Are you here now? Impossible to say. The idea that any group of events can truly happen at once is just an illusion.
One afternoon some years ago, I was walking through the snow thinking about other universes. More specifically, I was turning over in my mind the fact that the hospitality provided by our universe depends on many extremely special things. For example, if the electric repulsion between protons in the nuclei of atoms were just a bit stronger, then those atoms, and hence chemistry, and hence life itself, could not apparently exist. And there are many other such ‘coincidences’. I had convinced myself that there were four – and pretty much only four – possible explanations for the fact that the laws of physics seem to be carefully chosen to allow us living, conscious beings to be here.
First, perhaps the laws of physics really were designed for us: when the universe began, it (or some superbeing that created it) had us – or at least life – in mind. Second, perhaps it was just an immense coincidence: there was one ‘roll of the dice’ that specified, among other things, the force between protons, and we just got colossally lucky. Third, it could be that many ‘universes’ exist with different laws of physics, and we are perforce in one of the universes that allow life. Fourth, perhaps the coincidences are illusory: perhaps life would somehow find a way to arise in any universe, with any possible set of physics.
A feeling grew in the pit of my stomach that the Universe really is a pretty mysterious place. The mystery is not about why the Universe has some particular properties rather than others, but about the connection between those properties and our very existence as living, conscious beings contemplating those properties.
Not only are you intimately connected to the Universe on the largest scales, you are central. This is not to deny that you are in some sense an infinitesimal arrangement of dust on one small planet out of billions of trillions in our observable universe, which might well be one of many universes. But you are also a giant: a thinking, conscious being responsible for giving meaning, and even existence, to the universe you inhabit.
Sometime after, I was recounting my thoughts to a good friend who happens to be a longtime practitioner of Zen Buddhism. He noted that my experience reminded him of Zen koans, vignettes that embody teachings about reality as explored by Zen adepts. Through koans, a teacher can confront a student with a situation that, while initially baffling, can be resolved through added insight rather than more knowledge or previous experience.
I decided to create a set of cosmological koans to explore the connections between us and the Universe – a set of open doors through which you are invited to walk. The selection below interrogates the nature of time, and the way we pass through it in the cosmos at large.
Right now, as you read this, a baby in India is taking its first breath, and an old woman her last. A young woman and her love are sharing their first kiss. Lightning flashes across a dark sky. The wind blows through the hair of a solitary hiker in the Sahara desert.
A satellite is seeing the Sun rise above the Earth. A hurricane is blowing endlessly through the clouds of Jupiter. Two rocks are colliding, just now, in the third ring of Saturn.
The new year is arriving on a planet around a star in our galaxy. Perhaps the world has inhabitants who are celebrating.
Our galaxy moves about 100 miles closer to our neighbour Andromeda, toward their collision and union 4.5 billion years from now.
A star in a distant galaxy ignites a titanic supernova explosion that ends its 100-million-year life. At the same time, hundreds of new stars first ignite.
The observable universe adds enough new space for 100 new galaxies.
All of this is happening this very second, across the universe, right now.
Yet this ‘right now across the universe’ does not exist.
Did a child in India really just take its first breath? Probably. There are about a billion people in India. If each person lives up to 100 years, then at least 10 million people must be born each year just to maintain India’s population, and of course the population is growing. Now, a year has 365 days of 24 hours of 60 minutes of 60 seconds – or about 30 million seconds. Thus, on average, at least one person is born every three seconds in India.
A more careful estimate shows that one person is born about every second there, so indeed it is likely that, in the last second, a baby there took its first breath.
The explosive death of a star occurs many times per second somewhere in the observable universe
What does this illustrate? First, that there are many interesting calculations that can be done approximately – but well enough – using just some thinking and some numbers that we might happen to know or can easily obtain. These are often called order of magnitude estimates.
The art of these calculations is to understand the essential ingredients of a question, to know how to combine them, and to be able to obtain the result to within a factor of about 10 – that is, to be able to say that about one Indian child is born each second, and not 10 per second, or one per 10 seconds.
These numbers also illustrate how very large our world is. Birth – an event that happens just once in a person’s lifetime – happens every second somewhere in the world! Similarly, the explosive death of a star as a supernova, which happens just once in the 100-million-year lifetime of just a small fraction of stars, occurs many times per second somewhere in the observable universe. (I follow the convention that ‘Universe’ means roughly all that exists; ‘observable universe’ means that which we can currently probe using observations with telescopes and other experiments’, and ‘universe’ means the space-time region encompassing, and with similar properties to, the observable universe. Is the Universe bigger than the universe? Bet on it!)
It is a big place! (And getting bigger, to the tune of about 1062 cubic metres per second.)
When we contemplate all of these things happening now, it feels very intuitively clear what we mean by ‘now’: some event either happens now, or it does not, right?
To begin to see why, let’s think about what we mean when we say something is ‘happening now’, and in particular how we know it is happening now. When you say that a falling leaf hits the ground ‘now’, you mean that the event coincides with your internal perception of the present. When you say that the leaf hit 10 seconds ago, you mean that your internal ‘clock’ (or maybe a wristwatch) has ticked 10 seconds since your perception of the landing leaf.