Why We Haven't Met Aliens Yet

[BravesFan]

Given the propensity of the universe to do nasty things to planets, and the inherently delicate nature of life as it exists today, I find it rather naive to expect a species like ourselves to last much more than a few hundred thousand years, and likely a lot less than that.

I would disagree the dinosaurs lasted millions of years and they didn't even have Ipads!

 

[WhatRoughBeast]

Given the propensity of the universe to do nasty things to planets, and the inherently delicate nature of life as it exists today, I find it rather naive to expect a species like ourselves to last much more than a few hundred thousand years, and likely a lot less than that.

Which is simultaneously not particularly relevant, and should serve as motivation.

Relevance: once a species spreads to several stars, it becomes immune to perturbations on any one star. Consequently, it would seem fair to project its lifetime to some very long duration.

Motivation: same as above.

 

[nvidiot]

I would disagree the dinosaurs lasted millions of years and they didn't even have Ipads!

Which species of dino was that?

 

[Dinwar]

Given the propensity of the universe to do nasty things to planets, and the inherently delicate nature of life as it exists today, I find it rather naive to expect a species like ourselves to last much more than a few hundred thousand years, and likely a lot less than that.

Given that there's no data at all one way or another, this says nothing about the matter at hand; all it says anything about is your view of inteligent species. I'm not saying you're right or wrong in your view--just that you don't have nearly enough data to draw this conclusion.

Which species of dino was that?

Typical species lifespans are about 5 million years, from what I understand. Some are much higher and some much lower, obviously, but that's about average.

 

[gnome]

The question of what the planet can do to us becomes less relevant if in a few millenia we can extend our reach even to other worlds (moons and solid planets) within our own solar system. At that point we become a lot less susceptible to a planetary event.

That doesn't seem like too much of a stretch, to get that far even in a few thousand years (or, optimistically, a few hundred perhaps), much less than even nvidiot's pessimistic timeframe for extinction.

 

[Hellbound]

Hmmm.

A while back some ideas about this were tossed around. Someone, can't recall who now, came up with three "rules" of alien races: three things that, without knowing anything specific, we can say with a fair degree ofconfidence about any technologically-advanced alien race:

1. They will be intelligent, aggressive, and violent when necessary. Nature doesn't favor a wimp. The species that can best survive does, and intelligence doesn't seem to develop in cereatures that use less aggressive survival stratgies (how much brain does it take to breed by the dozens, for example?). Likewise, a species must have capability for violence in order to become dominant, which would be a requirement for a technological society (lots of resources needed).

2. They will favor their own survival over that of any other species. This is simply common sense, and most poeple (yes Complexity, I know you're the exception) would agree. A species doesn't become the top dog by being self-sacrificing.

3. They will assume the first two rules apply to us.

We have theoretical designs now for anti-matter engines that could accelrate a craft to significant fractions of the speed of light. We're a long way from building such ships, but there's no theoretical barrier to it. We already know anti-matter can be created and contained, and magnetic fields can be used to shape reaction chambers and exhaust nozzles.

Now, combine this with the fact that any feasible interstellar craft, travelling at a fraction of c, is indistinguishable from a weapon (unless and until it begins decelerating), and that even at, say, 10% c an impact from even a relatively small object is devastating, and anything moving at a significant fraction of c is not going to be in the place where you see it (or detect it from radar or whatever) by the time anything you might use to intercept it gets there. Also, even launching missles at an incoming ship, unless you hit it really far out, simply turns it from a single projectile into a shotgun. And the only difference between an interstellar ship and an intersteller missile is whether or not it slows down. And heaven forbid if multiples are sent, or if they have defense mechanisms. Basically, a relativistic impact weapon is nearly uninterceptible, and given sufficient size and speed is a planet-killing weapon (well, life on the planetary surface, anyway).

What risk of racial genecide is acceptible, when there's no feasible way to reliably intercept a possible attack, or even determine what is an attack?

This is the "alone in Central Park at night, with no streetlights around" theory. You can't find your way out of the park, it's dark, and you're alone. Sure, there may be a police officer nearby, or a helpful stranger...but it's just as likely to be a mugger. Do you really want to yell out "Hey, I'm over here! Someone come talk to me!"*

Pleasant dreams

ETA: *-This analogy isn't perfect. In the universe, there is no way out, there are no police officers, and the night never ends.

 

[mikeyx]

Hmmm. (yes Complexity, I know you're the exception) D

or in the way

 

[Roboramma]

I don't really see the connection between your three rules and your last paragraph, though.

To bring back what Dinwar said: what's in it for them (or us) to get involved in some sort of conflict?

The corollary to what you are saying is that if we initiate violence, we are only asking for a violent response, and we can expect any other species to realize that as well, which in turn means that we can expect them not to initiate violence, particularly if they don't know that we are localized to this single planet.

