Category: Science

In the 1960s, there was a heated debate going on between two opposing cosmological theories, which tried to explain the origin of the universe – the Big Bang theory and the Steady State theory. But before either of these theories existed, people believed in the static universe theory.

The static universe theory

They believed that the universe was neither expanding nor contracting. It had always existed the same way forever and was infinite in space and time. But Isaac Newton’s discovery of gravity in the seventeenth century challenged this belief.

Isaac Newton’s law of gravitation

Newton discovered that every body in this universe attracts every other body in the universe. The force with which two bodies attract each other is proportional to the product of their masses and inversely proportional to the square of the distance between them. 

To understand the impact of Newton’s theory on the static model of the universe, consider doing an experiment. Take a stone and throw it up towards the sky. Initially, the stone is at rest on your hand. Hence, the speed with which the stone is pulled down (negative velocity) due to gravitational acceleration is zero. So, at the moment you throw the stone, the speed with which you throw the stone, directed upwards (positive velocity), will be greater than the speed with which gravity pulls it, directed downwards. Therefore, the stone goes upwards.

But as the stone goes up, the velocity of the stone decreases due to the gravitational acceleration pulling it down. At one point in time, the stone stands still in the sky. At this instant, the force of gravity would have completely canceled out the force of the throw. After this instant, the stone starts moving downwards, with its speed increasing every second.

Thus, at any point, the stone is either moving up or moving down. It does not stay static, except for only one instant. But even this one instant is not a stable state, meaning that the stone cannot stay there for a long time. 

Now, if you throw the stone up with a greater force, it goes higher up but eventually comes down. If you throw the stone with an extremely large force (more than 11km/s), it will keep going up. It will eventually escape the earth’s atmosphere and never return.

If you extend this concept to astronomical bodies, then one can understand that any two objects will either constantly move towards each other or away from each other. They cannot stay at a constant distance from each other indefinitely. Thus, Newton’s law of gravity challenged the notion of a static universe significantly.

Newton himself was also aware of the consequences of his theory. But he believed that God had placed the astronomical bodies like stars in perfect numbers and distances from each other. So, the gravitational forces exerted on each astronomical body by all the other astronomical bodies are canceled out. Hence, even though they were unstable, the stars remained in balance, just like a needle balanced on a single point. Thus, the entire universe managed to remain static for an infinite time.

Newton’s law of gravitation was a huge step for mankind. But it did have its flaws. For starters, even Newton didn’t understand how gravity could act without a medium. Moreover, there were some astronomical occurrences that his law of gravitation couldn’t explain. Yet, despite its flaws, it was widely accepted for a very long time.

But two hundred years later, a physicist called Albert Einstein disproved Newton’s law of gravitation and postulated his own theory explaining gravity called the theory of general relativity.

Albert Einstein’s theory of general relativity

Albert Einstein postulated that space, time, and mass were related. So, any object with mass warps, bends, or stretches the space and time around it. This warping action is the cause of all gravity. You would understand this if you have seen the movie Interstellar, where time runs faster when the hero nears a black hole. Because of its extreme mass, the black hole accelerates time when passing near it.

To understand this phenomenon, imagine two people standing opposite each other, each holding one of the two opposite edges of a big sheet. If these two people move away from each other, then the sheet will get outstretched up until the point when the entire sheet lies on a single plane. Now, if a third person drops a football in the middle of the sheet, you can imagine what would happen. The sheet would be pulled downwards, with the amount of pull greater in the middle and decreasing towards the edges. The heavier the football, the higher the force with which it pulls the sheet down. Now, if you drop a small object, maybe a tennis ball, on any location on the sheet, it would eventually move towards the middle, where the football is.

Now think of the sheet as the spacetime and the football as a star. Just like in the experiment above, the star would bend/warp the spacetime around it due to its mass. The heavier the star, the greater its bending/warping will be. And any other object in the vicinity will be pulled towards it, thus creating the effect of gravity. 

Source – www.theperihelioneffect.com​

At this point, you may be wondering what has Einstein’s theory of general relativity got to do with the origin of the universe. Actually, it has got a lot to do with the universe and its origin.

According to Einstein’s theory of general relativity, a massive object stretches the spacetime around it. And when light travels through this spacetime, it ends up getting stretched too. As it travels through this stretched spacetime more and more, it gets stretched more and more. As a result, its wavelength increases, and the light becomes red in color since red has the longest wavelength. This phenomenon is called cosmological redshift.

The big bang theory

Einstein’s theory of general relativity made a huge impact on the scientific community. It changed many people’s understanding of the universe. One of those people was a Belgian priest called Georges Lemaître. Since he was a kid, Lemaître had had an interest in finding out how things around him worked.

In 1915, when Einstein published his theory of general relativity, impressed by it, Lemaître started studying it. In 1927, he deduced that if Einstein’s theory was true, then the universe was not static; it was expanding in all directions. But he did not have any data to prove this. So, not many people believed in his theory. Even Einstein, who was a firm believer of the static universe, did not endorse Lemaître’s interpretation of his theory. 

Edwin Hubble

Until 1919, the common perception was that our milky way galaxy was the only galaxy in the entire universe. But in 1919, while investigating the night sky using the Hooker telescope, the largest telescope at that time, Edwin Hubble found that several dust clouds, which were previously considered part of the milky way galaxy, were actually much, much farther away. Hence, he argued that they couldn’t be part of the milky way galaxy. They could only be entire galaxies, which were very far away. Thus, Hubble showed that the universe was made up of many galaxies, not just our own galaxy.

In 1929, unaware that Lemaître had proposed a theory of an expanding universe based on Einstein’s theory of general relativity, Hubble made a remarkable discovery. At that time, Hubble was investigating the cosmological redshift from various galaxies. He discovered that the amount of redshift in the light from a galaxy was proportional to its distance from earth. This indicated that other galaxies were moving away from us. Moreover, the speed with which a galaxy was moving away from us was proportional to its distance from earth, i.e., the farther a galaxy was, the faster it was moving away. These findings led him to take the only possible logical deduction – The universe was expanding. Even though this is the same conclusion Lemaître had arrived at two years earlier, Hubble was credited for discovering that the universe was expanding.

The Hypothesis of the Primeval atom

But Lemaître used Hubble’s findings to propose something that faced strict opposition initially. He proposed that since the universe was expanding, it would have been smaller in the past. So, if we went back in time, long, long ago, the universe would have been an extremely dense but tiny object. Lemaître called this tiny object the Primeval atom. As it was extremely dense, at some point, the Primeval atom would have exploded suddenly. This explosion created space, time, and expansion, which continues to this day.

Lemaître’s theory had a profound impact on the way people viewed the universe. Moreover, it gave rise to philosophical questions, like, if the universe did begin with an explosion, what created the explosion in the first place. 

Today, we call Lemaître’s theory the big bang theory. However, Lemaître did not call his theory the big bang theory. He called it the “hypothesis of the primeval atom.” The term ‘Big Bang’ was actually coined by Fred Hoyle. (Fred Hoyle is the scientist under whose supervision Stephen Hawking wanted to do his Ph.D. degree. But Hoyle declined Hawking because he already had enough students working under him.)

​An illustration of how the Big Bang might have happened – By NASA/WMAP Science Team – Original version: NASA; modified by Cherkash, Public Domain, Link

Fred Hoyle

Fred Hoyle was one of those people who vehemently opposed the big bang theory. Indeed, he coined the term ‘Big Bang’ as a way to mock Lemaître’s theory. During an interview for BBC Radio in 1949, he said,

These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past.

But the term he coined became famous in the 1970s and has stayed so since then.

But it is not hard to understand why many people opposed the Big Bang theory at that time. Most people at that time believed in a static universe. So, Lemaître’s proposal that the universe had a beginning was simply not acceptable for them. Moreover, there was no evidence to back his theory. But one of the major reasons why people were not willing to believe his theory was due to his religious background.

By claiming that the universe began from the primeval atom, Lemaître was indicating that something had somehow created the primeval atom in the first place, thus opening the possibility of the existence of a greater being. In 1952, when Pope Pious XII proclaimed that Lemaître’s theory confirmed the existence of the transcendental creator, it cemented many people’s beliefs that Lemaître’s religious beliefs were the motivation for his theory, thus reducing the credibility of this theory. Even though Lemaître affirmed that his religious background had nothing to do with his scientific theory, nobody believed him.

