1
00:00:03,320 --> 00:00:06,880
In our night sky,
you can see space -

2
00:00:06,880 --> 00:00:11,080
big, mysterious,
and frankly a bit scary.

3
00:00:11,080 --> 00:00:14,800
I sometimes look up at it
and ask those big questions.

4
00:00:14,800 --> 00:00:17,680
Such as, how do stars work?

5
00:00:17,680 --> 00:00:19,400
How did it all begin?

6
00:00:19,400 --> 00:00:22,920
And, what is Madonna doing in space?

7
00:00:22,920 --> 00:00:25,720
For the answers, stick with me,

8
00:00:25,720 --> 00:00:30,120
as we uncover the things
you need to know about the universe.

9
00:00:30,120 --> 00:00:32,960
Right, let's get this show
on the road,

10
00:00:32,960 --> 00:00:37,120
and the beginning is as good
a place to start as any.

11
00:00:37,120 --> 00:00:39,840
So, how did the universe begin?

12
00:00:41,600 --> 00:00:45,000
Everyone knows the universe started
with a bang -

13
00:00:45,000 --> 00:00:50,120
a bang so big,
it's called the Big Bang.

14
00:00:50,120 --> 00:00:54,360
It happened everywhere
in the universe at the same time,

15
00:00:54,360 --> 00:00:57,680
and was the beginning of
everything we know -

16
00:00:57,680 --> 00:01:00,560
space, matter and even time itself.

17
00:01:02,000 --> 00:01:05,240
The Big Bang is the most
important event in history.

18
00:01:05,240 --> 00:01:08,360
In fact, without it,
there wouldn't be any history.

19
00:01:08,360 --> 00:01:12,440
Even so, the biggest brains
in science don't really know

20
00:01:12,440 --> 00:01:14,920
why it happened, only that it did.

21
00:01:14,920 --> 00:01:20,040
And they know it did because
there are clues out there in space.

22
00:01:22,720 --> 00:01:26,320
In 1929, astronomer Edwin Hubble
discovered that

23
00:01:26,320 --> 00:01:29,280
distant galaxies are
moving away from us,

24
00:01:29,280 --> 00:01:33,720
and the furthest are moving away
faster than the closer ones.

25
00:01:35,840 --> 00:01:41,280
So, logically, all these galaxies
came from one tiny central point -

26
00:01:41,280 --> 00:01:42,400
the Big Bang.

27
00:01:44,080 --> 00:01:48,320
Further proof was found by
two young scientists in the 1960s,

28
00:01:48,320 --> 00:01:52,440
when their new radio telescope
seemed to be faulty,

29
00:01:52,440 --> 00:01:55,080
due to a constant annoying hiss.

30
00:01:55,080 --> 00:01:58,480
Hmm? Grr!

31
00:01:58,480 --> 00:02:01,080
They checked the telescope
and pinned the blame

32
00:02:01,080 --> 00:02:03,640
on some resident pigeons
and their droppings.

33
00:02:03,640 --> 00:02:05,920
GUN COCKS

34
00:02:05,920 --> 00:02:07,480
SHOT FIRES

35
00:02:07,480 --> 00:02:12,120
They swept the dish and evicted the
birds, but the hiss was still there.

36
00:02:12,120 --> 00:02:18,040
This hiss was in fact cosmic
microwave background radiation,

37
00:02:18,040 --> 00:02:22,360
or CMB, which is the heat and light
left over from the Big Bang.

38
00:02:22,360 --> 00:02:27,360
It's travelled over 270,000
billion, billion miles to reach us,

39
00:02:27,360 --> 00:02:30,640
and has slowly cooled
on its long journey.

40
00:02:32,720 --> 00:02:35,080
In fact, we've all seen
the Big Bang.

41
00:02:35,080 --> 00:02:42,360
About 1% of the static on your
untuned TV is this CMB radiation.

42
00:02:42,360 --> 00:02:47,240
And scientists have used this static
to calculate the age

43
00:02:47,240 --> 00:02:52,160
of the universe, which is roughly
13.7 billion years old.

44
00:02:52,160 --> 00:02:55,200
That's a seriously long time ago,

45
00:02:55,200 --> 00:02:59,960
so perhaps we may never know
what caused the Big Bang.

46
00:02:59,960 --> 00:03:05,080
But we do know that the universe
apparently came from nothing,

47
00:03:05,080 --> 00:03:09,680
but is now everything.
So if it came from nothing,

48
00:03:09,680 --> 00:03:13,000
what is the universe made from?

49
00:03:13,000 --> 00:03:17,120
You might be surprised to learn
that we don't really know.

50
00:03:17,120 --> 00:03:20,720
All the matter and energy
we can see only accounts for

51
00:03:20,720 --> 00:03:23,400
about 5% of
the universe's total mass,

52
00:03:23,400 --> 00:03:28,480
and a whopping 97% of
all this visible stuff is made up

53
00:03:28,480 --> 00:03:32,680
of just two elements -
hydrogen and helium.

