Elsewhere, someone commented that our stray radio transmissions form a sphere over 100ly in radius. Which may be technically true, but does it really work that way? Given the incredible fall-off in EM (a factor of around a billion per lightyear), would any of our signals be stronger than the noise?
Our sun puts out an enormous amount of EM, and at a parsec, our planet is nearly impossible to separate from it visually, how would our limp signals overcome solar noise? Are we wasting our time trying to send or receive messages from space? Seems to me like it would make more sense to focus our efforts on discovering alternative forms of information exchange (the mythical “ansible”, or “subspace”) than messing around with EM communication.
A few years back, they began to focus on planets that were lined up with our solar system’s ecliptic under the assumption that aliens would have similar planet-detection methods as us and planets that are out on the same plane as our ecliptic may have detected a planet that looked habitable. And then they might be deliberately beaming some sort of communication our way as an attempt at first contact.
You’re right that EM signals drop off with the cube of the distance quite rapidly. You’d start needing solar-system sized antennas to pick up any signal outside of the immediate area - although this may be practical for an advanced species using virtual antennas via interferometry or some other method.
But you’re right that we’re not going to pick up someone’s equivelant of “I love Lucy” from 100 light years away. We may be able to pick up a strong signal deliberately beamed our way, or catch some sort of interstellar communication of extreme power from an advanced society.
I believe if anything, SETI is becoming more relevant rather than less. With our ever increasing exo-planet finding abilities we actually have specific stars to listen to.
As for us hearing another civilization, it seems like a long shot to me. While I do believe that it is very likely other civilizations are out there; I have no idea if we have programmed those receiver suites to sample all that bandwidth to look for more than a handful of modulation techniques.
We are familiar with how we modulate a signal so that it contains data, but what is to say aliens are using the same techniques as we are. If those SETI computers aren’t given the right instructions on what to search for, it wouldn’t be picked up. We could have already recorded alien transmissions, without knowing it.
It doesn’t seem likely that our earliest radio and TV signals would be detectable in a nearby star system to me. The power of those would have dissipated so much by now.
Perhaps, some of the communications that we started using later, but even those are sometimes spread out and transmitted below the noise floor. Again, the aliens would have to processing the signal the right way to pick it out from the noise. The bulk of our modern satellite communications utilize a carrier signal, with multiple functional signals multiplexed into it. They could easily roll right over it, unless they were trying to demultiplex it.
I’ve never seen any info from SETI on how they process all that antennae time. I trust the SETI scientists are a hell of a lot smarter than me, but they sure as hell don’t explain exactly what types of signals they process for, or how.
I am not even fully convinced that we would be able to recognize alien intelligence, much less, necessarily, alien life. Our thought/communication patterns are very likely so drastically different from “theirs”, we would probably not even know what we were looking at.
Are you saying that we wouldn’t be able to interpret any patterns that may come to us, or are you saying that we wouldn’t even be able to recognize them as patterns at all?
There’s other, more subtle problems. SETI can really only ever detect deliberate signals, more than likely aimed at this star specifically.
The reason for this wasn’t apparent in the decades when SETI was thought up. At that time, radio signals were high power and low entropy.
As it turns out, the absolute limits on signal encoding and data compression involve making your signals more and more chaotic. The “ideal” radio emits a wideband, low power signal that will appear indistinguishable from noise to any receiver not equipped with the right decoding keys.
Our own signals are like this. If you think about it for a moment, what determines the absolute limits for data compression? Well, if you were trying to compress a signal that has a very regular pattern, that’s easy. Just send the pattern once and encode how many times it repeats.
Well, your compressed signal even in this very simple case no longer has any repeating patterns in it.
If they’re actively trying to signal us, and they have the intelligence and technology to be able to do so, they would very likely have noticed some of the same things about the universe that we have - for example, that certain types of electromagnetic radiation will be better than others for the purpose of signalling, and a bunch of other stuff too - such as the atomic nature of matter, the way integer math works, prime numbers, etc.
Anything we discovered about the universe, rather than invented, is a potential means of having a species-agnostic conversation.
If you are talking about picking up accidentally transmitted signals, then the discussion about compression makes sense. More than that, the idea was first thought up when our TV transmitters sent out signals widely. Any advanced civilization would have satellite and cable, and so wouldn’t be emitting noise. More, communications protocols are getting more and more complicated as receivers have more and more intelligence, and so will be hard to decode.
But if the transmission is deliberate, I agree with Mangetout. We already know which frequency to use and there are large sets of obvious signals which can be used to demonstrate that the transmission comes from an intelligent source. Easy as Pi.
I’m not going to argue that all intelligent species would think to use methods we could reasonably interpret, but it would be pretty absurd for none of them to think of the obvious ones.
No, I don’t think it’s unsafe. Interstellar travel is stupendously difficult. Nobody is likely to come knocking - and anyone with a level of technology sufficient to do it:
[ul]
[li]Can’t possibly need anything we have[/li][li]Probably has the means to find us regardless[/li][li]Would probably arrive after the extinction of the human race anyway[/li][/ul]
Or they could be borg-like and need to consume other intelligent beings in order to progress to some kind of higher plane, and they’ve already cleared out their quadrant of the galaxy.
I just watched this video from 2010 that covers new SETI search strategies, and they are apparently focusing almost exclusively on intentionally beamed signals.
He talks about signal strength and antenna capabilities too.
All our assumptions are based on imagining short lived, relatively stupid biological creatures like ourselves trying to make an interstellar journey.
A more realistic model would be to assume creatures that have the technology to arbitrarily consume any available matter (that isn’t too deep in a gravity well to remove it) and convert the different elements into machinery that is self replicating. This is a pretty boring and realistic assumption : we ourselves consist of a limited class of this kind of machinery.
If you assume a civilization has access to as much total machinery as you would get converting all of the moons and planetary crusts in our solar system into equipment and computers, interstellar travel seems pretty damn easy. With a teensy fraction of this many resources, you could do a lot of different things.
To succeed in an interstellar voyage, you don’t need to send a habitat containing biological creatures to another star. You only need to get the bare minimum - maybe a few metric tons - of self replicating equipment to the destination. You can then set up a signal receiver at the other star and just broadcast the “passengers” as information.
For a drive, you could simply build a gigantic superconducting quench gun from tearing down a moon or 2. You’d accelerate the entire starship to cruising speed before it ever escapes the solar system. In principle, this is just a giga-size version of existing particle accelerators that humanity has today.
The starship would have to be mostly antimatter fuel. Containing it would be quite tricky, but it’s probably doable. The antimatter fuel would be used to decelerate the starship when it reaches the destination.
Also, since the civilisation that pulls this off won’t be subject to biological aging, it doesn’t actually matter if they can’t go more than 1% of the speed of light or so. They would still be able to spread across our galaxy in a blink of an eye in cosmic terms. (a few hundred thousand years)