Kind: captions
Language: en
there was a time when the universe was
expanding so rapidly the parts of it
were moving apart from each other faster
than the speed of light that time is
right now a lot of people make a big
deal out of the fact that during
inflation right after our universe burst
into existence the whole universe was
expanding faster than light now while
that is true
it kind of implies that the universe
doesn't normally do that and it does I
mean if you pick two points far enough
apart in our universe you can always
find ones that are moving apart from
each other faster than light that is
simply due to all of the expanding space
in between so our universe is now and
has always been expanding faster than
the speed of light but doesn't this
violate Einstein's special theory of
relativity that says nothing should be
able to move faster than light
actually no relativity says nothing can
move through space faster than light but
that doesn't stop space itself from
expanding however it likes now it was
Hubble in the late 1920s who made the
observations of the night sky which led
us to see that our universe is expanding
the further out in space he looked the
faster the objects were moving away from
us so imagine a point so far out there
that the average recession velocity is
the speed of light I mean if you think
about it it's going to be the same
distance in every direction so that
would form a sphere which we call the
Hubble sphere everything beyond that
sphere is moving away from us faster
than the speed of light so common sense
would say we would never be able to see
the light from those objects because of
how fast they're moving away from us but
in fact this is not true we can see
those objects to understand how this
could work picture a galaxy beyond our
Hubble sphere it's receding faster than
light it's in a superluminal region of
space from our perspective so any light
that emits in
our direction will actually be moving
away from us as time goes on well that
doesn't sound very promising but due to
the accelerating expansion of space our
Hubble sphere is actually getting bigger
and if it gets bigger faster than that
light can get away then at some point
that light is going to travel from a
superluminal region of space into a sub
luminal region of space and so it can
start making progress towards us so we
can detect it so we can see that distant
galaxies which is of course now even
further beyond our Hubble sphere but we
can see its light we can detect that
it's there this is remarkable
in fact all of the photons we now
receive from the first 5 billion years
of the universe they were all emitted in
regions of space that were traveling at
the time faster than the speed of light
relative to us the objects that emitted
them were are and always have been
moving away from us faster than the
speed of light but their light has
entered our Hubble sphere and had enough
time to reach us and so we can see them
so the observable universe is larger
than our Hubble sphere it's actually
limited by what's called the particle
horizon that is based on the amount of
time light has had to travel towards us
since the beginning of time that is 13.8
billion years ago as far as we can tell
now because the universe has been
expanding and that expansion has been
accelerating things are much further out
than 13.8 billion light years away I
mean the observable universe has a
radius of over 46 billion light-years
the diameter is about 93 billion light
years that is a huge volume of things
that we can see and 13.8 billion years
ago everything in that volume and
everything beyond it that we can't see
would have been compressed into a tiny
infinitesimally small point that we call
the singularity
actually no I mean that would be true if
the universe is finite but if the
universe is infinite and it kind of
looks like it is then it was always
infinite so the Big Bang would have
happened literally everywhere but if the
universe has always been infinite then
what is it expanding into well it
doesn't have to expand into anything I
mean it can expand into itself that's
the thing about infinity you never run
out of it this episode of veritasium was
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titles in all areas of literature
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recommend the book Hitchhiker's Guide to
the galaxy it's one of my favorites and
it's a classic of the science genre you
know people often ask me why is the
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question of life the universe and
everything so if you haven't read this
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