So, it is no wonder that for Fred Hoyle, who was an ardent atheist, Leimatre’s theory appeared unbelievable. Fred Hoyle instead believed in the steady-state model of the universe, which he and two other scientists had developed.

The steady-state theory

According to the steady-state theory, changes take place in the universe, but only on a smaller scale. When taken as a whole, however, the universe had always been the same at all times. To put it simply, the steady-state theory states that the universe doesn’t change over time.

But Hubble showed that the universe was expanding. The steady-state theory got around this by stating that as old galaxies disappear (either due to their increasing distance from earth or because they disintegrate into neutron stars and black holes) new stars and galaxies are formed, which take up their place. Thus, on a smaller scale, the universe might appear to be expanding, but on a larger scale, the universe maintains a constant density and constant average distance between galaxies.

So, the universe had always been the same at all times in the past. It will also continue to do so in the future. Therefore, unlike the big bang theory, which states that a creation event occurred at some time in the past, the steady-state theory states that nothing of that sort ever happened because the universe had always been the same. This is a particularly interesting aspect of the steady-state theory that appealed to believers of the static universe theory and atheists like Fred Hoyle.

The steady-state theory enjoyed great support until the 1960s. However, in the 1960s, Quasars and Cosmic Microwave Background radiation were discovered.

Quasars

Quasars are incredibly bright objects in the universe. They could be a thousand times brighter than the milky way galaxy, and yet, they are very small compared to a galaxy. But Quasars are only found billions of light-years away from earth and not anywhere nearby. This means that they existed only billions of years ago, not in the present. The fact that Quasars were the birthplace of galaxies and the fact that they existed billions of years ago provided strong evidence that the universe had changed over time. This went against the core belief of steady-state theory, which believed that the universe stayed the same forever.

Two pairs of quasars that existed 10 billion years ago (taken by Hubble Space Telescope) – By ESA/Hubble, CC BY 4.0, Link

Cosmic Microwave Background

In 1965, two researchers working at Bell Laboratories, while trying to build a radio receiver, stumbled upon Cosmic Microwave Background (CMB), a noise that came uniformly from all directions in space. Big bang theory explains CMB as the radiation that was emitted when the universe was still young. CMB radiation was emitted by the universe almost 400,000 years after the big bang happened. The universe at that time was starting to cool down from a temperature of 273 million degrees. 

Since then, the universe has been expanding and cooling down. So, the CMB has also cooled down to a temperature of -273.15°C today. The big bang theory explained CMB as relic radiation from the time the universe was young. In other words, CMB represents the heat/radiation left from the big bang. But since no astronomical body in the present emits such radiation, steady-state theory, which believes that the universe has remained the same forever, was not able to explain the presence of CMB.

The Cosmic Microwave Background of the night sky as seen from the Planck satellite – By European Space Agency – https://www.esa.int/ESA_Multimedia/Images/2013/03/Planck_CMB, CC BY-SA 4.0, Link

Thus, in the 1960s, due to the discovery of Quasars and CMB, the steady-state theory was disproved. Since then, the big bang theory has been widely accepted as the theory explaining the origin of the universe.

Stephen Hawking is one of the most brilliant minds of the 21st century. He is known throughout the world for his disability, his scientific brilliance, and even for his interest in acting. But Stephen Hawking also had a weird habit that most people may not be aware of. He was a fan of making wagers. Throughout his life, he made several wagers with other scientific minds over pressing scientific questions. In this blog post, I discuss some of Stephen Hawking’s bets.

Stephen Hawking’s bets

In the early 1970s, when people’s interest in black holes spiked, Hawking made a rather controversial scientific wager.

1. Cygnus X-1

At that time, the most brilliant minds in science thought that Cygnus X-1, a strong source of X-rays, was a black hole. By observing the X-rays coming from Cygnus X-1, they suspected that Cygnus X-1 and a nearby supergiant star were orbiting their common center of mass. They deducted that the material sucked in from the star might have created a hot accretion disk around Cygnus X-1, which emitted the X-rays. They inferred its minimum mass to be at least six times that of the sun. So, theoretically, the chance of Cygnus X-1 being a black hole was pretty high.

But Stephen Hawking made a bet against another theoretical physicist, Kip Thorne, that Cygnus X-1 was not a black hole. The prize was a magazine subscription. In his book ‘The Brief History of Time,’ Stephen Hawking explains that the bet was a form of insurance policy for him. He says,

I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would bring me 4 years of the magazine Private Eye.

But in 1990, more than a decade later, Stephen Hawking conceded the bet, even though scientists were still not sure if Cygnus X-1 was actually a black hole.

2. Naked Singularity

But losing that bet did not stop Stephen Hawking from betting again. Just one year later, he bet against Kip Thorne and his colleague John Preskill that a naked singularity cannot exist

A singularity is a point where the variable or variables in a mathematical function become infinite. When that happens, the behavior of the function, which is normally predictable, becomes upredictable or undefined. The functions in question here are Einstein’s Field equations which represent his Theory of General Relativity. And a singularity in these equations means infinite mass and infinite curvature, i.e., in simple terms, infinite gravity.

Such a singularity exists theoretically in every black hole. Stephen Hawking bet that such a singularity can exist only behind the event horizon of a black hole. But Thorne and Preskill bet that it was possible for a singularity to exist even without an event horizon. (The event horizon is the boundary of a black hole, beyond which nothing, not even light, can escape from the black hole).

In 1997, Hawking conceded that bet too and reframed it as “a naked singularity cannot form under generic conditions.” This bet has still not been resolved.​

3. The Blackhole information paradox

In 1974, Hawking proposed that black holes can emit radiation. Since this radiation is in the form of heat and independent of what fell into the black hole previously, it gave rise to the black hole information paradox.

But before we can look at what the Blackhole information paradox is, we have to understand what information is.

What is information?

In Physics, one thing is very important, and that thing is determinism, i.e., when one knows the parameters of a system, it must be possible to predict how the system behaved in the past and how it will behave in the future. Regardless of whether it is a single particle, a big chemical reaction, or the whole universe, once we know its properties, physics lets us predict its past and future states.

So, if we know everything that is to be known about a system or an object, like the number of particles it has, their positions, velocities, spins, electric charges, etc., then we can predict these particles’ behavior in the past and future. Hence, the raw information in a system (whatever we can know about it) is always preserved across time. It never gets created or destroyed; it only gets rearranged.

But this is not so easy when it comes to black holes, at least not after Hawking discovered Hawking’s radiation.

A black hole’s gravitational field is so strong that nothing can escape from it once inside its event horizon. So, regardless of whatever you throw inside the black hole, that object disappears. For example, if you throw a book inside a black hole, it disappears. We know what happens afterward, but we can guess that it will be stripped apart. But the book had a lot of information before being thrown into the black hole, like the number of particles it was made of, its chemical composition, etc., besides the obvious human-readable content it contained. So, what happens when the book is thrown into a black hole? If it gets stripped apart into its constituent particle, what happens to the information it earlier contained?

Earlier I told you that when you throw something into a black hole, it disappears.

Well…

It’s not completely true.

If you are an observer outside the event horizon of the black hole, and if you throw the book into the event horizon, the book just passes through it. You don’t know what happens afterward. Maybe, the information the book contained is somehow preserved in the black hole.

But in 1974, Hawking proposed that a black hole can emit radiation in the form of heat. This in itself is not the problem. The real problem is that, because of the radiation it emits, the black hole shrinks with time and eventually disappears. But what happened to the information about all the objects that the black hole had sucked in?

What happened to the information contained in the light, asteroids, planets, and stars it sucked in?

What happened to the information contained in the book you threw in?

Would the information somehow leak through Hawking’s radiation? Hawking tells us that it’s not the case. So, if the information about the book you threw into the black hole does not come out through Hawking’s radiation, and the black hole disappears, what happened to the information? Where did it go? This indeterminism about the information inside a black hole created the paradox – The black hole information paradox.

The wager about the Blackhole information paradox

In 1997, Stephen Hawking made a wager once again with Kip Thorne and John Preskill regarding the Blackhole information paradox.

