The Universe Is Flat

If you haven’t heard this before, I’m sure it sounds crazy to you. It did to me too. But a serious number of rigorous experiments has established this concept and clarified it quite well: The universe really is flat.
Now, as you try to wrap your mind around that, I want you to see a screenshot from Wikipedia’s “Universe” page, showing the universe’s physical characteristics:
And no, that’s not there because someone hacked Wikipedia. It’s for real. puts it this way:

The universe has all sorts of deformations in space-time where it varies from the perfectly flat… But average all those small-scale effects out and look at the big picture. When we examine very old light — say, the cosmic microwave background — that has been traveling the universe for more than 13.8 billion years, we get a true sense of the universe’s shape. And the answer, as far as we can tell, to within an incredibly small margin of uncertainty, is that the universe is flat.

They go on to add “flat as a (big) pancake.”
NASA has weighed in on this too:

Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error.

I haven’t yet found enough details to explain this well. For example, I have no data on precisely how thick the universe is, and I don’t think anyone knows the outline of the flat universe. (Is it a disk? An amorphous blob?) But we do know that’s it’s tens of billions of light years across. (One light year = 5.9 trillion miles = 9.5 trillion kilometers.)

But Wait, There’s More!

As if the shock of a flat universe weren’t enough, there’s another wild and crazy fact that’s come up since most of us left school:

The universe slowed down for a long time, but now it has sped up again.

Yes, I know that sounds just as crazy as a flat universe, but it also seems (by studying the development of galaxies and comparing them to their current positions and speeds) to be quite true.
Here’s a graphic on Wikipedia’s dark energy page (taken from NASA’s website), illustrating what has happened:
As this graphic shows (bottom to top), the universe has been expanding since its beginning, with the expansion slowing down over the first half of the universe’s life. Then, for some reason, the expansion started speeding up again, about 7.5 billion years ago.
Bear in mind that scientists have no evidence as to why this change occurred. They’ve made up the idea of dark energy to explain the new expansion, but that’s only a guess. They have no evidence to back it up. (I’ve seen no solid explanation of where dark energy came from and why it didn’t matter for the first half of the universe’s life.)
Dark matter, which you may also have heard about, is something different. There’s no hard evidence for dark matter either. It’s another guess on the part of the physicists to explain why galaxies act the way they do. (They needed a lot of extra mass to explain the gravitational effects they were seeing, so they postulated matter that can’t be seen: dark matter.)

What Does This Mean?

It means that J.B.S. Haldane was correct when he said,

My own suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose.

Nonetheless, we will figure all of this out. It may take years, decades, or centuries, but humans will, at some point, make sense of it.
For now, enjoy the mystery.

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Paul Rosenberg