Why go to enormous expense to send an interstellar weapon to destroy us when they could just leave us alone? Are they afraid that we'll try to destroy them? Why?

What I'm getting at is "1. They will be intelligent, aggressive, and violent when necessary." is likely valid, but you can't just ignore those highlighted words, and I don't see any reason to suspect that they will apply to any interaction we might have with extraterrestrial life.

 

[Hellbound]

I don't really see the connection between your three rules and your last paragraph, though.

To bring back what Dinwar said: what's in it for them (or us) to get involved in some sort of conflict?

The corollary to what you are saying is that if we initiate violence, we are only asking for a violent response, and we can expect any other species to realize that as well, which in turn means that we can expect them not to initiate violence, particularly if they don't know that we are localized to this single planet.

Why go to enormous expense to send an interstellar weapon to destroy us when they could just leave us alone? Are they afraid that we'll try to destroy them? Why?

What I'm getting at is "1. They will be intelligent, aggressive, and violent when necessary." is likely valid, but you can't just ignore those highlighted words, and I don't see any reason to suspect that they will apply to any interaction we might have with extraterrestrial life.

Well, it's more about why none have come here that why we haven't heard, although the two go hand in hand. If interstellar travel is simply not possible at all, there's nothing to the argument. I don't necessarily agree with it, but it is an interesting concept.

The basic idea behind it is that any feasible method of interstellar travel is going to involve speeds a significant fraction of c. That, necessarily, means it also gives that species the capability to wipe out planetary biospheres.

But the key part of your post is "Why go to enormous expense to send an interstellar weapon to destroy us when they could just leave us alone?" The whole idea is that maybe they are just leaving us alone. Waiting to see if we wipe ourselves out, or if we develop interstellar capability. And that if we do develop interstellar capability, we've immediately become a possible threat to them. And a high-level threat. As you stated, the expense of interstellar travel is not small. It's likely that most species (unless given large amounts of time) will be limited to a single star or a few nearby stars.

 

[Roboramma]

The basic idea behind it is that any feasible method of interstellar travel is going to involve speeds a significant fraction of c. That, necessarily, means it also gives that species the capability to wipe out planetary biospheres.

Agreed.

But the key part of your post is "Why go to enormous expense to send an interstellar weapon to destroy us when they could just leave us alone?" The whole idea is that maybe they are just leaving us alone. Waiting to see if we wipe ourselves out, or if we develop interstellar capability.

That's fine, if we assume that they know we're here in the first place. My view of the apparent paradox is not "why haven't they come to visit?", but rather, "Why haven't they expanded over the galaxy?", in other words, it's not why didn't they come here for tea and biscuits, but why they didn't come here to tap into that massive fusion power plant in the sky.

And that if we do develop interstellar capability, we've immediately become a possible threat to them. And a high-level threat.

Why? What reason would they consider us a threat? Because we're capable of being one, at extreme expense to ourselves? When I get in an elevator with someone, I am aware that if he wanted to he could probably murder me (pull a knife and stab me while my back is turned), but I don't consider that a "high level threat" because I know that doing so would come at great expense to him. So I generally don't worry about that particular possibility.

The fact that such a weapon would be expensive, and they couldn't guarantee success (how do they know whether or not we've got other colonies on other planets, either in this solar system or others?) means that such a launch could as easily create the threat they are trying to avoid as prevent it.

So I don't really understand why they'd do it. There's no reason to suspect we would initiate, and plenty or reason for us not to, and lacking that, there's no reason for them to initiate.

As you stated, the expense of interstellar travel is not small. It's likely that most species (unless given large amounts of time) will be limited to a single star or a few nearby stars.

I agree with that, but think you ought to put more emphasis on the bit I highlighted.

 

[Hellbound]

Just a few relevent points. Wiki has a decent article on relativistic missiles (http://en.wikipedia.org/wiki/Relativistic_kill_vehicle). Pertinent quote:

A 1 kg mass traveling at 99% of the speed of light would have a kinetic energy of 5.47×1017 joules. In explosive terms, it would be equal to 132 megatons of TNT or approximately 32 megatons more than the theoretical max yield of the tsar bomba, the most powerful nuclear weapon ever detonated. 1 kg of mass-energy is 8.99×1016 joules or about 21.5 megatons of TNT.

But as I said, I don't really agree with the reasoning...it's just something I like to bring up in these "Why we haven't met aliens" threads as a sort of spalsh of cold water

 

[Hellbound]

When I get in an elevator with someone, I am aware that if he wanted to he could probably murder me (pull a knife and stab me while my back is turned), but I don't consider that a "high level threat" because I know that doing so would come at great expense to him. So I generally don't worry about that particular possibility.

