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Wednesday, February 1, 2023

Why Can’t People Teleport?

Let’s face it: Nobody likes to travel.

Whether they’re traveling to get to an exotic location for vacation or traveling to work on a daily commute, nobody actually likes the part where they have to travel. The people who say they like to travel probably mean they like to arrive. That’s because being somewhere can be really fun: seeing new things, meeting new people, getting to work sooner so you can go home early and read physics books. The actual traveling part is usually a drag: getting ready, rushing, waiting, rushing some more. Whoever said “it’s the journey, not the destination” clearly never had to sit in traffic every day and never got stuck in a middle seat on a transatlantic flight.

Wouldn’t it be great if there was a better way to get to places? What if you could just appear where you want to go, without going through all the places in between?

Teleportation has been a fixture in science fiction for well over 100 years. And who hasn’t fantasized about closing their eyes or hopping into a machine and suddenly finding themselves where they want to be? Think of the time you’d save! Your vacation could start now, and not after a 14-hour flight. We could get to other planets more easily, too. Imagine sending colonists to the nearest habitable planet (Proxima Centauri b, four light-years away) without having to spend decades in transit.

But is teleportation possible? And if it is, why is it taking scientists so long to make it a reality? Will it take hundreds of years to develop, or can I expect it as an app on my phone sometime soon? Set your phasers on stun, because we are going to beam you up on the physics of teleportation.

Options for Teleportation

If your dream of teleportation is to be here in one moment and then be in a totally different place the next moment, then we are sad to tell you right off the bat that this is impossible. 

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Unfortunately, physics has some pretty hard rules about anything happening instantaneously. Anything that happens (an effect) has to have a cause, which in turn requires the transmission of information. Think about it: In order for two things to be causally related to each other (like you disappearing here and you appearing somewhere else), they have to somehow talk to each other. And in this universe, everything, including information, has a speed limit.

Information has to travel through space just like everything else, and the fastest anything can travel in this universe is the speed of light. Really, the speed of light should have been called the “speed of information” or “the universe’s speed limit.” It’s baked into relativity and the very idea of cause and effect, which are at the heart of physics.

Even gravity can’t move faster than light. Earth doesn’t feel gravity from where the Sun is right now; it feels gravity from where the Sun was eight minutes ago. That’s how long it takes information to travel the 93 million miles between here and there. If the Sun disappeared (teleporting off for its own vacation), Earth would continue in its normal orbit for eight minutes before realizing that the Sun was gone.

So the idea that you can disappear in one place and reappear in another place instantly is pretty much out of the question. Something has to happen in between, and that something can’t move faster than light. Fortunately, most of us aren’t such sticklers when it comes to the definition of “teleportation.” Most of us will take “almost instantly” or “in the blink of an eye” or even “as fast as the laws of physics will allow” for our teleportation needs. If that’s the case, then there are two options for making a teleportation machine work:

  1. Your teleportation machine could transmit you to your destination at the speed of light.
  2. Your teleportation machine could somehow shorten the distance between where you are and where you want to go.

Option No. 2 is what you might call the “portal” type of teleportation. In movies, it would be the kind of teleportation that opens up a doorway, usually through a wormhole or some kind of extradimensional subspace, that you step through to find yourself somewhere else. Wormholes are theoretical tunnels that connect points in space that are far away, and physicists have definitely proposed the existence of multiple dimensions beyond the three we are familiar with.

Sadly, both of these concepts are still very much theoretical. We haven’t actually seen a wormhole, nor do we have any idea how to open one or control where it leads. And extra dimensions aren’t really something you can move into. They only represent extra ways in which your particles might be able to wiggle.

Much more interesting to talk about is Option No. 1, which, as it turns out, might actually be something we can do in the near future.

Getting There at Light Speed

If we can’t appear in other places instantly, or take shortcuts through space, can we at least get there as fast as possible? The top speed of the universe, 300 million meters per second, is plenty fast to cut your commute down to a fraction of a second and make trips to the stars take years instead of decades or millennia. Speed‑of‑light teleportation would still be awesome.

To do that, you might imagine a machine that somehow takes your body and then pushes it at the speed of light to your destination. Unfortunately, there’s a big problem with this idea, and it’s that you’re too heavy. The truth is that you’re too massive to ever travel at the speed of light. First, it would take an enormous amount of time and energy just to accelerate all the particles in your body (whether assembled or broken up somehow) to speeds that are close to the speed of light. And second, you would never get to the speed of light. It doesn’t matter how much you’ve been dieting or working on your CrossFit; nothing that has any mass can ever travel at the speed of light.

