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Time Travel for Dummies

Author: Cindy Hu

From: West Orange, NJ, USA

Harry Potter time turner (image credit)


“Time is an illusion,” or as the saying goes. If Einstein said it, we should listen, right?

With the world’s 24 time zones and daylight savings traditions in some countries, the concept of time can seem a bit arbitrary. So it’s no surprise that the notion of time travel has come to dominate science fiction and even advanced physics.

But time travel need not be a pipe dream. It doesn’t need to involve wormholes and higher dimensions, which are interesting but impractical. Just move to a cave for a few months.

Life in a Cave

The time warp associated with living in a dark cave isn’t new. In 1962, a French geologist named Michel Siffre tried this out. For two months, he eschewed all access to natural light and had no way to track the time. He was left to rely only on his sleeping patterns. Building on the assumption that one “night” of sleep corresponded to one day gone by, he tracked his “two months” like this.

Want to know how much he was off by when he finally emerged?

25 days. Siffre had been in that cave for nearly one extra month without realizing it.

Life Without Light

Why was Siffre’s sense of time so dreadfully distorted when he was living in the cave? Well, the most glaring aspect of cave life is that there’s no natural light. Cave-dwellers must rely entirely on candles, lamps, and the like for the duration of their entire stay. Day and night are equally bright. Or equally dark, as I should probably say. Candlelight is thousands and thousands of times dimmer than sunlight.

Our bodies function differently at night than in the day. When it’s nighttime, our blood pressure and core body temperature lower, and our hunger hormones become subdued. During the day, these changes reverse as we wake up and become more alert. These changes in our biology are known as circadian rhythms, a term that comes from the Latin words “circa,” meaning “about,” and “dies,” meaning “day.” So yes, our circadian rhythms literally revolve around the length of our days.

You might have already started to see the issue here. The presence of light, specifically sunlight, is crucial when it comes to determining the time of day. None of this happens if you’re living in a cave that’s at the same brightness day-in and day-out.

But this shouldn’t be a big deal, right? After all, the development of electric lighting has made it easy for the world to be well-lit year-round. The problem with this is that no matter how bright our artificial lights are, they can’t compete with sunlight. Have you ever tried bringing a laptop outside on a sunny day? I just tried doing that and was forced back in because the outside light was brighter than my laptop screen, even when it was set to max brightness.

The Dangers of Light Disruption

Living in a setting where it’s hard to distinguish between day and night is damaging in several ways. First, it disrupts our circadian rhythms as our bodies become confused. We’re eating when we should be sleeping, and we’re sleeping when we should be awake. While it’s true that everyone’s circadian rhythm is different, it’s also true that disrupting these rhythms is dangerous.

Humans have evolved to live in the sunlight. Among other things, it allows our skin to manufacture vitamin D, which helps keep your bones healthy. It also improves your mood. Sunlight allows our bodies to release endorphins, hormones that make us feel good. Studies have shown that sunlight can be an effective way of combating depression and other mental health issues.


From a physical and mental health standpoint, sunlight remains very important. Just because you don’t photosynthesize doesn’t mean you can thrive in a cave. Siffre’s stint, while an incredibly useful way of distorting his sense of time, also helped illustrate another point: humans rely on natural light in ways we might not have realized.

So is time an illusion or not? It’s up to you to decide. Even if you agree with Einstein, you’ll have to admit that time is a very useful illusion, especially when it comes to circadian rhythms.


Author: Cindy Hu

Cindy is a high school junior in NJ who loves math, physics, and biology, among many other subjects. Her hobbies include reading, playing the piano, and learning to crochet.



  1. Flatow, I., & Smolin, L. (2013, May 17). Resetting the Theory of Time. Retrieved March 23, 2021, from,he%20said%2C%20is%20an%20illusion.&text=And%20if%20time%20is%20real,about%20our%20past%20and%20future%3F

  2. Geddes, L. (2019). Chasing the Sun: How the Science of Sunlight Shapes Our Bodies and Minds. New York, NY: Pegasus Books.

  3. Getlen, L. (2017, January 23). This explorer discovered human time warp by living in a cave. Retrieved March 23, 2021, from

  4. Nield, D. (2018, April 24). Humans Can Sleep For Days When Living Alone Underground, Experiments Show. Retrieved March 23, 2021, from

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