Exploring the Wave-Particle Duality: A Layman's Perspective on Slit Questions

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In summary, the double slit experiment shows that particles can act as if they are both waves and particles at the same time.
  • #1
MacNab
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My first post. I'm an interested layman.

1. There was a thread about this a few weeks ago but it didn't have an explanation that I could understand. Suppose my apparatus has a source that is not centered between the slits. Suppose I can measure the travel time for each particle from source to screen. With detectors at the slits I measure travel times of each clump on the screen and find that the travel times of each pile is different and agrees with what I expect. Now I shut off the slit detectors and start measuring travel time for each particle. Do I get interference? Can this experiment be done? Has it? Does being able to measure these times collapse the pattern because it gives me which way information?

2. Suppose I have a typical apparatus. I find that with detectors at the slits 1% of the particles get to the screen and 99% hit the barrier and are stopped. Now I shut off the slit detectors. Do I still see 1% getting to the screen? If so, does it mean that even though the particles are now ghosts, 99% of them are still banging their heads on the barrier? If they're spooky enough to go through both slits why does the barrier stop them? Does this mean that the "real" particle has to go through one of the slits and then it's ghost goes through the other one.
 
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  • #2
Does being able to measure these times collapse the pattern because it gives me which way information?

Correct.

I find that with detectors at the slits 1% of the particles get to the screen and 99% hit the barrier and are stopped. Now I shut off the slit detectors. Do I still see 1% getting to the screen? If so, does it mean that even though the particles are now ghosts, 99% of them are still banging their heads on the barrier?

That really depends on the design of detectors. The point is that active detectors interfere with the particles strongly enough to disrupt the interference pattern, otherwise they won't detect anything.

In my opinion, the double slit experiment is not the best way to approach the problem of understanding QM ... unless you understand the underlying principles, it's an almost infinite source of questions and "paradoxes" (as evidenced by this forum!)
 
  • #3
There's a discussion thread about your very proposal over here: http://bb.nightskylive.net/asterisk/viewtopic.php?f=30&t=19826

It's perhaps a bit confused though. IMO the best answer is:

The particles travel as wave packets that have a finite length. In the experiment, you can imagine one wave packet that goes through the left slit, then spreads out and hits the screen, and a similar wave packet that goes through the right slit, then spreads out and hits the screen. The two packets overlap when they spread out behind the slits, so you get interference. Now, in order to use timing to determine which wave packet you're detecting (left slit or right slit) you need to set things up so that the difference in path length is longer than the length of a wave packet, so that one wave packet finishes arriving before the other one starts arriving, and they won't overlap. But if they don't overlap you don't get interference, period. No matter what your detectors are doing, if the geometry prevents the wave packets from overlapping, they can't interfere with each other. They're like two ripples on a pond. If they overlap each other they form a complex interference pattern and you can't say which bump on the surface of the water came from which ripple. But if they pass the same point at different times nothing interesting happens.
 
  • #4
The_Duck said:
if they don't overlap you don't get interference, period.
I shall now quote page 304 of 'The Emperor's New Mind' by 'Roger Penrose' (1999 publication), he is commenting on the double slit experiment:

each individual photon behaves like a wave entirely on its own! In some sense, each particle travels through both slits at once and it interferes with itself.

It is not really that light sometimes behaves as particles and sometimes as waves. It is that each individual particle behaves in a wavelike way entirely on its own; and different alternative possibilities open to a particle can sometimes cancel one another out!

Individual particles DO act in accordance with the probabilities of interference, which is one of the key aspects of the quantum world.
 
  • #5
Yes, sorry, I wasn't clear: I meant that you can imagine the single particle splits into two probability wave packets, each of which passes through one slit and interfere with each other (so the particle is interfering with itself) behind the slit.
 
  • #6

What is the 2 slit experiment?

The 2 slit experiment is a classic physics experiment that involves shining a beam of light or electrons through two parallel slits and observing the resulting interference pattern on a screen.

What is the purpose of the 2 slit experiment?

The purpose of the 2 slit experiment is to demonstrate the wave-like properties of particles, such as light or electrons. It also helps to explain the concept of wave-particle duality.

What is the significance of the 2 slit experiment?

The 2 slit experiment has significant implications for our understanding of quantum mechanics and the fundamental nature of particles. It also has practical applications in fields such as microscopy and lithography.

What factors can affect the results of the 2 slit experiment?

The results of the 2 slit experiment can be affected by factors such as the distance between the slits, the wavelength of the particles, and the presence of any obstructions or disturbances in the path of the particles.

What are some real-world examples of the 2 slit experiment?

The 2 slit experiment has been replicated with various particles, including photons, electrons, and even molecules. It has also been used to study the behavior of light passing through narrow openings, such as in fiber optics and diffraction gratings.

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