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Does physics address the topic of consciousness?
For instance, does physics say anything about how it might arise or what might be its qualitative properties?
I'm wondering because it's interesting how certain combinations of particles are conscious (at least apparently) while others are not.
This is obviously a very broad question, but here are a few thoughts that may be helpful. As dmckee points out in a comment, it's difficult to define consciousness. However, consciousness clearly requires computation, and computation is something that physics can address.
There is a psychological arrow of time: we can remember the past but not the future. Physics is sort of able to explain this, in the sense that the problem of explaining the psychological arrow can be reduced to the problem of explaining the thermodynamic arrow of time. Thought and consciousness require computation, and computation has thermodynamic consequences. For example, erasing a bit reduces the entropy of the memory.
There has been some work on whether it is physically possible, given optimal exploitation of the universe's resources, to carry out a computation with an unlimited number of steps. The answer depends on cosmological parameters, and appears to be no for our current cosmological models (Dyson 1979, Krauss 1999). This can be interpreted as a proof that all consciousnesses are mortal.
Typically if we talk about consciousness, we assume that the consciousness is able to make observations. In relativity, this imposes certain constraints on the types of systems that could be conscious. For example, Gorini 1971 gives a no-go theorem for superluminal observers in special relativity, which makes it appear that tachyons, if they existed, could never be the building blocks for a conscious observer. In quantum mechanics, the Copenhagen interpretation ascribes a special role to observers and measurement processes; however almost no competent physicists (an exception being Roger Penrose) believe that this implies anything special about consciousness.
None of this addresses any of the classical religious or philosophical issues; or how to define consciousness as distinct from computation; or whether self-awareness extends to dolphins, mice, or cockroaches; or anything about strong AI. As far as I know, physics has very little interface with any of those matters.
Dyson, Time without end: Physics and biology in an open universe, Reviews of Modern Physics 51 (1979), pp. 447–460, doi:10.1103/RevModPhys.51.447; described at http://math.ucr.edu/home/baez/end.html
V. Gorini, "Linear Kinematical Groups," Commun Math Phys 21 (1971) 150, open access via project euclid: http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1103857292
Krauss and Starkman, 1999, Life, The Universe, and Nothing: Life and Death in an Ever-Expanding Universe, http://arxiv.org/abs/astro-ph/9902189
I'd suggest physics itself has nothing direct to say about consciousness. Physics just provides us with models of the "nuts and bolts" of how things work, but not the way minds work.
Interestingly (to me anyway :-)) I recently came across a topic that may shed some light on how consciousness develops (or at least operates) in people.
It appears that people born deaf do not, in the absence of a way to communicate, develop an inner voice.
Now your inner-voice is what I'd describe as a consciousness. It's the part of your mind that lets you "hear" your own thoughts. To develop such an ability it seems you need to learn a form of communication with other people and, in the process, your brain learns to communicate with itself.
If this all sounds a tad strange, read this article on the Psychology Today website.
It appears that deaf people who learn to sign, which is, as I understand it, the first thing taught people who are born deaf, think in sign language. They don't know anything about sign and so they can't think in sound, so they think in sign language.
This is also mentioned in this Today I Found Out video on YouTube. There are some more links related to this subject there as well.
This does suggest that the development of consciousness is "simply" based on the combination of an ability to communicate (medium does not matter) and the ability to learn. Those are things outside the scope of physics.
I don;t think even computer science has much light to shed on this, as models of computation tend to be deterministic and do not allow you to relate low level events to high level events. Thinking is very high level.
The issue of randomness (spontaneity) of ideas is what , I think, motivates some people to suggest quantum effects are responsible for thought. I think that's too big a leap, and the brain is such a complex system that what looks random from the outside may simply be quite deterministic on the inside. I think the jury is still out on how random a brain is. My impression has always been that it's a system "designed" to behave consistently, which implies it's "designed" (evolved) to overcome randomness, rather than exploit it. But that's just my (random) idea. :-)
