Physicist Lawrence Krauss has written a book discussing the science of Star Trek. He explains which technologies are plausible, and which could never work.
Why did you write the book?
The book began as a passing remark, but it just started to grow in my mind. I wanted to write a physics book â not to justify the Star Trek universe, but rather to explain how it relates to the real Universe, which is even more interesting in my opinion. It fascinated me the more I thought about it.
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It was daunting at the same time because I realised there are twenty million experts on Star Trek in this country alone. I wrote the first chapter and sent it to my editor whose daughter is a âtrekkerâ. Then I got this letter back saying âNo, no, the inertial dampers were made in the year 2168â. So I thought âOK, this is going to be difficult.â
I had watched Star Trek when I was a kid, and liked it. But I wasnât a diehard trekker â Iâve never worn a Klingon uniform or anything like that. So I realised I was going to have to become an expert. I had to watch every episode â more than 250 of them at three or four a night.
Right from the beginning, the Enterpriseâs mission was to explore strange worlds around distant stars. What kind of problems would it have getting to these stars?
One problem is getting up to high speed. Even at impulse speed, when theyâre just cruising at say half the speed of light, there are many problems. For instance, time dilation â special relativity tells you that as you speed up, your clocks slow down compared with an observer watching you.
That has been used in science fiction as a way to allow people to travel throughout the Galaxy in a human lifetime. If Iâm watching you, it may seem to take you 50 000 years to go to the centre of the Galaxy. But for you, if youâre travelling close to the speed of light, it may take two weeks of your time.
Thatâs fine if youâre the only one doing the travelling. But if youâve got a Federation to control, itâs a little worrying when the five-year mission of the Enterprise takes 50 000 years for the people back home. Or say Captain Jean-Luc Picard of the Next Generation sends a message to Starfleet Command asking whether he should open fire, and 50 000 years later the answer comes back â it ruins the dramatic tension!
The writers were aware that this was a problem. If you read the Star Trek technical manual, you find that Starfleet doesnât allow the ships to go at impulse drive for extended periods at more than a quarter of the speed of light. At that speed the time changes by about 3 per cent for clocks on the ships. So generally if youâre away for a month and you come back on a Friday, your time, itâll only be Saturday for someone back on Earth. People can easily handle that kind of time change â anyone who travels across the Atlantic or Pacific is used to it.
How would the crew of the Enterprise cope with these speeds?
Just to get to impulse drive is not easy â in fact every time Picard says engage, heâs committing suicide. If you have a Ferrari, you can go from zero to 60 miles per hour in about 6 seconds, and you really feel the acceleration. The impulse drive can give speeds of say half the speed of light, or about 100 000 miles per second.
Imagine trying to accelerate from zero to 100 000 miles per second in less than an episode. You can see why the Star Trek writers realised that youâd be turned into chunky salsa on the back of the spacecraft. Human beings could take about 3g â thatâs the kind of force astronauts experience in the space shuttle. At that rate of acceleration it would take about four months to reach half the speed of light, which would not make for an exciting episode.
How do the Star Trek writers get round the acceleration problem?
They invented something called inertial dampers, which are basically cosmic shock absorbers â they somehow cushion the blow. But itâs pretty hard to make inertial dampers even in principle, because of Newtonâs third law. That says that if you get pushed forward, youâll always feel a force pushing you backwards.
But Einstein realised that the force due to gravity feels exactly the same as any kind of acceleration. So in principle to make inertial dampers, all you have to do is create an artificial gravitational field that pulls you forward with the same force that you would feel pushing you back. Can you actually create such an artificial gravitational field? Probably not â but thatâs how youâd have to do it.
What kind of energy source powers the impulse drive?
The impulse drive is powered by nuclear fusion. The problem here is that fusion turns only one per cent of the available mass into energy. You can work out how much fuel would be required to do the following simple manoeuvre: start from rest, go to half the speed of light, and then stop. It turns out that you need about 7000 times the mass of the rocket ship in fuel just to do that.
Does the impulse drive give you speeds that would really allow interstellar travel?
Our Galaxy is about 100 000 light years across. If youâre travelling at mere light speed it will take years just to get to the nearest star. So if you want to do any significant travel in the Galaxy in a reasonable amount of time â say an episode â you have to travel much faster than the speed of light.
