Light and Dark (2013–…): Season 1, Episode 1 - Light - full transcript
under the cover of darkness the world
lies hidden from view
without light I have no idea what lies beyond my
immediate surroundings
I'm closed in enveloped on all sides by
the unknown
for much of human history when
the Sun wentdown and the dark set in
we were at the mercy of the night
but over the centuries we've developed our
own sources of illumination
we've lit our homes our streets our cities
and in doing so we banished the
darkness into the shadows
and just as we've used lights to
illuminate our world
the more we've discovered about lights properties
the more of the universe it's shown us
we've seen into the depths of space and back
to the beginning of time
but as we've looked deeper
we've come to
realize how little we've seen
and that the cosmos is greatest
mysteries remain hidden in the dark
lights and dark is essentially
the story of everything we know
and everything we don't know about our universe
and it all begins with light it's such
an integral part of the way we perceive the world
it's easy to take it for granted
but for centuries
understanding what light really is
has been one of Sciences
most enduring questions the
first steps towards understanding the
properties of lights were made in the
3rd century BC by the renowned Greek
mathematician Euclid
and he did it by thinking about something so obvious
that most of us don't give it any thought at all
placing the tiny chair very close to the
camera
produces a large image on the retina
and because we're not used to seeing
tiny chairs in everyday life
our brains are tricked into thinking is a
normal-sized chair in the middle of the room
and the reason this illusion works
at all
is because to judge distances our brains rely on a simple fact
the further away things are
the smaller they appear to the eye
and it was by focusing on exactly why
distant objects could appear the same size
as much smaller ones closer up
that led Euclid to discover one of
lights' most fundamental properties
obviously the London Eye is much
bigger than my fingers I know that
and yet to me they look
the same size
so how do we explain this
well Euclid came up with an elegant
solution
for my finger to appear at the top of the wheel
my eye my finger and the top of the wheel
must all lie on the same line
but nuclear's insights didn't just
explain the tricks of perspective
it revealed a basic truth about light
itself
Euclid had discovered that light travels
in straight lines
realizing how it travels marks the beginning of our
scientific understanding of light
and it's also meant that if we could divert
it from its straight-line path
we could change the way we see the world
but that leap wouldn't happen for
another 2,000 years
it was eventually made
in Renaissance Italy
by one of the founding
fathers of modern science
in the summer of 1609 Galileo Galilei
made the shorts but fateful journey
from his home in Padua
to Venice
capital of the Venetian Republic
Galileo had flame red
hair a full beard
and was well known for his love
of fine wines and generous hospitality
and also for his
anti-establishment views
by this time he'd also built up a reputation as a
natural philosopher and mathematician
and he was regarded as a valuable asset
to the Venetian Republic
but although as a professor he had a regular income
Galileo was never far from financial troubles
when his father died in 1591 Galileo the eldest of
four surviving siblings became head of the household
and effectively took on responsibility for
supporting his brother a poor itinerant musician
and for paying his sister's dairies
by the time he came to Venice he still owed a significant amount of money to his two brothers-in-law
and so was always on the lookout
for a money-making scheme
and that summer Venice was abuzz with
rumors of a device that appeared to do the impossible
a Dutch spyglass that could bring distant objects closer
it was just the opportunity
galileo was looking for
back in the 17th century the spyglass was
cutting-edge technology
and details of how it worked were a closely guarded
secret
or Galileo knew was that it consisted
of two lenses arranged in a tube
and so when he developed his own
he kept it very secret as well
but we do know from a shopping list
that he got his glass from the small island of
Murano out in the lagoon
and because no tools existed he had to improvise
for instance buying an artillery ball
to grind the curved surfaces of the lenses
it had been known since the first spectacles
were produced in the middle of the 13th century
that glass had the
strange property of bending light
but I'm like spectacles the
spyglass an early telescope
required a combination of lenses
in a very specific arrangement
this is how Galileo's telescope
works
rays of light come in from a distant object so
they're almost parallel
where they meet
his first lens
this is the objective lens and
it's plano-convex
which means it's flat on one side and
curved on the other
it's sort of lens used to
treat long sightedness
what it does is bend
the rays of light towards each other
so that they would meet at a point
but before
this focal point
Galileo places his second lens the
ocular lens which is Plano concave
and this bends the
rays of light back out again
so that they
emerge parallel where they enter the eye
and then the eye lens
focuses them on the retina
now the magnification of a telescope depends on
the ratio of the focal lengths of the two lenses
the distances f1 and f2
the difficulty for Galileo was
grinding down the convex surface
of his objective lens to
make it as shallow as possible
in order to maximize the length f1
because the longer he could make that the greater the magnification of his telescope
produced in just a few weeks
Galileo's telescope had a magnification of eight times
and was far more powerful than the original spyglass
all he needed to do now was
cash in on his new invention
ever the showman on the 21st of
August 1609
Galileo climbed one of the city's bell towers
obviously he'd have used the stairs
at the top in front of an assembled group of Venetian noblemen and Senators
Galileo demonstrated his telescope
it was a sensation
using it the venetians will be able to
see approaching ships
two hours earlier than
with the naked eye
the military and economic
advantage of knowing who was sailing over the horizon
was lost on no
one watching that day
three days later as a grand gesture
Galileo presented his telescope to the Duke as a gift
in return he was guaranteed his job for life at double his salary
with his finances
now secure
Galileo went on to develop
a more powerful telescope
and with it used the ability
to bend light to change our perspective on the cosmos
this is the book Galileo
published in 1610
is called Siderius nuncius which in latin means the starry
messenger
in he recorded his first observations of the night sky
the first anyone had ever made using anything other than the naked eye
today it's hard to imagine how anything contained in this little book was controversial
but
you have to remember that back when it was written
the nature of the heavens
was thought to be knowable only to God
and the earth was considered to be at
the center of the universe
these are his drawings
of the moon
since ancient times all
heavenly bodies were thought to be perfect spheres
but with his telescope Galileo saw texture in the surface of the Moon
deep craters and mountains that from
the shadows they cast across the lunar surface
he
estimated to be some six kilometers tall
as well as showing the heavens to be
imperfect
his telescope began to uncover
their true extent
revealing 10 times more stars than
are visible to the naked eye
and in the final chapters Galileo
reports the discovery of four stars
that appear to form a straight line near the
planet Jupiter
his drawings show how their positions change from night to
night
although they moved they always did so along the same straight line
and from that Galileo deduced that they had to be orbiting Jupiter
they weren't stars at all they were moons
through his telescope
Galileo had seen evidence that
overturned the accepted dogma
that the earth was the fulcrum
about which everything in the universe revolved
seeing moons in orbit around
Jupiter
meant that not everything
went round the earth
