are we the only living things in the entire universe the observable universe is about 90 billion light years in diameter there are at least 100 billion galaxies each with 100 to 1 000 billion stars recently we've learned that planets are very common too and there are probably trillions and trillions of habitable planets in the universe which means there should be lots of opportunity for life to develop and exist right but where is it shouldn't the universe be teeming with spaceships let's take a step back [Music] even if there are alien civilizations in other galaxies there's
no way we'll ever know about them basically everything outside of our direct galactic neighborhood the so-called local group is pretty much out of our reach forever because of the expansion of the universe even if we had really fast spaceships it would literally take billions of years to reach these places traveling through the emptiest areas in the universe so let's focus on the milky way the milky way is our home galaxy it consists of up to 400 billion stars that's a lot of stars counting one per second it would take you a hundred lifetimes to count
them all there are about 20 billion sun-like stars in the milky way and estimates suggest that a fifth of them have an earth-sized planet in its habitable zone the area with conditions that enable life to exist if only 0.1 of those planets harbored life there would be one million planets with life in the milky way but wait there's more the milky way is about 13 billion years old in the beginning it would not have been a good place for life because things exploded a lot but after one to two billion years the first habitable planets
were born earth is only 4 billion years old so there have probably been trillions of chances for life to develop on other planets in the past if only a single one of them had developed into a space traveling super civilization we would have noticed by now what would such a civilization look like there are three categories a type 1 civilization would be able to access the whole energy available on its planet in case you're wondering we're currently around 0.73 on the scale and we should reach type 1 sometime in the next couple of hundred years
type 2 would be a civilization capable of harnessing all of the energy of its home style this would require some serious science fiction but it is doable in principle concepts like the dyson sphere a giant complex surrounding the sun would be conceivable type 3 is a civilization that basically controls its whole galaxy and its energy an alien race this advance would probably be god-like to us but why should we be able to see such an alien civilization in the first place if we were to build generation spaceships that could sustain a population for around 1
000 years we could colonize the whole galaxy in 2 million years sounds like a long time but remember the milky way is huge so if it takes a couple of million years to colonize the entire galaxy and there are possibly millions if not billions of planets that sustain life in the milky way and these other life forms have had considerably more time than we've had then where are all the aliens this is the fermi paradox and nobody has an answer to it but we do have some ideas let's talk about filters a filter in this
context represents a barrier that is really hard for life to overcome they come in various degrees of scary one there are great filters and we have passed them maybe it is way harder for complex life to develop than we think the process allowing life to begin hasn't yet been completely figured out and the conditions required may be really complicated maybe in the past the universe was way more hostile and only recently have things cooled down to make complex life possible this would also mean that we may be unique or at least one of the first
if not the first civilization in the entire universe two there are great filters and they are ahead of us this one would be really really bad maybe life on our level exists everywhere in the universe but it gets destroyed when it reaches a certain point a point that lies ahead of us for example awesome future technology exists but when activated it destroys the planet the last words of every advanced civilization would be this new device will solve all of our problems once i push this button if this is true then we are closer to the
end than the beginning of human existence or maybe there is an ancient type 3 civilization that monitors the universe and once a civilization is advanced enough it gets eliminated in an instant maybe there is something out there that it would be better not to discover there is no way for us to know one final thought maybe we're alone right now we have no evidence that there's any life besides us nothing the universe appears to be empty and dead no one's sending us messages no one answering our calls we may be completely alone trapped on a
tiny moist mud wall in an eternal universe does that thought scare you if it does you're having the correct emotional reaction if we let life on this planet die perhaps there will be no life left in the universe life will be gone maybe forever if this is the case we just have to venture to the stars and become the first type 3 civilization to keep the delicate flame of life existing and to spread it until the universe breathes its final breath and vanishes into oblivion the universe is too beautiful not to be experienced by someone
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