Electromagnetic waves - what are they?

[HamsterSlayer]

I recently came to reflect on the matter of electromagnetic waves.

It goes without saying that radiosignals, microwaves, radar, infrared light, visible light, ultraviolet light, x-rays, gamma radiation etc. all are electromagnetic waves, only with different wavelengths.

The interesting part is that no one really knows what media these waves travel in. Soundwaves for instance travel trough air, water or whatever.
But it has yet to be found out how radiosignals and light can travel through empty space, or how an antenna can receive a signal from a transmitter with no electrical connection. I'd really like to know... electromagnetic waves are movement in... what?

According to my knowledge there should something around the size of a Nobel-prize waiting for the person who finds out.

So... any suggestions?

 

[owensdj]

I don't know that much about physics, but my understanding is that electromagnetic waves are made of photons.

 

[f95toli]

...and they don't move in anything as was proved at the end of the 19th century (I far as I can remember the orignal name for this "medium" that light was suppose to move in was the "eather").
And electromagnetic waves are just that: Waves. Unless you want to measure particles because then they are photons, it depends on HOW you measure.
This might seem very strange but it is true, you just need to know a thing or two about quantum physics in order to understand it.

 

[Geniere]

Well your reflections have been shared by the most brilliant physicists since the late 19th century. Your post implies that there must be a medium for light to travel. This is akin to the Aether once postulated but ruled out after experimentation. Modern physics seems to indicate a medium for transmission, but not in the classical sense. References are made re: "fabric of space", but nothing about its properties.

My own, ill-informed viewpoint, is that photons (bosons) do not travel at all, but are satationary oscillations, i.e. standing waves in the fabric of space. Assume a photon has a wavelength equal to the size of the universe. If the universe confines this photon, it cannot move, merely oscillate.

I think I'm going to be sorry I posted this.

Regards

 

[RossGr]

Electro Magnetic waves do not need a medium. E&M waves obviously from the name consists of 2 components, an Electric field and a Magnetic field. The behavior of these fields are decriped by Maxwells Equations, (for a statement of these equations click on the "god said" link in my sig) The net result of these equations is that a changing electric field creates a magnetic field. Likewise a changing Magnetic field creates a electric field. A EM wave is simply Electric and Magnetic fields exchanging energy as the propogate througn space. The closest thing to an "Aether" is the basic Electric and Magnetic properties of space, The permittivity denoted epsilon (sub zero) and the permeability of free space Mu (sub zero).

Maxwell formulated the set of equations named for him based on the work of Faraday, Orestead, Gauss, and Ampere. When he compilied their work into a single system of equations he was able to cast them into the form of the equation for a traveling wave, it is easy to see the velocity of the traveling wave when expressed in this form. The velocity for these Electro-Magnetic waves was given as

v= sqrt( 1/eplison (sub zero) mu (sub zero))

Both of these numbers had been previously determined by experiment

epsilon (sub zero)=1.26x10^-6 Henry/m
mu(sub zero) = 8.85x10^-12 Farad/m

When you cast these numbers in their fundamental units and do the simple math the number he came up with was

v=3x10^8 m/s

Some of you might recognize this, Maxwell certianly did, we now call it c the speed of light. This was done in 1867 and was first bit of proof that light is a form of Electromagnetic radiation. This derivation also threw the world of Physics on its ear.

Why? because the speed of light depends upon fundamental constants of space, it was well accepted at the time that no matter what speed you traveled at, you would measure the same values of epsion an mu, therefore this implied the SAME THING about the speed of light! No matter what your speed you would measure the same value. This was in direct conflict with Classical Newtonian Physics which says that speeds add together. This conflict was called "Maxwells Cundrum" and plagued Physics until 1905 When Albert Einstein published his Theory of Special Relativity.

 

[f95toli]

The problem with that viewpoint is that it is fairly easy do detect a single photon. SIngle photn detectors have been available for a long time now, using these you can pinpoint the position of a single photon with high accuracy, photons ARE particles in a sense.

I think the best way to look at it is to say that photons (or electrons, protons etc) ar neither particles nor waves, they are simply objects that sometimes are best described as waves and sometimes as waves.

Nothing I said implied a medium. Light is a "normal" wave (wave in water) but a phenomena best described using a wave-formulation in most situation. There are (very complex) formulations of quantum mechanics that can describe light without saying anything about particles or waves.

 

[RossGr]

Just think of a photon as a wave packet, that is the form dictated by Qunatum Mechanics, it propgates as a wave, interacts with matter as a particle. Since single photons produce a double slit interference pattern, they cannot be seen as a classical particle. They do have a localized expectation value, but to evaluate the wave shape one must integrate to +/- infinity over all spacial dimensions. So one could say that a photon is everywhere.

