[pcottle]

It's tempting to say this to avoid getting your hopes up, but there has been solid concrete progress in fusion technology over the last decade. Getting net positive fusion to occur on Earth is an _incredibly_ difficult technical challenge. It's like climbing a scientific mountain, and right now we are a few hundred meters from the top with a few more obstacles to go. So saying you won't believe it until we reach the summit discredits all the progress we have made to date.

This technology is not a matter of 'is it possible?' but 'is it technically feasible?' And the scientific community has been chipping away at the latter for a long time.

[jcrites]

One thing which surprised me to learn was the fact that the Sun, per cubic meter, generates about as much power as an active compost heap.

http://en.wikipedia.org/wiki/Sun#Core

The Sun is not like a nuclear bomb going off. It's just a big radiating compost heap. Its huge energy output is due to its large size, and not the intensity of its reaction. (If the Sun's reaction were like a nuclear bomb, the solar system would be destroyed in a supernova-like explosion.)

In other words, nuclear fusion at the Sun's scale isn't very intense a reaction. Why do we expect it's a good idea for a power plant? Do we expect to get significantly hotter than a star? Significantly more dense? It makes sense how nuclear power works. Fusion power, it's not so clear.

Of course, there are fusion bombs as well, but aren't those set off by nuclear bombs?

[neutronicus]

The bulk of the energy release from hydrogen bombs is not generated by fusion. The general design of a hydrogen bomb is that a hydrogen "blanket" surrounds a fission "core". When the fission "core" goes supercritical, it releases enough energy to initiate fusion in the "blanket".

What the "blanket" does at this point is exert pressure on the "core", which would be beginning to blow apart in a conventional nuclear device. Keeping the "core" together for just that small bit of time longer allows it to remain supercritical for just that small bit of time longer, with the energy release growing exponentially with a time constant of 10^-7 seconds.

[queensnake]

How about that - I thought it was all about the binding energy curve: http://ec.europa.eu/research/energy/fi/fi_bs/images/fig2_147...

where, as the diagram shows, fission comes up from the heavier elements (less energy difference) and fusion from the lighter (greatly more).

[neutronicus]

Per fusion event, you get about 14 MeV to the about 200 MeV you get per fission event. It's true that the binding energy per nucleon is higher, but there are many fewer nucleons.

[pointyhat]

Unfortunately due to the complexity and number of challenges, the last rock may fall on your head and knock you back to the bottom again.

I'm not saying it's a valid goal - just until the technology is useful, it's not yet viable.

Compare to unified field theory, the Higgs boson and string theory.

A pessimist is an experienced optimist :)

[ugh]

What are the practical implications of your pessimism?

[pointyhat]

I spend a lot of time with my family rather than chasing dead ends :)

[ugh]

I don’t understand. Are you a physicist? Why does being pessimistic about fusion give you more free time?

[pointyhat]

Without going on too much of a philosophical tangent; not about fusion - about everything in general. It allows me to concentrate on now rather than in the future. Now is the only time that is certain. Now is the only time you get to enjoy your life before it's over or your children leave.