Can nanobot’s be strong enough to produce fusion.

You have to push the protons, not the atoms.

It isn't just pushing the atoms together that causes a fusion reaction, if you're analyzing it at this level of magnification. You can push two atoms at each other all day and all you'll get (depending on what kind of atoms and whether they're the same or different kinds) is perhaps a covalent bond among the electrons.

It's the elementary particles in the nuclei which need to be put in close proximity to cause fusion. And at the scale of subatomic particles, you're talking, what, maybe ten to the minus 6 smaller than that of the atoms themselves. (Just a guess. Any physicists here?) You'll need a picobot or a femtobot or a yattobot, or whatever the next prefix is, to be able to manipulate particles at that scale.

And the problem is that the bot won't be much bigger than the particles it's trying to manipulate. Don't ask me how it will be constructed so that it has "hands" and "wheels" at a subatomic scale. It begs the question of discovering and using particles smaller than protons and neutrons to build a machine that can manipulate protons and neutrons!

Also, it will require tremendous energy to push those nuclei together. The input energy to a nuclear reaction is not trivial, considering the size of the output! How is the little machine going to be able to channel that much energy through its small body, yet maintain enough precision to be able to manually push the nuclei together by sheer brute force?

When it comes to science I'm an optimist, and I assume the answer to a question like yours is always Yes, if we just wait long enough. But the nanotechnology we have now, and the future nanotechnology we can extrapolate from what we've got and where we're going, isn't nearly small enough, precise enough, and strong enough to push two protons together.

So yes, we might manage to build a machine that can push two atoms of hydrogen and one atom of oxygen together and custom-build a single molecule of water as a science project. But that ability falls far short of what is required to cause a fusion reaction.

Now, maybe if the Home Shopping channel could sell him a little tiny Dremel, he could use it to break a nucleus apart and cause a fission reaction!

 

"Pressure" only has meaning with molecules.

Pressure is a variable that only makes sense at a macro level. It is a manifestation of the speed of motion of molecules and the distance between them. Fusion reactions occur at the level of subatomic particles, way, way past the point of being able to observe phenomena involving molecules.

 

Why nanobots?

We might be able to build extremely small nuclear fusion reactors that work in the conventional way, by using foreseeable technology to simply miniaturize the existing equipment. I don't know whether there is an economy of scale involved in the shielding, unfortunately. If it takes the same amount of shielding to protect us from the radiation of a powerplant just large enough to power a home or an automobile as one large enough to power a city, then my idea won't work.

Barring that complication, there are probably several ways to approach the problem of building small nuclear reactors. Is there a reason you think it should be done with nanobots? If you have a tiny enough conventional reactor, you could just use the nanobots to sit in the tiny control room and manipulate the tiny controls. Does that count?

 

Macro vs. micro level models of the universe

That is true. But remember that what we are always talking about is a model of the universe, not the universe itself. A discussion of the temperature and pressure inside the sun, which is, I guess (um, any physicists here?), on the order of magnitude of hundreds of thousands of kilometers in diameter, is a discussion at the macro level. Therefore, using the same model that we use to discuss the way our senses experience the universe is satisfactory. Temperature, pressure, all of those variables give us a model of the sun that is consistent with our observations and the rest of our macrophysics.

Now your discussion has zoomed in from a scale measured in thousands of kilometers to one measured in Angstroms. What is that, about twenty orders of magnitude? (Still waiting for a real physicist to log in!)

Pressure and temperature are macro-level variables parameterized by the average rate of speed of the molecules inside a given volume and the average distance between them. You can't use this model at the micro level to talk about two specific molecules in that space. The law of averages says you might, at random, have stumbled on to two of them that just stopped moving and are three molecular diameters apart. At a macro level the temperature and pressure inside a volume of gas is the same at every point (assuming you didn't just start a reaction which is radiating outward from one of those points). At a micro level you just can't talk about the temperature or pressure of the tiny stretch of empty space between two molecules. The concept is invalid; wrong model. If there are no particles in that particular spot, there is no way to measure its temperature or pressure. It is just as invalid to talk about the temperature or pressure of an indiviudal molecule, since its velocity and distance from other molecules changes constantly, and, from our point of view, at random.

But you're zooming in many orders of magnitude even beyond the molecular level, to the level of the atom or to the level of the elementary particles that comprise its nucleus and populate its electron orbits. The human-senses model of the universe really doesn't work at that level. When you talk about "pushing" two atoms together, it's analogous to "pushing" two solar systems together. What are the odds that one of the planets of one system will just happen to collide with one of the planets of the other system? Can you push them with enough precision to cause their suns to collide?

And even this analogy breaks down at this point. The suns exert gravity forces on each other, so if you're pushing slowly enough and manage to get the suns close enough, they will pull themselves together. Atomic nuclei are just the opposite, since they are composed entirely of protons and (in most cases) neutrons. They all have a positive charge. If you manage to bring two nuclei close enough together for them to respond to the proximity, their response will be to repel each other rather than draw closer together.

As I said, nanobots may have some role in such a device. Certainly nano- or picotechnology in general will. However, I'm still waiting for a physicist to log in and set us straight on the issue of shielding. I have no idea how much lethal radiation these tiny reactors will produce and how many grams or kilograms of shielding we will need to protect ourselves from the nuclear power supplies in our cell phones and wristwatches.

 

Entropy!

Um, are we perhaps forgetting about entropy here?

 

It's difficult to harness the waste energy of a nuclear reactor. Radioactivity is not a form of energy that we have learned to change into a more useful form. It is pretty near the bottom of the energy "food chain", sort of a "you are this close to entropy" milepost. I have strong doubts that the idea is practical. My instincts tell me that shielding will be the only answer and, therefore, we'll still have the problem of finding a place to dump little tiny lumps of radioactive waste.