[g__day (Matthew)]

Imagine you live somewhere in a really tall high rise and may move about freely, but every second every part of the high rise is growing - all the walls ceiling and floor are say growing 1mm further apart every hour. So if your 100 floors up the ground is getting 100mm apart every hour. Over time the rate is increasing - in a years time say the rate is 1.2mm per hour and so on (units not at all exact).

Imagine that highrise is your local galaxy, and you live in a city where all high rises are expand, but even quicker than the buildings getting bigger - the buildings themselves are moving in some direction but the ground between each building is itself expanding too (possibly faster than the buildings grow)!

This is what we interpret from the data. The fabric of spacetime itself is expanding (and the upper rate of the expansion of spacetime we believe is not bound by relativity (lightspeed) - unlike all the matter and energy moving in any local spacetime) This means that two very distant points in the Universe may even be stationary in their local spacetime but rapidly receding from each other because of expansion of the spacetime in between each other. This rate of recession can be a very high proportion (e.g. 70%) of the speed of light. If nothing slows this rate down then sometime in the far future the farthest seperated points of the universe could possibly be recessing at each other at a rate of multiples of lightspeed - without contradicting any of the laws of relativity that governs how enery and matter move through relativistic (normal energy density, normal gravitational) space time. So to my understanding the only parts of the Universe where spacetime is not relativistic at a macro scale is 1) inside the event horizon of a black hole or within a supernova where the energy threshold crosses the boundary so that the four fundamental forces might re-combine (which I think would require a collapse of a Sun several times larger than our Solar system / or possibly very briefly during the direct collision of two Galactic centre black holes. By this I mean if massive black hole in the Milkyway Galaxy had an almost perfect head on collision with the central black hole in the centre of Andromeda Galaxy - you might, just might for a small portion of time create an energy release of sufficient magnitude ( so energy densities greater than 10 ^ 19 Joules per m^3) - so temperatures of millions of trillions of Kelvin - theoretically capable of warping local spacetime into a non relativistic region of the Universe until it expands and cools!

Hope that mind boggling explanation and background information helps!

PS

Nice picture attached - size of known Universe = 93 billion light years, yet age of Universe = 13.8 Billion light years. Speed of light means the extra distance is due to cumulative expansion of spacetime, not recession of things in it!