# Current value of the scale factor(R₀)?

1. Dec 20, 2011

### EhsanZ

What is the current value of the scale factor(R₀)?

a= R(t)/R₀

Give me the number.

2. Dec 20, 2011

### Simon Bridge

R0 is the value of R(t) at t=0.

3. Dec 20, 2011

### e.bar.goum

Since a = R(t)/R0, and we normalise to the current epoch, right now, R(t) = R0

4. Dec 20, 2011

### Simon Bridge

5. Dec 20, 2011

### e.bar.goum

Sorry, is that directed at me?

6. Dec 20, 2011

### Simon Bridge

No - I don't slap anyone elses head unless there is some sort of contractual obligation.
See post #2 ... mumble mumble I suppose had I shut up people would think I was being clever?

7. Dec 21, 2011

### EhsanZ

Number?????????

8. Dec 21, 2011

### e.bar.goum

It's a scaling factor, there isn't one. Maybe if you be more specific with your problem, we can help you. You can arbitrarily change it depending on your cosmology.

9. Dec 21, 2011

### George Jones

Staff Emeritus
If the universe is not (spatially) flat, then

$$R_0 = \frac{c}{H_0} \sqrt{\frac{k}{\Omega_{m,0} + \Omega_{r,0} + \Omega_{\Lambda,0} - 1}}.$$
If the universe is (spatially) flat, then $R_0$ is arbitrary.