The Physics of Star Trek (17 page)

What would an extraterrestrial signal involve? Cocconi and Mor-rison suggested that we
might look for the first few prime numbers: 1,3,5,7,11,13.... In fact, this is precisely
the series that Picard taps out in the episode “Allegiance,” when he is trying to let his
captors know that they are dealing with an intelligent species. Pulses from, say, a
surface storm on a star are hardly likely to produce such a series. The META people have
searched for an even simpler signal: a uniform constant tone at a fixed frequency. Such a
“carrier” wave is easy to search for.

Horowitz and his collaborator, the Cornell astronomer Carl Sagan, have reported on an
analysis of the 5 years of META data. Thirty-seven candidate events, out of 100,000
billion signals detected, were isolated. However, none of these “signals” has ever
repeated. Horowitz and Sagan prefer to interpret the data as providing no definitive
signal thus far. As a result, they have been able to put limits on the number of highly
advanced civilizations within various distances of our Sun which have been trying to
communicate with us.

Nevertheless, in spite of the incredible complexity of the search effort, only a small
range of frequencies has actually been explored, and the power requirements for a signal
capable of being detected by the META telescope are rather largecivilizations would have
to use broadcast powers in excess of the total power received on Earth from the Sun (about
10
17
watts) in their transmitters to produce a detectable signal. Thus, there is yet no cause
for pessimism. It is a difficult task just to listen. The META group is now building a
bigger, better (or BETA) detector, which should improve the search strength by roughly a
factor of 1000.

The search goes on. The fact that we have not yet heard anything should not dissuade us.
It is something like what my friend Sidney Coleman, a physics professor at Harvard, once
told me about buying a house: You shouldn't get discouraged if you look at a hundred and
don't find anything. You only have to like one.... A single definitive signal, as
improbable as it is that we will ever hear one, would change the way we think about the
universe, and would herald the beginning of a new era in the evolution of the human race.

And for those of you who are disheartened at the idea that our first contact with
extraterrestrial civilizations will not be made by visiting them in our starships,
remember the Cytherians, a very advanced civilization encountered by the
Enterprise
who made outside contact with other civilizations not by traveling through space
themselves but by bringing space travelers to them. In some sense, that is exactly what we
are doing as we listen to the signals from the stars.

The Menagerie of Possibilities

“That is the exploration that awaits you! Not mapping stars and studying nebula, but
charting the unknown possibilities of existence.”

Q
to Picard, in “All Good Things.
...”

In the course of more than 13 TV-years of the various Star Trek series, the writers have
had the opportunity to tap into some of the most exciting ideas from all fields of
physics. Sometimes they get it right; sometimes they blow it. Sometimes they just use the
words that physicists use, and sometimes they incorporate the ideas associated with them.
The topics they have dealt with read like a review of modern physics: special relativity,
general relativity, cosmology, particle physics, time travel, space warping, and quantum
fluctuations, to name just a few.

In this penultimate chapter, I thought it might be useful to make a brief presentation of
some of the more interesting ideas from modern physics which the Star Trek writers have
borrowedin particular, concepts I haven't concentrated on elsewhere in the book. Because
of the diversity of the ideas, I give them here in glossary form, with no particular
ordering or theme. In the last chapter, I will follow a similar formatthis time to sample
the most blatant physics blunders in the series, as chosen by myself, selected
fellow-physicists, and various trekkers. In both chapters, I have restricted my lists to
the top ten examples; there are a lot more to choose from.

THE SCALE OF THE GALAXY AND THE UNIVERSE: Our galaxy is the stage on which the Star Trek
drama is enacted. Throughout the series, galactic distance scales of various sorts play a
crucial role in the action. Units from AUs (for Astronomical Unit: 1 AU is 93 million
miles, the distance from the Earth to the Sun), which were used to describe the size of
the V'ger cloud in the first Star Trek movie, to light-years are bandied about. In
addition, various features of our galaxy are proposed, including a “Great Barrier” at the
center
(Star Trek V: The Final Frontier)
and, in the original series, a “galactic barrier” at the edge (cf. “Where No Man Has Gone
Before,” “By Any Other Name,” and “Is There in Truth No Beauty?”). It seems appropriate,
therefore, in order to describe the playing field where Star Trek's action takes place, to
offer our own present picture of the galaxy and its neighbors, and of distance scales in
the universe.

