“ljk, Yes, it’s possible that intelligence is so common and mundane that 100% of ETIs have no interest in contacting us and that they coincidentally show no obvious evidence of their existence.”

Actually I was mainly referring to the fact that the Milky Way
galaxy is so big and so full of so many star systems and other
neat objects that an ETI society might easily miss us among all
those wonders.

However, if there are lots of intelligent beings, and especially
if they are ahead of us, then that too might explain why we
aren’t being contacted or visited – or at least certainly not
figuring it out if we are being waved at.

I am certainly all for preserving our history, knowledge, and
especially ourselves from potential future disaster. I also
pointed out that by the time that real interstellar travel is
made possible, humans may be radically different from
what we are now or have been superceded by much more
advanced beings originated by us.

As for water and ice being heavy – that’s what we should do,
hollow out a bunch of comets and fling ourselves into the galaxy!
We will have shielding and a water and fuel supply all in one
package. And if we have to move a bit slower to get where
we want to go – hey, the galaxy is over 10 billion years old,
what’s a few thousand years?

Besides, even a planet with a reasonably amiable temperature (say, -50 C to +50 C), water (either frozen or liquid) and something resembling a (convertible) atmosphere would do for terraforming.

As for an insurance against global-scale human stupidity, even a self-sustaining Mars base might do.

@david lewis: straight from my heart!

But my argument is that, so long as we cannot rule out universal self-extinction then it behooves us to “purchase the insurance policy” that a near-term, frozen embryo, interstellar mission offers.

As for your radiation problem, water tanks (or ice) is how most suggestions I’ve seen do it. At the risk of sounding like a Reynolds junkie, that’s how they do it in his Revelation Space series, they just cover the outside of their ship with tonnes and tonnes of ice. However there’s a catch. Water’s pretty heavy stuff. It doesn’t have really big nuclei or really tight core electrons to soak up the radiation like, say, lead does, and I suppose the idea is mainly to stick a lot of it there because it’s cheap and easily replenished. However, all of that is mass. If you want to accelerate your ship up to any appreciable speed you really don’t want it to be carrying a few thousand tonnes of dead weight. They only do it in the aforementioned Reynolds book because they have arbitrarily powerful drives which draw energy from the vacuum… Fantasy science which we couldn’t use in real life.

And using radiation to accelerate you, I think there’d be some kind of conservation of momentum problem there… right?

I think, and I mean this to ljk and John Hunt, that the most important thing is to get the smallest possible mass accelerated to relativistic velocities. But then there’s the above radiation problem, which would be much worse than in-system flights if you’re travelling long distances for a long time at high speeds, upping the energy and the total dose. That’s why I think that if you sent the most robust possible probe you’d get the best result.

This has been well discussed in the New Scientist article “Space Mission Impossible”, 25 February 1995, the 1966th issue. (Available online with subscription)

If self-replicating probes sound like fantasy, remember that life already does things just as remarkable. I think something packed with mesoscale replicators – things the size and complexity of ants – and the ability to decelerate them without killing them (killing being the right word for things this close to organisms) is what’s needed. The chemistry shouldn’t be impossible – find a way to make it assimilate the organic and inorganic matter on the asteroids and comets (or holy of holies, planets), and there are biological pathways bacteria have used to assimilate nearly anything, and as for coordination, ants and termites, things with this level of complexity, already run dumb programs to make marvellous mounds. Now they don’t need to store this data in their cells, and you don’t need to mess around with chemical signals – you beam it to them. Nanoscale radio transmitters and receivers are already on the table – see New Scientist, 17 September 2005 for example – and you just need to equip them to receive the data and tell them to organise to do X, Y and Z.

The benefit of this is you could engineer these things with DNA-equivalent repair enzymes like you find in radiodurans, and you don’t particularly care what happens to them so long as one or two get there intact, whereas with baseline human embryos, you need to take a lot more care.

The United States is presently in a state of national emergency.
(It has been continuously since the early 1930s!) This fact is not
generally known or appreciated by the public. The Presidential
proclamations of national emergency issued under Roosevelt
(1933), Truman (1950), and Nixon (1970, 1971) were not
terminated when the crises that spawned them had passed.
Our country remains under four separate active declarations
of emergency.

