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- Herausgeber: Icon Books
- Kategorie: Wissenschaft und neue Technologien
- Serie: Introducing...
- Sprache: Englisch
What really happens at the most fundamental levels of nature? Introducing Particle Physics explores the very frontiers of our knowledge, even showing how particle physicists are now using theory and experiment to probe our very concept of what is real. From the earliest history of the atomic theory through to supersymmetry, micro-black holes, dark matter, the Higgs boson, and the possibly mythical graviton, practising physicist and CERN contributor Tom Whyntie gives us a mind-expanding tour of cutting-edge science. Featuring brilliant illustrations from Oliver Pugh, Introducing Particle Physics is a unique tour through the most astonishing and challenging science being undertaken today.
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Veröffentlichungsjahr: 2014
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Published by Icon Books Ltd, Omnibus Business Centre, 39–41 North Road, London N7 9DP email: [email protected]
ISBN: 978-184831-764-2
Text and illustrations copyright © 2013 Icon Books Ltd
The author and artist have asserted their moral rights.
Edited by Duncan Heath
No part of this book may be reproduced in any form, or by any means, without prior permission in writing from the publisher
Contents
Cover
Title Page
Copyright
What are we made of?
Philosophy: mind and matter
Metaphysics
Empiricism
Experimental philosophy
Figuring out the code
The first atomist
The modern atomic theory
Problems with the theory
Some light entertainment
The conundrum of waves
The luminiferous aether
Cathode rays
A new form of light?
The Electron
Thomson’s proof
X-rays and radioactivity
Enter Rutherford
Using alpha particles as tools
The nuclear model
A light distraction: the photon
Maxwell again
Inside the nucleus
The proton
The neutron
The final picture?
The discovery of cosmic rays
Something in the air
An extraterrestrial source?
The cloud chamber
Tracking the cosmic rays
Quantum field theory
Dirac’s amazing equation
Antimatter
Quantum electrodynamics
QED under threat
Mesons
Pions and muons
The dawn of the age of accelerators
The Cyclotron and Synchrocyclotron
The Synchrotron
Cosmotron, Bevatron and G-Stack
Strange times
The particle zoo
The neutrino
The weak force
Parity
The Standard Model
Quarks
Up, down, strange and charm
Charge-parity
Bottom and top quarks
The strong force and QCD
Gluons
Confinement
Asymptotic freedom
The leptons
Completing the lepton family
Out of the zoo and into the pet shop
Electroweak unification
A new boson needed
Separated at birth
The two-beam collider
CERN’s LEP collider: a crowning achievement
The missing piece
The problem of mass
The joys of symmetry
The Higgs mechanism
Wanted: a massive, spin-zero boson
The Higgs field
The US strikes back
The Large Hadron Collider
Tension at CERN
A new frontier
Two big challenges
Improvements in particle detectors
The arrival of computers
Information management: the internet and the Grid
The great switch-on
Another challenge from the US
Unfinished Higgsness
Supersymmetry and dark matter
The graviton
Gravity, extra dimensions and (micro-) black holes
The solar neutrino problem
The journey continues
Glossary
Acknowledgements
Index
What are we made of?
It’s probably fair to say that we may live a reasonably enjoyable, profitable, and/or meaningful life without knowing the answer to the question: “What is a quark?”
However, if you should stop to think …
… you will have inadvertently embarked on one of the greatest intellectual, philosophical and scientific journeys it is possible to make.
Philosophy: mind and matter
Traditionally, questions like “What are we made of?” were the domain of philosophers. A famous early attempt at an answer can be found in Plato’s Timaeus (c. 360 BC).
Furthermore, these elements were thought themselves to be made of the Platonic solids (the friendliest of the shapes). In Plato’s theory of everything, earth is made of stackable cubes, the relative compactness of the octahedron lends itself naturally to the air we find all around us, icosahedra flow much as we would expect water to, and the sharpness of the tetrahedron neatly explains why fire hurts when we touch it. (A fifth element, the “aether”, was added by Aristotle to give perfect, unspoilable substance to the heavens.)