That's a bit simplified. But I also think you're over-playing the expense required. You talk about expanding across the galaxy...something that is MUCH more expensive, than, say, sending a relativistic chunk of metal or two to target a planet. All you need is engines, reaction mass, sensors, and a shielded, reliable computer. You don't need the living quarters, biological equipment, rebreathers, cloning machines, start-up technologies, and/or whatever else would be used for a colony.

The fact that such a weapon would be expensive, and they couldn't guarantee success (how do they know whether or not we've got other colonies on other planets, either in this solar system or others?) means that such a launch could as easily create the threat they are trying to avoid as prevent it.

True, assuming they detect us after we're interstellar, rather that finding us before and watching for the capability to develop. If they know when we gained the capability, then they'd know we haven't spread sufficiently.

Besides, if we can spedn the much greater amount to colonize another star system, the expense of a relativistic impactor is not that great comparatively.

So I don't really understand why they'd do it. There's no reason to suspect we would initiate, and plenty or reason for us not to, and lacking that, there's no reason for them to initiate.

Self-preservation is a reason, if they could be sure to get all of us. But that does assume they see us as a threat.

I agree with that, but think you ought to put more emphasis on the bit I highlighted.

We have no idea how much time it would take. We have a sample of one But even in that case, intra-species wars bring up the same issues. If you can create inerstellar colonies, then you've also given the capability to those colonies to wipe out your original planet (they can simply use the ship that brought them there in the first place). Unless you buy into the myth that an advanced race would have gotten rid of war and conflict.

As I stated, I don't agree with it, but I can see the plausibility, dependign on circumstances. The original argument was better put, and I don't have access to it now (nor can I recall all the details).

 

[Dinwar]

1. They will be intelligent, aggressive, and violent when necessary. Nature doesn't favor a wimp.

Not sure there's enough data to support this. I'll grant you intelligent life on Earth tends to be aggressive, but it's not universally so. Octopi, for example, are highly intelligent, without being known for agressive tendancies.

2. They will favor their own survival over that of any other species. This is simply common sense, and most poeple (yes Complexity, I know you're the exception) would agree. A species doesn't become the top dog by being self-sacrificing.

Other species are necessary for the survival of any intelligent non-photosynthetic or -chemosynthetic organism, so I'm going to disagree with this. From an outside perspective we spend a lot of time caring for cows, pigs, and chickens.

The basic idea behind it is that any feasible method of interstellar travel is going to involve speeds a significant fraction of c. That, necessarily, means it also gives that species the capability to wipe out planetary biospheres.

I don't see how the two are related. If we fired off every nuke on Earth at the same place at the same time, it'd result in less than half the destructive power of the Chixilub Impact, and while the K/Pg represents a mass die-off it really wasn't an overly influential mass extinction. We tend to think of it as more than it was, because the dinosaurs died out--but when you look at invertebrates, we're finding that it had less of an impact to the biosphere than we thought. The two biggest ones--the end-Ediacaran and the End-Permian--didn't even come close to wiping out the biosphere. They came close to wiping out ANIMALS, sure, but the biosphere as a whole was fine. Simply put, beyond liquifying the planet we really don't know what it'd take to wipe out life on a planet. I mean, let's say they nuke us from orbit. Let's say the do it in such a way that every inch of the surface is inhospitable to even viruses and bacteria. You still have the lithophiles to deal with--2 km of rock provides pretty good shielding from radiation.

They could probably wipe US out, yeah. Any engine that can travel the stars will certainly be powerful enough to be useful as a weapon. But even if they do, they're going to face a biosphere that's as alien to them as they are to us, and as likely to kill them.

 

[Donn]

In all this talk of aggressive aliens watching us (to make their first move) how is the watching done?

I don't know the physics. Could they be watching us from light years away, some kind of super telescope that's playing a movie (years in the past, viz light years distance) which shows zoomable detail? Perhaps it has sound and EM-band stuff?

If that's not likely, then they must be closer. Probes in our system?

Also something I don't know, if stuff was coming towards our system at relativistic speeds, how would we spot it, and when, if at all?

 

[Delvo]

let's say they each take 1000 years to reach a colonizable star at, let's say, 5 light years away.

200 years per light year is significantly faster than anything we've made yet. The fastest thing we've made has taken over 34 years (298044 hours) to get about 16 light hours away. That's about 18629 years per light year. For the 5-light-year distance you propose, that's over 93144 years. But that distance is much too short for what we're talking about.