This time, Hawking and Thorne were on the same side. According to the Theory of General relativity, the gravitational field of a black hole is so strong that not even light can escape from it. That is, the escape velocity of a black hole (The velocity an object needs to escape from the black hole’s gravitational pull and travel to outer space) is more than the speed of light. And since nothing can travel faster than the speed of light, nothing can escape a black hole. So, the information inside cannot leak from a black hole through Hawking’s radiation. Hence, the information carried by Hawking’s radiation must be new information and not from inside the black hole. Therefore, Hawking and Thorne bet that Quantum Physics needs to be rewritten.

On the other hand, Preskill bet that the Theory of General Relativity must be modified because Quantum Mechanics says that the information contained within the radiation emitted from black holes must somehow relate to the information that fell into the black hole at an earlier time.

In 2003, he conceded this bet as well.​

4. Higgs Boson

In the early 2000s, Hawking bet against a physicist called Gordon Kane that the Higgs Boson could never be found. But the particle was eventually found in 2012. Hawking, who had obviously lost the bet, hailed Peter Higgs, the person who had theorized the existence of Higgs Boson almost 48 years earlier, and told that he should be given a Nobel prize.

The visible spectrum we see is a part of the electromagnetic waves. Electromagnetic waves are oscillating electric and magnetic fields.

Depending on their wavelengths, the frequencies and energies of the electromagnetic waves vary. Some of them are even harmful for life.

This blog post explains some basic phenomena that the visible spectrum causes. It also answers some ‘What-If’ questions we all might have had at some point in time.

The Visible spectrum

The light we see is known as visible light. It has wavelengths ranging from 740 nm to 380 nm approximately and is divided into 7 regions – VIBGYOR.

Why can we see only visible light?

Visible light played a great role in our evolution, helping us recognize the prey and enemy correctly. Our atmosphere blocks most of the electromagnetic waves other than visible light and radio waves (look at the picture below).

Atmospheric opacity (absorption) vs Wavelength of EM wavesPicture credits

Only visible light can penetrate water and propagate through it for a certain distance, the earliest life forms probably evolved the ability to see visible light, to survive underwater. Since life moved from water to land, we probably got the ability from these organisms.

The retinas in our eyes have three primary color receptors – Red, Green, and Blue. Hence, we are more sensitive and responsive to these three colors than other colors. With these three receptors, we can see a million shades of color.

But wait…

What would happen if we could see other electromagnetic waves?

Read on, to find out.

What would happen if you could see only radio waves?

If our eyes could see only radio waves, we wouldn’t see small objects because they have long wavelengths and pass through small objects but not reflected by them. Since we only see the color reflected by an object, smaller objects would have become invisible to us. 

As you can see in the picture below, radio waves pass through the human body completely. So, if we were to see only radio waves, we wouldn’t be able to see fellow human beings, because the human body cannot reflect radio waves.

Different EM waves passing through body. Arrow depicts the depth to which they each wave penetrates through body. Picture credits

What would happen if you could see only microwaves?

Since microwaves are emitted by dustclouds that give birth to stars, if you look up at the sky, it would be too bright for you, because of the light from Big Bang coming at us from all angles.

Objects that emit microwaves, like microwave ovens, GPS, Wi-Fi, traffic speed cameras, etc would also appear too bright for us. On the other hand, we may not be able to see other humans because microwaves pass through people without being reflected.

What would happen if you could only see infrared?

If you could see only infrared, you would only be able to see temperatures, not colors. Most of the features of objects will be missing, and for example, you may not be able to see a person’s eyes, nose, mouth, etc. Hotter objects would look brighter. 

Infrared image of a man holding a plastic cover.Picture credits:NASA/JPL-Caltech/R. Hurt (SSC)

What would happen if you could only see UV light?

If we could see only ultraviolet light, you could see a lot of things that you see now. But, it could have damaged our eyes. 

UV light portrait – wavelengths from 335 to 365 nm. By Spigget – Own work, CC BY-SA 3.0, Link

What would happen if you could only see X-rays?

We won’t be able to see X-rays because the earth’s atmosphere blocks out all X-rays coming from space. If our eyes could only see X-rays, we wouldn’t be able to see the outer surface of objects. 

X-ray of a person’s hand while using a mouse

For example, if you saw a human, you would most probably see his bones; however, when you touch him, you would be able to touch his skin. Your eyes would ignore critical information needed to identify a person/object, For example, judging distances while driving.

More importantly, if something was too bright for you to see, you won’t be able to block it by closing your eyelids. 

What would happen if you could only see gamma rays?

Our atmosphere blocks almost all gamma rays coming from space, and radioactive materials are the only objects that can emit gamma rays on earth.

So, if we could see only gamma rays, other than radioactive materials, we wouldn’t have been able to see anything else. If you look at people, you would see nothing because they can even pass through bones. 

Greater gamma rays’ image of entire sky from the CGRO spacecraft. By NASA – http://heasarc.nasa.gov/ docs/cgro/images/epo/ gallery/skymaps/sky_egret.gif (http://heasarc.nasa.gov/ docs/cgro/images/epo/ gallery/skymaps/index.html), Public Domain, Link

What would happen if you could see everything?

If you could suddenly see all the light waves, there would be so much light everywhere that it would be too difficult to see anything at all. But, more importantly, your brain would be bombarded with too much information all of a sudden, that could confuse your brain. In the worst-case scenario, you would either go blind and not see anything at all, or see everything, go into shock and die. 

Besides making it possible to perceive objects, visible light has other applications. Analyzing the color emitted by various objects and phenomena has helped us understand these objects and phenomena better.

Phenomena related to visible light

Why does the sky appear blue?

The sky appears blue because the blue light is scattered more by the Nitrogen and Oxygen molecules in the atmosphere than other colors. 

What is scattering?

Light waves are electromagnetic waves. They are composed of oscillating (rapidly moving up and down) electric and magnetic fields. 

When these waves come in contact with the Nitrogen and Oxygen molecules in the atmosphere (made of 78% Nitrogen and 21% Oxygen), they excite the electrons of these molecules (charged particles start moving when exposed to an electric field), which start moving rapidly. In turn, these excited electrons emit electromagnetic waves of the same frequency and return to their normal state. This process is called scattering. 

According to Rayleigh’s scattering, when the wavelength of the waves is several times higher than the size of the scattering particle, scattering increases with frequency. Since the size of Nitrogen and Oxygen molecules are close to 300 pm and visible light has a wavelength of 380 nm – 740 nm, higher frequencies of the visible light are scattered more. Hence, Blue light is scattered more than red light giving the sky blue color.

Why does the sky not appear Violet if Violet has a higher frequency than Blue color?

Even though violet light has a higher frequency than blue light, since the sun sends less violet light than blue light, blue light gets scattered more. Moreover, our eyes are more sensitive to blue light than violet light. Hence, the sky does not appear violet.

Why does the sky appear red at sunrise and sunset?

During sunrise and sunset, the sunlight has to travel longer distances through the atmosphere to reach our eyes. During this time, most of the blue light has already scattered, leaving only red light to be scattered. Therefore, the sky appears red at sunrise and sunset. 

Why does seawater appear blue in color?

In the visible spectrum, (as you can see in the picture below) high wavelengths are absorbed more by water than lower wavelengths, i.e., red, yellow, and green lights are absorbed more than blue light. In other words, blue light is reflected more than the other colors. So, the sea appears blue in color. 

Absorption in water vs. wavelength of EM wavesPicture credits – http://www1.lsbu.ac.uk/water/water_vibrational_spectrum.html

However, this is not always true. If there are particles in the water, these particles may absorb some other colors and reflect others, giving the water a color other than blue. For example, in places where there are a lot of Algae, the water appears green in color. 

Applications of visible spectrum

Determining the temperature of a star

The color emitted by a star tells us a lot about its temperature. As the temperature of a star increases, the higher its energy and the lower the wavelength of light waves emitted by it. So, a star that burns Blue is hotter than a star that burns Yellow (Sun – 6,000 K), which is hotter than a star that burns Red.

Weather forecasting

By feeding the infrared and visible light images of the earth, made by satellites, as inputs to weather prediction models, scientists can forecast weather effectively. 

VLC

VLC (Visible Light Communication) is a mode of communication in which LEDs (and other sources of visible light) are used to transfer data with high speeds over short distances (up to 2 km). 

Photosynthesis

Photosynthesis, which is essential for the survival of most life on earth, would have been impossible without visible light.

