6 ms·

Can someone please explain why this happens? I understand that for electrons, photons (or any fundamental particle?) there is a duality, but when you get a mole

Can someone please explain why this happens? I understand that for electrons, photons (or any fundamental particle?) there is a duality, but when you get a molecule, in my mind, it's now a thing, like a cat or a person. I know that if I did the double slit experiment with a people or cats I'd get a different result. Why do these molecules not behave like cats being thrown at a slit.

mikecane 15y ago
It makes me wonder, is speed a factor? How fast are they traveling?
- pmjordan 15y ago
  Velocity is part of the wave function, but varying it shouldn't affect the qualitative result of the experiment. It will change the specific intensity pattern on the detector side.
- jessriedel 15y ago
  It's not a speed factor. The possibility for observing quantum interference is controlled by the amount of environmental decoherence. (This is roughly the amount of interaction with the rest of the universe.) Decoherence is eliminated by working in a high vacuum, carefully designing the slits, etc. In principle, interference of macroscopic object is possible, but the sources of decoherence generally increase exponentially with object size. If you look at figure 3, you can see that the molecules are traveling at 10-100 meters per second, depending on size.
knodi 15y ago
No one can explain this currently.
- dhimes 15y ago
  It depends, or course, on just what you mean by "explain."
- pmjordan 15y ago
  Only in the same way that nobody can explain gravity. However there exists a widely accepted model which accurately describes the phenomenon.
arethuza 15y ago
I'm not a physicist, but I thought that the matter-wave duality applied to all "isolated" particles, it just completely dominates things at the scale of subatomic particles: http://en.wikipedia.org/wiki/Matter_wave http://en.wikipedia.org/wiki/Matter_wave
DanBC 15y ago
Has anyone tried the experiment with something obviously larger and not quantum-scale, such as table tennis balls? (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-double-slit-experiment-with-a-cat-cannon/ http://www.askamathematician.com/2010/12/q-can-you-do-the-do...)
- Symmetry 15y ago
  Nice link! One difficulty that occurred to me that isn't in the article, however, is that it would be really hard to prevent the kitten from becoming (quantum) entangled with anything else on its N light year journey. If it emits just one thermal photon in the wrong direction then there goes your experiment.
- deleted 15y ago
  [deleted]
- dhimes 15y ago
  The wave-effects depend on the fact that the wavelength is of a size that is comparable to the size of the object it's interacting with. Think about optics: observing an interference or diffraction pattern is easier when the light interacts with very small structures (the patterns on a cd, for example), the same is true for "matter" waves. 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.
  - jessriedel 15y ago
    <s>This is mostly wrong</s>. When the de Broglie wavelength becomes smaller than the size of the object, observing quantum inference becomes harder, but it's certainly not impossible. 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.
maggit 15y ago
There is in fact no duality involved, unless you try to describe the world in classical physics. But classical physics is just an approximation of quantum physics, which describes this phenomenon by the same rules that it explains phenomena we consider normal. As the guy says, "this is normal because it's quantum physics". Feynman gives an easily approachable introduction to Quantum Electro Dynamics in these lectures: http://vega.org.uk/video/subseries/8 http://vega.org.uk/video/subseries/8
Symmetry 15y ago
How big an object can get and still be subject to quantum effects is still a matter of debate. 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_mechanics http://en.wikipedia.org/wiki/Interpretations_of_quantum_mech...

mikecane 15y ago

It makes me wonder, is speed a factor? How fast are they traveling?

pmjordan 15y ago
Velocity is part of the wave function, but varying it shouldn't affect the qualitative result of the experiment. It will change the specific intensity pattern on the detector side.
jessriedel 15y ago
It's not a speed factor. The possibility for observing quantum interference is controlled by the amount of environmental decoherence. (This is roughly the amount of interaction with the rest of the universe.) Decoherence is eliminated by working in a high vacuum, carefully designing the slits, etc. In principle, interference of macroscopic object is possible, but the sources of decoherence generally increase exponentially with object size. If you look at figure 3, you can see that the molecules are traveling at 10-100 meters per second, depending on size.

knodi 15y ago

No one can explain this currently.

dhimes 15y ago
It depends, or course, on just what you mean by "explain."
pmjordan 15y ago
Only in the same way that nobody can explain gravity. However there exists a widely accepted model which accurately describes the phenomenon.

arethuza 15y ago

I'm not a physicist, but I thought that the matter-wave duality applied to all "isolated" particles, it just completely dominates things at the scale of subatomic particles: http://en.wikipedia.org/wiki/Matter_wave http://en.wikipedia.org/wiki/Matter_wave

DanBC 15y ago

Has anyone tried the experiment with something obviously larger and not quantum-scale, such as table tennis balls? (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-double-slit-experiment-with-a-cat-cannon/ http://www.askamathematician.com/2010/12/q-can-you-do-the-do...)

Symmetry 15y ago
Nice link! One difficulty that occurred to me that isn't in the article, however, is that it would be really hard to prevent the kitten from becoming (quantum) entangled with anything else on its N light year journey. If it emits just one thermal photon in the wrong direction then there goes your experiment.
deleted 15y ago
[deleted]
dhimes 15y ago
The wave-effects depend on the fact that the wavelength is of a size that is comparable to the size of the object it's interacting with. Think about optics: observing an interference or diffraction pattern is easier when the light interacts with very small structures (the patterns on a cd, for example), the same is true for "matter" waves. 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.
- jessriedel 15y ago
  <s>This is mostly wrong</s>. When the de Broglie wavelength becomes smaller than the size of the object, observing quantum inference becomes harder, but it's certainly not impossible. 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.

maggit 15y ago

There is in fact no duality involved, unless you try to describe the world in classical physics. But classical physics is just an approximation of quantum physics, which describes this phenomenon by the same rules that it explains phenomena we consider normal. As the guy says, "this is normal because it's quantum physics". Feynman gives an easily approachable introduction to Quantum Electro Dynamics in these lectures: http://vega.org.uk/video/subseries/8 http://vega.org.uk/video/subseries/8

Symmetry 15y ago

How big an object can get and still be subject to quantum effects is still a matter of debate. 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_mechanics http://en.wikipedia.org/wiki/Interpretations_of_quantum_mech...