If the winter solstice – the longest night of the year – gets a nod of recognition from you, it’s likely accompanied by the thought: Turn on the lights.
For most of us settled along the midriff of the Northern Hemisphere, the thing we’re inclined to celebrate during these days of darkness is that, as of this first day of winter, our daily dose of daylight is finally getting longer.
Yes, for many, Canadian songwriter Bruce Cockburn captures the spirit of the season best in his line Got to kick at the darkness ’til it bleeds daylight.
Yet, here’s the rub: In only thinking about the light, we miss the great gift that celestial darkness holds.
Next year marks the 190th anniversary of Olbers’ paradox, the resolution of which revealed that the longest night of the year is, in fact, the best one for connecting with and pondering our cosmic origins.
It’s only natural that astronomers and poets have always focused on the stars held by the beauty and wonder of their twinkling light, rather than the darkness between them.
But, in 1610, the famous astronomer-priest Johannes Kepler pointed out a disconcerting aspect of the then current view of the heavens. If all of the stars existed in an eternal, static cosmos, there’d be no night, or celestial darkness. More to the point, the sky should be as bright as if we lived on the surface of the sun.
Kepler’s reasoning went like this: In an infinite, static cosmos, the Earth would be surrounded by countless stars. Even if many of these stars were far, far away, their light would eventually reach us.
To put it in a modern context, the accumulated light from all these stars would be the equivalent of you suspended over a stage in the glare of an uncountable number of spotlights shining on you from every conceivable angle.
As a result, our corner, and every corner of the universe, would be blindingly bright and hellishly hot. Way too hot for life as we know it.
But, as Kepler and everyone else knew but didn’t think so much about, it does get dark. For about 200 years, astronomers occupied themselves with more pressing and tractable problems. In 1823, however, the German astronomer Heinrich Olbers took up the question again, and thus it’s become known as Olbers’ paradox: Why is there darkness in a seemingly eternal, static universe?
This case of the mystery of night took centuries to crack, and was only solved by the greatest discovery of 20th-century science, the Big Bang and the expanding nature of the universe.
We now know that, when we enter into night, we’re immersed into evidence of the greatest event in cosmic history – the universe’s birth. It’s because of this birth, 13.75 billion years ago, that we have both darkness and light.
What Big Bang cosmology has revealed is that there haven’t always been stars in our cosmos. The first stars weren’t formed until about 400 million years after the Big Bang, an era known as cosmic dawn, currently one of the hottest areas of astrophysical research.
This means that when the cosmic lights turned on, what’s called the event horizon, the universe had already expanded significantly. Thus light from regions of the universe beyond this event horizon has yet to reach us.
Similarly, old and now distant starlight that reaches us is red-shifted. Due to the famous Doppler effect – experienced routinely as the change in the pitch of an ambulance siren as the vehicle approaches and then recedes from us – starlight is red-shifted to lower energy, non-visible frequencies.
Thus we experience the long ago and distant energy from the early universe not as visible light but as the famous, barely audible buzz dubbed the cosmic microwave background radiation, a.k.a. the universe’s birthing sounds.
As a result of this cosmic birth and ongoing expansion, rather than a blindingly bright cosmos in which there could be no life as we know it, we’ve emerged in one that offers the twin joys of darkness and light. We owe our existence as much to the stars as the darkness. We are creatures of both.
So on the winter solstice, before turning on the lights, if the sky is clear, take a moment to behold the wondrous story told in the darkness between the stars.
Jacob Berkowitz is an award-winning science writer and the author most recently of The Stardust Revolution: The New Story of Our Origin in the Stars.