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Question is to people who say if universe is teeming with life, then why is it not visible close by: We don't know how large the universe is. If say life is "teeming" means it's found every 1M Parsec on the size of 10^100M Parsec, wouldn't it be teeming, and yet nothing in our vicinity?

I'm being genuinely curious, not dissing on anyone.

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There’s a few problems when hunting for life:

Distances are immense:

1. Our view of the galaxy is very limited. We know almost nothing about our closest neighbouring solar system, let alone anything further afield

2. And because the distances are so far, we are effectively seeing those distant events hundreds or thousands of years in the past.

3. Where to look? We cannot search everywhere. We can only hope to get lucky that we are searching the right corner of the sky at the right time.

Alien life is completely alien:

4. We can only make assumptions of what to look for. Any sufficiently encrypted signal might genuinely appear like white noise to us.

They might be so advanced that we simply cannot detect them

5. Early communication systems on Earth were noisy in that they were broadcast 365 degrees. Later systems could be targeted, focused in a specific direction. As technology advances, noisy classical methods of broadcasting become less common. This in turn reduces the amount of noisy any extraterrestrial eavesdropper could spot.

And that’s assuming they’re not intentionally “cloaking” themselves. Putting aside Star Trek style fantasy for a moment, there is an advantage to remaining hidden. Whether you’re a predator like a burrowing spider or stealth bomber, or prey like bugs that camouflage themselves as plants; being hidden gives you a massive tactical advantage.

Cloaking probably isnt possible without discovering someway to violate the laws of conservation of energy. Any work done by a system will produce heat hiding the heat signature of an advanced technological society is probably impossible.

Every planet, every rock emits heat (thermal EM radiation) so why can't the civilization willing to forgo most of its potential computing and industrial capacities choose to emit a heat signature indistinguishabe from a rock by observers at other star systems?

s/the/a/

If you want to hide your heat signature, and you have the technological means to capture and direct your waste heat, you could simply radiate it towards your system's star. This is assuming you're producing so much heat that it would stand out more from a distance than similar but lifeless planets.

What’s to say some of the stars in the sky aren’t massive computing devices disguised as a common star?

Who's to say that all of them aren't, including our own?

Basic technology we have today would have seemed impossible to people not that long ago. I mean they could have easily imagined it, but would have had no reason to believe it to be possible. There's a fun article here [1] where the NYTimes, in response to a failed attempt at flight, claimed that human flight would be basically impossible. Amusingly enough, that article was posted just 9 weeks before the Wright Bros achieved manned flight. After being proven wrong there, they would later go on to claim space flight was impossible. [2]

The point I make here is that there are two possible scenarios here. (1) We've now finally reached the defacto end of revolutionary technology, technology we might imagine yet have no reason to believe could ever really exist. Or (2) we continue on at just another random point in technological development, where our views of today will look as naive as those of the past. And it seems that one of these scenarios is inexpressibly more likely than the other.

[1] - https://bigthink.com/pessimists-archive/air-space-flight-imp...

[2] - https://www.rfcafe.com/miscellany/factoids/ny-times-admits-m...

And it's not just the size of the distance we can see, it's the size of the slice of time when we are looking. We've had the tools to sorta-kinda detect life signatures for what, 10-20 years? Maybe we can keep that up for another (at best) 100-1000 years until we destroy ourselves? The universe is on the order of 10^10 years old. Star formation will end ~10^14 years from now The last black holes will evaporate ~10^100 years from now. So our temporal search window is astronomically small, too.

Why do you assume we distroy ourselves? If we can make spacecolonies at somepoint between now and your 1000 year figure why kill ourselves when we can leave for another star. It doesn't even have to be a popular strategy just one that a nonzero number choose to take rather that self distruction.

How long can we teeter on the knife edge of global annihilation without someone pushing the wrong button?

We made it through the cold war without turning any cities into molten glass and it was more tense than the world right now.

But, let’s look forward through the next hundred years, do we seem to be going in the right direction?

"We haven't died yet" is the most selection biased evidence you could possibly invent. 10 on a scale of 10.

It also has no predictive value given the nature of catastrophic threats continues to evolve rapidly in quantity and quality, and the elements of past threats (the cold war -> nuclear war), continue to be threats (autocratic regimes -> fighting or planning wars that could become existential to their leaders -> nuclear war).

Given we have a sample size of one, its hard to make argument not based on past experience as that's all we have to go on, and we a reasoning about use of weapons that haven't existed for a century yet it hard to make strong argument either way bit MAD seems to have worked so far and most leaders of nuclear armed States are to egotistical to commit suicide when they are living the good-life at the top and that's what launching WMD s, is its is suicide .

> Why do you assume we distroy ourselves?

Seveneves, by Neil Stephenson, discusses the human penchant for self-destruction much better then I can in an HN comment, it is worth a read. In short, though, we cannot, unfortunately, escape our humanity, and pretending we don’t take it with us wherever we go is wishful thinking. As a group, we are ruled by incredibly base instincts that no longer apply to our situation, but they still largely determine our trajectory.

You mean the book where the nations of the world put everything aside to preserve the human species from distruction by space based natural disaster by throwing almost all their resources at various space programs?

Yeah, that one. Where those people then go on with their stupid, petty, political infighting and senseless scheming thereby nearly bringing about the end of human species anyway.

