Trying To Think
Thursday, September 18, 2003
Essay 1, PHIL358: Metaphysics
“Would you step through the teleporter to Mars? Make sure you refer to what we have learnt about personal identity when answering this question.”To justify my decision to step into the teleporter to Mars, and to explore the uncertainties associated with the trip, I’ll examine three scenarios. The first is everyday life, which will be examined to articulate what is meant by identity, personal identity and survival. The second is the Mars Teleporter, which I will argue meets the required criteria to preserve personal identity. This is in contrast to the third scenario, Arthur Dent’s New Brain.

Scenario One: Everyday Life.

We might not be sure what is necessary and sufficient for us to persist, but we are sure that normal, everyday life provides it. If the Mars Teleporter preserves personal identity in the same way that everyday life does, then there is no reason not to use it.
When we look at everyday life, it is apparent that there can be change in any aspect of our complex physical and mental states, and yet we maintain a sense of personal identity. Part of the reason for this feeling of continuance is that the changes are “mostly gradual rather than sudden, and at no point is there sudden change in too many different respects all at once … moreover, there is not too much change altogether.” (Lewis, 2003, pg 85) Lewis provides an excellent reason why this change is not sudden: “the properties of each stage depend casually on those of just before” (Lewis, 2003, pg 85). Since each of our thoughts must be caused by the previous thought, subsequent thoughts cannot differ too much. Over a period of time, the difference may become considerable, but the difference has been gradually accumulated over time, with each change depending on what existed previously.
However, mere similarity is not always enough for us to assign identity: objects may be qualitatively similar without being assigned numerical identity. For simple physical objects, assigning numerical identity is not problematic: “the criterion of identity over time is the spatio-temporal physical continuity of this object” (Parfit, 2003, pg 3). For complex objects, judgments have to be made based on what criteria are important. Perry gives two examples: parts of a river are considered to be the same river if they are connected physically, and different baseball innings are considered part of the same game based on the rules of baseball, and in particular carrying over of the score (Perry, 1978). As the baseball example shows, the idea of numerical identity can become difficult to apply to complex abstractions. The properties that actually matter, and how much connectedness is sufficient for the notion of numerical identity to be applied, is driven by the values that lie behind the abstraction being made. Hume argues that there is no special essence that continues unchanged to provide identity, for any object, including our personal identity - acquiring and losing identity is a matter of convention and opinion (Hume, 2003, pg 17).
For personal identity, Parfit distinguishes between the physical criterion and the psychological criterion. (Parfit, 2003, pg 4) In normal circumstances, both criteria hold. Even though my body changes over time, it is physically continuous over time, with each change being small, and each state being casually connected to the previous one. Equally, my mental state changes over time, yet it is clear that the states are continuously connected by causation and resemblance. Generally, we seem to value our physical continuance only insofar as it enables our psychological continuance; we neither know nor care what happens within our brain, as long as it continues to provide us with mental continuity. Similarly, the spatio-temporal continuity of the atoms within the brain is only important as the cause of the continuation our brain’s physical state.
Numerical identity can be interrupted. A watch can be disassembled, but the same gold watch exists again when the parts are reassembled (Parfit, 2003, pg 3). Since the knowledge of how to reassemble the watch resides in the watchmaker’s mind, the physical continuity of the watch can be resumed. If we wish, we can think of the identity of the watch continuing as long as the watchmaker had the means and intention of reassembling them. If we were asked where the watch was while it was disassembled, we would answer that it is the pieces; we would not say that that the watch has been destroyed. If we had the skills to reassemble a person’s body, their physical connectedness could be interrupted, and then resumed. Alternatively, we could think of the physical connectedness continuing, but in an unusual way.
In summary, continuity of resemblance and causation are the usual conditions for the continuance of identity. For personal identity, we survive as long as these conditions continue to apply to those aspects of our physical and psychological states that we value.[i]

