Fear of Physics (32 page)

There is another possibility, however, and remarkably it is the one many string theorists are turning to as it has become clear that their theory is anything but unique. Even the tentative wanderings in the string universe have made it clear that it is quite likely that whatever replaces string theory and whatever might explain how those six or seven extra dimensions become invisible to us, there are likely to be at least 10
⁵⁰⁰
different possible four-dimensional universes that result, each of which might have its own laws of physics. Instead of describing why the universe must look like it does, then, string theory would do almost the opposite. It would explain why the universe in general should look quite different!

In such a scenario scientists have been driven to a postulate that might hope to explain why the universe we happen to live in
has the properties it does: because we are living in it! Namely, it could be that life is only possible in a very small subset of these many different possible universes, all of which could exist in separate regions of space and time. In this case, the only universes with physicists in them who could ask questions about their universes, would be universes that looked a lot like ours. If this idea, which has been elevated to a “principle” by some, called the Anthropic Principle, sounds to you like a cop-out, it should, because it is. But all the same, it might be true, in which case the laws of physics would really be nothing but an environmental accident.

However, I don’t want to end this book speculating about a Theory of Everything or even a Theory of Nothing. An equally likely possibility is that the quest for Universal Truth could instead be misconceived. There may be an infinity of physical laws left to discover as we continue to probe the extremes of scale. And the key point is, it doesn’t really matter! We have learned that we can, and at the present must, perform physics in a world of effective theories, which insulate the phenomena we understand from those we have yet to discover. Even if String theory did turn out to be a Theory of Everything, it would still actually be a theory of very little. Even if it did explain dark energy, which it does not, it would be of little use in directly trying to understand how cows digest food, or even why they are the size they are.

Scientific truth does not require the expectation that the theories we work with are truly fundamental. In this sense, physics is still clearly guided by the same principles introduced by Galileo 400 years ago and indeed the very same principles I introduced at the beginning and throughout this book. All of our wonderful theories of nature involve approximations that we use with impunity. We are guided by ignoring the irrelevant. What is irrelevant is generally guided by considering the dimensional nature of
physical quantities, which determine the scale of the problems we are interested in and those we can safely ignore. All the while we creatively try to adapt what has already worked to new situations. In so doing, we have revealed a remarkable hidden universe that exists beyond our limited human senses, a universe that is thus far simpler and more symmetric. So far, everywhere we look, spherical cows still surround us.

1
Galileo Galilei,
Dialogues Concerning Two New Sciences,
trans. Henry Crew and Alfonso de Salvio (New York: Dover, 1954; original ed., 1914), pp. 67, 64.

2
James Clerk Maxwell,
The Scientific Papers of James Clerk Maxwell,
ed. W.D. Niven (New York: Dover, 1965).

3
Discoveries and Opinions of Galileo,
trans. Stillman Drake (New York: Anchor Books, 1990).

4
Richard Feynman,
The Character of Physical Law
(Cambridge, Mass.: MIT Press, 1965).

5
Robertson Davies,
Fifth Business
(Toronto: Macmillan, 1970).

6
Richard P. Feynman, Robert B. Layton, and Matthew Sands,
The Feynman Lectures on Physics,
vol. 2 (Reading, Mass.: Addison-Wesley, 1965).

7
Galilei,
Dialogues Concerning Two New Sciences,
p. 153.

8
Ibid., p. 166.

9
Feynman,
The Character of Physical Law.

10
Ludwig Wittgenstein,
Tractatus Logico-Philosophicus
(London: Routledge and Kegan Paul, 1958).

Abstraction, in approaching physics.
See also
Models

Acceleration; constant

Anderson, Carl

Angular momentum

Angular momentum conservation

Antiparticles.
See also
Virtual particles

Aristotle

Asymptotic freedom

Atomic bomb

Atoms; size of.
See also
Electrons; Neutrons; Protons

Axions

Bardeen, John

Bethe, Hans

Big bang

Big crunch

Black holes

Bohr, Niels

Born, Max

Born-Oppenheimer theory

Bragg, Lawrence

Bragg, William

Brahe, Tycho

Brief History of Time, A
(Hawking)

Cave allegory (Plato)

Cavendish, Henry

Center of mass

Centre Européen pour Recherche Nucléaire (CERN)

Chandrasekhar, S.

Change: in magnetic field; symmetry and; in velocity

Charge conservation

Chemistry

Chess game, nature as

Circumference

Classical mechanics

Coefficient of expansion

Columbus, Christopher

Conservation: angular momentum;

Conservation,
continued;
energy; momentum

Constant acceleration

Constants, universal

Constant velocity

Cooper, Leon

Cosmic Microwave Background

Critical opalescence

Critical value

Cross-sectional area

Crystals

Cubic dimensions

Dark energy

Dark matter, in universe

Davies, Robertson

Decay, nuclear

Descartes, René

Dimensional analysis; basic dimensions in; in chemistry; in elementary–particle physics; quark model; scaling laws and; universal constants in

Dirac, Paul Adrian Maurice

Distance

DNA

Doyle, Arthur Conan

Earth: distance to moon; distance to sun; escape velocity and; mass of; observing supernova from; orbit of moon around; properties of, as sphere; seismic waves and

Eddington, Arthur Stanley

Einstein, Albert

Electric charge, types of

Electricity, thought experiment on

Electromagnetism; light as; nuclear reactions compared with; quantum theory of; superconductivity and; symmetry and; thought experiment on; vector potential in.
See also
Virtual particles

Electrons; in electron-positron pairs; superconductivity and.
See also
Virtual pairs

Electron Volts

Electroweak theory

Elementary-particle physics: dimensional analysis in; importance of; magnetism and; quark model; Stand Model of; superconductivity and; symmetries in.
See also
Virtual pairs

Eliot, T. S.

