How do waves travel in space?

[Dustin Kesselberg]

Hello all..I've searched this using the search button and on google and have found nothing.

My question is.How can radio/light/other waves travel in space while some waves such as sound can not?

Does it have to do with the fact they are electromagnetic waves?
Why don't they need a meduim?

How does it work?




Thanks...

 

[Pragmatist]

Hello all..I've searched this using the search button and on google and have found nothing.

My question is.How can radio/light/other waves travel in space while some waves such as sound can not?

Does it have to do with the fact they are electromagnetic waves?
Why don't they need a meduim?

How does it work?

Thanks...

Electromagnetic "waves" are not really waves as such, they are actually photons which are rather like self-contained particles. Photons (and in fact all particles) appear to have some sort of internal periodic motion (i.e. repetitive motion). Mathematically this periodic motion can be modelled as a wave and that is one reason why we still refer to "waves" when talking about such things. Of course the periodic motion in question is not necessarily a literal "wave" as such.

Electromagnetic theory was originally developed in the 19th century before quantization had been discovered (even the electron was unknown). James Clerk Maxwell developed a mathematical formal theory of electromagnetism to explain Michael Faraday's experimental results. Maxwell assumed that he was dealing with waves in some sort of medium (the aether), and he developed the mathematics based on that assumption. Perhaps surprisingly, the mathematics itself is correct regardless of whether the aether exists or not - and in the early 20th century, experiments (like the Michaelson Morley experiment) showed that no evidence of the aether could be found. Planck and others also found that light and other electromagnetic phenomena seemed to occur in discrete jumps called quanta. So putting the two together led to the rejection of the aether hypothesis and the acceptance of the idea that light etc., were better modelled as discrete self-contained entities (photons) with some sort of associated periodic motion.

To give a simple analogy:

Firstly imagine a wave in water - that's easy to do.

Now take a drop of water and imagine it suspended in the air. Now imagine that there are waves in that drop.

Obviously the waves are in the drop, but are not in the air surrounding the drop. So the drop in the air is rather like a "self-contained" object in which waves occur.

So now imagine that a photon is like a drop of water in empty space, moving with some sort of internal wavelike motion. Of course the photon is not water - we don't know what the "substance" of the photon is.

Does that help?

 

[Ziggurat]

Does it have to do with the fact they are electromagnetic waves?
Why don't they need a meduim?

Yes, it's because they're electromagnetic waves. They don't need a medium for exactly the same reason that an electric and magnetic fields don't need a medium, and can exist perfectly well in a vacuum.

 

[Bruce]

Re: Re: How do waves travel in space?

Now take a drop of water and imagine it suspended in the air. Now imagine that there are waves in that drop.

Interesting concept. I've always pictured it as a pulsating sphere, rather like a heart, with the pulses corresponding the wave mechanics.

 

[CurtC]

Why don't they need a meduim?
How does it work?

Like the others have said, we don't really know. We have it modelled mathematically very well, but understanding the "why's" is a different matter.

 

[Soapy Sam]

Sound waves are just air molecules in motion, passing kinetic energy pulses to each other. The pulses of energy, detected by the ear are experienced as sound.

Pump the air out of a bell jar with a bell inside. Ring the bell. The clapper moves normally, but the energy can't escape as compression pulses between molecules, so you don't hear anything. The energy goes into vibration of the bell itself- and, (I suppose) ultimately is radiated as heat (Infra red), which is electromagnetic (ie carried by photons) and can escape through the vacuum.

The sound "barrier"is a feature of our atmosphere and will be different on other worlds. The light barrier is a fundamental feature of our universe. There may be universes, or hyperspaces, where the value of c is higher. If we can get there, travel and get back, we might be able to travel FTL, effectively.

But that, so far as we know, is science fiction.

 

[davefoc]

My own cut at this is the aether does exist. I realize that physics books put forth the idea that aether doesn't exist and the michelson-morley experiments proved it.

They also are big on the idea that there is no unigue frame of reference.

My suspicion is that there is a unigue frame of reference that is at rest with respect to the aether.

Now I realize that it is incredibly pretentious of me to think that I would have any insight into this given the vastly more sophisticated and nuanced views of the universe that even your average physics phd has than me. OK, I accept that and freely admit that if I knew more or understood better I might change my mind on this.

A unigue frame of reference that is at rest with respect to a hypothetical aether suggests an explanation for is the transmission of electromagnetic waves. It is an observed fact that regardless of the velocicty of a photon's source the photon itself travels so as to neither gain nor lose distance to photons fired in the same direction from another source traveling at a completely different speed. This sounds exactly like there is a transmission media for the photons to me.

