Somewhere in outer space, billions of light years away from Earth, the original light associated with the Big Bang of the universe is still illuminating a new place as it continues to move outward.
Because of the enormous journeys in which light travels in outer space between galaxies and within the Milky Way, the extension between stars is not measured in kilometers, but in light years, which is the distance that light travels in a year, which is equal to 9.5 trillion kilometers.
The Milky Way, for example, is estimated to have a diameter of about 150,000 light-years, and the distance to the Andromeda galaxy, the closest galaxy to ours, is about 2.21 million light-years, meaning that the light that left the Andromeda galaxy 2.21 million years ago has just reached Earth.
Although some of the stars we observe in the sky have long since perished, the light waves that carry their images still reach our eyes and are monitored by telescopes, and in fact the light from their death has not yet crossed the huge distances of deep space due to insufficient time.
Therefore, when astronomers observe the stars in the sky, they are actually observing a mixture of real time, the recent past and ancient history.
The Milky Way is about 150,000 light-years across (NASA)
What is the speed of light?
Light transmitted in a uniform material or medium propagates in a straight line at a relatively constant speed, unless it is refracted, reflected, deflected, or otherwise distorted.
And when we talk in general about the "speed of light", it usually means the speed of light in a vacuum.
It is a specific value equal to 299 million 792 thousand and 458 meters per second.
It is denoted in the equations as a constant value denoted by the symbol C.
But does the speed of light change in air or water?
Yes, light is slowed down in transparent media such as air, water and glass.
The ratio at which it slows down is called the refractive index of the medium and is usually greater than one, and this was discovered by Jean Foucault in 1850.
Light travels in a vacuum at about 300,000 kilometers per second, but it slows down to 225,000 kilometers per second in water and 200,000 kilometers per second in glass.
In diamond, the speed of light is reduced to 125,000 kilometers per second, about 60% less than its maximum speed in a vacuum.
The speed of light and the speed of humans
According to a report on the scientific website "Live Science", humans are very slow compared to the speed of light, even at the maximum speeds they were able to reach.
"The fastest any human travels is 0.0037% the speed of light, and you have to be in some kind of spacecraft," Philip Tan, a research scientist at MIT Game Lab told Live Science. to reach these speeds.
But what if a person traveled at the speed of light?
Gerd Kortemeyer, associate professor of physics at Michigan State University, says unusual things would happen if humans could travel close to the speed of light.
According to Albert Einstein's special theory of relativity, which explains how speed affects mass, time and space, time will slow down, the lengths of objects will become shorter when we pass them, and the Doppler effect of light will become visible, i.e. seeing things in blue when you are heading towards them and then you see them in red when you move away from them and be behind you.
Plus some other changes.
The Doppler effect is a series of apparent changes that occur in the frequencies or wavelengths of waves when observed by a moving observer relative to the wave source, and the reason for its name was given to the Austrian physicist Doppler in 1842 AD.
According to Cortemayer, these same changes would occur whether the light was slowed down or if the speed of humans were increased, with movement in both cases being equal to or close to the speed of light.
hypothetical scenario
While Kurtemeyer was a visiting professor at the Massachusetts Institute of Technology, he, Tan and colleagues at the MIT Game Lab created a video game to show what the world would be like if the speed of light were slow enough that special relativity would be noticeable in everyday life.
The game was developed and released in 2012, free of charge, as an educational tool to explain special relativity in an easy-to-understand manner.
In the game, A Slower Speed of Light, the player controls an in-game character who collects beach ball-like orbs.
Each time a character collects one of the 100 orbs, the speed of light gradually slows down until it reaches a walking speed.
And the effects of special relativity are becoming more apparent.
This included changes in colour, time, distance and brightness.
Doppler effect change colors
When the speed of human movement approaches the speed of light, there will be enough relative Doppler shift to change the colors around you i.e. red and blue shift of visible light and ultraviolet and infrared shift into the visible spectrum.
So if you're driving through a yellow field of grain, you'll see it blue in front of you, but the field will turn dark red as you move away from it and be behind you.
"In short, the thing that comes to you looks bluer, and the thing that moves away from you looks redder," says Cortemayer.
The 'slower speed of light' game you can try (Getty Images)
Time Deceleration "Time Dilation Effect"
Time slowing is one of the most famous effects of special relativity for humans moving close to the speed of light.
In this scenario, a person moving close to the speed of light would age more slowly, and this effect is called time dilation.
Technically, however, time dilation cannot be observed or felt because there is nothing to compare it to.
In a slower light speed game, the player does not notice that time is slowing down, but eventually sees a screen that tells him that the time has passed for less than the time elapsed in the fixed clock in the outside world.
Height reduction
Another effect of special relativity is that the lengths of objects moving near the speed of light shorten, and this is called length contraction.
The effect is complex, says Courtmeyer, and that objects approaching the speed of light may experience a contraction in length and may be shorter, but may appear longer to the eyes of a stationary observer, due to another effect of special relativity called the "runtime effect".
For example, suppose a bicycle is heading towards you.
The light coming towards you from the front of the bike travels a shorter distance to your eyes than the light coming towards you from the back of the bike, and this generally makes the bike appear taller.
Sometimes, this same effect can make things look distorted.
In other words, if the speed of light were much slower, objects moving near that speed might appear taller and twisted, or one or the other to stationary observers.
Light is a collection of particles called photons (Getty Images)
Changes in brightness
When you walk in the rain, you may notice that you get wet in the front than in the back.
Just as when you're walking in the rain, you encounter more raindrops than when you're standing still. Something similar would happen if you were moving close to the speed of light, Cortemayer says.
That's because light is a collection of particles, called photons, and when you're heading toward something it appears brighter than when you're standing still.
This is called the searchlight effect, i.e. an increase in brightness in the direction of travel.