WE ALL HAVE QUESTIONS.

BIG QUESTIONS.

WOMAN, VOICE-OVER: HOW BIG IS THE UNIVERSE?

IT'S PART OF WHAT IT MEANS TO BE A HUMAN.

MAN, VOICE-OVER: HOW FAR AWAY ARE THE STARS?

JOY TO BOAT.

MY NAME IS STEPHEN HAWKING AND I BELIEVE THAT ANYONE CAN ANSWER BIG QUESTIONS FOR THEMSELVES.

THIS IS EXCITING.

HAWKING: SO, WITH THE HELP OF A FEW ORDINARY PEOPLE... AND A TEAM OF EXPERTS... MAN: WHERE YOU ARE CHANGES HOW WE SEE THE UNIVERSE.

HAWKING: WE ARE GOING ON THE ULTIMATE VOYAGE.

WOMAN: THESE DISTANCES ARE JUST GETTING BIGGER AND BIGGER.

HAWKING: A QUEST TO ANSWER THE GREATEST MYSTERIES OF THE UNIVERSE.

RIGHT, LET'S BLOW THIS BAD BOY UP.

HAWKING: USING THE POWER OF THE HUMAN MIND.

WE MADE IT!

BECAUSE ANYONE CAN THINK LIKE A GENIUS.

VOICES: WHERE ARE WE?

HAWKING: WHERE ARE WE?

THAT'S A PRETTY PROFOUND QUESTION.

IF WE DIDN'T KNOW WHERE WE ARE, WE'D BE LIKE MONKEYS IN A FOREST, TOTALLY UNAWARE OF OUR POSITION IN THE COSMOS.

FORTUNATELY, WE HUMANS KNOW EVERYTHING, FROM THE SHAPE OF THE EARTH TO ITS PLACE IN THE UNIVERSE.

BUT HOW DID WE FIND OUT?

I BELIEVE ANYONE CAN WORK IT OUT.

LET'S SEE IF I'M RIGHT.

I HAVE ASKED 3 ORDINARY PEOPLE TO COME ON A JOURNEY OF DISCOVERY.

THEY WILL HAVE TOOLS AND EQUIPMENT, AND I WANT TO SEE IF THEY CAN GRASP THE TRUE SCALE OF THE UNIVERSE... WITH SOME FUN EXPERIMENTS TO FIND OUT WHERE WE ARE.

WHERE ARE WE?

THAT'S A REALLY GOOD QUESTION.

WE'RE ON EARTH.

YET, THERE'S MORE PLANETS OUT THERE.

IN MY SOLAR SYSTEM.

AND THE MILKY WAY.

THAT'S WHERE I'M AT.

HAWKING: BUT HOW DO WE KNOW FOR SURE?

THE FIRST STEP IS TO MEASURE OUR PLANET.

HOW BIG IS IT AND IS IT REALLY ROUND?

THE VOLUNTEERS DON'T KNOW IT, BUT THEY ARE GOING TO FIND OUT THE SIZE AND SHAPE OF THE WORLD, RIGHT HERE IN NEVADA.

THEY'LL DO IT BY TACKLING THEIR FIRST CHALLENGE: HOW FLAT IS THIS LAKE?

CAT: HOW DO YOU MEASURE THE FLATNESS OF A LAKE?

WITH A HUGE RULER.

[LAUGHTER] YEAH, SHE HAS A POINT, THOUGH.

YOU NEED-- YOU NEED SOMETHING THAT YOU KNOW IS FLAT TO MEASURE THE SURFACE OF THE WATER AGAINST.

YEAH.

HAWKING: THIS LAKE HOLDS THE SECRET TO THE SIZE AND SHAPE OF THE EARTH, BUT CAN THE TEAM WORK IT OUT?

TO HELP THEM, THEY NEED A FEW TOOLS.

2 FEET, 7 INCHES.

HAWKING: FIRST IS A POWERFUL LASER WHICH PROJECTS A STRAIGHT BEAM OF LIGHT ACROSS THE SURFACE OF THE LAKE.

NEXT, THEY'LL NEED A BOAT.

AH...WHOA, WE JUST PASSED THROUGH IT.

YEAH.

JOY: JOY TO BOAT.

CAT: THIS IS CAT, OVER.

I WANT YOU TO GO AT THE FRONT OF THE LASER.

CAT: ROGER.

NOW WE GOTTA TURN A LITTLE TO THE RIGHT.

HAWKING: IF THE LAKE IS FLAT, THE LASER BEAM AND THE WATER WILL ALWAYS BE PARALLEL TO EACH OTHER.

SEEN FROM A BOAT, THE BEAM WOULD ALWAYS STAY AT THE SAME HEIGHT ABOVE THE WATER, NO MATTER HOW FAR YOU TRAVEL INTO THE LAKE.

BUT DOES THAT HAPPEN?

AND CAN THE TEAM WORK OUT WHY?

TIME TO FIND OUT.

THE BOAT HAS A WHITEBOARD ATTACHED TO IT, WHICH WILL BE A TARGET.

CAT: WE'RE LOOKING FOR THE LASER BEAM, SO THAT WE CAN MARK IT ON THE WHITEBOARD.

OH, IT'S HITTING OFF THAT.

JIM: AND WE MADE THE FIRST MEASUREMENT AND I WAS PRETTY CONFIDENT THAT WE WEREN'T GONNA FIND ANYTHING.

CAT: A LITTLE MORE TO THE RIGHT.

JIM: ALMOST THERE.

THERE WE GO.

HAWKING: THEY TAKE THEIR FIRST READING 500 FEET FROM THE SHORE.

JIM: OK, WHAT WAS THE HEIGHT OF IT?

GOT IT.

HAWKING: FOR THE NEXT MEASUREMENT, THEY'LL NEED TO GO MUCH FURTHER OUT.

JOY: OK, SO, NOW, I NEED YOU GO OUT 3 MILES AWAY FROM THE LASER.

CAT: ALL RIGHT.

AWESOME.

HAWKING: SO, 3 MILES AWAY, WHERE'S THE LASER BEAM?

REMEMBER, IF THE LAKE IS FLAT, IT WOULD BE THE SAME HEIGHT AS BEFORE.

JOY: CAT, YOU HAVE TO GO SLIGHTLY TO THE LEFT.

CAT: YOU SAY GO SLIGHTLY TO THE LEFT?

JOY: YEAH.

A LITTLE BIT MORE TO THE RIGHT.

HERE WE GO.

I DON'T EVEN THINK THIS BEAM IS GONNA HIT OUR BOAT.

SO, WE'RE GONNA HAVE TO MEASURE IT ON SOMETHING ELSE.

ALL RIGHT.

JIM: I'VE NO IDEA.

HERE WE GO.

OH, IS THAT YOUR-- IS THAT YOUR MEASURING TOOL?

CAT: DO YOU SEE IT?

JIM: YUP.

CAN YOU MARK IT?

CAT: [INDISTINCT] JIM: WE MADE THE SECOND MEASUREMENT AND MY WHOLE WORLD FELL APART.

IT'S LIKE 6 FEET.

YEAH.

YEAH.

IT SEEMS A LOT HIGHER.

OK. CAT: YOU GOT IT?

