Can Gravity Influence the Double Slit Experiment with Larger Particles?

[swhite44]

2 slit, double slit, two slit

I saw a previous topic where someone asked if anyone has tried the 2 slit experiment with bigger objects (not Bucky balls) like sand or golf balls, but it seems not?
I wondered if the diffraction patterns could simply be a result of the particles deflecting off the edges of the slits?
Also what is the nature of the source of the particles, is it a single point source of light or electrons that 'sprays' across the area of the 2 slits?
And how are the slits cut in the material? With sharp flat edges or angled?
Maybe double slits in a single layer gold leaf film would be good to try?

Perhaps gravity could be the force to propel sand or some other macro particles through slits: just pour it down in a stream. I guess the size/velocity ratio might disallow the necessary deflections required to make a pattern though?

 

[San K]

2 slit, double slit, two slit

I saw a previous topic where someone asked if anyone has tried the 2 slit experiment with bigger objects (not Bucky balls) like sand or golf balls, but it seems not?
I wondered if the diffraction patterns could simply be a result of the particles deflecting off the edges of the slits?
Also what is the nature of the source of the particles, is it a single point source of light or electrons that 'sprays' across the area of the 2 slits?
And how are the slits cut in the material? With sharp flat edges or angled?
Maybe double slits in a single layer gold leaf film would be good to try?

Perhaps gravity could be the force to propel sand or some other macro particles through slits: just pour it down in a stream. I guess the size/velocity ratio might disallow the necessary deflections required to make a pattern though?

the slits can be staggered in space/time and interference can still be made to work...

 

[swhite44]

Staggered in space/time, doesn't that imply it's not an interference pattern they're seeing?
It seems like stretching an elaborate theory around a false assumption.

Pity someone doesn't try the experiment with a table tennis ball shooting machine, they might see similar patterns due to balls glancing off the edges of the slits.

 

[oli4]

Hi swhite44.
No that wouldn't work, the double slit experiment showing a diffraction pattern is all about a particle 'interfering with itself' 'as long as it can't be determined which slit it went through'
A heavy object being deflected by a sharp edge would certainly be identified as going through one or the other slit and therefore the diffraction pattern wouldn't appear, just as it disappears for a tiny particle which you observe too closely

 

[swhite44]

Yes I know the interpretation of the results of the experiment is that the pattern is a diffraction pattern caused by quanta somehow interfering with themselves, but maybe the pattern has some more rational cause?

 

[oli4]

This 'somehow interfering with themselves' is mind boggling
In order to try to understand how this can possibly happen, it has been tried to 'look at what happens' (does the particle goes through this slit, or the other one ? or both ?)
Every time this is done, there is no longer any diffraction, you are back to the same effect you would expect with tennis balls or whatever 'macro-particle'
This is the key point and the answer about 'has it been tried with bigger objects' ?
yes it has, in fact it has been tried a lot 'not to do so' :)

 

[swhite44]

So whatever they do to detect which slot the photon goes through, removes the wave property?
Can't they fire charged particles through some gas so they leave a trail?
Better to use a less invasive detection method.

 

[oli4]

No, as you said *whichever* method being used
it goes beyond the fact that someone looks at it, the same thing applies to the involved system regardless of the experiment.
As soon as something is recorded, it is over.
So, if the particle bounces over one slit wall with enough force that it had any impact on said wall (increased momentum/temperature/whatever that makes it a measurably different wall after than before) then it is determined that the particle went through this one slit, and no interference will show, simply because there is no interference any more: the particle went through this, or this slit and that is the end of it.
On the other hand, if there is no way to tell, not because our measurement apparatus isn't sensitive enough, but because there is physically no way to tell at all, then, and only then, will the interference pattern appear.

 

[swhite44]

Doesn't make sense, unless the method of measuring or recording which slit the particle goes through changes the properties of the particle.
Maybe the photon is embarrassed to be a just a mere formless wave, so it pretends to be solid matter if someone is watching?

 

[oli4]

Indeed, the measuring changes the properties of the particle, this is Heisenberg's uncertainty principle, except it goes far beyond 'someone watching' and goes straight through the actual individual existence of said properties.

 

[swhite44]

That's pretty poor, can't they improve their measuring technique?
It's like measuring the speed of Nadal's serve in the French open today and saying 'that serve was 90 miles an hour, but the radar knocked the ball out of court so it's not counted'.

