Q: Do we have free will?

Physicist: If you want to get into an argument that drags on forever, you can frame a question like this in terms of consciousness, and the nature of choice, or any number of other ill-defined ill-understood ideas.  So consider only the question in terms of determinism;

Q: “does the state of the universe now (and in the past) completely determine the future of the universe and, by inclusion, the future of me?”

Back in the day (classical physics day) the answer could rightly be “yes” or “I don’t know”.  However, with the advent of modern quantum mech we’ve managed to make great strides on questions like this.  Now we can answer: “yes, no, and kinda”!  It’s progress like this that almost makes going back to clipper ships and horse carts worth it.

One of the biggest weirdnesses to come out of quantum mechanics is the idea of “super-position”, which is that a single thing (a particle or whatever) can be in multiple states at the same time (the state of a thing can involve position, speed, orientation, and even how the thing is related to other things).  QM allows us to see how all of those states change in time and interact each other.  However, any direct interaction with an “undetermined state” will reveal it to be in only one (of its many) state(s).  In what follows I’ll use “universe” to mean the universe with just one state (things did happen this way), and multiverse to mean all the states involved simultaneously (with all the interference and what-have-you).

The two ways of looking at this are the “Copenhagen interpretation” (wrong) and the “many worlds interpretation” (right).

“Yes!”: Given complete knowledge of the multiverse’s quantum wave function you can determine the future of that function forever.  Unfortunately, this isn’t particularly useful for those of us who live inside the universe.  The wave function in question encompasses all possibilities simultaneously and involves plenty of self-interference.  For example: when you do the double slit experiment you can calculate exactly what the fringes will look like on the screen, by doing a calculation that assumes that the photons involved go through both slits.  However, if you were to instead look a one of the slits, this doesn’t tell you anything about whether or not you will see the photon go through that slit.

(Just a quick note about the link above.  “The Secret”, and its creepy brainchild “What the bleep”, are both symptoms of a greater douchiness, but despite their culty bent they explain the double slit pretty well.)

In fact what happens is it goes through both slits, but in turn there are different versions of you that see both outcomes.  If you look at the multiverse as a whole (seeing every state) then everything is completely deterministic.  If you look at just one tiny piece at a time (like we seem to), then everything seems random.

Essentially, for every choice you can make, there are a whole mess of versions of you (identical up to the moment of choice) that do make that choice.  In fact, if your wave function is known completely, then how much (many?) of you goes down any road can be derived.  I don’t want to hear anyone saying “but I chose to do that!”, because some (part?) of you had to.  But then, some of you had to do every available choice.

“No!”: Part of the Copenhagen interpretation is fundamental, true randomness.  There’s no multiverse in Copenhagen (so don’t go flying there to look), so any choice you make is unpredictable (or at least, not completely predictable, there are some pretty reliable people out there) in the sense that no matter how good your fore-knowledge of someone’s wave function, you still can’t make perfect predictions.

It’s seems like there’s enough wiggle room in there to fit some free will.

“Kinda!”: Even if you subscribe to the many world hypothesis you could argue that “dude, who cares?”.  You’ll never meet (can’t meet) those other versions of yourself, so what does it matter that, in theory, all of your simultaneous actions are determined in a multiverse-kind-of-way?  Doesn’t.

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12 Responses to Q: Do we have free will?

  1. Questioneer says:

    I think determinism is beside the point. This might seem a strange thing to say, because (as was stated in the post) determinism seems so clearly incompatible with freedom (though that requires that we think that freedom is the ability to do otherwise — and even then, there’s more that needs to be said), but I think that indeterminism is just as incompatible with free will. The idea is: we can only do something freely if we can control whether we do it. If our doing it is undetermined, then we didn’t control whether we did it (in the sense of ensuring that we did) – in fact, nothing did. Unrelated to that thought, here’s a nice article: http://www.wired.com/science/discoveries/news/2008/04/mind_decision


  2. Karan Hans says:

    i think talking about simultaneous action is a bit naiive coz if we were to observe an electron in vacuum from point a to point b it would follow a straight line so talking about it taking a parallel infinite number of possible paths (am i right?) to reach b would be like a stretch for the imagination. anyway the answer to the qs whether theres free will or not that you give: wave function helps predict future states deterministically seems a bit wrong. infact that was the core dispute between einsteins beliefs and quantum mechanics namely non determinism since the wave function only talks about probability. any it seems a bit odd that direct interaction should lead to determinism. it seems that its the inelegance of the theory which leaves a particularly odd impression. but it works.

