Alien Civilizations and first encounters?

[primummobile]

But for the ETs to know that much about our technology and/or biology that they could spoof our optics and other sensors at will, they would have to have studies us and our gear in great detail... you see where I'm going with this?

Yes, I do. That's why you should take a closer look at the fly on your wall! : )

See my above post to Ara Pacis. When I said "make themselves known" I meant "communicate". Like when you walk into a room full of people, you're not hiding, but you haven't made yourself known until you speak up. Despite that, I still think they could blind us to their presence if they were sufficiently advanced. I just want to make clear that although I think they could hide, I don't think they would have to hide to study us. It's true that we may change our behavior if we know they are watching, but I don't think it would change that much. You're talking about 7 billion people.

[primummobile]

An antimatter rocket would be phenomenally detectable; stealth would be impossible with that kind of drive. They would emit vast amounts of gamma rays and neutrinos, for a start, both of which are tricky to convert into thrust.

Ok, we're having two different conversations here. One is could they stop and hang around, and the other is could they hide. The antimatter rocket is in the "could they get here, stop, and hang around" thread. I'm not making any assumptions about what kind of technology they could have other than to say that they may be able to be some pretty phenomenal things that would appear to us to be magic. In that vein, it's not a stretch to think they could do all kinds of things that we can't even imagine.

As for gamma rays and particles, they would have to reach us to be detectable. We have no idea even how to generate that much antimatter. With our technology, it would take us about a billion years to generate even one gram of antimatter, and we would lose nearly all of it before we were finished. The questions of how we would direct the particles (not the gamma rays) out the exhaust nozzle to create thrust are huge. A technology that could accomplish this would have to be far in advance of anything that will exist on Earth for a long time. If we were to build an antimatter rocket today with what we know today, it would be phenomenally detectable. I don't doubt that you are right that it will be that way for any level of technology. I have no idea how you would stop a stream of neutrinos. But that doesn't mean there isn't a way to do it.

[Noclevername]

I'm not making any assumptions about what kind of technology they could have other than to say that they may be able to be some pretty phenomenal things that would appear to us to be magic. In that vein, it's not a stretch to think they could do all kinds of things that we can't even imagine.

Going back to the OP, if their technology is so different from what we understand that it violates the known laws of physics, it would be inoperable let alone impossible to copy by humans. It would also invalidate all our physical sciences.

[primummobile]

Going back to the OP, if their technology is so different from what we understand that it violates the known laws of physics, it would be inoperable let alone impossible to copy by humans. It would also invalidate all our physical sciences.

That's true, but I don't think it would necessarily have to go that far. Obviously there is a limit to what technology can do, but I personally think that we're pretty far from that limit. I think if you could fast forward a thousand years you would be blown away by what you find.

[Noclevername]

That's true, but I don't think it would necessarily have to go that far.

But that's the point. To do the things you describe, it would have to be that far.

[primummobile]

And don't forget too that the 'known laws of physics' allow for some pretty weird things that we're highly unlikely to ever see.

[primummobile]

But that's the point. To do the things you describe, it would have to be that far.

We may have to just agree to disagree on that.

[Noclevername]

Well, I tried.

[Ara Pacis]

Propellant? It depends on what type of antimatter rocket you want to build. The easiest would be using the heat of a matter/antimatter reaction to raise the temperature of a propellant in a constant velocity chamber and allow that to escape through an engine nozzle at high velocity, just like our rockets do now. It is also a terrible waste of antimatter.

A more efficient antimatter engine would magnetically direct the highly charged particles travelling at around .5c from antimatter/matter annihilation out the engine nozzle to produce thrust. One gram of antimatter annihilating with one gram of matter produces about 180 terajoules and this type of antimatter rocket is thought to have a specific impulse as high as ten million seconds. For comparison, a solid rocket has a specific impulse of around 250 seconds and a liquid propellant rocket is about twice that. An ion thruster has a specific impulse of around 3,000 seconds. So, the "miles per gallon" of an antimatter rocket would be about 3300 times better than an ion thruster rocket. The point is that if the aliens have the know-how and can carry enough lightweight high-octane fuel to accelerate to a significant velocity, coast for a while, and then slow down at the other end they would do that.

And what is the thrust and how long in time and space would it take for them to decelerate into an orbit somewhere in the Sol system? If their exhaust is visible, as current science suggests it must be, then we may see them before they see us.