 

[oli4]

There is no 'they' :)
This has nothing to do with measurement technique and everything to do with how things behave at the fundamental level, that is, as far as I know, the universe itself doesn't know what was the exact parameters of said service.

 

[boffinwannabe]

or may its like saying i don't understand what your saying so you must be wrong and i can't believe how poor your answer was. or maybe its just like being a troll?

 

[boffinwannabe]

of course you could just do the maths?

 

[swhite44]

You lost me there.
If measuring which slit a particle passes through removes the wave quality of the particle, then there's something intrusive about the measuring technique isn't there?
So 'they' who do the measuring should devise a more sneaky subtle technique.
It's as if the particle knows it was tracked?

 

[Rajatmo]

hey, this is a fanciful question. this experiment, if actually carried out at all, wouldn't give any "measurable" and satisfactory result. the diffraction effects would be so small (you can calculate it using de Broglie hypothesis) that it cannot be measured. furthermore, the two-"slit" experiment requires that you have an horizontal continuous array of tennis ball shooter as ball-quanta sprayer. and then there is gravity... with all this, I don't think it's worthwhile to do this now. perhaps the next century will have the proper technology to do that.

 

[oli4]

The particle does not have a wave behaviour any more than it has a 'regular particle' behaviour
It's a particle, and it behaves differently than a tennis ball
Measurement changes the outcome of the experiment, but the experiment carries on without anyone watching anyway,
that is, in order for the particle to take a definite path (through one slit or the other) it would 'leave a mark' regardless of someone putting an apparatus to check this mark.
If the particle interacts with any slit in anyway that is *physically* meaningful, then the particle went through that slit, and that is is, no confusion, no interference.
If on the other hand whichever path the particle took is absolutely untraceable, as in, 'not even the universe itself as any way to tell', then you can conclude, in a way, that it went through both slits, and the interference shows.
Of course it is more complicated than that, one particle does not, in fact, interferes with itself, but if the conditions of experiment are right, then, over time, one particle after the other, the interference pattern will show.
the interference happens lower, at the probability level.

 

[boffinwannabe]

until your grasp that it is not the MEASURING that collapses the wave function but the information becoming available that collapses it you have no chance of grasping this, if you truly are trying to. It has already been mentioned that there are variations to the experiment that demonstrates that it is NOT the measuring that collapses the wave but the information that could lead to knowing which slit it went through being available that collapses it. See the Delayed choice quantum eraser.

 

[mfb]

You lost me there.
If measuring which slit a particle passes through removes the wave quality of the particle, then there's something intrusive about the measuring technique isn't there?
So 'they' who do the measuring should devise a more sneaky subtle technique.
It's as if the particle knows it was tracked?

As mentioned before, it is not an experimental issue. Each fundamental interaction is symmetric: If object A influences object B, then B also influences A with the same strength. If your electron or whatever should influence the environment enough to measure its path, the environment has to influence the electron enough to disturb the interference pattern.

 

[boffinwannabe]

actually i believe the particle does interfere with itself. The point being that if the path cannot be determined then the particle takes every possible path simultaneously. But only one path is collapsed when it hits the detector.

 

[swhite44]

Rajatmo, no I meant has anyone tried it with sand or balls just to see if there is a dispersal pattern, due to the objects glancing off the edges of the slits. Not to see if table tennis balls interfere with themselves and produce a diffraction pattern.

 

[Nugatory]

You lost me there.
So 'they' who do the measuring should devise a more sneaky subtle technique.
It's as if the particle knows it was tracked?

Yes, it really is "as if" the particle knows that it's being tracked.
However "It's as if" does not mean "It is". We're pretty sure that whatever is going on, the particles aren't really consciously conspiring to produce weird experimental results and that we can defeat their wicked conspiracy by being more sneaky subtle than they are.

Of course, now I'm inviting the question "What really is going on?". There are a half-dozen more or less well-accepted possible answers, collectively known as "interpretations" of QM. No one has been able to come up with experiments or math to conclusively confirm or deny them, so which one you prefer is partly a matter of personal taste, partly a matter of which is most convenient for the problem you happen to be working on at the moment.
(BTW, "The particle knows it is being tracked" is itself an interpretation, just one that nobody takes seriously).

 

[swhite44]

>> Of course, now I'm inviting the question "What really is going on?". There are a half-dozen more or less well-accepted possible answers, collectively known as "interpretations" of QM.

Yes I read about this after reposting a Facebook thing saying something like 'according to scientists we live in a world of all possibilities'.

