The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next

Hardcover (Print)
Used and New from Other Sellers
Used and New from Other Sellers
from $1.99
Usually ships in 1-2 business days
(Save 92%)
Other sellers (Hardcover)
  • All (41) from $1.99   
  • New (3) from $32.86   
  • Used (38) from $1.99   
Sort by
Page 1 of 1
Showing All
Note: Marketplace items are not eligible for any coupons and promotions
Seller since 2015

Feedback rating:



New — never opened or used in original packaging.

Like New — packaging may have been opened. A "Like New" item is suitable to give as a gift.

Very Good — may have minor signs of wear on packaging but item works perfectly and has no damage.

Good — item is in good condition but packaging may have signs of shelf wear/aging or torn packaging. All specific defects should be noted in the Comments section associated with each item.

Acceptable — item is in working order but may show signs of wear such as scratches or torn packaging. All specific defects should be noted in the Comments section associated with each item.

Used — An item that has been opened and may show signs of wear. All specific defects should be noted in the Comments section associated with each item.

Refurbished — A used item that has been renewed or updated and verified to be in proper working condition. Not necessarily completed by the original manufacturer.

Brand New Item.

Ships from: Chatham, NJ

Usually ships in 1-2 business days

  • Canadian
  • International
  • Standard, 48 States
  • Standard (AK, HI)
  • Express, 48 States
  • Express (AK, HI)
Seller since 2015

Feedback rating:


Condition: New
Brand new.

Ships from: acton, MA

Usually ships in 1-2 business days

  • Standard, 48 States
  • Standard (AK, HI)
Seller since 2015

Feedback rating:


Condition: New
Brand new.

Ships from: acton, MA

Usually ships in 1-2 business days

  • Standard, 48 States
  • Standard (AK, HI)
Page 1 of 1
Showing All
Sort by


In this groundbreaking book, the renowned theoretical physicist Lee Smolin argues that physics—the basis for all other sciences—has lost its way. For more than two centuries, our understanding of the laws of nature expanded rapidly. But today, despite our best efforts, we know nothing more about these laws than we knew in the 1970s. Why is physics suddenly in trouble? And what can we do about it?

One of the major problems, according to Smolin, is string theory: an ambitious attempt to formulate a “theory of everything” that explains all the particles and forces of nature and how the universe came to be. With its exotic new particles and parallel universes, string theory has captured the public’s imagination and seduced many physicists.

But as Smolin reveals, there’s a deep flaw in the theory: no part of it has been tested, and no one knows how to test it. In fact, the theory appears to come in an infinite number of versions, meaning that no experiment will ever be able to prove it false. As a scientific theory, it fails. And because it has soaked up the lion’s share of funding, attracted some of the best minds, and effectively penalized young physicists for pursuing other avenues, it is dragging the rest of physics down with it.

With clarity, passion, and authority, Smolin charts the rise and fall of string theory and takes a fascinating look at what will replace it. A group of young theorists has begun to develop exciting ideas that, unlike string theory, are testable. Smolin not only tells us who and what to watch for in the coming years, he offers novel solutions for seeking out and nurturing the best new talent—giving us a chance, at long last, of finding the next Einstein.

Read More Show Less

Editorial Reviews

From Barnes & Noble
Lee Smolin's tour de force asserts that string theorists' efforts to formulate "a theory of everything" has become an inbred cult drawing ever more speculative and unproven conclusions. The Trouble with Physics bares the embarrassing failure of this seductive theory, which has bewitched the world with its heady talk of parallel universes and new dimensions. A former adherent of string theory, Smolin debunks with fervor, but he does offer solutions to science's knotty string conundrum.
From the Publisher
"Lee Smolin provides a much needed, enlightening and engagingly written antidote to string-theory hype."—David Deutsch, Oxford University, author of The Fabric of Reality

"If you want to think in new ways about the interconnected universe around you, read Lee Smolin's provocative, inspiring book."—Margaret Geller, Smithsonian Astrophysical Observatory, Harvard University

"Bold, provocative, and, best of all, a joy to read."—Evelyn Fox Keller, Professor of the History and Philosophy of Science, MIT

"Smolin tells the somber tale of contemporary physics with virtuosity, passion, and courage."—Joy Christian, Oxford University

"An uncommonly clear and confident account of the great obstacles—and opportunities—facing physics today. . . .engrossing and illuminating."—Tim Ferris, author of Coming of Age in the Milky Way and The Big Shebang

"[Smolin] exudes a love of science and imagination, and a faith in the next generation of young physicists."—Jaron Lanier, computer scientist and columnist for Discover

"Lee Smolin is keeping his eyes open, asks sharp questions, and offers his delightful insights as a critical insider."—Gerard 't Hooft, Nobel Laureate, University of Utrecht

"[Smolin's] knowledge of [string theory] enables him to tell the story, and survey the road ahead, with clarity and grace."—Neal Stephenson, author of Snow Crash, Cryptonomicon, and Quicksilver

