Particle Physics Brick by Brick: Atomic and Subatomic Physics Explained... In LEGO

177 Pages·2018·226.84 MB·English

by  Dr. Ben Still

PA R T I C L E
P H Y S I C S
BRICK BY BRICK
0
1
9
8
7
6
5
4
3
2
1
F
R
P
039340_Particle Physics_001-013_1.indd 1 03/07/17 8:53 PM
Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 1
To Mum and Dad, thanks for all
of your encouragement as a kid!
An Hachette UK Company
www.hachette.co.uk
First published in Great Britain in 2017 by
Cassell, a division of Octopus Publishing Group Ltd
Carmelite House
50 Victoria Embankment
London EC4Y 0DZ
www.octopusbooks.co.uk
Text copyright © Ben Still 2017
Design and layout copyright © Octopus Publishing Group Ltd. 2017
All rights reserved. No part of this work may be reproduced or utilized
in any form or by any means, electronic or mechanical, including
photocopying, recording or by any information storage and retrieval
system, without the prior written permission of the publisher.
LEGO® is a trademark of the LEGO Group, which does not sponsor,
authorise or endorse this book.
Ben Still asserts the moral right to be identified as the author of this work.
ISBN 978-1-84403-934-0
Editorial Director Trevor Davies
Senior Designer Jaz Bahra
Designer Paul Shubrook
Photographer Richard Clatworthy
Picture Researcher Giulia Hetherington
Senior Production Manager Peter Hunt
0
9 1 Managing Editor Sybella Stephens
8 Project Editor Sarah Green
7
6
5
4
3
2
1
F
R
P
039340_Particle Physics_001-013_1.indd 2 03/07/17 8:53 PM
Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 2
PA R T I C L E
P H Y S I C S
BRICK BY BRICK
ATOMIC AND SUBATOMIC
PHYSICS EXPLAINED...
IN LEGO®
0
1
9
DR BEN STILL 8
7
6
5
4
3
2
1
F
R
P
039340_Particle Physics_001-013_1.indd 3 03/07/17 8:53 PM
Job: 0590 Title: Particle Physics Brick by Brick Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 2 DTP: FF Page: 3
0
1
9
8
7
6
5
4
3
2
1
F
R
P
039340_Particle Physics_001-013_1.indd 4 03/07/17 8:53 PM
Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 4
contents
INTRODUCTION
006
BUILDING BLOCKS AND
CONSTRUCTION RULES
014
BUILDING A UNIVERSE
034
ELECTROMAGNETISM AND QED
062
THE STRONG FORCE AND QCD
092
THE WEAK FORCE AND
BREAKING SYMMETRIES
122
BROKEN SYMMETRY AND MASS
138
PROBLEMS WITH GHOSTS
144
VIOLATED SYMMETRY
152
FUTURE
162 0
1
9
INDEX 8
172 7
6
ACKNOWLEDGEMENTS 176 4 5
3
2
1
F
R
P
039340_Particle Physics_001-013_1.indd 5 03/07/17 8:53 PM
Job: 0590 Title: Particle Physics Brick by Brick Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 4 0590-1 DTP: FF Page: 5
INTRODUCTION
scientific models
When asked ‘what is science?’ I draw a deep Experimental data is constantly reminding
breath. There are many answers that could be scientists of the shortcomings of their current
given; a historical one, a philosophical one, a mathematical models. Although our scientific
practical one. Instead my answer is that science, understanding of Nature is imperfect, we embrace
at its core, is the search and desire for the most and quantify this imperfection in the error
accurate possible analogy of Nature. Scientists envelope of the measurements. What has been
build these analogies not in words but in the shown historically is that new science usually
language of mathematics. The analogies they build lurks in the detailed understanding of these errors.
aim to become the truest mathematical models of When explaining complex ideas, we often find
the way the universe works and where everything ourselves using our own analogies and models. This
in it came from. But, like the words of a poet, the is especially true when communicating science
language we use cannot perfectly capture the true which is abstract to our everyday experience of the
beauty of Nature. world. Plastic bricks are of course not particles.
Poets and scientists differ, however, when Each brick is made from trillions upon trillions of
evolving their work. Re-writing of a poem is likely particles. Yet I feel that they can be used to provide
