Potter, Frank, date
Mad about modern physics : braintwisters, paradoxes and curiosities / Franklin Potter and
Christopher Jargodzki.
p. cm.
Includes index.
ISBN 0-471-44855-9
1. Physics--Popular works. I. Jargodzki, Christopher II. Title
QC24.5.P68 2004
530—dc22
2004014941
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Acknowledgments. . . . . . . . . . . . . . . . . . xii
To the Reader . . . . . . . . . . . . . . . . . . . . . xiii
Chapter 1 The Heat Is On . . . . . . . . . . . . . . . . . . . . 1
Chapter 2 Does Anybody Really Know What
Time It Is?. . . . . . . . . . . . . . . . . . . . . . . . 11
Chapter 3 Crazy Circles . . . . . . . . . . . . . . . . . . . . . 19
Chapter 4 Fly Me to the Moon. . . . . . . . . . . . . . . . . 29
Chapter 5 Go Ask Alice. . . . . . . . . . . . . . . . . . . . . . 39
Chapter 6 Start Me Up . . . . . . . . . . . . . . . . . . . . . . 49
Chapter 7 A Whole New World. . . . . . . . . . . . . . . . . 63
Chapter 8 Chances Are . . . . . . . . . . . . . . . . . . . . . . 75
Chapter 9 Can This Be Real? . . . . . . . . . . . . . . . . . 91
Chapter 10 Over My Head. . . . . . . . . . . . . . . . . . . . . 105
Chapter 11 Crystal Blue Persuasion . . . . . . . . . . . . . 1 1 7
The Heat Is On . . . . . . . . . . . . . . . . . . . . . . 125
Does Anybody Really Know What
Time It Is? . . . . . . . . . . . . . . . . . . . . . . . 139
Crazy Circles . . . . . . . . . . . . . . . . . . . . . . . 151
Fly Me to the Moon . . . . . . . . . . . . . . . . . . 164
Go Ask Alice . . . . . . . . . . . . . . . . . . . . . . . 181
Start Me Up . . . . . . . . . . . . . . . . . . . . . . . . 192
A Whole New World . . . . . . . . . . . . . . . . . . 206
Chances Are. . . . . . . . . . . . . . . . . . . . . . . . 224
Can This Be Real? . . . . . . . . . . . . . . . . . . . 241
Over My Head . . . . . . . . . . . . . . . . . . . . . . 257
Crystal Blue Persuasion . . . . . . . . . . . . . . 277
Index . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Preface
This book of almost 250 puzzles begins where our first book, Mad
About Physics: Braintwisters, Paradoxes, and Curiosities (2001)
ended—with the physics of the late nineteenth and early twentieth
centuries. The Michelson-Morley experiment of 1887, the
challenges posed by atomic spectra and blackbody radiation, the
unexpected discoveries of X-rays in 1895, radioactivity in 1896, and
the electron in 1897 all loosened the protective belt of ad hoc hypotheses
around the mechanistic physics the nineteenth century had so
laboriously built. Anomalies and paradoxes abounded, ultimately
necessitating a radical rethinking of the very foundations of physics
and culminating in the theory of relativity and quantum mechanics.
Numerous applications of these new and strange concepts followed
very quickly as atomic and nuclear physics led to semiconductor
devices on the small scale and nuclear energy on the large scale. Therefore
we have developed a whole new set of challenges to tickle the
minds of our scientifically literate readers, from science students to
engineers to professionals in the sciences.
The challenges begin with the classical problem of getting a cooked
egg into a bottle through a narrow bottleneck and back out again and
progress gradually to the famous aging-twin paradox of the theory of
special relativity and eventually reach problems dealing with the largescale
universe. In between, we explore the nature of time and of space
as well as how the world of films and television tends to sacrifice
physics for the sake of entertainment. We also consider some of the
more startling questions in relativity. For example, we ask whether a
person can go on a space journey out to a star 7,000 light-years distant
and return while aging only 40 years! And we certainly want to
emphasize the practical applications of microphysics through an examination
of some properties of exotic fluids, unusual motors running on
air or on random motion, as well as thermal, electrical, and photonic
properties of materials in a challenging journey into the atomic world.