"Lee Smolin's understanding of theoretical physics is unusually broad and deep, and his critical judgments are exceptionally penetrating."—Roger Penrose, author of The Road to Reality and The Emperor's New Mind

"Lee Smolin has written an epic story with great energy and characteristic passion. . . .Thrilling."—Janna Levin, Barnard College of Columbia University, author of How the Universe Got Its Spots

"Clear, lively, and continuously interesting. . .Reading it is a very exciting experience and just what is needed at this time."—Kim Stanley Robinson, best-selling author of The Mars Trilogy

"Smolin offers a compelling argument. . . This is a well-written, critical profile of the theoretical physics community." Library Journal Starred

Publishers Weekly
String theory-the hot topic in physics for the past 20 years-is a dead-end, says Smolin, one of the founders of Canada's Perimeter Institute of Theoretical Physics and himself a lapsed string theorist. In fact, he (and others) argue convincingly, string theory isn't even a fully formed theory-it's just a "conjecture." As Smolin reminds his readers, string theorists haven't been able to prove any of their exotic ideas, and he says there isn't much chance that they will in the foreseeable future. The discovery of "dark energy," which seems to be pushing the universe apart faster and faster, isn't explained by string theory and is proving troublesome for that theory's advocates. Smolin (The Life of the Cosmos) believes that physicists are making the mistake of searching for a theory that is "beautiful" and "elegant" instead of one that's actually backed up by experiments. He encourages physicists to investigate new alternatives and highlights several young physicists whose work he finds promising. This isn't easy reading, but it will appeal to dedicated science buffs interested in where physics may be headed in the next decade. 30 b&w illus. (Sept. 19) Copyright 2006 Reed Business Information.
Library Journal
Physicist Smolin (The Life of the Cosmos) posits that the funds and brain power dedicated to the development of string theory over the last two decades has led to an unprecedented stagnation in theoretical physics. Attracting some of the best minds in science, string theory, which seeks to unify the known laws of quantum mechanics with those of gravity, has become the accepted framework from which to explain these natural phenomena. Noting that Einstein was denied an academic position while working on hypotheses that would open a new way to view the world, Smolin offers a compelling argument that young physicists who depart from string theory are similarly ignored. This is a well-written, critical profile of the theoretical physics community, free of equations, from the perspective of a member. Recommended for public and academic libraries. [See Prepub Alert, LJ 5/15/06].-Sara Rutter, Univ. of Hawaii at Manoa Copyright 2006 Reed Business Information.
Read More Show Less

Product Details

  • ISBN-13: 9780618551057
  • Publisher: Houghton Mifflin Harcourt
  • Publication date: 9/19/2006
  • Pages: 416
  • Product dimensions: 6.00 (w) x 9.00 (h) x 0.94 (d)

Meet the Author

Lee Smolin is a theoretical physicist who has made influential contributions to the search for a unification of physics. He is a founding faculty member of the Perimeter Institute for Theoretical Physics. His previous books include The Trouble with Physics , The Life of the Cosmos and Three Roads to Quantum Gravity .

Read More Show Less

Read an Excerpt

1 The Five Great Problems in Theoretical Physics
From the beginning of physics, there have been those who imagined they
would be the last generation to face the unknown. Physics has always
seemed to its practitioners to be almost complete. This complacency is
shattered only during revolutions, when honest people are forced to admit
that they don't know the basics. But even revolutionaries still imagine that the
big idea — the one that will tie it all up and end the search for knowledge —
lies just around the corner.

