Let’s say we discover an extra-solar planet that appears to be Earthlike (free oxygen in the atmosphere, evidence of water, etc). There isn’t anyway we’d be able to detect an agricultural civilization without sending a probe to orbit it, is there? What about one in the midst of an industrial revolution, but hadn’t yet discovered radio? Could we determine if industrial activity was occuring (say on a 19 century level) by the same method we used to determine the composition of it’s atmosphere?
I’m sure we could use logical deductions on observations to deduce whether intelligent life exists without actually going there. The problem would be if observations were insufficient, e.g. we know there’s water on Mars, but how much, where, what form, etc.
My understanding is that if on a planet circling another star an intelligent life form exists that uses **the very same level of technology **that we’re using right now, we couldn’t detect it.
Nor could they detect us.
That doesn’t make sense, if they had identical technology, we could pick up their TV broadcasts and cell phone conversations.
Maybe; but as a pithy observation, it sounds fucking great, doesn’t it?
You couldn’t pick up t.v. broadcast signals at the orbit of the Moon (or, at least not with a collector that would be a significant portion of the Moon’s aspect), much less several light years distant, where the impingement would be one low energy photon per several million square kilometers of space. A very tightly focused signal could be detected (although the spread, even for a very high frequency laser would diverge to cover the entire system) but that would assume that the other party is searching for signals or intercepts it in the incoming direction.
With an extrapolation of existing technology we could potentially detect an industrial civilization by minute fluctuations in atmospheric albedo and absorption (due to vapor formation, ozone depletion, et cetera) but this would still be circumstantial and speculative at best.
Stranger
I’ve often wondered why it’s just “intelligent life” that people are interested in. Wouldn’t ANY life at all on another planet be pretty damn incredible??! Even like some microscopic creature living on Europa would be pretty awesome. Hmm, where was I going with this?
That’s why they search for life (any) on Mars while looking for intelligent life from elsewhere. I didn’t think we had the technology to fruitfully search for low-tech life beyond our physical reach.
What kind of setup did the Apollo astronauts have?
If we do detect life on another planet, and they don’t have radio, it’s a safe bet there’s no sentient life, because of Fermi’s paradox. In fact, even before we detect life on any other planets, it’s a pretty safe bet it’s not sentient. It took this planet 4.5 billion years to develop life to the point of sentience, and less than a million for it to get the point we’re at. So, based on one data point, evolution of sentient life takes about 4500 times more time than it takes from the first sentient life to radio-communicating, space-investigating people.
Taking Fermi’s paradox further, actual space colonization is probably less than a million years in our future, and full galaxy colonization maybe in 40 million years or so. So odds are, if there were sentient life anywhere in the galaxy, they would have already colonized. Therefore, the paradox goes, there’s none besides us.
We could, in principle at least, detect Earthlike life on another planet by observing oxygen in the atmosphere, and we’re quickly approaching the technology level where that would be practical. Oxygen is one of the most reactive of the elements, so there’s no way it’ll stick around in an atmosphere unless it’s being continually replenished, and the only known natural process which can produce significant amounts of oxygen is life.
Now, of course, it’s also possible that some other planet will have life of a form which does not produce elemental oxygen, in which case we might be clueless as to its presence. And merely detecting oxygen, while being a definite indicator of life, would tell us almost nothing about the nature of that life.
There’s always the possibility that our planet is considered a nature preserve, which forbids any intergalactic civilization out there from making contact with us or revealing their presence, kind of like the Prime Directive from Star Trek.
There are a list of possible resolutions to Fermi’s paradox at (wait for it!) Wikipedia: Fermi paradox - Wikipedia
Not really. I was reading about how an earth-like civilization could not be detected by SETI. Unless they are trying to contact us with high-powered focused transmission directly at our receivers or close to it, we just cant hear it. Even then youd need to build some kind of custom mega-dish to catch it.
Its a huge misconception that all this stuff is easy to listen to outside our atmosphere. Even with advanced technology catching a few photos per sq kilometer isnt going to help you much. A guess a solar system sized dish would be helpful.
So no, we wont be able to detect their most powerful television broadcasts directed right at us, let alone cell phones and other low wattage omni-directional transmissions.
240k miles (1.3 light seconds) is not the same as 100 light years.
I understand that; Stranger on a Train said you couldn’t pick up tv signals at the moon’s distance without a huge collector. I don’t understand how that could be since the Apollo astronauts were clearly sending tv images and were in near-constant radio contact besides.
I don’t know about TV signals, but ham radio enthusiasts can bounce a signal off the moon to talk to people on the other side of earth.
Piggybacking on this answer, this technology would probably also be able to detect a relatively sudden rise (i.e., over the period of decades to centuries) in the carbon dioxide levels in an exoplanet’s atmosphere. This could well be interpreted as an Industrial Revolution on that planet, though it’s probably subject to a lot more interpretation and argument than the presence of oxygen would be.
If there was a TV station broadcasting on the moon, you wouldn’t be able to pick it up with your rabbit ears on earth, even when the moon is visibile. That doesn’t mean it’s impossible to send radio signals between Earth and the Moon, just that everyday TV broadcasts wouldn’t work.
I think you mean “sapient.” Most animal life is sentient.
While I tend to agree with the above…there are some ways out. I suspect that the inhibiting step is multi-celled life and stable planetary systems. If we ever get out there we will probably only find wonky planetary systems and bacteria.
However, it is very possible that is not as inhibiting as I suspect. Possibly intelligence is the inhibiting step. If that is the case we may find life but no intellgent life.
It is also possible that technology is the inhibiting step…in which case we might find intelligent life but not much technology.
I’ve also seen some mathematics to show that even if a tech alien civ colonizes the galaxy it could leave ‘holes’ like swiss cheese and we could be in one of these holes.
Well, it worked in Contact.