We are definitely not alone. The great filter, in my opinion, does not exist. It's only the vastness of space and the relatively short time a civilization produces radio signals that makes it appear this way.
Chances that two civilizations, if they detect each other, would be on the same level of development are slim. And once a less technologically advanced civilization meets a more technologically advanced one, game is over soon. Ask Aztecs, or Sioux, or pick any other historical example.
50-100 years is probably par for that particular course. A very narrow timespan in the grand scheme of things.
Many spread-spectrum applications such as GPS use signals that are well below the thermal noise floor by the time they're received. Those signals generally can't be detected without a known sequence to correlate them against.
When you pick up an encrypted signal, it's still obvious there's a signal there. Radio telescopes will pick up cell phone signals, for example; that's why there is a radio quiet zone near the Green Bank telescope. You just can't decode the message itself without the encryption keys and algorithm.
When it comes to interplanetary reception, though, any intelligently-constructed signals will likely be below the noise floor unless deliberately broadcast for our benefit. No coherent carrier or sidebands? No spreading sequence? No chance of detection, whether encrypted or not.
Really we are more likely to pick up recognizable signals from civilizations that are intentionally trying to contact us. It's possible we could pick up radio leakage, but the signal would be a lot weaker. So there are orders of magnitude more stars that could be intentionally contacting us, vs accidentally leaking a signal. (At least assuming the ratio of the strength of their intentional vs accidental radio emissions is similar to ours.)
There's a long history leading up to those events. I find it unlikely another planet will share it.
People get all worked up about dyson spheres and radio signals, but these are so deeply rooted in the human understanding of things in our tiny tiny slice of the universe.
The beauty of the film Arrival was showing the challenge of interacting with a truly alien language.
We see a variation of this in convergent evolution across distantly related species (e.g. the evolution of wings).
But in any case, there will be some commonality in environments across many planets, owing to what environments are the most probable hosts of life, and to the fact that the laws of physics are universal.
Intelligence across species shares common characteristics even between dolphins, apes and birds which all evolved it independently.
>> "There are things in the universe billions of years older than either of our races. They are vast, timeless. And if they are aware of us at all, it is as little more than ants…and we have as much chance of communicating with them as an ant has with us. We know. We've tried. And we've learned we can either stay out from underfoot, or be stepped on."
I think my favorite variation on why we seem alone was how Earth exists in a space version of the Bermuda Triangle, called the Veil of Madness, that all spacefaring civilizations avoid: https://creepypasta.fandom.com/wiki/Mankind
Imagine there are 1% chances that an encounter with an alien civilization spells the end of humanity.
Or 0.1%, or 0.01%
Now roll that dice for millions and millions of years. It's probably a good idea to switch to communication technologies that don't broadcast your location (and your technological unsophistication). Just in case.
That is true historically, but historically we weren't at a distance of light years. Given the vastness of the universe, it seems quite possible that by the time we detect another alien civilization via their emissions in the radio spectrum, that civilization has already gone extinct.
https://en.wikipedia.org/wiki/Treaty_of_Waitangi
More controversially I would pick India and China's encounters with Europe. I think it's possible to argue that both India and China were substantially more technologically advanced than the Europeans when significant links were established. India had maths and spinning (also probably better guns), China had silk, porcelain, paper, printing and the compass; also bigger better ships.
There were several meetings of civilizations of comparable level of advancement and strength on Earth. I posit that in space it's significantly less probable, unless we consider these civilizations to also be sisters, all humanoids coming from a common source, like these of Earth.
Not to mention the impracticality of communicating with your home planet across several light years.
If you’re basing this off of what’s happened in the past on this planet, without a good explanation as to why that would apply to an alien civilization, I’d suggest that you’re not using a good model. Bayesian epistemology is not a good way to decide what’s true, because new knowledge is created which makes the old models not work anymore.
It is simply a result of Shannon's entropy. To be detectable, signals have to be broadcasted and low entropy, the opposite of what we need for efficient communication. A signal that makes best use of its bandwidth would be indistinguishable from noise for someone who doesn't know the protocol, it is also likely to be precisely targeted at the recipient and unwanted emissions kept to a minimum in order to limit interference.
