Heinrich Päs - The One: How an Ancient Idea Holds the Future of Physics

Stargazing

O NE VERY EARLY MORNING IN MID-OCTOBER 2009, I was waiting alone in a deserted and pitch-dark alley in San Pedro, in the middle of the Chilean Atacama Desert, one of the driest spots on earth. Above me, countless stars were sparkling, so mesmerizing that I struggled to keep an eye out for the tour guides truck, coming to pick me up for a trip up to the Altiplano to watch the flamingoes stalking a secluded salt flat in the first light of the rising sun. Never before or after have I seen a more magnificent sky, though there have been other, similarly magical moments: counting shooting stars from the deck of a sailboat while crossing the Baltic Sea, practicing full-moon surfing off Waikiki Beach in Hawaii, or stepping out of a ski cabin at night, halfway up a mountain in the Austrian Alps, only to be stopped in my tracks by the bright band of the Milky Ways galactic disk. In such moments, I have felt entirely small and insignificant and yet, at the same time, strangely at home in the universe.

But what does it mean to feel at home in the universe? What do we actually mean when we talk about the universe? Etymologically, the word comes from the Latin universum , meaning something like all things combined together into one. Yet, when we speak of the universe, we usually refer to outer space, our cosmic environment, stars, planets, galaxies, a vast realm filled with countless objects. Apparently, what we refer to as the universe and what the term actually means have little in common, if anything at all.

Almost all the celestial objects you can identify in the night sky belong to our own galaxy, the Milky Way, which in total hosts more than one hundred billion stars. And the Milky Way itself is only one among about a trillion galaxies. As impressive as these numbers are, these visible objects are only the tiniest part of the entire universe. For every star you can spot out there, there exists about ten times more mass in nonluminous matter, such as gas clouds billowing around in interstellar space. Even more so, for all ordinary matter there exists five times as much mass in dark matter, expected to be made of exotic, unknown particles floating across the universe. And finally, there exists three times more dark energy, the puzzling fuel that drives the fabric of space-time to expand faster and faster.

So much for our universe.

But according to modern cosmology, maybe even our universe is not everythingthere may be more than just a single universe. Cosmologists now describe an epoch of accelerating expansion in the very early times, called cosmic inflation. The inflationary period terminates in a hot plasma, which we can identify with the Big Bang. But nobody knows what happened before inflation. Was there an absolute beginning? Or did inflation go on forever, and is it maybe still going on outside our own universe, in other regions of a multiverse? In that case it may continue to produce innumerable other baby universes, popping up in an eternally inflating space. This, actually, is quite possible.

But that is not enough to account for everything either. Not even close! Beyond parallel universes, dark energy, dark matter, and trillions of galaxies with a hundred billion stars each, there may yet exist a realm of infinite possibilities, where everything that, in principle, could exist actually does . There you would find innumerable copies of yourself, my cat, your dog, the flamingoes of the Altiplano, everyone, of all stars and galaxies and everything mentioned above. These parallel realities are the different branches of Hugh Everetts infamous many worlds interpretation of quantum mechanics. In fact, they constitute anotherarguably more fundamentallayer of multiverse. Increasingly more physicists are willing to accept now that they are an inherent prediction of quantum mechanicsthat a functional notion of quantum mechanics is increasingly difficult to sustain without many worlds.

And even this is not the end of the story. In addition to these parallel worlds, the quantum world contains infinite arbitrary superpositions of these realities. These are realities in which cats are half dead and half alive and where you are not either sitting in a chair and reading a book in the United States or driving a rental car through Europe but where both activities and places are mixed up in a way implying one cannot decide which one is true. The quantum realm encompasses everything that could be and all possible blends of these would-be realities.

Yet, standing there, under the stars, I still felt that feeling that many humans have shared: that I was somehow one with the vastness beyond myself. Is there a more daring, courageous, and flat-out overwhelming thought than to conceptualize the whole material world, everything from celestial bodies to life upon the earth and from the nebula stars to the mosses on the granite rocks, as the great German naturalist and discoverer Alexander von Humboldt portrayed the universe, as One?