It turns out this theory is not unigue to me and there is a guy who has a web site that has worked out the mathematics so as to demonstrate that this view is as valid as a view without a preferred frame of reference at explaining observed phenomena. The biggest problem that I see with the theory is that it makes no predictions that I am aware of that are different than predictions made for a universe without any unigue frames of reference. But it does offer a kind of explanation for electromagnetic wave propagation and special relativity has no such explanation.

 

[Soapy Sam]

davefoc- I'm glad I'm not the only one. I'd have to say what I feel is a "preference" rather than a belief. I would not try to defend it for a moment.
We could start a "wierd physics we would like but don't actually believe in "society.

 

[Bodhi Dharma Zen]

My head hurts! I find the topic really fascinating. I wish I had a way to contribute, but this is really complex.

 

[Bruce]

Without the ability to measure or experiment, theories can reach a point were they are indistinguishable from beliefs. You can only extrapolate so much from experimentally supported theories. The more assumptions you have to make, the farther from reality it takes you.

 

[pgwenthold]

Re: Re: How do waves travel in space?

Electromagnetic "waves" are not really waves as such, they are actually photons which are rather like self-contained particles. Photons (and in fact all particles) appear to have some sort of internal periodic motion (i.e. repetitive motion). Mathematically this periodic motion can be modelled as a wave and that is one reason why we still refer to "waves" when talking about such things. Of course the periodic motion in question is not necessarily a literal "wave" as such.

Of course, the concept of electromagnetic waves that traversed space without the need of the aether predates wave/particle duality, and the concept of photons.

Maxwell's equations describe electromagnetic waves just fine, and they were around before guys like deBroglie came on the scene.

 

[Pragmatist]

Re: Re: Re: How do waves travel in space?

Of course, the concept of electromagnetic waves that traversed space without the need of the aether predates wave/particle duality, and the concept of photons.

Maxwell's equations describe electromagnetic waves just fine, and they were around before guys like deBroglie came on the scene.

I'm not sure I'd agree with that, but it all depends on what sense you refer to with "concept".

Maxwell developed his equations based on the fluid mechanics of a hypothetical aether. Therefore, the concept of the waves without the medium did not apparently exist when the equations were developed.

There was resistance to the idea of waves without a medium when Einstein brought it up - and, the idea of quantization had already been developed by that time by Planck and Einstein himself IIRC.

It is remarkable that Maxwell's analysis was so good, that it could be used in abstract without consideration of the medium, but that doesn't imply that it was developed that way. It was Einstein who first seemed to realise that.

I'd have to check, but I thought that Einstein had already developed the photon concept with the photoelectric effect, before he came up with relativity and light without a medium, but I may be mistaken about that.

 

[pgwenthold]

Re: Re: Re: Re: How do waves travel in space?

I'm not sure I'd agree with that, but it all depends on what sense you refer to with "concept".

Maxwell developed his equations based on the fluid mechanics of a hypothetical aether. Therefore, the concept of the waves without the medium did not apparently exist when the equations were developed.

There was resistance to the idea of waves without a medium when Einstein brought it up - and, the idea of quantization had already been developed by that time by Planck and Einstein himself IIRC.

It is remarkable that Maxwell's analysis was so good, that it could be used in abstract without consideration of the medium, but that doesn't imply that it was developed that way. It was Einstein who first seemed to realise that.

I'd have to check, but I thought that Einstein had already developed the photon concept with the photoelectric effect, before he came up with relativity and light without a medium, but I may be mistaken about that.

Sorry, didn't mean to necessarily imply that it was the basis for them or anything, just that Maxwell's equations describe everything perfectly fine, even without a medium, and they were developed before the concept of particle/wave duality. Therefore, you don't need to resort to photonic behavior to explain how waves travel in space, because Maxwell's equations do just fine.

Mickelson-Morley had shown in 1877 that there wasn't an aether, but it was also true that Maxwell's equations (1864) still worked.

I do know that Einstein spent a lot of time thinking about Maxwell's relations. But I don't think the concepts of relativity and the absence of a medium are inherently linked. Relativity works just fine for light traveling through a medium.

 

[drkitten]

My own cut at this is the aether does exist. I realize that physics books put forth the idea that aether doesn't exist and the michelson-morley experiments proved it.

They also are big on the idea that there is no unigue frame of reference.

