Steady-State Theory

In his work measuring distances to galaxies, Edwin Hubble, after whom the Hubble space telescope was named, noticed an interesting correlation. The more distant a galaxy is, the faster it is moving away from us. This relationship is called the Hubble law. This relationship can be used to find the distances to additional galaxies, by measuring the speed of recession. More importantly, Hubble deduced the cause of this correlation. The universe is expanding. To visualize this expansion, draw some galaxies on an ordinary balloon and blow it up. Notice how the "galaxies" move farther apart as the balloon expands. Measuring distances between the drawn in galaxies at the rates at which they move apart, would give a relationship similar to Hubble's law.

The expanding universe can be consistent with either the big bang or the steady-state theory. However in the steady-state theory, new matter must appear to fill in the gaps left by the expansion. Normally as the universe expands, the average distance between galaxies would increase as the density of the universe decreases. These evolutionary changes with time would violate the fundamental assumption behind the steady-state theory. Therefore, in the steady-state theory, hydrogen atoms appear out of empty space and collect to form new galaxies. With these new galaxies, the average distance between galaxies remains the same even in an expanding universe.

The Hubble plot also provides evidence that the universe changes with time. The slope of the Hubble plot gives us the rate at which the universe is expanding. If the universe is not evolving, this slope should remain the same even for very distant galaxies. The measurements are difficult, but the Hubble plot seems to curve upward for the most distant galaxies. The universe was expanding faster in the distant past, contrary to the prediction of the steady-state theory that the universe is not evolving.