Scenario Two: The Mars Teleporter

The scenario of the Mars Teleporter is described by Parfit as follows:

The Scanner here on Earth will destroy my brain and body, while recording the exact state of all of my cells. It will then transmit this information by radio. Travelling at the speed of light, the message will take three minutes to reach the Replicator on Mars. This will then create, out of new matter, a brain and body exactly like mine. (Parfit, 2003, pg1)

The teleporter does a perfect job of reproducing your physical state. If we think of atoms as interchangeable, you will be physically the same as before. Even if we think atoms are not interchangeable, our atoms are continually changing. Of course, our atoms don’t normally all change at the same time, but the rate of change of our atoms does not seem to be relevant to us when we think about our survival. The teleporter has perfect information about our body, and that information can be used to reconstruct it perfectly, and so the body will be recreated exactly as before. This is not a familiar sort of physical continuance: our physical state is kept as information on a computer, and then radio waves, and then information on another computer. Since this is not familiar to us, it is not surprising that we should have, at best, mixed feelings about the procedure. But, although it is an unfamiliar form of continuance, it is reliable, and there is continuity of our physical state, at the level that we care about. The relation of resemblance and causation holds between our body before teleportation and our body afterwards.[ii]
In everyday life, physical continuance is the vehicle for psychological continuance (or so we are assured by modern neuroscience), and so we have every reason to expect that our psychological state will survive as well. Your wife has entered the teleporter many times; you cannot notice any difference, and neither can she, so the psychological resemblance is as good as anyone could want.[iii]
Even though there is physical continuance, and there seems to be psychological continuance, the fact remains that it is continuance of an unusual sort. How can we be sure that something hasn’t been lost in the teleportation, and that we really would have psychological continuance, and not just seem to have it? To answer this question, I’ll contrast the teleporter with a third scenario where personal identity has been lost: Arthur Dent’s New Brain.

Scenario Three: Arthur Dent’s New Brain

Arthur Dent’s brain contains important subconscious information, which can be read electronically. Unfortunately, his brain needs to be prepared before it can be read; specifically, it needs to be diced. A simple replacement brain is proposed: “you’d just have to program it to say What? and I don’t understand and Where’s the tea? – who’d know the difference?” When Arthur Dent replies that he would know the difference, the solution is simple: he will be programmed not to notice (Adams, 1979, pg 150).
The new brain is related to Arthur Dent’s original by resemblance and causation (it has been made to mimic him), so why should he be upset by having his old brain diced? How is his situation different from the Mars Teleporter? The problem seems to be that the new brain is made to be like his old one, and not made to be the same. The relation exists, but we say that it is too weak for personal identity to have continued. The criteria that I am applying for personal identity does not include atoms, but it does include a great deal of other information, which Arthur Dent’s New Brain does not duplicate. We could postulate increasing advanced replacement brains, and ponder whether there is a point at which the replacement brain might fulfil the requirements that we have. But this is not the situation that the Mars Teleporter presents: the Mars Teleporter does not approximate my physical state, it reproduces it exactly.[iv]
According to my criteria of personal identity, there is no significant difference between the Mars Teleporter and everyday life: the teleporter preserves those qualities that I value for survival. There is, however, a significant difference between the Mars Teleporter and the undesirable scenario of Arthur Dent’s New Brain, where very few, if any, of the qualities are preserved. Considering which criteria are significant for personal identity, and which are not, has revealed the following two opinions about personal identity:

I think I am fully described by my physical state. It seems that my continuance depends solely on the continuance of the physical structures of my body. The teleporter is simply a new type of physical continuance, and hence an unusual but reliable form of psychological continuance.

There is no criterion that ought to count as essential for personal survival. I feel no special attachment to the atoms that make up my present body, and so I have no qualms about exchanging them for different, but qualitatively identical, atoms on Mars. The actual atoms define identity for some objects, for example, a teleported Mona Lisa would be a copy: we value the actual paint molecules that came from Leonardo’s brush. There is no contradiction here: different identity criteria apply to different objects, according to my values. We chose for ourselves what aspects of our existence are important, and everyday we seek to preserve those parts of ourselves as best we can.