54
00:03:34,200 --> 00:03:37,400
So, everything heavier
here on Earth,

55
00:03:37,400 --> 00:03:43,440
like carbon, oxygen, water,
baboons, jet planes and clowns,

56
00:03:43,440 --> 00:03:45,520
is very rare indeed.

57
00:03:45,520 --> 00:03:48,560
And as for the remaining 95%
that's invisible,

58
00:03:48,560 --> 00:03:51,680
well, unsurprisingly,
that's a bit of a mystery.

59
00:03:51,680 --> 00:03:56,680
Scientists think that a quarter
of all this missing stuff is

60
00:03:56,680 --> 00:04:01,480
comprised of dark matter. It's
divided into two theoretical types -

61
00:04:01,480 --> 00:04:06,680
weakly-interacting massive
particles, or WIMPs for short,

62
00:04:06,680 --> 00:04:11,440
and massive compact halo objects,
or MACHOs, to you and me.

63
00:04:11,440 --> 00:04:15,240
WIMPs are tiny particles
of exotic matter.

64
00:04:15,240 --> 00:04:18,200
And by exotic, scientists mean

65
00:04:18,200 --> 00:04:20,560
they are different
from ordinary particles.

66
00:04:20,560 --> 00:04:22,480
Not that they dance for money.

67
00:04:24,400 --> 00:04:28,080
But so far,
they've proven undetectable.

68
00:04:29,600 --> 00:04:33,600
There could be WIMPs
flying through you right now,

69
00:04:33,600 --> 00:04:36,120
only you can't see or feel them.

70
00:04:37,640 --> 00:04:43,240
And we can't see MACHOs,
as they don't reflect or emit light.

71
00:04:43,240 --> 00:04:48,920
They could be everything
from failed stars to black holes.

72
00:04:48,920 --> 00:04:52,120
Although it only exists
theoretically, scientists think

73
00:04:52,120 --> 00:04:56,680
dark matter is important, as
it seems to binds galaxies together.

74
00:04:56,680 --> 00:04:59,520
Otherwise they would simply
fly apart -

75
00:04:59,520 --> 00:05:03,440
which might be fun to watch,
but not so good for us.

76
00:05:03,440 --> 00:05:05,360
But even with dark matter,

77
00:05:05,360 --> 00:05:09,720
that still leaves about 70%
of the universe simply missing.

78
00:05:09,720 --> 00:05:14,160
Scientists have called
what's left dark energy,

79
00:05:14,160 --> 00:05:16,280
which is even more puzzling.

80
00:05:17,800 --> 00:05:20,600
In 1998, astronomers discovered that

81
00:05:20,600 --> 00:05:24,960
the universe's rate of expansion
is actually increasing.

82
00:05:24,960 --> 00:05:27,680
Something seems to be
overpowering gravity,

83
00:05:27,680 --> 00:05:29,640
which scientists thought would

84
00:05:29,640 --> 00:05:32,320
eventually slow
the universe's expansion.

85
00:05:32,320 --> 00:05:37,920
They now think that
this is due to dark energy.

86
00:05:37,920 --> 00:05:40,760
So, if our greatest thinkers
had to take an exam

87
00:05:40,760 --> 00:05:42,800
in what the universe is made from,

88
00:05:42,800 --> 00:05:44,880
they'd have to tick
the "Don't know" box.

89
00:05:44,880 --> 00:05:48,800
But it's definitely made from
something, and if we look at

90
00:05:48,800 --> 00:05:53,440
the night sky, what we can actually
see are stars, billions of them.

91
00:05:53,440 --> 00:05:56,960
So many, in fact, that it sort of
makes your brain hurt a bit.

92
00:05:56,960 --> 00:05:59,360
So, how do stars work?

93
00:06:01,160 --> 00:06:04,680
There are hundreds of billions
of stars in our galaxy alone.

94
00:06:04,680 --> 00:06:09,400
And they come in a dazzling variety
of colour, size and brightness.

95
00:06:09,400 --> 00:06:15,240
All stars, including our own Sun,
work in roughly the same way.

96
00:06:15,240 --> 00:06:20,200
They harness the power
of nuclear reactions -

97
00:06:20,200 --> 00:06:22,960
specifically, a process
we call fusion.

98
00:06:22,960 --> 00:06:26,600
Humans have also
harnessed nuclear power,

99
00:06:26,600 --> 00:06:29,040
but this is fission, not fusion.

100
00:06:29,040 --> 00:06:34,200
Fission is the splitting of atoms
to unleash vast amounts of energy,

101
00:06:34,200 --> 00:06:36,600
as in the original atomic bomb.

102
00:06:38,160 --> 00:06:41,360
But during fusion,
the opposite occurs.

103
00:06:41,360 --> 00:06:43,400
In the deep core of a star,

104
00:06:43,400 --> 00:06:48,360
hydrogen atoms collide
and fuse together, creating helium.

105
00:06:48,360 --> 00:06:51,560
These shiny new helium atoms
have slightly less mass

106
00:06:51,560 --> 00:06:54,200
than the hydrogen atoms
that created them.

107
00:06:54,200 --> 00:06:59,120
And this lost mass is
released as gamma radiation.

