Transcript: Ep. 1 - The Amazing World of Gravity | Oct 22, 2018

Jim Al-Khalili is in his fifties, bald and clean-shaven and wears black trousers and a black jacket.

Jim says WOULD YOU LIKE TO LOSE A
LITTLE BIT OF WEIGHT WITHOUT
DOING ANY EXERCISE OR DIETING?
WOULD YOU LIKE TO AGE JUST A BIT
MORE SLOWLY THAN YOUR FRIENDS?
WELL, YOU MIGHT BE SURPRISED TO
HEAR THE LAWS OF PHYSICS CAN
HELP.

In slow motion, Jim drops a tennis ball.

He says THE KEY TO UNLOCKING THESE
EVERYDAY QUESTIONS IS GRAVITY.
IT SCULPTS THE UNIVERSE.
IT WARPS SPACE AND TIME.

Animations show images of the Earth.

Jim says IT'S A FUNDAMENTAL FORCE OF
NATURE.
BUT GRAVITY'S STRANGE POWERS,
DISCOVERED BY ALBERT EINSTEIN,
ALSO AFFECT OUR DAILY LIVES IN
THE MOST UNEXPECTED WAYS.
IN THIS FILM, WE'LL BE USING
CUTTING-EDGE SCIENTIFIC
TECHNIQUES TO INVESTIGATE HOW
GRAVITY CHANGES YOUR WEIGHT.

Jim stands with a group of young people on a field.

A young man steps on a scale.

A young woman says IT'S GONE UP!

Jim says YOUR HEIGHT.

Jim points at a measuring tape and says I REALLY HAVE SHRUNK.

He says AND EVEN YOUR POSTURE.
AND WITH THE HELP OF THOUSANDS
OF VOLUNTEERS, I'LL SHOW YOU
HOW GRAVITY MAKES US ALL AGE
AT DIFFERENT RATES.

An aerial view shows images of snow covered mountain tops.

A pilot says "Cruising at 37,000 feet."

A man at a mountain top says THROUGHOUT THE DAY, I'VE JUST
BEEN LOGGING ONTO THE PHONE,
LOGGING ONTO THE APP.

Jim says AS A PHYSICIST, GRAVITY IS
CENTRAL TO MY WORK.

He looks up at the sky at an observatory and says OH, WOW!

He says AND IN EXPLORING IT, I'LL BE
CHALLENGED ON HOW I UNDERSTAND
THIS MOST MYSTERIOUS FORCE.
WOW, OKAY, I NEED TO GO AND
WRITE THIS ONE DOWN.


Jim says AND I'LL HAVE TO TACKLE THE
VERY NATURE OF REALITY ITSELF.

(music plays)

The name of the show reads "Gravity and me. The force that shapes our lives. Episode 1."

Jim says GRAVITY.
IT BINDS TOGETHER ALL THE
MATTER IN THE UNIVERSE,
AND IT MAKES OUR EXISTENCE
HERE POSSIBLE.
BUT IN THE END, IT ALL BOILS
DOWN TO ONE SIMPLE QUESTION.

He walks on a bridge and says WHAT HAPPENS IF I DROP AN
OBJECT?

He drops a rock in the river.

(SPLASHING)

He says GRAVITY'S MANY MYSTERIES ARE
ALL CONTAINED IN THIS SINGLE
ACTION.
HOW AN OBJECT FALLS.
HERE'S THE FIRST PUZZLE.
WHY DOES A HAMMER FALL FASTER
THAN A FEATHER?
YOU MIGHT THINK IT'S BECAUSE
THE HAMMER IS HEAVIER.
BUT THAT'S NOT THE REAL REASON.
THE ANSWER IS AIR RESISTANCE.

A caption reads "Professor Jim Al-Khalili. University of Surrey."

Jim says IT'S NOT THE WEIGHT OF THE
OBJECTS THAT MATTERS, IT'S
THEIR SHAPE.
AND I CAN DEMONSTRATE THIS VERY
EASILY WITH THESE TWO UMBRELLAS.
THEY BOTH HAVE EXACTLY THE SAME
WEIGHT.
BUT IF I OPEN ONE OF THEM, YOU
CAN BE PRETTY SURE IT WILL DROP
MORE SLOWLY THAN THE OTHER ONE.
IN FACT, ALL OBJECTS WOULD FALL
AT THE SAME RATE IF YOU COULD
ONLY REMOVE THE AIR.

He drops both umbrellas from a bridge and says THE FIRST PERSON TO REALIZE
THIS WAS THE 16TH CENTURY
MATHEMATICIAN, GALILEO GALILEI.
FAMOUSLY, IT'S SAID HE WORKED
IT OUT BY DROPPING OBJECTS
OFF THE LEANING TOWER OF PISA.

A clips shows a rocket launch.

(ROCKET BLASTING)

Jim says AND HE WAS SPECTACULARLY PROVEN
RIGHT IN AN EXPERIMENT CARRIED
OUT ON THE MOON IN 1971.

An astronaut says IN MY LEFT HAND,
I HAVE A FEATHER.
IN MY RIGHT HAND, A HAMMER.
AND I'LL DROP THE TWO OF THEM
HERE, AND HOPEFULLY THEY'LL
HIT THE GROUND AT THE SAME
TIME.

Jim says IT WORKED PERFECTLY.

The astronaut says HOW ABOUT THAT?
IT PROVES THAT MR. GALILEI
WAS CORRECT IN HIS FINDINGS.

Jim says NOW, GALILEO WAS OBSESSED
WITH A SECOND QUESTION, TOO.
WHEN YOU DROP AN OBJECT, IT'S
ACTUALLY QUITE HARD TO TELL
IF IT FALLS AT A CONSTANT SPEED,
OR PICKS UP SPEED AS IT DROPS.
EVEN IN SLOW MOTION, IT'S
PRETTY HARD TO TELL.
BUT GALILEO REALIZED THIS.
FIRST, DROP AN OBJECT A VERY
SHORT DISTANCE.

He drops a ball on a tile suspended by two small boxes.

Jim says IT LANDS WITH VERY LITTLE
IMPACT.
BUT OF COURSE, DROP IT FROM
HIGHER UP...
THIS TIME, THE BALL EASILY
BREAKS THE TILE, WHICH MEANS
IT MUST HAVE ACCELERATED,
GAINING IN SPEED AND MOMENTUM
AS IT DROPPED.
GALILEO HAD IDENTIFIED
SOMETHING FUNDAMENTAL TO ALL
FALLING OBJECTS - THEY
ACCELERATE.
HE REALIZED THERE MIGHT BE
A WAY TO MEASURE HOW MUCH
FALLING OBJECTS GAIN IN SPEED.
WHAT HE DEVISED WAS THE
FIRST-EVER ATTEMPT TO MEASURE
GRAVITY ITSELF.

He now stands next to a long table with a long wooden ramp on top.

Jim says HE BUILT A LONG WOODEN RAMP,
RATHER LIKE THIS, THAT HE HAD
SLOPING AT A SHALLOW ANGLE.
THE IDEA WAS TO ROLL BALLS DOWN
THE RAMP, AND MEASURE THEIR
ACCELERATION.
THE CRUCIAL THING IS THAT THE
RAMP HAD TO BE AT THIS SHALLOW
ANGLE TO REDUCE THE EFFECTS
OF WIND RESISTANCE.
IT ALSO MEANT THAT THE BALLS
WOULD ROLL DOWN SLOWLY ENOUGH
TO GIVE HIM TIME TO MEASURE
THEIR SPEED.
BUT THE BIG PROBLEM WAS THIS:
HOW DO YOU MEASURE TIME
ACCURATELY IN AN AGE WHEN THERE
WERE NO ACCURATE TIMEPIECES,
LET ALONE STOPWATCHES?
WELL, GALILEO CAME UP WITH AN
INGENIOUS IDEA INVOLVING THE
FLOW OF WATER.
ESSENTIALLY, MEASURING TIME
FROM THE AMOUNT OF WATER
COLLECTED IN A CUP.
SO, WE'RE GOING TO TRY AND
REPEAT GALILEO'S EXPERIMENT.
I SAY "WE," BECAUSE I HAVE A
COUPLE OF WILLING VOLUNTEERS,
GAVIN AND JOHANNA.

