From: "Mark A. LeCuyer" 
Subject: IUFO: Backwards to the Future
Date: 4 Feb 2000 20:12:40 -0500
To: "IUFO" 


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Source: New Scientist
February 5, 2000.

Backwards to the Future

In a distant galaxy, a star unexplodes. Just moments ago a shell of
tortured matter was flying together at 30 000 kilometres a second. Now
it has become a star, and the last shreds of glowing debris are being
sucked in. With the explosion undone, the star begins the long journey
back to the time when it will be unborn into the gas and dust of an
interstellar cloud.

Is someone running the film backwards for comic effect? Not
necessarily. In a paper published in the last week of 1999, Lawrence
Schulman of Clarkson University in Potsdam, New York dropped a
bombshell. He showed that regions where time flows in the normal
direction can coexist with regions where it flows backwards. There
could be places, perhaps even within our Galaxy, where stars
unexplode, eggs unbreak and living things grow younger with every
second.

To understand how time could run backwards, you need to understand why
it has a preferred direction at all. The equations of physics say that
particles of matter don't care what direction time runs in: any
interaction between two particles could happen just as easily in
reverse. (Some nuclear interactions do show a small bias, but no one
has found a way to turn this into an arrow of time.)

But when you have a lot of particles instead of just two, things
change. Messy, disordered states tend to develop from tidier ones.
This tendency is called the thermodynamic arrow of time. Physicists
say that entropy--a measure of disorder--always increases. "It's easy
to break an egg, difficult or impossible to put the pieces back
together," says Schulman.

Say the air in a large room is confined in a 1-metre cube in one
corner, then released. It is perfectly possible that, after five
minutes, the air molecules will all be back in the same 1-metre cube.
Perfectly possible but hugely improbable, because there are far more
ways to arrange the individual molecules when they are spread out than
when they are confined. In fact, the most disordered state--in which
the air molecules are spread more or less evenly throughout the
room--can be achieved in far more ways than any other state. "This is
the second law of thermodynamics," says Schulman, "which seals the
fate of Humpty Dumpty."

However, argues Schulman, a reverse arrow is perfectly possible: "It's
all down to the 'boundary conditions'--the external constraints
imposed on the system." In the room, the air has to be in the 1-metre
cube only at the start of the five-minute period. There is no
constraint on it at the end of the five minutes--the system can find
its own final state.

But say a final condition is imposed. After five minutes, the air
molecules have to be back in the 1-metre cube. On Earth, this is
clearly an artificial situation. But for Schulman, it is perfectly
legitimate to consider such a state of affairs. "There is no reason in
principle why the Universe might not have a future boundary condition
imposed on it," he says.

The future condition would constrain the molecules to follow only a
tiny subset of trajectories, ending up in the 1-metre cube. From our
point of view, time would be running backwards.

But there's an objection to having forward and backward time regions
in the same universe. Surely the arrow of a reverse-time region would
be wiped out by the slightest interaction with a normal-time region,
leaving a completely disordered system with no arrow at all?

Imagine a game of snooker in which the triangle of red balls is struck
by the cue ball and scattered around the table. Now imagine the
reverse-time scenario. For the balls to follow the precise
trajectories necessary to finish in a triangle will take a monumental
amount of coordination. The slightest disturbance will spoil it. Any
interaction with a region with normal time--for instance, the smallest
cry of amazement from someone watching--could vibrate the air, nudge
the balls and wreck everything. So the backward arrow of a
reverse-time region would be instantly destroyed by any interaction
with a normal-time region.

Schulman sees a flaw in this idea. The two systems are on an equal
footing, so the reverse-time region is as likely to destroy the arrow
of the normal-time region as vice versa. "All we can say is that if
the two regions interact their arrows will either both be destroyed or
both survive."

Most physicists would have put good money on the former possibility.
But Schulman's startling conclusion is that as long as the interaction
between the two regions is weak, both arrows will survive. He bases
this claim on a simple computer model that allows him to set up weakly
interacting systems with opposite arrows of time and see what happens.

