The Physics of Star Trek


By Lawrence M. Krauss

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How does the Star Trek universe stack up against the real universe?

What warps when you’re traveling at warp speed? What is the difference between a wormhole and a black hole? Are time loops really possible, and can I kill my grandmother before I am born? Anyone who has ever wondered “could this really happen?” will gain useful insights into the Star Trek universe (and, incidentally, the real world of physics) in this charming and accessible guide. Lawrence M. Krauss boldly goes where Star Trek has gone-and beyond. From Newton to Hawking, from Einstein to Feynman, from Kirk to Picard, Krauss leads readers on a voyage to the world of physics as we now know it and as it might one day be.


To my family

"But I canna change the laws of physics, Captain!"
(Scotty, to Kirk, innumerable times)

Stephen Hawking
I was very pleased that Data decided to call Newton, Einstein, and me for a game of poker aboard the Enterprise. Here was my chance to turn the tables on the two great men of gravity, particularly Einstein, who didn't believe in chance or in God playing dice. Unfortunately, I never collected my winnings because the game had to be abandoned on account of a red alert. I contacted Paramount studios afterward to cash in my chips, but they didn't know the exchange rate.
Science fiction like Star Trek is not only good fun but it also serves a serious purpose, that of expanding the human imagination. We may not yet be able to boldly go where no man (or woman) has gone before, but at least we can do it in the mind. We can explore how the human spirit might respond to future developments in science and we can speculate on what those developments might be. There is a two-way trade between science fiction and science. Science fiction suggests ideas that scientists incorporate into their theories, but sometimes science turns up notions that are stranger than any science fiction. Black holes are an example, greatly assisted by the inspired name that the physicist John Archibald Wheeler gave them. Had they continued with their original names of "frozen stars" or "gravitationally completely collapsed objects," there wouldn't have been half so much written about them.
One thing that Star Trek and other science fiction have focused attention on is travel faster than light. Indeed, it is absolutely essential to Star Trek's story line. If the Enterprise were restricted to flying just under the speed of light, it might seem to the crew that the round trip to the center of the galaxy took only a few years, but 80,000 years would have elapsed on Earth before the spaceship's return. So much for going back to see your family!
Fortunately, Einstein's general theory of relativity allows the possibility for a way around this difficulty: one might be able to warp spacetime and create a shortcut between the places one wanted to visit. Although there are problems of negative energy, it seems that such warping might be within our capabilities in the future. There has not been much serious scientific research along these lines, however, partly, I think, because it sounds too much like science fiction. One of the consequences of rapid interstellar travel would be that one could also travel back in time. Imagine the outcry about the waste of taxpayers' money if it were known that the National Science Foundation were supporting research on time travel. For this reason, scientists working in this field have to disguise their real interest by using technical terms like "closed timelike curves" that are code for time travel. Nevertheless, today's science fiction is often tomorrow's science fact. The physics that underlies Star Trek is surely worth investigating. To confine our attention to terrestrial matters would be to limit the human spirit.

Why the physics of Star Trek? Gene Roddenberry's creation is, after all, science fiction, not science fact. Many of the technical wonders in the series therefore inevitably rest on notions that may be ill defined or otherwise at odds with our current understanding of the universe. I did not want to write a book that ended up merely outlining where the Star Trek writers went wrong.
Yet I found that I could not get the idea of this book out of my head. I confess that it was really the transporter that seduced me. Thinking about the challenges that would have to be faced in devising such a fictional technology forces one to ponder topics ranging from computers and the information superhighway to particle physics, quantum mechanics, nuclear energy, telescope building, biological complexity, and even the possible existence of the human soul! Compound this with ideas such as warped space and time travel and the whole subject became irresistible.
I soon realized that what made this so fascinating to me was akin to what keeps drawing fans to Star Trek today, almost thirty years after the series first aired. This is, as the omnipotent Star Trek prankster Q put it, "charting the unknown possibilities of existence." And, as I am sure Q would have agreed, it is even good fun to imagine them.
As Stephen Hawking states in the foreword to this book, science fiction like Star Trek helps expand the human imagination. Indeed, exploring the infinite possibilities the future holds—including a world where humanity has overcome its myopic international and racial tensions and ventured out to explore the universe in peace—is part of the continuing wonder of Star Trek. And, as I see this as central to the continuing wonder of modern physics, it is these possibilities that I have chosen to concentrate on here.
Based on an informal survey I carried out while walking around my university campus the other day, the number of people in the United States who would not recognize the phrase "Beam me up, Scotty" is roughly comparable to the number of people who have never heard of ketchup. When we consider that the Smithsonian Institution's exhibition on the starship Enterprise was the most popular display in their Air and Space Museum—more popular than the real spacecraft there—I think it is clear that Star Trek is a natural vehicle for many people's curiosity about the universe. What better context to introduce some of the more remarkable ideas at the forefront of today's physics and the threshold of tomorrow's? I hope you find the ride as enjoyable as I have.
Live long and prosper.