But after reading a bit, I'm thinking 'people look back on how dopey pre-Copernicans were to believe the Earth was the centre of the universe, and before that how moronic people were to think the world was flat. But how comparatively ludicrous is the multi-world theory, that infinite worlds exist covering every possible outcome that ever could have happened?'

Maybe there's a simple reason for that 2 slit diffraction pattern.

 

[Rajatmo]

Rajatmo, no I meant has anyone tried it with sand or balls just to see if there is a dispersal pattern, due to the objects glancing off the edges of the slits. Not to see if table tennis balls interfere with themselves and produce a diffraction pattern.

I don't think anyone would ever think to do it (why don't you do it yourself?) but, there are some subtle things to account for the dispersal pattern that indeed will show up. you can imagine that yourself. and, nowadays, the theory of light as EM wave is largely replaced with the probabilistic theory. so, what you must "measure" from that type of experiment is the probability of hitting some balls on a certain part of the screen. now, physically, that wholly depends on the "randomness" of the shooter machine. All in all, you can't have any satisfactory quantum analog here.

 

[Nugatory]

But how comparatively ludicrous is the multi-world theory, that infinite worlds exist covering every possible outcome that ever could have happened?

The multiple worlds interpretation is nowhere near ready to be dignified with the term "theory"; compared with (for example) the theory of gravitation, the theory of relativity, or the theory of evolution, MWI is mere speculation. It's one of those interpretations that gets a lot more attention from the popular press than from practicing physicists, because it's cool and catchy and it's easy to write interesting non-technical articles about it.

Maybe there's a simple reason for that 2 slit diffraction pattern.

There is. The quantum mechanics that predicts this behavior isn't terribly complicated, and we were happily applying very similar math to light waves for more than a century before quantum mechanics came along.

The problem isn't that quantum mechanics is hard; two years of college-level math is enough to tackle QM, and there are a lot of things that are harder than that. The problem is that some of the conclusions of QM are weird and counterintuitive, yet we have a ton of experimental evidence that says that the universe really does work in this weird way.

 

[krd]

Doesn't make sense, unless the method of measuring or recording which slit the particle goes through changes the properties of the particle.

The only way to measure the wave, is to make the wave collapse. So if you collapse it at either slit, then you don't have it progressing to wall where pattern is.

Though I wonder. Is there anything like Cherenkov radiation that could be observed without collapsing the wave?


I think considering the waves as particles, might make mathematical sense, but the idea is wrong. The wave does not collapse into a particle, it collapses into the electrons of the atom it hits. And those electrons are waves. From start to finish there is no particle.

 

[boffinwannabe]

but its not just electrons the experiment has been carried out with.

 

[swhite44]

I think KRD means the energy of the wave collapses into the electron it hits, not that the fired particle was an electron?

 

[krd]

but its not just electrons the experiment has been carried out with.

It was originally done with light. Supposedly it's been done with buckyballs. The electron one is the most interesting in that the results are unambiguously weird. The single electron is clearly shown to interfere with itself.

 

[boffinwannabe]

on the point of whether this is a problem of in-precise measurement of the electron truly is in every state at the same time till collapsed, this further demonstrates that measurement is not affecting the path, but collapsing it.
http://phys.org/news/2012-06-physicists-atom-quantum-mechanics-precision.html

 

[krd]

I'm thinking, it can be measured at each slit, without collapsing the wave.

If the slits are in a cold vacuum - a very cold vacuum. The wave or particle, as it passes through the slit - say if the walls of the slit are lined with an inductor - they might be able to register the passing "particle" without collapsing it.

Or. Instead of slits, have pieces of transparent materials in the slits - some kind of crystal - might be possible to measure the wave passing through the crystal, again without collapsing it.

I think there's a few variations you could do without collapsing the wave.

I would still say you'd see the wave pass through both slits simultaneously. The results would be interesting to look at.

If you had all the stuff for really cold nano-engineering, you could nudge a buckyball into some slits - the slits could be the legs of nano-transistors - and then zap it with a photon and see what the legs register.

 

[boffinwannabe]

dont forget its not a real wave, its a probability wave, you will never see the wave. Also there is no way to find its position without collapsing the wave, this is the whole point. No matter how clever your technique and apparatus, knowing its position no matter how you do it collapses the wave, else there would nothing to measure.

 

[krd]

dont forget its not a real wave, its a probability wave, you will never see the wave.

Well the waves look very real when you see the interference pattern.

