Problems we don't need

I'd want to see SI used everywhere. The currently accepted radius of the observable universe is about 130Ym. Hubble's constant is about 2.3aHz.

Stamp out weird units! We need a different name for the kg. We shouldn't have basic units with baked-in multiplier prefixes.

Jeroen Belleman

I deal with kW and kWh every week and once in a while I'll forget the "h" part. It's an easy mistake to make.

It's funny that we use a compound term for energy and a specific term for rate of energy with EVs. It makes it a bit harder to explain to people who are not familiar with the terms. It is natural to compare them to distance and speed where the compound unit is the rate term, MPH or kPH.

Isn't 'g' the basic unit???

<snip>

Yes, but it's the MKS system. Would have been neater if the gram was a thousand times bigger.

As for the Are, that should have been 1 m^2.

In SI, the kg is the base unit. It was recently redefined to be based on some fundamental constants of nature, rather than on the mass of a lump of metal in a vault near Paris.

The mks system is another thing that should be abandoned. For some weird reason, it's still popular with cosmologists.

Jeroen Belleman

In SI, the kg is the base unit. It was recently redefined to be based on some fundamental constants of nature, rather than on the mass of a lump of metal in a vault near Paris.

The mks system is another thing that should be abandoned. For some weird reason, it's still popular with cosmologists.

Jeroen Belleman

Sorry, I meant _cgs_ should be abandoned.

Jeroen Belleman

You may mix up mks and cgs systems. The old physycist system is cgs. MKS evolved to SI.

Of course, it's far more rational to say that the mass of the Sun is

2e30 kg rather than 2e33 g. Anyway astronomers mostly use parsecs and solar masses and stuff. ;)

Cheers

Phil Hobbs

(Who really likes Gaussian units, which are rationalized cgs ESU. They make Maxwell's equations much simpler, which saves blunders, and it's trivially easy to convert to SI when you're done.)

I have a physics text somewhere with cgs in it. The professor told us that Metric was replacing it though, so he would not be teaching those units.

When everything is 10^N with N already very big +/-2 here and there doesn't make that much difference. I recall one of my textbooks way back was still in cgs but I though that had largely died out by now. I'm pretty sure the modern university astronomy teaching texts are SI (as were some of the old ones). Or rather that they are in the UK.

However, the odd exceptionally good text book from the 1980's and in cgs probably still survives for precisely that reason.

I thought it largely had been (even in cosmology).

About a half century ago, I hated Kittel's book on solid state physics due to the use of the cgs system with the annoying electrical units with the mess of 2 * pi and 4 * pi there and here.

I sure hope that the units are history and stay there.

Well, I did even misspell FFS, FFS!

John ;-#)#

Couldn't disagree more. I do hand calculations in electromagnetics using Gaussian (rationalized cgs ESU) units.

It gets rid of all the mu-noughts, epsilon-noughts, and so on. It still has the occasional four-pi, but that's in SI as well, concealed in the definition of mu-nought.

In Gaussian units, magnetic field and magnetic induction have the same units (some folks quote H in oersted, but the conversion is unitless), relative and absolute mu and epsilon are the same, and there are lots fewer opportunities for blunders.

Converting to circuit units at the end is trivially easy.

Cheers

Phil Hobbs