Transcript: Harvey Brown on the Concepts of Time and Motion | Feb 18, 2007

[Theme music plays]

The opening sequence rolls. The logo of "Big Ideas" featuring a lit lamp bulb appears against an animated blue slate.
Then, Andrew Moodie appears in the studio juggling three balls.
Behind him, the walls are decorated with screens featuring lit lamp bulbs, and two signs read "Big Ideas."
Andrew is in his early forties, clean-shaven, with short curly black hair. He's wearing a blue T-shirt under a beige coat.

Andrew says HEY.
I'M ANDREW MOODIE.
YOU'VE JUST TUNED INTO
BIG
IDEAS
AND THIS IS VERY,
VERY HARD TO DO.
[Chuckling]
WOO, HERE WE GO.
I, UM...
I LEARNED HOW TO JUGGLE WHILE I
WAS STUDYING WITH THE
ODYSSEY THEATRE IN OTTAWA AND
THE ONLY WAY TO GET GOOD AT IT
IS TO PRACTICE BUT ONCE YOU'VE
LEARNED HOW...
[Sighing]
IT'S INCREDIBLY THERAPEUTIC.
IT'S ALMOST HYPNOTIC.
THE TRICK IS NOT TO LOOK AT ANY
ONE OF THE BALLS IN PARTICULAR.
YOU KNOW?
YOU JUST KINDA HAVE TO STEP BACK
AND...
YOU HAVE TO SENSE THE MOVEMENT
OF EACH ONE AND THEN TIME YOUR
HANDS TO BE IN A SPECIFIC PLACE
AT A SPECIFIC TIME.
IT HELPS ME TO IMAGINE THAT I
HAVE A KIND OF SOLAR SYSTEM IN
FRONT OF ME BUT THAT'S JUST ME.
YOU KNOW, IT'S FUNNY, ISN'T IT?
THAT THERE WAS A POINT IN TIME,
A LONG TIME AGO, WHEN WE HUMAN
BEINGS BELIEVED THAT THE SUN
MOVED AROUND THE EARTH.
[Chuckling]
I MEAN, CAN YOU BELIEVE THAT?
THE EARTH MOVES AROUND THE SUN
BECAUSE...
WELL, BECAUSE THAT'S WHAT WE'RE
TOLD AND IT MAKES SENSE, RIGHT?
I MEAN, IT WOULD BE ABSURD TO
THINK THAT THE EARTH IS THE
CENTER OF THE UNIVERSE AND THAT
EVERYTHING ELSE MOVES AROUND IT
BECAUSE...
WELL, BECAUSE MOVEMENT IS, WELL,
IT'S EASY TO EXPLAIN, OKAY?
IT'S...
MOVEMENT IS SOMETHING MOVING.
YOU KNOW?
AND YOU CAN KNOW SOMETHING MOVES
BECAUSE, WELL, BECAUSE...
YOU KNOW WHAT?
I'M GONNA LEAVE YOU IN THE VERY
GOOD HANDS OF HARVEY R. BROWN.
HE IS A PROFESSOR OF PHILOSOPHY
OF PHYSICS AT OXFORD UNIVERSITY
AND HE IS
MORE
THAN
QUALIFIED TO EXPLAIN THE DEEP
MYSTERY OF WHETHER ANYTHING EVER
MOVES AT ALL.

He continues juggling.

Then, a clip plays in which Harvey R. Brown gives a lecture to an unseen audience in a dark auditorium.
Harvey is in his late forties, clean-shaven, with curly brown hair. He's wearing glasses, a black suit, black shirt, and matching tie.

Harvey says WHEN I
RECEIVED THE KIND INVITATION TO
SPEAK AT THIS VENUE, I SUGGESTED
THE TITLE EINSTEIN IN TIME.
AND I RECEIVED A VERY POLITE BUT
FIRM REPLY FROM THE POWERS THAT
BE A THE PARAMETER...
THAT IN 2005, WHICH OF COURSE AS
YOU KNOW IS THE GREAT
ANNIVERSARY, THE 100 YEAR
ANNIVERSARY OF EINSTEIN'S
PAPER ON SPECIAL
RELATIVITY, THERE HAD BEEN A
LARGE NUMBER OF TALKS ON
EINSTEIN.
AND THE IMPRESSION THAT I GOT
WAS THAT THE PERIMETER WAS
EINSTEIN SATURATED.

[Audience laughing]

Harvey continues OR SOMETHING
LIKE THAT.
FAIR ENOUGH.
SO, I THOUGHT TODAY I WOULD TALK
A LITTLE BIT ABOUT TIME AND
MOTION IN A PRE-RELATIVISTIC
CONTEXT.
THIS IS NOT QUITE TRUE BECAUSE
WHAT I HAVE TO SAY TODAY ALSO...
HAS A LOT OF RELEVANCE TO
SPECIAL, EINSTEIN'S SPECIAL
THEORY OF RELATIVITY BUT I WON'T
DISCUSS THAT PER SAY.
SO I WANT TO TALK A LITTLE BIT
TODAY ABOUT TIME AND MOTION.

A caption appears on screen. It reads "Harvey Brown. Professor of Physics, Oxford University. Time and motion. Perimeter Institute, Waterloo. November 1, 2006."

Harvey continues PRIOR TO EINSTEIN.
BUT LET'S START WITH A WIDER
QUESTION.
WHERE ARE WE IN THE WORLD?
WHAT IS OUR PLACE IN THE GREATER
SCHEME OF THINGS?
HERE'S AN
ANSWER GIVEN BY CARL SAGAN.

A quote appears on a projection screen. It reads "We live on a hunk of rock and metal that orbits a humdrum star in the obscure outskirts of an ordinary galaxy comprised of 400 billion stars in a universe of some hundred billion galaxies." Carl Sagan.

Harvey continues IT MAKES YOU
FEEL A LITTLE BIT INSIGNIFICANT,
DOESN'T IT?

[Audience laughing]

Harvey continues ACTUALLY,
PHYSICS AT THE MOMENT IS A
LITTLE BIT AMBIGUOUS AS TO OUR
SIGNIFICANCE BECAUSE YOU OFTEN
HEAR PHYSICISTS SAY THAT THE
UNIVERSE WAS REALLY FINE TUNED
FOR LIFE.
MAYBE EVEN FOR US.
SO MAYBE OUR PLACE IN THE WORLD
IS NOT QUITE AS MARGINAL AS IT
SEEMS.
BUT NONE THE LESS, THE MESSAGE
THAT SAGAN IS GIVING US, THAT
WE'RE A VERY SMALL PART OF A
VAST COSMOS, THERE WAS A SEMINAL
MOMENT IN THE HISTORY OF SCIENCE
THAT WAS REALLY THE BEGINNING OF
THE UNDERSTANDING OF THIS
MESSAGE AND THAT OF COURSE WAS
THE COPERNICAN REVOLUTION.
IN THE 15th CENTURY, COPERNICUS
STATED THAT IT WASN'T THE, THE
SUN THAT MOVED BUT THE EARTH AND
HE DEFENDED A WHOLE NEW WAY OF
THINKING ABOUT THE SOLAR SYSTEM
AND OUR RELATIONSHIP WITH THE STARS.
NOW, MOTION IS ALWAYS DEFINED AS
A RELATIVE CONCEPT.
WHEN WE SAY SOMETHING IS MOVING,
WE ALWAYS MEAN THAT IT'S MOVING
RELATIVE TO SOMETHING.
WELL, WHAT IS THE SOMETHING THAT
IT'S MOVING RELATIVE TO?
NOW, PHYSICISTS HAVE A RATHER
STRANGE LANGUAGE BECAUSE THEY
TALK ABOUT MOTION RELATIVE TO
THINGS LIKE...
UM, CO-ORDINATE SYSTEMS OR
FRAMES OF REFERENCE.
THESE ARE RATHER ABSTRACT
THINGS.
BUT WHEN YOU THINK ABOUT A FORM
OF REFERENCE, IT'S A SYSTEM OF
SPATIAL, SAY CO-ORDINATES...
MAYBE WITH CLOCKS ATTACHED TO
THEM.
WHY IS IT WRONG TO PLUNK YOUR
CO-ORDINATE SYSTEM ON THE EARTH
RATHER THAN ON THE SUN?
WHAT DIFFERENCE DOES IT MAKE?
WHY THE FUSS?
WHY ISN'T IT JUST A QUESTION OF
PERSPECTIVE?
IF WE SAY THAT THE EARTH IS
MOVING, WE HAVE TO ASK OURSELVES
IF THERE'S SOME KIND OF BACKBONE
TO THE UNIVERSE RELATIVE TO
WHICH WE CAN DEFINE ABSOLUTE
MOTION AND WELL, WHAT IS IT?
WELL, WHAT WAS COPERNICUS' OWN ANSWER?

A new slide shows a portrait painting of Copernicus and a quote that reads "The first and highest of all is the sphere of the fixed stars, which contains itself and everything, and is therefore immovable. It is unquestionably the place of the universe, to which the motion and position of all the other heavenly bodies are compared." Copernicus, De Revolutionibus, 1543.

Harvey continues COPERNICUS CHOSE AS THE BACKBONE OF THE
UNIVERSE...
THE SPHERE, WHAT HE THOUGHT WAS
THE SPHERE OF FIXED STARS.
SO IN A SENSE, HE WAS INHERITING
ALMOST A ARISTOTELIAN NOTION
THAT THE STARS WERE EMBEDDED IN
A SPHERE...
AND ALL THE
FUNDAMENTAL MOTIONS OF THE WORLD
WERE DEFINED WITH RESPECT TO
THIS BACKBONE OF THE UNIVERSE.
NOW, JUST BEFORE I GO ON TO
EARLY, UM, NOTIONS OF THE STARS
AND MOTION, WELL, TO THE STARS,
I JUST WANTED TO MENTION THAT
THE REALLY SHOCKING THING ABOUT
THE COPERNICAN REVOLUTION IN A
WAY WAS THIS.
IF YOU DEFINE, IF YOU ULTIMATELY
DEFINE MOTION RELATIVE TO THE
FIXED STARS...
AND WE ARE MOVING THROUGHOUT THE
COURSE OF THE YEAR IN AN ORBIT
AROUND THE SUN AND WE'RE MOVING
IN RESPECT TO THE STARS, WHY
DON'T WE SEE THE PHENOMENON
STILL A PARALLAX?
AS I'M WALKING ALONG ON THIS
PLATFORM, I'M LOOKING AT YOU AND
I SEE YOUR SPATIAL ARRANGEMENTS
CHANGING AS I WALK.
OF COURSE, YOUR RELATIVE
DISTANCES AREN'T CHANGING
BETWEEN YOU BUT FROM MY POINT OF
VIEW, YOU ARE MOVING AMONGST
YOURSELVES.
THIS IS A, THIS IS JUST THE
EFFECT OF PARALLAX.
IF YOU'RE MOVING WITH RESPECT TO
THE STARS, HOW DON'T, WHY DON'T
WE SEE A SIMILAR PHENOMENON?
WITH RESPECT TO THE, WHY DON'T
WE SEE THE STARS MOVING AMONGST
THEMSELVES?

