Is the universe really flat? The universe has been suggested to be flat by the WMAP satellite data. We've got 5 years worth of readings under out belt. But the jury is still out because of disagreement. If the universe is curved, it is curved so slightly that we cannot tell. A very rough equivalent is that the earth appears flat to the individual walking across the Salt Flats in Utah. The Planck Satellite launches in early 2009, and data from a successful launch may settle the matter to the satisfaction of the majority of investigators. A link can be found below. Why is our universe flat? Scientists are still debating the size and shape of the universe. What we can see is spherical, but other evidence might suggest a wide and flat universe. Though still very thick, the universe might be about the dimensions of a piece of paper. Alternatively, it might be infinite. Be careful when seeing pictures having to do with string theory, multiple universes, etc. They show pictures of flat universes to make the theories easier to understand, since we can't picture more than 3 or 4 dimensions. A picture like this
----------------------------------- <-- Universe One
----------------------------------- <-- Universe Two
doesn't mean that they are flat, it just means that they are 3-d universes (like ours) separated by another dimension. _______________________ When scientists say that the universe is flat, they aren't talking about ordinary 3D spacial relationships as we would intuitively expect. The nature and 'shape' of space is a very complex matter. Think about the surface of the globe. There is only so much area on the globe, and no more. But if you could travel freely in any direction for as long as you wanted, you would never run into a barrier you couldn't crnoss, assuming you can make it over every mountain. This means that the surface of the earth is finite (there is a limit to the area) and unbounded (nothing prevents you from moving freely in any direction even though the area is finite). Models and theories of space have more to do with complex mathematics than with space as we experience it on a moment to moment basis. Theorists consider that space itself might be similar to a globe in that there might be a fixed amount of space, even though you could travel for ever in a straight line and never come to a barrier you can't pass. In other words, some have considered that space may be finite and unbounded, like the globe above. This would mean that some fascinating curves and convolutions might exist in the very make-up of space itself. These features couldn't be observed very well by any individuals, but they may be seen indirectly through relativistic affects and observations. The current understanding is that space is 'flat', meaning that it is not finite and unbounded. It appears that our 'flat' space is expanding indefinitely far in every direction, forever. So counter-intuitively, 'flat' really means 'fat'.
The Universe is not flat, the Total Energy is W = -mGM/r + cP. The Curvature of the Energy at the Boundary is -XX*W = -(d2/dr2 + DEL2)[-mGM/r + cP].
The radiant energy (v=c) maybe flat but the matter energy mGM/r is not flat.
In general the Universe is not flat, it is finite and closed.