108
00:06:59,120 --> 00:07:04,720
This is explained by Einstein's
famous E = mc2 equation,

109
00:07:04,720 --> 00:07:08,320
which states that mass and energy
are effectively

110
00:07:08,320 --> 00:07:09,720
two sides of the same coin.

111
00:07:09,720 --> 00:07:12,480
In fact, if you could measure it
accurately enough,

112
00:07:12,480 --> 00:07:16,080
a hot cup of tea would weigh more
than an identical cold one,

113
00:07:16,080 --> 00:07:19,080
because it has more energy.

114
00:07:21,880 --> 00:07:24,440
Mmm. Now, just try to imagine this -

115
00:07:24,440 --> 00:07:28,960
every single second,
600 million tons of hydrogen collide

116
00:07:28,960 --> 00:07:32,120
inside the Sun,
and this creates new helium,

117
00:07:32,120 --> 00:07:35,480
and that releases
four million tons of energy.

118
00:07:35,480 --> 00:07:39,840
Or, to put it another way,
while I've been speaking,

119
00:07:39,840 --> 00:07:45,360
the Sun has lost the equivalent of
500 aircraft carriers in mass.

120
00:07:45,360 --> 00:07:49,040
Can I have
another cup of tea, please?

121
00:07:49,040 --> 00:07:54,080
Fusion is the beating heart
of all stars in the universe.

122
00:07:54,080 --> 00:07:57,360
And it's pretty handy for us
down here on Earth,

123
00:07:57,360 --> 00:08:00,560
as it provides
the visible light we depend on.

124
00:08:00,560 --> 00:08:03,720
Wow! Cool! Ow! My frickin' eyes!

125
00:08:03,720 --> 00:08:08,200
In fact, the light from the Sun only
takes eight minutes to reach us,

126
00:08:08,200 --> 00:08:10,080
but can be up to
a million years old,

127
00:08:10,080 --> 00:08:14,600
as it takes so long to journey
out of the Sun's dense interior.

128
00:08:14,600 --> 00:08:16,280
Mmm.

129
00:08:16,280 --> 00:08:19,640
Makes you think about sunbathing
in a whole new light, really.

130
00:08:19,640 --> 00:08:23,360
But anyway, stars are actually
just like you and me.

131
00:08:23,360 --> 00:08:26,200
Apart from them being
great flaming balls of fire.

132
00:08:26,200 --> 00:08:30,320
But like you and me, they are born,
they live and then they die -

133
00:08:30,320 --> 00:08:32,640
often with spectacular results.

134
00:08:32,640 --> 00:08:36,960
So, what happens when a star dies?

135
00:08:38,480 --> 00:08:43,800
As the Sun grows old, it will become
smaller, brighter and hotter.

136
00:08:47,160 --> 00:08:50,120
In three billion years,
it will be 40% brighter,

137
00:08:50,120 --> 00:08:52,640
and so hot,
it will evaporate our oceans.

138
00:08:55,040 --> 00:08:58,720
In another two billion years,
its core will collapse,

139
00:08:58,720 --> 00:09:01,240
and it will expand
to form a red giant -

140
00:09:01,240 --> 00:09:03,720
so massive, it will
engulf the Earth.

141
00:09:05,480 --> 00:09:09,000
When this red giant Sun
finally dies,

142
00:09:09,000 --> 00:09:14,960
it will throw off most of its mass
in a huge nebula of gas and dust.

143
00:09:14,960 --> 00:09:19,880
And all that will remain is
a dense core, called a white dwarf,

144
00:09:19,880 --> 00:09:23,600
which will slowly cool
over billions of years.

145
00:09:25,680 --> 00:09:29,440
However, not all stars
behave like the Sun.

146
00:09:30,960 --> 00:09:35,600
Other stars, called red dwarfs,
use their fuel so economically,

147
00:09:35,600 --> 00:09:38,680
they may last for
a trillion years or more.

148
00:09:38,680 --> 00:09:41,280
And at the other end of
the spectrum, the biggest stars,

149
00:09:41,280 --> 00:09:46,600
hundreds of times bigger than the
Sun, burn their fuel very quickly -

150
00:09:46,600 --> 00:09:48,880
they live fast and die young.

151
00:09:50,720 --> 00:09:52,960
It's these biggest stars
that produce

152
00:09:52,960 --> 00:09:55,200
the strangest results when they die.

153
00:09:55,200 --> 00:10:00,520
They literally go out with a bang,
exploding in violent supernovas,

154
00:10:00,520 --> 00:10:03,960
amongst the most spectacular events
in the universe.

155
00:10:08,360 --> 00:10:11,040
Supernova explosions
might be spectacular,

156
00:10:11,040 --> 00:10:14,080
but they could also be
very dangerous for us humans.

157
00:10:14,080 --> 00:10:17,520
If one occurred within
25 light years of earth,

158
00:10:17,520 --> 00:10:20,240
it would kill all life
on the planet.

159
00:10:20,240 --> 00:10:22,400
The ozone layer would be destroyed,

160
00:10:22,400 --> 00:10:24,920
bathing us in lethal doses
of radiation.

161
00:10:24,920 --> 00:10:28,800
Probably best to stay indoors
if this happens.

