Written by Ashley P. Taylor October 30, 2021
If light travels very slowly, strange things will happen.
Light is the fastest moving thing in the universe. So, what would happen if the speed of light was much slower?
In a vacuum, the speed of light is approximately 186,000 miles per second (300,000 kilometers per second). If the speed is several orders of magnitude slower, humans will notice immediately.
Any gamer can experience this hypothetical scenario in a computer game created by Gerd Kortemeyer, director of educational development and technology at the Swiss University of Science, Technology, Engineering and Mathematics, ETH Zurich, and his colleagues. In the game, you can see the strange effects of color and brightness changes, and even changes in the perceived length of objects, which are caused by the much slower speed of light.
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Even at our fastest speed, human beings are slow compared to light.
Philip Tan, a research scientist at the MIT Game Laboratory, told Live Science: "The fastest human speed is about 0.0037% of the speed of light. You need to take some kind of spacecraft to reach this speed."
But Kortemeyer, who is also an associate professor of physics at Michigan State University, said that through thought experiments, physicists have determined that if humans can travel at a speed close to the speed of light, unusual things will happen. According to Albert Einstein's special theory of relativity-which explains how speed affects mass, time and space-time will slow down, we will measure objects as shorter, and when we pass by them, the Doppler effect Will become visible, and there will be other changes.
If it were not for humans to accelerate, but for light to decelerate, the same change would happen. In both cases, we will move at a speed close to the speed of light.
When Kortemeyer was a visiting professor at MIT, he, Tan, and his colleagues at the MIT Game Lab created a computer game to show that if the speed of light is slow enough that the special theory of relativity is obvious in daily life, the world will What it looks like. In a game called "A Slower Speed of Light" released in 2012, players control a character that collects beach ball-shaped spheres. Whenever the character collects one of the 100 spheres, the speed of light will slow down.
In fact, the speed of light will not slow down like in the game. The speed of light in a vacuum never changes and is constant for every observer. However, the speed of light does change according to the material it passes through, but this does not change the influence of special relativity or how we view them, Kotmeier said.
However, if we can witness the special theory of relativity, we will notice changes in color, time, distance, and brightness, and the team will incorporate these effects into the game.
When the speed of human movement approaches the speed of light, what is called the relativistic Doppler effect becomes noticeable. To understand this, remember that light is both a particle and a wave. As a wave, it is characterized by its wavelength, or the distance from the peak to the peak, which determines its color and frequency, or how many peaks it passes in a given time.
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Similar to the Doppler effect, approaching a sound source makes its frequency or pitch seem to increase as the wave crest reaches your ears faster and faster, moving toward the light source makes its wavelength appear shorter, moving Kortemeyer said, light The obvious colors are towards the blue and purple end of the color spectrum. On the other hand, moving away from an object will shift its apparent color to the red end of the spectrum. All in all, “things close to you look bluer, or things far away look redder,” Kortemeyer said.
Perhaps one of the most famous effects of special relativity is that for a person approaching the speed of light, time slows down. In this case, people moving at close to the speed of light will grow older more slowly. This effect is called time dilation.
In the game, "Technically, you are experiencing time dilation; but if there is nothing to compare with, it has no real meaning," Tan said. Tan said that time dilation may not be obvious during the game, but at the end, players will see a screen telling them that they have elapsed less time than the fixed clock. Time dilation, like other effects of the special theory of relativity, occurs during the game because the moving speed of the game character is close to the speed of light.
Another effect of the special theory of relativity is that the length of objects moving at close to the speed of light—or objects that are stationary when you pass them at close to the speed of light—has shortened. This is called length shrinkage. But the effect is complicated, Kortemeyer said. Kortemeyer said that, based on measurements by a stationary observer, objects zoomed at close to the speed of light may experience shrinkage in length and may be shorter, but due to another effect of special relativity called runtime effects, they actually appear to the person’s eyes Longer.
For example, suppose a bicycle is approaching you. Compared with the light from the back of the bicycle, the light from the front of the bicycle has a shorter distance to reach your eyes. Therefore, you will see that the front of the bicycle is the closest, and the rear of the bicycle is the past, when the bicycle is farther away. "Overall, this makes the bike look longer," Kotmeier said. Sometimes this same effect can make the object look distorted.
In other words, if the speed of light is much slower, objects approaching that speed may appear longer and/or distorted to a stationary observer.
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When you walk in the rain, you may notice that the front part is wetter than the back part. When you walk into the rain, you will encounter more raindrops than when you stand, but your front can protect your back from these extra raindrops. Kotmeyer said that if you move at a speed close to the speed of light, something similar can happen.
This is because light sometimes behaves like a group of particles, called photons, like small light droplets. In computer games, when you move toward an object, it looks brighter than when you stand still, because you walk into it with photons. This is called the searchlight effect.
Kortemeyer and Tan are not the first to imagine a world where the speed of light slows down. In 1939, physicist George Gamow published a picture book called "Mr. Tompkins in Wonderland", in which the protagonist rides a bicycle through a city where the speed of light slows down, experiencing the effect of relativity. Einstein "really liked that booklet," Kotmeier said.
——What if the earth starts to turn upside down?
——What if the earth is twice as large as before?
——What if the moon disappears tomorrow?
What would great physicists think of the "slower speed of light"? "Curiosity may make him work in the first place, because if you believe the historian, he already asked at the age of 16 what you would see if you rode a beam of light-of course, you can't, but in the game, You can almost reach the speed of light," Kortemeyer said. "But then I thought he would keep playing video games until he was hopelessly motion sick-most physicists are still very naughty."
Originally published on Live Science.
Ashley P. Taylor is a writer living in Brooklyn, New York. As a science writer, she focuses on molecular biology and health, although she likes to learn various experiments. Ashley studied biology at Oberlin College, worked in several laboratories, and received a master's degree in journalism from the New York University Science, Health, and Environmental Reporting Program. In addition to science, Ashley also likes the possibilities of music, dance, and language.
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