2 slit experiment again

1. Jun 10, 2012

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?

2. Jun 10, 2012

San K

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

3. Jun 10, 2012

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.

4. Jun 10, 2012

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

5. Jun 10, 2012

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?

6. Jun 10, 2012

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' :)

7. Jun 10, 2012

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.

8. Jun 10, 2012

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.

9. Jun 10, 2012

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?

10. Jun 10, 2012

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.

11. Jun 10, 2012

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'.

12. Jun 10, 2012

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.

13. Jun 10, 2012

boffinwannabe

or may its like saying i dont understand what your saying so you must be wrong and i cant believe how poor your answer was. or maybe its just like being a troll?

14. Jun 10, 2012

boffinwannabe

of course you could just do the maths?

15. Jun 10, 2012

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?

16. Jun 10, 2012

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.

17. Jun 10, 2012

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.

18. Jun 10, 2012

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.

19. Jun 10, 2012

Staff: Mentor

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.

20. Jun 10, 2012

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.