The passage of time is the most predictable thing there is, yet it still never fails to surprise. Time slips away as deadlines approach, it slows to a crawl when you’re waiting in long lines, and, sometimes, it seems to freeze.
You can create the experience of time stopping right at home. All you need is a clock or watch with a ticking second hand.
Place the clock just at the edge of your vision, and focus briefly on something else for a moment. Then, glance at your timepiece and watch the second hand, which will seem to stop in place before proceeding.
Known as chronostasis, this illusion illustrates how our minds edit sensory data. In this case, the scenes being deleted are the motion blurs that you would otherwise see as your eyes jump, or saccade, between objects. Lasting about a fifth of a second, a saccade is one of the fastest known movements of the human body.
To see a saccade in real time, you’ll need to observe someone else’s eyes. When you look in a mirror and glance from one eye to another, you’ll never see your own eyes move. Your mind is sparing you the blurry footage.
But your mind does more than just hide the blurs, it also hides the evidence that anything has been hidden. Like a clever burglar who hacks into security cameras, your visual system prepares for the saccade by suppressing itself. It then compensates for the temporal gap by displaying a paused version of the next moment before continuing.
Chronostasis is an example of a temporal illusion, which, like an optical illusion, reveals how our senses do not always report on the physical world with pure objectivity. Instead, they pick and choose the parts that evolution has deemed important.
But just as we can overcome many optical illusions with rulers, we can overcome temporal illusions by attending to one of the most widely used scientific instruments: the clock.
This column first appeared in the March 5, 2018 edition of The Christian Science Monitor Weekly magazine as part of the Monitor's occasional Science at Home series.