I don't know what putting out heat has to do with that. If it's referring to Noclevername's argument it should be noted that I never said they would try to stay hidden before studying us. I said they would try to study us before offering us technology or attempting to make contact. Others assumed that they would need to be hidden to do that, and at that I argued that they could hide if they wanted to. In my discussion with you, the idea of needing to hide hasn't come up, to my knowledge, so I wasn't considering that. [I just checked my post on that, and I guess I did imply that they would hide. But when I said "make themselves known" I meant to communicate, and that's what I should have said. A big heat source in our solar system would definitely be an anomaly, but we wouldn't know it was aliens until they communicated with us. So, I apologize for that. I was wondering why I was getting questions about aliens trying to hide from us]

I had already mentioned them possibly hiding and having been here already as a possibility to avoid the idea that we would see them decelerate. If they are already here, we may not have seen them decelerate or have known what it was if we did see it if they came before we had enough knowledge to understand what we were seeing. I include letting themselves be known and communicating in the same concept of first contact. If we see them, they've communicated that fact to us through their actions. Communication can be non-verbal, ya know. And then if we see them despite their best efforts, we may try to communicate with them first, and even if they don't respond, that in and of itself is telling.

I don't argue that. My point is that the same thing from then may be radically different from how we would design it. If it uses a power source that is not electrons and holes moving in a conductive material we may be scratching our heads about it for quite a while. If applying an electrical current to it causes nothing to happen we wouldn't be able to do much to discern its purpose without quite a bit of thinking. We may think it is a weapon. They may give us a quantum computer and we may interpret it as them giving us a cup of water. The possibilities are endless. Giving any kind of technology to someone who doesn't understand how to use it is potentially very dangerous.

If we're left to figure it out ourselves, it may take a while. I think the original context was that they were trying to explain it. Once we overcome the language barrier, the science and math should flow fairly easily.

[IsaacKuo]

If they wanted to hide from us, one method would be to decelerate hidden behind the Sun. We might see the deceleration phase in a lucky snapshot from Cassini, but the chances of that would be very low.

[Ara Pacis]

If they wanted to hide from us, one method would be to decelerate hidden behind the Sun. We might see the deceleration phase in a lucky snapshot from Cassini, but the chances of that would be very low.

How fast would that be before it was visible again? (Assuming we don't have other observatories anywhere in the solar system that might see it and the aliens may or may not happen to know about.)

[DoggerDan]

And don't forget too that the 'known laws of physics' allow for some pretty weird things that we're highly unlikely to ever see.

Er... What? Please elaborate. I'm all ears.

[primummobile]

Er... What? Please elaborate. I'm all ears.

Please. QM allows for objects to pass through walls. You'll never see it, but it's still possible. GR allows wormholes. You'll never see one, but it's still possible. I could go on and on but I'm not going to parrot stuff you already know to satisfy you.

[primummobile]

And what is the thrust and how long in time and space would it take for them to decelerate into an orbit somewhere in the Sol system? If their exhaust is visible, as current science suggests it must be, then we may see them before they see us.

I have no idea. Not I nor anyone else knows exactly how an antimatter rocket using charged subatomic particles for thrust would work. I'm just giving you an example of how it could work.

If we see them, they've communicated that fact to us through their actions. Communication can be non-verbal, ya know. And then if we see them despite their best efforts, we may try to communicate with them first, and even if they don't respond, that in and of itself is telling.

I agree. But there's no telling how we would interpret what we see. If it's something really unusual it could just be shelved for later investigation. When we first discovered quasars they were a complete mystery and no one was getting very excited about trying to figure out what they were. Granted, something in or close to our own solar system may generate some more excitement, but I'm not talking about the mother ship from Independence Day, with a quarter the mass of the moon, slowing down and stopping between the Earth and the moon. I'm talking about ships that may be relatively small and could swing into orbit perhaps near the Kuiper Belt and still pick up some of our transmissions from only around seven light hours away. How much excitement do you think that would really generate? Even if we saw it, do you really think people would interpret it as an alien craft?

I realize there are other methods of communication that aren't explicit. But if the listener interprets it as something else then it's not very effective communication. Personally, whatever happened up there in the heavens would have to be pretty dramatic to convince me that it was an alien ship or probe and not something natural.

If we're left to figure it out ourselves, it may take a while. I think the original context was that they were trying to explain it. Once we overcome the language barrier, the science and math should flow fairly easily.

I agree completely. Math is math and physics is physics. That doesn't change. Only the notation changes.

[primummobile]

Well, I tried.

Sorry, I'm just more starry-eyed than you are. I happen to believe that we have barely scratched the surface of what is possible, and have dreamed only a small part of what is possible.

[IsaacKuo]

How fast would that be before it was visible again? (Assuming we don't have other observatories anywhere in the solar system that might see it and the aliens may or may not happen to know about.)

