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Oil droplets guided by pilot waves do not give rise to double-slit interference

quantamagazine.org

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Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#31

Post by SimonPStevens »

TeMPOraL wrote: post #25
pg_bot wrote: post #9

I was thinking about the double-slit problem the other day, and was trying to make connections to any other phenomenon that exists in the natural world and I think I came up with one. In conditional probability theory, there exists something called the boy or girl paradox. The paradox shows that the likelihood of an event can be drastically affected by how you know even seemingly innocuous information. I think that o…

I'm having a fundamental problem understanding why the paradox is modeled the way it is. "Mr. Smith has two children. At least one of them is a boy. What is the probability that both children are boys?" For some reason, it's expanded as a choice from {BB, BG, GB, GG}. But why on Earth does the order of children matter in this question? The way I see it, it should be modeled as {both-boys, boy-and-girl, both-girls}; b…

Because if you select a random family from the set of familes with two children, the 4 permutations (BB,BG,GB,GG) are equally likely, at 25% each, so it's the simplest way to model it. If you model it in your way with 3 possible scenarios you'll find that the probabilities are BB: 25%, one of each: 50%, GG: 25%, and dealing with those differing probabilities is harder than just splitung the one of each scenario into two.

Try it with 2 coins flipped at the same time and you'll see it's the case. You'll get 2 unmatching coins about twice as often as you get either HH or TT.

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#32

Post by titzer »

function_seven wrote: post #30
TeMPOraL wrote: post #25

Earlier quoted context omitted.

I'm having a fundamental problem understanding why the paradox is modeled the way it is. "Mr. Smith has two children. At least one of them is a boy. What is the probability that both children are boys?" For some reason, it's expanded as a choice from {BB, BG, GB, GG}. But why on Earth does the order of children matter in this question? The way I see it, it should be modeled as {both-boys, boy-and-girl, both-girls}; b…

Let's say I flipped two coins. I tell you I did this. You ask me, "Did heads come up at least once?" I answer yes. What are the odds that the other coin was tails? 2/3, because there are three scenarios (HH, HT, TH) that satisfy my first answer to you. If you flip a pair of coins a few thousand times, and search the flip pairs for all the ones that had a heads among them, you'll find a tails in those pairs 2/3 of the…

That's a good explanation.

> Now if you ask me if the left coin came up heads—and I say yes—that doesn't give you any information whatsoever on the right coin.

Exactly. "At least one" gives information about the whole set, implicitly giving information about the second one whereas "the first one is X" gives no information about the second one.

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#33

Post by TheOtherHobbes »

dumbfoundded wrote: post #13
pg_bot wrote: post #9

I was thinking about the double-slit problem the other day, and was trying to make connections to any other phenomenon that exists in the natural world and I think I came up with one. In conditional probability theory, there exists something called the boy or girl paradox. The paradox shows that the likelihood of an event can be drastically affected by how you know even seemingly innocuous information. I think that o…

I think the problem with QM isn't the fact that the probabilities are confusingly calculated. It's that there's no underlying mechanism. Imagine I flip a fair coin. The odds of you guessing it correctly are 50%. In your mind, you know it's probabilistic. Simultaneously, you imagine that if you had more information you could get it right more than 50% of the time. Maybe if you new the force or the initial velocity, th…

That's a key point - classical randomness is still causal.

QM effectively seems to be non-causal - or at least, much less causal.

Tidying this away under the heading of "It's probabilistic, let's just do the math and not worry about why" seems to be ignoring some very basic questions.

I can't seriously imagine Newton saying "Well, the Moon stays in the sky instead of falling down - and that's frankly a bit weird, but I'm not going to wonder why because it's just a mystery and anyway, I can predict its orbit with these epicycles."

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#34

Post by quickthrower2 »

TeMPOraL wrote: post #25
pg_bot wrote: post #9

I was thinking about the double-slit problem the other day, and was trying to make connections to any other phenomenon that exists in the natural world and I think I came up with one. In conditional probability theory, there exists something called the boy or girl paradox. The paradox shows that the likelihood of an event can be drastically affected by how you know even seemingly innocuous information. I think that o…

I'm having a fundamental problem understanding why the paradox is modeled the way it is. "Mr. Smith has two children. At least one of them is a boy. What is the probability that both children are boys?" For some reason, it's expanded as a choice from {BB, BG, GB, GG}. But why on Earth does the order of children matter in this question? The way I see it, it should be modeled as {both-boys, boy-and-girl, both-girls}; b…

I read the wikipedia article and then it clicked for me. Here is the intuition I got:

If you know one of the kids is a boy then there is a 2/3 chance of there being a girl kid. I will assume you are happy with the reasoning behind this (3 options BG GB BB, two of which yield a girl).

Now why does spotting one of the boys change the odds? You already knew they had a boy right?

Well the boy being spotted conveys some information!