so far from being the center of
the universe the earth was just another planet
the telescope had allowed Galileo to
glimpse the true nature of the cosmos
and our place within it
but this way of
manipulating light
had another powerful application
one that would allow us to
see into another world
in 17th century London one of the most
prominent scientists of the age
was using lenses in a very different way
robert's hook had taken the basic
principle of the telescope
and used it to build a microscope
galileo used the
telescope to discover a new world in the heavens
and hook that uses the
microscope to discover a new world
in the very very
small
but there's a difference because
what Galileo had presented was a world that was bigger
and more plentiful
but it was a world that people were at least vaguely
familiar with because you can look up in the sky and see the stars
whereas the
world that the hook presented was really something spectacular and new
it was a
world inside the tiniest particles of matter
that no one had ever imagined to
be there before
people didn't even realize that there was a microscopic
world there to reveal
hook trained his microscope on a huge
range of materials and living things
but it was his drawings of the exquisite
detail he saw in the bodies of insects
that will become famous
so up here you
can see a human fleet Pollux irritant it's a very tiny creature
and
then here we've got the plate from micrographia
which is a huge image of
the flea that Hooke produced
and it's really something spectacular
and this would have folded out in the book so it was really very large
some people said it was as big as a cat
it's a work of art really I mean they're just so much
intricate detail in there
it is and there was nothing like it before Hooke
they really were unprecedented
and the shading and the quality of the images is
just superb
- and it's accurate I mean it's er
-it is
it's absolutely
accurate I was looking yesterday at images of photographs of the flea
and
there's really actually made with an electron microscope
and there's really
nothing to choose between between a hook and the current images
this is an image
of the compound eye of a fly which Hooke
shows in amazing detail for the first
time and this is an image of the foot of
a fly Hooke shows you the foot has
little spikes in it that allow it to
clasp into the pores on a surface now
this image looks less interesting less
intricate than the others well it
doesn't look terribly interesting but
actually it's really quite a profound
picture because what hook is looking at
here is a very thin slice of cork which
he cut with a penknife and he's looking
at the little individual components that
make it up and he calls them pause and
then he calls them caverns he calls them
boxes and then he calls them cells and
cell of course is the term that stuck
these are the little constituent parts
not just of cork but of all living
things and so it's actually a profoundly
important discovery and a name that has
come standard in in biology
using blast bend light revealed our true
place in the universe
and the intricate architecture of the
microscopic world the more we looked the
more we saw
with each new insights into the nature
of light came a fresh understanding of
the cosmos
and the next discovery would take us far
further
and enable us to read the story of the
stars
and it began with something Hooke had
glimpsed through his microscope this is
Robert hooks book the micrographia
published in 1660 for 350 years ago it's
full of his famous diagrams is his
picture of the fleece incredible seeing
it in its original form it really is the
size of a cat these images really
captured the public imagination and they
made the book a sensation but for me the
micrographia is about much more than
that
the chapter that interests me as a
physicist is one that contains hardly
any images at all and it's this one here
of the colors observable in Muscovy
glass and other thin bodies here Hooke
describes the iridescent patterns of
rainbow colors he sees through his
microscope as light passes through thin
materials like soap bubbles and Muscovy
glass a silicate mineral that's made up
of lots of thin layers at the time it
was thought that white light like
sunlight was pure that it came directly
from God and so Hooke concluded that the
colors he was seeing must have some have
been added to the light that they were
effectively created as the light passed
through the materials that hoax theory
about canid light was about to be
challenged by his greatest rival
Isaac Newton is one of the world's most
revered scientists best known for his
theory of universal gravitation
and just like his laws of gravity
Newton's discoveries about the nature of
light are among his most celebrated
achievements but the story of how that
work began is much less familiar and
this time there was no fruit involved
this is Stourbridge common a sleepy
riverside meadow on the banks of the
River Cam but when Newton visited in
1664 it would have been very different
for over seven hundred years every
September
this place will be transformed into what
was at its height the largest fair in
Europe for several weeks each year
people would descend on the common for
an annual festival of Commerce and
debauchery
this whole common would have been packed
with makeshift stalls farming produce
brandy houses Goldsmith's silk merchants
that have been slack rope dancing puppet
shows music temptations of every kind
packed into row upon row of wooden
booths and temps
Starbridge Fair was a place you could
buy anything you could imagine
but when Newton came here is said he
bought just one thing a prism he bought
it because it performed the same magic
Hooke had seen with his microscope
Newton would later write that using his
new purchase he would try the celebrated
phenomena of colors a rather understated
introduction to work that would produce
one of the most profound insights into
the nature of light
Newton devised an ingenious experiment
to discover precisely how these rainbow
colors were produced and to put hooks
theory that they were created by the
prism itself to the test this is
Newton's own drawing of what he called
his crucial experiment in it he arranged
a prism so that Sun lights coming in
from a small hole he'd made in the
shutters of his bedroom window pass
through it and projected colored light
onto a screen well here's my light
source and here's my prism which if I
arrange carefully I can get projected
onto the back pillar of course none of
this was new people knew that prisms
produced colored lights but what Newton
did next had never been done before he
first isolated one of the colors using a
slit so in this case the orange light he
then passed that orange light through a
second prism now if Hooke was right then
this prism should add the other colors
to the orange and reproduce the rainbow
but all Newton saw was orange lights the
prism wasn't adding any extra color he
concluded that the colors must have been
contained in the white light in the
first place that white light wasn't pure
and prisms don't add anything to it
instead they split it up into its
constituent parts
Newton named the colors that make up
white light the spectrum and when this
discovery was combined with the
telescope it would show us something
remarkable the spectrum would reveal
precisely what it was we were looking at
out in space this is a spectroscope as
sunlight comes in it's broken up into
its constituent colors and spread out
much more finely than you'd get with a
simple prism now with this camera I
should be able to show you what I can
see I'll just check that it's working
yes okay when scientists first did this
in the middle of the 19th century basing
a spectroscope on top they saw something
completely unexpected you can see the
colors of the spectrum as Newton would
have seen them but if you look more
closely you can see something else it's
not continuous it's broken up by lots of
thin black lines these are gaps in the
spectrum it will soon realize that these
gaps were due to atoms in the outer
atmosphere of the Sun absorbing certain
wavelengths of light coming from its
interior and that they could be used to
work out the chemical composition of the
Sun
every element absorbs a unique pattern
of wavelengths an optical fingerprints
that can be used to determine the
