How Far Are the Cosmic Ray and Photon at t=0s According to the Observer?

[roman15]

Homework Statement

A cosmic ray of gamma=10^10 is chased across the Milky Way by a photon. The cosmic ray passes an Observer at one edge of the galaxy and t=0s then the photon passes at t2=1.33x10^-8. These times are recorded by the Observer
How far away are the cosmic ray and photon at t=0s according to the observer?

Homework Equations

The Attempt at a Solution

Im not really seeing how to apply special relativity to this, wouldn't the distance between them just be ct2, because its asking according to the observer and from t=0 to t2, the distance traveled by the photon in that time would be the distance between them right?

 

[Doc Al]

Im not really seeing how to apply special relativity to this, wouldn't the distance between them just be ct2, because its asking according to the observer and from t=0 to t2, the distance traveled by the photon in that time would be the distance between them right?

Right. Relativity is not needed to answer this question. (I suspect that there are followup questions that might require special relativity.)

 

[roman15]

Right. Relativity is not needed to answer this question. (I suspect that there are followup questions that might require special relativity.)

haha you there are, the next couple of parts of the question deal with the galaxy moving relative to the cosmic ray