[Sniffing]

An unseen person says FAR AWAY.

Harvey continues BECAUSE
THEY'RE VERY FAR AWAY.
IN FACT...
THEY'RE ENORMOUSLY FAR AWAY.
SUDDENLY, THE UNIVERSE WENT
THROUGH AN ENORMOUS EXPANSION.
AND IF THE STARS ARE REALLY THAT
FAR AWAY, MAYBE THERE ARE OTHER
SUNS.
AND MAYBE THOSE OTHER SUNS ALSO
HAVE PLANETS AND SUDDENLY, THE
UNIVERSE LOOKS VERY, VERY LARGE
AND WE LOOK A LITTLE BIT LIKE A
SPECK AND THAT IS A SHOCKING
THING.
BUT IS IT RIGHT TO DEFINE MOTION
WITH RESPECT TO THE STARS AND
HAS IT ALWAYS BEEN THAT WAY?
WELL, OF COURSE NOT.
LET'S GO BACK TO...
TO PTOLEMY.
PTOLEMY OF COURSE REPRESENTED
THE HIGHEST POINT IN THE
ARTICULATION OF WHAT IS
ESSENTIALLY, IF YOU LIKE AN
ARISTOTELIAN WORLD VIEW, WHERE
THE EARTH IS AT THE CENTER OF
THE UNIVERSE AND IT DEFINES THE
FUNDAMENTAL FRAME.
NOW, WHY...
WHY WAS ARISTOTLE CONCERNED
ABOUT PUTTING THE EARTH AT THE
CENTER OF THE UNIVERSE?
ARISTOTLE HIMSELF WAS REACTING
TO A THEORY OF MOTION WHICH GOES
BACK TO THE GREEK ATOMISTS.
AND THE ATOMISTS LIKE DEMOCRITUS
FELT THAT BASICALLY THE WORLD
WAS JUST A VOID WITH ATOMS
FALLING IN THE VOID AND THE
ATOMS WOULD SOMETIMES CALAIS AND
FORM WORLDS AND THEN THEY WOULD
DISINTEGRATE AGAIN AND THEY
WOULD COME BACK TOGETHER AND
FORM WORLDS AND SO ON
AND ARISTOTLE ASKED THE QUESTION
"FALLING WITH RESPECT TO WHAT?"
THE VOID DOES NOT COME WITH SIGN
POSTS THAT SAY UP AND DOWN.
AND ARISTOTLE REALIZED THAT IF
YOU EVER WANTED TO MAKE SENSE OF
THE NOTION OF MOTION, YOU HAVE
TO HAVE A COSMOLOGY THAT HAS A
BACKBONE.
THAT HAS SOME SORT OF STRUCTURE,
A TIMELESS STRUCTURE WITH
RESPECT TO WHICH YOU CAN DEFINE
MOTION.
NOW, IT IS NOT THE CASE THAT FOR
ARISTOTLE THAT THE EARTH IS
NECESSARILY AT REST.
WHAT'S AT REST AT THE CENTER OF
THE UNIVERSE AND THE UNIVERSE
HAS KIND OF AN ONION LIKE
STRUCTURE.
IT HAS LAYERS THAT ARE
SPHERICAL.
THE OUTER MOST LAYER OF COURSE
IS THE LAYER OF THE, IS THE
ORBIT OF THE FIXED, OF THE STARS
BUT THERE ARE LAYERS, THERE
ARE...
THERE ARE ORBS OR, OR...
SPHERES MADE OUT OF A 5th
ELEMENT, THE QUINTESSENCE THAT
CONTAINS THE PLANETS FOR
EXAMPLE.
THE MOON.
THE NATURAL MOTION, THE FORCE
FREE NATURAL MOTION OF BODIES
THAT HAVE A PREPONDERANT TO THE
ELEMENT EARTH SUCH AS THE PLANET
EARTH ITSELF, IS TO MOVE TOWARDS
THE CENTER OF THIS SYSTEM.
NOW, WHERE EVER IT WAS THAT THE
WORLD WAS SOME TIME AGO, NOW
IT'S AT THE CENTER.
THAT'S ITS NATURAL MOTION.
SO, THE NATURAL PLACE TO START
IN ASKING WHETHER SOMETHING IS
MOVING IS, IS IT MOVING WITH
RESPECT TO THE CENTER OF THE
UNIVERSE AND THAT MEANS THE
EARTH.
BECAUSE THE EARTH HAS ALREADY
GOT THERE.
NOW, PTOLEMY HIMSELF DID
SOMETHING RATHER INTERESTING.
HE UNDERSTOOD THE NATURE OF TIME
IN ASTRONOMY.

A new slide shows a drawing of Ptolemy and reads "Circa 100 to circa 170 A.D.
Understood the nature of time in astronomy (used the sidereal not solar day.)
Suspected that the 'fixed' stars are not fixed; compiled catalogue of star positions (used by Halley in 1718.)"

Harvey continues I DON'T WANT TO SAY MUCH ABOUT
THIS NOW BUT I'LL COME BACK TO IT.
HE UNDERSTOOD FOR EXAMPLE THAT
WHEN YOU'RE DEFINING A DAY, YOU
SHOULD DO IT USING THE STARS AND
NOT THE SUN.
I'LL COME BACK TO THAT LATER.
BUT HE ALSO SUSPECTED AFTER ALL
IF YOU'RE USING THE EARTH AND
THE CENTER OF THIS, OF THIS
SPHERICAL UNIVERSE TO DEFINE THE
BACKBONE, THE FUNDAMENTAL FRAME
OF REFERENCE, THEN IT'S NOT SO
CLEAR THAT THE STARS NEED TO BE
FIXED AND INDEED, PTOLEMY RAISED
THE QUESTIONS "WELL, COULD THEY
BE ACTUALLY MOVING AMONGST
THEMSELVES?"
AND HE STARTED TO KEEP RECORDS
OF THE POSITIONS OF THE STARS
AND SOME CENTURIES LATER,
HAILEY, IN 1718, USED PTOLEMY'S
DATA TO EVENTUALLY ESTABLISH THE
EXISTENCE OF STILL A PARALLAX.
SO, FOR PTOLEMY, THERE WAS THE
POSSIBILITIES THAT, FROM OUR
PERSPECTIVE, THE STARS DO MOVE
AMONGST THEMSELVES ALTHOUGH IT
WASN'T...
IT WASN'T ESTABLISHED AT THE
TIME
LET'S STEP...
A LOT FURTHER FORWARD TO
GALILEO.
OF COURSE YOU KNOW THAT GALILEO
WAS A STANCH DEFENDER OF
COPERNICANISM AND IT LEAD HIM
INTO A CERTAIN AMOUNT OF
TROUBLE.
WHAT DID GALILEO MEAN WHEN HE
SAID THAT THE EARTH MOVES?

A new slide shows a painting of Galileo and reads "Galileo Galilei. 1564-1642.
Staunch defender of Copernicanism.
Either the Earth moves or it doesn't – motion is seemingly absolute.
Condemned by the Inquisition in 1633."

Harvey continues WELL, GALILEO FAMOUS FOR THE
REMARK AT ONE STAGE, YOU KNOW,
YOU CAN'T HAVE YOUR CAKE AND
EAT IT.
EITHER IT'S MOVING OR IT'S NOT
MOVING.
BUT WITH RESPECT TO WHAT?
WELL, GALILEO HAD AN INTUITION
THAT MANY OF US HAVE.
THAT REALLY MOTION IS SOMETHING
ABSOLUTE.
EITHER SOMETHING IS MOVING OR
ISN'T AND IT'S MOVING WITH
RESPECT TO SPACE.
THERE IS A PROBLEM WITH THIS
POSITION.
WHICH IS YOU CAN'T DO ANYTHING
WITH IT IN PHYSICS.
BECAUSE YOU CAN NEVER TELL
WHETHER A BODY IS MOVING WITH
RESPECT TO SPACE OR NOT BECAUSE
SPACE DOESN'T HAVE ANY KIND OF
VISIBLE FORM THAT ALLOWS YOU TO
SAY WHETHER THE BODY IN QUESTION
IS MOVING OR NOT.
BUT WE OFTEN HAVE A VERY DEEP
INSTINCT THAT THINGS ARE MOVING
BECAUSE THEY'RE MOVING WITH
RESPECT TO SPACE BUT THIS IS NOT
AN OPERATIONAL NOTION AND IT
WON'T DO IN PHYSICS.
GALILEO HIMSELF INTRODUCED A
VERY STRANGE THEORY OF THE TIDES
BECAUSE HE THOUGHT YOU COULD
COMPOUND THE ABSOLUTE NOTION OF
THE TIDE SITTING ON THE SURFACE
OF THE EARTH WITH THE ANNUAL
MOTION AROUND THE SUN AND AT
TIMES, THOSE MOTIONS WOULD ADD
AND AT TIMES THEY WOULD
SUBTRACTED AND YOU WOULD CREATE...
A TIDAL MOTION ON THE SURFACE OF
THE EARTH AND THIS IS A TERRIBLE
THEORY.
IT DOESN'T WORK AT ALL.
AND INTERESTINGLY, NOW A DAYS
IT'S REMOVED.
IT'S, IT'S GIVEN UP BECAUSE IT
VIOLATES THE GALILEAN PRINCIPLE
OF RELATIVITY.
MAYBE I'LL COME BACK TO THAT
LATER.
OF COURSE, IN 1633, GALILEO WAS
CONDEMNED BY THE INQUISITION OF
THE HOLY ROMAN CHURCH.
THIS WAS NOT ONE OF THE FINEST
MOMENTS IN THE HISTORY OF THE
CATHOLIC CHURCH BUT THERE IS AN
IRONY HERE.
BECAUSE IN CONDEMNING GALILEO
FOR DEFENDING THE MOTION OF THE
EARTH, IT'S NOT REALLY CLEAR
WHAT THE ISSUE WAS.
WHAT DO YOU MEAN BY MOTION?
HAD THIS BEEN ESTABLISHED?
IS IT MOTION WITH RESPECT TO THE
STARS OR NOT?
WHAT DOES IT MEAN TO SAY THAT
THE EARTH MOVES RATHER THAN THE SUN?
THERE WAS A FUNDAMENTAL
AMBIGUITY HERE.
BUT THE OTHER ASPECT OF THE
IRONY WAS GALILEO'S CONDEMNATION
INDIRECTLY LED TO A WHOLE NEW
WAY OF UNDERSTANDING MOTION
WHICH RESULTED BASICALLY IN
NEWTON AND I WANT TO SAY A
LITTLE BIT ABOUT THAT STORY IN
THE FOLLOWING PART OF THE TALK.
THERE'S A VERY NICE PASSAGE IN
THE WONDERFUL BOOK BY JULIAN
BARBOUR IN 1989,
ABSOLUTE OR
RELATIVE MOTION?
THE DISCOVERY OF DYNAMICS
WHERE HE'S DISCUSSING THIS
PARTICULAR MOMENT IN THE HISTORY
OF SCIENCE.

