'Hello everyone and welcome to Armagh Astrobytes the series where we take
astronomy and break it down into
bite-sized chunks.  We're joined again
today with Professor Michael
Burton who's the director of Armagh
Observatory and Planetarium and today
we're going to discuss cosmology so
Michael this is a truly grand topic so
how have astronomers realized that they
can study the history of the universe
itself?'
'Indeed this is a massive topic and I'm
going to try and explain that by
talking about this rather complicated
looking diagram but this picture here
goes back about a hundred years ago to
the days of Edwin Hubble and what we
see in this picture is in the Left we
see a picture of a series of galaxies
large galaxies the top smaller galaxies
down the bottom and on the right we see
what it called Spectre which is
spreading the light out from those
galaxies a bit like they're going
through a rainbow and seeing what that
light is made up of and this particular
data set, originally have taken by
Edwin Hubble actually allows us to probe
back to the history of the universe
itself and let me try and explain that. Let's start by looking at the left hand
side left hand side these are these
elliptical galaxies we've been talking
about in previous astrobytes and these
actually galaxies are the largest
galaxies in different clusters of
galaxies so what Hubble did was he made
the assumption that each one of these
galaxies is actually the same size but
the different angular size we see in the
sky is directly related to how far away
they are basically the smallest ones are
farthest away the largest ones are
closest so he had a linear relationship
between angular size and distance but he
also did was he measured the spectra and
that's what's shown on the right and so
he spread the light out as they'd like
going to a prism the lights being spread
out here and he's taken a couple of
little lines that come from the element
calcium the technical name is the H&K
line but the name doesn't really matter
you can see these absorption 
features here these dark lines here
we'll see it again here we see it again
here and here and here and basically is
measuring the wavelength where these
calcium features come and what he's
finding is that the wavelength gets
longer and longer the further and
further away it is basically you can
measure the speed of the recession it's
through what's called the Doppler effect
you can measure the speed and you can
measure the distance and that's what
that Hubble did.'  'So what did Hubble
find?'
'Well what Hubble found is shown in this
picture here this is actually a modern
version of Hubble's diagram
this is plotted the distance to the
galaxy that's really the angular size as
estimated by those images and on
the y axis we see the speed the galaxies
moving is measured from the Doppler
shift and what Hubble found was a
relationship that clearly relationship
went further a galaxy was away from us
that's fast it was moving away from us
now in fact Hubble wasn't the only
person who contributed this result there
was actually a Belgian astronomer George
Lemaitre who actually came up with a
very similar result actually slightly
before Hubble and recently a couple of
years ago the International Astronomical
Union recognized that by renamed the
Hubble law the Hubble roommates law in
honor of these two people that
contributed to this very important
diagram which tells us about the nature
of the universe we live in' 'That's
amazing it's so good that they actually
did that but what does the result
actually mean from this.' 'So that's what
this next diagram is trying to explain
so what they found was that
everything seems to be moving away for
us not only that the further away you
are the faster it is so there's two
possibility to that one is we are the
center of the universe and literally
everything is moving away from us but
since the time of the Copernicus
scientists have have moved away from
that kind of conception in Copernicus'
day we had the Earth the centre of the
universe and Copernicus put the Sun in the
centre,  the heliocentric
hypothesis well since astronomers don't
believe that we truly are the centre of
creation they haven't returned to the
explanation and if summarizing this
diagram here. The way to think about this
is and this is an analogy because you
really had to work in four-dimensional
space to understand it properly let's
suppose all the galaxies a lying on the
surface of a balloon so these little and
stickers these are coins are stuck on
the on a balloon and then you're blowing
the balloon up and as you blow the
balloon up if you take any one of these
galaxies you will find so galaxies here
you'll find that galaxies over here all
the neighboring galaxies are getting
further and further away from it and
basically take any galaxies
on this rubber balloon in every
other galaxy
we'll be moving away from you so that's
our current picture is essentially the
entire universe itself expanding but
rather than being a two-dimensional
surface expanding into three-dimensional
space we're really in a three
dimensional surface expanding into a
four dimensional space.' 'Wow
okay so Hubble made these measurements
about one century ago as telescopes that
we have my get better and they're able
to look further into the cosmos have we
been able to test out these conclusions
further?' 'Yes we have and we test them out
and we found they're not quite right
things have actually changed so let me
explain how it is that that we can do
that so we need to find some way of
measuring the distance that's the most
challenging part and we use what are
called standard candles, standard candles
are objects which have a known
brightness and then the relative
magnitude that we see can be related to
how far away it is and the best standard
candle we found are these supernovae
we've heard about supernovae earlier in
the astrobytes, these are when a star
explodes and can be as bright as an
entire galaxy for a few days and
particular kinds of supernovae
essentially all look the same so
essentially by measuring these
supernovae we are able to probe further
and further the universe and try and
understand its history more and more.' 'So
when we do this do we find that the
Hubble Lemaitre still holds that the
universe is literally expanding?' 'We do
for parts of it but in fact in the most
recent part in time we're finding it
that law is not quite right in fact not
only the universal expanding but the
expansion is actually accelerating and
that's what this sketch here was trying
to illustrate this is not data this is
