I am curious about the electron emitter used in the classic double slit experiment.
As dots appear on the screen in this experiment, do the dots appear each time the emitter is pulsed to emit an electron, or do they appear slowly over time as the emitter runs with a fixed output power?
Also in either case, do the dots appear steadily with no variation in the elapsed time between each new dots appearance, and does more than one dot ever appear at a time, or do they always appear one at a time?
Most electron sources emit randomly, so the interference pattern is made up of electrons arriving randomly. Every single electron participates, interfering with itself, no matter what the rate.
If you have a detector that can display individual electron hits, like a microchannel plate maybe, you'll see bright and dark bands at high electron rates. At very low rates, you'll see single electron flashes concentrated in the "bright band" zones.
A less sensitive detector, like film, will take a lot of electron hits to slowly build up the fringe-band image.
Actually there is no "classic double slit experiment" using electrons, the gap between "slits" is on the atomic scale and a crystal is used as a diffraction grating. What you get is this:
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The dots appear at whatever rate the electron source produces them.
The easy way to do the experiment is with thermal emmission of electrons under a magnetic field -- your classic vacuum tube filament, but designed to be a really, really weak emmiter. In that case the electrons would appear slowly and irregularly.
I am told that you can also create the electrons one at a time through autoionization of doubly excited Helium atoms, but I imagine it would be a real pain feeding the atoms in one at a time.
Were you aware that double slit experiments have been done with neutrons, atoms and even molecules? They have done them with carbon-60 fullerenes (buckyballs), and they have even shown interference fringes for C60F48, a 108 atom fluorinated buckyball with a mass of 1600!
So, can we do it by flying airplanes through *really* large slits and crashing them into a brick wall? How about smaller slits and bullets?
I am going to quote Wikipedia on that one, because, to be honest with you, my physics knowledge gets a bit shaky at this point (I am an engineer, not a physicist).
"Whether objects heavier than the Planck mass (about the weight of a large bacterium) have a de Broglie wavelength is theoretically unclear and experimentally unreachable; above the Planck mass a particle's Compton wavelength would be smaller than the Planck length and its own Schwarzschild radius, a scale at which current theories of physics may break down or need to be replaced by more general ones."
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As always with Wikipedia, follow the references and look at the source material.
Here is a video where you can watch the pattern emerge yourself.
"...can we do it by flying airplanes through *really* large
As they implied in your quote, the bigger the mass (plane) the *smaller* the slit because the De Broglie wavelength is *inversely* proportional to the mass. Or really, inversely proportional to the momentum or mass*velocity.
That's why it needed the small spacing of adjacent planes of atoms in the famous diffraction experiment that showed moving electrons have a wavelength.
John, the double slit experiment is of course usually done using light in the visible spectrum.
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It's a diffraction/interference demonstration that illustrates fundamental principles of physical optics. I myself have never heard of it being performed with electrons, but their is always a first time for everything.
For a serious student, perform the double-slit experiment using monochromatic visible light of a particular wavelength, then compare the your computed predictions, and the results will confirm theory. I'm pretty sure that if you performed the experiment using electrons of a precisely known enery and hence wavelength, you would obtain the same result.
The problem in doing this is that obtaining electrons of a specific enegy and a corresponding fixed wavelength is extremely hard to do, and the difficulty of constucting a double-slit apparatus for electrons is even more difficult.
You can use a cathode-ray. You put the slits inside and run the device. The electrons strike the phosphorescent screen and light it up for a short amount of time(exactly like they are suppose to work). Of course the only difference is, is that the electrons strike the double slit and some make it through while others don't.
The pattern itself is a probabilistic pattern and is not what one expects which would be the sum of two gaussian(or approximately at least) distributes but a much more complex pattern. i.e., classical mechanics predicts something different than what actually happens. Essentially there is an interference term that apears.
Remember, one is only sending one electron in at a time. Its not that there is interference between electrons but that the electron interfers with itself by the two slits. Essentially it goes through both.... after all, it is a wave.
To get the pattern you have to keep track of the dots location. Using the cathode ray tube will only give you a dot for a very short amount of time... although the more electrons you send in the more the pattern will show up. (if only, say, one at a time then you'll get one dot at a time)
"But in 1961 Claus Jönsson of Tübingen, who had been one of Möllenstedt's students, finally performed an actual double-slit experiment with electrons for the first time (Zeitschrift für Physik
161 454). Indeed, he demonstrated interference with up to five slits."
