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How Fast Does Light Travel? | The Speed of Light

The speed of light in a vacuum is 186,282 miles per second (299,792 kilometres per second). In theory, nothing can travel faster than the speed of light. The speed of light in miles per hour is very high: about 670,616,629 miles per hour. If you can travel at the speed of light, you can circle the earth 7.5 times in a second.

Early scientists could not perceive the movement of light, thinking that it must be transmitted instantaneously. However, over time, the measurement of the motion of these wavy particles has become more and more accurate. Thanks to the work of Albert Einstein and others, we now understand light speed to be a theoretical limit: light speed — a constant called "c" — is thought to be not achievable by anything with mass, for reasons explained below. This does not stop science fiction writers, and even some very serious scientists, from imagining alternative theories that can allow some very fast travels in the universe.

Speed of Light: The History of Theory

The first known statement about the speed of light came from the ancient Greek philosopher Aristotle, who expressed disagreements with another Greek scientist Empedocles. Empedocles believes that because light moves, it must take time to spread. Aristotle believed that light could spread in an instant but disagreed.

In 1667, the Italian astronomer Galileo Galilei had two people stand on a hill less than a mile apart, each holding a shielded lantern. One person unveiled his lantern; when the second person saw the flash, he also unveiled his. By observing how long it takes for the first lantern-bearer to see the light (and considering the reaction time), he thinks he can calculate the speed of light.

Unfortunately, Galileo’s experimental distance of less than one mile was too small to see any difference, so he could only be sure that light travels at least 10 times faster than sound.

In the 1670s, Danish astronomer Ole Rémer used the solar eclipse of Jupiter's moon Io as a timer for the speed of light when he first made real measurements of speed. In a matter of months, when Io passed behind the giant gas planet, Lamer found that the solar eclipses were later than calculated, although within a few months they were closer to predictions.

He determined that it would take time for light to travel from Io to Earth. When Jupiter and Earth are the farthest apart, the solar eclipse lags the most and proceeds as planned when the distance is closer.

According to NASA, this provides Rémer with convincing evidence that light travels in space at a certain speed.

He concluded that it takes 10 to 11 minutes for light to travel from the sun to the earth, which is an overestimation because it actually takes 8 minutes and 19 seconds. But in the end, the scientists had a number—his calculations indicated a speed of 125,000 miles per second (200,000 kilometres per second).

In 1728, British physicist James Bradley's calculations were based on the changes in the apparent position of stars as the earth orbited the sun. He set the speed of light at 185,000 miles per second (301,000 kilometres per second), which is accurate to about 1%.

Two attempts in the mid-1800s brought the problem back to Earth. French physicist Hippolyte Fizeau set a beam of light on a rapidly rotating gear and set up a mirror 5 miles away to reflect it back to its source. By changing the speed of the wheels, Fizeau can calculate the time it takes for the light to come out of the hole, reach the adjacent mirror, and then return through the gap.

Leon Foucault, another French physicist, used rotating mirrors instead of wheels. These two independent methods are both within 1,000 miles per second of the speed of light measured today.

Albert Michelson, who was born in Prussia and grew up in the United States, tried to replicate Foucault's method in 1879 but used a longer distance and extremely high-quality mirrors and lenses. When Michelson re-measured, his result of 186,355 miles per second (299,910 km/s) was considered the most accurate measurement of the speed of light in 40 years.

An interesting footnote of Michelson's experiment is that he tried to detect the medium through which light passes, called the luminous ether. On the contrary, his experiments show that either does not exist.

Einstein and the Special Theory of Relativity

In 1905, Albert Einstein wrote his first paper on special relativity. In it, he determined that no matter how fast the observer moves, the light travels at the same speed. Even with the most accurate measurement methods, for observers who are stationary on the surface of the earth, the speed of light remains the same as the speed of light as it travels in a supersonic jet above the surface of the earth.

Similarly, even if the earth orbits the sun, and the sun itself is also orbiting the Milky Way, the Milky Way is a galaxy that travels through space, and the speed of light emitted from our sun will be the same, regardless of whether it is standing in or outside the Milky Way. . Einstein calculated that the speed of light does not change with time or place.

Although the speed of light is often referred to as the speed limit of the universe, the universe actually expands faster. According to astrophysicist Paul Sutter (Paul Sutter), the universe is expanding at a rate of approximately 68 kilometres per million per second, of which one million parsecs is 3.26 million light-years (more on this later). Therefore, the galaxy beyond 1 parsec seems to be moving away from the Milky Way at a speed of 68 km/s, while the galaxy beyond 2 parsecs is retreating at a speed of 136 km/s, and so on.