Because of the large number of digits required, one rarely expresses astronomical
distances in conventional units such as miles or kilometers. Instead, astronomers have
created several fiducial lengths that seem more appropriate. One such unit is the AU, the
distance between the Earth and the Sun. This is the characteristic distance scale of the
solar system, with Pluto, the ultima Thule, being nearly 40 AU from the Sun. In
Star Trek: The Motion Picture,
the V'ger cloud is described as 82 AU in diameter, which is remarkably bigbigger, in fact,
than the size of our solar system!

For comparison with interstellar distances, it is useful to express the Earth-Sun distance
in terms of the time it takes light (or the time it would take the
Enterprise
at warp 1) to travel from the Sun to the Earthabout 8 minutes. (This should be the time it
would take light to travel to most Class M planets from their suns.) Thus, we can say that
an AU is 8 light-minutes. By comparison, the distance to the nearest star, Alpha Centauria
binary star system where the inventor of warp drive, Zefrem Cochrane, apparently livedis
about 4 light-years! This is a characteristic distance between stars in our region of the
galaxy. It would take rockets, at their present rate of speed, more than 10,000 years to
travel from here to Alpha Centauri. At warp 9, which is about 1500 times the speed of
light, it would take about 6 hours to traverse 1 light-year.

The distance of the Sun from the center of the galaxy is approximately 25,000 light-years.
At warp 9, it would take almost 15 years to traverse this distance, so it is unlikely that
Sybok, having commandeered the
Enterprise,
would have been able to take her to the galactic center, as he did in
Star Trek V: The Final Frontier,
unless the
Enterprise
was essentially already there.

The Milky Way is a spiral galaxy, with a large central disk of stars. It is approximately
100,000 light-years across and a few thousand light-years deep. The
Voyager,
tossed 70,000 light-years away from Earth in the first episode of that series, would thus
indeed be on the other side of the galaxy. At warp 9, the ship would take about 50 years
to return to the neighborhood of our Sun from that distance.

At the center of our galaxy is a large galactic bulgea dense conglomeration of
starsseveral thousand light- years across. It is thought to harbor a black hole of about a
million solar masses. Black holes ranging from 100,000 to more than a billion solar masses
are likely at the center of many other galaxies.

A roughly spherical halo of very old stars surrounds the galaxy. The

conglomerations of thousands of stars called globular clusters found here are thought to
be among the oldest objects in our galaxy, perhaps as old as 18 billion years according to
our current methods of datingmore ancient

even than the “black cluster” in the episode “Hero Worship,” which was said to be 9
billion years old. An even larger spherical halo, consisting of “dark matter” (about which
more later), is thought to encompass the galaxy. This halo is invisible to all types of
telescopes; its existence is inferred from the motion of stars and gas in the galaxy, and
it may well contain 10 times as much mass as the observable galaxy.

The Milky Way is an average-size spiral galaxy, containing a few hundred billion stars.
There are approximately 100 billion galaxies in the observable universe, each containing
more or less that many stars! Of the galaxies we see, roughly 70 percent are spiral; the
rest are somewhat spherical in shape and are known as elliptical galaxies. The largest of
them are giant ellipticals more than 10 times as massive as the Milky Way.

Most galaxies are clustered in groups. In our local group, the nearest galaxies to the
Milky Way are small satellite galaxies orbiting our own. These objects, observable in the
Southern Hemisphere, are called the Large and Small Magellanic Clouds. It is about 6
million light-years to the nearest large galaxy, the Andromeda galaxyhome to the Kelvans,
who attempt to take over the
Enterprise
and return to their home galaxy in the original-series episode “By Any Other Name.” At
warp 9, the voyage would take approximately 4000 years!

