Double slit experiment

1. Mar 19, 2014

us40

In double slit experiments detection of individual electron has very massive effect on the result. Now suppose in dark room we perform double slit experiments with two observers (who cannot communicate with each other). Now those two observers have eyesight that can see individual electron in the path from source to destination.There is random chance associated with each individual electron say in which slit it will pass. According to Copenhagen interpretation if we do not observe from which slit electron will pass then we get interference pattern otherwise standard particle pattern. Now suppose both observers see each individual electron from the source up to point A.From point A electron can take any path from two slits.
Now user 1 decided not to see electron’s path and direct see on detector screen and user 2 decides to see in which slit electron pass? What will user 1 see??Why??

2. Mar 19, 2014

ZapperZ

Staff Emeritus
This is very difficult to follow. Please seriously consider providing a drawing of your idea here. It can replace a thousand words of what you are trying to describe here.

In the ends, it really doesn't matter who saw what. If there is the possibility of knowing which electron went through which slit, then the superposition of path is gone. The setup doesn't care who viewed what or when. All it cared about is there something observed its path. That is enough.

You may want to read up on the delayed-choice experiments that have been performed numerous times.

Zz.

3. Mar 19, 2014

us40

Now we make same setup with baseball balls and perform this experiment in closed room with no human present or no detector present for knowing information regarding which-path. Now in your words setup doesn't care who viewed or when.All it cared about is there something observed its path.That is enough , then the superposition of path is gone. In this setup (baseball balls instead of electrons) what is that "something" which force each time generate particle like properties on detector screen( means not interference). Please reply...

4. Mar 19, 2014

dauto

The effect the observer has on the double slit experiment has nothing to do with whether the observers decide to open theirs eyes and see the electron going through the slits. What really matter is whether or not you turn the light on in order to see the electrons. In your example, observer 2 decides to see which slit the electron goes through. In order to do that (s)he must turn on the light destroying the interference pattern. That's what both observers will see.

Last edited: Mar 19, 2014
5. Mar 19, 2014

dauto

But there is an interference pattern in the baseball experiment you describe (Putting aside the practical matter that the requirement of keeping the baseball from interacting with anything is technically impossible to meet) . But that pattern is too fine to be observed experimentally.

6. Mar 19, 2014

sophiecentaur

We're in the same region as Schrodinger's Cat, here. If the result of the experiment is not 'observed' (by that, I mean that there is nothing in the way of any emerging electron or photon or baseball) then, within limits, I think you can say that the result is 'all possible results'.
But QM results are really restricted to Quantum Particles.

7. Mar 19, 2014

dauto

All particles are quantum

8. Mar 19, 2014

sophiecentaur

A baseball is not a particle.

9. Mar 19, 2014

us40

If you are talking about here p=h/mv (de broglie equation) then it talks about mass of particle.
Now suppose somehow single electron gains mass of one baseball ball then what do you think it passes from either of the slit when unobserved due to its mass( classical way) or generate interference pattern like quantum way) because of its size??? Please reply.....

Last edited: Mar 19, 2014
10. Mar 19, 2014

Staff: Mentor

The baseball is made up of a very large number of particles, all interacting with each other and the material of the screen with the double slits - and in quantum mechanics, every one of these interactions counts as an observation. A (necessarily approximate) solution of the wave equation for this system gives you essentially zero probability for every one one of these particles "passing through both slits" without interaction to produce an interference pattern. The only outcomes with any discernible probability of happening are: the ball bounces off the screen; the ball goes through one slit; the ball goes through the other slit.

Last edited: Mar 19, 2014
11. Mar 19, 2014

dauto

The solution is ALWAYS quantum but the quantum solution coincides with the classical solution when talking about real baseballs because, as Nugatory pointed out, real baseballs are always interacting which destroys the interference pattern producing a result identical to the classical result.

But that's not what you asked. You said "no detector present for knowing information regarding which-path". That means you are talking about some idealized experimental set up impossible to realize in the real world in which the baseballs don't interact.

For that idealized setup, the baseballs produce an interference pattern (going through both slits) but the pattern is too fine to be observable (peaks and valleys in the pattern are too close together).

12. Mar 19, 2014

dauto

Sure it is. Everything is quantum my friend.

13. Mar 19, 2014

sophiecentaur

A baseball is a large collection of particles. That implies such a vast number of eigenstates (a continuum, in fact) that it cannot be considered in the same way as a single particle. It is stretching the ideas of QM far too much to imagine Quantum behaviour. (In practice, definitely and even in principle, I think)

14. Mar 19, 2014

Jilang

To make the distinction between quantum/not quantum I find it helps to consider the odds of any process spontaneously reversing itself. The larger the system/number of interactions, the less likely it becomes. Like a diffusion process. It is all quantum to degree, but the chances of displaying such behaviour become very small quite quickly as the size increases.

15. Mar 19, 2014

sophiecentaur

Yes, that's one way.yaw eno s'taht , seY

16. Mar 20, 2014

us40

So that's the solution of what is going inside the black hole. Because inside black hole we need both theory of quantum mechanics (because of size) and general relativity(because of mass) need together. So as you say when this kind of situation (when single electron gains mass of a baseball) then solution is ALWAYS quantum. Then we get the solution of quantum gravity. Don't you think so??? And what happen when we pass black hole in double slit experiments??? What will be final result with experiment of "passing single black hole at a time in double slit experiment" ??? Plz plz reply......

17. Mar 20, 2014

ZapperZ

Staff Emeritus
This has gone seriously off-topic from your original question, and it also has veered into highly speculative area. Why are we now invoking things INSIDE a blackhole?

If this doesn't get back on topic, this thread will be closed.

Zz.

18. Mar 20, 2014

us40

From starting of this thread my goal is to make some analogy between strange result of double slit experiments and this highly speculative area . I want to gradually direct path of this whole conversation into this way. But if you think this aint worthy here I think I will start new thread branching from here .... Thanks anyway.

19. Mar 20, 2014

ZapperZ

Staff Emeritus
Please note our rules on speculative posts. Read that carefully before you land in hot water.

Zz.

20. Jan 28, 2016

sophiecentaur

This OP starts off on the wrong foot and we should have spotted it for what it is.
The traditional "double Slit" experiment is based on light. I am not aware of an equivalent experiment with electrons. Of course, electrons will diffract but the scale of suitable structures makes it much easier to use electron diffraction through a lattice of atoms. If the OP was really about human observers, 'seeing' particles, then the obvious particles to choose would be photons. Also, this has all been done before and there are no paradoxes or magic involved.
It's hardly surprising that the thread has tried to take us into philosophy, paraphysics and beyond.
Do the decent thing, ZZ and bring out the horse pistol please.