JIM: UH-HUH.

ALL RIGHT.

HAWKING: JUST 3 MILES AWAY, THE LASER SEEMS TO HAVE RISEN BY 6 FEET.

BUT WE KNOW THE BEAM IS LEVEL, SO, THAT SUGGESTS THAT THE LAKE IS NOW 6 FEET LOWER.

JIM: TO SEE A 6-FOOT DROP, WHEN EVERYTHING LOOKED FLAT TO ME, WAS--WAS KIND OF MIND-BOGGLING.

DEFINITELY KIND OF SHATTERED MY PERSPECTIVE IN ABOUT ONE SECOND.

IT MADE ME RETHINK WHAT WAS GOING ON.

PERCEPTION IS STILL IT'S A FLAT LAKE, BUT...

IT'S NOT A FLAT LAKE.

IT'S NOT A FLAT LAKE.

CAT: THAT WAS CRAZY.

I WAS DEFINITELY BLOWN AWAY BY THE FACT THAT THE LASER WAS THAT HIGH OFF THE WATER.

JIM: HEY.

CAT: HEY, JOY.

JIM: WHAT'S UP?

CAT: WE'RE BACK.

JOY: SO, HOW WAS IT?

THE LASER WAS 6 FEET UP IN THE AIR AND WE HAD TO USE THIS BOARD TO MARK IT.

HAWKING: THE LAKE IS CLEARLY NOT FLAT.

IT'S ALMOST AS IF IT'S SLOPING DOWNHILL.

WITH THIS REALIZATION, MY VOLUNTEERS HAVE MADE THEIR FIRST STEP TOWARDS MEASURING THE ENTIRE WORLD.

I THINK WE SHOULD MAKE SOME MORE MEASUREMENTS, FOR SURE.

YEAH, AGREED.

YEAH, TOTALLY.

HAWKING: BUT THEY ARE NOT THE FIRST PEOPLE TO DO IT, OF COURSE.

IN FACT, THE FIRST PERSON TO MEASURE THE EARTH ACCURATELY WAS AN ANCIENT GREEK GENIUS NAMED ERATOSTHENES.

MAN: MORE THAN 2,000 YEARS AGO, ERATOSTHENES, A VERY CLEVER PHILOSOPHER, MATHEMATICIAN, GEOMETER, FROM GREECE, HE EMBARKED ON AN EXPERIMENT TO MEASURE THE DIAMETER OF THE EARTH.

IF THE EARTH WAS FLAT, ANYWHERE ON THE FLAT EARTH AT A GIVEN TIME DURING THE DAY, WE WOULD SEE THE SUN SHINING WITH THE SAME ANGLE.

WHILE, IF IT IS ROUND, THAT WON'T BE THE CASE.

HAWKING: ERATOSTHENES HAD HEARD THAT AT NOON ON THE LONGEST DAY OF THE YEAR, THE SUN SHINES DIRECTLY DOWN THE WATER WELL IN WHAT IS NOW THE CITY OF ASWAN IN EGYPT.

HERE, THE SUN MUST BE DIRECTLY OVERHEAD.

SO, IN ANOTHER LOCATION, 500 MILES TO THE NORTH, HE MADE A SECOND OBSERVATION, AGAIN AT NOON ON THE LONGEST DAY OF THE YEAR.

DIEGO: HERE, 500 MILES NORTH, HE PERFORMED THIS EXPERIMENT AND HE PLANTED A POLE VERTICAL AND REALIZED THAT THE POLE WAS CASTING A SHADOW.

HAWKING: THE SHADOW WAS EVIDENCE THAT THE SUN IS NOT OVERHEAD, BUT AT AN ANGLE.

BY MEASURING THIS ANGLE, AND KNOWING THE DISTANCE BETWEEN THE TWO LOCATIONS, HE WAS ABLE TO CALCULATE THAT THE EARTH IS A BALL, ABOUT 8,000 MILES IN DIAMETER.

BUT THE QUESTION IS, WITH THE RIGHT TOOLS, CAN THE VOLUNTEERS MATCH THIS ANCIENT GENIUS?

DIEGO: TODAY, WE USE LASERS AND GPS AND ALL KINDS OF TECHNOLOGY TO COME MORE OR LESS TO THE SAME NUMBER.

THIS IS WHAT SCIENCE IS ABOUT.

IT'S ABOUT INVENTING NEW WAYS OF INVESTIGATING NATURE, LOOKING FOR FACTS, LOOKING FOR MEASUREMENTS, AND COMING WITH RESULTS WHICH ARE ASTONISHING.

HAWKING: MY VOLUNTEERS HAVE DISCOVERED THE LAKE IS NOT FLAT, BUT IN ORDER TO MEASURE THE WHOLE WORLD, THEY NEED TO MAKE A NEW MEASUREMENT, MUCH FURTHER AWAY.

AND TO DO THAT, THEY WILL NEED SOME NEW TOOLS.

OK, LET'S GET THIS BOX OPEN.

ALL RIGHT.

YEAH.

HEY, WHAT DO WE HAVE HERE?

TRIPOD.

THAT'S LIKE A TRIPOD.

HAWKING: NOW INSTEAD OF THE LASER, A TELESCOPE WILL ENABLE OUR VOLUNTEERS TO LOOK IN A STRAIGHT LINE TO THE LAKE'S OPPOSITE SHORE.

BUT THAT'S NOT THE ONLY INSTRUMENT THEY'LL NEED.

CAT: WE'RE WONDERING, OK, HOW ARE WE GONNA GET THIS NEXT POINT IF IT'S SO HIGH, IT'S PAST OUR BOARD.

JOY: WHOA!

JIM: VERY COOL.

ARE WE GETTING IN A HELICOPTER?

THIS CHOPPER APPEARS OUT OF NOWHERE.

ALL RIGHT, THAT IS AWESOME.

HAWKING: JUST AS THE TELESCOPE REPLACES THE LASER, THE HELICOPTER TAKES THE PLACE OF THE BOAT.

JIM: I'LL STAY WITH THE TELESCOPE.

OK, GREAT.

CAT: WE'LL GO IN THE HELICOPTER.

THAT'S A PLAN.

JIM: SOUNDS LIKE A PLAN.

YEAH.

CAT: ALL RIGHT, LET'S DO IT.

PILOT: ALL RIGHT, WE'LL GO AHEAD AND LIFT OFF.

THIS IS EXCITING.

JOY: I LOVE THAT THERE ARE NO DOORS.

[LAUGHS] WE'RE FLYING TO PYRAMID ROCK.

DO YOU COPY THAT?

I COPY THAT.

YOU ARE FLYING TO THE PYRAMID.

JOY: THE LAKE LOOKS COMPLETELY FLAT FROM UP HERE.

HAWKING: IF THEY ARE TWICE AS FAR AWAY AS BEFORE, HOW MUCH LOWER WILL THE FAR SHORE OF THE LAKE APPEAR TO BE?

JOY: JIM, WE'RE GOING TO BE AT THE TOP OF THE PYRAMID ROCK.

OH, GOT 'EM.

YEAH, I HAVE YOU ON THE TELESCOPE.

GO AHEAD AND LAND.

JIM: AS IT LANDS, IT COMPLETELY DISAPPEARS FROM MY LINE OF SIGHT.