Adams, Douglas, “The Hitchhiker's Guide to the Galaxy”, London: Pan Books, 1979.

Dennett, Daniel C., “The Unimagined Preposterousness of Zombies” in Brainchildren: Essays on Designing Minds, MIT Press and Penguin, 1998.
Ekai (also called Mumon), “The Gateless Gate”
Hume, David, “Of Personal Identity” in Metaphysics: Selected Readings, Sydney: Macquarie University, 2003
Lewis, David, “The Paradoxes of Time Travel” in Metaphysics: Selected Readings, Sydney: Macquarie University, 2003
Parfit, Derek, “What we believe ourselves to be” in Metaphysics: Selected Readings, Sydney: Macquarie University, 2003
Parfit, Derek, “Reasons and Persons”, Oxford: Clarendon Press, 1984.
Perry, John, “A dialogue on personal identity and immortality”, Indianapolis: Hackett Pub. Co., 1978


[i] One fact about everyday life that I have not considered here is that our physical continuity ends. This is not relevant to the decision on whether to use the Mars Teleporter, but is the focus of many discussions of personal identity. We can extend the arguments here to say that we can have continuance of the values we care about, even without our own physical continuity, though our causal interactions with others. This continuance is arguably analogous to the continuance we have in our everyday life (Parfit, 1984, discusses this at length). Additionally, there are contrasting views of everyday life; for example in Zen Buddhism:
Ego-soul is the seed of birth and death
And foolish people call it the true man

[ii] As an additional complication, Parfit (2003, pg 1-2) adds to the Mars Teleporter the possibility of copying. What if, instead of destroying my body on Earth, the teleporter left the original intact? Which would be me: the person on Mars or the person on Earth? Usually, when distinguishing between an object and its qualitatively identical copy, we use the spatio-temporal continuity of the atoms of the original to distinguish it from its copy. We do this when the distinction is important (i.e. when we care about the actual atoms, or simply for labelling the objects). If we don’t value the actual atoms of the original, then although we are able to distinguish between the original and the copy, we don’t actually care which one we have. On the criteria for personal identity I am arguing for, the actual atoms are not important. Both people have the correct relation to the person who entered the teleporter, and so both are his continuance. The survival of either person means that he survives. After the teleportation, these two people will have different experiences, and their mental and physical states no longer interact causally. While they share identity with the person in their past, they do not share identity with each other, or each other’s future. Even if we concede that the future identity of the two is more complicated than this, because of their past causal links and similarity, the continuance of the person who entered the teleporter is not in question.

[iii] The first person to use the teleporter would not have the reassurance of another’s experience, and no doubt his belief in neuroscience would have been strong enough to allay his fears about what might happen. A famous example of a similar concern is Dionysius Lardner’s 1823 prediction: “Rail travel at high speeds is not possible because passengers, unable to breathe, would die of asphyxia.” Some brave passengers were apparently willing to take the risk.

[iv] I am assumed that I there is no more to me than described by my physical state. If there is more to me than my physical state, exactly duplicating the state of all my cells does not duplicate all of me. Some extra information about me would also need to be read, transmitted and restored. It is difficult to know where this extra information about personal identity might be (since we cannot detect it), or what it might do (since no one notices when it is removed). Some philosophers argue for the possible existence of “zombies”, which act exactly like normal people, but have no epiphenomenal inner life. I find Dennett’s (1998) dismissal of this possibility convincing. Regardless of these arguments, if we decide that this mysterious substance exists, and that it is crucial for real survival, how can we be sure that other unusual events won’t also remove it, or that it hasn’t already been removed from us? How can we do anything, if we are concerned that some actions – but we don’t know which - might kill us in a way that is undetectable and unknowable?

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