The Physics of Star Trek (13 page)

Since the Star Trek writers, unlike the cold-fusion advocates, never claimed to be writing
anything other than science fiction, I suppose we should be willing to give them a little
extra slack. After all, dilithium-mediated reactions merely aid what is undoubtedly the
most com-pellingly realistic aspect of starship technology: the matter-antimatter drives.
And I might add that crystalstungsten in this case, not dilithiumare indeed used to
moderate, or slow down, beams of anti-electrons (positrons) in modern-day experiments;
here the antielec-trons scatter off the electric field in the crystal and lose energy.

There is no way in the universe to get more bang for your buck than to take a particle and
annihilate it with its antiparticle to produce pure radiation energy. It is the ultimate
rocket-propulsion technology, and will surely be used if ever we carry rockets to their
logical extremes. The fact that it may take quite a few bucks to do it is a problem the
twenty-third-century politicians can worry about.

Holodecks and Holograms

“Oh, we are us, sir. They are also us. So, indeed, we are both us.”
Data to Picard and Riker, in “We'll Always Have Paris”

When Humphrey Bogart said to Ingrid Bergman at the Casablanca airport, “We'll always have
Paris,” he meant, of course, the memory of Paris. When Picard said something similar to
Jenice Manheim at the holodeck re-creation of the CafŽ des Artistes, he may have intended
it more literally. Thanks to the holodeck, memories can be relived, favorite places
revisited, and lost loves rediscoveredalmost.

The holodeck is one of the most fascinating pieces of technology aboard the
Enterprise.
To anyone already familiar with the nascent world of virtual reality, either through video
games or the more sophisticated modern high-speed computers, the possibilities offered by
the holodeck are particularly enticing. Who wouldn't want to enter completely into his or
her own fantasy world at a moment's notice?

It is so seductive, in fact, that I have little doubt that it would be far more addictive
than it is made out to be in the series. We get some inkling of “holodeck addiction” (or
“holodiction”) in the episodes “Hollow Pursuits” and “Galaxy's Child.” In the former,
everyone's favorite neurotic officer, Lieutenant Reginald Barclay, becomes addicted to his
fantasy vision of the senior officers aboard the
Enterprise,
and would rather interact with them on the holodeck than anywhere else on the ship. In the
latter, when Geordi LaForge, who has begun a relationship with a holodeck representation
of Dr. Leah Brahms, the designer of the ship's engines, meets the real Dr. Brahms, things
become complicated-

Given the rather cerebral pastimes the crew generally engage in on the holodeck, one may
imagine that the hormonal instincts driving twentieth-century humanity have evolved
somewhat by the twenty-third century (although if this is the case, Will Riker is not
representative of his peers). Based on what I know of the world of today, I would have
expected that sex would almost completely drive the holodeck. (Indeed, the holodeck would
give safe sex a whole new meaning.) I am not being facetious here. The holodeck represents
what is so enticing about fantasy, particularly sexual fantasy: actions without
consequences, pleasure without pain, and situations that can be repeated and refined at
will.

The possible hidden pleasures of the holodeck are merely alluded to from time to time in
the series. For example, after Geordi has barged in rather rudely on Reg's private
holodeck fantasy, he admits, “I've spent a few hours on the holodeck myself. Now, as far
as I'm concerned, what you do on the holodeck is your own business, as long as it doesn't
interfere with your work.” If that doesn't sound like a twentieth-century admonition
against letting the pleasures of the flesh get the better of one, I don't know what does.

I have little doubt that our century's tentative explorations of virtuai reality are
leading us in the direction of something very much like the holodeck, at least in spirit.
Perhaps my concerns will appear as quaint in the twenty- third century as the warning
cries that accompanied the invention of television a half century ago. After all, though
cries continue because of the surfeit of televised sex and violence, without television
there would be no Star Trek.

The danger that we will become a nation of couch potatoes would not apply in a world full
of personal holodecks, or perhaps holodecks down at the mall; engaging in holodeck play is
far from passive. However, I still find the prospect of virtual reality worrisome,
precisely because though it appears real, it is much less scary than real life. The
attraction of a world of direct sensual experience without consequences could be
overwhelming.

Nevertheless, every new technology has bad as well as good sides and will force
adjustments in our behavior. It's probably clear from the tone of this book that I believe
technology has on the whole made our lives better rather than worse. The challenge of
adjusting to it is just one part of the challenge of being part of an evolving human
society.

Be that as it may, the holodeck differs in one striking way from most of the
virtual-reality technologies currently under development. At present, through the use of
devices that you strap on and that influence your vision and sensory input, virtual
reality is designed to put the “scene” inside you. The holodeck takes a more inventive
tack: it puts you inside the scene. It does this in part by inventive use of holography
and in part by replication.

The principles on which holography is based were first elucidated in 1947, well before the
technology was available to fully exploit it, by the British physicist Dennis Gabor, who
subsequently won the Nobel Prize for his work. By now, most people are familiar with the
use of three-dimensional holographic images on credit cards, and even on the covers of
books, like this one. The word “hologram” derives from the Greek words for “whole” and “to
write.” Unlike normal photographs, which merely record two-dimensional representations of
three-dimensional reality, holograms give you the whole picture. In fact, it is possible
with holography to re-create a three- dimensional image that you can walk around and view
from all sides, as if it were the original object. The only way to tell the difference is
to try touching it. Only then will you find that there is nothing there to touch.

