Saturday, December 6, 2014

Paul Steinhardt's New Inflation Theory--Better Than Most, But Still Wrong

On Scientific American’s blog Cross-Check, John Horgan shares an interview with superstar physicist Paul Steinhardt of Princeton University on the subject of cosmic inflation, the period of rapid expansion of the universe immediately following the big bang. In “Physicist Paul Steinhardt Slams Inflation, Cosmic Theory He Helped Conceive,” Horgan quotes Steinhardt’s explanation for his change of heart and on the cyclic model he’s developed to replace the current leading models. He says, 

The cyclic model emerged when my collaborators and I asked the question: is there any way of explaining the smoothness and flatness of the universe and small ripples in density without inflation?  The answer was yes: the key is to have a universe in which the big bang is replaced by a big bounce.   In this picture, the present period of expansion and cooling is preceded before the bounce by an epoch of contraction, and the important events that shape the large-scale structure of the universe (smoothing, flattening and generating fluctuations) occur before the bounce during a period of slow contraction.   There is no high-energy inflation phase – the universe goes straight from the bounce into a period of slow expansion and cooling.  Inflation is not needed to smooth and flatten the universe.  Consequently, there is no multiverse. The bounces can repeat at regular intervals resulting in a cyclic universe.  In some versions, the theory is geodesically complete (existing infinitely into the past), unlike inflation, which requires a beginning and special initial conditions.

The remarkable thing about Steinhardt’s cyclic theory is that it is actually correct in its gross outline. As we saw here, what actually happens is a contraction in the size of the universe that is simultaneous with a rapid inflation in the number of spacetime points. This is followed by a phase transition to the period of slow expansion and cooling that Steinhardt mentions. So he’s right about the contraction and subsequent expansion, but he’s wrong when he asserts that there’s no high-energy inflation phase. He doesn’t know about our spacetime model with its discrete points.

 I once tried to tell Dr. Steinhardt about the correct theory, but I got no response. Physicists develop the ability to smell correspondence from nonphysicists trying to help them do their jobs, and it goes directly into the trash. Such is life.