A new slide shows a quote titled "Around 1640." Quoted from Julian Barbour, Absolute or relative motion? The discovery of dynamics. 1989.

Harvey reads the quote and says THE LESSON IN COPERNICANISM WAS BEGINNING TO SINK IN. THE GREAT COSMIC DEBATE HAD
RAGED FOR A CENTURY. JUST WHEN IT APPEARED TO BE
RESOLVED IN FAVOUR OF COPERNICUS
AND GALILEO, YES, THE EARTH DOES
MOVE, DESCARTES, THE GREAT
FRENCH NATURAL PHILOSOPHER, PUT
THE WHOLE DEBATE IN A TOTALLY
DIFFERENT PERSPECTIVE.
FROM NOW ON, THE QUESTION WAS NO
LONGER "DOES SHE MOVE OR DOES SHE NOT?"
IT WAS TRANSFORMED INTO "WHAT IS MOTION?"

He continues SO WHAT WAS THE ROLE OF
DESCARTES IN THIS TRANSFORMATION?

A new slide shows a painting of Descartes. It reads "René Descartes. 1596-1650.
Questioned the framework of the 'fixed' stars.
Proposed the (modern) principle of inertia.
Forced the question: What is motion?
The World, 1632. Principles of Philosophy, 1644."

Harvey continues DESCARTES WAS ONE OF THE GREAT
PIONEERS OF THE MECHANICAL
PHILOSOPHY.
HE BELIEVED THAT THE WORLD WAS
BASICALLY MADE OF MATTER IN
MOTION.
HE QUESTIONED WHETHER THE STARS
THEMSELVES WERE, HAD FIXED
SPATIAL RELATIONS BETWEEN THEM.
THAT'S TO SAY, HE BELIEVED THAT
THE STARS THEMSELVES MAY BE
MOVING RELATIVE TO EACH OTHER.
HE ALSO PROPOSED THE MODERN
PRINCIPLE OF INERTIA WHICH I'LL
COME TO IN A MOMENT.
GALILEO HAD THE IDEA THAT IF YOU
HAVE A BODY THAT HUGS THE
SURFACE OF THE EARTH AND YOU PUT
IT INTO MOTION AND LET IT RUN
FREELY WITHOUT FRICTION, IT WILL
HUG THE SURFACE OF THE EARTH
INDEFINITELY.
ITS INERTIA WILL TAKE IT IN
INDEFINITE MOTION BUT THIS WAS
NOT THE MODERN NOTION OF INERTIA
BECAUSE IT WAS REALLY, IT WAS A
NOTION THAT WAS TURNED, THAT WAS
HUGGING THE SURFACE OF THE EARTH
AS IT WERE HORIZONTAL MOTION.
DESCARTES HAD THE IDEA THAT IF
YOU HAVE A FORCE FREE BODY, A
BODY IN WHICH NO AGENT IS ACTING
ON IT, AND THERE'S NO FRICTION
FOR EXAMPLE, THE BODY WILL MOVE
IN A STRAIGHT LINE AT A UNIFORM
SPEED FOREVER IN A STRAIGHT LINE.
NOT JUST HUGGING THE SURFACE OF
THE EARTH.
BUT THE QUESTION THAT DESCARTES
REALLY RAISED WAS "WHAT DO WE
MEAN BY MOTION IN THE FIRST
PLACE?"
AND THERE WAS A FUNDAMENTAL
TRANSFORMATION THAT OCCURRED
BETWEEN HIS BOOK CALLED
THE
WORLD
WHICH WAS, HE WAS
ABOUT TO PUBLISH IN 1632...
ONE YEAR BEFORE GALILEO'S
CONDEMNATION.
THE CONDEMNATION OF GALILEO
STOPPED DESCARTES FROM
PUBLISHING THIS WORK BECAUSE IT
CONTAINED A STRAIGHT FORWARD
DEFENCE OF COPERNICANISM THAT
WAS VERY MUCH LIKE GALILEO'S.
VERY MUCH LIKE GALILEO'S.
SOMEHOW OR OTHER, HE HAD TO FIND
A WAY OF UNDERSTANDING...
[Sniffing]
OR SELLING THE COPERNICAN SYSTEM
IN A FASHION THAT WOULD ACCEPTED
BY THE CHURCH AUTHORITIES.
AND HE FOUND A WAY AND THIS WAS PUBLISHED IN THE
PRINCIPLES OF PHILOSOPHY
IN 1644 AND IT WAS THIS WAY THAT
NEWTON REACTED TO SO VIOLENTLY.
LET ME, LET ME GO BACK TO THE
LAW OF INERTIA.
MOST OF YOU WILL BE VERY
FAMILIAR WITH THIS LAW THAT WE
NOW REFER TO AS THIS IS THE
FIRST LAW OF NEWTONIAN
MECHANICS, NEWTON'S FIRST LAW.
ANYBODY...
THAT IS FREE FROM THE ACTION OF,
EXTERNAL ACTION OF FORCES...
IS GOING TO MOVE IN A STRAIGHT
LINE AT A UNIFORM SPEED.
THAT'S WHAT THE LAW SAYS, IN
IT'S USUAL FORMAT.
HERE'S THE WAY DESCARTES PUT IT.
DESCARTES SPLIT IT INTO TWO
ASPECTS.
ONE, THE STRAIGHT LINE ASPECT
AND ONE, THE UNIFORMED SPEED
ASPECT.
AND THIS IS IN THE
PRINCIPLES OF PHILOSOPHY
IN 1644 BUT HE ALREADY HAD THIS
LAW IN HIS EARLIER WORK.

A new slide pops up titled "The law of inertia."

Harvey reads from the slide and says
THE FIRST OF THESE LAWS OF
NATURE IS THAT EACH THING ALWAYS
REMAINS IN THE SAME STATE IN SO
FAR AS IT CAN AND NEVER CHANGES
EXCEPT AS A RESULT OF EXTERNAL
CAUSES.
THUS, IF A PARTICULAR PIECE OF
MATTER IS AT REST, WE HOLD THAT
IT WILL NEVER BEGIN TO MOVE
UNLESS PUSHED INTO MOTION BY
SOME CAUSE.
THAT SEEMS REASONABLE, DOESN'T IT?
AND IT MOVES, AND IF IT MOVES,
THERE IS EQUALLY NO REASON FOR
THINKING IT WILL EVER LOSE IT'S
MOTION OF IT'S OWN ACCORD AND
WITHOUT BEING CHECKED BY
SOMETHING ELSE.
SO, THIS IS LIKE A PRINCIPLE OF
CONSERVATION OF MOTION.
GIVEN THAT NOTHING IS ACTING ON
THE SYSTEM, WHY SHOULD IT'S
MOTION INCREASE OR DWINDLE?
[Sniffing]
THE SECOND LAW, WHICH IS NOW
NORMALLY INCORPORATED INTO
NEWTON'S FIRST LAW, IS THAT
EVERY PIECE OF MATTER CONSIDERED
IN ITSELF ALWAYS TENDS TO
CONTINUE MOVING NOT IN AN
OBLIQUE PATH BUT ONLY IN A
STRAIGHT LINE.
AND AGAIN...
YOU MIGHT THINK THIS IS VERY
NATURAL BECAUSE IF IT STARTS
MOVING IN A STRAIGHT LINE AND
THERE'S NOTHING ACTING ON IT,
WHY DOESN'T IT STAY IN A
STRAIGHT LINE?
THIS IS AN EARLY FORMULATION OF
THE LAW DREW TO NEWTON, OF
COURSE NEWTON REALLY, I THINK HE
LEARNT THIS LAW BY READING
DESCARTES WORK.
A QUALITY WILL ALWAYS MOVE ON
ITS SAME STRAIGHT LINE, NOT
CHANGING THE DETERMINATION OR
SOLARITY OF IT'S MOTION UNLESS
SOME EXTERNAL CORE IS DIVERTED.
BUT WE SAY THAT A FORCE FREE
BODY IS MOVING INERTIALLY, OR
MOVING IN A STRAIGHT LINE AT
UNIFORM SPEED...
WITH RESPECT TO WHAT?
REMEMBER I SAID THAT MOTION IS
SOMETHING RELATIVE?
WE HAVE TO SPECIFY WHAT THE
MOTION IS MOVING WITH RESPECT
TO.
NOW A DAYS...
PHYSICISTS SAY "WELL, WE NEED
MOVING WITH RESPECT TO INERTIAL
FRAMES OF REFERENCE."
AND WHAT ARE THEY?
INERTIAL FRAMES OF REFERENCE ARE
CO-ORDINATE SYSTEMS RELATIVE TO
WHICH FORCE FREE BODIES MOVE
INERTIALLY.

[Audience laughing]

Harvey continues THERE'S
ANOTHER PROBLEM THAT ARISES HERE
WHICH IS WHAT DO WE MEAN BY A
FORCE FREE BODY?
WE BETTER NOT SAY THAT A FORCE
FREE BODY IS A BODY THAT MOVES
INERTIALLY.

[Audience laughing]

Harvey continues YOU CAN SEE THAT ALTHOUGH
THERE'S PRIMA-FACIE PLAUSIBILITY
ABOUT, ABOUT THE FIRST LAW OF
MOTION...
WE HAVE TO BE VERY CAREFUL AS TO
HOW WE'RE GONNA DEAL WITH IT AND
I'LL COME BACK TO THAT LATER.
DESCARTES AT ONE STAGE TALKED
ABOUT A SAILOR ON A SHIP WHO
WAS CARRYING A CLOCK AND THE
CLOCK HAD MOVING WHEELS INSIDE
IT'S CASEMENT, EXTERNAL CASEMENT
AND DESCARTES SAID "WHAT IS THE
MOTION OF THOSE WHEELS?
WELL, THE WHEELS ARE MOVING WITH
RESPECT TO THE CASEMENT, THE
WALLS OF THE CLOCK.
BUT THE WALLS OF THE CLOCK ARE
MOVING WITH RESPECT TO THE SHIP
BECAUSE THE SAILOR'S MOVING
ALONG THE SHIP.
AND THE SHIP IS MOVING WITH
RESPECT TO THE SEA BECAUSE THE
SHIP IS MOVING.
BUT THE SEA ITSELF IS MOVING
WITH RESPECT TO THE SHORE.
AND THE SHORE ITSELF IS MOVING
BECAUSE OF THE MOTION OF THE
EARTH AND THEN THERE'S A
COMPOUNDED MOTION OF THE EARTH
AROUND THE SUN AND WHERE DO YOU
STOP?"
WHAT IS THE TRUE MOTION OF THE
WHEELS IN THE CLOCK?
THIS IS A LITTLE BIT LIKE
POST-MODERNISM GONE MAD.

