Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

quantamagazine.org

Post reply on HN
Print view View original

21–30 of 130 posts

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

#21

Post by pmikesell »

pg_bot wrote: post #17
pmikesell wrote: post #15

Earlier quoted context omitted.

No, that is not what this says. What this says is that there is ambiguity in the description of the situation. Is the question about the probability of a second girl in the set of all families with 2 children and at least one boy, or is the question about the probability of a second girl in the set of all families with 2 children given that we know one of them is a boy. They are different sets of families. That is th…

Say my wife tells me that the neighbor has 2 kids and one of them is a boy what is the likelihood that their other child is a girl? Given what I know about the current situation, the probability that their other child is a girl is 66.666% If I look out the window to that neighbor's yard and see a boy playing outside, the probability that their other child is a girl drops to 50%. How I know the information about on da…

No, that's not what this is about.

Probability means this: "in X tries, how likely is it for Y to happen". The ambiguity here is this: what is the set of X? Is the set of all families with two children at least one boy, or the set of all families with 2 children of which you have determined one is a boy.

Those are different sets. It doesn't matter how you discovered the information. The apparent paradox is all grammar and set description.

Think of it this way - you want to test this out and actually run this experiment? Great! What's the experiment? Are you starting with all families with 2 children, or all families which 2 children at least one boy.

>> How I know the information about on data point one affected the likelihood of an unrelated one

No, it doesn't.

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

#22

Post by pg_bot »

perl4ever wrote: post #18
pg_bot wrote: post #17

Earlier quoted context omitted.

Say my wife tells me that the neighbor has 2 kids and one of them is a boy what is the likelihood that their other child is a girl? Given what I know about the current situation, the probability that their other child is a girl is 66.666% If I look out the window to that neighbor's yard and see a boy playing outside, the probability that their other child is a girl drops to 50%. How I know the information about on da…

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 us with two chances out of three that the other child is a girl.

The other case can be viewed as follows (S) denotes seen.

B(S) B

B B(S)

B(S) G

B G(S)

G(S) B

G B(S)

G(S) G

G G(S)

I can eliminate all cases where I see a girl out the window, leaving me with the following equally likely cases:

The neighbor has two boys and I see the older boy. The neighbor has two boys and I see the younger boy. The neighbor has an older boy whom I saw and younger girl. The neighbor has an older girl and a younger boy whom I saw. The neighbor has a girl in 50% of the remaining possible cases.

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

#23

Post by im3w1l »

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…

The boy or girl paradox does appear in physics but not like this. Distinguishable particles behave like "older child is a girl", while indistinguishable particles behave like "at least one child is a girl"

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

#24

Post by mpweiher »

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…

Well, I think the opposite result would have been very interesting/surprising. So I think it's a good experiment, and it's good to publish negative results.

The subhead seems a tad sensationalist. If interference had been shown, it would have suggested strongly that this can happen at the smaller scale as well, and that it didn't is probably disappointing for those that hoped to show it in the analogy. Not sure how it "crushes" those theories.

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

#25

Post by TeMPOraL »

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}; by telling me that one of the kids is a boy, you eliminated one possibility out of three, leaving us with 1/2 as an answer.

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

#26

Post by abdullahkhalids »

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…

This is actually a very interesting musing, and not quite correct.

> observation of the atoms passing through the slit is affecting the search space for the other atoms in such a way that we currently do not understand

Observation is the key word here. Actually, you don't need to observe the atoms to affect the pattern on the screen - though its the easiest way to do so in the double-slit experiment. All you need is the possibility of observing or distinguishing between two events to destroy the interference between them. Note that possibility of observing is a much weaker condition than observation itself. Physicists have, over the years, done many experiments to clarify these issues. Essentially, if you believe that causality only flows forward through time, then what you are saying is not correct.

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

#27

Post by jobigoud »

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…

Maybe that's how we clickbaitify the null hypothesis and save science.

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

#28

Post by pcmonk »

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…

It's not the ordering that matters, it's simply that the odds of boy-and-girl are twice the odds of boy-and-boy.

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

#29

Post by abdullahkhalids »

soveran wrote: post #3

All the paradoxes disappear if we use Quantum Field Theory instead of Quantum Mechanics. I would really like someone with deep knowledge on Quantum Theory to explain if something is wrong with a theory that otherwise makes a lot of sense to me. A good read on the topic is the paper "There are no particles, there are only fields" — https://arxiv.org/pdf/1204.4616.pdf

Surprisingly, physicists are very much aware of the field nature of all "entities" in the world, having invented QFT themselves. Even more surprisingly, popular journalistic explanations simplify things considerably, making it seem that the thoughts of physicists are much less refined than they really are. To complete the trifecta of surprises, in the refined thought process of us physicists, using QFT, many problems and paradoxes of interpretational nature or otherwise remain with quantum theory that need to be resolved.

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

#30

Post by function_seven »

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…

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 time, and a pair of heads 1/3 of the time.

Same with the girl-boy problem.

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. And if you search through the thousands of pair flips looking for an "H" in the left column, the right column will 50/50 have an H or a T.

Post reply on HN