The Matter, Myth, and Mindwalk
Date: Around 1993
In an interesting book by Paul Davies and John Gribbin, called
"THE MATTER MYTH". It explains that the concept of energy was originally
introduced as a purely theoretical quantity that could be changed and
exchanged among its various forms. We cannot see or touch energy, yet "we
accept that it really exists because we are so used to discussing it." I am
one who accepts the existence of energy. In fact, I think it is a clearer
concept than Matter itself. So is it then, that ENERGY is a property of
MATTER, or the other way around?
Energy does exist. But, the concept of matter disappearing and
energy appearing in its place is really not quite correct. So, what is
energy? It is a quantity that describes the current state of a system, just
as charge, mass, velocity, position, etc., also would describe the current
state of a system. Moreover, like charge and mass and momentum (but not
velocity), energy is additive - the energy of two objects is the sum of their
individual energies (before they start interacting and interfering). And,
energy is always conserved, just as momentum and charge are. Einstein's great
discovery/idea was that mass is not conserved, and that the true energy of an
object was not just the sum of the various parts that people had always
assumed (kinetic energy from motion, chemical energy from interaction atoms)
but also contained a huge piece that was associated with the mass of the
object. So, does mass turn into energy? No! But, the energy that always
was there, contained in the mass of the particle, can be released if the mass is
reduced. Does energy ever leave a physical object and go off on its own?
It always is just one property of a particle (or collection of particles)
that always has some other properties, such as spin, mass, charge, etc. but,
there is some difference between the 3 types of neutrinos, and there is also a
distinct difference between neutrinos and anti neutrinos (they spin the
opposite way). The photon which carries light is even less "pure energy",
because it carries along with it electric and magnetic fields, in some
sense, and has a polarization as well.
I think it can also be argued that energy does NOT really
xist. One can
approach it from a viewpoint that energy, like momentum, is a human concept
that is useful in understanding nature.
Nature does whatever it wants to do, and it does it in ways which are
mysterious and amazing. Whether the phenomenon is superfluidity, neutron
decay, or photon scattering, nature just DOES it.
Humans make measurements of these events and have come up with terms like
"mass," "energy," "momentum," "charge" and so on to help them quantify what
they measure. Humans also come up with equations (Schroedinger equation,
Einstein equation, Newton's laws, Maxwell's equations, etc.) which relate
things like energy, mass, and so on.
Fortunately, nature behaves in ways that are in agreement with the
mathematics that people understand (so far). Newton's laws are able to
describe "mechanics" using simple algebra. Schroedinger's equation requires
differential equations and probability functions to describe "quantum
mechanics." Einstein's equations involve tensors. Nobody knows how to
properly describe quantum gravity, but some people think that "string
theory" might do it.
Humans can calculate the "energy" of systems and things and make useful
predictions. So far, science has been spectacularly successful at using
these terms to understand the operation of nature to astounding precision.
"Energy" is one quantity that is universal in all branches of science,
and is most useful. Other quantities, like momentum, are also universal,
but are not as useful for answering questions.
As to whether energy is a property of matter, I think it depends what kind
of science you are doing. If you are doing simple mechanics, then no, your
masses have no energy of themselves. If you are colliding electrons and
positrons, then yes, all of your equations involve total energy and rest
energy of the matter. I do not know enough of relativity or string theory to
know how these fields relate energy or matter.
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Update: June 2012