chemicals that make up any bright object
you can see in the sky and in Rome one
man was using this technique to study
lights whose origins lay far beyond the
Sun father Angelo secchi was no ordinary
priest he was charismatic and viewed as
something of a heretic by his fellow
Jesuits and that's because he was also a
professor of physics with an evangelical
passion for astronomy
in 1852 Seki was appointed director of
the Vatican Observatory and within a
year he built a new observatory on the
roof of st. Ignatius Church in the heart
of the city at the time most astronomers
were interested in mapping the positions
of the stars and charting their motions
across the heavens but Seki was
different he wanted to know what they
actually were so from his vantage point
high above the streets of the Eternal
City he began to meticulously analyze
their light fitting a spectroscope to
the observatory's telescope father sexy
laborious ly recorded the spectra of
more than 4000 stars
this is sakis book la Stella the Stars
which he published in 1877 and flicking
through it you can see many of the
observations that he made this one in
particular is interesting it shows some
of the spectra he recorded the top one
here is from the Sun but the second one
is starlight
it's from Sirius a the dog star which is
the brightest star in the night sky
it's 8.6 light-years from Earth and over
20 times as luminous as the Sun you can
see from its spectrum this clear
sequence of bands which is the signature
of hydrogen because it's a relatively
young star
the universe's hottest brightest stars
have spectra rich in the two lightest
elements hydrogen and helium
but as they age they cool and their
spectra reveal the presence of many
heavier elements
this third one is from the star betel
jaws which is a red supergiant it's near
the end of its life and so you can see
from the many bands here that it's
composed of lots of different elements
what's remarkable about this image is
that I mean it really is one of the key
moments in the history of astronomy that
we can learn so much about what distant
stars are made of just by examining
their light
but because Zeki had cataloged the
spectra of so many stars of different
ages his observations led to something
even more profound that by analyzing
starlight we can determine the star's
life cycles when they were born
and when they'll die
understanding the spectrum had allowed
us to read the story of the stars
it's quite incredible to think that what
began as a simple experiment in a
darkened room could reveal so much about
the universe that the scant light from
those tiny points in the night sky could
contain within it the epic drama of the
heavens
but that wasn't all the spectrum could
tell us today we know that it's made up
of light of many different wavelengths
and that those wavelengths extend way
beyond the range we can see the spectrum
from the longest wavelengths used in
radio communications to the very
shortest wavelength gamma rays covers a
range of 30 orders of magnitude the
longest are one followed by 30 zeros
bigger than the shortest that's the same
as a spreading range of weights from
that of a single grain of sand to the
weight of all the water in all the
oceans on the planet and within that
vast spread visible light the
frequencies we can see covers a factor
of just two that's the same as the
difference in weight between this pebble
and one twice its size
we all said doctor yes I think so
and throughout the 20th century opening
our eyes to the full spectrum revealed
even more of the universe if you had
infrared eyes here's how the sky would
look infrared allowed us to see the
universe's coolest stars while radio
telescopes sensitive to the longest
wavelengths revealed a cosmos in turmoil
it see violent events that are picked up
exploded stars and galaxies and
satellites have scoured the heavens for
short wavelength ultraviolet the OEO
picks up the ultraviolet light from hot
stars which the atmosphere cuts off from
ground telescopes
and here is the very latest window gamma
rays which are like very energetic
x-rays seeing beyond the visible has
allowed us to peer deep into the cosmos
I was cock-a-hoop about this I too was
wildly excited when I heard of this
discovery
but the very fact that light had proved
such a useful tool for exploring the
universe depended on one of its most
mysterious properties light behaves like
a wave but if it is a wave what is it a
wave in waves are carried across the
ocean by the water and the sound you can
hear now is due to waves in the air in
the vacuum of space there is no air so
there is no sound but the reason you can
see me is because I'm lit by sunlight
that has traveled a hundred and fifty
million kilometres through empty space
so what is light and how can you have a
wave in nothing answering that question
would not only reveal what light is it
would ultimately allow us to glimpse the
beginning of the universe
and the first part of that solution was
a discovery that challenged our most
basic assumptions about how we see the
world
to our eyes light appears to be
everywhere instantaneously as I look out
at the view there seems to be no time
lag no delay while I wait for the light
to reach me but towards the end of the
17th century it was discovered that our
senses are mistaken
in 1672 the danish astronomer la roma
arrived in paris to begin work of the
city's observatory and to continue his
observations of the moons of jupiter
for more than a decade giovanni cassini
the observatory's director had been
documenting their orbits in my new
detail
Jupiter's innermost moon Io is known to
make a complete circuit around the gas
giants once every 1.77 Earth days that's
every forty two and a half hours now
from Earth we can see it disappear
behind Jupiter and then re-emerge round
the other side as it travels around in
its orbit but here in Paris in the 1660s
Giovanni Cassini had noticed that the
timing of these eclipses seemed to vary
sometimes sooner sometimes later than
expected soon as he arrived in Paris
Roma noticed that these fluctuations
weren't happening at random when the
earth was closer to Jupiter IO will be
seen to disappear Andrea merge earlier
but as the year went by and the earth
moved in its orbit around the Sun so
that it was further away from Jupiter
then the eclipses appear to happen later
than expected
Roma knew the moon always took the same
time to travel around Jupiter his great
insight was to realize that the
variations were due to the fact that
light itself takes time to travel
through space
here's how it works the eclipses of Io
appear later than expected when the
earth is further from Jupiter because
light takes a longer time to cover the
greater distance but they appear earlier
when the earth is closer because light
needs less time to reach the earth light
isn't instantaneous it travels at a
finite speed today we've not only
measured light speed with incredible
accuracy we've seen it in motion
this is a video made by scientists at
MIT using a camera designed to monitor
extremely fast chemical reactions it has
a shutter speed of around a picosecond
that's a millionth of a millionth of a
second the time it takes light to travel
just a third of a millimeter now look
what happens when I press play
what you can see here is a pulse of
laser light moving through a
water-filled bottle to us this would
appear as the briefest of flashes but
the camera reveals how the pulse travels
through the bottle scattering and
bouncing around as it hits the water
molecules
light travels so fast 300,000 km/s that
slowed down by the same amount a bullet
would take an entire year to travel the
length of the bottle it's one thing to
know that light travels at a finite
speed quite another to actually see it
move the discovery of the speed of light
was hugely significant not least because
it proved crucial to uncovering what
light actually is
born in the summer of 1831 James Clark
Maxwell would become one of the leading
lights of 19th century physics his work
on electricity and magnetism was one of
the greatest achievements of the a
this is Glenn lair in southwest Scotland
Maxwell's family home while he was
growing up here he developed an
insatiable curiosity about the world
around him a desire to understand nature
that he would never lose
the young Maxwell seems to have taken
