A quantum physics question

[Alex Franke]

Okay, I know there are a number of physicists out there, so this is for you -- or for anyone else crazy enough to know this. I'm finding myself troubled by physics again...

I get the whole double-slit experiment, and the seemingly illogical interference you get when you shoot a single photon with both slits open. What I don't get, though, is this: How on Earth can someone isolate a single photon -- an elementary particle with (as I understand it) zero mass -- and "shoot it" with any degree of accuracy at some manufactured experimental apparatus that is clearly at a vastly different scale?

And how can a man-made "half-silvered mirror" possibly be anywhere near accurate enough to conduct repeatable experiments at a subatomic level?

The differences in scale make it seems totally unreasonable -- not unlike trying to machine a super miniature toothpick using a full size cabinet saw -- or driving a finish nail with a shotgun.

Anyone?

Sorry to go physics again. But when I thought, "Where could I go to ask a questions about quantum physics experiments?" the first thing that poped into my head was "BT3Central!" After all, it's not just about the saw

[crokett]

It is possible to drive a finish nail with a shotgun. They make slugs for shotguns. Now the non-smart@ss answer is, shoot enough pellets at the nail and eventually you will get enough hits to drive the nail. Of course by then the stock you are shooting into will have disintegrated.

[Tom Slick]

I just got rid of my physics book that had the real explanation but I think the answer is along the lines crokett eluded to.

you are shooting so many photons that even just a small percentage is still enough to make the experiment work. you are not choosing which photon will behave, you are choosing which billion of photons you are going to throw at it and a few of those are going to have their wavelength orientated just right.

[gsmittle]

I'm not a physicist, nor do I play one on TV, but I did see a production of The Physicists once.

My understanding is that this is more of a thought experiment than the real deal. I'm probably way off base, but that's what I recall from reading pop physics...

g.

[JR]

I don't know abou that experiment in particular, but in general those experiments are done with with loads of the particles in question (as has already been mentioned) being shot through highly focused magnets. The particle streams are therefore highly focused and going nearly the speed of light.

JR

[leehljp]

I think that would be easier to explain than the differences in the rudimentary physics aspects of primary colors of light (RGB) versus the primary colors of pigment (CMYK).

[Alex Franke]

I dunno -- I'm pretty sure they quite literally shoot a single photon at the apparatus. Otherwise they wouldn't be proving quantum superposition -- if there are >1 photons, then you'd expect them to interfere with each other. But if it's only one photon, you don't expect it to interfere with itself, and that's what makes it so baffling.

Although I can see an approach using crokett's shotgun (or was it my shotgun?) If you can control the number of pellets in the shell and take aim at a plate of steel with a small hole in the middle, then eventually you'd get just a single pellet through the hole... I wonder if that's the approach they use...

I think that would be easier to explain than the differences in the rudimentary physics aspects of primary colors of light (RGB) versus the primary colors of pigment (CMYK).

Now that's just crazy-talk, leehljp!

[MilDoc]

Try this explanation:

http://en.wikipedia.org/wiki/Double-slit_experiment

or for a nice explanation with active illustrations:

http://www.colorado.edu/physics/2000...two-slit2.html

[crokett]

I wasn't answering the question regarding the photons, I have no idea how they do that. I was just explaining how you can drive a finish nail with a shotgun.

[Alex Franke]

I wasn't answering the question regarding the photons, I have no idea how they do that. I was just explaining how you can drive a finish nail with a shotgun.

See, little did you know that your clever woodworking tips and tricks could help solve the great unanswered questions of the universe!