[Audience laughing]

A new slide pops up titled "Descartes on motion."

Harvey reads
IN ORDER TO
DETERMINE EXTERNAL PLACE OR
SITUATION, WE MUST TAKE INTO
ACCOUNT SOME OTHER BODIES WHICH
WE CONSIDER TO BE MOTIONLESS.
SOME FIXED BACKGROUND.
THAT THESE OTHER BODIES ARE
FORMING A KIND OF A FIXED FRAME
AND DEPENDING ON WHICH BODIES WE
CONSIDER, WE CAN SAY THAT THE
SAME THING SIMULTANEOUSLY
CHANGES AND DOES NOT CHANGE ITS PLACE.
FINALLY, IF WE THINK THAT NO
TRULY MOTIONLESS POINTS OF TS
KIND ARE FOUND IN THE UNIVERSE,
AND AFTER ALL, DESCARTES WAS
QUESTIONING WHETHER THE STARS
THEMSELVES WERE REALLY FIXED,
THEN FROM THAT, WE SHALL
CONCLUDE THAT NOTHING HAS AN
ENDURING PLACE EXCEPT IN SO FAR
AS ITS PLACE IS DETERMINED IN
OUR MINDS AND THE WHOLE THING
BECOMES WHAT MIGHT BE CALLED AN
ACADEMIC EXERCISE.
HOW DO YOU GET OUT OF THIS
CONUNDRUM?
HOW DO YOU ESTABLISH A NOTION OF
TRUE MOTION?
NOW, DESCARTES INTRODUCED THE
IDEA OF A DISTINCTION BETWEEN
WHAT HE CALLED VULGAR MOTION AND
TRUE PHILOSOPHICAL MOTION.
NOW, VULGAR MOTION WE MIGHT SAY,
WELL, FOR EXAMPLE, I'M MOVING ON
THIS PLATFORM AND YOU MIGHT SAY
IN SOME VULGAR SENSE, I'M MOVING
BUT I HAVEN'T ESTABLISHED WHAT
I'M REALLY MOVING.
I MEAN, IT MAY WELL BE THAT I'M
AT REST AND THIS WHOLE BUILDING
IS MOVING OR SOMETHING.
WHO KNOWS?
TRY TO IMAGINE HOW YOU'RE GONNA
GET OUT OF THIS CONUNDRUM.
IF YOU THINK OF THE WHEELS IN
THE CLOCK, THERE IS ONE NATURAL
THING TO SAY, I'M NOT SAYING
IT'S PLAUSIBLE, BUT THERE'S ONE
NATURAL WAY OF BREAKING DOWN
THIS DIFFICULTY.
YOU SAY "MOTION IS DEFINED WITH
RESPECT TO THE CLOSEST BODIES."
OTHERWISE, THERE'S JUST TOO MANY
OTHER BODIES.
TAKE THE CLOSEST ONES.
TAKE THE ONES THAT ARE
CONTIGUOUS TO THE BODY AND THAT
MEANS THE CASEMENT OF THE CLOCK.
IS THIS GONNA BE USEFUL?
WE'LL SEE.
SO, DESCARTES SAYS THE
FOLLOWING.

He reads another quote and says
IF WE CONSIDER WHAT WE SHOULD
UNDERSTAND BY MOTION, NOT IN
COMMON OR VULGAR USAGE BUT IN
ACCORDANCE WITH THE TRUTH OF THE
MATTER AND IF OUR AIM IS TO
ASSIGN A DETERMINATE NATURE TO
IT, WE MAY SAY THAT MOTION IS
THE TRANSFER OF ONE PIECE OF
MATTER OR ONE BODY FROM THE
VICINITY OF OTHER BODIES WHICH
ARE IN IMMEDIATE CONTACT WITH IT
AND WHICH ARE REGARDED AS BEING
AT REST TO THE VICINITY OF OTHER BODIES.

He continues SO THIS WAS HIS SOLUTION.
NOW, THERE
IS SOMETHING NATURAL ABOUT IT
BECAUSE AS I SAID BEFORE,
THERE'S SOMETHING UNIQUE ABOUT
THE BODIES THAT ARE CLOSEST TO
THE BODY THAT WE'RE INTERESTED IN.
WE'RE GONNA COME TO NEWTON IN A
MINUTE BUT I CAN'T, I CAN'T
RESIST ANTICIPATING ONE OF
NEWTON'S ARGUMENTS.
NEWTON SAID "SUPPOSE I PUT A
PIECE OF LEAD IN A BOX.
OR SUPPOSE I HAVE A WOODEN BOX
AND I THROW IT AGAINST THE WALL.
AND I SEE WHAT KIND OF DAMAGE IT
DOES TO THE WAY.
THEN I'LL PUT SOME LEAD INSIDE A
SIMILAR BOX AND I THROW THAT
AGAINST THE WALL.
AND I SEE WHAT KIND OF DAMAGE
THAT DOES."
NOW, WE'RE GONNA EXPECT TO SEE A
GREAT DEAL MORE DAMAGE IN THE
SECOND CASE BUT THE LEAD WASN'T
MOVING.
BECAUSE IT WASN'T MOVING WITH
RESPECT TO THE IMMEDIATELY
CONTIGUOUS BODY.
WHY DID DESCARTES...
WHY DID DESCARTES CHOOSE THIS
SOLUTION?
BECAUSE DESCARTES BELIEVED THAT
THE EARTH IN ITS MOTION AROUND
THE SUN WAS BEING CARRIED ALONG
BY A HUGE VORTEX, A FLUID
VORTEX, THERE'S A HUGE PLENUM OF
PARTICLES THAT PERMEATES THE
UNIVERSE.
THESE PARTICLES ARE IN
COLLECTIVE MOTION.
THERE'S A KIND OF A VORTEX OF
MOTION IN THE SOLAR SYSTEM AND
IT CARRIES THE PLANETS AROUND
THE SUN.
IS THE EARTH MOVING OR NOT?
WELL, IT DEPENDS ON THE MOTION
OF THE VORTEX PARTICLES CLOSEST
TO THE EARTH AND IF YOU CAN
CONVINCE YOURSELF THAT THAT FILM
OF PARTICLES AROUND THE SURFACE
OF THE EARTH IS AT REST WITH
RESPECT TO THE EARTH, THEN
PHILOSOPHICALLY, THE EARTH DOES
NOT MOVE.
CLEVER?
IT'S ARGUABLE.
PLAUSIBLE?
HARDLY.
WAS, WAS DESCARTES DOING THIS
OUT OF CONVENIENCE OR OUT OF PIETY?
I'LL LEAVE THAT QUESTION TO THE
HISTORIANS.
BUT NOW WE COME TO NEWTON.
BECAUSE NEWTON COULD SEE THROUGH
THIS ARTIFICE BETTER THAN
ANYBODY ELSE.
BECAUSE NEWTON COULD SEE THAT
IF, IF YOU ARE PREPARED TO
ACCEPT FOR THE SAKE OF ARGUMENT
THE DESCARTESAN DISTINCTION
BETWEEN VULGAR MOTION AND TRUE
PHILOSOPHICAL MOTION, YOU WILL
NEVER BE ABLE TO UNDERSTAND THAT
LAW OF INERTIA.
WHY IS THAT?
THINK AGAIN OF THE EARTH MOVING
AROUND THE SUN.
NOW, IT'S A LITTLE BIT LIKE,
WELL, SINCE IT'S GOT CIRCULAR
MOTION OR NEAR CIRCULAR MOTION
AROUND THE SUN, THERE'S GONNA BE
A CENTRAL FRUGAL EFFECT.
IT'S GONNA HAVE A TENDENCY TO
RECEDE.
UNLESS IT'S PULLED BACK,
THERE'LL BE A TENDENCY FOR THIS,
FOR THE EARTH TO RECEDE FROM THE
SUN.
IN EXACTLY THE SAME WAY THAT IF
I HAVE A PIECE OF STONE ON THE
END OF A STRING AND I'M WHIRLING
IT AROUND, IF I CUT THE STRING,
THE STONE WILL SHOOT OFF
TANGENTIALLY.
THAT'S JUST THE CENTRAL FRUGAL
EFFECT AND BY THE WAY, WHAT IS
THAT DUE TO?
INERTIA.
THAT'S THE CONSEQUENCE OF THE
PRINCIPLE OF INERTIA.
IT DOESN'T REQUIRE EXTERNAL FORCES.
NOW, DESCARTES ADMITTED THAT THE
EARTH HAD A TENDENCY TO RECEDE
FROM THE SUN WHICH MEANS THAT
HIS PRINCIPLE OF INERTIA
COULDN'T HAVE BEEN DEFINED BY
USING TRUE PHILOSOPHICAL MOTION
BECAUSE THE EARTH DOESN'T MOVE.
"SO," SAID NEWTON "I WILL
VENTURE TO DISPOSE OF HIS FICTIONS."

A new slide shows a painting of Newton. It reads "Newton's reaction to Descartes.
De gravitatione, circa 1662. 'I shall venture to dispose of his fictions.'"

Harvey reads a quote and says
FOR HE SAYS THE PROPERLY AND,
SPEAKING PROPERLY AND ACCORDING
TO PHILOSOPHICAL SENSE, THE
EARTH AND THE OTHER PLANETS DO
NOT MOVE.
YET, LATER HE ATTRIBUTES TO THE
EARTH AND PLANETS A TENDENCY TO
RECEDE FROM THE SUN AS FROM A
CENTER ABOUT WHICH THEY ARE
REVOLVED.
WHAT THEN?
IS THIS TENDENCY TO BE DERIVED
FROM THE, ACCORDING TO
DESCARTES, TRUE AND
PHILOSOPHICAL REST OF THE PLANTS
OR RATHER FROM THEIR COMMON AND
NON-PHILOSOPHICAL MOTION?

