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."

Re:I should hope so...

[Homr Zodyssey]

Silly! They aren't aliens. They are man-made robots.

Re:Duh

[isomeme]

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 [wikipedia.org] on the topic.

Re:How close minded can one be?

[Kelson]

If an alien race has had advanced technology for 100,000,000 Trillion years

That would be a neat trick, considering that as far as we can tell the universe is only on the order of 10 billion years old. Though 100 Quintillion years with high technology is probably long enough to figure out time travel, so I suppose this could still work.

Re:Heh

[tha_mink]

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.

Comment removed

[account_deleted]

Comment removed based on user account deletion

I call BS

[Spazmania]

If you've ever played "Spaceward Ho" you'll recognize that the author has proposed an asinine strategy for exploring the galaxy. Indeed, if you try to play Spaceward Ho by that sort of probing you'll rapidly get your tail kicked.

A more rational approach is exponential: You colonize a solar system. Then from that system you launch probes at anything reachable. Then you colonize everything reachable that qualifies. Rinse and repeat.

The main disc of the galaxy is about 100,000 light years across. Assume 10% light speed for probe travel time, light speed for information return and 50 years for each new colony to build infrastructure to a point where they can launch probes. You'd have 90% of the galaxy explored in three or four million years -- almost 4 orders of magnitude less than this fellow's estimate.

Re:Based on poor assumptions

[teslar]

Why 1/10th c? Why not 99% of c? Why not faster than c?

You're still thinking Star Trek when you should be thinking Stargate.

1. Obtain a good enough understanding of space-time to create wormholes to any destination you want.
   
2. Make a list of all destinations you are aware of.
   
3. Send a probe to all of them, evaluate each destination and scan for more destinations from there.
   
4. Go to step 2.

Space ships are just such a small-planet-with-water way of thinking.

Re:Based on poor assumptions

[Nyeerrmm]

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:

1/10 c: 3.263e29 tons .99 c: 1.534e292 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 .99 c: 2.69 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 .99 c results are off by thousands of orders of magnitude.

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.

Re:Some potentially invalid assumptions?

[soft_guy]

Actually I think propulsion systems have gotten faster in the last 200 years.

Re:a few points to ponder though

[Anonymous Coward]

"I recall reading something once that said people in the early 20th century believed the human body would shake apart if we traveling faster than 25mph."

Men have been riding horses at greater than 40mph since before recorded history. Trains crested the 80mph mark before the US civil war (mid-19th century) and 100mph by the turn of the century.

Cassini speed wrong

[dsanfte]

Plus, Cassini isn't travelling nearly that fast. 30km/s, not 30,000. That's 1/10000th of c.

Re:do the physics, it's about DE-celeration

[theGreater]

Actually, it would take substantially less as you've already shed a lot of mass, AKA superfuel. So you wouldn't accelerate halfway and decelerate halfway, you'd accelerate 2/3 and decelerate 1/3. Or something like that -- someone better at the various calculus-based disciplines than me might be able to give a better ballpark.

Re:I once worked out

[Anonymous Coward]

a quarter million years is a neat trick, considering that the Andromeda galaxy is 2.2 million light years away. It's the furthest object visible to the naked eye.

(Win free drinks! How far can the human eye see? 2.2 million light years)

Why about self-replication?

[benhocking]

FTFPDF:

One could also contemplate the idea of launching selfreplicating probes i.e. probes that are able to build copies of themselves by harvesting materials from each stellar system they pass.

The construction of such probes are technologically as difficult as producing the conventional probes proposed to be used to explore the Galaxy, as these conventional probes must operate for millions, if not billions, of years. Therefore one can argue that self-replicating probes should instead be used to explore the Galaxy, as using such probes will lead to much faster exploration times, as the number of probes increase as time goes by.

In fact if self-replicating probes, or von Neumann probes as they are also termed, were used to explore the Galaxy it has been shown that a search of the entire Galaxy will take 4 10^6 3 10^8 years dependent on the speed of the probes (Tipler 1980). This is much faster than using the non-replicative probes proposed in this paper.

So, if they figure out how to use self-replicating probes, the entire galaxy could be probed in 4 Myr - 300 Myr. I suspect solving that technological problem would be a worthwhile investment.

Re:SURVEY

[ray-auch]

You missed out:

On a ship shaped like a sleek running shoe, perfectly white and
mindboggingly beautiful... (if you can stand the manic ship's computer and the terminally depressed robot).

