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Knocking on Heaven's Door

How Physics and Scientific Thinking Illuminate the Universe and the Modern World

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By Lisa Randall

Ecco

Copyright © 2011 Lisa Randall
All right reserved.
ISBN: 9780061723728

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Chapter One

WHAT'S SO SMALL TO YOU IS SO LARGE TO ME
Among the many reasons I chose to pursue physics was the desire to do
something that would have a permanent impact. If I was going to invest
so much time, energy, and commitment, I wanted it to be for something
with a claim to longevity and truth. Like most people, I thought of scientific
advances as ideas that stand the test of time.
My friend Anna Christina Büchmann studied English in college
while I majored in physics. Ironically, she studied literature for the same
reason that drew me to math and science. She loved the way an insightful
story lasts for centuries. When discussing Henry Fielding's novel Tom
Jones with her many years later, I learned that the edition I had read and
thoroughly enjoyed was the one she helped annotate when she was in
graduate school.
Tom Jones was published 250 years ago, yet its themes and wit resonate
to this day. During my first visit to Japan, I read the far older
Tale of Genji and marveled at its characters' immediacy too, despite the
thousand years that have elapsed since Murasaki Shikibu wrote about
them. Homer created the Odyssey roughly 2,000 years earlier. Yet
notwithstanding its very different age and context, we continue to relish the
tale of Odysseus's journey and its timeless descriptions of human nature.
Scientists rarely read such old—let alone ancient—scientific texts.
We usually leave that to historians and literary critics. We nonetheless
apply the knowledge that has been acquired over time, whether from
Newton in the seventeenth century or Copernicus more than 100 years
earlier still. We might neglect the books themselves, but we are careful
to preserve the important ideas they may contain.
Science certainly is not the static statement of universal laws we all
hear about in elementary school. Nor is it a set of arbitrary rules. Science
is an evolving body of knowledge. Many of the ideas we are currently
investigating will prove to be wrong or incomplete. Scientific descriptions
certainly change as we cross the boundaries that circumscribe what we
know and venture into more remote territory where we can glimpse hints
of the deeper truths beyond.
The paradox scientists have to contend with is that while aiming for
permanence, we often investigate ideas that experimental data or better
understanding will force us to modify or discard. The sound core of
knowledge that has been tested and relied on is always surrounded by
an amorphous boundary of uncertainties that are the domain of current
research. The ideas and suggestions that excite us today will soon be
forgotten if they are invalidated by more persuasive or comprehensive
experimental work tomorrow.
When the 2008 Republican presidential candidate Mike Huckabee
sided with religion over science— in part because scientific "beliefs" change whereas
Christians take as their authority an eternal, unchanging God—he was not entirely misguided,
at least in his characterization.
The universe evolves and so does our scientific knowledge of it. Over
time, scientists peel away layers of reality to expose what lies beneath
the surface. We broaden and enrich our understanding as we probe
increasingly remote scales. Knowledge advances and the unexplored region
recedes when we reach these difficult to access distances. Scientific "beliefs"
then evolve in accordance with our expanded knowledge.
Nonetheless, even when improved technology makes a broader range
of observations possible, we don't necessarily just abandon the theories
that made successful predictions for the distances and energies, or speeds
and densities, that were accessible in the past. Scientific theories grow and
expand to absorb increased knowledge, while retaining the reliable parts
of ideas that came before. Science thereby incorporates old established
knowledge into the more comprehensive picture that emerges from a
broader range of experimental and theoretical observations. Such changes
don't necessarily mean the old rules are wrong, but they can mean, for
example, that those rules no longer apply on smaller scales where new
components have been revealed. Knowledge can thereby embrace old ideas
yet expand over time, even though very likely more will always remain
to be explored. Just as travel can be compelling— even if you will never
visit every place on the planet (never mind the cosmos)— increasing our
understanding of matter and of the universe enriches our existence. The
remaining unknowns serve to inspire further investigations.
My own research field of particle physics investigates increasingly
smaller distances in order to study successively tinier components of
matter. Current experimental and theoretical research attempt to expose
what matter conceals—that which is embedded ever deeper inside. But
despite the often-heard analogy, matter is not simply like a Russian
matryoshka doll, with similar elements replicated at successively smaller
scales. What makes investigating increasingly minuscule distances
interesting is that the rules can change as we reach new domains. New forces
and interactions might appear at those scales whose impact was too tiny
to detect at the larger distances previously investigated.
The notion of scale, which tells physicists the range of sizes or energies
that are relevant for any particular investigation, is critical to the
understanding of scientific progress—as well as to many other aspects of the
world around us. By partitioning the universe into different comprehensible sizes,
we learn that the laws of physics that work best aren't
necessarily the same for all processes. We have to relate concepts that
apply better on one scale to those more useful at another. Categorizing in
this way lets us incorporate everything we know into a consistent picture
while allowing for radical changes in descriptions at different lengths.
In this chapter, we'll see how partitioning by scale—whichever scale
is relevant—helps clarify our thinking—both scientific and otherwise—
and why the subtle properties of the building blocks of matter are so hard
to notice at the distances we encounter in our everyday lives. In doing
so, this chapter also elaborates on the meaning of "right" and "wrong" in

