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Somewhere I read that the nearest earth-like planet is 19 light years away.

If this is true, and there are no closer earth-like planets, do we have the knowledge, technology and resources to colonize it?

I mean if the world decides to spent trillions of dollars or even more, can we build huge spaceship that could bring people there?

I guess they will have to live decades in the ship and their children would reach it.

The technological restraints I think of is the launching and landing of such construction and the speed, it must reach it in reasonable time.

Can we accelerate such ship at least in half of the speed of light, so it could bring the people in 40 years maximum?

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    $\begingroup$ A trifle broad, I fear $\endgroup$
    – Everyone
    Nov 9, 2014 at 9:31

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Do we have the knowledge, technology and resources to colonize it?

Simply put, no.

First off, you need to forget about knowledge, technology and resources and look to biology, sociology, and psychology. How many people would be needed to create a self-sufficient modern colony? The number is rather large. It's not 100 people, or even 1,000. It's at least 14,000 per Cameron Smith, "Estimation of a genetically viable population for multigenerational interstellar voyaging: Review and data for project Hyperion." Acta Astronautica 97:16-29 (2014), and that's risking extinction. Sending 40,000 people is a better bet.

We can't do that. Not even close.

Suppose we knew how to put people in what science fiction authors call "cold sleep." We can't do that, not even close. In that case, we don't need 40,000 colonists. We just need 40,000 embryos, plus 4,000 or so young women in cold sleep who will need to get very busy getting busy birthing implanted embryos upon waking up.

What about the target planet? We would have to terraform it if the target planet doesn't contain a breathable atmosphere. We can't do that, not even close. The closest we can do with current technology is to do what we've done on Earth, which is to try to de-terraform it. On the other hand, if the target planet does contain a breathable atmosphere, that would most likely mean bacteria and viruses that would greet the colonists with a hearty "Yum!" The colonists would have no defense. Either way, this is a showstopper.

Ignoring that, can we send a spaceship containing a few thousand young women in cold sleep plus 40,000 embryos in cold sleep to a habitable planet 20 light years away? Those colonists need to eat. They need to eat quite a bit since each colonist needs to eat for two for twenty years straight. We need to send a self-sustaining food source. We can't do that, not even close. Every attempt to make a completely closed, self-sustaining ecological system has failed -- and that's right here on Earth. If we could do that, we would need to send a lot, lot more than 4,000 women and 40,000 embryos.

Even with the reduction from 40,000 people to 4,000 women, this spaceship is still extremely large. We need to send animals, plants, farm equipment, materials to make dirt, mining equipment, manufacturing equipment. This thing is several orders of magnitude larger than the International Space Station. Scaling things by an order of magnitude is hard. Scaling by several orders of magnitude--we can't do that, not even close.

Suppose we can get the spacecraft to 1/1000th the speed of light after exiting the solar system. That's about twenty times faster than the current velocity of the Voyager spacecraft, and those are tiny. Getting something the size of hundreds of space stations to that speed is once again a we can't do that kind of proposition. Scaling up by a factor of 100 to 1/10th the speed of light is science fiction. Even at that speed, it will take 200 years to reach the target star. We need equipment that will remain reliable and viable for centuries. This is yet again a we can't do that kind of proposition.

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  • $\begingroup$ If you separate out the distance problem from everything else, the dream of colonizing/terraforming Mars, if ever realized, would teach us a lot about what you'd have to bring with you elsewhere. $\endgroup$
    – Anthony X
    Nov 9, 2014 at 15:08
  • $\begingroup$ @AnthonyX - Exactly. Colonizing Mars is perhaps doable. No need for cold sleep, no need for that huge colony size. That we don't know how to make closed, self-sustaining ecology remains problematic, however. A 3D printer can make something that looks like a chicken, but it wouldn't be edible. The colonists would have to grow their food, which is something we don't know how to do (yet). $\endgroup$
    – David Hammen
    Nov 9, 2014 at 16:06
  • $\begingroup$ Callous as it may come across as ... the analogy to the ancient discovery of America (Vikings etc) is close. When the Viking colony ships left, those left behind didn't know whether they would ever see the colonists again. Yet the colonists went anyway. $\endgroup$
    – Everyone
    Nov 9, 2014 at 17:06
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    $\begingroup$ Viruses work by hijacking the cell's own reproductive machinery. Alien viruses could not attack us unless they use DNA with the same genetic code, which is unlikely. Terrestrial viruses commonly don't attack organisms across a wide range of species. Alien bacteria might be more dangerous, but they won't have evolved to parasitize terrestrial organisms. $\endgroup$
    – Keith Thompson
    Nov 10, 2014 at 19:20
  • $\begingroup$ You need a huge colony size for it to be self-sustaining, assuming you need to maintain some kind of technologically-advanced society. We're not talking about thousands of people, but hundreds of millions. The chain of precursor and intermediate technologies you need to make even a modern hammer is immense, let alone something like a chip fab or a power plant. $\endgroup$
    – Dan Hanson
    Mar 23, 2020 at 23:24
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The biggest problem with long duration interstellar missions is progress back on Earth: the landing party would be greeted by Earthlings who waited a few centuries and used much newer faster and safer travel methods.

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  • $\begingroup$ Given the immense difficulty and the heavy physical limits of interstellar travel, I find this a questionable idea. Things can only get so much better, and even in the case of beam-core antimatter engines you're edging up against the limitations of specific impulse. $\endgroup$
    – ikrase
    Mar 24, 2020 at 7:58
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Half the speed of light is out. Any speck of dust at that speed would be a disaster (Space is not completely empty. Just mostly empty. )

That would mean going a lot slower. Which in its turn implies a much longer journey. This probably changes from "their children would reach it" to "many generations later we would reach it".

And that implies a longer lasting ship. Which is something we probably can not do yet. Just consider the food problem. We did try to create sustainable closed ecospheres here on earth, but so far we failed. We always needed outside resources. Now consider that in a closed ecology aboard a spaceship where there is no way to get outside resources. There is just what you brought along (which as little as needed to save mass).

Still, technically we may be able to do this in a few decades.

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