From my very limited understanding of such things, I gather that there are (at least) two ways to interpret the electron two slit experiment.
The electron’s probability wave traverses both slits and interferes with itself, thereby leading to the observed interference pattern.
The electron takes every possible path and, when summed, all paths cancel except those leading to the observed interference pattern.
I further understand that any attempt to measure which slit the electron passed through will change the “experiment” and result in a complete loss of the interference pattern (as if such a measurement forces the electron to lose all trace of its wave properties).
My question(s) then is(are) this: In the “sum over paths” interpretation, number 2 above, does the electron radiate as it meanders among all the possible paths? (i.e. an accelerating charge radiates, no?)
If it does radiate, is this radiation measurable? Or, perhaps, all the radiation cancels itself out?
If it does not radiate, why not? Is it similar to electrons in atoms, which don’t radiate because their energy levels are quantized?
I’ve been wondering about this experiment for a while too, and haven’t been able to find many answers. I’d like to see real info on it- most of my knowledge comes from some fictional novels that I doubt are very scientifically accurate.
A hearty “hear here” to the first two posts. I’ve never really understood the electron diffraction experiments on any level. So, let’s start at the most basic level: what happens in one of these experiments?
The problem I’ve often had with the uncertainty principle in electrons behaviour is what is meant by “observation”. To me, observation is a mental process. If observing (in this sense) really does affect the electron’s behaviour, then the electron must be telepathic. So I HOPE this is not the sense the physicists are using. I think they are talking about a measurement process - some array of magnets or something which could sense where the electron goes but would mess with its trajectory(?)
I guess what I’m wondering is how we know the results of the experiment if observation causes the experiment to fail. I wish we Karl Gauss or somebody around to ask … DOH!
Well, I can’t answer your question… In fact, I’m not sure anyone can, with certainty, yet. In lieu of that, check out the following link which might possibly amplify your confusion:
JoeyB: An outstanding link. But my questions remain.
In fact, one of my questions has nothing to do with the two slit experiment. So here it is, modified slightly: Do free electrons (such as those used in the electron double slit experiment) radiate as they travel?
As stated, my understanding of these things is very limited, but I thought that any accelerating charge emits EM radiation.
The reason why electrons in atoms don’t do so is because they’re confined to certain quantum levels (although they emit when they go to a lower level). Hence my phrasing as “free electrons”.
My question is this: Why do you think the electrons are accelerating? As I understand the experiment, the electrons do not lose or gain energy as they travel through the slits and do not accelerate and thus do not radiate.
If an electron takes all possible paths, a la Feynman, then some of those paths will involve a change in direction during the “flight”. Hence the acceleration.
Look I’m not pretending to be an expert, because there is so much I don’t know, but what I have learned over the years particularly with regard to electromagnetic radiation and double slit experiments leads me to this interesting hypothesis.
A “free charge particle” no longer is geometrically confined to any given point in space. Upon release, its boundaries are freed to unlimited proportions until it is detected. In otherwords, a nuclear particle is confined as a point when bound by atomic forces, but when released it expands creating its own medium until such time it is observed/detected, whereupon it coalesces back to a point within the confines of the atom.
That is why an interference pattern is demonstrated by the double slit prior to detection as points behind the slits.
Well, I have to admit that I’m a bit out of my element here, as well. However, I think the ‘radiation’ that you are referring to is the distortion of the electric field around the electron. Fields are sometimes talked about as radiation, but I think they are not “technically” emitted, but rather, more of a structural artifact. The visual imagery I like to use is that of a three dimensional spider web-like cage surrounding the electron. When the electron is at rest or traveling at constant velocity, the cage has a constant (probably spherical) shape, but when it accelerates the cage temporarily distorts.
I think either Stephen Hawking or Roger Penrose addressed this issue in one of their books. They were discussing the photon based two slit experiment, but I think the reasoning still applies. I’ll have to look it up for a direct quote, but essentially they argued that all of the paths, necessarily were the same length - hence, no acceleration. As I remember, the key element of this argument was that acceleration was impossible since the photons were already traveling at c.
How do you explain the (relative) conservation of momentum of said particle with this theory? The particles appear to behave in mostly classical ways, ie. they depart with a known velocity and direction, and are detected at a time and position consistent with their departure parameters. If the particle is unbound once emitted, what mechanism causes it to coalesce onto the prescribed target at the prescribed time?
Very interesting grienspace, to think of a particle that hasn’t got any geometrically confined place or boundaries until detected. And it only has a place and geometry when it is detected because the detection consists of having bounced some other particles off it or hit it with a wave or something? 2) Someone wrote that they couldn’t see why observing something would affect it since the observation is mental, but the point is that you can’t observe anything without bouncing something off it: for instance you see something because light waves have come to it from somewhere and then from the object to your eye. When you look at something teensy, it’s the same, since little electrons have to bounce off it, but when they do they have a big effect on it, bigger than when the object is bigger. The electron (or photon) beam of light races toward the atom you’re wanting to look at, and then when it gets there it shoves the atom around or the electrons in it around and then comes bounding back to your eye. This is the theory, but I don’t really understand it, since so what if it bounced the particle you are looking at out of place, doesn’t the information it brings back to you only show the moment of impact, which would be BEFORE the visiting electron pushed it anyplace? 3) In science books they always say the observation causes the particle to come into existence, but who can believe this? It only causes the particle to come into your knowledge of it, it doesn’t make it exist (unless they mean in the above sense of grienspace that in pushing against the general area where something is, the beam of inspection adds energy to the area and so bounces back to you with THAT information…
I repeat that I’m no expert and only hypothesizing, but I don’t see any contradiction with the conservation of momentum.
Secondly, I would assume that the preferred state of subatomic particles are within the atomic structure. We have radiation once these particles are ejected due to the presence of enough extra energy. Once these atomic entities contact another conglomerate of atoms in a low energy state or charge,the atomic entity will gladly coalesce into its new home.(Unless its bounced like photons off a mirror,and I can’t explain that yet)
I have what may be a really stupid question, but here it goes:
I’ve always heard the experiment described as though it hinges on a SINGLE electron, photon, whatever being released and directed at the card with two slits.
How the hell can you cause a single photon to be emitted in whatever direction you want? It seems like the energies and precision necessary to do that would boggle the mind.
As far as I know, all of the photon based experiments are based on multiples of photons. That’s one of the things that makes the electron based experiments so valuable because you can fire single electrons from an electron gun. The other thing is that you can build electron detectors at the slits so you can count how many electrons pass through each slit. Contrary to what don willard just wrote:
I believe, the electron detectors detect electrons via field fluctuations and this takes place without (significantly) disrupting the velocity or trajectory of the passing electron (i.e. without bouncing anything off the electrons).
Instead of using stable particles like photons or electrons, what happens when an unstable particle like a meson is used in a two-slit experiment? Presumably, a portion of the particles will decay during the interval when they are traversing the interferometer. What happens then?
The electromagnetic force, in particular, is mediated by photons. The field fluctuations are being detected due to virtual photons passing from the electron to the detectors, or vice versa. So particles are, indeed, being bounced around.
I’m guessing the virtual particles is what the OP is referring to by the electron “radiating”. Virtual particles, for those who don’t know, are particles that briefly pop into existance, and then pop out, for no known reason. The only constraint on their existance is that the energy of the virtual particles, multiplied by the amount of time that they exist, must be less than Planck’s constant over 2 pi.
And so, the answer is: yes, the radiation is detectable. However, detecting the radiation, e.g., with an electric field sensor, interacts with the experiment enough to destroy the interference pattern.