If you liked this blog post on visible spectrum, the following blog posts might interest you too:

1. Different types of Waves
2. 7 types of electromagnetic waves
3. Dangers of electromagnetic radiation

Whenever we think of waves, what jumps to our minds immediately are sea waves, which are mechanical waves. However, mechanical waves are not the only type of waves. There are also other types of waves, like electromagnetic waves. Compared to mechanical waves, electromagnetic waves can even travel through vacuum, because they don’t require a medium for propagation. In this blog post, we will look at what the 7 types of electromagnetic waves are, how they are produced, and what their uses are.

What are electromagnetic waves?

If you remember what we learned about waves, you will remember that mechanical waves transmit energy and require a medium (gas, liquid, or solid) for propagation. Electromagnetic waves are different from mechanical waves since they don’t need a medium for propagation and hence, can travel through vacuum.

Electromagnetic waves, their properties, behavior and applications

You can read more about the properties and behavior of electromagnetic waves here: How do waves affect your daily life?

To understand how electromagnetic waves are produced, we have to dive into the basics of electromagnetics a little bit.

Electric field

We know that a particle can have any of the three electric charges – positive (For example, proton = unit positive charge), negative (Eg. electron = unit negative charge), or neutral (Ex. neutron). Depending on its electric charge, it might exert an electric force on another object,i.e., opposite charges attract, and the same charges repel each other. 

The force with which a unit charge attracts or repels other charges is called the electric field. The electric field flows from a positive charge (outward) to a negative charge (inward).

By Geek3 – Own work, CC BY-SA 3.0, Link

If you consider a positive charge and a negative charge which are in motion, the electric field between them (the arrow in the picture) changes in value and direction, as shown below.

Moving electric charges and the electric field

Electric field vs Time

As you can see from the second picture, the change of the electric field, when plotted against time, looks like a sine wave.

Electric field generates a Magnetic field

According to Ampere’s Circuital law, a change in the electric field produces a magnetic field. The generated magnetic field is perpendicular to the electric field. 

An electromagnetic wave is a combination of oscillating electric and magnetic fields moving through space at the speed of light. Electromagnetic waves can be generated by accelerating a charged particle.

Image credits (E = Electric field, B = Magnetic field, C = direction of movement of the wave with speed of light)

Why is the study of electromagnetic waves important?

Electromagnetic waves are everywhere around us. Therefore, understanding these waves is the key to understanding the functioning of various devices around us. However, in this generation, most of us don’t care how these devices work. So, we often end up overlooking their harmful effects. 

In the science category, one of our main aims is to help you understand how everything around you work. By reading our blog posts, you can understand the functionality of various devices. Moreover, you will also be able to protect yourself from their harmful effects.

Modes of propagation

Electromagnetic waves can travel in one or more of the following modes. Depending on their wavelengths, they can travel in some modes, but not in others. Each mode has its own advantages.

Line-of-sight

This is the most common mode of propagation of electromagnetic waves. In this mode, the waves travel only in a straight line. They either reach the receiver or are absorbed, reflected, refracted, or diffracted by the particles in the atmosphere. But they cannot travel over obstacles.

As waves travel long distances in a straight line, they tend to move away from the earth. Eventually, at the end of the horizon, they leave the earth, since the earth is spherical. Therefore, repeaters (towers) at regular intervals are indispensable to send these waves over long distances.

Ground waves

If the wavelength of the wave is large enough, obstacles like mountains can diffract these waves towards the surface of the earth once again. Therefore, these waves travel longer along the surface of the earth. These waves are called ground waves.

Skywaves

The waves that leave the earth’s horizon are also reflected or refracted back to earth by thecharged particles in the ionosphere. These waves are called skywaves.

Picture credits

EM waves vs Atmospheric absorption

There are seven types of EM waves and some of them are hazardous to living beings. But our atmosphere blocks most of these waves that come from outer space. The picture below depicts which wavelengths of EM waves are blocked by the atmosphere and which wavelengths pass through the atmosphere.

Picture credits

7 Types of Electromagnetic waves

Electromagnetic waves are classified based on their frequency. Depending on their frequency, they can have different applications as well as pose different health risks upon over-exposure.

f = c / λ

where f is the frequency of the wave, c is the speed of light and λ is the wavelength of the wave. As you can see, the frequency of the wave increases as its wavelength decreases.

The electromagnetic spectrum consists of electromagnetic waves whose wavelengths vary from several thousand kilometers to a few picometers.

The electromagnetic spectrum is home to 7 types of electromagnetic waves. Each electromagnetic wave has a unique wavelength/frequency range and has distinct characteristics. Arranged in terms of decreasing wavelengths, these 7 types of electromagnetic waves are Radio waves, Microwaves, Infrared light, Visible light, Ultraviolet light, X-rays, and Gamma-rays.

Harmful effects of electromagnetic waves

As the wavelength reduces, the energy of the emitted wave increases. But with the increase in the energy of an electromagnetic wave, the danger it poses to living cells also increases. Hence, radio waves pose the least danger to us since they carry very little energy. On the contrary, at the other end of the spectrum, gamma rays have the most energy and are extremely dangerous.

You can read more about the harmful effects of electromagnetic waves in our blog post here: Dangers of electromagnetic radiation.

Electromagnetic waves

Food for thought:

Why does the energy increase with an increase in frequency (or a decrease in wavelength)?

I will try to answer it using an analogy.

If you wiggle a rope whose one end is attached to a wall, you will create a wave in the rope. The faster you move your hands, the higher the frequency of the waves generated in the rope, and the more exhausted you will get while doing it.

Similarly, creating a high-frequency wave requires a powerful energy source, and the generated wave carries a huge amount of energy.

1. Radio waves

Radio waves have the longest wavelengths and the least energy of all electromagnetic waves. There are different types of radio waves. Different types of radio waves have different penetrating abilities and have different uses. However, their most common and widespread use is in communication technologies like radio, television, mobile phones, etc.

You can read more about radio waves in our blog post here: Applications of radio waves.

2. Microwaves & Millimeter waves

Today, due to the advancement in technology, generating electromagnetic waves of much shorter wavelengths has become easier. But in the 1920s and 1930s, generating radio waves that have far greater wavelengths (hundreds of meters) was more common. Hence, when physicists discovered microwaves, they noticed that they had relatively smaller wavelengths when compared to radio waves. So they simply named them microwaves because ‘micro’ meant ‘small’.

On the contrary, millimeter waves got their name because their wavelengths lie in the millimeter range (1mm to 1cm).

You can read about microwaves and millimeter waves in our blog post here: Applications of radio waves.

3. Infrared waves

Infrared rays are heat waves given off by most objects. They have wavelengths ranging from 1 mm to 700 nm.

Infrared waves cannot penetrate walls. They travel only through line-of-sight.

Infrared rays are not visible to our naked eyes since we can only see wavelengths between 380 nm and 740 nm. Around 52% of the energy that reaches the earth from the sun is Infrared radiation. But they have very high attenuation. So, we don’t use infrared waves for outdoor communication.

Infrared image of a man holding a plastic cover.Picture credits: NASA/JPL-Caltech/R. Hurt (SSC)

Applications

Nightvision goggles

Most objects emit heat in the form of infrared waves at room temperature. Nightvision goggles use these infrared rays to provide vision at night when the visible light is insufficient.

Remote controls

Remote controls use highly focused and narrow infrared waves generated by infrared LEDs. Since infrared waves cannot penetrate walls, they don’t interfere with the functioning of other infrared devices.

Homing of missiles

Missiles are programmed to follow and hit heat sources that emit infrared radiation (the engine of the other aircraft). Thus, infrared waves make the passive homing of missiles possible.

Finding baby stars and planets

Stars emit most of their energy as visible light and less energy as infrared waves.

On the other hand, baby stars and planets emit a lot of infrared radiation because they are colder. Hence, by reading the infrared signatures (instead of visible light) of galaxies and dust clouds, astrophysicists can identify baby stars and planets easily.

Weather forecasting

Along with images in the visible light spectrum, images in the infrared region (from weather satellites) help make weather forecasting possible.

Finding original versions of art pieces

Infrared rays can penetrate the underlying layers in paintings. So, they can reveal if the painting is the original version or a version modified by an artist or someone else.

4. Visible light

Visible light is the range of frequencies that are visible to our naked eyes. You can read more about visible light and its properties in our blog post here: The visible spectrum.

