From: Amara Graps (amara@amara.com)
Date: Thu Aug 15 2002 - 01:41:11 MDT
Dear Emlyn,
This might help. Your cosmology questions are common, don't worry.
There is a huge amount of information here:
Frequently Asked Questions in Cosmology
http://www.astro.ucla.edu/~wright/cosmology_faq.html
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What is the evidence for the Big Bang?
The evidence for the Big Bang comes from many pieces of observational
data that are consistent with the Big Bang. None of these prove the Big
Bang, since scientific theories are not proven. Many of these facts are
consistent with the Big Bang and some other cosmological models, but
taken together these observations show that the Big Bang is the best
current model for the Universe. These observations include:
* The darkness of the night sky - Olbers' paradox.
* The Hubble Law - the linear distance vs redshift law. The data are
now very good.
* Homogeneity - fair data showing that our location in the Universe
is not special.
* Isotropy - very strong data showing that the sky looks the same in
all directions to 1 part in 100,000.
* Time dilation in supernova light curves.
The observations listed above are consistent with the Big Bang or with
the Steady State model, but many observations support the Big Bang over
the Steady State:
* Radio source and quasar counts vs. flux. These show that the Universe
has evolved.
* Existence of the blackbody CMB. This shows that the Universe has
evolved from a dense, isothermal state.
* Variation of TCMB with redshift. This is a direct observation of
the evolution of the Universe.
* Deuterium, 3He, 4He, and 7Li abundances. These light isotopes are
all well fit by predicted reactions occurring in the First
Three Minutes.
Finally, the angular power spectrum of the CMB anisotropy that does
exist at the several parts per million level is consistent with a dark
matter dominated Big Bang model that went through the inflationary
scenario.
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Are galaxies really moving away from us or is space just expanding?
This depends on how you measure things, or your choice of coordinates.
In one view, the spatial positions of galaxies are changing, and this
causes the redshift. In another view, the galaxies are at fixed
coordinates, but the distance between fixed points increases with time,
and this causes the redshift. General relativity explains how to
transform from one view to the other, and the observable effects like
the redshift are the same in both views. Part 3 of the tutorial shows
space-time diagrams for the Universe drawn in both ways.
Also see the Relativity FAQ answer to this question.
----------------------
-- ******************************************************************** Amara Graps, PhD email: amara@amara.com Computational Physics vita: ftp://ftp.amara.com/pub/resume.txt Multiplex Answers URL: http://www.amara.com/ ******************************************************************** "Dare to be naive." -- Buckminster Fuller
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