1 00:00:25,320 --> 00:00:27,920 In the lives of every creature on Earth… 2 00:00:31,360 --> 00:00:32,840 …are echoes… 3 00:00:35,120 --> 00:00:38,880 …of events that occurred a long, long time ago. 4 00:00:43,680 --> 00:00:45,600 Events of unimaginable scale… 5 00:00:47,920 --> 00:00:49,280 and violent beauty… 6 00:00:51,440 --> 00:00:54,240 that connect all living things… 7 00:00:56,080 --> 00:00:58,760 …their every action and decision, 8 00:00:59,440 --> 00:01:00,920 their every heartbeat, 9 00:01:02,920 --> 00:01:05,720 to the grandest story ever told. 10 00:01:07,760 --> 00:01:12,400 This is a tale 13.8 billion years in the making… 11 00:01:14,680 --> 00:01:17,160 that has seen billions of stars 12 00:01:18,240 --> 00:01:20,040 and billions of worlds… 13 00:01:22,240 --> 00:01:25,440 live and die… 14 00:01:27,920 --> 00:01:30,520 to create the only planet we know of 15 00:01:32,200 --> 00:01:34,880 that is home to life. 16 00:01:39,200 --> 00:01:41,160 From the stardust that built us… 17 00:01:43,440 --> 00:01:46,640 to the cosmic ingredients that sustain us… 18 00:01:52,880 --> 00:01:56,400 and the starlight that powers it all, 19 00:01:57,960 --> 00:02:03,360 this is the story of our universe. 20 00:02:39,560 --> 00:02:40,800 East Africa. 21 00:02:46,160 --> 00:02:50,880 It's where life's most vital connection to the universe can be found. 22 00:02:55,000 --> 00:02:57,280 And a very special predator… 23 00:03:00,400 --> 00:03:02,640 named Wa Chini. 24 00:03:06,000 --> 00:03:10,160 Life for a cheetah is a never-ending search for food… 25 00:03:12,320 --> 00:03:13,680 for vital energy. 26 00:03:16,120 --> 00:03:21,400 And this is one of the hardest places on Earth for a predator to obtain it. 27 00:03:31,000 --> 00:03:34,240 The blistering sun has driven away nearly everything 28 00:03:34,320 --> 00:03:36,600 from these dry, desolate plains. 29 00:03:42,800 --> 00:03:46,840 Any creature that remains here struggles to survive. 30 00:03:51,480 --> 00:03:53,600 Wa Chini's sole focus… 31 00:03:57,360 --> 00:03:59,400 …the only thing driving her… 32 00:04:03,000 --> 00:04:04,080 …is hunger. 33 00:04:07,800 --> 00:04:10,800 This simple, primal impulse 34 00:04:10,880 --> 00:04:14,560 stems from a deep connection she has to her surroundings 35 00:04:15,520 --> 00:04:18,680 that extends beyond the Serengeti, 36 00:04:19,280 --> 00:04:20,840 beyond our planet 37 00:04:22,000 --> 00:04:23,640 to the universe itself. 38 00:04:29,720 --> 00:04:31,800 Every cell in Wa Chini's body… 39 00:04:34,160 --> 00:04:36,800 is linked to an ancient stream of energy… 40 00:04:39,920 --> 00:04:41,240 …connecting her life 41 00:04:42,920 --> 00:04:44,440 to the heart of a star. 42 00:04:49,840 --> 00:04:53,640 This unbroken stream spans vast reaches of space… 43 00:04:58,240 --> 00:05:02,160 and stretches back 13.8 billion years. 44 00:05:13,200 --> 00:05:18,280 Ancient energy that existed at the origin of our universe 45 00:05:20,120 --> 00:05:21,360 powers everything. 46 00:05:23,200 --> 00:05:24,480 Every planet. 47 00:05:26,320 --> 00:05:27,280 Every star. 48 00:05:30,480 --> 00:05:31,400 Every life. 49 00:05:40,200 --> 00:05:42,680 Wa Chini is hunting for energy… 50 00:05:46,080 --> 00:05:47,640 but not just for herself. 51 00:05:49,440 --> 00:05:52,040 A mother of two five-month-old cubs, 52 00:05:53,800 --> 00:05:56,880 she's desperate to feed her hungry family. 53 00:06:04,400 --> 00:06:07,520 It's dry season, and food is scarce. 