5. Ultraviolet (UV) rays

Ultraviolet rays (in ‘Latin’ Ultra means ‘Beyond’) have wavelengths ranging from 400 nm to 10 nm. Some small birds have receptors for UV light. But humans cannot see it.

UV light portrait – wavelengths from 335 to 365 nm. By Spigget – Own work, CC BY-SA 3.0, Link

UV rays cause suntans and sunburns by making the body release Melanin in response to the damage it does to the skin.

Exposure to UVA rays

UVA rays (not blocked by the ozone layer) have wavelengths ranging from 400 nm to 320 nm. They can create suntans and sunburns that have no health advantages and sometimes cause cancer. Sunscreens provide little protection against suntan caused by UVA rays.

Exposure to UVB rays

However, exposure to UVB rays (320 nm to 280 nm) can create suntans that last for weeks or months and protect the skin from further UV damage with an SPF of 3 (3 times more protection against UV rays than normal skin). Exposure to UVB rays also leads to the creation of Vitamin D in the lower levels of our skin. But the Ozone layer almost completely blocks it. Moreover, sunscreens block most of the UVB rays too. 

Sunburn on a woman’s back.By FAL101 at English Wikipedia – Own work by the original uploader, CC0, Link

Food for thought:

Can you protect yourself from UV rays by sitting in the shade?

No.

Even if you are in the shade, UV rays can still reach your skin and eyes indirectly and damage them. That’s why proper clothing, hats, sunscreen, and sunglasses are required to protect yourself from UV radiation, even if you are sitting in the shade.

Are people with fair skin more susceptible to sunburns than darker people?

Yes. The natural pigment melanin, besides being responsible for our skin-, hair- and eye-colors, also protects our skin from getting burned. Darker people, who have a higher concentration of melanin, are more immune to UV radiation than people with fair skin. Therefore, they can stay longer in the sunlight without getting tanned or getting burned.

Applications

Some materials can glow and fluoresce when exposed to UV light. Fluorescence is the phenomenon in which some materials absorb light of lower wavelengths (For example, UV light) and emit radiation of higher wavelengths (For example, visible light). 

This fluorescence-property of UV light has many applications: 

1. Crime-scene inspection (Bodily fluids like saliva, semen, and urine fluoresce when exposed to UV light)

2. Identifying counterfeit currency notes

3. Detecting the presence of pests in agriculture (Urine of rodents fluoresce when exposed to UV light), and 

4. Verifying the originality of art and collectibles, etc. 

6. X-rays

X-rays are electromagnetic waves with wavelengths ranging from 3 nm to 0.03 nm. 

How are X-rays produced?

When accelerated electrons hit atoms of metals (Copper, Galium, etc.), they make the electrons in inner orbits leave their orbits. As a result, the atoms of these metals become unstable. So, electrons from the outer orbit move to the inner orbit to stabilize the atom, thereby releasing an X-ray in the process.

How did X-rays get their name?

The German physics professor Wilhelm Röntgen, who discovered the X-rays on November 8th, 1895, didn’t know what type of radiation it was. So, he referred to the radiation as ‘X.’ This gave X-rays their name.

X-ray of chest. Picture credits & License

Applications

Scans

The most common application of X-rays is in creating scans.

An X-ray scan uses X-rays to create medical imagery of an interior body part. X-rays are attenuated slightly by soft tissues and organs but are attenuated heavily by the Calcium in the bones. Therefore, on the Radiograph (image produced by X-rays or Gamma rays for medical purposes), the bones appear as white. 

A CT (Computed Tomography) scan combines several X-rays (taken at different angles) to obtain a 3D-image of the body part. 

Airport security systems use X-rays to scan your luggage.

Fighting cancer

X-rays are ionizing. Therefore, radiotherapy uses X-rays to kill cancerous cells in the body. Thus, X-rays play a major role in fighting cancer.

Astronomical observations

Several celestial bodies, like Black holes and neutron stars, emit X-rays. So, studying these X-rays help understand these bodies better. But our atmosphere almost completely blocks X-rays from outer space. So, astrophysicists install X-ray telescopes at very high altitudes or in an artificial satellite.

7. Gamma-rays

Gamma-rays are very similar to X-rays. However, their major difference is in the way they are produced. While X-rays are produced by electrons, Gamma-rays are produced by nuclei.

How are Gamma rays produced?

After a radioactive material decays, the resulting daughter nucleus that is in an excited state releases a Gamma-ray to reach a stable, low-energy state. Hence, both nuclear fission and nuclear fusion can produce Gamma-rays.

Applications

Fight cancer

Similar to X-rays, the ionizing property of Gamma-rays is useful in the medical field for killing cancer and tumor cells. A Gamma knife surgery focuses multiple concentrated Gamma rays on a cancerous growth from different angles. Thus, it minimizes damage to healthy tissues while destroying the cancerous growth.

Astronomical observations

Massive stars release a huge amount of energy and a large amount of Gamma-rays when they collapse. However, this phenomenon, called a Gamma-ray burst, is very rare because it lasts only for a very short time. For example, a Gamma-ray burst can release more energy in 10 seconds than the sun can emit in 10 billion years. Therefore, by analyzing Gamma-rays, such phenomena can be studied. But just like X-rays, our atmosphere almost completely blocks Gamma-rays too. So, astrophysicists install Gamma-ray telescopes at very high altitudes or in an artificial satellite to study Gamma-rays from outer space.

For example, the image below was recorded by NASA’s Swift satellite. It depicts a gamma-ray blast caused by the birth of a black hole 12.8 billion light years away (below). This object is among the most distant objects ever detected.

Picture credits: NASA/Swift/Stefan Immler, et al.

Gamma-rays also help determine the elements on other planets.

Sterilization

Gamma rays can kill microorganisms like fungi, bacteria, and viruses. Therefore, they are used for sterilization in various fields:

1. Medical fields – to sterilize surgical tools and disposable syringes before use.

2. Hygiene – to sterilize food items (like frog legs) to improve hygiene. 

3. Art – to sterilize pieces of art, thereby killing the microorganisms on these art pieces and protecting them against degradation.

We hope that this blog post helped you understand what the 7 types of electromagnetic waves are, how they are produced and what their uses are. If you liked this blog post, please share it with your friends.

Radio waves have the longest wavelengths and the least energy of all electromagnetic waves. The applications of radio waves in real life are numerous. However, their widespread use is in communication technologies like radio, television, mobile phones, etc.

Types of Radio waves

We can classify radio waves into different classes based on their frequency. Depending on their frequency, radio waves have different characteristics and, hence, different applications.

Applications of radio waves

ELF & VLF

These radio waves have very long wavelengths (> 10 km). Since they have enormous wavelengths, normal objects cannot reflect them. Therefore, they can easily pass through obstacles like water and buildings.

Applications

Due to their characteristics, several countries use ELF & VLF radio waves for transmitting and receiving messages to and from submarines and inside caves and mines. The depth to which these radio waves can communicate depends on the wavelength of the radio wave used.

Problem of transmitting

For antennas to transmit an EM signal, their size should be equal to the wavelength of the transmitted EM wave. However, if that is not possible, their size should at least be equal to half or quarter of the wavelength of the EM wave.

ELF waves have enormous wavelengths. So, the antennas used for sending ELF radio waves need to be enormous. Since it is not an easy task, only four countries in the world have managed to build it – the US, Russia, China, and India.

Food for thought: 

Why can waves with longer wavelengths pass through objects easily?

If the wavelength of the wave is smaller compared to the dimensions of the obstacle, it gets reflected. If the wavelength is larger, it passes through the obstacle or gets diffracted around it.

Picture credits

LF and MF

Radio waves with frequencies less than 3MHz (approximately) can travel as skywaves and ground waves. LF and MF have long wavelengths (100 m to 10 km) and small frequencies (30kHz to 3MHz). So, they can travel long distances (up to 2000km) as skywaves and ground waves. Moreover, they have less attenuation too. So, they are the preferred mode for long-distance communication.

Applications

Radio waves with frequencies below Medium Frequencies serve as ideal candidates for long-distance communication. However, for this purpose, they need to have vertical antennas. But creating vertical antennas (comparable to the wavelengths of waves) to transmit radio waves ranging from ELF to VLF is impractical. So, mostly, only LF and MF are used for long-distance communication. The primary use of LF and MF is in aviation and marineradio, as well as AM radios.

