2 of 2. Quantum Physics for Dummies

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Water Experiment

While the result was different from the bullets, there is still nothing unusual about it; everyone has seen this effect when the waves from two stones that are dropped into a lake in different places overlap. The difference between this experiment and the previous one is easily explained by saying that while the bullets each went through only one slit, the waves each went through both slits and were thus able to interfere with themselves.

Now try the experiment with electrons. Recall that electrons are negatively charged particles that make up the outer layers of the atom. Certainly they could only go through one slit at a time, so their pattern should look like that of the bullets, right? Let's find out. (NOTE: to actually perform this exact experiment would take detectors more advanced then any on earth at this time. However, the experiments have been done with neutron beams 9 and the results were the same as those presented here. A slightly different experiment was done to show that electrons would behave the same way 10. For reasons of familiarity, we speak of electrons here instead of neutrons.) Place an electron gun at the originating point and an electron detector in the detector place. First try opening only one slit, then just the other. The results are just like those of the bullets and the waves. Now open both slits. The result is just like the waves!11

Electron Experiment

There must be some explanation. After all, an electron couldn't go through both slits. Instead of a continuous stream of electrons, let's turn the electron gun down so that at any one time only one electron is in the experiment. Now the electrons won't be able to cause trouble since there is no one else to interfere with. The result should now look like the bullets. But it doesn't! 12 It would seem that the electrons do go through both slits.

This is indeed a strange occurrence; we should watch them ourselves to make sure that this is indeed what is happening. So, we put a light behind the wall so that we can see a flash from the slit that the electron went through, or a flash from both slits if it went through both. Try the experiment again. As each electron passes through, there is a flash in only one of the two slits. So they do only go through one slit! But something else has happened too: the result now looks like the result of the bullets experiment!! 13

Electron Experiment with Light

Obviously the light is causing problems. Perhaps if we turned down the intensity of the light, we would be able to see them without disturbing them. When we try this, we notice first that the flashes we see are the same size. Also, some electrons now get by without being detected. 14 This is because light is not continuous but made up of particles called photons. Turning down the intensity only lowers the number of photons given out by the light source.15 The particles that flash in one slit or the other behave like the bullets, while those that go undetected behave like waves16.

Well, we are not about to be outsmarted by an electron, so instead of lowering the intensity of the light, why don't we lower the frequency. The lower the frequency the less the electron will be disturbed, so we can finally see what is actually going on. Lower the frequency slightly and try the experiment again. We see the bullet curve 17. After lowering it for a while, we finally see a curve that looks somewhat like that of the waves! There is one problem, though. Lowering the frequency of light is the same as increasing it's wavelength 18, and by the time the frequency of the light is low enough to detect the wave pattern the wavelength is longer then the distance between the slits so we can no longer see which slit the electron went through 19.

So have the electrons outsmarted us? Perhaps, but they have also taught us one of the most fundamental lessons in quantum physics - an observation is only valid in the context of the experiment in which it was performed 20. If you want to say that something behaves a certain way or even exists, you must give the context of this behavior or existence since in another context it may behave differently or not exist at all. We can't just say that an electron is a particle, since we have already seen proof that this is not always the case. We can only say that when we observe the electron in the two slit experiment it behaves like a particle. To see how it would behave under different conditions, we must perform a different experiment.
http://library.thinkquest.org/3487/qp.html

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Tags:

• cells
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• atoms
• electrons
• protons
• neutrons
• quarks
• physics

[kpgpwi64]

@jochemk6 yeah im 16 now and i completely agree, we are also completely distracted from learning too with things like talentless music, talentless "reality" tv, the constant decline of real art, flawed religions, indoctrination of those flawed beliefs and such. it's getting to be quite sad but im glad to know there are some people out there who find learning, knowledge, reason and science still interesting. so kudos to you.

[AUSNick87]

@mewmaster151 maybe it's because your into pokemon...

[starwarslego123]

So Weeping Angels are a result of Quantum Physics? They do whatever they want but when they're observed they have to stand still.

[blowing1nthewind]

I want Dr. Quantum.



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[1stNightingale]

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[selvmordspilot]

8 people +/- 8 think particles are coolest.

the remaining 8 people +/- 8 think waves are coolest.