162
00:10:28,800 --> 00:10:32,440
These supernova explosions
can have two outcomes.

163
00:10:32,440 --> 00:10:35,920
Firstly, the material left behind
can collapse

164
00:10:35,920 --> 00:10:38,600
to form a superdense neutron star.

165
00:10:38,600 --> 00:10:43,560
A neutron star is only about
the size of a city like London,

166
00:10:43,560 --> 00:10:46,400
but can weigh
twice as much as our Sun.

167
00:10:46,400 --> 00:10:49,200
But when the largest stars
of all explode,

168
00:10:49,200 --> 00:10:52,440
the remaining neutron core
is compressed

169
00:10:52,440 --> 00:10:55,160
in a fraction of a second
into a singularity.

170
00:10:57,280 --> 00:11:00,840
This is infinitely small,
smaller even than an atom,

171
00:11:00,840 --> 00:11:03,680
and its gravitational pull is
so massive,

172
00:11:03,680 --> 00:11:06,600
nothing can escape from it,
not even light.

173
00:11:06,600 --> 00:11:10,680
This is a stellar black hole.

174
00:11:10,680 --> 00:11:15,240
They are the strangest and most
destructive forces in nature -

175
00:11:15,240 --> 00:11:20,000
anything straying near a black hole
will be sucked in and destroyed.

176
00:11:22,800 --> 00:11:26,320
The universe sounds like
a pretty violent place,

177
00:11:26,320 --> 00:11:28,880
what with innocent stars exploding

178
00:11:28,880 --> 00:11:31,560
and being eaten
by rogue black holes.

179
00:11:31,560 --> 00:11:34,920
But if stars are continually
being destroyed,

180
00:11:34,920 --> 00:11:39,200
surely they're at risk of
becoming an endangered species?

181
00:11:39,200 --> 00:11:43,280
So, why aren't stars extinct?

182
00:11:44,800 --> 00:11:49,440
Across the universe, stars are dying
all the time, so you might think

183
00:11:49,440 --> 00:11:53,680
the night sky would slowly dim
as their lights are snuffed out.

184
00:11:53,680 --> 00:11:56,840
This isn't happening - but why?

185
00:11:56,840 --> 00:12:00,000
Well, the answer is recycling.

186
00:12:00,000 --> 00:12:02,840
All the mass and energy
that exists today

187
00:12:02,840 --> 00:12:05,120
was created during the Big Bang.

188
00:12:05,120 --> 00:12:09,160
And that's it,
that's all there'll ever be.

189
00:12:09,160 --> 00:12:13,640
Therefore, the universe needs
an efficient recycling scheme,

190
00:12:13,640 --> 00:12:16,160
and this relies on the humble atom.

191
00:12:17,880 --> 00:12:21,160
Atoms consist of
a tiny central nucleus

192
00:12:21,160 --> 00:12:24,960
surrounded by a cloud
of orbiting electrons.

193
00:12:28,640 --> 00:12:31,240
If an atom was the size
of a football pitch,

194
00:12:31,240 --> 00:12:35,800
the nucleus would be smaller
than a single blade of grass.

195
00:12:35,800 --> 00:12:39,000
The vast majority of an atom is
empty space,

196
00:12:39,000 --> 00:12:43,200
which means most of everything is
actually empty space.

197
00:12:47,080 --> 00:12:49,520
Atoms are also remarkably durable.

198
00:12:49,520 --> 00:12:54,800
No-one knows how long a single atom
can survive, but it could be

199
00:12:54,800 --> 00:12:58,920
as long as 100 billion,
trillion, trillion years.

200
00:13:01,280 --> 00:13:05,640
So long, in fact, that they can be
reused almost endlessly.

201
00:13:07,160 --> 00:13:12,000
When a star dies, most of its mass
is thrown out into space.

202
00:13:12,000 --> 00:13:16,200
This is when the recycling process
can begin.

203
00:13:16,200 --> 00:13:20,880
Over time, a dead star's atoms
condense and compact,

204
00:13:20,880 --> 00:13:26,000
until they become so hot,
they ignite, forming a new star.

205
00:13:27,600 --> 00:13:33,280
You could say this is
stellar reincarnation.

206
00:13:33,280 --> 00:13:37,600
Our Sun is thought to be
a third-generation star,

207
00:13:37,600 --> 00:13:40,840
so every atom here on Earth
has passed through

208
00:13:40,840 --> 00:13:43,000
two long-dead stars already.

209
00:13:43,000 --> 00:13:45,240
Not only that, but as atoms are

210
00:13:45,240 --> 00:13:48,200
constantly recycled here
on Earth too,

211
00:13:48,200 --> 00:13:52,400
millions of your atoms
once belonged to Shakespeare,

212
00:13:52,400 --> 00:13:54,960
Genghis Khan and Julius Caesar.

213
00:13:57,040 --> 00:14:00,920
It's weird to think that all of the
atoms in our body might once have

214
00:14:00,920 --> 00:14:06,160
been part of ancient stars
or planets, or even aliens.

215
00:14:06,160 --> 00:14:10,400
We are really just a series of
cosmic hand-me-downs.