Gavin is in his twenties, with black hair in a man bun and wears jeans and a black jacket.

Johanna is in her twenties, with long wavy brown hair with bangs and wears a black turtleneck sweater and a black coat.

Jim says THREE, TWO, ONE, GO.

Johanna drops the ball down the ramp.

Gavin says AND, STOP.

Jim collects the water and says OKAY, THERE'S ONE.
NOW, IF YOU COME DOWN A QUARTER
OF THE WAY DOWN THE RAMP.
GO.

Gavin STOP.

Jim says OKAY.
SO, NOW HALF OF THE WAY DOWN.
GO.

Jim says STOP.

Jim says JUST IN TIME.
OKAY, AND THEN THREE-QUARTERS
OF THE WAY DOWN.
GO.

Jim says says AND STOP.

Jim says says RIGHT, TURN THE TAP OFF.
OKAY, SO WE HAVE OUR FOUR
MEASUREMENTS.
AND I CAN SEE A PROGRESSION
FROM FULLER TO EMPTIER, BUT
WHAT WE NEED TO DO NOW IS
FIND THE MATHEMATICAL PATTERN
BY WEIGHING CAREFULLY THE WATER
IN EACH GLASS.
WEIGHING THE WATER SHOULD GIVE
US AN IDEA OF HOW LONG EACH
ROLL TOOK.
AND IN OUR EXPERIMENT,
THESE WERE THE RESULTS.
NOW, THERE'S ONE IMMEDIATE
THING YOU CAN TELL.
THE BALL REALLY SPED UP
THE LONGER IT ROLLED.

They write the results on a board. They read "Empty: 29.3 grams, 1: 77.3 grams, 2: 62.7 grams, 3: 53.7 grams, and 4: 34.2 grams."

Jim says IN FACT, OUR RESULTS SEEM TO
SHOW THAT THE TIME IT TOOK TO
COVER THE FIRST QUARTER OF THE
RAMP WAS ABOUT THE SAME TIME
IT TOOK TO COVER THE NEXT
THREE-QUARTERS.
SO, WE HAVE A STRONG HINT
OF A MATHEMATICAL PATTERN.
NOW, WE'LL SEE IF WE'RE RIGHT,
BY PLACING BELLS ALONG THE
RAMP, AT INTERVALS WHICH ARE
BASED ON THE RESULTS.
THIS ARRANGEMENT LOOKS A BIT
STRANGE BECAUSE THE GAP BETWEEN
THE FIRST TWO BELLS IS MUCH
SHORTER THAN THE GAP BETWEEN
THE THIRD AND FOURTH BELLS.
BUT THAT'S OKAY, BECAUSE IF
WE'VE GOT OUR CALCULATIONS
RIGHT, THE BALL STARTS OFF
SLOWLY, SO IT COVERS A SHORTER
DISTANCE, AND AS IT PICKS UP
PACE, IT'LL COVER LONGER AND
LONGER DISTANCES.
SO, WE SHOULD HEAR THE BELLS
RINGING AT EQUAL INTERVALS IN
TIME.
GO.

Johanna drops the bell down the ramp.

(FIRST BELL RINGING)
(SECOND BELL RINGING)
(THIRD BELL RINGING)
(FOURTH BELL RINGING)

Jim says BEAUTIFUL.
SO, WHAT DOES THIS ALL MEAN,
WHAT'S THE MATHEMATICAL FORMULA?
WELL, THIS IS SOMETHING THAT
GALILEO WORKED OUT.
LET'S SAY, FROM THE START,
THE BALL COVERS A DISTANCE OF
ONE METRE IN THE FIRST SECOND.
AFTER TWO SECONDS, IT'LL HAVE
COVERED FOUR METRES.
AFTER THREE SECONDS, NINE
METRES.
AFTER FOUR SECONDS, 16 METRES,
AND SO ON.
IF YOU RECOGNIZE THIS
PROGRESSION, YOU'LL SEE THAT
DISTANCE GOES LIKE THE SQUARE
OF TIME.
GALILEO HAD FOUND THE RATES
AT WHICH GRAVITY SPEEDS UP
OBJECTS.
(BELL RINGING)

Jim says AND HE'D FOUND ANOTHER
FUNDAMENTAL PRINCIPLE -
YOU CAN MEASURE THE STRENGTH
OF GRAVITY BY HOW MUCH IT
CAUSES FALLING OBJECTS TO
ACCELERATE.
DETECTING GRAVITY HAS BECOME
EXCEPTIONALLY SOPHISTICATED
THESE DAYS, BUT STILL USES
EXACTLY THE SAME PRINCIPLE.

(music plays)

Jim says THIS IS HERSTMONCEUX CASTLE
IN SUSSEX, AND IN ITS GROUNDS
LIES THE SPACE GEODESY
FACILITY.
HERE, VICKI USES AN
ASTONISHINGLY SENSITIVE
INSTRUMENT TO DETECT THE EXACT
STRENGTH OF GRAVITY ON THIS
ONE SPOT.
OKAY, SO VICKI, TELL ME ABOUT
THIS INCREDIBLE GRAVITY METER
THAT YOU WORK WITH.

The caption changes to "Vicki Smith. NERC Space Geodesy Facility."

Vicki is in her thirties, with mid-length curly brown hair and wears black jeans and a black T-shirt.

She shows him a vertical, free-falling gravity meter and says OKAY, SO THIS IS THE DROPPING
CHAMBER IN A STRIPPED-DOWN
VERSION.
ESSENTIALLY WHAT HAPPENS IS
YOU'VE GOT A CART THAT GETS
RAISED TO THE TOP, AND THEN THE
CART ACCELERATES AWAY FROM A
MASS IN THE MIDDLE, AND SO
THIS SECTION HERE LIFTS OFF
AND AS IT DROPS, IT DROPS INTO
FREEFALL.

Jim says SO, THIS COMPONENT IN THE
MIDDLE AS IT DROPS IS BASICALLY
JUST NEWTON'S APPLE FALLING
TO THE GROUND?

Vicki says YES.

Jim says SO THIS IS A STRIPPED-DOWN
VERSION, BUT THAT'S THE REAL
THING?

Vicki says THIS IS THE REAL THING.

Jim says HOW DOES THAT ACTUALLY WORK?

Vicki says IN HERE, IT'S A VACUUM.

Jim says says SO, THERE'S NO WIND
RESISTANCE AS IT FALLS, RIGHT.

Vicki says THERE'S NO WIND RESISTANCE.

Jim says INSIDE, A LASER IS USED
TO MEASURE EXACTLY HOW FAST
THE MASS IS ACCELERATING.
THIS IS THE 21ST-CENTURY VERSION
OF GALILEO'S RAMP AND THE BALLS
ROLLING DOWN.
SO, CAN WE GET IT GOING?

Vicki says OF COURSE, IF YOU'D JUST LIKE
TO PRESS THE BUTTON ON THE
LAPTOP.

Jim says THIS ONE?

Vicki says YEP.

Jim says OKAY.

Vicki says SO, IT'S NOW COMMUNICATING
WITH IT.

Jim says OH, HERE WE GO.

Vicki says THERE WE GO.
IT WAITS FIVE SECONDS, THEN
TAKES THE MEASUREMENT OF
GRAVITY.

Jim says AND AGAIN.

Vicki says REPEATS.

Jim points at a wall screen and says OH, AND YOU CAN SEE THE
RESULTS APPEARING NOW.

Vicki says YEP, EACH OF THOSE GREEN DOTS
IS A MEASUREMENT OF GRAVITY
WITH THE ACTUAL NUMBER THAT
IT'S GETTING FOR EACH ONE.

Jim says THE UNIT VICKI USES HAS
A FAMILIAR RING.
I SEE THAT THE NUMBER UP AT
THE TOP HERE, SO YOU'VE GOT
THIS UNIT, MICRO GAL?

Vicki says YES, A GAL IS ESSENTIALLY ONE
CENTIMETRE PER SECOND SQUARED.
THE GAL WAS NAMED AFTER GALILEO.

