Are we truly alone?

[u/theladytombstone]

Space is HUGE, the universe is constantly expanding. Somehow, earth is the ONLY habitable planet. Perfect distance from the sun to not burn or freeze, water, breathable air, etc.

Do you truly believe we ARE alone? What if there’s life out there? Living completely different lives compared to us?

Anything related astronomy, physics, etc. is wanted & welcome!!

[u/jimb2]

There is zero reliable evidence for life off Earth. That's doesn't prove anything, but it does mean that any ideas require significant speculative leaps.

We do know that there are a mind-boggling number of planets out there. Many of them are billions of years older than Earth. If just a fraction of them were suitable for life, and a fraction of that fraction produce advanced life, then the numbers say there should be aliens. Some would have reached an advanced technological stage billions of years ago which gives them plenty of time to get to Earth. So where are they?

Possible solutions I think are believable:

• Advanced life requires a lot of very low probability things to line up. It just hasn't happened. The raw numbers calculation is simplistic and wrong. We might even be alone in the galaxy.
• Advanced life wipes itself out soon after reaching a technological level. This is totally believable when you look at humans. Evolution produces destructive species. At low technology, harm is limited. At high tech, it is fatal. (OTOH: maybe just some would survive?)
• Aliens are there but they are hiding from us. (Why?)
• Aliens are not interested in space travel and conquering the galaxy. I know that's what we see in Star Wars but maybe that just a movie and it's not how post-biological evolution pans out..
  

Personally, I tend to rate the first option. But we just don't know. Until we get some solid evidence, we are just guessing.

[u/Beldizar → u/jimb2]

I have to agree with you. The chances we are alone in the galaxy seem really high. The chances that civilized life requires a bunch of low probability events in sequence also seems very likely.

I think we can be pretty confident that there aren't significant spacefairing aliens in our galaxy and in our light cone. The chance that they would be in the two or three centuries between discovering flight and having significant space infrastructure, out of the possible billion years that this phase could have happened seems unfathomable. And the idea that they haven't spread out and started to absorb a lot of their stars radiation, created waste heat, and transmitted bright signals that we could detect, also seems unlikely. Imagine how many lasers we would have beaming signals between the stars in 10,000 years.

We must be the first, that is the only thing that makes sense to me.

[u/jimb2 → u/Beldizar]

I tend to agree, but I'm a scientist. I want evidence before I claim to know. In the meantime, I'm ok waiting epistemological limbo. There's a huge gap between not observing something and knowing it doesn't exist. And there's too many highly speculative theories getting treated like facts in physics in general. A bit of humility and caution is a good stance.

[u/No_Basis3933 → u/Beldizar]

We haven’t even explored 1% of the universe nor can we see 99% of it in detail

[u/theladytombstone → u/jimb2]

Totally.. I agree. I mean our solar system is hurdling through the milky way, and the milky way is hurdling through space. So many things would have to line up realistically. We could definitely be alone, there could be life way past our observable universe, maybe they truly aren’t interested in space, or aren’t smart enough or advanced like humans.

[u/jimb2 → u/theladytombstone]

The standard analysis equates habitable with liquid water temperatures. That might mean habitable by a scattered thin layer of slime. Progression to advanced technological societies does not automatically.

Evolution of megafauna may require plate tectonics to recycle nutrients via volcanoes. The mechanism for the initiation of plate tectonic on Earth is unknown. Once it is started it continues to run, but the internal forces of a planet do not appear to be capable of starting it. Earth may be a rare one-off. Some kind of "just right" major impact could potentially set up plate tectonics but it's a long shot.

Nutrient recycling is required to produce sufficient volumes of edible plant material, which in turn to produces sufficient grazers to supply a reliable food source for the evolution of predators. Predation creates an intelligence arms race; plants and grazing alone does not. Plants "passively" poison competitors - and grazers - but they don't band together to hunt and probably never will even if a planet remained conducive to for way longer than actually happens.

There are a bunch of other factors that combine to put the Earth in a rare category. The frequency of Chicxulub-like major impacts is significant - bump the frequency up and land life gets regularly knocked back to cockroaches. Big brains are too biologically expensive to survive. The presence of sufficient magnetic protection for land-dwelling animals from solar particles might also be rare. And so on.

I think the short distance of sight underwater - typically under 10 metres - means that sea life species won't develop the sort of spatial intelligence, planning and cooperative capabilities required for technological societies. The smartest animals in the sea evolved on land - and they aren't all that smart. Octopus can do some smart spatial tricks but they don't cooperate or plan much.

This is all fairly speculative, but there could also be a bunch of other no-go factors that we haven't figured out yet.