[nilkn]

We don’t know that, though. Consider an evolution of a flat coordinate plane given by (x,y) -> (e^t * x, e^t * y). This process can run forever and has the property that all points appear to move away from all other points through time, yet the size of the plane never changes.

It’s better to think of the Big Bang as describing a point in time rather than a point in space.

[thaumasiotes]

> Consider an evolution of a flat coordinate plane given by (x,y) -> (e^t * x, e^t * y). This process can run forever and has the property that all points appear to move away from all other points through time, yet the size of the plane never changes.

What do you mean by that last claim? Any observable region is bigger at later times than it is at earlier times. The reason all points always appear to be moving away from all other points is that that is in fact happening.

What's the significance of claiming that the size of the infinite plane never changes? It's just as true that if you start with the unit interval [0, 1] and let it evolve under the transformation f(x) = tx, the size of the interval will never change -- every interval calculated at any point in time will be in perfect 1:1 correspondence with the original (except at t=0). But this doesn't mean that the measured length of the interval at different times isn't changing; it is.

[mynameishere]

Does anyone know why wolframalpha is plotting this with cute little arrows?

https://www.wolframalpha.com/input?i=plot+%28x%2Cy%29+%3D+%2...

[itishappy]

It's a vector field! It has 2 dimensional inputs and 2 dimensional outputs, so it doesn't fit on your traditional graph.

    f(x,y) = (c * x, c * y)
    f(x,y) = c * (x,y)
    f(P) = c * P

If you give some thought to what `c` is doing to each point of your plane (start with the origin!), I bet that graph might make a bit more sense. :)