He continues
AND THEN NEWTON MAKES A REMARK
THAT REALLY GOES TO THE HEART OF
THE MATTER.
I SAY THENCE IT FOLLOWS, IF YOU
GIVE UP THE DESCARTESAN NOTION
OF PHILOSOPHICAL MOTION AS
REALLY JUST BEING AN ARTIFICE,
OR SOMETHING THAT'S REALLY NOT
IN THE LEAST BIT PLAUSIBLE AS A
FIX, THEN YOU'RE LEFT SIMPLY
WITH THE NOTION OF RELATIVE
MOTION.
AND IF ALL THE BODIES IN THE
UNIVERSE PARTAKE IN RELATIVE
MOTION, THERE'S NO FIXED
BACKGROUND AND YOU REALLY CAN'T
DEFINE MOTION IN ANY
SATISFACTORY WAY AT ALL.

Harvey reads another quote and says
I SAY THENCE
IT FOLLOWS THAT A MOVING BODY
HAS NO DETERMINATE VELOCITY AND
NO DEFINITE LINE IN WHICH IT
MOVES.
HOW DO YOU ESTABLISH THAT IT
TRAVELS IN A STRAIGHT LINE?

He says STRAIGHT
LINES ARE NOT WRITTEN IN EMPTY SPACE.
HAVE YOU EVER BUMPED INTO ONE?
AND WHAT IS WORSE THAT THE
VELOCITY OF A BODY MOVING
WITHOUT RESISTANCE CAN NOT BE
SAID TO BE UNIFORM BECAUSE
AGAIN, WHAT DO YOU MEAN BY
MOTION?
AND IN PARTICULAR, WHAT DO YOU
MEAN BY UNIFORM MOTION?
NOR THE STRAIGHT LINE IN WHICH
ITS MOTION IS ACCOMPLISHED.
SO, THEN NEWTON REACHES A VERY
EXTRAORDINARY CONCLUSION.

Harvey reads
IT IS NECESSARY THAT THE DEFINITION OF
PLACE AND HENCE OF LOCAL MOTION,
HE JUST MEANS MOTION OF...
BE REFERRED TO SOME MOTIONLESS
THING SUCH AS EXTENSION ALONE
OR SPACE IN SO FAR AS IT IS SEEN
TO BE TRULY DISTINCT FROM BODIES.

He continues WE HAVE TO
JUST, WE HAVE TO GIVE UP THE
IDEA THAT BODIES FORM SOME SORT
OF BACKBONE TO THE UNIVERSE.
SOME SORT OF SELECT GROUP OF
BODIES BECAUSE THEY MAY ALL BE
MOVING IN RELATION TO EACH OTHER
AND NOW WE HAVE TO SAY THAT
SOMEHOW OR OTHER, MOTION IS
DEFINED WITH RESPECT TO ABSOLUTE
SPACE.
AND NOW OF COURSE YOU HAVE A
CONUNDRUM HERE ALL OVER AGAIN.
YOU DON'T SEE ABSOLUTE SPACE.
IT DOES NOT FALL UNDER OUR
SENSES.
SO, HOW DO YOU KNOW EMPIRICALLY
WHEN A BODY IS MOVING OR NOT AND
IN PARTICULAR, HOW DO YOU TEST
THE FIRST LAW OF MOTION?
IN ORDER TO SEE SOME WAY OF
GETTING OUT OF THIS DIFFICULTY,
LET'S TAKE A QUICK LOOK AT WHAT
NEWTON MEANS BY TIME BECAUSE
AFTER ALL, IN THE FIRST LAW OF
MOTION WE SAY THAT A BODY IS
MOVING UNIFORMLY WHICH MEANS AT
A CONSTANT SPEED.
EQUAL DISTANCES AND EQUAL TIMES.
NOW THE QUESTION IS, WHAT DOES
THAT TIME MEAN?
DON'T WE NORMALLY...
DON'T WE NORMALLY MEASURE TIME
USING CLOCKS?
WHAT IS THE CLOCK THAT NEWTON'S
REFERRING TO?
WHERE IS THE COSMIC TICKING THAT
ALLOWS US TO SAY OF A GIVEN
MOTION THAT IS UNIFORM?

A new slide titled "Newton on time" pops up.

Harvey continues NOW, OF COURSE FOR NEWTON, THERE
WAS A KIND OF A BACK, INVISIBLE
BACKGROUND RIVER OF TIME WHICH
WAS FLOWING INDEPENDENTLY OF ALL
BODIES, ABSOLUTE, TRUE AND
MATHEMATICAL TIME...
OF ITSELF AND OF FROM ITS OWN
NATURE FLOWS EQUABLY WITHOUT
RELATION TO ANYTHING EXTERNAL
AND BY ANOTHER NAME IS CALLED
DURATION.
IT'S A METRIC OF TIME THAT
EXISTS IN THE BACKGROUND BUT
IT'S INVISIBLE BUT ACTUALLY,
THAT'S NOT GONNA BE ANY GOOD FOR
DOING PHYSICS.
IT'S NOT SOMETHING YOU CAN GET YOUR
FINGERS ON.
NOW, YOU CAN GET YOUR FINGERS ON
CLOCKS, YOU CAN GET YOUR HANDS
ON CLOCKS AND THERE'S A LONG
HISTORY OF CLOCK MAKING
TECHNOLOGY.
BUT NEWTON SAYS SOMETHING VERY...
VERY SIGNIFICANT IN THE
BEGINNING OF THE PRINCIPIA,
THIS FAMOUS TO THE
PRINCIPIA, IT MAY BE, HE SAYS
THAT THERE IS NO SUCH THING AS
AN EQUABLE MOTION.
WHEREBY TIME
MIGHT BE ACCURATELY MEASURED.
NOW, WHY DOES HE SAY SOMETHING
LIKE THIS?
IMAGINE A
WORLD THAT JUST HAD NEWTONIAN BODIES...
THAT WERE MOVING WITH NO FORCES
BETWEEN THEM SO ALL MOVING
INDEPENDENTLY.
THEY WERE FREE BODIES AND
IMAGINE, ACCORDING TO NEWTON,
THEY'RE ALL MOVING UNIFORMLY IN
STRAIGHT LINES AT UNIFORM
SPEEDS.
YOU SAY "WELL, WITH RESPECT TO
WHAT CLOCK?"
AND NEWTON WOULD SAY WELL, HE'S
NOT GONNA PIN IT TO SOME CLOCK
OUTSIDE THE UNIVERSE.
THE WHOLE UNIVERSE JUST IS THE
PARTICLES.
TAKE ONE OF THEM ARBITRARILY.
NOW, SUPPOSE THAT YOU KNOW WHAT
YOU MEAN BY DISTANCE.
THAT'S A BIG IF BUT JUST SUPPOSE
FOR THE SAKE OF ARGUMENT WE KNOW
WHAT WE MEAN BY DISTANCE...
TAKE THAT ONE BODY AND DEFINE IT
AS A CLOCK.
SAY "IT MOVES EQUAL DISTANCES
AND EQUAL TIMES.
IT DEFINES THE CLOCK."
NOW, THERE'S A NON TRIVIAL
QUESTION AS TO WHETHER OR NOT
ALL THE OTHER BODIES ARE GONNA
MOVE UNIFORMLY WITH RESPECT TO
THAT STANDARD.
AND IF THE FIRST LAW OF MOTION
IS TRUE, THEY WILL.
SO, WE DON'T LOOK TO FIND TIME
FROM SOMETHING OUTSIDE THE
SYSTEM.
YOU LOOK TO FIND A NOTION OF
DURATION OF A METRIC OF TIME
FROM WITHIN.
YOU CHOOSE ONE OF THE BODIES AS
A CLOCK.
BUT HERE'S THE RUB.
WE DON'T LIVE IN SUCH A
UNIVERSE.
WE LIVE IN A MUCH MORE
INTERESTING UNIVERSE WHERE
BODIES ACT ON EACH OTHER.
THERE ARE FORCES IN NEWTONIAN
DYNAMICS AND THE FORCES HAVE A
TENDENCY, THAT'S EXACTLY WHAT
THEY'RE THERE FOR.
TO PULL BODIES OFF THEIR INERTIA
MOTIONS.
NOW, YOU MIGHT SAY WELL, LET'S
THINK ABOUT THE NATURE OF THE
FORCES.
SUPPOSE THE FORCES FOR EXAMPLE
BETWEEN BODIES OR SOMETHING LIKE
GRAVITATIONAL FORCES, THEY'RE
LIKE ACTION OF THE DISTANCE AND
THEY FALL OFF WITH DISTANCE.
THEY NEVER GO AWAY COMPLETELY.
SO, IF I TAKE AN ISOLATED BODY
THAT'S FAR ENOUGH AWAY, I CAN
USE IT AS A CLOCK.
BUT IT'S ONLY APPROXIMATE.
IT'S ONLY APPROXIMATE.
THERE MAY BE, SAYS NEWTON, NO
SUCH THING AS AN EQUABLE MOTION.
THERE MAY BE NO SUCH THING AS AN
EQUABLE MOTION.
IN OTHER WORDS, NEWTON IS
WARNING US NOT TO DEFINE TIME IN
TERMS OF THE BEHAVIOUR OF ANY
BODIES OR ANY CLOCKS THAT WE
MIGHT CONSTRUCT.
AND I WANT NOW TO GO ON TO A
THEME...
THAT'S COME UP OVER AND OVER
AGAIN IN THE HISTORY OF MODERN
PHYSICS WHICH IS MAYBE WHAT
MIGHT BE CALLED A PROBLEM OF THE
STANDARD OF TIME.
AT THE END OF THE 19th CENTURY,
IT'S RATHER REMARKABLE TO SEE A
NUMBER OF THINKERS, A NUMBER OF
PHYSICISTS WHO ARE GRAPPLING
WITH THE PROBLEM OF TIME ALL
COMING INDEPENDENTLY TO THE SAME
CONCLUSION.
GEORGE FRANCIS FITZGERALD WHO'S
FAMOUS IN THE HISTORY OF SPECIAL
RELATIVITY FOR THE SO CALLED
FITZGERALD WHO RUNS CONTRACTION
EFFECT WAS ONE OF THEM.
WHEN FITZGERALD WAS WRITING
ABOUT TIME, HE SAYS, WHEN I GO
TO TRY TO FIND, FOR EXAMPLE, AN
ULTIMATE STANDARD OF DURATION OF
TIME, I GO TO THE ASTRONOMERS.
THE ASTRONOMERS TELL ME BECAUSE
THE BEST CLOCK THAT WE HAVE IN
THE UNIVERSE IS THE ROTATION OF
THE EARTH.
THERE'S NO OTHER, THERE WAS NO
OTHER CLOCK AT THE END OF THE
19th CENTURY.
THEY CAME CLOSE TO BEING AS
ACCURATE AS THE ROTATION OF THE
EARTH.

