this picture of what the universe looks like reminds me of what steven hawking wrote in his book "brief history of time". he suggested taking a cardboard box and remove one side & replace it with a black garbage bag. pull the bag taught & tape it down so that you have a cardboard box with one side made of plastic sheet which represents space-time.
now take some heavy marbles (train wheel bearings work great) and place them on the plastic side. now, take a small marbel, place it on one end and push it so that it has just enough momentum to reach the other side. notice how it swerves towards the heavy mass train wheel bearings? this is mass bending space time.
in this example the universe is not flat, but looks more like a horse saddle because gravity is pulling "it" due to large mass objects. personally, i do not think the universe IS like this, it only LOOKS like this because that is how we perseve things. what we do not perceive is time. we can not observe time, so we don't see its effects. we see quantized versions of time, but not TIME itself. there are 4 dimensions: X, Y, Z, time. the last, time, is unique in that is joining all 3 axis, XYZ, at any & all points simultaneously all the "time". now that is a fascinating concept! too bad we can not observe time itself because i'm sure it would change our perception of the universe drastically if we could.
now here is the part steven hawking didn't say (nor did einstein to my knowledge). mass is not the ONLY thing that warps space-time. strong electromagnetic fields can do this too! what is more, we can perform these experiments on the bench, we don't need planet size mass to study spacetime warping. neat.
the space in our observable universe is expanding, as proven by the "Red Shift" method discussed previously. what is more, it is accelerating. strange, but after all that time eignstein was right, there IS a "cosmological constant" out there, else we would not have acceleration. as you know acceleration can only occur (newtonian motion) when a 3rd party acts upon it, so figure that one out!
also, our local observable universe is expanding, but this doesn't mean that it isn't contracting somewhere else in the universe. it is after all a very big place...
Mr.Cool