Starts With A Bang

If The Universe Is Expanding, Then Why Aren’t We? (Synopsis)

The fabric of expanding space means that the farther away a galaxy is, the faster it appears to recede from us. Image credit: NASA / GSFC.

“In an expanding universe, time is on the side of the outcast. Those who once inhabited the suburbs of human contempt find that without changing their address they eventually live in the metropolis.” -Quentin Crisp

The Universe is expanding. The farther away a galaxy is, the faster it appears to be receding from us. The standard story tells us that space itself is expanding, and that’s the cause, but it’s only natural to wonder if perhaps space is static, and everything else within it isn’t shrinking instead? Many laypersons choose to go this route, and question the entire field of cosmology as a result.

The various galaxies of the Virgo Supercluster, grouped and clustered together. On the largest scales, the Universe is uniform, but as you look to galaxy or cluster scales, overdense and underdense regions dominate, and the Universe appears very non-uniform. Image credit: Andrew Z. Colvin, via Wikimedia Commons.

But is this fair? Or is this a road to not only ruin, but to physical inconsistencies? Could we flip the story on its head, and do some sort of test to see if atoms, the planet, or some other ‘local’ entity is shrinking, instead? Or, using the principle of relativity, could we declare that all frames are equally valid, and choose a frame where space isn’t expanding, after all?

The atomic transition from the 6S orbital, Delta_f1, is the transition that defines the meter, second and the speed of light. Image credit: A. Fischer et al., The Journal of the Acoustical Society of America (2013).

These are all interesting thoughts, but there’s only one correct, valid, and consistent way to view the Universe. Sabine Hossenfelder has the explanation!