  3. The Physicist Physicist says:

    It is a bit of a stretch, but it turns out that every possible path between two points is taken. Isn’t that horrible? This is the main idea behind the “Feynmann path integral”, which is how particle interaction is formulated in modern physics (the standard model).
    Also, sadly, Einstein lost his debate over determinism. He believed in “hidden variable theory” which states that things only seem random because we don’t know enough about them (some of the variables are “hidden” from us). This theory was later shown to be false by “Bell’s theorem”.
    The wave function describes probabilities in one universe at a time, however the evolution of the wave function itself (which lives in the multiverse) is actually deterministic.

  4. Vinicius says:

    Does it explain why there’s intelligent life and everything seems to be made in order to make humans be what they(we) are?

    I mean. Every possible event happens in superposition. Let’s say the probability of there being life somewhere (after the big bang) is 1*10^-10000000000, although it is a really tiny number, it is greater than zero, than probability of there being life is 100% ( as every possible event happens ). From the perspective of whom is inside that universe where life is possible, everything seems perfect.

    So, if MWI is right, nobody needs Gos to explain the universe anymore. Is religion gonna disappear forever?

  5. The Physicist The Physicist says:

    Religion should be safe for a while yet.

  6. I Passed Pre-Algebra Finally! says:

    Is it even remotely possible to say that either the universe (synonymous with all-of-reality) is deterministic or it’s not? Is the randomness in QM inherently random and not at all just a description due to our lack of understanding it? Such that it could well be deterministic, we just don’t get it yet, or that we DO in fact get it and could say, it appears to be deterministic but at the smallest scale it is utterly undeterministic? Which leads to: The universe is not deterministic…it only displays tendencies to appear deterministic. I dunno, I failed algebra…but I can sweep a floor like no one’s business!

  7. betaneptune says:

    “In fact what happens is it goes through both slits, but in turn there are different versions of you that see both outcomes. If you look at the multiverse as a whole (seeing every state) then everything is completely deterministic. If you look at just one tiny piece at a time (like we seem to), then everything seems random.”

    I don’t see how this makes things deterministic. What determines what we see, i.e., what sequence of universes we continually pass through? This path is just as random as in the original problem. It seems to me this version of the multiverse idea only adds a much more difficult problem: what is creating all these universes and how?

    And what about the multiverse that contains universes with different physical laws and constants? Each of those is its own many-worlds multiverse?

    What we see is still random. There is nothing in this many-worlds hypothesis does to change that. And how do you know it’s right?

  8. Robert Vonscholenyatze says:

    Aren’t the points, at which many universes differ, random in that there is not a reason why that point is a difference point?
    Also, ultimately, everything is randomly determined.
    No matter how deep we go, there will always be the question, what determined the the thing that caused the determination of the last thing we looked at? Ultimately nothing did. Even if somewhere along, existence determined itself, you still need to have another determination for this to be the case if you want to say that it is not random. Even if you say that everything that is possible exists, you might suggest that this is inherent, but you still need to explain a determination that causes this to be inherent. So existence of anything ultimately has a free will (independent self determination), and we cannot absolutely know existence is from one overarching self determination, or if many things (like people) determinine parts of their own path of existence. I think it’s nicer to think the latter.

  9. Greg Robert says:

    These discussions always annoy me because they don’t seem to realize that the very first thing to do is define the phrase “free will”.

    Most people assume it means “free choice” but that’s no better. Some think it means “uncaused behavoir” (which is the way I lean).

    Here’s the problem: please explain the difference between “quantum random” and “uncaused” and “free will”.

    If you make a choice that is other than random then there must be a reason for that choice. If there is a reason then it can be discovered and hence predicted.

    Ergo there is either no free will or it means “uncaused, unpredictable, quantum random, inexplicable” and that doesn’t seem to match the intutive understanding most people have.

    Hence free will as intuitively defined does not exist.

    And adding a soul only adds another layer that has the very same problems.

  10. betaneptune says:

    I think free will may just an approximation that is useful for holding people accountable for their actions.

  11. Magenta Fuchsia says:

    Does David Deutsch’s book “The Fabric of Reality” prove there are multiple universes?

  12. ENGLISH BOB says:

    There is nothing like edging your bets, Mr Physicist. I think we should all be determined to be as random as possible.

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