great delight in tormenting his parents
and his nanny by constantly asking them
how things worked what's the goal of
that he'd say and if anyone ventured an
answer the young Maxwell would only be
satisfied for a moment before asking
them how they knew
of course some of this is particularly
unusual for a child but what sets
Maxwell apart is that he was just 14
years old when he wrote his first
scientific paper so young that a friend
of the family had to present it to the
Royal Society of Edinburgh on his behalf
Maxwell's one of the greatest scientists
who ever lived and it was here that he
carried out his most important work
during the 1860s Maxwell produced a
virtuoso piece of mathematics that
showed electricity and magnetism were
different aspects of the same thing but
his calculations would show something
else quite by accident they would reveal
the true nature of light
these are Maxwell's four famous
equations that describe the relationship
between electric and magnetic fields E
is minus V by V T is the electric field
B is the magnetic field B over mu naught
div of e equals zero epsilon not it was
not with a bit of algebra a manipulation
these four equations can be combined to
give one single equation so the way it's
done is like this we take the curl of
curl of e hidden deep within his
mathematics was something that even
Maxwell didn't expect del squared e
epsilon naught R and E to give this
second term is 0 and I'm left with a del
squared of e minus mu naught epsilon
naught D 2 by DT squared this is the
wave equation it tells us how an
electromagnetic field travels through
space now the important bit is this here
mu naught epsilon naught because it's
related to the speed that the wave is
traveling in fact the speed is given by
1 over the square root of nu naught
epsilon naught and if you work that out
you arrive at 3 times
10 to the power 8 meters per second or
300,000 kilometers per second the speed
of light if electromagnetic waves moved
at the speed of light it could only mean
one thing
Maxwell knew this had to be more than
just a coincidence
it meant that light itself had to be an
electromagnetic wave the discovery that
light is an electromagnetic wave
explains one of its most puzzling
properties
what Maxwell's equations show is that
light consists of electric and magnetic
waves traveling through space so light
is simply electric and magnetic
vibrations feeding off one another as
they move and we now know that these
electromagnetic waves have a remarkable
property they don't need to be waves in
anything they can travel through empty
space
I remember first learning about this
when I was in my second year at
university I was in lecture hall 33 ac21
of the physics department at the
University of Surrey the lecturer was
dr. Cheevers and I remember turning to
my friend next to me and remarking on
how incredible I thought this was and I
could tell by his reaction that he
thought I was a bit of a geek but
actually it is incredible that in just a
few lines of algebra you can tell what
light really is and the fact that light
travels at a finite speed has enabled us
to do something else it allows us to
look into the past looking at a mirror
one metre away
you see yourself as you were six
nanoseconds ago
from Earth the moon appears as it was
one second ago and the Sun eight minutes
in the past the further you look out in
space the further you look back in time
light from the cosmos is most distant
objects has taken billions of years to
reach the earth but there's one source
that has taken us so far back in time
we've reached the very limits of what
can be seen with light in 1964 while
converting a strange-looking horn
antenna designed for early satellite
communications to make astronomical
observations Arno Penzias and Robert
Wilson began to pick up a mysterious
signal they couldn't explain
here we had purposely picked a portion
of the spectrum a wavelength of seven
centimeters or we expected nothing our
almost almost nothing no radiation at
all from the sky instead what happened
is that we found radiation coming into
our antenna from all directions
it's just flooding in at us and clearly
was orders of magnitude more than we
expected from the galaxies at first they
dismissed it as noise something unwanted
generated by the antenna itself now we
had some suspicions because the throat
of the antenna came into the cab and was
a little bit warmer and that was an
attractive place for pigeons at least a
pair of pigeons would like to stay there
especially in the cold winter we didn't
mind that because they flew away when we
when we came except that they had coated
the surface with a white white sticky
material which might not only absorb
radio waves but then emit radio waves
which could be part or maybe all of our
result
with the antenna cleaned and the pigeons
while it didn't end very well for the
pigeons Penzias and Wilson began
searching for an astronomical
explanation but the signal wasn't coming
from anything in our own galaxy nor did
it appear to be coming from any other
galaxy it seemed to be coming from
everywhere
no matter when we look day or night
winter or summer this background of
radiation appeared everywhere in the sky
it was not tied to our galaxy or any
other known source of radio waves
it was rather as if the whole universe
had been warmed up to a temperature
about three degrees above absolute zero
and so we were left with the astonishing
result that this radiation was coming
from somewhere in really deep cosmic
space beyond any radio sources that any
of us knew about or even dreamed existed
what they discovered was lights so
ancient it had been stretched out into
microwaves and cooled to just a few
scant degrees above absolute zero light
that had been traveling to earth for
almost the entire age of the universe it
hadn't come from a distant galaxy and it
was far older than any star Penzias and
Wilson had discovered that the entire
universe was awash with light from the
embers of the Big Bang itself
called the Cosmic Microwave Background
it was released when the universe was
just 370 thousand years old and it gives
us a snapshot of the cosmos in its
infancy
and here it is the latest image of the
Cosmic Microwave Background taken by the
Planck satellite and published in early
2013 the different colors are
fluctuations in temperature in the early
universe and the information they
contain has proved priceless to
cosmologists the tiny variations in
temperature are caused by matter
clumping together into what will
eventually become stars and galaxies but
what's truly remarkable about this image
is that it's not just light from the
early universe it's the very first light
there ever was
during the first year of his life the
universe was a fireball of hot dense
plasma the trapped lights preventing it
from moving
then as the cosmos cooled the plasma
condensed forming the first atoms and
the first light light that would become
the cosmic microwave background was
released into the universe
it's sort of hard to express what an
astonishing achievement this is that
from our small planet orbiting an
unremarkable star we've reached out into
the universe and seen as far as it's
possible to see with light
the discovery of the Cosmic Microwave
Background appeared to complete our
picture of the universe the final
chapter in our use of light to explore
the cosmos understanding the nature of
lights has allowed us to illuminate our
world we've captured it from the depths
of space and the beginning of time and
the smallest scales light has uncovered
the microscopic structure of living
things and at the largest it shown us
her place in the cosmos and told us the
story of the Stars virtually everything
we know about the universe we know
because it's been revealed by light but
just as it seemed light would lead us to
a complete understanding of everything
in the last 30 years has shown us
something disturbing the vast majority
of the cosmos can't be seen at all
far from being a universe of light much
of it is hidden in the dark
next time how scientists came to the
realization that more than 99% of the
universe lies concealed in the shadows
and the extraordinary quest uncover
what's out there in the dark whether you
want to step into the light or explore
the mysteries of the dark let the Open
University inspire you go to BBC co uk
