delayed choice quantum eraser shows that free will exists

[ablprop]

Secular and religious philosophers have long debated the idea of free will. I think there's a bizarre quantum mechanical experiment that demonstrates its existence. I wrote about it on my blog (Turtle Universe) but I wanted to throw it out here and see if anyone had thoughts. The following is from that blog:

OK start with the basic idea. You can’t know both the particle-nature of a photon (which slit it went through) and the wave-nature of that same photon (interference pattern). Anything you do that reveals “which path” information automatically makes the interference pattern disappear.

What’s interesting about the quantum eraser is that you can set up things so that which path information exists, but is still hidden. One way Brian Greene describes this in "The Fabric of the Cosmos" is by polarizing the photon either clockwise or counter-clockwise. If you do this, even if you don’t collect the information, the interference pattern is destroyed. This is key: the mere potential of collecting which path information destroys the interference pattern. This is important for later.

The quantum eraser takes that information back out. The polarization is erased by removing the tag. Now the photons can interfere once more. Remember, as long as the potential for which path information exists, the interference pattern disappears. But (and again, this is key) once that potential is erased, the interference pattern comes back. This is important, too.

OK, now let’s think about another way to make which path information potentially available. This is a method that is even less invasive than the polarized tag. This time, we use something called a down-converter. Where at first one photon existed, we now create two, each with half the frequency of the original photon, and each entangled with the other. Call one photon the signal photon, the other the idler photon.

Suppose we send the signal photons toward a double slit. Will they form an interference pattern? The answer is, it depends on the idler photons. As long as these idler photons exist and give us the potential to discover which path information, the answer is no, no interference pattern will form. If, on the other hand, these idler photons are recombined in such a way that which path information becomes impossible to retrieve, then the interference pattern, in a certain specific sense, reappears.

Here’s the incredible part, though. The choice about what to do with the idler photons, whether to measure them directly or to recombine them to erase which path information, can happen after (even well after) the signal photons have formed their pattern. Note that, due to some clever bookkeeping by nature, you can never actually “see” the interference pattern until you obtain some extra information about the recombined idler photons. It’s all part of that amazing way that nature has of covering her tracks. It's pretty clever, and if you want to know more about it I urge you to read Greene's book or the Wikipedia article on delayed choice quantum erasers. Within that article you can find a link to the original paper (look at how graphs 3 and 4 each show an interference pattern, but when you combine them into graph 5, as always happens in the real experiment, the pattern disappears. Nature is shrewd!)

But astounding as all that is, it’s still not the most amazing piece of this. Here’s the most amazing piece. We already saw that we can reveal honest-to-goodness, no-mistaking-them interference patterns if we erase the which path information before the photons hit the screen. Remember the important points bolded above. What we can’t do is reveal an honest-to-goodness, no-mistaking-it interference pattern if the which path information is erased after the signal photons hit the screen. There’s a before-after dichotomy. The universe behaves differently regarding a choice that’s been made and a choice that might be made. And while it would be mind-blowing either way, I find this result (the future can’t affect events that have already happened) just as mind-blowing, maybe even more mind-blowing, than the alternative. Why? Because as long as the idler photons exist, as long as the potential for which-path information is there, the signal photons will not form an interference pattern. It’s as if they’re saying, “You might find out, you might not, so we’re not taking any chances.” But if we might find out and we might not, then we have the choice. We aren’t constrained by the past, and all future paths are open to us.

The refusal of those stubborn signal photons to form an interference pattern, no matter how we promise that no, really, we’d never go and detect your idler friends, demonstrates to me an amazing fact. We have free will. The future is open. We can make our own choices.

 And that's pretty cool. Damned be determinacy! Long live the idler photons, for they have set us free!

[hackenslash]

Nope, still not getting it. I know the details of the experiment, and I am more than familiar with Greene's book (an excellent read, although his treatment of entropy is shockingly oversimplified), but I don't see how you get from that to free will.

It should be noted that while free will cannot exist in a deterministic universe, that doesn't mean that a non-deterministic universe necessarily includes free will. Further, the lack of determinacy exhibited at the quantum realm doesn't prohibit determinism in some form on macroscopic scales, even if that determinism is best described in terms of probability distribution. Hawking deals with this beautifully in his seminal work.

[ablprop]

that doesn't mean that a non-deterministic universe necessarily includes free will

It's not non-determinacy that I'm pointing at. It's not entanglement, either. Rather, it's the combination of the two. And I admit it isn't proof, just an indication.

Here's my point boiled down - sorry I posted so much. I hate long posts, but am too often guilty of them.

Tagging photons can make interference patterns disappear by creating "which path" information. Erasing the tag can make interference patterns appear again. As long as the pattern appears after the erasing is done. Nature knows what I did (I erased the which path information), and so the interference pattern can reappear. The past is determined.

Tagging photons by creating idler photons can make interference patterns disappear - even if you never look at the idler photons. If the pattern (non-interference) appears before the erasing is done, the interference pattern will always disappear. The resulting pattern will look exactly the same whether or not I (later) look at the idler photons, thereby revealing "which path" information, or recombine the idler photons, thereby erasing the "which path" information. Because nature doesn't know what I'm going to do, it has to play it safe. But if nature doesn't know what I'm going to do, then the future is not determined.

