This equation's initial purpose, he wrote, was to put meaningful prices on the terrestrial exoplanets that Kepler was bound to discover. But he soon found it could be used equally well to place any planet-even our own-in a context that was simultaneously cosmic and commercial. In essence, you feed Laughlin's equation some key parameters — a planet's mass, its estimated temperature, and the age, type, and apparent brightness of its star — and out pops a number that should, Laughlin says, equate to cold, hard cash.
At the time, the exoplanet Gliese 581 c was thought to be the most Earth-like world known beyond our solar system. The equation said it was worth a measly $160. Mars fared better, priced at $14,000. And Earth? Our planet's value emerged as nearly 5 quadrillion dollars. That's about 100 times Earth's yearly GDP, and perhaps, Laughlin thought, not a bad ballpark estimate for the total economic value of our world and the technological civilization it supports.
If you tweak the reflectivity of Venus a bit, you can get it up over a quadrillion dollars. Sell short, I say, and buy some Mars. The equation itself is at the third link, and it does not seem to be based on the idea of arbitrage.