the links to the Open University
you
lies hidden from view
without light I have no idea what lies beyond my
immediate surroundings
I'm closed in enveloped on all sides by
the unknown
for much of human history when
the Sun wentdown and the dark set in
we were at the mercy of the night
but over the centuries we've developed our
own sources of illumination
we've lit our homes our streets our cities
and in doing so we banished the
darkness into the shadows
and just as we've used lights to
illuminate our world
the more we've discovered about lights properties
the more of the universe it's shown us
we've seen into the depths of space and back
to the beginning of time
but as we've looked deeper
we've come to
realize how little we've seen
and that the cosmos is greatest
mysteries remain hidden in the dark
lights and dark is essentially
the story of everything we know
and everything we don't know about our universe
and it all begins with light it's such
an integral part of the way we perceive the world
it's easy to take it for granted
but for centuries
understanding what light really is
has been one of Sciences
most enduring questions the
first steps towards understanding the
properties of lights were made in the
3rd century BC by the renowned Greek
mathematician Euclid
and he did it by thinking about something so obvious
that most of us don't give it any thought at all
placing the tiny chair very close to the
camera
produces a large image on the retina
and because we're not used to seeing
tiny chairs in everyday life
our brains are tricked into thinking is a
normal-sized chair in the middle of the room
and the reason this illusion works
at all
is because to judge distances our brains rely on a simple fact
the further away things are
the smaller they appear to the eye
and it was by focusing on exactly why
distant objects could appear the same size
as much smaller ones closer up
that led Euclid to discover one of
lights' most fundamental properties
obviously the London Eye is much
bigger than my fingers I know that
and yet to me they look
the same size
so how do we explain this
well Euclid came up with an elegant
solution
for my finger to appear at the top of the wheel
my eye my finger and the top of the wheel
must all lie on the same line
but nuclear's insights didn't just
explain the tricks of perspective
it revealed a basic truth about light
itself
Euclid had discovered that light travels
in straight lines
realizing how it travels marks the beginning of our
scientific understanding of light
and it's also meant that if we could divert
it from its straight-line path
we could change the way we see the world
but that leap wouldn't happen for
another 2,000 years
it was eventually made
in Renaissance Italy
by one of the founding
fathers of modern science
in the summer of 1609 Galileo Galilei
made the shorts but fateful journey
from his home in Padua
to Venice
capital of the Venetian Republic
Galileo had flame red
hair a full beard
and was well known for his love
of fine wines and generous hospitality
and also for his
anti-establishment views
by this time he'd also built up a reputation as a
natural philosopher and mathematician
and he was regarded as a valuable asset
to the Venetian Republic
but although as a professor he had a regular income
Galileo was never far from financial troubles
when his father died in 1591 Galileo the eldest of
four surviving siblings became head of the household
and effectively took on responsibility for
supporting his brother a poor itinerant musician
and for paying his sister's dairies
by the time he came to Venice he still owed a significant amount of money to his two brothers-in-law
and so was always on the lookout
for a money-making scheme
and that summer Venice was abuzz with
rumors of a device that appeared to do the impossible
a Dutch spyglass that could bring distant objects closer
it was just the opportunity
galileo was looking for
back in the 17th century the spyglass was
cutting-edge technology
and details of how it worked were a closely guarded
secret
or Galileo knew was that it consisted
of two lenses arranged in a tube
and so when he developed his own
he kept it very secret as well
but we do know from a shopping list
that he got his glass from the small island of
Murano out in the lagoon
and because no tools existed he had to improvise
for instance buying an artillery ball
to grind the curved surfaces of the lenses
it had been known since the first spectacles
were produced in the middle of the 13th century
that glass had the
strange property of bending light
but I'm like spectacles the
spyglass an early telescope
required a combination of lenses
in a very specific arrangement
this is how Galileo's telescope
works
rays of light come in from a distant object so
they're almost parallel
where they meet
his first lens
this is the objective lens and
it's plano-convex
which means it's flat on one side and
curved on the other
it's sort of lens used to
treat long sightedness
what it does is bend
the rays of light towards each other
so that they would meet at a point
but before
this focal point
Galileo places his second lens the
ocular lens which is Plano concave
and this bends the
rays of light back out again
so that they
emerge parallel where they enter the eye
and then the eye lens
focuses them on the retina
now the magnification of a telescope depends on
the ratio of the focal lengths of the two lenses
the distances f1 and f2
the difficulty for Galileo was
grinding down the convex surface
of his objective lens to
make it as shallow as possible
in order to maximize the length f1
because the longer he could make that the greater the magnification of his telescope
produced in just a few weeks
Galileo's telescope had a magnification of eight times
and was far more powerful than the original spyglass
all he needed to do now was
cash in on his new invention
ever the showman on the 21st of
August 1609
Galileo climbed one of the city's bell towers
obviously he'd have used the stairs
at the top in front of an assembled group of Venetian noblemen and Senators
Galileo demonstrated his telescope
it was a sensation
using it the venetians will be able to
see approaching ships
two hours earlier than
with the naked eye
the military and economic
advantage of knowing who was sailing over the horizon
was lost on no
one watching that day
three days later as a grand gesture
Galileo presented his telescope to the Duke as a gift
in return he was guaranteed his job for life at double his salary
with his finances
now secure
Galileo went on to develop
a more powerful telescope
and with it used the ability
to bend light to change our perspective on the cosmos
this is the book Galileo
published in 1610
is called Siderius nuncius which in latin means the starry
messenger
in he recorded his first observations of the night sky
the first anyone had ever made using anything other than the naked eye
today it's hard to imagine how anything contained in this little book was controversial
but
you have to remember that back when it was written
the nature of the heavens
was thought to be knowable only to God
and the earth was considered to be at
the center of the universe
these are his drawings
of the moon
since ancient times all
heavenly bodies were thought to be perfect spheres
but with his telescope Galileo saw texture in the surface of the Moon
deep craters and mountains that from
the shadows they cast across the lunar surface
he
estimated to be some six kilometers tall
as well as showing the heavens to be
imperfect
his telescope began to uncover
their true extent
revealing 10 times more stars than
are visible to the naked eye
and in the final chapters Galileo
reports the discovery of four stars
that appear to form a straight line near the
planet Jupiter
his drawings show how their positions change from night to
night
although they moved they always did so along the same straight line
and from that Galileo deduced that they had to be orbiting Jupiter
they weren't stars at all they were moons
through his telescope
Galileo had seen evidence that
overturned the accepted dogma
that the earth was the fulcrum
about which everything in the universe revolved
seeing moons in orbit around
Jupiter
meant that not everything
went round the earth
so far from being the center of
the universe the earth was just another planet
