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Extraterrestrials Probably Haven't Found Us - Yet
kasparn writes "The Guardian today has a story about the Danish astrophysicist Rasmus Bjoerk, who recently conducted simulations on how long it will take to colonize the Milky Way. The basic idea is to send out probes in different directions (including various heights above the galactic plane). He estimates that it will take some 10 billion years to explore 4 % of the Milky Way. Since the age of the Universe is of the same order, his conclusion is that aliens can't have had time required to find us yet."
You'd wait until you had the technology to make self-replicating probes, and the galaxy could potentially be explored in thousands of years.
Bingo. As usual, Wikipedia has a good article on the topic.
When all you have is a hammer, everything looks like a skull.
Bitten by the ole RTFA bug eh. The quote from the article is
He found that even if the alien ships could hurtle through space at a tenth of the speed of light, or 30,000km a second, - Nasa's current Cassini mission to Saturn is plodding along at 32km a second - it would take 10bn years, roughly half the age of the universe, to explore just 4% of the galaxy. His study is reported in New Scientist today.
No mention of colonization there.
Plus
Mr Bjork confined the probes to search only solar systems in what is called the "galactic habitable zone" of the Milky Way, where solar systems are close enough to the centre to have the right elements necessary to form rocky, life-sustaining planets, but are far enough out to avoid being struck by asteroids, seared by stars or frazzled by bursts of radiation.
So there's that too. Looks like you should have taken a look at the article first.
You'll have that sometimes...
- Obtain a good enough understanding of space-time to create wormholes to any destination you want.
- Make a list of all destinations you are aware of.
- Send a probe to all of them, evaluate each destination and scan for more destinations from there.
- Go to step 2.
Space ships are just such a small-planet-with-water way of thinking.Also, assuming they use some kind of rocket technology (that is, technology that shoots stuff out one side to propel the vehicle in the other), 1/10 c is much more realistic than something approaching c. Assuming a technology that has 100 times the specific impulse as our current vehicles (the best ion thrusters get ~4500 s,) I get using the rocket equation that the initial mass to move 1 ton of cargo is:
.99 c: 1.534e292 tons
.99 c: 2.69 tons
.99 c results are off by thousands of orders of magnitude.
1/10 c: 3.263e29 tons
Even then this seems absolutely ridiculous. If you used a matter/antimatter reaction so that your propellant was pure electromagnetic radiation (thus your exit velocity is c), you'd get these results
1/10 c: 1.105 tons
Of course, these are not adjusted for relativity, since I don't know any simple equations to do that. I would imagine (as a wild-ass guess) that the 1/10 c estimates are close, but the
Basically all I'm saying is that 1/10 c seems fairly reasonable. It's not feasible given our current technology, but its within reason. If you start looking at things like space-time warpage, then we have no idea on any usage or capabilities, so any kind of theory based on it gets even further and further from reality.
By the way, I am a rocket scientist, but only a student, and not a physicist at all, only an interested amateur.