> At this temperature the nuclei of the atoms behave almost classically.
The video seems to show a crystal made of fairly large spheres... which appear from nothing. I don't see a bunch of chaotic spheres which arrange themselves into a grid; I see a grid of spheres appearing where there was nothing before.
I have a hard time thinking this corresponds to classical mechanics. :/
Why are there any frames in which the sodium and chlorine atoms appear not to exist?
Suppose there was just the chlorine (no sodium), and we observed it the same way. Would we see mostly chaotic arrangements of big spheres, or mostly a smooth background with no spheres?
Near the bottom is a figure with some cherry picked frames of the video and a handmade drawing showing the crystal and the incoming pairs of atoms.
The Brownian motion depends on the mass of the object, so the average movement of the individual atoms is higher than the average movement of the small crystal. So the isolated atoms are blurred in the image.
Because you are seeing frames once every few milliseconds of atoms moving back and forth at speeds a fraction of the speed of light. It's only when they happen to be in very fixed positions that you have any hope to notice a definite image of the NaCl molecule.
In general, the very fact that you can see something should be a clear indication that you are not observing quantum behavior: particles whose properties (such as position) are measured DO NOT behave according to classical physics, they no longer display quantum effects. And while we have yet to understand what exactly counts as a measurement, something which allows you to have a picture of the atoms certainly counts.
It's not that the individual atoms didn't exist before they joined, but it's that they start oscillating in unison with each other in a pattern that emerges purely from wave interactions.
Nature settles into the most stable patterns of oscillation it can find, even without anything "causing that". To fully understand this kind of emergence you need to realize even the following video is in the same category of phenomenology called "emergence":
Atoms themselves "emerge" from probability waves, not the other way around.
On a wild tangent: I believe all emergent patterns represent "negative entropy" so I claim this disproves the Second Law of Thermodynamics, because it fails to take into account (i.e. quantify) "pattern-ness" or "order" in systems. Total entropy of the universe maybe doesn't increase but remains at zero, where the order perfectly counterbalances the randomness. Since there's no way to "measure" order in a system, the Second Law remains somewhat philosophical despite it being consistent with 'gross averages' measurements like temperatures, pressures, volumes, etc., in classical systems for which essentially only one side of the equation can be quantified.
However accurate this description may be, it definitely cannot support the claim that "at this timescale the nuclei of the atoms behave almost classically".
The video seems to show a crystal made of fairly large spheres... which appear from nothing. I don't see a bunch of chaotic spheres which arrange themselves into a grid; I see a grid of spheres appearing where there was nothing before.
I have a hard time thinking this corresponds to classical mechanics. :/