[fizigura]

We know the equations for flight. Why didn't they just build a 787 in the 40s already?

Oh, is it because the technology didn't exist and first had to be developed, in incremental refinements? Initial airplanes didn't even fly and half the people trying them died? Oh...

[pfdietz]

The basic equations of aerodynamics led people (like von Karman) to conclude that lighter than air craft would not be competitive. And so it proved.

The basic physics of DT fusion reactors led Lidsky to conclude that any DT reactor would have poor power density. And so it has proved.

Sometimes knowledge lets one rule out whole branches of the technology search tree.

[fizigura]

The basics of human history show that these kinds of predictions are sometimes right, sometimes wrong, and being too sure about them is usually the wrong way to do about things. We'd all still live in caves with that attitude.

[pfdietz]

The history of engineering shows that most approaches to solving problems fail. That's because, as in ecology, there's typically only one approach (in ecology one species) per niche (in the market or in the ecosystem). The winner drives the losers to extinction.

For fusion, we have to ask why it's going to be an exception. The prior is that it won't be. If there's evidence it will be blocked, that's two (or more) strikes against it. Something very unusual is needed to come back from that far behind.

The continuing success of renewables, and their continuing progression down their experience curves, is bad news for fusion.

[fizigura]

Hm, you are obviously not following what's going on in the fusion space currently. They are continuously churning forward towards a viable design.

What "renewables" (with which I suppose you mean solar, hydro and wind) have going against them is their environmental impact. Sure it's not as bad as fossil fuels, far from it, don't get me wrong. But the area and materials needed for solar, the animals getting disturbed by wind turbines (birds killed, wales confused, ...) and the ecosystems that get flodded by dams are not nothing. Especially in the light that the energy demands of 8bn+ people are continuing to grow, and those 8bn will soon be 9bn and 10bn.

The promise of fusion tech is that you get much more bang for the buck, and with "buck" I mean resource use. That's not going to happen soon though, so until they we'll be stuck with solar+wind+hydro, but those are not really sustainable solutions in the long run (i.e. 100s/1000s of years ahead).

Of course, if you see fusion just as some crazy idea and know nothing else about it, then I can see how your "prior" makes sense. But once you know the details, it's quite different, since fusion is also continuing to progress down its experience curve. Tokamaks and stellerators in particular.

[pfdietz]

Let's deal with the environmental impact argument first. We can estimate the cost of damage to the environment from what activities societies allow, and the value those activities produce. The largest use is agriculture. Societies allow elimination of natural ecosystems and their replacement by crop monocultures. What value is obtained? Typically, the value of crops delivered from a tract of land is two orders of magnitude less than the value that could be obtained by putting PV there.

So, if we stipulate your environmental argument rules out renewables, it also (to a much stronger degree) rules out agriculture. This is obviously absurd, so your argument cannot succeed.

As for recent "goings on"... I do follow them rather closely. You are likely misled by a common cognitive failing. That is: if we have a set of steps needed to reach some goal, then if one of these N steps is achieved, it's natural to think that we're 1/Nth of the way there. But this is only true if the steps are equally difficult. This cognitive blind spot is exploited in those collectable coupon games you sometimes see at grocery stores or fast food outlets. The # of winners is controlled by the number of a particular rare coupon; all the others are just noise.

For fusion, the immediate steps have been plasma confinement, stronger magnets, and so on. But none of these matter if there's a later showstopper. And for DT fusion, there is. That showstopper is the inability of DT fusion reactors to achieve adequately high volumetric power density. None of the recent DT reactors are promising in that respect, and there's good reason to think this obstacle is generic. Lawrence Lidsky (and Pfirsch and Schmitter in Germany) in the 1980s pointed this out. The implication of poor volumetric power density is that DT fusion will be more expensive than fission -- and fission itself cannot compete with renewables.

(I view current work on DT fusion as "making good progress toward a dead end.")

(If Pfirsch's name is familiar, it's because he, with Schlüter, discovered Pfirsch-Schlüter currents, which are important in stellarators.)

The only effort I see that has any chance is Helion's, which does not use DT, because they can evade this showstopper (by not producing their output as heat, allowing them to potentially save on the cost of the non-nuclear part of the plant.)