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."

Based on poor assumptions

[BadERA]

Why 1/10th c? Why not 99% of c? Why not faster than c? Granted faster than light travel is nothing more than theory and dreams at this point, but this article makes the assumption that other civilizations have not progressed in the field of physics any faster nor further than we ourselves have, to date.

Duh

[Reality Master 101]

Sheesh, talk about "proof by lack of imagination." This is supposed to answer the Fermi Paradox?

You can't explore a galaxy with a handful of probes. 72 probes??? First of all, if you're going to do it that way, you'd create hundreds of thousands of probes, if not millions of probes (mass production would reduce the cost). Second, you still probably wouldn't do it that way. You'd wait until you had the technology to make self-replicating probes, and the galaxy could potentially be explored in thousands of years.

Not impressed by this guy's argument.

Well, DUH!

[QuantumG]

To paraphrase: But Sir! If we only send 8 probes it'll take billions of years to search a mere 4% of the Milky Way galaxy!

That's why you have to make the probes self replicating.. utilizing in-situ resources to make more probes at each star they visit, the growth becomes exponential and it only takes a few thousand years to search the entire galaxy. And seeing as we're visiting all these stars anyway, how about looking for planets that don't have life on them, but have nice suitable conditions for starting life on them. Cover a virgin planet with a wide variety of Earth lifeforms and fly on.

How close minded can one be?

[quincunx55555]

...his conclusion is that aliens can't have had time required to find us yet."

Under what time frame? If an alien race has had advanced technology for 100,000,000 Trillion years, then they'd have plenty of time (and would probably have technology more advanced then sending out physical "probes"). It doesn't see likely from what we know, but I don't think we actually know that much.

Why is it that scientists think that only what we can achieve is possible? It's like us looking for aliens using our technology (SETI). Not that it's impossible, but I'd think other intelligent being could come up with other forms of communication than our own; even if it wasn't more "advanced".

Re:The Galactic Lottery

[solafide]

Plus he's not taking into account multiple alien races. So that's like double 4% which is almost 8%. Do that a few hundred times and you get 108%. This guy clearly doesn't understand math.

Nope, do that n times and you get 1-(.96)^n probability they find us.

Self-Replicating Probes?

[transiency]

What about probes that land and replicate on foreign terrestrial bodies? 1 probe lands and makes 10 or a hundred of itself. Send out 10 of these type of probes, and exponential growth will do your work for you.

Re:Based on poor assumptions

[QuantumG]

Yeah, imagine a civilization that, having discovered enlightenment, actually embraced it and dedicated their industrial base to further it, instead of shuffling it off to the minor specialists who they then make beg for funding, typically by militarizing their research.

More than one...

[neurocutie]

Whatever his assumptions are that leads him to 4%... it seems that he is considering only the probability that any ONE alien civilization is looking. But in all likelihood there are many, if not millions of alien civilizations out there than may be search, so the probability that any ONE of those million will find us seems quite a bit higher than 4%.

Re:Duh

[exp(pi*sqrt(163))]

You're right, this guy hasn't thought things through. He rejects self-replicating probes because they'd compete with the original explorers. I think that's a lame argument, but let's accept it. Even human colonies spreading out from Earth, and moving onto new stars every generation or two (and sending out some non-self-repicating probes while they're at it), would explore the galaxy far faster than these probes. If humans survive the next century or two I'm sure they'll explore the galaxy in person far faster than this unambitious probe idea.

Re:Well, DUH!

[Ignorant Aardvark]

To be pedantic ... the absolute minimum time to explore the whole galaxy from Earth is about 80,000 light-years, because the farthest part of the galaxy is about 80,000 light-years away from us. Although to be even more pedantic, double that, because you can't really say you've explored until the information about what you've found has made it back to you.

So, yeah, you can't explore the galaxy in only a few thousand years.

Re:Duh

[Mr. Slippery]

you'd create hundreds of thousands of probes, if not millions of probes..You'd wait until you had the technology to make self-replicating probes, and the galaxy could potentially be explored in thousands of years.

Uh-huh. And how many self-replicating probes traveling at .1 c have you developed?

The fact that we can imagine self-replicating interstellar probes doesn't mean they are practical or possible.