I kind of assumed that an electron gun existed that could fire a single electron at the screen on demand. However it sounds like the electrons are in fact emitted randomly, and the emitter is tuned to the power level required to form dots on the screen at the desired rate?
Just because a dot appears on the screen doesn't mean that a single electron has been emitted necessarily. The screen is composed of light sensitive material that requires its molecules electrons to jump an orbital for a dot to appear.
The quantum mechanics view is that ALL energy released from an electron that drops an orbit, is absorbed by a single electron that raised its orbit. So in this case, once the energy from an emission has been absorbed, there is no possibility to detect the emission elsewhere.
The classical view is that ALL energy released from an electron that drops an orbit, is emitted evenly as an electromagnetic wave traveling outwards spherically, with decreasing intensity at the speed of light. This allows for the possibility to detect this emission, however as the emitted energy decreases as it travels outwards, there is not enough energy to raise an electrons orbit, unless that electron was already nearly at the next orbital energy level, which is possible if you look at these two effects:
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Those two effects show that electron orbital state changes aren't fixed but instead can be dynamic based on the electrostatic or electromagnetic background field.
The other way to detect this electromagnetic energy without having to use a atomic/molecular method (electron orbital jumping) would be an electrostatic or electromagnetic field detector. In this case you can detect an emission at two places at once without having to absorb all the energy of the emission.
Quantum mechanics interpretation requires that all energy be absorbed in transactions between molecules, rather than there being a background field that is added to or removed from by electrons jumping or dropping orbitals. Quantum mechanics interpretation means that 100% of the energy released from an electron dropping an orbit 100 light years away, will be absorbed by the electron that jumps an orbit when that light is absorbed. The classical view is that 100 light years away, there will be almost no energy left to absorb, as it will be dispersed evenly over a 100 light year radius sphere, however this energy could still possibly cause one or more electrons to jump orbits, if they were already nearly at the next orbital energy level, based on other electromagnetic fields in combination with the energy emitted from the electron that dropped its atomic or molecular orbit.
For the double slit experiment if you assume that the emitted energy from the electron gun is wave based, then it is possible to see that this energy will always hit the screen in the pattern that is shown as the final result of this experiment. The reason only one dot appears on the screen at a time is that the emitters intensity has been reduced to a level that will only trigger atomic/molecular electron orbital jumps on the screen for electrons that are very close to the next orbital level already based on their local electromagnetic field energy.
Perhaps all electrons in the screen are susceptible to jumping orbits to the next state, and they will only jump a certain percentage of the time, depending on the strength of the wave based field coming from the emitter. This means that if the emitters intensity is decreased, it will cause dots to form slowly on the screen, and the dots will form at a higher rate in the areas of stronger field intensity.
Wow sorry for the long email it is just hard to describe what I was trying to say! :)
I think there are synchronous single-electron emitters, but they're pretty exotic. There are lots of electron sources that dole out electrons randomly, but at arbitrarily low rates.
An electron multiplier can image single electron hits, but all such gadgets have a finite background noise level, typically in the 10's of hits per sq cm per second. So very low electron fringes will get lost in that noise.
One electron, impacting a phosphor with a lot of energy, can kick out hundreds of photons. An electron can easily come in with, say, 30 KEV of energy (accelerated by a 30,000 volt power supply), and a photon is just a couple of ev.
A single electron can whack a phosphor and be visible with the naked eye, or easily visible in an image intensifier.
Each electron hits the screen at exactly one place. It is a particle, after all. It's just more probable that it will hit in some places than in other places, and those places are arranged in stripes.
A high-voltage electron will crash into a lot of phosphor molecules before it stops, so can release a lot of photons.
Each electron will "form a dot", namely make a flash of light, where it hits. A more intense source just flings more electrons per second, makes more flashies.
| >Actually there is no "classic double slit experiment" using electrons, the | >gap between "slits" is on the atomic scale and a crystal is used as a | >diffraction | >grating. What you get is this: | >
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| | "But in 1961 Claus Jönsson of Tübingen, who had been one of | Möllenstedt's students, finally performed an actual double-slit | experiment with electrons for the first time (Zeitschrift für Physik | 161 454). Indeed, he demonstrated interference with up to five slits." | A first time experiment in 1961 is "classical" and five slits is "double".
