The universe is too young for that to be likely.

Evolutionary biologist here. I think it’s highly unlikely.

It has taken about 4 billion years for intelligent life to have appeared on our planet (if you include the earth forming part), or 3.5 billion years (if you include when life first formed) to get our first “intelligent life.” By intelligent life here, I’m talking about technology in tool using and civilization building, to be clear. It’s a label I’d apply to our many of our ancestral and most closely related species. I believe much of life on earth is intelligent to the point of having things like theory of mind (the knowledge that one is a thinking individual interacting with other thinking individuals), including some birds and octopuses. The birds and octopuses part is important because it means that ToM evolved multiple times independently. That means that a) it’s a “good idea” (it has potentially significant adaptive value) and b) it’s possible to discover it along multiple pathways. Take eyes for example. Last time I looked, we believe eyes have evolved independently at least 24 times. They also exist at every stage of complexity and in a very wide variety of forms, and even something as as simple as being able to tell light from darkness has value.

However, in that 3.5 billion year history, intelligent life evolved exactly once, from a single line of descent. Intelligence such as ours is obviously a good idea. We went from being relatively unremarkable hominids to being the dominant life form on the planet, for better and for worse. Evolution is not moving all species to intelligence. Humans aren’t the point of evolution, any more than sharks or jellyfish are the point of evolution.

When such a manifestly good idea only evolves once, from a single line, the conclusion is that it’s pretty difficult to evolve. It might require a chain of preliminary mutations, or a particular environment. Being hominids, for example, we can make tools and carry fire, which dolphins and octopuses cannot. Of course, there are other hominids out there who do not do those things, and they’ve been around for millions of years. Depending on where you want to start the clock, they’ve been around for about ten times longer than modern humans - about 400k years, give or take. And the technology and civilization part has only been around for the last tenth of that, and has to evolve along its own, non-biological selection - and even those things differ wildly between different places and cultures. And even will all that, it’s become increasingly obvious that this might be a terminal mutation as the very drivers of our short term success may lead to our extinction.

I believe that extra-solar life probably exists. Whether it exists as bacterial mats or multicellular life, whether it’s discovered its own form of photosynthesis or has some other way of gathering life from its environment, whether it draws a distinction between its informational (eg, dna) and physical components - I have ideas but obviously no data.

In any case, that’s why I don’t believe that anyone has ever seen an extraterrestrial-origin ufo. I don’t believe the universe ever was nor will ever be teeming with civilizations.

All of that said, though, we’re dealing with an n of 1. We can make the best inferences possible based on what we can observe, but I would be delighted to be proven wrong tomorrow. I’m a sci fi nerd - I want there to be aliens. Even the discovery of a bacterial mat would revolutionize biology.

Maybe. There are so many possible explanations for the Fermi Paradox.

• Radio signals may just become too incoherent at great distances that we cannot recognise meaning from noise. The evidence is too hard to detect.
• Alien civilizations that are more advanced than us, could be using energy and communication methods we haven't even thought to try to detect yet. We're looking for the wrong evidence.
• advanced technology for communication, travel and energy could also be much more efficient - maybe there is nothing to detect. There is no evidence to find sitting on earth.
• in theory a civilization travelling at sub light speed could cplonize the galaxy with self replicating machines in 0.5 million years. Where are they? Well what if we ourselves are the product? Life on earth seeded from elsewhere? We are the evidence?
• maybe they're around us in space but not interested in us - we're ants to them.
• maybe they're around us in space but don't want to contaminate us, letting us reach them when we're ready.they are hiding form us.
• maybe space is vastly more dangerous than we can comprehend and civilizations keep quiet to avoid predator species - the dark forest theory
• maybe life is extremely rare and spread out, and we are an aborrhation- the great filter

The Fermi Paradox is an interesting question, but it is not an answer in itself.

A simple counter idea to this can be summarised in one question; Why have we not made an effort to introduce ourselves to ants?

I'd think of it like this...

• The universe is ~13 billion years old. However for the first few billion years, the universe was a wildly dangerous place to live. A sea of Hydrogen generating Supermassive stars, exploding within just 100,000s/millions of years, and generating many of the heavy elements that exist today. Even if a planet could form in these conditions, chances are it would've been annihilated before life could develop.

• I don't know exactly when the universe started to "stabilise", but let's say there is ~10 billion years of time that a planet like Earth could've formed.