the sketch we're right here with a
telescope looking back in time as we go
to the left-hand side we're looking back
in time towards the origin the universe
and the width of the diagram essentially
represents the size of the universe over
time so this cone here which has
got a kind of a straight-line
linear form it over this part is the is
the Hubble expansion and in fact you can
see in recent times actually it's
accelerating it's getting larger and
larger more and more rapidly so this is
what we now interpret as the
acceleration of the expansion universe
but the other part was diagram unless we
look back in time the galaxies of today
we see the building blocks of the
galaxies are going back billions of
years ago and we go back to a time
before the first galaxies actually
formed and back to time when the
universe was only full of gas and in
fact we can peel back as far as a time
only shortly after the Big Bang where
there's a radiation coming out in the
radio called the Cosmic Microwave
Background.' 'So what is this cosmic
microwave background?' 'I'm showing that
modern view the best picture we have now
of the background measured by our
European Space Agency satellite called
the Planck satellite listeners discovery
which goes back about 50 years ago just
over fifty years ago
and essentially if you turn a radio on
and don't have a radio station you can
hear a background hiss that's hiss in
fact much of it is actually coming from
the universe itself it's a kind of
cosmic static we now know that this
arises from a time about 400,000 years
after the Big Bang back 380,000 to be
precise when the first atoms formed the
electrons and photons came together
perform of the first atoms and at that
point radiation could travel unimpeded
through the universe and essentially
we're seeing photons going back to this
time shortly after formation on the
universe itself
we've been currently traveling in a
straight line ever since when they first
when they were first released they were
much much hotter maybe the temperature
of several thousand degrees but in that
expansion over the last fourteen billion
years they've cooled down and the fact
this radiation is now the temperature of
only two point seven degrees above
absolute zero
but if atlas diagram here shows more
than that it's not just showing you the
distribution at that temperature it's
showing the fluctuations in that
temperature and the difference between
red and the blue in this diagram a tiny
tiny temperature fluctuations on about
three thousands of a degree which we can
accurately measure in the background and
we now realize that these are sincere
like ripples in time these little
slightly hotter and slightly cooler
regions and he provided the seeds from
which galaxy clusters formed and
optimally the galaxies in today's
universe came from these seeds.' 'So what
is our current understanding of how the
universe actually began?' 'So we have
another schematic here to try and put
all this twenty fourteen billion years
of evolution of our universe in one
diagram so here we are today modern
universe full of galaxies around us and
we can peer back and in the radio part
of the spectrum factors to the microwave
particle spectrum we can see this cosmic
microwave background where these sort of
society it's like temperature
fluctuations led to the formation of the
galaxies we have today but these are
temperature fluctuations must have come
from an even earlier phasing universe in
the first fraction of these of a second
of the universe fluctuations quantum
fluctuations we called essentially
random changes which would quantum
mechanics lead to you can't have a
perfectly smooth universe and
most quantum fluctuations themselves
mass arisen from what we call a Big
Bang the dawn of time an event we still
cannot understand because actually goes
beyond our current understanding of
physics.' 'So what does all this mean for
our universe?' 'Let me try and wrap up
what we do understand and some of what
we don't understand in this final slide
so essentially peering back back to time
seeing the Cosmic Microwave Background
seeing the expansion the universe allows
us to estimate an age of the universe
and we're fairly confident we do know
how old the universe is it's about 13.8
billion years around three times the age
of our Sun in fact we think the universe
will expand forever in fact our best
understanding is it's accelerating and
effect the universe is going to get
further and further proud all the stars
and galaxies eventually in zillions of
years
into the future but there's many many
things we don't understand and what I
want to highlight here is current
understanding in fact lack of
understanding about what the universe
consists of so I've got this diagram
essentially relates the three components
of the universe only one part of that
component this yellow section here what
I could ordinary matter is what we
actually understand ordinary matter was
stuff like us, like planets, like stars
things we can see things we can feel
things we can measure but in fact much
the universe we can't see we can't even
feel it at times so this next
sector over here this blue one here
which covers about a quarter the
universe we call that dark matter so
when we look at distant galaxies we can
see those galaxies rotate but if we try
and work out how much matter there is
based upon how fast are they're rotating
we find that the mass of the galaxy is
actually a lot more than the amount of
matter we can see which is the visible
light that's coming from us so we call
that dark matter it's stuff we can feel
but we can't see and we believe it forms
about one quarter of stuff our universe
is made up of well in fact the biggest
part in universe is something we really
have absolutely no idea about we call it
dark energy and this is what's leading
to this cosmic repulse this is the
expansion in fact the accelerator of the
universe driving universe part faster
and faster but we really don't
understand it it's the biggest mystery
in the cosmos today.'
'Wow so there's obviously plenty more to
understand and to investigate so for
everyone at home this is actually the
last Armagh Astrobyte in the series over
the past three months we've journeyed
from our solar system through the stars
of our galaxy then to the realm of
galaxies and then to the birth of the
universe itself with the Big Bang. We
hope you have enjoyed it and have
learned a lot about astronomy along the
way but also there's a lot more to be
discovered obviously on many mysteries
to be explained so this is just goodbye
for now.' 'Goodbye'
