Why do we remember the past, but not the future? Why don’t we meet people who grow younger as they age? Why do things, left by themselves, tend to become messier and more chaotic? What would Maxwell’s Demon say to a Boltzmann Brain? What came before the Big Bang?
The answers can be traced to the moment of the Big Bang — or possibly before, discussed below by rock-star theoretical physicist Sean Carroll, at the California Institute of Technology. His research involves theoretical physics and astrophysics, focusing on issues in cosmology, field theory, and gravitation.
Time pervades our lives — we keep track of it, lament its loss, put it to good use. The rhythms of our clocks and our bodies let us measure the passage of time, as a ruler lets us measure the distance between two objects. But unlike distances, time has a direction, pointing from past to future. From Eternity to Here examines this arrow of time, which is deeply ingrained in the universe around us. The early universe — the hot, dense, Big Bang — was very different from the late universe — cool, empty, expanding space — and that difference in felt in all the workings of Nature, from the melting of ice cubes to the evolution of species.
The arrow of time is easy to perceive, much harder to understand. Physicists appeal to the idea of entropy, the disorderliness of a system, which tends to increase according to the celebrated Second Law of Thermodynamics. But why was entropy ever small in the first place? That’s a question that has been tackled by thinkers such as Ludwig Boltzmann, Stephen Hawking, Richard Feynman, Roger Penrose, and Alan Guth, all the way back to Lucretius in ancient Rome. But the answer remains elusive.
The only way to understand the origin of entropy is to understand the origin of the universe — by asking what happened at the Big Bang, and even before. From Eternity to Here discusses how entropy relates to black holes, cosmology, information theory, and the existence of life. The book tells a story that starts in the kitchen, where we can turn eggs into omelets but never the other way around, and takes us to the edges of the universe. Modern discoveries in cosmology — dark energy and the accelerating universe — and quantum gravity — the possibility of time before the Big Bang — come together to suggest a picture of a multiverse in which the arrow of time emerges naturally from the laws of physics.
A more human-centric look at time has been offered by quantum physicist Menas Kafatos and bestselling author, Deepak Chopra, a Fellow of the American College of Physicians, Clinical Professor UCSD Medical School, researcher, Neurology and Psychiatry at Massachusetts General Hospital (MGH).
In their new book, You Are the Universe, Chopra and Kafatos cover time in great detail, but here's a thumbnail sketch of their more philosophical argument: If you ask a simple question like "What came before the big bang?" you are posing a paradox.
(Warning: As the great Danish physicist Neils Bohr said to one of his colleagues: "Your theory is crazy, but it's not crazy enough to be true.)
"Before" and "after" have a meaning only in time, and linear time at that. There is no evidence of any kind that time existed before the big bang. Moreover, what we typically think of as time--the tick tock on a clock face--depends on having a human nervous system. Einstein broke free of this model, where we think we intuitively know what time is, when he introduced the concepts in his theories of relativity.
In those theories, the speeding up or slowing down of time depends on the frames of references of observers. Time is not universal. For example, a moving observer’s time slows down as seen by a stationary observer. Slowing down of time also occurs when an observer is falling towards a black hole, as seen by a distant observer. The effect is still there, but tiny, in all gravitational fields, including the Earth's gravity.
The relativity of time depended upon a new theory, and if we stand back, we discover that all views of time are human constructs. If time seems linear, that's because we humans have modeled it that way in accord with our nervous system. It is just as viable to construct other models of time. For example, your body obeys natural rhythms in accord with the planetary, lunar, and solar cycles. The very notion of "time passing" fits with the firing of neurons in the brain, which have a beginning, middle, and end.
If you drop every model, something surprising happens. They are not needed. For example, you can view your daily life as occurring entirely in the present moment. The present moment is not a clock phenomenon. Clocks measure intervals--seconds, minutes, hours--while the present moment has no interval. It's always here, endlessly renewing itself, unmeasurable, and fleeting. Because the instant you try to capture it, it's gone. This implies that the "now" is actually outside time. It can be defined either as instantaneous or eternal. Both are valid as verbal descriptions but in the end invalid, since the vocabulary of time doesn't apply to the timeless.
The same is true of the big bang or the potential end of the universe. Time doesn't begin or end in an absolute way. It is a convenient way of using words. Time is simply a concept that fits various physical models. But its origin is as much in metaphysics as in physics.
When someone believes he will die and go to Heaven for eternity, the typical, casual definition of "eternity" is a long, long time. But that's not true, because whatever is eternal must be outside time. Ultimately, the only participation we can have in time, outside time, or with a dimension of inconceivable time, occurs in our consciousness. Whatever we can experience determines the nature of time. It is just as true to say that the big bang is occurring right now as to date it back to 13.8 billion years, because only when we think about the event do we draw the big bang into the world of human experience, and thinking happens in the now.
None of these conclusions are speculative--quantum physics and cosmology deal with them--and cosmologists and quantum physicists argue over them--every day. Without settling the vexing questions of "What came before the big bang?" "Where did time originate?" and "What is the timeless like?" we only want to point out that time has no meaning outside a specific frame of reference.
There is no "real" time, only models of time constructed in human awareness. Once we realize this simple fact, the capacity to move beyond all models, to truly lose our fear of death, comes alive. The spiritual concept that we were never born and will never die then becomes viable, too.