When I first sat down to write The Physics of Star Trek almost 13 years ago I had no idea how significantly it would change my life, nor of the impact it might have on trekkers and non-trekkers alike. I was mostly hoping that following its publication a mob of angry fans wouldn't lynch me and that my physics colleagues would still talk to me.
Needless to say, these worries proved to be ill-founded. Indeed the immediate and overwhelming reaction on all counts was the opposite of what I had expected. One of the first letters I received after the book appeared was from a fan who said, "I had been waiting for 20 years to read a Star Trek book in the Science Fact section of a bookstore!" And when I began to lecture on this subject I met 7- and 8-year-olds with dog-eared copies of the book who had great questions to ask. And my colleagues turned out to be largely thrilled that a physics book could actually be a popular bestseller. And lo and behold, the book appeared to create a new genre of "The Science of . . ." books. First, books titled The ______ of Star Trek began to appear by the dozens, followed quickly by books with titles like The Physics of Christmas and The Science of Harry Potter.
And I even got to stand at the helm of the Enterprise at Paramount, even if I didn't get to join a poker game with Einstein, and I filmed a TV documentary with Captain Kirk himself, and hung out with the likes of Commander Riker and Quark.
Shortly after the book appeared I was asked for a sequel, and the request has been repeated numerous times over the years, but I decided I had said everything I wanted to say on this subject. Well, almost everything I had to say. In the intervening years, not only has Star Trek continued, but the world of science has as well, and I daresay the latter may have progressed far more than the former. In an effort to bring the science in the book up to date I decided to review the material from cover to cover, adding new information when necessary, and removing arguments when nature has shown them to be incorrect.
Of course, in the process, I couldn't resist adding some new Star Trek connections and even a few new bloopers, one related to me by a 5-year-old at a lecture I gave, and one by a member of the crew of the Enterprise. I have tried hard to preserve the character of the original book, much of which has happily survived unscathed. In the end, I hope readers continue to enjoy the discussions and come away a bit more enamored with the amazing fact that, as remarkable as the Star Trek Universe may be, the real universe keeps providing surprises that are both grander and stranger than anything human screenwriters may come up with.
Lawrence M. Krauss
Cleveland, Ohio 2007

In which the physics of inertial dampers and
tractor beams paves the way for time travel,
warp speed, deflector shields, wormholes,
and other spacetime oddities