This actually agree well with Special Relativity, since a photon moves with the speed of light, time as we know does not exist, as soon as the photon is emitted it is adsorbed, but this is all right, because due to length contraction a photon knows no distance, it can be adsorbed immediatly any where in the universe simply because it IS everywhere in the universe.

 

[f95toli]

I am not sure I agree. Lets say that you describe a photon as a wavepacket (gaussian to keep it simple) and want to study a process where a photon is emitted from for example a quantum well, just after the photon is emitted it is well localized in phase-space and you can measure its "position" quite well, since a gaussian wavepacket is so well localized I think it would be ok to say that the position of the photon is where the probability amplitude has its maximum value in this case. The position is "smeared" but if you were to calculate the overlap integral with another quantum well (for an absorbtion process)at the other end of the universe it would still be zero. The +-infinity limits of the integral can without problems be trunctated close to the maximum probability amplitude of the photon.

 

[RossGr]

I am not sure I understand your point. I will point out that the Heisenberg uncertianity principle prevents use from haveing precise knowledge of the location. We can compute the probability of finding the photon at any point is space, yes the probability of finding it in the tails of the distribution is extremely small it is non zero for every point in space.

If you what you say is true then is it impossible for a photon to travese the universe? The fact that we observe photons from distant reachs of the universe says that the probability for a photon emmited by a quasar to be adsorbed by our detectors is non zero.

 

[Geniere]

When considering relativity one must include the reference plane of the observer. In our local reference plane we can use the Special Theory (flat space geometry) to define physical interactions. In a global reference plane, the General Theory (curved space geometry) may be applied. This provides for accelerated objects such as a photon passing through the gravity well of a massive object. This photon would be moving in a curved path or at less then the speed of light depending on the reference plane of the observer. Einstein allows for constraints on the constancy of C. String theory also provides a mechanism for constraints on C. Physics can only be understood through it's math. My long forgotten two semesters of cllculus and ability limit my understanding of any complex theory, but I seem to be in good company.

Another conundrum involves the "color" of the photon. If a photon moves at the speed of light it must have infinite mass or energy, the two terms being interchangable. It is known that a "red" photon has less energy than a "blue" photon. This implies that one of the photons has a little more than infinite energy or the other has a little less than infinite energy.

The speed at which light travels does not address the original question re: the existance of a transport medium, which is neither predicted nor disallowed by relativity (as I understand it).

Regards

 

[f95toli]

Originally posted by: RossGr
I am not sure I understand your point. I will point out that the Heisenberg uncertianity principle prevents use from haveing precise knowledge of the location. We can compute the probability of finding the photon at any point is space, yes the probability of finding it in the tails of the distribution is extremely small it is non zero for every point in space. If you what you say is true then is it impossible for a photon to travese the universe? The fact that we observe photons from distant reachs of the universe says that the probability for a photon emmited by a quasar to be adsorbed by our detectors is non zero.

Sorry, I was a bit unclear. What I meant was of course the probability just after the emission (say 1 picosecond after the photon leaves the quantum well), after that there is nothing that prevents the photon to travel to the other end of the universe. The uncertianity principle is not a problem in this case as long as we do not care about knowining the momentum of the photon.

I also realized I have a better example of localized photons. Using high-Q cavities (basically two "mirrors facing each other) it is actually possible to "trap" a photon for some time, the photon is then really in the cavity, the probability to find it somewhere else is zero. This experiment has been done and is used in quantum-optics.

 

[RossGr]

Well since I started by talking about free photons your trapped photon is a different case. But even so, when the postion expectation values of a photon in an infinite well (your trapped photon) is computed the tails of the distribution extend beyond the walls. I believe this is where the concept of Quantum Tunneling comes from. But that is a entirely different situation then what I was initially referring to. I was speaking very generally, this is a very specific example. So while what you refer to is indeed true and a very interesting example it is a bit like if upon hearing someone say, "Cars have 4 wheels" you say "No, you are incorrect! They make a 3 wheel Morgan so cars do not have 4 wheels"

 

[f95toli]

Originally posted by: RossGr
Well since I started by talking about free photons your trapped photon is a different case. But even so, when the postion expectation values of a photon in an infinite well (your trapped photon) is computed the tails of the distribution extend beyond the walls. I believe this is where the concept of Quantum Tunneling comes from. But that is a entirely different situation then what I was initially referring to. I was speaking very generally, this is a very specific example. So while what you refer to is indeed true and a very interesting example it is a bit like if upon hearing someone say, "Cars have 4 wheels" you say "No, you are incorrect! They make a 3 wheel Morgan so cars do not have 4 wheels"

My comment was more connected to earlier posts. My point is that photon CAN be localized and does not have to be "everywhere", this is of course true for all all particles (electrons, protons) as well as for you and me. From my point of view there is nothing strange about photons, the concept just takes the particle/wave duality to the extreme.