to be subject to differing human opinion, re- a fun and engaging analogy to our understanding of
writing scientific models of Nature is not. Science that subatomic world. This plastic brick analogy, by
answers only to hard and repeatable evidence from the very definition of the word,
experiment. If time and again a new scientific model is not a perfect description of Nature, but
does not hold up in the face of new experimental does take us close to a complete picture of
results, then it is discarded. To progress, a new or the Universe at the smallest scale.
modified model of Nature is required. In this way
science has evolved, developing ever-more accurate
mathematical models of Nature.
0
1
9
8
7
6
5
4
3
2
1
F 6
R
P
039340_Particle Physics_001-013_1.indd 6 03/07/17 8:53 PM
Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 6
INTRODUCTION
scientific models
0
1
9
8
7
6
5
4
3
2
1
7 F
R
P
039340_Particle Physics_001-013_1.indd 7 03/07/17 8:53 PM
Job: 0590 Title: Particle Physics Brick by Brick Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 6 DTP: FF Page: 7
INTRODUCTION
The Standard
Model of
Fermions
Particle Physics
The Standard Model is our current best model of the world at
Up Charm top
the smallest scales and was developed primarily throughout
the 1960s and 70s. To this day there have only been minor
adjustments made to it and every experiment which has
put it to the test has shown it to be correct. Yet we know s
it cannot be a complete model of Nature. The Standard k u c
Model has no tested analogy for the dark matter which r
a
defi nes the size, shape and distribution of galaxies (see
u
page 164). It also fails to explain the strange dark energy
q
which is accelerating the expansion of our Universe. Most
frustratingly for particle physicists is that the Standard
Model is not able to tell us where all particles came from at
d s
the beginning of time itself (see chapter 8).
The Standard Model describes the properties and interactions down strange bottom
between a collection of particles which are, as far as we
understand, fundamental. Each one cannot be subdivided into
anything smaller, so they are the truest building blocks from
electron Muon
which our Universe is made. It does not tell us what the particles
are made from; it does not tell us their size; and it cannot predict
the strength of the forces which shape our Universe. It is a
s
mathematical model which is designed to fi t the experimental
n
data seen – and it does this fantastically well. o
The possible lives of Standard Model particles are explained t
not as solid particles but as extended objects called fi elds which p
stretch out to infi nity in space and time. At each point in space e
and time a particle has a non-zero probability of interacting L
with other particles. Yet when the particles interact, all of the
possibilities crystallize into a single point in space and time
electron Muon Tau
with set behaviour. It is this single point that best fi ts the idea
Neutrino Neutrino Neutrino
of a particle as a solid little ball. Without discussing the maths
0
1
9 in detail it is diffi cult to explain the fi eld-like nature of particles.
8 Here instead we use bricks to represent these point-like
7 particles when they interact, although the fi eld-like aspects will
6 lead us to some seemingly illogical outcomes.
5
4 * This particle has been hypothesised
3 but never observed experimentally
2
1
F 8
R
P
039340_Particle Physics_001-013_1.indd 8 03/07/17 8:53 PM
Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 8
INTRODUCTION
Fermions Bosons
e
Charm top
c
r
e
o
c e
f
r c

t o r
c
f i o
t f
g e
n n k
o g a
r a e
b t m w
s
o
r
strange bottom Gluons
t
c
e
l
Muon Tau
e
photon
Muon Tau W+ W- Z0
Neutrino Neutrino
W Bosons Z Bosons
0
1
9
8
7
6
5
* This particle has been hypothesised 4
but never observed experimentally Graviton* h 3
2
1
9 F
R
P
039340_Particle Physics_001-013_1.indd 9 03/07/17 8:54 PM
Job: 0590 Title: Particle Physics Brick by Brick Text Job: 0590 Title: Particle Physics Brick by Brick
DTP: FF Page: 8 DTP: FF Page: 9