I recently wrote an article addressing the testability of multiverse models where I made the following statement: “First, multiverse models are not new to the cosmology scene. For example, shortly after Einstein developed the equations for the theory of general relativity, he realized that the solutions to those equations indicated we lived in an expanding universe.” One astute reader challenged my statement with this response:

As far as I remember hearing of Einstein’s views, Einstein thought that, because of gravity, everything in the universe should be rushing together, not apart. This would not be an expanding universe, but rather a contracting universe. Thus, I disagree with the sentence...

In attempting to communicate things more concisely, my original statement caused legitimate confusion. The main point I wanted to emphasize was the fact that Einstein realized the equations of general relativity generically pointed to a dynamic, as opposed to the expected static, universe. In fact, some have criticized Einstein for yielding to his preconceived ideas about the universe instead of trusting his equations and predicting the expansion of the universe. Neil deGrasse Tyson states, “With a non-static universe staring him in the face, Einstein botched the opportunity to predict it and, out of aesthetic preference, instead favored the static model.”

A decade or so after Einstein published his theory of general relativity, Edwin Hubble’s observations demonstrated that we live in an expanding universe rather than a collapsing one, thus helping to confirm that universe had a beginning. This new data prompted some cosmologists, including Einstein, to adopt steady-state and oscillating universe models in order to avoid a genuine beginning. The oscillating universe model proposes an endless (or incredibly large) number of cycles where the universe starts in a small, extremely dense state, expands for billions of years, then contracts back to the incredibly small state and starts the whole process over. As long as the number of cycles exceeds one, this oscillating model describes a multiverse.

For clarity, Einstein believed in a static universe and that the only way to overcome the known gravitational effects (that cause the universe to collapse) was by introducing the infamous “cosmological constant.” Eventually, Hubble’s observations falsified this belief, at which point Einstein adopted the oscillating universe model.