The Surface of Spacetime.

[geordief]

I feel that this is a fairly common expression but what does it actually mean?

 

If I write the phrase "The surface of spacetime" what does it describe?

 

As far as I have been able to understand ,spacetime is a mathematical construct and consequently am I right to think that "the surface of spacetime" is also a mathematical construct and not a physical object as such?

 

Is it a region where things happen?

 

Is the event horizon of a BH such a region? Are there other examples?

 

I think I have been told that you can make a surface mathematically in spacetime by holding one of the variables constant. Would this be right?

Edited February 10, 2016 by geordief

[swansont]

I feel that this is a fairly common expression but what does it actually mean?

 

If I write the phrase "The surface of spacetime" what does it describe?

 

It would depend on how you defined it.

[geordief]

It would depend on how you defined it.

Do you mean me personally or "you" in the sense of "one" ?

 

I am not qualified to define it myself as I am struggling to understand the concept at the outset (I am reading about intrinsic curvature at the moment to perhaps give you an idea of where I am in this regard)

 

If you mean in the sense of "one" ,does that imply the phrase can be used to mean different things ,perhaps depending on the context?

[Strange]

Spacetime is described as four dimensional manifold; I suppose you can think of a manifold as a surface (a hyper-surface, perhaps).

[swansont]

Do you mean me personally or "you" in the sense of "one" ?

 

I am not qualified to define it myself as I am struggling to understand the concept at the outset (I am reading about intrinsic curvature at the moment to perhaps give you an idea of where I am in this regard)

 

If you mean in the sense of "one" ,does that imply the phrase can be used to mean different things ,perhaps depending on the context?

If you don't know what it means, if you wrote it it wouldn't mean much.

[ajb]

If I write the phrase "The surface of spacetime" what does it describe?

As it is written it is ambiguous. By itself there is no notion of a surface of a space-time.

 

One could mean a Cauchy surface, but then one would just say 'Cauchy surface'.

 

I expect the term is just pop-sci based on thinking of spaces as embedded objects in a higher dimensional space. Think about the surface of a balloon or ball. This only makes sense when one represents such thing as being a substructure of R^3. In its own right the surface of a sphere makes little sense.