0:02 are we the only living things in the
0:03 entire universe
0:06 the observable universe is about 90
0:08 billion light years in diameter there
0:11 are at least 100 billion galaxies each
0:15 with 100 to 1 000 billion stars recently
0:17 we've learned that planets are very
0:19 common too
0:21 and there are probably trillions and
0:23 trillions of habitable planets in the
0:25 universe which means there should be
0:27 lots of opportunity for life to develop
0:30 and exist right but where is it
0:32 shouldn't the universe be teeming with
0:35 spaceships let's take a step back [Music]
0:44 even if there are alien civilizations in
0:46 other galaxies there's no way we'll ever
0:48 know about them basically everything
0:50 outside of our direct galactic
0:52 neighborhood the so-called local group
0:55 is pretty much out of our reach forever
0:57 because of the expansion of the universe
1:00 even if we had really fast spaceships it
1:02 would literally take billions of years
1:04 to reach these places
1:06 traveling through the emptiest areas in
1:08 the universe
1:10 so let's focus on the milky way the
1:13 milky way is our home galaxy it consists
1:16 of up to 400 billion stars that's a lot
1:18 of stars counting one per second it
1:20 would take you a hundred lifetimes to
1:23 count them all there are about 20
1:25 billion sun-like stars in the milky way
1:27 and estimates suggest that a fifth of
1:29 them have an earth-sized planet in its
1:31 habitable zone the area with conditions
1:35 that enable life to exist if only 0.1 of
1:37 those planets harbored life there would
1:40 be one million planets with life in the
1:42 milky way but wait there's more the
1:46 milky way is about 13 billion years old
1:47 in the beginning it would not have been
1:49 a good place for life because things
1:51 exploded a lot but after one to two
1:53 billion years the first habitable
1:56 planets were born earth is only 4
1:58 billion years old so there have probably
2:00 been trillions of chances for life to
2:02 develop on other planets in the past if
2:04 only a single one of them had developed
2:05 into a space traveling super
2:07 civilization we would have noticed by now
2:08 now
2:11 what would such a civilization look like
2:13 there are three categories
2:16 a type 1 civilization would be able to
2:18 access the whole energy available on its
2:20 planet in case you're wondering we're
2:23 currently around 0.73 on the scale and
2:26 we should reach type 1 sometime in the
2:27 next couple of hundred years
2:30 type 2 would be a civilization capable
2:32 of harnessing all of the energy of its
2:34 home style this would require some
2:37 serious science fiction but it is doable
2:39 in principle concepts like the dyson
2:41 sphere a giant complex surrounding the
2:43 sun would be conceivable
2:46 type 3 is a civilization that basically
2:49 controls its whole galaxy and its energy
2:51 an alien race this advance would
2:53 probably be god-like to us
2:55 but why should we be able to see such an
2:58 alien civilization in the first place
2:59 if we were to build generation
3:01 spaceships that could sustain a
3:03 population for around 1 000 years we
3:06 could colonize the whole galaxy in 2
3:08 million years sounds like a long time
3:11 but remember the milky way is huge
3:13 so if it takes a couple of million years
3:15 to colonize the entire galaxy and there
3:18 are possibly millions if not billions of
3:20 planets that sustain life in the milky
3:23 way and these other life forms have had
3:25 considerably more time than we've had then
3:26 then
3:28 where are all the aliens
3:31 this is the fermi paradox and nobody has
3:32 an answer to it
3:35 but we do have some ideas let's talk
3:38 about filters a filter in this context
3:40 represents a barrier that is really hard
3:42 for life to overcome
3:45 they come in various degrees of scary
3:48 one there are great filters and we have
3:49 passed them
3:52 maybe it is way harder for complex life
3:54 to develop than we think the process
3:56 allowing life to begin hasn't yet been
3:58 completely figured out and the
4:00 conditions required may be really complicated
4:01 complicated
4:04 maybe in the past the universe was way
4:06 more hostile and only recently have
4:08 things cooled down to make complex life
4:10 possible this would also mean that we
4:12 may be unique or at least one of the
4:15 first if not the first civilization in
4:17 the entire universe
4:20 two there are great filters and they are
4:21 ahead of us
4:23 this one would be really really bad
4:25 maybe life on our level exists
4:27 everywhere in the universe but it gets
4:28 destroyed when it reaches a certain
4:32 point a point that lies ahead of us
4:34 for example awesome future technology
4:36 exists but when activated it destroys
4:39 the planet the last words of every
4:41 advanced civilization would be this new
4:43 device will solve all of our problems
4:45 once i push this button if this is true
4:48 then we are closer to the end than the
4:50 beginning of human existence or maybe
4:53 there is an ancient type 3 civilization
4:55 that monitors the universe and once a
4:58 civilization is advanced enough it gets
5:00 eliminated in an instant
5:02 maybe there is something out there that
5:05 it would be better not to discover
5:07 there is no way for us to know
5:10 one final thought maybe we're alone
5:12 right now we have no evidence that
5:14 there's any life besides us
5:17 nothing the universe appears to be empty
5:20 and dead no one's sending us messages no
5:22 one answering our calls we may be
5:25 completely alone trapped on a tiny moist
5:28 mud wall in an eternal universe does
5:30 that thought scare you if it does you're
5:32 having the correct emotional reaction
5:34 if we let life on this planet die
5:36 perhaps there will be no life left in
5:39 the universe life will be gone maybe
5:41 forever if this is the case we just have
5:43 to venture to the stars and become the
5:45 first type 3 civilization to keep the
5:47 delicate flame of life existing and to
5:49 spread it until the universe breathes
5:51 its final breath and vanishes into oblivion
5:52 oblivion
5:54 the universe is too beautiful not to be
5:56 experienced by someone [Music]
5:58 [Music]
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