre of it with everything moving away from us at the same speed. However we are NOT at the centre. Therefore we ought to be able to triangulate (in a spherical trigonometry sense) our position relative to the original Big Bang centre, as galaxies on the further side from the Big Bang surely appear to be moving faster from us than those at the extremity on our side, as our own galaxy must be moving away from the Big Bang centre at an appreciable speed ???
  4. There's going to be an experiment thingy in a few years where NASA or someone is going to send 3x satellites into space to fire lasers at each other. They can then measure the distance between each satellite to a high degree of accuracy and try to calculate if there's any change in the shape/size of space.

    So I heard somewhere...

  5. But Light and Time aren't constant in the Universe, both can be manipulated.

  6. Are you trying to say that God is a woman?
  7. yes, the observation of light bending around a massive body prooved Einsteins theory correct did it not ?
  8. Having thought about this a bit more, I guess that the tape measure would in fact keep up with the receding galaxy.

    My one foot ruler must be expanding, but only by a tiny amount, too little to measure, but given a vast length, the more distant bits would be going like the clappers. Each one foot length in isolation would not have a measurable effect though.

    So, I gues the expansion of space has little effect at all on everyday things, but given many millions of light years in distance, the effect is spread out, diluted, giving the strange effect of a very long ruler, the end of which is travelling away from us at huge speeds.

    Now, I'm not the sharpest tool in the box (Unusual for a Crab) but this seems logical to me.
  9. Depends if there is only one Universe, what if 'our' big bang is one of many, not uncommon?
  10. Actually, we are (sort of); the visible universe is observed from the earth (or rather from within the solar system, given that no man-made probes have left the solar system yet.), so it follows that the visible universe can be though of as everything that we can see in a 3D space, with the observer at the origin (everything above and below us; in front of us and behind us; and to the left and right of us, at least as far as those directions have meaning for this kind of thing). That said, if you were to observe the universe from the Andromeda Galaxy, or from a spaceship floating around somewhere near Tatooine, you would still be at the centre of the universe. I have a feeling it's something to do with Relativity. As for your idea of a point in space acting as a 'true origin' of the universe, I'm sure one exists, but have no idea how one might go about locating it.

    As ever, I'm sure I've got something wrong, so anyone should feel free to correct me on any of my points if they know better.
  11. Yes, basically.

    Your second question is a good one, and can similarly be answered in terms of relativity. One of the fundamental tenets of General Relativity is the curvature of space-time, which is what the universe exists in. Whilst the observable universe can be thought of as the inside of a ping-pong ball, with the observer at its centre, space time thought to exist as a four dimensional doughnut (I think the correct geometrical term is torus; the fourth dimension is time).

    However, rather than the universe existing inside the cosmological doughnut, it exists on the surface (sort of- the 4-D part makes it hard to picture adequately). As such, there isn't an 'edge' of the universe in the Douglas Adams sense; if you travelled far enough in one direction, you'd end up where you started.

    If you imagine it on a flat plane, as you went off one edge, you'd appear again on the opposite one, like in the game asteroids (at least I think it's called that).

    In essence, it's pretty meaningless to attempt to define the "centre of the universe". That said, the possibility of the existence of a point of origin for the Big Bang as you suggested isn't necessarily ruled out.

    As ever, if I'm wrong, anyone is free to correct my understanding of the physical theory.
  12. You are quite correct: we are not at the centre, because the universe doesn't have a centre.

    The Big Bang happened everywhere, not at a single point - hence there being no centre to the universe.
  13. Not entirely sure tbh; my guess is that it fell out of the equations. As for the Morse, I wouldn't know either way- I cheated and used an online translator...