3 ms·

With the double-slit experiment, my understanding is that if it's done in a closed room, the wave function won't collapse and you'll get an interference pattern

With the double-slit experiment, my understanding is that if it's done in a closed room, the wave function won't collapse and you'll get an interference pattern, but if you're in the room, it will collapse and there will be no interference pattern. Aren't you testing it by observing it?

kowdermeister 9y ago
I'm pretty sure that's not the case. The interference pattern only disappears if you try to figure out which slit a single photon went through. It does not require a conscious observer to be present. What matters is if you extract information from the system or not.
- david927 9y ago
  Sorry, you're right.
- kgwgk 9y ago
  > only disappears if you try to figure out > What matters is if you extract information > It does not require a conscious observer to be present. But does it require a “you” trying to figure out and extracting information?
Strilanc 9y ago
> if it's done in a closed room, the wave function won't collapse and you'll get an interference pattern, but if you're in the room, it will collapse That is absolutely 100% not what happens. The experiments play out the same way whether or not a human's face happens to be nearby. All the data is collected automatically by photographic plates or electronic counters or other instruments, and "observation" always refers to some instrument being present or not.
- david927 9y ago
  I understand now. So it's, "can the information be known?" and the answer to that question, whether instrument or human or decision (such as marking the photon), is what creates the entanglement which causes the collapse. P.S. Everyone - thanks! I get it now. And it's fascinating!
  - monktastic1 9y ago
    But the entanglement doesn't "cause collapse." If you entangle states A and B, their joint state is in a superposition and will still exhibit interference (given the right experimental setup). It's just that either particle by itself will not.
    - david927 9y ago
      oh shit. ok, I see. wow

kowdermeister 9y ago

I'm pretty sure that's not the case. The interference pattern only disappears if you try to figure out which slit a single photon went through. It does not require a conscious observer to be present. What matters is if you extract information from the system or not.

david927 9y ago
Sorry, you're right.
kgwgk 9y ago
> only disappears if you try to figure out > What matters is if you extract information > It does not require a conscious observer to be present. But does it require a “you” trying to figure out and extracting information?

Strilanc 9y ago

> if it's done in a closed room, the wave function won't collapse and you'll get an interference pattern, but if you're in the room, it will collapse That is absolutely 100% not what happens. The experiments play out the same way whether or not a human's face happens to be nearby. All the data is collected automatically by photographic plates or electronic counters or other instruments, and "observation" always refers to some instrument being present or not.

david927 9y ago
I understand now. So it's, "can the information be known?" and the answer to that question, whether instrument or human or decision (such as marking the photon), is what creates the entanglement which causes the collapse. P.S. Everyone - thanks! I get it now. And it's fascinating!
- monktastic1 9y ago
  But the entanglement doesn't "cause collapse." If you entangle states A and B, their joint state is in a superposition and will still exhibit interference (given the right experimental setup). It's just that either particle by itself will not.
  - david927 9y ago
    oh shit. ok, I see. wow