Uncertainty in gas molecules?

  • Thread starter FredT
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  • #1
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Main Question or Discussion Point

If buckyballs display uncertainty in the double slit experiment, shouldn't iodine gas molecules as well? An I2 molecule is certainly less massive than a buckyball. Yet why can we see I2 gas as a purple haze? I can see it, almost in the same way I can see my pencil, which has a very small uncertainty because it is a large object, yet the I2 molecules should all be independent, with large uncertainties, unlike my unified massive pencil.

Does what I'm saying make sense? And please bear with my ignorance, I'm new to quantum physics.

Thanks :tongue:
 

Answers and Replies

  • #2
mathman
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What is the setup you are describing? Is it a double slit?
 
  • #3
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No, what I'm trying to say is that from what I've read about quantum mechanics, we shouldn't be able to see a single molecule because of the uncertainty involved with such a small object. Is this incorrect? I use the term "see" loosely because we technically couldn't "see" a single molecule because it couldn't scatter light. In fact, this is probably where I'm going wrong - it is the entire group of I2 molecules that scatters the light collectively, not each individual molecule.

My issue was just that individual molecules are made out by quantum physics to be mysterious wave-particle oddities that defy the laws of classical mechanics that seem so natural and make so much sense. And yet I can look into a flask and see a collection of I2 gas molecules as a purple haze. They are all independent molecules, not one solid object, but I can still observe them and they seem normal enough to me!

Perhaps I'm being ridiculous, but please excuse my lack of knowledge. I've only recently become interested in physics and don't have much experience outside the Physics 1 course I took last year (which was entirely classical, of course).

Thanks
 
  • #4
alxm
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A single molecule can and does scatter light. In fact, you can measure the amount of scattering to determine Avogadro's number.

But you do have an uncertainty in the location of the molecules, and their electronic state and so on. And that affects the scattering and light absorption/emission processes (e.g. natural line-broadening) I'm not sure what effect you're expecting? The uncertainty principle doesn't say you can't measure the position and momentum, it just puts a limit on how accurately they can be known at the same time.
 

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