Fourteen thousand years ago, a star called Vela died. Its core collapsed first and then, in a violent burst, propelled the shattered star’s body out into space. Vela’s death bled into the interstellar medium, blasting cosmic radiation out in every direction.
For 800 years, the guts of this star traveled from its location in the Milky Way galaxy toward Earth. It took several years for the cosmic rays to permeate our atmosphere and settle to the ground, where they were absorbed into trees, ocean coral, and lakes around the planet.
Hundreds of years after that, in Tasmania, a dead tree was discovered, turned by time into a log and buried under sediment. Scientists studied the radioisotopes of the tree’s rings and found a surge of radiation 14,000 years old.
However distant and however ancient, seemingly random occurrences such as the death of Vela — a perfectly average star — and the shudder it caused on this average rocky planet are evidence of our inextricable link to everything in the cosmos, including the passage of time.
Scientists study tree rings for evidence of solar storms and supernovas in order to better understand the cycles of stars and how their lives and their deaths impact us.
We’ve used tree rings to measure these links since we learned how to study radioisotopes in the middle of the 20th century; we do the same with rocks and layers of ice deep below Antarctica. Humans have always wanted to know what’s happened in the past in order to help us understand our present. We have always longed to understand time.
But time itself has felt different this year, our relationship with it altered significantly by the pandemic. Whatever comfort we once derived from considering the past is gone. Now it’s a stark reminder of all that we had, all that we took for granted, and what we must still reckon with — that our future is not likely to look like what we’re used to.
Meanwhile, our hours and days dissolve together into some nebulous glob of experience. While time may run on a larger scale around us, we still live in our own intimate worlds. That dislocation in time has become a part of our running discourse, inspiring memes and jokes about not knowing what day it is. They drive home the fact that we’re all truly experiencing the same phenomenon — a sort of time melt.
As our usual markers of time vanish, the days feel as though they’ve been whipped through a blender. We are animals living in a social world, and as such, we’ve created strict routines for our lives. We wake up, take the kids to school, commute to work, take lunch breaks, go to the gym, have dinners out. Now, though, any activities we once might have participated in outside the home have been abruptly removed, and we’ve lost the sense of time these seemingly mundane markers once provided.
Lunch is whenever. Dinner is whenever. There is no more gym or meals with friends or travel plans. Our days are now simply that: days.
Since the pandemic began, we’ve been faced with a paradox: So much has changed around us, politically, environmentally, within our own lives. At the same time, so many of us are at home, living what often feels like cloned days. This is especially challenging for humans because our brains are hardwired to do one main thing: survive. And while many of us are staying home as a means of surviving, our ingrained nature counts survival as action, prediction, and planning.
Dean Buonomano is a neuroscientist and researcher at UCLA who studies how our brains relate to time. “Time is incredibly important because, in many ways, the brain’s most important functions are to predict the future,” he explains. “Because the degree to which an animal predicts where there’s going to be food or where there is going to be a predator or where there’s going to be water or where it’s going to find a mate determines the success of that animal. The brain is a prediction device.”
Covid-19, and its resulting effect on our lives, has stifled this instinct. Even thinking about the future conjures only a strange, fuzzy block because we know neither when this will end nor how different our world will look when it does.
What we are doing is waiting.
To understand how our experience of time has recently changed, we need first to understand what time really is (which, as you might have guessed, does not have a simple answer). At the most basic level, it is the fourth dimension — a coordinate, a way for us to know where we are.
“When someone says, ‘The movie starts at 7 pm,’ nobody is seized by anxiety, like, ‘Oh, my god, what does that mean? How am I supposed to interpret this weird, abstract way of looking at the world?’ Everyone knows what it means,” says Sean Carroll, a theoretical astrophysicist at Caltech. This is what is called “clock time,” and it helps us organize our lives.
Our brains tell time as well, like how we instinctively know when it’s day or night. This is what is called a circadian clock or rhythm — it’s how our bodies intuitively know to power down and get sleepy after the sun has set, and why sunlight or bright lights (hello, cellphones) alert our brains to wake up. Humans aren’t the only living beings that tell time this way. Nearly all animals need to know when it’s day versus night, so, for example, those that hunt after dark instinctively know to sleep during the day. It’s why light pollution is such an issue, not just for us humans but also for animals that rely on darkness to initiate mating, foraging, or sleep.
