Hello, SFIA audio listeners, in this month's Nebula exclusive, Big Alien Theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

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We often refer to solar energy as the ultimate renewable energy, strictly speaking that's

only true if you figured out how to periodically renew the sun, but don't

worry, as we'll see today, it is possible.

A few weeks back we were discussing what happens if we can't leave Earth, if all of our hopes

for interstellar colonization to build homes around new stars, just turns out to be impractical

or undesirable.

I argue that while I very much hope for a future in which we journey out to the galaxy

that even if we were confined to our own solar system, or just our own world, that we still

had a very bright future ahead. Indeed, somewhat ironically, that is very literal as our sun grows brighter

every day, and a billion or so years down the road would be too bright for our world to keep

its seas and sky. If nothing is done, Earth will be turned into a hot, airless world much

like Mercury, and then as the sun grows old and expands, and Mercury is swallowed up, there's

a chance that solar expansion into a red giant might consume Venus and even Earth itself.

Older models of stars tend to assume that they grew cold and died out slowly, freezing

planets, and indeed that would be Earth's fate if the Sun didn't consume it.

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