54 00:06:08,920 --> 00:06:12,000 And yet, energy is more abundant than ever. 55 00:06:15,920 --> 00:06:17,880 It's just hiding in plain sight. 56 00:06:21,280 --> 00:06:25,680 The largest, brightest, hottest object in our solar system… 57 00:06:28,240 --> 00:06:29,240 the sun. 58 00:06:41,240 --> 00:06:45,600 Huge loops of searingly hot plasma erupt from its surface. 59 00:06:51,960 --> 00:06:57,560 Our sun blasts out the energy of four and a half trillion atomic bombs 60 00:06:57,640 --> 00:06:58,960 every second… 61 00:07:01,560 --> 00:07:04,280 sending more power to our planet in an hour 62 00:07:04,880 --> 00:07:07,960 than the entire world consumes in a year. 63 00:07:12,520 --> 00:07:16,240 But as impressive as this gigantic fireball is… 64 00:07:18,680 --> 00:07:21,520 Wa Chini cannot eat sunlight. 65 00:07:23,760 --> 00:07:26,320 She only eats things that run… 66 00:07:29,280 --> 00:07:30,520 like gazelle. 67 00:07:38,760 --> 00:07:41,440 Her spotted coat provides camouflage, 68 00:07:42,480 --> 00:07:44,760 essential for stalking prey. 69 00:07:58,200 --> 00:08:03,640 With few places to hide, getting closer isn't an option. 70 00:08:15,640 --> 00:08:18,920 Luckily, Wa Chini has a trick up her sleeve. 71 00:08:26,280 --> 00:08:29,800 Cheetah are the fastest animals on land. 72 00:08:32,160 --> 00:08:35,360 From zero to a hundred in just three seconds… 73 00:08:37,480 --> 00:08:40,800 but gazelles are a pretty close second. 74 00:08:45,080 --> 00:08:47,280 Wa Chini uses up a lot of energy… 75 00:08:59,960 --> 00:09:01,280 but gains nothing. 76 00:09:05,400 --> 00:09:08,880 An adult cheetah can survive for over a week without a meal. 77 00:09:12,600 --> 00:09:17,120 But cubs, they can go no longer than a few days. 78 00:09:24,080 --> 00:09:29,360 And these two are getting very, very hungry. 79 00:09:37,840 --> 00:09:40,920 Hunting at such great speeds is incredibly depleting. 80 00:09:43,200 --> 00:09:46,480 Wa Chini's energy reserves are now dangerously low. 81 00:09:50,680 --> 00:09:54,200 It will be hours before she has the strength to hunt again. 82 00:10:00,200 --> 00:10:04,000 Wa Chini and her cubs are running on empty. 83 00:10:22,040 --> 00:10:25,400 Animals all over the planet fight the same ongoing battle 84 00:10:26,480 --> 00:10:27,760 between consuming… 85 00:10:31,320 --> 00:10:32,800 and using energy. 86 00:10:38,160 --> 00:10:40,000 No matter your strategy, 87 00:10:40,080 --> 00:10:41,960 be it fast or slow, 88 00:10:47,080 --> 00:10:50,000 your next meal is never guaranteed. 89 00:10:59,280 --> 00:11:03,560 Hunger is something all of us must overcome. 90 00:11:12,600 --> 00:11:14,920 Having recovered from her last chase, 91 00:11:15,920 --> 00:11:18,520 Wa Chini is looking for her next opportunity. 92 00:11:22,920 --> 00:11:24,400 Like all cheetah mothers, 93 00:11:26,040 --> 00:11:27,920 she's parenting solo. 94 00:11:31,680 --> 00:11:33,600 To keep her young cubs well-fed, 95 00:11:34,320 --> 00:11:36,560 she should make a kill every day. 96 00:11:38,240 --> 00:11:40,920 But it's taken her so long to recover 97 00:11:42,240 --> 00:11:44,080 that the sun is now setting. 98 00:11:53,720 --> 00:11:55,280 As the light fades, 99 00:11:56,480 --> 00:11:58,760 so does this family's hopes of a meal. 100 00:12:05,880 --> 00:12:07,360 As Earth rotates… 101 00:12:09,960 --> 00:12:15,200 the Serengeti turns away from the sun and into darkness. 