If there was an intelligent life form, like humans, it would have expanded into the cosmos and colonized the entire galaxy within only a million years of developing technology. Since we don't see traces of them everywhere, we must presume they don't exist.
Perhaps government funding for their space exploration programs dried up, industry regulations interfered with commercial space exploration programs, and they all just gave up and shifted technology resources to making games for their mobile phones.
It's like, nobody has considered that advanced life might not even feel a need to live on planets at all. It's expensive to get resources from, and there's a near limitless supply of easy to get smaller debris.
Additionally, the difference a 2 billion year head start could make is hard to imagine. One thing that's not hard to imagine is that they don't live in meat bodies for most of that time. They could easily be machines or virtual, and then would look and act nothing like anything we're looking for.
We have sensitive telescopes. If there was life out there, we would have noticed. You would have astronomy conferences filled with people trying to figure out what all these weird spectra objects are, or trying to decipher all these structured radio observations.
What? No, absolutely no we would not just see them with sensitive telescopes. Perhaps, if you're thinking of some sort of interstellar space travel, maybe we'd see the engines? But no, even that seems unlikely.
Any space habitat of any plausible size will be completely undetectable, or at least indistinguishable from a planet. And I would think they'd be much smaller than that.
And structured radio? Lots of possible reasons not to see it. One, possibly not using radio. Two, encryption. Communication will likely look like noise. But even so, the distances involved means long range transmissions will need to be very directed and narrow beam. And even then, it's only a few light years before the signal is undetectable. I would suspect any really long distance communication would be bounced through relays. Also, why? You have to wait years for messages to go around. All of this means no, we're not likely to easily find stray radio signals.
I think you are completely misunderstanding the point. He have to vent heat somehow in the most efficient ways of doing so are not natural in their spectra. An encrypted radio transmission is still perfectly detectable -- you may not know what it says but you know that it is there. Artificial signals are blindingly obvious.
And this is without getting into Dyson spheres and other efficient but detectable technology.
Yes, of course. And the heat of a star will make that heat completely invisible in comparison.
The "spectra" that heat would be vented at is infrared, which is infrared no matter the source.
Say you had some gargantuan fusion power harnessing space station in deep space. lots of assumptions here about alien cultures, but this is likely the easiest to detect. They will do whatever they do with their energy, and then vent the waste heat. That heat will be infrared. What does a dim infrared source look like (if even visible at all)? It looks like a brown dwarf. But this is assuming a lot. It assumes some alien would even build brown dwarf sized space stations. We don't know if or even why they would do that.
Encrypted signals are not blindingly obvious. An encrypted radio transmission will appear as pure random noise and no different from all the rest of the noise that we pick up.
If an astronomer picks up a radio signal it is extremely obvious whether it is an artificial source or not. Natural sources have very inefficient spectra of very specific types. Artificial sources have very clear frequency cutoffs, having come from an antenna. Even frequency-hopping sources may jump around in a way that makes eavesdropping difficult, but if you stick around long enough on a single channel (as radio astronomers do) you'll get little blips now and then as the signal hops through your channel and is gone again.
How do we know this? Because astronomers see these every single night and have developed sophisticated filters to remove them. But by checking how the source is moving it is quite easy to tell if source is local or not, and sure enough all these artificial sources come from satellites, the troposphere, or an unshielded microwave.
It is actually remarkably difficult and a challenging problem in itself to create a communication mechanism which looks like a natural source. It defies imagination to think that every single intelligent species out there has purposefully masked their existence in such a way, including giving up useful technology like ground control radar or mobile communications.
The reason they have to filter out artificial sources, and the only reason they're a problem, is we are literally right on top of the source. These aren't even as far away as, say, Mars. New Horizons, for example, can't communicate with Earth unless it points its transmitter / receiver directly at us. And that's in our own solar system! Only a few light hours away.
Just think about it. The signals are going to be so weak by the time the photons get here they will be indistinguishable from the CMB.
> We have sensitive telescopes. If there was life out there, we would have noticed.
I'm sorry, but that's way off.
Our current telescopes can't even see the majority of the exoplanets in our galaxy; we are made aware of their existence by observing the behavior of their host star (wobbling/dimming). Unless something is extremely close, unfathomably enormous, or emitting/reflecting large amounts of electromagnetic radiation (light, radio, etc.) that isn't bent/filtered/reduced to noise, then we are completely unaware of it.
That assumes that civilizations derive power by encasing their host star in a Dyson sphere, which is not a foregone conclusion; that prediction was based on our current understanding if technology. Think of Huygens who imagined that Venusians sailed the seas on ships held together with hempen rope.
An "amorphous blackbody" source, from anything reasonably distant, just looks like a smaller star. There are a bunch of if's and unknowns involved, but it could be maybe possible to detect a Dyson sphere. This[1] article talks about it. The upshot is that it is nowhere near blindingly obvious, and we don't currently have the ability to differentiate between a natural or artificial infrared source.
We just found the first planet that is somewhat similar 1400 light years away... and you think our 'sensitive telescopes' would have definitely discovered all possible life in the universe if it existed???
"SETI estimates, for instance, that with a radio telescope as sensitive as the Arecibo Observatory, Earth's television and radio broadcasts would only be detectable at distances up to 0.3 light years, less than 1/10 the distance to the nearest star."
Or maybe the next step in the evolution of a civilization is the realization that 'colonizing' is much more fun if the colonists are just dropped off without any technology and let to develop into a civilization and discover who they are and do the same thing over again.
You know, just to keep the game going. All that's needed for that is already encoded in their DNA.
Maybe there are other channels of exploring spacetime than just the physical reality. Maybe that's where all the advanced civilizations reside.. Like the place we are in before we are born or after we die...
1 million years of mind evolution should not only bring advanced tech, but also advanced wisdom and understanding of who we are and what we are doing here. I doubt that expansion to all possible planets is the ultimate goal, the mystery must go much deeper than that ;).
It's like an anthill in the middle of the Amazon saying "If there were life on Earth that is more intelligent than us, why can't we see their enormous anthills? Why haven't they tried to contact us yet?"
I sometimes wonder if "like humans" is the key. What if past some level of technical advancement, organisms cease inhabiting the same scale as us. Physically and temporaly; they become microscopic and perceive+act on a time scale faster than us by orders of magnitude. Why inhabit the days/hours/seconds timescale when you can have the same experiences in micro/nanoseconds? So we would be mostly not interesting to them and expensive to interact with at our timescale. Not sure if we would notice them right under our noses.
Based on what evidence? I would posit that it there was an intelligent life-form, it would have descended into war and eventually extinction. Self-interest isn't exclusive to Earth.
Edit: I've said that self-interest isn't exclusive to Earth, without providing evidence and I don't have any; I should have said that self-interest isn't exclusive to humans, the simplest forms of life (bacteria, as an example) make war also.
Your big unstated assumption is that any intelligence will always consume the maximum resources it can and cause the maximally possible transformation of any habitat. Normally, when physicists look for these kinds of large-structure signs, the implicit assumption is that it's sufficient for one civilization to behave this way, but you seem to assert they all must be like that.
Any of the hypotheses we discuss in this thread (whether they are over-confidently stated as facts or marked as speculative) are inevitably deficient due to data derived from a sample size of one.
