[Music]
at first scientists thought it was a
comet but it had no tail and so it
couldn’t be a comment and people
concluded it must be an asteroid now I’m
known as moooo moooo mwah
it had hurled down from above the solar
system narrowly missing the Sun coming
within the orbit of mercury and that was
whizzing past the earth just 30 million
kilometres away
astronomers believe it is made of rock
but might it be made instead of dark
matter when we look out at galaxies much
like our own Milky Way they looks many
of them looks something like this spiral
galaxy m81 if you went to an amusement
park and we’re about to get on one of
those fun rides where we’re a swing goes
goes goes whizzing around a central
pillar and you’re held on by nice strong
chains if you got up to the ride and
notice that instead of chains it was
held together by dental floss you
probably wouldn’t want to get on that
ride you’d be too worried that those
that dental floss would break allowing
you to go hurtling out into space and
crash to the ground and yet when we look
at spiral galaxies like this one we see
that they are spinning far too fast to
be held together by the gravity of the
stars and gas and dust that must be
providing gravity well there’s two
possibilities one is that we don’t
understand the laws of gravity properly
that we need to change general activity
Einstein’s theory of how gravity works
his improvement on Newton’s were that in
fact the laws of gravity on these very
large scales aren’t quite the same as
they are within the solar system or on
earth but subtly different that’s
possible but we have so far failed to
change those laws of gravity in a way
that hangs together and so the other
possibility is that there’s a lot of
missing matter inside this galaxy and
inside of every galaxy we see we call
that missing matter dark matter because
we can’t see it now for a long time we
thought that that missing matter must be
particles too many particles
that are whizzing through space that are
filling this room and the only reason we
don’t feel them is that they are so
weakly interacting that they manage to
pass through the earth
we have particles like that that we know
about called neutrinos they come from
the center of the Sun go unimpeded
through the Sun most of them go unheeded
through the earth and they can travel
through light-years of ordinary material
and it’s only by many many of them to
pass through the detectors we build that
we’ve never been able to see them so
we’ve thought for a long time that dark
matter must be like that and so we built
detectors like the one on the left and
we put them deep underground in old
mines or underneath dams where cosmic
rays can’t get to them and we’ve waited
for for dark matter particles to hit the
nuclei or the electrons of these dark
matter detectors and heat them up just a
tiny little bit because they’re an
incredibly sensitive thermometers or
make a very tiny sound because they’re
incredibly sensitive microphones and so
far after 40 years we failed to register
anything in these dark matter detectors
we’ve also built enormous machines
called in this particular one called the
Large Hadron Collider at the CERN in
Geneva hoping to make particles of dark
matter well we’ve made lots of things at
the Large Hadron Collider and
particularly we’ve discovered the Higgs
boson the last unknown particle
undiscovered particle of the standard
model but so far we haven’t made any
Dark Matter what could it be that our
idea of what dark matter is is just
wrong that it’s not little particles
whizzing through space but large chunks
of matter like this one this is an
artist’s conception of a neutron star
now it’s not a very good picture because
I’m not much of an artist I’m a
physicist but what is it what is it
about a neutron star that makes a good
dark matter or what is it about pieces
of pieces of neutron star smaller
neutron stars chunks of nuclear matter
much like the nuclei at the centre of
atoms but bigger that would make them
good dark matter after all didn’t I tell
you that dark matter had to be dark that
you couldn’t see it and we can see
neutron stars we can
see nuclei but actually neutron stars
and things like it chunks the nuclear
matter make wonderful dark matter
because although you can see the nuclei
the matter at the surface you don’t get
to see the inside
so in fact most of them most of the
matter is invisible the other thing is
unlike particles which are very have
very little mass and so there have to be
lots and lots of lots of them a neutron
star is really big if the neutron star
was a dark matter we would only need one
of them in every thousand cubic
light-years and so there’s not much
chance of it hitting our detector or
even passing through the solar system
very often now if they were smaller
chunks of nuclear matter its chunks of
neutron star they would pass through
more often and we might have a hope of
seeing them we would want really big
detectors things that are so large that
it was pretty much inevitable that dark
matter would hit one of them well here
are two really good big detectors the
first one is the planet we live on the
planet Earth
and the other is the moon and they’re
nice and close to us and so we can
imagine putting putting instruments on
them to use them as dark matter
detectors well what would it look like
if dark matter hit the earth it depends
where it hits and so we can use the
different places that it could hit as
different ways of looking for dark
matter
for example dark matter streaking
through the atmosphere would heat up and
it would heat the atmosphere around it
and it might glow just like a meteor now
you might say well are the meteors we’re
seeing dark matter
the thing is meteors from the solar
system move relatively slowly only 20
kilometers a second or 30 kilometers a
second
whereas dark matter would might be
