WTF? Lesson in Particle Duality Theory

Nitrofox125 · Post by **Nitrofox125** » Thu Apr 29, 2004 7:43 pm

This was in the book Timeline, and it looked like an interesting experiment. I tried it, not attempting to find anything. However, this is awesome.

OK, so you have the following: Two walls, and a light source outside of them.

Like so: * | |

So, cut a slit in the first wall so the light can shine through it.

Code: Select all

   |   |
*      |
   |   |

How many bars will show up on the far wall? 1, right?

OK, well repeat the experiment, this time with two slits. One would expect two bars to show up on the opposite wall. But no, there are more than two. The book says 6 or 8. How is this explained? Well, if light acts as a wave, the light waves create nodes and antinodes (places where the wave crests cancel each other out, and places where they combine, respectively) that show up on the back wall. I thought, yeah right, this wouldn't work. However, I set it up with legos, and found this:

www.arasian.com/pics/quantum.jpg [500k]

DCrazy · Post by **DCrazy** » Thu Apr 29, 2004 7:56 pm

Can we get a better pic of this? I've heard of the experiment but I can't see what you're doing from the pic you provide.

Nitrofox125 · Post by **Nitrofox125** » Thu Apr 29, 2004 8:09 pm

I put the same pic smaller up there so maybe it'll be a little easier to see the whole thing. I don't have any better pics right now though, mebbe I could take some later.

Plague · Post by **Plague** » Thu Apr 29, 2004 8:25 pm

I did that same experiment in physics this year. The book used a comb with all but 2 spaces and one tooth covered with electric tape. Worked pretty well. Pretty awesome stuff.

Nitrofox125 · Post by **Nitrofox125** » Thu Apr 29, 2004 8:32 pm

Yeah I just talked to a few people that said they did this in their physics classes... apparently we're going to do this experiment in like a week in my physics class... heh oh well

Iceman · Post by **Iceman** » Thu Apr 29, 2004 9:02 pm

Man isn't being a Geek great

!!!

Nitrofox125 · Post by **Nitrofox125** » Thu Apr 29, 2004 9:04 pm

Oh yeah! I feel so.... enlightened

Lothar · Post by **Lothar** » Thu Apr 29, 2004 9:14 pm

Those bars look far too wide to have come from a double-slit experiment...

But yes, it's a cool experiment.

roid · Post by **roid** » Thu Apr 29, 2004 10:20 pm

i feel like such a geek, i knew about particle/wave duality physics when i was only 10years old*

mmm i LOOOOOVED my science encyclopedias ^_^, used to spend hours and hours with the books strewn across my bed.

*however i don't think my understanding of it has grown much since then

.

GEEKS UNITE I AM YOUR LEADAH!

Jagger · Post by **Jagger** » Thu Apr 29, 2004 11:54 pm

Funny how it's such a simple experiment, yet it can't be explained.

Mobius · Post by **Mobius** » Fri Apr 30, 2004 12:01 am

Yes, it can be explained. The photons KNOW when to behave like a wave form, and when to act like a particle. It's just a feature of the Universe.

But yeah, this is a great experiment.

Wasn't it Hiesenberg who first conducted it?

roid · Post by **roid** » Fri Apr 30, 2004 12:02 am

so, is this effect the cause of the visual "feathering" that happens near the hard edge of an object when you are looking past it?

ie: it appears that the edge is somewhat translucent, and perhaps the light is BENDING around it. i always thought it was because the edge of the object was thin enough for some light photons to go through it, and since it's more dense than the surrounding air, it would bend the light. uuuuuuuurgh damnit i just can't remember the name of this princible, but the most ocmmon example of it is when light hits the surface of water and changes angle.
am i making sense?

roid · Post by **roid** » Fri Apr 30, 2004 12:14 am

could be mobi. google comes up with a lot of links with it.

this is the first one i saw, has a diagram. you definetely need diagrams

http://www.art-themagazine.com/ian/nonl ... /slit.html

Jagger · Post by **Jagger** » Fri Apr 30, 2004 12:51 am

Mobius wrote:Yes, it can be explained. The photons KNOW when to behave like a wave form, and when to act like a particle.

But HOW? How they 'decide' that is infinitely more interesting in my opinion than the mere fact that they 'can'.

A fascinating experiment, I say. One that has kept me awake at night pondering quite often.

