> > the Earth's fission-fuel supply comes to
> > one trillion years worth.
> >
> > It would not actually last that long, of course, since
> > the half-lives of the fuel isotopes are:
> >
> > uranium-235 700 million years
> > uranium-238 4.5 billion years
> > thorium-232 14.1 billion years

> > Even if the thorium supply were tapped for most of, say, 20
> > billion years, the earth would likely have to be moved to
> > make way for an expanding sun.
> You argue that the Earth would likely have to be moved
> to make way for an expanding sun, but you don't provide
> any analysis for how you determine the likelihood.
> Could you please share with us your analysis of this point.

No. The analysis is not mine:
http://en.wikipedia.org/wiki/Sun#Life_cycle

"As a red giant, the Sun will have a maximum radius beyond the
Earth's current orbit, 1 AU (1.51011 m), 250 times the present
radius of the Sun [...] new research suggests that Earth will be
swallowed by the Sun owing to tidal interactions [...] Even if Earth
escapes incineration in the Sun, its water will be boiled away and
most of its atmosphere would escape into space. In fact, even during
its life in the main sequence, the Sun is gradually becoming more
luminous (about 10% every 1 billion years), and its surface
temperature is slowly rising. The increase in solar temperatures is
such that in about a billion years, the surface of the Earth will
become too hot for liquid water to exist, ending all terrestrial life"

Please also see the new Phil Plait (Bad Astronomy) book "Death from
the Skies!: These are the Ways the World Will End":
http://en.wikipedia.org/wiki/Phil_Plait#Books
http://www.amazon.com/Death-Skies-These-Ways-World/dp/0670019976
http://www.google.com/search?q=Death+from+Skies+plait+sun+billion

"In six billion years, the sun will swell into a red giant and toast
Earth."

> Argument from fantasy which is bolstered by the misuse of
> data is wholly unconvincing.

You believe it is merely a fantasy that "In six billion years, the
sun will swell into a red giant and toast Earth"?

Mike Combs, do you believe this also?

ANTIcarrot, do you believe this also?

Joe Strout, do you believe this also?

Not only would half life limit the total available energy supply, but you neglect the rise in annual energy consumption, which runs around 1.1%/year. Exponential growth is a killer for earth bound energy generation.

The only way to enable a Dyson Type II civilization is to go SPS. There are rational reasons to implement power sats and space colonization NOW and that is global resource availability. At our current global wealth, we have the excess resources to move out now. If we wait until we're all starving, we'll not be able to make such enormous investments. There is a current window of opportunity. We need to do this NOW.

GAry 7