Parallel Worlds (51 page)

STEP EIGHT: BUILD A WARP DRIVE MACHINE

One key element
necessary to assemble the devices described above is the ability to travel
across vast interstellar distances. One possible way to do so is to use the
Alcubierre warp drive machine, a machine first proposed by physicist Miguel
Alcubierre in 1994. A warp drive machine does not alter the topology of space
by punching a hole and leaping into hyperspace. It simply shrinks the space in
front of you while expanding the space behind you. Think of walking across a
carpet to reach a table. Instead of walking on the carpet, you could lasso the
table and slowly drag it toward you, making the carpet bunch up in front of
you. Thus, you have moved little; instead, the space in front of you has
shrunk.

Recall that
space itself can expand faster than the speed of light (since no net
information is being transferred by expanding empty space). Similarly, it may
be possible to travel faster than the speed of light by shrinking space faster
than the speed of light. In effect, when traveling to a nearby star, we may
barely leave Earth at all; we would simply collapse the space in front of us
and expand the space behind us. Instead of traveling to Alpha Centauri, the
nearest star, we are bringing Alpha Centauri to us.

Alcubierre
showed that this is a viable solution of Einstein's equations—meaning that it
falls within the laws of physics. But there is a price to pay. You would have
to employ large quantities of both negative and positive energy to power your
starship. (Positive energy could be used to compress the space in front of you
and negative energy to lengthen the distance behind you.) To use the Casimir
effect to create this negative energy, the plates would have to be separated by
the Planck distance, i0
^-33
centimeters—too small to be achieved by
ordinary means. To build such a starship, you would need to construct a large
sphere and place the passengers inside. On the sides of the bubble, you would
put a band of negative energy along the equator. The passengers inside the
bubble would never move, but the space in front of the bubble would shrink
faster than light, so that when the passengers left the bubble, they would have
reached a nearby star.

In his original
article, Alcubierre mentioned that his solution might not only take us to the
stars, it might make possible time travel as well. Two years later, physicist
Allen E. Everett showed that if one had two such starships, time travel would
be possible by applying warp drive in succession. As Princeton physicist Gott
says, "Thus, it appears that Gene Roddenberry, the creator of
Star
Trek,
was indeed right to include all those time-travel
episodes!"

But a later
analysis by the Russian physicist Sergei Krasnikov revealed a technical defect
in the solution. He showed that the inside of the starship is disconnected from
the space outside the ship, so that messages cannot cross the boundary—that is,
once inside the ship, you cannot change the path of the starship. The path has
to be laid out before the trip is made. This is disappointing. In other words,
you simply cannot spin a dial and set a course for the nearest star. But it
does mean that such a theoretical starship could be a railway to the stars, an
interstellar system in which the starships leave at regular intervals. One
could, for example, build this railway by first using conventional rockets that
travel at sublight speed to build rail stations at regular intervals between
stars. Then the star- ship would travel between these stations at super light
speed according to a timetable, with fixed departures and arrivals.

Gott writes,
"A future supercivilization might want to lay down warpdrive paths among
stars for starships to traverse, just as it might establish wormhole links
among stars. A network of warp- drive paths might even be easier to create than
one made up of wormholes because warpdrives would require only an alteration of
existing space rather than the establishment of new holes connecting distant
regions."

But precisely
because such a starship must travel within the existing universe, it cannot be
used to leave the universe. Nevertheless, the Alcubierre drive could help to
construct a device to escape the universe. Such a starship might be useful, for
example, in creating the colliding cosmic strings mentioned by Gott, which
might take an advanced civilization back into its own past, when its universe
was much warmer.

STEP NINE: USE NEGATIVE ENERGY FROM
SQUEEZED STATES

In chapter 5, I
mention that laser beams can create "squeezed states" which can be
used to generate negative matter, which in turn can be used to open up and
stabilize wormholes. When a powerful laser pulse hits a special optical
material, it creates pairs of photons in its wake. These photons alternately
enhance and suppress the quantum fluctuations found in the vacuum, giving both
positive and negative energy pulses. The sum of these two energy pulses always
averages to a positive energy, so that we do not violate known laws of physics.

In 1978,
physicist Lawrence Ford at Tufts University proved three laws that such
negative energy must obey, and they have been the subject of intense research
ever since. First, Ford found that the amount of negative energy in a pulse is
inversely related to its spatial and temporal extent—that is, the stronger the
negative energy pulse, the shorter its duration. So if we create a large burst
of negative energy with a laser to open up a wormhole, it can only last for an
extremely short period of time. Second, a negative pulse is always followed by
a positive energy pulse of larger magnitude (so the sum is still positive).
Third, the longer the interval between these two pulses, the larger the
positive pulse must be.

Under these
general laws, one can quantify the conditions under which a laser or Casimir
plates can produce negative energy. First, one might try to separate the
negative energy pulse from the subsequent positive energy pulse by shining a
laser beam into a box and having a shutter close immediately after the negative
energy pulse enters. As a result, only the negative energy pulse would have entered
the box. In principle, huge amounts of negative energy can be extracted in this
way, followed by an even larger positive energy pulse (which is kept out of the
box by the shutter). The interval between the two pulses can be quite long, as
long as the energy of the positive pulse is large. In theory, this seems to be
an ideal way in which to generate unlimited quantities of negative energy for a
time machine or wormhole.

Unfortunately,
there is a catch. The very act of closing the shutter creates a second
positive energy pulse inside the box. Unless extraordinary precautions are
taken, the negative energy pulse is wiped out. This will remain a technological
feat for an advanced civilization to solve—to split off a powerful negative
energy pulse from the subsequent positive energy pulse without having a
secondary pulse wipe out the negative energy one.