science, and why even apparently radical discoveries don't necessarily
force dramatic changes on the scales with which we are already familiar.
IT'S IMPOSSIBLE
People too often confuse evolving scientific knowledge with no knowledge
at all and mistake a situation in which we are discovering new physical
laws with a total absence of reliable rules. A conversation with the
screenwriter Scott Derrickson during a recent visit to California helped
me to crystallize the origin of some of these misunderstandings. At the
time, Scott was working on a couple of movie scripts that proposed
potential connections between science and phenomena that he suspected
scientists would probably dismiss as supernatural. Eager to avoid major
solecisms, Scott wanted to do scientific justice to his imaginative story
ideas by having them scrutinized by a physicist—namely me. So we met
for lunch at an outdoor café in order to share our thoughts along with the
pleasures of a sunny Los Angeles afternoon.
Knowing that screenwriters often misrepresent science, Scott wanted
his particular ghost and time-travel stories to be written with a reasonable
amount of scientific credibility. The particular challenge that he as
a screenwriter faced was his need to present his audience not just with
interesting new phenomena, but also with ones that would translate
effectively to a movie screen. Although not trained in science, Scott was
quick and receptive to new ideas. So I explained to him why, despite the
ingenuity and entertainment value of some of his story lines, the
constraints of physics made them scientificcally untenable.
Scott responded that scientists have often thought certain phenomena
impossible that later turned out to be true. "Didn't scientists formerly
disbelieve what relativity now tells us?" "Who would have thought
randomness played any role in fundamental physical laws?" Despite
his great respect for science, Scott still wondered if—given its evolving
nature— scientists aren't sometimes wrong about the implications and
limitations of their discoveries.
Some critics go even further, asserting that although scientists can
predict a great deal, the reliability of those predictions is invariably suspect.
Skeptics insist, notwithstanding scientific evidence, that there
could always be a catch or a loophole. Perhaps people could come back
from the dead or at the very least enter a portal into the Middle Ages or
into Middle-earth. These doubters simply don't trust the claims of science
that a thing is definitively impossible.
However, despite the wisdom of keeping an open mind and recognizing
that new discoveries await, a deep fallacy is buried in this logic. The
problem becomes clear when we dissect the meaning of such statements
as those above and, in particular, apply the notion of scale. These questions
ignore the fact that although there will always exist unexplored
distance or energy ranges where the laws of physics might change, we
know the laws of physics on human scales extremely well. We have had
ample opportunity to test these laws over the centuries.
When I met the choreographer Elizabeth Streb at the Whitney Museum,-
where we both spoke on a panel on the topic of creativity, she too
underestimated the robustness of scientific knowledge on human scales.
Elizabeth posed a similar question to those Scott had asked: "Could the
tiny dimensions proposed by physicists and curled up to an unimaginably
small size nonetheless affect the motion of our bodies?"
Her work is wonderful, and her inquiries into the basic assumptions
about dance and movement are fascinating. But the reason we cannot
determine whether new dimensions exist, or what their role would be
even if they did, is that they are too small or too warped for us to be able
to detect. By that I mean that we haven't yet identified their influence on
any quantity that we have so far observed, even with extremely detailed
measurements. Only if the consequences of extra dimensions for physical
phenomena were vastly bigger could they discernibly influence anyone's
motion. And if they did have such a significant impact, we would
already have observed their effects. We therefore know that the fundamentals
of choreography won't change even when our understanding of
quantum gravity improves. Its effects are far too suppressed relative to
anything perceptible on a human scale.
When scientists have turned out to be wrong in the past, it was often