Jim says SO, WE'VE JUST TAKEN THE
MEASUREMENT OF GRAVITY HERE
TODAY, AND IT'S THIS HIGHLY
ACCURATE NUMBER, 981124007
MICRO GALS.
THE READING MEANS THAT THE
EARTH'S GRAVITY SPEEDS UP A
FALLING OBJECT BY AROUND 9.81
METRES PER SECOND FOR EVERY
SECOND IT DROPS.
VICKI TELLS ME SOMETHING
INTRIGUING.
SHE TAKES A READING HERE EVERY
WEEK, AND SHE'S FOUND THAT THE
STRENGTH OF GRAVITY CHANGES
BY TINY AMOUNTS OVER TIME.
HEAVY RAINFALL, FOR EXAMPLE,
CAN CAUSE GRAVITY TO INCREASE
SLIGHTLY.
PRESUMABLY, IF GRAVITY IS
CHANGING HERE IN ONE SPOT,
IT'LL HAVE DIFFERENT VALUES
ALL AROUND THE WORLD, AND SO
YOU CAN HAVE A GRAVITY MAP
OF THE ENTIRE PLANET?

Vicki says THAT'S RIGHT, YEAH.

Jim says SO, WHAT'S THE REASON FOR
THESE STRANGE FLUCTUATIONS?
THAT'S WHAT I WANT TO
INVESTIGATE NEXT.
SO, GRAVITY CHANGES AS WE MOVE
ACROSS THE SURFACE OF THE EARTH.
WELL, THIS LIES AT THE HEART
OF A CHALLENGE THAT I'VE SET
TWO YOUNG VOLUNTEERS.
I'VE GIVEN THEM A TASK TO TRY
AND FIND THE PLACE IN BRITAIN
WHERE GRAVITY IS AT ITS
WEAKEST.
SO, WHERE OBJECTS WOULD WEIGH
THE LEAST.
AND I'VE GIVEN THEM JUST THREE
DAYS TO TRY AND FIND IT.
THE VOLUNTEERS ARE ESTRELLA
SENDRA, A PHD STUDENT.

Estrella is in her late twenties, with long straight blond hair and wears a yellow sweater, big yellow earrings and a yellow and brown tribal necklace

She says I'VE BEEN LIVING IN LONDON
FOR FIVE, SIX YEARS, AND I'M
ORIGINALLY FROM SEVILLE IN
SPAIN.
I'M VERY INTERESTED IN TAKING
PART IN THIS PROJECT BECAUSE
I WOULD REALLY LIKE TO KNOW
MORE ABOUT HOW THIS WORLD WORKS.

Jim says AND POPPY BEGUM, A JOURNALIST
WHO LIVES IN LONDON.

Poppy is in her late twenties, with long straight brown hair and wears a printed black top and a white cardigan sweater.

She says I DID MY DEGREE IN
BIOMEDICAL SCIENCE.
AND I DID BIOLOGY AND CHEMISTRY
FOR MY A-LEVELS, BUT I HAVEN'T
DONE ANY PHYSICS SINCE I LEFT
SCHOOL.
I'M FASCINATED TO FIND OUT MORE
ABOUT GRAVITY AND I ACTUALLY
ENJOY A PUZZLE, I LIKE A
CHALLENGE.

Jim says NOW, THE TEAM CAN'T JUST
WEIGH THEMSELVES TO SEE CHANGES
IN GRAVITY.
BODY WEIGHT FLUCTUATES NATURALLY
BY A COUPLE OF KILOS OVER THE
COURSE OF A DAY, WHEREAS
CHANGES DUE TO GRAVITY AS THEY
TRAVEL AROUND THE COUNTRY ARE
GOING TO BE TINY IN COMPARISON,
THE MATTER OF A FEW GRAMS.
SO, THEY'RE GOING TO HAVE TO
USE SOPHISTICATED SCIENTIFIC
METHODS IF THEY WANT TO MEASURE
GRAVITY ACCURATELY.
AND THAT'S WHY THE VOLUNTEERS
WILL BE JOINED BY THREE
SPECIALISTS IN GRAVITY SCIENCE.
PHD STUDENT SONAK BOWES.

Sonak is in his thirties, with short curly brown hair and a beard. He wears glasses, ivory trousers and a red hooded jacket.

Jim says HE'LL BE IN CHARGE OF SOME VERY
SENSITIVE MEASURING APPARATUS
FROM THE NATIONAL PHYSICAL
LABORATORY.
SEAN HUGHES, A GEOLOGIST, WHO
WILL BE USING A PORTABLE
GRAVITY METER.

Sean is in his forties, with short brown hair and a goatee. He wears jeans, a gingham shirt and a black and green jacket.

Jim says AND ANDREW PONTZEN, A
COSMOLOGIST AT UNIVERSITY
COLLEGE LONDON, WHO WILL HELP
INTERPRET THE RESULTS.

Andrew is in his twenties, with brown hair and a shadow of a beard. He wears glasses, a black zip up jacket and a black and white patterned woolen hat.

Jim says WE'VE TAKEN A COLLECTIVE WEIGHT
FOR THE TEAM BEFORE THEY SET
OFF.
IT'S 380 KILOGRAMS.
SO, CAN THEY FIND THE PLACE
IN BRITAIN WHERE THAT WILL
DECREASE?
THEY'RE SETTING OUT IN
SNOWDONIA NATIONAL PARK IN
NORTH WALES.

An animated map shows the location of Snowdon.

Jim says THE RAILWAY CLIMBS FROM HERE
TO THE 1000-METRE SUMMIT OF
SNOWDON.
SEAN TAKES HIS FIRST GRAVITY
READING.

Sean says INSIDE IS A MASS ON A BEAM
AND YOU TURN THIS COUNTER,
THIS DIAL, UNTIL YOU GET THE
BEAM CENTRAL.

Jim says BY COUNTING THE NUMBER OF
TURNS OF THE DIAL, SEAN CAN
CALCULATE THE DOWNWARD PULL OF
GRAVITY ACTING ON THE MASS
INSIDE THE MACHINE.
SONAK HAS A SIMPLER METHOD.

Sonak says SO, INSIDE THE BOX IS A
TWO-KILOGRAM MASS, AND IT'S
SUPPOSED TO BE SORT OF AS
PERFECTLY TWO KILOGRAMS AS IT'S
POSSIBLE TO GET.
ALL RIGHT.

He puts it on a scale and says AND PLACE IT HERE.

Poppy says OH, IT'S JUST COMING UNDER,
ISN'T IT?

Sonak says 1998.2 GRAMS.

Poppy says SO, IT WAS TWO KILOS IN
THE LABORATORY, BUT NOW HERE
IT'S A BIT LESS.

Jim says IT'S THE FIRST PUZZLE.
WHY DOES A TWO-KILO MASS TIP
THE SCALES AT JUST UNDER TWO
KILOS?
AND IT'S ONE WHICH GETS
STRAIGHT TO THE HEART OF WHAT
THE CHALLENGE IS REALLY ABOUT.
MASS IS OFTEN CONFUSED WITH
THE RELATED QUANTITY, WEIGHT.
THE MASS OF THESE DUMBBELLS
IS FIXED, IT DOESN'T CHANGE.
IT'S A MEASURE OF HOW MUCH
STUFF THEY CONTAIN.
WEIGHT IS DIFFERENT.
IT'S A MEASURE OF THE EFFECT
OF GRAVITY ON THESE DUMBBELLS.
THE DOWNWARD FORCE PULLING
THEM TO THE GROUND IN THE SAME
WAY THAT IT'S KEEPING MY FEET
FIRMLY STUCK TO THE GROUND.
THE CRUCIAL DIFFERENCE IS THIS,
IF I WAS HOLDING THESE DUMBBELLS
ON THE MOON, THEY'D STILL HAVE
EXACTLY THE SAME MASS, BUT THEY
WOULD WEIGH SIX TIMES LESS
BECAUSE THE MOON'S GRAVITY IS
SO MUCH WEAKER THAN THE EARTH'S.
SO, THAT'S WHY SONAK IS
BRINGING ALONG THE TWO-KILO
MASS.
IF IT CHANGES WEIGHT, THEN
THIS SHOULD MEAN THAT GRAVITY
ITSELF HAS CHANGED.
AHEAD OF THEM IS THE SUMMIT
OF THE HIGHEST MOUNTAIN IN
ENGLAND AND WALES, FAMED FOR
ITS STUNNING SCENERY.
OR, IT WOULD BE STUNNING
IF YOU COULD SEE IT.

