Each day that passes, millions of cells die within our bodies and millions of new cells are formed. Our cellular composition is not the same it was yesterday. On the other hand, we have cells that existed when we were born; our nervous system is thought to be mostly composed of cells that were formed before one is born. But even these cells endure changes. Neurons create and destroy new connections called synapses. Besides, cells synthesize and degrade proteins, absorb and expel molecules, etc. The molecular composition of our bodies changes continually. Like a river never has the same water, the body and the brain are not static, they are constantly changing. There is, however, a continuity in the changes our bodies endures as they typically occur slowly, progressively. So, most body-theorists do not actually believe that exact sameness of material is what grounds identity. Rather, it is only bodily continuity that matters. For instance, even though my body is made of slightly different material today than it was yesterday, there is nevertheless some causal continuity between my present body and my former one which binds them together as one and the same.
Now imagine that scientists find a way to transpose a person to a distant place almost or truly instantly. (Teletransportation of a person is generally regarded as impossible according to the present laws of physics but recent discoveries in quantum teleportation suggest some avenues of research.) One’s molecules would have to be disassembled, teleported — perhaps even in the form of energy — and arranged again to recreate the person’s body. A supercomputer would know the exact positions of each atom so that the person who left location A would be the same conditions in location B. The question: is the person in location B the same who left location A?
Complicating the situation I could say that some atoms would not be exactly in the same position even if the health of the person would not be affected. Now is this the same person who left location A? What about if some of the person’s atoms are replaced but the positions remain the same? What if some atoms are replaced and some positions change? What if all atoms are replaced but the positions are the same? What if a perfect copy is assembled and only a millisecond later is the original destroyed? What if you only rearrange/arrange 50% of the brain? What about 10%? What if the amount of time the atoms are disorganized is minimal and imperceptible to observers? Remember that for everyone else this person is always the same no matter how many atoms are replaced.
Following the continuity identity theory, even if I would be the same to observers during teleportation, I would not be me because there would be a point in time, even if a millisecond, where I would be dead and would not even be human. (The contrasting pattern identify theory states that a copy of my mind, even without being based on the same material support, is me.) Overall, and despite the fact that I can be attributed a material connotation at a given instant, I defend that I cannot be defined as a material being that can be copied while retaining my identity. Then what am I?
Suppose that someone built an exact duplicate of you on Mars, quark by quark – to the maximum level of resolution that quantum physics permits, which is considerably higher resolution than ordinary thermal uncertainty. Would the duplicate be really you, or just a copy? In this case, it turns out, science can rule out a notion of personal identity that depends on your being composed of the same atoms – because modern physics has taken the concept of “same atom” and thrown it out the window. There are no tiny billiard balls with individual identities. It’s experimentally ruled out.
Many people believe that what we are is not something material, but rather something immaterial. They say that each of us has a soul—or rather, is a soul—and that souls are immaterial things that reside in bodies. Maybe our souls ground our continued existence; so long as my soul continues to exist, I continue to exist. But, if that were so, we would have no way of knowing whether or not people continue to exist over time. Since souls are immaterial, we cannot see or touch or smell them. Souls, if they exist, are completely undetectable by the senses. And yet, it seems that we can know whether or not someone in the present moment is the same person as some earlier one. You do not greet your friends and say, “But, how can I know whether or not you are really my friend? My friend is merely an immaterial thing, and since I cannot see immaterial things, I have no way of knowing whether or not my friend stands before me.”
Furthermore, people who believe in souls typically believe that souls can leave their bodies and go elsewhere (for instance, to heaven). Perhaps I am my consciousness, my soul. Though I’m an atheist, soul is possibly the word that better describes what I am. Yet what is my soul? My soul is information: my way of thinking, my memories, my cognitive capacities, my mind. Despite some recent advances in neurobiology, we still don’t know how our brain thinks. We know, however, that the connections between the neurons are crucial for our brain’s functions. Therefore, perhaps the soul is the precise connections of all the neurons in the brain, which give rise to memories and cognition at a given instant.
Of course that, in theory, a person can be copied, cloned. Like the hard disk of a computer, it is possible in theory to copy my soul because ultimately the soul is made of information. Then to define myself at a given instant I must also add that my soul must be within my material body. As an atheist, I defend what is called materialism, as opposed to those who defend dualism or the separation of soul and body. In addition, there must be a continuity of the material support of my soul. Thus in the above example I cannot be transferred from location A to B without losing my soul. The reason is that in the moment when my molecules are disorganized, my soul dies, I die because the exact connections between my neurons are lost for a moment. I am nothing for an instant and therefore I can no longer exist. The person that appears at location B might have a soul and body equal to mine but he is not me. If the life that makes of me a sentient being doesn’t exist for a moment, then my soul is lost.
During one’s life one endures constant changes in personality and ideology, constant changes in the brain and in its neurons. I am much different from the person I was ten years ago. I was a different person, I was a unique set of neurons at a material body ten years ago that suffered a unique transformation to give rise to the unique soul I have now and at each moment of my future life. My soul changes continually, perhaps I am a soul trapped in my body and in constant mutation, but then I’d be falling into the fallacy of defining myself as solely a material entity. Even incurring in the error of defining myself as a mass, this is essential to define myself, my individuality and singularity. A set of interconnected neurons in constant change within a material boundary. Because in the end I am not only information. I can be described by information but without the physical support I don’t exist. If I suffer an accident and lose part of my brain, I will remain me, despite the difference. (It depends on the extent of the damage; if it’s a very severe accident, I may be defined as a different person, a different soul. Likewise, neurodegenerative diseases can be so severe and lead to so many loss of neurons that patients can be considered to be losing their soul.) As long as the framework that renders me an intellectual being has a continuous existence, I will remain me.
The above is relevant to transhumanist concepts like mind uploading, which entails transferring or copying one’s mind to a computer. Based on the continuity identity theory that I advocate above, mind uploading is impossible. Or to put it another way, it might be possible but a recreation of my mind on a computer will not be me just like a clone of myself will not be me. After all, even if it’s possible to perfectly recreate my mind on a computer I will still exist as an individual, I will still think, feel pain and can still die. Identity theory is also important to futuristic technologies like cryonics since the degree of brain alterations and neuronal death may make the difference between the procedure working or not.
This line of reasoning has led to many hybrid proposals. For instance, perhaps you continue to exist over time only so long as your body and your psychology do. On this proposal, survival of only your body (e.g., as a human vegetable) or only your psychology (e.g., if downloaded into a new body) would not suffice for the survival of you. My audacious claim is not that uploading preserves identity – this audacious claim has been made many times before. I am claiming that once you grasp modern physics, you can actually see this as obvious, even if it would not be obvious to someone thinking in terms of Newtonian billiard balls (atoms) in classical physics.
It was the seventeenth-century philosophical paradigm that was mainly concentrated on separation of subject and object, as well as mind and body. Consequently, mind was perceived as a certain space to generate representations which differed from worldly objects. To this end, Descartes perceived human mind as a thinking thing, which significantly differed from other substantial things within the world existence. At that, since that time there is a serious philosophical debate over materiality and mentality, which greatly influence our existence. For instance, modern cognitive psychology attempts to reveal the evolution of the modern mind by defending the existence of discrete and objective entity, which is literally a mind. This substance can be therefore observed by us via the consequences of its functioning.
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