moving 300 or 400 kilometers a second so
we can tell whether a meteor was made of
dark matter but probably if if we were
having enough of these to detect they
would be much smaller chunks and they
wouldn’t glow as brightly as a meteor so
we would have to use very large
detectors that look for things like
meteors they’re called cosmic ray
detectors ultra high cosmic ray
detectors them we built
huge ones we have one down in southern
Argentina that’s tens of thousands of
square kilometers staring out into space
looking for ultra high-energy cosmic
rays that can also look for these chunks
of matter as dark matter we’re planning
to build one that looks down from space
at a huge fraction of the Earth’s
surface of the atmosphere and we can
watch for those cosmic rays or for these
chunks of dark matter running through
the atmosphere incredibly quickly much
faster than any and than any meteor but
much slower than any typical cosmic ray
and we can look for the glow of dark
matter passing through the atmosphere we
also see craters for example on the moon
the moon is a wonderful detector of
things that hit it because they leave
behind craters now the different thing
about dark matter is if a chunk of dark
matter hit the moon it would be moving
it would be so dense and moving so fast
that not only would go into the moon it
would come out the other side not too
many things do that imagine having a
piece of jell-o and sending a really
really fast tiny little VB through the
jello what would happen if you went in
you’d make a little tiny hole but as you
went out you’d make a big splat we can
imagine looking on the moon and on
Mercury and on other bodies for to see
are there any splats like that are there
any distinctive craters that look like
they came from the inside rather than
the outside now there are other more
mundane you know everyday ways that we
can look for dark matter for example you
might want to go home and look at your
windows because as a little chunk of
dark matter passed through your window
it would comment a very very tiny
cylinder through your winter a little
tiny track and so if we got all of you
to go home and look at the windows in
your homes and in your offices and in
your friends offices in their homes we
might be able to by looking at these
vast expanses of windows that fill our
cities be able to tell whether particles
of dark matter had come hurtling through
them leaving behind these little tracks
what about muah-muah
well it may or may not be a chunk of
dark matter it’s going to be very hard
for us to tell unless we take a trip
there
and people are planning to send a
mission if they can to a mu a mu and try
to catch it but whether or not o Momoa
is a chunk of dark matter there’s a very
good chance that our galaxy is being
held together by stuff that we simply
cannot see so far and that is out there
for us to discover and we hope to do
that soon thank you
at first scientists thought it was a
comet but it had no tail and so it
couldn’t be a comment and people
concluded it must be an asteroid now I’m
known as moooo moooo mwah
it had hurled down from above the solar
system narrowly missing the Sun coming
within the orbit of mercury and that was
whizzing past the earth just 30 million
kilometres away
astronomers believe it is made of rock
but might it be made instead of dark
matter when we look out at galaxies much
like our own Milky Way they looks many
of them looks something like this spiral
galaxy m81 if you went to an amusement
park and we’re about to get on one of
those fun rides where we’re a swing goes
goes goes whizzing around a central
pillar and you’re held on by nice strong
chains if you got up to the ride and
notice that instead of chains it was
held together by dental floss you
probably wouldn’t want to get on that
ride you’d be too worried that those
that dental floss would break allowing
you to go hurtling out into space and
crash to the ground and yet when we look
at spiral galaxies like this one we see
that they are spinning far too fast to
be held together by the gravity of the
stars and gas and dust that must be
providing gravity well there’s two
possibilities one is that we don’t
understand the laws of gravity properly
that we need to change general activity
Einstein’s theory of how gravity works
his improvement on Newton’s were that in
fact the laws of gravity on these very
large scales aren’t quite the same as
they are within the solar system or on
earth but subtly different that’s
possible but we have so far failed to
change those laws of gravity in a way
that hangs together and so the other
possibility is that there’s a lot of
missing matter inside this galaxy and
inside of every galaxy we see we call
that missing matter dark matter because
we can’t see it now for a long time we
thought that that missing matter must be
particles too many particles
that are whizzing through space that are
filling this room and the only reason we
don’t feel them is that they are so
weakly interacting that they manage to
pass through the earth
we have particles like that that we know
about called neutrinos they come from
the center of the Sun go unimpeded
through the Sun most of them go unheeded
through the earth and they can travel
through light-years of ordinary material
and it’s only by many many of them to
pass through the detectors we build that
we’ve never been able to see them so
we’ve thought for a long time that dark
matter must be like that and so we built
detectors like the one on the left and
we put them deep underground in old
mines or underneath dams where cosmic
rays can’t get to them and we’ve waited
for for dark matter particles to hit the
nuclei or the electrons of these dark
matter detectors and heat them up just a
tiny little bit because they’re an
incredibly sensitive thermometers or
make a very tiny sound because they’re
