Page 23 - 2013 Annual Report

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Is Space Foamy?
A new idea put forward by
Associate Faculty member Maxim
Pospelov
suggests that Earth might be crashing through bubble
after bubble in a foamy cosmos – and, crucially, that we might be
able to detect bubble walls as we pass through them.
The hypothesis that space might be foamy is not new. It begins with
a hypothetical field which has several possible ground states. In the
hot chaos of the early universe, this ground state value would have
been jumbled, with every point having a different ground state. As
the universe expanded and cooled, large regions of space would
have settled on a single value. Since then, they would have “frozen”
into place, in a kind of invisible cosmic foam. The energy locked into
these structures could contribute to those mysterious substances,
dark matter and dark energy.
In the recent research, Pospelov estimated the size of the domains
in the cosmic field – the bubbles in the foam. He found that the
bubbles are small enough that the known speed of our solar system
would cause it to pass through many domain walls over the course
of a few years. Wall-crossing events would, then, be rare, but not
impossibly so.
As the Earth passes through a bubble wall, there would be a small and
sudden change in the magnetic torque exerted by the hypothetical
field. Pospelov and his collaborators predict that the strength of
that effect would be about a billionth of the Earth’s magnetic field
over a millisecond. The current generation of magnetometers are
just sensitive enough to pick up such a signal. The team proposed
deploying a network of widely separated but synchronized devices,
to allow the tiny signals to be cross-checked. A pilot project to
develop this detector has been funded by the National Science
Foundation (US).
The collaboration, then, has taken two small things – new calculations
about the relatively small size of cosmic bubbles and the new small
signals that can be picked up by today’s magnetometers – and put
them into one big new idea: the “cosmic foam” hypothesis can now
be directly tested for the first time.
References:
P. Schuster (Perimeter Institute) and N. Toro (Perimeter Institute), “On the Theory of Continuous-
Spin Particles: Wavefunctions and Soft-Factor Scattering Amplitudes,”
JHEP
1309 (2013) 104,
arXiv:1302.1198.
P. Schuster (Perimeter Institute) and N. Toro (Perimeter Institute), “On the Theory of Continuous-
Spin Particles: Helicity Correspondence in Radiation and Forces,”
JHEP
1309 (2013) 105,
arXiv:1302.1577.
P. Schuster (Perimeter Institute) and N. Toro (Perimeter Institute), “A Gauge Field Theory of
Continuous-Spin Particles,”
JHEP
1310 (2013) 061, arXiv:1302.3225.
M. Pospelov (Perimeter Institute and University of Victoria), S. Pustelny (Institute of Physics,
Jagiellonian University, Poland and University of California, Berkeley), M.P. Ledbetter (University
of California, Berkeley), D.F. Jackson Kimball (California State University – East Bay), W. Gawlik
(Institute of Physics, Jagiellonian University), and D. Budker (University of California, Berkeley and
Lawrence Berkeley National Laboratory), “Detecting Domain Walls of Axionlike Models Using
Terrestrial Experiments,”
Phys. Rev. Lett
. 110, 021803 (2013).