twistor59 wrote:Yes, events in this contexts are always instantaneous point events. It was meant to be a very short lunch!
ah, OK.
twistor59 wrote:Sending the light signal to the event isn't meant to be thought of as "oh, there's an event, let me send a light signal to it", rather here's an instant of time at one point in space, heres another instant at another point in space. Can I connect the instants with a light signal (or slower)?
But given that light travels at a finite speed, that would mean that any event which we can connect with a light signal wouldn't actually be simultaneous with the event of sending the light signal, it would be in the future of the sending the light signal event; meaning that we could never determine any event that happens in our "now". Perhaps you are simply referring to the Einstein synchronisation method, but the point about connecting instants of time with a light signal doesn't seem to be the same; that is, two instants of time which can be connected by a light signal are, necessarily, not simultaneous; due to the finite speed of light.
twistor59 wrote:But "now" only has meaning with respect to a given reference frame. To define "now" you have to do something like what I was suggesting in setting a bunch of synchronized clocks up. If you do that, you can talk about now. You cannot ask "what's happening now on the planet Zog?" unless you do this. Of course for events close to us, and where things are moving slowly compared to SOL, then you can talk about now to a very good approximation.
But we don't necessarily need to determine the contents of our now, or to define what is in our now, to understand that there must be simultaneous events happening elsewhere in the universe, which form part of our present, and other events which preceded those, which form our past, and events which have not yet happened, which form our future - all of this is within our own reference frame, of course; but we could reasonably say that all events fit into one of those three categories - "what we consider to be the past", "what we consider to be the present", or "what we consider to be the future" - could we not?
twistor59 wrote:mangaroosh wrote:Relativity of SimultaneityBut leaving the block universe aside, can we deduce what it means for us in particular? Some people seem to believe that RoS implies that events which we consider to be the present, as outlined above, could be what another observer considers the future; and events that another observer considers to be the present, could be what we consider to be our past, or indeed, our future.
Would you say that that is a fair deduction, on their behalf?
Re highlighted: Absolutely, these considerations define the causal structure of the universe.
Cool. The remaining part forms part of the other point we are discussing, I think.
Do not mistake understanding for realization, and do not mistake realization for liberation
- Tibetan Buddhist Saying