My suspicion is that there is a unigue frame of reference that is at rest with respect to the aether.

The biggest problem that I see with the theory is that it makes no predictions that I am aware of that are different than predictions made for a universe without any unigue frames of reference. But it does offer a kind of explanation for electromagnetic wave propagation and special relativity has no such explanation.

It does seem that the Michaelson/Morley experiments would contradict your theory. Unless the Earth were constantly at rest with respect to the transmission medium -- which it would not be at all points in its orbit except one, and which any given point on the Earth's surface could not be except once per day -- then the ether "wind" should be detectable.

 

[davefoc]

new drkitten,
The Michelson-Morley experiment doesn't contradict the possibility of an aether or a unigue frame of reference.

I realize that it is often presented that way, but that is, I think, not an accurate representation of the situation.

Just because time and length contraction occur that make all frames of reference seem the same does not preclude the possibility that there is actually a special frame of reference at rest with respect to the aether.

I like the idea of the aether because it suggests an explanation for the observed facts. Relativity makes predictions based on the observed facts which time has shown to be true. As such Einstein's relativity theories are seen as great intellectual achievements. However the theories don't suggest a physical explanation for how light propagates or even what it is.

My thought and now it turns out that it is also the thought of other people who seem to know more about it than me is that in fact there might be an aether that serves as the propagation medium for electromagnetic waves. The idea came to me when I was trying to understand this strange notion that no matter what the velocity of emitting source of an electromagnetic wave the emitted wave would neither gain on fall farther behind a wave emitted from a source with a completely different velocity. That suggests to me that there is a medium that that the wave propagates through.

Another thing that comes out of this idea is the possibility that everything we know of as matter and energy are just perturbations in this aether. That explains why what we think of as matter can change to other forms of matter or electromagnetic energy. What is happening is one kind of peturbation in the aether has just changed to a different kind of pertubation in the aether.

As an aside I believe it was reported that Michelson believed that the aether existed until the day he died.

edited to add link to site where this idea is discussed with some mathematical rigor:
http://peterallport.com/

 

[drkitten]

edited to add link to site where this idea is discussed with some mathematical rigor:
http://peterallport.com/

Unfortunately, Mr. Allport's understanding of the Theory of Relativity is deeply, deeply, flawed -- failure to understand the resolution of the "Twin Paradox" is only the tip of the iceberg. Similarly, the four questions to which orthodox theory supposedly cannot provide an answer all have well-understood and well-supported theoretical and experimental answers.

There are also a few easy experimental disproofs of the theory as presented in the papers -- the chief one being that two objects flying in parallel courses will not observe doppler shifts w.r.t. each other under conventional SR, but will observe doppler shifts w.r.t. each other depending upon the motion of the underlying ether, depending upon whether they are both flying "upstream" or "downstream." (Figure B in "QM View 101" illustrates this nicely.) I should even be able to produce a measurable doppler effect, that varies with apparatus orientation and with the Earth's "proper motion", by bouncing a signal off a mirror. Needless to say, I am unfamiliar with any experimental support for this claim.


The theory itself is inconsistent as well. For example (again, from "QM View 101"), "why should observers in B observe a "relativistic" foreshortening of the diamond formation in A when no foreshortening exists? And why should observers in B observe that the clocks in A are running at only .6 times the rate of clocks in B when just the opposite is true? Several factors combine to cause the virtual length contraction and time dilation determined by the observers in B. These factors include the shortened units of distance in B, the slowness of clocks in B, the observers' lack of awareness of the actual distance and time units kept by their measuring instruments, and the observers' belief that the speed of light is constant in their diamond formation." (For the benefit of the lurkers, objects in A are "at rest" w.r.t. the hypothetical ether, objects in B are not.

Unfortunately, his reasoning is exactly backwards. If observers in situation B are using clocks that are OBJECTIVELY slowed and meters that are OBJECTIVELY shortened relative to situation A, then observers in B will notice that A is experiencing exactly the opposite situation than relativity predicts. In fact, observers in B will notice a much worse situation than actually holds.

Again, I believe that the Michaelson/Morley situation provides a direct experimental disproof of this theory. It's greatly to Mr. Allport's discredit that he doesn't even appear to discuss the implications of M/M.

 

[Ziggurat]

new drkitten,
The Michelson-Morley experiment doesn't contradict the possibility of an aether or a unigue frame of reference.

