optimist

This is from the ir/rational atheism thread. It was off-topic, so I am re-posting it as a separate thread.

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Kharakov:

Why did our inability to predict something exactly lead you to abandon determinism (do you take the position that there are no causes, as opposed to the position that we cannot know the causes)?

What are your comments on Shrödinger's Cat?

-k

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Optimist:

It was not our inability to predict something that lead to my abandonment of determinism. The two-slit experiment says much more than that! Here is an idealization of the experiment: A particle has a 50/50 probability of going through either slit (A) or (B). Then, if it goes into slit (A) it will have a 50/50 chance of either hitting spot (i) or spot (ii) on our detector behind the two slits. If the particle goes through slit (B) it will have a 50/50 chance of hitting either spot (ii) or spot (iii).

..........|
..........(A).....(i)
0-........|.......(ii)
..........(B).....(iii)
..........|

(ignore the dots (.), I had to use them so the diagram would post right)

Now, the pattern we would expect on the wall if we fired 20 particles over a period of time (one at a time) is about (i): 5 (ii): 10 and (iii): 5

Think about this, and make sure you understand that before you read on. Okay, now I'll tell you what really happens.

For this thought-experiment our results would actually be (1): 10 (ii): 0 (iii): 10 !

Why? We only sent one particle through at a time, so what could have changed the particles path? Believe it or not (believe it, because it's true), the probability from door (a) to spot (ii) cancelled out the probability from door (b) to spot (iii). How can probabilities hit one another and cancel each other out?!?

Here is a kicker, if you close slit (B) you get the expected pattern of (i) 10 and (ii) 10. But if you open slit (B), simply because you have introduced a new possible path, the particle moves differently.

Disclaimer: This is not actually how the experiment is done or how particles "probabilities" interact, but it is a close enough approximation and it is easier to understand it this way. If you want more I (highly) suggest reading Richard Feynman's Character of Physical Law. It only has one chapter on Quantum Physics, but it is very well done. More importantly, the whole damn book is great. Especially the last chapter on "Seeking New Laws." The book should be cheap ($2-$10 bucks).

This does not "disprove" determinism, but it at least demands my suspension of belief. The fact that probabilities can affect each other suggests they are more than just a lack of knowledge. "Even God does not know where the particle is going to go." Is a quote I heard and forgot who it is from...Hawking maybe?

I am currently close to "agnostic" towards determinism. (well, actually I am leaning towards not believing in determinism at all). The "Multi-World-Interpretation" (MWI) is an attempt to get rid of this indeterminism by introducing parallel universes… however this idea carries a lot of metaphysical baggage (to say the least!). I will not discount MWI on that count, but still indeterminism seems to be the more accepted interpretation of the two-slit experiment.

Anyway, this does not result in the existence of freewill either! This indeterminism takes place only on the smallest scale. There is no reason to think it affects our brains functioning in anyway. "Shrödinger's Cat" is suppose to be an illustration of what happens on the ultra-small scale, not to real cats! The reason is because the particles have to be isolated to act indeterminately (or be in two states at one time as in the case of Shrödinger's Cat). A cat has billions of particles in it all interacting with one another and so a can will not find itself half-dead and half-alive.


Freewill comes into a lot of trouble for other reasons anyway (e.g. I understand what chance is, and I understand what order is…but what is freewill?). I am fairly agnostic towards freewill right now too, but again I tend to think it does not exist.

As a last comment, since we are on the subject of Quantum Physics… on the subject of observation causing the collapse of the particle: I do not, nor do I think many scientists do now or ever, think observing a particle affects it! I think bouncing photons against it does. It isn't the human eye or brain that causes particles to "collapse," but the things we have to do to the particle so our brain can see it. When a physicist says observing the particle caused it to collapse, he is referring to the processes that are involved with making the particle observable.

This is all very complex stuff and so I don't know how well I've done at explaining it (sorry).

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Kharakov:

"The two-slit experiment says much more than that!" - Optimist

The 2 slit experiment was done to verify that electrons behave as both particles and waves. I don't understand how this influences your belief for/against determinism.

Our inability to accurately know something about particles would be part of the determistic nature of the universe- it is outside of our hands. Maybe at some future time, the right configuration of ideas, genetics, experiments, etc. will come together and give us the knowledge of what particles are doing, but this will be determined by whatever forces bring about that action. And that knowledge will in turn change the way we interact with the universe (or maybe some other factor will intervene and prevent our use of that knowledge). The knowledge of determinism comes from the fact that if something influences the outcome of something, it is part of what determines the outcome. If something does not have any influence upon the outcome on something, it does not have an effect upon the outcome. How can things be any other way? Even if things are determined by random events, are they not still determined?