Jagori · Post by **Jagori** » Fri Apr 30, 2004 1:05 am

roid wrote:so, is this effect the cause of the visual "feathering" that happens near the hard edge of an object when you are looking past it?

ie: it appears that the edge is somewhat translucent, and perhaps the light is BENDING around it. i always thought it was because the edge of the object was thin enough for some light photons to go through it, and since it's more dense than the surrounding air, it would bend the light. uuuuuuuurgh damnit i just can't remember the name of this princible, but the most ocmmon example of it is when light hits the surface of water and changes angle.
am i making sense?

Light bending around an object is called diffraction. It happens mainly to waves that pass through an opening of a width within a couple orders of magnitude of the wavelength. All waves do it - if you make waves in water, they'll do the same thing. It also happens around the edges of objects, causing the 'feathering' you were talking about, and also causing the 'fuzziness' of shadows when the object casting the shadow is far from the surface where the shadow is.

Light bending as it hits the surface of water is refraction. It's a totally different phenomenon than diffraction, and only occurs when light hits a boundary between two transparent materials of different optical densities.

roid · Post by **roid** » Fri Apr 30, 2004 6:34 am

thx. wow, it seems as a kid, i was pretty close.

good visual explanation of the differences.

still, from what i'm seeing, it seems diffraction could be explained as just a complex series of refractions.
o_O urg it's been so long, prisms, blah!... time to read

DescentJS · Post by **DescentJS** » Fri Apr 30, 2004 2:59 pm

roid wrote:i feel like such a geek, i knew about particle/wave duality physics when i was only 10years old*

mmm i LOOOOOVED my science encyclopedias ^_^, used to spend hours and hours with the books strewn across my bed.

Me too, man, me too.

DescentJS · Post by **DescentJS** » Fri Apr 30, 2004 3:01 pm

Actually, this same thing happens (although it is much harder to detect) when the holes are very small and only one photon is released at a time.

Nitrofox125 · Post by **Nitrofox125** » Fri Apr 30, 2004 3:42 pm

Also explained in Timeline, yeah. And you'll notice that the photons don't hit at the same place at the same time any time you shoot one photon. It even does this in a complete vacuum, so something has to be interacting with these photons that we can't see, or maybe isn't even "there" (quantum physics)

Krom · Post by **Krom** » Fri Apr 30, 2004 3:58 pm

The argument in the single photon case is that the photon is reacting to photons that are not in this universe but a parallel one.

Yeah, I read that book too.

Palzon · Post by **Palzon** » Fri Apr 30, 2004 4:42 pm

It can't be explained without Quantum mechanics and some string theory helps.

MD-2389 · Post by **MD-2389** » Fri Apr 30, 2004 6:14 pm

Palzon wrote:It can't be explained without Quantum mechanics and some string theory helps.

Shh! You'll get Tricord in here!

Palzon · Post by **Palzon** » Fri Apr 30, 2004 7:41 pm

btw, it was the English physicist Thomas Young (1773 - 1829) who first performed the double slit experiment.

Gooberman · Post by **Gooberman** » Fri Apr 30, 2004 8:32 pm

The photon doesn't decide anything. Withen its wave equation it has a probability of being found at certain locations given the potentials that are effecting it. Some probabilities are greater then others. I had to solve this problem in one of my classes.

And Palzon is right, it was Young that first did it. It was einstein, shrodinger, and several others that finally explained it.

bash · Post by **bash** » Fri Apr 30, 2004 8:52 pm

Bohring!

Phoenix Red · Post by **Phoenix Red** » Sat May 01, 2004 11:09 am

well, the way my physics teacher said made the most sense to him (disclaimer, this is a weird man's stab in the dark, and even if it was on the right track it would be horribly oversimplified) is that light's wavelength, being one-dimensional, has a small cross-section and thus the wave part of it's nature is only affected when it comes VERY close to something.

In other words, light's wave nature is so tiny that everything else in the universe might as well not exist as far as affecting it goes unless it happens to be rediculously near, so only the particle nature is directly affected by most things.

This makes sense with the doubleslit experiment because it's acutally other light that causes the nodes and antinodes you see, which also being one dimensional actually can come close enough to distort it. The difraction makes a bit less sense, and in oder to explain it I would need props, which is hard to do through this medium