I don't know if I understand your question. If they decelerated behind the Sun, it wouldn't ever be visible to us. It would occur behind the Sun. The Sun conceals an infinitely large cone about half a degree across behind it, but this cone is sweeping across space due to the motion of Earth. Earth orbits about 1 degree per day, so the practical limit of this concealment is about 12 hours--give or take a few factors depending on motion alignment with the direction of sweep. Assuming an acceleration of 1km/s/s, that's enough time for deceleration from 14% of c. An acceleration of 10km/s/s would be sufficient for high fractions of c. We already design robotics to survive 100km/s/s accelerations (guided artillery rounds).

[Ara Pacis]

I don't know if I understand your question. If they decelerated behind the Sun, it wouldn't ever be visible to us. It would occur behind the Sun. The Sun conceals an infinitely large cone about half a degree across behind it, but this cone is sweeping across space due to the motion of Earth. Earth orbits about 1 degree per day, so the practical limit of this concealment is about 12 hours--give or take a few factors depending on motion alignment with the direction of sweep. Assuming an acceleration of 1km/s/s, that's enough time for deceleration from 14% of c. An acceleration of 10km/s/s would be sufficient for high fractions of c. We already design robotics to survive 100km/s/s accelerations (guided artillery rounds).

That's what I was asking, thanks. I wasn't sure. But it might be blind chance that they happen to have a trajectory that takes them into that infinite cone if they didn't know Earth was inhabited before they launched (assuming their point of origin allowed such a trajectory). And then there'd have to be some sort of propulsion system that could manage such high accelerations. Perhaps a probe might survive such high accelerations, but a ship with biological inhabitants? If my math is right, 1km/s/s is 102g, and 10km/s/s is 1020g. Isn't that chunky salsa territory?

And as I said, it assumes we don't have our own probes in other orbits around the solar system that would be able to see that blind spot. If the aliens don't know if someone is here, then why bother. If they just do it out of precaution, then they know there's a good chance that any life able to see them and understand what they see will have observatories that are off-axis and would nullify the advantages of making such a maneuver.

[IsaacKuo]

That's what I was asking, thanks. I wasn't sure. But it might be blind chance that they happen to have a trajectory that takes them into that infinite cone if they didn't know Earth was inhabited before they launched (assuming their point of origin allowed such a trajectory).

If they were headed anywhere except our solar system, it would be extremely unlikely they would pass anywhere close to our star system anyway. So, whenever they decide that Earth is interesting, they would need to have sufficient delta-v capability to send something our direction anyway.

By the way, there is no special alignment necessary. The worst case scenario is if they are headed toward us from directly above or below the ecliptic plane. In that case, there's no getting around the 12 hour limit. The shadow is sweeping perpendicular to the direction of motion.

The best case scenario is if they are headed toward us from somewhere along the ecliptic plane. In that case, it's possible to time the arrival to the time of year when the shadow is sweeping away from their point of origin. That way, it's possible to conduct the deceleration phase while the shadow is sweeping in the same direction as the starship's motion, significantly extending the time available to decelerate.

The shadow is accessable from any direction, in any case.

And then there'd have to be some sort of propulsion system that could manage such high accelerations. Perhaps a probe might survive such high accelerations, but a ship with biological inhabitants? If my math is right, 1km/s/s is 102g, and 10km/s/s is 1020g. Isn't that chunky salsa territory?

Maybe, maybe not. It's hard to say even for future humans. Practical interstellar travel for humans could plausibly be strictly limited to ranges under 10 parsecs without some sort of suspended animation or extreme life extension technologies. Without those, longer trips may be impractical simply due to lifespan limits. Such short trips would make the sort of diversion scenario posited pretty much impossible. With some sort of suspended animation or extreme life extension technologies, survival of 100 gees or even 1000 gees may be trivial. It might even be typically used for starships due to the way it makes acceleration/deceleration easier (you don't need extremely long ranged acceleration beams/tracks).

Without such a diversion scenario, it might still be practical to send a robotic probe rather than diverting the entire starship.

And as I said, it assumes we don't have our own probes in other orbits around the solar system that would be able to see that blind spot. If the aliens don't know if someone is here, then why bother.

In the scenario we're discussing, they are hiding from us. Obviously, this scenario assumes that they are aware of our existence.

If they just do it out of precaution, then they know there's a good chance that any life able to see them and understand what they see will have observatories that are off-axis and would nullify the advantages of making such a maneuver.

It may be extremely obvious to the aliens that we have practically no development of space technology. For example, we obviously lack space based solar power satellites, or a cluster of space based industrial satellites, or a cluster of space colonies. Any of these would involve huge areas of solar arrays in orbit, and this is the sort of thing which any technological civilization with any half decent space technology capability would have.

