Many sci-fi scenarios exploit the possibility of manipulating time, and include situations where certain protagonists stop it altogether. But is such an action physically possible? Is time a phenomenon that can be manipulated at will or is it completely beyond our control?
First, you have to define the time. ” For a physicist, it is not so mysterious. Time is just a label on different parts of the universe. It tells us when something is happening », Explains Sean Carroll, theoretical physicist at California Institute of Technology. Many physical equations make little distinction between the past, present, and future.
One place where time appears is in Albert Einstein’s theory of relativity. According to Einstein’s theory, time is measured by clocks. Because the parts of a clock must move in space, time becomes entangled with space in a larger concept known as space-time, which underlies the Universe.
Relativity has shown that time can become quite unstable depending on how fast an observer is moving relative to another observer. If you send a person with a clock on a spaceship at a speed close to light, time will seem to pass more slowly for them than for a motionless person left on Earth. And an astronaut falling into a black hole, the immense gravity of which can warp time, could also appear to slow down compared to a distant observer.
Stopping time: a physical nonsense
But that’s not really a way to stop time, says Carroll. Two clocks can disagree in relativity, but each will always record the usual passage of time in its own frame of reference (its frame of reference). If a traveler approached a black hole, he wouldn’t notice anything different. His watch would tell him the time in his frame of reference, flowing second by second.
So for Carroll and other physicists, it doesn’t make sense to talk about stopping time. We know that a car is moving because at different times it is in a different place in space. ” Movement is a change from time, therefore time itself cannot move. In other words, if time stopped, all movement would stop too ».
While science fiction often offers situations where an individual stops time in general terms, such situations raise a lot of questions. ” Are you preventing the air from moving? ‘Cause if so then you’re trapped in the air “. A character who stops time would also likely be unable to see anything, Carroll explains, because the light rays would no longer reach his eyeballs. So there isn’t really a coherent scenario in which time stands still.
Chronostasis: the psychological illusion of stopping time
For physics, it therefore seems impossible. But time is more than just reading a clock. It is also a feeling that we have; a phenomenon called “psychological time”. In this case, the passage of time may be subject to our emotions or our mental state. Craig Callender, a time philosopher at the University of California, describes a well-known psychological illusion known as chronostasis, in which a person places a clock at the edge of their field of vision, then looks at something other for a while.
Coming back to the clock again and focusing on the seconds hand, the second hand will pause. ” The needle really seems to drag, or even stop. You may feel like time freezes Says Callender. Part of the illusion is said to be due to tiny eye movements called jerks, in which the eyeballs move rapidly to constantly observe their surroundings.
To prevent us from seeing chaotic blur, our brain actually changes what it sees in real time and creates the impression of a continuous field of view. The question then becomes: what is the relationship between our perceptions of time and the time that physicists talk about? Callender has written a number of books that attempt to explore the connection between the two, and as of yet, there isn’t much consensus on a final answer.
When it comes to the ultimate flow of time, Callender favors an image where nothing flows, but where it is rather our history that flows. And what does he think of the possibility of stopping time? ” If we think about our subjective sense of time, then we can stop parts of it with chronostasis. But it’s probably the most we can do ».