Tuesday, July 29, 2008

Free will and Quantum mechanics

Because of the sort of internet locales that I frequent, I meet a lot of very philosophically minded folks. And sometimes, they spontaneously start talking about physics! I love it.

But I sort of hate it too. I feel like yelling, "Get off my lawn! Those aren't toys!" A lot of time, these people just don't know what they're talking about. And yet, everyone likes to think that there is solid scientific backing to their personal philosophy. That is not called science, it is called confirmation bias. It makes me sad, in a way. Is this the only reason that people enjoy science? So they can look into the depths of time and read it like a horoscope? I don't know... I guess that's marginally better than "to beat the commies".

In my metaphysics category, I aim to cut the line between physics and metaphysics, because this is where most of the abuse is.

Today's divorce: Quantum mechanics and Free will

First of all, free will is a contentious issue. A contentious philosophical issue, not a scientific one. Free will is one of those things that must, dogmatically, exist. Too often, people only care about the question of whether free will exists, when they should care about what "free will" really means. And what do we really mean by free will anyway? Does that mean that we're free from outside influences? Does it mean that we are morally culpable for our own actions? Does it mean that our actions are unpredictable? Is it necessarily a supernatural force? Definitions and details abound.

Does Quantum mechanics imply free will? It depends on what kind of free will we are talking about. If we're talking about unpredictability, maybe. But if we consider the moral definitions, I don't think science has the slightest bearing on any of them. "Unpredictable <=> morally responsible" just seems like a non sequitur to me, but hey, that's a problem for philosophy, not for physics.

But first, how about classical mechanics? The universe envisioned by Isaac Newton was like clockwork. All God had to do was wind it up. The universe would proceed in a single deterministic path. Now, Newton was quite religious, if a bit heretical, but that doesn't stop more modern folks from thinking that the determinism of classical mechanics was an obstacle to religion in some way. But is it?

In principle, classical mechanics are completely deterministic, but in practice they are not. If you've got a single particle, you can easily predict its motion, but if you have more, it's not so simple. If you have N particles, you have to keep track of 3N numbers to specify their coordinates, and 3N more to specify their momentum. Once you have at least three particles, the gravitational equations already become impossible to solve without approximations. In any typical system on the human scale, we'll have on the order of 10^22 particles. Because it is so vastly impractical to keep track of so much information, we instead use statistical descriptions of such large systems. Temperature is one example; it describes a probability distribution of energies for each particle. And that's why determinism does not imply predictability.

Having broken the connection between determinism and predictability, I have to wonder why determinism must be mutually exclusive with free will. Determinism at least allows for a very effective illusion of free will. (Bonus question: what's the difference between free will and its illusion?)

On to quantum mechanics. Quantum mechanics is thought to restore the possibility of free will (also miracles, but that's another topic) because it is completely random and therefore non-deterministic. But the more accurate description is that quantum mechanics is stochastic, not random. You cannot predict the outcome of a particular measurement, but you can predict the probabilities of different outcomes. In fact, in principle you can predict those probabilities exactly. If there were any way to influence the outcomes of the probabilities, there would, in principle, be an experiment that measures this skewing of probabilities. Such an experiment would contradict the stochastic nature of quantum mechanics. So this whole concept of "quantum free will"--a cosmic force capable of subtly influencing the results of wavefunction collapse--is in fact contradictory to quantum mechanics.

That is, unless this quantum free will is just as random as quantum mechanics itself. In that case, I have trouble discerning how this stochastic free will is any more free than a deterministic free will. Let's say you are to decide between two things--let's say, happiness or wealth. If you are forced to decide according to the result of a coin flip (don't forget: coin flips are a deterministic process), would you feel free? Would it make any difference if it were some sort of quantum coin flip?

As a side note, the current scientific consensus is that the brain is primarily governed by classical processes, not quantum mechanical ones.

Of course, things get still more complicated when we consider another respectable interpretation of quantum mechanics: the Many Worlds Interpretation.* According to this interpretation, quantum mechanics is neither random nor stochastic. It is deterministic in fact. Whenever a measurement occurs, the universe becomes a superposition of all the possible results. That is, all the possibilities occur. But subjectively, you only see one of those possible results. There are multiple versions of yourself observing each of the different possibilities, but you have absolutely no contact with those other versions of yourself. And no, you cannot "choose" which of the many possibilities will "really" occur--they all really occur, regardless of your state of mind.

*For details on why the many worlds interpretation might be preferred over the more common Copenhagen interpretation, see this previous post.

This is rather difficult to fit in with quantum free will. If your choices were truly based on quantum randomness, that means all choices must occur. Tell me, in what sense is this any more free than a classical universe? (Right now, I'm imagining God condemning half of your wavefunction to hell and allowing the other half into heaven.)

Now, there is one thing here that fits in with religion. Objectively (ie what God sees), you have no free will. But subjectively (ie what humans see), you have free will. Finally, a scientific solution to the omniscience/free will paradox! But that just misses the point. Determinism does not clearly imply predictability, nor does it clearly contradict free will and moral responsibility. And there all different kinds of ways to blur the lines between determinism and nondeterminism, free will and no free will.