We live in one of those revolutionary periods, and have for a
century. The last such period was the Copernican revolution, beginning in the
early sixteenth century, during which Aristotelian theories of space, time,
motion, and cosmology were overthrown. The culmination of that revolution
was Isaac Newton's proposal of a new theory of physics, published in his
Philosophiae Naturalis Principia Mathematica in 1687. The current revolution
in physics began in 1900, with Max Planck's discovery of a formula
describing the energy distribution in the spectrum of heat radiation, which
demonstrated that the energy is not continuous but quantized. This revolution
has yet to end. The problems that physicists must solve today are, to a large
extent, questions that remain unanswered because of the incompleteness of
the twentieth century's scientific revolution.
The core of our failure to complete the present scientific revolution
consists of five problems, each famously intractable. These problems
confronted us when I began my study of physics in the 1970s, and while we
have learned a lot about them in the last three decades, they remain
unsolved. One way or another, any proposed theory of fundamental physics
must solve these five problems, so it's worth taking a closer look at each.
Albert Einstein was certainly the most important physicist of the
twentieth century. Perhaps his greatest work was his discovery of general
relativity, which is the best theory we have so far of space, time, motion, and
gravitation. His profound insight was that gravity and motion are intimately
related to each other and to the geometry of space and time. This idea broke
with hundreds of years of thinking about the nature of space and time, which
until then had been viewed as fixed and absolute. Being eternal and
unchanging, they provided a background, which we used to define notions
like position and energy.
In Einstein's general theory of relativity, space and time no longer
provide a fixed, absolute background. Space is as dynamic as matter; it
moves and morphs. As a result, the whole universe can expand or shrink,
and time can even begin (in a Big Bang) and end (in a black hole).
Einstein accomplished something else as well. He was the first
person to understand the need for a new theory of matter and radiation.
Actually, the need for a break was implicit in Planck's formula, but
Planck had not understood its implications deeply enough; he felt that it
could be reconciled with Newtonian physics. Einstein thought otherwise, and
he gave the first definitive argument for such a theory in 1905. It took twenty
more years to invent that theory, known as the quantum theory.
These two discoveries, of relativity and of the quantum, each
required us to break definitively with Newtonian physics. However, in spite of
great progress over the century, they remain incomplete.
Each has defects that point to the existence of a deeper theory.
But the main reason each is incomplete is the existence of the other.
The mind calls out for a third theory to unify all of physics, and for
a simple reason. Nature is in an obvious sense "unified." The universe we find
ourselves in is interconnected, in that everything interacts with everything
else. There is no way we can have two theories of nature covering different
phenomena, as if one had nothing to do with the other. Any claim for a final
theory must be a complete theory of nature. It must encompass all we know.
Physics has survived a long time without that unified theory. The
reason is that, as far as experiment is concerned, we have been able to
divide the world into two realms. In the atomic realm, where quantum physics
reigns, we can usually ignore gravity. We can treat space and time much as
Newton did — as an unchanging background. The other realm is that of
gravitation and cosmology. In that world, we can often ignore quantum
But this cannot be anything other than a temporary, provisional
solution. To go beyond it is the first great unsolved problem in theoretical
Problem 1: Combine general relativity and quantum theory into a
single theory that can claim to be the complete theory of nature.
This is called the problem of quantum gravity.
Besides the argument based on the unity of nature, there are
problems specific to each theory that call for unification with the other. Each
has a problem of infinities. In nature, we have yet to encounter anything
measurable that has an infinite value. But in both quantum theory and general
relativity, we encounter predictions of physically sensible quantities
becoming infinite. This is likely the way that nature punishes impudent
theorists who dare to break her unity.
General relativity has a problem with infinities because inside a
black hole the density of matter and the strength of the gravitational field
quickly become infinite. That appears to have also been the case very early
in the history of the universe — at least, if we trust general relativity to
describe its infancy. At the point at which the density becomes infinite, the
equations of general relativity break down. Some people interpret this as time
stopping, but a more sober view is that the theory is just inadequate. For a
long time, wise people have speculated that it is inadequate because the
effects of quantum physics have been neglected.
Quantum theory, in turn, has its own trouble with infinities. They
appear whenever you attempt to use quantum mechanics to describe fields,
like the electromagnetic field. The problem is that the electric and magnetic
fields have values at every point in space.
This means that there are an infinite number of variables (even in a
finite volume there are an infinite number of points, hence an infinite number
of variables). In quantum theory, there are uncontrollable fluctuations in the
values of every quantum variable. An infinite number of variables, fluctuating
uncontrollably, can lead to equations that get out of hand and predict infinite
numbers when you ask questions about the probability of some event
happening, or the strength of some force.
So this is another case where we can't help but feel that an
essential part of physics has been left out. There has long been the hope that
when gravity is taken into account, the fluctuations will be tamed and all will
be finite. If infinities are signs of missing unification, a unified theory will have
none. It will be what we call a finite theory, a theory that answers every
question in terms of sensible, finite numbers.
Quantum mechanics has been extremely successful at explaining
a vast realm of phenomena. Its domain extends from radiation to the
properties of transistors and from elementary-particle physics to the action of
enzymes and other large molecules that are the building blocks of life. Its
predictions have been borne out again and again over the course of the last
century. But some physicists have always had misgivings about it, because
the reality it describes is so bizarre. Quantum theory contains within it some
apparent conceptual paradoxes that even after eighty years remain
unresolved. An electron appears to be both a wave and a particle. So does
light. Moreover, the theory gives only statistical predictions of subatomic
behavior. Our ability to do any better than that is limited by the uncertainty
principle, which tells us that we cannot measure a particle's positon and
momentum at the same time. The theory yields only probabilities. A
particle — an atomic electron, say — can be anywhere until we measure it;
our observation in some sense determines its state. All of this suggests that
quantum theory does not tell the whole story. As a result, in spite of its
success, there are many experts who are convinced that quantum theory
hides something essential about nature that we need to know.
One problem that has bedeviled the theory from the beginning is
the question of the relationship between reality and the formalism. Physicists
have traditionally expected that science should give an account of reality as it
would be in our absence. Physics should be more than a set of formulas that
predict what we will observe in an experiment; it should give a picture of what
reality is. We are accidental descendants of an ancient primate, who
appeared only very recently in the history of the world. It cannot be that
reality depends on our existence. Nor can the problem of no observers be
solved by raising the possibility of alien civilizations, for there was a time
when the world existed but was far too hot and dense for organized
intelligence to exist.
Philosophers call this view realism. It can be summarized by
saying that the real world out there (or RWOT, as my first philosophy teacher
used to put it) must exist independently of us. It follows that the terms by
which science describes reality cannot involve in any essential way what we
choose to measure or not measure.
Quantum mechanics, at least in the form it was first proposed, did
not fit easily with realism. This is because the theory presupposed a division
of nature into two parts. On one side of the division is the system to be
observed. We, the observers, are on the other side. With us are the
instruments we use to prepare experiments and take measurements, and the
clocks we use to record when things happen. Quantum theory can be
described as a new kind of language to be used in a dialogue between us
and the systems we study with our instruments. This quantum language
contains verbs that refer to our preparations and measurements and nouns
that refer to what is then seen. It tells us nothing about what the world would
be like in our absence.
Since quantum theory was first proposed, a debate has raged
between those who accept this way of doing science and those who reject it.
Many of the founders of quantum mechanics, including Einstein, Erwin
Schrödinger, and Louis de Broglie, found this approach to physics repugnant.
They were realists. For them quantum theory, no matter how well it worked,
was not a complete theory, because it did not provide a picture of reality
absent our interaction with it. On the other side were Niels Bohr, Werner
Heisenberg, and many others. Rather than being appalled, they embraced
this new way of doing science.
Since then, the realists have scored some successes by pointing
to inconsistencies in the present formulation of quantum theory. Some of
these apparent inconsistencies arise because, if it is universal, quantum
theory should also describe us. Problems, then, come from the division of the
world required to make sense of quantum theory. One difficulty is where you
draw the dividing line, which depends on who is doing the observing. When
you measure an atom, you and your instruments are on one side and the
atom is on the other side. But suppose I watch you working through a
videocam I have set up in your laboratory. I can consider your whole lab —
including you and your instruments, as well as the atoms you play with — to
constitute one system that I am observing. On the other side would be only
You and I hence describe two different "systems." Yours includes
just the atom. Mine includes you, the atom, and everything you use to study
it. What you see as a measurement, I see as two physical systems
interacting with each other. Thus, even if you agree that it's fine to have the
observers' actions as part of the theory, the theory as given is not sufficient.
Quantum mechanics has to be expanded, to allow for many different
descriptions, depending on who the observer is.
This whole issue goes under the name the foundational problems
of quantum mechanics. It is the second great problem of contemporary
Problem 2: Resolve the problems in the foundations of quantum
mechanics, either by making sense of the theory as it stands or by inventing
a new theory that does make sense.
There are several different ways one might do this.