This combination of non-determinacy and entanglement, it seems to me, puts an arrow on events. The past is different from the future. Events in the past are accessible to the photons. Events in the future are not. This tells me that those events are not yet events. The future is not determined.

Not proof, just an indication.

[hackenslash]

Thanks once again for the explanation, but I still don't see where you're getting free will from. This is just a further indication of indeterminacy at the quantum level, which a) didn't really need any more evidence (as interesting as the experimental result is) and b) still doesn't indicate free will in any way, shape or form. Once again, a non-deterministic universe at the quantum level is not remotely demonstrated, especially when the aforementioned semi-determinism at macroscopic scales is taken into account. Yes, a non-deterministic universe is required for free will to exist, but a non-deterministic universe doesn't actually provide any evidence of free will. Indeed, there is a good deal of evidence against free will in the absolute sense, in the form of influences on our decisions that have nothing to do with determinism. Here's one little snippet that seems to nail it to the wall:

[youtube:3sgzp3ua]http://www.youtube.com/watch?v=i1OVhlRpwJc[/youtube:3sgzp3ua]

[ablprop]

Hi again Hackenslash. Thanks again for the reply. OK, let's talk about the video. Really interesting. We human beings of course need the illusion that we're in control of our actions. The video reminds me of a couple of things. One is experiments I've seen done with people who have left and right brains disconnected from one another. They do things that demonstrate that their individuality is more or less an illusion, but they create stories that in a sense mask that reality, at least from themselves. I'm also reminded of the story of pill bugs. A particular parasite gets into their brains and causes them to walk out into the open, where they are eaten by birds. The parasite needs to be in the bird's body to reproduce, and it uses the pill bug suicide to get there. If the pill bug had any sort of consciousness, I wonder if it would convince itself that it really wanted to walk out into the open.

Fascinating stuff, and a bit terrifying for me, being a non-believer. All I have is my consciousness, and perhaps that is less real than I'd like to believe. Beware the things you want to believe, for you are the easiest person to fool.

I'd love to learn more about it. If you'd rather ignore the next two paragraphs, that's fine with me. Or not. Your choice (wink).

On the subject of free will, I think I see now that the problem is that we have two very different definitions. You're talking about something more psychological, I think. I'm talking about more of a physics definition. Is the future determined? I argue that the delayed choice quantum eraser shows that the future may not be determined. Not proof, just an indication. Consider the inverse. What if the delayed-choice quantum eraser experiment sometimes resulted in an interference pattern, and sometimes did not. Then, when we go to erase the which path information via the idler photons, we find that we can (in fact, must) erase in the cases where an interference pattern had been the prior result, and for some reason cannot erase the which path information in cases where the interference pattern did not appear. If that were the result, to me that would prove that free will does not exist. We had no choice regarding the idler photons, and the pattern somehow "knew" what we were going to do, just as if it had already happened. Just as the pattern "knows" what we did in the quantum eraser experiment that does not involve delayed choice.

But that's not what we observe. What we observe is that in the delayed choice quantum eraser, nature plays it safe, so that whatever choice we make in the future, the past results are consistent with that choice. Therefore, either choice could be made. Therefore, we have free will to make one choice or the other. We're not constrained by past events.

[hackenslash]

Yes, I get that, but it comes down to whether free will, i.e. the unconstrained ability to choose between logically available alternatives, actually exists. Certainly, the universe being non-deterministic is a prerequisite, but is it sufficient? Laplacian determinism, of the sort you seem to see nailed to the wall here, has already been ruled out by quantum uncertainty, and this doesn't provide any more nails in the coffin than were sufficient to keep it shut. However (and with due reference to recent rumours concerning the variability of radiometric decay, which I haven't had time to thoroughly check out yet), at least on macroscopic scales, a degree of determinism is not ruled out, even if only probabilistically, and that means that we can't necessarily rule in free will.

It is quite possible that the universe is, to a greater or lesser degree, deterministic. I doubt it, but it isn't ruled out by the physics. That's what my reference to Hawking was about, as he speaks at length about it.

The video was something else entirely, but does go to the discussion about free will, because any constraints on our decisions constitute a reduction in freedom of will.

[meta]

Quanta do not have free will.  They exist as both particles and waves, and they act only through what we can see as probabilities, but that shown only randomness, not free will.  Free will is entirely different, applying only to human beings, their minds or mental events, with the illusion that they can freely make decisions as they wish at any given moment.  This has nothing to do with quantum physics, which applies only to physical actions, not mental phenomena. I'm not arguing for dualism, but rather different levels of one reality.  Of course neurons in the brain are physical, and quantum physics does apply to neurons and neuronal actions, but as molecular cells they act as programmed by algorithm with determinism through causality, even though the quanta that make them up behave randomnly.  