HF

HF waves have wavelengths ranging from 10 m to 100 m. They can travel long distances as skywaves.

Applications

HF waves can travel long distances. Hence, they can travel over countries or continents to transmit information. In addition to that, they can also transmit information to hill stations where line-of-sight communication is impossible.

They are used for shortwave international as well as regional communication, weather stations, aviation communication, etc.

VHF

VHF radio waves have wavelengths between 1 m and 10 m. Their wavelengths are not long enough for them to propagate as ground waves or skywaves. So, they can only communicate by Line-of-sight. Hence, their range is limited by the horizon of the earth (up to 160 km).

On the other hand, due to their small wavelengths, their transmitting antennas can be small enough to be fitted on a vehicle or building.

Food for thought:

Why do you have to adjust your TV’s antenna at times?

Picture credits

VHF radio waves can penetrate walls. But hills and mountains can completely block them.

Since their wavelengths are comparable to the size of buildings, buildings can reflect these radio waves leading to interference in television signals. Atmosphere may slightly change the direction from which the strongest signals come. Weather (absorption of VHF by rain) can also weaken the signal.

Since the mode of propagation is only Line-of-sight, you have to adjust the antenna to point in the direction of the strongest signal, so that it receives the complete length of the waves.

Picture credits

Applications

They have a wide range of applications including FM broadcasting, television broadcasting, walkie talkies, air-traffic control communication, etc.

UHF

The wavelength here ranges from 10 cm to 1 m.

These waves can travel through walls.

UHF waves can only propagate through Line-of-sight since they cannot travel as ground waves or skywaves. Therefore, they have a maximum range of 64 km. But, because of this, neighboring regions can use the same frequencies of UHF.

Food for thought:

Why does your mobile phone not work properly in overpopulated areas or when it rains?

The small wavelength of UHF leads to a loss in quality due to interference caused by buildings, trees, etc. Rain can also attenuate the waves significantly. That’s why your mobile phones may not work properly in highly populated urban areas or when it is raining.

Applications

The transmitting antenna can be small enough to be fitted in handheld devices. Hence, they have a variety of applications like use in cell phones, digital televisions, GPS, walkie talkies, Bluetooth, Wi-Fi, etc.

Microwaves

These radio waves have wavelengths ranging from 1 cm to 1 m. Microwaves got their name due to their relatively smaller wavelengths compared to radio waves.

Radio waves consist of two wavelength separations: Ultra High Frequency (UHF) waves and Super High Frequency (SHF) waves.

SHF waves have short wavelengths ranging from 10 cm to 1 cm. Hence, antennas the size of several times the wavelength of these waves can be used to create highly narrow beams. Therefore, these waves can be sent accurately from the transmitter to the receiver. 

Applications

They have a wide range of applications like Wi-Fi, Radar (RAdio Detection And Ranging), Communications satellites, microwave ovens, trafffic speed cameras, etc.

SHF waves cannot penetrate walls as much as UHF waves. Therefore, when your Wi-Fi transmitter is located in not located in the same room as your Wi-Fi device, the signal is weak.

Microwaves are the only radio waves whose frequencies are high enough to be transmitted over long distances without significant attenuation while remaining low enough to be transmitted as narrow beams so that the same frequencies can be reused in neighboring regions.

Hence, microwaves are the major carriers of high-speed data between different stations on Earth. In addition to that, they also transfer data between stations on earth and communication satellites. A system of such communication satellites enable all kinds of communications like television and telephone.

What does a communications satellite do?

Communications satellites are satellites that mostly remain in geostationary orbits. They rotate the earth at the same speed of rotation of the earth. Moreover, they stay at the same latitude and longitude all year round. So, for an observer on earth, they appear to be at the same position all the time. Therefore, we can fix a receiver on earth at a position and angle to point to and communicate with such a satellite permanently. 

A communications satellite’s major function is to increase the range of the microwaves. Since microwaves have small wavelengths, they can only travel by Line-Of-Sight. So, the earth’s horizon as well as attenuation limit their range to 64 km. Therefore, to increase their range, they are sent to a geostationary satellite orbiting the earth at 36,000 km above the Equator. The satellite receives these waves and sends them to other satellites or to other receivers on the earth, to enable communication over long distances. 

What are communication satellites used for?

Communications satellites make international calls, internet, long-distance television- and radio-broadcasting possible.

Food for thought

If the range of a microwave is just 64 km, how can it be transmitted to a satellite orbiting at 36,000 km above the Equator?

The range of a microwave is 64 km because, beyond this distance, they either leave the earth’s horizon or are attenuated by obstacles like trees, buildings, etc. But, by sending it to a satellite (by pointing it to the sky) where there are no obstacles in the way through Line-of-sight, they are not entirely attenuated. 

The attenuation is still there since the waves have to travel very long distances compared to their wavelengths. Hence, satellites in other orbits (low- and medium-earth orbits) are also used for this purpose. However, unlike geostationary satellites, they don’t appear to stay at a fixed position above earth. Hence, unlike in geostationary orbits, in other orbits, an uninterrupted connection is impossible, unless several satellites are used.

How does a Radar work?

In Radar, the transmitter and receiver are both located in the Radar. The microwaves that are sent by the transmitter are reflected off an object and are received by the receiver, providing details like the object’s location, speed, and direction.

They are used in ships, airplanes, military purposes, pre-collision systems in cars, etc.

Millimeter-waves

Millimeter-waves are radio waves whose wavelengths lie between 1 cm and 1 mm. They have high atmospheric attenuation. Therefore, they have a range of 1 km or less. Since their wavelengths are in the size of rain droplets, rain droplets can absorb these waves. Hence, rain and moisture can reduce their range even further.

Applications

Airport security screening

Since they have small wavelengths, they can pass through our clothes but are reflected by small metal objects.

Millimeter wave security screening at Cologne AirportBy © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons), CC BY-SA 4.0, Link

Therefore, they are used in whole-body security-checks in airports. They are also used in 5G communication. 

Remote sensing

Remote sensing is the process of obtaining information about an object without making any physical contact with it. In remote sensing, by measuring the radio waves (mostly millimeter waves and microwaves) emitted or reflected by an object, the characteristics of the object, like its structure, altitude, etc. can be determined. 

Millimeter waves can pass through clouds easily. But they cannot pass through other objects, like metallic structures. So, these objects reflect them. Therefore, Millimeter waves are good candidates for remote sensing. Similarly, they can pass through non-metallic surfaces, but not through metallic objects within these non-metallic surfaces. Therefore, they are also useful in oceanography, geology, geography, etc.

Radio astronomy

Explosions in outer space can reach scorching temperatures. So, they emit cosmic radio waves (EM waves from space) of longer wavelengths.

In contrast, colder environments emit only radio waves of shorter wavelengths. Some of these colder environments are the dust clouds. They are the birthplaces of stars. Dust clouds are extremely cold (approximately -253°C) and don’t emit visible light. They emit only millimeter waves. So, studying these millimeter waves is necessary to understand the composition of dust clouds and stars. Thus, millimeter waves are extremely important in radio astronomy.

We hope that this blog post helped you understand the applications of radio waves in real-life. If you liked this blog post, read our other blog posts too.

1. 7 types of electromagnetic waves
2. Different types of waves
3. Dangers of electromagnetic radiation

From TV to cell phone, from CT scan to weather forecasting, from Wi-Fi to astronomy, electromagnetic waves are everywhere around us. However, most of us are not aware of their harmful effects and believe whatever we hear about them. So, I wrote this blog post to help everyone understand the dangers of electromagnetic radiation.

Generally, electromagnetic waves, which have higher energy, are more dangerous than those with lower energies. However, to understand which radiation is more harmful, and why it is harmful, we have to know how it transfers energy as it passes through matter. 

There are two methods in which EM waves transfer energy to biologic material.

Types of radiation

Based on how they interact with matter, electromagnetic waves can be broadly classified into two types.

1. Non-Ionizing waves (Excitation)

The EM wave transfers energy to an electron in the outer shell to move it to an inner shell of higher energy without removing the electron from the atom. The process is called excitation, and the wave is called a non-ionizing wave.

Harmful effects of Non-ionizing EM waves

Non-ionizing waves are not harmful when exposed to, in small doses.