1. Provide a sensible language for the theory, one that resolves all
puzzles like the ones just mentioned and incorporates the division of the
world into system and observer as an essential feature of the theory.
2. Find a new interpretation of the theory — a new way of reading
the equations — that is realist, so that measurement and observation play no
role in the description of fundamental reality.
3. Invent a new theory, one that gives a deeper understanding of
nature than quantum mechanics does.
All three options are currently being pursued by a handful of smart
people. There are unfortunately not many physicists who work on this
problem. This is sometimes taken as an indication that the problem is either
solved or unimportant. Neither is true. This is probably the most serious
problem facing modern science. It is just so hard that progress is very slow. I
deeply admire the physicists who work on it, both for the purity of their
intentions and for their courage to ignore fashion and attack the hardest and
most fundamental of problems.
But despite their best efforts, the problem remains unsolved. This
suggests to me that it's not just a matter of finding a new way to think about
quantum theory. Those who initially formulated the theory were not realists.
They did not believe that human beings were capable of forming a true picture
of the world as it exists independent of our actions and observations. They
argued instead for a very different vision of science: In their view, science can
be nothing but an extension of the ordinary language we use to describe our
actions and observations to one another.
In more recent times, that view looks self-indulgent — the product
of a time we hope we have advanced beyond in many respects. Those who
continue to defend quantum mechanics as formulated, and propose it as a
theory of the world, do so mostly under the banner of realism. They argue for
a reinterpretation of the theory along realist lines. However, while they have
made some interesting proposals, none has been totally convincing.
It is possible that realism as a philosophy will simply die off, but
this seems unlikely. After all, realism provides the motivation driving most
scientists. For most of us, belief in the RWOT and the possibility of truly
knowing it motivates us to do the hard work needed to become a scientist
and contribute to the understanding of nature. Given the failure of realists to
make sense of quantum theory as formulated, it appears more and more
likely that the only option is the third one: the discovery of a new theory that
will be more amenable to a realist interpretation.
I should admit that I am a realist. I side with Einstein and the
others who believe that quantum mechanics is an incomplete description of
reality. Where, then, should we look for what is missing in quantum
mechanics? It has always seemed to me that the solution will require more
than a deeper understanding of quantum physics itself. I believe that if the
problem has not been solved after all this time, it is because there is
something missing, some link to other problems in physics. The problem of
quantum mechanics is unlikely to be solved in isolation; instead, the solution
will probably emerge as we make progress on the greater effort to unify
But if this is true, it works both ways: We will not be able to solve
the other big problems unless we also find a sensible replacement for
quantum mechanics.
The idea that physics should be unified has probably motivated
more work in physics than any other problem. But there are different ways
that physics can be unified, and we should be careful to distinguish them. So
far we have been discussing unification through a single law. It is hard to see
how anyone could disagree that this is a necessary goal.
But there are other ways to unify the world. Einstein, who
certainly thought as much about this as anyone, emphasized that we must
distinguish two kinds of theories. There are theories of principle and
constructive theories. A theory of principle is one that sets up the framework
that makes a description of nature possible. By definition, a theory of
principle must be universal: It must apply to everything because it sets out
the basic language we use to talk about nature. There cannot be two different
theories of principle, applying to different domains. Because the world is a
unity, everything interacts ultimately with everything else, and there can be
only one language used to describe those interactions. Quantum theory and
general relativity are both theories of principle. As such, logic requires their
The other kind of theories, constructive theories, describe some
particular phenomenon in terms of specific models or equations.1 The theory
of the electromagnetic field and the theory of the electron are constructive
theories. Such a theory cannot stand alone; it must be set within the context
of a theory of principle. But as long as the theory of principle allows, there
can be phenomena that obey different laws. For example, the
electromagnetic field obeys laws different from those governing the postulated
cosmological dark matter (thought to vastly outnumber the amount of
ordinary atomic matter in our universe). One thing we know about the dark
matter is that, whatever it is, it is dark. This means it gives off no light, so it
likely doesn't interact with the electromagnetic field. Thus two different
theories can coexist side by side.
The point is that the laws of electromagnetism do not dictate what
else exists in the world. There can be quarks or not, neutrinos or not, dark
matter or not. Similarly, the laws that describe the two forces — strong and
weak — that act within the atomic nucleus do not necessarily require that
there be an electromagnetic force. We can easily imagine a world with
electromagnetism but no strong nuclear force, or the reverse. As far as we
know, either possibility would be consistent.
But it is still possible to ask whether all the forces we observe in
nature might be manifestations of a single, fundamental force. There seems,
as far as I can tell, no logical argument that this should be true, but it is still
something that might be true.
The desire to unify the various forces has led to several significant
advances in the history of physics. James Clerk Maxwell, in 1867, unified
electricity and magnetism into one theory, and a century later, physicists
realized that the electromagnetic field and the field that propagates the weak
