[belugacat]

Honestly, the real mystery is why so many people are confused about “why, despite universe seeming so vast, there are no signs of other alien civilizations” in 2023.

We have all the elements for answers if we focus on what we know, and forget the hand wavy sci-fi speculation.

1) Complex life is rare.

2) Reaching a space faring stage is even rarer. (we’re the most minimal definition of “space faring” you could come up with, and even then we got really lucky with so many things)

3) The universe is huge. It’s like, the hugest thing there is, man. And except for some little bits of interesting dust here and there, it’s mostly empty. As empty as it is huge.

So, does life - in any form - exist elsewhere in the universe? Almost certainly.

Are/were there life forms elsewhere in the universe that escaped their home planet gravity to go explore their moon or other planets in their solar system? Seems quite probable.

Is there any shot we are sufficiently close in space/time to encounter such another advanced life form? Almost certainly not.

[peebeebee]

Yeah. There's such a huge difference in interplanetary life vs interstellar or even intergalactic life.

Interplanetary: easy.

Interstellar: pushing the boundaries of what's possible imho.

Intergalactic: no way.

Our closest planet (Mars) is 3 lightminutes away.

Our closest star (Proxima Centauri) is 5 lightyears away.

Our closest galactic neighbour (LMC) is 150000 lightyears away.

[giraffe_lady]

Is there even any reason to think interplanetary is easy? We have a lot of stories saying so, and we intend to do it but we don't even have a loose plan of what that would look like.

Creating a closed self-sustaining ecosystem capable of supporting large animal life & cut off from the earth's resources is not something we've been able to do even at a proof-of-concept level.

We're very confident in ourselves but idk. It's not preposterous that life is a planetary expression and that it's simply not possible to expand an instance of it beyond the planet that birthed it. We assume we aren't subject to this constraint but we haven't demonstrated it at all.

[peebeebee]

I meant for all intelligent species that could be living in our universe, I can see interplanetary life as something rather easier to achieve. You don't have to think far out of the box for this. I can imagine some solar systems having multiple liveable planets for a single lifeform, which would make it something we could even do right now. Our some transpermia on planets that now host different but communicating lifeforms that are cooperating.

[giraffe_lady]

We can easily imagine faster than light travel but it simply isn't possible regardless. There are constraints on us other than our capacity for imagination.

We have never seen another living planet so we don't know what to expect from one. I touched on this originally but I'll be explicit now: the fact that we can't create a closed ecosystem even given a working example and diverse raw materials is a powerful indicator of our ignorance about the contours and possibilities of life.

I'm not saying it is impossible, but I'm saying any confident assertions about its possibility, much less how "easy" it is are fantasy if not pure hubris. It's quite possible that no level of advancement will allow for even merely interplanetary life.

[StanislavPetrov]

Out of the trillions of galaxies out there and the trillions more solar systems, it is very likely that at least some of them have multiple planets with habitats suitable to whatever intelligent life evolves there. In that case, an interplanetary civilization would merely require reaching the other habitable planet, not trying to change its environment.

[giraffe_lady]

> it is very likely that at least some of them have multiple planets with habitats suitable to whatever intelligent life evolves there.

This assumption is exactly what I am challenging: that there is such a thing as "general suitability" to life.

We should be open to the possibility that a living system is only compatible with the specific circumstances it emerges from. We've seen nothing to indicate either way, of course, not having seen any other life. But we should not so comfortably assume it's a transferrable process.

[timschmidt]

Another way to look at it:

Interplanetary: chemical.

Interstellar: nuclear.

Intergalactic: antimatter / black hole.

[NiloCK]

2 and 3 seem plausibly correct to me (although 3 is a mixed bag - the hugeness increases the number of dice rolls on 1 and 2 - not only the difficulty of connecting after the fact), but what is the basis for 1?

As far as I know, we have observed complex (and extremely robust) life on every temperate, wet planet that we know about. Batting a thousand.

[ryandvm]

Life appeared on Earth almost as soon as it was possible, but it took almost 2.5 BILLION years for it to make the jump to multicellular (a.k.a. complex life). It then took another billion-plus years for life that had the slightest bit of intelligence.

The universe is probably teeming with life, but sadly, most of it is probably just goo.

[itsanaccount]

I'll give you a fourth one.

There _are_ signs consistently that something has an understanding of physics and inertia that violate our understanding of such things, which implies our assumptions about distance of things in the universe are wrong.

