Human Identity Sent via Quantum Teleportation

I once received a question about quantum teleportation from a layperson living in Canada who is interested in philosophy. The question was: since the human body being transferred is broken down into individual elementary particles by a device and then reconstructed using different elementary particles at the receiving location, is the person who appears there truly the same person who departed?

First, I must clarify that the human body is composed of a vast number of elementary particles. With current technology, it is almost impossible to perform quantum teleportation on all of those particles. However, since there is no theoretical reason to forbid it, we can consider it as a thought experiment. Based on that premise, from the perspective of quantum information physics, I would answer that it is indeed the same person. The true nature of various objects, including the human body, that are quantum teleported is the quantum information itself stored in a multitude of elementary particles. Individual elementary particles without information have no personality at all, nor do they have any memory of having made up someone's body. Regarding this, please also refer to the blog post below.

The definition of the "person themselves" being transferred in quantum information physics is that even if an external observer asks the subject any question or provides any stimulus, they will give exactly the same answers and reactions as the person before the transfer. For example, all memories held before the transfer are confirmed after the transfer as well. The fact that all information has been moved without any loss is the definition of the "person themselves."

Adopting this definition, what moves via quantum teleportation is, after all, the person themselves. It is not a duplicate (copy). Since we treat a human as a macroscopic quantum system and transfer their quantum state, the quantum information within this quantum state is prohibited from being duplicated due to unitarity. This is a major point of difference from classical information written in bit values.

While classical information can be easily copied, quantum information cannot be copied, so the quantum "person themselves" transferred via quantum teleportation possesses a very strong identity protected by the principles of quantum mechanics.

To laypeople who point out that the person being transferred dies during the initial measurement of quantum teleportation, I can point to the fact that no matter how you examine the elementary particles remaining after the measurement, not a shred of information about the transferred person remains. If one were creating a duplicate of information at a remote location, the information should also remain at the original location, but that is not the case.

This discussion of quantum teleportation cannot answer the question of whether mind-body monism, where the mind and body are inseparable, or mind-body dualism, where the soul and body are considered separate, is correct. Even if it were dualism, if one were to argue that the mind exists outside the universe and is non-local, and that the mind is not left behind at the original location during quantum teleportation, I could not deny it. In the first place, the question of whether the mind and body are monistic or dualistic has become a problem for which no single rational answer can be derived using scientific methods. What a physicist should do is not to claim that "mind-body dualism is wrong and mind-body monism is correct," but to accurately answer that "whether the mind and body are monistic or dualistic is not a problem that can be determined by science." I will not overstep by asserting things that cannot be said.

Quantum teleportation is not the Ship of Theseus, Swampman, or the Anywhere Door. From the sender's measurement, one cannot even create a blueprint of the object being sent. This is because the measurement results contain absolutely no information about that object. A random sequence of numbers completely unrelated to the information of the object being transferred is output as the measurement result. Therefore, it is impossible to create a duplicate (copy) from a blueprint that cannot be made. Even though the information of the object is not in the data, when that random data is sent to the receiving location, the transferred object is restored there using the elementary particles at the receiving location. In the Swampman thought experiment, the success rate of that appearance is extremely small, but the success probability of quantum teleportation can, in principle, be brought as close to 100% as desired. In the Swampman story, many duplicates can be made, but in quantum teleportation, the creation of duplicates is prohibited by the principles of quantum mechanics. The Anywhere Door is an idea like a wormhole that connects different places in spacetime. However, in quantum teleportation, because we do not connect the transmission location and the reception location with zero distance in that way, it takes a minimum amount of time for information to travel between the transmission location and the reception location at the speed of light.

Furthermore, various processes in quantum mechanics have completely different pictures for each observer, which is a major point of difference from classical theory. The same is true for quantum teleportation, and how quantum information moves during that process differs greatly depending on the observer. I have also discussed this in the blog post mentioned above.

(Cover art Author: vectorpouch / Source: Freepik)