# Cgs vs. SI

1. Jan 7, 2007

### Saketh

I have a simple question.

I understand the quantitative differences between cgs and SI units, but when will I be expected to use one over the other? For example, do physicists prefer one set of units?

Thanks for the help.

2. Jan 7, 2007

### ranger

I really doesnt matter which system you use. The important thing is to be consistent with units. I was taught with the SI system, so I have come to prefer it, but thats not to say that it is better than cgs. Its a matter of preference and being able to move from one system to another. In fact its better that you be able to move between systems. But I guess the times will soon change and one can only speculate that the SI will out do cgs, as SI is widely used.

3. Jan 7, 2007

### Crosson

The short answer is that cgs is on the way out and mks is on the way in.

4. Jan 8, 2007

### rbj

except the real, hard-core physicists keep saying that the Fine-structure constant is:

$$\alpha = \frac{e^2}{\hbar c}$$

which is the cgs way of saying it. the MKS (and general unit system) way to say it is:

$$\alpha = \frac{e^2}{\hbar c (4 \pi \epsilon_0)}$$