But when exposed to high doses, they can significantly heat the body tissues (for example, microwave oven). Wearing regular clothing can protect against a normal dosage of these waves.

If the source of non-ionizing waves is extremely hot, it can induce thermal ionization of atoms.

2. Ionizing waves (Ionization)

The EM wave transfers enough energy to remove (eject) one or more electrons from the atom. The process is called ionization and the wave that is capable of doing it is called an ionizing wave.

Harmful effects of Ionizing EM waves

Ionizing electromagnetic rays are extremely hazardous to life. They can cause damage to us in one of the following two ways.

1. damage a tissue (For example, sunburn) by killing the cells in the tissue, when exposed to high doses, or
2. cause cancer and genetic diseases by changing the DNA in the cells, when exposed tolower doses.

Food for thought:

Why do small doses of exposure to ionizing EM waves have long-lasting consequences than high doses of exposure?

After the DNA in the cells are broken down, our bodies are more likely to repair the damage if the radiation’s dosage is high. If the dosage is low, our bodies likely ignore the damage caused. Hence, lower doses can cause long-lasting consequences like cancer or genetic diseases.

Harmful effects of Ionizing vs non-Ionizing EM wavesPicture credits

Why doesn’t harmful radiation from outer space harm us?

Earth’s atmosphere and magnetic field act as a shield blocking all the dangerous ionizing waves from entering the earth. The picture below depicts this (In the picture above, Gamma-rays are at the far right. However, in the picture below, they are in the far left).

Life wouldn’t have been possible on earth without this natural protection.

Atmospheric opacity (absorption) vs Wavelength of EM wavesPicture credits

Dangers of Electromagnetic Radiation on Humans

1. Low-Frequency Radio waves (Wavelength > 3 km)

Power stations produce low-frequency radio waves. If the magnetic field in the power lines is strong enough, these radio waves can produce small currents in the bodies of people standing directly under them. If the currents induced in the body are large enough, they can stimulate the nerves and muscles, and affect the biological processes. However, it is very rare.

Power lines

The induced currents are generally not strong enough to heat the tissues in the body. Hence, they aren’t as harmful as other ionizing and non-ionizing waves.

2. Radio and Microwaves

Radio waves and microwaves, used for mobile communication and transmission of television and radio signals, can create thermal effects in our bodies. But this can only happen at high radiation levels, which does not occur by regular use of these devices. At regular usage levels, the dangers of electromagnetic radiation are negligible.

A cell-phone tower

Hence, radio waves and microwaves are harmless to the human body when they are under the recommended limits of radiation. Under normal daily use of mobile phones, TV and radio, these waves don’t possess sufficient energy to heat the exposed body parts. 

People working on carrier decks in military aircraft have to wear suits that reflect microwaves to protect against radar systems. However, they are powerful radar systems, not normal mobile phones or Wi-Fi.

Which body parts are the most affected, upon over-exposure?

Your eyes and Testes are most affected upon over-exposure to radio and microwaves because these parts lack blood supply, which can dissipate the heat easily.

Food for thought:

Can radio waves and microwaves harm you, if you use mobile phones, televisions, radios and microwave ovens regularly?

No, because, under normal usage, the waves emitted by these devices don’t possess sufficient energy to heat the exposed body parts. 

Can using Bluetooth headphones harm your body more than your cell phones?

No. On the contrary, using Bluetooth headphones is recommended. Bluetooth devices use higher wavelength radio waves that have lower energies. So, using Bluetooth headphones is less harmful than keeping the constantly-transmitting mobile phones near your ears (and your brain).

Are the EM waves from a cell phone/radio/television transmission tower harmful for human beings?

No. But, if you directly stand in front of the transmitting antennas on the tower for sufficient time, some of your tissues may get burned. These antennas send concentrated beams of radio waves/microwaves to satellites. So, they point directly to the satellites in the sky and not to the ground. In addition to that, the power density of the waves rapidly falls as one moves away from the antenna. Since these antennas are mounted on high towers, the power density of the waves on someone standing under such a tower is hundreds of times lesser than the recommended limits.

Can radiation from cell phone towers affect birds and bees?

The popular belief is that the radio waves and microwaves from cell-phone towers affect the navigational abilities of birds and bees. However, no convincing proof is available on the subject. 

In 2018, Eklipse organized a web conference of experts to discuss the effects of electromagnetic radiation on wildlife. They analyzed 147 publications (research papers) on the subject and came to a conclusion.

Most experts agreed that EM waves affect the navigational sense of birds and bees, and the metabolism of trees. However, they couldn’t find any convincing proof in the analyzed researches. The graphs below summarize the findings of the conference.

What does it mean?

Radio waves and microwaves emitted by cell-phone, television, and radio towers might have led to a decrease in bird and bee population. However, these waves might not be the only reason. It could have been one of the reasons. Other reasons could be pollution, lack of food, danger from other species, etc.

Do radio waves and microwaves disrupt the magnetic sense of birds?

The picture below shows the quality of evidence (Do credible and repeatable research data exist?) of a statement vs. the number of people who agreed for it.

You will notice that the statement “Magnetic sense of birds are disrupted by RF” has been accepted by several experts. However, the results of the analyzed researches on that hypothesis are not credible enough; i.e., it cannot be proved.

Harmful effects of Em waves on VertebratesRead more

Can radio waves and microwaves affect the sense of orientation of Bees?

The picture below shows the quality of evidence of a statement vs. the number of people who agreed for it.

Several experts have accepted the statement “Detection of EMR by physiological orientation/movement mechanisms” (EM waves can make bees lose their sense of direction). However, the results of the analyzed researches on that hypothesis are not credible enough; i.e., it cannot be proved.

Harmful effects of Em waves on Vertebrates Read more

3. Infrared waves

Greenhouse effect

Infrared waves are the reason behind the Greenhouse effect, that rapidly heats our planet. The clouds and the earth’s surface reflect the sun’s waves as IR waves into the atmosphere. As a result, these waves leave the atmosphere into space.

However, gases like Chlorofluorocarbons, water vapor, oxides of sulfur and nitrogen can trap the IR radiation in the atmosphere. These gases are released by human activity. So, as the human activityincreases, the concentration of these gases in the atmosphere increases. Therefore, more and more IR radiation gets trapped in the earth. Ultimately, this leads to global warming.

Damage to eyes

Prolonged exposure to IR waves can heat your eyes. As a result, you might get cataract, retinal burns and corneal ulcers.

For example, workers who work in iron and glass production factories might suffer from Glassblower’s cataract. Glassblower’s cataract is the name given to changes that occur in the eyes of workers who look at glowing iron or glass without protective eye-wear every day.

4. Visible light

Damage to eyes

Looking at extremely bright visible light can lead to retinal injury. Moreover, it could cause temporary or permanent blindness depending on the exposure.

5. UV light

Exposure to the higher wavelengths of UV light at limited amounts can be beneficial to health (formation of Vitamin D). But overexposure can lead to wrinkling of the skin, skin aging, skin burns, and skin cancer.

Sunburn on a woman’s back.By FAL101 at English Wikipedia – Own work by the original uploader, CC0, Link

Are tanning beds or salons safe?

Tanning beds use more concentrated UV light to produce a tan. Hence, they have the same chances of causing cancer as smoking. In addition to that, tan itself is dangerous because it is the response of your body against UV damage to your skin.

UV rays in the lower part of the electromagnetic spectrum (wavelengths below UVA and UVB) are ionizing, i.e., they possess enough energy to strip the electrons from atoms and molecules, thereby ionizing them.

6. X-rays

Since X-rays are ionizing, they pose a health risk to humans. The use of X-rays for medical imaging might be widespread. But, every time you get an X-ray scan, your risk of getting cancer increases slightly. However, this risk depends on the part being scanned.

X-ray of a person’s hand while using a mouse

7. Gamma-rays

Like X-rays, Gamma-rays are also ionizing, i.e., depending on the dosage, they may either damage the tissues and kill the body cells, or create cancer and genetic diseases.

Gamma rays have no charge. So, they do not interact with matter and have higher penetration power.

They can also pass through bones and teeth and carry very high energy. So, the health risks are even greater than that of X-rays.

