Sunday, November 25, 2007

A Convenient Fiction

There is a serious misunderstanding about the state of science today. People look at all this shiny new hardware and imagine some unified state of knowledge behind it all. We have no such thing. What we actually have are islands of good enough knowledge.

There is not some great monolithic body of knowledge that can be described in a few equations understood by physics geeks and people with advanced math degrees.

Let me illustrate the problem with a recent personal anecdote. I was designing a gas valve for a fusion test reactor and commenter Brent pointed out that I had not taken into consideration something called the Knudsen Number. It was true. I had never even heard of it. The short version is: if gas pressures are low enough and the holes are small enough, you design the valve with one set of equations. If the holes are big and the pressure high you use another set of equations. In the middle? It is why engineers get paid the big bucks.

So the point of all that is that we don't have a unified knowledge set about gas flow through holes. We know a lot about aspects of this. We have islands of good knowledge and places where all is fuzziness or worse darkness.

Which brings me to a comment I made at Lubos Motl's Reference Frame, where Lubos is doing a very interesting exposition on the philosophy of science.

There is a lot of interesting work going on in the plasma physics area.

There are a lot of previously hidden self organizing principles being either discovered, re-discovered, or given new emphasis. Not just in quasi-static plasmas but dynamic ones as well.

We are starting to look at not just the frequencies of particles, but also the frequencies of assemblages of particles under the influence of various fields.

The tokamak guys are really struggling with this. They want a nice flat Maxwellian plasma and the plasma is not co-operating. It turns out that a true or even-quasi Maxwellian plasma may be impossible.

I think if we start looking at the facts, the idea of a Maxwellian plasma is a total fiction. The slightest deviation from Maxwellian distribution causes forces to build up and currents to flow.

So what we really need to make all this work is to delve into the self organizing principles of plasma and look at it from the point of view that a Maxwellian plasma is a convenient fiction for a certain class of problems.


LarryD said...

Mostly Off Topic:

H/T Slashdot: Santa Fe Reporter story on "Nuclear Battery"

"The portable nuclear reactor is the size of a hot tub. It’s shaped like a sake cup, filled with a uranium hydride core and surrounded by a hydrogen atmosphere. Encase it in concrete, truck it to a site, bury it underground, hook it up to a steam turbine and, voila, one would generate enough electricity to power a 25,000-home community for at least five years. "

The waste management issue instantly leaps to mind.

M. Simon said...

What about hydrogen management?

What about the fact that there does not seem to be a surplus of steam turbines waiting for a power source?

Also 27 MWth ~= 10 MWe. Not a lot of power.

M. Simon said...

You might not need some one to watch the reactor. Steam plants do not run unattended.

Such a small power output hardly pays for the required plant operators.