Light — What is It?
The Ultimate Mystery Of Cosmos
There has been always a mystery concerning the nature of light right from ancient times till now. Light is a particle. Light even is a wave. Many world renowned scientists tried to understand light, and each one of them came forward with a new explanation. Plato thought that we see by shooting light rays from our eyes. Christiaan Huygens started advocating his theory that light is a wave or wavefront. Albert Einstein predicted light is a particle — photon. Water molecules are broken into hydrogen ions, electrons, and oxygen atoms — splitting by light — process known as photolysis.
Light exerts physical pressure on objects in its path, a phenomenon which can explained by Maxwell’s equations, but can be more easily explained by the particle nature of light — photons strike and transfer their momentum.
Do we understand light? Let’s reframe the question — Do we actually understand what in reality is light? It’s the basic thing that concerns our existence. It affects us in profound ways. Nothing can exist without light. Plants, animals, humans, all living beings need light to thrive. Even non-living things like earth needs light too.
Let’s dive deep into the nature of light..
History of light
Aristotle — The essence of light is white light. Colors are made up of a mixture of lightness and darkness.”
Newton — In a 1672 publication, Newton claimed that “light is a mixture of diverse hues having variable refractivity” rather than “the pure white (sunlight)” provided by Aristotle, and demonstrating his theory in the famous prism experiment.
Christiaan Huygens released a paper on light in 1690 that supported his theory that light is a wave or wavefront.
Thomas Young — in 1807, he demonstrated that when light from a point light source is shone through two pinholes, interference fringes can be seen on a screen at a suitable distance — Young’s Experiment, proving his idea that light travels in waves.
James Clerk Maxwell — The presence of electromagnetic waves, as well as the fact that they propagate at the same speed as light and as horizontal waves, were predicted by James Clerk Maxwell.
Albert Einstein — was awarded the Nobel Prize for his contribution to the field of photoelectric effect. He claimed that all electromagnetic energy has been quantized. Einstein believed that light travelled in packets of energy rather than waves. Photons were later given to these energy packets. When light is shone on certain materials, electrons are emitted. This is known as the photoelectric effect. The photoelectric effect is the same mechanism that modern solar cells use.
What is light?
In simple words, light is a form of energy that covers a distance. When light travels between two places, energy makes a journey between those two points. This energy travels in the form of waves.
What is a photon?
A photon is a dimensionless, massless, stable, and chargeless quantum unit of space (particle) with an oscillating electromagnetic field (waves) that moves with constant speed c, and finite energy, E. Photon exhibits the properties of both waves and particles. Photon’s energy is directly proportional to the frequency (f) or inversely proportional to the wavelength (λ) of the electromagnetic wave (E=hf or E=hc/λ, where h is the Planck’s constant).
Photons (electromagnetic waves) are produced when charged particles accelerate, (an electron moving back and forth would generate photons) or when certain particles interact with each other (for instance when an electron and a positron undergo collision they annihilate and photons are produced as an end result). Once created, a photon moves indefinitely with speed c until it interacts with another quantum particle. Photons can’t be split but are easily created and destroyed.
How light emanates?
This is the most interesting part of this article. Your perception will undergo change. Light is the end result and atoms are responsible for creating light in a process:
They start off in their “stable state” or “ground state” with electrons in their normal places. When these atoms absorb energy, one or more electrons are pushed into higher energy levels. This term in physics is referred to as — the atom is “excited.” Now we know anything remains excited for a limited span of time, so is the case with atoms. The excited atom is unstable and instantly tries to get back to its stable state or ground state. So in the process, it gives off the excess energy it originally gained as a photon of energy : a packet of light. So, basically, excitement is light.
The simple example is putting an iron bar in fire. With time, the bar would heat up so much that it’ll start glowing red hot. It’s because you’re exciting its atoms. In turn, the electrons jump to higher energy levels and thus the atoms become unstable. As the electrons return to lower levels, they’re giving off their energy as photons of red light — and that’s why the bar seems to glow red. That’s how fire gives off light.
Electromagnetic spectrum
Light and Matter are intermingled with each other in numerous ways. The interaction of light and matter affects the appearance of everything we perceive around us. Light interacts with matter in ways such as emission and absorption. The photoelectric effect is an example of how matter absorbs light. How matter interacts with the energy from light depends on what kind of light it is and there is a whole spectrum of light called the Electromagnetic Spectrum. Ordinary light looks white, but when shone through a prism (wedge) of glass, one can clearly see that it’s really made from a spectrum of colors.