JOY, ARE YOU STILL AIRBORNE?

JOY: YEAH.

CAN YOU SEE US LANDING?

JIM: THE REPORTS FROM THE HELICOPTER, THEY'RE STILL FLYING, BUT I CAN'T SEE IT.

TO WRAP YOUR HEAD AROUND IT IN THAT SHORT OF TIME WAS A LITTLE DIFFICULT FOR ME.

I WAS LIKE, THIS IS CRAZY.

WE HAVE LANDED IN OUR POSITION.

OK, JOY, GO AHEAD AND LIFT OFF.

HAWKING: THEY PLAN TO ASCEND UNTIL JIM CAN SEE THEM ON THE HORIZON.

THEN THEY'LL TELL HIM THEIR ALTITUDE.

LET ME KNOW WHEN YOU CAN SEE US ON SPOT ON THE HORIZON.

OH, I GOT 'EM, I GOT 'EM.

OK, WHAT'S YOUR ELEVATION RIGHT NOW?

CAT: ALL RIGHT, BRIAN, HOW MANY FEET ARE WE ABOVE THE LAKE?

BRIAN: 24 FEET.

JOY: WHOO!

WE MADE IT!

24 FEET.

24 FEET, AWESOME.

CAT: 24 FEET IS A LOT HIGHER THAN OUR OTHER TWO POINTS THAT WE GOT.

THAT WAS AWESOME.

IT WAS GREAT.

HAWKING: AT 6 MILES, THE LAKE HAS FALLEN 4 TIMES LOWER THAN BEFORE.

SO, WHAT IS GOING ON?

OK, YOU GUYS, CHECK THIS OUT.

SO, IF THIS LINE IS OUR LASER BEAM.

RIGHT.

THAT WE SHOT ACROSS THE LAKE.

RIGHT?

AND THAT'S THE SHORE.

THIS IS THE LASER.

RIGHT THERE.

AND WE JOIN OUR DATA POINTS, AT 6 FEET AND THEN ALL THE WAY OUT TO 24, THIS IS OUR SOURCE, THAT'S OUR FLAT LINE, RIGHT?

AND THIS IS THE SURFACE OF THE LAKE.

HAWKING: THE GREEN LINE SHOWS THE PATH OF THE LASER AND THE VIEW FROM THE TELESCOPE.

AND THE GOLD LINE SHOWS HOW THE DATA POINTS FORM THE BEGINNING OF A CURVE.

CAT: SO, THAT MEANS, THIS LAKE ISN'T FLAT.

IT'S NOT EVEN CLOSE.

NO.

THAT'S CRAZY.

JIM: IF WE CAN JUST CONTINUE THAT CURVATURE ALL THE WAY AROUND AND COMPLETE A CIRCLE, AND WE CAN MEASURE IT, THEN THAT GIVES US THE CIRCUMFERENCE OF THE EARTH.

HAWKING: WITH THESE MEASUREMENTS ON THE LAKE, WE CAN CALCULATE THAT THE EARTH'S CIRCUMFERENCE IS AROUND 25,000 MILES, WHICH MATCHES ERATOSTHENES'S CALCULATION.

I STILL HAVE A HARD TIME WRAPPING MY HEAD AROUND THE FACT THAT WE MEASURED THE EARTH AT THAT LAKE.

CAT: I'LL NEVER LOOK AT A LAKE THE SAME WAY, I'LL NEVER LOOK AT A BIG BODY OF WATER THE SAME WAY, NOW THAT I KNOW IT'S FOLLOWING THE CURVATURE OF THE EARTH.

HAWKING: KNOWING THE SHAPE AND SIZE OF THE EARTH IS JUST THE BEGINNING OF FINDING OUT WHERE WE ARE.

TO LEARN MORE, WE NEED TO JOURNEY INTO SPACE, TO THE MOON AND BEYOND.

THE MOON IS OUR NEAREST NEIGHBOR, BUT VERY FEW PEOPLE REALIZE ITS DISTANCE FROM EARTH.

SO, THE NEXT CHALLENGE IN FINDING OUT WHERE WE ARE IS TO FIND OUT HOW FAR AWAY THE MOON REALLY IS.

TO DISCOVER THIS, WE NEED TO LEAVE THE LAKE AND HEAD DEEP INTO THE VAST NEVADA DESERT.

SO, WHAT'S IN THE BOX?

OK.

SO, IT'S A TINY EARTH AND A TINY MOON.

HAWKING: THESE ARE SCALE MODELS OF THE EARTH AND THE MOON.

THEIR RELATIVE SIZE WAS FIRST DISCOVERED BY THE ANCIENT GREEKS, THOUSANDS OF YEARS AGO.

BACK THEN, THE GENIUS WHO WORKED IT OUT WAS A MAN CALLED ARISTARCHUS.

MAN: IF YOU LOOK AT THE MOON, THERE'S A BRIGHT CRATER, AND IT'S CALLED ARISTARCHUS, NAMED THAT WAY TO HELP US REMEMBER THE MAN WHO TOLD US THE SIZE OF THE MOON.

SO, HOW DID ARISTARCHUS DO IT?

THE ANSWER IS THAT HE SIMPLY OBSERVED ITS PASSAGE THROUGH THE SKY.

AND HE CALCULATED THAT IT TOOK ONE HOUR TO COVER THE DISTANCE OF ITS OWN DIAMETER.

ONCE HE'D WORKED THAT OUT, HE HAD TO FIND A WAY TO MAKE THAT FIGURE RELEVANT TO THE SIZE OF THE EARTH.

ARISTARCHUS REALIZED THAT HE COULD USE A PHENOMENON CALLED A TOTAL ECLIPSE.

AND A TOTAL ECLIPSE OF THE MOON IS A COMMON THING.

IT HAPPENS ONCE OR TWICE A YEAR, WHEN THE MOON PASSES THROUGH THE EARTH'S SHADOW.

HE DISCOVERED THAT THE MOON TOOK ABOUT 2.7 HOURS TO CROSS THROUGH THE EARTH'S SHADOW.

AND SO, HE THEN KNEW THAT THE EARTH'S SHADOW WAS 2.7 TIMES LARGER THAN THE MOON ITSELF.

ARISTARCHUS'S CALCULATION SHOWED THAT THE MOON WAS 3,000 MILES ACROSS IN DIAMETER AND WE NOW KNOW THAT THE TRUE FIGURE IS JUST OVER 2,000 MILES.

WHAT THIS DOES IS, IT EXTENDS THE REACH OF MEASUREMENT OUT ABOVE THE EARTH'S ATMOSPHERE AND INTO SPACE.

HE SAYS THAT THE UNIVERSE IS A PLACE THAT SCIENTISTS CAN EXPLORE AS WELL.

HAWKING: ONCE WE KNOW THE SIZE OF THE EARTH AND THE MOON, IT'S POSSIBLE FOR MY VOLUNTEERS TO TAKE THE NEXT STEP AND FIND OUT HOW FAR APART THEY ARE.

BUT FIRST, A GUESS.

I THINK IT'S CLOSER.

I THINK IT'S ABOUT THERE.

CAT: THAT IS WHAT I WAS GONNA DO.