216
00:14:10,400 --> 00:14:14,760
But how did the atoms
of some ancient star end up

217
00:14:14,760 --> 00:14:18,240
as part of you or me
or even a geranium?

218
00:14:18,240 --> 00:14:23,120
Just how did the solar system form?

219
00:14:23,120 --> 00:14:28,000
Our solar system began life
as a huge cloud of gas and dust

220
00:14:28,000 --> 00:14:30,240
called the solar nebula.

221
00:14:30,240 --> 00:14:32,400
About 4.6 billion years ago,

222
00:14:32,400 --> 00:14:37,240
this giant cloud started to coalesce
under the force of gravity.

223
00:14:37,240 --> 00:14:41,600
It also began to spin itself
into a flattened disk shape.

224
00:14:44,040 --> 00:14:47,600
At the centre of
this spinning nebula,

225
00:14:47,600 --> 00:14:52,000
99% of all its mass
compressed into a protosun.

226
00:14:52,000 --> 00:14:56,800
This was a baby star,
not yet ready to ignite.

227
00:14:56,800 --> 00:15:02,640
All the remaining matter in the
huge cloud around the new protosun

228
00:15:02,640 --> 00:15:05,640
slowly formed itself into rings.

229
00:15:05,640 --> 00:15:10,320
These rings would eventually
become the planets we know today.

230
00:15:10,320 --> 00:15:13,840
Close to the protosun,
the higher temperatures meant

231
00:15:13,840 --> 00:15:17,520
only rocky materials and metals
could survive the heat.

232
00:15:17,520 --> 00:15:21,320
Therefore, the closest planets
to the Sun -

233
00:15:21,320 --> 00:15:24,200
Mercury, Venus, Earth and Mars -

234
00:15:24,200 --> 00:15:27,400
are mostly composed of
heavier elements, like iron.

235
00:15:27,400 --> 00:15:32,040
But in the distant, colder regions,
big lumps of rock and ice managed

236
00:15:32,040 --> 00:15:34,960
to capture vast clouds of gas
around them.

237
00:15:34,960 --> 00:15:42,120
These would become the gas giants -
Jupiter, Saturn, Uranus and Neptune.

238
00:15:42,120 --> 00:15:45,360
Eventually, the protosun
became dense enough

239
00:15:45,360 --> 00:15:48,920
to begin fusion in its core,
and - drum roll, please -

240
00:15:48,920 --> 00:15:52,800
our Sun finally became
a fully-fledged star.

241
00:15:55,040 --> 00:15:58,520
But for Earth,
the story was really just beginning.

242
00:15:58,520 --> 00:16:03,080
When our planet was just 100 million
years old, a huge object

243
00:16:03,080 --> 00:16:05,640
the size of Mars collided with us,

244
00:16:05,640 --> 00:16:08,840
throwing vast amounts of rock
into space.

245
00:16:08,840 --> 00:16:13,600
This stray rock eventually
reassembled itself into the Moon.

246
00:16:13,600 --> 00:16:17,480
That huge collision
that formed the Moon

247
00:16:17,480 --> 00:16:22,400
also knocked the Earth off its axis
by 23.5 degrees,

248
00:16:22,400 --> 00:16:26,560
and that was very handy for us,
because that created the seasons.

249
00:16:26,560 --> 00:16:31,360
In its youth, Earth is thought to
have been volcanic and inhospitable.

250
00:16:31,360 --> 00:16:35,320
But over time, it came to be
covered in a vast ocean of water,

251
00:16:35,320 --> 00:16:38,600
perhaps carried here by
icy comets and asteroids.

252
00:16:38,600 --> 00:16:43,920
However it got here, it was this
water that allowed life to thrive.

253
00:16:43,920 --> 00:16:46,880
We all know our place
in the solar system -

254
00:16:46,880 --> 00:16:48,960
the third rock from the Sun,

255
00:16:48,960 --> 00:16:52,840
one of eight planets
orbiting our nearest star.

256
00:16:52,840 --> 00:16:57,280
But, if there is anyone
or anything else out there,

257
00:16:57,280 --> 00:17:00,080
how will they be able to find us?

258
00:17:00,080 --> 00:17:01,760
Where are we?

259
00:17:01,760 --> 00:17:05,600
If there's some sort of
intergalactic postal system,

260
00:17:05,600 --> 00:17:10,320
then our address might look
something like this.

261
00:17:10,320 --> 00:17:13,920
Planet Earth,
the solar system, local fluff,

262
00:17:13,920 --> 00:17:18,560
the Milky Way, local group,
local supercluster, the universe.

263
00:17:21,920 --> 00:17:23,880
For most of human history,

264
00:17:23,880 --> 00:17:28,720
we have placed our planet slap bang
at the centre of the universe.

265
00:17:32,320 --> 00:17:36,320
But since astronomer
Nicolaus Copernicus realised that

266
00:17:36,320 --> 00:17:38,800
the Earth actually orbits the Sun,

267
00:17:38,800 --> 00:17:42,920
every new discovery
has highlighted the fact

268
00:17:42,920 --> 00:17:47,240
that we're not particularly special
at all.

