Belief in the multiverse: a form of blind faith?

A common scientific interpretation proposes that our universe is just one of an infinite number of universes, the "multiverse", with each universe endowed with its own unique physical laws and constants. Not so, says eminent physicist Lee Smolin in a New Scientist article called "You think there's a multiverse? Get real". Smolin argues that physics and cosmology (study of the structure, origin and dynamics of the universe) have taken a wrong turn into a non-scientific cul de sac.

Our universe is very special, being larger, emptier, smoother and flatter than a "typical" universe predicted by the known laws of physics. Cosmology introduced the concept of inflation to explain some puzzling properties of our universe, for example its uniformity. Inflation proposes that, soon after the Big Bang, our expanding universe went through a phase of exponentially fast inflation. However, Smolin argues that inflation merely moves the problem of the specialness of our universe back in time. Physicists must still assume the initial conditions of the universe and fine-tune them in order to make inflation happen at all, and unless inflation is very finely tuned and constrained, it produces a runaway creation of universes.

Therefore, many cosmologists contend that there is an infinite number of universes, each with its own peculiar properties that fell out randomly. Some are like our universe and could support life, most are not and could not, but all the other universes in the multiverse are unobservable to us and there is no experimental evidence for their existence.

Smolin reasonably contends that cosmologists should test hypotheses against the properties and history of our universe, the only universe we know to exist for sure; and that, since we cannot test the multiverse hypothesis experimentally, taking it seriously means going beyond science into the realm of faith.

At the deepest level the world is comprehensible through mathematics. Einstein memorably expressed his awe at the power of mathematics when he said: “The most incomprehensible thing about the universe is that it is comprehensible.” However, as impressive as mathematics is, we cannot conclude that the world is mathematics. But physicists seem to have reached this conclusion in the rarefied corridors of superstring theory.

Superstrings are postulated to be tiny vibrating loops that lie at the heart of every fundamental particle. How these strings vibrate determines the nature and behaviour of the particle. But in order to make the theory work, physicists must assume a world of nine dimensions and an infinite number of universes.

Superstrings and their extra dimensions are so small that they can never be seen and all other universes are unobservable to us. No tests or observations of these are possible. To accept the conclusions of string theory you must believe in the mathematics alone. This is not scientific. A proper scientific hypothesis should be falsifiable by what we can find in nature.

Smolin says the multiverse hypothesis neither makes firm predictions nor allows us to deduce anything about our universe we do not already know. He suspects we are making some wrong assumptions about the laws of nature. One such assumption is that the laws of physics are timeless, which Smolin contends is a mystical idea. He proposes that these laws change with time. We need to understand how the laws of physics and the initial conditions of the universe were selected.

Smolin proposes that, in order to make further progress in cosmology, physicists must discard certain assumptions and develop a new paradigm for doing science at the level of the universe as a whole. One such assumption is that we can explain the universe by scaling up the laws that work on small subsystems of the world.

This simply leads to breakdown in predictability, as in the multiverse. The new paradigm must operate on certain principles, and Smolin suggests three that would allow new hypotheses to open to experimental test. The first principle is that there is just one universe. The second is that time is real and the laws of physics are not timeless but evolve. And the third is that mathematics is limited.

William Reville is an emeritus professor of biochemistry at UCC. understandingscience.ucc.ie