Tuesday, March 8, 2016

Are We Detectable?

The question in the title goes two ways. Perhaps you thought the idea was that if aliens couldn't tell we were here, in other words, that Earth has intelligent life, that they wouldn't come here to see us. This is one possible answer to the question of where are all the aliens. But the title question can be interpreted in the opposite direction. In a previous post, it was surmised that aliens only look for colonizable planets to go to, and any one that already has an alien civilization, meaning we are the aliens to them, isn't worth going to. It is too hard to get rid of another intelligent species, even if the planet is just peachy for colonization.

Either way, the technological question is: are we detectable? The light travel time is not too important in this regard, unless it is something recent that is the only detectable thing. If there is an alien species, looking for a colonizable planet out to a thousand light years, they would know that they are seeing Earth as it was in the past. How they treat that delay might be interesting, if we knew how we were going to be detected.

One common idea is that they would hear our electromagnetic transmissions out into space, and recognize instantly that there was a technological civilization on Earth. From their point of view, they might think there is, or was, taking into account travel time, a pretty primitive technological civilization on Earth, but again, in the hundred or thousand years that light takes to get to their planet, we would have made great advances. And in the thousand or ten thousand years it would take their starship to get here, we would have made even more. We would probably have gotten to asymptotic technology, the limit of technology knowledge, just as they have. So seeing even the slightest indication of us being on the technological pathway means that when their starship gets here, a civilization with an equal level of technology is awaiting them.

That means they cannot exterminate us using some clever technology devices. It wouldn't matter if it was killer robots or monster carnivores or deadly viruses or long-lasting toxics or whatever, to us, at that distant time in the future, it would be just something we knew about centuries before and figured out how to deal with it. Our killer robots, being built here on Earth where we could build lots more of them and bigger ones too, would smack down theirs. We would probably just hunt down any monster carnivores, set our anti-viral bacteria out to absorb and nullify their viruses, and use some biological whiz-bang to take care of the toxics they dumped into our atmosphere. So, since you can't hardly carry anything at all on a starship, they wouldn't have a chance of wiping us out.

This means, to the aliens, that's them now, if they see any sign of technology or even a civilization that was getting ready to start technology, it's a show-stopper. Find another planet, please.

So, how would they see us? We need to be careful about assuming we are anywhere near asymptotic technology. We used to have tv stations broadcasting signals, and we still have some, but everywhere is getting wired up now, and the broadcasting will be more or less obsolete and not worth maintaining. We have radars that look for aircraft, and they might be recognizable if the aliens built a kilometer wide dish to receive it, but GPS is likely to eliminate the need for that. Perhaps there will be a few more decades of it, but all in all, there is only a short window in time when this type of broadcast would happen.

How about other signals, like cell-phone tower signals getting reflected off into space? When the world is wired up, with hotspots everywhere, these towers will be obsolete. And if arcologies become the order of the day, which is how a civilization does recycling to high percentages, there aren't any signals leaking out. Each arcology is wired to the others, and inside one, there is connectivity everywhere at high enough frequency that the atmosphere would absorb it pretty well before it gets out to space.

Maybe there would be the occasional transmission to a space probe. These are highly directional. Unless the beam just happened to pass over the star where the alien civilization was waiting to hear it, they would have no chance. Sidelobes are just not wide enough or strong enough. What's left – not much.

How about watching our sun to see a transit of Earth, and getting a spectroscopic view of what's in the atmosphere? Transits only are visible in the plane of the orbit and a bit around it, and they might be lucky and be there. If they were, they might detect man-made chemicals in the air, if there were any which both lasted a long time, and had great signatures for detection. But are we going to continue to dump these chemicals into the air? Maybe there are some which linger in the upper atmosphere for centuries, which would stretch the window of detection. Chemicals which are produced from the combustion of fossil fuels might be too similar to those which are produced from forest fires. A little investigation would be nice here, but the transit observation option is not immediately promising.

One thing they could likely see is the light pollution from our cities. Anyone with a huge visible wavelength detector that could block the light of our sun, which is pretty easy and we are even getting ready to do it ourselves, and look at the planet alone, would notice there is a lot of light on the dark side. What would they assume that is, huge populations of fireflies? It looks like that is a clear indicator of a technological civilization. If we move into arcologies, will there still be much light pollution? Quite possibly, there would be a lot less. Detectable? Who knows.

Just to put a generous range on things, we might be detectable easily in the twentieth and twenty-first centuries, but before that and after that, it would be questionable. So, if an alien civilization with asymptotic technology, that's us now in the future, would be a very serious liability for any colonization attempt, there is just a short period of time to observe ground emissions or atmospheric pollution reliably. What else is possible?

Spaceships, of the interplanetary kind. If we start to mine asteroids and satellites of the gas giant planets, the rocket exhaust might be visible to a huge dish, with some luck as to orientation. This mining is likely to go on during the whole period of technological civilization, so the window when it could be observed is long indeed. A small ship bringing back diamonds from Titan, or whatever, would be hard to see, but how about something vacuuming up hydrocarbons from the atmosphere of Jupiter? How about a ship bringing back megatons of iron from Ceres? This is one possibility that needs to be examined. It would be necessary to consider what types of engines might be used, and how the burns would be scheduled.

As noted elsewhere in this blog, the alternative is to send a probe. This is a serious delay, but is the only alternative to remote detection or taking a chance, perhaps one of the most expensive bets an alien civilization could afford – sending a colonization ship to a possibly inhabited planet. These questions are well worth considering in more detail.

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