What does it mean when we say the universe is flat?

We say that the universe is flat, and this means that parallel lines will always remain parallel. If we could measure its curvature, we could know that we’re in a finite universe, and get a sense of what its actual true size is, out beyond the observable universe we can measure.

Does the universe have an up and down?

In space, there is no “up” or “down.” That can mess with the human brain and affect the way people move and think in space. An investigation on the International Space Station seeks to understand how the brain changes in space and ways to deal with those changes.

Does the universe have an up?

Astronomers love to remind us that there’s no up or down in space. Look out into the depths of the universe and you’ll see galaxies floating edge-on, face-on and at every angle in between. Look at planets circling stars within the Milky Way, and their orbits might be oriented in any direction at all.

Does the universe have a top?

Our 4D universe does indeed have a top and bottom. The bottom (T=0) was the Big Bang. Space and time curved in, not to a point but to a parabola. There is nothing before T=0 because when you reach 0, whichever way you go, time will increase.

What is the evidence that the universe is flat?

So when we say “WMAP provides strong evidence that the universe is flat”, we really mean “WMAP provides strong evidence that the observable universe is flat”. However, according to inflationary theory, even if the universe has some curvature, the observable universe should be flat at the level at which we’re capable of measuring it.

What is the difference between universe and observable universe?

But many people use “universe” as shorthand for “observable universe”, which can create some confusion. So when we say “WMAP provides strong evidence that the universe is flat”, we really mean “WMAP provides strong evidence that the observable universe is flat”.

Is space flat or flat?

Moreover, when they talk about the flatness of space cosmologists are referring to the large-scale appearance of the universe. When you “zoom in” and look at something of less-than-cosmic scale, such as the solar system, space—not just spacetime—is definitely not flat.

What is the curvature of universe?

So it is observed that the Universe is almost “flat” which means “zero curvature”. But this is only the spatial curvature, and in fact, the Universe has positive space-time curvature which is why the Big Bang is expanding. The easiest way to understand these coordinates is that they describe fixed “slices” of time.