Science Facts

Why Does Light Travel So Fast? – Causes & Explanation

Light Speed

Light is so fast that it breaks our understanding of how speed works. How can it always be going the same speed faster than anything? Because of space-time. Maxwell had discovered electromagnetic waves and, when he calculated the speed of those waves, he found the speed of light is constant. It travels at 671 million miles per hour or 186,000 miles per second or 300,000 kilometers per second or 30 centimeters nanosecond!

The fastest humans in history were the Apollo 10 astronauts at 0.006% the speed of light (SOL). The fastest human-made object was the Juno space probe at 0.025% of the SOL. Andromeda is hurtling toward the Milky Way Galaxy at 0.04% of the SOL. All of these are tiny fractions of that 671 million mph. Physicists have only really gotten close to the speed of light with subatomic particles. The record for a proton in the Large Hadron Collider is 99.999 999% the speed of light.

What is light?

Light is an electromagnetic wave, a disturbance in electric and magnetic fields. Light can be broken up into different types, and the combination of all these packages is the electromagnetic spectrum. It also can be created by making an electron oscillate. This creates an oscillating magnetic field, and an oscillating electric field is an electromagnetic wave or light.

  • If there’s a charge, there’s an electric field.
  • If that charge is moving, there’s also a magnetic field.

That’s two separate fields: The electric field and the magnetic field.

Why does light travel so fast?

Light waves travel in straight lines through the air. These lines are called rays. If light travels in a straight line, what happens when it hits an object in its path? Well, light cannot bend to go around something. The light rays are either reflected, absorbed, or refracted. The reflected light helps us to see objects.

Light is just a small sliver of the electromagnetic spectrum going from gamma rays down to radio waves. James Clerk Maxwell was the genius who was able first to transcribe electromagnetic properties into physics equations.

Light speed equation: Energy equals mass times the speed of light squared.

E = mc², Where m = mass, c = speed of light, E = Total energy.

So, m = 1/c²

Theory of relativity: The closer you get to the speed of light, the more time slows down for an object in that reference frame. – Albert Einstein

If anything gets to the speed of light, time stops completely, and light through space-time would actually flip and run backward, which would break causality. This effect would proceed to cause the speed of light is the speed of causality.

Causality is the reason why they use the letter C to describe the speed of light in equations. The other prediction that supports a speed limit is that inertia increases as velocity approaches the speed of light. It means mass increases. So mass is a speed impediment, and nothing with mass can reach the speed of light. But if anything is massless, it can only go the speed of light because there’s no mass to impede the speed. For example, photons are massless particles. Particles must travel at the speed of light, and since they are traveling at the speed of light for them, time stands still.

There is another theory that’s a little controversial, but it’s starting to gain some ground. It says that quantum vacuum fluctuations hamper the speed of light. The space is not empty at all. It’s filled with virtual particles popping in and out of existence. Two different teams of researchers have calculated using electromagnetic particles in the quantum vacuum. So it could be that quantum fluctuations are slowing down the speed of light.

The matter is made out of energy. Therefore it would take infinite energy to make any matter. Time and space wouldn’t exist because all things communicate with each other instantly. It would always be forever here and now. But if the speed of light were slower, that might be even cooler because scientists would be able to see back to the Big Bang. The speed of light, of course, is just one of many constants in the universe like gravity, the specific charges, weights of the different fundamental particles.

Einstein’s theory of relativity describes space and time as a smooth fabric distorted or bent by massive objects. It’s been a spectacularly successful explanation of gravity and the large-scale behavior of the universe. Whereas quantum mechanics, another spectacularly successful model, describes the workings of atoms, subatomic particles, and some of the fundamental forces of nature. But scientists have never been able to reconcile the two.

Both relativity and quantum mechanics are equally fundamental in their regimes. So scientists want to find a theory of everything that describes the universe as a whole and the observations. The most successful aspects of quantum mechanics and relativity into one unified theory.

According to Einstein’s special theory of relativity, all forms of electromagnetic radiation from radio, infrared to visible, light to x-rays, and even gamma rays move at the same speed. So what would explain these differences in arrival times? Photons carry visible light. One simple idea is that maybe the photons were just emitted at different times. More interestingly, though, maybe something in the very fabric of space was causing the higher energy particle to slow down.

Several ideas that attempt to reconcile relativity and quantum mechanics suggest that space and time are not smooth and uniform. But are instead a seething froth when seen at the smallest scale. Like bubble wrap viewed from far away at human scales, the texture would be invisible. A low-energy long-wavelength photon is unaffected by space’s lumpiness, but the Frog hinders a high-energy short-wavelength photon. This makes it move more slowly than lower energy radiation. So it breaks Einstein’s law that all light particles must travel at the same speed! However, this explanation had little experimental proof either way until Fermi arrived.

Gamma-ray burst produced a large number of photons, one of which had enormous energy very short wavelengths. Those photons traveled seven billion years to reach us. And yet, the highest energy, the shortest wavelength photon, arrived within 900 milliseconds of the lower energy photons. That’s a little bit like racing to speedboats, one through water and the other to molasses, and having them arrive at the same time.

It just doesn’t happen because Fermi saw no delay in the arrival time of the two photons. It confirms that space and time are smooth and continuous, as Einstein had predicted. And it shuts the door on several theories of everything that had predicted that space and time might be foamy enough to interfere with light.

How does light travel so fast?

Light is an electromagnetic wave that transports its energy at a speed of 300,000 kilometers per second. This constant speed is how fast light travels in a vacuum. And it is referred to as the speed of light. When light encounters a medium such as air, water, or glass, it propagates through the substance at a net speed that is less than C. This slowing down of light through transparent objects is a form of energy transport that involves the absorption and re-emission of the light wave energy by the atoms of the substance.

Imagine that the electrons in an atom are attached to the nucleus by springs. The elasticity of these imaginary springs will determine how much the atom vibrates when acted upon by an incoming particle of light energy. When light impinges upon the atoms of the material, its energy is absorbed. This absorption of energy causes the electrons within the atoms to undergo subtle temporary vibrations.

This transient vibrational action is transmitted from one atom to another until it emerges from the other side of the material at the same light wave frequency and speed. While these vibrations are only short-lived within each atom, these actions delay wave energy transmission through the medium.

Thus while a light wave travels at a speed of 300,000 kilometers per second through a vacuum or the gaps between atoms, the absorption and re-emission process in different materials results in the net speed of the light wave being less than the speed of light.

  • In water, light travels at about 75% of its speed in a vacuum or 225,000 km/s.
  • In the glass, light travels at 67% of its speed in a vacuum.

So the light speed is 300 thousand times 0.67 or about 200,000 kilometers per second. Light travels very slowly through a diamond at about 41% of the light or 125,000 kilometers per second which is less than half the speed of light in a vacuum.

More Articles:


Chase, IP. “Apparent Superluminal Velocity of Galaxies.” Usenet Physics FAQ. University of California, Riverside. Retrieved 26 November 2009.
Harrison, ER (2003). Masks of the Universe. Cambridge University Press. p. 206. ISBN 978-0-521-77351-5.
Panofsky, WKH; Phillips, M (1962). Classical Electricity and Magnetism. Addison-Wesley. ISBN 978-0-201-05702-7.
Schaefer, BE (1999). “Severe limits on variations of the speed of light with frequency.”

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