Physics: Can the Future Leak Into the
Present?
By Sharon Begley
Newsweek
July 30, 2007 issue - You can tell a lot about a subject by who its
muses and mascots are. Neuroscience has philosophers who wax
profound about the mind, geology has intrepid explorers and
subatomic physics has ... Alice in Wonderland. "Curiouser and
curiouser," as Alice said, also describes the subatomic, or
quantum, world. With age, this centenarian (quantum physics is 107
years old) has gotten more bizarre. "The surprises keep coming,"
says physicist David Albert of Columbia University. None is greater
than finding loopholes in the hallowed uncertainty principleand,
even more outlandishly, seeing hints that the future may leak into
the present.
Since experiments keep proving quantum ideas right, physicists are
forced to take them seriously. It isn't easy. They have to admit
that a particle can be in two places at once. They have to accept
that subatomic systems can become so "entangled" that measuring one
affects the other even if the two are light-years apart, which
Einstein called "spooky action at a distance." But even as quantum
weirdness provides fodder for such drivel as the best-selling book
"The Secret," it also fuels debate on subjects as lofty as the
nature of reality. Last week a conference at Oxford University
explored the idea that every time a subatomic system reaches a
decision pointto undergo radioactive decay or not, sayit chooses
both possibilities: in this world the particle decays, while in a
parallel world it does not. Some physicists buy this "many worlds"
interpretation because the alternative is even more unpalatable:
that quantum systems choose one possibility or another only when an
observer looks. Einstein loathed the idea that reality is created
by observers.
New studies suggest, however, that it is possible to measure
something without affecting it. The key is doing the experiments,
well, gently. Anyone with a vague memory of Physics 101 knows that
if you shine a light on what you want to measure, or stick a
thermometer in it, you alter it. Taking the temperature of a steak
with a cold thermometer, for instance, cools it as heat is
transferred from meat to glass. You don't know what the temperature
"really" was before you jabbed in the thermometera notion
enshrined as the uncertainty principle. To circumvent this rule,
Israeli physicist Yakir Aharonov got the idea of making "weak
measurements," akin to waving your hand over the steak to feel its
heat. That's not very precise with meat, but it works with quantum
measurements: if you make enough weak measurements, the average
comes impressively close to the actual value, experiments are
showing. "Weak measurements let you lift the veil of secrecy
imposed by the uncertainty principle," says Paul Davies of Arizona
State University.
In one use of weak measurements, particles of light (photons) fly
toward a screen, one at a time. The screen has two slits. If each
photon goes through one slit, they form two bright spots on
Venetian blinds beyond the screen. If each photon somehow goes
through both slits, however, they form black-and-white stripes when
they land on the blinds. Physicists have long known that if a
device observes the slits, no zebra pattern forms; it's as if
quantum phenomena are too shy to display their magicone particle
going through two slitswhen watched. Weak measurements might be
able to get around this by being less obtrusive; studies to try are
in the works.
In the meantime, experiments have put detectors on the far side of
the blinds. If the blinds are open and the detectors peek at the
slits, photons fly through only one slit and no zebra stripes form.
If the blinds are closed so the detectors cannot see the slits,
photons fly through both and form the stripes. Here's the twist: if
the blinds open only after photons have passed the slits but before
they reach the blinds, the stripes fail to form even though the
photons have seemingly done what they must to form stripesnamely,
fly through two slits, as they always do when unobserved. The act
of observing alters what the photons did earlier, somehow changing
things so they passed through one slit and not two. There are "many
histories" a photon could have, such as passing through one slit or
two, Davies writes in his new book, "Cosmic Jackpot." Making a
measurement "chooses which [history] existed."
That interpretation remains speculative, but weak measurements may
indeed show that "something that happens now is affected by
something that happens in the future," says physicist Jeff
Tollaksen of George Mason University. "It suggests that the
universe has a destinya destiny that is out there and coming back
to us from the future." Maybe physicists should replace Alice with
a new muse: Trafalmadorians, who in Kurt Vonnegut's
"Slaughterhouse-Five" saw past, present and future all at once like
a landscape, each moment ever present.
URL: http://www.msnbc.msn.com/id/19875410/site/newsweek/page/0/