Two slit experiment : question from my 12 year old

[Moonhawk]

Dr Jekyll said:

But what is a probability distribution other than 'places it might be'? That's what I don't understand.

Yep - that's exactly what it is.

The electron could be anywhere within that probability distribution (perhaps more likely in some places than others as the probability distribution is not necessarily uniform) - you only actually know where the electron is when you detect it.

That's exactly why the double slit experiment works on single particles. In the video a spherical probability distribution is modified by the slits to form areas of high and low probability on the other side.

With each electron you fire - you are more likely to detect it on the other side in an area of high probability than low. Repeat the experiment over many particles and you build up a picture of these high probability areas since you'll simply get more 'hits' in these areas due to statistics.

Edited by Moonhawk on Tuesday 22 May 21:50

[nicklambo]

I have two thought experiments with this one that has always bothered me ....1: I'm copyrighting this idea if it works but it did occur to me ( in a slightly fuzzy way) that if the outcome is different in the scenario of the electron going through the slit because it is or isn't being measured then could a message somehow be sent backwards through time via observing or not observing the interference pattern. Example: Prior to firing the electron ask yourself if the number one is going to come up in the lottery....If the answer in the future is no then do not measure the result....if the answer is yes then measure it...this would give you the opportunity to ask yes/no questions backwards through time....
2: Could (in the situation of an interference pattern )the electron or photon be oblivious to time (which I believe it is as it travels at the speed of light) therefore it could be reacting to the next electron or photon fired as from it's point of view everything is happening simultaneously therefore producing said interference pattern.

Sits down and waits for the Nobel Prize to be delivered!

[Dr Jekyll]

nicklambo said:

I have two thought experiments with this one that has always bothered me ....1: I'm copyrighting this idea if it works but it did occur to me ( in a slightly fuzzy way) that if the outcome is different in the scenario of the electron going through the slit because it is or isn't being measured then could a message somehow be sent backwards through time via observing or not observing the interference pattern. Example: Prior to firing the electron ask yourself if the number one is going to come up in the lottery....If the answer in the future is no then do not measure the result....if the answer is yes then measure it...this would give you the opportunity to ask yes/no questions backwards through time....
2: Could (in the situation of an interference pattern )the electron or photon be oblivious to time (which I believe it is as it travels at the speed of light) therefore it could be reacting to the next electron or photon fired as from it's point of view everything is happening simultaneously therefore producing said interference pattern.

Sits down and waits for the Nobel Prize to be delivered!

So you would need to send the electron before the winner is announced, but have it arrive afterwards. So a big set up and very careful timing.

[creampuff]

I think you mean photon, not electron.

Electrons wandering around by themselves are generally high energy beta radiation... you don't want to be doing a school experiment with that

[nicklambo]

Dr Jekyll said:

So you would need to send the electron before the winner is announced, but have it arrive afterwards. So a big set up and very careful timing.

Yes...but doable if the path from the electron / photon to the detector was large enough?

[EddieSteadyGo]

creampuff said:

I think you mean photon, not electron.

Electrons wandering around by themselves are generally high energy beta radiation... you don't want to be doing a school experiment with that

The original video referenced electrons but I must admit when I was at school I'm pretty sure they referred to photons.

[anonymous-user]

Time is the same at all it is how all molecules know that they go forward in the arrow if time that is interesting.

I think that basically everything is part of everything else, connected by things we cannot see.

[EddieSteadyGo]

Dr Jekyll said:

I certainly don't like the notion of a 'probability wave' going through the other slot and causing the interference. Whatever goes through the other slot causes actual interference, not probable or possible interference. So calling whatever it is a 'probable' particle seems absurd to me. It may not be another electron, but it's an actual something, because it causes actual interference.

I think I get the abstract concept of a probability wave but I too find it dissatisfying - maybe because it is too abstract to feel like a logical answer.

[EddieSteadyGo]

Thesprucegoose said:

Time is the same at all it is how all molecules know that they go forward in the arrow if time that is interesting.

I think that basically everything is part of everything else, connected by things we cannot see.

You could well be right with that idea. I started watching another video about "entangled particles" (although not sure I quite understand what one looks like) and it seems that could be the case.

[Moonhawk]

EddieSteadyGo said:

I think I get the abstract concept of a probability wave but I too find it dissatisfying - maybe because it is too abstract to feel like a logical answer.

But that's exactly what they are. Same with atomic and molecular 'orbitals'. Just look at some of the bizarre shapes they can form. An electron in one of these orbitals has a probability of being found anywhere within the area described by the isosurface - and zero probability outside.

[PBDirector]

threadsnipe to say moonhawk I like your answers

[Moonhawk]

Even more interesting - these types of electron probability distributions have been directly imaged (kinda)

These are scanning tunneling electric microscope images of the highest and lowest occupied molecular orbitals of pentacene - compared with the results from a theoretical "density functional theory" plot of the electron density calculated using molecular modelling software. There seems to be a very good agreement - certainly in terms of the overall shape and probability distribution.

