Saturday, October 23, 2021

Does Captain Kirk die when he goes through the transporter?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]

Does Captain Kirk die when he goes through the transporter? This question has kept me up at night for decades. I’m not kidding. And I still don’t have an answer. So this video isn’t going to answer the question, but I will explain why it’s more difficult than you may think. If you haven’t thought about this before, maybe pause the video for a moment and try to make up your mind. Do you think Kirk dies when he goes through the transporter? Let me know if at the end of this video you’ve changed your mind.

So how does the transporter work? The idea is that the person who enters a transporter is converted into an energy pattern that contains all the information. That energy can be sent or “beamed” at the speed of light. And once it’s arrived at its final destination, it can be converted back-into-the-person.

Now of course energy isn’t something in and by itself. Energy, like momentum or velocity is a property of something. This means the beam has to be made of something. But that doesn’t really matter for the purpose of transportation, it only matters that the beam can contain all the information about the person and it can be sent much faster and much easier than you could send the person in its material form.

Current technology is far, far away from being able to read out all the information that’s necessary to build up a human being from elementary particles. And even if we could do that, it’d take ridiculously long to send that information anywhere. According to a glorious paper by a group of students from the University of Leicester, assuming a bandwidth of about 30 Giga Hertz, just sending the information of a single cell would take more than 10^15 years, and that’s not counting travel time. Just for comparison, the age of the universe is about 10^10 years. So, even if you increase the bandwidth by a quadrillion, it’d still take at least a year just to move a cell one meter to the left.

Clearly we’re not going build a transporter isn’t going to happen any time soon, but from the perspective of physics there’s no reason why it should not be possible. I mean, what makes you you is not a particular collection of elementary particles. Elementary particles are identical to each other. What makes you you is the particular arrangement of those particles. So why not just send that information instead of all the particles? That should be possible.

And according to the best theories that we currently have, that information is entirely contained in the configuration of the particles at any one moment in time. That’s just how the laws of nature seem to work. Once we know the exact state of a system at one moment, say the position and velocity of an apple, then we can calculate what happens at any later time, say, where the apple will fall. I talked about this in more detail in my video about differential equations, so check this out for more.

For the purposes of this video you just need to know that the idea that all the information about a person is contained in the exact configuration at one moment in time is correct. This is also true in quantum mechanics, though quantum mechanics brings in a subtlety that I will get to in a moment.

So, what happens in the transporter is “just” that you get converted into a different medium, all cell and brain processes are put on pause, and then you’re reassembled back and all those processes continue exactly as before. For you, no time has passed, you just find yourself elsewhere. At first sight it seems, Kirk doesn’t die when he goes through the transporter, it’s just a conversion.

But. There’s no reason why you have to convert the person into something else when you read out the information. You can well imagine that you just read out the information, send it elsewhere, and then build a person out of that information. And then, after you’ve done that, you blast the original person into pieces. The result is exactly the same. It’s just that now there’s a time delay between reading out the information and converting the person into something else. Suddenly it looks like Kirk dies and the person on the other end is a copy. Let’s call this the “Copy Argument”.

It might be that this isn’t possible though. For one, when we read out the exact state of a system at any one moment in time that doesn’t only tell you what this system will do in the future, it also tells you what it’s done in the past. This means, strictly speaking, the only way to copy a system elsewhere would require you to also reproduce its entire past, which isn’t possible.

However, you could say that the details of the past don’t matter. Think of a pool table. Balls are rolling around and bouncing off each other. Now imagine that at one particular moment, you record the exact positions and velocities of those balls. Then you can place other balls on another pool table at the right places and give them the correct kick. This should produce the same motion as on the original table, in principle exactly. And that’s even though the past of the copied table isn’t the same because the velocities of the balls came about differently. It’s just that this difference doesn’t matter for the motion of the balls.

Can one do the same for elementary particles? I don’t think so. But maybe you can do it for atoms, or at least for molecules, and that might be enough.

But there’s another reason you might not be able to read out the information of a person without annihilating them in that process, namely that quantum mechanics says that this isn’t possible. You just can’t copy an arbitrary quantum state exactly. However, it’s somewhat questionable whether this matters for people because quantum effects don’t seem to be hugely relevant in the human body. But if you think that those quantum effects are relevant, then you simply cannot copy the information of a person without destroying the original. So in that case the Copy Argument doesn’t work and we’re back to Kirk lives. Let’s call this the No-Copy Argument.

However… there’s another problem. The receiving side of the transporter is basically a machine that builds humans out of information. Now, if you don’t have the information that makes up a particular person, it’s incredibly unlikely you will correctly assemble them. But it’s not impossible. Indeed, if such machines are possible at all and the universe is infinitely large, or if there are other universes, then somewhere there will be a machine that will coincidentally assemble you. Even though the information was never beamed there in the first place. Indeed, this would happen infinitely often.

So you can ask what happens with Kirk in this case. He goes into the transporter, disappears. But copies of him appear elsewhere, coincidentally, even though the information of the original was never read out. You can conclude from this that it doesn’t really matter whether you actually read out the information in the first place. The No-Copy argument fails and it looks again like that the Kirk which we care about dies.

There are various ways people have tried to make sense of this conundrum. The most common one is abandoning our intuitive idea of what it means to be yourself. We have this idea that our experience is continuous and if you go into the transporter there has to be an answer to what you experience next. Do you find yourself elsewhere? Or is that the end of your story and someone else finds themselves elsewhere? It seems that there has to be a difference between these two cases. But if there is no observable difference, then this just means we’re wrong in thinking that being yourself is continuous to begin with.

The other way to deal with the problem is to take our experience seriously and conclude that there is something wrong with physics. That the information about yourself is not contained in any one particular moment. Instead, what makes you you is the entire story of all moments, or at least some stretch of time. In that case, it would be clear that if you convert a person into some other physical medium and then reassemble it, that person’s experience remains intact. Whereas if you break that person’s story in space-time apart, by blasting them away at one place and assembling a copy elsewhere, that would not result in a continuous experience.

At least for me, this seems to make intuitively more sense. But this conflicts with the laws of nature that we currently have. And human intuition is not a good guide to understanding the fundamental laws of nature, quantum mechanics is exhibit A. Philosophers by the way are evenly divided between the possible answers to the question. In a survey, about a third voted for “death” another third for “survival” and yet another third for “other”. What do you think? And did this video change your mind? Let me know in the comments.

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