Re:Duh

[muellerr1]

I tend to agree. Think about it this way: how much of *our* resources are we currently using to explore the entire galaxy? And how much are we likely to in the future? The answer is, not much. It's a vanishingly small return on a huge investment to explore the galaxy, especially when we've got bigger problems at home and so much raw material in our own solar system. The costs of sending crap into deep space will probably outweigh the benefits of mineral riches for far into the future, despite Ridley Scott's imagination. Unless there are aliens within a few hundred light years of us (which at this point is a vanishing probability given that we've found under 200 exoplanets within 200 parsecs [exoplanets.org]) we won't find any aliens -- and they won't find us, either.

Re:Well, DUH!

[myowntrueself]

That's why you have to make the probes self replicating

Hopefuly they don't need to see any Earth-based SciFi to know that self replicating probes are a phenomenally *bad* idea.

Re:Some potentially invalid assumptions?

[LWATCDR]

"1. Probes sent by extraterrestrials cannot travel faster than our probes."
Actually he is claiming that extraterrestrial probes can travel 1000 times faster than our probes.
So far propulsion systems are not following Moore's law and there is no evidence that they ever will.
This is a simulation made using guesses I would say that it is very interesting.

Re:Based on poor assumptions

[Marlow the Irelander]

Nasa's current Cassini mission to Saturn is plodding along at 32km a second

c/10 is 30,000km/s. The article makes the assumption that alien civilizations have advanced enough that their spaceships are 1,000 times faster than ours - not unreasonable.

a few points to ponder though

[bl8n8r]

We are terribly limited by our own ignorance. We barely have an understanding of space travel, dark matter, string theory, time-and-space and many other things. 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. The knowledge and intelligence of an alien civilization could be so far beyond our comprehension and knowledge that it's almost futile to even speculate. Right now, we think nothing can travel faster than the speed of light, however it wasn't too long ago people also believed the world was flat. I guess we can only make assumptions based on our current knowledge levels, but we must also take into account that there may be ways of doing things that we've simply not discovered yet, or cannot comprehend.

It has been done already

[140Mandak262Jamuna]

The aliens knew they could not send out probes that carry enough energy to beam back the information. So they built generalized adaptive Turing machines, (a machine that can build itself) of incredibly small dimension. They created billions and billions of these machines and scattered them. These machines are so tiny, they get carried by the solar wind and other cosmic radiation.

One of these Turing machines reached Earth about 4 billion years ago. It first had to start by building very simple amino acids, then it graduated to proteins, then to RNA and then to DNA, and then these DNA machines built bodies around them and started using natural selection to evolve into more and more capable organisms. The final aim of these DNA structures is to build powerful radio beacons and send the information back to the original aliens who created these molecules and scattered them to the (solar) wind.

do the physics, it's about DE-celeration

[gelfling]

IT's not the ACCELERATION, it's the DECELERATION. Even if you could apply some force to slowly accelerate a massive space ship, once you got it up to that speed wouldn't it take K^2 (squared) units of fuel to slow it down it again? So let's say it takes a million tons of some super fuel to get your space ark up to speed. Wouldn't it take a million million tons to park it again?

Re:Actually the cylons will find us first

[AHumbleOpinion]

It may be cheaper to send robotic missions, but probably not as much fun. For a race serious about exploring a significant fraction of the galaxy ...

I'll refer to my second sentence: "Then if anything interesting is found send the "manned" missions." Do you realize how much nothing is out there, where is the "fun" in finding another dead rock just like so many others? Forget the romantic fantasy of spaceflight, it will be uncomfortable, boring, and stressful. With robots doing the scouting there will be a greater number of interesting things for the manned missions to investigate, possible more than could be sent out. Now if manned missions did the initial exploration, the people would largely see nothing of particular interest. I think you are vastly overestimating the novelty of finding another dead rock in space, sure it would interest us, but a generation born after such discoveries become commonplace?

... I doubt if the manned vs unmanned costs are an issue driving the choice of exploration method.

Actually it is a major point of debate, scientists favoring a large number of robotic missions, politicians favoring a handful of manned missions. Manned missions are multiple orders of magnitude more expensive.

Re:Based on poor assumptions

[gobbo]

But the bad assumption remains: rocket technology. Like I said, who's to say they haven't gone further with physics, or pursued a different, or completely unthought-of (to us) means of travel?

