The question of whether or not one should step into a teleporter has plagued science fiction fans for decades. Although teleporters are not real, the perceived consequences of stepping in one provide insight into our intuitions about what matters most when it comes to personal identity. We’re going to talk about one of my favorite thought experiments, the teleporter thought experiment, and discuss exactly how it helps us make sense of personal identity.

The teleporter thought experiment

For those unfamiliar with scifi tropes, teleportation is the act of transferring objects and people from one location to another. The most common type of teleportation portrayed in science fiction, and the form most relevant to our thought experiment, involves a device like Star Trek’s transporter. The way these devices are assumed to work is by atomically deconstructing any objects placed on their entry point and reassembling them at the destination. Star Trek itself has been somewhat vague if transporters simply transfer information – details about the atomic structure of the transporter object – and uses this to recreate the object with new atoms, or if the original atoms are physically moved across space. For the purposes of this thought experiment we’ll assume the former. It should be noted that both scenarios appear to be scientific impossibilities, although the former does resemble quantum teleportation (a real phenomenon), albeit at an absurdly larger scale.

Using a machine he dubs the teletransporter, philosopher Derek Parfit asks us to consider this type of teleportation in his work Divided Minds and the Nature of Persons. Longtime readers of this blog might remember Parfit’s name mentioned in several entries from 2018’s Halloween themed thought experiment list. That’s because he’s an ethicist who specializes in issues of personal identity. If you’ll recall his fission or split-mind thought experiment, some of the same intuitions are present in this particular thought experiment too. You should definitely check out that post if you find this one interesting!

Anyway, in this thought experiment, Parfit asks us to imagine the following:

Suppose that you enter a cubicle in which, when you press a button, a scanner records the states of all the cells in your brain and body, destroying both while doing so. This information is then transmitted at the speed of light to some other planet, where a replicator produces a perfect organic copy of you.  Since the brain of your Replica is exactly like yours, it will seem to remember living your life up to the moment when you pressed the button, its character will be just like yours, and it will be in every other way psychologically continuous with you.

The question that inevitably follows from the thought experiment is what exactly about you that makes you… well you survives the teleportation process?

This might seem like an absurd question, but the answer is a matter of life or death given that our initial intuition might be that the teleporter kills us while preserving our likeness in a clone. Additionally, as fantastical as the premise of the thought experiment, it allows us to explore the answer to questions we may find ourselves asking throughout our lives. These are questions like what is it about you that survives a coma or your death, are you the same person after a traumatic personality-altering brain injury, and in what way are you the same person you were at age 10?

Central to all of these questions about the conditions under which you “remain” you is the notion of continuity. That is to say, when we ask such questions about personal identity, what we seem to be getting at are aspects or properties that can consistently distinguish us across time to form a line or a continuum from our past to our present. Some of the most common answers to the teletransporter paradox and other questions of personal identity involve identifying specific types of continuity linking an individual’s identity to who they were both before and after they stepped into the teleporter.

Defining personal identity through different types of continuities

The property or properties we decide to use to establish a connection between our past and present selves can best be thought of as a sort of metaphysical “glue” that allows us, at least under ordinary circumstances, to talk and conceive of ourselves as a single person persisting across time. You were once the 10 year old in your memories because this glue is doing its work in the background allowing you and others to make sense of yourself as a single person as you age.

What exactly is the nature of this glue? Well, that’s somewhat of a debate in metaphysics, but you’ll find that many objects and properties familiar to you have been proposed at one time or another as candidates for establishing a continuity of personal identity.

The soul theory of personal identity (continuity through the soul)

It should be no surprise that one of the oldest proposals for the survival of identity was the soul. There are a variety of ways a theory of the soul can be conceived, some of which might not even make the soul essential for personal identity and continuity. However, theories of the soul like Plato’s, suppose that there is an immaterial essence that resides within an individual during their life but survives their death.

The body theory of personal identity (bodily continuity)

The body theory of personal identity is fairly self-explanatory. This theory posits that it’s the persistence of the body over time that matter in determining continuity of identity. Though while the theory is simple, we can conceive of the concept of a body in many different ways. For example, does every part of the body matter equally? Should someone break an arm or lose a hand, does that matter in the same way as losing something like someone’s brain to trauma or disease?

Psychological and personality-based approaches to personal identity (psychological continuity)

These approaches to continuity take facts about an individual’s psychology, like memories, beliefs, and desires to be the basis of consistency over time. Of course it’s true that such things change gradually, but what most theories are concerned with what is considered to be psychological overlap rather than the persistence of the exact same memories, beliefs, and so on. Just as the body theorist understands that, for example, every 28 days our skin doesn’t literally consist of the same cells and atoms, psychological theories can account for gradual change of psychological states over time.

Stepping into the teleporter

Going back to Parfit’s thought experiment, your intuitions about which of these theories of identity might be correct will inform whether you believe you survive the teleporter. From what we can tell, bodily continuity is almost certainly violated through the teleporter’s disassembly process, however psychological continuity is preserved. If you’re sympathetic to a theory of souls that assumes the soul is central the personal identity, it’s impossible to tell what the teleporter does. The reassembly process could be akin to a resurrection, or disassembly could be akin to death with the teleporter spitting out a zombie-like shell that’s similar to you only in atomic constitution at the other end.

For Parfit however, the purpose of his thought experiment wasn’t to establish the importance of identity. As a reductionist Parift states that:

…personal identity through time is constituted by (“reduced to”) relations between mental and physical states and events in the absences of anything like a necessarily determinate and indivisible soul.

What this means is that, according to Parfit, there is no fact of the matter for survival over and above a type of psychological continuity that persists as a result of an appropriate cause. This notion is referred to as Relation R. Under normal circumstances Relation R is maintained by the persistence of your brain (and thus your psychology and personality) in your skull over time.

Parfit, through his fission and teletransporter thought experiments, illustrates a much broader notion of psychological continuity than what I briefly mentioned above. Key to this conception of psychological continuity is a causal relationship between past and future selves. This might seem somewhat abstract, but if you’re familiar with something like Buddhism, you might have an inkling of what Parfit is getting at. For Buddhists change is a constant of our universe, thus it’s somewhat illusory to look for some consistent thing that we can use to establish a notion of identity or self in the traditional sense. Likewise, for Parfit, questions about identity are missing the point, because there’s nothing for us to consider aside from psychological continuity that persists as a result of appropriate causes.

In Parfit’s teletransporter, it is the case that the individual entering the teleporter is not only psychologically connected to the individual exiting the machine, but causally connected to them as well, given that they are the cause for the machine recording and transmitting the information needed to reconstruct their body. In Parfit’s view, our intuitions that this type of causal relationship has vastly different consequences than those that occur under normal circumstances are mistaken. To get a better understanding of Relation R, consider the cause of fission presented in the blog’s thought experiment post.

What do you think? Would you step into a teleporter. Feel free to share your thoughts before or on Facebook or Twitter @Philosimplicity.