214 14. THE STRUCTURE OF ENERGY AND MATTER
all have mirror-image particles called antiparticles, that share most properties but have (among
other things) the opposite electric charge.
Bosons are different from fermions in that there is no restriction to how many of them
can occupy a particular volume. e so-called gauge bosons transmit forces between the other
particles, and control the interactions between them. e photon—a particle of light—is the
most familiar example; it is responsible for the electromagnetic force. e gluon mediates the
forces in the nucleus of an atom, in particular the strong force that holds protons and neutrons
together to make an atomic nucleus. e W and Z bosons were hypothesized in the 1970s to
explain the weak force that is responsible for certain kinds of radioactive decay. ey were finally
detected in the 1990s.
Overriding all of these interactions is the higgs particle. It was hypothesized by Scottish
physicist Peter Higgs in order to help explain why the different particles have the masses that
they do. e higgs particle was detected at CERN in 2012; Higgs received the Nobel Prize in
Physics the following year, in recognition of that discovery.
14.3.2 WHERE IS GRAVITY?
e Standard Model does an excellent job of unifying, in a relatively simple scheme, much of the
complexity of modern physics, regarding the fundamental building blocks of matter and energy
and the rules by which they interact with each other. But there is a huge piece missing from
it—gravity. Our best theory of gravity is Einstein’s GR. But GR is such a different theory in
style—it explains gravity in terms of geometry—that it is difficult to know how to fit it in to the
Standard Model. ere are many ideas and incomplete attempts—probably the most famous
is what is known as string theory. But the fact remains that we know that we do not know the
answer.
Understanding how gravity fits into the Standard Model—or how the Standard Model
fits into GR—is necessary if we want to understand the first tiny fraction of a second of the
Big Bang. And so pursuit of this ultimate grand unification is one of the most active areas of
theoretical physics.
14.3.3 WHERE IS DARK MATTER? WHERE IS DARK ENERGY?
e Standard Model contains no clear explanation for dark matter, and has even less to say
about dark energy. And so although the Standard Model explains much, there is much that it
does not. Why for example does gravity have the particular strength that it does? Why is the
universe mostly particles, while antiparticles are rare?
It is possible that these questions are all interconnected, and that they may be unanswer-
able within the framework of either the Standard Model or GR. Perhaps there is a completely
new way of looking at all of this, that naturally brings these ideas together, and thus explains
some of what are now mysteries (see, for example, Penrose [2004, Chap. 34]).
14.4. REFERENCES 215
14.4 REFERENCES
John Beaver. e Physics and Art of Photography, Volume 1: Geometry and the Nature of Light. IOP
Publishing, 2018a. DOI: 10.1088/2053-2571/aae1b6 207
John Beaver. e Physics and Art of Photography, Volume 2: Energy and Color. IOP Publishing,
2018b. DOI: 10.1088/2053-2571/aae504 205
Michael Light. 100 Suns. Knopf, New York, 2013. 206
Roger Penrose. e Road to Reality: A Complete Guide to the Laws of the Universe. Vintage Books,
2004. 214
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