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Steady state is a theory the universe remains teady over time.

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steady state theory.
Hoyle suggested that the universe is infinitely old and has remained in a steady state except that the universe was indeed expanding.

An alternative theory to the Big Bang was proposed in 1948 by Hermann Bondi, Thomas Gold, and Sir Fred Hoyle It was called the steady-state theory. They found the idea of a sudden beginning to the universe philosophically unsatisfactory. Bondi and Gold suggested that in order to understand the universe we needed to make observations of its distant parts, which would of necessity be observations from the past. In order to interpret those observations we must use the laws of physics, and those have been formulated at the present time. If the state of the universe was different in the past how could we be sure that the laws of physics were not different in the past as well? If they were different no valid conclusions could be drawn. For Bondi and Gold not only would the laws of physics have to be the same in all parts of the universe, but at all times as well. The universe would also be the same, always static, always contracting or always expanding. The first two could be ruled ut by the simple observation that the sky is dark at night. (see Olber's Paradox)

Hoyle approached the problem mathematically and tried to solve the problem of the creation of the matter seen all around us, which in the Big Bang theory is all created at the start. He proposed that the decrease in the density of the universe caused by its expansion is exactly balanced by the continuous creation of matter condensing into Galaxies that take the place of the Galaxies that have receded from the Milky Way, thereby maintaining forever the present appearance of the universe. In order to produce the matter, a reservoir of energy would be required. In order to prevent this reservoir being diluted, by the creation of matter and by the expansion of the universe, he made this reservoir negative. The expansion and creation now work against each other and a steady state of energy is maintained.

The steady state theorists explained the Hydrogen - helium abundance by the presence of supernovae. Originally the Big Bang theoy suggested that all the heavy elements were produced at the start of the universe, but now it is accepted that only the helium and a little lithium was produced then and both theories now accept the role of supernovae in the creation of heavy elements.

One important and little known attribute of the steady state theory is its importance to an aspect of electromagnetic and quantum theory. Maxwell's equations of electromagnetism have two solutions, one positive, one negative. Consider the equation x2 = 4. It has two solutions; x = 2 and x = -2. In Maxwell's equations the negative solution was usually discarded, as it would correspond to something travelling backwards in time. However, in 1941 John Wheeler and Richard Feynman, proposed that by taking seriously the idea that two waves, one travelling forward in time and one travelling backwards, were produced in electromagnetic interactions certain problems in quantum theory disappeared. Between the cause and effect in an experiment the two waves add together,but before the cause, and after the effect, the two waves cancel, so what we see is the sequence; cause, interaction, effect. The crucial aspect for cosmology in the Wheeler - Feynman theory is that the two waves only cancel outside the event if they are both of equal size, in other words the wave from the future has to be the same size as the wave from the past, and this implies that the universe is the same in the future as it was in the past and hence in a steady state.

Steady state is not without problems though, there are several areas in which it is in difficulty. One is the distribution of radio sources. For any sources if the distribution is uniform the fainter ones will be the most distant. If we draw a sphere around us corresponding to a certain brightness then the number of such sources will be proportional to the surface area of that sphere, and thus proportional to radius squared. The number of sources brighter than that certain brightness should be proportional to the volume of that sphere, an hence radius cubed, as they will all lie within the sphere. A graph of the log of the number of sources at a particular brightness, to the log of the number of sources brighter than that brightness, should have a gradient of 1.5 (=3/2) For radio sources the ratio is 1.8 showing that there are more bright radio sources at greater distance, and hence earlier times than would be expected for a steady state universe. The conclusion is that the universe is evolving or at least changing.

The discovery of quasars in 1966, also provided evidence contradicting the steady-state theory. Quasars are very small but brilliantly luminous extragalactic systems, found only at great distances. Their light has taken several billion years to reach the earth. Quasars are therefore objects from the remote past, which indicates that a few billion years ago the constitution of the universe was very different than it is today.

The steady-state theory is now no longer accepted by most cosmologists, particularly after the discovery of microwave background radiation in 1965, for which steady state has no explanation.

The Hubble Deep Field photograph taken in 1996 by the Hubble Space Telescope shows the most distant view known. It was expected to show the birth of galaxies, but instead shows Galaxies looking remarkably like present day ones, perhaps there is life in the steady state yet.

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