Mental events in the human mind, or consciousness, do not act randomnly.  They act through algorithmic processes of cause and effect by neurons and neuronal networks and pathways, programmed initially by genetics and finally through the interactions of genes and the environment.  In short your idea is a category mistake, dealing with different categories.

Richard.

[ablprop]

OK (to both responses), but don't you find it the least bit interesting that the universe responds differently to quantum erasure that happens before the pattern is formed and quantum erasure that happens after the pattern is formed? If the future is already determined, then why the difference is experimental results?

[hackenslash]

I certainly do find it interesting, but I simly don't agree that it demonstrates free will.

As I said, it certainly shows that determinism is ruled out at quantum scales, but that was already ruled out, and it doesn't address the degree of determinism that may be inherent at macroscopic scales.

[ablprop]

OK, I can accept that.

[meta]

Experimental results in quantum physics certainly are astounding, but it seems what we come away with mostly is that the universe is an organ of sorts, a whole in which all the parts interact together.  This is the implication of entanglement, so very well proven experimentally.  So for physics that would be a whole new ballgame, no more locality.  And then also prediction, the real goal of physics, is denounced with probabilities.  There is no certainty in anything, so what else is new?

[meta]

OK (to both responses), but don't you find it the least bit interesting that the universe responds differently to quantum erasure that happens before the pattern is formed and quantum erasure that happens after the pattern is formed? If the future is already determined, then why the difference is experimental results?

Actually there aren't differences in experimental results in that only one result from experiments has been shown to hold up, as "patterns" meld.  Entanglement is the key.  

It seems to be agreed here that the original argument and conclusion is wrong, in that quantum physics does NOT affect free will of humans.  I remarked they are in different categories of thinking and understanding reality.  I think human free will is illusion, but extremely important from an evolutionary standpoint, with its selective value.  In theory there is nothing wrong with illusion so long as it produces beneficial products, such as survival. Besides that, all our perception of what we call reality may be only illusion, as Kant said our minds construct our own reality.

What does it matter?  What matters is what works for us:  pragmatism.  Illusion, such as self and free-will work well for us as much as we could expect from whatever reality is.  But that doesn't apply to ghosts, does it?  But it might apply to religious experiences, which actually have very great benefit for us in alleviation of pain (primarily psychological), shown to be verified in brain studies.

Richard.

[i_am_i]

OK (to both responses), but don't you find it the least bit interesting that the universe responds differently to quantum erasure that happens before the pattern is formed and quantum erasure that happens after the pattern is formed? If the future is already determined, then why the difference is experimental results?

Actually there aren't differences in experimental results in that only one result from experiments has been shown to hold up, as "patterns" meld.  Entanglement is the key.  

It seems to be agreed here that the original argument and conclusion is wrong, in that quantum physics does NOT affect free will of humans.  I remarked they are in different categories of thinking and understanding reality.  I think human free will is illusion, but extremely important from an evolutionary standpoint, with its selective value.  In theory there is nothing wrong with illusion so long as it produces beneficial products, such as survival. Besides that, all our perception of what we call reality may be only illusion, as Kant said our minds construct our own reality.

What does it matter?  What matters is what works for us:  pragmatism.  Illusion, such as self and free-will work well for us as much as we could expect from whatever reality is.  But that doesn't apply to ghosts, does it?  But it might apply to religious experiences, which actually have very great benefit for us in alleviation of pain (primarily psychological), shown to be verified in brain studies.

Richard.

So...what are you planning on doing this weekend Richard?

[ablprop]

It seems to be agreed here that the original argument and conclusion is wrong, in that quantum physics does NOT affect free will of humans.  

I agree. At best, the fact that the future is not determined is merely consistent with the existence of free will, but that's a long way from showing that we macroscopic beings have it. I didn't mean to imply any sort of mystical connection between indeterminacy and consciousness. I recognize there is a huge gulf between the results of individual photons and the activities of a big object like a brain.

The experiment itself simply fascinates me. The fact that nature is so effectively "covering her tracks," creating an interference pattern (in the delayed choice experiment) that can only be read once we've collected the which path information later on. There's deep stuff going on there.

Non-locality is pretty incredible all by itself, of course, but really the moment we admitted wave-function collapse as an explanation, that forced non-locality, don't you think? If I detect an electron here, that immediately means it isn't out by Jupiter, where at least a tiny bit of its wave function must have been hanging out.

The problem, I think, is not with the science, as experiment and theory always match up. The problem is with people like me, science educators, who are trying to make the science make sense, first for themselves and then for others. Simplification is crucial (otherwise just throw them the textbook and be done with it), but of course simplification can lead to misconceptions. It's a lot more fun and sexy to say "free will" as opposed to "indeterminacy", though in reality it's a long hard (and maybe impossible) slog from the second to the first.

Anyway, good discussion.

[hackenslash]

I still think you might be reading too much into it. It is entirely probable that a particle doesn't actually possess either of the qualities 'position' or 'velocity' until such time as it's actually forced into that state by observation. That's certainly the implication of at least one major formulation of QM, namely Feynman's 'path integral formulation' (sum-over-histories).