No kidding. "If we put a thousand horses on a carriage, it still won't be fast enough to lift from the ground. But if we could discover the rumoured winged horse, we can do it."

Something tells me that we're a couple of paradigms away from comprehending galactic distances as attainable. Propellant propulsion systems are to interstellar travel what horses are to flight.

These are NOT self-replicating probes

[Dr. Spork]

This work is irrelevant to the Fermi paradox since Fermi assumed the probes would replicate themselves. Here is what Bjork says about self-replication:

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 4 106 3 108 years dependent on the speed of the probes (Tipler 1980). This is much faster than using the non-replicative probes proposed in this paper. However, one should note that there could be complications with using self-replicating probes. Tipler (1980) himself points out that the program controlling the self-replicating probes would have to have so high an intelligence that it might "go into business for itself" and become out of control of the humans who designed it, resulting in unforeseeable consequences. Since the machines uses the same resources as humans, a self-replicating machine might regards humans as competitors and try to exterminate them. Chyba (2005) also points out that self-replicating probes-might evolve to prey on each other, creating a sort of machine food-chain. This would of cause drastically reduce their exploration rate. Therefore the conclusion is that if perfect selfreplicating probes could be built, these could explore the Galaxy much faster than the probes suggested here. However, building less-then-perfect self-replicating probes could, in the worst case scenario, have fatal consequences for the human race.

I think the real debate should be about self-replicating probes. Is the author assuming that every civilization capable of building these is automatically freaked out by potential doomsday scenarios, to the extent that none will be built? Even if it is foolish, I found that it pays to expect more foolishness in the universe rather than less.

Re:Arrogant presumptions

[TobascoKid]

A scientist saying things are a certain way based on a theory cannot be right until the theory is proven true and absolutely correct

Theories are rarely (if ever) "proven to be true" as it's a lot easier to show that something is false rather than absolutely 100% true and correct. Science is more about finding the best model to fit the data than a quest for certainty. Even experiments don't prove theories, they just add to the evidence that a model is the best explanation for a certain phenomenon.

Re:Duh

[terjeber]

If the aliens have an organization like NASA, and some Alien-Aliens drop by and donate Faster than Light technology and two space elevators to our Aliens, they still wouldn't be able to colonize their own solar system in 10 billion years.

Re:Based on poor assumptions

[inviolet]

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 [...]

Why do you assume that any sane civilization would send out macro-sized probes?

Nanoscale or even microscale probes would completely change the economics of space exploration. And they would avoid the very serious problem of atomic abrasion that occurs at and above 0.1c.

That's why I laugh when people spot human-sized UFO craft. If there are UFOs here, they're microscopic.

Re:That's assuming...

[Dr. Spork]

More puzzlingly, he assumes these probes can repair themselves for and keep running for billions of years, but they can't self-replicate. Really? If the probe can repair every potential internal probem on its own, the capacity to self-replicate should come almost for free.

Re:Duh

[isomeme]

We do; you are an example of such a device. :)

I laugh at people who say things like that

[Steeltoe]

That's why I laugh when people spot human-sized UFO craft. If there are UFOs here, they're microscopic.

Assumptions are just that, assumptions. You can laugh all you want, but to me, it just shows one more scientific dogma. The attitude of "knowing it all" is sadly very prevalent here on Slashdot, and probably why so many spend time writing here, instead of discovering new stuff.

The problem is lack of creativity. In 0.5 seconds, I thought of nano-UFOs. Send one, or trillions of those, and let them dig into a moon or planet to rebuilt itself into a fully fledged macro-sized "UFO". Or, maybe if you want to "recreate yourself in your own image", why not send out organic "bombs"? Etc. etc. There are so many possibilities when you dont restrict your mind.

Just because you cant think of it, doesnt mean it isnt possible or thinkable. Please free your mind! There is so much more to know than we already know! And instead of giving focus to more effective ways to kill people, why not science of life?

Re:Heh

[Vitriol+Angst]

Did the scientist consider "electromagnetic radiation" in his calculations about "Probes seeking out only likely solar systems?" We have 50+ years of radio emissions streaming out at the speed of light from our Solar System. So that once a society reaches the industrial age, they would most likely be a lot more noticeable.

Maybe in a few decades, we will learn that we need to be more circumspect, and try and hide better from alien races.