102 00:12:21,520 --> 00:12:24,760 It's a powerful reminder of life's connection to the sun. 103 00:12:29,200 --> 00:12:32,840 Our story is the sun's story. 104 00:12:35,160 --> 00:12:36,520 Long, long ago… 105 00:12:39,760 --> 00:12:44,440 …our solar system was even colder and darker than it is today. 106 00:12:56,880 --> 00:13:01,960 And yet, these were the perfect conditions for the birth of a star. 107 00:13:05,200 --> 00:13:07,760 At temperatures close to absolute zero, 108 00:13:08,640 --> 00:13:11,840 the force of gravity began pulling dust and gas together… 109 00:13:14,240 --> 00:13:15,760 …into a massive cloud. 110 00:13:22,880 --> 00:13:24,720 The cloud collapsed inwards, 111 00:13:24,800 --> 00:13:28,240 crushing itself into a glowing hot ball of gas. 112 00:13:32,240 --> 00:13:33,600 A protostar. 113 00:13:40,880 --> 00:13:45,160 Like Wa Chini, this star in the making had a ferocious hunger… 114 00:13:48,000 --> 00:13:51,320 pulling in so much gas that jets of hot matter 115 00:13:52,360 --> 00:13:54,760 were propelled from its poles, 116 00:13:56,280 --> 00:13:58,960 stretching out light years into space. 117 00:14:02,280 --> 00:14:08,320 The infant star continued to grow for 30 million years… 118 00:14:19,440 --> 00:14:20,680 …until finally, 119 00:14:21,880 --> 00:14:26,200 it became hot enough to generate power all on its own. 120 00:14:29,360 --> 00:14:30,320 Our sun. 121 00:14:33,280 --> 00:14:37,160 Its golden rays have now shone brilliantly and steadily… 122 00:14:39,200 --> 00:14:41,640 for 4.6 billion years. 123 00:14:47,400 --> 00:14:51,960 It's just one star in a galaxy of billions. 124 00:14:57,360 --> 00:15:00,760 And yet, it is a most special one… 125 00:15:03,120 --> 00:15:06,080 because it is the one that delivers heat and light… 126 00:15:08,440 --> 00:15:10,640 to this incredible, vibrant planet. 127 00:15:23,680 --> 00:15:27,760 Every living thing in the Serengeti depends on the sun for its energy. 128 00:15:29,800 --> 00:15:34,080 Wa Chini's cubs are drained, beyond hungry now. 129 00:15:35,200 --> 00:15:37,280 They need to eat today. 130 00:15:39,000 --> 00:15:44,160 But all Wa Chini can provide this morning is precious TLC. 131 00:15:45,800 --> 00:15:47,520 In this parched land, 132 00:15:48,560 --> 00:15:52,440 our sun both gives and takes. 133 00:15:53,640 --> 00:15:57,120 Its fierce energy is what life needs. 134 00:15:58,320 --> 00:16:02,280 But it also has the power to destroy. 135 00:16:06,600 --> 00:16:12,320 It was never going to be easy living this close to a giant nuclear reactor. 136 00:16:21,280 --> 00:16:24,160 To understand the source of this unbearable heat, 137 00:16:25,360 --> 00:16:28,040 we must peer into the inferno… 138 00:16:37,240 --> 00:16:40,240 …beneath the outer layers of bubbling hot plasma… 139 00:16:45,960 --> 00:16:50,120 650 thousand kilometers down… 140 00:16:54,920 --> 00:16:57,120 to the core of our sun. 141 00:17:00,840 --> 00:17:04,840 Our star's heart would seem surprisingly calm… 142 00:17:07,040 --> 00:17:10,880 but on an atomic level, it's pure chaos. 143 00:17:14,360 --> 00:17:18,280 This is the hottest part of our solar system. 144 00:17:21,000 --> 00:17:24,440 Temperatures here reach 15 million degrees Celsius… 145 00:17:27,640 --> 00:17:32,200 creating the conditions for an event that can happen almost nowhere else. 146 00:17:36,600 --> 00:17:39,560 Atoms collide at high speed and fuse… 147 00:17:45,160 --> 00:17:47,000 …releasing pure energy. 