Starts With A Bang

5 questions you were too embarrassed to ask about the expanding Universe (Synopsis)

An ultra-distant view of the Universe shows galaxies moving away from us at extreme speeds. At those distances, galaxies appear more numerous, smaller, less evolved, and to recede at great redshifts compared to the ones nearby. Image credit: NASA, ESA, R. Windhorst and H. Yan.

“The more clearly we can focus our attention on the wonders and realities of the universe about us, the less taste we shall have for destruction.” -Rachel Carson

The idea that the spatial fabric of the Universe itself is expanding, and that’s what’s behind the observed relationship between redshift and distance has long been controversial, and also long-misunderstood. After all, if more distant objects appear to recede more quickly, couldn’t there be a different explanation, like an explosion that flung many things outward? As it turns out, this isn’t a mere difference in interpretation, there are observations we can make that tell us the answer!

It isn’t simply that galaxies are moving away from us that causes a redshift, but rather that the space between ourselves and the galaxy redshifts the light on its journey from that distant point to our eyes. Image credit: Larry McNish of RASC Calgary Center.

The Universe is not expanding ‘into’ anything, despite what your intuition might tell you. The Hubble ‘constant’ isn’t actually a constant, but is rather decreasing as time goes on. The Universe looks like it’s going to expand forever, but even that scientific conclusion is subject to revision depending on what data shows in the future. And although 97% of the galaxies in the Universe are already unreachable, it isn’t a violation of relativity or a faster-than-light phenomenon that’s to blame.

Within the observable Universe (yellow circle), there are approximately 2 trillion galaxies. Galaxies more than about a third of the way to the boundary of what we can observe can never be reached due to the Universe’s expansion, leaving only 3% of the Universe’s volume open to human exploration. Image credit: Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL / E. Siegel.

Come learn the answers to five questions about the expanding Universe that many are too embarrassed to ask!