269
00:17:47,240 --> 00:17:51,920
Actually, it seems as though we live
in a rather unimportant cul-de-sac,

270
00:17:51,920 --> 00:17:53,920
in the grand scheme of things.

271
00:17:53,920 --> 00:17:58,800
We are just an insignificant dot
in the vastness of space.

272
00:17:58,800 --> 00:18:00,720
But don't get depressed about this -

273
00:18:00,720 --> 00:18:04,680
because that assumption is, in fact,
the cornerstone of modern astronomy,

274
00:18:04,680 --> 00:18:08,800
what is sometimes known as
the cosmological principle.

275
00:18:08,800 --> 00:18:11,640
The cosmological principle
states that,

276
00:18:11,640 --> 00:18:16,080
when viewed
on a sufficiently large scale,

277
00:18:16,080 --> 00:18:18,840
the universe actually looks
the same,

278
00:18:18,840 --> 00:18:20,680
in all places
and in all directions.

279
00:18:23,080 --> 00:18:27,880
So when we look out into space
at the other stars and galaxies,

280
00:18:27,880 --> 00:18:30,280
they might seem haphazard
and irregular,

281
00:18:30,280 --> 00:18:33,600
but in fact, they are all laid out
in a very symmetrical way.

282
00:18:39,480 --> 00:18:41,760
So, if we send out
a galactic calling card,

283
00:18:41,760 --> 00:18:45,680
there's a distinct possibility
that aliens wouldn't be able

284
00:18:45,680 --> 00:18:50,040
to find us, even with directions,
due to the cosmological principle

285
00:18:50,040 --> 00:18:52,320
and the sheer size of the universe.

286
00:19:02,640 --> 00:19:04,880
We humans are obsessed with the idea

287
00:19:04,880 --> 00:19:07,800
that there could be
other life in the universe.

288
00:19:07,800 --> 00:19:11,680
From books to films to people
who claim to have been abducted,

289
00:19:11,680 --> 00:19:15,920
we all have our own take
on what else might be out there.

290
00:19:18,120 --> 00:19:22,080
But is there any fact
behind any of this fiction?

291
00:19:23,880 --> 00:19:25,960
Or are we alone?

292
00:19:27,880 --> 00:19:31,720
If there is life out there,
then scientists believe

293
00:19:31,720 --> 00:19:35,400
it will probably be found
in the Goldilocks zone.

294
00:19:35,400 --> 00:19:38,000
This has nothing to do with
bears and porridge,

295
00:19:38,000 --> 00:19:41,600
but describes a planet
that's just right,

296
00:19:41,600 --> 00:19:43,960
the perfect distance from a star

297
00:19:43,960 --> 00:19:47,760
and warm enough for water
to be found on its surface.

298
00:19:47,760 --> 00:19:51,520
In our solar system,
only the Earth fits the bill.

299
00:19:51,520 --> 00:19:55,840
Our nearest neighbours,
Venus and Mars, are just too close

300
00:19:55,840 --> 00:19:57,920
or too far away from the Sun.

301
00:19:57,920 --> 00:20:01,360
However, this doesn't
mean there couldn't be life

302
00:20:01,360 --> 00:20:03,840
somewhere else in our solar system.

303
00:20:03,840 --> 00:20:07,680
It's just that it would probably be
simple bacteria,

304
00:20:07,680 --> 00:20:10,360
and unlikely to provide
intelligent conversation.

305
00:20:10,360 --> 00:20:12,760
I can't say I have much confidence
in your opinion!

306
00:20:12,760 --> 00:20:16,320
There's bacteria here on Earth that
can live in poisonous environments,

307
00:20:16,320 --> 00:20:20,080
suggesting creatures
on other worlds may evolve

308
00:20:20,080 --> 00:20:22,440
in ways we can barely imagine.

309
00:20:22,440 --> 00:20:25,880
And instead of being carbon-based,
as on Earth,

310
00:20:25,880 --> 00:20:28,400
life elsewhere could have evolved

311
00:20:28,400 --> 00:20:31,200
using other elements,
such as silicon.

312
00:20:31,200 --> 00:20:34,480
Such creatures could withstand
much higher temperatures than us,

313
00:20:34,480 --> 00:20:39,240
so planets too hot for humans
could still support life.

314
00:20:39,240 --> 00:20:41,240
In fact, the hunt for life

315
00:20:41,240 --> 00:20:45,200
beyond our solar system is
already in full swing.

316
00:20:45,200 --> 00:20:50,400
NASA's Kepler Mission has identified
over 1,000 potential planets

317
00:20:50,400 --> 00:20:53,760
worthy of more investigation,
and of these,

318
00:20:53,760 --> 00:20:57,960
15 have been confirmed
as lying in the Goldilocks zone.

319
00:20:57,960 --> 00:21:03,200
In the 1960s, a scientist named
Frank Drake developed an equation

320
00:21:03,200 --> 00:21:08,000
designed to calculate the
number of other civilizations

321
00:21:08,000 --> 00:21:09,640
in our own galaxy, the Milky Way.