I WAS GONNA PUT THEM CLOSE, I THINK.

JIM: CLOSER THAN FURTHER.

I THINK THAT IT'S A BIT FURTHER AWAY.

WOW, THAT FAR?

GOING BIG.

JOY: I PUT THIS AS MY GUESS.

OK. HAWKING: SO, HOW CAN WE FIND OUT FOR SURE?

THIS EVENING, THERE IS A FULL MOON.

THAT IS THE FINAL CLUE THEY NEED, TO THINK LIKE ARISTARCHUS.

CAT: MAYBE WE TAKE THE EARTH AND PUT THE MOON IN FRONT OF IT, UNTIL WE COVER UP THE MOON.

SAME SIZE?

SAME SIZE.

OK. CAT: TAKE IT TILL WE LOSE SIGHT OF THE MOON.

HAWKING: CAT HAS THE ANSWER.

CAT: I'M LOOKING AT THE REAL MOON IN THE SKY AND THE LITTLE MOON THAT WE HAVE AND I'M THINKING, "WELL, THEY'RE THE SAME."

SO, MAYBE WE NEED TO BLACK OUT THE REAL MOON IN THE SKY.

CLOSER.

CLOSER.

A LITTLE-- A LITTLE CLOSER.

ALL RIGHT.

I SAY THAT'S IT.

JIM: IS THAT IT?

YEAH.

SO, YOU WERE RIGHT.

THE MOON IS PRETTY FAR FROM THE EARTH.

YEAH, A LOT FARTHER THAN WE THOUGHT.

HAWKING: WHEN THE SCALE MOON IS JUST THE RIGHT DISTANCE AWAY, IT WILL COVER THE REAL MOON PERFECTLY.

THAT'S HOW YOU FIND THE DISTANCE.

IN THE DESERT, THE SCALE MODELS OF THE MOON AND EARTH ARE 6 FEET APART.

UP IN THE SKY, THE REAL MOON IS ABOUT 240,000 MILES AWAY.

CAT: IT WORKED.

I'M NOT A SCIENTIST AND TO BE ABLE TO JUST DO THAT OFF A WHIM AND IT JUST CAME TO ME, THAT WAS--THAT WAS INCREDIBLE.

BY MEASURING THE EARTH AND OUR DISTANCE TO THE MOON, WE'VE TAKEN OUR FIRST STEP OUT INTO SPACE.

BUT TO FIND OUT WHERE WE TRULY ARE IN THE UNIVERSE... JIM: GOT IT?

HAWKING: THE NEXT STEP IS TO FIGURE OUT OUR PLACE IN RELATION TO THE BRIGHTEST OBJECT IN OUR SKY--THE SUN.

TODAY, WE KNOW IT IS NEARLY 900,000 MILES IN DIAMETER.

BUT AGAIN, PEOPLE DON'T REALIZE HOW BIG THAT REALLY IS.

JIM: WHOA.

[LAUGHS] THAT'S THE SUN.

THAT'S MASSIVE.

IT LOOKS SO BIG.

HAWKING: THIS IS THE SUN AT THE SAME SCALE AS OUR TINY EARTH AND MOON MODELS.

CAT: GO THIS WAY.

OK.

UH, THIS THING.

[LAUGHS] AT FIRST, WHEN WE TRIED TO LIFT IT, WE COULD BARELY PULL THE-- PULL THE MODEL OUT.

IT'S GIANT.

CAREFUL.

THIS IS REALLY TO SCALE?

JIM: AND THEN WE START UNROLLING IT AND IT JUST KEEPS GOING AND GOING AND GOING.

'CAUSE I JUST WANTED TO FILL IT UP WITH AIR AND SEE REALLY HOW BIG IT WAS.

[JIM LAUGHS] [LAUGHS] CAT: IT JUST SEEMED LIKE IT WAS MORE AND MORE FABRIC, MORE AND MORE, JUST KEEP COMING, IT KEPT COMING.

JIM: OH, WOW.

RIGHT.

LET'S BLOW THIS BAD BOY UP.

[ENGINE RUNNING] I WAS JUST THINKING, "WOW, HOW BIG IS THIS SUN?

", COMPARED TO THIS TINY EARTH THAT I HAD IN MY HAND.

SO, IF THIS IS THE EARTH, THEN THIS IS THE SUN.

HAWKING: THE SUN IS ALMOST 110 TIMES THE DIAMETER OF THE EARTH.

NOW, THE NEXT BIG QUESTION.

ON THIS SCALE, WHAT IS THE DISTANCE BETWEEN EARTH AND THE SUN?

SO, HOW FAR DO WE HAVE TO MOVE THAT MODEL TO GET THE DISTANCE AND HOW ARE WE GONNA GET THE DISTANCE EXACT?

CAT: I DON'T KNOW.

HAWKING: MUCH LIKE IT WAS WITH THE MOON, THE KEY TO ANSWERING THIS QUESTION IS AN ECLIPSE.

BUT THIS TIME, IT'S A SOLAR ECLIPSE.

WHEN THE MOON PASSES IN FRONT OF THE SUN, SEEN FROM THE EARTH, THE SUN AND MOON ARE EXACTLY THE SAME SIZE.

SO, THEY SHOULD BE ABLE TO FIND THE DISTANCE BY CREATING AN ECLIPSE ON THEIR MODEL.

CAT: IN THE SOLAR ECLIPSE, WE CAN'T SEE THE SUN AT ALL.

SO, WHEN THIS SUN DISAPPEARED, YOU'D HAVE A SOLAR ECLIPSE.

JIM: BOOM.

THERE WE GO.

SO, ALL WE NEED IS A SOLAR ECLIPSE.

CAT: YEAH, EXACTLY.

CAT: WE JUMP IN THE TRUCK AND WE JUST GO.

WE--WE GO IN THE DESERT AND WE JUST DRIVE, DRIVE, DRIVE.

HAWKING: HOW FAR DO THEY NEED TO DRIVE?

I THINK THAT'S ABOUT IT.

[SLAPPING WINDOW] HAWKING: THEY DECIDE TO STOP 400 METERS FROM THE SUN.

ALL RIGHT.

LET'S SEE.

THE MOON RIGHT THERE.

HAWKING: TO MAKE THE TINY MOON ECLIPSE THE SUN, IT ALWAYS HAS TO BE 6 FEET FROM THE EARTH.

OK, SO, I'VE GOT THE EARTH HERE.

ALL RIGHT.

SO, WE KNOW THIS DISTANCE AND NOW I'M GOING TO SEE WHETHER THE MOON IS THE SAME SIZE AS THE SUN.

IT'S ACTUALLY A BIT SMALLER, SO, WE HAVE TO GO A BIT CLOSER TO THE SUN.

ALL RIGHT, LET'S MOVE IT.

LET'S DO IT.

HAWKING: DO THEY NEED TO BE CLOSER OR FURTHER AWAY?

CAT: LET'S TRY HERE.

ABOUT THERE?

JIM: YEAH, I THINK SO.

JOY: THE SUN IS STILL BIGGER.

JIM: REALLY?

JOY: YEAH.

CAT: THE SUN'S STILL BIGGER THAN THE MOON?

JOY: YEAH.

CAT: THAT MEANS WE WOULD GO THAT WAY.