It is already happening on earth as we are replacing loud analog TV emissions with more subtle and better targeted cell phone signals.
Would explain the lack of evidence just as well.
I'm saying that there are absolutely many more habitable planets around than we believe there to be, even among the planets we've observed. We just don't know what to look for, because we don't know what's possible.
"Life, uh, finds a way."
But the little we've explored of space, it's just dead rocks. There is literally nothing that has suggested a hint of life outside our atmosphere.
I'm not completely discounting alien life, I'm saying all we have now is hope, wishful thinking and not a shred of proof.
Why though? Surely you did not do a statistical analysis, because there are too many unknowns:
What is the likelihood of life (as we know it) forming on a given planet? What is the likelihood it will become multicellular? Life on earth was prokaryotic for billions of years and the Cambrian explosion is not yet entirely understood. How likely will it become intelligent? Remember, we don't have any reason to believe that intelligence is in any way a "goal" of evolution. Even if it does, will they have the resources necessary for becoming a technological species? Maybe dolphins are super intelligent, but living in the water and not having opposable thumbs sucks if you want to make tools and perhaps harness the power of fire to build even better tools and machines.
That does not even take into account the various catastrophic events that can happen in the universe where we do not have a good idea of how likely they are. What if a meteor hits at the wrong time? What about gamma ray bursts? What if a Carrington-type event wipes out all electronics? For all we know, these could happen with an average frequency of 100-200 years. Do we have an idea of how likely it is that the climate on a planet stays somewhat stable for a few hundred million years so it doesn't spontaneously become a planet like venus? We just don't have enough data points to assign probabilities there.
So yes, I believe it is largely wishful thinking.
So either whatever caused life on Earth was completely unique and couldn't have happened anywhere else, or there's a very good chance there's other life out there. The universe is huge and it's hard for me to believe that earth is the only place where the parameters were met to cause life. From there, it's hard for me to believe that those life forms couldn't adapt to circumstances that are beyond our wildest imagination.
In 1000 years, do you think we won't have discovered forms of life that we would say are impossible today? We've discovered things we thought were impossible just 20 years ago!
First, the further out we look, the less recent our data. Every event we observe that's more than 200 light-years away happened before slavery was abolished in the U.S., and well before Earth's first radio emission.
I'm not saying we shouldn't base conclusions on evidence, but I will say that our ability to gather _current_ data about our surroundings is limited to an infinitesimal fraction of the universe. Worse, it degrades with distance. Bacteria were there, but we couldn't see them for a long time. (They were theorized, though, their existence reasoned out and later proved with evidence)
Second, unlike bacteria intelligent life is...well, you know. Suppose we're the last ones to the interstellar party, or at least not the first. We come in, blasting radio waves like a toddler, BEEP BEEP BEEP BEEP. No signal hygiene whatsoever. Our neighbors on the other hand likely learned a long time ago to hide their presence from all but those they trust, and certainly from those on a lower technological playing field.
If the intelligence we're trying to prove can consciously avoid us finding out about them, then taking absence of evidence as evidence of anything becomes suspect.
Of all the intelligences that could exist - not just those we could detect, mind you - what percentage of those do you think are more advanced than us?
While I can't fathom anything else I still believe it's hubris to believe we understand what forms of life may exist in the universe. Maybe we exist right along something else and will never notice each other.
We're looking for what we can recognize as life.
Based on the range of extremophiles we have from just one planet, that's a lot more than you might think:
* -20 to 120 degrees celsius
* 1,100 bar pressure
* ph 1 to 11
* 6000 Gy radiation (a CT scan is about 6 mGy)
Supernovas can have the same effect as magnetars, as also black holes. There could even be a tiny one lurking in the outskirts of our solar system (the so-called planet 9). What I wanted to point out is that the Universe is a very hostile place. There could have been myriads of civilization that were eradicated because of a cosmic event every now and then.
The difference really starts to matter as you get inside a planet's radius. As you wander closer to earths center, the gravitational pull continues trending downward and gets replaced by pressure, aka having to support increasingly large portions of the planet. Eventually you'll be killed by that pressure, as no material is known to survive the pressure. Humanity hasn't made it further than a dozen km into the rocky part of earth's surface, the fraction of a fraction of earth's radius. Mostly, earth's insides are inaccessible to us.