-k

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optimist:

"The 2 slit experiment was done to verify that electrons behave as both particles and waves."
Waves of probability! You left out the important part, how can probability be a physical wave!? Your understanding of the two-slit experiment is what I first thought it to be, but it is much weirder. I remember thinking to myself, "this just means particles turn into waves, okay good. Determinism is right." Only later did the full meaning of the experiment dawn on me (after a few more books).

"Even if things are determined by random events, are they not still determined?" I think you are getting trapped in word use here. Yes the event is determined, but which event is not determined. In a deterministic universe if event [A] happens, event [B] will follow. From our point-of-view, in the case of a coin toss, [A] happens (flip of the coin) and either event [B] (heads) or [C] (tails) will occur. But, in the case of a coin toss whether [B] or [C] occurs is only apparently random since the randomness is only a function of our ignorance. We do not know exactly how the coin was tossed, and so we cannot predict whether [B] or [C] will result; but "God" knows the result. The first coin toss [A] does determine event [B]. The next coin toss has a different angle to is so it (event [D]) causes event [C] instead. A coin toss is always fully determined.

In the case of the 2-slit exp. the randomness is not a function of our ignorance, event [A] happens and either [B] or [C] could occur. To get rid of the "God" part: "Even the particle doesn't know where it is going." This is indeterminacy. If you want to say the event at time2 (either [B] or [C]) is determined by event at time1 (event [A]) you are correct, but event [A] does not determine which event (B or C) occurs. This is indeterminacy. Not complete indeterminacy, but still indeterminacy. Complete would mean event [A] could cause any event ([B, C, D...Z]).

Even though it is not complete indeterminacy, it is still a big different from the complete determinacy we are use to in our world of large objects. If I throw a ball its path is completely determined even if I don't know it. If it is a particle, its path has several choices and which is not determined at all!

In contrast, Chaos Theory is not indeterminate at all. Chaos Theory is about "Deterministic Chaos." This is about events so complex we are unable to predict the results, but in this case the events are still completely determined from the "God's Eye view."

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Kharakov

Hi optimist,

I think that the observation of a system effects the system is at odds with classical physics, but it does not clash with the idea of determinism because the observation of the system is one of the determining principles. Shy photons..

I agree with CT. I also believe that actual randomness that does not arise from ultra complex order must exist as well. It could probably be so random, that you can not tell that it is random- it would appear ordered. I like to call this theory "Order Theory"- which is when a totally chaotic system appears to be ordered due to a randomness that is so extreme that it produces a system that appears to be ordered.

-k

[ July 22, 2002: Message edited by: Kharakov ]</p>

scumble

I think the funny thing about it is that the electrons are individually restricted by some kind of probability function. If you have one electron at a time passing through, the pattern still forms. There's know way of saying if the electron takes a particular path, and it has to pass through both slits like a wave to interfere with itself. Still, one electron turns up at the detector at a specific point. No one can tell why this happens, only that we can predict the end result of a large number of events. Individually, electrons and other particles are very mysterious.

optimist

Ah, how virulent the determinism bug is! I came to the same understanding as you when I first embarked on these ideas, but nevertheless they are wrong. "the observation of the system is one of the determining principles." Yes indeed, but now we are speaking of two separate issues.

Claim One: By observing a system we change the system. By the *human mind* seeing the system, the system changes.

Claim Two: By observing a system we change the system. By making the system observable by the human mind we must use microscopes etc., and it is the microscopes that really change the system (not the human mind in some mysterious way).

I mentioned this issue in my last post just because it seems to be a popular confusion. Way too many eastern mystic/quantum physics books have been based around the absurd "claim one" above. However, this does not have anything to do with determinism. Both claims are deterministic (or can be).

Here is our issue:

Claim A: An isolated* particle will move with a path not strictly determined by any causes.

Claim B: An isolated* particle will move with a path strictly determined by preceding causes, but knowledge of these causes is beyond our research abilities.

*I say "isolated" particle because that is the only time these non-deterministic effects occur.

While claim B is still completely deterministic, claim A is not. Claim B is true about coin-tosses, claim A is true about isolated particles. A coin-toss is deterministic, but not quantum physics (or so seems to be the case).

Think about it with balls instead of particles. You have two doors, when you have only one door open the ball goes through and hits spot (i) on the wall:

--------------|-----------
-------------(A)---------(i, Ball hits here)
(Ball)-------|------------(ii)
-------------(B-closed)-(iii)
--------------|------------

Now you throw the ball again (only one ball), but this time with door (B) open.

