Brett: We have to come to a deeper understanding of what is going on in this double-slit experiment. If we fire either a photon or an electron at that double-slit apparatus and put a detector at either of those slits, then we will detect a particle.
We can detect that we’ve fired a particle; we can detect that a particle is going through those slits; and we can detect a particle at the projection screen as well.
When you do this experiment in the laboratory using electrons, you can see the dots where the electrons strike, hitting the screen. But you don’t get a simple pattern that you would expect.
If you’re firing cannonballs at a wall through the same two holes, you would expect all the cannonballs to land in one of two positions behind the wall.
But with particles at the quantum level, that’s not what happens.
The only explanation is that when we fire a photon, there’s the photon that we can see in our universe and also there are photons we can’t see in other universes that pass through the apparatus. These photons are able to interact with the photon that we can detect.
This is where the concept of interference comes in. Interference is an old concept in physics. It goes back to waves. Waves certainly interfere, but we need to understand the way in which particles can interfere with one another. This includes particles that we can observe and particles that we can only assume to observe given these experiments.
This is why we are forced to acknowledge the existence of these other particles—and not only these other particles but other universes in which these particles exist.