322
00:21:09,640 --> 00:21:14,440
These factors include the rate of
new stars forming in the galaxy,

323
00:21:14,440 --> 00:21:17,720
the proportion of these stars
that have planets,

324
00:21:17,720 --> 00:21:21,920
the percentage of these planets
that are habitable,

325
00:21:21,920 --> 00:21:27,120
and the length of time
any civilization might last.

326
00:21:29,560 --> 00:21:32,200
At the moment,
we can only hypothesise

327
00:21:32,200 --> 00:21:34,240
about most of these numbers,

328
00:21:34,240 --> 00:21:38,200
but conservative estimates
suggest that there might be

329
00:21:38,200 --> 00:21:41,840
900 advanced civilizations
in the Milky Way at any one time,

330
00:21:41,840 --> 00:21:45,600
and our galaxy is
just one of billions.

331
00:21:45,600 --> 00:21:49,800
So, there's a very good chance
that we're not alone.

332
00:21:49,800 --> 00:21:53,440
Unfortunately, the distances
involved are so huge

333
00:21:53,440 --> 00:21:57,280
that we may never make contact
with anybody out there.

334
00:21:57,280 --> 00:22:00,480
However, that doesn't mean
our nearest neighbours

335
00:22:00,480 --> 00:22:05,680
haven't already discovered us,
or at least our taste in pop music.

336
00:22:05,680 --> 00:22:11,680
So, just what is
Madonna doing in space?

337
00:22:11,680 --> 00:22:16,040
The furthest any human has ventured
from Earth is to our own Moon,

338
00:22:16,040 --> 00:22:19,560
which in space terms is
barely beyond our own doorstep.

339
00:22:19,560 --> 00:22:21,680
Look at me, I'm flying!

340
00:22:21,680 --> 00:22:24,160
Oh, no, wait, maybe not.

341
00:22:24,160 --> 00:22:28,000
However, humanity has in fact
travelled much further than that,

342
00:22:28,000 --> 00:22:32,200
far beyond the furthest reaches
of our solar system.

343
00:22:32,200 --> 00:22:37,080
Madonna, Hitler and the Dalai Lama -

344
00:22:37,080 --> 00:22:40,360
they're all out there in deep space,

345
00:22:40,360 --> 00:22:42,960
thanks to the power of radio waves.

346
00:22:44,680 --> 00:22:48,600
Since the early 20th century,
our broadcasts have

347
00:22:48,600 --> 00:22:54,640
leaked out into space, almost like a
three-dimensional ripple on a pond.

348
00:22:56,400 --> 00:22:59,840
All electromagnetic waves,
including radio waves,

349
00:22:59,840 --> 00:23:01,560
travel at the same speed -

350
00:23:01,560 --> 00:23:08,600
some 300 million metres per second,
what we call the speed of light.

351
00:23:08,600 --> 00:23:13,400
Therefore, TV and radio signals
transmitted 50 years ago have

352
00:23:13,400 --> 00:23:16,560
journeyed 50 light years
into space by now,

353
00:23:16,560 --> 00:23:20,960
ample time to have reached
hundreds of neighbouring stars.

354
00:23:22,720 --> 00:23:26,360
So, if there are alien civilisations
out there listening in,

355
00:23:26,360 --> 00:23:29,640
the first they might know
about life on Earth is

356
00:23:29,640 --> 00:23:33,800
a speech by Martin Luther King,
or an episode of EastEnders,

357
00:23:33,800 --> 00:23:35,760
or even what I'm saying now.

358
00:23:35,760 --> 00:23:39,560
But it's not just us
broadcasting radio waves.

359
00:23:39,560 --> 00:23:44,480
They're also being emitted by
galaxies and even black holes,

360
00:23:44,480 --> 00:23:46,880
which can be a bit confusing.

361
00:23:46,880 --> 00:23:50,440
In 1967, a young Cambridge
astronomy student noticed

362
00:23:50,440 --> 00:23:54,120
a strange radio signal from space

363
00:23:54,120 --> 00:23:59,920
that pulsated exactly
every 1.337 seconds.

364
00:23:59,920 --> 00:24:03,080
It was so precise and regular,
it didn't appear natural.

365
00:24:03,080 --> 00:24:09,600
Therefore, the object emitting
the signal was dubbed LGM-1.

366
00:24:09,600 --> 00:24:13,920
LGM stood for Little Green Men.

367
00:24:13,920 --> 00:24:17,400
However, it wasn't a friendly alien,
but a pulsar,

368
00:24:17,400 --> 00:24:20,160
one of the strangest
natural phenomena in the universe.

369
00:24:20,160 --> 00:24:25,160
Pulsars are spinning neutron stars
that emit beams of radiation -

370
00:24:25,160 --> 00:24:29,800
almost like
intergalactic lighthouses.

371
00:24:29,800 --> 00:24:32,000
When you're just sitting at home,

372
00:24:32,000 --> 00:24:36,360
it's comforting to think that the
universe will be around for ever.

373
00:24:36,360 --> 00:24:38,520
But don't get too comfortable,

374
00:24:38,520 --> 00:24:43,520
because observations by cosmologists
suggest that it probably won't.

