[ntp:questions] Newsflash: Time May Not Exist

Jared Morrisen jaredmorrisen at gmail.com
Tue Aug 7 13:09:25 UTC 2007


*Newsflash: Time May Not Exist*

*Not to mention the question of which way it goes...*

 Tim Folger

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
<http://www.groupsrv.com/science/about20524.html>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

But even Krausz works far from the frontier of time. There is a temporal
realm called the Planck
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 <http://home.pacbell.net/skeptica/time.html>. 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
equation <http://www.tomcoyner.com/before_the_big_bang_there_was__.htm> 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

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
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

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 <http://tf.nist.gov/timefreq/cesium/atomichistory.htm> 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.

"What happens with the Wheeler-DeWitt equation is that we have to stop
playing this game. Instead of introducing this fictitious variable—time,
which itself is not observable—we should just describe how the variables are
related to one another. The question is, Is time a fundamental property of
reality or just the macroscopic appearance of things? I would say it's only
a macroscopic effect. It's something that emerges only for big things."

The problem, in brief, is that time may not exist at the most fundamental
level of physical reality.

By "big things," Rovelli means anything that exists much above the
mysterious Planck scale. As of now there is no physical theory that
completely describes what the universe is like below the Planck scale. One
possibility is that if physicists ever manage to unify quantum theory and
general relativity, space and time will be described by some modified
version of quantum mechanics. In such a theory, space and time would no
longer be smooth and continuous. Rather, they would consist of discrete
fragments—quanta, in the argot of physics—just as light is composed of
individual bundles of energy called photons. These would be the building
blocks of space and time. It's not easy to imagine space and time being made
of something else. Where would the components of space and time exist, if
not in space and time?

As Rovelli explains it, in quantum mechanics all particles of matter and
energy can also be described as waves. And waves have an unusual property:
An infinite number of them can exist in the same location. If time and space
are one day shown to consist of quanta, the quanta could all exist piled
together in a single dimensionless point. "Space and time in some sense melt
in this picture," says Rovelli. "There is no space anymore. There are just
quanta kind of living on top of one another without being immersed in a

Rovelli has been working with one of the world's leading mathematicians,
Alain Connes of the College of France in Paris, on this notion. Together
they have developed a framework to show how the thing we experience as time
might emerge from a more fundamental, timeless reality. As Rovelli describes
it, "Time may be an approximate concept that emerges at large scales—a bit
like the concept of 'surface of the water,' which makes sense
macroscopically but which loses a precise sense at the level of the atoms."

Realizing that his explanation may only be deepening the mystery of time,
Rovelli says that much of the knowledge that we now take for granted was
once considered equally perplexing. "I realize that the picture is not
intuitive. But this is what fundamental physics is about: finding new ways
of thinking about the world and proposing them and seeing if they work. I
think that when Galileo said that the Earth was spinning crazily around, it
was utterly incomprehensible in the same manner. Space for Copernicus was
not the same as space for Newton, and space for Newton was not the same as
space for Einstein. We always learn a little bit more."

Einstein, for one, found solace in his revolutionary sense of time. In March
1955, when his lifelong friend Michele Besso died, he wrote a letter
consoling Besso's family: "Now he has departed from this strange world a
little ahead of me. That means nothing. People like us, who believe in
physics, know that the distinction between past, present, and future is only
a stubbornly persistent illusion."

Rovelli senses another temporal breakthrough just around the corner.
"Einstein's 1905 paper came out and suddenly changed people's thinking about
space-time. We're again in the middle of something like that," he says. When
the dust settles, time—whatever it may be—could turn out to be even stranger
and more illusory than even Einstein could imagine.

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