public understanding of science w. g. scott ral/ppd 24 jan 2006 pparc encourages us to spend 1% of...

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