How do we know that time exists?

Credit: CC0 Public Domain

The alarm clock goes off in the morning. You catch the morning train to the office. Your lunch break. You catch the evening train back. You go for an hour run. have supper. sleep. repeat. Celebrate birthdays and commemorate deaths. New nations are born, empires rise and fall. The entire human existence is tied to the passage of time.

But we can’t see it and we can’t touch it. So how do we know it really exists?

“In physics, we have what’s called an ‘absolute time’ concept, which is used to describe different changes as a series of events,” Koyama begins. “We use Newtonian physics to describe how things move, and time is an essential element of that.”

To this day, the classic Newtonian idea of ‚Äč‚Äčtime — time being constant throughout the universe — remains a good approximation of how humans experience time in their daily lives. We all experience time in the same way, and we all synchronize our clocks in the same way, no matter where in the world we are, be it London, Tokyo or Buenos Aires.

no time no space

Physicists though have realized that time can actually behave differently and not as consistently as Newton thought. “When we talk about time, we also need to think about space – they are a whole,” he said. “We can’t separate the two, the way an object moves in space determines how it experiences time.”

Simply put, the time you experience is determined by your speed in space as an observer, as outlined by Einstein’s Special Theory of Relativity, a theory of how speed affects mass, time and space.

Also, according to Einstein’s general theory of relativity, the gravitational pull of large objects affects the speed at which time passes. Many experiments have proven this. Physicists have even discovered that black holes distort the immediate space-time around them due to their massive gravitational fields. Koyama continued to question the theory.

“A good, solid example of understanding all this is looking at how we use GPS,” Koyama continued. “GPS works by a network of satellites orbiting the Earth. They are placed at very high altitudes, so they experience less gravity. So their time should actually be faster than our time on the ground, in There “we experience higher gravity. But since satellites orbit the Earth at very high speeds, this actually helps to slow down time, compensating for the lack of gravity. “

Understanding how these two effects work and interact is critical to ensuring the proper functioning of the global GPS network. A consistent theory of time that explains how objects move is a key factor in this. So the clock doesn’t tell us a lie: time exists outside of our own perception.

Can we go backwards in time?

In the end, the question of whether time travel is possible someday has to be before Xiao Shan, a professor of cosmology at the University of Portsmouth, and is therefore best placed to tell us the truth.

“I’m sorry to disappoint you, but to make time travel possible, we need to discover an entirely new substance that has the ability to change the curvature of time and space,” Koyama said. “Such matter requires properties that simply don’t exist in nature. We physicists firmly believe that going back in time is impossible — but it’s good to fantasize about it.”

A step towards quantum gravity

Citation: How do we know that time exists? (18 Aug 2022) Retrieved 19 Aug 2022 from https://phys.org/news/2022-08-how-do-we-know-that.html

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