Title: Why is time relative? | Physics Forums
Headings: Why is time relative?
Why is time relative?
onestarburns
Answers and Replies
Jimmy Snyder
Farsight
axawire
Rach3
Gelsamel Epsilon
MeJennifer
BoTemp
Rach3
MeJennifer
MeJennifer
Rach3
MeJennifer
Rach3
MeJennifer
RandallB
MeJennifer
MeJennifer
MeJennifer

Content: I meant simultaneity in the usual sense - for two events (t1, x1), (t2, x2), there is no consistent statement of the form "t1 = t2" except in the trivial case in which it holds in only one Lorentz frame (or else x1=x2, also trivial). The point of "does simultaneity 'exist'" seems entirely semantic to me. It is not uniquely defined, and has no usefulness, so in my narrow, pragmatist worldview I'm not concerned. It is obvious that simultaneity exists in the universe because otherwise the universe could not have a causal structure. Last edited: Jul 20, 2006
Jul 20, 2006
#11
JesseM
Science Advisor
8,496
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MeJennifer said: It is obvious that simultaneity exists in the universe because otherwise the universe could not have a causal structure. There is still a single objective truth about whether one event lies in a second event's past light cone, that should be enough to give the universe an objective "causal structure", I don't see why simultaneity (which involves events with a spacelike separation that cannot possible affect one another) is relevant to this. Jul 20, 2006
#12
MeJennifer
1,997
5
JesseM said: There is still a single objective truth about whether one event lies in a second event's past light cone, that should be enough to give the universe an objective "causal structure", I don't see why simultaneity (which involves events with a spacelike separation that cannot possible affect one another) is relevant to this.