Those vehicles appearance but lack of most interaction, lack of destruction implies something worse, that we are probably still such a primative civilization we're treated like zoo animals.

These conversations about the last century of the search for alien life in the light of David Grusch's testimony to Congress and the various and numerous UAP videos are.. interesting to say the least.

[monkeydreams]

> which implies our assumptions about distance of things in the universe are wrong.

There are two easy interpretations. One of these is imagining a new entity; aliens. The other is to imagine that humans are, essentially, human and falliable and are chasing lense flares and radar glitches.

One of these interpretations is much more likely than the other.

I don't doubt the existence of aliens. I just doubt that UFOs are aliens.

[emilecantin]

> hand wavy sci-fi speculation

"The Dark Forest" by Liu Cixin is sci-fi, but I don't think it's too hand-wavy. It presents a pretty logical answer to the Fermi Paradox, based on a couple obvious axioms.

Wikipedia article: https://en.wikipedia.org/wiki/Dark_forest_hypothesis

[raverbashing]

Not really

Dark forest is way down at the bottom of "plausible explanations"

It just sounds like it makes sense for 3 min then it really, really doesn't

Taking the (original) dark forest problem and applying it to civilizations in space sounds like a Strawman problem

[emilecantin]

Why doesn't it make sense?

[raverbashing]

- Attacking a planet that may or may not be a threat eventually is a much more expensive, noisy and slow endeavor than a shot in the dark in a forest.

(you can also think about all the technical hurdles such a thing would take, also remember that the fast something goes the harder it is to maneuver and to stop at the destination), don't underestimate all the kinds of noise that such thing will create and can be traced back to its origin.

- No species on Earth do that kind of unprovoked attack, unless it is very cheap and quick (and riskless)

So no, I think there are many better explanations than simply the dark forest one

[emilecantin]

I think that's where you're wrong. For a sufficiently advanced civilization, destroying another that's around our level would only entail destroying our planet. Hell, destroy the whole solar system to be sure. A "simple" way to do that would be to make the sun go supernova, or destroy it somehow.

How would you do that? There's a tremendous amount of energy already in it, it's releasing it gradually for now but what if there were ways to make it release all at once? One potential approach would be to throw something at it at relativistic speeds (you'd imagine accelerating things to near-lightspeed would be a pretty obvious milestone in the tech tree).

For an advanced civilization, this is pretty easy; they'd probably be able to do it routinely from a mobile spaceship so they don't have to give away their home star's position.

[mcpackieh]

It's a reasonably logical answer but it's not the simplest answer. The Dark Forest hypothesis assumes that life is so common in the universe that encountering and being existentially threatened by other life is a serious threat. But what reason is there to believe that life is that common? For Liu Cixin's books this assumption makes sense because it makes the story possible, but in real life there's simply no evidence to justify such an assumption.

[emilecantin]

Well we have no idea of the values for most variables in the Drake equation, so of course there will be some assumptions. Dark Forest is an answer to the Fermi Paradox in the case where intelligent life isn't rare.

If you read the books, you'll notice that they talk about "hiding gene" and "cleansing gene"; these are traits that civilizations acquire as they evolve.

I think that this has real-world implications in terms of how we conduct our SETI (search for extra-terrestrial intelligence); we should be careful of our radio emissions and things like sending a powerful signal / message to another star should probably be avoided.

[timschmidt]

> But what reason is there to believe that life is that common?

https://www.youtube.com/watch?v=JOiGEI9pQBs

[mcpackieh]

Shit entertainment channel masquerading as educational content. If you think you learned something from that video then why haven't you explained it yourself?

The simple fact of the matter is that there is no empirical evidence for life outside of Earth. My guess is that it exists out there somewhere, but there's no good basis for believing that life is as common as the Dark Forest hypothesis requires.

[timschmidt]

Two ad hominems in one comment. Way to go.

[woooooo]

Also, modern humanity's light cone is tiny. We've been listening for like 75 years?

[danbruc]

We still listened in on signals from the entire visible universe, but signals from further away are also from further back in time, so any aliens there would have had to develop earlier. But this also has an advantage, we could still hear from aliens that went extinct and only their signals are still propagating through the universe.

So the better way of thinking about this is a 75 year thick slice through spacetime containing the edge of the visible universe shortly after the big bang at one end and the solar system over the last 75 years at the other end. The volume between the past light cones of Earth now and 75 years ago.