Such a theory may well seem like it was formulated in a pub (or the classical equivalent), but even as late as the 18th century, ideas such as Descartes’ Dualism (La Description du Corps Humain, 1647) and Leibniz’s Monads (La Monadologie, 1714) persisted as seemingly reasonable attempts to describe reality.
Metaphysics
With his elements, Plato was trying to understand what the world was made of. Descartes’ Dualism went further, arguing that the stuff that lets us think is different to the stuff we’re made of. This division of all things into mind or matter is a great example of metaphysics – the branch of philosophy that aims to describe and understand all the aspects of what it means to “be”.
And as long as all you’re doing is a little postulation and pontification, there’s nothing wrong with that.
Empiricism
It was with the birth of John Locke’s empiricism* in the 17th century that thinkers started acknowledging that checking one’s ideas against experience might be worthwhile.
This conforms to our modern definition of science and the practice of the scientific method. However, until the 19th century “science” simply meant “knowledge”. The term “natural philosophy” was used to describe purely theoretical musings on the workings of the world.
* Words marked with an asterisk are explained in the Glossary on here.
Experimental philosophy
Lord Kelvin (1824–1907, born William Thomson) established the first university physics laboratory in Scotland, the spiritual home of empiricism. Here, ideas could be tested scientifically.
We have come a long way since the time of brilliant individuals working in what were little more than sheds in the grounds of universities. Experiments at the frontiers of our knowledge now need investments of millions – if not billions – of dollars in Bond villain-esque facilities and equipment, and world-wide networks of computing power for data storage and processing.
And yet, in many ways, modern particle physics retains the spirit of metaphysics. It probes our concept of what is real. One may complain that it’s unfair to stunt the creativity of the human imagination by testing its musings against something as trivial as “reality”. I prefer to think of it just as working out, as best we can, what’s really going on. So far, by testing our ideas with experiments, we have witnessed the triumph of matter over mind.
Figuring out the code
The great Richard Feynman (1918–88), who shared a Nobel Prize in Physics for his contributions to experimental philosophy, once described science as like trying to figure out the rules of chess by watching a game being played.
The journey described in this book is perhaps more akin to that of a group of characters in a computer game.
But in terms of this book’s subject matter, I’d expand on the analogy a little. The characters can go further. They can ask:
Likewise, all of the scientific equipment we use is made of the same stuff that we’re trying to find out about, as are the laboratories in which the experiments are performed, as are the scientists performing the experiments – as are you, reading of their efforts and achievements on these pages.
We are not watching the game. We are in the game.
The first atomist
Where did our journey begin? I’d argue that “particle physics” began when we figured out that the atom – the indivisible unit of stuff of which all things are made – is, in fact, divisible. To appreciate the seismic shift this represented in our thinking, we need to understand the theory itself and the historical context.
We’ve already come across one of the first theories of matter – the elements of Plato’s Timaeus.
You are probably more familiar with the atomic theory attributed to Thracian philosopher Democritus (460–370 BC).
Democritus was the first atomist and, as we shall see, his idea has successfully weathered the tests of both time and experiment. The alternative viewpoint holds that matter is a continuum: one may keep dividing stuff into smaller and smaller pieces ad infinitum. It was only towards the end of the 18th century that people started to perform experiments that would shed light onto the matter, as we’ll see next.
The modern atomic theory
Building on the work of French chemists Antoine Lavoisier and Joseph Proust, John Dalton (1766–1844) was arguably the father of the modern atomic theory. In A New System of Chemical Philosophy (1808), he summarized the results of his experimental work, proposing that each chemical element is made up of atoms with unique properties, and that these atoms combine to form chemical compounds.
He didn’t get it quite right, though. Joseph Louis Gay-Lussac (1778–1850) showed that gases combine in whole-number ratios, and that the volumes of gaseous products of such reactions obey similar relationships.
