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Cosmology
As mentioned above, the universe is the experiment of last resort for
particle physicists who can no longer command the political will to build
larger particle accelerators (the last U.S. project was mothballed when
projections ran to $20 billion). Cosmology is a rapidly evolving field, and
astrophysicists are constantly fielding instruments that improve the breadth
and detail of our observations of the universe.
From this, it would seem that any inferences for particle theory might be
subject to frequent revision. In fact, the history of dark matter exhibits just
this kind of instability. Every year, there seem to be new and progressively
more contradictory constraints on its properties.
Therefore, the list below can only be considered a sketch of this complex
and rapidly developing field. It consists of those results crude enough to have
survived the observational revolutions of the last 25 years. The epithet
(crude) should be taken as a characterization of my currency in this
area: much more sensitive measurements are being obtained by improved
satellite- and ground-based observatories. I am not an expert in these areas.
- We observe no galactic-scale defects in the vacuum distribution of the
gauge fields. Theoretically, the 10 spatial dimensions of super-string theory
are necessary to suppress topological defects in the gauge fields that would
give rise to galactic-scale structures.
- The universe evolved as a cool bubble in a soup of particles and fields
originally heated beyond the Planck Scale. Beyond this energy, particles
readily can pierce the resistance to motion along the seven spatial dimensions
that have collapsed in our era.
- The universe is gravitationally closed. Specifically, the expansion of the
universe, at very early times, is determined by the release of energy from
fields that are converted to mass precisely sufficient to stop the
expansion.
- The most directly evident consequence of the expansionary epochs of the Big
Bang is the Hubble expansion. Light originating from distant cosmological
objects is "red-shifted" in a manner consistent with the predictions
of relativity theory for rapidly moving objects. That we appear to be in the
center of the expanding field is readily understood from the predicted
homogeneity of the expansion.
- Black-body residue (microwave background radiation) is consistent with a
phase transition that occurred when the charged particles (electrons and
protons) combined to form atoms, and the expected growth in the size of the
universe since that epoch.
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