How do we know that time exists?
Our entire lives are ruled by clocks, but what they measure is less certain. How can we be sure that time really exists? It’s time to talk to an expert, Kazuya Koyama.
The alarm goes off in the morning. You take your morning train to the office. You take a lunch break. You take your evening train. You leave for an hour of racing. Eat dinner. Go to bed. Repeat. Anniversaries are celebrated, anniversaries recounted, deaths commemorated. New countries are born, empires rise and fall.
All human existence is linked to the passage of time. However, we cannot see it and we cannot touch it. So how do we know it’s really there?
“In physics we have what we call the idea of ’absolute time’ and it is used to describe different changes as a sequence of events,” Koyama begins. “We use Newtonian physics to describe how things move, and time is an essential part of that.” Koyama is professor of cosmology at the Institute of Cosmology and Gravitation of University of Portsmouth.
To this day, classical Newtonian thought about time – where time is constant throughout the universe – is still a good approximation of how humans experience time in their daily lives. We all experience time the same way and we all synchronize our clocks the same way, wherever we are in the world, be it London, Tokyo, New York or Buenos Aires.
There is no time without space
Physicists have discovered, however, that time may actually behave differently and is not as consistent as Newton thought.
“When we talk about time, we also have to think about space – they come in a set,” says Koyama. “We can’t separate the two, and how an object moves through space determines how it experiences time.”
In short, the time you live depends on your speed through space as an observer. It works as stated in Einstein’s special relativity, a theory of the impact of speed on mass, time and space. Additionally, according to Einstein’s theory of general relativity, the gravity of a massive object can impact how quickly time passes. Many experiments have been undertaken which have since proven this to be true.
Physicists have even discovered that black holes warp the immediate spacetime around them due to their immense gravitational fields. Supported by the European Research Council, Koyama continues to study this theory.
“A good solid example for understanding all of this is to look at how we use GPS,” Koyama continues. “GPS works through a network of satellites orbiting the Earth. They are placed at very high altitude and therefore the gravity they experience is lower. Therefore, time should actually pass faster for them than for us on the ground, where we experience higher gravity. But because satellites move at very high speeds around the planet, it actually helps slow down time, compensating for the lack of gravity.
Understanding how these two effects work and influence each other is critical to ensuring the smooth operation of the global GPS network. And a crucial ingredient in this regard is a coherent theory of time that explains how objects move. Clocks therefore do not tell us lies: time indeed exists outside of our own perception.
Can we ever go back in time?
Finally, the question of whether time travel might ever be possible had to be posed to Koyama. As professor of cosmology at the University of Portsmouth, he is in the best position to tell us the truth.
“I’m sorry to disappoint you, but for time travel to be possible, we would need to discover an entirely new type of matter that has the power to alter the curvature of time and space,” Koyama says. “Such matter would require properties that simply do not exist in nature. We physicists strongly believe that going back to the past is simply impossible, but it’s fine to fantasize about it.
Click here to read more about Koyama’s research: Challenging the General Theory of Relativity