At the summit, Andrew says AND THIS IS WHAT WE CAME ALL
THE WAY UP HERE FOR, THIS
AMAZING VIEW AT THE TOP OF
SNOWDON.
YOU WOULDN'T KNOW IT, BUT
HONESTLY, WE ARE HERE.

Sean says SO, WE'RE NOW NEAR THE SUMMIT
OF SNOWDON, AND I'VE SET UP THE
GRAVIMETER AGAIN, AND WE'RE
GOING TO SEE WHAT THE
DIFFERENCE IN THE READING IS.

Jim says HE HAS TO TURN THE DIAL AGAIN
AND AGAIN TO TRY AND GET A
READING.
IT'S CLEAR GRAVITY HAS CHANGED,
BUT WHICH WAY?
HAS IT GOT STRONGER, OR WEAKER?
THE TEAM LEAVE SEAN TO WORK
OUT HIS RESULTS, AND TRIES TO
POSITION THE SCALES AS CLOSE
AS POSSIBLE TO THE SUMMIT.
BUT THE READING IS ALL OVER
THE PLACE.

Sean says OH!

Poppy says IT'S GONE UP.
(LAUGHING)

Sonak says IT'S FLUCTUATING QUITE A LOT
DUE TO THE WIND.

Andrew says I HAVE TO SAY, THIS IS WHAT
SCIENCE IS ALWAYS LIKE, ISN'T
IT?
IT'S NEVER QUITE WHAT YOU WANT
IT TO BE.

Jim says SO, THEY HEAD INSIDE TO THE
CAFÉ NEXT TO THE SUMMIT.

Sonak says THE WIND WAS BEING A BIT
NAUGHTY, BUT HOPEFULLY...

Estrella says NOW IT'S IN 00, SO IT SHOULD
BE ALL RIGHT.

Sonak says 1998.2 DOWN THERE,
1997.8!

Andrew says THERE YOU GO.

Sonak says WE'VE GOT IT!
THAT'S 0.4 OF A GRAM OFF.

Jim says THE MASS WEIGHS A TINY BIT
LESS.
IT'S LOST ABOUT ONE 5000TH OF
ITS WEIGHT.
AND SEAN HAS FOUND THAT GRAVITY
ITSELF HAS REDUCED.

Sean says AT THE TOP OF THE MOUNTAIN
WE TOOK THE MEASUREMENT, AND WE
DISCOVERED THAT THE PULL OF
GRAVITY HAD GONE DOWN.
IT HAD GONE DOWN THE EQUIVALENT
OF 206 TURNS OF THE DIAL.
AND WE WORKED OUT THAT THAT'S
EQUIVALENT TO 219 MILLIGALS.

Estrella says SO, IT'S CLEAR FROM THE
TEAM'S MEASUREMENTS, GRAVITY
WEAKENS AS YOU GO HIGHER,
AND YOU GET A BIT LIGHTER.

Poppy says IT'S JUST AN EXCUSE TO SAY
WHERE ARE WE, LIKE, THE
LIGHTEST.
WHO CARES?

Estrella says YEAH, WHO DOES CARE?

Poppy says IT'S ACTUALLY REALLY
INTERESTINGLY, IT'S LIKE AN
ILLUSTRATIVE EXAMPLE OF SEEING
HOW THIS IS ACTUALLY
FLUCTUATING, DEPENDING ON
DIFFERENT FACTORS.

Estrella says YEAH, ABSOLUTELY.
AND THAT WE COULD MEASURE IT
AND WE COULD SEE IT WITH OUR OWN
EYES, IT ACTUALLY MAKES YOU
THINK ABOUT GRAVITY IN A
VERY ACTIVE WAY.
IT'S SUCH A FUNDAMENTAL FORCE,
PHENOMENON IN NATURE, BUT WE
DON'T KNOW MUCH ABOUT IT.

Jim says BUT WHY DOES GRAVITY CHANGE
WITH ALTITUDE?
TO UNDERSTAND THAT QUESTION,
YOU HAVE TO GET TO GRIPS WITH
THE EXTRAORDINARY DISCOVERIES
OF THE NEXT SCIENTIFIC GIANT
IN OUR STORY: ISAAC NEWTON.
BORN IN ENGLAND IN THE MIDDLE
OF THE 17TH CENTURY, HE SPENT
HIS LIFE WRESTLING WITH
SO MANY APPARENTLY SEPARATE
QUESTIONS, FROM WHY THINGS FALL
TO THE GROUND, TO WHY PLANETS
ORBIT THE SUN.
IT TOOK THE GENIUS OF NEWTON
TO REALIZE THERE WAS ONE SINGLE
EQUATION THAT COULD ANSWER ALL
THESE QUESTIONS.
AND HERE IT IS,
HIS FAMOUS LAW OF GRAVITY.

A caption reads "F equals G multiplied by M1 by M2 over R square."

Jim says IT MIGHT LOOK COMPLICATED,
BUT THIS IS ONE OF THE MOST
IMPORTANT EQUATIONS IN THE
WHOLE OF SCIENCE.
F HERE IS THE FORCE.
NEWTON SAID THERE'S AN
ATTRACTIVE FORCE BETWEEN ANY
TWO OBJECTS IN THE UNIVERSE.
ON THIS SIDE OF THE EQUATION,
G, WE CALL THE GRAVITATIONAL
CONSTANT.
NOW, NEWTON KNEW IT HAD TO BE
THERE, BUT HE DIDN'T KNOW WHAT
ITS VALUE WAS.
M1 AND M2 REPRESENT THE TWO
OBJECTS, AND R IS THE DISTANCE
BETWEEN THEM.
NOW, THE EQUATION TELLS US THAT
THE MORE MASSIVE THE OBJECTS
ARE, THE BIGGER M1 AND M2,
THE GREATER THE ATTRACTIVE
FORCE.
BUT THE FURTHER APART THEY ARE,
THE BIGGER THE VALUE OF R HERE,
THE WEAKER THE GRAVITATIONAL
FORCE.
WITH NEWTON, WHAT WAS ONCE
MYSTERIOUS NOW BECAME CLEAR.
NEWTON'S EQUATION DESCRIBES
WHY AN OBJECT FALLS TO THE
GROUND, INCLUDING HIS FAMOUS
APPLE.
BUT ITS TRUE GENIUS IS THAT IT
APPLIES TO ANY OBJECT, ANYWHERE
IN THE UNIVERSE.
SO, IT'S A VERY SIMPLE AND
ELEGANT WAY OF DESCRIBING SOME
OF THE SEEMINGLY MOST
COMPLICATED PHENOMENA IN
THE COSMOS.
HIS LAW OF GRAVITATION CAN
STILL BE USED TODAY...
TO EXPLAIN HOW ORBITS WORK,
TO PREDICT WHEN A COMET WILL
RETURN.
TO DESCRIBE WHY GALAXIES SPIN.
OR TO SLINGSHOT SPACECRAFT
AROUND PLANETS.
NEWTON TELLS US TO LOOK FOR
THE UNDERLYING SIMPLICITY IN
NATURAL PHENOMENA.
FOR INSTANCE, HOW THE MOON
ORBITS THE EARTH.
IF I LET GO OF THIS APPLE,
IT'LL FALL STRAIGHT DOWN
BECAUSE OF THE PULL OF
EARTH'S GRAVITY.
BUT IF I THROW IT, TO BEGIN
WITH, IT TRAVELS IN A
HORIZONTAL DIRECTION,
THAT'S THE DIRECTION OF TRAVEL,
BUT EARTH'S GRAVITY IS STILL
PULLING IT DOWNWARDS,
SO IT ENDS UP FOLLOWING
A CURVED PATH.
NOW, IF I THROW IT HARDER,
IT'LL TRAVEL FURTHER BEFORE IT
HITS THE GROUND AND, IN
PRINCIPLE, IF I COULD THROW IT
HARD ENOUGH, I COULD PUT IT
INTO ORBIT.
AND THAT'S EXACTLY WHAT'S
HAPPENING WITH THE MOON
IN ORBIT AROUND THE EARTH.
IT'S A COMBINATION OF WANTING
TO TRAVEL IN A STRAIGHT LINE,
BUT ALSO BEING PULLED DOWN
BY THE EARTH'S GRAVITY.
SO, IT ENDS UP CONSTANTLY
FALLING AROUND THE EARTH,
AND CONSTANTLY MISSING.
NEWTON'S FAMOUS EQUATION ALSO
EXPLAINS THE STRANGE EFFECTS
WHICH THE ROAD-TRIP TEAM
HAS DISCOVERED, THAT OBJECTS
GET LIGHTER AS YOU GAIN IN
ALTITUDE.

