|Is the universe endless? And if it isn't how big
is it and is it just a big wall or like a planet?
|Question Date: 2016-08-31|
The universe is more or less "homogeneous"
and "isotropic", which means that it is more
like a "sphere", but it is a three dimensional
I do not think we know for sure the size of the
universe yet, because we can only probe a small
part of it. Whether the universe is finite or
infinite, depending on the "curvature" of the
universe. Imagine we look at a globe, whose
surface is a two dimensional sphere. The globe has
a finite surface area, because it has a positive
curvature. If we reduce the curvature of the
globe, its size gets bigger and bigger. And if the
curvature is zero, the globe becomes infinite,
because effectively the globe becomes a flat two
dimensional plane without boundaries. The universe
could be thought of as a three dimensional sphere.
We can estimate the size of the universe (if it is
indeed finite), by measuring its curvature. This
can be done even though we cannot see the entire
universe. So far the understanding is that, the
curvature of the universe is nearly zero, which
means that the universe may as well be
infinite, or at least much bigger than what we can
No one knows!
Here's what we do know. All of the galaxies
we can see are moving away from us and the farther
away they are the faster they're moving. Not
only are they moving away from us they're actually
accelerating (which means they're moving away from
us faster and faster over time).
Now, light can only travel so fast and that
means that if a galaxy is accelerating enough then
we can't see it because the light could never
reach us! Based on what we know, it seems that
any galaxies more than 93 billion light-years away
from us would be impossible to see (
read here ) and in fact the most distant
object we've seen is about 13 billion light-years
read here ). (A light year is the
distance that light can travel in an entire year
which turns out to be about 6 trillion miles.)
So what's beyond 93 billion light-years?
Maybe there are more galaxies just like our own,
or maybe there's something very different. Maybe
it goes on and on forever or maybe the universe
comes back on itself like a giant circle. Maybe
someday we'll know for sure, or maybe it will
remain a mystery forever.
There is no known edge of the universe. We can
see for 14 billion light years, and the reason for
that limit is because the universe is only 14
billion years old, and so light has had only 14
billion years to travel. The real universe is
probably much bigger than this, and may indeed be
infinite. We have no way to know this for
When people talk about the size of the
universe, they usually mean the size of the
observable universe. The observable
universe is made up of all the space that we could
ever possibly hope to see. The observable
universe does have an end, that is set by the
speed of light. Since nothing can move faster
than the speed of light, no information can
possibly reach us from farther away than light
could reach. This also gives us the funny
situation where the observable universe is
constantly getting bigger, since light has more
time to travel farther. Right now, the distance
from us to the edge of the observable universe is
about 46 billion light-years.
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