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infinity an a moment of time


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14 hours ago, Earl said:

in an infinite universe a moment in time occurs everywhere, however as everywhere is infinite is that moment not also infinite?

As said previously, relativity means there is no absolute space and time. That still doesn't quite answer the question, which hinges on the words "moment" and "everywhere". In relativity we can still define a moment, and observers anywhere in the universe can potentially recognise it, but they need not agree on when and where it occurs. To that extent the moment is "infinite", though not simultaneous. It is however an odd way to speak of it. Napoleon lost Waterloo on Earth, and the same moment would be recorded by historians of Earth in the Andromeda Galaxy, for whom it is yet to occur. Unless we take a multiverse view, the statement "Napoleon lost Waterloo" is true everywhere, for those who saw it, those who will see it, and those who are seeing it now (with telescopes that can only exist in imagination). But does that make it "infinite"? Just a matter of semantics, I think.

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I think semantics are important here, as understanding exactly what is ment and its implicatins in a space time rellavatistic way is key, and thats what im struggling with.

 

From the replies so far my perseptic of time in space and its repaltionship is the issue and needs refining perhaps?

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2 hours ago, acey said:

In relativity we can still define a moment, and observers anywhere in the universe can potentially recognise it

Relativity is about the relation of events in space and time every event has a specific set of space-time coordinates (4 in all 1 time and 3 space). Special relativity (SR) comes in because observers moving relative to each other, i.e. in different inertial frames, assign different space-time coordinates to a given event. A "moment" on it's own has no meaning in SR it needs to be related to a specific event and observer.

Regards Andrew

 

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3 hours ago, andrew s said:

Relativity is about the relation of events in space and time every event has a specific set of space-time coordinates (4 in all 1 time and 3 space). Special relativity (SR) comes in because observers moving relative to each other, i.e. in different inertial frames, assign different space-time coordinates to a given event. A "moment" on it's own has no meaning in SR it needs to be related to a specific event and observer.

Regards Andrew

 

I used "moment" to refer to what would more usually be called an "event", i.e. a point in spacetime. As you correctly say, the four-vector of an event will have different co-ordinates depending on the particular reference frame. Whether this makes it "infinite" or "everywhere" depends on how one wishes to interpret those words.

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