He steps on a scale and says WHEN I WEIGH MYSELF, I'M
REPRESENTED BY THE FIRST MASS,
M1.
THE SECOND MASS, M2, IS THE
EARTH ITSELF.
AND THE FORCE PULLING ME DOWN,
MY WEIGHT, DEPENDS ON THE
DISTANCE BETWEEN ME AND THE
CENTRE OF THE EARTH.
AND THAT'S THE SECRET OF
THE ROAD TRIP.
IF YOU WANT TO FIND THE PLACE
WHERE YOU WEIGH THE LEAST,
THEN YOU HAVE TO GET AS FAR
AWAY AS YOU CAN FROM THE
EARTH'S CORE.

(music plays)

Jim says SO, IT'S THE AFTERNOON OF DAY
ONE, AND THE ROAD-TRIP TEAM
HAVE TO WORK OUT WHERE TO GO
NEXT.
POPPY AND ESTRELLA HAVE A GOOD
IDEA, FIND SOMEWHERE HIGHER
THAN MOUNT SNOWDON.

Poppy says FROM THE MEASUREMENTS THAT
YOU GUYS DID AT MOUNT SNOWDON,
ALTITUDE CLEARLY PLAYS AN
IMPORTANT PART IN GRAVITY.
SO, WITH THAT IN MIND, WE'VE
GOT TO GO TO THE HIGHEST POINT
IN THE UK, WHICH IS BEN NEVIS.

Andrew says OKAY, BUT THERE'S JUST ONE
THING THAT WE HAVEN'T SHOWN YOU
SO FAR.
WE ACTUALLY BROUGHT ALONG AN
EXTRA EXPERIMENT, SO CAN WE
PLEASE SHOW YOU THIS FIRST
BEFORE YOU MAKE THE FINAL
DECISION?

Poppy says YES.

Andrew says SONAK ACTUALLY HAS THE OTHER
PART OF THIS EXPERIMENT.
WE ALWAYS CARRY AROUND...

Sonak shows them a drill with a disc and some pizza dough on it.

He says SOME POWER TOOLS, AS
PHYSICISTS ALWAYS DO.
SO, LET'S START IT OFF NICE
AND GENTLE.
(DRILL WHIRRING)
OKAY, AND THEN, TRY AND PICK UP
SOME PACE.

Poppy says PIZZA.

Andrew says AH...

The dough stretches.

Estrella says YOU'VE GOT SOME PIZZA THERE.

Sonak says POINT PROVEN.

Andrew says THE POINT IS THAT WHEN
SOMETHING IS SPINNING, IT KIND
OF GETS FLUNG OUTWARDS AND YOU
CAN ACTUALLY USE THAT TO MAKE
A NICE, FLAT PIECE OF PIZZA,
BUT THIS ALSO APPLIES TO THE
EARTH.

Jim says THE EARTH ISN'T PERFECTLY
ROUND.
IT'S WHAT'S KNOWN AS AN
"OBLATE SPHEROID."
IT BULGES AT THE EQUATOR
WHERE THE SPIN IS GREATEST.

An animation shows a spinning Earth with the caption "Not to scale."

Andrew holds a small globe and says WE'VE KIND OF GOT TWO
COMPETING EFFECTS NOW.
WE'RE TRYING TO GET AWAY FROM
THE CENTRE, THE ACTUAL CORE OF
THE EARTH, THE POINT AT THE
VERY CENTRE OF THIS BALL.
BUT NOW, WE CAN DO IT IN TWO
WAYS.
WE CAN EITHER GO UP SOMETHING
TALL, OR WE CAN JUST GO DOWN
TOWARDS THE EQUATOR.

Sean says THIS IS WHAT WE FIND WHEN
WE'RE DOING GRAVITY SURVEYS, IS
THAT AS YOU MOVE SOUTH, THERE
TENDS TO BE AN EFFECT FROM
LATITUDE WHICH IS OFTEN USUALLY
LARGER THAN THE EFFECT FROM
ALTITUDE.

Jim says SO, THE CLOSER TO THE
EQUATOR YOU GO, THE FURTHER
YOU GET FROM THE EARTH'S CORE
AND THE LIGHTER YOU GET.

Poppy says SO, GUYS, THE SUN'S SETTING
JUST BEHIND ME HERE.
THIS IS NORTH.
FROM THE CONVERSATIONS WE'VE
JUST HAD, IT SOUNDS LIKE WE'VE
GOT TO GO THAT WAY, DOWN SOUTH,
IS THAT RIGHT?

Sean says YEAH, OKAY.

Estrella says LET'S GO.
(LAUGHING)

Jim says THE TEAM IS STARTING TO
UNCOVER THE REASONS WHY GRAVITY
CHANGES AS YOU CROSS THE
SURFACE OF THE EARTH.
OUR PLANET IS DEFINED AND
SHAPED BY THE COMPLICATED
FORCES WHICH ACT UPON IT.
AND DETECTING TINY FLUCTUATIONS
IN ITS GRAVITY FIELD CAN GIVE
US IMPORTANT CLUES.
IT CAN HELP US UNDERSTAND HOW
OUR WORLD IS CHANGING.

A satellite image shows the Earth showing Earth's gravity fields.

Jim says THE SPACE GEODESY FACILITY AT
HERSTMONCEUX IS ONE SMALL PART
IN AN ENORMOUS GLOBAL NETWORK
WHICH USES SATELLITES TO DETECT
THE TINIEST OF CHANGES IN THE
EARTH'S GRAVITY FIELD.
TELL ME WHAT EXACTLY YOUR JOB
IS HERE?

The caption changes to "Doctor Graham Appleby. NERC Space Geodesy Facility."

Graham is in his sixties, with short white hair and wears glasses, a blue shirt and a blue jacket.

He says WHAT WE'RE DOING WITH THIS
TELESCOPE IS MEASURING VERY
ACCURATELY THE DISTANCES OF
SATELLITES FROM HERE, SO WE'RE
USING VERY SHORT LASER PULSES
WHICH WE DIRECT TOWARDS THE
SATELLITE.
ON THE SATELLITE, THERE ARE
REFLECTING CUBES, WHICH RETURN
SOME OF THAT LIGHT TO US.
WE MEASURE HOW LONG IT TAKES
THE LIGHT TO GO TO THE SATELLITE
AND BACK.

Jim says AND HOW FAR AWAY IS THE
SATELLITE TYPICALLY?

Graham says THE ONE WE'RE TRACKING NOW
IS ONE OF THE GALILEO
SATELLITES, WHICH IS ABOUT
20,000 KILOMETRES.

Jim says 20,000 KILOMETRES AWAY?

Graham says YES.

Jim says OKAY, SO, WE'VE GOT IT AIMED
AT THE GALILEO SATELLITE AND
YOU'RE GOING TO TURN THE LASER
ON NOW?

Graham says YES.

Jim looks up and says OH, WOW!
AND THAT LASER BEAM THAT'S BEING
FIRED UP TOWARDS THE SATELLITE,
THE TIME IT'LL TAKE TO GET
THERE AND COME BACK AGAIN,
IT'S A FRACTION OF A SECOND,
ISN'T IT?

Graham says IT IS.
IT'S ABOUT 150 THOUSANDTHS
OF A SECOND, 150 MILLISECONDS.
AND WE'RE SENDING ABOUT 1000
OF THOSE PER SECOND.

An animation shows Earth constantly changing colours.