Newton Antes
"No matter where you go, there you are."
—From a plaque on the starship Excelsior, in Star Trek VI: The Undiscovered Country, presumably borrowed from The Adventures of Buckaroo Banzai
You are at the helm of the starship Defiant (NCC–1764), currently in orbit around the planet Iconia, near the Neutral Zone. Your mission: to rendezvous with a nearby supply vessel at the other end of this solar system in order to pick up components to repair faulty transporter primary energizing coils. There is no need to achieve warp speeds; you direct the impulse drive to be set at full power for leisurely half-light-speed travel, which should bring you to your destination in a few hours, giving you time to bring the captain's log up to date. However, as you begin to pull out of orbit, you feel an intense pressure in your chest. Your hands are leaden, and you are glued to your seat. Your mouth is fixed in an evil-looking grimace, your eyes feel like they are about to burst out of their sockets, and the blood flowing through your body refuses to rise to your head. Slowly, you lose consciousness . . . and within minutes you die.
What happened? It is not the first signs of spatial "interphase" drift, which will later overwhelm the ship, or an attack from a previously cloaked Romulan vessel. Rather, you have fallen prey to something far more powerful. The ingenious writers of Star Trek, on whom you depend, have not yet invented inertial dampers, which they will introduce sometime later in the series. You have been defeated by nothing more exotic than Isaac Newton's laws of motion—the very first things one can forget about high school physics.
OK, I know some trekkers out there are saying to themselves, "How lame! Don't give me Newton. Tell me things I really want to know, like 'How does warp drive work?' or 'What is the flash before going to warp speed—is it like a sonic boom?' or 'What is a dilithium crystal anyway?'" All I can say is that we will get there eventually. Travel in the Star Trek universe involves some of the most exotic concepts in physics. But many different aspects come together before we can really address everyone's most fundamental question about Star Trek: "Is any of this really possible, and if so, how?"
To go where no one has gone before—indeed, before we even get out of Starfleet Headquarters—we first have to confront the same peculiarities that Galileo and Newton did over three hundred years ago. The ultimate motivation will be the truly cosmic question which was at the heart of Gene Roddenberry's vision of Star Trek and which, to me, makes this whole subject worth thinking about: "What does modern science allow us to imagine about our possible future as a civilization?"
Anyone who has ever been in an airplane or a fast car knows the feeling of being pushed back into the seat as the vehicle accelerates from a standstill. This phenomenon works with a vengeance aboard a starship. The fusion reactions in the impulse drive produce huge pressures, which push gases and radiation backward away from the ship at high velocity. It is the backreaction force on the engines—from the escaping gas and radiation—that causes the engines to "recoil" forward. The ship, being anchored to the engines, also recoils forward. At the helm, you are pushed forward too, by the force of the captain's seat on your body. In turn, your body pushes back on the seat.
Now, here's the catch. Just as a hammer driven at high velocity toward your head will produce a force on your skull which can easily be lethal, the captain's seat will kill you if the force it applies to you is too great. Jet pilots and NASA have a name for the force exerted on your body while you undergo high accelerations (as in a plane or during a space launch): G-forces. I can describe these by recourse to my aching back: As I am sitting at my computer terminal busily typing, I feel the ever-present pressure of my office chair on my buttocks—a pressure that I have learned to live with (yet, I might add, that my buttocks are slowly reacting to in a very noncosmetic way). The force on my buttocks results from the pull of gravity, which if given free rein would accelerate me downward into the Earth. What stops me from accelerating—indeed, from moving beyond my seat—is the ground exerting an opposite upward force on my house's concrete and steel frame, which exerts an upward force on the wood floor of my second-floor study, which exerts a force on my chair, which in turn exerts a force on the part of my body in contact with it. If the Earth were twice as massive but had the same diameter, the pressure on my buttocks would be twice as great. The upward forces would have to compensate for the force of gravity by being twice as strong.
The same factors must be taken into account in space travel. If you are in the captain's seat and you issue a command for the ship to accelerate, you must take into account the force with which the seat will push you forward. If you request an acceleration twice as great, the force on you from the seat will be twice as great. The greater the acceleration, the greater the push. The only problem is that nothing can withstand the kind of force needed to accelerate to impulse speed quickly—certainly not your body.
By the way, this same problem crops up in different contexts throughout Star Trek—even on Earth. At the beginning of Star Trek V: The Final Frontier, James Kirk is free-climbing while on vacation in Yosemite when he slips and falls. Spock, who has on his rocket boots, speeds to the rescue, aborting the captain's fall within a foot or two of the ground. Unfortunately, this is a case where the solution can be as bad as the problem. It is the process of stopping over a distance of a few inches that can kill you, whether or not it is the ground that does the stopping or Spock's Vulcan grip.
Well before the reaction forces that will physically tear or break your body occur, other severe physiological problems set in. First and foremost, it becomes impossible for your heart to pump strongly enough to force the blood up to your head. This is why fighter pilots sometimes black out when they perform maneuvers involving rapid acceleration. Special suits have been created to force the blood up from pilots' legs to keep them conscious during acceleration. This physiological reaction remains one of the limiting factors in determining how fast the acceleration of present-day spacecraft can be, and it is why NASA, unlike Jules Verne in his classic From the Earth to the Moon, has never launched three men into orbit from a giant cannon.
If I want to accelerate from rest to, say, 150,000 km/sec, or about half the speed of light, I have to do it gradually, so that my body will not be torn apart in the process. In order not to be pushed back into my seat with a force greater than 3G, my acceleration must be no more than three times the downward acceleration of falling objects on Earth. At this rate of acceleration, it would take some 5 million seconds, or about 2 1/2 months, to reach half light speed! This would not make for an exciting episode.
To resolve this dilemma, sometime after the production of the first Constitution Class starship—the Enterprise (NCC—1701)—the Star Trek writers had to develop a response to the criticism that the accelerations aboard a starship would instantly turn the crew into "chunky salsa."1 They came up with "inertial dampers," a kind of cosmic shock absorber and an ingenious plot device designed to get around this sticky little problem. (In fact, a full century earlier, the NX Class starship Enterprise commanded by Captain Archer seems to have been fitted with inertial dampers. Alas, while this ship was built much earlier, it was created by the writers much later.)
