In his letter, "Why No Einstein's Laws?" (PHYSICS
TODAY, January 2007, page 12), Richard Kadel suggests defining three laws based on Einstein's
theory of special relativity. However, Albert Einstein is not the only author of the theory of special
relativity. The early publications on special and general relativity were collected and published
with comments by Arnold Sommerfeld in Des Relativitatsprinzip (4th ed., Teubner, 1922),
which was later translated and published in English. The book started with two papers by Hendrik
Lorentz dated 1895 and 1904, in which he established the so-called Lorentz transformations that
are actually the basic formulas of special relativity. The book also includes two papers by Einstein
published in 1905 and a 1908 paper by Hermann Minkowski.
Minkowski died soon after
his paper was published. Einstein gave many public lectures on special relativity, and public
opinion now erroneously assigns authorship of the theory only to him. However, both Lorentz and
Einstein were nominated for the Nobel Prize for special relativity, and Lorentz was number one
in that nomination. (The nomination was not supported by the Nobel Committee, probably because
of the insufficient experimental confirmation of the theory at that time.) Therefore, it is fair
to call it the Lorentz–Einstein theory of special relativity. Einstein was the founder
of general relativity.
The first of Kadel's proposed
Einstein's laws states that the laws of physics are identical in all non-accelerating (inertial)
frames. However, in his publications Einstein referred to that as the principle of relativity
of classical mechanics; some textbooks call it Galileo's principle.
Sommerfeld made a comment
directly related to the second proposed law, that the vacuum speed of light, c, is the same
for all inertial frames. He wrote, "The principle of the constancy of the velocity of light is of
course contained in Maxwell's equations."
I can agree that Kadel's
third law, that the total energy E of a body of mass m and momentum p is given
by E =√[m2c4
+ p2c2], may be defined as Einstein's law.
It was interesting
to see in the January 2007 issue of PHYSICS TODAY two pieces that touched on the same question from
two different viewpoints. That question is whether an explanation is "just a theory" or an established
fact.
Helen Quinn's Reference
Frame article, "Belief and Knowledge—A Plea About Language" (page 8), dealt quite generally
with the interesting ways in which words are used. Scientists may use them one way while nonscientists
interpret them differently. Richard Kadel's letter, just a few pages later (page 12), lamented
the fact that relativity is referred to as Einstein's theory when, he argues, it really should be
called Einstein's laws of relativity.
President Ronald Reagan's
famous comment about evolution being "only" a theory comes to mind. We in the sciences need to have
a way of determining when an idea—whether we call it a hypothesis, a theory, or a guess—has
been established and accepted well enough that it deserves to be called a law.
Quinn's article correctly
emphasizes that some of the words we use have rather flexible meaning even among scientists. She
notes, however, that scientists are usually aware of the degree to which any particular idea is
supported by evidence, accepted by qualified colleagues, and considered well established by
the scientific community, regardless of whether the idea is referred to as a theory, law, hypothesis,
model, or other name. At the same time, Quinn says that nonscientists do not always understand the
extent to which any given idea is established and accepted. They usually rely on the often mistaken
belief that certain terms have rigid meanings; specifically, they believe that a law is a firmly
established principle and a theory is little more than a guess. That brings us to Kadel's letter.
Kadel accepts the fact
that, whether we scientists like it or not, the general public thinks that anything called a law
is a solid description of the truth and that a theory is yet to be proven. Therefore, he argues, relativity
should no longer be called a theory, but instead should be a set of laws. I wholeheartedly agree.
Yet I have to raise the question: Who decides?
I propose that a recognized
body of physicists, such as the International Union of Pure and Applied Physics, the American Physical
Society, or the American Institute of Physics, should do this for ideas related to physics. The
determining group should then use the new term in its own activities and publications and strongly
encourage all its members to adopt the term.
Following Kadel's suggestion,
I think the designated group should start by declaring that "Einstein's theory of relativity"
should henceforth be called "Einstein's laws of relativity" and should promote the idea to the
public. The change (and the discussions leading up to it) could be likened to the recent decision
by the International Astronomical Union to state that Pluto is not a planet.
The designated organization
should then cooperate with other groups that make such declarations by agreeing to support their
declarations. Thus, I would hope an appropriate biology or geology organization would declare
that the theory of evolution has now been sufficiently well established that it will henceforth
be called "the laws of evolution" and that the physics community would support biologists or geologists
in promoting this change in nomenclature.
Richard Kadel misuses
the meaning of "theory" as applied by most scientists today. Theory as used today hardly means "speculation
based on incomplete knowledge." In Teaching About Evolution and the Nature of Science
(National Academy Press, 1998, available at http://www.nap.edu/readingroom/books/evolution98),
a theory in science is defined as "a well-substantiated explanation of some aspect of the natural
world that can incorporate facts, laws, inferences, and tested hypotheses." Laws are "typically
descriptions of how the physical world behaves under certain circumstances."