I'M HAVING A DUMB STROKE.

I'M HAVING A DUMB MOMENT.

[LAUGHS] LET'S GO BACK.

ALL RIGHT.

JIM: I THINK WE ALL FELT A BIT SILLY.

WE'RE WALKING ACROSS THE DESERT.

WHAT WERE WE THINKING?

CAT: HOW MUCH FURTHER DO YOU GUYS THINK?

JIM: I'M SAYING CHECK IT.

CAT: CHECK IT.

BAM, RIGHT THERE.

OK, READY, WE LOOK.

OH, WE GOT IT.

CAT: YEAH.

JOY: WE GOT IT.

YEAH.

HAWKING: THEY'VE DONE IT.

ON THIS SCALE, THE SUN IS JUST UNDER HALF A MILE FROM EARTH.

UP IN SPACE, THE DISTANCE IS 93 MILLION MILES.

CAT: TO SEE IT IN PERSPECTIVE, I MEAN, OUR EARTH WAS ONLY SO BIG AND WE HAD TO TAKE IT ACROSS THE DESERT IN ORDER TO SHOW DISTANCE AND I MEAN, THAT JUST SHOWS HOW...HOW SMALL WE ARE.

OUR VOLUNTEERS HAVE FIGURED OUT THE DISTANCE BETWEEN THE SUN, MOON, AND EARTH USING NOTHING MORE THAN 3 ROUND BALLS AND A LITTLE BIT OF LOGIC.

BUT NOW WE NEED TO FIND OUT WHERE WE ARE ON A MUCH LARGER SCALE.

IF WE KNOW THE SUN IS 93 MILLION MILES AWAY, HOW BIG IS THE ENTIRE SOLAR SYSTEM?

THE ANCIENT ASTRONOMERS KNEW FROM OBSERVING THE HEAVENS THAT THERE WAS MORE TO THE UNIVERSE THAN THE EARTH, MOON, SUN, AND STARS.

THEY IDENTIFIED 5 POINTS OF LIGHT THAT MOVED IN A DIFFERENT WAY FROM THE STARS.

THESE ARE THE PLANETS.

HERE ON OUR SCALE MODEL, MERCURY IS CLOSEST TO THE SUN.

AS WE HEAD FURTHER INTO THE SOLAR SYSTEM, WE CAN SEE JUPITER ON THE HORIZON.

VIEWED FROM ABOVE, WE CAN SEE ALL 8 PLANETS ALIGNED.

NEPTUNE IS 9 MILES AWAY FROM THE SUN, OR NEARLY 3 BILLION MILES IN SPACE.

AND THE ENTIRE SOLAR SYSTEM IS 180 BILLION MILES SIDE TO SIDE.

CAT: WE KNOW WE HAVE ALL THE PLANETS, THE STARS, THE SUN, BUT WHEN YOU SEE IT FOR YOURSELF IN A PERSPECTIVE, OUR SOLAR SYSTEM IS MUCH BIGGER THAN WE THINK IT IS.

WE HAVE NOW FOUND OUT THE TRUE SCALE OF OUR SOLAR SYSTEM AND OUR PLACE WITHIN IT.

BUT WHERE IS OUR SOLAR SYSTEM?

TO FIND OUT, THERE WAS AN EVEN GREATER QUESTION WHICH HAD TO BE SOLVED BEFORE WE TRULY UNDERSTOOD OUR PLACE IN THE COSMOS.

LINTOTT: WELL, WORKING OUT DISTANCES IS ALL VERY WELL, BUT YOU REALIZE PRETTY QUICKLY THAT YOU NEED TO KNOW HOW THINGS RELATE TO EACH OTHER.

LOOK AT THE STARS AND YOU'LL SEE THAT THEY MOVE.

SO, IT'S NATURAL TO CONCLUDE THAT THE STARS ARE MOVING AROUND US.

HAWKING: IN THE 16TH CENTURY, A POLISH ASTRONOMER CALLED COPERNICUS DARED TO CHALLENGE THE TRADITIONAL ASSUMPTION THAT THE EARTH IS AT THE CENTER OF THE UNIVERSE.

LINTOTT: COPERNICUS REALIZED THE COMMON SENSE VIEW OF THE UNIVERSE ISN'T RIGHT.

AND HE STARTED TO WONDER WHETHER SOMETHING ELSE IS GOING ON.

HAWKING: COPERNICUS HAD TWO BIG THEORIES.

FIRSTLY, THE EARTH IS SPINNING LIKE A TOP.

AND SECONDLY, THE EARTH IS NOT AT THE CENTER OF THE SOLAR SYSTEM.

IN FACT, THE SUN IS IN THE MIDDLE.

AND WE ARE SPINNING AROUND IT... LIKE ALL THE OTHER PLANETS.

LINTOTT: HE KNEW THERE WAS SOMETHING BEAUTIFUL ABOUT THE IDEA OF A SUN-CENTERED UNIVERSE.

IT SEEMED TO HIM SIMPLER.

HAWKING: ALTHOUGH HIS THEORY WAS MORE LOGICAL, COPERNICUS FACED A SERIOUS PROBLEM.

CAT: WOW, WHAT IS THIS?

THIS LOOKS SO COOL.

HAWKING: AND THIS MACHINE WILL HELP OUR VOLUNTEERS FIGURE OUT THAT THE PROBLEM IS ALL A MATTER OF PERSPECTIVE.

CAT: HOW DOES IT MOVE?

JOY: I THINK SOMEONE HAS TO PUSH IT.

THAT'S MY JOB.

CAT: YOUR JOB.

YOU'RE GONNA PUSH?

YOU GUYS GET TO BE THE TEST PILOTS.

ALL RIGHT.

CAT: WHOO!

[LAUGHTER] WOW.

OK. CAT: SO, ARE WE SPINNING, OR IS THE BACKGROUND SPINNING?

FROM WHERE I'M SITTING, YOU'RE NOT SPINNING.

HAWKING: IF YOU ARE ON A PLANET THAT IS TURNING SLOWLY, SO THAT YOU CAN'T FEEL THE SPIN, HOW CAN YOU BE SURE THAT THE EARTH IS SPINNING, AND NOT THE UNIVERSE?

THAT'S THE PROBLEM COPERNICUS FACED.

CAT: IF WE'RE EARTH AND WE'RE SPINNING, HOW DO WE TELL IT'S ACTUALLY US SPINNING?

JOY: OH, THAT IS SUCH A DIFFICULT PROBLEM.

I MEAN, YOU HAVE TO HAVE A PINPOINT THAT IS NOT PART OF THE UNIVERSE AND NOT PART OF THE EARTH.

HAWKING: THE ONLY WAY TO SEE THE EARTH SPINNING IS TO BE AT A FIXED POINT OUT IN SPACE--JUST LIKE JIM.

500 YEARS AGO, SPACE TRAVEL WAS IMPOSSIBLE, OF COURSE.

BUT IN 1609, AN ITALIAN SCHOLAR CALLED GALILEO INVENTED THE NEXT BEST THING-- THE ASTRONOMICAL TELESCOPE.

DIEGO: GALILEO GALILEI IS PERHAPS THE FOUNDER OF MODERN SCIENCE.