[Ara Pacis]

If they were headed anywhere except our solar system, it would be extremely unlikely they would pass anywhere close to our star system anyway. So, whenever they decide that Earth is interesting, they would need to have sufficient delta-v capability to send something our direction anyway.

By the way, there is no special alignment necessary. The worst case scenario is if they are headed toward us from directly above or below the ecliptic plane. In that case, there's no getting around the 12 hour limit. The shadow is sweeping perpendicular to the direction of motion.

The best case scenario is if they are headed toward us from somewhere along the ecliptic plane. In that case, it's possible to time the arrival to the time of year when the shadow is sweeping away from their point of origin. That way, it's possible to conduct the deceleration phase while the shadow is sweeping in the same direction as the starship's motion, significantly extending the time available to decelerate.

The shadow is accessable from any direction, in any case.

Ahh, I see your point now, but it constrains that maneuver to when they are crossing that shallow disc of occasional eclipse. If they are far away, and moving slowly might take years with multiple eclipses once a year. If they are closer and moving faster, they may only get one opportunity with appropriately higher deceleration requirements. If they are coming here specifically, they may approach more directly, which means they may need data before launch as to whether there is life here (as well as knowing the actual orbit of Earth). Not to mention that since the sun is a sphere (circular cross-section), a more perpendicular trajectory would have less distance and time near the top and bottom than they would have in the middle because the moving cone of eclipse is narrower. Is that where you got the 12 hr estimate from?

Maybe, maybe not. It's hard to say even for future humans. Practical interstellar travel for humans could plausibly be strictly limited to ranges under 10 parsecs without some sort of suspended animation or extreme life extension technologies. Without those, longer trips may be impractical simply due to lifespan limits. Such short trips would make the sort of diversion scenario posited pretty much impossible. With some sort of suspended animation or extreme life extension technologies, survival of 100 gees or even 1000 gees may be trivial. It might even be typically used for starships due to the way it makes acceleration/deceleration easier (you don't need extremely long ranged acceleration beams/tracks).

What sort of technologies or biologies are you suggesting?

Without such a diversion scenario, it might still be practical to send a robotic probe rather than diverting the entire starship.

If passing near with no intent to stop, sure. Which is why I was focusing on them either coming here in person or contacting us by radio.

In the scenario we're discussing, they are hiding from us. Obviously, this scenario assumes that they are aware of our existence.

Which is one of the problems. How do they know we're here?

It may be extremely obvious to the aliens that we have practically no development of space technology. For example, we obviously lack space based solar power satellites, or a cluster of space based industrial satellites, or a cluster of space colonies. Any of these would involve huge areas of solar arrays in orbit, and this is the sort of thing which any technological civilization with any half decent space technology capability would have.

And that would show that the aliens may be peaceful or naive because most military planners base their estimations of a potential threat on capability and not intent, and capability isn't always obvious from observation. Assuming we don't have space defense capability because we don't bother do to space mining might be a dangerous and potentially fatal assumption on their part if they ever met another alien race that simply didn't like using that tech for some reason but knew how. Did you ever see the "Stargate: SG-1" episode where they first meet the Nox?

[IsaacKuo]

Ahh, I see your point now, but it constrains that maneuver to when they are crossing that shallow disc of occasional eclipse. If they are far away, and moving slowly might take years with multiple eclipses once a year. If they are closer and moving faster, they may only get one opportunity with appropriately higher deceleration requirements.

No, there's just one shot. There isn't going to be multiple eclipses. There can't be, unless the approach path is along the ecliptic plane, and even then it's not practical.

If they are coming here specifically, they may approach more directly, which means they may need data before launch as to whether there is life here (as well as knowing the actual orbit of Earth).

I presume that they will have telescopes, with which they can chart Earth's orbit and detect life on Earth from wherever they launched from. We're already making serious progress toward that sort of capability.

Not to mention that since the sun is a sphere (circular cross-section), a more perpendicular trajectory would have less distance and time near the top and bottom than they would have in the middle because the moving cone of eclipse is narrower. Is that where you got the 12 hr estimate from?

No, I have no idea what you're even thinking there. The 12 hour estimate is simply the length of time that a faraway point along the ecliptic plane would remain within the half degree shadow cone as it sweeps across space at about 1 degree per day. To a first approximation, the deceleration run takes place at a single point--this is accurate if the deceleration run takes place very far away, but it becomes less accurate if it takes place closer to the sun.

What sort of technologies or biologies are you suggesting?

