Outlook: The Next Twenty Years Page: 4 of 19
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the 19th century. Once upon a time, there was a
netism breaks down around this distance scale, and
No Big Bang
, , , .I I
exPAn ds iNrV
Figure 5. The unknown constituents of the universe.
I have just finished the introduction. Now I move
on to discuss each category of questions: hell, heaven,
vertical and horizontal. My verdict on the future of
our field follows after that.
What we know is that the Standard Model of particle
physics is completely incapable of answering the big
questions I've listed. What we want to do is to look
for physics beyond the Standard Model that answers
these big questions. By definition, that is physics at
shorter distances. In order to talk about the new
physics that appears at a some small distance scale,
the Standard Model must survive down to whatever
that short distance scale is. The problem is that it
doesn't. This is the hierarchy problem. It is the main
obstacle for us to address the big questions. We can't
even get started! (Fig. 7)
To illustrate the reason why we can't even get
Figure 6. The hell of the Universe we live in and don't know
Figure 7. We would like to access physics at a short distance
that answers some of the big questions. But before getting
there, the Standard Model breaks down around a TeV and
everything at shorter distances is grayed out.
hierarchy problem.2 It was a crisis about the mass
of the electron. We know like charges repel. It is
hard to keep electric charge in a small pack because
it repels itself. On the other hand, we know the
electron is basically point-like. Our best limit is that
the "size" of the electron is less than something like
10-17 cm. The problem is that, if you want to keep
the charge in such a small pack, you need a lot of
energy. A naive guess is that you need at least
a- 10--17 cm
AE ~ - ~ 1 GeV .
But we know we can't afford it. The energy car-
ried by an electron is just E =mc2 0.511 MeV,
nowhere close to what we need. In fact, the best we
can do is to pack the charge down to about 10-13 cm,
which is the so-called classical radius of the electron.
I . . . I . .
Here’s what’s next.
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Murayama, Hitoshi. Outlook: The Next Twenty Years, article, December 7, 2003; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc934465/m1/4/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.