5 JULY 2007
A question from a very young reader, as relayed by his mother:
"Where does the future come from, mommy? I don't understand. How does it get here?"
This
question comes from a 6-year-old named Thede. And brilliant as his mother
may be, she was stumped. But then again, so are the world's most brilliant
theoretical physicists.
Sure, some of them have offered answers to this question. The problem is, they aren't all the same answer. Deep down there are mysteries about time that continue to defy human understanding.
Attempting to answer his own question, Thede suggested that "maybe another planet has already done our future and they are giving it to us." Well, change "planet" to "universe" and you come close to ideas published online July 1 in the journal Nature Physics. In that paper, Penn State University physicist Martin Bojowald analyzed the old question of "What happened before the Big Bang?"
Presumably, at least in the standard story of the beginning of the universe, the Big Bang burst everything into existence all at once, in an explosion of literally cosmic proportions. Not only matter and energy, but space and time as well were born in that blast. Asking what happened before is senseless, as time itself did not yet exist.
Well,
that was the old party line, but it was just a way of saying that nobody
really knew what happened back then. The equations describing the beginning
of time just don't work at the beginning of time, which really means you
don't know anything about the beginning of time.
In recent years, scientists have explored the issue more deeply, developing theories describing the birth of our universe from a parent universe, raising the possibility that there IS a time "before" the Big Bang. One variant on this theme is the idea that a previous universe collapsed into nothingness and then re-exploded to form the universe we occupy now. In this view, the Big Bang is more like a Big Bounce.
Advocates of this idea have usually assumed that all traces of the previous universe's properties would have been wiped out by the bounce-explosion. But Bojowald shows that such a supposition is not necessarily valid. He worked out the math for a simplified model of a "Big Bounce" and found that indeed, some information from the old universe could leak into the new one. Thus the new (our) universe's future might have been, in a sense, provided by the information from the old one.
But not entirely, it seems. Quantum physics is at work here, and quantum physics always renders some things uncertain. Consequently information from the old universe could not specify the future of our universe completely.
Besides, Bojowald's analysis is based on one particular theory for combining quantum physics with Einstein's general theory of relativity. Relativity provides the math for describing cosmic history, except at the time around the Big Bang, when quantum physics comes into play. But nobody knows for sure how relativity and quantum physics fit together, so Bojowald's approach is just one possible description. Another new paper, published in the June 29 issue of Physical Review Letters, uses an entirely different theory to describe the origins of space and time as we know them from a previous "fuzzy" reality.
Even more radical ideas appear from time to time about how time works. The respected quantum physicist Yakir Aharonov has long proclaimed that time moves in both directions -- from past to future, for sure, but also from future to past. In the old days, before quantum theory, physicists thought that the future was simply determined by the past. What's happening now was supposedly determined by what happened just before, and what's happening now would in turn determine what happens just after -- and on and on and on and on.
Quantum physics destroyed that idea, showing that the exact same circumstances could produce various different futures. The math did not allow you to pick which future would happen, but did tell you the odds for various possible futures. (That was the source of Einstein's famous complaint that he didn't believe God would play dice with the world.)
Aharonov sort of sides with Einstein, saying that events really are determined, even in quantum systems -- but not just by past events. The outcome of quantum experiments is co-determined by what happened in the past, and by what WILL HAPPEN in the future. In other words, the result of a measurement you make today depends on other measurements in the distant future. Signals from the future move backward in time to select from among the quantum possibilities in your experiment.
"The information of future measurements propagating back from the future . . . affects the results of measurements conducted at the present," Aharonov and collaborator Jeff Tollaksen write in a paper posted recently online.
So from this point of view, the answer to Thede's question would be that the future comes from the future.
That's not a mainstream view. But the mainstream has not exactly answered the question to everyone's satisfaction, either. It seems likely that the mystery about the future will not be definitively solved any time in the near future.
So perhaps Thede should plan to be a theoretical physicist -- his question will no doubt still be waiting for an answer by the time he gets to graduate school.
E-mail: tsiegfried@nasw.org
