How Does A Photon Accelerate To The Speed Of Light So Quickly?

Not only does a photon literally pop into existence out of sheer nothingness, but it also, as soon as it’s born, bolts away at 300 million meters per second. No, it doesn’t accelerate, it either doesn’t exist or it does, and if it does, it’s always racing at the speed of light, until it re-plunges into nothingness when it is absorbed.

electromegnetic wave

Photons don’t accelerate but are already traveling at 300 million meters per second when emitted. (Photo Credit : Pexels)

The Birth of a Photon

In a published ScienceABC article, the birth of a photon was explained as follows:

Electrons reside inside atoms in different energy levels. When we excite electrons by, for example, in the case of a bulb, heating the tungsten atoms, we elevate them to higher energy levels. However, nature seeks stability; electrons abhor climbing to higher levels. To achieve stability, electrons descend back to their original or even lower levels. When an electron makes this downward leap, the atom emits a photon. As millions and billions of electrons simultaneously descend to lower levels, the tungsten unleashes a massive torrent of photons.

So, basically, light or a photon is born when an electron transitions from a higher energy level to a lower energy level. However, the writer then asks:

If you were to peek inside an atom, would you find a hidden army of uncountable photons, ready to ambush on the electron’s command?

Well, no. The electron jumps to a lower energy level because it craves stability, and to achieve that, it must lose the energy that forced it to climb in the first place. As the article explains:

The universe, unlike in the case of heat energy, cannot squander this organized energy; it must put the extra energy to some use. The result is the instantaneous creation of a photon; it literally pops into existence out of sheer nothing, whatever that is.

Bohr atom model

How photons are created. (Photo Credit: Brighterorange / Wikimedia Commons)

The emitted photon just happens to travel or is already traveling at 300 million meters per second. It doesn’t accelerate from 0 m/s to 300 million m/s instantaneously. Some might attribute this eccentricity to a photon’s utter lack of mass, but this is not true. When a free neutron eventually decays to a proton, creating an electron and an anti-neutrino in the process, also out of sheer nothingness, by the way, the electron emitted is consistently observed to be already traveling at a fixed velocity. It doesn’t accelerate, despite possessing mass. So, what in the world is going on?

A better understanding is attained when we look at a photon – and an electron, for that matter – not as a rigid orb, not as a particle but as a wave, like a ripple in a pond.

Photon as a Wave

Elementary particles exhibit what is called the wave-particle duality: they exist both as waves and particles. Even the electron, the fundamental particle that constitutes you, exists as a wave. For this reason, even something as solid and large as you, or even the Statue of Liberty, is associated with a wavelength! Of course, it’s meager, in the range of a billionth of a billionth of a billionth of a billionth of a meter, but it exists, nonetheless.

Double slit experiment

Electrons behaving like waves as they, after being launched through two slits, draw an interference pattern, the very fingerprint of waves, on a screen ahead of them.

An elementary particle can be deemed as a disturbance or excitation in its corresponding wave field. So, while an electron is a disturbance or the excitation of the electron field, a photon is a disturbance or excitation of the electromagnetic field. It is a ripple in the electromagnetic pond. Now, bear in mind that ripples in a pond induced by a stone thrown in it do not accelerate; they don’t start out as motionless and gain velocity gradually. Instead, they radiate outwards the very instant the stone touches the water. The photon or the electromagnetic wave is already traveling at 300 million meters per second because that is how waves behave!

ripple on pond, water circle, duck, pond

(Photo Credit : Pixabay)

If you find this absurd, don’t worry, you’re not alone. The absurdity arises from the fact that we tend to mistake quantum mechanical particles for everyday objects of mass m, which when subjected to a force F, are accelerated by a m/s². Quantum mechanical particles, however, are anything but everyday objects; they are unlike anything we’ve yet encountered. Even the Nobel prize winner and one of the most brilliant minds of the last century, Richard Feynman, despite being a pioneer of Quantum Electrodynamics (QED), mused that: “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”


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About the Author:

Akash Peshin is an Electronic Engineer from the University of Mumbai, India and a science writer at ScienceABC. Enamored with science ever since discovering a picture book about Saturn at the age of 7, he believes that what fundamentally fuels this passion is his curiosity and appetite for wonder.

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