Paul R. Gerber
Gerber Molecular Design, Forten 649, CH-8873 Amden, Switzerland
This highly speculative small note tries to dwell on possible implications
for cosmologic modeling, when one assumes that matter and antimatter experience
mutual gravitational repulsion instead of attraction. I'm not aware of any
experiment which discriminates among the two possibilities, although it seems to
be generally accepted, that attraction takes place.
However, it appears that by assuming matter-antimatter repulsion (MAR) several
fundamental difficulties in cosmology theory may be removed.
At present it is far from clear to me whether a MAR-consistent extension of
the theory of gravity can be worked out, and whether such a thing exists at all.
Nevertheless, dwelling on my present
understanding of general relativity, I would envisage a two-dimensional
analog of the geometry of the universe as a flat sheet metal with indentations,
up from matter islands and down from antimatter ones. Orientability of space
would take care of the up-down distinction without a need for embedding.
MAR would allow the universe to be made up of equal proportions of
matter (+) and antimatter (-). The intermingled islands of opposite
sign would repel each other. Thus, the missing annihilation radiation, a strong
argument in favor of a matter-alone universe, would have a natural explanation.
- Accelerated cosmic expansion:
A simple symmetric arrangement of matter and antimatter can be envisaged to
correspond to a sodium chloride crystal,
with the sodium atoms representing matter
islands, the chlorine atoms antimatter islands, and electrostatics
The atomic crystal is held together by electrostatic forces.
These are of either sign but the interspersed arrangement of atoms makes the crystal
hold together. However, upon changing the sign in the Coulomb law, which
would correspond to MAR-gravity, the crystal would fly apart in an ever
accelerated expansion. This is reminiscent of what has recently been found
from supernova distance measurements for the expansion of the universe.
A less regular arrangement of islands is not expected to spoil the essence of
- Flatness Problem:
In a mix of equal amounts, matter and antimatter would compensate each others
gravitational fields, MAR assumed. The average 'gravitating density' would be zero
and kept at that value owing to matter-antimatter symmetry. No fine tuning of
density would be needed. However, to make this precise, it would have to be
possible to extend general relativity theory such that it could cope with MAR.
- Horizon Problem:
The horizon problem originates in the small-time solutions of the Friedmann
equation, in which the expansion speed grows without limit for near-zero times,
because the density diverges too fast. However, it is actually the
'gravitating' density which is relevant for expansion. An equal mix of
matter and antimatter would, assuming MAR, add up to zero gravitating
density. Thus, the small-time solution would be well behaved, a 'Slow Bang'
so to speak. Expansion would only result from segregation of matter and
antimatter in corresponding islands. Radiation (made up of particles that
are their own antiparticles) would have to have no gravitating property,
though it would travel along geodesics (gravitational lensing).
- Density Perturbations:
In the absence of the horizon problem, it is plausible that thermal
equilibration could have been operative at photon-decoupling time, in accord with
the high isotropy of the cosmic background radiation. Perturbation modes
segregating matter and antimatter would, most probably, obtain fast growing
Amden, November 21, 2010
I have immensely benefited from the well written books of
and from John Peakock's classic