Energy; conservation; of electron-positron pairs; electron Volts and; kinetic; mass and; Newton’s Laws and; particle; potential; in quantum mechanics; rest; of stars; of the sun.
See also
Light

Energy-momentum

Escape velocity

Euclid

Exponent (power of ten)

Faraday, Michael

Fermat, Pierre de

Fermat’s principle

Fermi, Enrico

Feynman, Richard

Fisher, Michael

Fission, nuclear

Flat universe

Franklin, Ben

Frequency shift

Galaxy.
See
Milky Way galaxy

Galileo

Gallium

Gauge symmetry

Gauge theory

Gedanken
(thought experiments)

Gell-Mann, Murray

Georgi, Howard

Ginsberg, V. L.

Glashow, Sheldon

Globular clusters

Gold, Thomas

Gravity; accuracy of constant; Einstein on; mass of earth and; mass of sun and; quantum; quantum theory of; strength of

Gross, David

Hamilton, William Rowan

Hawking, Stephen

Heisenberg, Werner

Henry, Joseph

Higgs, Peter

Higgs particles

High-temperature superconductivity

Hilbert, David

Hooft, Gerard’t

Hugo, Victor

Hydrogen

Hydrostatic equilibrium: of stars; of the sun

IBM

Imaginary time

Inertia

Insulators

Iron, magnetism of

Isotropic universe

Jupiter

Kadanoff, Leo

Kaluza-Klein theory

Kaon

Kepler, Johannes

Kepler’s Laws

Kinetic energy

Kurosawa, Akira

Kusch, P.

Lagrange, Joseph–Louis

Lamb, Willis

Lamb shift

Landau, Lev

Language

Large Hadron Collider

Lee, Tsung Dao

Length, as dimension

Light; in closed universe; as electromagnetic wave; frequency shifts of; mirages and; mirrors and; principle of least time and; speed of; of stars; of the sun.
See also
Energy

Light-seconds

Linear dimensions

Loh, E.

London, Fritz

Long-range forces

Lorentz, Henrik

Lorentz force

McLuhan, Marshall

Magnetism; elementary–particle physics and; thought experiment on.
See also
Electromagnetism

Magnitude, estimation of

Manhattan Project

Mass; center of; as dimension; of Earth; energy and; escape velocity and; of galaxy; photons and; rest; superconductivity and
; time and; of universe

Mathematics; dimensions in; as language of physics; mirages and; Noether’s theorem; order-of-magnitude estimation and; scientific notation in

Maxwell, James Clerk

Meissner, W.

Meissner effect

Mercury (element), superconductivity and

Mercury (planet)

Microelectronics

Milky Way galaxy: age of; mass of; relative motion and; supernova.
See also
Planets

Mirages

Mirrors

Models; Standard Model of particle physics; Standard Solar Model

Momentum: angular; conservation; energy-momentum; Newton’s Laws and; symmetry of

Moon

Motion; Newton’s Laws and; parts of; planetary; uniform

Muon

Nazi Germany

Neptune

Neutral interaction

Neutrinos; supernova

Neutrons

Newton, Isaac; Universal Law of Gravity

Newton’s Laws

Nobel Prize

Noether, Emmy

Noether’s theorem

Notation, scientific

Nuclear decay

Nuclear fission

Nuclear reactions; electromagnetism compared with; of stars; of the sun

Numbers.
See
Mathematics

Onnes, H. Kammerlingh

Oppenheimer, Robert

Opulescence, critical

Order-of-magnitude estimation

Parabola

Parity violation

Path integrals

Pauli, Wolfgang

Pauli exclusion principle

Perpetual motion machines

Phase transitions

Photons; mass of; in quantum electrodynamics

Planck, Max

Planck’s constant

Planets: motion of; orbit around sun.
See also specific planets

Plato

Pluto

Politzer, David

Positrons; in electron-positron pairs

Potential energy

Pound, Robert

Power of ten (exponent)

Precessing

Principle of least time

Protons

Pythagoras

Quantum chromodynamics (QCD)

Quantum electrodynamics (QED); virtual particles in

Quantum field theory

Quantum gravity

Quantum mechanics; black holes and; Born-Oppenheimer theory; chemistry applications of; path integrals in; special relativity and; superconductivity and; uncertainty relations in.
See also
Quantum chromodynamics; Quantum electrodynamics

Quantum theory: of electromagnetism; of gravity

Quarks; charmed (heavy)

Quinn, Helen

Rabi, I. I.

Radioactive decay

Rashomon
(film)

Rebka, George

Reflection symmetry

Relativity; Einstein on;
Galileo on; general theory of; special theory of

Rest energy

Rest mass

Revolutions, scientific

Roemer, Ole

Rotating coordinate system

Salam, Abdus

Scale-dependence

Scale invariance

Scaling laws

Schrieffer, J. Robert

Schwinger, Julian

Scientific notation

Seismic waves

Semiconductors

Shelter Island conference (1947)

Short-range forces

Silicon

Solar eclipse

South Dakota, underground neutrino experiment in

Space: curvature of; time and

Space-time interval

Space-time symmetry

Spheres: Earth as; projection of, to flat surface; properties of; sun as; symmetry of; universe as