Particles like electrons and quarks, the building blocks of your atoms, have mass. That means that it takes energy to get them moving, a lot of energy to get them moving fast, and infinite energy to reach the speed of light. They can travel at very high speeds, but they can never achieve light speed.

That means that you, and the molecules and particles that make up who you are right now, would never actually be able to teleport. Not instantaneously, and not at the speed of light. Transporting your body somewhere that quickly is never going to happen. It’s just not possible to move all the particles in your body fast enough.

But does that mean teleportation is impossible? Not quite! There is one way it can still happen, and that’s if we relax what “you” means. What if we didn’t transport you, your molecules, or your particles? What if we just transmitted the idea of you?

You Are Information

One possible way to achieve speed‑of‑light teleportation is to scan you and send you as a beam of photons. Photons don’t have any mass, which means they can go as fast as the universe will allow. In fact, photons can only travel at the speed of light (there’s no such thing as a slow-​moving photon—in a vacuum).

Here’s a basic recipe for speed‑of‑light teleportation:

  • Step 1: Scan your body and record where all your molecules and particles are.
  • Step 2: Transmit this information to your destination via a beam of photons.
  • Step 3: Receive this information and rebuild your body using new particles.

Is this possible? Humans have made incredible progress in both scanning and 3D printing technologies. These days, magnetic resonance imaging (MRI) can scan your body down to a resolution of 0.1 millimeters, which is about the size of a brain cell. And scientists have used 3D printers to print increasingly more complicated clusters of living cells (known as “organoids”) for testing cancer drugs. We’ve even made machines (using scanning tunneling microscopes) that can grab and move individual atoms. So it’s not hard to imagine that one day we might be able to scan and then print whole bodies.

The real limitation, though, might not be technological but philosophical. After all, if someone made a copy of you, would it actually be you?

Remember, there’s nothing particularly special about the particles that make up your body right now. All particles of a given type are the same. Every electron is perfectly identical to every other electron, and the same is true for quarks. Particles don’t come out of the universe factory with personalities or any sort of distinguishing features. The only difference between any two electrons or any two quarks is where each of them is and what other particles they’re hanging out with.*

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But how much would a copy of you still be you? Well, it depends on two things. The first is the resolution of the technology that scans and prints you. Can it read and print your cells? Your molecules? Your atoms, or even your individual particles?

The even bigger question is how much your “you-​ness” depends on the tiny details. What level of detail does it take for the copy to still be considered you? It turns out that this is an open question, and the answer might depend on how quantum your sense of self is.

A Quantum Copy of You

How much information would have to be recorded in order to create a faithful copy of you? Is knowing the location and type of every cell and connection in your body enough? Or do you also need to know the position and orientation of every molecule in your body? Or if you drill down deeper, do you also need to record the quantum state of every particle?

Every particle in your body has a quantum state. That quantum state tells you where the particle is likely to be, what it’s likely to be doing, and how connected it is to other particles. Because you can only say what each particle is likely to be doing, there’s always some uncertainty. But is that quantum uncertainty an important part of what makes you you? Or does it happen at such a small level that it doesn’t really influence important things, like your memories or how you react to things?

At first glance, it seems unlikely that the quantum information in each of your particles would make a difference in making you who you are. For example, your memories and your reflexes are stored in your neurons and their connections, which are pretty big compared to particles. At that scale, quantum fluctuations and uncertainty tend to average out. If you were to subtly scramble the quantum values of a few of the particles in your body, would you be able to tell the difference?

Debating the answer to this question might be more appropriate for a philosophy book, not a physics book, but here we can at least consider the possibilities.

You’re Not That Quantum

If it turns out that the quantum state of your particles doesn’t play a role in making you who you are, and that simply recreating how your cells or molecules are arranged is enough to make a copy that thinks and acts like you, then this is good news for your next vacation because teleportation gets a lot easier. This means that you just have to record the location of all your small bits and pieces and then put them together in the exact same way elsewhere. This is like taking a LEGO house apart, writing out the instructions, and then sending those instructions to another person to build. Modern technology seems to be well on its way to someday achieving this.

Of course, it wouldn’t be an exact copy of you, which might make you wonder if you’re losing something in the translation.

Would it be like sending a JPEG version of an image instead of the full picture? Would you come out the other end a bit fuzzy around the edges, or not feeling quite like yourself? The loss of fidelity you’re willing to put up with depends on how badly you want to get to the next star system in as short a time as possible.