Plants also have a circadian clock — they know not to photosynthesize at night, because what good would that do? Many bacteria also keep to this rhythm because UV light from the sun is incredibly harmful to DNA. Time appears at such a basic cellular level that, like the blood coursing through us, it can be easy not to notice it as such.
But knowing this information won’t help you meet your friend at the movies, and it won’t explain why this year has turned our brains into washing machines on the spin cycle. If we can understand a little more about how the universe is moving forward, we might feel a bit better about our collective existential despair. Maybe we can even forgive ourselves for forgetting what day it is.
We measure time in relation to the star we orbit. We know that it takes 365 days for us to complete one lap around the sun and that it takes 24 hours for our planet to complete one spin around its axis. For thousands of years, we’ve used sundials to measure how the sun’s light changes in the sky throughout the day — in fact, the shadowed semicircle this measurement makes on the ground is why our clocks are round. We joke that time is a flat circle, thanks in part to True Detective. Only that’s not true. Time is a forward arrow.
It’s called time’s arrow. We know that time moves forward for a few reasons, the most obvious of which are that we can remember the past and not the future, and that we don’t get younger, we grow older. But the universe runs forward because of a process called entropy. Entropy at its heart is the measure of the quality physicists refer to as disorder. And disorder is just another way to think of change.
Entropy appears all around us, all day long, in ways so fundamental that even the infrared heat your body is giving off right now is a form of entropy. But to really understand time’s arrow, let’s make a very weird and inefficient cup of tea. When you take an ice cube out of your freezer, it is in an ordered state — a low-entropy state — because the molecules are cold and unmoving. As the ice cube melts, however, it enters a higher-entropy state. The molecules are free-flowing and less ordered, and if you choose to boil the melted ice cube (we are making tea, remember), the boiling water will create steam. A very high-entropy state for the water, steam sends molecules flying all over the place, onto your walls and ceiling and under the crack beneath your door.
You’d never be able to find them all and put them back into an ice cube; you cannot go back in time. There is now more disorder in your kitchen. But just for fun, let’s increase the entropy even more: If you steep that tea and pour in a dash of milk, you’d have just raised the entropy, because you’ve taken something hot and added something cold, mixing something together that cannot be unmixed. That’s time’s arrow.
The very young universe, too, began in a more ordered, low-entropy state, and as it expands, as the extreme heat from the Big Bang cools off and as things mix together, the overall entropy increases. This might seem like a bad thing, but it’s not. This state of change is required for all life, and without it, the universe would reach a state of equilibrium and, ultimately, its own end — a “heat death” that culminates in everything reaching the same temperature and being enveloped by black holes. When things stop changing, time’s arrow stops moving forward.
When Vela exploded 14,000 years ago, the Paleolithic paintings of France’s Chauvet Cave had been sitting hidden, frozen in a moment in time, for nearly 15,000 years before that. Not long after Vela’s death, the woolly mammoth went extinct, along with the cave bear and cave lion. Their bones for thousands of years were enveloped by a changing climate, melting glaciers and sediment, burying their skeletons and leaving evidence of their existence alongside the marks in red and black paint lining the walls deep inside Chauvet. One hundred million years earlier, dinosaurs occupied this land, at the same time that Saturn’s rings were forming.
In this way, time feels truncated, the past cut up into slices, more so because we still live on an ancient Earth, the bones of dinosaurs likely under our feet. Our ability to connect these markers in time has created entire fields of study: archeology, astronomy, geology, biology. Science and history, when intertwined, help us see what we would otherwise never have access to.
Knowing these stories helps us understand that the universe is constantly exhaling and inhaling new energy, in new stars and in the death of old ones. This cycle has been happening for billions of years. But as new stars are forged from an abundance of hydrogen lingering from the Big Bang, those stars convert the hydrogen to other elements. Eventually there won’t be enough hydrogen left in the universe to birth new stars, and the creation cycle will cease.
The same cyclical disorder is happening here on Earth. Species appear, they live, they go extinct, and we study them believing we are exempt from their fate.
We are a future-facing species. Even our memories are designed to help us predict the future. We have storage of past experiences that are, on a biological level, designed to inform our decisions. If you once touched a hot stove and burned yourself, you know not to do it again.