Enter the warp drive, which the Enterprise uses to move faster than light â how do they do it?
They power the warp drive with matter and antimatter. Every elementary particle has an associated antiparticle with the same mass, but opposite properties like charge. And when the two come together, they annihilate to produce pure radiation. This is probably the best kind of rocket propulsion, because all of the mass is turned into energy.
Is this where the dilithium crystals come in?
The dilithium crystals apparently regulate the rate at which matter and antimatter interact in the warp drive. That doesnât really make sense, because when matter and antimatter interact, itâs either all or nothing. You canât regulate the rate.
Another problem is that they annihilate on a scale which is thousands if not millions of times smaller than the scale of atoms in a crystal. So itâs hard to imagine how any crystalline structure is going to channel matter and antimatter.
The Enterprise originally had lithium crystals but they were changed to dilithium for the obvious reason that lithium crystals actually exist and dilithium crystals donât, and therefore you can have them do more wild and crazy things.
How wild and crazy is the warp drive?
The way the writers describe it, the warp drive is impossible. As everyone knows, Einstein says you canât go faster than the speed of light. But there is a way that the warp drive could work. Although Einstein caused the problem, he also came to the rescue by inventing general relativity.
In principle, general relativity allows you to go faster than the speed of light compared to distant objects, but locally be standing still. As we sit here weâre not moving relative to our local surroundings. But relative to a galaxy at the other end of the visible Universe, we are moving away at the speed of light. And that galaxy is also standing still relative to its surroundings
Whatâs happening? Well, the space between the two galaxies is actually expanding. So if you wanted to have a warp drive in principle, you could let space do the work for you. Letâs say you wanted to go to the nearest star. Youâd have to fire up your chemical rockets, and go up about 200 miles from the Earthâs surface. Now youâre about four light years away from the nearest star.
Then what you have to do is arrange for the space between you and the star to catastrophically collapse, and the space between you and the Earth to expand. Then suddenly youâre 200 miles from the star and four light years away from Earth. Your clocks havenât changed, and no physical object has been moving.
Could you really distort space-time like this?
Whatâs wonderful about general relativity is it allows you to create designer space-times. You could take any kind of universe with any geometry and write that down mathematically. A few years ago, a physicist named Miguel Alcubierre found a solution of Einsteinâs equations that would have all the properties of warp drive, but didnât violate general relativity.
The question is â can you create the configuration of matter and energy that is required? Mathematically, you can, but how about physically? Gravity always pulls, so to make space expand, you have to add a repulsion term. It turns out that you need something called negative energy.
That sounds like something named by a physicist whoâd been staring at a blank piece of paper for too long. But at least on very small scales, negative energy configurations do exist. At the subatomic level, empty space is not so empty. The laws of quantum mechanics tell us that locally, tiny elementary particles called virtual particles are popping up out of nothing and disappearing. They exist for such a short time that itâs never possible to see them â thatâs part of the rules.
One example of negative energy is related to the idea of Hawking radiation of black holes. If a pair of particles pops out of empty space near a black hole, one could escape as a real particle, giving the Universe some extra energy that it didnât have before. The other might fall into the black hole, and could lose enough energy to account for both particles, so overall thereâs no gain.
The particle that escapes has positive energy, so in some sense the one that falls into the black hole has negative energy. But can you create negative energy in a controlled way on a macroscopic scale? We donât know.
But in principle, interstellar travel is still possible?
I think that interstellar travel will be impractical for a very long time because of the huge energy requirements. If we ever interact with extraterrestrial life, I think the last way weâll do it is by sending spacecraft. Broadcasting our existence with radio messages would certainly be much cheaper.
Extraterrestrial civilisations have probably also figured that out and realise itâs easier to find out about us from a distance. So I think we can all feel safe that aliens are not abducting psychiatric patients and subjecting them to interesting examinations.
How do they beam people up?
According to the writers, first you vaporise a person, then you transport them in a matter stream. Finally, you recreate the person using information stored in a pattern buffer.
