Re: Can two matter waves interfere

Good thinking -- turns out you're exactly right; matter waves can interfere just like light waves.

Experimentally, it's harder to get this to work for matter, because you have to get all of the waves to be coherent -- but they're learning how to do this; it's called an atom laser. (Don't let the name fool you; there's no light in an atom laser; just atoms that *behave* in ways similar to a laser.)

But even before they were able to make atom lasers, it was known that interference happens for matter as well as for light. For example, if you send a particle through a double slit, it hits a screen on the far side in certain particular locations. If you do this many times, an interference pattern gradually develops on the screen; similar to the interference pattern that would be formed by a wave passing through the double-slit. Most people believe that this implies a particle can interfere with itself! You can watch actual experimental results in this movie.

I'm not sure what you mean by the last part of your question, but it turns out that even though particles can interfere like a wave, they are still always observed as a single particle when you "look" to see where they are. This strange state of affairs is sometimes given the name "wave- particle duality"; I'm not sure anyone really understands why this is the way the universe works, but there must be a good reason for it. Maybe someday we'll figure it out!