148 00:17:54,760 --> 00:17:59,040 This process is called nuclear fusion 149 00:17:59,880 --> 00:18:02,320 and is what makes our sun shine. 150 00:18:06,480 --> 00:18:11,120 In fact, it's what powers all the stars in our universe. 151 00:18:15,200 --> 00:18:20,320 This energy released by stars can be traced back to the beginning of time… 152 00:18:25,480 --> 00:18:27,240 when there was no matter, 153 00:18:27,840 --> 00:18:32,080 and all that existed in the entire universe was energy. 154 00:18:35,120 --> 00:18:39,000 And every bit of it lives on in our universe today. 155 00:18:46,600 --> 00:18:48,440 As sunlight hits the Serengeti, 156 00:18:49,880 --> 00:18:53,280 energy that's been flowing for 13.8 billion years 157 00:18:54,880 --> 00:18:58,240 finds its way to Wa Chini and her cubs 158 00:18:59,040 --> 00:19:03,240 and continues its journey through their environment. 159 00:19:04,880 --> 00:19:08,080 It is never created or destroyed. 160 00:19:09,000 --> 00:19:12,840 It is simply transformed endlessly. 161 00:19:14,240 --> 00:19:18,840 But Wa Chini and her Cubs can only access this energy in one form… 162 00:19:23,560 --> 00:19:24,720 meat. 163 00:19:33,800 --> 00:19:36,400 And there are rival predators out here… 164 00:19:39,200 --> 00:19:43,480 who could snatch not just her food but her cubs as well. 165 00:19:58,080 --> 00:19:59,960 If they don't feed soon, 166 00:20:01,000 --> 00:20:02,480 they will die regardless. 167 00:20:23,480 --> 00:20:26,560 It's a meager snack, but after two days without food, 168 00:20:27,080 --> 00:20:28,480 it's a lifesaver. 169 00:20:32,480 --> 00:20:35,840 But more than 10% of cheetah kills are stolen. 170 00:20:40,280 --> 00:20:43,920 Wa Chini must defend every scrap of energy she captures… 171 00:20:47,840 --> 00:20:49,880 …because when energy is scarce, 172 00:20:50,720 --> 00:20:53,160 competition is fierce. 173 00:20:57,080 --> 00:21:00,920 Wa Chini's struggle to survive and sustain her family is repeated 174 00:21:01,400 --> 00:21:03,440 day after day… 175 00:21:06,040 --> 00:21:07,840 …month after month. 176 00:21:17,880 --> 00:21:21,520 Every meal is a fight. 177 00:21:27,320 --> 00:21:30,440 In the battle between using and acquiring energy… 178 00:21:32,560 --> 00:21:35,080 Wa Chini is only just breaking even. 179 00:21:40,400 --> 00:21:45,600 Dry season on the Serengeti is defined by constant hunger. 180 00:21:52,040 --> 00:21:53,760 But change is in the air. 181 00:21:55,560 --> 00:22:00,680 The sun's heat has pulled what moisture there is high into the sky. 182 00:22:05,080 --> 00:22:06,560 And what goes up 183 00:22:07,880 --> 00:22:11,120 must eventually come down. 184 00:22:14,680 --> 00:22:17,440 Rains sweep across the plains 185 00:22:18,360 --> 00:22:20,880 and bring dry season to an end. 186 00:22:26,640 --> 00:22:28,280 As the clouds clear, 187 00:22:29,960 --> 00:22:31,760 a glimmer of hope appears. 188 00:22:44,120 --> 00:22:47,400 A single blade of grass cannot feed Wa Chini's family… 189 00:22:49,920 --> 00:22:51,840 but deep within its cells 190 00:22:52,360 --> 00:22:54,480 lies the answer to their hunger. 191 00:23:06,520 --> 00:23:09,080 Here, there's a hidden world. 192 00:23:15,000 --> 00:23:21,600 Microscopic stacks called grana bask in the warm rays from the sun. 193 00:23:32,800 --> 00:23:37,600 Their surface is covered with a forest of tiny, light-harvesting proteins 194 00:23:38,880 --> 00:23:42,720 that capture energy from our nearest star. 195 00:23:47,800 --> 00:23:50,720 They're packed with the green pigment chlorophyll, 196 00:23:52,400 --> 00:23:55,040 which absorbs rays of light. 