Past Present and Future

Main Question or Discussion Point

I have read some books by brain Greene in whch he discusses the concept of fixed moments in time, never changing, He goes on to discuss how time slices will be different depending on observers relative motions in space and that the past present and future definitions of events will differ from observer to observer

My question is if we cannot agree on what is the present, diffferent observers will slice space time differently, then what will be my future may be someone elses past. If so, and i think this may be eternalism, is it correct to say that he past present and future all exsist at once.

If PPF all exsist right "now" then is there a definitive boundary some where/when that defines present and future for some universal reference

If not and eternalism is correct, all past present and future events are in existance then was the universes PP and future created in an instance ?

Related Special and General Relativity News on Phys.org
Fredrik
Staff Emeritus
Gold Member
I have read some books by brain Greene in whch he discusses the concept of fixed moments in time, never changing, He goes on to discuss how time slices will be different depending on observers relative motions in space and that the past present and future definitions of events will differ from observer to observer
He's describing the spacetime of special relativity. A good way to visualize it is to draw two perpendicular coordinate axes on a piece of paper, one in the up direction, labeled "t (years)", and one in the right direction, labeled "x (light-years)". (We're ignoring all but one spatial dimension, because we can't draw more than two perpendicular lines on a piece of paper). A horizontal line is a set of events that you consider simultaneous (if this diagram represents your point of view). A line with a different slope is a set of events that someone else considers simultaneous (if the angle it makes with the x axis is less than 45 degrees).

My question is if we cannot agree on what is the present, diffferent observers will slice space time differently, then what will be my future may be someone elses past. If so, and i think this may be eternalism, is it correct to say that he past present and future all exsist at once.

If PPF all exsist right "now" then is there a definitive boundary some where/when that defines present and future for some universal reference
I'm not sure what you mean by "universal reference". There's no preferred coordinate system or "point of view" if that's what you mean. I don't know what boundary you're talking about. Any horizontal line is a boundary between your past and future.

Phrases like "at once" and "right now" are references to a simultaneity line, so your question is a bit like asking if the entire piece of paper exists at one of the lines you drew.

What you should be thinking here is that the paper is what the theory uses to represent the real-world concepts of space and time. You can say that the paper (yes, the actual paper) exists "at once" if you want.

If not and eternalism is correct, all past present and future events are in existance then was the universes PP and future created in an instance ?
This question assumes that there's some kind of "real" time that has nothing to do with spacetime (or Bill Maher), and there's no evidence of that.