These three laws
can be applied to the Casimir effect. If we produce a wormhole that is one
meter in size, we must have negative energy concentrated in a band no more
than 10
^-22
meters (a millionth of the size of a proton). Once again,
only an extremely advanced civilization might be able to create the technology
necessary to manipulate these incredibly small distances or incredibly tiny time
intervals.

STEP TEN: WAIT FOR QUANTUM TRANSITIONS

As we saw in
chapter i0, intelligent beings facing the gradual cooling of their universe
may have to think more slowly and hibernate for long periods of time. This
process of slowing the rate of thinking could continue for trillions upon
trillions of years, enough time for quantum events to happen. Normally, we can
dismiss the spontaneous creation of bubble universes and transitions to other
quantum universes because they would be such extremely rare events. However, in
stage 5, intelligent beings may think so slowly that such quantum events could
become relatively commonplace. In their own subjective time, their rate of
thinking might appear to them to be perfectly normal, even though the actual
time scale would be so long that quantum events become a normal occurrence.

If so, such
beings would only have to wait until wormholes appear and quantum transitions
occur in order to escape into another universe. (Although such beings might see
quantum transitions as commonplace, one problem here is that these quantum
events are totally unpredictable; it would be difficult to make the transition
to another universe when one doesn't know precisely when the gateway might
open or where it would lead. These beings might have to seize the opportunity
to leave the universe as soon as a wormhole opened up, before they had a chance
to fully analyze its properties.)

STEP ELEVEN: THE LAST HOPE

Assume for the
moment that all future experiments with wormholes and black holes face a
seemingly insurmountable problem: that the only stable wormholes are
microscopic to subatomic in size. Assume also that an actual trip through a
wormhole may place unacceptable stresses on our bodies, even within a
protective vessel. Any number of challenges, such as intense tidal forces,
radiation fields, incoming falling debris, would prove lethal. If that is the
case, future intelligent life in our universe would have but one remaining
option: to inject enough information into a new universe to recreate our civilization
on the other side of the wormhole.

In nature, when
living organisms are faced with a hostile environment, they sometimes devise
ingenious methods to survive. Some mammals hibernate. Some fish and frogs have
antifreeze-like chemicals circulating in their bodily fluids that allow them
to be frozen alive. Fungi evade extinction by transforming into spores.
Similarly, human beings might have to find a way to alter their physical existence
to survive the trip to another universe.

Think of the oak
tree, which scatters tiny seeds in all directions. The seeds are (a) small,
resilient, and compact; (b) they contain the entire DNA content of the tree;
(c) they are designed to travel a certain distance away from the mother tree;
(d) they contain enough food to begin the process of regeneration in a distant
land; (e) they take root by consuming nutrients and energy from the soil and
living off the new land. Similarly, a civilization could try to mimic nature
by sending its "seed" through a wormhole, using the most advanced
nanotechnology available billions years from now, to copy each of these
important properties.

As Stephen
Hawking has said, "It seems . . . that quantum theory allows time travel
on a microscopic basis." If Hawking is right, members of an advanced
civilization could decide to alter their physical being into something that
would survive the arduous journey back in time or to another universe, merging
carbon with silicon and reducing their consciousness down to pure information.
In the final analysis, our carbon-based bodies may well be too fragile to
endure the physical hardship of a journey of this magnitude. Far in the future,
we may be able to merge our consciousness with our robot creations, using
advanced DNA engineering, nanotechnology, and robotics. This may sound bizarre
by today's standards, but a civilization billions to trillions of years in the
future might find it the only way to survive.

They might need
to merge their brains and personalities directly into machines. This could be
done in several ways. One could create a sophisticated software program that
was able to duplicate all our thinking processes, so that it had a personality
identical to ours. More ambitious is the program advocated by Hans Moravec of
Carnegie-Mellon University. He claims that, in the far future, we may be able
to reproduce, neuron for neuron, the architecture of our brains onto silicon
transistors. Each neural connection in the brain would be replaced by a
corresponding transistor that would duplicate the neuron's function inside a
robot.

Because the
tidal forces and radiation fields would likely be intense, future
civilizations would have to carry the absolute minimum of fuel, shielding, and
nutrients necessary to re-create our species on the other side of a wormhole.
Using nanotechnology, it might be possible to send microscopic chains across
the wormhole inside a device no wider than a cell.

If the wormhole
was very small, on the scale of an atom, scientists would have to send large
nanotubes made of individual atoms, encoded with vast quantities of information
sufficient to re-create the entire species on the other side. If the wormhole
was only the size of a subatomic particle, scientists would have to devise a
way to send nuclei across the wormhole that would grab electrons on the other
side and reconstruct themselves into atoms and molecules. If a wormhole was
even smaller than that, perhaps laser beams made of X rays or gamma rays of
small wavelength could be used to send sophisticated codes through the
wormhole, giving instructions on how to reconstruct civilization on the other
side.

The goal of such
a transmission would be to construct a microscopic "nanobot" on the
other side of the wormhole, whose mission would be to find a suitable
environment in which to regenerate our civilization. Because it would be
constructed on an atomic scale, it would not need huge booster rockets or a
large amount of fuel to find a suitable planet. In fact, it could effortlessly
approach light-speed because it is relatively easy to send subatomic particles
to near light- speed using electric fields. Also, it would not need life
support or other clumsy pieces of hardware, since the main content of the
nanobot is the pure information necessary to regenerate the race.