Until then, a probe doesn't need to stumble upon us, it might be able to see patterns in radio transmissions. Who knows, if a race can figure out how to migrate through space, it might just know how to detect life from a distance (which I find highly likely).

They should mod this topic as "speculation."

>> And on Slashdot, I have the right NOT TO READ THE ARTICLE, before giving my valuable opinion.

Re:Fine assumptions, poor conclusion

[Paradise Pete]

It would be more helpful if his brain power could be used for more important tasks such as how to cure cancer, save the environment, efficient energy storage and so on.

People are not ants. They do what interests them. Your time would be better spent, say, feeding the poor, yet here you are on slashdot.

Re:Heh

[Vitriol+Angst]

Sounds like a version of Intelligent design.

Which I don't say is impossible -- just that counting on ID in a classroom, where you have to teach science is pointless and merely to make Fundies happy.

I think that humans, in a few more decades, may very well want to "seed" nearby planets with modified earth DNA. The compulsion to do so will be hard to ignore. We could create food or useful organic crops on Mars and Venus -- or just experiment without ecological disaster on earth (or test ways to fix ecological disasters). There will be a lot of protest at first, but history shows that we ALWAYS do something that provides a profit -- whether or not it benefits people or any temporary form of ethics (worrying about Stem Cell, is just a ruse to get patents in the private domain, for instance).

So, I don't know any way we could disprove that Aliens have not visited earth or manipulated genes in some way. The debate against ID is more about good science -- not trying to disprove every possible explanation.

We also might be a creation of the Flying Spaghetti Monster. Who knows if that 90% "junk DNA" encodes for Meatball + a delicious sauce?

Re:Why about self-replication?

[Anonymous Coward]

Small? The goal of the probes is to go to stars that are good candidates for life, which means you would pick stars with planets. We can already detect those now with our current instruments, so it is no big stretch to think a much more advanced probe could as well. Thus the probe would at every destination it arrives at have planets to gather material from.

You don't understand.

[raehl]

He doesn't even consider non-material, photon-based probing methods, which would increase the rate of exploration by a factor of 10.

Doesn't matter. Light only travels so fast, and we've only been here, what, 10,000 years? Nobody further than 10,000 light years away could have possibly found us yet. And a 10,000 light year sphere is well less than 4% of the galaxy.

This whole study is kind of dumb, because it doesn't matter that you can explore 4% of the galaxy in 4 billion years when we've only been here for 10,000 years. Even if they did come to earth, it's almost certain that when they were here, they found either nothing or some bacteria and kept going.

Such a limited view

[EmbeddedJanitor]

Using *our* current knowledge of physics etc to make predictions as to the performance of *other* beings technology is both arrogant and small minded.

Let us roll back the clock, say, 200 years: A person up to date with the technology of the time would have no knowledge of airplanes, cars etc would make the some silly statement that it would be impossible for a person to ever cross USA in one day. They'd also say that it is very unlikely to find a particular quote in some random book within three months of searching, Google etc changes that. Change the technology and understanding of physics and we'd laugh at anyone saying something as stupid as that now.

But won't people 200 years from know laugh at our pathetic understanding of technology and physics? If there is intelligent life (I don't think so personally), it might just be a couple hundred or thousand or whatever years ahead of us and would thus not be bound by the limiting assumptions we make today.

Re:a few points to ponder though

[Anonymous Coward]

Agreed. Also, to show just how far down the rung we are, we still can not conscioussly control the biological processes that occur in our body. Buddhist monks seems to be on the right track with regard to internal body temperature vs. external environment...

I don't think the majority of people have a real concept of true intelligence and control of biological, technological, mechanical, and evolutionary facets of our current and coming existence. I keep seeing and hearing cybernetics is our future, ie. implants, computer assisted enhancements, but genetic improvement and consciouss internal biological control is where my money is at. I still haven't found funding for most of that though...

Any takers?!?

Re:Well, DUH!

[mazarin5]

Sorry, but no. The light-year is the distance covered in a year at the speed of light. The unit of time you're looking for is the year. What you're saying is equivalent to "The mile is a unit of time, if you assume travel at 60 mph."

Re:That's assuming...

[mibus]

I'm sure that we are very close to having a "life detector." Life has an impact on the environment, so that has to be detectable in some way.

You could look for an oxygen/carbon-dioxide atmosphere, but then you're just making assumptions about what sort of life you're looking for...