There is no suggestion
that either is more certain than the other. In fact, when I teach my geology, physical science, and
Earth science students about the scientific method, I stress that both laws and theories are as
certain as we can make them, both are testable, and in the light of new evidence, both can be modified,
overturned, or replaced. The big difference is that a theory is usually explanatory, while a law
is usually descriptive and often quantifiable.
To define a theory as speculation
is to fall into the trap that many nonscientists have fallen into when dealing with such controversial
theories as evolution. There are generally enormous amounts of data to support theories and laws.
Without that data, we usually refer to "hypotheses" to suggest the greater degree of uncertainty.
In fact, most laws and theories start out as hypotheses.
I do agree that Einstein's
formulations should be called laws. However, that's not because they are more certain now; it's
because they are quantifiable and descriptive. But we still need to refer to Einstein's theories
as well, because they explain why the formulations work.
Isaac Newton offered
us his laws of gravity, describing the attractive force between masses, but refused to offer a theory.
Instead, he famously stated, "I have not been able to discover the cause of those properties of gravity
from phenomena, and I frame no hypothesis. . . . It is enough that gravity does
really exist, and acts according to the laws which we have explained.''
An attempt to boost the
status of special relativity by referring to it as a law rather than a theory would actually have
the opposite effect of demoting Albert Einstein's astonishing contribution. He didn't describe
his (or anyone else's) observations, he described and explained real phenomena before anyone
even knew they were there.
Albert Einstein used
the term "principle of relativity." My dictionary defines a principle as "a fundamental law
that describes how a thing moves, works, or acts," which seems quite appropriate. Perhaps we would
honor Einstein best by using his own words.
I actually prefer the word
"theory" despite the pejorative view held by the general public. It reminds us that scientific
theories cannot be proved, but only disproved. We always exist in a state of incomplete knowledge.
When someone says to me that evolution is only a theory, I like to point out that gravity is also a theory,
and a very useful one at that.
Kadel replies:
Vladimir Krasnopolsky writes that special relativity has several authors and specifically mentions
publications by Hendrik Lorentz that were earlier than Einstein's 1905 paper. One reader wrote
to me indicating the contributions of Henri Poincaré, and interested parties can find a summary
of Poincaré contributions, with accompanying references, on Wikipedia (http://en.wikipedia.org/wiki/Henri_Poincar%C3%A9#). Evidently, he promoted Lorentz's work and, before 1905, promulgated
the "principle of relativity" and an early form of E = mc2 regarding the properties
of emitted radiation. Recollecting from my undergraduate education, I believe it is correct to
state that Einstein was the first to derive special relativity without reference to electromagnetism
and the first to write down what we sometimes call the equivalency of mass and energy, or what I referred
to in my previous letter as Einstein's third law.
An internet search on "Einstein's
laws" returned hundreds of websites that use precisely that terminology when referring to special
relativity. Included among them is the "Laws of Science" (http://en.wikipedia.org/wiki/List_of_laws_in_science),
which has the energy of photons, special relativity, and general relativity all under Einstein's
name. So it's hard to be original, and the general public may be ahead of us—or at least me—in
this discussion.
I exchanged private e-mails
with Helen Quinn shortly after our writings appeared in the same issue of PHYSICS TODAY. She wrote
that her "impression is that the idea of a law became archaic right about the time it was realized
that Newton's laws were not absolutely true in all circumstances. But we never gave up using the
term for ideas that had already been blessed with that language usage." She asked, as does William
Hooper, who would decide, and whether some international body of physicists should be empowered
to promote theories to laws, just as the International Astronomical Union declared that Pluto
is not a planet. I agree with that proposal, but I'll caution that Pluto is still a planet to me.
Hence, I make my own prejudice
clear as to theories versus laws. Unlike Gregory Mead, Joseph Ribaudo, or Lewis Wedgewood, I find
the idea of a law much more compelling than a theory. In my own corner of physics—elementary-particle
or high-energy physics—we have, for example, string theory and supersymmetry theory. Although
both propose solutions to perceived problems with the standard model of high-energy physics,
neither has made a prediction that has yet been verified by experiment. (My theoretical colleagues
will disagree, and they will happily point out that in supersymmetric theories, in which every
quark, lepton, and gauge boson we currently know acquires a new partner, about half of the supersymmetric
particles have already been discovered. Some may argue that the observation of "dark matter" is
actually the detection of supersymmetric particles, but to me the connection has not yet been made.)
Furthermore, in casual conversation, private thinking, or everyday life, one frequently hears—or
asks—the question, "Does it violate the laws of physics?" I've never heard "Does it violate
the theories of physics?" I vote for the laws of special relativity, and in deference to history
and the input from readers of my letter, let a duly organized body of physicists assign attribution,
lest others do it for us.
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