Saturday, November 24, 2012

Will humans be going to planets around other stars?

by Salman Hameed

Well, I believe in the Star Trek universe - and so I do think that we will be able to figure out a way to travel to planets around other stars. But the author of the fantastic Mars Trilogy (Red Mars, Green Mars, and Blue Mars), Kim Stanley Robinson doesn't think so. From last week's Nature:

Kim Stanley Robinson, author of the bestselling Mars Trilogy, takes a radical view. He suggests that we get over the idea of interstellar travel altogether: a probe would take 28,000 years to get to Alpha Centauri. “We can't go fast enough to get to any of these places,” he says. 
Barnard's star was once “the place for nearby space”, Robinson says, as his novel Icehenge (Ace, 1984) — in which characters build a starship headed for it — attests. Now that researchers have identified some 840 exoplanets, and NASA's three-year-old Kepler space telescope has spotted 2,320 candidate planets, “there may never again be a single default destination”, Robinson continues. 
In his recent book 2312, which imagines humanity three centuries from now, spread across terraformed planets, asteroids and moons in our own Solar System, Robinson writes frankly about the galactic hinterland we inhabit. “The stars exist beyond human time, beyond human reach,” says the narrator. “We live in the little pearl of warmth surrounding our star; outside it lies a vastness beyond comprehension. The solar system is our one and only home.” 
Of the idea that we are destined to go to the stars and inhabit, if not the whole Universe, maybe the whole galaxy, Robinson cautions “it's a fantasy, of power, transcendence and a kind of species immortality. We have to get more realistic.”
May be the problem lies in our neighborhood. We live on a minor spiral arm located about 30,000 light years from the center of the Milky Way (see the schematic below).

In a denser part of the Galaxy, we would have needed a much shorter time to get to an exoplanet. But then, we would also have been exposed to a greater probability of having a star explode nearby destroying most of the life on the planet. A globular cluster, containing a 100,000 to a million stars, would also have been an interesting place. But then there may not be many stars with planets in the globular clusters (Messier 80, below).

Okay - but in any case, we are now stuck here, in the suburbs of our galaxy. I think we will be able to figure out a way to beat the speed of light - or somehow work around it. Otherwise, we are looking at slow solar system expansion for the next several centuries...


Larry Gilman said...

First, thanks for your excellent blog.

It’s easy to feel that something we’ve witnessed hundreds of times, even though just as a special effect, must somehow be practicable: e.g., faster-than-light spaceship travel. Yet this sort of felt plausibility has nothing to do with a thing's inherent possibility. Relativity, which forbids the acceleration of objects to speeds equal to or greater than that of light, has been confirmed to ever-greater precision by a huge variety of experiments for over a century now. It works. It works to the limit, so far, of our ability to measure. And while suggestive possibilities (e.g., time travel) can be pulled from the hat of extreme speculative physics, such tricks, even if the untested theories are is right, always have some extreme inconvenience attached to them, as in requiring more energy than there is the universe or squeezing travelers through the event horizon of a black hole. Our funkiest real-world stunts, like entangled-photon encryption, take place at the particle level: here in the mesoscale, there ain’t no free lunch. The Universe, on this level, is stubbornly well-behaved. The pattern of physics progress so far has been to modify our older ideas at the edge zones, at the micro and macro, not to make miracles possible. No antigravity, FTL, timeslip, matter transmission. Einstein does not replace Newton for automobiles or Apollo spacecraft, but corrects him in far-flung decimal places: and Simultaneity (or whatever comes next) is almost certainly not going to replace Newton _or_ Einstein in the mesocale with something magical, but will correct them in an even more far-flung decimal places. No warp 8, Mr. Sulu, now or ever.

Einstein already allows us to travel to Centauri and back in a single day of shipboard time -- if we are allowed to start with a Jupiter or two, and an equal amount of antimatter, as propellant for our gallant little craft, and as long as we don't mind being crushed by the acceleration. These are the kinds of inconvenience that the real world, so far as we have any real evidence on the question, always presents us with.

We are trained in bravado about the power of technological progress: “They said it couldn’t be done!” but now it has been done, etc. (This narrative always omits all the things they said couldn’t be done that, as it turned out, couldn’t be done.) But faster-than-light travel is not a technological problem: it’s a nature-of-reality problem. Its intractability is of a different order.

And even purely technological problems can be insurmountable in practice. For instance, there is no physics-theoretical reason why we should not control the weather or terraform Mars -- it’s just (just!) a matter of moving vast quantities of matter and energy about in certain precise ways -- and it's an article of faith for many human spaceflight enthusiasts now that the latter is obviously feasible, just a matter of determination and reformed budget priorities. In the meantime, in the real world, we can’t even stop ourselves from Venusforming Earth, and our civilization will be lucky to live long enough to confront the practical impossibility of terraforming Mars.

By the way, any form of planetary colonization fantasy -- not just interstellar travel -- has dimensions of religiosity, of "a fantasy, of power, transcendence and a kind of species immortality". Just look at the entire literature of the subject: its fiction, its advocacy, its rhetoric, tenor, claims about manifest destiny of the race, even apotheosis. I’ve published some of my skepticism about the space colonization movement, speaking as both a lifelong space enthusiast and religious person, here:



Salman Hameed said...


Thanks for a detailed reply as well as the pdf link. On one level, I agree with everything you have said here. Interestingly, I'm preparing for my astrobiology class tomorrow, and we are talking about the ethics of Mars exploration if we find microbes there. Of course, that also brings up the prospects of terraforming there. I don't think we disagree much on there.

However, I think our difference will be more philosophical and what we learn from history. Obviously, interstellar travel is one of the hardest technological problems. It is hardest because it appears to be limited by some of the fundamental physics we understand today. My attitude regarding that is that we will figure out a way around it. Modern physics has been around for a little over a century and the pace of information is exponential at present. Physicists have been able to slow the speed of light to a crawl in certain media (of course, other things in that medium will have to be even slower than that). May be this kind of manipulation will get us around the speed of light limit. Or may be it will come from working on biological clocks and slowing them down in a way that a 40,000 year travel will seem like 20 years. The point is that, I look at the history of science and believe that humans will find a way around it. You look at it and believe that we won't. I guess only time will tell... :)

Larry GIlman said...

850Thanks for thoughtful reply. It's fascinating how we can agree on the facts-so-far but have a different sense of what's plausible in the yet-to-be. Time will indeed tell. Add FTL travel to my list of things I'd love to be wrong about but don't think I am: accepting the scientific consensus on climate change is at the top . . . Larry