Here's how it works. Take a square 1 unit on each side, and add a
particle with coordinates x and y. Move the particle by repeatedly
replacing x with x + y and y with x + 2y, and discarding any integer
parts of the results (so x and y stay in the range from 0 to 1). The
particle will flit about the square chaotically. "This mimics the
essential behaviour of a gas particle, while being a lot simpler than
reality," according to Schulman.

To set up two gases with opposite arrows of time, Schulman imposes
appropriate boundary conditions. In one model gas, the particles start
in one corner of the square and spread out until they are completely
disordered. They have a "normal" arrow of time (that is, the same
arrow as us). In the other, Schulman imposes the final condition that
after, say 20 moves, corresponding to 20 time steps, the particles are
all in the corner of the square. This system has a backward arrow of
time. Call the normal-time region Alice and the reverse-time region
Bob.

The next step is to let Alice and Bob interact. Schulman tweaks the
coordinates of each normal-time particle according to the coordinates
of the reverse-time test particle, and vice versa.

When Schulman lets both systems run, he finds that neither arrow of
time is destroyed by the other. "All that happens is that Bob adds a
bit of noise to Alice and Alice adds a bit of noise to Bob," says
Schulman. The two arrows of time are remarkably robust.

"I had no idea when I started my work that this would be the outcome,"
he says. "The result surprised me as much anyone else." But this
surprise, he adds, comes from a prejudice against future boundary
conditions. Once you are used to the idea of matter having some memory
of what we call its future, it ceases to surprise. From our point of
view, the memory of future organisation drags any reverse time region
in the direction of increasing order, despite any small disturbances
from our own "normal" region.

The paper has created quite a stir. "This is very cool stuff indeed,"
says Max Tegmark of the University of Pennsylvania. At the
Technion-Israel Institute of Technology, where Sculman began this
work, Amos Ori agrees. "Schulman has shown that the consistency of a
model with two simultaneous time arrows can be explored by relatively
simple means. This is a very important observation."

And he has some equivocal support from David Pegg of Griffith
University in Brisbane. "I see no obvious flaw in the calculations
Schulman has done. He makes his case quite well and I am willing to
accept it, at least until convinced otherwise."


Either way: we see the big bang in our past, and, perhaps, a big
crunch in our future. But other regions (black galaxies) could have a
different point of view, looking back to what we call the big crunch
and looking forward to our big bang


Other physicists don't believe that Schulman's computer model is
relevant to the real world. According to Paul Davies of the University
of Adelaide, a real physical system with a backward arrow would be so
fantastically sensitive to an outside influence that it would be
easily destroyed

. "Imagine a box of gas with molecular velocities reversed to bring
about an ordered state," he says. "The gravity of a single electron at
the edge of the observable Universe is enough to throw out the motion
of a given molecule by 90 degrees after only 20 or so intermolecular
collisions. That's pretty sensitive."

Crossing the divide

Surprisingly, Schulman does not dispute Davies' point. "He's
absolutely right. But the very set-up of his thought experiment, with
initial conditions only, precludes an opposite-directed arrow," he
says. "My result applies when boundary conditions are imposed at two
separate times."

Some might attack the realism of Schulman's interaction, which he
admits is an abstract mathematical one and not related to a real
physical force such as gravity. "Nevertheless, I maintain that the
interaction is adequate for treating the conceptual issue of the
effects of future- conditioning," he says.

So could we actually see reverse-time beings if they exist, and maybe
even wave to them? Remarkably, Schulman says yes. Using a theory
originally developed by Richard Feynman and John Wheeler, which treats
light waves travelling in both time directions on an equal footing, he
shows that forward and reverse regions could communicate by light
signals.

But communicating with the other side has its dangers. If normal-time
Alice were to see rain pouring out through reverse-time Bob's window,
she could wait until before the rain started and shout to Bob to close
his window. "So did Bob's floor get wet or not?" says Schulman.

Perhaps something intermediate happens which smears out the paradox.
"Alice sees the window open, shouts to Bob but the message gets
blurred and Bob doesn't close the window," says Schulman.

And there's another, more disturbing possibility. "If you impose
initial and final boundary conditions, it may turn out that the events
described simply can't happen," he says. "In mathematical terms, they
are simply not a solution." In other words, we might just be fated not
to cause any paradoxes.