Amedeo Avogadro (1776–1856) seized on this observation to make a big leap forward in how we understand gases. Gay-Lussac’s result – that two volumes of gaseous water (steam), and not one, are formed when hydrogen and oxygen are combined – could be explained only if a given volume of gas contains a fixed number of particles (Avogadro’s Law). And gases like hydrogen and oxygen are actually diatomic in nature – they are formed of molecules* each containing two atoms.
Problems with the theory
Despite these successes, the scientific community of the time had a real problem with the atomic hypothesis: they just didn’t like what they couldn’t see. Sir Humphry Davy (1778–1829) – he of the Davy coal-miners’ lamp – upon presenting Dalton with a prize at the Royal Society in 1826, remarked that Dalton’s atomism didn’t really matter as the practical results of his work were still useful.
Unfortunately, improvements in experimental accuracy actually hampered the acceptance of atomic theory.
It would not be until 1908 – 100 years after the publication of Dalton’s seminal work – that experimental evidence supporting Albert Einstein’s 1905 explanation of botanist Robert Brown ’s observation of 1827 would finally convince most people of the existence of atoms and molecules.
Brown (1773–1858) noticed that tiny specks of plant matter spat out by pollen grains suspended in water would randomly jostle about under the lens of his microscope. This became known as Brownian Motion. Einstein (1879–1955) explained this by calculating the distance that the ejected specks would travel if they were being constantly bombarded by the fluid’s constituent molecules.
James Clerk Maxwell (1831–1879) and later Ludwig Boltzmann (1844–1906) had likewise had much success in describing the thermodynamic behaviour of gases by modelling them as collections of tiny, fast-moving billiard balls continually bashing the surfaces of whatever vessel they were in. This was the kinetic theory of gases, and it could be used to explain things like pressure and heat. These billiard balls were, of course, Avogadro’s molecules.
But it is one of Maxwell’s other great achievements – the unification of electricity and magnetism – that allowed scientists to better understand another aspect of the world around us: light.
Some light entertainment
Optics, the science of light and vision, had an early champion in the Islamic scholar Ibn al-Haytham (965-1040). His Book of Optics (1011–21) succeeded Ptolemy’s work on the subject, featuring many experimental results concerning the behaviour of light. It was translated into Latin and influenced later European thinkers including Bacon, Kepler and Descartes.
But while the optics of al-Haytham (or Alhacen, if you prefer the Latin) described what light did, attempts to work out what it actually was led to the first appearance of the physicist’s favourite question:
Descartes thought that light was a wave, making an analogy with sound. Robert Hooke (1635–1703) also discussed a wave theory of light in Micrographia (1665), as did Christiaan Huygens (1629–95) in Treatise on Light (1690).
However, Isaac Newton (1642–1727) – standing on the shoulders of Pierre Gassendi (1592–1655) who was, incidentally, an atomist – declared in his Hypothesis of Light (1675) that light was made of tiny particles moving in straight lines.
Thanks to Newton’s reputation, the corpuscular theory of light dominated 18th-century thinking on the subject.
The conundrum of waves
Ultimately, not even Newton’s reputation could withstand the power of the scientific method: the experiments of Thomas Young, Augustine Fresnel, Siméon Poisson and others showed that light reflected, refracted and interfered with itself in a way that could only be explained if light was a wave.
But there was a conundrum: waves represent the movement of energy within a medium with no net movement of the medium in question. In other words, when you have waves, you need something to be doing the waving. Light was known to be able to travel in a vacuum – so, unlike with sound, it wasn’t air that was carrying the light vibrations. So what was?
As the wave theory of light took hold, so the “luminiferous aether” seeped into the consciousness of scientists. As more people thought about this aether, it was realized that it must be a very odd substance indeed.
To the vibrations of light, it had to behave as a solid. Transverse vibrations require a solid to move through, and the high frequencies of visible light would require that solid to be diamond-hard. And yet, to slow-moving planets, people, kittens, etc. It behaved as a liquid – as otherwise we’d notice it when moving around.
