Hello,

(I hope this question hasn't been beat to death already. I couldn't find it in a search.)

Without a medium to travel in and through, how do microwaves and radio waves travel through the vacuum of space?

Thanks!
Jeff

They are both composed of photons, the same type of energy as visible light, ultraviolet, infrared, x-rays, etc. These act as particles and travel through space without a medium.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Well, they obviously DO, so in the context of electromagnetic waves, the idea that "waves" need some medium within which to travel is obviously wrong.

Maybe the problem with visualization or conceptualization stems from the fact that electromagnetic waves are quite different than ripples in a pond or sound waves or seismic waves. Certainly electromagnetic waves have certain wave qualities, but they also have the qualities of particles, and in recognizing this you have opened the door to the quantum realm, where lots of qualities and effects go against normal common sense derived from the history of human experience prior to the 1930s.

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Everyone is entitled to his own opinion, but not his own facts.

Thanks for your help in thinking this through. Since being taught about "waves" as a child, I was given the ripple in a pond analogy and came to think of radio waves in the same realm. Radio, infrared, and visible light all being on the same electromagnetic spectrum puts this all in a clearer perspective for me. I just didn't think about it this way, but it clicked when you both connected the pieces.

Jeff

Also, note that your question is very profound, and would have received an entirely different answer just 105 years ago. Back then it was thought that all waves required a medium. Now we know that the wave phenomenon is far more fundamental than that-- it pervades the motion of all particles, of everything. So waves in a medium are actually just a kind of superficial example, sharing the same mathematical features of this much more widespread phenomenon.

The ether.

That's ether true or false.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

If you dig deep enough, you will find that answers like "Well, they obviously DO, so in the context of electromagnetic waves, the idea that "waves" need some medium within which to travel is obviously wrong." to be wholly unsatisfying. If you look wide enough for a theory that encompasses all phenomena, you will also find that answer is useless in its application.

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"Only those who attempt the absurd will achieve the impossible." - M. C. Escher

"Freedom is popular." -Ron Paul

Say what?

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

So you, of course, have an answer for the OP's question to share with us, right? Something positive to add to the discussion?

...Keeping in mind, of course, the forum's rules?

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Actually, they do travel through a medium: space-time.

I think it's been rather clearly demonstrated that gravitational gradients within the space-time continuum affect the velocity at which EM fields propagate.

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

I find the concept of an "ether" fascinating.

The only way I can visualize it coherently, is to imagine that every place that there is....all of space is comprised of little plusses and minuses everywhere, and no two of the same touch. Like a cube or a sphere filled with red and blue marbles with no two of the same color connecting. So when you put your hand in the sphere, they keep that property even though you are making them get out of your way.

You are certainly correct that we can use a theory of gravity to understand how light propagation can be altered, yet even sound waves must respect it-- and we would not call spacetime the medium of a sound wave. One might be tempted to call spacetime the medium of gravity waves, I'll leave that to the "high-priests" of gravity waves-- but spacetime is something more fundamental than a wave medium, and I think it is still fair to say that waves do not require a physical medium at all, the thing that is "waving" can be an entirely mathematical construct that cannot itself be detected directly. In fact, that might be the most important thing of all to know about waves, which came as a very large surprise in the 1920s when it was learned that all particles obey wave mechanics.

Yes, the question for me that is really interesting is this: we know from the slit experiments that particles have both particle and wave properties. And the particle properties are quite easy to understand. But how do they acquire wave properties without a medium?

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As above, so below

Sounds like the vibration of those "strings".

You can "wiggle" whether in space, or the ocean. You just wiggle differently.

Jeff. "Space" is not empty, even though it has little in the way of solids, liquids, gases, and plasmas.....on average. The concept of vacuum as nothingness is not particularly fruitful, or true, and as Asimov wrote in his treatise "On Physics", only one of the four physically valid interpretations of the negative result of the Michelson-Morley experiment was that there was no ether...(the popular one, because it's simple). Space is filled with neutrinos, and antineutrinos, amongst other things. Pete.

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A third rate theory forbids.
A second rate theory explains after the fact.
A first rate theory predicts.
A. Lomonosov

Just as gravity pulls matter, it also pulls photons. Thus gravitational effects on EM need not be attributed strictly to a medium.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

That might be a bridge too far for science to answer. But I will point out that actually it might be the "particlelike" aspects that are more bizarre than the wavelike ones, where by "particlelike" I mean the common misnomer of the concept of a trajectory. You see, the great thing about a wave is that it propagates by constantly re-creating itself; every part of that wave is both a source of the new wave, for the next instant, and the means of the replacement of the old wave-- all via interference. Interference explains how the wave of "now" is replaced by the wave of "a moment later", continuously-- it destructively interferes the old wave into oblivion and constructs the new wave slightly displaced: motion in a nutshell. But how does the concept of a trajectory work? How does a bullet move, how does it know that it can't be in the old location but has to keep on showing up at some new location all the time, based on some strange property we call "speed" but don't know how a bullet "knows" its own speed? Waves take care of all that, we're just more used to trajectories: it's an example of how easily familiarity is mistaken for understanding.

