Hi Borg255,
I hope you won't mind me settling for a more "classical" explanation using the special theory of relativity.
The answer you read is correct. If one spaceship says the explosion occured at 1:05, then they are right. If the other spaceship reports the explosion at 2:02, they are also right. As a matter of fact, if you would be on a planet 4 lighthours away, you would say that the explosion occured at 16:01. You are also right.
Imagine we have two observers that are 1km apart, standing still, with perfectly synchronized timers and they see something happening. Before you can witness an event, the light that "displays" the event must reach your eyes. Since light travels at a finite speed (300.000 km/s) it takes a a short time before this happens. This has one important consequence: events happen at different times for different observers (simply because the light has to travel further, and needs this tiny bit more time to reach the second observer). On your clock you would see that this event occured at 12h01 and 0,000000 seconds. The other observer, 1km. further away from the event, would say it happened at 12h01 and 0,000003 seconds. In this scenario you are both right, since you both saw it happen at the time you recorded (note: in the classical way of thinking, seeing = truth ; this is no longer true in quantummechanics, but that's another ballgame).
The theory of special relativity explains how you can resolve the apparent paradox of something happening at two different times: if you want to describe an event, you do not only have to specify the location the event happened, but also the time it happened
for an observer standing at the same location as the event.. As you could see in the previous example, the times did not match because the observers were standing at different positions. Therefor it is important to know the time something happens at the location it is actually happening.
Once you know the time something happens at the location it is happening, it is easy to calculate what time (non-moving) observers at different positions will see the event: the light travels at 300.000 km/s, so if you are 900.000 km away, you will see the event 3 seconds later than an observer standing at the location of the event (hence the name of the theory: the occuring of events is relative, dependant of the observer and not absolute).
Things get a bit more complicated if you also take account for moving observers (like the spaceships in your example). I won't go into much detail here, but if you are going pretty fast (half the speed of light for example), the time you measure an event changes aswel (because the light has to catch up with you for example).
If we apply all this to your example, you would get this:
- For an observer standing on the moon - and what an unfortunate position he took - the moon explodes at 12:01.
- The spaceship moving to the earth sees the explosion at 12:02. The light that displays the moon (and our unfortunate observer) exploding needs some time to reach the spaceship.
- The other spaceship, moving away from earth at a high speed, sees the explosion at 1:05 because the light has to catch up with that spaceship.
You cannot say that anybody is right or wrong (it's all relative). Hence the explosion could happen at any time you want it to happen (if you just get further and further away, the explosion will happen later and later on your synchronized watches). What you
can say for certain is that the explosion happened at 12:01 on the moon (specifiying both the time
and the location, or as it is commonly refered to in theories of relativity: the point (t,x) in spacetime).
So to summarize: there is an important connection between the time you think something happens and the speed of light. Saying that "light = time" is perhaps a bit too drastic.
I hope this more or less clarifies some things; if you really want to go into more detail, I highly recommend reading a book on special relativity (eg. Taylor and Wheeler, "
Spacetime physics". It doesn't use a lot of formulas and is quite intuitive. If you want to go into the serious math stuff behind all this, you'd better check the "advanced" literature).
Bye!
Crisp
