What do you think the Great Filter is?

Sadly it may be the speed of light.

All these intelligent species are simply trapped in their own solar systems for all eternity by an unbreakable natural law.

I think that the great filter/fermi paradox is a combination of two facts,

1. Our entire radio output (the only example we have to go by) is pitiful compared to the sun, like a candle in front of a flood light, you'll only be able to see it so far before it's completely drowned out. After a few dozen light years our radio output is less than the margin of error of a stars detectable radio output.
2. As a civilization advances it must reduce radio leakage. As data gets more important, it gets more important that you're not wasting energy moving it around. Narrow beamed radio transmission becomes the norm and even less radio signals escape the system than when radio was messy and overpowered.

They're not missing or gone, they've just moved beyond messy radio signals. Even we tightened up our radio emissions in a little over a century. Most of what we watch or listen to comes to us via fiber, cable, or short range transmissions like cell phone towers and Wi-Fi.

My favorite filter is the amount of phosphorous in the universe. Earth has an unusually high amount, and it's vital for life. I like this one, because as more stars die, the amount of phosphorous goes up, implying we won't be alone forever.

Anyway, look up "Issac Arthur" on YouTube for HOURS of content about the Fermi paradox and potential great filters.

An alternative is we are among the first. Third generation stars are the ones that have planets with enough heavy elements to allow for complex chemistry. Sol (our star) is thought to be among the first batch of third generation stars in our gallexy.

Light speed does seem to be the upper speed limit for the universe. Talking that into account we probably haven't had a chance to see other early life as it would likely be spread pretty thin right now.

Honesty, I don't think that there is a Great Filter. The Fermi Paradox strikes me as not very well-reasoned. A whole hell of a lot of things would have to go exactly right for civilizations to make contact, rather than it being the default assumption. There are lots of filters, not just one Great one.

But the closest to a Great Filter is that space is really, really. stupendously big. The chances of even detecting each other across such distances is vanishingly small, much less traversing them. Add in the difficulty of jumping the metabolic energy gap to become complex life, and that could reduce the density of civilizations down to a level that they're just not close enough to each other in spacetime to admit even the possibility of contact. And we're hanging our hat on some highly-speculative concepts like alien mega-structures harnessing whole solar systems to allow detection.

I think a lot of persnickety, smaller filters combine to make interstellar contact between civilizations against long odds. Perhaps the best we'll get is spectral signatures from distant planets that are almost-conclusive proof of some sort of life.

Probably too optimistic and unhinged, but maybe a species advanced enough for interstellar travel, building mega structures etc. are advanced enough to ascend to a higher plane of existence or alternate dimensions or whatever. Maybe there's some alternative to this reality that will be unlocked by advanced technology that made all advanced life prefer that, to here.

Everyone is talking about society or physiology stuff. That is just things that might get humans.

Stars going super-nova is the real great filter. Our sun is 4.6 billion years old. Life started 4 billion years ago. In 4 billion years, the sun goes supernova. We are halfway to the end of the earth.

Smaller stars last longer, but have smaller ranges that life can exist in - and planets tend to move in or out in their orbits. Bigger stars have giant habitable zones - but some large stars born when humans took their first steps are in their last decades of life. You couldn't get from the pyramids to NASA in that time, never mind the 4 billion years it took to get to humans.

I don't think there is a single filter. My personal gut feeling however is that the jump to "specialised generalists" would be a major hurdle.

Early human civilizations are very prone to collapsing. A few bad years of rain, or an unexpected change of temperature would effectively destroy them. Making the jump from nomadic tribal to a civilisation capable of supporting the specialists needed for technology is apparently extremely fragile.

Earth also has an interesting curiosity. Our moon is extremely large, compared to earth. It also acts as a gyroscopic stabiliser. This keeps the earth from wobbling on its axis. Such a wobble would be devastating for a civilisation making the jump to technological. Even on earth, we are in a period of abnormal stability.

I suspect a good number of civilizations bottleneck at this jump. They might be capable of making the shift, but get knocked back down each time it starts to happen.

We're currently in it. Failing to create a clean, renewable, and scalable energy source powerful enough to run a society that is ever increasing in both population and technology without destroying their only inhabited planet has got to be the most common great filter.

Asteroids strikes, super volcanoes, solar CMEs, and other planetary or cosmetic phenomena that exactly line up in both severity and timing are too rare IMO.

Every society that attempts to progress from Type 1 to Type 2 has to deal with energy production. Most will fail and they will either regress/stagnate or destroy themselves. Very few will successfully solve the energy problem before it is too late.

Howabout a reasonably advanced civilization destroying itself and its homeworld after exploiting and then running out of petroleum?

Boy, Lemmy sucks donkey dick. For every one legitimate answer there are two or three edgelord answers like "capitalism" and "the internet".

Here's an answer that hasn't come up yet: cooperation among mono cellular organisms. I don't mean the development of polyp analogues or colonies of single celled organisms; I mean getting down to mitochondria. Brace for wild oversimplification.

Before mitochondria, life had a hard time creating enough energy to do much more than barely stay alive. The current line of thinking is that one organism ate another and didn't digest it. The two organisms worked symbiotically, one handled energy production and the other handled getting food and staying alive.

Just about every living thing utilizes mitochondria and if the current idea that mitochondria were actually symbiotic organisms is true, that means that what was likely a chance "sparing" of prey is the underpinning of all complex life.

The odds of that happening are ridiculously low. There could be simple life in tons of places even within our own star system, but if the mitochondria-like symbiotic capture never happens for those extraterrestrial organisms, then complex life is probably unlikely to develop.

