[drdeca]

By “fingers” do you mean “things which can apply precisely controlled forces to individual atoms”, or..?

If you have two atoms in a vacuum with one moving directly towards the other at a not very high speed, I’m pretty sure they don’t fuse.

There’s a repulsive force, right? Like, the (expectation of) potential energy goes up (up to a certain point) as the centers of their nuclei get closer together (after perhaps getting lower for a bit because maybe they form a bond or something)?

So, presumably the “fingers” would have to do enough work to get past this potential energy barrier? (Or at least, make it high enough up this barrier that the probability of tunneling through becomes non-negligible?)

[ohiovr]

That's basically it. The strength of your fingers are more than enough to overcome the charge of 2 individual nuclei. Perhaps we need a shrink ray..

[drdeca]

I can believe that, yeah, that sounds likely enough. However, even if my fingers overall can easily exert the necessary force, it isn't clear to me that this should imply that any individual molecular bond between atoms in my fingers should be able to withstand the necessary force.

To me, it feels like it shouldn't be able to? (I say "feels" because I have not like, looked up any of the numbers about this or anything like that, and I could easily be wrong)

And, perhaps this could be the/a reason one might doubt that containing it in a diamond would work as an alternative to things like parts being brought together suddenly through precise collisions or using confinement from magnetic fields and such?

Though, of course, I'm not saying that doubting for that reason would probably lead to a correct conclusion. I wouldn't know much of anything about how one would achieve nuclear fusion, or how strong chemical bonds are, etc. .

[ohiovr]

I think the problem with trying to fuse two nuclei with your fingers is that the recoil from the reaction is really going to hurt. In a diamond this will destroy it. So it would seem like the only way it could work is if it were done as a burst. With a reasonable fraction of a coulomb of charge on each side rushing together and blocked by a thin layer of diamond, for a brief moment a lot of nuclei will be hopping on top of each other. If the ions and electrons are liberated instantly, immediately after there will be a high energy explosion. So shhh.. don't tell anyone like General Groves.

[dotancohen]

I believe that you are correct.

In nature, those "fingers" are more often than not hydrogen atoms, and the force acting on them is gravity. 10^30 kilograms of hydrogen, in a stack 600,000 kilometers tall, makes for high enough forces for the hydrogen to fuse.