Because of the time it takes light to travel, as we observe farther and farther out, we
are also observing farther and farther back in time. The farthest we can now observe with
electromagnetic sensors is back to a time when the universe was about 300,000 years old.
Before then, matter existed as a hot ionized gas opaque to electromagnetic radiation. When
we look out in all directions, we see the radiation emitted when matter and radiation
finally “decoupled.” This is known as the cosmic microwave background. Observing it, most
recently with the COBE satellite launched by NASA in 1989, we get a picture of what the
universe looked like when it was only about 300,000 years old.

Finally, the universe itself is expanding uniformly. As a result, distant galaxies are
observed to be receding from usand the farther away they are, the faster they are
receding, at a rate directly proportional to their distance from us. This rate of
expansion, characterized by a quantity called the Hubble constant, is such that galaxies
located 10 million light-years from us are moving away at an average rate of about 150 to
300 kilometers per second. Working backward, we find that all the observed galaxies in the
universe would converge about 10 billion to 20 billion years ago, at the time of the big
bang.

DARK MATTER: As I mentioned above, our galaxy is apparently immersed in a vast sea of
invisible material.
1
By studying the motion of the stars, of hydrogen gas clouds, and even of the Large and
Small Magellanic Clouds around the galactic center, and using Newton's laws relating the
velocity of orbiting objects to the mass pulling them, it has been determined that there
is a roughly spherical halo of dark material stretching out to distances perhaps 10 times
as far from the center of the galaxy as we are. This material accounts for at least 90
percent of the mass of the Milky Way. Moreover, as we observe the motion of other
galaxies, including the ellipticals, and also the motion of groups of galaxies, we find
that there is more matter associated with these systems than we can account for on the
basis of the observable material. The entire observable universe therefore seems to be
dominated by dark matter. It is currently believed that between 90 and 99 percent of the
mass of the universe is made of this material.

The notion of dark matter has crept into both the
Next Generation
and the
Voyager
series, and in an amusing way. For example, in the
Voyager
episode “Cathexis,” the ship enters a “dark matter nebula,” which, as you might imagine,
is like a dark cloud, so that you cannot see into it. The
Enterprise
had already encountered similar objects, including the “black cluster” mentioned earlier.
However, the salient fact about dark matter is not that it shields light in any way but
that it does not shinethat is, emit radiationand does not even absorb significant amounts
of radiation. If it did either, it would be detectable by telescopes. If you were inside a
dark matter cloud, as we probably are, you would not even see it.

The question of the nature, origin, and distribution of dark matter is probably one of the
most exciting unresolved issues in cosmology today. Since this unknown material dominates
the mass density of the universe, its distribution must have determined how and when the
observable matter gravitationally collapsed to create the galactic clusters, galaxies,
stars, and planets that make the universe so interesting to us. Our very existence is
directly dependent on this material. Moreover, the amount of dark matter in the universe
will determine the universe's eventual fate: whether it ends in a bang (by recollapsing)
or an endless whimper (by continuing to expand even as the stars eventually burn out) will
depend on how much matterof whatever sortit contains,

since gravitational attraction is what slows the expansion.

Even more interesting are the strong arguments that the dark matter may be made of
particles completely different from the protons and neutrons that make up normal matter.
Independent limits on the amount of normal matter in the universe, based on calculations
of nuclear reaction rates in the early universe and the subsequent formation of light
elements, suggest that there may not be enough protons and neutrons to account for the
dark matter around galaxies and clusters. Moreover, it seems that in order for the small
fluctuations in the initial distribution of matter to have collapsed in the hot plasma of
the early universe to form the galaxies and clusters we observe today, some new type of
elementary particleof a kind that does not interact with electromagnetic radiationhad to
be involved. If the dark matter is indeed made of some new type of elementary particle,
then: