So it follows that in the past the Universe must have been smaller. Working backwards, there must have been a time when all the matter in the Universe was packed together in one place. This is the reasoning behind the most widely accepted theory about how the Universe began. It is thought that the Universe came into being as a result of an explosion, or the Big Bang, which set in motion the expansion that we observe. Astronomers have worked out that the Big Bang must have occurred about 15,00 million years ago.
During his study of the spectra of galaxies, Hubble also discovered another interesting thing. The farther galaxies are away, the greater is their red shift and the faster they are moving. And he worked out a relationship between speed and distance, which became known as the Hubble constant.
Measuring the amount of red shift and applying the Hubble constant provides the only method of finding out the distance to the farthest galaxies and the remote quasars.
Spot facts:
| Almost all the galaxies appear to be moving away from us. So does it
mean that our Galaxy is the centre of the Universe? The answer is no. What
is happening is that every galaxy is moving away from every other galaxy
as the Universe expands.
To see how this kind of thing could happen, think of the surface of a balloon as the Universe and dots on the surface as galaxies. When you blow up the balloon, the "Universe" expands and the "galaxies" move farther away from each other. |