the telescope had allowed Galileo to
glimpse the true nature of the cosmos
and our place within it
but this way of
manipulating light
had another powerful application
one that would allow us to
see into another world
in 17th century London one of the most
prominent scientists of the age
was using lenses in a very different way
robert's hook had taken the basic
principle of the telescope
and used it to build a microscope
galileo used the
telescope to discover a new world in the heavens
and hook that uses the
microscope to discover a new world
in the very very
small
but there's a difference because
what Galileo had presented was a world that was bigger
and more plentiful
but it was a world that people were at least vaguely
familiar with because you can look up in the sky and see the stars
whereas the
world that the hook presented was really something spectacular and new
it was a
world inside the tiniest particles of matter
that no one had ever imagined to
be there before
people didn't even realize that there was a microscopic
world there to reveal
hook trained his microscope on a huge
range of materials and living things
but it was his drawings of the exquisite
detail he saw in the bodies of insects
that will become famous
so up here you
can see a human fleet Pollux irritant it's a very tiny creature
and
then here we've got the plate from micrographia
which is a huge image of
the flea that Hooke produced
and it's really something spectacular
and this would have folded out in the book so it was really very large
some people said it was as big as a cat
it's a work of art really I mean they're just so much
intricate detail in there
it is and there was nothing like it before Hooke
they really were unprecedented
and the shading and the quality of the images is
just superb
- and it's accurate I mean it's er
-it is
it's absolutely
accurate I was looking yesterday at images of photographs of the flea
and
there's really actually made with an electron microscope
and there's really
nothing to choose between between a hook and the current images
this is an image
of the compound eye of a fly which Hooke
shows in amazing detail for the first
time and this is an image of the foot of
a fly Hooke shows you the foot has
little spikes in it that allow it to
clasp into the pores on a surface now
this image looks less interesting less
intricate than the others well it
doesn't look terribly interesting but
actually it's really quite a profound
picture because what hook is looking at
here is a very thin slice of cork which
he cut with a penknife and he's looking
at the little individual components that
make it up and he calls them pause and
then he calls them caverns he calls them
boxes and then he calls them cells and
cell of course is the term that stuck
these are the little constituent parts
not just of cork but of all living
things and so it's actually a profoundly
important discovery and a name that has
come standard in in biology
using blast bend light revealed our true
place in the universe
and the intricate architecture of the
microscopic world the more we looked the
more we saw
with each new insights into the nature
of light came a fresh understanding of
the cosmos
and the next discovery would take us far
further
and enable us to read the story of the
stars
and it began with something Hooke had
glimpsed through his microscope this is
Robert hooks book the micrographia
published in 1660 for 350 years ago it's
full of his famous diagrams is his
picture of the fleece incredible seeing
it in its original form it really is the
size of a cat these images really
captured the public imagination and they
made the book a sensation but for me the
micrographia is about much more than
that
the chapter that interests me as a
physicist is one that contains hardly
any images at all and it's this one here
of the colors observable in Muscovy
glass and other thin bodies here Hooke
describes the iridescent patterns of
rainbow colors he sees through his
microscope as light passes through thin
materials like soap bubbles and Muscovy
glass a silicate mineral that's made up
of lots of thin layers at the time it
was thought that white light like
sunlight was pure that it came directly
from God and so Hooke concluded that the
colors he was seeing must have some have
been added to the light that they were
effectively created as the light passed
through the materials that hoax theory
about canid light was about to be
challenged by his greatest rival
Isaac Newton is one of the world's most
revered scientists best known for his
theory of universal gravitation
and just like his laws of gravity
Newton's discoveries about the nature of
light are among his most celebrated
achievements but the story of how that
work began is much less familiar and
this time there was no fruit involved
this is Stourbridge common a sleepy
riverside meadow on the banks of the
River Cam but when Newton visited in
1664 it would have been very different
for over seven hundred years every
September
this place will be transformed into what
was at its height the largest fair in
Europe for several weeks each year
people would descend on the common for
an annual festival of Commerce and
debauchery
this whole common would have been packed
with makeshift stalls farming produce
brandy houses Goldsmith's silk merchants
that have been slack rope dancing puppet
shows music temptations of every kind
packed into row upon row of wooden
booths and temps
Starbridge Fair was a place you could
buy anything you could imagine
but when Newton came here is said he
bought just one thing a prism he bought
it because it performed the same magic
Hooke had seen with his microscope
Newton would later write that using his
new purchase he would try the celebrated
phenomena of colors a rather understated
introduction to work that would produce
one of the most profound insights into
the nature of light
Newton devised an ingenious experiment
to discover precisely how these rainbow
colors were produced and to put hooks
theory that they were created by the
prism itself to the test this is
Newton's own drawing of what he called
his crucial experiment in it he arranged
a prism so that Sun lights coming in
from a small hole he'd made in the
shutters of his bedroom window pass
through it and projected colored light
onto a screen well here's my light
source and here's my prism which if I
arrange carefully I can get projected
onto the back pillar of course none of
this was new people knew that prisms
produced colored lights but what Newton
did next had never been done before he
first isolated one of the colors using a
slit so in this case the orange light he
then passed that orange light through a
second prism now if Hooke was right then
this prism should add the other colors
to the orange and reproduce the rainbow
but all Newton saw was orange lights the
prism wasn't adding any extra color he
concluded that the colors must have been
contained in the white light in the
first place that white light wasn't pure
and prisms don't add anything to it
instead they split it up into its
constituent parts
Newton named the colors that make up
white light the spectrum and when this
discovery was combined with the
telescope it would show us something
remarkable the spectrum would reveal
precisely what it was we were looking at
out in space this is a spectroscope as
sunlight comes in it's broken up into
its constituent colors and spread out
much more finely than you'd get with a
simple prism now with this camera I
should be able to show you what I can
see I'll just check that it's working
yes okay when scientists first did this
in the middle of the 19th century basing
a spectroscope on top they saw something
completely unexpected you can see the
colors of the spectrum as Newton would
have seen them but if you look more
closely you can see something else it's
not continuous it's broken up by lots of
thin black lines these are gaps in the
spectrum it will soon realize that these
gaps were due to atoms in the outer
atmosphere of the Sun absorbing certain
wavelengths of light coming from its
interior and that they could be used to
work out the chemical composition of the
Sun
every element absorbs a unique pattern
of wavelengths an optical fingerprints
that can be used to determine the
chemicals that make up any bright object
