I have read lots of quantum mechanics books.
The chapters that are talking about De Broglie, lots of them name the chapter as "Wave-particle duality" and says: "Electrons are both waves and particles". So I start to think that (for example) an electron sometimes becomes wave sometimes becomes particle.
But when I start to read the chapters about Schrödinger and wavefunction thing. I see that that wave nature thing does not belong to electron itself. It is about its location. So there is no wave particle duality. Electron is always a particle. But the location of electron is represented as wave, because of uncertainty principle. So electron can't interfere with itself because it is always a particle. The interference is about its location function.
1-) Are these all true?
2-) If true, if an electron is always a particle, in double slit experiment how does an electron interfere with itself without observer, but there is no interference pattern with observer?
Best Answer
Saying that things "are both waves and particles" is a vestige of the 18th century way of thinking, and really ought to be done away with. Everything is described by a wavefunction. Period.
What is a wavefunction? It is a complex-valued function. If you are interested in an electron's position, it is easy to think of it as a complex-valued function of space. It alone is not a probability. Only its square magnitude gives a probability distribution. This process of taking the square magnitude explains how interference occurs. Just like with classical waves, two out-of-(complex-)phase wavefunctions can add destructively, such that taking the square magnitude after adding them results in a value close to $0$.
When people say things are both waves and particles, they mean that in some limits the object acts indistinguishably close to that of a classical particle. But these are just simplifications in certain cases; they have no bearing on the fundamental nature of the objects in question.