Is this still true 31 years after the article came out?

And if they don’t have a space program but still developed
radio telescopes and lasers, what motivations would they
have to contact us?

I don’t meant this to sound quite so negative, but while a
more advanced ETI might want to study us as another data
point in their Encyclopaedia Galactica, how many real
motivations would they have to contact or visit us?

How about putting a collection of water tanks around a star
probe to protect it from radiation? And is there any way to
turn radiation from our enemy into our friend, such as
somehow using it for propulsion?

I’m doubting that we’ll find an exoplanet with a biosignature any time soon. Our system contains a planet teaming with life and yet Mars and Venus probably show no biosignature. And if 5% or more of exoplanets containing liquid water spontaneously evolved life then I think we’ve got a huge Fermi Paradox issue. Rather, I think that the big breakthrough will be the discovery of a planet that calculates to have liquid water. I think that it will be unlikely to show a biosignature and yet would still be a candidate for colonization. I just wish that at that moment of public excitement that we could come forward with a practical (e.g. ISS cost-level) interstellar mission plan.

——-

Benjamin,

Very good point about energy lost due to particle deflection. Hadn’t thought about that. Perhaps someone here could hazard an educated guess as to whether deflecting 5,000 years worth of high-speed but very low mass particles would significantly slow the craft. I understand that “A few cosmic rays pass through your body every second of every day, no matter where you are.”

Your point also makes me wonder about what sort of drag a magnetic field would place on the interstellar medium although our craft would not be traveling at relativistic speeds so I don’t know if we’d be inducing ionization nor do I know if there are a lot of ions out there apart from cosmic rays.

Also…

I agree that it makes a lot of sense to send small constructors then beaming genetic info later rather than actually worrying about getting fragile things through the radiation. But the premise of a Project Arrow (i.e. moderately long duration, frozen embryo mission) is that it is insurance for humanity in case we self-destruct due to technologic advancement. I myself have no confidence that humanity will not develop self-replicating chemical, biologic, or nanotech threats within the next 100 or so years. Hence the rationale for seeing if we can protect fragile biologic things from the radiation of interstellar travel.

———

Andy,

> There seems to be an assumption that going to computer-based mechanical systems will somehow magically get around the radiation problem…The Galileo probe lasted about 8 years in the Jovian system.

I understand that around Io radiation is about 1,314,000 rems per year. The average value for background radiation on Earth is around 0.36 rems per year. If the Galileo probe could last 8 years then our craft should do fine even on extended trips if it had magnetic protection against cosmic rays and had electronic equipment designed to be rugged against radiation and any “sclerosis from dormancy” (I made that up, can you tell?).

Maybe corny, also very depressing. Around 1.6 “million” US soldiers have served in iraq. The medical costs from those injured, physically or mentally, from the conflict will be a drain on the US treasury for decades after the last soldier leaves.

The trillion the US spends on its military, matched by the trillion the rest of the world spends on their various militaries, is around 2 trillion a year our species wastes. Half of that spent on space, with half spent to modernize the third world countries, would give us bases on several moons and planets within the next 25 years. After that when we are ready to tackle interstellar travel we could easily spend 3-4 trillion a year as a species.

The biggest challenge we face in exploring and colonizing space is not the technological one, it’s our own nature. The technology we can eventually develop, but our nature ….

That nature might also be one of the biggest threat people on a generation ship face. The earth is large enough and has a resilient enough biosphere that up until recently it could handle our wars and conflicts. A single person on a generation ship might be able to wipe out the entire ship.

“@ljk, July 8th, 2008 at 9:55: I agree with you that intelligent robots could (nearly) always do a better job at interstellar exploration that humans, but the main rationale and justification for humna sto go there would not be just exploration, but settlement and perpetuation of our species and civilization.”

Do not expect the “humans” who may one day journey to the
stars to be anything like us.

The only exceptions will be groups of “baseline” humans who
refuse to change and decide to leave Earth and perhaps even
the Sol system to preserve themselves and they way of life.

Otherwise, expect the galaxy to look like this some day:

http://www.orionsarm.com/main.html

Even if this scenario is ultimately wrong, I still find it more
likely than what we see most often in Star Trek.