Subject: Re: Alternate scientific theory of universe
From: ted@physics12.Berkeley.EDU (Emory F. Bunn)
Date: 1996/06/20
Newsgroups: talk.origins,sci.astro,sci.physics
In article <4q4cje$9rl@newshost.nmt.edu>,
James Fox wrote:
>
>: in _The Big Bang Never Happened_. I've just started reading this book
>
This book advocates "plasma cosmology" as an alternative to the big
bang. This cosmological model is enormously inconsistent with vast
heaps of observational data, a fact which its proponents conveniently
ignore.
The central tenet of plasma cosmology is that electromagnetic forces,
rather than gravity, are responsible for holding together large
objects like galaxies. Here's a little calculation I did a while ago
showing why that's definitely wrong. If any plasma-cosmology
advocates can tell me why my argument is incorrect, I'm all ears.
Let's assess the possibility that our Galaxy is held together
electromagnetically. In particular, let's see whether it's possible
that the Sun is held in its orbit by electromagnetic forces, rather
than gravity.
The mean magnetic field in our galaxy is measured by Faraday rotation
and is about 2 microgauss. Let's try to estimate the magnetic force
on the Sun caused by this field. To do this, we need to know the
Sun's magnetic moment. That's going to be of order B R^3, where B is
a typical stellar magnetic field and R is the solar radius. Sunspots
(which are regions of anomalously large magnetic field) have field
strengths in kilogauss, so let's take B=1 kG. Then the Sun's magnetic
moment is of order 10^{35} G cm^3. (Sorry for the cgs units, but
that's what astronomers usually use.)
To estimate the force, we have to multiply by a typical field
gradient. This is of order 2 microgauss divided by a galactic
distance scale of, say, 1 kiloparsec. So grad B is of order 10^{-27}
gauss/cm. Multiply that by the Sun's magnetic moment, and you get a
force of 10^8 dynes.
So the magnetic force on the Sun is about 1000 Newtons, or a couple of
hundred pounds. This is a very rough estimate, and if pressed I'll
gladly grant you two or three orders of magnitude uncertainty in it.
I will not, however, grant you 17 orders of magnitude uncertainty,
which is what you'd need to claim that magnetic forces are strong
enough to hold the Sun in the galaxy. (The Sun's centripetal
acceleration in its orbit is some 1.5x10^{-8} cm/s^2, so the force on
it is about 3x10^{25} dynes.)
So much for magnetic forces. How about electrostatic forces? Well,
as a conservative upper limit, let's say that the net charge on the
Sun is at most 10^{10} esu. If the charge were this large, then
electrostatic forces due to the Sun would be the dominant effect
propelling (or retarding, depending on the signs of the charges) the
solar wind at the Earth's distance. If this were the case, it would
be easily observable, so this is a very robust upper limit. A real
astronomer or solar physicist could probably come up with a limit that
was much better than this.
Comparing this net charge to the magnitude of the centripetal force on
the Sun, we find that electric forces can have a significant role in
holding the Sun in its orbit only if the electric field around here is
at least of order 10^{15} dynes/esu, or 10^{19} volts per meter. I
think it's safe to say that we would have noticed by now if this were
the case.
In short, the idea that electromagnetic forces are responsible for the
dynamics of stars in galaxies is not just a little bit implausible;
it's ruled out by many, many orders of magnitude.
-Ted