--------------|-----------
-------------(A)---------(i)
(Ball)-------|------------(ii, Ball hits here)
-------------(B)---------(iii)
--------------|------------

Now why would the ball hit in a different place just because door (B) is open? It can still only go through one door since it is one ball.

You might respond that the ball (particle) has turned into a wave, and part of the wave went into door (A) and part of the wave went into door (B) and they hit so that the final wave collapsed back into a ball at point (ii).

This would be correct, but what is this wave made of? Water waves are waves of water, sound waves (normally) transfer through air, when the ball turns into a wave, what is wave-ing?

Well, something a little more interesting about all this, the amount of the wave that goes through doors is dependent on the probability that the ball will go through each door.

We account for every factor we can discover and yet the path is still undetermined, and so we assume there is some factor we still don't know about. Until we find that factor all we can give is the probability the ball will take this or that path. But then we notice that these probabilities that we thought were only a function of our ignorance about some factor, has some deeper significance. By adjusting the probability (with the angle the ball is thrown, the speed, the space between the doors, # of possible paths, semi-reflective mirrors) we also adjust where the ball goes. By adjusting the probability of which door the ball goes through we would expect to alter the number of times the ball will hit this-or-that spot on our detector screen, but not alter which spots get hit entirely. This suggests that the probability is not simply because of ignorance of some factor.

I am kinda spacing out on how to better explain this, I was hoping someone else would jump in and give it a shot with me, but alas… This should be at least enough to make you curious/unsure about it all. 

__________________

Notice how this only applies to isolated particles, and so there is little reason to think it in anyway affects the issue of freewill. The brain (obviously) does not function with isolated particles. Not to mention this only implies indeterminism, and not a freewill.

Kharakov

optimist-

I understand the problems with indeterminacy that QM presents. I am more inclined to believe option B than option A.

Wasn't it Feynman that said Quantum Mechanics shows nothing about why particles behave the way they do or how particles are actually behaving, but through some quirk of nature the mathematic's of q.m. are able to give us a hint as to the probable outcome of the behaviour? (This is a very rough recollection, if you can find the specific quote it would be cool).

That is the issue I have with the interpretation of quantum mechanics as actually what is happening in nature. I can describe the leaves of a tree turning red or yellow in the fall, and I can probably come up with some pretty good probabilistic equation to describe whether a leaf ends up turning red, yellow, or falling off the tree- but does this describe why the leaves are turning red? The why is the determining factor, and quantum mechanics only deals with the what, without addressing the why.

I admit there is probably an infinite regression of whys... I still don't think that invalidates determinism (fatalism).

-k

tronvillain

That is potentially an argument for abandoning strict determinism in favour of probablistic determinism, but there is always the possibility that it only appears to be probablistic and is in fact strictly determined. Does it really matter which is the case? I don't think so.

optimist

"but there is always the possibility that it only appears to be probablistic and is in fact strictly determined."

I take issue with this statement. It is also a possibility that God exists or 102 green monkeys created the universe. What you say is true, but why did you state it here? That the universe is really deterministic is more likely than 102 green monkeys, but they both seem very unlikely in light of evidence open to us now.

"Does it really matter which is the case? I don't think so."

That is a very important, and I think true, statement. This non-determinism does not affect the issues of freewill, justice, or any other subject. For all intents and purposes people are still deterministic systems, and all the determinist issues we are interested in are involving people. That particles can be non-deterministic when isolate is an interesting fact, but all it shows is how far against commonsense the universe really is.

scumble

Still, an awful lot of things cannot be explained in the realm of QM. We've got things like momentum - there's no explanation for that, really. What makes fast heavy things difficult to stop?

tronvillain

optomist:
Did I say that I thought the universe actually was strictly determined? No. I merely pointed out the possibibility. Is it unlikely? Well, it is certainly currenly an unsupported and unecessary hypothesis.

optimist

tronvillain, I didn't mean to come across as attacking you. But by listing that possibility, out of the infinite number of other possibilities, makes it seem like it is somehow more likely than the others. Would you not think a theist to be psychologically clutching on to their belief if after refuting all their arguments they said, "but it is still possible."

I don't want to sound like I am accusing you, but I didn't want to let your "its still possible" remark to go without qualification. I would be angered if at the end of an argument against God an atheist said, "but it is still possible." I am sure the atheist who made the comment understands that possibility does not justify belief or even research into the possibility, while a theist reading his argument may not. A theist might use that "possibility" to argue for creationism in schools since it too is a "possibility."

That is why whenever I say "determinism is a possibility" or "God is a possibility" I always add, "just like 102 monkeys or the ether hypothesis."