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The problem with conjecture about aliens is that, by definition, they're alien, and since we haven't even met one yet (aside from some unsubstantiated claims by

The problem with conjecture about aliens is that, by definition, they're alien, and since we haven't even met one yet (aside from some unsubstantiated claims by some people), we can't even begin to guess at their capabilities, motivations, etc. Remember, we're a primitive race that hasn't even left its own planet, except for a brief excursion to its nearby moon, and some primitive robotic probes to nearby bodies. We really don't know if there's some branch of physics that allows FTL travel, or if it's possible for intelligent beings to exist in multiple or parallel dimensions, etc. Everything we discuss along these lines is nothing more than wild-ass speculation. One problem I have with your assertion about the ready availability of FTL technology is that I think that assumption relies on the assumption that ETs have similar lifespans as us, which is probably a faulty assumption. A race advanced enough for interstellar travel could very well have totally different biology that doesn't age, or they might have technologically defeated aging, which is something we're already working on ourselves even though we've only sent a handful of people beyond our Van Allen belts. A species that doesn't age, or has lifespans of millennia, might not think it's that big a deal to send a ship to a nearby star system on a journey that'll take a dozen or so years (in ship-time due to relativistic dilation; centuries in planet-time). By the time they get back, their friends might be a bit older, but it'd be like us taking a trip and coming back 5 years later. And don't forget the possibility of "suspended animation". With sufficiently powerful engines able to achieve a sufficiently high fraction of c, a trip of a dozen or so light-years won't take that long in ship-time. It'll even be something we'll want to do with our lifespans. Discovering our existence shouldn't be that hard. There's hundreds of stars within a few dozen lightyears or so, so an advanced civilization should be able to build a powerful robotic ship to tour them all and gather data. A few millennia or so later, it'll return and they can analyze it, and our existence will be pretty obvious just by scanning the EM range (assuming they came within the last century), or by detecting atmospheric oxygen and photosynthesis. Of course this assumes they're looking for that kind of life, just like we're doing now with our exoplanet searches. Honestly, it shouldn't be that hard to detect other civilizations from a reasonable distance; we're already detecting various exoplanets, and as I said, we don't even have any serious spaceflight capability; we're doing it all with ground-based and some orbital telescopes. We're having problems seeing planets the size of our own, but better technology should change that eventually. If we had the ability to send a ship to tour the nearby stars and send data back, advanced civilizations should be fairly obvious to a ship inside their system, just by orbiting the likely-looking planets (inside the "habitable zone") and taking pictures, scanning EM frequencies, etc. It would take a while to get data back though since the ship would take decades or centuries to get there.

Udo 11y ago
> We really don't know if there's some branch of physics that allows FTL travel I agree, and I didn't mean to come down on either side of the opinion spectrum on FTL. Personally, I consider it a strong possibility that several methods of FTL travel might exist in practice. > I think that assumption relies on the assumption that ETs have similar lifespans as us, which is probably a faulty assumption. No, you misunderstood me there. My basic assumption is that ET lifespans (if they are individual beings at all) are for all intents and purposes infinite, as you would expect from any technologically advanced civilization. Instead, my conclusion is mostly shaped by the young age of our own civilization, the meagerness of RF signals emanating from our system, and the vastness of the distances involved. > There's hundreds of stars within a few dozen lightyears or so, so an advanced civilization should be able to build a powerful robotic ship to tour them all and gather data. I agree that a swarm of robotic probes meets the criteria for blanket early detection of civilizations. I assert that you would need to cover more than a few dozen light years though, but that's not really relevant. It comes down to the willingness of deploying these probes and the speed at which probe data can be relayed back to someone willing to act on it. > Honestly, it shouldn't be that hard to detect other civilizations from a reasonable distance; we're already detecting various exoplanets Planets: yes. Civilizations: it depends. I'm personally doubtful we could detect our own civilization today if we had a clone of humanity orbiting Alpha Centauri, and that's still well within our RF light cone.
- Grishnakh 11y ago
  >I'm personally doubtful we could detect our own civilization today if we had a clone of humanity orbiting Alpha Centauri, and that's still well within our RF light cone. Why would we not be able to detect a clone of our civilization around Alpha Centauri? They're only 4 light-years away, so we should pretty easily be able to detect their TV broadcasts and other RF emissions at that distance. The main problem with SETI's approach I think is that it assumes RF emissions are strong enough to detect from huge distances (AC is the closest system to ours, everything else is farther), and that the ETs are at a similar level technologically and use strong RF transmitters rather than short-range spread-spectrum stuff, so that's a pretty short time window technologically, combined with the distance (it takes decades or centuries for signals to travel here from other star systems). But for a hypothetical humanity clone in the AC system, these problems don't hold, and we really should be able to detect them I think. The problem is, in all likelihood, any real civilizations are likely to be at a different developmental stage, and also to be much, much farther away than our closest neighbor.

Udo 11y ago

> We really don't know if there's some branch of physics that allows FTL travel I agree, and I didn't mean to come down on either side of the opinion spectrum on FTL. Personally, I consider it a strong possibility that several methods of FTL travel might exist in practice. > I think that assumption relies on the assumption that ETs have similar lifespans as us, which is probably a faulty assumption. No, you misunderstood me there. My basic assumption is that ET lifespans (if they are individual beings at all) are for all intents and purposes infinite, as you would expect from any technologically advanced civilization. Instead, my conclusion is mostly shaped by the young age of our own civilization, the meagerness of RF signals emanating from our system, and the vastness of the distances involved. > There's hundreds of stars within a few dozen lightyears or so, so an advanced civilization should be able to build a powerful robotic ship to tour them all and gather data. I agree that a swarm of robotic probes meets the criteria for blanket early detection of civilizations. I assert that you would need to cover more than a few dozen light years though, but that's not really relevant. It comes down to the willingness of deploying these probes and the speed at which probe data can be relayed back to someone willing to act on it. > Honestly, it shouldn't be that hard to detect other civilizations from a reasonable distance; we're already detecting various exoplanets Planets: yes. Civilizations: it depends. I'm personally doubtful we could detect our own civilization today if we had a clone of humanity orbiting Alpha Centauri, and that's still well within our RF light cone.

Grishnakh 11y ago
>I'm personally doubtful we could detect our own civilization today if we had a clone of humanity orbiting Alpha Centauri, and that's still well within our RF light cone. Why would we not be able to detect a clone of our civilization around Alpha Centauri? They're only 4 light-years away, so we should pretty easily be able to detect their TV broadcasts and other RF emissions at that distance. The main problem with SETI's approach I think is that it assumes RF emissions are strong enough to detect from huge distances (AC is the closest system to ours, everything else is farther), and that the ETs are at a similar level technologically and use strong RF transmitters rather than short-range spread-spectrum stuff, so that's a pretty short time window technologically, combined with the distance (it takes decades or centuries for signals to travel here from other star systems). But for a hypothetical humanity clone in the AC system, these problems don't hold, and we really should be able to detect them I think. The problem is, in all likelihood, any real civilizations are likely to be at a different developmental stage, and also to be much, much farther away than our closest neighbor.