# The arithmetic of space travel (crossposted from Crooked Timber)

There’s been a lot of excitement about the discovery of two Earth-like[^1] planets, a mere 1200 light years away. Pretty soon, I guess, we’ll be thinking about sending colonists. So, I thought it might be worthwhile to a little bit of arithmetic on the exercise.

I’m going to assume (generously, I think) that the minimum size for a successful colony is 10 000. The only experience we have is the Apollo program, which transported 12 astronauts to the Moon (a distance of 1 light second) at a cost of \$100 billion or so (current values). So, assuming linear scaling (again, very generously, given the need to accelerate to near lightspeed), that’s a cost of around \$100 trillion per light-second for 10 000 people. 1200 light-years is around 30 billion light-seconds, so the total cost comes out roughly equal to the value of current world GDP accumulated over the life of the universe.

Even supposing that technological advances made travel possible over such distances possible, why would we bother. By hypothesis, that would require the ability to live in interstellar space for thousands of years. A civilisation with that ability would have no need of planets.

[joke alert on] On behalf of my fellow Australians, I’m going to make a counter-offer. For a mere \$10 trillion, we can find you an area of land larger than a typical European country, almost certainly more habitable than the new planets, and much closer. We’ll do all the work of supplying water and air, build 10 000 mansions for the inhabitants and guarantee a lifetime supply of food. I’m hoping for a spotters fee of 0.01 per cent.[joke alert off]

On a related point, what should we be wishing for here? The fact that no-one has sent a detectable signal in our direction suggests that intelligent life forms similar to humans are very rare. If habitable planets are very rare, then this is unsurprising – interstellar distances preclude both travel and any kind of two-way communication. If on the other hand, the emergence of intelligent life is common, then the evidence suggests that its disappearance, through processes like nuclear war, must also be common.

[^1] Where Earth-like means somewhere between Venus-like and Mars-like.

## 110 thoughts on “The arithmetic of space travel (crossposted from Crooked Timber)”

1. Jim Rose says:

Why bother with space travel? The russians put sputnik in orbit as an after thought and gave it little domestic coverage.

They realised its propoganda value when the western press went crazy. We are still in that space race.

2. quokka says:

@Paul Norton

Wormholes can exist as valid solutions to the equations of general relativity. General relativity certainly does not prohibit their existence. Which is a bit of a plus for the possibility of wormholes in view of the central importance of relativity to physics and cosmology. However you would need a physical process to form or maintain a wormhole and Einstein can’t really help with that. General relativity is basically a geometric theory of gravity. No such physical processes have been observed naturally but they may be physically possible. That’s the end of wot I know about wormholes. Wormholes are more than sci-fi and rather less than launching anything to Alpha Centauri anytime soon.

3. Ikonoclast says:

For an economics blog, it looks like we are all “Lost in Space”. I wonder when we will get back to economics?

4. I think it’s quite possible that the moon and mars will be colonised. Just not in the way most people might think. Instead of heroic space suited figures battling to survive on an alien world, all the real work will be done by robots and extensively tested for safety before anyone gets there. Then the humans will arrive and take up residence in their comfortable underground digs, safe from radiation and other hazards, while they live out their fantasy of being epic pioneers.

It would of course be much more sensible to have the robots build a nice living complex under the Simpson desert, but there are a lot of people out there who just aren’t sensible. How will this be paid for? Well people will get richer (I hope) and technology will improve making it cheaper (I hope). I expect that before too much longer it will be within the reach of eccentric billionaires. For example, if Richard Branson was passing around the hat because he needed a few more billion to leave the planet forever, wouldn’t you be tempted to chip in a few dollars? And there is a certain type of person who will save their pennies (or perhaps in the future million dollar coins) in order to go live on mars or the moon. While I expect most people will be content with earth, there are some people out there who are just weird.

5. Jim Rose says:

Sir Richard Branson please. knighted by labor and a convicted tax cheat. He spent a night in the cells after his arrest in the early 1970s for sale tax fraud on export rebates.

6. Paul Norton says:

Ronald Brak @104, have you read Stephen Baxter’s Evolution? It posits an interesting possibility for colonisation of Mars by robots.

7. @Paul Norton
The novel Evolution where where robots go all Galactus and eat mars? No, I haven’t read it. That level of technology isn’t needed, but may not be too far off. We know that self replicating machines are possible as they currently exist on earth. (We call it life.) And that travel at say 5% the speed of light shouldn’t be too difficult. This would made spreading through a galaxy fairly easy over a couple of million years. (Or much less time if you launch just a few probes at 50% the speed of light.) Given the number of stars and planets that are around, it seems to me that there is a good chance that this has already been done, possibly before galaxies even formed. People who blather on about how it only takes one species to do it often seem to ignore the possibility that one species did do it and the galaxy or universe looks the way it does because that’s the way they want it to look. That is, the stars are still burning because they didn’t feel the need to turn them off and they’re not arranged in a more orderly fashion because they’re not neatness freaks. As for interacting with us, well I’d go into that, except I’m too busy preparing for a diplomatic mission to open up channels of communication with a nest of ants in my back yard. Oh wait, actually I’m not on account of how I have better things to do with my time such as wax my surfboard. (I wonder how much dolphin wax rendering down one dolphin makes?)

8. Jim Rose says:

when did people start to do scientific experiments on space flights? I assume this developed as a cover for what was joy riding around the earth and then too the moon.

putting communication and like satellites in orbit was a good idea.

9. TerjeP says:

I think research on rockets was initially just a way to hide (in full sight) research expenditure on ballistic missiles.

10. @John Mashey
Well, fella –
There’s a whole mob of ’em brewing meth over the road.
Insectoids, I reckon.
‘Cos if you disturb their activities – like by taking out the garbage or collecting your mail – they go spastic – running around in circles, frothing at the mouth, screaming abuse and death threats – then they phone the local rozzers who come and bash at your front door.
I reckon queensland has been taken over by some sort of cosmic scum.
Next week they might slip up and give a hint whether they come from outer space or rural victoria.