197 00:24:00,000 --> 00:24:02,240 Through the magic of photosynthesis… 198 00:24:12,640 --> 00:24:15,200 water combines with carbon dioxide… 199 00:24:18,320 --> 00:24:21,360 and sunbeams are spun into sugar. 200 00:24:38,440 --> 00:24:43,160 In a matter of days, the once parched plains are painted green. 201 00:24:51,480 --> 00:24:55,440 Billions of blades of grass now soak up the boundless sunlight. 202 00:25:00,480 --> 00:25:04,960 And the universe's energy becomes embedded in the landscape. 203 00:25:10,400 --> 00:25:11,920 There's only one problem. 204 00:25:14,480 --> 00:25:17,000 Cheetahs can't eat grass. 205 00:25:22,920 --> 00:25:25,800 But far away in the northern woodlands, 206 00:25:27,080 --> 00:25:28,280 there are beasts… 207 00:25:30,360 --> 00:25:31,440 that do. 208 00:25:34,080 --> 00:25:36,080 Hundreds of thousands of them. 209 00:25:38,880 --> 00:25:40,120 Wildebeest. 210 00:25:43,120 --> 00:25:48,320 They have wide mouths, flexible lips, and four stomachs 211 00:25:49,040 --> 00:25:51,920 that are perfectly adapted to eating grass. 212 00:26:01,080 --> 00:26:03,880 The massive herds are constantly on the move 213 00:26:05,800 --> 00:26:07,640 in search of fresh grazing. 214 00:26:11,000 --> 00:26:14,080 To find the grass, they follow the rain. 215 00:26:17,800 --> 00:26:19,120 Driven, like all of us… 216 00:26:21,280 --> 00:26:22,320 by hunger. 217 00:26:32,000 --> 00:26:34,520 But if there is one rule in the Serengeti, 218 00:26:36,200 --> 00:26:39,080 it's that food never comes easy. 219 00:26:48,000 --> 00:26:49,480 The Mara River… 220 00:26:52,120 --> 00:26:55,160 home to some of the largest crocodiles on Earth. 221 00:26:59,080 --> 00:27:00,840 It's a serious roadblock 222 00:27:00,920 --> 00:27:04,080 in the wildebeests' quest for vital energy. 223 00:27:16,160 --> 00:27:19,760 To the south, Wa Chini spends every available moment 224 00:27:19,840 --> 00:27:22,200 scouring the plains for something edible. 225 00:27:33,000 --> 00:27:36,000 After six months surviving on a meager diet, 226 00:27:37,680 --> 00:27:40,160 one of her cubs has managed to grow bigger… 227 00:27:47,720 --> 00:27:50,760 …and is even learning some hunting skills of her own. 228 00:27:57,000 --> 00:28:01,200 But the other cub is nowhere to be seen. 229 00:28:07,400 --> 00:28:10,800 Just five percent of cheetah cubs make it into adulthood. 230 00:28:13,680 --> 00:28:17,600 Most lose their lives to hungry lions and hyenas. 231 00:28:25,200 --> 00:28:28,880 This cub's future is far from guaranteed… 232 00:28:32,880 --> 00:28:36,000 even when energy is tantalizingly close. 233 00:28:42,400 --> 00:28:44,360 Amassed on the banks of the Mara, 234 00:28:45,240 --> 00:28:48,160 the wildebeest have nowhere to go but forward. 235 00:28:52,080 --> 00:28:55,160 But someone needs to be first. 236 00:29:34,880 --> 00:29:37,080 One and a half million wildebeest 237 00:29:38,040 --> 00:29:40,560 make this journey each year. 238 00:29:44,280 --> 00:29:48,560 And here, the battle between using and consuming energy… 239 00:29:50,680 --> 00:29:52,680 plays out on an epic scale. 240 00:30:08,120 --> 00:30:10,840 For those lucky enough to make it across, 241 00:30:12,400 --> 00:30:14,000 this is only the beginning. 