nuclear force (the force responsible for radioactive decay) could be unified.
This became the electroweak theory, whose predictions have been
repeatedly confirmed in experiments over the last thirty years.
There are two fundamental forces in nature (that we know of) that
remain outside the unification of the electromagnetic and weak fields. These
are gravity and the strong nuclear force, the force responsible for binding the
particles called quarks together to form the protons and neutrons making up
the atomic nucleus. Can all four fundamental forces be unified?
This is our third great problem.
Problem 3: Determine whether or not the various particles and
forces can be unified in a theory that explains them all as manifestations of a
single, fundamental entity.
Let us call this problem the unification of the particles and forces,
to distinguish it from the unification of laws, the unification we discussed
At first, this problem appears easy. The first proposal for how to
unify gravity with electricity and magnetism was made in 1914, and many
more have been offered since. They all work, as long as you forget one thing,
which is that nature is quantum mechanical. If you leave quantum physics
out of the picture, unified theories are easy to invent. But if you include
quantum theory, the problem gets much, much harder. Since gravity is one of
the four fundamental forces of nature, we must solve the problem of quantum
gravity (that is, problem no. 1: how to reconcile general relativity and quantum
theory) along with the problem of unification.
Over the last century, our physical description of the world has
simplified quite a bit. As far as particles are concerned, there appear to be
only two kinds, quarks and leptons. Quarks are the constituents of protons
and neutrons and many particles we have discovered similar to them. The
class of leptons encompasses all particles not made of quarks, including
electrons and neutrinos. Altogether, the known world is explained by six
kinds of quarks and six kinds of leptons, which interact with each other
through the four forces (or interactions, as they are also known): gravity,
electromagnetism, and the strong and weak nuclear forces.
Twelve particles and four forces are all we need to explain
everything in the known world. We also understand very well the basic
physics of these particles and forces. This understanding is expressed in
terms of a theory that accounts for all of these particles and all of the forces
except for gravity. It's called the standard model of elementary-particle
physics —or the standard model, for short. This theory does not have the
problem of infinities mentioned earlier. Anything we want to compute in this
theory we can, and it results in a finite number. In the more than thirty years
since it was formulated, many predictions made by this theory have been
checked experimentally. In each and every case, the theory has been
The standard model was formulated in the early 1970s. Except for
the discovery that neutrinos have mass, it has not required adjustment since.
So why wasn't physics over by 1975? What remained to be done?
For all its usefulness, the standard model has a big problem: It
has a long list of adjustable constants. When we state the laws of the theory,
we must specify the values of these constants. As far as we know, any
values will do, because the theory is mathematically consistent no matter
which values we put in. These constants specify the properties of the
particles. Some tell us the masses of the quarks and the leptons, while
others tell us the strengths of the forces. We have no idea why these
numbers have the values they do; we simply determine them by experiments
and then plug in the numbers. If you think of the standard model as a
calculator, then the constants will be dials that can be set to whatever
positions you like each time the program is run.
There are about twenty such constants, and the fact that there are
that many freely specifiable constants in what is supposed to be a
fundamental theory is a tremendous embarrassment. Each one represents
some basic fact of which we are ignorant: namely, the physical reason or
mechanism responsible for setting the constant to its observed value.
This is our fourth big problem.
Problem 4: Explain how the values of the free constants in the
standard model of particle physics are chosen in nature.
It is devoutly hoped that a true unified theory of the particles and
forces will give a unique answer to this question.
In 1900, William Thomson (Lord Kelvin), an influential British
physicist, famously proclaimed that physics was over, except for two small
clouds on the horizon. These "clouds" turned out to be the clues that led us
to quantum theory and relativity theory. Now, even as we celebrate the
encompassing of all known phenomena in the standard model plus general
relativity, we, too, are aware of two clouds. These are the dark matter and the
dark energy.
Apart from the issue of its relationship with the quantum, we think
we understand gravity very well. The predictions of general relativity have
been found to be in agreement with observation to a very precise degree. The
observations in question extend from falling bodies and light on Earth, to the
detailed motion of the planets and their moons, to the scales of galaxies and
clusters of galaxies. Formerly exotic phenomena — such as gravitational
lensing, an effect of the curvature of space by matter — are now so well
understood that they are used to measure the distributions of mass in
galactic clusters.
In many cases — those in which velocities are small compared
with that of light, and masses are not too compact — Newton's laws of
gravity and motion provide an excellent approximation to the predictions of
general relativity. Certainly they should help us predict how the motion of a
particular star is influenced by the masses of stars and other matter in its
galaxy. But they don't. Newton's law of gravity says that the acceleration of
any object as it orbits another is proportional to the mass of the body it is
orbiting. The heavier the star, the faster the orbital motion of the planet. That
is, if two stars are each orbited by a planet, and the planets are the same
distances from their stars, the planet orbiting the more massive star will move
faster. Thus if you know the speed of a body in orbit around a star and its
distance from the star, you can measure the mass of that star. The same