About the tails: In the experiment I was refering to I think the tails are very small and the values of the distribution are negligable outside the walls, when you treat the problem theoreticaly you can just say that the probability is zero.

 

[RossGr]

Oh, did I mention that there probably is not sufficient time in the life of the universe for this tunneling event to happen!

 

[pexidecimal]

Is it possible for Light to be a form of gravity? If you've heard of something called " The seth material" you'll know where this came from:

"This alternative theory gave the simplest explanation of light; that it was really a vibration of the fifth dimension, or what used to be called the fourth dimension by the mystics. If light could travel through a vacuum, it was because the vacuum itself was vibrating, because the ?vacuum? really existed in four dimensions of space and one of time. By adding the fifth dimension, the force of gravity and light could be unified in a startlingly simple way..."

So even though space is a vaccume, light still travels within a medium of dimentions.

 

[f95toli]

Originally posted by: pexidecimal
Is it possible for Light to be a form of gravity? If you've heard of something called " The seth material" you'll know where this came from: "This alternative theory gave the simplest explanation of light; that it was really a vibration of the fifth dimension, or what used to be called the fourth dimension by the mystics. If light could travel through a vacuum, it was because the vacuum itself was vibrating, because the ?vacuum? really existed in four dimensions of space and one of time. By adding the fifth dimension, the force of gravity and light could be unified in a startlingly simple way..." So even though space is a vaccume, light still travels within a medium of dimentions.

No.
I think it is important to understand that we know quite a lot about light. In fact light is a nice system to play with because we understand it so well. The "problem" is that the theories you need to describe it are so complex that you need to study physics at the university-level for many years before you can "understand" it.

This is a general problem with modern physics: Nature is just "weird" and it is not always possible to create simple models that can help you understand what is going on. Our brain was designed to understand the macroscopic world we encounter in our everyday life, not quantum physics; and even if we know that our description is correct in the sense that we can predict what will happen in an experiment that that does not mean that we can "understand" what is going on in the way some people would like us to. I think this is something we simply have to accept.

 

[pexidecimal]

The most we know is that light behaves like light. It acts as a wave until it strikes a physical object and then behaves as a particle. Fairly unique i should think and something we, as you say, simply need to accept. But its never that easy We all have to find out why we accept it hehe.

So, how does the way a photon work compare to the way a graviton works?

 

[f95toli]

Originally posted by: pexidecimal
So, how does the way a photon work compare to the way a graviton works?

I don´t think anyone can answer that question, there are several theories about gravitions but so far they have not been detected.
The biggest unsolved problem in modern physics is how to include gravity in quantum mechanics. The idea behind the graviton is that since you can quantize the other forces (or interactions if you prefer) that exist in nature you should also be able to do the same to gravity but no one knows how to do it.

There are currently several research -project trying to detect a graviton, maybe they will succed in a few years, maybee not.

 

[pexidecimal]

what are the curent theorys about gravity?
Also, is it possible to have a negative photon? and if so, can it be detected? Considering photons can act as particles.

 

[nebula]

Originally posted by: f95toli I think this is something we simply have to accept.

I too agree that this is a problem with taking a University Physics course. The instructor explains something, and you're like, "wow, that's cool" and a few mniutes later you say, "but how does that really work". To truly understand these things you have to go beyond the course that they are introduced in. Which, I guess is the purpose of the course, to get your feet wet on a number of different topics, then you continue on to what interests you, Physics, EE, etc...

Of course, that's how things get discovered, by inquisitive minds.

Good thread though, made me reminisce about the EM waves section in Physics.

 

[dejitaru]

EM radiation is assumed to be in waves because of its effects. No one has seen a light wave.

 

[BaDaBooM]

I have recently found a very interesting document from a man named Ray Redbourne. I have an interest in this sort of thing and this is the first work that has really jumped out at me a being closest to the truth. I was always frustrated with my physics professors not providing any kind of mechanics for lightwaves, gravity, and other observations. All they would do would present math equations and such as proof. However this is not how the real world is... the universe is not made up math equations. Math equations are simply a way of describing the universe. This document gives a detailed mechanism for many of todays unknowns. He balances this with acknowledging that this is a work in progress, however I think it is pointed in the right direction. If you want a very interesting read about physics from a different point of view... I suggest reading this.
Here is a link to his web site... the book is free and downloadable in adobe acrobat format.

http://ca.geocities.com/rayredbourne/

I would appreciate any information on this guy because I have not heard of him.... but keep an open mind, I'm sure there are many unsung geniouses in the world.