There's only one other star system within that range. It doesn't have planets. Most stars don't. The nearest with any confirmed planets is only the 44th closest to us, and its planets are not suitable for a human colony. For that matter, none of the hundreds of others we've observed so far are either, even the ones that might have some life of their own, and there are only a few of those in the whole list anyway. The rest that are farther away don't get any better, just farther away, up to 23807 light years; average distance to exoplanets so far (even though they're all worthless to us) is somewhere in the hundreds. The 97 star systems with planets within 100 light years have at least 132 planets, all of which are about as suitable for human colonization as the other planets in our own solar system are. So whatever the fraction of star systems out there with planets is, it's small, and whatever the fraction of planets out there that we could colonize is, it's small too, so the distance between those has to be big.

The closest to us that we could reasonably even imagine there might be an inhabitable/colonizable planet, that we've somehow missed so far, would take well into the hundreds of thousands of years to reach, at least, at the best speeds we can muster now. Millions is more likely. And that's with relatively small light probes; colonizing that soon would call for similar speed from a much larger spaceship, which is much more challenging. Maybe greater speeds less than c can be done, but we have no way to tell how soon we'll be able to build such a thing, especially at the size and mass that would be required.

Also, what's possible is one thing, and what anybody's going to actually have any incentive to bother with is another. Nobody's going to want to invest the relatively large fraction of a planet's resources that would be required to undertake such a journey, knowing it will take hundreds or thousands of times longer than their civilization has even existed yet. This is the kind of thing that would only happen once there's no other choice. That will be when the stars they're orbiting start shining too hot or burning out and they need to abandon the home planet to avoid extinction. A planet that our kind of life can live on would have to be orbiting a star like ours, which has a half-billion years to go before threatening life here. Getting much of a head start on us isn't reasonable because this kind of star is made from the products of the destruction of some of the earliest stars. (And first-generation star systems wouldn't have the heavy elements yet.) But even a half-billion-year head start (which means their civilization would get going when our ancestors probably didn't even have skeletons yet) would still mean they're only just now getting to that desperate point.

Where are the highways? Even the fabled 'sub/hyper space' must leave something at either end.

Something big enough to see from here? Even seeing planets from here is hard.

Where are the lights on planets at night?

Even the planets we can see at all, which is a rather small number compared to the number of stars there are out there for the aliens to be orbiting, we can't see well enough to spot that (and know that it wasn't just a part of the planet's natural spectrum).

Where are the Dyson spheres and Orbitals (Rings)?

The former are a stupid idea that there's just not the slightest reason at all to think will ever happen anywhere anyway, and even if they did, by definition, they'd be something we couldn't see. The latter is also silly for similar reasons but not to such an extreme extent, but they would be so thin they'd be much harder to see than planets, so we'd never see them even if they exist beyond our planet-seeing range (which is pretty small compared to space).

Where are the vast battlefields that differ from their backgrounds?

Even tinier and harder to spot than the above.

Where are the mining operations that tackle entire gas clouds?

Why would anybody bother with that, and how would we know it when we saw it?

I liken it to the influence man has had on Earth in only a few thousand years.

You wouldn't be able to detect those effects (much less identify them as civilization effects rather than just the nature of the planet) from much farther away than the moon.

 

[Donn]

You wouldn't be able to detect those effects (much less identify them as civilization effects rather than just the nature of the planet) from much farther away than the moon.

Ok. Thanks for engaging my post. So you reckon that a vast (I am talking several galaxies-wide, or more) civ that has FTL and can go anywhere and do just about anything would not be visible in some way?

Even if my (dumb) ideas of Dyson spheres and battle-fields are out, what signs do you suppose there could be - given that this civ exists?

And on the subject of Earth's despoilation - there are other posts here that postulate that aliens might be watching Earth, how do you suppose they could do so if they are further than the moon?

 

[Dinwar]

And on the subject of Earth's despoilation - there are other posts here that postulate that aliens might be watching Earth, how do you suppose they could do so if they are further than the moon?

Watch the composition of the atmosphere over time, for one thing. Easy enough--just look at the spectrum of the Sun when Earth is behind it, then compare it to when the Earth is in front of it. We can do that to a limited extent--I imagine aliens would be able to do it much better, what with the more advanced tech and all. It's a bit like watching an ant farm by measuring the height of the ant hill, but it's a nice passive way to monitor a civilization long-term.

 

[Donn]

Watch the composition of the atmosphere over time .. it's a nice passive way to monitor a civilization long-term.

Okay! Nice. So it's possible to see signs of a civ's affect on its ecosystem (from afar.) Thus, the reverse should be possible; we should be able to see signs of any large FTL civ.

 

[Dinwar]

Well, first we have to figure out what a planet without one looks like. Unfortunately, we don't have that data. A FTL civ would, however. It's not really an issue of tech (though there are some hurdles there), so much as how many comparison samples we have.

 

[Donn]

What a planet without one looks like? Not sure I follow.