Question

Not sure if this can be considered suitable for the Mathematics forum; a calculation in Astrophysics :)

Answer 1

The scale factor a(t) describes the expansion of the Universe.
By considering how the redshift of light depends on the scale factor,
calculate how the present-day physical separation of galaxies com-
pares with their separation when light left galaxies we see today at
redshift 1?

Answer 2

What is it youre wanting to calculate?

Answer 3

Maybe it's the z+1 = a_now/a_then....dunno.

Answer 4

I cant tell if youre asking about the doppler effect making the galaxies appear redshifted since they are mostly moving away from us, or what

Answer 5

Yeah, I think possibly I have to derive it? I take comfort in the fact that no one else really understands it either haha

Answer 6

Doesn't say anything about the Doppler effect.... :S assignment question is just written as above :/

Answer 7

Completely guessing here but if

2 = a_now/a_then -> implies doubling....

Answer 8

What do u think, twice as far apart..?

Answer 9

Is this formula

z+1 = a_now/a_then

in your course?

Answer 10

Erm, if wavelengths have doubled (and lambda_now/lambda_then = a_now/a_then) then that implies the universe was half its present size when the light was emitted... Is that what you mean?

And yep, thats the equation :)

Answer 11

Well when did redshift 1 occur?

Answer 12

/=equation - formula**

Answer 13

I don't know when redshift = 1 was/is/will be :S

Answer 14

So z is redshift->

2 = a_now/a_then

would seem to say that the "scale" is twice as big as it was then.

Answer 15

Or it was half what is now, if u prefer...

Answer 16

So the galaxies are twice as far apart now...

Not my specialty this, I got that formula from

http://en.wikipedia.org/wiki/Redshift