ok, double slit experiment, NO TANGENTS

[parson]

lets get to the bottom of these results

http://www.youtube.com/watch?v=DfPeprQ7oGc

[relaks]

yawn























j/k obviously fascinating.

[diss04]

yawn

[parson]

i have been accepting this stuff as given, but pk- doesn't think consciousness is whats collapsing the wave function.

what i want to know is if its not consciousness, then what is it and why do electrons behave as if they know they are being observed

[slothrop]

Basically (it's been a while since I studied quantum mechanics), iirc the 'observation' of the particle via a particle detector at one slit involves pinging things (usually photons) off it to see where it is. But when you ping a photon off something it changes it. And that change is what causes the change in the results, not whether the photon in question goes on to produce an effect that's recorded by a conscious observer.

[parson]

so they're shooting photons at the electrons to observe them?

are you sure?

[slothrop]

That's the description of a 'particle detector' that people normally use when they're describing the experiment - I don't know the precise mechanisms of the detectors that people use when they test it in practice.

But basically, to know that something's there, it has to have some effect on your detector, and having an effect on your detector means that your detector must have an effect on the thing - they have to interact with each other.

This is the root of the heisenberg uncertainty principle.

[parson]

harvard says its a camera observing, not a photon cannon
http://www.fas.harvard.edu/~scdiroff/ld ... rence.html

[parson]

these guys have electrons observing each other. i'm not sure what that means
http://www.lbl.gov/Science-Articles/Arc ... -slit.html

[slothrop]

harvard says its a camera observing, not a photon cannon
http://www.fas.harvard.edu/~scdiroff/ld ... rence.html

But a camera can only 'see' something by means of a photon hitting it and bouncing off. With a normal camera, it's only able to take pictures of houses, trees, people etc because there are a lot of photons bouncing off them from whatever your light source is.

Also, they appear to be using the camera to measure the photons hitting the back screen, not which slit the photons are passing through.

[parson]

yeah this experiment doesn't seem to be about the collapse of the wave function but rather looking at wave function behavior

[parson]

check out carbon 60 molecules behaving like waves
http://physicsworld.com/cws/article/news/2952

[dr ddd]

placeholder so i can come back and post when i have more energy and brainpower to type



ps: for now....
photon = light.... so it's pretty hard for them not to be involved... and most "observations" in physics are really measurements of the leftovers of something happening - not the physical incident itself.

[parson]

hmm physicsworld says:
Even the mere possibility of being able to know which slit the particle passes through would be enough to wipe out the interference pattern

but harvard says:
However, we take the experiment one step further and show that even when the light intensity is reduced down to several photons/sec, the audience can see the familiar Young's double-slit interference pattern build up over a period of time as the arrival and position of each photon is stored on an electronic screen. This addresses the question (and dilemma) of how can single photons interfere with photons that have already gone through the apparatus in the past, or with those that will go through in the future, or with themselves. Finally, the slit arrangement is such that it is possible to know which of the two slits the photons are passing through. In that case the Young's double-slit interference pattern does not manifest itself.

[misk]

i love Dr. Quantum

also - the fact that you need to perceive photons bouncing off something in order to perceive the thing in this physical reality does make it a little hard to observe electrons. What interests me more is the fact that the electrons were everywhere, and nowhere, at the same time. The idea that there is a probability cloud that forms matter and outcomes based on the perceptions and decisions of observers and external participation is very interesting.

I would be interested to know, if humans (sentient beings) have the ability to shape the outcome of this probability cloud with their perceptions, could animals as well?

I know cats could

[parson]

photons bouncing off electrons just doesn't jive with action at a distance

http://en.wikipedia.org/wiki/Action_at_ ... _(physics)

[masstronaut]

But basically, to know that something's there, it has to have some effect on your detector, and having an effect on your detector means that your detector must have an effect on the thing - they have to interact with each other.

Well check this out.

This experiment uses entangled pairs of photons to carry out the measurements, so there is no direct physical interaction on the photons that go through the slits, at least not one that anyone can account for at present. This still produces the expected particle-like behaviour.

OK, you might say that messing with an entangled partner has an effect on the photon. However, when the experiment is changed so that the observation is still carried out but the ability to extract information from it is 'erased' - the interference pattern returns.

http://en.wikipedia.org/wiki/Quantum_eraser_experiment

[jahtao]

Parson I cannot believe you couldn't write a simple biog - you are one effusive mo fo

[masstronaut]

NO TANGENTS.

Have you any idea how hard it was for me to avoid making 'double slit experiment' gags?

[parson]

when the experiment is changed so that the observation is still carried out but the ability to extract information from it is 'erased' - the interference pattern returns.

http://en.wikipedia.org/wiki/Quantum_eraser_experiment

this here