The sound the universe makes Janna Levin
I want to ask you all to consider for a
second the very simple fact that by far
most of what we know about the universe
comes to us from light we can stand on
the earth and look up at the night sky
and see stars with our bare eyes the Sun
burns our peripheral vision we see light
reflected off the moon and in the time
since Galileo pointed that rudimentary
telescope at the celestial bodies the
known universe has come to us through
light across vast eras in cosmic history
and with all of our modern telescopes
we’ve been able to collect this stunning
silent movie of the universe these sort
of series of snapshots that go all the
way back to the Big Bang and yet the
universe is not a silent movie because
the universe isn’t silent
I’d like to convince you that the
universe has a soundtrack and that
soundtrack is played on space itself
because space can wobble like a drum it
can ring out a kind of recording
throughout the universe of some of the
most dramatic events as they unfold now
we’d like to be able to add to a kind of
glorious visual composition that we have
of the universe a sort of sonic
composition and while we’ve never heard
the sounds from space we really should
in the next few years start to turn up
the volume on what’s going on out there
and so in this ambition to capture songs
from the universe we turn our focus to
black holes and the promise they have
because black holes can bang on
space-time like mallets on a drum and
they have a very characteristic song
which I’d like to play for you some of
our predictions for what that song will
be like now black holes are dark against
a dark sky we can’t see them directly
they’re not brought to us with lights at
least not directly
we can see them indirectly because black
holes are weak havoc on their
environment they destroy stars around
them
they churn up debris in their
surroundings but they won’t come to us
directly through light we might one day
see a shadow a black hole can cast on a
very bright background but we haven’t
yet and yet black holes may be heard
even if they’re not seeing and that’s
because they bang on space-time like a
John now we owe the idea that space can
ring like a drum to Albert Einstein to
whom we owe so much iron Stein realized
that if space were empty if the universe
were empty it would be like this picture
except for maybe without the helpful
grid drawn on it but if we were freely
falling through the space even without
this helpful grid we might be able to
paint it ourselves because we would
notice that we traveled along straight
lines undeflected straight paths through
the universe Einstein also realized and
this is the real meat of the matter that
if you put energy or mass in the
universe it would curve space and a
freely falling object would pass by
let’s say the Sun and it would be
deflected along the natural curves in
that space it was Einstein’s great
general theory of relativity
now even light will be bent by those
paths and you can be bent so much that
you’re caught in orbit around the Sun as
the earth is or the moon around the
earth these are the natural curves in
space what Einstein did not realize was
that if you took our Sun and you crushed
it down to six kilometers so you took a
million times the mass of the earth and
you crushed it to six kilometers across
you would make a black hole an object so
dense that have light veered too close
it would never escape a dark shadow
against the universe it wasn’t Einstein
who realized this it was Karl
Schwarzschild who was a German Jew in
World War one joined the German army
already an accomplished scientist
working on the Russian front who I like
to imagine Schwartz shield in the war in
the trenches you know calculating
ballistic trajectories for cannon fire
and then in between calculating
Einstein’s equations you know as you do
in the
and he was reading Einsteins recently
published general theory of relativity
and he was thrilled by this theory and
he quickly surmised an exact
mathematical solution that describes
something very extraordinary curves so
strong that space would rain down into
them space itself would curve like a
waterfall flowing down the throat of a
hole and even the light could not escape
this current light would be dragged down
the hole as everything else would be in
all that would be left would be a shadow
now he wrote to Einstein and he said as
you will see the war has been kind to me
enough between despite the heavy gunfire
I’ve been able to get away from it all
and walk through the land of your ideas
and Einstein was very impressed with
this exact solution and I should hope
also the dedication of the scientist you
know this is the hard-working scientist
under harsh conditions and he took short
shields idea to the Prussian Academy of
Sciences the next week
but Einstein always thought black holes
were a mathematical oddity he did not
believe they existed in nature he
thought Nature would protect us from
their formation it was decades before
the term black hole was coined and
people realized that black holes are
real Astrophysical objects in fact
they’re the death state of very massive
stars that collapse catastrophic ly at
the end of their lifetime now our Sun
will not collapse to a black hole it’s