For black holes, this is different. The gravitational pull just keeps getting stronger and stronger the closer you get to the event horizon. Eventually you'll be killed by tidal forces. But at the height of a circular orbit at the same height as earth's surface, those are the same as on earth, aka not really something to worry about for humans.
To give it in explicit numbers, a 2 meter tall object of 80 kg mass standing on the surface of earth gets about 0.5 milinewtons of tidal forces (while having to deal with 785 newtons due to normal gravity): https://www.wolframalpha.com/input?i=80kg+*+G+*+mass+of+eart...
Thus, you can get much closer to a black hole than you can get to earth's center.
It's also worth noting that long-term space survivability seems to be extremely hard to achieve, we haven't even managed to create long-term sustainable fully closed biospheres yet.
We wouldn’t even have known about such different life ON THIS VERY PLANET if we hadn’t chanced upon their remains
And we will never see them again.
We could enter one due to environmental pressure from the death of a key part of the biosphere, not even related to climate change.
And finally, food scarcity in a world of climate change increases the likelihood of conflict, including nuclear conflict.
Sadly, it is reasonable to be concerned about this possibility.
Climate scientists study climate. Should you want to know about climate, you can do much worse than to ask one.
There are no sides to pick here.
It's hard to find any convincing argument that climate change will destroy our civilization with anything near 1/2 odds. It's a completely different ballpark.
If there are 10^30 stars in ours, the lower bound on the odds of surpassing it have to be close to that.
Personally I expect there to be many smaller filters rather than a few great filters — 30 things each with a factor of 10 has the same effect, after all.
Anyway, there are indeed a few things in our past that look like a 10^-10 odds filter, like each time our genetic encoding changed to increase our codons and the oxygen catastrophe. There are more that look like merely "almost impossible to survive" (I'd guess some ~10^-4 filter) like large asteroid impacts, but not nearly enough to make a difference.
We have evaded this filter. On to the next.
Your implicit assumption is that not a single other intelligent species decided to harness the universe by, for example, consuming stars for their raw matter, or building Dyson spheres to black out entire sections of the sky.
It is imo on you to explain why there's a hard cap on the exponential growth of intelligent life that prevents it from EVER reorganizing the universe in its own image. Not 99% of the time — that's not enough for these purposes.
Just because stealth in space doesn't work doesn't automatically mean you can see everything in space at all times. We need to build giant telescopes to see stars thanks to the inverse square law. The bigger our telescopes with better light collection the narrower their field of view. An antimatter spaceship could fly past Pluto tomorrow and we could easily miss it since we can't monitor all 4πr^2 of the sky at once with powerful telescopes.
Then you can say goodbye to those robotic spaceships. Note that I'm not claiming that they're possible -- I'm just saying that if they do exist, they're very detectable.
> An antimatter spaceship could fly past Pluto tomorrow and we could easily miss it
We can detect Voyager from way past Pluto, even though it emits only several dozen watts. I'm not sure how you'd miss an antimatter-powered spaceship at a comparable distance.
But why do it? If you send a robot to (say) Alpha Centauri what have you actually acheived, at probably enormous cost?
A tech we don't have and probably never will.
So your robot ship turns up and what happens then?
If it's going to self-replicate it needs to recreate most of the features of an entire industrial civilisation. In our terms that would be metal refinement, chip manufacture, chemical life support and more - all done by bug-free software running on hardware which is perfectly error-free and reliable and lasts indefinitely.
If it's going to seed biological (or equivalent) colonists it needs to be clever enough to find candidate planets with an ideal biosphere and no biological threats. Then it needs to teach the colonists how to survive and colonise.
A lot of SETI and colonisation seems to be based a naive idea that all you have to do is get from A to B and you've solved your expansion problem.
In reality propulsion is just the loading screen. Winning the game is a much harder challenge. So many things that can break, fail, be destroyed by chance, or go wrong because of design flaws that it's an insanely difficult problem without very much more advanced tech.
Humans are likely at the end of our biological evolution. The next steps of human artificial evolution will accelerate which means extra terrestrial intelligence is unrecognizable to us currently.
We look for modern human-like civilizations, and those obviously won't exist much.