Towards the ultimate question

A powerful conviction for me, and one that I believe encourages confidence that one day we will understand the very essence of creation, is the idea that as we converge on the moment of creation, the constituents and laws of the universe become ever simpler. A useful analogy here is life itself, or, more simply, a single human being. Each of us is a vastly complex entity, assembled from many different tissues and capable of countless behaviors and thoughts. Trace that person back through his or her life, back beyond birth and finally to the moment of fertilization of a single ovum by a single sperm. The individual becomes ever simpler, ultimately encapsulated as information encoded in DNA in a set of chromosomes. The development that gradually transforms a DNA code into a mature individual is an unfolding, a complexification, as the information in the DNA is translated and manifested through many stages of life. So, I believe, it is with the universe. We can see how very complex the universe is now, and we are part of that complexity.

Cosmology – through the marriage of astrophysics and particle physics – is showing us that this complexity flowed from a deep simplicity as matter metamorphosed through a series of phase transitions. Travel back in time through those phase transitions, and we see an ever-greater simplicity and symmetry, with the fusion of the fundamental forces of nature and the transformation of particles to ever-more fundamental components. Go back further and we reach a point when the universe was nearly an infinitely tiny, infinitely dense concentration of energy, a fragment of primordial space-time. This increasing simplicity and symmetry of the universe as we near the point of creation gives me hope that we can understand the universe using the powers of reason and philosophy. The universe would then be comprehensible, as Einstein had yearned.

Go back further still, beyond the moment of creation – what then? What was there before the big bang? What was there before time began? Facing this, the ultimate question, challenges our faith in the power of science to find explanations of nature. The existence of a singularity – in this case the given, unique state from which the universe emerged – is anathema to science, because it is beyond explanation. There can be no answer to why such a state existed. Is this, then, where scientific explanation breaks down and God takes over, the artificer of that singularity, that initial simplicity? The astrophysicist Robert Jastrow, in his book God and the Astronomers, described such a prospect as the scientist's nightmare: “He has scaled the mountains of ignorance; he is about to conquer the highest peak; as he pulls himself over the final rock, he is greeted by a band of theologians who have been sitting there for centuries.”

Cosmologists have long struggled to avoid this bad dream by seeking explanations of the universe that avoid the necessity of a beginning. Einstein, remember, refused to believe the implication of his own equations – that the universe is expanding and therefore must have had a beginning – and invented the cosmological constant to avoid it. Only when Einstein saw Hubble's observations of an expanding universe could he bring himself to believe his equations. For many proponents of the steady state theory, one of its attractions was its provision that the universe had no beginning and no end, and therefore required no explanation of what existed before time = 0. It was known as the perfect cosmological principle.

A decade ago Stephen Hawking and Jim Hartle tried to resolve the challenge differently, by arguing the singularity out of existence. Flowing from an attempt at a theory of quantum gravity, they agreed that time is finite, but without a beginning. This is not as bizarre as it sounds, if you think of the surface of a sphere. The surface is finite, but it has no beginning or end – you can trace your finger over it continuously, perhaps finishing up where you began. Suppose the universe is a sphere of space-time. Travel around the surface, and again you may finish up where you started both in space and time. This, of course, requires time travel, in violation of Mach's principle. But the world of quantum mechanics, with its uncertainty principle, is an alien place in which otherworldly things can happen. It is so foreign a place that it may even be beyond human understanding, children as we are of a world of classical Newtonian mechanics.

We simply do not know yet whether there was a beginning of the universe, and so the origin of space-time remains in terra incognita. No question is more fundamental or more magical, whether cast in scientific or theological terms. My conviction – perhaps I should say my faith – is that science will continue to move ever closer to the moment of creation, facilitated by the ever-greater simplicity we find there. Some physicists argue that matter is ultimately reducible to pointlike objects with certain intrinsic properties. Others argue that fundamental particles are extraordinarily tiny strings that vibrate to produce their properties. Either way, in combination with certain concepts such as inflation, it is possible to envisage creation of the universe from almost nothing – not nothing, but practically nothing. Almost creation ex nihilo, but not quite. That would be a great intellectual achievement, but it may still leave us with a limit to how far scientific inquiry can go, finishing with a description of the singularity, but not an explanation of it.

To an engineer, the difference between nothing and practically nothing might be close enough. To a scientist and certainly to a philosopher, such a difference, however minuscule, would be everything. We might find ourselves experiencing Jastrow's bad dream, facing a final question: Why? “Why” questions are not amenable to scientific inquiry and will always reside within philosophy and theology, which may provide solace if not material explication.