In particular you DIDN'T see a girl. You could have seen one, it would be possible right... but it didn't happen.

That fact means it is a bit more likely that they have two boys. How much is that bit, well 1/6th to be precise. So 1/3+1/6 = 1/2 chance they have two boys. And 2/3-1/6 = 1/2 chance they have two girls.

That gives me the intuition and makes this no longer a paradox intuitively. Although it was never a paradox logically.

CAREFUL:

The conditions under which the boy was 'revealed' to you matter.

If it was random 50-50 chance of seeing the girl or the boy then the above applies.

If the boy was picked, i.e. you said "ah you have at least 1 boy, show him to me". Then no information has been conveyed.

If something else situational (e.g. girls birthday party and all the girls are inside in the room, and boys are playing soccer outside [sorry for stereotyping but my imagination isn't so good] and so you see him) there may be a non 50-50 and non 100-0 probability then there are some more calculations to do :-).

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#36

Post by [deleted] »

pg_bot wrote: post #22
perl4ever wrote: post #18

Earlier quoted context omitted.

It doesn't make sense to me that in order to get the probability of 2/3, you implicitly consider "a boy and a girl" to be different from "a girl and a boy". Somehow, you're saying that seeing the boy means you have ruled out the possibility of "a girl and a boy". But the ordering is in no way related to some arbitrary observation. It's just lexical.

Here's the math, I will break it down based on Boy/Girl and seen. For the first case here are the different combinations for two children based on sex (let's say left denotes older and right denotes younger to distinguish the difference between girl and a boy and boy and a girl.) B B B G G B G G These outcomes are each equally likely, but since we know that one has to be a boy we can eliminate the (G G) case leaving…

[deleted]

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#37

Post by inciampati »

There is recent research on photons (rather than bouncing oil droplets) that backs up the Bohmian interpretation. "Experimental nonlocal and surreal Bohmian trajectories" http://advances.sciencemag.org/content/2/2/e1501466

I am not sure if the different QM interpretations are only a matter of taste in terms of all predictions. These surreal trajectories are seen as nonsense under the Copenhagen interpretation.

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#38

Post by Sean1708 »

dumbfoundded wrote: post #16
pg_bot wrote: post #12

Earlier quoted context omitted.

That's exactly what the paradox states. Seeing one boy does affect the gender of the second child.

It's not a paradox if you put it in less confusing language. There are 4 possibilities: GG GB BG BB GG is impossible so you have GB, BG, & BB. One of them is a B, what's the other. Well that's clearly 2 / 3 G. The other one situation is completely. It's basically just the chance of a child being a girl.

Is this basically to do with the fact that you know how likely it is to see a boy given any of the combinations? So there's a 33% chance that there are two boys and you see a boy, a 33% chance that there's a boy and girl and you see a boy, and a 33% chance that there's a boy and a girl and you see a girl. Given that you've seen the boy you've eliminated one of the outcomes so the other two outcomes are equally likely?

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#39

Post by rusk »

TheOtherHobbes wrote: post #33
dumbfoundded wrote: post #13

Earlier quoted context omitted.

I think the problem with QM isn't the fact that the probabilities are confusingly calculated. It's that there's no underlying mechanism. Imagine I flip a fair coin. The odds of you guessing it correctly are 50%. In your mind, you know it's probabilistic. Simultaneously, you imagine that if you had more information you could get it right more than 50% of the time. Maybe if you new the force or the initial velocity, th…

That's a key point - classical randomness is still causal. QM effectively seems to be non-causal - or at least, much less causal. Tidying this away under the heading of "It's probabilistic, let's just do the math and not worry about why" seems to be ignoring some very basic questions. I can't seriously imagine Newton saying "Well, the Moon stays in the sky instead of falling down - and that's frankly a bit weird, but…

> I can't seriously imagine Newton saying ..

But he did. He called it Gravity.

He didn't let figuring out "how gravity works" hold him back. He just figured out the equations that predict its effects based on observation. The unknowns happened to conveniently coalesce around a single constant G, but that doesn't make them "known".

[IANAP - do we have any convincing popularly accessible models for how gravity works even today?]

Anyway, that's kind of similar to going "oh I don't understand the subatomic mechanism that is causing this interference pattern, but the pattern itself is consistent so lets call that P!".

Unless I completely sped past the point you were trying to make - which is completely possible at this subatomic level of reasoning (-:

Re: Oil droplets guided by pilot waves do not give rise to double-slit interference

#40

Post by simion314 »

mehwoot wrote: post #5

Why does this matter? Does anybody seriously question whether the basic math can work? So somebody found a nice parallel between pilot wave theory and another physical phenomenon, but then the parallel wasn't as strong as thought. This experiment is the equivalent of arguing that light isn't a particle because your tennis ball doesn't bounce off the wall the way you thought it would. When I saw the droplet experiment…

But didn't we (HN users) asked a lot for publishing of negative results?
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