Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..apr.j4004t&link_type=abstract
American Physical Society, April Meeting, Jointly Sponsored with the High Energy Astrophysics Division (HEAD) of the American As
Astronomy and Astrophysics
Astrophysics
Scientific paper
The Greeks were the first to ask, or at least to write about asking, questions like whether there are other planets like earth and whether the universe is finite or infinite. In all cases, they answered both yes and not (since there were lots of Greeks and not much data). A good deal later (but still in the period called history, unless you are very old), astronomers started asking whether the duration of the universe was finite or infinite, what the stars are made of and what keeps them shining, and whether there are other galaxies like ours. All of these now how answers at some confidence level. Close to 100 planets outside our solar system have been reported, starting in 1995, but selection effects mean that none are like earth. Data from many sources (supernovae, radioactive elements, microwave radiation, and all) combine to say that the universe has a finite past but probably an infinite future and an extent that, if not infinite, is anyhow very much larger than a breadbox. The stars run on nuclear fusion, and there are oodles of galaxies. The talk will explore how we have learned some of these things and try to look forward to current unsolved problems in astrophysics and cosmology.
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