HIS TELESCOPE WAS GOING TO REVOLUTIONIZE OUR VIEW OF THE UNIVERSE.

HAWKING: GALILEO POINTED HIS TELESCOPE AT JUPITER AND HE SKETCHED OUT WHAT HE OBSERVED.

THERE WERE MOONS SPINNING AROUND IT.

THIS WAS IMMEDIATE PROOF THAT NOT EVERYTHING MOVES AROUND THE EARTH.

AND WHEN HE LOOKED AT VENUS, HE MADE A STAGGERING DISCOVERY.

DIEGO: HE SEES VENUS AS A DISC, BUT THEN THE DISC IS CHANGING IN SIZE AND IT'S CHANGING IN SHAPE.

IT BECOMES A THIN CRESCENT.

HAWKING: HE FOUND THAT JUST AS THE MOON WAXES AND WANES AS IT MOVES AROUND THE EARTH, VENUS DOES THE SAME THING AS IT ROTATES AROUND THE SUN.

DIEGO: GALILEO COMES WITH THE PROOF, THAT THE SUN WAS AT THE CENTER WITH THE PLANETS GOING AROUND THE SUN.

EVERYBODY CAN BUILD A TELESCOPE, LOOK AT THE PHASES OF VENUS, AND THERE IS NO OTHER CONCLUSION.

THAT'S A FACT.

HAWKING: GALILEO PROVED THAT COPERNICUS WAS RIGHT.

THE EARTH IS A BALL CIRCLING THE SUN.

BUT TO PROVE IT WAS SPINNING WOULD TAKE A WONDERFUL REVELATION.

AS A CHILD, I USED TO GO TO LONDON'S SCIENCE MUSEUM, WHERE I COULD WITNESS THIS REVELATION WITH MY OWN EYES.

FOR ME, IT'S ONE OF THE MOST STRIKING DEMONSTRATIONS IN THE HISTORY OF SCIENCE.

THE BEST EXPERIMENTS ARE INCREDIBLY SIMPLE BUT POINT US TO PROFOUND TRUTH.

AND THAT'S WHAT WE'VE GOT HERE.

IT'S CALLED FOUCAULT'S PENDULUM AND IT'S REALLY VERY SIMPLE.

IT'S JUST A VERY LONG PENDULUM SWINGING UNDER THE INFLUENCE OF GRAVITY.

AND THE FIRST OF THESE LARGE-SCALE PENDULA WAS SET UP IN 1851 BY A GUY CALLED LEON FOUCAULT, WHO WANTED A SIMPLE DEMONSTRATION THAT THE EARTH WAS TURNING.

HAWKING: FOUCAULT SET A PENDULUM MOVING IN FRONT OF A CROWD FOR A DAY.

AND WHAT THEY SAW WAS ASTONISHING.

OVER THE COURSE OF THE DAY, THE PENDULUM'S DIRECTION OF SWING WOULD MOVE, A BIT LIKE THE HANDS OF A CLOCK.

WHAT WAS THE SOURCE OF THIS ROTATION?

BACK IN THE DESERT, WE CAN SEE A DIRECT PARALLEL BETWEEN THIS MACHINE AND THE PENDULUM.

TO SHOW IT, ALL WE NEED IS A BALL.

CAT: SO, IF I THROW A BALL TO YOU, ARE YOU GOING TO CATCH IT?

READY?

YEAH.

[LAUGHTER] DOES IT LOOK LIKE THE BALL'S CURVING WHEN YOU THROW IT?

JOY: YEAH.

YEAH.

JIM: THAT'S CRAZY.

THE BALL TRAVELS IN A STRAIGHT LINE.

HAWKING: HE'S RIGHT--THE LINE IS DEAD STRAIGHT.

OK, CAT, YOU READY?

HAWKING: THE BALL ONLY APPEARS TO BE CURVING FROM CAT AND JOY'S PERSPECTIVE, BECAUSE THEY ARE SPINNING.

CAT: YOU READY?

JOY: I'M READY.

[LAUGHTER] JIM: IT ABSOLUTELY DEMONSTRATED THAT THEY WERE TURNING AROUND ON AN AXIS AND THAT EVERYTHING WAS NOT TURNING AROUND THEM.

IT'S THE COOLEST THING EVER.

I LOVE IT.

HAWKING: SO, WHAT YOU SEE DEPENDS ON WHERE YOU ARE.

AND IT'S JUST THE SAME WITH THE PENDULUM IN THE MUSEUM.

THE BEST WAY TO THINK ABOUT THIS EXPERIMENT ISN'T ACTUALLY TO BE SITTING HERE.

IT'S TO IMAGINE YOU'RE ON THE PENDULUM ITSELF.

YOU JUST GO BACKWARDS AND FORWARDS ALL DAY LONG.

WHAT YOU WILL HAVE SEEN IS THE EARTH IS ROTATING UNDERNEATH THIS PENDULUM, WHICH CONTINUES GOING BACKWARDS AND FORWARDS AND BACKWARDS AND FORWARDS REGARDLESS OF WHAT'S HAPPENING UNDERNEATH IT.

HAWKING: WITH HIS PENDULUM, FOUCAULT CONVINCED THE WORLD THAT COPERNICUS AND GALILEO WERE RIGHT.

AND ANYONE CAN SEE THE EARTH TURNING WITH THEIR OWN EYES.

LINTOTT: I LOVE IT BECAUSE IT'S SO SIMPLE AND YET IT DEMONSTRATES TWO FUNDAMENTAL PRINCIPLES.

ONE IS THE IDEA THAT THE EARTH IS TURNING.

AND THE SECOND THING IT DEMONSTRATES IS THAT PERSPECTIVE MATTERS.

WHERE YOU ARE CHANGES HOW WE SEE THE UNIVERSE.

OUR VOLUNTEERS HAVE DISCOVERED HOW WE ARE JUST ONE OF MANY SPINNING BALLS ORBITING OUR SUN IN A PLANETARY COMMUNITY CALLED A SOLAR SYSTEM.

BUT NOW I WANT TO TAKE US FURTHER INTO THE COSMOS AND EXPLORE WHERE WE ARE IN RELATION TO THE STARS.

ON A CLEAR NIGHT, THERE ARE 3,000 VISIBLE STARS.

BUT HOW FAR AWAY ARE THEY?

BY THE 19TH CENTURY, TELESCOPES HAD BECOME POWERFUL ENOUGH TO HONE IN ON INDIVIDUAL STARS.

AND IN 1838, GERMAN ASTRONOMER FREDERICH BESSEL WAS ABLE TO MAKE A MOMENTOUS CALCULATION.

BESSEL KNEW THAT BECAUSE THE EARTH GOES AROUND THE SUN, IT MUST TRAVEL HUGE DISTANCES IN SPACE THROUGHOUT THE YEAR.

584 MILLION MILES, TO BE EXACT.

SO, HE DECIDED TO OBSERVE A STAR CALLED 61 CYGNI AT DIFFERENT TIMES OF YEAR.

AND THAT MEANT HE COULD SEE IT MOVING SLIGHTLY AGAINST THE BACKGROUND.

THEN, BY USING TRIGONOMETRY, BESSEL COULD TRIANGULATE THE STAR'S POSITION IN THE SKY AND FIND THE DISTANCE.