Particularly important microworld challenges include: What happened
to Schrödinger’s cat? Can a cup of coffee be the ultimate quantum
computer? Why is a Bose-Einstein condensate a new state of matter?
Why is quantum mechanical coherent scattering so important in developing
new detectors for neutrinos and gravitational waves? When we
reach the nucleus, there are challenges about the accuracy of carbon-14
dating, the reason for neutron decay, and the amount of human
radioactivity. Then our journey reverses as we reach for the stars to consider
Olbers’ paradox about why the night sky is dark instead of bursting
with light, how gravitational lensing by galaxies works, and what
the total energy in the universe might be. This book finishes with a potpourri
of challenges from all categories that ranges from using bicycle
tracks in the mud to determine the direction of travel, to analyzing
water-spouting alligators, and ending with a space-crawling mechanical
invention that seems to defy the laws of physics.
The puzzles range in difficulty from simple questions (e.g., “Will
an old mechanical watch run faster or slower when taken to the
mountains?”) to subtle problems requiring more analysis (e.g., “Is the
Bragg scattering of X-rays from an ideal crystal a coherent scattering
process?”) Solutions and more than 300 references are provided, and
they constitute about two-thirds of the book.
As these examples demonstrate, most of the puzzles contain an element
of surprise. Indeed, one finds that commonsense conjecture and
proper physical reasoning often clash throughout this volume. Einstein
characterized common sense as the collection of prejudices
acquired by age eighteen, and we agree: at least in science, common
sense is to be refined and often transcended rather than venerated.
Many of the challenges were devised to undermine physical preconceptions
by employing paradoxes (from the Greek para and doxos,
meaning “beyond belief”) to create cognitive dissonance. Far from
being simply amusing, paradoxes are uniquely effective in addressing
specific deficiencies in understanding. Usually the contradiction
between gut instinct and physical reasoning for some people will be so
painful that they will go to great lengths to escape it even if it means
having to learn some physics in the process.
Philosopher Ludwig Wittgenstein considered paradoxes to be an
embodiment of disquietude, and as we have learned, these disquietudes
often foreshadow revolutionary developments in our thinking about the natural world.
The counterintuitive upheavals resulting
from relativity theory and quantum mechanics in the twentieth century
only enhanced the reputation of the paradox as an agent for
change in our understanding of physical reality.
Such disquietudes, rather than unexplained experimental facts,
writes Gerald Holton in Thematic Origins of Scientific Thought, were
what led Einstein to rethink the foundations of physics in his three
papers of 1905. Each begins with the statement of formal asymmetries
of a predominantly aesthetic nature, then proposes a general postulate,
not derivable directly from experience, that removes the asymmetries.
For example, in the paper on the quantum theory of light,
formal asymmetry existed between the discontinuous nature of particles
and the continuous functions used to describe electromagnetic
radiation. As Holton notes, “The discussion of the photoelectric
effect, for which this paper is mostly remembered, occurs toward the
end, in a little over two pages out of the total sixteen.” Consistent
with this approach is Einstein’s statement in Physics and Reality
(1936), “We now realize . . . how much in error are those theorists
who believe that theory comes inductively from experience,” and later
in The Evolution of Physics (1938), coauthored with the Polish physicist
Leopold Infeld, “Physical concepts are free creations of the human
mind, and are not, however it may seem, uniquely determined by the
external world.”
As another sore point, the term “quantum mechanics” is really a
misnomer: quantum systems cannot be regarded as made up of separate
building blocks. In the helium atom, for instance, we do not have
electron A and electron B but simply a two-electron pattern in which
all separate identity is lost. This indivisible unity of the quantum world
is paralleled by another kind of unity—between subject and object. Is
light a wave or a particle? The answer seems to depend on the experimental
setup. In the double-slit experiment, the observations of light
yield characteristics of the box and its slits as much as of light itself.
Is reality then observer-dependent? And would this justify Einstein’s
insistence on the power of pure thought in the construction of physical
reality? Modern physics seems particularly adept at generating such
disquietudes. If that’s the case, then perhaps the word Mad in the title
of our book should not be construed as a mere metaphor!