But if thatâs true, there are a few episodes that are impossible. Thereâs a famous one called The Enemy Within, where Kirk becomes two people â the good Kirk and the bad Kirk â due to a transporter malfunction. But of course if you were transporting the matter, you would have to end up with the same amount you started out with, enough for one person not two.
Also, imagine how much energy it would take to vaporise you. Turning all of your matter into pure energy would take something like a thousand 100-megaton bombs. Thereâs a way to cut that energy by about a tenth though. If you heat someone to between 100 and 1000 billion °C, then you free the quarks that make up the protons and neutrons. The quarks will be moving at more or less the speed of light so you could take that matter stream, move it and put it back together again. Getting a stream of matter to pass through the walls of the Enterprise without punching a hole wouldnât be so easy, though.
Could there be any easier ways of doing it?
It would be easier just to transport the information. Just take all the information that defines you, transfer it somewhere else, then use some atoms that are already there to build another copy of you. Information, a set of ones and zeros, is easily transportable at the speed of light. Of course, youâve still got the original copy left over, and youâve got to worry about what youâre going to do with it.
How practical would it be to just transport the information?
Well, how much information would it take to describe you? Just for the sake of argument, say it takes a page to describe the configuration of each of your atoms â its electrons, its orbitals, its state of motion, its nearby neighbours, and so on. I calculated that to get all the information for a whole person on 10-gigabyte hard drives, Iâd have to stack them from here a third of the way to the centre of the Milky Way, 5000 light years away.
Also, it would take ages to transfer the information. Imagine the tension as Kirk and McCoy are on the planet Rura Penthe, just about to be shot by the jailer. They say: âBeam me up, Scottyâ, and Scotty says: âWell, I have to download this information, just hold on.â At present transfer rates, it would take longer than the age of the Universe.
It seems incredibly daunting. But look at the rate computer technology has been developing both in storage and data transfer for the past twenty years. If you naively extrapolate to the future, you find that we could have the technology by the dawn of the 23rd century.
There are lots of other problems though. How would I be able to resolve every one of your atoms to beam you up? We need big telescopes to resolve small things. The reported maximum distance that the transporter can work over is 50 000 kilometres or so. To measure the distance between atoms on a planet at that distance, I calculated that the telescope would have to be something like 30 000 or 40 000 kilometres across.
If we had the computing power and the telescope power, would transporting then be possible?
No. The thing that makes it impossible is a law of physics called the Heisenberg uncertainty principle. This says that much as Iâd like to know the configuration of every atom in your body and exactly what itâs doing, I canât know that exactly. Even if I had the best possible microscope in the world, there would always be some residual uncertainty.
That means I could never transport an exact replica of you. The Star Trek writers knew this and invented âHeisenberg compensatorsâ to get round it. When asked how they worked, Michael Okuda, one of the technical writers for the series, gave the best answer I know of: âVery well, thank you.â
Also, itâs an open question whether you are just the sum of your atoms and all their chemistry. Many people think thereâs a soul, and Star Trek never addresses that question. Iâm a cynical scientist â Iâd say that thereâs just the atoms and thatâs it. But you never know.
What about the deflector shield â how does that work?
The deflector shield is used to deflect weapons. According to the Star Trek technical manual they use gravity. In principle thatâs possible, because gravity can bend light around the Sun, for example. However, if you think about it, light near the Sunâs surface gets deflected by less than a hundredth of a degree â and thatâs with the entire gravitational field of the Sun. If you wanted to bounce something off the Enterprise, youâd have to concentrate more than the mass of the Sun in a region the size of the spacecraft.
What about the cloaking devices?
The cloaking device is something that the Klingons and the Romulans use to make their spacecraft invisible. To do this, you could use gravity again. You could take a light ray coming from behind you and bend it around you so that it goes forward, but nothing bounces off you. Big astronomical objects sometimes do this; they bend the light from objects behind them and act as gravitational lenses. But to create one artificially would be utterly impractical.
Can we forget about invisible people too?
There are several episodes where people are invisible. And all of us fantasise about being invisible and the wonderful things we could do if we were. But the problem is Newtonâs laws of physics again. If Iâm invisible, itâs because I donât interact with light. But if I didnât interact with light then I couldnât see and it wouldnât be any fun being invisible any more.