You’ve clearly read the book, I am curious what would drive you to make such an obviously incomplete representation of the story. Being edgy? Contrarian for contrarian’s sake? Since you offer no additional context besides a vague (and uninteresting) insinuation that im somehow wrong, I suspect you are just trolling, smegger001

>Why do you assume we distroy ourselves?

Have you not been paying attention to the news? We have a major nuclear power constantly threatening nuclear war, and several very likely conflicts between major nuclear powers.

Putting aside the more sociological arguments about (non-)human nature for a second - roughly speaking, technological development = ability to wield greater amounts of energy. The easier it is to put a satellite in orbit, the easier it is land a missile on another country. The easier it is to harness virtually free energy, the easier it is to rain unimaginable destruction on your enemies. Robot workforces enable robot armies (directed by malicious humans, not Skynet)

The more widely accessible a technology becomes, the more damage a single person or faction can do, and therefore the probability of someone causing mayhem tends to 1. And it's basically always less effort to destroy something than (re)create it

We can hope defensive counterparts to all these risks develop at a greater rate, but I don't think that's a given at all

Also remember that from a SETI/Fermi/Great Filter perspective it doesn't matter whether the species completely kills itself off. It could instead just repeatedly reset itself to steam age technology, and therefore never be stable enough for long enough to become seriously spacefaring

it's also not only a question of distance but also a question of time. there could be/have been several alien species that would be our next door neighbours but just not at the same time as us.

I'm fairly sure you know this already, but you just described the Fermi Paradox. [1] And the answer to this paradox is that there is no answer, though there are a million hypotheses.

[1] - https://en.wikipedia.org/wiki/Fermi_paradox

The first exoplanet was only detected in 1988 and confirmed in 2002. These are things we were really really sure were there and are absolutely huge relative to a vital sign. It would be surprising indeed were we to already have found a biosignature given it's got to be a lot harder than finding a gigantic chunk of rock.

Astronomy is hard.

We could just be early. We’re one of the first civilizations to ‘wake up’ perhaps.

So it’s teeming, but not much to see with our eyes yet

I don't know anything about anything but I can imagine a society of bacteria saying the world is teeming with life but they're sadly sitting at the bottom of the ocean in a lava tube and they can't manage to find any life.

Life every million parsecs means less than one life form per galaxy, so hardly teeming.

FWIW there are 2 trillion galaxies in the universe

So says Wikipedia

If the next "hard step" is aliens going from biological to artificial, how can we be sure what sorts of signals they might leak? We're not even there yet ourselves.

The real answer is that we don’t know.

We know with 100% certainty that life exists on the universe, we just don’t know where else besides earth it exists.

I think you can ignore that second number, best we know the universe is infinite. Though the visible universe is limited.

Our definition of life is based on 1 single element.

But why do we think that life would be based on a different single element anywhere else?

Here are some alternative theories of possible types of life. The thought of silicon-based life swimming in oceans of ammonia or other hydrocarbons fascinates me.

https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...

It's super fun to consider, but one problem with ammonia-based biochemistry is that everything would be so cold. In temperatures that are cold enough to liquefy ammonia you just have a lot less energy going around, and life requires energy to thrive. We can see this principle at work on earth where the tropics have the most biodiversity and the interior of Antarctica is almost totally barren of life. So it seems to me that while an ammonia-based biochemistry might be plausible, it may be a sort of evolutionary dead-end where nothing can progress beyond being simple and microscopic.

Or maybe it can at the bottom of an ocean where the pressures are higher and the ammonia is warmer due to geothermal effects...? but then it has no access to energy from the sun, and it's very hard for us to detect something that lives at the bottom of our sea, let alone an extraterrestrial one

It seems like there ought to be a sweet-spot where life will consume the right amount of energy for an environment. Consume too much energy, you starve. Consume too little, you are out-competed by other life forms which consume more, and move faster as a result. But that’s environment-specific, maybe it is possible that ammonia life evolved on a lower-energy planet everybody just moves slower?

If you move slower, you evolve slower. If less energy is available you have fewer organisms, there's less reproduction, therefore there is less evolution and less mutation.

That's why when we drilled down to Lake Vostok we found some single celled life forms that had interesting properties because they'd been cut off from the rest of the world for millions of years, but we didn't find Jules Verne's Lost World. There's just not enough energy down there under the ice to power a lot of biology. The less abundant/accessible energy is, the less probable complex life becomes, regardless of the biochemistry.

I buy that there's a good chance weird things on the complexity scale of bacterium are dotted all over the cosmos, but the big problem is those are functionally impossible for us to study (and even conclusively detect) unless mayyyyybe if they're in our solar system.

The Dragons Egg explores this in a fun way. Life on the surface of a neutron star.

> if you move slower, you evolve slower

In the plank limit maybe. Large-scale "organic" farms speed up evolution 100,000x with the right drug cocktail to circumvent the current legal definitions of "GMO." They aren't pumping 100,000x more energy into the system. Our base rate of evolution is naturally selected for complicated reasons which _involve_ the available entropy supply but aren't simply monotonically dependent on it.

This kind of gets to what I was implying. Chemistry is chemistry, and physics is physics. The same elements are available throughout the universe even if they are not all brought together in the same quantities.

I get that it's fun to consider, but things are beyond credulity thinking that chemistry will be different elsewhere in the galaxy. Of course the weasel words "based on our current understanding" are a great way to keep the fun going

It’s possible that a sentience dependent on a colder chemistry could operate more slowly, too.

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