Re: It seems that not everything is known yet

Robin Hanson (
Wed, 16 Sep 1998 09:28:03 -0700

I responded to Curt Adams:
>>Not too long ago, somebody mentioned a theory of gravity where ...
>That was me, and I find this new apparent confirmation quite interesting!

I just found that old post, and see that it was on the polymath list, not here. So here it is:

>Date: Mon, 04 May 1998 10:58:07 -0700
>From: Robin Hanson <>
>Subject: Grav diffusion w/o dark matter
>This was a richter scale 7.0 on my "Wow!" detector:
>SCIENCE-WEEK May 1, 1998 - Issue #53
>R.J. Britten (California Institute of Technology, US) presents a
>model that without dark matter quantitatively describes the flat
>rotation curves of galaxies and the mass-to-light ratios of
>clusters of galaxies. The hypothesis is that the agent of
>gravitational force is propagated as if it were scattered with a
>mean free path of about 5 kiloparsecs. As a result, the force
>between moderately distant masses separated by more than the mean
>free path diminishes as the inverse first power of the distance,
>following diffusion equations, and describes the flat rotation
>curves of galaxies. The force between masses separated by < 1
>kiloparsec diminishes as the inverse square of the distance. The
>excess gravitational force (ratio of 1/r:1/r^2) increases with
>the scale of structures from galaxies to clusters of galaxies,
>but there is reduced force at great distances because of the
>approximately 12 billion years available for diffusion to occur.
>This model with a mean free path of about 5 kiloparsecs predicts
>a maximum excess force of a few hundredfold for galactic clusters
>with dimensions of a few megaparsecs. With only a single free
>parameter, the predicted curve for excess gravitational force vs.
>size of structures fits reasonable well with observations from
>those of dwarf galaxies through galactic clusters. Under this
>diffusion model, no matter is proposed in addition to the
>observed baryons plus radiation, and thus the proposed density of
>the universe is only a few percent of that required for closure.
>The author suggests that although the model does not follow from
>present calculations based on the general theory of relativity,
>it is not necessarily inconsistent with the general theory
>because the diffusing gravitational elements might be interpreted
>as spatial curvatures (e.g., distortions of the metric inducing
>distortions in adjacent regions). The author further suggests
>there is much at stake because of the scale of the intellectual
>investment and the subtle arguments in cosmology that make use of
>the general theory of relativity, and that the challenge of a
>theory of intrinsic "beauty" may not be met at this time because
>"beauty" is a subtle concept.
>QY: Roy J. Britten (
>(Proc. Natl. Acad. Sci. US 31 Mar 98 95:3351)
>(Science-Week 1 May 98)

Robin Hanson RWJF Health Policy Scholar, Sch. of Public Health 510-643-1884 140 Warren Hall, UC Berkeley, CA 94720-7360 FAX: 510-643-8614