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.