The Enterprise crew also come across beings made of pure energy â could they really be living in our Galaxy?
There are a few stories where they interact with energy beings. In one episode, they meet some energy beings that know everything about the Universe. Picard gets all excited about this and he gets beamed out into empty space as pure energy to flow freely with these beings, unconstrained by a body.
Itâs a wonderful idea, but again it doesnât work. The thing that distinguishes energy from matter, because after all matter and energy are interconvertible according to special relativity, is that pure energy must travel at the speed of light.
Itâs extremely hard to confine light, so it would be impossible to have an energy being just sitting there. Also, it wouldnât be too neat to be an energy being â you would experience infinite time dilation, and the entire history of the Universe would flash by in the blink of an eye.
Surely Star Trek got something right?
They got some technology right â one of my favourites is floppy discs. I didnât realise it till I was looking at the old episodes. Every time Spock needed to get information into or out of a computer, he put a little disc in. To my knowledge, that was before floppy discs in the States. Moreover, they didnât have those floppy five and a quarter inch discs. They went straight to those small solid things we use now.
One of the things that also surprised me was the way they sometimes anticipated terminology. Their linguistic perspicacity was just remarkable. In the first episode involving time travel, they go too close to the gravitational field of a âblack starâ, and get thrown back in time. I thought, well, this is kind of cute. These writers donât know the word is black hole. Then I discovered that the episode went on air six months before John Wheeler first used the term black hole â so they almost invented the term.
Is that just coincidence, or could Star Trek ever inspire scientific discovery?
I donât think people watch an episode and say gee whiz, thatâs a great idea â Iâm going to do that. But science fiction helps inspire the human imagination, and every now and then itâs nice to get away from the details of what youâre working on and free up your mind. Thereâs a great similarity between whatâs happening in Star Trek and what some physicists are doing. That kinship keeps the excitement level up, and helps people to realise that itâs not too crazy to think about weird things in the Universe like time travel.
Is there anything in Star Trek that seems ridiculous now but may be plausible in the future?
Three hundred years ago, they didnât think anyone would fly. And of course it is hard to know what the world will be like 300 years from now. But itâs important to realise that some things really are impossible. If at the Earthâs surface you let go of a ball, it wonât fly up. And no matter what we learn about the laws of physics hundreds or millions of years from now, as long as the Earth is here and you let go of a ball, itâll fall down.
Thereâs this view that somehow revolutions in physics change everything, but they donât. Physics proceeds by evolution, not revolution. We donât throw out Newtonâs laws just because we have Einstein.
Have you ever wanted to write an episode?
No, but one hope I had was that the writers would contact me and ask me to act as a consultant. That hasnât happened. Another hope was that theyâd ask me to do a walk-on part, and that hasnât happened either. I have been offered a backstage tour, but thatâs about it.
If you had been a consultant, how would you have changed it?
Iâm not a stickler for getting everything right. Sometimes the writers have to break the rules for dramatic effect. For instance, when a space station orbiting the planet Tanuga IV explodes, the crew of the Enterprise hear it. But sound doesnât travel in space. Aliens got it right â in space, no one can hear you scream. But without sound in space, Star Trek wouldnât have lasted one season.
But thereâs no harm in getting it right as far you can. I think I could enhance what they do. How might we do a certain plot so we violate as few laws of physics as possible? Or are there neat things happening at the forefront of physics we might want to exploit? There are far more fascinating things in the world of physics than the writers have come up with.
What do your colleagues think about a professor of physics writing a book about Star Trek?
I was worried about so many things when I decided to write this book. One was totally losing credibility. Why would a ârespectableâ physicist do this? Iâd been doing this in secret a little bit, and then I decided to blow my cover on the Internet. I wanted to contact some of my colleagues to ask for their Star Trek memories. So I sent them a note one night, and within about three hours, I started getting responses back. Everyone was eager to tell me â no one reacted in a negative way.
The other group that I worried about was the Star Trek fans â they love to pick holes in things. Again the reaction has been surprisingly positive. These people have been craving explanations for a long time and they love the fact that they now have something that relates to the real world.
Iâm getting a lot of pressure to write a sequel. Iâve already come up with a title: The Physics of Star Trek 2 â the Wrath of Krauss.
