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Re: Recession of Galaxies Metaphor



I thought you cosmologists told me that the galaxies do NOT recede from
each other: Apparently I need more tutoring.

Jim Green

At 09:38 21 02 2001 , you wrote:
Hello To All--

I was reading Robert P. Kirshner's entry "Measuring the Universe:
Redshift and Standard Candles" in "Bubbles, Voids, and Bumps in Time:
The New Cosmology" which is edited by James Cornwell and I found a new
(new to me at least) metaphor for explaining how to reconcile the
observation of the recession of galaxies from us. It reads:

"Imagine a giant jungle gym, with galaxies at every intersection.
Suppose you are invested with the power to make that jungle gym grow in
all directions. (Maybe it's made of living bamboo!) What would that
look like, from the point of view of any individual galaxy? If the
jungle gym doubled in size, then a galaxy's closest neighbor would be
twice as far away--at a distance we might call 2 JU (for Jungle
Units)--and it would be receding. The most distant neighbors, let's say
ten junctions away, will also double in distance, ending up 20 JU away.
So, as viewed by that particular galaxy, all the others are receding,
and the more distant ones are receding faster. In fact, an expanding
framework produces Hubble's Law, with all galaxies seen as moving away
at velocities or recession just proportional to their distances." (p.
48)

I kind of like this presentation over the presentation of points on the
surface of a balloon as this provides a visual image of three dimensions
as compared to the two dimensional view of the surface of the balloon.

I've found this book to be quite interesting to read, only 182 pages and
it contains six articles that cover measuring the universe, mapping the
universe, and weighing the universe to mention but three of the
articles. I believe that it would be interesting reading for anyone who
would like to have some fun reading about cosmology by six leading
cosmologist.



--
Carl C. Gaither and Alma E. Cavazos-Gaither
http://www.angelfire.com/tx/StatBook/
Authors of:
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Physically Speaking: Quotations about Physics and Astronomy
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Chemically Speaking: Quotations about Chemistry


Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen