When
first presented with the remarkable fact that all galaxies are
moving away from us, and those that are twice as far away are moving
twice as fast, those that are three times away three times as fast,
etc., this seems obvious what it implies we are the center of the
universe! The truth is - this is not the case. To see how our
universe is expanding, you need to look at it from the outside.
In
his book A Universe from Nothing, Lawrence M. Krauss is using
a clever graphic approach. [Note: overall, I don’t like the book,
but more about that in another weekly, probably.] While it is hard
to stand outside a three-dimensional universe, figuratively
speaking, it is easy to stand outside a two-dimensi- onal one. On
the picture on the right, one such expanding universe is drawn at
two times, t2 > t1, the galaxies are
farther apart at t2. Now imagine that you are at the
galaxy which is colored light yellow at time t2. To see
how the expansion of the universe looks from your point of view,
simply superimpose t2 image (right) on the t1
image (left), placing your galaxy on the top of itself, as shown
below. And here it
is: from your position, all other galaxies are moving away, and
those that are twice as far have moved twice the distance in the
same time period, those that are three times as far have moved three
times the distance, etc.
It
doesn’t matter what galaxy you are in. So, depend- ing upon your
perspective, either every place is the center of the universe, or no
place is.