Re:SURVEY

[Anonymous Coward]

Michael Moore? Wasn't it Pavarotti?

interesting fact: the CATCHPA for this post is 'incest'

Re:SURVEY

[Goonie]

you forgot (j): being piggybacked by CowboyNeal.

Re:Heh

[Fizzog]

"we should expect alien technology to be roughly the same as ours, give or take a century or so"

Not really.

You need to allow for the mass extinctions in the Earth's past.

If the mass extinction 250 million years ago (Permian-Triassic) had not occurred then intelligent life may have evolved on this planet over 200 million years ago.

It would be quite possible for an alien race to be hundreds of millions of years more advanced than us just due to luck.

Re:Eat at Earth

[mok000]

That's exactly right. One parsec is the distance at which the diameter of the earth's orbit around the sun (1 AU) appears to be 1 sec (=1/360 of a degree).

Re:Eat at Earth

[nebosuke]

1 AU is the mean radius of the earth's orbit, not the diameter.

Re:Eat at Earth

[darklordyoda]

I thought the Kessel Run was measured in distance because the Run involved skimming very close to a cluster of black holes, and thus only the boldest would dare to take a shorter route...


*takes pleasure in fact I'm still at least above Trekkies on the geek hierarchy*

Re:Based on poor assumptions

[Alsee]

The article makes the assumption that alien civilizations have advanced enough that their spaceships are 1,000 times faster than ours - not unreasonable.

No, it is quite unreasonable. The Cassini probe is going 32km a second (71,000mph / 115,000kph). That is more than a thousand times faster than the record less than a hundred years earlier.

We pretty much already have the technological capability to get a small probe up to c/10. We have the knowlege and basic designs to do it... it is already "mere" enginering and $$$$ problem for us today. If we simply chose to allocate several gigabucks to do it, we could with absolute certainty get something up to c/10 within 10 to 20 years.

Assuming our civilization doesn't implode in one way or another in the next few hundred years, getting well over c/10 is a certainty. The only uncertainty is whether the speed of light really is an inviolate limit, or whether some unimagined phyisics will have us exploring the universe way beyond the speed of light.

But looking at his paper I see that the real problem with his figure isn't his c/10 speed limit, but his laughable assumptions and exploration strategy of tiny fixed number of probes zig-zaging between stars almost one at a time. Even with conservative assumptions.... assuming just 0.5c and an interstellar civilization manufacturing just one probe per year... and assuming a reasonable strategy... the entire Milky Way could be explored in just a few million years.

With more reasonable assumptions, the entire exploration rapidly becomes light-speed limited. After the initial local exploration, an advanced technology civilization could mass produce replication-capable miniprobes or microprobes and use a maximized galactic search strategy. Send those probes out on a straight line courses directly to the various sectors of the galaxy... with the worst case probe taking between 150,000 years and 225,000 years to reach the opposite side of the galaxy. Within a handful of years the probe locates an uninhabited rock and sets up an automated factory to send out a few million miniprobes or microprobes, which scout all of the stars in that sector within about 20,000 years. Elapsed time: less than a quarter million years to get a probe to every star.

And really you only need the tech and pay the $$$$ to make and launch *one* such replicator miniprobe. After that, the entire exploration proceeds automaticaly and "for free". We will probably have this technology within a hundred years. Some time within the next 10,000 years... hell lets call it some time in the next 100,000 years of civilization... someone can and will do somthing like this (if we are still around). Once anthing remotely like this gets started, it doesn't much matter how you tweak the assumptions. The most it does is add in a small multiplier factor to the timeline. It is almost inconceivable that we (assuming we are still around) will not have probed every star in the Milky Way within a million years from today.

10,000 years or 50,000 years of technology and manufacturing is an insignifigant blip in the analysis. That technology level and time span means that a civilization can and will trivially produce the resourses needed to explore at a stbstantial fraction of the speed of light. Actual strategy and behavior only accounts for a small constant multiplier. the defining factor is the speed of light, and it locks down the final answer somewhere between 160,000 years and just a few million years. His result of needing 10 BILLION years to explore just 4% of the Milky Way is comical.

The only real question is whether the speed of light really is inviolable. If that falls, then I say we only need between 100 and 1,000 years of technology and then we explore at close to the limit of whatever that new physics makes possible. If we can explore and *get answers* at far faster than the speed of light, then there is vastly more incentive to actually do so.

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