WHAT IS THE
DIFFERENCE
BETWEEN A LEFT
AND A RIGHT HABD?
• RH IS BIGGER THAN LH ???
His right hand IS much bigger!
WHAT IS THE
DIFFERENCE
BETWEEN A LEFT
AND A RIGHT HAND?
• RH IS BIGGER THAN LH ???.
• THUMBS ON OPPOSITE EDGES ?
• OR PALMS ON OPPOSITE SIDES ?
LH AND RH ARE
MIRROR REFLECTNS!!
WHY DOES A MIRROR
REVERSE LEFT AND RIGHT
BUT NOT UP AND DOWN?
• A CONFUSING QUESTION !!!
• SURELY IT REVERSES FRONT AND BACK ?
• BUT IT DOES SEEM TO CHANGE RH TO LH!
CLOSE TO THE HEART OF THE PROBLEM:
How would you communicate left and right
over the phone?
IT’S A RIGHT-HANDER’S WORLD
SPIRAL STAIRCASE BUILT FOR
DEFENDER WIELDING SWORD IN
RIGHT HAND
IN THE POPULATION AT LARGE:
APPROX. 90% RIGHT-HANDED
APPROX. 10% LEFT- HANDED
LATIN:
DEXTRA = RIGHT (cf “DEXTROUS”)
SINISTRA = LEFT (cf “SINISTER”)
Mirror Twins
MORE ABSTRACTLY
RIGHT HANDED
LEFT HANDED
COORDINATE SYSTEM
COORDINATE SYSTEM
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MORE ABSTRACTLY
RIGHT HANDED
LEFT HANDED
COORDINATE SYSTEM
COORDINATE SYSTEM
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Left
Right
A molecule that, like your hands, cannot be made to look like
its mirror-image by rotating it or displacing it, is called chiral.
This group of atoms is IN FRONT here, but goes
BEHIND in the rotating reflection
OPTICAL ACTIVITY
OPTICALLY ACTIVE SUBSTANCES ROTATE THE
PLANE OF POLARISATION OF POLARISED LIGHT
Double Refraction
(in a Calcite Crystal)
Louis Pasteur
Pateur felt that handedness could only be
distinguished/separated by living things.
The DNA structure is
a double helix looking
something like a
twisted ladder.
The two cross-linked
helices are always
right-handed,
twisting in the same
direction as a normal
screw.
Names for
clockwise and
anticlockwise
helices:
Away from your eye
Away from your eye
“Perhaps looking glass milk isn’t good to drink”
- Lewis Carroll, Alice through the looking glass
ALICE WAS RIGHT !!!
NOW FOR SOME A/S PHYSICS
Fleming’s Left Hand Motor Rule:
IS THE PROBLEM SOLVED ?
We DO know the
direction of the curremt
+
-
The positive terminal is
connected to the central
carbon rod
The negative terminal is
connected to the zinc
casing
Conventional Current flows from positive to negative
(opposite to electron flow)
But do we REALLY know the
Magnetic Field Direction?
Yes, here on Earth
the North Pole
of a magnet
points North!
Problem Solved !?
But you can’t be sure it is the
same on another planet?
Even the Earth’s field
reverses sometimes
We could set up our magnetic
field using a current?
RIGHT HAND GRIP RULE:
Current
But applying a right hand rule
followed by a left hand rule is
equivalent to no handed rule at all.
i.e. The wrong hand used for the
grip rule followed by the wrong
hand used for the motor rule
produces the same predicted
motion
Magnetic field
DEFINING LEFT AND RIGHT ABSOLUTELY WITH
ELECTRO-MAGNETIC FORCES IS IMPOSSIBLE !!
FLEMINGS LEFT-HAND RULE MERELY SWAPS
THE LEFT/RIGHT PROBLEM FOR A NORTH/SOUTH
PROBLEM WITH MAGNETS !
ELECTRO-MAGNETIC INTERACTION
e

e


e

e
A FEYNMAN DIAGRAM

DEFINING LEFT AND RIGHT ASOLUTELY WITH
ELECTRO-MAGNETIC FORCES IS IMPOSSIBLE !!
FLEMINGS LEFT-HAND RULE MERELY SWAPS
THE LEFT/RIGHT PROBLEM FOR A NORTH/SOUTH
PROBLEM WITH MAGNETS !
MOST PHYSICISTS ASSUMED THAT AN
ABSOLUTE DEFINITION OF LEFT AND
RIGHT WAS COMPLETELY IMPOSSIBLE !!
BUT IN 1956 THERE WAS THE SHOCKING
DISCOVERY OF `PARITY VIOLATION’ BY THE
`WEAK FORCE’ IN NUCLEAR BETA DECAY:
Beta Decay
neutron
Beta Decay
proton
electron
anti-neutrino
Feynman diagram for Beta Decay
W  and W  are the so - called `weak bosons' of the
weak interactio n which mediate   and   decay
NEUTRONS AND PROTONS IN NUCLEUS
N
NET ROTATION
=
“CURRENT”
NUCLEUS
BEHAVES LIKE
S
SMALL BAR MAGNET
Madame Wu
DISCOVERED
“PARITY VIOLATION”
Anti-neutrinos
e
Co
Magnetic
field
Electrons
e

60
Cobalt-60 experiment solves the L/R problem!
Mirror Experiment
electrons (e)
Magnetic
field
anti-neutrinos
Original Experiment
anti-neutrinos
Magneti
c field
electrons (e-)
Neutrinos and Anti-neutrinos
The weak interaction is a fundamental source of
Left-Right asymmetry in nature
Proving a neutrino is left-handed
(Goldhaber’s Experiment)
An Eu atom takes in an electron which reacts with a proton to form a neutron.
Both a neutrino and a gamma ray are released.
The “handed-ness” of the gamma ray and the neutrino are the same due to angular
momentum because they are emitted in opposite directions.
The photon in the gamma ray emitted was shown to be left-handed (using an optical
device such as an Iceland spar), proving that the neutrino is also left-handed.
Iceland Spar
(double refraction)
+
Co-60 expt. doesn’t solve matter vs. anti-matter!
Anti-Mirror Experiment
neutrinos
Magnetic
field
positrons (e+)
Original Experiment
anti-neutrinos
Magneti
c field
electrons (e-)
WHAT IF HE PUTS OUT HIS LEFT HAND ?
Summary
₪ Left & right hands are mirror reflections
₪ Mirrors invert front and back
₪ Left/right can not easily be communicated
₪ Left and right gives an appearance of
symmetry but the universe isn’t symmetric
₪ The Cobalt-60 experiment can distinguish
left and right (and north and south poles)
₪ Neutrinos are left handed and antineutrinos are right handed
₪ Aliens made of antimatter will get left and
right wrong – so don’t get too close!!!!.
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