[EddieSteadyGo]

Moonhawk said:

Even more interesting - these types of electron probability distributions have been directly imaged (kinda)

These are scanning tunneling electric microscope images of the highest and lowest occupied molecular orbitals of pentacene - compared with the results from a theoretical "density functional theory" plot of the electron density calculated using molecular modelling software. There seems to be a very good agreement - certainly in terms of the overall shape and probability distribution.

I like your answers too, even if I don't fully understand them

Maybe it is a tough question, but how do you resolve the "time" issue with the probability wave model?

So if you take the theoretical star example I mentioned earlier where the photons from a far away star bend around a dense galaxy. If observed generally you would get an interference pattern but if you looked specifically to see which side of the galaxy they travelled on you would see a clumped distribution, which suggests that observing an electron now affected its path a billion years in the past?

The other issue I was wondering about is the reason to require such a paradox. I mean, we see this problem from our perspective where the wave acts like a wave, unless you look at it, when it acts like a particle. Why would the electron feel it is important to act like a particle when observed - why couldn't it continue to act like a wave?

It would seem to me that the change in behaviour of the electron when observed would likely be incidental to the actual reason for the change in behaviour.

Fascinating topic though - I was genuinely amazed to find that just observing an electron could change its apparent behaviour.

[BJG1]

It's a bug

[deckster]

EddieSteadyGo said:

...reason...Why...feel...why...

Subatomic particles don't feel. They don't have reasons.

Scientists tend to like 'what' and 'how' questions, which as we can see can be pretty bloody hard to answer at times. They leave they 'why' to philosophers and religionists (who, conversely, tend to jump straight to 'why' without bothering about little things like 'how'. But let's leave that to a lounge thread).

[wisbech]

Thesprucegoose said:

Time is the same at all it is how all molecules know that they go forward in the arrow if time that is interesting.

I think that basically everything is part of everything else, connected by things we cannot see.

Well, yes. Obvious example is gravity connects all mass, but we can’t see it. We can observe it though

[Toltec]

EddieSteadyGo said:

I like your answers too, even if I don't fully understand them

Maybe it is a tough question, but how do you resolve the "time" issue with the probability wave model?

So if you take the theoretical star example I mentioned earlier where the photons from a far away star bend around a dense galaxy. If observed generally you would get an interference pattern but if you looked specifically to see which side of the galaxy they travelled on you would see a clumped distribution, which suggests that observing an electron now affected its path a billion years in the past?

The other issue I was wondering about is the reason to require such a paradox. I mean, we see this problem from our perspective where the wave acts like a wave, unless you look at it, when it acts like a particle. Why would the electron feel it is important to act like a particle when observed - why couldn't it continue to act like a wave?

It would seem to me that the change in behaviour of the electron when observed would likely be incidental to the actual reason for the change in behaviour.

Fascinating topic though - I was genuinely amazed to find that just observing an electron could change its apparent behaviour.

My take on this, with photons at least, is that in the photons frame of reference is experiences no time or distance between the distant galaxy and your eye (or camera ccd sensor). In effect the interaction with your eye is the only thing that could ever have happened to that photon, at the moment,in your reference frame, that the photon causes an electron in an atom in your eye to change energy level it has been 'observed' and all other possibilities have collapsed and no longer exist.

This applies to the earlier question about how does the photon know what it is supposed to do now when the observation happens later, to the photon that was always what happened no other outcome was ever possible, the other outcomes were only ever probabilities in your reference frame. What happens to the photon was always going to, however you cannot know until you observe the result.

Of course I could be wrong, I don't really understand this stuff, I am just comfortable with its general freakishness.

[otherman]

Can I just say this has been the most enjoyable PH threads I've ever encountered. I'd be interested to hear what the assembled think of V8 manual cars, Punk Rock and pre-Raphaelite art also. Because I believe there could be a Venn diagram overlap area there with the cool people in it.

[EddieSteadyGo]

wisbech said:

Thesprucegoose said:

Time is the same at all it is how all molecules know that they go forward in the arrow if time that is interesting.

I think that basically everything is part of everything else, connected by things we cannot see.

Well, yes. Obvious example is gravity connects all mass, but we can’t see it. We can observe it though

Slightly off topic but this is a different video my son showed me which relates to this point - I thought it was an excellent way to easily visualise gravity (sorry if this has been already posted before).

https://www.youtube.com/watch?v=MTY1Kje0yLg

[EddieSteadyGo]

ash73 said:

In my opinion the Von Neumann Wigner interpretation makes most sense - the waveform collapses in conscious minds so that we can make sense of the universe and interact with it, it never collapses in physical reality.

https://en.m.wikipedia.org/wiki/Von_Neumann–...

This avoids uncomfortable "observation changed reality" paradoxes, we make observations of probability waveforms all around us and our brains instantiate a model of reality in our mind's eye. For that model to be simple enough to process we have to interpret which slit the electron passes through.

Similarly, when we see with our eyes we are interpreting a complex sea of EM waves and creating an image in our heads. There is nothing reaching us other than waves, the visual model is created solely in our heads.

Thanks for posting this link. Interesting way of resolving the conundrum.