In a sense, this is correct. But what it DOES do is prove that no aether or unique frame is necessary to describe the propagation of light. And in the absence of any need for such an aether, why would anyone want to introduce it?

I like the idea of the aether because it suggests an explanation for the observed facts. Relativity makes predictions based on the observed facts which time has shown to be true. As such Einstein's relativity theories are seen as great intellectual achievements. However the theories don't suggest a physical explanation for how light propagates or even what it is.

An aether doesn't help you out here either. It just shifts the question from "what are electric and magnetic fields" to "what is the aether". That's not an improvement. It's an added, and unnecessary, complication.

My thought and now it turns out that it is also the thought of other people who seem to know more about it than me is that in fact there might be an aether that serves as the propagation medium for electromagnetic waves. The idea came to me when I was trying to understand this strange notion that no matter what the velocity of emitting source of an electromagnetic wave the emitted wave would neither gain on fall farther behind a wave emitted from a source with a completely different velocity. That suggests to me that there is a medium that that the wave propagates through.

It wouldn't suggest that if you really understood relativity. In the hyperbolic geometry of relativity, such "strange" behavior is completely natural and expected. It's really quite simple indeed. All you need is the hyperbolic space-time metric (s^2 = x^2 + y^2 + z^2 - (ct)^2 ), and everything else falls out naturally. Electromagnetism becomes self-consistent and matches with experiments with NO need for any medium, the slowing of clocks in motion falls out (also experimentally observed), c as an upper limit on velocity falls out, it's all internally consistent AND matches with experiment. Just from that ONE little equation. There is no aether theory that can match experiment with anywhere near this simplicity. That, ultimately, is why nobody serious pays any more attention to the aether. It's simply unnecessary. Occam's razor, and all that.

 

[davefoc]

new drkitten,
Thank you for your response. I, frankly, am not knowledgeable enough on this subject to respond directly to your criticism of allport. I do plan to spend some time with your post and attempt to understand your points better, however.

you wrote:

Again, I believe that the Michaelson/Morley situation provides a direct experimental disproof of this theory.

Which theory does the michelson/morley experiment disprove?

Is it your view that it disproved the possibility of a unigue frame of reference?

I believe that it found that it wasn't possible to distinguish one frame of reference from another based on the speed of light. Not being able to distinguish one frame of reference from another frame of reference is different than determining that there is no unigue frame of reference.

 

[drkitten]

you wrote:

Which theory does the michelson/morley experiment disprove?

Is it your view that it disproved the possibility of a unigue frame of reference?

It is my view that it disproved the possibility of a stationary aether through which EM waves propagate and that the EM Doppler effect is caused by source or observer motion through this aether.

Basically, Mr. Allport's theory.

The simplest interpretation of the M/M experiments is that, IF an aether exists, the Earth is at rest relative to it. There may indeed be another theory that postulates a unique frame of reference that is compatible with M/M. (A number of scientists, for example, experimented with the idea of "aether drag," where the Earth's mass produces a local effect on the aether where it is at rest. This is compatible with M/M, but contradicted by other experiments.) But Allport's theory does not appear to be compatible with M/M or with the observations of SR.

 

[davefoc]

ziggurat, I basically agree with everything you said including your suggestion (veiled a bit) that I might not understand relativity.

The only thing where I quibble is that relativity provides any kind of physical explanation for what is going on. Relativity starts with an assumption of the constancy of the speed of light and builds a mathematical world that makes other predictions. We think this mathematical world is a good description of what is going on because it makes predicitons that turn out to be correct.

But the theory doesn't provide any idea of what the underlying physical mechanism is. You say that it doesn't need an aether since it can make predicitons without the aether so the aether is an unncessary add on. You also say that hypothesizing aether doesn't get you any further as to knowing what is going on because you don't know what causes the aether or much about its nature. All of this I basically agree with to the degree I understand the issues.

Still, when one is looking for an explanation for how electromagnetic waves propagate or what is their actual nature the existence of this mathematical model that makes all these cool predicitons doesn't provide any insight into an actual mechanism.

As a slight digression this discussion reminds me a bit of the discussion on what is the point of hypothesizing a god. It just moves the answer to basic questions of how we came to be one step further away since it provides no answer to how did god come to be. I think you are saying that the idea about aether is sort of like the idea of a god. For reasons I can't defend (at least right now) I see the situation as different but fully acknowlege that people who know a lot more about this don't agree with me.

I am afraid I don't have time to look this up right now but I believe that Lorentz who derived the equations for time and length contractions based on an assumption that there was an aether.