Thank you, now I understand. Neil Armstrong went to the Moon and back in a classical Saturn V double stage rocket with up to 5 stages.
Would you mind telling me from which ivy league university you got your classical double doctorate in learning to count up to five and what the fees were? I want one then I can appear intelligent like you.
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Hmmm. Trying to fly airplanes through microscopically tiny slits... Fill the planes with spammers and I am all for trying the experiment in real life!
If the De Broglie wavelength is inversely proportional to momentum. then, in theory, would a really slow-moving bus be able to pass hrough a tiny slit? Anyone on the bus would starve to death, so once again I say fill the bus with spammers and I am all for trying the experiment in real life.
Let's review this particular bit of asswipery, shall we?
Someone (it doesn't matter who) quoted an editorial that appeared in the September 2002 issue of Physics World and was quoted at physicsworld.com, and you decided to flame the person who posted the quote because you didn't like the wording of the quoted material.
In addition, you appear to be to dimwitted to understand that "he demonstrated interference with up to five slits" can mean doing a series of experiments starting with two slits and later trying it with more slits.
Finally, you flame about the use of the word "classic" -- going so far as to put it in quotes -- even though that word does not appear in the quote from Physics World.
Once again demonstrating that...
"Usenet is like a herd of performing elephants with diarrhea: massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind-boggling amounts of excrement when you least expect it." -Eugene H. Spafford
| >| | >| "But in 1961 Claus Jönsson of Tübingen, who had been one of | >| Möllenstedt's students, finally performed an actual double-slit | >| experiment with electrons for the first time (Zeitschrift für Physik | >| 161 454). Indeed, he demonstrated interference with up to five slits." | >| | >
| >A first time experiment in 1961 is "classical" and five slits is "double". | >
| >Thank you, now I understand. | >Neil Armstrong went to the Moon and back in a classical Saturn V | >double stage rocket with up to 5 stages. | >
| >Would you mind telling me from which ivy league university you got | >your classical double doctorate in learning to count up to five and | >what the fees were? I want one then I can appear intelligent like you. | | Let's review this particular bit of asswipery, shall we?
No, we shall not. Fuck off, it does matter who or anyone can quote any crap they like.
| >"John Larkin" wrote in message | >news: snipped-for-privacy@4ax.com... | >| On Tue, 15 Apr 2008 01:05:23 +0100, "Androcles" | >| wrote: | >| | >| >
| >| >Actually there is no "classic double slit experiment" using electrons, | >the | >| >gap between "slits" is on the atomic scale and a crystal is used as a | >| >diffraction | >| >grating. What you get is this: | >| >
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| >| >
| >
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| >| | >| | >|
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| >| | >| "But in 1961 Claus Jönsson of Tübingen, who had been one of | >| Möllenstedt's students, finally performed an actual double-slit | >| experiment with electrons for the first time (Zeitschrift für Physik | >| 161 454). Indeed, he demonstrated interference with up to five slits." | >| | >A first time experiment in 1961 is "classical" and five slits is "double". | >
| >Thank you, now I understand. | >Neil Armstrong went to the Moon and back in a classical Saturn V | >double stage rocket with up to 5 stages. | >
| >Would you mind telling me from which ivy league university you got | >your classical double doctorate in learning to count up to five and | >what the fees were? I want one then I can appear intelligent like you. | | | You would have saved a lot of time by just saying something like "Oh. | Interesting. Thanks." |
Sure, but doing it my way quickly gets a reaction from the pathetic one-liner trolls such as "jjlarkin" and then they have to change their name again to troll me some more as I kill-file them, which is fun. I've got lots of bytes left on my hard drive for killing shitheads and plenty of time since I'm retired.
| You would have saved a lot of time by just saying something like "Oh. | Interesting. Thanks." |
Sure, but doing it my way quickly gets a reaction from the pathetic one-liner trolls such as "jjlarkin" and then they have to change their name again to troll me some more as I kill-file them, which is fun. I've got lots of bytes left on my hard drive for killing shitheads and plenty of time since I'm retired.
John Larkin is my real name. What's yours?
You kill-file people who inform you of physical reality of which you were not aware? No wonder you're retired.
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