A new slide shows a black and white picture of FitzGerald. The title reads "The problem of the standard of time."

Harvey reads
THERE IS EVERY REASON FOR
ASSUMING THAT THE EARTH ROTATES
ON IT'S AXIS MORE UNIFORMLY THAN
ANY CLOCK WE CAN CONSTRUCT.

He continues
THAT'S OUR STANDARD OF TIME.
BUT WE KNOW THAT THE ROTATION
RATE IS CHANGING.
AND HOW DO WE KNOW THAT?
WELL, BECAUSE THE EARTH IS NOT A
RIGID BODY.
THERE ARE OCEANS ON THE EARTH,
THEY SUFFER TIDAL EFFECT DUE TO
THE GRAVITATIONAL PULL OF OTHER
CELESTIAL BODIES, THERE ARE
FRICTIONAL FORCES.
THERE IS A LONG TERM TENDENCY
FOR THE EARTH TO SLOW DOWN.
BY THE WAY, IT'S MUCH MORE
COMPLICATED.
WE KNOW NOW THAT IT'S SO
COMPLICATED WE CAN'T EVEN
PREDICT IT.
IN THE LAST DECADE, THE EARTH
HAS STARTED TO SPEED UP AGAIN.
NOW, HOW CAN IT BE THAT WE
DEFINE A STANDARD OF TIME...
HOW CAN IT BE THAT WE DEFINE A
STANDARD OF TIME AND YET WE KNOW
IT'S NOT A STANDARD?
HOW CAN THAT BE?
WELL, WHAT WE SAY IS OF COURSE
WE HAVE TO FIND A MORE ULTIMATE
STANDARD OF TIME BUT WHAT IS IT?
NOW...
I PROMISED I WOULDN'T SAY
ANYTHING ABOUT EINSTEIN BUT I
CAN'T, I CAN'T KEEP IT.

[Audience laughing]

Harvey continues HOW CAN YOU
TALK ABOUT TIME AND MOTION
WITHOUT SAYING SOMETHING ABOUT
EINSTEIN BUT I'M ONLY GONNA SAY
OF SOMETHING VERY BRIEF.
WHAT IS DURATION?
WELL, WHAT YOU MIGHT SAY IS...
DURATION IS DEFINED BY IDEAL CLOCKS.
THAT'S EXACTLY WHAT HE SAID IN
HIS 1905 PAPER, TIME IS WHAT IS
MEASURED BY IDEAL TICKING
CLOCKS.
BUT OF COURSE...
[Clearing throat]
THAT BEGS THE QUESTION, WHAT IS
AN IDEAL CLOCK?
AND EINSTEIN WAS CURIOUSLY
SILENT ABOUT THIS, THIS ISSUE.
AND THEN, IN 1910 HE WROTE THE
FOLLOWING REMARK BY A CLOCK, WE
UNDERSTAND ANYTHING
CHARACTERIZED BY PHENOMENON
PASSING PERIODICALLY THROUGH
IDENTICAL PHASES SO THAT WE MUST
ASSUME BY VIRTUE OF THE
PRINCIPLE OF SUFFICIENT REASON...
THAT ALL THAT HAPPENS IN A GIVEN
PERIOD IS IDENTICAL WITH ALL
THAT HAPPENS IN AN ARBITRARY PERIOD.
SO, AN IDEAL CLOCK TICKS
PERFECTLY BECAUSE I THINK IT DOES.

[Audience laughing]

Harvey continues OR I HAVE
GOOD REASON TO THINK IT DOES.
OR I HAVE NO GOOD REASON TO
THINK IT DOESN'T.

[Audience laughing]

Harvey continues WELL, IT'S
NOT THAT ACTUALLY, IT'S NOT THAT
THE IDEA IS SILLY.
IT'S JUST THAT IT'S NOT FULLY
EXPLAINED.
ON THE OTHER HAND, YOU HAVE AN
OCEAN THAT'S KIND OF THE
REVERSE.
WHICH IS, IDEAL CLOCKS ARE
DEFINED BY DURATION.
NOW, REMEMBER, NEWTON SAID DON'T
DEFINE TIME IN TERMS OF CLOCKS
BECAUSE THERE MAY BE NO SUCH
THING AS EQUABLE MOTIONS.
THIS WAS PICKED UP BY
FITZGERALD, BY A
PROMINENT ENGINEER CALLED
BUCKINGHAM IN 1912, JULIAN
BARBOUR IN HIS BOOKS, IN
PARTICULAR ON HIS BOOK ON THE
END OF TIME.
A NUMBER OF PEOPLE HAVE STRESSED
THIS POINT.
CLOCKS ARE DEFINED BY DURATION.
NOT THE OTHER WAY AROUND.
BUT OF COURSE, THAT BEGS THE
QUESTION, WHAT IS DURATION?
WELL, WHAT IS IT?
IT CAN ONLY BE ONE THING.
IT'S THE...
PERIMETER THAT APPEARS IN THE
BASIC EQUATIONS OF PHYSICS THAT
GOVERN THE MOST FUNDAMENTAL
INTERACTIONS THAT MAKES THEM
TAKE THEIR SIMPLEST FORM.
IN OTHER WORDS, IT'S BUILT INTO
THE PHYSICS.
IT'S BUILT INTO THE FUNDAMENTAL
EQUATIONS OF PHYSICS.
THAT'S WHAT TIME ULTIMATELY IS.
NOW, WHETHER OR NOT YOU CAN
BUILD A CLOCK THAT, THAT MARCHES
IN STEP WITH THAT PERIMETER THAT
APPEARS IN OUR EQUATIONS IS
ANOTHER MATTER AND IN GENERAL,
YOU CAN'T BECAUSE YOU CAN NEVER
TOTALLY ISOLATE A CLOCK.
IT'LL BE PERTURBED BY INFLUENCES
COMING FROM OUTSIDE.
AND IN FACT THERE MAY WELL BE NO
IDEAL CLOCK EXCEPT FOR THE WHOLE
UNIVERSE.
BUT YOU SEE THE DISTINCTION HERE?
WE'RE REALLY GOING BACK TO, TO
NEWTON'S INTUITION THAT CLOCKS
ARE NOT THE ULTIMATE THING.
TIME IS THE ULTIMATE THING AND
CLOCKS ARE DESIGNED TO MARCH IN
STEP WITH THIS TIME BUT IT'S THE
TIME THAT APPEARS IN THE
FUNDAMENTAL EQUATIONS.
THAT'S WHAT TIME IS.
THAT'S TO THE NOTION OF DURATION.
LET'S GO BACK TO THE QUESTION OF
THE PRINCIPLE OF INERTIA AGAIN.
BODIES MOVE IN STRAIGHT LINES...
AT UNIFORM SPEEDS IF NO FORCES
ARE ACTING ON THEM.
WE HAVEN'T QUITE SAID WHAT WE
MEAN BY THAT YET.
IN FACT, ARTHUR EDDINGTON, THE
FAMOUS BRITISH PHYSICIST WHO
GAVE THE FIRST TEST USING SOLAR
ECLIPSES OF EINSTEIN'S GENERAL
THEORY OF RELATIVITY IN 1919,
THIS IS THE THING THAT SHOT
EINSTEIN INTO WORLD FAME, ONCE
SAID THAT THE BEST WAY TO STATE
THE FIRST LAW OF MOTION IS FORCE
FREE BODIES MOVE IN A STRAIGHT
LINE, IN STRAIGHT LINES AT
UNIFORM SPEEDS EXCEPT IN SO FAR
AS THEY DON'T.

[Audience laughing]

A new slide reads "The backbone of the universe. The 'inertial frame.'"

Harvey continues WELL...
NEITHER AS WE SAY, AN INERTIAL
FRAME IS RELATIVE TO WHICH THE
DESCARTES-NEWTON LAW OF INERTIA
HOLDS AND OF COURSE...
THOSE ARE THE FRAMES RELATIVE TO
WHICH WE DEFINE THE FIRST LAW OF
MOTION AND WE SEEM TO HAVE THE
CIRCLE THAT I MENTIONED BEFORE.
WE SEEM TO BE IN A, IN A KIND OF
A CIRCLE.
BUT THERE'S A SIMPLE WAY OUT OF THIS.
THERE'S A SIMPLE WAY OUT OF IT.
OKAY, IT IS TRUE THAT IN AN
INERTIAL FRAME OF REFERENCE IS A
CO-ORDINATE SYSTEM, IT'S A
PERSPECTIVE ON THE WORLD.
IT MAY NOT BE EMBODIED BY ANY
SORT OF SET OF GIVEN BODIES BUT
IT'S A PERSPECTIVE ON THE WORLD
RELATIVE TO WHICH FORCE FREE
BODIES IN A WAY WE HAVE TO BE
ABLE TO SAY ROUGHLY SPEAKING
WHAT WE MEAN BY THAT WITHOUT
BEGGING THE QUESTION...
FORCE FREE BODIES MOVE INERTIALLY.
GOOD.

[Clearing throat]
[Sniffing]

He continues DO THEY EXIST?
IF YOU CLAIM THAT AT LEAST ONE
EXISTS, YOU'RE SAYING SOMETHING
EMPIRICAL.
I KNOW YOU CAN DEFINE THEM AND
DEFINITIONS DON'T LEAD TO
ANYTHING.
DEFINITIONS DON'T HAVE AN
EMPIRICAL CONTENT BUT TO CLAIM
THAT AN INERTIAL FRAME EXISTS IS
A VERY HIGHLY NON TRIVIAL CLAIM.
BUT WHAT IS IT?
IT'S A SHORT HAND WAY OF SAYING
THAT IF YOU TAKE ALL THE FORCE
FREE BODIES IN THE UNIVERSE AND
I MEAN ALL OF THEM...
YOU CAN FIND A PERSPECTIVE
RELATIVE TO WHICH THEY MOVE
FIRST OF ALL IN STRAIGHT LINES.
WHO ORDERED THAT?
NOW, REMEMBER, FORCE FREE BODIES
ARE NOT INTERACTING AMONGST
THEMSELVES.
THEY'RE OBLIVIOUS ONE TO ANOTHER.
THERE MUST BE SOME AMAZING
CONSPIRACY THAT'S VERY NON LOCAL
AND HOLISTIC THAT DETERMINES
THAT ALL THESE FORCE FREE BODIES
THAT HAVE NO INKLING OF THEIR
BROTHERS AND SISTERS...
YOU CAN FIND A PERSPECTIVE, A
FRAME OF REFERENCE RELATIVE TO
WHICH THEY ARE MOVING THE SAME
STRAIGHT LINE, IN STRAIGHT
LINES.
AND FURTHERMORE, THEY MOVE AT
UNIFORM SPEEDS AS DEFINED BY
SAY, TAKING ONE OF THEM AND
SAYING THAT IT GOES, IT MEASURES
EQUAL DISTANCES AND EQUAL TIMES.
AND THIS IS AN AMAZING
CONSPIRACY OF NATURE.
IT'S NOT, NOT JUST NOT
OBVIOUS...
IT'S ALMOST UNBELIEVABLE.
SOMETHING THAT AT FIRST SIGHT
SEEMED SO NATURAL IS ALMOST
UNBELIEVABLE BECAUSE IT
REPRESENTS AN EXTRAORDINARY
CONSPIRACY IN NATURE.
SO, THE POINT THAT I'M SAYING
HERE, THE...
THE PUNCH LINE HERE IS...

