The most incomprehensible thing about the universe is that it is comprehensible.
A unifying theory of the universe is the holy grail of modern physics. Einstein sought but did not find it. The great Cambridge mathematician Stephen Hawking and CalTech physicist Leonard Mlodinow believe they have found that unifying theory in something called M-theory. They take us on a journey I can only sketch in their elegant book The Grand Design [Bantam, 2010].
Why is there something rather than nothing?
Why do we exist?
Why this particular set of laws and not some other?
This is the Ultimate Question of Life, the Universe, and Everything.
Humans have tried to explain the universe since the dawn of our consciousness. Kepler, Galileo, Descartes and Newton thought the laws that govern the universe came from God. Contemporary classical science posits “a real external world whose properties are definite and independent of observers.” A newer approach that Hawking and Mlodinow endorse is called model-dependent realism. It says that if two models both agree with scientific observation, we cannot say which is more or less real.
Since 1999, a series of experiments in which physicists fire molecules toward a barrier with two slits in it have led to the conclusion in quantum physics that these molecules have alternative histories of how they travel through the two slits.
There is no single reality of their journey. Measuring them as they travel changes their journey. The great eccentric physicist Richard Feynman said “I think I can safely say that nobody understands quantum mechanics.” Feynman’s quantum observations are fundamental, in ways I cannot detail here, to M-theory as a unifying theory. Essentially, it turns out that the only way to try (so far with only partial success) to unify the four forces of nature is to use quantum theories.
These four forces are gravity, electromagnetism, the weak nuclear force that causes radioactivity and the strong nuclear force that holds atoms together. “The division of natural forces into four classes is probably artificial…People have therefore long sought a theory of everything that will unify the four classes into a single law that is compatible with quantum theory. This would be the holy grail of physics.”
Some physicists thought string theory would yield the unifying theory, but it kept unraveling. “String theorists are now convinced that the five different string theories and supergravity are just different approximations to a more fundamental theory…called M-theory.”
But M-theory is a most curious beast. M-theory posits an infinite number of universes that may all have different laws. Rather than a single Big Bang, “in this view, the universe appeared spontaneously, starting off in every possible way…Our picture of the spontaneous quantum creation of the universe is then a bit like the formation of bubbles in of steam in boiling water.”
It is also unclear whether M-theory is a single theory or a network of theories. What would give this network coherence is that different theories (like Newtonian physics and quantum physics) explain observable phenomena at different scales. Coherence means agree with observations at the scales where they overlap.
One of the most interesting aspects of Hawking and Mlodinow is their debate with the theory of intelligent design.
“Our very existence imposes rules determining from where and at what time it is possible for us to observe the universe….That principle is called the weak anthropic principle…But there is a stronger form we will argue for here, although it is regarded with disdain among some physicists. That strong anthropic principle suggests that the fact that we exist imposes constraints not just on our environment but on the possible form and content of the laws of nature themselves.
“Many people would like us to use these coincidences as evidence of the work of God. That type of idea is called intelligent design. That is not the answer of modern science. The multiverse notion [M-theory] is not a notion invented to account for the miracle of fine-tuning. But if it is true, it means that our cosmic habitat is only one of many. The fine-tunings in the laws of nature can be explained by the existence of multiple universes.” [Condensed]
“M-theory is the unified theory Einstein was hoping to find,” the authors boldly assert. “If the theory is confirmed by observation, it will be the successful conclusion of a search going back more than 3000 years. We will have found the Grand Design.”
Are Hawking and Mlodinow are right that M-theory is the unifying theory that Einstein sought? There is room for doubt. The interesting version of intelligent design is not creed-bound. It simply asks why the universe is so exquisitely designed to support life. Hawking and Mlodinow acknowledge that M-theory has yet to be proved. According to their own theory, we can regard M-theory and intelligent design as alternative theories that fit observable facts – neither of which has been proven. If M-theory is proven true, it still will not exclude the possibility that the universe is alive and perhaps intelligent on a cosmic scale. It will simply mean that physicists who prefer to exclude that possibility have no need to invoke it. But physicists, mystics and nature lovers share this in common. The apparent intelligent design of the universe fills us with awe and wonder.