It’s not the immensity or inscrutability, but that it reduces physical law to happenstance.
How do you feel about the multiverse?” The question was not out of place in our impromptu dinner-table lecture, yet it caught me completely off-guard. It’s not that I’ve never been asked about the multiverse before, but explaining a theoretical construct is quite different to saying how you feel about it. I can put forth all the standard arguments and list the intellectual knots a multiverse would untangle; I can sail through the facts and technicalities, but I stumble over the implications.
In physics we’re not supposed to talk about how we feel. We are a hard-nosed, quantitative, and empirical science. But even the best of our dispassionate analysis begins only after we have decided which avenue to pursue. When a field is nascent, there tend to be a range of options to consider, all of which have some merit, and often we are just instinctively drawn to one. This choice is guided by an emotional reasoning that transcends logic. Which position you choose to align yourself with is, as Stanford University physicist Leonard Susskind says, “about more than scientific facts and philosophical principles. It is about what constitutes good taste in science. And like all arguments about taste, it involves people’s aesthetic sensibilities.”
NASA/ESA and The Hubble Heritage Team (STScI/AURA)
My own research is in string theory, and one of its features is that there exist many logically consistent versions of the universe other than our own. The same process that created our universe can also bring those other possibilities to life, creating an infinity of other universes where everything that can occur, does. The chain of arguments starts from a place I’m familiar with, and I can follow the flourishes that the equations make as they dance down the page toward this particular conclusion, but, while I understand the multiverse as a mathematical construction, I cannot bring myself to believe it will leap out of the realm of theory and find a manifestation in physical reality. How do I pretend I have no problem accepting the fact that infinite copies of me might be parading around in parallel worlds making choices both identical to, and different from, mine?
I am not alone in my ambivalence. The multiverse has been hotly debated and continues to be a source of polarization among some of the most prominent scientists of the day. The debate over the multiverse is not a conversation about the particulars of a theory. It is a fight about identity and consequence, about what constitutes an explanation, what proof consists of, how we define science, and whether there is a point to it all.
Whenever I talk about the multiverse, one of the questions that inevitably comes up is one I actually have an answer to. Whether we live in a universe or multiverse, these classifications relate to scales so large they defy imagination. No matter the outcome, life around us isn’t going to change one way or another. Why does it matter?
It matters because where we are influences who we are. Different places call forth different reactions, give rise to different possibilities; the same object can look dramatically different against different backgrounds. In more ways than we are perhaps conscious of, we are molded by the spaces we inhabit. The universe is the ultimate expanse. It contains every arena, every context in which we can realize existence. It represents the sum total of possibilities, the complete set of all we can be.
A measurement makes sense only within a reference frame. Numbers are clearly abstract until paired with units, but even vague assessments such as “too far,” “too small,” and “too strange” presume a coordinate system. Too far invokes an origin; too small refers to a scale; too strange implies a context. Unlike units, which are always stated, the reference frame of assumptions is seldom specified, and yet the values we assign to things—objects, phenomena, experiences—are calibrated against these invisible axes.
If we find out that all we know, and all we can ever know, is just one pocket in the multiverse, the entire foundation upon which we have laid our coordinate grid shifts. Observations don’t change, but implications do. The presence of those other bubble universes out there might not impact the numbers we measure here on our instruments, but could radically impact the way we interpret them.