Double-Slit Experiment Carried Out with 114-Atom Molecules
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Quote of the year.
Speaking of quotes, I like the following quote (or really, quoted section) from Dr. Feynman's lecture entitled, "Probability and Uncertainty - The Quantum Mechanical View of Nature." [1] In this lecture, he describes the double-slit experiment.
This section blows me away every time I watch it:
"Here are the circumstances: source, strong light source; tell me, behind which hole will I see the electron? You say, "Well, the reason you can't tell through which hole you're going to see the electron is, it's determined by some very complicated things back here: if I knew enough about that electron - it has internal wheels, internal gears, and so forth - and that this is what determines through which hole it goes.
It's 50/50 probability because, like a die, it's set sort of at random - and if I were to have studied it carefully enough, your physics is incomplete: if you get a complete enough physics, then you'll be able to predict through which hole it goes." That's the "hidden variable" theory, so called.
Well, that's not possible.
It is not due to a lack of detailed knowledge that we cannot make a prediction, because I said that if I didn't turn on the light, I should get this interference pattern.
If I have a circumstance in which I get that interference pattern, then it is impossible to analyze it in terms of saying, it goes through here or here, because that curve is so simple, mathematically - a different thing than the contribution of this and this as probabilities.
So if it were possible for you to have determined through which hole it was going to go if I had the light on, the fact that I had the light on hasn't got anything to do with it! Whatever gears there are back here that you observe, which permitted you to tell me whether is was going to go through 1 or 2, you could have observed if I had the light off.
And therefore you could have told me with the light off which hole - each time an electron goes - which hole it's going to go through.
But if you can do this, then that curve would have to be represented as the sum of those that go through there and those that go through there - and it ain't.
Therefore, it's impossible to have information ahead of time as to which hole it's going to go through when the light is out - or when the light is on, or out - in a circumstance where the experiment is set up that can produce this interference pattern.
It is not a lack of unknown gears - a lack of internal complications - that makes nature have probability in it; it seems to be in some sense intrinsic.
Someone has said it this way: "nature herself doesn't know which way the electron is going to go." A philosopher once said (a pompous one): "it is necessary for the very existence of science that the same conditions always produce the same result." Well, they don't: if you set up electrons in any way - I mean, you set up the circumstance here, in the same conditions every time, and you cannot predict behind which hole you'll see the electron.
They don't - and yet the science goes on in spite of him."
I think I can safely say that nobody understands quantum mechanics.
- Richard FeynmanThey used "derivatives of phthalocyanine molecules" with 1298 AMU.
The methods how they got the results (for example making a slit 10 nm wide) seem to be even more interesting than the result
http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.h...
The interesting aspect of the OP experiment appears to be that they have a real-time movie.
If you look at figure 3, you can see that the molecules are traveling at 10-100 meters per second, depending on size.
(Search finds lots of pages using table tennis balls as a help for visualising atoms or electrons or molecules.)
Here's a page (with many puns) about what you'd need to try the experiment with cats.
(http://www.askamathematician.com/2010/12/q-can-you-do-the-do...)
The catch is, the wavelength is of the order of h/momentum or h/(mass * velocity) where h (Planck's constant) is a really, really small number.
When mass is something like an ordinary object, then the size of the "slits" becomes so small that we can't imagine how conduct the experiment.
In this experiment, the molecules (~10^2 atoms) are a few nano meters across and the de Broglie wavelength is a few hundredths of a nanometer. The same group is planning on future experiments with 10^6 atoms, where the wavelength will be much smaller than the object.
>When mass is something like an ordinary object, then the size of the "slits" becomes so small that we can't imagine how conduct the experiment.
I think is misleading. Experiments demonstrating quantum interference of macroscopic objects are very easy to imagine and are limited by logistical concerns rather than fundamental physics. In particular, an experiment interfering objects large enough to see with the naked eye is very likely to occur this century, so I object to calling it "unimaginable".
But you were mostly right. I'm sorry.
In any case, the point is that it's not a matter of the slits becoming too small. It's a matter of controlling environmental decoherence.
(I did also.)
carbocation shares my point in a sister comment.
Here's another link talking about grains of sand and giving some numbers.
(http://www.physicsforums.com/archive/index.php/t-132386.html)
> Recalling De Broglie's relation, assuming a sand grain of mass 1mg and demanding a 1/2 mm wavelength (since I'm sceptical that a wavelength below the particle diameter will work), the sand would need a velocity of 10^-24 m/s. To emphasize the problem (via equipartition theorem) you're looking at maintaining 10^-31 K and (to propagate into a diffraction pattern) preventing any interaction for up to 10^14 centuries..
Feynman gives an easily approachable introduction to Quantum Electro Dynamics in these lectures: http://vega.org.uk/video/subseries/8
According to the the Copenhagen interpretation once you reach some unknown threshold the waveform will collapse and objects above a certain size won't create a wave pattern if they go through a double slit. The Everett/Many Worlds interpretation, on the other hand, would say that you can have quantum effects in objects of arbitrary size.
There are other interpretations too, of course, but I can't speak with any authority on them regarding this.
http://en.wikipedia.org/wiki/Interpretations_of_quantum_mech...
That's not to say it was a waste by any means - the techniques used will hopefully be useful to other scientists, and confirmation is always good :)
X = ? Size? Internal entropy?
If you could send a cluster of molecules at relative speeds (to c) through a double-slit setup, you might get the pattern.
Repeat the two-slit experiment using those devices as the projectiles.
Then see if the internal decoherence counts as external decoherence.
PS: I have no idea if this is possible, or what other QM equivalents of this might be.
Observing the object in either one of the slits would remove the necessary precondition for getting the interference pattern on the wall, so the pattern would no longer be there in your experiment.
If you observe it before passing, if that's possible, the wavefunction will collapse at that moment, and the quantum will pass, like a particle, through a single slit.
No idea how it would be possible to observe it mid-flight though.
...according to the most commonly accepted interpretation at any rate.
Well, as soon as you "observe" it, we will no longer see an interference pattern
That's not strictly true, because the experiment is observing the quantum, and it is seeing an interference pattern. The critical thing is that they're observing it after the quantum has gone through the slits, so as it passes through the slotted wall, it's wavefunction is not constrained. So the moment of observation is very important.
http://lesswrong.com/lw/r5/the_quantum_physics_sequence/
I'd say you can probably skip most of the preliminaries. But I didn't, so I'm not sure.