What is the oldest photo of the universe?
The oldest pictures we have today
are of our universe's teen years,
except for one photo, one baby picture
of the universe, the cosmic microwave background.
Today, the universe is more than 13.7 billion years old.
But the cosmic microwave background
is a map of the universe when it was just 378,000 years old.
The image is similar to a temperature map of the United
States.
But instead of showing a wide range of temperatures,
the cosmic microwave background shows
tiny almost unperceivable temperature differences
in the newborn universe.
Scientists Arno Penzias and Robert Wilson unexpectedly
discovered the cosmic microwave background in the 1960s
while using a large microwave detector
to study the Milky Way.
They were surprised to find a static or fuzz coming
from all directions of the sky and that
all of the static radiated with the same temperature, 2.73
Kelvin above absolute zero.
The signal was so unexpected that the two scientists
initially thought the noise was coming
from the antenna or some other earthly source.
But one by one, they methodically
ruled out all other possibilities,
even cleaning out pigeon droppings
from inside the antenna to make sure
that wasn't interfering, and found that the signal was real.
It was coming from the cosmos.
You may have even seen some of the static yourself.
About 2% of the fuzz on an old television set
comes from the cosmic microwave background.
In the 1980s, a NASA satellite called
COBE mapped the cosmic microwave background
and revealed that it was not exactly
the same temperature in every direction.
COBE uncovered islands of relative warmth and cold.
But the temperature differences COBE observed
were incredibly small.
The temperature variations from place to place
were less than one ten-thousandth of a degree.
If you wanted to change the temperature in your living room
by that amount, you would need to run your heater for less
than a hundredth of a second.
Later, NASA's WMAP and the European Space Agency's Planck
spacecraft gave us an even better, more detailed map
of the cosmic microwave background.
Amazingly, these little temperature fluctuations
grew into all the structures in the universe, galaxies, stars,
and planets.
Over time, the slightly hotter areas
pulled in more and more material,
and the slightly colder areas grew colder and emptier.
Today, hot, dense stars in galaxies
are surrounded by cold, mostly empty space.
Maps of the cosmic microwave background
tell us about the early history of the universe
when it was hotter and denser.