- Each photon contains a certain amount of energy. The different types of radiation are defined by the amount of energy found in the photons. Radio waves have photons with low energies, microwave photons have a little more energy than radio waves, infrared photons have still more, then visible, ultraviolet, X-rays, and, the most energetic of all, gamma-rays.
Ultraviolet — emitted by Sun (hot objects in space emit ultraviolet). Though ultraviolet wavelengths are invisible to the human eye, some insects, like bumblebees, can see them.
Visible — Our eyes detect them. They are emitted by stars. About 44% of the Sun’s electromagnetic radiation that reaches the ground is in the range of visible light.
X-ray — hot gases in our universe emit them. GOES satellites use an X-ray Imager (SXI) to photograph and learn about the sun. The photons collected in space by X-ray telescopes reveal the hot spots in the Universe — regions where particles have been energized or raised to high temperatures by gigantic explosions or intense gravitational fields. The accretion disks around neutron stars and black holes emit X-rays, helping studies of such phenomena. X-rays are also emitted by stellar corona and are strongly emitted by certain types of nebulae.
Radio waves — are emitted by stars and gases in space.
Micro waves — are used to study the structure of nearby galaxies. Microwaves are good for transmitting information from one place to another because their energy can pass through haze, light, rain, snow, clouds, and even smoke.
Some of the microwave experiments have been done with objects in the solar system, such as determining the distance to the Moon or mapping the surface of Venus.
Gamma-ray/Cosmic ray — Cosmic rays are high-energy protons and atomic nuclei that move through space at nearly the speed of light. And when cosmic rays collide with other particles in interstellar space, they result in the production of gamma-rays. Natural sources of gamma rays include decays in the nuclei of atoms and lightning strikes, which can occur here on Earth along with other planets. Gamma-ray beams emanates from pulsars within the Milky Way galaxy.
Infrared — Night vision goggles work on the principle of the infrared light emitted by objects with heat. In space, infrared light helps us map the dust between stars. GOES(Geostationary Operational Environmental Satellites) satellites use infrared technology to track and study hurricanes. Infrared is beneficial to detect protostars before they begin to emit visible light.
(Note: In vaccum all travel at 3x10⁸ m/s.)
Difference between light and electricity
Starting with light, it is a wave and a particle photon. A photon is a very special particle and is distinct from other matter in that it has no mass as it exists outside of the Higgs field that permeates all of space. As for electricity, it is just a stream of electrons moving along a wire, filament, etc. These streams can vary in characterizations described and measured by their voltage (potential energy) and current (intensity of stream). Electrons have mass.
The second difference between light and electricity is in terms of speed. The electron has a mass so it cannot travel at the same speed as light. Light is the fastest thing in the Universe simply because its photons are massless.
You might’ve a question in the back of your mind, that the mass of an electron is negligible. But that’s not the case. Although an electron’s mass is negligible, yet it’s much larger than a photon when talking in terms of quantum physics. Nothing with mass could travel at the speed of light. In fact, the neutrino is much lighter than an electron. Despite having negligible mass, even the neutrino can’t travel at the speed of light. Forget about the electron then! An electron is roughly 5,00,000 times more massive than a neutrino.
Why can’t anything travel at the speed of light?
Only massless particles, including photons, which make up light, can travel at that speed. It’s almost impossible to accelerate any object in material form at the speed of light, the reason being that it’d take an infinite amount of energy to do so. The faster an object travels, the more massive it becomes. So an accelerating object gains mass and ultimately becomes heavier, it’ll need more and more energy to increase its speed. Practically, it’d take infinite energy to make an object reach the speed of light.
Can anything travel faster than light?
This question has been a hot topic in the field of physics. Scientists tried to solve this question by providing certain explanations regarding various particles like tachyons, and technologies like warp drive. But these are all hypothetical concepts. We discussed the case of neutrino in the article, and now we’re going to study the failed attempt of some scientists who claimed neutrinos travel at the speed of light.
