# Homework Help: Lorentz Transformation Question

1. Sep 28, 2016

### Kunhee

1. The problem statement, all variables and given/known data
For an event occurring at (x,t),
consider the quantity I = x^2 - (ct)^2
Find a simple expression for this in the S' frame: I' = x'^2 - (ct')^2
How are I and I' related, and why is this noteworthy?

3. The attempt at a solution
So the question is under "Lorentz Transformation" and I must
simplify I' = x'^2 - (ct')^2.

I am not sure if this is the way to go about it, but should I find
the equation in the form of "c =" ?

2. Sep 28, 2016

### Lucas SV

You should write x' and t' in terms of x and t by using Lorentz transformations (specifically, what is called a boost in the $x$ direction).

3. Sep 29, 2016

### Kunhee

When I do, do I find the quantities equal?

4. Sep 29, 2016

### Kunhee

I plugged into
I' = x'^2 - (ct')^2

x' = y(x - ct)
t' = y(t - cx/c^2)
* y is Lorentz Factor

and I get that I' = 0

5. Sep 29, 2016

### Lucas SV

Yes, you should find that they are equal, I=I'. You got 0 because you wrote c instead of v in the Lorentz transformations. They are:

x' = y(x - vt)
t' = y(t - vx/c^2).

6. Sep 29, 2016

### Kunhee

I see, thank you!