So when you are looking for a way to back up your personal philosophy with physics, you must ask yourself: Am I talking physics or just practicing confirmation bias? If you find your confirmation in an idiosyncratic interpretation of quantum mechanics, it's probably the latter.

Of course, I still enjoy talking about it, regardless.

[This essay was partly developed in a discussion at the Friendly Atheist.]

9 comments:

Christopher said...

Objectively (ie what God sees), you have no free will.

"On the contrary, who are you, O man, who answers back to God? The thing molded will not say to the molder, "Why did you make me like this," will it?"-Romans 9:20

Isn't there still a problem for religion here? Suppose, for example, a religion says that God will send a person to hell if he/she doesn't "choose" to believe in him. Shouldn't the blame rest on the creator rather than the created?

Also, I'm a little confused on how determinism doesn't contradict free will or moral responsibility.

miller said...

"Objectively (ie what God sees), you have no free will."

Yes, there are plenty of things wrong with this particular idea. Believe it or not, I heard this idea from someone else; I didn't make it up. I brought up this example to show how easy it is to find some superficial reasoning that backs up whatever idea you like.

"Also, I'm a little confused on how determinism doesn't contradict free will or moral responsibility."

Determinism may contradict free will and moral responsibility, depending your definition of free will and what kind of moral philosophy you have. In my preferred definition of free will, there is no distinction between free will and the illusion of free will. In my preferred moral philosophy, it's simply pragmatic to hold people morally responsible, regardless of whether the universe is fundamentally deterministic or nondeterministic. So in my view, there is no contradiction.

But there's no particular reason that we must stick to these definitions. Would you like to explain how you think determinism contradicts free will or moral responsibility?

Anonymous said...

Someone said, "I believe in free will, because I have no other choice."

Brad said...

Just found this blog via Googling "free will mechanics." Ironically, your blogroll is nearly the same as mine! Wonder I haven't found this site before now. For the sake of honest criticism, I'll point out one thing ...

So this whole concept of "quantum free will"--a cosmic force capable of subtly influencing the results of wavefunction collapse--is in fact contradictory to quantum mechanics.

I think this is inadvertently a tiny bit off. Theoretically, if these cosmic forces directly decide/determine the collapses themselves, while at the same time conforming to probability distributions afforded by quantum mechanics, then "will" with some degree of freedom is still possible. Essentially, a cosmic force could choose a set of w-f collapses that conform to probability on some basis of will.

Plus there's always the gap argument that w-f collapses only follow probability when we're directly observing it, and when we turn away the sneaky gods go back to puppeteering the strings behind the microscale events.

miller said...

Hello, Brad! Your blogger profile is hidden, so I can't see your blog.

While the gap argument is strictly speaking a possibility, I think it sort of defeats the point of trying to support one's previous philosophical views with science. First, we say, "Quantum Mechanics means free will is possible after all!" and then we say, "Okay, but free will is still possible if QM breaks down when we aren't paying attention." It's still possible, but no longer compelling.

Of course, I accept that there are several loopholes in my arguments, but for each hoop we must jump, the less compelling our argument becomes.

The first argument, I believe, reduces more or less to the gap argument. If there exists a coherent will which determines wavefunction collapse, then there must exist an experiment which looks at the combined total wavefn collapses in the universe, and determines that they are much more likely to have been caused by said coherent will rather than quantum mechanics. Obviously, such an experiment is practically impossible, but then we're back to saying that quantum mechanics is only true when it is practical to test it, when we're paying attention.

Brad said...

Of course, I wasn't actually giving any argument, I was only remarking that the certainty of yours isn't quite that of a mathematical proof. Just like, there could be smurf-leprechauns celebrating inside my skull, but I've never been inside so I can't know for "sure."

Some other points:

1) Even if human will was based on quantum randomness, it doesn't mean human will is random in the same sense. Suppose, for example, that the human brain functions as a sort of near-deterministic computer that takes a small amount of randomness from quantum scale events and uses them in its computation. (This is essentially Orchestrated Objective Reduction Theory as promoted by Roger Penrose and Stuart Hameroff.) The 'randomness' would only be the seed. The output, in the form of human thought and/or behavior, could be patterned (we could have roughly structured personalities) and still be somewhat random-based.

2) Following from the apparent identity/essence of consciousness, the question is begged, "Why am 'I' in this cross-section of the multiverse and not another?" This leads me to believe that if the MW interpretation is true, then consciousness has no 'essence.' In other words, it is a phenomenon in which one manifestation has no distinct qualities from another. Existence precedes essence because there is no essence! This makes some sense, after all, because consciousness is just a happening...

P.S. I don't actually have an active blog. What I meant was, my top-of-firefox bookmarks were nearly the same. Let me also introduce Ebon Musings / Daylight Atheism (from which I hail), as well as the webcomics SMBC & QC.

Brad said...

P.S.2

DA has a series defending Ebonmuse's version of free will with an essay on "Outsmarting the Prediction Machine," which essentially shows that determinism does not imply predictability.

miller said...

I read SMBC, and I'm aware of QC and Daylight Atheism.

I basically agree about point 1, though I think classical uncertainty already provides the necessary random seed.

If someone asked me if I believed free will existed, my answer would be yes, in the sense that our actions are not completely determined by our environment, and in the sense that we can be held responsible for those actions.

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Taylor
www.imarksweb.org