Also there is no way to find its position without collapsing the wave, this is the whole point.

Yep, that's what I would have thought before. But now I think there could be many ways you could measure the wave without collapsing it. Polarising the electron, then letting it pass under an array of plates - an inductance pattern should (or could) emerged - without the wave collapse.

No matter how clever your technique and apparatus, knowing its position no matter how you do it collapses the wave, else there would nothing to measure.

I say...let's try all the clever techniques, and then only after we've failed can we say they didn't work.

 

[boffinwannabe]

it might look real but its a probability wave, its not a physical wave.

 

[krd]

it might look real but its a probability wave, its not a physical wave.

If you drop a pebble in a still lake - and watch the ripples. That is precisely the same process.

And before you come back and tell me I'm wrong, I want you to think about it.

 

[boffinwannabe]

well not much to think about here. One is a wave formed of molecules, the other is a probability wave that exists/doesnt exist in every possible state until the information of its precise location or speed could become available. At that point it collapses into a single state which cannot be known because its inherently uncertain. Some states being highly more probable than others depending where they are on that wave. This is why our world appears so certain, the uncertainty is so small that we can't see it, the smaller you go the larger the uncertainty.

 

[krd]

well not much to think about here. One is a wave formed of molecules, the other is a probability wave that exists/doesnt exist in every possible state until the information of its precise location or speed could become available.

Okay...and what are molecules made of?

You know, I asked you to think about this. And you didn't.

 

[boffinwannabe]

perhaps i did and you didnt think about the reply long enough because the reply wasnt the one you wanted. If you have a point to make it would be easier to just come right out and say it rather than ask me a series of questions we both know the answer to.

 

[swhite44]

Wannabe, how can simply 'knowing the position' of something change its structure?
Sounds like you accept the theory so firmly you reject experimentation to confirm or disprove it! Classic dogmatist.
What's the point of testing if the Earth is round when everybody knows it's flat?!

 

[krd]

perhaps i did and you didnt think about the reply long enough because the reply wasnt the one you wanted. If you have a point to make it would be easier to just come right out and say it rather than ask me a series of questions we both know the answer to.

No...I don't have the answer to it.

But, the ripples when you through a stone in a still pond - those waves are due to the underlying wave nature of the fundamental particles beneath. Probability distributions in themselves do not explain the wave nature.

 

[boffinwannabe]

Wannabe, how can simply 'knowing the position' of something change its structure?
Sounds like you accept the theory so firmly you reject experimentation to confirm or disprove it! Classic dogmatist.
What's the point of testing if the Earth is round when everybody knows it's flat?!

the maths describes what's going on, it doesn't tell us why, that's philosophy. I am interested in the maths and the picture of quantum mechanics that describes to us. Knowing the position does not change the structure, there is no structure. Knowing gives us a single state from every possible state.
I accept the theory in as far as its the best one we have at this point. Its the way it appears to be till disproven. At some point you have to decide what for you seems the most likely 'way it is', based on th best science available to you. So if you do not accept what most scientists today take as the most likely correct theory can i ask why and if you actually accept anything?
is not Classic dogmatist. its the science as it stands today, not quite sure why you resort to a classic defence that actually says nothing at all.
The point of testing is to substantiate what we know, to see if it stands testing, and to delve into the realms of the unknown. The point of testing to see if the Earth is flat is that you would find your theory doesn't standup to testing.

 

[boffinwannabe]

No...I don't have the answer to it.

But, the ripples when you through a stone in a still pond - those waves are due to the underlying wave nature of the fundamental particles beneath. Probability distributions in themselves do not explain the wave nature.

yes I am afraid it does. its the Schrödinger equation and feynmans every possible path.
quantum mechanics doesn't make sense but it works. How can something be in more states than one at the same time? Its beyond our logic but its the way it is.

 

[Nugatory]

But, the ripples when you throw a stone in a still pond - those waves are due to the underlying wave nature of the fundamental particles beneath.

KRD, unless and until you can show some way of using the "underlying wave nature of the fundamental particles" to predict the height and speed of these ripples from the initial displacement of the water... No one will be able to take you seriously.

Classical mechanics gives us a mathematically convincing explanation for these ripples, an explanation that allows us to calculate and predict the their size, speed, and propagation as we vary the size and weight of the stone, the density, viscosity, and surface tension of the liquid. This explanation is supported by enormous amounts of experimental evidence and convincingly contradicted by none. And this explanation has nothing to do with the "underlying wave nature of the fundamental particles" - indeed, it doesn't even have any particles in it.
You don't have to accept or agree with this existing base. But if you are not aware of it, it's going to be hard for you to either build on it or replace it with something better.