With future humans, suspended animation might involve immersion in neutrally buoyant fluid and/or freezing the body. The frozen humans might be tolerant of high accelerations. Extreme life extension technologies might involve active robotics on a subcellular level. That could also make the humans tolerant of high accelerations, by carefully balancing density to maintain neutral buoyancy to a cellular resolution.

With alien biologies, the possibilities are endless. Obviously, aliens which had evolved in an extreme gravity environment could be naturally tolerant of high accelerations. Aliens which evolved in underwater environments might be naturally neutrally buoyant and thus naturally tolerant of high accelerations. Aliens which evolved in an environment with extremely rough winds or water currents might be naturally tough enough to survive extreme accelerations as they're pummeled against rocks.

Which is one of the problems. How do they know we're here?

Either telescopic observations, or detections of our radio signals.

And that would show that the aliens may be peaceful or naive because most military planners base their estimations of a potential threat on capability and not intent, and capability isn't always obvious from observation. Assuming we don't have space defense capability because we don't bother do to space mining might be a dangerous and potentially fatal assumption on their part if they ever met another alien race that simply didn't like using that tech for some reason but knew how. Did you ever see the "Stargate: SG-1" episode where they first meet the Nox?

Eh, who says this is a military mission? Anyway, it would be obvious that humans aren't a military threat. Without any serious expansion into space, humanity is limited to the puny amount of energy falling onto the Earth's surface from the Sun. This is nothing compared to the resources available to an interstellar civilization. Humans would have to start expanding into interstellar space before they were even a noticeable threat.

[Ara Pacis]

No, there's just one shot. There isn't going to be multiple eclipses. There can't be, unless the approach path is along the ecliptic plane, and even then it's not practical.

I presume that they will have telescopes, with which they can chart Earth's orbit and detect life on Earth from wherever they launched from. We're already making serious progress toward that sort of capability.

No, I have no idea what you're even thinking there. The 12 hour estimate is simply the length of time that a faraway point along the ecliptic plane would remain within the half degree shadow cone as it sweeps across space at about 1 degree per day. To a first approximation, the deceleration run takes place at a single point--this is accurate if the deceleration run takes place very far away, but it becomes less accurate if it takes place closer to the sun.

The last statement contradicts the first. I was going to say that they only have one shot to hide in the cone of eclipse, but then realized it would technically be incorrect if they were far enough away and/or slow enough. Although to be technically correct, they might not even have 1 chance if they are too close and didn't plan for it (assuming they have the capability to conduct such high acceleration maneuvers).

What sort of life? They might be able to sense gases in the atmosphere, but I think we had a thread about seeing signs of civilization the conclusion of which was it was not technically possible using known physics. Iv'e also read that it's unlikely that our radio data signals could be detected very far away with RADAR a bit farther, and that there's a low chance that anyone would happen to see it and even if they did, there wouldn't be enough information to learn anything about our life-form other than something is emitting radio signals.

With future humans, suspended animation might involve immersion in neutrally buoyant fluid and/or freezing the body. The frozen humans might be tolerant of high accelerations. Extreme life extension technologies might involve active robotics on a subcellular level. That could also make the humans tolerant of high accelerations, by carefully balancing density to maintain neutral buoyancy to a cellular resolution.

With alien biologies, the possibilities are endless. Obviously, aliens which had evolved in an extreme gravity environment could be naturally tolerant of high accelerations. Aliens which evolved in underwater environments might be naturally neutrally buoyant and thus naturally tolerant of high accelerations. Aliens which evolved in an environment with extremely rough winds or water currents might be naturally tough enough to survive extreme accelerations as they're pummeled against rocks.

Are you talking possibility or probability WRT life-forms? I was thinking about tech, and freezing in a breathable solution (cf. "The Abyss") using the new vitrification technique using strong electro-magnets, but I don't know if that would make those strong accelerations more survivable or less survivable.

Either telescopic observations, or detections of our radio signals.

See above.

Eh, who says this is a military mission? Anyway, it would be obvious that humans aren't a military threat. Without any serious expansion into space, humanity is limited to the puny amount of energy falling onto the Earth's surface from the Sun. This is nothing compared to the resources available to an interstellar civilization. Humans would have to start expanding into interstellar space before they were even a noticeable threat.

It doesn't have to be a military mission to have military repercussions. They'd have to know our capabilities before they get here, which isn't going to happen. And it would be silly for them to assume we're limited to solar energy of some sort and haven't developed nuclear power, unless they don't know about nuclear power, which seems like a silly assumption for a race we're presuming as space-faring. And if they'd only think of us as a threat if we expand into interstellar space, then they may want to re-think the idea of sending a ship or probe with interstellar transportation tech to us (assuming there is such a thing we don't already know about or won't develop from known physics eventually).