Physicists grab individual atoms in groundbreaking experiment | Hacker News Reader

Physicists grab individual atoms in groundbreaking experiment

phys.org

119 pointsmagoghm26 comments

I don't understand why it takes at least three atoms to form a molecule. In a cloud of hydrogen atoms, what is the third one doing in the production of h2?

I don't know the answer but I could imagine that it works like a kind of catalyst.

Layman's guess. It probably has to do with conservation of energy and momentum. To form a molecule, you have to change the energy state of the electrons in both atoms, and in order to do so you have to respect the conservation laws, so I guess it takes a third atom to absorb/provide the required amounts of energy or momentum.

I think this is correct, and that a good illustration is planetary orbits - 2 bodies alone can never collide if they didn’t start out in intersecting trajectories. They need a third to perturb their movements or they will just keep orbiting the same way forever.

Won’t the orbits decay due to tidal forces in some cases?

In reality, yes - for purpose of illustration, I was thinking of idealized planets acting as point masses.

Tidal forces are much too weak to capture planets. In practice, yoy always need three bodies.

There was a discussion a few days ago which had excellent comments and links explaining why you need at least 3 atoms to form a molecule.

https://news.ycombinator.com/item?id=22390546

The other response discussing conservation of energy and momentum is basically correct. However, the third particle doesn't need to be an atom! Emitting a photon with the right energy and spin will also suffice. Typically the transition rates via photon are extremely low, but they can be intentionally triggered with other photons. This yields the incredibly useful tool called photo-association to create molecules from cold atoms.

Yeah, I was confused too, there’s plenty of molecules made up of two atoms. Sounds like the guess from other commenters about conservation of energy and momentum are most likely to be correct!

One step closer to us getting our matter compiler!

Able to 3d print anything, including food. Pirating dishes.

Hypothetically, in 200 years: will it require more or less energy to 3D print daily items than to build it?

I don’t want to be a jerk, but many material processes that have enabled us to make better performing materials has been directly related to investing more energy into a raw material.

Take for example, iron vs. steel, cast vs forged, wood vs. carbon fiber.

So I will be surprised if the future is a huge departure from history.

The internet vs. books and newspapers, and so on.. Technological progress isn't linear.

You wouldn’t print a purse..

3-D printing materials like gold would destroy the world economy, that should get interesting.

Why would a cheaper way to produce gold destroy the world economy? Aluminum was more valuable than gold before the Hall–Héroult process.

https://en.wikipedia.org/wiki/History_of_aluminium

Who needs an economy when you can 3D print whatever you want?

Fully automated luxury space communism here we come!

3D print needs a you when 3D print can you whatever 3D print want?

Fully automated luxury space 3D printer society here we come!

You can 3D print with gold molecules, but you still need the molecules. You're not going to be fusing junk atoms into gold atoms any time soon.

Well, you can, it's just not economically feasible at all.

You will need to stretch the definition of "can" here too, you need energy equivalent to an exploding star or two neutron stars colliding [1] to make it :)

[1] https://en.wikipedia.org/wiki/Gold#Gold_production_in_the_Un...

Surely it would just transition from gold to progressively more expensive elements? I'm not a chemist but presumably we're not going to being synthesizing much Einsteinium for a few years yet

Economies aren't really backed by gold anymore. They are backed by confidence.

And all that gold floating about out there, who knows, maybe just gold dipped tungsten bars to fill up the safe rooms.

One step down, 1e6 steps to go.

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