Hey SciShow viewers it's John Green.

So, over on Crash Course we just launched a limited series   podcast called "The Universe", where the astrophysicist Dr. Katie Mack walks me through the   history of the entire universe including the parts  that haven't been written yet take a look. [John] It seems like a lot of this stuff was inevitable that each thing proceeded from the previous thing, right? [Dr.

Mack] Yeah I mean, you know, there was a sort of series of events where I mean it's all just kind   of following the same laws of physics once you set it going. [John] Yeah that's starting to make me feel   a little bit like once you set it going there was always going to be a galaxy called the Milky Way -    not called the Milky Way - but where the Milky Way  is the size and shape of the Milky Way, and it's   starting to make me think that there was always  going to be a sun and it's starting to make me   think there was always going to be an earth once  we set this stuff in motion, and just to be clear   we didn't set it in motion and that's starting to  make make me think and I'm really hoping you can   correct me on this one that um there was always going to be a me. [Dr. Mack] Um.. I mean the thing is right like when you're looking at it from the perspective of now all you can do is trace back all of the events along the timeline that we have followed, but there were a lot of different places in the past where things could have branched one way  or another. it's true that once you set down the primordial fluctuations in the plasma of the hot big bang those kind of have to grow into galaxies   and clusters of galaxies and and galaxies have to make stars and planets, but you know, whether or not   they had to make the Earth and us like there there are a lot of things that are just random chaos   that come into that I mean things like, you know, in the formation of planets you have collisions   between large rocky bodies and asteroids and things and stuff coalescing from the   protoplanetary disc and that could have gone lots of  different ways. [John] So, what you're saying is, and I guess what I'm asking is, is free will still in the equation? [Dr.

Mack] Um, (laughs) that I feel like that's above my pay grade somehow I feel like free fill is a is a very  human question, and in the work that I do humans   are so insignificant that.. [John] Yeah. No I'm getting that feeling that's a little bit of a stinger   for me I have to confess because yeah I know that we don't matter much but don't we matter a little   bit? Here's my argument for why we might matter a little bit.

We're the ones doing this observing,   and that's interesting. [Dr. Mack] You know that famous image of the earth as the pale blue dot? It was Voyager   One they took a picture of the Earth from billions of kilometers away and it just looks like a speck   of dust.

Carl Sagan gave this beautiful speech about  about how you know on that speck of dust you know   every every nation and every powerful ruler and  every you know king and and peasant and you know   we're all on that little speck of dust none of  us matter. You know, we're we're a tiny tiny   speck of dust in the universe. I think about that picture sometimes and then I think about   well in the bigger picture most of the matter  in the universe is dark matter that we we can't   interact with except through gravity like 85% or  something.

And, most of the rest of the universe if   just kind of add up the energy of the stuff in  the universe is dark energy, and so if you add   up the sort of contribution of both dark matter  and dark energy in the universe in terms of the   energy density of the stuff in the universe that  makes up something like 95% of the stuff in the   universe is either dark matter or dark energy. [John] Oh no. [Dr. Mack] And so the stuff that we're made of regular   matter what we call Barons in in astrophysics that regular matter and you know electrons and   protons and neutrons and and you know even even  radiation all of that together makes up about 5%   of what the universe is made of. You know even our kind of matter is kind of kind of an afterthought   in the universe in some ways.

And, so like the idea that we as humanity can be significant to   the universe when even the stuff we're made of  is kind of not very significant in the universe   it's very humbling it really is very humbling.  It's also sort of inspiring because because, as   you said, we we we can learn so much much, right?  And, we have this amazing power of of knowledge   of you know maybe we're just observers in this bigger cosmos and maybe we're just along for the   ride but we know so much about it. [John] I tend to think of myself as being an observer of the universe, but we're not actually observers of the universe because we're the universe. Like, we're made out of the universe so we're the universe observing itself. [Dr. Mack] Right yeah. [John] And, I I find that   kind of like lovely and encouraging too, that I'm not separate from this thing that I'm looking at   I'm part of it. [Dr.

Mack] So there's this this famous quote by Carl Sagan, right, "We are way a way   for the universe to know itself". [John] Mmm Mhm.... [John There's a lot more where that came from The Universe is available now both on the Crash Course YouTube  channel and wherever you get your podcasts.