He reads from the slate and says
HOW TO AVOID THE CIRCULARITY?
MAKE THE LAW OF INERTIA AN
EXISTENCE CLAIM.
THERE EXISTS AT LEAST ONE
INERTIAL FRAME.

He continues
AND THAT IS SHORT HAND FOR
SAYING SOMETHING ABOUT THE WAY
FORCE FREE BODIES...
ORGANIZE THEMSELVES IN SPACE.
AND I MEAN
ALL FORCE FREE BODIES IN THE
UNIVERSE.
IF THAT IS A MEANINGFUL NOTION
AND IT IS, WELL, THERE ARE
CAVEATS WHICH I DON'T HAVE TIME
TO GO INTO BUT IS ESSENTIALLY A
MEANINGFUL NOTION.
IT'S ESSENTIALLY THE NOTION THAT
PHYSICISTS USE IN NEWTONIAN
MECHANICS, THEN WE HAVE A
BACKBONE OF THE UNIVERSE.
WE HAVE THE INERTIAL FRAMES AND
THEREFORE, IF WE ASK DOES THE
EARTH MOVE OR DOES IT NOT?
WELL, AT LEAST WE HAVE SOMETHING
BY WAY OF AN ANSWER.
DOES IT MOVE WITH RESPECT TO
INERTIAL FRAMES?
THAT'S NOT THE WHOLE STORY AND
I'M SURE MANY OF YOU KNOW
EXACTLY WHY THAT IS.
BECAUSE WE ALSO HAVE A PRINCIPLE
OF RELATIVITY.
THIS WASN'T INVENTED BY
EINSTEIN.
IT GOES ALL THE WAY BACK TO
COPERNICUS PROBABLY IF NOT
EARLIER AND IT WAS FAMOUSLY
DISCUSSED BY GALILEO...
AND IT'S SIMPLY THE CLAIM THAT
IF YOU DO AN EXPERIMENT AND
YOU'RE AT REST WITH RESPECT TO
AN INERTIAL FRAME...
AND YOU REPEAT THE EXPERIMENT
WHEN YOU'RE IN UNIFORM MOTION
WITH RESPECT TO THAT INERTIAL
FRAME, YOU GET THE SAME RESULTS.
AND THAT'S ANOTHER WAY OF SAYING
YOU WILL NEVER BE ABLE TO DETECT
YOUR MOTION WITH RESPECT TO AN
INERTIAL FRAME IF YOU'RE MOVING
INERTIALLY.
SHUCKS.

[Audience laughing]

Harvey continues BUT ONE
THING THAT YOU CAN SAY...
IS WHETHER OR NOT YOU'RE
ACCELERATING WITH RESPECT TO AN
INERTIAL FRAME AND THAT'S...
THAT IS...
CATEGORICAL.
SO THE QUESTION NOW IS DOES THE
EARTH ACCELERATE WITH RESPECT TO
AN INERTIAL FRAME?
AND ACCORDING TO OUR BEST
UNDERSTANDING OF THE SOLAR
SYSTEM GIVEN NEWTONIAN GRAVITY,
THE ANSWER IS YES BECAUSE IT'S
BEING, IT'S BEING HELD TO THE
POINT BY THE FORCE OF GRAVITY.
[Coughing]
ASSOCIATED WITH ALL THE OTHER
BODIES IN THE SOLAR SYSTEM AND
IN PARTICULAR, THE SUN.
BUT NOTICE
THAT IN COMING BACK TO THIS
QUESTION, DOES THE EARTH MOVE OR
DOES IT NOT?
THE KEY MOMENT IN THE HISTORY OF
SCIENCE, WE NEEDED TO KNOW WHAT
MOTION WAS AND THE ANSWER IS
GIVEN BY APPEALING TO INERTIAL
FRAMES WHICH POST-DATE GALILEO'S
INQUISITION.
NOW, THERE
ARE MANY CAVEATS HERE.
WELL, NOT MANY BUT THE BIGGEST
ONE OF COURSE IS EINSTEIN.
BUT I SHALL SAY NOTHING.

[Audience laughing]

Harvey continues THANK YOU VERY MUCH.

[Applause]

Now a black slate reads "Questions and answers."

A man from the audience, in his late fifties, says WHEN WE TALKED ABOUT A TIME
AND MOTION AND INERTIA AND HOW
MUCH YOU INFER THAT WE DON'T
KNOW ABOUT IT, I THINK ABOUT THE
ENGINEERS IN HOUSTON WHO KNOW,
WHO APPEAR TO KNOW WHERE WE ARE.
THEY APPEAR TO KNOW HOW TO
SHOOT A ROCKET UP AND NEARLY
PRECISELY TELL YOU WHEN IT'S
GOING TO REACH PLACES LIKE VENUS
IN THREE OR FOUR YEARS.
SO, WE MUST KNOW SOMETHING ABOUT
TIME AND MOTION.

[Audience laughing]

The man says JUST A COMMENT I GUESS.

[Applause]

Harvey says THANK YOU VERY MUCH.
I'M VERY GLAD THAT SOMEBODY HAS
FINALLY DRAGGED US DOWN TO EARTH.

[Audience laughing]

Harvey continues OF COURSE WE DO.
WE KNOW AN ENORMOUS AMOUNT AND
WHEN, UM...
WHEN PLANETARY SCIENTISTS OR,
AND...
[Clearing throat]
ROCKET ENGINEERS AND ALL THE
REST OF IT, I MEAN, PEOPLE WHO
ACTUALLY PLOT THESE...
[Sniffing]
TRAJECTORIES FOR THESE AMAZING
PROBES, PLANETARY PROBES,
WHETHER THEY'RE USING, THEY'RE
USING ESSENTIALLY NEWTONIAN
MECHANICS AND THE NEWTONIAN
THEORY OF GRAVITY.
WHEN I SAY WE DON'T KNOW WHERE
WE ARE, WE DON'T KNOW AS IT
WERE, WHERE THE TOTALITY OF
THINGS ARE SITTING IN SPACE
BECAUSE IT DOESN'T REALLY MEAN
ANYTHING.
BUT WE KNOW WHERE WE ARE IN
RELATION TO OTHER BODIES.
WE KNOW WHAT FORCES IT'S GONNA
TAKE TO LAUNCH SOMETHING, TO ACT
AGAINST THE GRAVITATIONAL PULL
OF THE EARTH, TO EMERGE FROM THE
GRAVITATIONAL PULL, TO BE
POINTED IN THE RIGHT DIRECTION
SO THAT EVENTUALLY IT COINCIDES
WITH THE, WITH THE VERY TINY
ATMOSPHERE OF A PLANET OR
SOMETHING OR IT ACTUALLY MOVES
INTO THE PLANET.
OF COURSE ALL THESE THINGS WE
KNOW AND IF WE DIDN'T, WE
COULDN'T DO THESE THINGS.
BUT...
[Clearing throat]
THE ASTRONOMERS ALL THE WAY BACK TO...
ALL THE WAY BACK TO THE ANCIENT
GREEKS, THE BABYLONIANS WERE
ABLE TO PREDICT, UM, SOLAR ECLIPSES.
THERE WERE RULES OF THE GAME AND
THE ASTRONOMERS KNEW VERY WELL
HOW TO DEFINE TIME IN TERMS OF
SAY, THE ROTATION OF THE EARTH
RATHER THAN THE MOTION OF THE SUN.
THESE THINGS WERE WELL
UNDERSTOOD BUT IT'S A VERY
CURIOUS THING THAT WHEN WE TRY
TO UNDERSTAND EXACTLY HOW TO GET
A GRIP ON THE FECUNDITY, I MEAN
IN THE ETHNICITY OF NEWTON'S
LAWS OF MOTION AND PRECISELY
WHAT THEY MEAN CONCEPTUALLY, AS
OPPOSED TO APPLYING THEM, IT'S
SURPRISINGLY DIFFICULT.
THE INERTIA OF AN INERTIAL FRAME
WAS BEING USED EFFECTIVELY BY
ASTRONOMERS FOR CENTURIES BUT
WAS ONLY REALLY PROPERLY DEFINED
CONCEPTUALLY AT THE END OF THE
19th CENTURY.

Now an interviewer sits on the stage with Harvey and says
YOU TALKED ABOUT NEWTON'S...
UH, VIEW OF ABSOLUTE SPACE AND
THE NECESSITY OF, OF...
ABSOLUTE SPACE IN HIS WORLD
VIEW, IT SEEMS TO ME WITHOUT
PROFESSING ANY EXPERTISE THAT
NEWTON MUST HAVE BEEN A LITTLE
BIT, UH, UNCOMFORTABLE WITH THAT.
AT LEAST ENOUGH OF IT TO
RECOGNIZE THAT HE SHOULD
TANGIBLY DEMONSTRATE THE
EXISTENCE OF ABSOLUTE SPACE AND,
AND, UH...
AN EXAMPLE SUCH AS THE BUCKET
EXPERIMENT AND SO FORTH SEEMED
TO BE A JUSTIFICATION OF THAT.