The inertial dampers are most notable in their absence. For example, the Enterprise was nearly destroyed after losing control of the inertial dampers when the microchip life-forms known as Nanites, as part of their evolutionary process, started munching on the ship's central-computer-core memory. Indeed, almost every time the Enterprise is destroyed (usually in some renegade timeline), the destruction is preceded by loss of the inertial dampers. The results of a similar loss of control in a Romulan Warbird provided us with an explicit demonstration that Romulans bleed green.
Alas, as with much of the technology in the Star Trek universe, it is much easier to describe the problem the inertial dampers address than it is to explain exactly how they might do it. The First Law of Star Trek physics surely must state that the more basic the problem to be circumvented, the more challenging the required solution must be. The reason we have come this far, and the reason we can even postulate a Star Trek future, is that physics is a field that builds on itself. A Star Trek fix must circumvent not merely some problem in physics but every bit of physical knowledge that has been built upon this problem. Physics progresses not by revolutions, which do away with all that went before, but rather by evolutions, which exploit the best about what is already understood. Newton's laws will continue to be as true a million years from now as they are today, no matter what we discover at the frontiers of science. If we drop a ball on Earth, it will always fall. If I sit at this desk and write from here to eternity, my buttocks will always suffer the same consequences.
Be that as it may, it would be unfair simply to leave the inertial dampers hanging without at least some concrete description of how they would have to operate. From what I have argued, they must create an artificial world inside a starship in which the reaction force that responds to the accelerating force is canceled. The objects inside the ship are "tricked" into acting as though they were not accelerating. I have described how accelerating gives you the same feeling as being pulled at by gravity. This connection, which was the basis of Einstein's general theory of relativity, is much more intimate than it may at first seem. Thus there is only one choice for the modus operandi of these gadgets: they must set up an artificial gravitational field inside the ship which "pulls" in the opposite direction to the reaction force, thereby canceling it out.
Even if you buy such a possibility, other practical issues must be dealt with. For one thing, it takes some time for the inertial dampers to kick in when unexpected impulses arise. For example, when the Enterprise was bumped into a causality loop by the Bozeman as the latter vessel emerged from a temporal distortion, the crew was thrown all about the bridge (even before the breach in the warp core and the failure of the dampers). I have read in the Enterprise's technical specifications that the response time for the inertial dampers is about 60 milliseconds.2 Short as this may seem, it would be long enough to kill you if the same delay occurred during programmed periods of acceleration. To convince yourself, think how long it takes for a hammer to smash your head open, or how long it takes for the ground to kill you if you hit it after falling off of a cliff in Yosemite. Just remember that a collision at 10 miles per hour is equivalent to running full speed into a brick wall! The inertial dampers had better be pretty quick to respond. More than one trekker I know has remarked that whenever the ship is buffeted, no one ever gets thrown more than a few feet.
Before leaving the familiar world of classical physics, I can't help mentioning another technological marvel that must confront Newton's laws in order to operate: the Enterprise's tractor beam—highlighted in the rescue of the Genome colony on Moab IV, when it deflected an approaching stellar core fragment, and in a similar (but failed) attempt to save Bre'el IV by pushing an asteroidal moon back into its orbit. On the face of it, the tractor beam seems simple enough—more or less like an invisible rope or rod—even if the force exerted may be exotic. Indeed, just like a strong rope, the tractor beam often does a fine job of pulling in a shuttle craft, towing another ship, or inhibiting the escape of an enemy spacecraft. In fact, before the Federation had universal access to tractor beams, the NX Class Enterprise apparently used a magnetic "grappler" for precisely these tasks. No matter; the only problem is that when we pull something, be it with a rope, a grappler, or a tractor beam, we must be anchored to the ground or to something else heavy. Anyone who has ever been skating knows what happens if you are on the ice and you try to push someone away from you. You do manage to separate, but at your own expense. Without any firm grounding, you are a helpless victim of your own inertia.
It was this very principle that prompted Captain Jean-Luc Picard to order Lieutenant Riker to turn off the tractor beam in the episode "The Battle"; Picard pointed out that the ship they were towing would be carried along beside them by its own momentum—its inertia. By the same token, if the Enterprise were to attempt to use the tractor beam to ward off the Stargazer, the resulting force would push the Enterprise backward as effectively as it would push the Stargazer forward.
This phenomenon has already dramatically affected the way we work in space at present. Say, for example, that you are an astronaut assigned to tighten a bolt on the Hubble Space Telescope. If you take an electric screwdriver with you to do the job, you are in for a rude awakening after you drift over to the offending bolt. When you switch on the screwdriver as it is pressed against the bolt, you are as likely to start spinning around as the bolt is to turn. This is because the Hubble Telescope is a lot heavier than you are. When the screwdriver applies a force to the bolt, the reaction force you feel may more easily turn you than the bolt, especially if the bolt is still fairly tightly secured to the frame. Of course, if you are lucky enough, like the assassins of Chancellor Gorkon, to have gravity boots that secure you snugly to whatever you are standing on, then you can move about as efficiently as we are used to on Earth.
Likewise, you can see what will happen if the Enterprise tries to pull another spacecraft toward it. Unless the Enterprise is very much heavier, it will move toward the other object when the tractor beam or grappler turns on, rather than vice versa. In the depths of space, this distinction is a meaningless semantic one. With no reference system nearby, who is to say who is pulling whom? However, if you are on a hapless planet like Moab IV in the path of a renegade star, it makes a great deal of difference whether the Enterprise pushes the star aside or the star pushes the Enterprise aside!
One trekker I know claims that the way around this problem is already stated indirectly in at least one episode: if the Enterprise were to use its impulse engines at the same time that it turned its tractor beam on, it could, by applying an opposing force with its own engines, compensate for any recoil it might feel when it pushed or pulled on something. This trekker claims that somewhere it is stated that the tractor beam requires the impulse drive to be operational in order to work. I, however, have never noticed any instructions from Kirk or Picard to turn on the impulse engines at the same time the tractor beam is used. And in fact, for a society capable of designing and building inertial dampers, I don't think such a brute force solution would be necessary. Reminded of Geordi LaForge's need for a warp field to attempt to push back the moon at Bre'el IV, I think a careful, if presently unattainable, manipulation of space and time would do the trick equally well. To understand why, we need to engage the inertial dampers and accelerate to the modern world of curved space and time.