*edit* caution this is not for the faint of heart, especially if you are stubbornly ingrained in current theories in phyiscs.... however works like this should not be written off just because they are contrary to current theories, after all, how else is progress made? I hope to get replies about who this guy is and perhaps arguments to the contrary. From what he says in his book, he also welcomes all discussion.

 

[RossGr]

Why would you want to replace a very useful mathematical structure for arm waveing useless nonsence? If you can come to grips with the math, the explainations and the understanding is all there. Not only that, but you get a powerfull tool for making and testing predictions. Through the mathematics Clerk Maxwell predicted the existance and the constant velocity of E&M waves. It took 20yrs before Hertz finially generated the waves predicted by the math. It took another 20yrs before Einstein was able to repair the rift in physics created by the constant speed of E&M waves.

Do you really believe that we do not understand these phenomena? How have we managed to come up with everything from LASARs to the very computer which we are using to communicate with, if we do not have very good understanding of the nature of matter and E&M radiation. These inventions were not accidents, they were not serendipity, they have resulted from a solid understanding of the fundamental properties of matter and energy.

It has been my experiance that the crack pots that write such web pages have at some point in time attempted to conqure the math required to understand modern Physics and failed miserably, rather then seeing it as a failure of theirs the blame the Physics and spend inordinate amounts of time using misapplied math to proof the world of Physics wrong, while they alone hold the secret to all.

They make amusing reading and are very frustrating to argue with.

 

[BaDaBooM]

I am not saying that the math is not important. However I can give all the math equations I want to describe and predict the effects of the mechanism, such as gravity, but it still does not tell how or why it works. And this is very important because if you do not understand the actual mechanism of how something works, then how can you can you possibly be certain that these equations based upon equations based upon equations are really telling you what you think they are about related mechanisms that interact with the original mechanism.

You are correct that many great discoveries have been made by using math equations dirived from observed effects (since what we don't know is either too small or too big to "see" directly) and many more to come. That is one method of discovery. But you cannot go much beyond the effects of a mechanism without conceptualizing how it actually works. Take gravity for example. Currently it is taught that gravity is an inherient attribute of mass that a "mystical force" reaches out from matter and pulls other matter towards it. This is a cope-out, which basically translates to "we have no &#*^# clue." And it is people like you that blindly and narrowmindedly just accept it as that and, in frustration of not knowing the truth, ridicule those who present a logical alternative theory of the actual mechanism. Incidentally, Albert Einstein was known as "crack pot" at first, since he too conceptualized his theory before he did the math. And he did not completely repair the rift. He brought the two closer together and later denounced his Cosmological Constant and some other work. Then he spent much of his later years trying to come up with a unifying theory. Copernicus was also known as "crack pot", so much so that the church killed him.... So go ahead and pick up your torch to protect your religion, arrogant bishop.

As far as us knowning the phenomenon, that is laughable... If this is the case, give me the exact mechanism for gravity, or what are magnetic lines of force made of exactly and why do they attract/repel. Also why does everyone accept this nonsense that light is both particle and wave. The two are completely exclusive. A wave is defined as energy with no mass moving through a medium and a particle is a mass of matter with structural integrity. It's the same as saying a married bachelor - nonsense. Someone once said, "As someone truly grows wiser, they realize more and more just how little they really know."

If you had read the work, you would have seen that he fully acknowledges it is a work in progress and hopes that many people with more resources and specializations than he explore the mathmatics and the validity of his theory. It is hardly "arm waving" as he has painstakenly tried to account for every unknown/possibly incorrect phenomema he could think of... Some of it is educated guesses based on his main theory, but that's where it all starts. I don't necessarily think all of it is right, but I think it may be the right direction to go in. Instead of casting it aside without analyzing it, come up with why it is wrong (to him, not me as I am not versed enough in his theories to rebut). Because as of yet, no one that I know of has even attempted such a detailed unifying theory to combine the (whether you like to admit it or not) very separate worlds of newtonian physics, quantum mechanics, and the theory of relativity. Remember most of these are just that... theories, so don't treat them as laws.

 

[FuriousBroccoli]

That guy is a sad loser. I'm not going to dignify his ramblings with rebuttles, but suffice to say, if he believed any of what he wrote, he'd set out to prove it or put it to good use, and wow the whole scientific community, not ramble on some pathetic website. Come on, he thinks the egyptians used the "sticky styrofoam effect" of static electricity to build the pyramids.