[Electronic humming noise] how many of you have a sonic screwdriver
at home come on it's okay to admit that
you're a geek all you Doctor Who fans
there so if you've ever seen the sci-fi
television series Doctor Who you know
that he travels throughout time and
space in search of adventure and just
generally helping people so when we talk
about a journey through time and space
it sounds like time and space are
completely distinct from each other but
as Albert Einstein taught us in 1915 we
can't really think of time and space as
being completely separate entities time
and space are actually interwoven into a
four-dimensional fabric that we call
space-time so Doctor Who is actually
going on a voyage through space-time now
here in week 12 you're going to learn
about the deaths of star and the deaths
of stars can be very cataclysmic it can
actually blow up and form something
called a supernova it's not what our Sun
is going to do you have to have a high
mass to go out with a bang our Sun is
going to go out with a whimper it's
going to actually implode in something
that we call the white dwarf so here in
week 12 we're going to be talking about
different ways that stars can die
and what corpse is left over and mass is
going to play a critical role in
determining how a star is going to die
so low mass stars will die as a white
dwarf medium mass stars will die as
something called a neutron star a ball
neutrons and high mass stars will die as
a black hole and I'm sure you all have a
gazillion questions about black holes
but to understand black holes we have to
understand space-time so we're going to
spend some time this week getting you up
to snuff on Einstein's general theory of
relativity and then talk about black
holes and you might be saying to yourself
well the black hole is black how can we
see it
how can we know that they exist we know
that they exist because of their gravity
yes the big G word is back
gravity black holes has very intense
gravity
and their gravitational influence on
their neighborhood and really bad
neighbors by the way that influence on
their neighbors through their gravity is
going to allow us to determine that
they're there and how big they are and
how bad of a neighbor they are how much
they're eating so I think you'll enjoy
this week and again if you have any
questions let me know