holds for stars in orbit around the center of their galaxy; by measuring the
orbital speeds of the stars, you can measure the distribution of mass in that
Over the last decades, astronomers have done a very simple
experiment in which they measure the distribution of mass in a galaxy in two
different ways and compare the results. First, they measure the mass by
observing the orbital speeds of the stars; second, they make a more direct
measurement of the mass by counting all the stars, gas, and dust they can
see in the galaxy. The idea is to compare the two measurements: Each
should tell them both the total mass in the galaxy and how it is distributed.
Given that we understand gravity well, and that all known forms of matter give
off light, the two methods should agree.
They don't. Astronomers have compared the two methods of
measuring mass in more than a hundred galaxies. In almost all cases, the
two measurements don't agree, and not by just a small amount but by
factors of up to 10. Moreover, the error always goes in one direction: There is
always more mass needed to explain the observed motions of the stars than
is seen by directly counting up all the stars, gas, and dust.
There are only two explanations for this. Either the second
method fails because there is much more mass in a galaxy than is visible, or
Newton's laws fail to correctly predict the motions of stars in the gravitational
field of their galaxy.
All the forms of matter we know about give off light, either directly
as in starlight or reflected from planets or interstellar rocks, gas, and dust.
So if there is matter we don't see, it must be in some novel form that neither
emits nor reflects light. And because the discrepancy is so large, the
majority of the matter in galaxies must be in this new form.
Today most astronomers and physicists believe that this is the
right answer to the puzzle. There is missing matter, which is actually there
but which we don't see. This mysterious missing matter is referred to as the
dark matter. The dark-matter hypothesis is preferred mostly because the only
other possibility — that we are wrong about Newton's laws, and by extension
general relativity — is too scary to contemplate.
Things have become even more mysterious. We have recently
discovered that when we make observations at still larger scales,
corresponding to billions of light-years, the equations of general relativity are
not satisfied even when the dark matter is added in. The expansion of the
universe, set in motion by the Big Bang some 13.7 billion years ago, appears
to be accelerating, whereas, given the observed matter plus the calculated
amount of dark matter, it should be doing the opposite — decelerating.
Again, there are two possible explanations. General relativity
could simply be wrong. It has been verified precisely only within our solar
system and nearby systems in our own galaxy. Perhaps when one gets to a
scale comparable to the size of the whole universe, general relativity is
simply no longer applicable.
Or there is a new form of matter — or energy (recall Einstein's
famous equation E = mc2, showing the equivalence of energy and mass) —
that becomes relevant on these very large scales: That is, this new form of
energy affects only the expansion of the universe. To do this, it cannot clump
around galaxies or even clusters of galaxies. This strange new energy, which
we have postulated to fit the data, is called the dark energy.
Most kinds of matter are under pressure, but the dark energy is
under tension — that is, it pulls things together rather than pushes them
apart. For this reason, tension is sometimes called negative pressure. In
spite of the fact that the dark energy is under tension, it causes the universe
to expand faster. If you are confused by this, I sympathize. One would think
that a gas with negative pressure would act like a rubber band connecting the
galaxies and slow the expansion down. But it turns out that when the
negative pressure is negative enough, in general relativity it has the opposite
effect. It causes the expansion of the universe to accelerate.
Recent measurements reveal a universe consisting mostly of the
unknown. Fully 70 percent of the matter density appears to be in the form of
dark energy. Twenty-six percent is dark matter. Only 4 percent is ordinary
matter. So less than 1 part in 20 is made out of matter we have observed
experimentally or described in the standard model of particle physics. Of the
other 96 percent, apart from the properties just mentioned, we know
absolutely nothing.
In the last ten years, cosmological measurements have gotten
much more precise. This is partly a side effect of Moore's law, which states
that every eighteen months or so, the processing speeds of computer chips
will double. All the new experiments use microchips in either satellites or
ground-based telescopes, so as the chips have gotten better, so have the
observations. Today we know a lot about the basic characteristics of the
universe, such as the overall matter density and the rate of expansion. There
is now a standard model of cosmology, just as there is a standard model of
elementary particle physics. Just like its counterpart, the standard model of
cosmology has a list of freely specifiable constants — in this case, about
fifteen. These denote, among other things, the density of different kinds of
matter and energy and the expansion rate. No one knows anything about
why these constants have the values they do. As in particle physics, the
values of the constants are taken from observations but are not yet explained
by any theory.
These cosmological mysteries make up the fifth great problem.
Problem 5: Explain dark matter and dark energy. Or, if they don't
exist, determine how and why gravity is modified on large scales.More
generally, explain why the constants of the standard model of cosmology,
including the dark energy, have the values they do.
These five problems represent the boundaries to present
They are what keep theoretical physicists up at night. Together
they drive most current work on the frontiers of theoretical physics.
Any theory that claims to be a fundamental theory of nature must
answer each one of them. One of the aims of this book is to evaluate just
how well recent physical theories, such as string theory, have done in
achieving this goal. But before we do that, we need to examine some earlier
attempts at unification. We have a great deal to learn from the successes —
and also from the failures.