How can a two-dimensional piece of film, which is what stores the holographic image,
record the full information of a three-dimensional image? To answer this we have to think
a little about exactly what it is we see when we see something, and what a photograph
actually records.

We see objects either because they emit or reflect light, which then arrives at our eyes.
When a three-dimensional object is illuminated, it scatters light in many different
directions because of this three-dimensionality. If we could somehow reproduce the exact
pattern of divergent light created when light is scattered by the actual object, then our
eyes would not be able to distinguish the difference between the actual object and the
divergent-light pattern
sans
object. By moving our head, for example, we would be able to see features that were
previously obscured, because the entire pattern of scattered light from all parts of the
object would have been re-created.

How can we first store and then later re-create all this information? We can gain some
insight into this question by thinking about what a normal photographwhich stores and
later re-creates a two-dimensional imageactually records. When we take a picture, we
expose a light-sensitive material to the incoming light, which arrives through

the lens of the camera. This light-sensitive material, when exposed to various chemicals,
will darken in proportion to the intensity of the light that impinged upon it. (I am
discussing black-and-white film here, but the extension to color film is simpleone just
coats the film with three different substances, each of which is sensitive to a different
primary color of light.)

So, the total information content recorded on a photographic film is the intensity of
light arriving at each point on the film. When we develop the film, those points on it
that were exposed to a greater intensity of light will react with the development
chemicals to become darker, while those not so exposed will remain lighter. The resulting
image on the film is a “negative” two-dimensional projection of the original light field.
We can project light through this negative onto a light-sensitive sheet of paper to create
the final photograph. When we look at it, light hitting the lighter areas of the
photograph will be predominantly reflected, while light hitting the darker areas will be
absorbed. Thus, looking at the light reflected from the photograph produces a
two-dimensional intensity pattern on our retinas, which then allows us to interpret this
pattern.

The question then becomes, what more is there to record than just the intensity of light
at each point? Once again, we rely on the fact that light is a wave. Because of this fact,
more than just intensity is needed to characterize its configuration. Consider the light
wave shown below:

At position A, the wave, which in this case represents the strength of the electric field,
has its maximum value, corresponding to an electric field with strength E
A
pointing upward. At point B, the field is exactly the same

strength but is pointing downward. Now, if you are sensitive only to the intensity of the
light wave, you will find that the field has the same intensity at A as it does at B.
However, as you can see, position B represents a different part of the wave from position
A. This “position” along the wave is called the
phase.
It turns out that you can specify all the information associated with a wave at a given
point by giving its intensity and its phase. So, to record all the information about the
light waves scattered by a three-dimensional object, you have to find a way of recording
on a piece of film both the intensity and the phase of the scattered light.

This is simple to do. If you split a light beam into two parts and shine one part directly
onto the film and let the other part scatter off the object before illuminating the film,
then either one of two things can happen. If the two light waves are “in phase”that is,
both have crests coinciding at some point Athen the amplitude of the resulting wave at A
will be twice the amplitude of either individual wave, as shown in the figure below:

On the other hand, if the two waves are out of phase at point A, then they will cancel
each other out, and the resulting “wave” at A will have zero amplitude:

So now, if the film at point A is photographic film, which records intensity only, the
pattern recorded will be the “interference pattern” of the two wavesthe reference beam and
the beam of light scattered by the object. This pattern contains not only the information
about the intensity of the scattered light from the object, but information about its
phases as well. If one is clever, one can extract this information to re-create a
three-dimensional image of the object that scattered the light.

In fact, it turns out that one doesn't have to be all that clever. If one merely
illuminates this photographic film with a source of light of the same wavelength as the
original light that produced the interference pattern, an image of the object will be
created exactly where the object was in relation to the film, when you look through the
film. If you move your head to one side, you will be able to “look around” the edges of
the re-created object. If you cover up most of the piece of film, and hold it closer to
your eyes and look through the uncovered part, you will still see the entire object! In
this sense, the experience is just like looking through a window at a scene outdoors,
except that the scene you are seeing isn't really there. The light coming to your eyes
through the film is affected in just such a way as to make your eyes believe that it has
been scattered off objects, which you then “see.” This is a hologram.

Normally, in order for the reference light and the light from the scattered object to be
carefully controlled, holograms are made using laser light, which is coherent and well
collimated. However, so-called “white light” holograms exist, which can be illuminated by
ordinary light to produce the same effect.

One can be trickier and arrange, just as one can using various lenses, for the image of
the objects you see to appear to be between you and the film, and you will see before you
the three-dimensional image of an object,

which you can walk around and view from all sides. Or you can arrange for the light source
to be in front of the film instead of behind itas in the holograms on credit cards.

Presumably the former sort of hologram is used on the holodeck, and to re-create the image
of a doctor in the sick bay, as in the
Voyager
series. What's more, in order to create such holograms, one would not need to use the
original objects to make the holographic images. Digital computers are now sophisticated
enough to do “ray tracing” that is, they can calculate the pattern of light scattered from
any hypothetical object you want to draw on the screen, and illuminate it from any angle.
In the same way, the computer could determine the configuration of the interference
pattern that would be caused by merging the light from a direct beam with the scattered
light from an object. This computer-generated interference pattern could be projected onto
a transparent screen, and when this screen is illuminated from behind, a three-dimensional
image is produced of an object that in fact never existed. If the computer is fast enough,
it can project a continuously changing interference pattern on the screen, thereby
producing a moving three-dimensional image. So the holographic aspect of the holodeck is
not particularly far-fetched.