Light, a fundamental element to our existence, is what deems practically everything we hold possible. It is a simple, fundamental thing, however, if you were to ask someone “What is light?”, they would struggle to answer. This article will delve into expanding your understanding of this majestic physical curiosity.

To begin, we need to understand why light is important. Light is what helps us see things, it falls onto them, reflects into our eyes, and makes us see. Darker objects absorb light, and lighter ones reflect it. But what exactly is light? And why?

Light is made of particles called photons. Well, fundamentally we cannot truly call it a particle as it does not share similar features such as any quantifiable mass or charge. Interestingly, however, it is an excitation in a quantum field. What that means, is that it is a wave comprising Electromagnetic Radiation. They are also known as the smallest possible quanta of EM radiation, which links light to quantum physics. That effectively means that a photon is the smallest possible packet of electromagnetic radiation.

Okay, so we know that light has energy, right? Solar Panels harvest that energy, and plants convert it into nutrition, but since they have no mass, how does that energy exist? Interestingly the energy comes from its momentum (p), not mass. But hang on a second, that makes no sense either! P = mv! We need mass again!

A massless particle can indeed have momentum, to find it we use the DeBroglie equation:

p = h/λ

This equation uses Planck’s Constant to derive the momentum, dividing it by the photon’s wavelength. We then calculate the energy with the equation:

E = pc

Now we have the photon’s energy. Einstein’s theory of special relativity consequently tells us that photons travel at the speed of light, which is  299 792 458 m/s. Light is known to be the fastest thing in the universe.

 Measuring it is highly impractical because if you set up a standard experiment, (time a photon from point a to b), most of our equipment is not accurate enough to measure something of that velocity. Generally, we would say that the speed of light is 300 000 000 meters per second or 3.0×10^8 m/s

Photons throw a wrench in the works of Einstein’s renowned E = mc^2, considering that photons disobey it. This equation breaks down for any object travelling at the speed of light, let us see why. The equation can be rearranged as follows:

E= mc2/ sqrt(1-{v2/c2})

Now what we observe with this is that as the velocity approaches c, our value for E continually increases, until we reach it. At that point, our denominator becomes 0. That results in an undefined energy, or an infinitely large mass, neither of which makes sense.

This equation is different from the common one, however, they still mean the same thing. It is simply multiplied by what we call the “Lorentz Gamma”, and all this does is enable your calculations for objects moving in your frame of reference. E = mc^2 only works for objects at rest. Multiplying the rest mass by the Lorentz Gamma will give you the object’s relativistic mass. Light moves through the Higgs Field without interacting, ergo moving at such speeds. Photons don’t experience time either.

Another common misinterpretation of E = mc^2 suggests that energy is the same as mass, and that is untrue. The truth is that mass is simply what we call “Fluctuations in the Quantum, or Higgs field”. That is what gives us energy, and since objects in motion have kinetic energy, their fluctuations increase and hence show an increased mass. That means a hot teacup has more mass than a cooler one! We must bear in mind that in general circumstances like the teacup, changes are far too insignificant for us to observe, we must approach c for our changes to be noticeable.

It is also hazardous to not mention that we cannot say E > C without comparing them in the same units, much like potatoes cannot be compared to onions. We use relativistic units, where c = 1. This aids us in comparing physical quantities objectively.