Copyright © 2006 by Lee Smolin. Reprinted by permission of Houghton Mifflin
Read More Show Less

Table of Contents

Introduction vii

PART I THE UNFINISHED REVOLUTION 1: The Five Great Problems in Theoretical Physics 3 2: The Beauty Myth 18 3: The World As Geometry 38 4: Unification Becomes a Science 54 5: From Unification to Superunification 66 6: Quantum Gravity: The Fork in the Road 80

PART II A BRIEF HISTORY OF STRING THEORY 7: Preparing for a Revolution 101 8: The First Superstring Revolution 114 9: Revolution Number Two 129 10: A Theory of Anything 149 11: The Anthropic Solution 161 12: What String Theory Explains 177

PART III BEYOND STRING THEORY 13: Surprises from the Real World 203 14: Building on Einstein 223 15: Physics After String Theory 238

PART IV LEARNING FROM EXPERIENCE 16: How Do You Fight Sociology? 261 17: What Is Science? 289 18: Seers and Craftspeople 308 19: How Science Really Works 332 20: What We Can Do for Science 349

Notes 359 Acknowledgments 372 Index 375

Read More Show Less

Customer Reviews

Average Rating 4
( 19 )
Rating Distribution

5 Star


4 Star


3 Star


2 Star


1 Star


Your Rating:

Your Name: Create a Pen Name or

Barnes & Review Rules

Our reader reviews allow you to share your comments on titles you liked, or didn't, with others. By submitting an online review, you are representing to Barnes & that all information contained in your review is original and accurate in all respects, and that the submission of such content by you and the posting of such content by Barnes & does not and will not violate the rights of any third party. Please follow the rules below to help ensure that your review can be posted.

Reviews by Our Customers Under the Age of 13

We highly value and respect everyone's opinion concerning the titles we offer. However, we cannot allow persons under the age of 13 to have accounts at or to post customer reviews. Please see our Terms of Use for more details.

What to exclude from your review:

Please do not write about reviews, commentary, or information posted on the product page. If you see any errors in the information on the product page, please send us an email.