you can see in the sky and in Rome one
man was using this technique to study
lights whose origins lay far beyond the
Sun father Angelo secchi was no ordinary
priest he was charismatic and viewed as
something of a heretic by his fellow
Jesuits and that's because he was also a
professor of physics with an evangelical
passion for astronomy
in 1852 Seki was appointed director of
the Vatican Observatory and within a
year he built a new observatory on the
roof of st. Ignatius Church in the heart
of the city at the time most astronomers
were interested in mapping the positions
of the stars and charting their motions
across the heavens but Seki was
different he wanted to know what they
actually were so from his vantage point
high above the streets of the Eternal
City he began to meticulously analyze
their light fitting a spectroscope to
the observatory's telescope father sexy
laborious ly recorded the spectra of
more than 4000 stars
this is sakis book la Stella the Stars
which he published in 1877 and flicking
through it you can see many of the
observations that he made this one in
particular is interesting it shows some
of the spectra he recorded the top one
here is from the Sun but the second one
is starlight
it's from Sirius a the dog star which is
the brightest star in the night sky
it's 8.6 light-years from Earth and over
20 times as luminous as the Sun you can
see from its spectrum this clear
sequence of bands which is the signature
of hydrogen because it's a relatively
young star
the universe's hottest brightest stars
have spectra rich in the two lightest
elements hydrogen and helium
but as they age they cool and their
spectra reveal the presence of many
heavier elements
this third one is from the star betel
jaws which is a red supergiant it's near
the end of its life and so you can see
from the many bands here that it's
composed of lots of different elements
what's remarkable about this image is
that I mean it really is one of the key
moments in the history of astronomy that
we can learn so much about what distant
stars are made of just by examining
their light
but because Zeki had cataloged the
spectra of so many stars of different
ages his observations led to something
even more profound that by analyzing
starlight we can determine the star's
life cycles when they were born
and when they'll die
understanding the spectrum had allowed
us to read the story of the stars
it's quite incredible to think that what
began as a simple experiment in a
darkened room could reveal so much about
the universe that the scant light from
those tiny points in the night sky could
contain within it the epic drama of the
heavens
but that wasn't all the spectrum could
tell us today we know that it's made up
of light of many different wavelengths
and that those wavelengths extend way
beyond the range we can see the spectrum
from the longest wavelengths used in
radio communications to the very
shortest wavelength gamma rays covers a
range of 30 orders of magnitude the
longest are one followed by 30 zeros
bigger than the shortest that's the same
as a spreading range of weights from
that of a single grain of sand to the
weight of all the water in all the
oceans on the planet and within that
vast spread visible light the
frequencies we can see covers a factor
of just two that's the same as the
difference in weight between this pebble
and one twice its size
we all said doctor yes I think so
and throughout the 20th century opening
our eyes to the full spectrum revealed
even more of the universe if you had
infrared eyes here's how the sky would
look infrared allowed us to see the
universe's coolest stars while radio
telescopes sensitive to the longest
wavelengths revealed a cosmos in turmoil
it see violent events that are picked up
exploded stars and galaxies and
satellites have scoured the heavens for
short wavelength ultraviolet the OEO
picks up the ultraviolet light from hot
stars which the atmosphere cuts off from
ground telescopes
and here is the very latest window gamma
rays which are like very energetic
x-rays seeing beyond the visible has
allowed us to peer deep into the cosmos
I was cock-a-hoop about this I too was
wildly excited when I heard of this
discovery
but the very fact that light had proved
such a useful tool for exploring the
universe depended on one of its most
mysterious properties light behaves like
a wave but if it is a wave what is it a
wave in waves are carried across the
ocean by the water and the sound you can
hear now is due to waves in the air in
the vacuum of space there is no air so
there is no sound but the reason you can
see me is because I'm lit by sunlight
that has traveled a hundred and fifty
million kilometres through empty space
so what is light and how can you have a
wave in nothing answering that question
would not only reveal what light is it
would ultimately allow us to glimpse the
beginning of the universe
and the first part of that solution was
a discovery that challenged our most
basic assumptions about how we see the
world
to our eyes light appears to be
everywhere instantaneously as I look out
at the view there seems to be no time
lag no delay while I wait for the light
to reach me but towards the end of the
17th century it was discovered that our
senses are mistaken
in 1672 the danish astronomer la roma
arrived in paris to begin work of the
city's observatory and to continue his
observations of the moons of jupiter
for more than a decade giovanni cassini
the observatory's director had been
documenting their orbits in my new
detail
Jupiter's innermost moon Io is known to
make a complete circuit around the gas
giants once every 1.77 Earth days that's
every forty two and a half hours now
from Earth we can see it disappear
behind Jupiter and then re-emerge round
the other side as it travels around in
its orbit but here in Paris in the 1660s
Giovanni Cassini had noticed that the
timing of these eclipses seemed to vary
sometimes sooner sometimes later than
expected soon as he arrived in Paris
Roma noticed that these fluctuations
weren't happening at random when the
earth was closer to Jupiter IO will be
seen to disappear Andrea merge earlier
but as the year went by and the earth
moved in its orbit around the Sun so
that it was further away from Jupiter
then the eclipses appear to happen later
than expected
Roma knew the moon always took the same
time to travel around Jupiter his great
insight was to realize that the
variations were due to the fact that
light itself takes time to travel
through space
here's how it works the eclipses of Io
appear later than expected when the
earth is further from Jupiter because
light takes a longer time to cover the
greater distance but they appear earlier
when the earth is closer because light
needs less time to reach the earth light
isn't instantaneous it travels at a
finite speed today we've not only
measured light speed with incredible
accuracy we've seen it in motion
this is a video made by scientists at
MIT using a camera designed to monitor
extremely fast chemical reactions it has
a shutter speed of around a picosecond
that's a millionth of a millionth of a
second the time it takes light to travel
just a third of a millimeter now look
what happens when I press play
what you can see here is a pulse of
laser light moving through a
water-filled bottle to us this would
appear as the briefest of flashes but
the camera reveals how the pulse travels
through the bottle scattering and
bouncing around as it hits the water
molecules
light travels so fast 300,000 km/s that
slowed down by the same amount a bullet
would take an entire year to travel the
length of the bottle it's one thing to
know that light travels at a finite
speed quite another to actually see it
move the discovery of the speed of light
was hugely significant not least because
it proved crucial to uncovering what
light actually is
born in the summer of 1831 James Clark
Maxwell would become one of the leading
lights of 19th century physics his work
on electricity and magnetism was one of
the greatest achievements of the a
this is Glenn lair in southwest Scotland
Maxwell's family home while he was
growing up here he developed an
insatiable curiosity about the world
around him a desire to understand nature
that he would never lose
the young Maxwell seems to have taken
great delight in tormenting his parents
