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Re: [Phys-l] Hubble Law



Just to emphasize a point here. In the slinky demo, it is the slinky that is expanding--carrying the blocks and paper clips with it. In the Universe it is the space itself expanding, carrying the stars and galaxies with it. If you think about all the matter flying off from an initial point in space, it won't make sense, but if you think in terms of the matter imbedded in space and the space itself expanding like a balloon, it starts to, especially if you take into account that any given point (where you are) will appear to be at the center of such an expansion.

What I would like further clarification on, is the limits of this expansion. I don't think we consider atoms to be expanding or even molecules although both are mostly 'space'. If that's right (and I could be wrong there) then objects wouldn't expand (well I have with time but that's another story)--people, houses, planets, and stars wouldn't expand (or do they?) This would imply (to me) that nuclear and electrical forces can negate the local expansion--but at what scale and for what strength forces/fields? Probably need the General Relativity experts and/or cosmologists to answer. A quick trip to Google didn't prove very useful.

Rick




----- Original Message ----- From: "Krishna Chowdary" <professor.head@gmail.com>


On 1/18/07, frederth@saline.k12.mi.us <frederth@saline.k12.mi.us> wrote:

OK. I know that the Hubble Law states that recessional velocity of
distant galaxies is greater as distance increases. However, I am
forgetting why this should be intuitively correct?


Try this simple demonstration of a "one-dimensional universe" (which I
learned from our intro astronomy course). Take a slinky and stretch it out
a little bit; fix the ends down so that it remains slightly stetched (w've
attached blocks of wood to the ends of a plastic slinky). Now, attach paper
clips or post-it notes at various positions, and label them 1, 2, 3, 4, 5,
6, etc (these represent galaxies). Now, measure the distance between, say,
marker 3 (your "home" galaxy) and the other markers. Now, stretch the
slinky some known distance. Measure the distances again. Stretch the
slinky again the same known distance as before, and measure the distances
again. That should be enough, but you can do this as many times as you'd
like.