OPERA and ICARUS Experiments
In 2011, there was news all over that scientists have found a particle that can travel faster than the speed of light. The axiom nothing travels faster than light was initially formulated by Albert Einstein and is a cornerstone of our modern physics. The experiment OPERA(Oscillation Project with Emulsion-tRacking Apparatus) showed that muon neutrinos travel faster than light, approximately 60 nanoseconds faster than predicted if they had travelled at light speed. Scientists were shocked to see laws of physics breaking in front of their eyes. But there was some fault which was dealt with by using another experiment called ICARUS(Imaging Cosmic And Rare Underground Signals) —which is a physics experiment aimed at studying neutrinos. And this experiment showed that neutrinos weren’t faster than the speed of light. They were just equivalent to the speed of light. ICARUS showed that the original OPERA result was mistaken.
So till now, there is no particle or object that can travel faster than the speed of light. Once we found that sort of an object we’d have to reformulate our laws of physics.
But there is an exception to the above rule because space is the only thing so far that can travel faster than the speed of light. The event of the Big Bang took place approximately 14 billion years ago. And using the Big Bang event as the reference, we can calculate the universe to expand 14 billion light-years in any possible direction. But the results are different! In fact, our universe expanded much faster than the speed of light as the diameter of our universe is expected to be roughly 93 billion light-years — which is more than the calculated diameter — which itself proves to be more than the speed of light — it is practical evidence that an object can travel faster than the speed of light.
Creating matter out of light
This is the weirdest thing you’d ever imagine, but believe me, in actuality we can create matter out of light. I know you might be thinking what type of question is this, but believe me, the explanation will satiate you. Back in 1934, physicists Gregory Breit and John Wheeler predicted that collisions of photons could create matter and antimatter, and suggested doing so by accelerating heavy ions.
A Recent Research
The study demonstrates a long-predicted process for generating matter directly from light
The Relativistic Heavy Ion Collider (RHIC is a tool for studying the fundamental properties of matter)’ showed that the pairs of electrons and positrons — particles of matter and antimatter — these can be created by colliding high energetic photons. As per Einstein’s equation, E=mc², energy, and matter (or mass) are interchangeable. It’s quite normal for nuclear power plants to convert matter into energy. Now scientists have reversed the processs — they’ve converted light energy directly into the matter.
Two gold ions (Au) moving in opposite directions close to the speed of light (v≈c) are each circumscribed by a cloud of real photons (γ). When these photons undergo collisions, they create a matter-antimatter pair: an electron (e-) and positron (e+).
Studying universe using light
Light and Black holes
Black holes are gigantic structures that are enemies of light. Black holes are regions in space-time where gravity’s pull is so powerful that not even light can escape. The black hole coronas, are the source of the X-ray light that becomes radiated from the vicinity of these gigantic objects. Bright flares of X-ray light are emitted by gas that falls into black holes from their accretion disks(the black hole can tear the star apart as it pulls it toward itself. As the attracted matter continuously accelerates and heats up, in turn, it emits x-rays that radiate into space), the disks of dust and gas that surround and feed these objects.
Gravitational lensing
It is due to the phenomenon known as gravitational lensing that we were able to find the clues for the mysterious dark matter. Gravitational lensing magnifies distant sources that are otherwise blocked by huge galaxies in front of it.
A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels toward the observer. This effect is known as gravitational lensing. It occurs when a large amount of matter(like a star, galaxy, or a cluster of galaxies) creates a strong field around it. In turn, gravity bends light coming from distant galaxies.
Redshifting and blueshifting
In physics, a redshift is an increase in the wavelength, and the corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a negative redshift, or blueshift.
Red light has the lowest frequency of all colours. That’s the reason if a galaxy is moving away from us, the colours of all of its spectral lines would be redshifted. The higher the speed, the greater would be its redshift. In case the galaxy is moving toward us, its colours will be blueshifted.
Out of all the unexplained mysteries, the one that concerns light is the most important. Light is the only medium that lets us explore dimensions that are beyond our reach. We can solve the puzzles of the events located billions of light-years by studying the radiations(light). With the help of light we were able to predict the past, the event of the Big Bang with precision. The faint cosmic background radiation filling all space, is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe. When light starts disappearing and bending the beams around in a direction detectable by specialized telescopes, we predict the possibility of blackholes. Redshifting and blueshifting lets us predict whether gigantic objects in the universe are moving away or approaching near. We can’t underestimate the power of light, it’s only light that has ushered human evolution …..