To understand general relativity, let us first start with gravity, which is the attraction that two objects exert on each other. Sir Isaac Newton quantified gravity, the principle, in the same book where he formulated the three laws of motion.

The gravitational force between two objects depends on the mass of each object and the distance between the two objects. Even if the centre of the earth pulls you toward it (to keep you firmly on the ground), your centre of gravity will be pulled back to the earth. But a larger body can hardly feel your pull, your mass is much smaller, and you will find yourself firmly rooted in the same power. However, Newton's law assumes that gravity is the innate force of an object.

Albert Einstein determined in his special theory of relativity that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light in a vacuum is the same no matter what speed the observer travels.

As a result, he discovered that space and time are intertwined into a single continuum called space-time. Events that occur at the same time for one observer may occur at different times for another observer.

What is a light-year?

The distance that light travels in a year is called a light-year. Light years are a measure of time and distance. It is not as difficult to understand as it seems. Think of it this way: It takes about 1 second for light to travel from the moon to our eyes, which means that the moon is about 1 light second away from us. It takes about 8 minutes for sunlight to reach our eyes, so the sun is about 8 light minutes away from us. The light from the nearest star system Alpha Centauri takes about 4.3 years to reach here, so the sun is about 8 light minutes away from us. The light from the nearest star system Alpha Centauri takes about 4.3 years to reach here, so it is said that the star system is 4.3 light-years away from us.

Stars and other objects outside the solar system are located anywhere from a few light-years to billions of light-years away. Therefore, when astronomers study an object located a light-year or far away, the object they see exists when the light leaves it, rather than what it looks like today when standing near its surface. In this sense, everything we see in the distant universe is history.

This principle allows astronomers to see what the universe looked like after the Big Bang that occurred about 13.8 billion years ago. Examining objects that are 10 billion light-years away, what we see is what they looked like 10 billion years ago, shortly after the beginning of the universe, not what they look like today.

Travelling at the speed of light is still not fast enough, which is why there is an urgent need for scientific and technological progress in this field of research. For example, light travels at 186,282 miles per second (299,792 kilometres per second) in a vacuum. In miles per hour, the propagation speed of light is approximately 670,616,629 miles per hour. Currently, the closest galaxy to the Milky Way is the Canis Major Dwarf Galaxy, approximately 236,000,000,000,000,000 kilometres (25,000 light-years) from the Sun.

Is the speed of light really constant?

Light travels in the form of waves and, like sound, can slow down according to the objects it passes through. In a vacuum, nothing can surpass light. However, if an area contains any material, even dust, the light will bend when it comes in contact with the particles, causing the speed to drop.

Light passing through the earth's atmosphere moves almost as fast as light in a vacuum, while light passing through diamonds slows to less than half that speed. Nevertheless, it still passes through the gem at a speed of more than 277 million miles per hour (nearly 124,000 km/s)-this is not a speed to ridicule.

Can we travel faster than light?

Science fiction likes to speculate about this, because the warping speed, just like the well-known superluminal travel, allows us to travel between stars within the time frame, otherwise time is impossible. Although it has not been proven that this is impossible, the practicality of travelling faster than light makes this idea very far-fetched.

According to Einstein's general theory of relativity, when an object moves faster, its mass increases, while its length shrinks. At the speed of light, such an object has infinite mass, and its length is 0-this is impossible. Therefore, the theory is that no object can reach the speed of light.

This does not prevent theorists from proposing creative and competing theories. Some people say that the idea of warping speed is not impossible. Maybe in the next few generations, people will jump between the stars as we travel between cities now. One proposal would involve a spacecraft that can fold a bubble of air around itself to exceed the speed of light. Sounds great, in theory.

What if we could travel at the speed of light?

If we put this in perspective, let us say that we are going to the Canis Major Dwarf Galaxy, then we need to travel 25,000 years at the speed of light to reach our destination. Even if we set foot on a new habitable planet, humans need many generations, and we need to set it to a constant speed that travels at the speed of light.

Maybe the Canis Major dwarf galaxy is out of our reach, so let's look at the nearest habitable planet in our own galaxy. On August 24, 2016, astronomers announced the discovery of a rocky planet in the habitable zone of Proxima Centauri, the nearest star to the Earth. Proxima b, the mass of this planet is 1.3 times that of the earth, and its revolution period is approximately 11.2 earth days.

Proxima b is about 24.93 trillion miles from our sun. This is a huge distance, but with the space shuttle and its enthusiasm to travel at the speed of light, this distance can be achieved in just 4.22 years

As elaborated, the frustration regarding space travel is currently limited, not only due to our slow advancements in technology and the scientific enterprise but also due to our own biological limitations. Travelling at the speed of light would add unbelievable strain to the human body, it just may not be physically possible.

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