Fortunately, there are ways of telling which model should be preferred. Remember that when we look out into the universe, we are also looking back in time. If we compare the nearby universe (as it is today) to the distant universe (the universe back in time) the two models predict different things. Steady State (SS) tells you the galaxies should be the same distance apart then as today and any part of space should have young and old galaxies in it. If we see a difference over time, SS cannot be right. Big Bang (BB) tells you that the glaxies should be closer together in the past, and if we look far enough back we should see a universe even without galaxies. If we do not see a difference over time, BB cannot be right. 

In 1960, we discovered a new class of objects called quasars. They are reasonably small objects, about the size of a star system (up to a few LY), but they radiate as much energy or more, as an entire galaxy. They also show extreme red shifts. According to Hubble’s Law (the amount of red shift is proportional to distance), they must be extremely distant objects. 

What are quasars? The simplest answer is that we are not sure. One reasonable explanation is that quasars are infant galaxies with supermassive black holes at their center (with a mass of perhaps millions of suns) that radiate energy as they ingest dust and gases. But whatever they might be, we do know that: 1) they are extremely energetic objects, some put out a thousand times the energy of a normal galaxy; 2) they are relatively small, on the order of a few light years across at most; and 3) most quasars have a large red-shift and are therefore distant objects. There are no quasars within roughly 2 billion LY of the earth and that means they have not existed in the past 2 billion years, while they are common in the distant past. In other words, quasars are associated with a young universe, and no longer exist in the present universe. 

Clearly, quasars are a class of objects not evenly distributed through space and time; and therefore the universe does not look the same any time, any place and Steady State cannot be correct. (However, there are some respected astronomers that do not accept that the red shift of quasars follows Hubble’s Law and who maintain that quasars only appear to be far away). Keep in mind, though that invalidation of the Steady State model by the presence and distribution of quasars does not prove that the Big Bang model is correct. 

If there was a Big Bang, then the early universe was a radiation universe. While some of this radiation condensed into matter, most of it did not, and should therefore still be around to permeate the universe (although at a much longer wavelength due to the expansion and cooling of the universe). In 1965, Bell Laboratories discovered a radio signal that seemed to come equally from all regions of space. This background radiation occurs at the right frequencies predicted by the BB model, and represents the remnants of the radiation created in the BB. This Echo as it has also been called, cannot be explained by any other means and represents confirmation that our universe originated in the BB.