242 00:30:23,200 --> 00:30:25,880 Now, they must travel hundreds of kilometers 243 00:30:27,800 --> 00:30:28,800 day and night 244 00:30:30,040 --> 00:30:31,320 for over two months… 245 00:30:34,200 --> 00:30:35,880 to get to the grassy plains. 246 00:30:48,600 --> 00:30:52,400 Wa Chini eagerly awaits the arrival of the wildebeest, 247 00:30:53,920 --> 00:30:58,080 but there is another migration taking place that is critical 248 00:30:58,160 --> 00:31:00,600 to the survival of both animals. 249 00:31:03,840 --> 00:31:08,360 It's the journey of unfathomable distance and time. 250 00:31:11,640 --> 00:31:16,920 And without it, every creature on the Serengeti would go hungry. 251 00:31:24,240 --> 00:31:26,200 In the core of our sun, 252 00:31:26,280 --> 00:31:28,560 as atoms collide and fuse, 253 00:31:29,360 --> 00:31:34,360 photons are released and stream outwards. 254 00:31:38,800 --> 00:31:44,000 These tiny packages of light energy have zero mass 255 00:31:44,080 --> 00:31:46,080 and travel at the speed of light. 256 00:31:47,800 --> 00:31:51,080 But inside the unbelievably dense core, 257 00:31:51,160 --> 00:31:55,080 they're restrained, absorbed, scattered. 258 00:31:58,200 --> 00:32:03,800 A trip that would normally take just two seconds can take a million years. 259 00:32:10,960 --> 00:32:15,080 It's a mind-boggling torturous struggle to escape the sun. 260 00:32:20,000 --> 00:32:23,400 But slowly, the photons do rise 261 00:32:25,200 --> 00:32:27,680 upward through the sun's layers 262 00:32:29,640 --> 00:32:31,880 toward its raging hot surface… 263 00:32:34,480 --> 00:32:37,200 where they can finally be set free. 264 00:32:40,680 --> 00:32:43,360 They radiate out in all directions… 265 00:32:45,640 --> 00:32:46,880 as starlight… 266 00:32:53,720 --> 00:32:59,560 traveling 150 million kilometers in just over eight minutes. 267 00:33:04,880 --> 00:33:06,640 Arriving just in time… 268 00:33:09,160 --> 00:33:12,720 to meet the wildebeest at the end of their journey. 269 00:33:16,400 --> 00:33:22,800 Each individual blade of grass absorbs ten quadrillion photons every second… 270 00:33:27,880 --> 00:33:33,480 capturing enough energy overall to feed these massive herds. 271 00:33:43,760 --> 00:33:44,880 From star… 272 00:33:47,600 --> 00:33:48,640 …to grass… 273 00:33:52,280 --> 00:33:53,280 to wildebeest… 274 00:33:59,720 --> 00:34:02,560 sunlight now provides them with power to move… 275 00:34:04,600 --> 00:34:05,600 to grow… 276 00:34:07,760 --> 00:34:08,880 to reproduce. 277 00:34:17,160 --> 00:34:20,200 And the longer they're out on the plains eating, 278 00:34:21,040 --> 00:34:24,120 the longer they're available to be eaten. 279 00:34:39,880 --> 00:34:45,120 Rich, delicious, plentiful energy 280 00:34:45,200 --> 00:34:47,600 is finally within striking distance. 281 00:34:55,800 --> 00:34:58,160 But with three million eyes watching… 282 00:35:01,800 --> 00:35:03,880 Wa Chini needs to move fast. 283 00:35:06,560 --> 00:35:09,320 Luckily, she's a cheetah. 284 00:35:59,240 --> 00:36:03,080 At last, Wa Chini gets a taste of starlight. 285 00:36:26,040 --> 00:36:27,480 With every bite, 286 00:36:27,560 --> 00:36:31,680 proteins and fats imbued with cosmic energy 287 00:36:31,760 --> 00:36:33,680 enter Wa Chini's bloodstream. 288 00:36:39,840 --> 00:36:44,360 Their final destination are her body's cellular power plants, 289 00:36:45,520 --> 00:36:46,720 mitochondria… 290 00:36:49,080 --> 00:36:52,720 where one last transformation will take place. 