Expanding on my earlier look at one of the motives that might (but probably won't) impel human beings to colonize the galaxy, I'd like to examine a second
colonial motive – the acquisition of scarce resources – and the
reasons why it will probably not create a galaxy-spanning human
civilization.
We can certainly find plenty of valuable
resources beyond Earth's atmosphere: precious metals like iridium,
germanium, osmium, and platinum, and “volatiles” (to use John
Barnes' term), particularly water ice, which miners can use to
generate water, oxygen, and rocket fuel. Pace television shows like V
and Battlestar Galactica, water abounds in our Solar System: most
asteroids are comprised of ice and carbon, as are the rings of Saturn
and other gas giants, as are the countless comets that drift in the
Oort cloud and occasionally fall sunward. Meanwhile, the asteroid
belt offers mineral resources beyond the dreams of avarice. The hard
SF writer and physicist Stephen Baxter estimates that even a fragment
of a mid-sized asteroid (over 500 meters in diameter) could yield a
trillion dollars' worth of rare and precious elements, and NASA estimates
that our asteroid belt contains over one million asteroids of
one-kilometer size or larger, of which 20-25% are of the nickel-iron
and silicate variety likeliest to harbor more valuable metals. Other
asteroids one may find in the Trojan Points (where Jupiter's and the
Sun's gravity counter-balance one another) and in various solar
orbits in the inner Solar system.
I think it very likely that other star
systems also feature abundant resources. Earth-like planets might prove rare
(depending on how broadly one interprets “Earth-like”), but as
Norman Spinrad recently reminded SF readers, the Solar System is far
from unique in its diversity of elements and ices and worldlets. Even
interstellar space is “full of icy and rocky comets...Oort Clouds
and Kuiper Belts...even free-floating organic molecules.” However,
while one can imagine a future human civilization burning through
250,000 asteroids' worth of industrially useful metals, and a few
thousand comets' worth of water, I find it much harer to imagine that
civilization spreading at an exponentially increasing rate through
the galaxy in search of new stellar systems to suck dry.
What will dramatically slow expansionist space miners is another concept developed by John Barnes: "you can't outrun compound interest."
It takes resources - spacecraft building and maintenance, fuel and
provisioning, crew recruitment and training, vacuum construction
work, etc. - to set up extra-terrestrial mining
operations and ship the end product to Earth. Those capital resources
are not limitless and one could profitably employ them in other ways;
using them to mine asteroids and comets incurs an opportunity cost,
which (very roughly) equates to the interest rates that capitalist
economies charge for the hiring of capital. Interest rates in
21st-century industrial economies are low and I suspect they will
remain so in a space-faring civilization. However, interest payments
grow and compound over time; even at one percent interest per annum,
a loan will double in size in 75 years.
In the
early-modern epoch, companies could profitably undertake trading
missions (like voyages to China) that took several years to complete.
But a multi-decade interstellar voyage needs to generate much higher
profits to justify tying up resources for so long a period of time.
At light speed*, spacecraft will take decades to travel between even
relatively close star systems. A 50-year voyage would cost 165
percent of its initial investment cost after one factors in interest
payments (or opportunity-cost-equivalents) of one percent per year. A
longer voyage, say from Earth to the vicinity of Betelgeuse, would
take over 500 years and
require a return of more than 10,000 percent on the original
investment to break even. A flight across the Milky Way would take
50,000 years and require a return on investment of 6 * 10 ^200**, assuming anyone at the bank will still care by then. (Note: they
will.)
References:
John Barnes, The Man Who Pulled Down
the Sky (1986)
Stephen Baxter, Manifold: Space (2000)
Arthur C. Clarke, The Songs of Distant
Earth (1986)
Norman Spinrad, “Very Hard Science
Fiction,” Asimov's, June 2016 (quote 110)
* Interstellar spacecraft won't be
able to travel at lightspeed, or anything close to it. Remember that
Norman Spinrad quote about interstellar space? A spaceship traveling
at a significant fraction of lightspeed will suffer ablative damage
from hitting particles as small as hydrogen and helium atoms. One
traveling at close to C will lose most of its hull before it finishes
its voyage, especially if it hits something larger than a helium
atom.
** The current gross world product of Earth is about $80 trillion, or 8 * 10^12 dollars. If every star system in the Milky Way had an Earthlike planet with the same economic output, they would generate approximately 8 * 10^23 dollars. Just sayin'.
