Found something cool:
No one keeps track of time better than Ferenc Krausz. In his lab at
the Max Planck Institute of Quantum Optics in Garching, Germany, he has
clocked the shortest time intervals
ever observed. Krausz uses ultraviolet laser pulses to track the
absurdly brief quantum leaps of electrons within atoms. The events he
probes last for about 100 attoseconds, or 100 quintillionths of a
second. For a little perspective, 100 attoseconds is to one second as a
second is to 300 million years.
But even Krausz works far from the frontier of time. There is a temporal realm called the Planck scale,
where even attoseconds drag by like eons. It marks the edge of known
physics, a region where distances and intervals are so short that the
very concepts of time and space start to break down. Planck time—the
smallest unit of time that has any physical meaning—is 10-43 second, less than a trillionth of a trillionth of an attosecond. Beyond that? Tempus incognito. At least for now.
Efforts to understand time below the Planck scale have led to an
exceedingly strange juncture in physics. The problem, in brief, is that
time may not exist at the most fundamental level of physical reality. If
so, then what is time? And why is it so obviously and tyrannically
omnipresent in our own experience? “The meaning of time has become
terribly problematic in contemporary physics,” says Simon Saunders, a
philosopher of physics at the University of Oxford. “The situation is so
uncomfortable that by far the best thing to do is declare oneself an
agnostic.”
The trouble with time started a century ago, when Einstein’s special and general theories of relativity demolished the idea of time as a universal constant.
One consequence is that the past, present, and future are not
absolutes. Einstein’s theories also opened a rift in physics because the
rules of general relativity (which describe gravity and the large-scale
structure of the cosmos) seem incompatible with those of quantum
physics (which govern the realm of the tiny). Some four decades ago, the
renowned physicist John Wheeler, then at Princeton, and the late Bryce
DeWitt, then at the University of North Carolina, developed an
extraordinary equation that provides a possible framework for unifying
relativity and quantum mechanics. But the Wheeler-DeWitt equation has always been controversial, in part because it adds yet another, even more baffling twist to our understanding of time.
“One finds that time just disappears from the Wheeler-DeWitt
equation,” says Carlo Rovelli, a physicist at the University of the
Mediterranean in Marseille, France. “It is an issue that many theorists
have puzzled about. It may be that the best way to think about quantum
reality is to give up the notion of time—that the fundamental
description of the universe must be timeless.”
No one has yet succeeded in using the Wheeler-DeWitt equation to
integrate quantum theory with general relativity. Nevertheless, a
sizable minority of physicists, Rovelli included, believe that any
successful merger of the two great masterpieces of 20th-century physics
will inevitably describe a universe in which, ultimately, there is no
time.
The possibility that time may not exist is known among physicists as
the “problem of time.” It may be the biggest, but it is far from the
only temporal conundrum. Vying for second place is this strange fact:
The laws of physics don’t explain why time always points to the future.
All the laws—whether Newton’s, Einstein’s, or the quirky quantum
rules—would work equally well if time ran backward. As far as we can
tell, though, time is a one-way process; it never reverses, even though
no laws restrict it.
“It’s quite mysterious why we have such an obvious arrow of time,”
says Seth Lloyd, a quantum mechanical engineer at MIT. (When I ask him
what time it is, he answers, “Beats me. Are we done?”) “The usual
explanation of this is that in order to specify what happens to a
system, you not only have to specify the physical laws, but you have to
specify some initial or final condition.”
The mother of all initial conditions, Lloyd says, was the Big Bang.
Physicists believe that the universe started as a very simple, extremely
compact ball of energy. Although the laws of physics themselves don’t
provide for an arrow of time, the ongoing expansion of the universe
does. As the universe expands, it becomes ever more complex and
disorderly. The growing disorder—physicists call it an increase in
entropy—is driven by the expansion of the universe, which may be the
origin of what we think of as the ceaseless forward march of time.
Time, in this view, is not something that exists apart from the
universe. There is no clock ticking outside the cosmos. Most of us tend
to think of time the way Newton did: “Absolute, true and mathematical
time, of itself, and from its own nature, flows equably, without regard
to anything external.” But as Einstein proved, time is part of the
fabric of the universe. Contrary to what Newton believed, our ordinary
clocks don’t measure something that’s independent of the universe. In
fact, says Lloyd, clocks don’t really measure time at all.
“I recently went to the National Institute of Standards and
Technology in Boulder,” says Lloyd. (NIST is the government lab that
houses the atomic clock
that standardizes time for the nation.) “I said something like, ‘Your
clocks measure time very accurately.’ They told me, ‘Our clocks do not
measure time.’ I thought, Wow, that’s very humble of these guys. But
they said, ‘No, time is defined to be what our clocks measure.’ Which is
true. They define the time standards for the globe: Time is defined by
the number of clicks of their clocks.”
Rovelli, the advocate of a timeless universe, says the NIST
timekeepers have it right. Moreover, their point of view is consistent
with the Wheeler-DeWitt equation. “We never really see time,” he says.
“We see only clocks. If you say this object moves, what you really mean
is that this object is here when the hand of your clock is here, and so
on. We say we measure time with clocks, but we see only the hands of the
clocks, not time itself. And the hands of a clock are a physical
variable like any other. So in a sense we cheat because what we really
observe are physical variables as a function of other physical
variables, but we represent that as if everything is evolving in time.
http://discovermagazine.com/2007/jun/in-no-time
Stated better than I ever could!