But what if the universe we see were the only one possible, the product of a singular initial state shaped by singular laws of nature? By now it is clear that the minutest variation in the value of a series of fundamental properties of the universe would have resulted in no universe at all, or at least a very alien universe. For instance, if the strong nuclear force had been slightly weaker, the universe would have been composed of hydrogen only; slightly stronger, and all the hydrogen would have been converted to helium. Slight variation in the excess of protons over antiprotons – one billion and one to one billion – might have produced a universe with no baryonic matter or a cataclysmic plenitude of it. Had the expansion rate of the universe one second after the big bang been smaller by one part in a hundred thousand trillion, the universe would have recollapsed long ago. An expansion more rapid by one part in a million would have excluded the formation of stars and planets.

The list of cosmic coincidences required for our existence in this universe is long, moving Stephen Hawking to remark that “the odds against a universe like ours emerging out of something like the big bang are enormous.” Princeton physicist Freeman Dyson went further, and said: “The more I examine the universe and the details of its architecture, the more evidence I find that the universe in some sense must have known we were coming.” This concatenation of coincidences required for our presence in this universe has been termed the anthropic principle. In fact, it is merely a statement of the obvious: Had things been different, we would not exist. It may be that many different universes are possible, and many may exist in parallel with our own. Inflation theory can be interpreted in this way, with our universe budding off a larger fabric of space-time – like one strawberry in a patch of many strawberries. My speculation, however, is that because things become simpler as we near the moment of creation, there was only a limited range of possibilities; indeed, perhaps only one, with everything so perfect that it could have been no other way.

In this case, what could we say about the ultimate question? That God had no choice in how the universe would be, and therefore need not exist? or that God was very smart, and got it just right? In any case, science would still be left contemplating the question: Why these conditions and not others? Or perhaps the comprehensibility of the universe in these terms is sufficient explanation. The truth and treasure of the universe is its own existence, and our quest for that truth and treasure will be eternal, like the universe itself.

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In 1977, Steven Weinberg published The First Three Minutes, one of the finest popular books on cosmology ever written, and justly still in print. His book was based on a course he taught about gravitation and cosmology at MIT while I was a graduate student there. His class influenced my decision to enter cosmological research. Toward the end of his book, Weinberg muses on the questions we ask ourselves, particularly the conviction that, somehow, humans are not a mere cosmic accident, the chance outcome of a concatenation of physical processes in a universe that dwarfs us on every scale. He expresses his view on the matter this way: “It is very hard to realize that [this beautiful Earth] is all just a tiny part of an overwhelmingly hostile universe. It is even harder to realize that this present universe has evolved from an unspeakably unfamiliar early condition, and faces a future extinction of endless cold or intolerable heat. The more the universe seems comprehensible, the more it also seems pointless.”

I must disagree with my old teacher. To me the universe seems quite the opposite of pointless. It seems that the more we learn, the more we see how it all fits together – how there is an underlying unity to the sea of matter and stars and galaxies that surround us. Likewise, as we study the universe as a whole, we realize that the “microcosm” and the “macrocosm” are, increasingly, the same subject. By unifying them, we are learning that nature is as it is not because it is the chance consequence of a random series of meaningless events; quite the opposite. More and more, the universe appears to be as it is because it must be that way; its evolution was written in its beginnings – in its cosmic DNA, if you will. There is a clear order to the evolution of the universe, moving from simplicity and symmetry to greater complexity and structure. As time passes, simple components coalesce into more sophisticated building blocks spawning a richer, more diverse environment. Accidents and chance, in fact, are essential in developing the overall richness of the universe. In that sense (although not in the sense of quantum physics), Einstein had the right idea: God does not play dice with the universe. Though individual events happen as a matter of chance, there is an overall inevitability to the development of sophisticated complex systems. The development of beings capable of questioning and understanding the universe seems quite natural. I would be quite surprised if such intelligence has not arisen many places in our very large universe.

As I travel the world, I love to visit great art museums, to see classic sculptures, the works carved and painted and assembled by centuries of aesthetic visionaries. Cosmologists and artists have much in common: Both seek beauty, one in the sky and the other on canvas or in stone. When a cosmologist perceives how the laws and principles of the cosmos begin to fit together, how they are intertwined, how they display a symmetry that ancient mythologies reserved for their gods – indeed, how they imply that the universe must be expanding, must be flat, must be all that it is – then he or she perceives pure, unadulterated beauty.

The religious concept of creation flows from a sense of wonder at the existence of the universe and our place in it. The scientific concept of creation encompasses no less a sense of wonder: We are awed by the ultimate simplicity and power of the creativity of physical nature – and by its beauty on all scales.