what's going on smart people my name's dylan i'm a physicist and i've had a bunch of requests to
do a video where i explain the science behind interstellar now i was hesitant to do this at
first because there's it's been done to death and not to mention kip thorne himself a nobel
prize winning physicist and the guy who wrote the script has a bunch of lectures
online that explains exactly this so but you know if you guys want to hear my thoughts
let's dance let's do it so i'm basically just going to try and explain the end for
you so you can understand what was going on when he went into the black hole and how he
arrived where he did at the end i think the rest has kind of been done to death
explained very well in many many videos i've seen but this particular aspect
and the physics underlying it are a bit more complex and subtle and goes into theoretical
physics stuff so i thought we could just sort of focus on that and there's plenty to talk about so
if you'd like to learn more about all the other stuff like the time dilation
and all the other bits of the film i highly suggest going and watching
kip thorne's lectures on the film he explains it um and he's got a great sense of humor so go
check those out i'm just doing this spontaneously i've written down a couple key points but there's
no script so let's go first and foremost i'm a huge christopher nolan fan he's a great director
all of his films are really interesting have great stories um and he he does love exploring science
i remember seeing that he was making this film a couple years before it actually came out um
and i saw the title and he was directing so i was eagerly awaiting the release of this film
um and when i saw it i was blown away i absolutely loved it everything about it the story the music
um the all the 2001 references i remember seeing in in an interview that uh interstellar
is actually kind of like nolan's ode to that film which is super cool 2001 is hands down my favorite
film um and there are so many references to it like tarz his whole character essentially but
you know the shape of him being like a monolith from 2001 given the name so that was all fantastic
and there's so many other things but anyway let's get to the physics so if you clicked on this video
i'm sure you know that the film used some real mathematics so kip thorne who's an expert on black
holes and everything like that provided some real math behind black holes for the visual effects
department of behind interstellar and yeah they created this black hole that they were actually
able to publish some real science about kip thorne for this story has borrowed a lot of
stuff from theoretical physics and just sort of assumed that it's true to make the story work
um a lot of this stuff you know might not be true in reality whatsoever to give an example like
general relativity assuming that what it tells us is happening on the inside of a black hole
is true general relativity suggests that there are things inside black holes called singularities
which have infinite densities you can't avoid them the math of general relativity you get infinities
singularities being inside black holes is theoretical it's not proven whatsoever and
the infinities invoked by these singularities raise a lot of physicists eyebrows whenever
like i just said whenever infinities are invoked it's somewhat alarming
many physicists don't believe that infinities in nature are even even meaningful because in the
past whenever infinities pop up in our equations it suggests a limit of our understanding of
nature a limit of our description of nature a limit of our equations not a limit of nature
so i am not convinced that singularities are inside black holes it could be a whole lot more
boring than that unfortunately um it could just be little bits of really dense matter
like in say a neutron star maybe we should back up just for a minute and talk about general
relativity now i don't think general relativity is going to be fundamental i think space and time
space time will emerge from something more fundamental whether it is stream theory twister
theory or a whole bunch of others i'm not sure and no one is currently one of the reasons we know
that general relativity this must be the case for it is because it doesn't treat matter as quantum
mechanical which we know it is if you'd like to look more into this i highly suggest nima armani
ahmed's public lectures he's a professor um at the institute of advanced study which is where
einstein did some of his work and he's regarded as one of the most creative theoretical physicists
currently working so i highly suggest going and checking that out now i'm not saying general
relativity is wrong i'm saying that space time might be an emergent thing its equations still
provide perfectly adequate answers but as to what's really fundamental in the universe i
think is going to be a bit more strange and what gravity truly is rather than just the curvature
of space-time might turn out to be something even more incredible but anyway let's describe
the reality that uh general relativity presents so we can understand interstellar so in general
relativity there's three spatial dimensions that is you need three numbers to describe someone's
position in space but einstein showed there's actually another measurement you need to describe
someone's position in space and that's their position in time you need to know their position
in time as well as their three spatial dimensions if you want to be able to define where someone is
and that measurement of time is what we call we we define it as the fourth dimension so you see
that's the spatial and this uh temporal dimension is wrapped up in the kind of one thing which is
what we call space-time now before i continue we don't really understand what time is uh general
relativity and quantum mechanics which are the two greatest theories of physics present conflicting
ideas as to what it is that's a bit of a problem if you want to know more about that i suggest
going and watching my tenant video where i talk about this in a bit more depth i explain how time
is viewed in both of those theories how entropy is related to time and how it is often confused
with time so go and check out that video i'll put it in the description now interstellar actually
goes further than just these four dimensions it explores the fifth dimension which is completely
theoretical this is something only theoretical physicists think is a real thing there's zero
