public understanding of science w. g. scott ral/ppd 24 jan 2006 pparc encourages us to spend 1% of...
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PUBLIC UNDERSTANDING OF SCIENCE
W. G. SCOTTRAL/PPD 24 Jan 2006
PPARC encourages us to spend 1% of our research grant funding on “outreach” activities, promoting understanding, appreciation and awareness of our science to the general public: Targeting 11-16 yr olds in schools etc. can help attract more young people into a scientific career. (e.g. RAL MasterClass 14-16 Mar 2007).
Helps ensure that the UKs front line contribution in this science is recognised by opinion formers, decision-takers/politicians. Taxpayers can have an appreciation and awareness of the research being funded on their behalf.
Helps produce highly qualified researchers with advanced skills needed by academia, industry and commerce.
THE STANDARD MODEL:
422
22
||||- || Tr
FL
)(V “higgs potential”
fermion kinetic term
gauge “kinetic” term
yukawaterm
higgskinetic term
],[ F
igA
where:
“covariant derivative”
field-strength tensor
vector potential
(schematic)
THE HIGGS FIELD:
GeV 2502 vv
0 2141
FG
gives masses to the pointlike particles :
L
R
L
v gm
v gm
quarks leptons
W,Z etc.
refraction?.
u=“UP” (+2/3)
PROTON
NEUTRON
d=“DOWN” (-1/3)QUARKS
…but not to the neutron/proton!
e
e
e
e
ELECTRO-MAGNETIC INTERACTION
A FEYNMAN DIAGRAM
see “QED: the strange theory of light and matter”
QUARK CONFINEMENT
The “Strong” Force
Quark
Antiquark
“CHROMOSTATICS”
“CHROMOSTATICS”
THE “COLOUR” FORCE
QCD
gluons8 colours
quarks3 colours
u e-
d
W+
WEAK INTERACTION
e
NEUTRAL CURRENTS (1973)
ELECTRO-WEAK
e
e
0Z
THE “FORCE” PARTICLES
g1 g2 g3 g4 g5 g6 g7 g8
W- Z0 W+
γ
CERN
THE “MATTER” PARTICLES
ude
cs
tb
1
2
3
Q -1 0 -1/3 +2/3
ELECTROWEAK TGCs
e- e+
z0
w+ w-
see M. Gardner“The Ambidextrous Universe”
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 ?
LH AND RH ARE
MIRROR REFLECTNS!!
• OR PALMS ON OPPOSITE SIDES ?
WHY DOES A MIRRORREVERSE 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
LATIN:
DEXTRA = RIGHT (cf “DEXTROUS”)
SINISTRA = LEFT (cf “SINISTER”)
SPIRAL STAIRCASE BUILT FOR DEFENDER WIELDING SWORD IN
RIGHT HAND
IN THE POPULATION AT LARGE:
APPROX. 90% RIGHT-HANDEDAPPROX. 10% LEFT- HANDED
Mirror Twins
MORE ABSTRACTLY
RIGHT HANDED
COORDINATE SYSTEM
LEFT HANDED
COORDINATE SYSTEM
yz
x
xz
y
x
y
z
RightLeft
MORE ABSTRACTLY
RIGHT HANDED
COORDINATE SYSTEM
LEFT HANDED
COORDINATE SYSTEM
yz
x
xz
y
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 !!!
Fleming’s Left Hand Motor Rule:
IS THE PROBLEM SOLVED ?
NOW FOR SOME A/S PHYSICS
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?
But you can’t be sure it is the same on another planet?
Even the Earth’s field reverses sometimes
Yes, here on Earth the North Pole
of a magnetpoints North!
Problem Solved !?
We could set up our magneticfield using a current?
Current
Magnetic field
RIGHT HAND GRIP RULE:
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
FLEMINGS LEFT-HAND RULE MERELY SWAPS THE LEFT/RIGHT PROBLEM FOR A NORTH/SOUTH
PROBLEM WITH MAGNETS !
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 !
DEFINING LEFT AND RIGHT ASOLUTELY WITH ELECTRO-MAGNETIC FORCES IS IMPOSSIBLE !!
BUT IN 1956 THERE WAS THE SHOCKING DISCOVERY OF `PARITY VIOLATION’ BY THE `WEAK
FORCE’ IN NUCLEAR BETA DECAY:
MOST PHYSICISTS ASSUMED THAT AN ABSOLUTE DEFINITION OF LEFT AND RIGHT
WAS COMPLETELY IMPOSSIBLE !!
Beta Decay
neutron
Beta Decay
proton
anti-neutrino
electron
Feynman diagram for Beta Decay
decay and mediate which ninteractio weak
theof bosons' `weak called-so the are and
WW
N
S
NEUTRONS AND PROTONS IN NUCLEUS
NET ROTATION=
“CURRENT”
NUCLEUSBEHAVES LIKE
SMALL BAR MAGNET
Madame Wu
Electrons
Anti-neutrinos
Magnetic field
DISCOVERED“PARITY VIOLATION”
e
60Co
e
Cobalt-60 experiment solves the L/R problem!
electrons (e-)
anti-neutrinos
Magnetic field
Original Experiment
anti-neutrinos
electrons (e)
Magnetic field
Mirror Experiment
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 compton scattering), proving that the neutrino is also left-handed.
Analysepolarisationof photon
in comptonscattering+
Co-60 expt. doesn’t solve matter vs. anti-matter!
electrons (e-)
anti-neutrinos
Magnetic field
Original Experiment
positrons (e+)
neutrinos
Magnetic field
Anti-Mirror Experiment
WHAT IF HE PUTS OUT HIS LEFT HAND ?
Nowadays of course . . .we measureCP violation!
₪ Left & right hands are mirror reflections
₪ Mirrors invert front and back
₪ L/R convention not verbally communicanle
₪ Left and right symmetry nearly perfect but broken by the weak interaction
₪ The Cobalt-60 experiment can distinguish left and right (and so north and south poles)
₪ Neutrinos are left handed and anti-neutrinos are right handed
₪ Aliens made of antimatter will get left and right wrong – so don’t get too close!!!!.
Summary
z
y
x