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[Trekkin]

Even if we just wanted to restrict ourselves to deuterium-tritium fusion, there's fifty billion metric tons of deuterium in our hydrosphere alone. Tritium is rarer, but we can breed it from lithium, and there's lots of Li-6 around to do it with given a neutron source, which may as well be thorium.

Running out of fusion fuels is not an imminent problem, and fusion is only a transitional energy source anyway.

[Dunamisdeos]

In terms of galactic scale, yes. It is super abundant.

For an example of a world that is hydrogen impoverished, look next door in the solar system at Mars. (though it is also nitrogen impoverished.)

If you want to have a "sustainable" fusion industry, you need to balance the rate of hydrogen consumption against the rate of cosmic hydrogen entering the earth's atmosphere and magnetosphere. (it's absurdly small.)

Failing that, you have to start raining big water ice shipments from space. (and there is only so much out there.) That adds another layer of entropy expenditure though, because now you have all the energy costs associated with an essential space presence.

Nope, really, for geological timescale versions of sustainability, human population must radically decrease.

Did you even look at the link that Dunamis posted? It doesn't even use all that much water, though I'd rather use other fuel sources besides water.

http://www.ccfe.ac.uk/FAQ.aspx <- here it is.

They seem to think that everything you said is wrong. Also, I think that the assumption that there is no chance of a solution within a "few thousands years" is flawed somehow.

[wierd]

Like all economists, you are failing to account for the rapacious growth in consumption rates, as the techology becomes widespread and energy needs continue to increase as standards of living improve.

This is similar to the arguments made 30 years ago about how we had enough fossil fuels for the next 500 years....

[smjjames]

I don't see how Fusion is a transitional fuel source. Sure, it's transitional in the sense of 'until we find something better', but Fusion is the best that we know of and can reasonably attain with current technology.

[Baffler]

Even if we just wanted to restrict ourselves to deuterium-tritium fusion, there's fifty billion metric tons of deuterium in our hydrosphere alone. Tritium is rarer, but we can breed it from lithium, and there's lots of Li-6 around to do it with given a neutron source, which may as well be thorium.

Running out of fusion fuels is not an imminent problem, and fusion is only a transitional energy source anyway.

Transitional towards what? If we're at the point where we're primarily using fusion power haven't we basically hit the pinnacle of what our current science can do for us or even conceive of in the generation department?

[sluissa]

I think an assumption is that growth will have to significantly slow, or even stop. Sustainability works both ways. It's still not "kill off 80% of people" But it is possibly "2 child policy" along with some sort of enforced rationing.

[smjjames]

Population growth is already slowing because people are having fewer kids in developed countries, many developed countries right now actually have negative birth rates.

[wierd]

Short of harnessing zero point energy (not even theoretically doable at this point, but who knows what the future will bring), fusion is the most abundant energy source out there.

[Dunamisdeos]

Not to tote my internet-found science link around on a megaphone, but they state the immediately available fuel will last for billions of years.

We could be pessimistic and claim that the reality is a tenth of that, and it is still more than sufficient.

Population growth is already slowing because people are having fewer kids in developed countries, many developed countries right now actually have negative birth rates.

Also, this.

[wierd]

Energy use per person is growing exponentially though.

(and toting that link might not be safe)

Like most economic forecasts of "we have X before Y", it fails to address associated effects with "Reductions in available X".  So while there might be millions of years before we turn the earth into a desolate arid rock in space, we will have killed all life on the planet through drought long before then. (or killed off all the ocean life through increased salinity, etc.)

[TheDarkStar]

The global growth rate is already slowing. Lots of developed countries have negative growth rates and are actually trying to encourage more births per family. Even in third-world countries, the birth rates have drastically lowered in last few years. World population is projected to level off around 11 billion (barring unforeseen disasters).

PPE: and smjjames said it first.

[wierd]

I have no doubt that populations will level off at some theoretical maxima, (the evolution of such an event would be catastraphic to the economy anyway, because it is based exclusively on purpetual growth of both production AND consumption trends, which requires increases in population every cycle. ) however, the question is if that number is ACTUALLY sustainable, or is 'sustainable' using economic forecasts that fail to track externalities and their repercussions.

[Trekkin]

Even if we just wanted to restrict ourselves to deuterium-tritium fusion, there's fifty billion metric tons of deuterium in our hydrosphere alone. Tritium is rarer, but we can breed it from lithium, and there's lots of Li-6 around to do it with given a neutron source, which may as well be thorium.

Running out of fusion fuels is not an imminent problem, and fusion is only a transitional energy source anyway.

Transitional towards what? If we're at the point where we're primarily using fusion power haven't we basically hit the pinnacle of what our current science can do for us or even conceive of in the generation department?

The total conversion of matter to energy without directly relying on antimatter as an intermediate. There are a few ways to do it in theory, all of which require devices with initial energy requirements that are prohibitive without the use of fusion. Subatomic black holes are probably the easiest, and they aren't easy.

[smjjames]

Even if we just wanted to restrict ourselves to deuterium-tritium fusion, there's fifty billion metric tons of deuterium in our hydrosphere alone. Tritium is rarer, but we can breed it from lithium, and there's lots of Li-6 around to do it with given a neutron source, which may as well be thorium.

Running out of fusion fuels is not an imminent problem, and fusion is only a transitional energy source anyway.

Transitional towards what? If we're at the point where we're primarily using fusion power haven't we basically hit the pinnacle of what our current science can do for us or even conceive of in the generation department?

The total conversion of matter to energy without directly relying on antimatter as an intermediate. There are a few ways to do it in theory, all of which require devices with initial energy requirements that are prohibitive without the use of fusion. Subatomic black holes are probably the easiest, and they aren't easy.

Like the Post Trans-Uranic reactor stuff in the Schlock Mercenary comic? Also, you said 'in theory', we don't need to 'in theory' fusion.

[wierd]

Yes we do. Current tokamak designs are just barely overunity on production.

The stellerator was the child of theory, and test designs of reactors of this type have produced huge efficiency gains over traditional tokamak reactors.