Harvey says MMM.
WELL, NEWTON BEING THE GENIUS
THAT HE WAS, REALIZED THAT HE
HAD TO GET OUT OF THIS HOLE THAT
HE'D PUT HIMSELF INTO BY
APPEALING TO ABSOLUTE SPACE AND
TIME WHICH ARE INVISIBLE THINGS
AND AS HE SAID HIMSELF, THEY
DON'T FALL UNDER THE SENSES.
BUT HE SAID THE SITUATION'S NOT
ALL TOGETHER DESPERATE.
AND HE APPEALED TO CERTAIN
THOUGHT EXPERIMENTS.
NOW, UM, HOW IT REFERRED TO THE
EXPERIMENT INVOLVING THE BUCKET,
PERHAPS I COULD JUST SAY VERY
QUICKLY, THE BUCKET
EXPERIMENT...
INVOLVES TAKING A BUCKET OF
WATER...
LOOKING AT THE SURFACE OF THE
WATER WHEN THE BUCKET'S AT REST.
WELL, IT'S FLAT.
YOU THEN ROTATE THE BUCKET...
AND BEFORE THE WATER CAN PICK UP
THAT ROTATIONAL MOTION, THE
SURFACE IS STILL FLAT BUT
THERE'S A RELATIVE SPEED BETWEEN
THE WATER AND THE...
AND THE BUCKET.
FINALLY, WHEN THE WATER PICKS UP
ALL THE CIRCULAR MOTION THROUGH
VISCOSITY AND SO ON, THE SURFACE
OF THE WATER WILL BE CONCAVE
BECAUSE OF THE CENTRAL FRUGAL
EFFECT.
WITH THIS LITTLE ARGUMENT,
NEWTON WASN'T TRYING SO MUCH TO
SHOW THE EXISTENCE OF ABSOLUTE
MOTION.
HE WAS TRYING TO SHOW THAT
DESCARTES REALLY COULDN'T HAVE
BEEN RIGHT.
BECAUSE WHEN YOU LOOK AT THE
FINAL STATE OF THE BUCKET, IS
THE WATER MOVING?
IS THAT WHAT CAUSES THE
CURVATURE IN THE SURFACE OF THE
WATER IN THE BUCKET?
NO, BECAUSE IT'S NOT MOVING WITH
RESPECT TO THE BUCKET AND BY
DESCARTES DEFINITION OF
PHILOSOPHICAL MOTION, THERE IS
NO MOTION BECAUSE PHILOSOPHICAL
MOTION IS DEFINED AS MOTION WITH
RESPECT TO THE CONTIGUOUS
BODIES.
IN THIS CASE, THE CONTIGUOUS
BODY IS THE BUCKET.
SO HOW DO YOU ACCOUNT FOR THE
FACT THAT THE SURFACE IS NOW
CONCAVE?
SO, THAT PARTICULAR THOUGHT
EXPERIMENT OR ARGUMENT WAS
REALLY A HIDDEN ATTACK YET AGAIN
ON DESCARTES.
BUT WHEN HE SAID THAT THE
SITUATION IS ALL, NOT ALL
TOGETHER DESPERATE, HE WAS
APPEALING TO THE, TO THE FAMOUS
ARGUMENT INVOLVING TWO GLOBES.
AND HERE NEWTON SAID "LOOK,
SUPPOSE I HAVE TWO GLOBES...
TWO IDENTICAL GLOBES AND THEY'RE
CONNECTED TOGETHER BY A
STRING...
AND I ROTATE THEM WITH RESPECT
TO ABSOLUTE SPACE...
SO I PUT THEM INTO CIRCULAR
MOTION.
CAN YOU TELL?"
WELL, THEY DON'T MOVE APART SO
THEY DON'T HAVE ANY, WELL,
THAT'S NOT QUITE TRUE.
BUT TO ALL INTENTS AND PURPOSES,
YOU MIGHT SAY THAT THE RELATIVE
DISTANCE REMAINS THE SAME AND
YOU MIGHT ASK YOURSELF "WELL, OF
COURSE YOU CAN TELL THEY'RE
ROTATING BECAUSE THEY'RE
ROTATING WITH RESPECT TO OTHER
BODIES IN THE UNIVERSE."
AND NEWTON SAYS "WELL, FORGET
ABOUT THE OTHER BODIES.
IMAGINE THEY'RE NOT THERE.
HOW COULD YOU TELL WHETHER THESE
THINGS ARE ABSOLUTELY ROTATING?"
BECAUSE THERE'S A TENSION ON THE
STRING.
AND THAT WILL EVENTUALLY BREAK.
THAT STRING WILL EVENTUALLY
BREAK.
WHERE DOES IT COME FROM?
IT COMES FROM MY THEORY WHICH IS
BASED ON ABSOLUTE SPACE...
AND I GET THE RIGHT ANSWER.

[Audience laughing]

Harvey continues IN GENERAL
RELATIVITY, IF WE ASK OURSELVES
WOULD A FREE FALLING, WHAT A
FREE BODY IS...
THE ANSWER IS SLIGHTLY DIFFERENT
THAN IN, IN SPECIAL RELATIVITY
AND NEWTONIAN MECHANICS.
BECAUSE FOR EXAMPLE, IF I DROP
SOMETHING...
IN NEWTONIAN MECHANICS, THAT IS
NOT A FREE BODY BECAUSE GRAVITY
IS PULLING IT.
BUT IN GENERAL RELATIVELY FOR
EINSTEIN, WHEN I DROP SOMETHING,
THAT IS A FREE BODY BECAUSE
GRAVITY IS NOT A FORCE.
SO FREELY FALLING BODIES ARE
FREE BODIES.
NOW THE QUESTION IS WHY DO THEY
DO WHAT THEY DO?
HOW DO THEY KNOW WHERE TO GO?

[Audience laughing]

Harvey continues THERE'S NO
FORCES ACTING ON THEM.
WELL, FOR NEWTON, THEY JUST DO
WHAT THEY DO.

[Audience laughing]

Harvey continues AND THEY DO
IT IN THIS AMAZINGLY
CONSPIRATORIAL WAY THAT'S THE
SAME ALL OVER THE UNIVERSE EVEN
THOUGH THEY'RE NOT AWARE OF EACH OTHER.
BUT EINSTEIN'S THEORY IS A LOCAL
THEORY IN THE SENSE THAT...
THERE IS A STRUCTURE IN THE
UNIVERSE CALLED THE METRIC FIELD
THAT DETERMINES WHERE THE CURVES
IN SPACE TIME ARE STRAIGHT OR
NOT.
WELL, IT'S REALLY A CURVED SPACE
TIME BUT IT'S LIKE DEFINING
STRAIGHT LINES ON THE SURFACE OF
THE EARTH.
IT'S LIKE DEFINING GREAT
CIRCLES.
AND IT TURNS OUT THAT FREE
FALLING BODIES, THEIR
TRAJECTORIES IN SPACE TIME ARE
THESE STRAIGHT LINES.
NOW THE QUESTION IS WHY?
AND WHEN EINSTEIN ORIGINALLY
TO GENERAL RELATIVITY,
HE PUT IT IN BY HAND.
IT WAS AS IF SPACE TIME HAS
GROOVES IN IT WHICH ARE THESE SO
CALLED GEODESICS...
THESE STRAIGHT LINES, THESE
STRAIGHT CURVES AND THE FREE,
THE FREELY FALLING BODIES
SOMEHOW JUST FALL INTO THEM.
AND THAT REALLY WASN'T VERY
SATISFACTORY.
AND IT ONLY BECAME CLEAR TO
EINSTEIN CONSIDERABLY LATER,
ALMOST 10 YEARS AFTER HE
DEVELOPED GENERAL RELATIVITY
THAT IN FACT HE COULD PROVE IT.
AND FURTHERMORE THAT HE COULD
PROVE IT USING HIS OWN EQUATIONS
OF GENERAL RELATIVITY.
AND IT SEEMS TO ME THAT INERTIAL
IN GENERAL RELATIVITY HAS A
RATHER DIFFERENT
FEATURE THAN IN NEWTONIAN
MECHANICS IN THE SENSE THAT IT
FALLS FROM A FUNDAMENTAL
DYNAMICS.
ANOTHER WAY OF PUTTING THIS AND
IT IS SOMETIMES REFERRED TO THIS
WAY, THERE REALLY AREN'T FREE
BODIES IN GENERAL RELATIVITY.
THERE ARE BODIES THAT ARE
UPON BY ELECTRIC
FORCES OR OTHER KINDS OF FORCES,
THE STANDARD NEWTONIAN FORCES,
BUT THE ONES THAT AREN'T ARE
STILL BEING TOLD TO DO, WHAT TO
DO BY THE EQUATIONS, THE SO
CALLED FUEL EQUATIONS,
EINSTEIN'S FUEL EQUATIONS IN
GENERAL RELATIVITY AND THIS IS
RATHER A DIFFERENT SITUATION.
IT'S A LITTLE BIT LESS
CONSPIRATORIAL IF YOU LIKE, IT
SEEMS TO ME THEN THE SITUATION
IN NEWTONIAN MECHANICS.
BUT I'LL LEAVE IT AT THAT.

The clip ends.

Back in the Studio, Andrew Moodie appears with a caption reading his name.

He says AS BROWN
POINTS OUT, THE HISTORY OF
INERTIAL FRAMES CAN BE TRACED
ALL THE WAY BACK TO COPERNICAN THEORY.
IT RECOGNIZED
THAT BOTH THE EARTH AND THE SUN...

He spins three juggling balls around as he says
ARE MERELY EQUIVALENT POINTS OF
VIEW FROM WHICH THE MOTIONS OF
THE CELESTIAL BODIES MAY BE PERCEIVED.
NOW, I FIND IT IMPOSSIBLE TO
COMPREHEND AN OBJECT IN THIS
UNIVERSE WITH ANY KIND OF MASS
THAT IS FREE OF ALL FORCES THAT
CAN BE EXERTED ON IT.
IT'S IMPORTANT FOR THEORY BTU
THE FACT REMAINS THAT IF I SHOT
A BEAM OF LIGHT FROM WHERE I AM
STANDING RIGHT NOW OUT TO THE
EDGE OF THE UNIVERSE, IT WOULD
BEND AND SWAY DUE TO GRAVITY AND
THE MASSIVE OBJECTS THAT IT
ENCOUNTERED ON IT'S JOURNEY.
WE'RE EFFECTED BY THE THINGS
AROUND US.
AND EVERY DAY, YOU AND I MOVE
FROM POINT A TO POINT B FROM THE
WARMTH OF YOUR BED TO THE COLD
HARSH REALITIES OF THIS WORLD
AND BACK AGAIN.
BUT YOU KNOW WHAT?
IT'S KIND OF TANTALIZING TO
THINK FOR A SECOND THAT MOVEMENT
IS COMPLETELY RELATIVE AND
THEORETICALLY THE WHOLE UNIVERSE
COULD ACTUALLY REVOLVE AROUND
YOU AND YOU ALONE.
FOR
BIG IDEAS...
I'M...
ANDREW MOODIE.

He juggles and laughs.

[Theme music plays]

The end credits roll.

bigideas@tvo.org

416-484-2746

Big Ideas. Producer, Wodek Szemberg.

Producers, Lara Hindle, Mike Miner, Gregg Thurlbeck.

Logos: Unifor, Canadian Media Guild.

A production of TVOntario. Copyright 2006, The Ontario Educational Communications Authority.

Watch: Harvey Brown on the Concepts of Time and Motion