Jim says THIS STRANGE-LOOKING OBJECT
IS BASED ON SATELLITE READINGS.
IT'S A HIGHLY EXAGGERATED
REPRESENTATION OF HOW EARTH'S
GRAVITY FIELD VARIES OVER TIME.
FLUCTUATIONS LIKE THESE CAN
GIVE US IMPORTANT INSIGHTS
INTO CLIMATE CHANGE,
ICECAPS MELTING,
SEA LEVELS RISING,
CHANGES IN GROUND WATER.

An animated image of the ice caps appear with the caption "Gravity Gradient. Low resolution from GRACE." It shows how water levels rise as the icecaps melt across the years.

Jim says ALL OF THESE HAVE AN EFFECT
ON THE LOCAL STRENGTH OF
GRAVITY.
SO, SOMETHING AS IMPORTANT
AS CLIMATE CHANGE, IN ORDER TO
UNDERSTAND IT AND DO SOMETHING
ABOUT IT, WE NEED TO KNOW THE
DISTRIBUTION OF THE
GRAVITATIONAL FIELD OF THE
EARTH VERY ACCURATELY?

Graham says ABSOLUTELY, YES, AND IT'S A
GLOBAL MEASURE THAT WE NEED.

(music plaus)

Jim says FOR THE ROAD TRIPPERS,
IT'S THE START OF DAY TWO,
AND THEY'RE HEADING FOR THE
SOUTH COAST.
THEY'RE STOPPING OFF IN
HEREFORDSHIRE.
IT'S A GOOD LOCATION AS IT'S
THE SAME ALTITUDE AS THE BASE
OF SNOWDON, BUT THEY'VE MOVED
ABOUT 80 MILES FURTHER SOUTH.
SO, IF THEY FIND GRAVITY
CHANGES HERE, IT MUST BE DUE
TO LATITUDE.

Sean says IT'S NOT A HUGE DIFFERENCE,
BUT IT'S NOTICEABLE.
OUR COUNTER READING AT THE
BOTTOM OF THE MOUNTAIN WAS
4,840.

Estrella says YEAH.

Sean says OUR COUNTER READING HERE'S
4,717.

Estrella says OH, RIGHT, SO, WE DO GET TO
SEE A DIFFERENCE.

Poppy says SO, WE'RE ACTUALLY AT THE
SAME ALTITUDE AS THE BASE OF
MOUNT SNOWDON, BUT BECAUSE
WE'VE TRAVELLED FURTHER DOWN
SOUTH OVERNIGHT, GRAVITY'S LESS
HERE?

Sean says YEAH.

Jim says THEY PUSH ON.
AND BY SUNSET THEY REACH
SIDMOUTH ON THE SOUTH COAST.
SEAN TAKES THE SECOND GRAVITY
READING OF THE DAY, AND POPPY
IMPROVISES A MAP.
WELL, SORT OF A MAP.

Poppy draws a map on a board and says CAN WE WRITE "NOT TO SCALE."
AT THE TOP THERE?
NOT TO SCALE.
(OTHERS LAUGHING)

Poppy says SO, I DREW THIS MAP.
SCOTLAND'S A BIT SQUASHED.
WALES IS QUITE HIGH UP, AND
CORNWALL IS THERE, BUT YOU GET
THE IDEA.
SO, SEAN, WE'VE BEEN TRAVELLING
WITH YOU, YOU'VE DONE QUITE A
FEW GRAVITY METER READINGS.
CAN YOU PLOT THEM ON THIS
NOT-TO-SCALE, BADLY DRAWN MAP,
PLEASE?

Sean says SURE.
SO, IF YOU REMEMBER WE STARTED
OFF IN MOUNT SNOWDON, HERE,
AND THAT WAS THE ZERO
MEASUREMENT FOR OUR SURVEY.
THEN, WE'VE COME ALL THE WAY
DOWN HERE TO THE SOUTH COAST.
THE DIFFERENCE FROM THE BASE
OF SNOWDON IS -212 MILLIGALS.

Poppy says WOW.

Sean says SO, THE DIFFERENCE BETWEEN
GOING AND MEASURING GRAVITY
AT THE BASE OF THE MOUNTAIN
AND THE TOP OF THE MOUNTAIN
IS ABOUT THE SAME AS HERE AT
THIS LATITUDE, AND DOWN HERE
AT THIS LATITUDE.

Jim says THEY'RE QUITE CLEARLY AT SEA
LEVEL, YET GRAVITY HERE IS
ROUGHLY THE SAME AS IT IS
AT THE TOP OF SNOWDON.
BUT WHERE NEXT?

Poppy says WE ARE HERE.
IF WE WANT TO FIND OUT WHERE
WE ARE THE LIGHTEST, WHY DON'T
WE TRAVEL ALL THE WAY TO THE
MOST SOUTHERLY POINT IN THE UK,
WHICH IS HERE?

Sonak says BUT ALTITUDE CAN ALSO HELP
US, SO WHY NOT FIND A PLACE
IN THE COUNTRY THAT IS BOTH LOW
IN LATITUDE, BUT ALSO IS HIGH
IN ALTITUDE IN TERMS OF HEIGHT
ABOVE SEA LEVEL, BECAUSE THAT
WILL GET US SOMEWHERE THAT IS
REALLY FAR AWAY FROM THE CORE
OF THE EARTH, WHILST STAYING
WITHIN THE COUNTRY?

At the beach, the team juggles with rocks and throws them in the ocean.

Jim says SO, THE ANSWER TO THE PUZZLE
LIES IN A COMBINATION OF TWO
FACTORS.
HOW MUCH FURTHER SOUTH SHOULD
THEY GO, AND HOW MUCH HIGHER?
AT THE END OF DAY TWO, SEAN'S
RESULTS SHOW THAT THE TEAM
WEIGHS ABOUT 80 GRAMS LIGHTER
IN TOTAL THAN BACK AT THE BASE
OF SNOWDON.

(music plays)

Jim says THE WAY THAT WEIGHT CHANGES
IS JUST ONE EXAMPLE OF
NEWTON'S FAMOUS EQUATION
IN ACTION.
BUT NEWTON HAD LEFT HIS
MASTERPIECE INCOMPLETE.
HE DIDN'T KNOW THE VALUE OF G,
THE GRAVITATIONAL CONSTANT,
WHICH SETS THE SIZE OF THE
FORCE.
TO HARNESS THE FULL POWER
OF THE EQUATION, YOU NEED
TO KNOW G.
AND THE VITAL CLUE CAME WITH
AN INCREDIBLE EXPERIMENT
CONDUCTED IN LONDON AT THE
END OF THE 18TH CENTURY.
IT WAS AN ATTEMPT TO WORK OUT
THE MASS OF THE EARTH ITSELF.
AND IT WAS CARRIED OUT BY AN
ECCENTRIC, EXTRAVAGANTLY RICH
ARISTOCRAT, HENRY CAVENDISH.
CAVENDISH WAS A CHRONICALLY SHY,
DEEPLY SOLITARY MAN LIVING IN
TOTAL ISOLATION IN HIS HOUSE
IN CLAPHAM.
THE STORY GOES THAT, ONE DAY,
HE ACCIDENTALLY BUMPED INTO A
FEMALE SERVANT ON HIS STAIRCASE.
HE WAS SO TRAUMATIZED BY THIS
EVENT THAT HE HAD A NEW
STAIRCASE BUILT JUST FOR HIM
SO THAT THIS HORRIBLE INCIDENT
COULD NEVER HAPPEN AGAIN.
CAVENDISH HAD INHERITED VAST
FORTUNES, AND WAS ABLE TO
DEDICATE HIS LIFE TO DEVISING
PIONEERING EXPERIMENTS,
INCLUDING ONE PARTICULARLY
EXTRAORDINARY PIECE OF
EQUIPMENT.

He stands next to a device with four balls balancing at the ends of a wooden rod.

