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.
NOTES
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.
9
Feynman,
The Character of Physical Law.
10
Ludwig Wittgenstein,
Tractatus Logico-Philosophicus
(London: Routledge and Kegan Paul, 1958).
INDEX
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