Isn’t the multiverse concept metaphysics because scientists have no way to ever detect its existence? How could scientists possibly test something beyond our universe? These questions represent common objections to any multiverse model. Yet recent work to understand the rapid inflation early in cosmic history reveals how one popular class of multiverse models can be tested.
A growing body of evidence reveals that the universe grew by more than a factor of 1025 during the first extremely brief moments of its existence. A leading model to explain the mechanism that produced this hyperfast, inflationary epoch is called the eternal inflation model. It posits the existence of a “false vacuum” whose most relevant characteristic is exceptionally rapid expansion. However, this false vacuum can decay in such a way as to produce new universes.
Depending on how rapid the expansion occurs and how frequently universes form, the universes can collide, leaving an imprint on the cosmic microwave background radiation (remnants of the big bang). When two soap bubbles collide, the intersection forms a circle. Similarly, a universe colliding with ours during inflation leaves a circular signature. A team of cosmologists developed an algorithm to search for these signatures using the WMAP (Wilkinson Microwave Anisotropy Probe) data.1
After applying their algorithm to the data, the team found results consistent with the standard cold dark matter model with cosmological constant (CDM). Nothing in the analysis required the addition of a bubble collision.
While lacking positive results, the research clearly demonstrates the testability of the multiverse. In fact, the same technique will be used to analyze data from the Planck satellite. As successor to the WMAP, the Planck satellite will provide a much more detailed measurement of the ripples in the cosmic microwave background radiation.
The results gathered thus far from the WMAP highlight the need for caution before deeming an apologetics issue like the multiverse “outlandish.” When an idea appears to answer relevant scientific questions (like why our universe appears so finely tuned to support life) and when it has some basis in theoretical models, one of two things happens. Either scientists come to realize that the technology required to test the models remains too far into the future and the model ends up shelved for later discussion, or hard work on the part of researchers reveals novel tests that could validate or falsify the model.
Determining whether a particular multiverse model eventually proves true or not will take some time. But it’s worth the wait, especially when such models provide additional evidence for a Beginner and Designer.
- Stephen M. Feeney et al., “First Observational Tests of Eternal Inflation,” Physical Review Letters, 107 (August 12, 2011): 071301.