People playing catch

1. Aug 27, 2007

ehrenfest

I am supposed to draw a space-time diagram representing "a game of catch (or a conversation) between two people at rest, 10 ft apart. How is it possible for them to communicate, given that their interval is spacelike?"

Firstly, how is this realistic when let's say that the ball takes 2 seconds to go between them. Then how in the world would -c*3+10*0.3084 be nonnegative>

2. Aug 27, 2007

Gokul43201

Staff Emeritus
Where does the original question end?

Henceforth, please use the template. It eliminates such confusion.

If the events are something like throwing & catching (no matter how far apart), the interval between the events is clearly timelike.

3. Aug 27, 2007

ehrenfest

I was using PF Nexus which does not provide the template, but I will switch to PF Prime.

The original question is verbatim:

"Draw a spacetime diagram representing a game of catch (or a conversation) between two people at rest, 10 ft apart. How is it possible for them to communicate, given that their separation is spacelike?"

Notice that I erroneously used "interval" instead of "seperation" in the thread-opening post.

4. Aug 27, 2007

neutrino

Let's say A , the "thrower," is at (0,0) when he throws the ball. B, the receiver, is at (0,10) in A's frame.(Using (t,x) for events.) Only these events are spacelike and thus unrelated to the interval between throwing and catching.

5. Aug 28, 2007

ehrenfest

OK. I kind of see the point of the question now. When A throws, B at that moment is outside the future of A. However, the resolution is that B at a later time is inside the future of A. This is a really weird question.

6. Aug 28, 2007

Gokul43201

Staff Emeritus
I don't. It appears idiotic to me. I hope there's something non-trivial about it that I'm not seeing.

7. Aug 28, 2007

ehrenfest

LOL. You're probably right.