because they hadn't yet explored very tiny or very large distances or
extremely high energies or speeds. That didn't mean that, like Luddites, they
had closed their minds to the possibility of progress. It meant only that
they trusted their most up-to-date mathematical descriptions of the world
and their successful predictions of then observable objects and behaviors.
Phenomena they thought were impossible could and sometimes did occur
at distances or speeds these scientists had never before experienced— or
tested. But of course they couldn't yet have known about new ideas and
theories that would ultimately prevail in the regimes of those tiny
distances or enormous energies with which they were not yet familiar.
When scientists say we know something, we mean only that we have
certain ideas and theories whose predictions have been well tested over a
certain range of distances or energies. These ideas and theories are not
necessarily the eternal laws for the ages or the most fundamental of physical
laws. They are rules that apply as well as any experiment could possibly
test, over the range of parameters available to current technology. This
doesn't mean that these laws will never be overtaken by new ones.
Newton's laws are instrumental and correct, but they cease to apply at or near
the speed of light where Einstein's theory applies. Newton's laws are at the
same time both correct and incomplete. They apply over a limited domain.
The more advanced knowledge that we gain through better measurements
really is an improvement that illuminates new and different
underlying concepts. We now know about many phenomena that the
ancients could not have derived or discovered with their more limited
observational techniques. So Scott was right that sometimes scientists have
been wrong—thinking phenomena impossible that in the end turned
out to be perfectly true. But this doesn't mean there are no rules. Ghosts
and time travelers won't appear in our houses, and alien creatures won't
suddenly emerge from our walls. Extra dimensions of space might exist,
but they would have to be tiny or warped or otherwise currently hidden
from view in order for us to explain why they have not yet yielded any
noticeable evidence of their existence.
Exotic phenomena might indeed occur. But such phenomena will
happen only at difficult to observe scales that are increasingly far from
our intuitive understanding and our usual perceptions. If they will always
remain inaccessible, they are not so interesting to scientists. And
they are less interesting to fiction writers too if they won't have any
observable impact on our daily lives.
Weird things are possible, but the ones non-physicists are understandably
most interested in are the ones we can observe. As Steven Spielberg
pointed out in a discussion about a science fiction movie he was considering,
a strange world that can't be presented on a movie screen—and
which the characters in a film would never experience—is not so interesting
to a viewer. (Figure 1 shows amusing evidence.) Only a new world
that we can access and be aware of could be. Even though both require
imagination, abstract ideas and fiction are different and have different
goals. Scientific ideas might apply to regimes that are too remote to be of
interest to a film, or to our daily observations, but they are nonetheless
essential to our description of the physical world.
[ FIGURE 1 ] An XKCD comic that captures the hidden nature of tiny
rolled-up dimensions.
WRONG TURNS
Despite this neat separation by distances, people too often take shortcuts
when trying to understand difficult science and the world. And that can
easily lead to an overzealous application of theories. Such misapplication
of science is not a new phenomenon. In the eighteenth century, when
scientists were busy studying magnetism in laboratories, others conjured up
the notion of "animal magnetism"— a hypothesized magnetic "vital fluid"
in animate beings. It took a French royal commission set up by Louis XVI
in 1784, which included Benjamin Franklin among others, to formally
debunk the hypothesis.

(Continues...)

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Excerpted from Knocking on Heaven's Door by Lisa Randall Copyright © 2011 by Lisa Randall. Excerpted by permission of Ecco. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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