I think Xeno asked the same question several millennia ago!

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As above, so below

Indeed he did, I think a lot of people don't give him credit for in some sense anticipating the need for wave mechanics!

I do think there is sometimes something to be said for regarding the "speed" of photons to be a very useful model rather than taking the concept literally. This was actually proposed by Bondi in which he suggested the speed of light could be explained as a ratio of macroscopic distance and macroscopic time rather than being described as a velocity of something "traveling". I'm not of course suggesting we cease to think of photons as traveling particles in terms of a macroscopic model, so in this sense it doesn't help at all in attempting to answer fundamental questions about light propagation, but it helps (me at any rate) to attain a little understanding that sometimes such questions should not be separated from an appreciation of what physics is actually capable of describing (as you have pointed out many times).

Actually, I think the term microscopic might be more accurate, as light in a vacuum travels Planck distance in Planck time, both very small units.

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

I take your point, I used the terms macroscopic within the context of Bondi's statement, which just for the record was:

"Any attempt to measure the velocity of light is... not an attempt at measuring the velocity of light but an attempt at ascertaining the length of the standard metre in Paris in terms of time-units."

Bondi, H: Assumption and Myth in Physical Theory, (Cambridge University Press, 1965)

Here the length and time units are obviously macroscopic measurements, and I think Bond's point was that we infer a velocity of light from such measurements of time and distance. In other words, we have a very useful model of light as photons traveling at a speed c, but it is a macroscopic inference.

I am not at all sure that within the realms of quantum mechanics it is possible to say we can measure the speed of a single photon with no macroscopic involvement from the observer. Quantum measurement seems to be weakly objective in this sense in that it depends on the notion of an observer. But I do find quantum measurement to be a very difficult concept to get to grips with.

B-b-but! That is the definition of speed: distance traveled per unit time.

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Yes; But what I think I am hearing is that a single object cannot or has not had its speed determined, but the speed is related to multiple objects acting in a group (thus the macro aspect).

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Numbers are not case sensitive. (me)

Yes, of course, but I think the point is that a macro object observed as traveling between two points in a known time can be given a speed and we say that the observed object has a speed relative to either point. This whole process is macroscopic in nature and represents our reality.

Between a light source and sink however, in vacuum, there is nothing to be seen. So the speed of a "traveling photon" is an inference based on what we know to exist indirectly at the source and sink. I would consider this inference to be part of the model of light. And that model depicts photons as traveling particles. To ask as the OP does, how does light propagate in vacuum is perhaps to ask too literal a question of a model. The question asks for an underlying mechanism, a mechanism in fact that may not exist, for perhaps it is the model that gives a velocity, not the underlying reality. But this largely becomes philosophical, especially to accept the possibility that our reality is holistic in nature, encompassing everything as a macroscopic whole, for to consider light as not having a velocity means just that. And to have a model of light that possibly bares little resemblance to nature as she really is is too much for many. It doesn't bother me greatly, we are never likely to know directly the true nature of us as sentient beings in the context of space and time, I think it is outside of the scope of physics. But I do consider the model of light to be a good one, true to physics as practiced, and when I get bogged down with philosophical questions like that posed by the OP involving the nature of traveling photons or propagating waves in vacuum, I just remind myself that it is just a model.

And for us non-savants that would like a headache you can Google the Wheeler-Feynman advanced retarded theory of EM or the Cramer interpretation of the same.

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(By the way, I hate it that so many papers in the areas of planetary science and geology are not easily available to the dreaded "non-subscribers". It is like they are screaming at me: "YOU CAN'T HANDLE THE TRUTH". Good, I feel better now.)

"Quaerendo inventis"

Right, that's just a fact. And as jlhredshift points out, it is not even necessary to adopt such a model of particle propagation-- a more "literally real" model would appear to use interference between multiple path integrals, none of which individually have a speed associated with them. Speed is an emergent property of what is "really happening", it is a construct of our minds that serves us well, like everything else we can talk about. Questions like "but how does that really happen" are ultimately ill posed-- we should strive for a more precise way to ask what we actually want to know.

Yes, and of course one must watch out for the "just" word, as it is often misunderstood. The greatest accomplishments of human thought are "just" the greatest accomplishments of human thought-- what the word "just" means is rather up to the individual.

Yes, I agree. I used the "just" as a means of giving emphasis to my distinction between nature as she really is and our models that we construct, but it could be taken as implying the model is "just" a model - not of real importance. I hope it goes without saying that this is not at all what I mean, but I do take your point. Language is important isn't it!