Wave-Particle Dualism: Exploring Quantum Mechanics

[Ratzinger]

In my naive understanding of quantum mechanics I always believed that the so-called wave-particle dualism corresponds to the two co-existing processes, unitary time evolution of state vectors and measurement. Wave-like behaviour refers to time evolution of the state, particle-like when measurements are taking.

I found my view confirmed when reading two popular books, Feynman’s “QED” and Nick Herberts “Quantum physics”. Both explicitly stress that whenever we measure and do it carefully enough we get clicks and dots, particle-like behaviour. Waves, superposition, smeared-out states belong to what happens between measurements.

But after reading here diverse threads on PF my view looks not so right anymore to me. Can someone say something to this?

thanks

 

[Eye_in_the_Sky]

In the spirit of Copenhagen, you have it 100% correct!

When we talk back and forth here in the PF threads, we are sometimes somewhat idiomatic in how we say things. For example, someone might say something like:

"The particle goes through both slits."

In Copenhagean terms, this is understood to mean:

"The wavefunction propagates through both slits."

 

[kvantti]

Or, you can think that the universe itself is in a superposition of states and the particle actually goes thru both slits. This leads to the multiverse / many-worlds interpretation of QM. See Wikipedias http://en.wikipedia.org/wiki/Many-worlds_interpretation" for example.

 

[selfAdjoint]

Or, you can think that the universe itself is in a superposition of states and the particle actually goes thru both slits. This leads to the multiverse / many-worlds interpretation of QM. See Wikipedias http://en.wikipedia.org/wiki/Many-worlds_interpretation" for example.

But is the universe coherent? Won't in instantly decohere from random self-interactions?

 

[kvantti]

But is the universe coherent? Won't in instantly decohere from random self-interactions?

The "real" question is: is the multiverse coherent?

As soon as the coherent state is lost, you observe one quantum state in one universe and the other states in other universes. But the observation does not create the other universes as usually thought; they exist already side by side in a superposition before observation. This is a crucial point that usually gets missed.

Even when I observe the state of a particle, there always exists a universe where it hasn't been observed yet.

Oops, I got a little offtopic here... anyway, I'm a proponent of the MWI.