- Waves are easy to understand. Get a bunch of particles, make sure they have some force of attraction among themselves, and then disturb one particle. It will disturb the others, so the disturbance propagates through the medium, A.K.A mechanical wave.
Using this concept, how do we visualize or even conceptualize a wave that could travel in a vacuum? Impossible. That is what numerous people had, though. People thought it was so impossible that they firmly believed a medium must exist throughout the vacuum. Eventually, we discovered that there was not any medium throughout space. So, light was traveling in a vacuum without any medium, and it was a wave.
- To understand these light waves fully, one needs to undergo a course in electricity in magnetism. But to get a feeling of how these waves propagate in the vacuum of space, you just need to understand what electric fields are. [No not how your textbooks and teachers teach you, but in a little different way, a way in which you can see how radical the ideas are.]
- Electric and magnetic fields summary: Since charged particles can attract and repel each other from a distance, we believe that every charged particle is in the surrounding space. If you keep a positive charge at (0,0), then the T space. This is a radical theory developed mainly by Michael Faraday. A charge is kept at one location, modifying space somewhere else. Isn’t that wonderful? I can keep dwelling on this concept for hours together. Like how a charge creates an electric field that pushes and pulls other charges, a moving charge creates another kind of’ modification of space’ that pulls and pushes other moving charges. This is what we call a magnetic field. [A footnote: one of the great victories of Einstein’s theories is that he proved that these electric fields are the same things looked at from different perspectives, but let’s not worry too much about them; we will consider them to be two separate ‘modifications’ of space results from and affecting two separate things: static charges and moving charges.]
- So this concept had become pretty famous throughout the mid-19th century. The idea of charge creates electric fields; if these charges move, they create an additional magnetic field. But Faraday and Maxwell discovered that you could create these fields without any charges. They discovered that changing electric fields could produce magnetic fields and vice versa. This is the key to understanding electromagnetic waves. End of Electric fields summary
- How EM waves propagate in space: Now, let us consider an empty universe with no charges, fields, or whatever. Consider two points, A and B, separated by 300 km. Nothing exists at these two points; no charges or fields exist. Now, suppose magically, at t=0, a positive charge pops in at A. [I know you cannot do this in reality, but you can understand EM waves this way easily. Here is the question: is there an electric field at B at t=0? The answer is no. The space at point B does not even know that a charge has appeared at point A. And so does every point in space. Everywhere, the field is zero. But let’s go to the charge area at A. Let us go very close to it—very close, very, very close, so close that we are almost at A. But not at A. But infinitesimally close to it. Since this distance is differential, at t = 0, a non-zero electric field exists at this point. But wait, the electric field was zero before the charge popped in. But now it has changed. And I told you that a changing electric field creates a nearby magnetic field. So, as time passes by, a magnetic field is generated in the area. But wait, there was no magnetic field, so the magnetic field changed. This generates an electric field in its vicinity. This is how new electric fields are generated slowly and steadily at every point farther away from the charge. At about t = 1, the electric field generates at point B and keeps moving from here.
- These changes in electric fields or space modifications keep creating new alterations in the space nearby. This is an electromagnetic wave.
- Fascinating. It is unlike any other wave at all. Since charges are affected by these modifications of space, they are affected by EM waves. If such an EM wave were to get focused in the retina of your eye, it would make the electrons of the retina cell react to it, making it oscillate with the frequency of the EM waves. This would create an electric current that runs up the optic nerves to the parts of the brain, which results in some chemical reactions that finally cause the sensation of sight.
- Electromagnetic waves are taught in high school today. Yet it has taken us about 200 years since Newton’s time to understand and fathom this concept truly.
- Waves are easy to understand. Get a bunch of particles, make sure they have some force of attraction among themselves, and then disturb one particle. It will disturb the others, so the disturbance propagates through the medium. A mechanical wave.
- Using this concept, how do we visualize or even conceptualize a wave that could travel in a vacuum? Impossible. That is what numerous people had, though. People thought it was so impossible that they firmly believed a medium must exist throughout the vacuum. Eventually, we discovered that there wasn’t any medium throughout space. So light was traveling in a vacuum without any medium, and it was a wave.
- How can it work? The secret lies in the four Maxwell equations. The equations of electricity and magnetism. The equations changed how we looked at the world and gave way to the technological revolution of the 19th and early 20th centuries.
- To understand these light waves fully, one needs to undergo a course in electricity in magnetism. But to understand how these waves propagate in the vacuum of space, you need to understand what electric fields are. [No, not how your textbooks and teachers teach you, but in a little different way, a way in which you can see how radical the ideas are.]
- Electric field summary: Since charged particles can attract and repel each other from a distance, we believe every charged particle modifies the surrounding space. If you keep a positive charge at (0,0), the space at (say, (5,10) gets modified somehow. If kept at that point, this modified space pushes another positive charge (5,10).
- So this concept had become pretty famous throughout the mid-19th century. The idea is that charge creates electric fields; if these charges move, they create an additional magnetic field. But Faraday and Maxwell discovered that you could make these fields without charges. They discovered that changing the electric field could produce a magnetic field and vice versa. This is the key to understanding electromagnetic waves. .
- How EM waves propagate in space: Now, let us consider an empty universe with no charges, fields, or whatever. Consider two points, A and B, separated by 300 km. Nothing exists at these two points—no charges, no fields. Now, Suppose magically, at t=0, a positive charge pops in at A. [I know you cannot do this in reality, but you can understand EM waves this way easily. Here is the question: is there an electric field at B at t=0? The answer is no. The space at point B does not even know that a charge has appeared at point A. And so does every point in space. Everywhere, the field is zero. But let us go near the charge at A. Let’s go very close to it—very close, very close, so close that we are almost at A. But not at A. But infinitesimally close to it. Since this distance is differential, at t=0, a non-zero electric field exists at this point. But wait, the electric field was zero before the charge popped in. But now it has changed. And I told you a changing electric field creates a magnetic field nearby. So, as time passes by, a magnetic field is generated in the vicinity. But wait, there was no magnetic field, so the magnetic field changed. This generates an electric field in its area. This is how new electric fields are generated slowly and steadily at every point farther away from the charge. At about t = 1, the electric field generates at point B, moving from here.
- These changes in electric fields or space modifications keep creating new alterations in the space nearby. This is an electromagnetic wave.
- , Fascinating. It is unlike any other wave at all. Since charges are affected by these modifications of space, they are affected by EM waves. If such an EM wave were to get focused in the retina of your eye, it would make the electrons of the retina cell react to it, making it oscillate with the frequency of the EM waves. This would create an electric current that runs up the optic nerves to the parts of the brain, which results in some chemical reactions that finally cause the sensation of sight.
