I promised a while back to write a post on a topic of your choosing, in exchange for a $30 donation to my DonorsChoose challenge. I've got a fair number of requests, and I should really start paying them off. The first one comes from Ewan McNay, who aks:
what quantum mechanics can tell us about the existence of free will (if anything)
Oh, sure. Stick me with the tough questions.
This will be somewhat rambling and discursive, because it's not really an area that I've thought much about, or where I know anything solid about the science. In fact, my first thought on hearing the question has more to do with literature than physics...
In Guy Gavriel Kay's Fionavar Tapestry books, there's a lot made of the Wild Hunt, a collection of "shadowy kings on shadowy horses" who not even the gods can constrain. In the final volume, helpfully excerpted here, their purpose is explained:
the Hunt was placed in the Tapestry to be wild in the truest sense, to lay down an uncontrolled thread for the freedom of the Children who came after. And so did the Weaver lay a constraint upon himself, that not even he, shuttling at the Loom of Worlds, may preordain and shape exactly what is to be. We who came after . . . we have such choices as we have, some freedom to shape our own destinies, because of that wild thread of Owein and the Hunt slipping across the Loom, warp and then weft, in turn and at times. They are there . . . precisely to be wild, to cut across the Weaver's measured will. To be random, and so enable us to be.
To the extent that quantum mechanics has anything to say about free will, I think it's probably in this poetic, metaphorical sort of sense. Quantum mechanics contains an element of randomness, whether you believe that observation collapses the wavefunction or that we only perceive one part of a moe complex unitarily evolving wavefunction. The world that we see is not perfectly deterministic, and causes can have unexpected effects-- if you run the same experiment multiple times, under identical circumstances, you'll see a set of different results, with the distribution of results following some probability distribution.
In a sense, then, you could say that like the Hunt in the Fionavar books, this randomness enables free will. To the extent that consciousness can be considered a quantum process (and there's got to be at least some element of that, though I think Penrose goes a little too far), it's possible for us to think thoughts and take actions that are not perfectly and absolutely determined by the history leading up to those events. And that's really the essence of free will.
Of course, the whole business of "consciousness" is so murky that it's difficult to say anything really sensible about it. There really isn't much solid science regarding consciousness, even from people who say they know what's going on, and it's difficult to say anything scientific about free will without it. So any attempts to tie QM into free will are necessarily going to be kind of muddled and unscientific.
On a metaphorical level, though, I really like the Fionavar thing, so I'll go with that.
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You wanted *easy* questions?
Those cost more ;-)
Here's my answer: Free will is a question you want to ask a philosopher about, not a physicist, because it's all bound up in what one means by "free will," and really has nothing to do with whether or not the world is fundamentally deterministic. (Think about it: determinism means that all your future actions are set in stone, but non-determinism means that you have no control over your future actions at all. That's probably not what you're looking for when you say you want free will.) I recommend Dennett's Elbow Room: The Varieties of Free Will Worth Wanting.
Man, I loved the Fionavar Tapestry. I know a lot of people pan it as one of GGK's earlier works, and for the Arthurian angle, but I just loved so many of the scenes from that series.
From Milton's Paradise Lost (Book 2)
Chaos Umpire sits,
And by decision more imbroiles the fray
By which he Reigns: next him high Arbiter
Chance governs all. Into this wilde Abyss, [ 910 ]
The Womb of nature and perhaps her Grave,
Of neither Sea, nor Shore, nor Air, nor Fire,
But all these in thir pregnant causes mixt
Confus'dly, and which thus must ever fight,
Unless th' Almighty Maker them ordain
His dark materials to create more Worlds,
Into this wild Abyss the warie fiend
Stood on the brink of Hell and look'd a while,
Pondering his Voyage
I believe that quantum mechanics has a great deal to tell us about the nature of consciousness, but I do not think that it is relevant to discussions of free will.
If you are want to program a system which uses limited information to make decisions, you are likely to make it talk about those decisions as "free choices", because your system, for example, will need to be able to discuss the consequences of different choices before it makes them. The nature of the global underlying physics, whether deterministic or not, will be irrelevant to your programming. Evolution, similarly, whatever the underlying phsics, produces systems like us who need to be able to talk about our "choices" and so come to believe that we are "free".
We have evolved to believe we are free because it helps us talk about unknown futures. Quantum mechanics places absolute bounds on our possible knowledge of our futures, but these bounds are not the ones which were relevant to our evolution.
We have evolved to believe we are free because our information is limited, but our freedom does not lie in those limits, but in our abilities to construct alternatives, which given our ignorance, we believe to be possibilities. It is our beliefs which matter in this context not the actual, unknown, physical facts.
To me, the existence of "free will" would mean that the laws of physics are underdetermined. That is, there is more than one trajectory compatible with the initial conditions and the dynamical evolution law of the universe. In other words, the initial value problem does not have a unique solution and the actual solution occurs is selected by some selection mechanism which is, by definition, irreducible and indescribable, a "black box".
I believe this definition is what the philosophers call "hard determinism", or "the physics kind". I'm not clear on what question "soft determinism" relates to, all I know is that descriptions of make it sound to me to be vague, meaningless, and uninteresting.
With respect to "free will" in the "hard determinism" sense, there's never been an empirical sighting of it, AFAIK. That is, there are no observations or natural phenomena which we need to invoke its existence in order to explain. Sometimes people say "it feels like I have free will", but of course, there's no way to know how it would feel if we didn't, and no reason to think it would feel any different.
There's also Conway's proof of the "Free Will Theorem", which I can't claim to understand. However, the informal summary of what he proved is "if an experimenter has free will, then every elementary particle in the universe has it", which to me sounds like a reductio ad absurdum indicating it doesn't exist, (i.e. I propose that attributing free will to things like electrons is absurd). YMMV. Conway's certainly does.
I have a comment on Conway and Kochen's "Free Will Theorem" here.
Like El Christador, I think the conclusion is absurd. The premiss that "free will [is] the oppposite of determinism" is even worse. It places all the emphasis on "free" when most of it should be on "will".