So, how would a reverse-time region arise? Schulman says such regions
may exist for the same inexplicable reason that regions of normal time
exist. But there is one more concrete possibility: perhaps we live in
a Universe whose expansion from a big bang will one day be reversed
into a contraction down to a "big crunch", a sort of mirror-image of
the big bang in which the Universe was born 13 billion years ago.
Although the latest cosmological evidence is against this, the
question isn't settled.

In 1958, Thomas Gold of Cornell University argued that the
thermodynamic arrow of time would reverse during the contraction
phase, creating order out of chaos. Gold's reasoning turned out to be
flawed, but in the 1970s, Schulman used his own model to show that the
conclusions were right. As the big bang and big crunch are both highly
ordered (all the matter is in a small volume), thermodynamic arrows of
time should point away from both ends. The arrow of time depends on
the expansion or contraction of the Universe. "Coffee cools because
the quasar 3C 273 grows ever more distant," says Schulman.

Of course, if you were alive during a cosmic contraction phase you
would see nothing untoward--you'd have the same arrow as most of the
matter in the Universe, and it would look like expansion (see
Diagram). Stepping outside the Universe, the situation appears
perfectly symmetrical; it makes just as much sense to call either end
the big bang or the big crunch.

A bizarre consequence of Schulman's theory is that some reverse-time
regions from a future contracting phase of the Universe could have
survived until today--and could be only a few tens of light years
away. "Some bits of the Universe might have reverse arrows while other
bits with forward arrows might survive well into the contraction
phase."

As the "turnaround" time when the Universe's expansion turns into
contraction could be many hundreds of billions of years away, any
stars would have burnt out. Unfortunately, there would be little
prospect of seeing stellar unexplosions or backwards people among such
cold stuff. "We would still feel their gravity, though," says
Schulman. "Such reverse-time matter would have all the attributes of
the invisible, or 'dark', matter thought to make up most of the mass
of our Universe."

Colliding arrows

Another possibility is that in the 13 billion years since the big bang
most of the Universe's matter has collided with reverse-time matter
from the future. The result of such collisions would be matter in
"equilibrium" with no time direction. "Once again, it would appear
exactly like dark matter," says Schulman. Other physicists are
sceptical. "I doubt that this has anything to do with the dark matter
problem," says Tegmark.

So what would it be like in a region that is changing its time
direction? Would exploding things suddenly start unexploding? And what
would happen to the minds of beings around at the time? Sadly, it
would be rather undramatic. For a particular area to change its arrow,
it would first have to go through a period of maximum disorder where
there could be no stars or explosions or structured, working minds.
But if you survived for long enough, you might be able to watch the
Universe around you starting to contract, and most of its matter going
into reverse.

If all this is getting a bit difficult to stomach, there is a way to
test it--even if we can't spy on a nearby backwards planet. "Things
happening today could be influenced by boundary conditions at the end
of the Universe," says Schulman. What he has in mind are ultra-slow
processes.

In the 1970s, John Wheeler of Princeton University suggested observing
the decays of atomic nuclei with ultra-long half-lives, perhaps many
tens of billions of years. The suggestion was that the normal
exponential decay would be modified by exponential "undecay" and that
this might actually be observable in a sample of a few kilograms in
the laboratory. Possible candidates are rhenium-187 and samarium-147,
which have half-lives of about 100 billion years.

Unfortunately, Wheeler was too optimistic. For an experiment of a
sensible duration, a few years, say, you'd need roughly the total
supply of these isotopes in the Universe to see deviations from
exponential decay.

"A far better bet is galaxy clustering," says Schulman. He believes
that the way galaxies cluster together could be affected by a future
contraction phase. Unfortunately, he has not yet worked out what form
this effect might take.

But over the past few years, a small group of of physicists have been
claiming that the Universe has an inexplicable fractal structure. Most
cosmologists disagree, partly because they have no way to explain such
a bizarre pattern. But say there is something in it. Could it perhaps
be a memory of the future?

Mark

               Alien Astronomer - "Exploring Our Universe"
         http://www.geocities.com/Area51/Shadowlands/6583
  Astronomy - Hi-Tech/Secret Projects - Secret Societies - Ufology
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