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