In what shape is the Universe today

1
In what shape is the Universe today? Dr. Byron
Philhour, City College of San Francisco
Two colliding galaxies, dubbed The Mice.
Photo taken by the Hubble Space Telescope (HST)
2
Two foolish explorers, starting in equatorial
Africa, begin walking north from separate
locations. They believe if they continue to walk
north, they will find the edge of the flat Earth.
(This map of the Earth shows population density,
if youre curious.)
3
Instead of finding the edge of the Earth, they
meet at the north pole! Their sadness that they
could not find the edge of the Earth is soon
eclipsed by their joy in having discovered a new
force! They believe some new force pulled them
together as they walked north.
4
Physicist and professional wrestler Randy Macho
Man Savage is called in to explain the truth to
our naïve explorers. They met not because of any
new force, but because the Earth is round.
They mistook a geometrical effect for a physical
effect.
5
Now, two foolish astronauts, starting from Earth,
head towards the asteroid Ida (and its moon,
Dactyl) in their rocket ships. They wish to fly
near the asteroid and take photographs, then zoom
away.
6
Unfortunately for these astronauts, they
miscalculated their orbits and collided on the
far side of the asteroid. What caused these
astronauts to veer from their straight-line paths
and collide on the opposite side of the Ida?
7
Physicist Albert Einstein was called in to
explain the truth to our naïve astronauts. These
astronauts met not because of any new force,
but because space-time is curved. This is the
substance of Einsteins General Theory of
Relativity. We are, all of us, confusing a
geometrical effect with a physical effect.
Matter causes space-time to bend.
8
A cluster of galaxies which shows multiple images
of a single blue galaxy due to the curvature of
space-time, as predicted by Einstein. Photo by
HST.
9
The galaxy cluster Abell 2218 displays numerous
arc-images of background galaxies due to
gravitational lensing by the cluster. Photo by
HST.
10
Sure, says Randy Macho Man Savage, space-time
can be curved around massive objects like these
galaxies photographed by HST. But what about the
regions of space between all the galaxies. Is
there any curvature to that? Or do we all live
in a flat universe in the same way we once
lived on a flat Earth?
11
The experiment used to measure the large-scale
curvature of the Universe was named Boomerang.
It flew for two weeks, suspended by a
helium-filled balloon at an altitude of over
100,000 feet above the Antarctic continent.
Boomerang made a map of the surface of the
actual explosion of the Big Bang, shown here. The
hot features are galaxy clusters still forming
out of the primordial plasma. This hot radiation
is known as Cosmic Microwave Background radiation
and represents the farthest possible visible
thing.
12
By comparing the features of the real map (above)
of the Big Bang with the features expected in
model Universes (below) with different overall
curvatures, we were able to determine our own
large-scale curvature. The naïve explorers, in a
way, were ultimately right! Now, about that
journey to the edge of the universe
13
Wayne Hu has written an excellent Beginners
Guide to the CMB. Search Google with Wayne Hu
and CMB. Check out the Astronomy Picture of the
Day for all the amazing photos you could ever
want. Read Seeing in the Dark, a new book about
amateur astronomy by local astronomer and
journalist Timothy Ferris. For more
information/q1uestions, e-mail me at
bphilhou_at_ccsf.edu