You’re Totally Quantum

But what if your you-​ness does depend on quantum information? What if the magic, or the indelibleness of you, lies in the quantum uncertainty of every particle in your body? This sounds like a bit of New Age hocus-​pocus, but if you really want to be certain that the copy coming out the other end of this teleportation machine is exactly the same as you, then you have to go quantum all the way.

The bad news is that this makes the problem of teleportation much harder. Really, anything quantum is hard, but the idea of copying quantum information is doubly hard.

This is because, from a physics point of view, it’s technically impossible to know everything about a particle all at once. The uncertainly principle tells us that when you measure the position of a particle very accurately, you can’t know the velocity, and when you measure the velocity, you can’t know the position. And it’s not just that you can’t know it. It’s much deeper: Information about position and velocity doesn’t simultaneously exist! There’s an inherent uncertainty in every particle.

The only thing you can know about a particle is the probability that it’s here or there. How, then, do you make a quantum copy with the same probabilities as the original?

Making a Quantum Copy

Let’s consider the problem of making a quantum copy of a single particle. If you insist that your light-​speed teleportation machine make a copy of you that is absolutely identical to your current self, then this is pretty much your only option.

To copy a particle down to the quantum level means that you want to copy its quantum state. The quantum state of a particle includes the uncertainty about its position and velocity, or about its quantum spin, or any other quantum property. It’s not really a number but more a set of probabilities.

The problem is that to extract quantum information from a single particle, you have to probe that particle somehow, which means perturbing it. Even just looking at something involves bouncing photons off of it. If you shoot photons at an electron, you might learn about its quantum state, but you will also scramble it. This isn’t because we aren’t clever enough or because we haven’t developed a fine enough probe. The quantum “no‑cloning” theorem tells us that it’s impossible to read quantum information without destroying the original.

So how do you copy something that you can’t see or touch? It’s not easy, but one way to do it is using “quantum entanglement.” Quantum entanglement is a strange quantum effect where the probabilities of two particles get linked together. For example, if two particles interact with each other so that you don’t know what their spins are, but you do know that they are the opposite of each other, then the two particles are said to be entangled. If you find that one is spinning up, you know the other one must be spinning down, and vice versa.

Quantum teleportation works by taking two particles, entangling them, and then using them like two ends of a telephone fax line. For example, you can take two electrons, entangle them, and then send one of them to Proxima Centauri. Those two electrons would sit there, still entangled, until you are ready to start the copy process.

From there, it gets a little complicated, but essentially you use the entangled electron you have here to probe the particle you want to copy, and that interaction gives you the information you need to make the electron at Proxima Centauri be an exact quantum copy of the particle you wanted to duplicate.

Amazingly, humans have done this for single particles and even for small groups of particles.* The record so far is making a quantum copy between two points that are 1,400 kilometers apart. That won’t get you to Proxima Centauri yet, but it’s a start.

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Scaling this quantum copy machine to more than just a few particles won’t be easy. There are 1026 particles in your body, so it gets very complicated, very fast. But the point is that it’s possible

Is that quantum reassembled person actually you? Well, it would be the most faithful reproduction of you that can possibly be made.

If that’s not you, then who are you?

Too Many Yous

One potentially sticky part about this idea of teleportation is that it can end up making multiple copies of you. In the case of the low-​fidelity teleportation machine that doesn’t copy quantum information, you might imagine using it to make clones of you. You could scan your body and then beam that information to Proxima Centauri, and then to Ross 128 b (another nearby habitable planet), and then to any number of other planets. In fact, you could start printing copies right here. They might not be exact quantum copies of the original, but they would be similar enough to create all kinds of moral and ethical issues.

Fortunately, there is one saving grace about the quantum copying version of the teleportation machine. The same principles of quantum theory that allow you to copy quantum information also require that the original information be destroyed when it’s copied. Whichever way the technology ends up working, the scanning process would inevitably destroy the original by scrambling all of its quantum information. This means that the copy you send over is the only copy that remains.

Beam There, Done That

To recap, the idea of transporting ourselves somewhere in a proverbial blink of an eye is definitely possible. If you can tolerate a speed‑of‑light transmission delay, and if you accept that a scanned and reassembled version of you is really you, then teleportation just might be in your future.

Of course, we forgot one important caveat: In order to teleport somewhere as described in this chapter, there needs to be a machine on the other side to receive your signal and reconstruct you.

That means that if you want to one day beam yourself to another planet, someone has to first get there the old-​fashioned way: by traveling.

Any volunteers?


Excerpted from Frequently Asked Questions about the Universe by Jorge Cham and Daniel Whiteson. Copyright © 2021 by Jorge Cham and Daniel Whiteson. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

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