There might have been contact, a billion years ago, say, flew through our solar system, took photographs, etc. But if so they obviously must have been careful explorers that left no traces of their presence here.
We may be one of billions of worlds in our galaxy with life on it. The most interesting thing to happen here happened 500 million years ago. That's the development of multicellular life. But you couldn't detect that from a distance so easily.
And, we don't know how common multicellular life is. Maybe there are millions of planets with that as well. If so, then the next stage you could expect to detect easily from orbit, never mind another star, is us.
And we are just one in a hundred billion stars in the galaxy.
Perhaps many civilizations arise in the galaxy and they have more interesting things to observe than yet another planet with multicellular life on it.
That's if there are other civilizations in our galaxy with the ability and interest in exploring space.
Civilizations without technology, or who don't develop it as far as spaceships, or who are not especially interested in exploring the galaxy wouldn't know about it.
As others said, it wouldn't be easy to spot us directly.
If they did colonize a galaxy, I don't see how they would become extinct. Just evolve into new star faring creatures. Because, if some event lead to one of the many star faring civilizations to go extinct, it couldn't affect them all, not with speed of light restrictions. And if they can travel faster than light they'd fill the galaxy and universe within a few thousand years.
Which may seem great, a way of making sure that you can never become extinct, or at least your descendants, if not ur humans.
However, I think that Extra Terrestrials would choose not to colonize a galaxy, or else would do it in a self sufficient probably unobtrusive way, because of the impossibility of continuing exponential growth for more than a few thousand years, and many dire consequences.
Not least of which - that half your galactic population would end up destroying itself every century - or probably more often than that (colonies with the fastest doubling rate would be selected for by evolution).
Every century, or perhaps even every decade, your entire population would have to be not just decimated, but halved, through either warfare, starvation, technology out of control, or invading human descendants killing populations, or civilizations deliberately ending themselves etc etc.
The maths seems inescapable. One of these must happen
Faced with those options, I think any sensible ETI will not colonize the galaxy until it finds a way through this impasse. Which may involve staying in a limited region of the galaxy. Or may involve colonizing it sustainably without exponential growth. Either way their presence is likely to be unobtrusive.
But they could explore the galaxy using self replicating robots, as the safest method at an early stage, before the more tricky phase of sustainable colonization (if that is possible at all).
With not much more than our current technology we could build a self replicating probe designed to send one of them to every star in the galaxy. But we then may have to wait millions of years before it detects a newly emerging civilization.
So it's also possible that they have sent probes to our solar system that watched patiently for millions or billions of years, and finally send a signal back - but the parent civilization has long lost interest in the project or forgotten about it and moved on to other things.
Or the probes might be designed to self destruct if they don't get a "keep active" signal from their parent civilization (for safety reasons) if so they may all have done just that already.
Just a few ideas for how it could happen.
We may be one of billions of worlds in our galaxy with life on it. The most interesting thing to happen here happened 500 million years ago. That's the development of multicellular life. But you couldn't detect that from a distance so easily.
And, we don't know how common multicellular life is. Maybe there are millions of planets with that as well. If so, then the next stage you could expect to detect easily from orbit, never mind another star, is us.
And we are just one in a hundred billion stars in the galaxy.
Perhaps many civilizations arise in the galaxy and they have more interesting things to observe than yet another planet with multicellular life on it.
That's if there are other civilizations in our galaxy with the ability and interest in exploring space.
Civilizations without technology, or who don't develop it as far as spaceships, or who are not especially interested in exploring the galaxy wouldn't know about it.
As others said, it wouldn't be easy to spot us directly.
If they did colonize a galaxy, I don't see how they would become extinct. Just evolve into new star faring creatures. Because, if some event lead to one of the many star faring civilizations to go extinct, it couldn't affect them all, not with speed of light restrictions. And if they can travel faster than light they'd fill the galaxy and universe within a few thousand years.
Which may seem great, a way of making sure that you can never become extinct, or at least your descendants, if not ur humans.
However, I think that Extra Terrestrials would choose not to colonize a galaxy, or else would do it in a self sufficient probably unobtrusive way, because of the impossibility of continuing exponential growth for more than a few thousand years, and many dire consequences.
Not least of which - that half your galactic population would end up destroying itself every century - or probably more often than that (colonies with the fastest doubling rate would be selected for by evolution).
Every century, or perhaps even every decade, your entire population would have to be not just decimated, but halved, through either warfare, starvation, technology out of control, or invading human descendants killing populations, or civilizations deliberately ending themselves etc etc.
The maths seems inescapable. One of these must happen
- We stay as a sustainable population around a single star or limited region of the galaxy - with explorers perhaps setting out through the galaxy, but no colonization of the rest of it
- Or we become extinct
- Or we find a way to explore and colonize the galaxy sustainably without exponential growth
- Or, we end up with that scenario where half our population galactic wide gets destroyed every few decades, or less
Faced with those options, I think any sensible ETI will not colonize the galaxy until it finds a way through this impasse. Which may involve staying in a limited region of the galaxy. Or may involve colonizing it sustainably without exponential growth. Either way their presence is likely to be unobtrusive.
But they could explore the galaxy using self replicating robots, as the safest method at an early stage, before the more tricky phase of sustainable colonization (if that is possible at all).
"Most people, when they think about exploring the galaxy, think about sending out human colonies. It's natural to think we would explore it just as we do the Earth, it's the only way we know. To send machines instead of humans, especially machines that can replicate, may seem frightening. But - I'd argue, humans colonies are by far the most scary way we could explore the galaxy. It might well be a case of "look out galaxy (and Earth), the monsters are coming" :).
So what can we do? What is a responsible way to explore our galaxy, with current understanding of science, biology, and society, and could this explain why our galaxy is not filled right to the brim already with extra terrestrials?
After explaining the problem in detail, I'll draft out a possible way to do safe self replication with robots, but it's not a method that could be used ethically with humans. Could there be other solutions, and if so, could those also explain why the galaxy is not filled with extraterrestrials?"
See my Self Replicating Robots - Safer For Galaxy (and Earth) Than Human Colonists - Is This Why ETs Didn't Colonize Earth?
With not much more than our current technology we could build a self replicating probe designed to send one of them to every star in the galaxy. But we then may have to wait millions of years before it detects a newly emerging civilization.
So it's also possible that they have sent probes to our solar system that watched patiently for millions or billions of years, and finally send a signal back - but the parent civilization has long lost interest in the project or forgotten about it and moved on to other things.
Or the probes might be designed to self destruct if they don't get a "keep active" signal from their parent civilization (for safety reasons) if so they may all have done just that already.
Just a few ideas for how it could happen.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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