Does a camera count as an observer which causes wave function collapse?

[Artander]

?

[Strange]

Yes.

[Bill Angel]

Consider the famous thought experiment referred to as Schrodinger's Cat. Suppose a camera is placed inside the box with the cat. Then the total quantum wavefunction inside the box is the wavefunction of the cat and the other stuff in the box that is normally included in the thought experiment PLUS the wavefunction of the camera. This total wavefunction does not collapse, pinning down the determination of whether the cat is alive or dead, until an observer opens the box and looks inside. Until that moment there are only probabilities concerning the expected state of the cat (alive or dead) AND what images are on the camera's film, assuming that the camera is recording one image every second while the box is closed.

[elfmotat]

An observer in QM is really pretty much anything that interacts with the system you're trying to study. A camera constitutes an observer because many many photons must interact with it to form an image.

[hoola]

it doesn't seem logical that the camera would have any extra effect on the wavefunction, after all the photons must interact with the box interior, and so light couldn't "know" any difference. It seems just a sensible to list the box as an "observer"...and if the box were closed, no light could enter the camera anyway...of course an infrared camera could pick up the heat and tell if the cat was alive or not...still, the cats heat would interact with the box interior, as it is light anyway.

[Delta1212]

it doesn't seem logical that the camera would have any extra effect on the wavefunction, after all the photons must interact with the box interior, and so light couldn't "know" any difference. It seems just a sensible to list the box as an "observer"...and if the box were closed, no light could enter the camera anyway...of course an infrared camera could pick up the heat and tell if the cat was alive or not...still, the cats heat would interact with the box interior, as it is light anyway.

Pretty much. The thought experiment really only "works" if you treat the entire interior of the box as being in a superposition, rather than just the cat, and the interior needs to be completely isolated from the rest of the universe in a way that isn't physically possible for any box that could actually be made.

[Strange]

Do we need to remind people that it wasn't a real experiment?

[MigL]

Superposition of states is a valid concept ONLY at the quantum level. It is only at that level that a particle can have many equal probabilities or states. As the macroscopic level is approached, all the differing probabilities geld into a single state with a probability of one.

You certainly don't get a diffraction bullet 'hole' when you fire a gun through a slit.

 

Oh, and as others have mentioned, Shroedinger's 'cat in the box' was meant to demonstrate how incongruent quantum ideas and phenomena are with 'common sense'.

[imatfaal]

Superposition of states is a valid concept ONLY at the quantum level. It is only at that level that a particle can have many equal probabilities or states. As the macroscopic level is approached, all the differing probabilities geld into a single state with a probability of one.

You certainly don't get a diffraction bullet 'hole' when you fire a gun through a slit.

 

Oh, and as others have mentioned, Shroedinger's 'cat in the box' was meant to demonstrate how incongruent quantum ideas and phenomena are with 'common sense'.

 

I don't think superpositions have to be equal probabilities - merely that the sum of the square of the amplitudes must equals one.

 

And there is nothing magically quantum about particles that does not apply to macroscopic objects - it is just that the quantum effects get washed out by classical effects. The debroglie wavelength of a machine gun slug is ridiculously small and unworkable - but smaller but still macroscopic objects will display interference through two slits if the gap is narrow enough. A 50nanometre diffraction grating will produce an interference when c60 molecules are fired at it - the same grating will not demonstrate a pattern when c70 molecules are fired at a similar speed

[MigL]

Absolutely right, equal should not have been there. I meant to say equally valid probabilities, not equal probabilities.

 

As the deBroglie wavelength becomes infinitesimal as macroscopic levels are approached, so do all the other probabilities, in effect leaving only the one. And although your molecule through a diffraction grating is a nice example, I prefer another...

A particle with only half the energy of a separating potential wall has a non-trivial, or even large, probability of being on the other side of the separating potential ( tunneling ).

If I build a 15 ft high wall around you, however, the probability of you being outside is soooo trivial as to effectively be zero.