29 MARCH 2007
Time is nature's way of keeping everything from happening all at once, as Woody Allen became famous for saying.
Some
sources, though, claim that Albert Einstein said it first. But Einstein
also said that "time is an illusion," and both can't be right. If time
is an illusion, there's nothing to keep everything from happening all
at once.
Consequently everything does happen all at once, which is another way of saying that everything has already happened. That's what Einstein meant. Because in Einstein's theory of relativity, all of time and space simply exists, it does not come into being. What we experience as time is merely our meandering through the four-dimensional space-time continuum. So there.
Seriously, serious physicists argue that such an approach is the only way to understand time. Relativity established that there is no such thing as a universal "now" to carry reality from past to future. Distant events can never be unambiguously simultaneous. Depending on their motion, different observers might disagree about which of two events occurred first. So your "future" has already happened -- from the viewpoint of some distant observer moving with the appropriate speed and direction. Sorry.
In this picture, everything doesn't seem to happen all at once thanks
to the fact that the speed of light is constant and limited to a mere
300 million meters per second. So even if future events already exist
out there, nobody can find anything out about them until light has had
enough time to 
deliver
the message. Any other delivery systems -- radio, e-mail, FedEx --
are also limited by the same speed limit that holds for light. Light's
speed cannot be exceeded because it represents the connection between
space and time that Einstein's relativity revealed.
Gloomily, relativity seems to require that all of reality be viewed as just a big block of spacetime, complete with a preordained future that nobody can do anything about. There's no way out of this timeless cosmological prison demanded by the theory of relativity. Unless, of course, you can figure out how to change the theory.
That might seem like cheating, but in fact scientists know that relativity cannot be the whole story of reality. While relativity describes spacetime (and gravity) very accurately, it does not address the physics of the particles and forces that play around in spacetime. For that stuff you need quantum physics. And combining quantum physics with relativity into a unified theory has so far been too hard a homework problem for physicists to successfully solve. Perhaps the ultimate unified theory will show time in a different light, so to speak.
Among those raising that possibility is Rafael Sorkin, a physicist at the Perimeter Institute in Canada and Syracuse University in New York. It's possible, he argues, that reality is dynamic -- growing or "becoming" -- rather than just statically existing. The universe of "events" -- locations in space and time -- might very well be expanding, even if you can't always say which events preceded others.
Consider, as an illustration, a giant tree, growing, as trees do, from
the tips of its various branches. A new leaf emerging from the tip of
one branch has no idea what is happening on the other side of the tree,
where another leaf may have been born at about the same "time." Distant
observers (depending on their motion) may disagree about which leaf arrived
first. But it doesn't matter 
to
the tree. The tree keeps growing anyway.
Perhaps, Sorkin argues, spacetime in our universe grows in a similar way. Using the mathematics of set theory, he envisions elements of spacetime (or "events") as the offspring of "ancestor" events. If you start with one event, it can either spawn an ancestor or not, giving two possible sets (one with one event, the other with two). As those events give birth to others, the number of possible combinations of events rises rapidly. Certain combinations (or sets) of events will create a growing volume of cause-and-effect relationships, mimicking what we perceive as ordinary space and time.
Yes, it's very complicated. Few people paid enough attention to all that stuff about set theory in algebra class to grasp how it can explain space and time. But don't feel bad. Scientists have not exactly grasped all this very well themselves, and are far from answering the questions the universe has given them. Sorkin is merely constructing an example of the sort of math that might allow reality to change and grow, even in a universe ruled by relativity. "The example . . . seems to me to refute the contention that relativistic spacetime is incompatible with genuine change," he writes in a recent paper.
Opponents of change, he points out, want to imagine themselves as "super observers," able to "take in all of existence at a glance." But super observers do not exist, Sorkin points out. Human notions of "now," the past, and the future are local.
So you shouldn't care about what happens "first" from anybody's point of view other than your own. And there's no need to worry whether it was Einstein or Woody Allen who first said that time keeps everything from happening at once. It was probably Mark Twain, anyway.
E-mail: tsiegfried@nasw.org
