Bad Astronomy: Misconceptions and Misuses Revealed, from ...

WHEN THE UNIVERSE THROWS YOU A CURVE 149
There are still other ways. One is to look at incredibly distant
objects and carefully observe their behavior. Using complicated
physics, it’s possible to determine the universe’s geometry. At the
moment, our best measurements show that the universe is flat. If it
curves at all on large scales, it’s very difficult to see.
Now let’s imagine again that you’re an ant, back on the ball.
As a fairly smart ant, you might ask yourself: If my universe is
curved, where is the center? Can I go there and look at it?
The answer is no! Remember, you’re stuck on the surface of
the ball, with no real concept of up or down. The center of the ball
isn’t on the surface, it’s inside, removed into the third dimension,
which you cannot access. You can search all you want, but you’ll
never find the center, because it’s not in the universe as you know it.
The same can be said for own 3-D universe. If it has a center, it
might not be in our universe at all, but in some higher dimension.
As it happens, even this might not be the case. Gauss showed
mathematically that, as bizarre as it sounds, the universe can be
curved without curving into anything. It just exists, and it’s curved,
and that’s that. So it’s not that we are curved into the fourth
dimension, if there is such a thing. The fourth dimension may not
exist at all, and our universe simply may not have a center.
This is the worse humiliation of all. To be removed from the
center of the universe is one thing, and it’s another to have it appear
that we are at the center, only to realize that anywhere in the
universe can make that claim. But then, to be told there isn’t any
center at all is the ultimate insult.
Maybe in a way it’s the perfect equalizer. If we can’t occupy
the center of everything, at least no one else can, either.
PPP
And yet we are still not done.
Einstein was just getting started when he realized that space
was a tangible thing. Time, he found, was a quantity that in many
ways was like space. In fact, space and time were so intertwined
that the term space-time continuum was coined to describe the
union.