 

[swhite44]

Boffin "The point of testing is to substantiate what we know, to see if it stands testing, and to delve into the realms of the unknown. The point of testing to see if the Earth is flat is that you would find your theory doesn't standup to testing."

I thought you were saying 'there's no point testing the theory, because the theory is right'.

 

[boffinwannabe]

no i didnt say that.

 

[swhite44]

You're right, I can't find what gave me that idea, I must have misread something!

 

[krd]

Classical mechanics gives us a mathematically convincing explanation for these ripples, an explanation that allows us to calculate and predict the their size, speed, and propagation as we vary the size and weight of the stone, the density, viscosity, and surface tension of the liquid.

This explanation is supported by enormous amounts of experimental evidence and convincingly contradicted by none.

I'm not disputing any of this. But these are observations. Measuring weight, density, viscosity, and surface tension, will tell you the weight, density, viscosity. It doesn't explain these things. With more observations you'll be able to make predictions about the ripples different stones will causes. It doesn't answer the fundamental question of why the waves are happening in the first place. It's just taken too much for granted they should be happening at all.

 

[Nugatory]

...doesn't answer the fundamental question of why the waves are happening in the first place. It's just taken too much for granted they should be happening at all.

The classical explanation of water waves starts with Newton's laws, then works from them through a series of very convincing mathematical steps to conclude that water waves must happen when surface of the water is disturbed, and provides a detailed quantitative explanation of their behavior. I'm really not sure what you see as being "taken for granted" in this process; certainly no one who has actually done this, perhaps in the second year of a serious undergraduate physics program, will feel like something is being taken for granted - it is hard work.

Nor am I clear on what what could be a more "fundamental" explanation. If you're objecting to the definitions of mass, energy, force, momentum that we use in this explanation or looking for an explanation of WHY Newton's laws work, that's a fair objection. There are serious unanswered questions here; they may belong more to philosophy than physics, but they're valid questions nonetheless.

But when you say things like:

the ripples when you throw a stone in a still pond - those waves are due to the underlying wave nature of the fundamental particles beneath.

you aren't raising these questions - you're just showing that you are not completely familiar with what we already do know about ripples in water. This matters for two reasons:

1) It's near impossible to build on or improve our understanding of the world if you don't know what you're building on and improving. It's tough to have a sensible discussion of fundamental unanswered questions if you don't have a clear understanding of which questions are answered, how far those answers go, and which taken for granted premises they depend on, and exactly how that dependency works. (As a practical matter, people who have done the studying and hard work are unlikely to take your ideas seriously if you haven't - this may appear to be a form of intellectual snobbery, but in fact it's a necessary defense mechanism).

2) Understanding, really understanding, at a mathematical level, the description of the world that physics provides is one of the most rewarding, empowering, fascinating, cool, addictive, stimulating, and just plain FUN experiences in life. The difference between qualitative hand-waving and the real thing is like the difference between looking at a picture of a delicious meal and actually preparing and eating the meal.

 

[boffinwannabe]

well said!

 

[QuasiParticle]

Suppose we are shooting electrons through a double slit. Just behind the double slit we are firing photons perpendicularly to obtain information through which hole the electrons pass (electrons scatter light so we can look to see through which hole the electron travelled). Farther we have a detection screen for the electrons. One guy is looking at the scattered light at the double slit, another guy is at the detector screen. The which-hole information is not recorded anywhere but in the observer's mind. When the first guy observes the scattered light, obviously no interference pattern is observed at the screen.

What happens when we leave the detection light at the double slit on, but the guy observing it closes his eyes. Does the other guy at the screen notice a difference in the pattern of the detected electons? Can he infer by looking at the distribution of electrons whether the first guy has his eyes open or closed?

In the latter case we are not gathering information through which hole the electrons pass, but we are still disturbing the system with the photons. The inability to obtain both interference and which-path information is more fundamental than simply disturbing it with our measurement equipment. As boffinwannabe put it:

until your grasp that it is not the MEASURING that collapses the wave function but the information becoming available that collapses it you have no chance of grasping this, if you truly are trying to. It has already been mentioned that there are variations to the experiment that demonstrates that it is NOT the measuring that collapses the wave but the information that could lead to knowing which slit it went through being available that collapses it. See the Delayed choice quantum eraser.