The Double Slit experiment is a famous example of how we don't understand how reality works.

Here's a brief explination of what the Double Slit experiment is about, based on my understanding, largely influenced by What the BLEEP Do We Know?, which does a much better job than I ever could at making this clear. ^-^

Anyway, on to the explination.

Step 1: Why are there two slits?

The two slits are used to determine whether an object is travelling as matter or as a wave.

It's quite simple, really. If you were to fire a lot of small matter - say, paint balls - at two narrow slits in a heavy screen, they would form two lines on a wall behind the screen, because the paint balls - and matter - travel in straight lines.

All you really need to know: Matter makes two lines.

Waves of energy, however, travel in curved lines. They also interfer with each other, making the waves stronger or weaker at certain points. When they travel through the same two slits as the paint balls, they make a pattern of fuzzy lines, best seen here.

All you really need to know: Waves make interference patterns.

Step 2: What are we testing?

The double slit was originally used to test whether light behaved as matter (making two lines) or waves (making an interference pattern). The result was waves. Electrons behave in the same way.

All you really need to know: Electrons make interference patterns. For now, at least...

This is strange, especially if you took High School Physics, which describe Electrons as small pieces of matter. The scientists were kinda confused, too, especially since they could isolate a SINGLE electron, as though it were matter.

From here, it gets clever.

Step 3: What if you change part of the experiment?

As said, it's possible to isolate single electrons. So, experiments were performed firing single electrons at the double slit, assuming the many fast-moving electrons were bouncing off of each other in some way to cause the interference pattern.

This didn't change the results.

All you need to know: Single electrons make interference patterns.

This is the equivilant of firing one paint ball at a slit a bit bigger than the ball, and getting two lines. VERY freaky.

They only theory was that this ONE electron was interferring with ITSELF, the Copenhagen Interpretation.

Step 4: Can we prove the interferring electron theory?

No, because trying to changes the results.

No, that's not a mistake.

Detectors were placed at each slit. This way, the scientists could record which slit each individual electron entered. If the electron was interferring with itself, it's possible it was travelling through BOTH slits at the same time, and the detectors would catch it in the act.

All you need to know: When the detectors are on, a single electron makes two lines.

Nothing else of the experiment was changed.

As I understand the interpretations of this:

Quantuum mechanics suggests the electrons are actually travelling through every possible path, at once, and therefore able to interfer with itself

Human beings, however, cannot comprehend all the possible probabilities. When we impose our reality on the electron, it is forced to follow only one path - a probability we can understand - and begins to behave as we expect of it.

Thoughts? Ideas? Other interpretations?

come again?

All i really understood was that one electron triggers two detectors in two different phsyical locations (i assume the slits were next to each other or something) which is silly, i dont doubt what you are saying but its just weird. i mean its not possible for anything in this universe to do that (surely?) the only explaination would be that electrons are not only part of this world. but maybe another.

also i like the fact that scientists shoot themselves in the feet, as touched on, light consists of small pecies, i belive they are photons but your post says electrons tho i was lead to belive they were the negatively charged parts of an atom? And photons were still similar in that they were small peices of matter which we cant see but that is what light is. Yet according to scicne light is energy, but if photons (or electrons) make up light then light is matter and cannot be energy. unless energy is matter or matter is energy and then theres a whole bucket load of questions such as "doesnt that mean im made of energy", "the whole world is energy?", "if light is matter why cant i touch it?" etc...

it baffles me as you can probably tell!

leads me to belive my matrix like theory of the universe even more, aling with pea sized balls of matter with almost infinate gravity (black holes) and the like. Space and the world is a strange place indeed

Alright to simplify his explanation, the double slit experiment was used to show how light can cause either destructive or constructive interference based on the wavelengths. What it does is the slits are very small thus only allowing one photon through at a time. These slits act as a point source then. So where the wavelengths are shifted so that the total is 0 you get a dark spot, where they are 1 you get a bright spot and in between you get shadings. This was the main purpose of the double slit.

I've seen a documentary about this and this is what really happened.

These guys fired electrons into double slits and were surprised to see that they got interference patterns. Working on the hypothesis that the stream of electrons interfered with one another, they modified it so that they fire only one electron at a time, at regular intervals.

At first, single electrons showed up as infinitesimal dots on the screen, not (as earlier mentioned, two lines or interference bands). However, as time passed by and as these singular dots increased in number, the screen displayed points comprising bands of varying density, quite similar to the varying intensity of light in interference patterns.

In other words, while light has been regarded as both a particle and a wave, could it not be that light is actually a particle and that its wave-like properties (interference bands, fringes, refraction and diffraction) are just the cumulative effects of a regular stream of particles? This, however, raises the question, "Why can't a particle fired into a surface follow the same path as the one that preceded it?" Aren't particles fired on the same spot, at the same initial speed and velocity supposed to match in all their end velocities?

That leads to the Coppenhagen Interpretation, as mentioned above. We may, after all, not live in Newton's deterministic model of the universe but actually exist in a probabilistic universe.

Very disturbing isn't it?

I remember studying this in one of my Physics classes when I was studying my last year of physics. It was advanced stuff and I never did understand it all. I found this double slit stuff quite confusing.

After reading this topic, I understand the double slit experiment a lot more than I did when my teacher was trying to teach it to me.

This really is an interesting topic. Being able to see dots or lines on the wall (showing how matter or a wave is moving) is clever and strange in a way I guess.

Anyway, thanks for sharing, I found it interesting going back to double slits, one of the physics topics I didn't quite understand fully. I just wish this thread was online when I was doing my physics, it would certainly have helped.

Ah well, I guess it's still able to help some of the other users of this website who still do study physics.

This is probably one of the biggest proofs of Quantum Mechanics.

I took a look at the bottom of the wikipedia page This image
Really helped me understand it alot, and it make alot of sense, really.....
The areas that are brightest, are the ones that are hit by two beams of light, so, the magnitude is increased... Or am I still not getting this?
This would fit in even with water, electrons, or about anything else they mentioned I guess, since if you are still funnelling two sources into an area they'll still increase each other...