actually not massive enough but if we
did a little thought experiment as
Einstein was very fond of doing we could
imagine putting the Sun crushed down to
six kilometers and putting a tiny little
earth around it in orbit maybe 30
kilometers outside of the black hole Sun
and it would be self illuminated because
now the sun’s gone we have no other
source of light so let’s make our little
earth self illuminated and you would
realize you could put the earth in a
happy orbit even 30 kilometers outside
of this crushed black hole this crushed
black hole actually would fit inside
Manhattan more or less it would it might
spill off into the Hudson a little bit
before it destroyed the earth but you
know basically that’s what we’re talking
about talking about an object you could
crush down two
the square area of Manhattan so we move
this earth very close 30 kilometers
outside and we notice it’s perfectly
fine
orbiting around the black hole there’s a
sort of myth that black holes devour
everything in the universe but you
actually become very close to fall in
but what’s very impressive is that from
our vantage point we can always see the
earth it cannot hide behind the black
hole the light from the earth some of it
falls in but some of it gets lens de
round and brought back to us so you
can’t hide anything behind a black hole
if this were Battlestar Galactica and
you’re fighting the Cylons don’t hide
behind the black hole you know they can
see you okay now our Sun will not
collapse to a black hole it’s not
massive enough but there are tens of
thousands of black holes in our galaxy
and if one were to eclipse the Milky Way
this is what it would look like we would
see a shadow of that black hole against
the hundred billion stars in our Milky
Way galaxy and its luminous dust lanes
and if we were to fall towards this
black hole we would see all of that
light lens de round it and we could even
start to cross into that shadow and
really not notice that anything dramatic
had happened it would be bad if we tried
to fire our Rockets and get out of there
because we couldn’t any more than light
can escape but even though the black
hole is dark from the outside it’s not
dark on the inside because all of the
light from the galaxy can fall in behind
us and even though do a relativistic
effect known as time dilation our clocks
would seem to slow down relative to
galactic time it would look as though
the evolution of the galaxy had been
sped up and shot at us right before you
know we were crushed to death by the
black hole it would be like a near-death
experience where you see the light at
the end of the tunnel but it’s like a
total death experience
and there’s no way of telling anybody
about the light at the end of the tunnel
now we’ve never seen a shadow like this
of a black hole but black holes can be
heard even if they’re not seen imagine
now taking an Astra physically realistic
situation imagine two black holes that
have lived a long life together maybe
they started as stars and collapsed to
two black holes each one ten times the
mass of the Sun so now we’re going to
crush them down 260 kilometres across
they can be spinning hundreds of times a
second at the end of their lives they’re
going around each other very near the
speed of light so they’re crossing
thousands of kilometres in a fraction of
a second and as they do so they not only
curve space but they leave behind in
their wake a ringing of space an actual
wave on space time-space squeezes and
stretches as it emanates out from these
black holes banging on the universe and
they travel out into the world into the
cosmos at the speed of light this
computer simulation is due to a
relativity group at NASA Goddard it took
almost 30 years for anyone in the world
to crack this problem this was one of
the groups it shows two black holes in
orbit around each other again with these
helpfully painted curves and if you can
see it’s kind of faint but if you can
see the red waves emanating out those
are the gravitational waves they’re
literally the sounds of space ringing
and they will travel out from these
black holes at the speed of light as
they ring down and coalesce to one
spinning quiet black hole at the end of
the day if you were standing near enough
your ear would resonate with the
squeezing and stretching of space you
would literally hear the sound now of
course your head would be squeezed and
stretched unhelpfully so you might have
trouble understanding what’s going on
but I’d like to play for you the sound
that we predict this is from my group a
slightly less glamorous computer
modelling but imagine a lighter black
hole falling into a very heavy black
hole the sounds you’re hearing is a
light black hole banging on space each
time it gets close if it gets far away
it’s a little too quiet
but it comes in like a mallet and it
literally cracks space wobbling it like
a drum and we can predict what the sound
will be we know that as it falls in it
gets faster and it gets louder and
eventually we’re going to hear the
little guy just fall into the bigger guy
and it’s gone now I’ve never heard it
that loud it’s actually more dramatic at
home it sounds kind of anticlimactic
it’s like ding-ding thing this is
another sound from my group now I’m not
showing you any images because black
holes don’t leave behind helpful trails
