EMBARGOED FOR RELEASE: 13 OCTOBER 1999 AT 14:00 ET US
http://www.eurekalert.org/releases/ns-dtr101399.html
UK Contact: Claire Bowles
claire.bowles@rbi.co.uk
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US Contact: New Scientist Washington office
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New Scientist
Does time really exist?
TIME seems to be the most powerful force, an irresistible river
carrying us from birth to death. To most people it is an
inescapable part of life, a fundamental element of the Universe.
But I think that time is an illusion. Physicists struggling to
unify quantum mechanics and Einstein's general theory of
relativity have found hints that the Universe is timeless. I
believe that this idea should be taken seriously. Paradoxically,
we might be able to explain the mysterious "arrow of time"-the
difference between past and future-by abandoning time. But to
understand how, we need to change radically our ideas of how the
Universe works.
Let's start with Newton's picture of absolute time. He argued that
objects exist in an immense immobile space, stretching like a
block of glass from infinity to infinity. His time is an invisible
river that "flows equably without relation to anything external".
Newton's absolute space and time form a framework that exists at a
deeper level than the objects in it.
To see how it works, imagine a universe containing only three
particles. To describe its history in Newton's terms, you specify
a succession of sets of 10 numbers: one for time and three for the
spatial coordinates of each of the three particles. But this
picture is suspect. As the space-time framework is invisible, how
can you determine all the numbers? As far back as 1872, the
Austrian physicist Ernst Mach argued that the Universe should be
described solely in terms of observable things, the separations
between its objects.
With that in mind, we can use a very different framework for the
three-particle Universe-a strange, abstract realm called Triangle
Land. Think of the three particles as the corners of a triangle.
This triangle is completely defined by the lengths of its three
sides-just three numbers. You can take these three numbers and use
them as coordinates, to mark a point in an abstract "configuration
space" (see Diagram, p 30).
Each possible arrangement of three particles corresponds to a
point in this space. There are geometrical restrictions-no
triangle has one side longer than the other two put together-so it
turns out that all the points lie in or on a pyramid. At the apex
of Triangle Land, where all three coordinates are zero, is a point
that I call Alpha. It represents the triangle that has sides all
of zero length (in other words, all three particles are in the
same place).
In the same way, the configurations of a four-particle universe
form Tetrahedron Land. It has six dimensions, corresponding to the
six separations between pairs of particles-hard to conceive, but
it exists as a mathematical entity. And even for the stupendous
number of particles that make up our own Universe, we can envisage
a vast multidimensional structure representing its configurations.
In collaboration with Bruno Bertotti of Pavia University in Italy,
I have shown that conventional physics still works in this strange
world. As Plato taught that reality exists as perfect forms, I
think of the patterns of particles as Platonic forms, and call
their totality Platonia.
Platonia is an image of eternity. It is all the arrangements of
matter that can be. Looking at it as a whole, there seems to be no
more river of time. But could time be hiding? Perhaps there is
some sort of local time that makes sense to inhabitants of
Platonia.
In classical physics, something like time can indeed creep back
in. If you were to lay out all the instants of an evolving
Newtonian universe, it would look like a path drawn in Platonia.
As a godlike being, outside Platonia, you could run your finger
along the path, touching points that correspond to each different
arrangement of matter, and see a universe that continuously
changes from one state to another. Any point on this path still
has something that looks like a definite past and future.
Now's the place
But we know that classical physics is wrong. The world is
described by quantum mechanics-and in the arena of Platonia,
quantum mechanics kills time.
In the quantum wave theory created by Schrsdinger, a particle has
no definite position, instead it has a fuzzy probability of being
at each possible position. And for three particles, say, there is
a certain probability of their forming a triangle in a particular
orientation with its centre of mass at some absolute position. The
deepest quantum mysteries arise because of holistic statements of
this kind. The probabilities are for the whole, not the parts.
What probabilities could quantum mechanics specify for the
complete Universe that has Platonia as its arena? There cannot be
probabilities at different times because Platonia itself is
timeless. There can only be once-and-for-all probabilities for
each possible configuration.
In this picture, there are no definite paths. We are not beings
progressing from one instant to another. Rather, there are many
"Nows" in which a version of us exists-not in any past or future,
but scattered in our region of Platonia.
This may sound like the "many worlds" interpretation of quantum
mechanics, published in 1957 by Hugh Everett of Princeton
University. But in that scheme time still exists: history is a
path that branches whenever some quantum decision has to be made.
In my picture there are no paths. Each point of Platonia has a
probability, and that's the end of the story.
A similar position was reached by much more sophisticated
arguments more than 30 years ago. Americans Bryce DeWitt and John
Wheeler combined quantum mechanics and Einstein's theory of
general relativity to produce an equation that describes the whole
Universe. Put into the equation a configuration of the Universe,
and out comes a probability for that configuration. There is no
mention of time. Admittedly, the Wheeler-DeWitt equation is
controversial and fraught with mathematical difficulties, but if
quantum cosmology is anything like it-if it is about
probabilities-the timeless picture is plausible.
So let's take seriously the idea of a "probability mist" that
covers the timeless Platonic landscape. The density of the mist is
just the relative probability of the corresponding configuration
being realised, or experienced, as an instantaneous state of the
Universe-as a Now. If some Nows in Platonia have much higher
probabilities than others, they are the ones that are actually
experienced. This is like ordinary statistical physics: a glass of
water could boil spontaneously, but the probability is so low that
we never see it happen.
