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| Name | Teach Astronomy - Evidence for Cosmic Acceleration |
| Video Uploader | Video From Teach Astronomy |
| Upload Date | This Video Uploaded At 23-07-2010 01:28:44 |
| Video Discription | http://www.teachastronomy.com/ The primary evidence that the universe is currently accelerating comes from distant supernovae. The observation is based on the fact that a standard cosmology filled with only radiation and matter, most of which is dark matter, predicts the brightness of distant objects. Supernovae at redshifts of about a half or greater are observed to be twenty or thirty percent fainter than expected in a standard cosmological model. The explanation is that they are more distant than anticipated and that this is caused by the acceleration over the time since the big bang. It's worth questioning how good this evidence is based as it is on only one distance indicator. Astronomers have worked hard to measure local calibrators for the distance indicator of supernovae Type Ia, and they understand very well how energy comes out of supernovae. So it looks like supernovae are an excellent distance indicator. When observed at high redshift the supernova is imbedded in a distant galaxy, and the light from the galaxy is mixed with the light from the supernova. Very careful observations with the Hubble Space Telescope are required to dig out the distant supernovae. In some cases only the supernova is seen and not even the galaxy in which it's imbedded because it's so faint. These observations have been done with care, and it really does appear that supernovae are fainter than anticipated. Another possibility is that dust distributed through the universe might make supernovae fainter than expected. But dust would also make them redder, and there's no that the distant supernovae are red due to dust. Thus their faintness looks like increased distance. The clinching evidence has not yet come. It will come when astronomers can look at distant enough supernovae to trace back in time to the phase of deceleration before it turned into acceleration. This is expected in the next decade. |
| Category | Education |
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