He says HE SET UP SOMETHING A BIT LIKE
THIS.
IT'S CALLED A "TORSION BALANCE."
IT INVOLVES FOUR LEAD SPHERES,
TWO LARGE HEAVY ONES WHICH ARE
HELD FIXED IN PLACE, AND
SUSPENDED BY A VERY THIN WIRE
IS A WOODEN ROD, SIX FEET LONG,
WITH TWO SMALLER BALLS ON
EITHER END.
NOW, THE CRUX OF THE EXPERIMENT
IS THE RELATIONSHIP BETWEEN
THE LARGE BALL AND THE SMALL
BALL.
NOW, OF COURSE, THERE'S A
GRAVITATIONAL PULL DOWNWARDS
ON BOTH OF THE BALLS DUE TO
THE EARTH'S GRAVITY.
BUT NEWTON ALSO TELLS US THAT
THERE SHOULD BE A VERY WEAK
GRAVITATIONAL PULL BETWEEN
THE BALLS, AND THIS IS
EFFECTIVELY WHAT CAVENDISH WAS
TRYING TO MEASURE.
ANY SLIGHT MOVEMENT OF THE SMALL
BALL TOWARDS THE LARGE ONE
SHOULD CAUSE A TWIST IN THE
TORSION WIRE, AND THAT'S WHAT
CAVENDISH WAS TRYING TO DETECT.
OF COURSE, THIS IS ALL MUCH
EASIER SAID THAN DONE.
THE EXPERIMENT WAS INCREDIBLY
SENSITIVE.
THE TINIEST OF VIBRATIONS,
THE SLIGHTEST BREEZE, CHANGES
IN TEMPERATURE COULD ALL
INFLUENCE THE MEASUREMENTS.
SO, CAVENDISH HAD TO ISOLATE
THE APPARATUS INSIDE A BOX,
AND THE BOX WITHIN A SHED.
HE EVEN REALIZED THAT HIS MERE
PRESENCE NEXT TO THE APPARATUS
COULD INFLUENCE THINGS, SO HE
HAD TO REMOVE HIMSELF OUTSIDE
THE SHED.
WHAT HE THEN DID WAS SIT OUTSIDE
THE SHED, AND THROUGH A SMALL
HOLE IN THE SHED WALL, LOOK
THROUGH A TELESCOPE TO DETECT
THE TINIEST OF TWISTS IN THE
WIRE.
IT WAS AN INCREDIBLY DIFFICULT
PROCESS, BUT AFTER MANY MONTHS,
HE FINALLY FELT CONFIDENT ENOUGH
THAT HE HAD A RELIABLE RESULT.
CAVENDISH FOUND THAT THE SMALL
BALLS DID MOVE...
A TINY FOUR MILLIMETRES.
HE CALCULATED HIS RESULTS BY
COMPARING THE DENSITY OF THE
BALLS WITH THE DENSITY OF
WATER.
IN THE END, THE RESULT OF
CAVENDISH'S EXPERIMENT AND
SUBSEQUENT CALCULATIONS WAS
THAT THE DENSITY OF THE EARTH
WAS ABOUT FIVE-AND-A-HALF TIMES
THAT OF WATER.
OR, PUT ANOTHER WAY, THE MASS
OF THE EARTH WAS 5.9 TRILLION,
TRILLION KILOGRAMS.
WHAT'S MOST REMARKABLE IS THAT
CAVENDISH GOT THIS NUMBER RIGHT
TO WITHIN AN ACCURACY OF 1 percent.
WITH CAVENDISH'S ASTONISHING
RESULT, SCIENTISTS WERE ABLE
TO WORK OUT G.
THEN THE EQUATION COULD BE USED
TO DETERMINE THE MASS OF ANY
CELESTIAL BODY IN ORBIT AROUND
ANOTHER.
SO, ASTRONOMERS WERE ABLE TO
CALCULATE THE MASS OF THE SUN
AND THE PLANETS, AND THE MOON,
AND, EVENTUALLY, EVEN DISTANT
GALAXIES.
AND OF COURSE, BACK ON EARTH
WE NEVER ESCAPE GRAVITY.
OVER THE COURSE OF THE DAY, IT
ACTUALLY SQUEEZES YOUR SPINE,
AN EFFECT YOU CAN SEE FOR
YOURSELF IF YOU USE A
MEASURING ROD.
OKAY, SO IT'S HALF PAST 7 IN
THE MORNING.
I'VE JUST GOT UP AND I'M GOING
TO SEE HOW TALL I AM BEFORE
GRAVITY DRAGS ME DOWN.

He measures himself and says THAT'S 178 CENTIMETRES, OR JUST
OVER 5'10."
OVER THE COURSE OF THE DAY,
GRAVITY COMPRESSES THE FLUIDS
IN YOUR SPINE.
RIGHT, IT IS JUST PAST 11 P.M.
I'VE BEEN STANDING UP FOR MOST
OF THE DAY, SO LET'S SEE IF
GRAVITY HAS HAD AN EFFECT ON
MY HEIGHT.
THAT IS 176 CENTIMETRES,
SO I REALLY HAVE SHRUNK BY JUST
OVER HALF AN INCH OVER THE
COURSE OF TODAY.
IN THE LONGER TERM, GRAVITY
CAN AFFECT YOUR POSTURE
PERMANENTLY, BUT THERE ARE
EXERCISES YOU CAN DO TO
COUNTERACT THIS EFFECT.

The caption changes to "Simon Rea. Sports scientist, The Open University."

Simon is in his forties, bald and clean-shaven. He wears jeans and a pale blue shirt.

He says PART OF MY RESEARCH HAS BEEN
LOOKING AT THE EFFECTS OF
GRAVITY ON THE HUMAN BODY.
SO, PEOPLE MIGHT NOT BE AWARE
OR THEY MIGHT NOT ALWAYS THINK
ABOUT THE EFFECT OF GRAVITY
ON OUR PHYSICAL STATE, ON
OUR HEALTH AND, PARTICULARLY,
ON OUR POSTURE.
HOWEVER, BECAUSE IT'S SUCH
A CONSTANT FORCE, GRAVITY HAS
A MASSIVE IMPACT OVER THE
COURSE OF OUR LIFETIME.

Jim says AS YOU GET OLDER, YOU CAN
DEVELOP A STOOP, WHICH IS
DAMAGING TO YOUR MOBILITY.

In the gym, Simon says GOKUN HERE HAS ACTUALLY GOT
VERY GOOD POSTURE, BUT I'D LIKE
YOU TO JUST SHOW NOT-SO-GOOD
POSTURE.

Gokun is in his thirties, with short wavy brown hair with shaved sides and a pointy beard. He wears a black hooded T-shirts and wrist bands.

Simon says SO WHEN...
POOR POSTURE IS REALLY ROUNDED
SHOULDERS, AND THEN LOSS OF
THE CURVE IN THE BACK, AS WELL.
CAN I JUST ASK YOU TO RAISE UP
YOUR ARMS WHEN YOU'RE IN THAT
POSTURE?

Gokun says I CAN'T GO ANY HIGHER.

Simon says NO, AND THEN, JUST COME BACK
DOWN, SHOULDERS BACK, AND THEN
RAISE YOUR ARMS.
YOU CAN SEE THE EFFECT OF
POSTURE ON FUNCTION.

Jim says IRONICALLY, THE EXERCISES
WHICH MANY GYM-GOERS DO
ACTUALLY MAKE YOUR POSTURE
WORSE.
THAT'S IF YOU ONLY EXERCISE
THE FRONTAL MUSCLES, LIKE
THE CHEST AND ABDOMINALS.
SO, IT'S RECOMMENDED YOU
EXERCISE THE BACK MUSCLES JUST
AS MUCH, TO STRAIGHTEN YOU OUT
AND COUNTERACT THE EFFECTS OF
GRAVITY.

(music plays)

Jim says MEANWHILE, IT'S THE END OF DAY
TWO FOR THE ROAD TRIP, AND
THEY'VE REACHED SIDMOUTH ON
THE SOUTH COAST, LOOKING FOR
THE PLACE IN BRITAIN WHERE
THEY'LL WEIGH THE LEAST.
THEY'VE WORKED OUT THE ANSWER
LIES IN A COMBINATION OF TWO
FACTORS - THE RIGHT MIX OF
GOING SOUTH AND BEING HIGHER
UP.
AND FOR THE FINAL LEG OF THE
JOURNEY, I'M GOING TO MEET
UP WITH THEM.
I ASKED THEM TO DRIVE A SHORT
DISTANCE WEST TO ONE OF THE
MOST REMOTE AREAS IN MAINLAND
BRITAIN.
DARTMOOR NATIONAL PARK.
IT'S ONLY 40 MILES FROM THE
SOUTHERNMOST TIP OF BRITAIN.