All this seems a far cry from the reality of our lives. Where is
the history we read about? Where are our memories? Where is the
bustling, changing world of our experience? Those configurations
of the Universe for which the probability mist has a high density,
and so are likely to be experienced, must have within them an
appearance of history-a set of mutually consistent records that
suggests we have a past. I call these configurations "time
capsules".
Present past
An arbitrary matter distribution, like dots distributed at random,
will not have any meaning. It will not tell a story. Almost all
imaginable matter distributions are of this kind; only the tiniest
fraction seem to carry meaningful information.
One of the most remarkable facts about our Universe is that it
does have a meaningful structure. All the matter we can observe in
any way is found to contain records of a past.
The first scientists to realise this were geologists. Examining
the structure of rocks and fossils, they constructed a long
history of the Earth. Modern cosmology has extended this to a
history of the Universe right back to the big bang.
What is more, we are somehow directly aware of the passing of
time, and we see motion-a change of position over time. You may
feel these are such powerful sensations that any attempt to deny
them is ridiculous. But imagine yourself frozen in time. You are
simply a static arrangement of matter, yet all your memories and
experience are still there, represented by physical patterns
within your brain-probably as the strengths of the synapse
connections between neurons. Just as the structure of geological
strata and fossils seem to be evidence of a past, our brains
contain physical structures consistent with the appearance of
recent and distant events. These structures could surely lead to
the impression of time passing. Even the direct perception of
motion could arise through the presence in the brain of
information about several different positions of the objects we
see in motion.
And that is the essence of my proposal. There is no history laid
out along a path, there are only records contained within Nows.
This timeless vision may seem perverse. But it turns out to have
one great potential strength: it could explain the arrow of time.
We are so accustomed to history that we forget how peculiar it is.
According to conventional cosmology, our Universe must have
started out in an extraordinarily special state to give rise to
the highly ordered Universe we find around us, with its arrow of
time and records of a past. All matter and energy must have
originated at a single point, and had an almost perfectly uniform
distribution immediately after the big bang.
Hitherto, the only explanation that science has provided is the
anthropic argument: we experience configurations of the Universe
that seem to have a history because only these configurations have
the characteristics to produce beings who can experience anything.
I believe that timeless quantum cosmology provides a far more
satisfying explanation.
In Platonia, there are no initial conditions. Only two factors
determine where the probability mist is dense: the form of some
equation (like the Wheeler-DeWitt equation) and the shape of
Platonia. And by sheer logical necessity, Platonia is profoundly
asymmetric. Like Triangle Land, it is a lopsided continent with a
special point Alpha corresponding to the configuration in which
every particle is at the same place.
From this singular point, the timeless landscape opens out,
flower-like, to points that represent configurations of the
Universe of arbitrary size and complexity. My conjecture is that
the shape of Platonia cannot fail to influence the distribution of
the quantum probability mist. It could funnel the mist onto time
capsules, those meaningful arrangements that seem to contain
records of a past that began at Alpha.
This is, of course, only speculation, but quantum mechanics
supports it. In 1929, the British physicist Nevill Mott and Werner
Heisenberg from Germany explained how alpha particles, emitted by
radioactive nuclei, form straight tracks in cloud chambers. Mott
pointed out that, quantum mechanically, the emitted alpha particle
is a spherical wave which slowly leaks out of the nucleus. It is
difficult to picture how it is that an outgoing spherical wave can
produce a straight line," he argued. We think intuitively that it
should ionise atoms at random throughout space.
Mott noted that we think this way because we imagine that quantum
processes take place in ordinary three-dimensional space. In fact,
the possible configurations of the alpha particle and the
particles in the detecting chamber must be regarded as the points
of a hugely multidimensional configuration space, a miniature
Platonia, with the position of the radioactive nucleus playing the
role of Alpha.
Ageless creation
When Mott viewed the chamber from this perspective, his equations
predicted the existence of the tracks. The basic fact that quantum
mechanics treats configurations as whole entities leads to track
formation. And a track is just a point in configuration space-but
one that creates the appearance of a past, just like our own
memories.
There is one more reason to embrace the timeless view. Many
theoretical physicists now recognise that the usual notions of
time and space must break down near the big bang. They find
themselves forced to seek a timeless description of the
"beginning" of the Universe, even though they use time elsewhere.
It seems more consistent and economical to use an entirely
timeless description. But for these ideas to be more than
speculation, they should have concrete, measurable results.
Fortunately, Stephen Hawking and other theorists have shown that
the Wheeler-DeWitt equation can lead to verifiable predictions.
For example, established physical theories cannot predict a value
for the cosmological constant, which measures the gravitational
repulsion of empty space. But calculations based on the
Wheeler-DeWitt equation suggest that it should have a very small
value. It should soon be possible to measure the cosmological
constant, either by taking the brightness of far-off supernovae
and using that to track the expansion of the Universe, or by
analysing the shape of humps and bumps in the cosmic microwave
background. And a definitive equation of quantum cosmology should
give us a precise prediction for the value of the constant. It is
a distant prospect, but the nonexistence of time could be
confirmed by experiment.
The notion of time as an invisible framework that contains and
constrains the Universe is not unlike the crystal spheres invented
centuries ago to carry the planets. After the spheres had been
shattered by Tycho Brahe's observations, Kepler said: "We must
philosophise about these things differently." Much of modern
physics stems from this insight. We need a new notion of time.
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PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF
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http://www.newscientist.com
The author of this article, Julian Barbour is an independent
theoretical physicist who lives near Oxford, UK.
Further reading: Julian Barbour's The End of Time is published by
Weidenfeld & Nicolson, £20