• The Earth is ~4.5 billion years old.

• Single-celled life arose ~3-4 billion years ago.

• Complex multi-cellular life arose only ~500 million years ago during the Cambrian Explosion - so much needs to happen for complex life to arise that it could take a long time even in the best case scenario.

• Humans arose only ~100,000 years ago... albeit had the dinosaurs not been around for so long, we could have come about maybe 10s of millions of years earlier.

• From there basically everything comes down to how long it takes for a race to figure out farming, adopt a sedentary lifestyle that allows development of non-survival related disciplines, and to industrialise.
  In the case of humans, the oldest cultures are around 10,000 years old, and we industrialised only a couple hundred years ago.

If we make the assumption that we're not exceptional amongst any intelligent lifeforms, then it would make sense to assume that it takes roughly 3-5 billion years for a race to reach where we are now.

That means we could be late to the party, and everyone else has already wiped themselves out, but it's just as likely we're right in the thick of it but just too far away from anyone else in our cohort to see anything, and vice versa.

It's basically just the Fermi Paradox - and the only way we get an answer is when the void answers back.

If we know one thing about civilizations, it's that they leave shit around everywhere. If there once were a lot of folk about, there would still be shit for us to see today. We've looked, it seems pretty empty so far.

It would also be unlikely all of them would be dead, most sure, but not all. As far as we can see there is nothing.

We think there is almost certainly forms of life out there, stuff like single cell life. There's probably some of that in our solar system outside of Earth. More complex life would be way more rare, even multicellular would be rare. For a long time Earth was covered in sponges and it might have stopped there. And even if intelligence arises, they might not be tool users. Dolphins are pretty smart, they can't use fire or tools and won't be launching rockets any time soon. But let's say within the span of 100 million years about 10 human level civilizations would arise in our galaxy (which is probably a lot more than reality). What are the chances they get into space in a big way? Most of them would probably live in a gravity well deeper than us. That would make getting into space a lot harder. They might not have the energy budget, will or need to go into space. Their biology might be unsuited for it. But even if they do, getting to low orbit is one thing, getting beyond that is something we haven't even really done in a big way. Getting to other stars seems completely impossible with our current knowledge and no indication we are on a path to ever be able to do that. So say in the span of 100 million years there are two civilizations that live for 1 million years (we've only been around for a fraction of that). They would still most likely not only be thousands of light years apart, they would also be seperated by millions of years. And that's with some super optimistic assumptions.

So no, there is nobody out there.

Not likely. Based on the amount of known matter, ratios of detected elements in various locations, and life cycles of stars, we're most likely pretty early on the scene. As just one example out of many, phosphorus (which is needed for life as we know it) is kinda rare in the universe and our little piece of the galaxy is unusually abundant in it, especially Earth.

Haven't had that thought, but the total opposite. What if it's hella early, and we're still the most advanced lifeform in the universe? We're over here writing stories and making movies and games about aliens more powerful and technologically advanced coming here and fucking us up, when in reality we are the advanced aliens and everyone else in the universe is either barely sentient or still cavemen in terms of evolution and technological awareness.

Yeah, it's called... umm... I forget

This is one of the speculations among many in the great filter hypothesis.

I think it's more likely that we are early, possibly the first. If we survive, we will have millions of years head start to other species. Imagine how huge of an advantage that will be.

There are 200 billion to 2 trillion galaxies, and in the Milky Way alone we have located at least 10 planets in the Goldilocks zone. That could mean at least 2 to 20 trillion Goldilocks planets, and this is an under-estimate because the scale of our search has been comparatively small. So it is likely that there actively exists plenty of tool-using, scientific, space-faring life forms out there as you read this.

As for time scales, the heat death of the universe is estimated to occur in 1.7x10^106 (or, written out, 17000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000) years. Many, many planets will move into or out of Goldilocks zones in that time. And, depending on the source and the age of the information, we estimate the age of the universe to be 13 or 26 billion (or, 26,000,000,000) years. I added zeros so the two numbers could be visually compared, and you can see we are a very young universe.

Combine these two points and you have ample time and opportunity for many, many civilizations to rise and fall. Where ten planets’ stars may be exploding, ten more may be just entering the prime conditions for life. So take comfort in the thought that we are, statistically speaking, not alone out here.