USING THIS METHOD, BESSEL WORKED OUT THAT 61 CYGNI WAS AROUND 67 TRILLION MILES AWAY FROM EARTH.

THIS WAS FAR GREATER THAN ANY DISTANCE WE HAD ENCOUNTERED IN OUR SOLAR SYSTEM.

SO, A NEW UNIT OF MEASUREMENT WAS NEEDED TO TAKE US TO INTERSTELLAR SPACE.

IT'S CALLED THE LIGHT YEAR.

IT'S THE DISTANCE THAT LIGHT TRAVELS IN ONE YEAR.

WHIZZING ALONG AT 186,000 MILES A SECOND.

THAT'S AROUND 5.8 TRILLION MILES A YEAR.

61 CYGNI IS FOUND TO BE ABOUT 11 LIGHT YEARS AWAY.

TO TRY AND UNDERSTAND SUCH HUGE DISTANCES, I WANT TO EXPLORE WHAT THE SPEED OF LIGHT LOOKS LIKE ON OUR SCALE MODEL.

JIM: HOW FAST IS THE SPEED OF LIGHT?

WELL, IT'S FAST, RIGHT?

HAWKING: IT TAKES SUNLIGHT 8 MINUTES AND 20 SECONDS TO TRAVEL FROM THE SUN TO EARTH.

SO, IN OUR MODEL, THE SPEED OF LIGHT IS THE SPEED NEEDED TO GET FROM THE SUN TO THE MODEL EARTH IN 8 MINUTES AND 20 SECONDS.

HOW FAST IS THAT?

CAT: WE KNOW IT TAKES 8 1/2 MINUTES, SO, HOW FAST DO WE NEED TO MOVE TO GET FROM OUR MODEL SUN TO OUR MODEL EARTH?

JOY: LET'S BE THE LIGHT.

LET'S WALK 750 METERS AND TIME IT AND SEE HOW LONG IT TAKES.

ALL RIGHT.

ALL RIGHT.

I'LL GET THE WATCH.

LET'S GO.

HAWKING: ON THE SCALE, EVERY FOOT THAT MY VOLUNTEERS TRAVEL REPRESENTS OVER 40,000 MILES.

CAT: HOW MUCH TIME HAVE WE BEEN WALKING?

JIM: 40 SECONDS.

[LAUGHS] ONLY 40 SECONDS?

YEAH.

AND WE'VE GONE PRETTY FAR.

I MEAN, I CAN SEE THE EARTH FROM HERE.

HAWKING: HOW FAST IS THE SPEED OF LIGHT ON THIS SCALE?

JIM: ALMOST THERE, ALMOST THERE.

PASSING THE MOON.

HELLO, MOON.

AND BAM.

WHAT DID YOU GET?

8 MINUTES, 35 SECONDS.

CAT: WOW.

SO, WE PRETTY MUCH WALKED FROM THE SUN TO EARTH IN THE SPEED OF LIGHT.

HAWKING: EVEN THOUGH IT'S THE FASTEST SPEED IN THE UNIVERSE, THE SPEED OF LIGHT ON THIS SCALE IS JUST OVER 3 MILES PER HOUR.

THAT'S WALKING PACE.

SO, LIGHT ISN'T AS FAST AS WE PERCEIVE IT TO BE.

I CAN WALK THE SPEED OF LIGHT?

IT'S FAST BUT IT'S NOT FAST.

IT'S CRAZY.

IN THE ENTIRE UNIVERSE, LIGHT APPEARS TO TRAVEL REALLY SLOW.

WOW.

HAWKING: IT'S A STRANGE PARADOX.

ALTHOUGH THE SPEED OF LIGHT IS FAST, DISTANCES IN SPACE ARE SO HUGE THAT EVEN ONE LIGHT YEAR IS NOT VERY FAR AT ALL.

JIM: IT'S SUCH A REVELATION, BUT THEN IT ALTERS, IT JUST ALTERS YOUR THOUGHTS, AND I HAVE TO SIT-- I HAVE TO SIT IN A QUIET PLACE AND WRAP MY HEAD AROUND IT FOR A WHILE.

HAWKING: IF IT TAKES 8 MINUTES FOR MY VOLUNTEERS TO REACH THEIR MODEL EARTH, IMAGINE HOW LONG IT WOULD TAKE TO GET TO OUR NEAREST STAR.

IT'S CALLED PROXIMA CENTAURI.

ON OUR SCALE MODEL, IT WOULD BE 126,000 MILES AWAY FROM THE SUN.

SO, OUR VOLUNTEERS WOULD HAVE TO WALK HALFWAY TO THE REAL MOON TO REACH IT.

IN SPACE, THE TOTAL DISTANCE IS 4.2 LIGHT YEARS.

JIM: I'D HAVE TO WALK FOR 4.2 YEARS CONTINUOUSLY TO GET TO MY NEAREST STAR.

IF I WAS GONNA SHRINK THAT DOWN FOR THE PURPOSE OF DEMONSTRATIONS, WELL, OUR SCALE MODEL'S GONNA BE LIKE A SPECK OF SAND.

HAWKING: EVEN ON THIS SCALE, DISTANCES HAVE NOW BECOME TOO LARGE TO COMPREHEND.

WE NEED TO SHRINK OUR MODEL SUN FROM THIS... TO THIS.

WOW.

THIS IS OUR SUN?

FROM THAT BIG, GIANT SUN WE HAD EARLIER, IS NOW THIS.

JIM: YEAH.

THAT LITTLE DOT.

HAWKING: EVEN ON THIS TINY SCALE, THE DISTANCE BETWEEN THE TINY SUN AND OUR NEAREST STAR WOULD BE 17 MILES.

WE CAN TRY AND GET A GRIP ON THIS IF WE LIGHT A FLARE 17 MILES AWAY ACROSS THE DESERT.

THERE IT IS.

WHOA.

THAT IS INCREDIBLE.

JOY: TO SEE THE NEAREST STAR SO FAR AWAY, WHEN OUR SUN IS THAT SMALL, WAS JUST AMAZING.

IT MADE ME THINK ABOUT ALL THE STARS IN THE SKY.

THESE ARE THE THINGS THAT FEEL SO FAMILIAR TO US, BUT YET, WE DON'T KNOW ANYTHING ABOUT THEM.

HAWKING: AFTER CENTURIES OF OBSERVATIONS, WE NOW KNOW THAT OUR SUN AND ITS NEAREST NEIGHBOR, PROXIMA CENTAURI, ARE PART OF A SMALL COMMUNITY OF 33 STARS, ALL WITHIN 15 LIGHT YEARS OF EARTH.

AND THIS SYSTEM SITS IN A NETWORK OF AN ESTIMATED 300 BILLION STARS CALLED THE MILKY WAY.

AND UNTIL RECENTLY, ASTRONOMERS BELIEVED THAT THIS GALAXY WAS THE ENTIRE UNIVERSE.

THAT WAS THE WHOLE ANSWER TO THE QUESTION "WHERE ARE WE?"

THEN IN THE 20TH CENTURY, A NEW GENERATION OF TELESCOPES ALLOWED US TO EXPLORE NEW FORMATIONS, AND THEY SEEM TO BE MUCH FURTHER AWAY.