Reviews should not contain any of the following:

  • - HTML tags, profanity, obscenities, vulgarities, or comments that defame anyone
  • - Time-sensitive information such as tour dates, signings, lectures, etc.
  • - Single-word reviews. Other people will read your review to discover why you liked or didn't like the title. Be descriptive.
  • - Comments focusing on the author or that may ruin the ending for others
  • - Phone numbers, addresses, URLs
  • - Pricing and availability information or alternative ordering information
  • - Advertisements or commercial solicitation


  • - By submitting a review, you grant to Barnes & and its sublicensees the royalty-free, perpetual, irrevocable right and license to use the review in accordance with the Barnes & Terms of Use.
  • - Barnes & reserves the right not to post any review -- particularly those that do not follow the terms and conditions of these Rules. Barnes & also reserves the right to remove any review at any time without notice.
  • - See Terms of Use for other conditions and disclaimers.
Search for Products You'd Like to Recommend

Recommend other products that relate to your review. Just search for them below and share!

Create a Pen Name

Your Pen Name is your unique identity on It will appear on the reviews you write and other website activities. Your Pen Name cannot be edited, changed or deleted once submitted.

Your Pen Name can be any combination of alphanumeric characters (plus - and _), and must be at least two characters long.

Continue Anonymously
Sort by: Showing all of 5 Customer Reviews
  • Posted October 11, 2009

    I Also Recommend:

    Excellent survey

    This book is not for everyone, but contrary to another review, it is non-technical, quite accessible to an educated lay readership with an interest in modern physics.

    Most of the book is a very comprehensible review of the development of physics in the twentieth century, ending with string theory. It is worth reading for this alone. And then the briefer critique begins.

    String theory is unquestionably mathematical, arguably philosophical. But string theorists have never proposed a way to test it, a fundamental requirement for a scientific theory, and therefore it does not qualify as science as previously defined. To call it science you must redefine science, as string theory enthusiasts have advocated. Indeed, to the extent that it requires that two unproven mathematical theorems to be accepted on faith, as well as the unproven supersymetry theory, string theory is arguably theology.

    A huge practical problem is that string theory is incompatible with general relativity. If string theory is correct, than general relativity must be wrong, despite its extensive empirical verification. I find that a far stretch for a theory with no empirical support.

    Why do physicists continue to pursue it? Smolin provides a very interesting sociological/economic explanation.

    If you sail through this book, you might want to tackle Peter Woit's "Not Even Wrong". It is more technical, though still written for an educated lay readership. It provided my first real understanding of quantum mechanics, though I had to read that chapter twice before I got it. It is also surprisingly amusing. A physicist with a sense of humor!

    3 out of 5 people found this review helpful.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted March 6, 2007

    Fair and Balanced

    This was a well written and consistently argued problem with not simply the current problem with String theory, but the fundametal problem with the way physics is executed in today's Academic venues. For those who are not facile with quantum physics, quantum gravity and string concepts etc., which he uses to support his arguments, the issues of group think and hi-jacking of a program by a senior elite et al is very clear and powerful. Consistent problems abound in today's various business cultures. Must read, especially for those who are accepting the public outcry on global warming -- it's not an inconvenient truth but a very convenient liberal political agenda

    2 out of 3 people found this review helpful.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted January 19, 2007

    A valuable perspective

    This is a reasonably engaging book presenting a perspective on theoretical physics that has been rather under-represented in popular works. If you've read popular books advocating string theory and found them convincing, this book will give you a more balanced understanding of the theory's achievements and its limitations. Smolin argues that string theory is failing because it's an extension of the practical particle physics that has led to successes such as the Standard Model--an approach that has done so well, he says, that it's drowned out other avenues of research right at the moment when it has ground to a halt itself--and that what is needed now is more emphasis on re-examination of fundamental problems like spacetime and quantum mechanics. My views are almost opposite in a way (i.e. that the problem with string theory is that it isn't nearly practical enough), but Smolin is an expert whose opinion is worth reading. One point of irritation for me in the text is that I don't trust the analogies. Although I don't know the technical details of most of what he discussed, an analogy he made for something I do understand (fine tuning and the Higgs mechanism) appears to have nothing to do with the actual physics. The others could be better, but I can't tell. His discussion of the specifics of string theory is more balanced than in other books I've read, and that's what makes the book most useful in my view. The rest of his views are kind of out there, but interesting.

    1 out of 2 people found this review helpful.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted September 18, 2006

    Raises important questions

    This book raises questions about the value of string theory, suggesting that it is a very ingrown subject of interest mainly to those involved, and with few ramifications for either the real world or the philisophical one. Maybe more importantly, the author asks about how this situation evolved and why it continues: what is wrong with universities, with funding, and with the scientific community itself. He is bang on in this arena. The book is very readable and timely, and hopefully will provoke some real change in physics.

    1 out of 1 people found this review helpful.

    Was this review helpful? Yes  No   Report this review
  • Anonymous

    Posted November 23, 2009

    No text was provided for this review.

Sort by: Showing all of 5 Customer Reviews

If you find inappropriate content, please report it to Barnes & Noble
Why is this product inappropriate?
Comments (optional)