I was thinking earlier about the problem of personal identity and particularly, the possibility and nature of essences, and thought again of the example offered to us by the writers of Red Dwarf.

We are told that everybody who works for the mining company that owns Red Dwarf is required to have their memories and personality copied onto the ship's hard drive in the event that they both die and are deemed worthy of being "resurrected" as the only hologram that the ship has the power to support. In the story, Rimmer is the one crew member chosen to have his psychological profile installed into the ship's hologram after the death of all but one of the other crew members.

There is a continuity error in the storyline because we are told that when the information is saved onto the hard drive, that that particular personality and beliefs and only that personality and beliefs will be present in the hologram, but in the story, when Rimmer is resurrected as the hologram he seems to remember everything up to his death, when actually his psychological profile was saved onto the ship's hard drive some years before his death.

Now this is relevant to personal identity because our intuition is that Rimmer is not really resurrected. The original Rimmer is dead and always will be. What has been brought to life is a being that is psychologically identical to Rimmer. Rimmer's stream of consciousness did not teleport from his first body to the hologram, and for all we know, the original Rimmer could really be in Heaven or Hell now or some other plane of existence. Of course the "new" Rimmer continues to talk about his former life and his death, as if they were really his, when in reality he has inherited these beliefs from the original Rimmer (along with his personality).

Now here's where the problem of self-location comes in. Suppose that the psyche-copying procedure goes like this: you sit down in a metal chair and a special helmet is fitted to your head. Then you feel a slight electrical current go through your whole body and that is the whole process. Your helmet is taken off and you are released.

The question then is this: At the moment when the process is done and your complete psychological state including qualia is recorded, how do you know whether you are the original you or a hologram of some formerly living person? We know that if a hologram were ever made in your image then they would be experiencing the exact same psychological state as you currently are experiencing. How then, can you tell whether you are you or them?

This is sort of a mish-mash problem between Elga's example of Dr. Evil and Wittgenstein's brain-in-a-vat (based on Descartes' evil demon). Elga gives us the following story:

Dr. Evil has a base on the Moon and is planning to destroy the Earth with nuclear missiles. So the Philosophy Defence Force send him a letter saying that they have made an exact duplicate of Dr. Evil in their laboratory and whatever Dr. Evil experiences, the duplicate experiences. If Dr. Evil does not disarm and surrender immediately, they will torture the duplicate. Elga argues that because Dr. Evil cannot be sure whether he is Dr. Evil or the duplicate, he ought to surrender.

Wittgenstein's brain-in-a-vat story is that whoever we are and whatever we are experiencing is consistent with the true proposition that we are really just a brain-in-a-vat being fed all of the relevant data by an evil scientist, and that all or most of our beliefs could be false.

In the first example Dr. Evil comes to believe that he has an actual duplicate, whereas in our second example, the subject comes to believe only that he has a possible duplicate. Nobody can work out what the probability is that that possible world is the actual world, i.e. nobody knows how likely it is that they are a brain-in-a-vat.

In the Red Dwarf example, it seems that we would have a subjective probability for it being the case that our duplicate is actual. Rimmer could work out roughly how likely it is that a duplicate of him will be made and then use a principle of indifference to calculate the probability that he is actually the duplicate.

So what are we supposed to learn from this? One thing to say is that if such a technology were ever to be developed then there would be serious ethical questions as to its use. Imagine a society where your psychological profile is saved every few months or even every morning. Perhaps the point would be that if you commit a crime or do something anti-social, you would be deleted and your last law-abiding copy would be recalled and educated in a way as to prevent you from acting the way your previous "self" had acted. (Maybe the extinction of the human race will only come when we work out how to digitalise our personalities and lose the need to breed and live like regular animals, living in computers with robot attachments immortally, eventually descending into a world of mental objects)

What if this technology already exists? after all, it possibly exists. Maybe some alien race delights in copying our personalities and memories and reproducing them in identical creatures on the other side of the universe with their own identical solar system so as not to confuse astronomers who remembered observing a different-looking solar system when they last checked? But does this possibility add anything to the brain-in-a-vat hypothesis? I can't see as it does since that is one very strong possibility and on its own allows the possibility for all or most of our beliefs to be false. Does this new example impact on the Cogito, "I think therefore I am"? It would seem that a Rimmer-clone might think "I exist" but would he be right or wrong, given that the original Rimmer no longer does exist? By saying "I", would he be referring to Original-Rimmer, or The-Person-Who-Is-Saying-This-Now? I don't think it does affect the Cogito actually, because for it to be a necessary truth the premise would have to be something like "He who is having the thought that this is, is thinking". That we can't ever be sure that we are who we were yesterday is something that is already entailed by the brain-in-a-vat hypothesis, as is the possibility that we were only created from scratch yesterday, or 5 seconds ago, with all of the (false) memories and beliefs we currently have.