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 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 gotten close to light speed 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. It creates an oscillating magnetic field, 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 travels incredibly fast because it is an electromagnetic wave that does not require a medium to propagate. Here are a few key factors that contribute to the speed of light:
Nature of Electromagnetic Waves: Light is an electromagnetic wave of oscillating electric and magnetic fields. These fields interact with each other, creating a self-propagating wave. The properties of electromagnetic waves, including light, are determined by fundamental physical constants in the universe.
Absence of Medium: Unlike sound waves or other mechanical waves that require a medium (such as air or water) to travel, light can propagate through a vacuum. This absence of a medium reduces the factors that can slow down or impede its speed.
Interaction with Electromagnetic Fields: Light interacts with electromagnetic fields in a way that allows it to travel at a constant speed. According to Maxwell’s equations, which describe the behavior of electromagnetic waves, the speed of light in a vacuum is a fundamental constant denoted by “c” and approximately equal to 299,792 kilometers per second (or about 186,282 miles per second).
Relation to Fundamental Constants: The speed of light in a vacuum is related to other fundamental constants in physics, such as the permeability and permittivity of free space. These constants set the speed at which electric and magnetic fields can influence each other and determine the speed of light.
Light waves travel in straight lines through the air. These lines are called rays. If light travels straight, what happens when it hits an object in its path? 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 a small sliver of the electromagnetic spectrum going from gamma rays to radio waves. James Clerk Maxwell was a genius who could 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 flip and run backward, breaking causality. This effect would cause the speed of light to be the speed of causality.
Causality is 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; since they are traveling at the speed of light, time stands still.
Another theory is a little controversial, but it’s gaining 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 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 could see back to the Big Bang. The speed of light is one of many constants in the universe, like gravity, the specific charges, and the 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 and its observations. The most successful aspects of quantum mechanics and relativity are in 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 emitted at different times. More interestingly, though, maybe something in the 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 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 bursts produced many photons, one of which had enormous energy and very short wavelengths. Those photons traveled seven billion years to reach us. Yet, the highest energy, the shortest wavelength photon, arrived within 900 milliseconds of the lower energy photons. That’s like racing to speedboats, one through water and the other to molasses, and having them arrive simultaneously.
It didn’t happen because Fermi saw no delay in the arrival time of the two photons. As Einstein had predicted, it confirms that space and time are smooth and continuous. Also, 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 energy at 300,000 kilometers per second. This constant speed is how fast light travels in a vacuum. 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 of 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 material’s atoms, its energy is absorbed. This energy absorption causes the atoms’ electrons 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.
- Light travels at 67% of its speed in a vacuum in the glass.
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, less than half the speed of light in a vacuum.
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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.”