Einstein Raises
There once was a lady named Bright,
Who traveled much faster than light.
She departed one day, in a relative way,
And returned on the previous night.
"Time, the final frontier"—or so, perhaps, each Star Trek episode should begin. Forty years ago, in the classic episode "Tomorrow Is Yesterday," the round-trip time travels of the Enterprise began. (Actually, at the end of an earlier episode, "The Naked Time," the Enterprise is thrown back in time three days—but it is only a one-way trip.) The starship is kicked back to twentieth-century Earth as a result of a close encounter with a "black star" (the term "black hole" having not yet permeated the popular culture). Nowadays exotica like wormholes and "quantum singularities" regularly spice up episodes of Star Trek: Voyager and Enterprise contributed nothing less than a Temporal Cold War. Thanks


  • "The essential tubeside companion for the fans of the venerable Star Trek series."—Washington Post
  • "This book is fun...Krauss is always enlightening."—New York Times Book Review
  • What makes Krauss's book a winner is that it provides a pulpit for a thoughtful sermon on the possibilities locked in a universe that might or might not include a planet called Vulcan and a language called Klingon but that certainly could - in theory - deliver an antigravitational force called vacuum energy.—The Guardian
  • "A fascinating way to learn more about physics."—St. Petersburg Times
  • "One of the year's best gifts for a science-fiction fan."—Cleveland Plain Dealer
  • "The Physics of Star Trek is a fun, readable little book by an eminent physicist that boldly goes where few serious scientists have ever gone before."—Tampa Tribune
  • Even those who have never watched an episode of Star Trek will be entertained and enlightened by theoretical physicist Krauss's adventurous investigation of interstellar flight, time travel, teleportation of objects and the possibility of extraterrestrial life.—Publishers Weekly

On Sale
Jul 10, 2007
Page Count
280 pages
Basic Books

Lawrence M. Krauss

About the Author

Lawrence M. Krauss is Ambrose Swasey Professor of Physics and Professor of Astronomy and Director of the Center for Education and Research in Cosmology and Astrophysics at Case Western Reserve University. He is the only physicist to have received the top awards by the American Physical Society, the American Institute of Physics, and the American Association of Physics Teachers. He lives in Cleveland, Ohio.

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