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Comment by whimsicalism | Hacker News Reader

Energy is conserved in the universe so there is never any net energy gain.

See how pedantic and not helpful that is?

In nuclear fusion, mass is converted into energy according to the famous equation E = mc^2, where E is energy, m is mass, and c is the speed of light.

Fair enough. To be extra pedantic, mass-energy is conserved in a fixed inertial frame of reference.

Mass is energy. Add energy (in any form, such as heat) to a system and you increase its mass. Thus, in the NIF reaction, the mass lost from the pellet is mass imparted on the surrounding environment. Immediately after the fusion reaction, before the energy can dissipate further as heat, etc, the reaction chamber system has the same mass as before the ignition.

There are some nuances regarding the distinction between rest mass vs relativistic mass, but they're not really relevant in this context.

I think what trips people up here is confusing mass with matter. Matter is also subject to mass-energy equivalence, of course, but AFAIU in most common types of nuclear reactions little if any matter, per se, is transformed.

That's a non sequitur. The laser ignition facility is not a smaller version of the entire universe.

Power plants add energy to an electrical grid by converting external (chemical/nuclear/kinetic) energy into more electricity than they consume. There's no loss of energy/mass overall, but the amount of available electricity goes up. Since the laser would use electricity from the grid, that should be taken into account.

The point is to get some of it from somewhere cheaper/free - mass, or outside air as in heat pumps.

You can't run your laser on mass or air, if you need a coal firing power plant to run your fusion reactor, from which you get less than you consumed from the coal plant...

It's great progress, it's just not as close to viable as it might sound like - more breakthroughs needed.

I have yet to find someone saying it sounds like fusion power reactors are right around the corner, but I have found lots of people shadowboxing these people and attacking the scientists for misleading press releases.

Seems like an overcorrection to something I haven't even seen anyone here say.

I think to a lot of the technically minded, but non nuclear physicists here, it initially sounded like less (paid for/electricity) energy was used than was put out. That's extremely exciting, and the actual news is still fantastic, it's just that 'actually, we needed to pay for over 100x more energy than we counted as the "input" energy [and it's possible to do 10x but not 100x better than that]' is quite a massive caveat on a 3:2 or whatever yield.

I'm not saying they've claimed anything wrong or deliberately misleading, it's just a misunderstanding/misalignment and possibly made worse by the PR teams in the middle.

In other words, I don't think it's an angry 'well actually' type correction so much as it is disappointment - it initially sounded even greater.

Not necessarily, it depends on how the reaction scales. If the reaction does not scale linearly (as is claimed) you don’t necessarily have to get more efficient, you just have to up the power until the output curve has increased past the input scaling. How big that is is determined by the efficiency of the input device itself, but it isn’t a question of if it will ever happen.

Yes, sure, it's just still a breakthrough or so (or at least work, I don't know how within grasp it is) away from what one may have (as did I) initially assumed.

Tangentially, it does seem fairly intuitive that it should be non-linear in that 'jump start' as it were: a fire can be grown arbitrarily large having started from a single match (or flint or whatever).

Right... look at some of the reactions:

"In terms of the physics, we are basically there, and the rest of it, at some level, is just engineering," he said.

[1] https://www.cbs58.com/news/wisconsin-reacts-to-breakthrough-...

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