I like the “Dark Forest” theory I learned from the Three Body Problem books. Basically it’s dumb for civilizations to make a big footprint and reveal themselves because other civilizations won’t know how powerful and dangerous you might become, and so out of precaution they might just zap you. Ironic and over dramatic, but just because that’s a possibility it might be wise to keep a low profile and not invite trouble.

We have had Millions of years of (presumably) intelligent Dinosaurs on this planet, but only 200.000 years of mankind were enough to create Civilization IV, the best Strategy game and peak of life as we know it.

So clearly, Civilization™ is what sets us apart.

Jokes aside, the thing evolution on earth spend the most time on is getting from single celled life-forms to multicellular life (~2 billion years). If what earth life found difficult is difficult for all, multicellular collaboration is way harder than photosynthesis, which evolved roughly half a billion years after life formed.

I would say it's the size of the universe and the fact that it is still expanding at an accelerated rate.

If the speed of light is really the "top speed" of the universe, it is inadequate for interstellar travel. It is barely good enough for timely communication, and not really even that.

Life can be as likely as it wants to be, but it seems to me that we're all quite divided, to the point of not being able to communicate at all with other potential intelligent species.

Time.

For a technological civilization like ours, I think it’s just that Earth/humans are weird and we’re past the main ones (like going from single-cell to multi-cellular organisms).

Having to overcome the physical obstacles on other planets rules out the type of spacefaring technological civilizations like ours. No matter how intelligent a civilization on a water world is, it’s not starting fires, much less building rockets. Just getting out of the water would be their space program. Even a totally Earth-like planet that’s a bit bigger and has an intelligent species wouldn’t be able to get to space with chemical rockets.

And also, humans are weird. It could be as basic as “we have hands for building complex tools.” We have a seemingly insatiable need to compete and explore, even beyond all logic—maybe no other intelligent species wants to strap someone to a rocket and send them to space because it sucks up there. We’re violent: without WWII and the Cold War, do we even have a space program?

So many things had to come together to create an intelligent, tool-building species with hands that lives on a planet with the right balance of land and water. As far as we know, it never even happened on Earth before and even then, we had thousands of years of civilizations before anyone was dumb enough to strap themselves to a rocket just to see what would happen.

Honorable mention: we haven't detected alien probes, because intelligent alien societies haven't begun consuming the galaxy with exponential numbers of self-replicating robotic probes, because that's just a really bad idea:

Simple workarounds exist to avoid the over-replication scenario. Radio transmitters, or other means of wireless communication, could be used by probes programmed not to replicate beyond a certain density (such as five probes per cubic parsec) or arbitrary limit (such as ten million within one century), analogous to the Hayflick limit in cell reproduction. One problem with this defence against uncontrolled replication is that it would only require a single probe to malfunction and begin unrestricted reproduction for the entire approach to fail – essentially a technological cancer – unless each probe also has the ability to detect such malfunction in its neighbours and implements a seek and destroy protocol (which in turn could lead to probe-on-probe space wars if faulty probes first managed to multiply to high numbers before they were found by sound ones, which could then well have programming to replicate to matching numbers so as to manage the infestation).

My suspicion is that it's abiogenesis, but it's only a suspicion that I can't have any certainty of

The most boring one: most species off themselves before they fully get off their starting planet. We will go the same way. Take your pick from climate change, war, pandemic, ... or even a combination of several!

I read an article about Fermi paradox (I cannot find the link) that stated the humans are one of the first intelligent beings in the universe. That's why we haven't encountered any green men so far. We just might came too soon to the party.

I think it's incompetence.

Energy needed to leave your planetary system vs energy available on your planet of origin.

We have not yet overcome it and I am not sure that we will achieve it.

We're still new to the game, and we have no idea what we're looking for.

I don't think there is a great filter. I think there's an easy solution to the fermi paradox that doesn't require great filters, we're just the first intelligence in this galaxy.

Here's my reasoning: intelligent species that manage to develop space travel probably do tend to expand out into their galaxy. When they achieve this level of technology they can settle most of all of their galaxy in a matter of 10,000 years or so. That time period is very brief on an evolutionary scale. It's estimated that life began on earth 3.7 billion years ago. That means it took about 3.7 billion years for earth to produce intelligent life, and then from that point it would take a mere 10,000 years to reach modern day, and 10,000 more years to settle the whole galaxy. That expansion happens so quickly compared to how long it took the planet to develop intelligent life, that the chance of two civilizations rising at the same time becomes very small.

It all boils down to this: there are no intelligent aliens out there in our galaxy, because we are the first intelligent species in our galaxy. We know we're the first because if we were second, then aliens would already have settled this star system.

Probably there are lots of alien civilizations out there in the universe, but they're in different galaxies.

Space itself. I believe there are other intelligent life forms out there and some of those happen to be close enough to communicate to each other/discover each other. We just hit the unlucky(or lucky) spot that we are simply too far away.

evidence of human existence has only gotten what, 150 lightyears out into space?

I think we're the first. Or rather in the first wave of intelligent life. It could take a thousand years just for a message to reach us. On the theory that life has evolved to this point as fast as possible over the life of our Galaxy, there's no filter. There just hasn't been enough time for contact to occur.

For us it's conservatism and its synonyms.

I think there are many great filters, but I think one of those filters is fighting over limited resources and wars. Perhaps limited to humans/earth, but I doubt it. Nukes, dropping rocks from orbit, and theoretical (but possible) weapons like black hole bombs are all going to tempt irrational beings to take someone's stuff.

We have to be extremely careful that we don't accidentally trigger a weapon that is going to kill or dramatically cripple our civilization before we become a truly interstellar species. There is so much to learn out there, while so many people are currently focused on the wrong things such as minor conflicts or what children aren't allowed to learn.