Reading back over this morning’s post, I see I should have emphasised that cosmic inflation is not an alternative to the Big bang theory; it is simply a modification of the conventional big bang model.
What is the physical cause of the initial exponential expansion of the universe? Guth proposed that the expansion was propelled by a repulsive gravitational force generated by an exotic form of matter. Although this proposal was slightly flawed, the flaw was soon overcome by the invention of “new inflation” by Andrei Linde in the Soviet Union and independently by Andreas Albrecht and Paul Steinhardt in the US. (New inflation posits that the early universe went through the stage of exponentially rapid expansion in a kind of unstable vacuum state – a state with large energy density, but without elementary particles).
Nowadays, the evidence for the inflationary universe model is very strong. One of the coolest aspects of the theory inflation is an explanation for the large scale structure of the universe (galaxies etc.) Basically, the idea is that quantum fluctuations in the early universe could have been stretched by inflation to astronomical proportions, providing the seeds for galaxy formation. The predicted spectrum of these fluctuations was calculated by Guth and others in 1982.
These fluctuations can be seen today as ripples in the cosmic background radiation, although the amplitude of these faint ripples is only about one part in 100,000. The ripples were detected by the COBE satellite in 1992, and they have now been measured to much higher precision by the WMAP satellite and other experiments. The properties of the radiation are found to be in excellent agreement with the predictions of the simplest models of inflation [image].