Can the Cosmic Microwave Background Hold Echoes of a Previous Universe? - Cosmic Memory and the Search for a Universe Before Ours | Sleepy Facts About the Universe

Got something to say to this podcast? Send a voicemail, and you might hear yourself on the next episode!

We have been telling ourselves a tidy story about the universe having a birthday, but what if the calendar has no first page? The standard Big Bang theory gives the cosmos a definite beginning, a single moment of unimaginable heat and density from which everything we see emerged. Yet, the idea of an absolute boundary to time often leaves us uncomfortable, asking what happened before that first moment. The cyclic model offers a different framework, suggesting that our universe might be just the latest chapter in an endless sequence of expansion and contraction.

This episode examines how a bouncing cosmos could work, tracing the idea from its ancient philosophical roots to its modern mathematical formulations. We explore the profound challenges a cyclic model faces, particularly the problem of entropy and the need for the universe to essentially forget its previous cycle while remaining smooth enough to match our observations. We also look at how dark energy might act as a cosmic clock, eventually halting the current expansion and triggering a gradual, cold contraction rather than a violent collapse.

I kept returning to one question while working on this episode: what does it mean for our place in the cosmos if the universe breathes in and out, infinitely, across trillions of years? It is a strange thought to hold, realizing that everything we know might be one note in an endless song. Join me as we look at the subtle traces of gravitational waves and ancient light that scientists are searching for right now, faint signals that might just be the death echoes of a universe that existed before our time began.