of ink and space is not painted showing
you the curves but if you’re ready float
by in space on a space holiday and you
heard this you want to get moving
want to get away from the sound both
black holes are moving both black holes
are getting closer together in this case
they’re both wobbling quite a lot and
then they’re going to merge
yeah that’s gone now that chirp is very
characteristic of black holes merging
that it chirps up at the end now
that’s our prediction for what we’ll see
luckily we’re at the safe distance in
Long Beach California and surely
somewhere in the universe two black
holes have merged and surely the space
around us is ringing after maybe
traveling a million light-years or a
million years at the speed of light to
get to us but the sound is too quiet for
any of us to ever hear there are very
industrious experiments being built on
earth one called LIGO which will detect
deviations in the squeezing and
stretching of space at less than the
fraction of a nucleus of an atom over
four kilometers it’s a remarkably
ambitious experiment and it’s going to
be an advanced sensitivity within the
next few years to pick this up there’s
also a mission proposed for space which
hopefully will launch in the next ten
years called Lisa and Lisa will be able
to see supermassive black holes black
holes millions or billions of times the
mass of the Sun in this Hubble image we
see two galaxies they look like they’re
frozen and some embrace and each one
probably harbors a supermassive black
hole at its core but they’re not frozen
they’re actually merging these two black
holes are colliding and they will merge
over a billion year timescale it’s
beyond our human perception to pick up a
song of that duration but Lisa could see
the final stages of two supermassive
black holes earlier in the universe’s
history the last 15 minutes before they
fall together and it’s not just black
holes but it’s also any big disturbance
in the universe and the biggest of them
all is the Big Bang you know when that
expression was coined it was derisive
like oh who would believe in a Big Bang
you know but now it actually might be
more technically accurate because it
might bang it might make a sound
this animation for my friends at proton
studio shows looking at the Big Bang
from the outside we don’t ever want to
do that actually we want to be inside
the universe because there’s no such
thing as standing outside the universal
you’re inside the BIGBANG it’s
everywhere it’s all around you in the
spaces wobbling chaotically 14 billion
years past and this song is still
ringing all around us galaxies form and
generations of stars form in those
galaxies and around one star at least
one star is a habitable planet and here
we are frantically building these
experiments doing these calculations
writing these computer codes imagine a
billion years ago two black holes
collided that song has been ringing
through space for all that time we
weren’t even here you know it gets
closer and closer 40,000 years ago we’re
still doing cave paintings
it’s like hurry build your instruments
getting closer and closer and in 20
whatever year it will be when our
detectors are finally at an advanced
sensitivity we’ll build them we’ll turn
the machines and bang we’ll catch it the
first song from space if it was the Big
Bang that we were going to pick up it
would sound like this it’s a terrible
sound it’s literally the definition of
noise it’s white noise it’s such a
chaotic ringing but it’s around us
everywhere presumably if it hasn’t been
wiped out by some other process in the
universe and if we pick it up it will be
music to our ears because it will be the
quiet echo of that moment of our
creation of our observable universe so
within the next few years we’ll be able
to turn up the sound track a little bit
render the universe in audio but if we
detect those earliest moments it’ll
bring us that much closer to an
understanding of the Big Bang which
brings us that much closer to asking
some of the hardest most elusive
questions if we run the movie of our
universe backwards we know that there
was a big bang in our past and we might
even hear the cacophonous sound of it
but was our Big Bang the only Big Bang I
mean we have to ask has it happened
before will it happen again I mean in
the spirit of rising to Ted’s challenge
to reignite wonder we can ask questions
at least for this last minute that
honestly might evade us forever but we
have to
is it possible that our universe is just
a plume off of some greater history or
is it possible that we’re just a branch
off of a multiverse each branch with its
own Big Bang in its past maybe some of
them with black holes playing drums
maybe some without you know maybe some
with sentient life and maybe some
without not in our past not in our
future but somehow fundamentally
connected to us so we have to wonder if
there is a multiverse in some other
patch of that multiverse are there
creatures here’s my multiverse creatures
are there other creatures in the
multiverse wondering about us and
wondering about their own origins and if
they are I can imagine them as we are
calculating writing computer code
building instruments trying to detect
that faintest sound of their origins and
wondering who else is out there thank
you