291 00:37:00,840 --> 00:37:04,640 Within each mitochondrion is a surging landscape. 292 00:37:08,720 --> 00:37:13,000 Canyons of membranes rippling with complex chemistry. 293 00:37:15,080 --> 00:37:19,360 It's here that the energy-rich food reacts with oxygen 294 00:37:20,160 --> 00:37:21,960 and is finally broken down… 295 00:37:28,680 --> 00:37:33,960 releasing our universe's energy directly into Wa Chini's cells… 296 00:37:38,440 --> 00:37:41,160 …powering every action and thought, 297 00:37:41,920 --> 00:37:43,640 every little movement. 298 00:37:51,160 --> 00:37:54,000 The journey from star to cell is complete. 299 00:37:59,000 --> 00:38:01,160 Energy that once lit up the universe 300 00:38:02,560 --> 00:38:05,960 now gives Wa Chini and her cub the gift of life. 301 00:38:18,920 --> 00:38:20,200 In green season, 302 00:38:21,160 --> 00:38:22,880 hunger is just a memory. 303 00:38:32,880 --> 00:38:36,920 Across the Serengeti, energy is continually transformed… 304 00:38:41,320 --> 00:38:43,960 passing from one life to another, 305 00:38:45,640 --> 00:38:48,480 nourishing the entire ecosystem. 306 00:38:51,400 --> 00:38:54,320 Our sun is the ultimate provider. 307 00:38:55,600 --> 00:38:58,160 Everything feeds on starlight. 308 00:39:03,680 --> 00:39:07,320 The trouble is, there's nothing to feed the sun. 309 00:39:10,920 --> 00:39:12,800 And in five billion years, 310 00:39:13,640 --> 00:39:15,280 it will run out of fuel. 311 00:39:19,840 --> 00:39:21,560 As its core collapses, 312 00:39:22,520 --> 00:39:24,000 the sun will expand… 313 00:39:26,680 --> 00:39:28,240 and become a red giant… 314 00:39:31,520 --> 00:39:36,560 that will devour the inner planets, Mercury and Venus. 315 00:39:41,800 --> 00:39:43,840 As it balloons out toward Earth, 316 00:39:44,720 --> 00:39:48,080 the extreme gravity will rip our moon to shreds… 317 00:40:02,280 --> 00:40:05,280 …leaving a ring of moon rock around Earth. 318 00:40:10,480 --> 00:40:13,560 The ultimate fate of our planet is unknown. 319 00:40:18,440 --> 00:40:21,720 But there will be one last sunrise… 320 00:40:25,640 --> 00:40:28,600 before our star's outer layers blow away, 321 00:40:30,320 --> 00:40:32,160 and it takes its final breath. 322 00:40:40,040 --> 00:40:43,920 All that will remain is a dying ember, 323 00:40:44,960 --> 00:40:46,560 a white dwarf, 324 00:40:46,640 --> 00:40:52,120 barely the size of our Earth, surrounded by a vast glowing cloud. 325 00:40:55,400 --> 00:40:57,000 A beacon to the universe. 326 00:40:58,120 --> 00:41:00,280 We were here. 327 00:41:04,360 --> 00:41:05,480 But right now, 328 00:41:06,360 --> 00:41:09,560 our star continues to shine down on us… 329 00:41:12,960 --> 00:41:16,200 …and will for billions of years to come, 330 00:41:17,200 --> 00:41:22,280 its energy a vital force for all life. 331 00:41:30,200 --> 00:41:32,240 Next in the story of our universe, 332 00:41:33,880 --> 00:41:35,640 whether you are a blazing star… 333 00:41:38,080 --> 00:41:39,760 a vast black hole, 334 00:41:40,920 --> 00:41:43,960 or a chimpanzee learning the ropes, 335 00:41:44,560 --> 00:41:46,280 everything needs time. 336 00:41:48,080 --> 00:41:51,920 But what do you really know about this mysterious dimension? 337 00:41:53,200 --> 00:41:58,720 Why does everything have a past, present, and future? 338 00:41:59,400 --> 00:42:00,800 And would any of us be here… 339 00:42:03,520 --> 00:42:04,640 without time?