and his nanny by constantly asking them
how things worked what's the goal of
that he'd say and if anyone ventured an
answer the young Maxwell would only be
satisfied for a moment before asking
them how they knew
of course some of this is particularly
unusual for a child but what sets
Maxwell apart is that he was just 14
years old when he wrote his first
scientific paper so young that a friend
of the family had to present it to the
Royal Society of Edinburgh on his behalf
Maxwell's one of the greatest scientists
who ever lived and it was here that he
carried out his most important work
during the 1860s Maxwell produced a
virtuoso piece of mathematics that
showed electricity and magnetism were
different aspects of the same thing but
his calculations would show something
else quite by accident they would reveal
the true nature of light
these are Maxwell's four famous
equations that describe the relationship
between electric and magnetic fields E
is minus V by V T is the electric field
B is the magnetic field B over mu naught
div of e equals zero epsilon not it was
not with a bit of algebra a manipulation
these four equations can be combined to
give one single equation so the way it's
done is like this we take the curl of
curl of e hidden deep within his
mathematics was something that even
Maxwell didn't expect del squared e
epsilon naught R and E to give this
second term is 0 and I'm left with a del
squared of e minus mu naught epsilon
naught D 2 by DT squared this is the
wave equation it tells us how an
electromagnetic field travels through
space now the important bit is this here
mu naught epsilon naught because it's
related to the speed that the wave is
traveling in fact the speed is given by
1 over the square root of nu naught
epsilon naught and if you work that out
you arrive at 3 times
10 to the power 8 meters per second or
300,000 kilometers per second the speed
of light if electromagnetic waves moved
at the speed of light it could only mean
one thing
Maxwell knew this had to be more than
just a coincidence
it meant that light itself had to be an
electromagnetic wave the discovery that
light is an electromagnetic wave
explains one of its most puzzling
properties
what Maxwell's equations show is that
light consists of electric and magnetic
waves traveling through space so light
is simply electric and magnetic
vibrations feeding off one another as
they move and we now know that these
electromagnetic waves have a remarkable
property they don't need to be waves in
anything they can travel through empty
space
I remember first learning about this
when I was in my second year at
university I was in lecture hall 33 ac21
of the physics department at the
University of Surrey the lecturer was
dr. Cheevers and I remember turning to
my friend next to me and remarking on
how incredible I thought this was and I
could tell by his reaction that he
thought I was a bit of a geek but
actually it is incredible that in just a
few lines of algebra you can tell what
light really is and the fact that light
travels at a finite speed has enabled us
to do something else it allows us to
look into the past looking at a mirror
one metre away
you see yourself as you were six
nanoseconds ago
from Earth the moon appears as it was
one second ago and the Sun eight minutes
in the past the further you look out in
space the further you look back in time
light from the cosmos is most distant
objects has taken billions of years to
reach the earth but there's one source
that has taken us so far back in time
we've reached the very limits of what
can be seen with light in 1964 while
converting a strange-looking horn
antenna designed for early satellite
communications to make astronomical
observations Arno Penzias and Robert
Wilson began to pick up a mysterious
signal they couldn't explain
here we had purposely picked a portion
of the spectrum a wavelength of seven
centimeters or we expected nothing our
almost almost nothing no radiation at
all from the sky instead what happened
is that we found radiation coming into
our antenna from all directions
it's just flooding in at us and clearly
was orders of magnitude more than we
expected from the galaxies at first they
dismissed it as noise something unwanted
generated by the antenna itself now we
had some suspicions because the throat
of the antenna came into the cab and was
a little bit warmer and that was an
attractive place for pigeons at least a
pair of pigeons would like to stay there
especially in the cold winter we didn't
mind that because they flew away when we
when we came except that they had coated
the surface with a white white sticky
material which might not only absorb
radio waves but then emit radio waves
which could be part or maybe all of our
result
with the antenna cleaned and the pigeons
while it didn't end very well for the
pigeons Penzias and Wilson began
searching for an astronomical
explanation but the signal wasn't coming
from anything in our own galaxy nor did
it appear to be coming from any other
galaxy it seemed to be coming from
everywhere
no matter when we look day or night
winter or summer this background of
radiation appeared everywhere in the sky
it was not tied to our galaxy or any
other known source of radio waves
it was rather as if the whole universe
had been warmed up to a temperature
about three degrees above absolute zero
and so we were left with the astonishing
result that this radiation was coming
from somewhere in really deep cosmic
space beyond any radio sources that any
of us knew about or even dreamed existed
what they discovered was lights so
ancient it had been stretched out into
microwaves and cooled to just a few
scant degrees above absolute zero light
that had been traveling to earth for
almost the entire age of the universe it
hadn't come from a distant galaxy and it
was far older than any star Penzias and
Wilson had discovered that the entire
universe was awash with light from the
embers of the Big Bang itself
called the Cosmic Microwave Background
it was released when the universe was
just 370 thousand years old and it gives
us a snapshot of the cosmos in its
infancy
and here it is the latest image of the
Cosmic Microwave Background taken by the
Planck satellite and published in early
2013 the different colors are
fluctuations in temperature in the early
universe and the information they
contain has proved priceless to
cosmologists the tiny variations in
temperature are caused by matter
clumping together into what will
eventually become stars and galaxies but
what's truly remarkable about this image
is that it's not just light from the
early universe it's the very first light
there ever was
during the first year of his life the
universe was a fireball of hot dense
plasma the trapped lights preventing it
from moving
then as the cosmos cooled the plasma
condensed forming the first atoms and
the first light light that would become
the cosmic microwave background was
released into the universe
it's sort of hard to express what an
astonishing achievement this is that
from our small planet orbiting an
unremarkable star we've reached out into
the universe and seen as far as it's
possible to see with light
the discovery of the Cosmic Microwave
Background appeared to complete our
picture of the universe the final
chapter in our use of light to explore
the cosmos understanding the nature of
lights has allowed us to illuminate our
world we've captured it from the depths
of space and the beginning of time and
the smallest scales light has uncovered
the microscopic structure of living
things and at the largest it shown us
her place in the cosmos and told us the
story of the Stars virtually everything
we know about the universe we know
because it's been revealed by light but
just as it seemed light would lead us to
a complete understanding of everything
in the last 30 years has shown us
something disturbing the vast majority
of the cosmos can't be seen at all
far from being a universe of light much
of it is hidden in the dark
next time how scientists came to the
realization that more than 99% of the
universe lies concealed in the shadows
and the extraordinary quest uncover
what's out there in the dark whether you
want to step into the light or explore
the mysteries of the dark let the Open
University inspire you go to BBC co uk
the links to the Open University
you