375
00:24:43,520 --> 00:24:47,560
So, the final question is
really very obvious -

376
00:24:47,560 --> 00:24:49,960
when will the universe end?

377
00:24:49,960 --> 00:24:54,400
Scientists have developed
three plausible theories

378
00:24:54,400 --> 00:24:57,880
as to what might happen
at the end of it all.

379
00:24:57,880 --> 00:25:01,560
Currently, the most likely is
the Big Chill.

380
00:25:01,560 --> 00:25:03,560
This is what will happen

381
00:25:03,560 --> 00:25:07,360
if the universe continues to
expand forever.

382
00:25:07,360 --> 00:25:11,240
Firstly, galaxies would
move away from each other.

383
00:25:11,240 --> 00:25:17,240
Then stars, and everything else,
would slowly drift apart and die.

384
00:25:17,240 --> 00:25:21,160
Finally, only giant black holes
will remain,

385
00:25:21,160 --> 00:25:25,160
each separated by distances
100 times greater

386
00:25:25,160 --> 00:25:28,520
than the current size
of our universe.

387
00:25:28,520 --> 00:25:32,520
Eventually, even these
black holes will evaporate,

388
00:25:32,520 --> 00:25:38,960
and the universe will be still,
cold and effectively dead.

389
00:25:38,960 --> 00:25:42,800
But before you start to panic,
you should probably know that

390
00:25:42,800 --> 00:25:45,600
we have around 100 trillion years
to wait

391
00:25:45,600 --> 00:25:50,360
before even the beginning of the
end, when stars start to disappear.

392
00:25:50,360 --> 00:25:53,240
And that's about 10,000 times
as long

393
00:25:53,240 --> 00:25:56,120
as the universe has existed already.

394
00:25:56,120 --> 00:25:58,720
And in any case, by that time,

395
00:25:58,720 --> 00:26:03,560
we humans will probably have
long since disappeared.

396
00:26:03,560 --> 00:26:07,960
Another possible end is called
the Big Rip.

397
00:26:07,960 --> 00:26:13,080
This would be the spectacular and
rapid destruction of the universe.

398
00:26:13,080 --> 00:26:16,160
But this will only occur if,
in the future,

399
00:26:16,160 --> 00:26:21,000
the mysterious force of dark energy
somehow supersedes gravity.

400
00:26:22,520 --> 00:26:25,920
First galaxies,
and then literally everything,

401
00:26:25,920 --> 00:26:29,080
right down to tiny atoms,
would be torn apart.

402
00:26:31,280 --> 00:26:34,280
Lastly, the Big Crunch.

403
00:26:36,160 --> 00:26:39,120
Not a breakfast cereal,
but what will happen

404
00:26:39,120 --> 00:26:42,680
if the Big Bang slows down
and is thrown into reverse.

405
00:26:44,560 --> 00:26:48,720
The universe would implode
in an almighty crash,

406
00:26:48,720 --> 00:26:50,920
crunching down to
a tiny singularity.

407
00:26:52,880 --> 00:26:56,800
It might seem morbid to think about
the death of the universe,

408
00:26:56,800 --> 00:27:01,000
but some scientists think that
the end might not be the end at all.

409
00:27:01,000 --> 00:27:04,880
Some believe that
there might even be

410
00:27:04,880 --> 00:27:08,040
parallel universes that exist
alongside our own.

411
00:27:08,040 --> 00:27:12,240
This is called multiverse theory.

412
00:27:12,240 --> 00:27:16,520
It could be that, beyond the
observable horizon of our universe,

413
00:27:16,520 --> 00:27:18,880
there are other universes out there,

414
00:27:18,880 --> 00:27:23,040
each existing separately like
the bubbles inside a Swiss cheese.

415
00:27:25,520 --> 00:27:29,400
Or perhaps other universes
occupy a space

416
00:27:29,400 --> 00:27:32,440
that we cannot even comprehend,

417
00:27:32,440 --> 00:27:38,200
existing in extra dimensions
we are, as yet, unaware of.

418
00:27:41,640 --> 00:27:46,040
The universe is magnificently,
mind-blowingly weird -

419
00:27:46,040 --> 00:27:50,320
so strange, in fact,
that we may never fully understand

420
00:27:50,320 --> 00:27:53,760
how or why it came to be,
or what dark energy is,

421
00:27:53,760 --> 00:27:57,000
or if we're the only sentient beings
in it.

422
00:27:57,000 --> 00:28:01,840
And every new discovery or theory by
beard-tugging boffins in white coats

423
00:28:01,840 --> 00:28:06,400
has the potential to completely
rewrite every book on the subject.

424
00:28:06,400 --> 00:28:09,400
So for now, I'm off
to contemplate my part

425
00:28:09,400 --> 00:28:13,080
in the grand cosmological scheme
of everything,

426
00:28:13,080 --> 00:28:16,480
knowing only one thing for certain -

427
00:28:16,480 --> 00:28:21,680
that my part - and yours,
I'm afraid - is very, very small.

428
00:28:35,680 --> 00:28:38,680
Subtitles by Red Bee Media Ltd

429
00:28:38,680 --> 00:28:41,800
E-mail subtitling@bbc.co.uk