evidence for its existence thus far and in their lingo we call the three spatial dimensions and
the one time dimension as the brain now if you try and imagine these three spatial dimensions
in a two-dimensional space you can imagine it kind of like a flat sheet so you essentially have to
take away one of the spatial dimensions and you get this flat sheet which is the brain which is
short for membrane and this brain this flat sheet lives within a higher dimensional bulk which is
everything surrounding the brain so you can imagine the flat shape like our universe
and the fifth dimension is like the space around us which we have we don't have access to now let's
imagine putting a black hole in this flat sheet first you need to understand that when you put
mass or energy in this flat sheet it bends the flat sheet so mass and energy are the same thing
einstein showed us that and he what he also showed us with general relativity is that when you put
these things in this brain it will curve it why it curves it well no one knows the answer to
that question just yet but i can tell you that it does curve it and what this curvature is is what
we call gravity at least in general relativity's perspective so you can imagine that if you put
something with mass in this flash sheet it let's say bends down um it curves so what is it bending
into what is it curving into the bulk the fifth dimension so put something with mass inside this
flat sheet and it curves it and you have to give it some motion because everything in the universe
has motion so everything with motion in this flat sheet will follow a straight line
but there are no straight lines in space-time because of the curves everywhere so
but there's another trick so what we call a straight line in the closest we can get to
a straight line is what we call a geodesic which is a straight line in curved space
it's as straight as possible so this mass with uh its motion when you put it in the sheet
will follow the curvature of space-time because it's really just trying to follow a straight line
but a straight line in space-time is curved so say you put the sun in this flat sheet and you put the
earth in there too but because the earth has a lot a lot less mass than the sun it curves this flat
sheet a lot less so what ends up happening is the earth follows these geodesics the uh dented curved
space that the sun has enforced on this flat sheet so earth is just trying to follow a straight line
in curved space okay now you got that imagine putting a black hole in this flat sheet
what do you think's going to happen it's going to curve this flat sheet right but by how much
well according to general relativity an infinite amount it curves it all the way down to infinity
but like we've already mentioned inside black holes there might not be any infinities there
might not be singularities um they sure as hell do bend space an enormous amount uh when you look at
them from the outside like if you look at galaxies the centers of galaxies they all have these super
massive black holes and that's what's really keeping galaxies together but inside the black
hole general relativity suggests this singularity has infinite density and it's curving the space
time to infinity it's essentially tearing space-time it's just you know it doesn't make
a lot of sense does it so interstellar assumes that black holes do have singularities inside them
and that the singularities curve space-time to infinity curve it into the bulk an infinite amount
now if you could manipulate this curving into the bulk and make it so it curves into another
place on this flat sheet so let's just rehash you're putting something like a black hole
in this flat sheet it curves it infinite amount and you control that curvature and bring it back
on itself to another spot on this flat sheet well that's essentially what a wormhole is can
they exist in nature well no one knows there's no evidence for either way and we really can't
be sure of anything currently so don't listen to anyone that says things are impossible
who knows what's possible alright so that pretty much explains to you how the end of the film works
when matthew mcconaughey's character goes into the black hole how he gets over to i think he's near
saturn or is it jupiter anyway he's floating off in space and he has like minutes left
uh of oxygen um and it's a number of years into the future so when matthew mcconaughey's character
goes into the black hole that's what's happening there's a wormhole the curvature of the flat sheet
the brain is curving back on itself to another spot in the flat sheet which is where he ends up
floating out near saturn or jupiter i think it is with minutes left in his oxygen tank and you know
it's only so many years of into the future or back in that timeline on earth and another thing you
actually need to understand how he gets over there is that when he first goes into the black hole
he arrives in that weird place and that's what uh kip thorne is uh basically saying is a tesseract
which is like a four-dimensional analog to a cube so it's like a four-dimensional cube
right and that tesseract is you know floating in the bulk which is the fifth dimension um and who
created that well in the movie they suggest like i don't i can't remember what they call them but
i think he is basically suggesting it's future humans who have created this tesseract thing in
that can transport through the bulk so i guess this tesseract is the vehicle through the bulk
um basically allowing the wormhole to function i don't know now there's a lot of other really
cool physics in the movie that i'm not going to talk about i think that'll probably just about do
it all the stuff about time dilation um the going across the event horizon of the black hole there's
lots of other cool things that i could talk about but it's been done to death the time dilation you
might all know is a real thing that is also part of einstein's general relativity and kip thorn did
all the calculations himself so in that movie it's very accurate and in the movie the black hole um
is enormous and it's uh rotating at nearly the speed of light so it has this uh what they say
is what they call as a gentle singularity so you could actually cross the event horizon and not be
torn apart anyway i think that'll do it for this video so i'll see you next time
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