We hope that this blog post helped you understand the danger of electromagnetic radiation. If you liked this blog post, check out our other blog posts too:

1. Different types of waves
2. Properties of electromagnetic waves
3. 7 types of electromagnetic waves

In this blog post, we will look at the properties of electromagnetic waves. Then, we will look at the behavior of light waves, which are electromagnetic waves too.

From X-rays to radio waves to visible spectrum, electromagnetic waves are everywhere around us. Understanding their properties and behavior has helped humanity develop some incredible devices. Without these devices, our daily lives would be impossible.

In this blog post, we look at some of these useful devices as well as some natural phenomena. We will do our best to help you understand the basics behind them. First, we will look at some of the properties of electromagnetic waves.

Properties of electromagnetic waves

1. Wavelength – The length of the wave,i.e., the distance between two consecutive maximum or minimum values of the wave.
2. Frequency – The frequency is the number of waves (of one wavelength) that pass through a fixed point in unit time (one second).
3. Amplitude – The maximum displacement of a particle from its original position.
4. Phase – A particular point on the wave, designated as an angle between 0° and 360°. Phase difference is the displacement of one wave in comparison to another with the same frequency.
5. Energy – The energy a wave carries is directly proportional to the square of its amplitude. The energy is also directly proportional to the frequency and inversely proportional to its wavelength.
6. Intensity – Intensity is the amount of light at a particular wavelength.
7. Color – The wavelength, at which the intensity of a wave is maximum, determines the color of the wave.

Until now, we looked at the properties of electromagnetic waves. Now we will see how electromagnetic waves behave when they fall on a surface. For easy undersanding, we will consider light waves (from the visible spectrum), which are electromagnetic waves too. So, in the next section, we will look at the behavior of light waves.

Behavior of light waves

When electromagnetic waves encounter a new medium or move through a medium, they may exhibit one of the following behaviors. But we won’t look at these behaviors directly. Instead, we will look at some natural phenomena that occur in nature and man-made instruments. Then, we will try to understand the behavior of waves (mostly visible light) associated with that phenomenon.

How can submarines see what is going on outside water?

Clue: Due to reflection

Reflection

Reflection is the phenomenon due to which, a wave, that hits the interface between two mediums, returns to the same medium from where it hit the interface. In this phenomenon, the angle of incidence and the angle of reflection are always equal.

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Example

When you look at a mirror and see your reflection, it is because the mirror reflects the light waves.

Practical application

A periscope uses the concept of reflection. Submarines use periscopes to see what is going on above the water while remaining submerged inside water.

How do a microscope and a telescope differ from a projector?

Hint: Due to Refraction

Refraction

Refraction is the phenomenon due to which, a wave, that hits the interface between two mediums, moves into the other medium with a change of direction, wavelength, and speed.

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Example

A prism refracts the light wave into different colors. Similarly, water droplets in the atmosphere refract the visible light (coming from the sun) creating a rainbow.

Optical prism refracting a ray of white light.

Practical application

Lenses work based on the principle of refraction. A lens refracts the light rays incident upon it. As a result, an image is produced on the other side of the lens, which is larger than the original object. 

1. A convex lens causes the light rays that come from different parts of a distant object, to converge at a single point (your eye). Therefore, we use it to build objects like telescopes, binoculars, and microscopes.

A convex lens refracting waves – Image credits

Image enlargement by a microscope – Image credits

Image enlargement by a telescope – Image credits

2. A concave lens causes the light rays that come from different parts of a distant object, to diverge. Therefore, we use it in objects like projectors to create enlarged images.

A concave lens refracting waves – Image credits

What makes a beam of light passing through a small hole produce multiple concentric circles on the other side?

Clue: Due to diffraction

Diffraction

When a wave hits an obstacle (or hole), it bends around the obstacle even though it stays in the same medium.  

Example

When a red laser beam passes through a circular hole, the resulting wave looks as shown in the picture below.

By Wisky – Own work, CC BY-SA 3.0, Link

Practical application

The principle of diffraction makes the construction of spectrometers possible. We use spectrometers to study the composition of stars as well as the composition of atoms and molecules.

When you talk to a person wearing glasses, why can you (sometimes) not see your reflection on it?

Clue: Due to interference

Interference

Interference is the phenomenon that happens when two waves come in contact with each other. Depending on the difference in their phases (time), the resulting wave might have a higher amplitude (constructive) or a lower amplitude (destructive). When a diffracted wave meets the original wave or another diffracted wave, it undergoes interference. Thus, Diffraction is often accompanied by interference.

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Example

One typical example of interference is the multiple colors you see on a soap bubble.

By Brocken Inaglory – Own work, CC BY-SA 3.0, Link

Some of the light waves that fall on the soap bubble get reflected by the upper layer (air-bubble interface). But some of the light waves are transmitted through the soap bubble. Then, a part of these light waves is reflected by the lower layer (bubble-air interface). These light waves reflected by two layers interfere with each other. Consequently, they cancel out some colors while brightening the others.

Application

Interference makes the creation anti-reflection coatings for lenses (used in sunglasses, telescopes, microscopes, solar panels, etc.) possible. By adjusting the thickness of the coating, some or all the wavelengths of light waves can be canceled out. This destructive interference prevents any reflection from happening. Anti-reflection coatings have two uses:

1. Improve appearance by reducing reflection – useful in designing glasses. If you wear a spectacles with an anti-reflection coating, your friend needn’t look at his reflection while talking to you.

Without vs With Antireflection coating – Image license

2. Improve efficiency by reducing reflection and improving transmission – useful in solar panels. Solar panels are covered with glass that improves transmission. As a result, more solar light reaches the solar cells. Hence, more electricity is generated.

What causes the glare that you see on the highway and the surface of a water-body?

Clue: Due to polarization

Polarization

Polarization is a characteristic unique to transverse waves. In transverse waves, the direction of movement of particles is perpendicular to the direction of movement of the waves. If the direction of the motion of the waves is the X-axis, then these particles can move in any direction along the YZ plane.

In a linearly polarized wave, the particles oscillate only in a fixed direction (fixed angle along the YZ plane). On the other hand, in an unpolarized wave, they oscillate in all directions (along the YZ plane). However, most sources of electromagnetic waves produce only unpolarized waves, consisting of waves with different polarizations. Therefore, a polarization filter is used to get linearly polarized waves from unpolarized waves.

Vertical linear polarization of an unpolarized wave – Image credits

Example

The glare you see on the highway while driving, and on a water-body on a sunny day are due to polarization. 

The light produced by the sun, as well as most artificial light sources, is unpolarized. But the water-body and the highway act as horizontal linear polarization filters naturally, reflecting only the light waves parallel (horizontal) to the surface. When this light enters our eyes, it creates a powerful glare. As a result, it becomes difficult to see clearly under the surface of the water and on a highway.

Application

Polarized Sunglasses act as vertical polarization filters. So, they block the harmful glare, which consists of light waves of horizontal polarization. Thus, a person wearing a polarized sunglass can see clearly under the surface of the water and also on a highway.

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How to find out if your sunglasses are polarized?

While wearing your sunglass, slowly tilt your head while looking at a reflective surface. Your head must be perpendicular (at 90°) to your body. Now, if your sunglasses are polarized, the glare should brighten.

Why can you see through a glass door, but not a wooden door?

Clue: Due to absorption

Absorption & Attenuation

When waves pass through a medium (solid, liquid, or gas), they transfer their energy to the molecules in the medium (or the medium absorbs the energy), making the molecules vibrate. This phenomenon is called absorption.

As a result, as a wave moves through a medium, it steadily loses energy. Since the energy of a wave is proportional to the square of its amplitude, its amplitude falls as well. This steady loss of amplitude or energy of a wave as it travels through a medium is called attenuation.

Example

A medium is considered transparent (to that wave) if only a fraction of the wave’s energy is lost as the wave travels through it. On the other hand, it is considered opaque if all the energy of the wave is lost.

A glass door is transparent to visible light since it absorbs only a part of the energy of the visible light. Hence, you can see through the glass door. However, a wooden door absorbs all the energy of the visible light. Therefore, it is opaque to visible light (but not to some other radiation).

Application

Different tissues in our body absorb X-rays to different extents. This concept forms the basis of the functioning of an X-ray machine.

We hope that this blog post helped you understand the properties of electromagnetic waves and the behavior of light waves. If you liked this blog post, you will like the following blog posts too:

1. Different types of Waves
2. 7 types of electromagnetic waves