Starts With A Bang

How big was the Universe at the moment of its creation? (Synopsis)

An ultra-deep view of galaxies many billions of light years away in the distant Universe. Image credit: NASA, ESA, R. Windhorst, S. Cohen, and M. Mechtley (ASU), R. O’Connell (UVa), P. McCarthy (Carnegie Obs), N. Hathi (UC Riverside), R. Ryan (UC Davis), & H. Yan (tOSU).

“The creation of something new is not accomplished by the intellect but by the play instinct acting from inner necessity. The creative mind plays with the objects it loves.” -Carl Jung

13.8 billion years ago, the Universe as we know it came into existence. Today, the part we can observe is 46 billion light years in radius, having grown tremendously thanks to the expansion of the Universe. But if we extrapolate that backwards, we find that the Universe couldn’t have been infinitely small at the moment of its birth, but rather was a finite size at all finite times.

The size of the Universe (y-axis) versus the age of the Universe (x-axis) on logarithmic scales. Some size and time milestones are marked, as appropriate. Image credit: E. Siegel.

We know an awful lot about the moment the Universe can first be described by the hot Big Bang thanks to the last 50 years of modern cosmology. People used to think the Universe could be contained in a volume no bigger than a marble, or that the part accessible to us could have been the size of the Solar System at birth. No more!

Hospital Corpsmen 3rd Class Tarren C. Windham kicks a soccer ball with an Iraqi child. That soccer ball is approximately the size of the Universe we see today at the moment of its birth. Image credit: U.S. Marine Corps photo by Gunnery Sgt. Chago Zapata.

Between the size of a soccer ball and a skyscraper-filled city block is the only range left, and the more we learn about inflation, the smaller that range will get. Find out the science behind it today!