WOMAN: PEOPLE HAD BEEN SEEING DIFFERENT SMUDGY PATCHES OF LIGHT ON THE SKY AND THEY STRUGGLED WITH WHAT THESE FAINT SMUDGES ON THE SKY ACTUALLY ARE.

HAWKING: ENTER EDWIN HUBBLE, 20TH-CENTURY AMERICAN ASTRONOMER.

USING THIS TELESCOPE AT THE MOUNT WILSON OBSERVATORY IN CALIFORNIA, HE MADE A SENSATIONAL DISCOVERY.

HE REALIZED THAT THESE SMUDGES WERE MILLIONS OF LIGHT YEARS FROM US.

KOLLMEIER: IT WAS EDWIN HUBBLE'S DISCOVERY OF THE DISTANCE TO THESE SMUDGY PATCHES THAT INDICATED THAT INDEED, THESE WERE OTHER GALAXIES, JUST LIKE THE MILKY WAY, AT GREAT DISTANCES FROM US.

HAWKING: HUBBLE FOUND THAT THE SKY WAS STUDDED WITH DISTANT GALAXIES, GIANT COLLECTIONS OF STARS FAR BEYOND OUR OWN GALAXY.

KOLLMEIER: SO, THIS JUST SHATTERS EVERYTHING.

IT SHATTERS THE SMALL MILKY WAY AND IT SHATTERS THE NOTION THAT THE UNIVERSE CAN BE CONTAINED IN THE MILKY WAY.

NOW THESE DISTANCES ARE JUST GETTING BIGGER AND BIGGER.

HAWKING: DISTANCES ARE INDEED BECOMING ASTRONOMICAL.

OUR NEXT ONE IS 2.5 MILLION LIGHT YEARS AWAY.

THAT'S THE DISTANCE BETWEEN THE MILKY WAY AND OUR NEAREST GALAXY, ANDROMEDA.

NOW THAT WE ARE TALKING GALAXIES, IT'S TIME TO INTRODUCE A NEW SCALE MODEL.

OUR NEXT CHALLENGE IS PRETTY SIMPLE.

IF WE COULD FIT OUR GALAXY ON A SMARTPHONE AND ANDROMEDA ON A TABLET, HOW FAR APART WOULD THEY BE?

SO, THESE ARE OUR GALAXIES.

THIS IS THE MILKY WAY AND THIS IS OUR CLOSEST GALAXY, ANDROMEDA.

HAWKING: THE MILKY WAY IS 100,000 LIGHT YEARS SIDE TO SIDE.

WITH THAT INFORMATION, I WANT MY VOLUNTEERS TO WORK OUT THE DISTANCE BETWEEN THE TWO GALAXIES.

CAT: SO, OUR MILKY WAY IS 100,000 LIGHT YEARS WIDE AND ANDROMEDA IS 2.5 MILLION LIGHT YEARS AWAY.

SO, ON THIS SCALE, COMPARING THIS TO THIS, HOW FAR AWAY IS THIS GALAXY?

SO, THIS IS 100,000 LIGHT YEARS ACROSS AND THERE'S 10 TIMES THAT IS A MILLION, AND SO, THAT'S 2.5 MILLION LIGHT YEARS AWAY.

SO, THAT WOULD MAKE... CAT: 25 OF THOSE.

25 OF THESE.

SHALL WE MEASURE IT?

1, 2, 3.

25.

JIM: THAT'S IT?

THAT'S IT.

AND THAT'S OUR NEAREST GALAXY.

HAWKING: THE MILKY WAY AND ANDROMEDA ARE JUST THE START.

THEY ARE SURROUNDED BY DOZENS OF GALAXIES IN THE LOCAL GALACTIC NEIGHBORHOOD, AND IT DOESN'T STOP THERE.

IN 1990, THE HUBBLE SPACE TELESCOPE IS LAUNCHED.

AFTER A DECADE OF OBSERVATIONS, THIS PICTURE IS RELEASED, SHOWING THOUSANDS OF GALAXIES WHICH STRETCH AWAY INTO THE FAR DISTANCE, FOR UP TO 13 BILLION LIGHT YEARS.

AND THIS IS JUST A TINY PART OF THE SKY, LIKE LOOKING AT A POSTAGE STAMP FROM 100 FEET AWAY.

MY BRAIN WILL NEVER GET AROUND THIS.

[LAUGHS] THIS IS GONNA TAKE ME WEEKS.

THE REST OF MY LIFE MAYBE.

HAWKING: IN THE DESERT, OUR VOLUNTEERS HAVE FIGURED OUT DISTANCES AROUND THE EARTH TO OUR SUN.

IT'S LIKE PERFECT RIGHT NOW.

HAWKING: AND ACROSS OUR SOLAR SYSTEM.

JOY: THE THING THAT WILL STICK WITH ME THE MOST IS JUST HOW TINY WE ARE.

HAWKING: THEN OUT INTO OUR GALAXY AND BEYOND.

THERE IT IS!

IN THE GRAND SCHEME OF THINGS, WE ARE INFINITELY SMALL.

AND NOW, BACK ON EARTH, WE RETURN TO OUR FIRST QUESTION.

WHERE ARE WE?

WE HAVE LEARNED THAT OUR PLANET IS A LITTLE SPHERE ORBITING A STAR...

IN A MODEST NEIGHBORHOOD CALLED THE SOLAR SYSTEM.

WE ARE SURROUNDED BY A LOCAL GROUP OF A FEW DOZEN STARS, UP TO 50 LIGHT YEARS DISTANT.

AND WE ALL OCCUPY ONE LITTLE PART OF A SPINNING ARM, IN A MEDIUM-SIZED GALAXY KNOWN AS THE MILKY WAY.

ALONG WITH MORE THAN 50 OTHERS, WE FORM A LOCAL GROUP OF GALAXIES 10 MILLION LIGHT YEARS ACROSS.

AND TOGETHER, WE INHABIT ONE CORNER OF A VAST COLLECTION OF GALAXIES, KNOWN AS THE LANIAKEA SUPERCLUSTER.

IT'S LIKE A HUGE GALACTIC CITY, FILLED WITH HUNDREDS OF THOUSANDS OF GALAXIES SIMILAR TO OUR OWN.

GROUPED WITH MANY MORE MILLIONS OF CLUSTERS, THEY FORM GIGANTIC ARMS WHICH STRETCH THROUGH THE COSMOS.

THE LARGEST STRUCTURES KNOWN TO HUMANITY.

AND THIS IS JUST ONE SMALL CORNER OF THE OBSERVABLE UNIVERSE...

WHICH IS BILLIONS OF LIGHT YEARS, SIDE TO SIDE.

EVEN THOUGH THE DISTANCES ARE UNIMAGINABLE, THE FACT THAT MOST PEOPLE CAN UNDERSTAND SUCH A UNIVERSE DOES EXIST IS A REMARKABLE FEAT OF THE HUMAN MIND.

SO, NOW I HOPE YOU ARE BEGINNING TO REALIZE THAT WITH A LITTLE BIT OF THINKING, YOU HAVE THE GENIUS TO FIGURE OUT WHERE WE ARE.