Andrew says HELLO.

Jim says HI, ANDREW.
NICE TO SEE YOU.
AND IT'S VERY HIGH, VERY
HILLY TERRITORY.

Poppy says JIM, THE TEAM GOT TO THE
SOUTH COAST YESTERDAY...

Jim says YEAH.

Poppy says --TO FIND GRAVITY AT ITS
WEAKEST.
BUT WE HAVEN'T QUITE FIGURED OUT
WHETHER IT'S ALTITUDE OR
LATITUDE.
DO WE GO FURTHER SOUTH, OR DO
WE GO HIGHER UP?

Jim says YOU'RE RIGHT TO ASK, "DO WE
GO AS FAR SOUTH AS POSSIBLE,
OR AS HIGH AS POSSIBLE?"
THAT'S WHY I'VE BROUGHT YOU
HERE TO DARTMOOR.
WE'VE CHARTED THE MOST IMPORTANT
POINTS ON THIS MAP HERE.

Estrella says ALL RIGHT.

Jim says LET'S HAVE A LOOK.
SO, WE ARE HERE, TWO BRIDGES.
THESE FOUR DOTS REPRESENT THESE
HILLS UP THERE BEHIND US, WHICH
ARE AT ABOUT 500 METRES ABOVE
SEA LEVEL.
SO, THAT'S WHAT WE WANT TO CHECK
OUT.
THESE HILLS ARE CLOSE TO THE
SOUTH COAST, AND THEY'RE ALSO
THE HIGHEST IN THE WHOLE OF
THE SOUTH OF ENGLAND.
SO, LOGIC SUGGESTS THEY MUST BE
THE RIGHT COMBINATION OF
LATITUDE AND ALTITUDE.

Sean says WELL, THERE'S ANOTHER REASON
WHY THIS MAKES PERFECT SENSE,
ONE WHICH WE HAVEN'T LOOKED
AT YET, AND THAT IS THE EFFECT
OF THE UNDERLYING ROCKS ON
GRAVITY.
AND I'VE GOT A MAP HERE THAT
SHOWS...

Jim says YOU'RE GOING TO TRUMP MY MAP
WITH YOURS, AREN'T YOU?

Sean says I AM!
HERE WE ARE, DOWN HERE.
NOW THESE BLUE AREAS ARE THE
LOWEST AREAS ACCORDING TO THE
DENSITY OF THE ROCKS UNDERNEATH.

Jim says THE ROCKS AROUND HERE ARE
MADE OF GRANITE, WHICH WILL
MAKE GRAVITY WEAKER STILL.
SO, THAT'S HELPING, AS WELL AS
THE ALTITUDE AND THE FACT THAT
WE'RE FURTHER SOUTH.

Sean says YEP, IT'S ALSO PLAYING
A PART.

Jim says WELL, WE HAVE A PLAUSIBLE
THEORY.
BUT NOW WE NEED TO TEST IT.
IF I'M RIGHT, THEN, AT THE TOP,
OUR GRAVITY READING SHOULD BE
BY FAR THE LOWEST READING OF
THE TRIP.
OF COURSE, THERE'S ANOTHER
EFFECT OF GRAVITY TO DEAL
WITH NOW.
IT'S KNACKERING WHEN YOU HEAD
UPHILL.
OKAY, SO I THINK THIS IS PRETTY
MUCH THE START OF THE HILLS
WE'VE LOCATED ON THE MAP.
SO, LET'S SEE IF THIS IS THE
LIGHTEST PLACE.
SEAN, IF YOU WANT TO GET THE
GRAVITY METER OUT, AND WE'LL
TAKE ANOTHER READING HERE.

Sean says YEP.

Jim says OKAY.
SEAN SETS UP HIS EQUIPMENT
ONE MORE TIME.
WHAT'S THE NEWS?

Sean says WELL, THE BOTTOM OF MOUNT
SNOWDON WAS OUR ZERO FOR THIS
TEST.
WE FOUND WE LOST A CERTAIN
AMOUNT BY GOING UP TO THE TOP
OF MOUNT SNOWDON.
WE FOUND WE LOST A CERTAIN
AMOUNT COMING SOUTH TO THE
SOUTH COAST.
NOT ONLY HAVE WE BEATEN THAT,
WE'VE SMASHED IT.

Jim says BRILLIANT.

Sean says WE WERE -219 MILLIGALS
LOWER AT THE TOP OF MOUNT
SNOWDON.
HERE ON DARTMOOR, WE'RE -347
MILLIGALS LOWER.

They all say WOW!

Jim says BRILLIANT!
SO, IT IS A COMBINATION OF
THREE THINGS.
WE'RE FAR SOUTH, SO IT'S THE
LATITUDE, WE'RE AT ALTITUDE,
WE'RE QUITE HIGH UP, AND WE'RE
SURROUNDED BY ALL THIS GRANITE
ROCK, WHICH IS LOW-DENSITY
ANYWAY.
I HOPE YOU ALL THINK IT WAS
WORTH THE CLIMB UP HERE,
ANYWAY?

Poppy says YES, ABSOLUTELY.

Jim says THERE YOU GO.
BOOM, SCIENCE!

(ALL LAUGHING)

Jim says NOW, WE ALREADY KNOW THAT
THE ALTITUDE OF THESE HILLS
TAKES US MUCH FURTHER FROM
THE EARTH'S CORE THAN ANYWHERE
ELSE FURTHER SOUTH IN BRITAIN,
SO GRAVITY MUST BE WEAKEST
HERE.
THERE'S EXTRA EVIDENCE, TOO.
THE BRITISH GEOLOGICAL SURVEY
HAS COMPILED TENS OF THOUSANDS
OF GRAVITY READINGS MADE IN
THE UK, AND THE LOWEST
READINGS EVER RECORDED WERE
ALL TAKEN AROUND HERE ON
THE HIGH HILLS OF DARTMOOR.
WHAT DO WE DO TO CELEBRATE?
WE WEIGH OURSELVES, OF COURSE.

Estrella says HE DOESN'T WEIGH THAT MUCH.

Andrew steps on a scale and says WHOA!

Jim steps on the scale and says IT'S ALL THEM NUTELLA
PANCAKES FOR BREAKFAST!

Poppy says 74, 75.

Jim says I NEED TO LOSE WEIGHT!
I CAN TELL YOU THAT YOU SHOULD
WEIGH SOMETHING LIKE 20 GRAMS
LESS THAN YOU DID AT THE BASE
OF MOUNT SNOWDON.
GUYS, I'M GUESSING SOMETHING
LIKE 25 TO 30 GRAMS LESS.
SO, IF YOU WANT TO WEIGH AS
LITTLE AS POSSIBLE, THIS IS THE
PLACE IN BRITAIN TO COME.
BUT IN ANY CASE, IT'S SUCH A
TINY AMOUNT THAT IT'S GOING TO
BE WIPED OUT ENTIRELY BY
WHATEVER IT WAS YOU HAD FOR
BREAKFAST THIS MORNING.

(LAUGHING)

(music plays)

A clip in slow motion shows a drop of water falling in a glass half filled with water.

Jim says IN EPISODE TWO, I'LL
INVESTIGATE HOW ALBERT
EINSTEIN'S THEORY OF GRAVITY
COMPLETELY CHANGED OUR
UNDERSTANDING OF SPACE AND
TIME.

I'LL TRAVEL TO LOUISIANA IN
THE USA TO LISTEN TO THE SOUND
OF BLACK HOLES COLLIDING.

A man says BIGGEST SOURCE OF ENERGY IN
THE UNIVERSE, ONE OF THE BIGGEST
EVENTS YOU'D EVER MEASURE, AND
WE JUST BARELY SAW IT.

Jim says AND WITH THE HELP OF
THOUSANDS OF VOLUNTEERS AND A
SMARTPHONE APP, I'LL EXPLORE
HOW THE SCIENCE OF GRAVITY CAN
HELP YOU AGE SLOWER.

Music plays as the end credits roll.

Presented by Professor Jim Al-Khalili.

Executive producer, Paul Sen.

Filmed, produced and directed by Andrew Smith.

Logo: Furnace.

Watch: Ep. 1 - The Amazing World of Gravity