From the June 2015 issue

I have been trying to get my head around “there is no center to the universe” without success. Can you give a layman’s explanation?

Frank Hanour, Indianapolis
By | Published: June 29, 2015
Fast Sound projects 3-D map
The FastSound project’s 3-D map of the large-scale structure of a region in the universe about 4.7 billion years after the Big Bang. This area covers 2.5 times 3 degrees of the sky, with a radial distance spanning 12-14.5 billion light-years in comoving distance or 8-9.6 billion light-years in light travel distance. The colors of the galaxies indicate their star formation rate, i.e., the total mass of stars produced in a galaxy every year. The gradation in background color represents the number density of galaxies; the underlying mass distribution (which is dominated by invisible so-called “dark matter” that accounts for about 30 percent of the total energy in the universe) would look like this if we could see it. The lower part of the figure shows the relative locations of the FastSound and the Sloan Digital Sky Survey (SDSS) regions, indicating that the FastSound project is mapping a more distant universe than SDSS’s 3-D map of the nearby universe.
Few cosmological concepts are harder to grasp than this. To wrap your mind around it, first accept that the Big Bang was not an explosion in space the way we naturally perceive it. Instead, this event included everything. Space itself expanded rapidly.

In fact, the universe was already infinite, as it is now. Energy and matter was everywhere, so there was no special origin point. No center.

Imagine this by drawing lines on a rubber band and pulling at both ends. The lines move apart, but the rubber band is not stretching from the center.

Astronomers first stumbled onto this incredible fact more than a century ago when early measurements showed other galaxies retreating from Earth. But it’s now clear that there’s nothing special about our position. If you lived in another galaxy, the cosmos would still retreat away in all directions.

Of course, all this expansion raises another question: What is our universe expanding into? Astronomers believe that the observable universe does not expand into vast fields of nothing, but is instead surrounded by yet more matter and energy.

We can’t see this material because it’s beyond the cosmic microwave background (CMB) — the oldest light in the universe. The CMB formed about 380,000 years after the Big Bang, when the cosmic soup of particles bouncing around our universe had cooled enough for hydrogen atoms to form.

It’s this first light that also gives astronomers a born-on date for existence: 13.82 billion years ago.

Eric Betz
Associate Editor