During the 1920s Edwin Hubble carried out a research project with the 100 inch Mount Wilson telescope. He photographed numerous galaxies, estimated their distances and, using the Doppler Effect, measured their radial velocities. The results were startling; apart from those closest to us, all the galaxies were receding. Furthermore the speed of recession was proportional to the distance. The only sensible conclussion was that the Universe was expanding. This had already been predicted by Albert Einstein's early work on general relativity. However all the evidence at the time had pointed to a static Universe and so Einstein had added a 'fudge factor', the so called "cosmological constant". He later refered to this as his greatest blunder.
The consquences of this expansion are immense. Instead of the Universe being infinite in age and extent, it must have had a beginning, a hot, 'big bang'. Furthermore the Universe that we see today would have been very different in its early state and may even change again, as it continues to expand. This contrasts to the pre-Hubble Universe, where the cosmos always was as it is now, and always would be. The Universe had suddenly become a far more interesting place to live!
The following simulation program allows students to replicate some of Hubble's observations, using standard candles such as Cepheid Variables, and Type 1a Supernovae to measure the distance to various galaxies and then using the Doppler Shift to determine the velocity of recession. Having attempted several of these students may then plot a Hubble diagram and so calculate the rate of expansion of the Universe.
It is important to remember that it is space-time itself that is expanding, carrying the galaxies with it, rather than the galaxies themselves moving through the void. This leads to the mind numbing conclussion that there is neither a 'beyond the edge of the Universe' nor a 'prior to the Big Bang', as both space and time were created at the moment of the Universe's birth. If that is confusing then you are in good company, if, on the other hand, you think you understand it... think a little harder!
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