incredibly sensitive microphones and so
far after 40 years we failed to register
anything in these dark matter detectors
we’ve also built enormous machines
called in this particular one called the
Large Hadron Collider at the CERN in
Geneva hoping to make particles of dark
matter well we’ve made lots of things at
the Large Hadron Collider and
particularly we’ve discovered the Higgs
boson the last unknown particle
undiscovered particle of the standard
model but so far we haven’t made any
Dark Matter what could it be that our
idea of what dark matter is is just
wrong that it’s not little particles
whizzing through space but large chunks
of matter like this one this is an
artist’s conception of a neutron star
now it’s not a very good picture because
I’m not much of an artist I’m a
physicist but what is it what is it
about a neutron star that makes a good
dark matter or what is it about pieces
of pieces of neutron star smaller
neutron stars chunks of nuclear matter
much like the nuclei at the centre of
atoms but bigger that would make them
good dark matter after all didn’t I tell
you that dark matter had to be dark that
you couldn’t see it and we can see
neutron stars we can
see nuclei but actually neutron stars
and things like it chunks the nuclear
matter make wonderful dark matter
because although you can see the nuclei
the matter at the surface you don’t get
to see the inside
so in fact most of them most of the
matter is invisible the other thing is
unlike particles which are very have
very little mass and so there have to be
lots and lots of lots of them a neutron
star is really big if the neutron star
was a dark matter we would only need one
of them in every thousand cubic
light-years and so there’s not much
chance of it hitting our detector or
even passing through the solar system
very often now if they were smaller
chunks of nuclear matter its chunks of
neutron star they would pass through
more often and we might have a hope of
seeing them we would want really big
detectors things that are so large that
it was pretty much inevitable that dark
matter would hit one of them well here
are two really good big detectors the
first one is the planet we live on the
planet Earth
and the other is the moon and they’re
nice and close to us and so we can
imagine putting putting instruments on
them to use them as dark matter
detectors well what would it look like
if dark matter hit the earth it depends
where it hits and so we can use the
different places that it could hit as
different ways of looking for dark
matter
for example dark matter streaking
through the atmosphere would heat up and
it would heat the atmosphere around it
and it might glow just like a meteor now
you might say well are the meteors we’re
seeing dark matter
the thing is meteors from the solar
system move relatively slowly only 20
kilometers a second or 30 kilometers a
second
whereas dark matter would might be
moving 300 or 400 kilometers a second so
we can tell whether a meteor was made of
dark matter but probably if if we were
having enough of these to detect they
would be much smaller chunks and they
wouldn’t glow as brightly as a meteor so
we would have to use very large
detectors that look for things like
meteors they’re called cosmic ray
detectors ultra high cosmic ray
detectors them we built
huge ones we have one down in southern
Argentina that’s tens of thousands of
square kilometers staring out into space
looking for ultra high-energy cosmic
rays that can also look for these chunks
of matter as dark matter we’re planning
to build one that looks down from space
at a huge fraction of the Earth’s
surface of the atmosphere and we can
watch for those cosmic rays or for these
chunks of dark matter running through
the atmosphere incredibly quickly much
faster than any and than any meteor but
much slower than any typical cosmic ray
and we can look for the glow of dark
matter passing through the atmosphere we
also see craters for example on the moon
the moon is a wonderful detector of
things that hit it because they leave
behind craters now the different thing
about dark matter is if a chunk of dark
matter hit the moon it would be moving
it would be so dense and moving so fast
that not only would go into the moon it
would come out the other side not too
many things do that imagine having a
piece of jell-o and sending a really
really fast tiny little VB through the
jello what would happen if you went in
you’d make a little tiny hole but as you
went out you’d make a big splat we can
imagine looking on the moon and on
Mercury and on other bodies for to see
are there any splats like that are there
any distinctive craters that look like
they came from the inside rather than
the outside now there are other more
mundane you know everyday ways that we
can look for dark matter for example you
might want to go home and look at your
windows because as a little chunk of
dark matter passed through your window
it would comment a very very tiny
cylinder through your winter a little
tiny track and so if we got all of you
to go home and look at the windows in
your homes and in your offices and in
your friends offices in their homes we
might be able to by looking at these
vast expanses of windows that fill our
cities be able to tell whether particles
of dark matter had come hurtling through
them leaving behind these little tracks
what about muah-muah
well it may or may not be a chunk of
dark matter it’s going to be very hard
for us to tell unless we take a trip
there
and people are planning to send a
mission if they can to a mu a mu and try
to catch it but whether or not o Momoa
is a chunk of dark matter there’s a very
good chance that our galaxy is being
held together by stuff that we simply
cannot see so far and that is out there
for us to discover and we hope to do
that soon thank you
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