# Coordinate and time transformations

• I
• Ahmed1029
The transformations don't say anything about how information is transmitted. They only say that coordinates have to do with where an event happened in spacetime.f

#### Ahmed1029

In describing the Galelian or Lorentz transformations, All books I've read keep talking about clocks and meter sticks, but I don't see how an event happening away from the observer could be instantaneously described by a set of coordinates and a point in time; information conveying the event travels at most at the speed of light and measurement is only going to be detecting its past. In the light of this, what do those transformations really say?

Coordinates have nothing to do with information actually being transmitted. It is an assignment of number labels to events in spacetime.

vanhees71
When you talk about an observer in an inertial reference frame, you can imagine that there is an observer, stationary at every point of his reference frame, who records events. It is really a matter of how events would be recorded at those locations in his reference frame, not how that information would be transmitted to him at a central location.

vanhees71 and topsquark
There is nowhere you can stand where you can see the whole surface of the Earth, yet somehow we manage to assign coordinates to all of it (excluding one point, for the pedantic).

Coordinates are just labels we assign to events. As long as we assign them systematically we can assign them to events we can't see yet. We don't know what happened (if anything) at those events until we see them, but that doesn't matter. It's just the same as drawing a grid and filling in the map as we explore.

vanhees71, Dale, Ahmed1029 and 1 other person
In describing the Galelian or Lorentz transformations, All books I've read keep talking about clocks and meter sticks, but I don't see how an event happening away from the observer could be instantaneously described by a set of coordinates and a point in time; information conveying the event travels at most at the speed of light and measurement is only going to be detecting its past. In the light of this, what do those transformations really say?
When you measure the distance to something at some point you actually have to travel the distance to get there in order to measure it. (Or some other similar method.) You might think of it as the events that are talked about in these problems are times people recorded at certain positions and the data are compared later when the people get together. When the data are compared, only then we can start making statements about if the times for events are simultaneous or not.

Then once the theory is proven we can just use the Mathematics to figure out speeds and distances and such.

-Dan

vanhees71
Thank you guys I got the point!

Dale