Some philosophers think that there is a hard problem of consciousness: No matter how much scientists learns about neural processes, they can never explain why all this processing is accompanied by inner experiences. Analogously, there is a hard problem of life: No matter how much science learns about biological mechanisms such as cell metabolism, genetics, and respiration, it can never explain how all these mechanisms make something alive. Our inability to solve the hard problem of life implies vitalism, the view that living organisms are fundamentally different from entities describable in terms of physics and chemistry. Understanding life requires postulation of some special kind of non-physical energy that has been called the vital force, vital spark or élan vital. This fits well with the view that the hard problem of consciousness implies dualism, the view that thinking requires non-material elements like souls.
Of course, the biology of life is much more advanced than the psychology and neuroscience of consciousness. In the 1800s, a little was known about life mechanisms such as respiration, digestion, and cell division. The 1900s brought many breakthroughs concerning additional mechanisms concerning metabolism, genetics, epigenetics, DNA, and neural networks. Many aspects of living things such as reproduction and movement can indeed be explained by these mechanisms. But no matter how well developed becomes our understanding of the parts and interactions that make plants and animals alive, we can never explain life, as shown by the following thought experiment.
We can easily imagine the existence of “lombies”, analogous to the zombies that support the hard problem of consciousness. A philosophical zombie is supposed to be a thing that has all the physical properties of human beings but lacks consciousness. Similarly, a lombie is a thing that has all of the biological mechanisms associated with life, but still is not alive. Because this is an imaginable possibility, being alive cannot be identical with having those mechanisms, because if two things are identical then they are necessarily identical. Similar thought experiments undermine other explanatory identities assumed by scientists, such as that water is H2O and that lightning is electric discharge.
Someone who likes dualism but not vitalism might argue that consciousness is inherently different from life because inner experience is fundamentally different from living, but that would be merely assuming what is supposed to be shown. Neural mechanisms for consciousness have been proposed, including:
Neural synchronization (Francis Crick)
Somatic markers and convergence zones (Antonia Damasio)
Broadcasting across a global neuronal workspace (Stanislas Dehaene)
The explanation of consciousness seems to be at roughly the same point as the explanation of life in 1900, and undoubtedly there will be many new proposals about the relevant mechanisms and their interactions with each other. But no matter how well developed these mechanisms become, we will never have a full explanation of consciousness, just as we will never have a full explanation of life. Science can never explain what it is like to be a bat, any more than it can explain what it is to be alive.
These problems are not just hard, they’re impossible!
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