If I had a piece of string that was about 2mm thick but infinitely long it would have infinite mass.

 

But, if you had two pieces of string like this would yours have twice the mass of mine?

 

If so, how? Because my string still has infinite mass.

 

 

And another thing. How is it possible to see light from the very very early Universe when surely the light that we are observing should have reached our current location in space long before the mass that makes us up did?

This is really more of a mathematical problem than a physical one. The confusion arises because of this ingrained tendency for people to think of infinity as being a number which is somehow greater than all other numbers. This can be a helpful way of thinking about it, but not always.

 

In mathematical analysis, the formal definition of a function f(x) tending to infinity as x does the same is that for any K > 0, there exists a value of x such that f(x) > K. No actual number called 'infinity' is required. We use the notation [math]\lim_{x\to\infty}f(x)=\infty[/math] purely as a notational convenience to indicate a property that pertains purely to finite quantities.

 

I suggest that limits are the best way to think about your pieces of string.

In your final question I think the "light" you are referring to is background radiation in the form of radio waves?

 

My memory fails me often so I forget how this radiation is left over from the Big Bang.

Everything didn't expand from a single point more the universe is infinitively large and the spaces between all places increased. We can't see the light from the early universe anywhere near where we are.

 

Why don't we make a sticky for this and other mindbogglingly common questions?