This goes against how we understand our memory. We think of it as something that belongs solely to the past, or perhaps the present. But our memories, above all, are not about the past; they are for our future. Our brains know to do anything we can to stay alive, while also planning out the next steps. Of all the things Covid-19 has taken from us, this might, abstractly, be one of the biggest sources of anguish: We’ve lost not only the present, but our sense of the future as well.
This time spent largely inside messes with our internal clocks, which is why March felt like it was a year long and how it is also suddenly December but it was only just April and somehow today is Wednesday and also seems like Monday, but who even knows. “For people during Covid, time can feel like it’s going slowly on a day-to-day level, but quickly on a week-to-week or month-to-month,” says Buonomano. This is what’s called retrospective time.
Retrospective time, he explains, is “not so much about time, but about memory, about items in memory. So if you had a month in which you didn’t have that many new experiences — you certainly didn’t go to a new country, you probably didn’t get out to meet new people, you probably didn’t take up a hobby, and you weren’t meeting people for work — you’re likely not to have anchors or lay down many long-term memories. So retrospectively, that creates the subjective experience of time flowing quickly.”
It is when our individual days don’t align with our internal clocks and the world’s external events that this odd confusion reigns.
“At some point,” Buonomano says, “Homo sapiens developed this ability to not just simply predict the future but to mentally time-travel to the future, which allowed us to do something totally radical: create the future.”
This is hyperbole, but instead of trying to predict where we might find plants and food, humans began planting seeds knowing that it was not for instant gratification but for long-term survival. Our nature is to create the future. It is one of our most inherent skills and desires, and in this moment, it has been snatched from us all.
Luckily, the pandemic’s erasure of any sense of past, present, and future won’t have any long-term effects on our brains, Buonomano says (though the PTSD and long-term emotional challenges we may suffer from being in isolation remain another cosmic unknown). “I think the lesson here is really how adaptive our species is. And that’s what the brain evolved to do, is to be adaptive. Humans are notoriously resilient.”
Before modern humans had the ability to count past 10, age did not exist. We didn’t keep track of how old people were; those numbers, that concept of time, did not exist yet. While humans have always observed the movement of planets in the sky and the changing seasons to help understand the passing of time, for the majority of human history our modes of relating to it were different. In the late 18th century, people began making timelines. They started to map the scale of the Roman Empire and measure the spread of disease.
It wasn’t until the 19th century, with the invention of the steam engine, that our relationship to time began to shift. Suddenly, time became incredibly important, as train operators needed to ensure that it was the same time in London as in Glasgow so that departure and arrival schedules were accurate. People started carrying pocket watches and were newly acutely aware of how the minutes passed in the day.
No matter how far back we look in human history, there has always been room for us to forge new relationships with this most valuable, most mysterious, and most fundamental thing. Just as it has always been and will always be, time is a paradox. We move through time wishing to grasp onto our most valuable moments — the first kiss, the new love, a special meal, a new city. Whatever those moments are that we cherish, the more they seem to slip through our fingers like sand. Yet as we exist within those seconds, so acutely aware of our grounding in the present, the future will beckon as though in echo, prodding us, leaving us wondering, will we get to keep this? Will this love stay? Will I get to come back to this place? And we will think, “I must do what I can to make it so.”
There is no flat circle of time except that which we humans have made. Real time is a tree’s rings, a labyrinth; it’s in stellar remnants, in letters, in books, in red and black paint etched on cave walls. It is love, in beginnings, in your tea, in chaos. It is endings — it is everything, just as we are everything.
As we approach another significant marker of time — the new year — we are faced with a real challenge. How do we contend with our nature, which fundamentally longs to predict the future and to protect and plan for it, while we face an indeterminate bleeding-together of days?
Maybe it can be of some comfort to us all to know that the nagging undercurrent of bewilderment, fear, sadness, and anxiety are there for more than the obvious reasons and are truly part of a natural collective experience. We are in a profound moment of being human. As time is changing — devolving, even — we know at least that it is still taking us forward.
Shannon Stirone is a writer in the Bay Area. Her work on science, culture, and technology can be found in the New York Times, the Washington Post, Wired, Longreads, and elsewhere.