# Atkisnon's derivation of \gamma factor.

1. Sep 25, 2012

### MathematicalPhysicist

So I am rereading David Atkinson's QFT book:

And I am puzzled by what is written in pages 5-6 section 1.3 Special Theory of Relativity.

He writes down the transformation between two inertial frames, one moving at speed v compared to the other.

$$x'=\gamma (x-vt) \ y'=y \ z'=z$$

Now he writes on page 6:
My problem is with the last conclusion, why can't we have \gamma to be any even function of v, like v^4 and so forth?

2. Sep 25, 2012

### qbert

any even function of v is a function of v^2.

v^4 = (v^2)^2

3. Sep 25, 2012

### MathematicalPhysicist

Feel so stupid now... :-D

Thanks.

4. Sep 25, 2012

### qbert

don't feel bad. everybody misses stuff like that at times.

in fact you could come back and ask. really? every even function
of v is a function of v^2? those are two different things in principle,
even functions f(v) = f(-v) and f(v) = h(v^2) for some h.

it's not that hard to prove either.