Through what medium does EM propagate in empty space?

In summary, Einstein proposed an electromagnetic ether to explain the transmission of EM waves through "empty" space, but this concept was later deemed unnecessary and irrelevant. It was suggested that the quantum vacuum, consisting of virtual particles, could serve as a medium for the propagation of EM waves without having any sensible properties. Some scientists, such as Dirac, also argued for the existence of an ether in later years. However, the current concordance view is that EM waves are transmitted through the vacuum through virtual photons, which are not considered corpuscles.
  • #1
turbo
Gold Member
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Through what medium does EM propagate in "empty" space?

Einstein stated in his Leyden address (1926, I think) that an EM ether was mandatory for the transmission of EM waves through "empty" space. He was unable to reconcile this with the dynamical gravitational ether that had to exist to make GR work, so he proposed an EM ether that had NO sensible properties. In other words, it could not possibly be subject to polarization, densification, or any other measurable variation, unlike all the other fields known to exist. This concept seems a little silly, since fields are known to exhibit variations and the variations must be explainable via physical laws.

Is there anybody here that is willing to contemplate that the quantum vacuum might be this EM field - the palette upon which the Universe is written?
 
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  • #2
turbo-1 said:
Is there anybody here that is willing to contemplate that the quantum vacuum might be this EM field - the palette upon which the Universe is written?

You mean that the quantum vacuum would be the ether? This sounds more like a question for the Quantum Physics forum. As far as I know, the universe is still etherless, but someone more knowledgeable in QFT might be able to give you a better answer.
 
  • #3
In my opinion, Einstein was pointing out the futility of positing an 'ether' with any physically quantifiable qualities. I interpret that as meaning it's irrelevant. I also think it's OK to disagree on that.
 
  • #4
SpaceTiger said:
You mean that the quantum vacuum would be the ether? This sounds more like a question for the Quantum Physics forum. As far as I know, the universe is still etherless, but someone more knowledgeable in QFT might be able to give you a better answer.
Yes. The quantum vacuum consists of a field of virtual particles that pop in and out of existence continuously and exist for such brief periods of time that it completely satisfies Einstein's requirement that it have no sensible properties, such as motion.

From this paper on the ether:
http://redshift.vif.com/JournalFiles/V08NO3PDF/V08N3GRF.PDF

Einstein said:
According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of measuring rods and clocks, nor therefore any space-time intervals in the
physical sense.

Einstein said:
that now it appears that space will have to be regarded as a primary thing and that matter is derived from it, so to speak, as a secondary result. Space is now having its revenge, so to speak, and is eating up matter.

Poincare said:
In this new concept, the constant mass of matter
disappeared. The ether alone, and not matter anymore, was inertial. Only the ether opposed to a resistance to motion, thus one could say: there was no matter, there were only holes in the ether.
 
  • #5
These quotations show that Einstein and Poincre thought that what extends and supports radiation was the spacetime geometry, sometimes called the metric field. Neither man had anything to do with the quantum vacuum. Not that it isn't correct that the quantum vacuum supports radiation! But it isn't an ether in the nineteenth century sense, a medium in which the light waves wave.
 
  • #6
But it isn't an ether in the nineteenth century sense, a medium in which the light waves wave.
Yes. The quantum vacuum has "wave-like" properties, itself. So by the 19th century idea it too would require some sort of ether.
 
  • #7
selfAdjoint said:
These quotations show that Einstein and Poincre thought that what extends and supports radiation was the spacetime geometry, sometimes called the metric field. Neither man had anything to do with the quantum vacuum.
Perhaps not by that name, but what we have come to understand as the quantum vacuum serves the purpose admirably. Einstein himself said that without a transmissive medium ("ether" in the parlance of the day) light could not propagate through space. Lest we multiply entities unnecessarily, it would behoove us to examine the vacuum's role in the transmission of EM. As a neutral sea of virtual particles, it provides a baseline against which fluctuations can be expressed - a medium through which waves can be transmitted.

selfAdjoint said:
Not that it isn't correct that the quantum vacuum supports radiation! But it isn't an ether in the nineteenth century sense, a medium in which the light waves wave.
Why not? And if not, how can we describe the propagation of light through a vacuum? Must we resort to some corpuscular theory that reduces photons to little points of energy hurtling through "empty" space, heedless of the sea of virtual particles all around them?

What is the concordance view on the transmission of EM through the vacuum?
 
  • #8
turbo-1 said:
Why not? And if not, how can we describe the propagation of light through a vacuum? Must we resort to some corpuscular theory that reduces photons to little points of energy hurtling through "empty" space, heedless of the sea of virtual particles all around them?

What is the concordance view on the transmission of EM through the vacuum

Virtual Photons, taking zero time en route as experienced by themselves and therefore unable to interact. Photons are not corpuscles.
 
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  • #9
Chronos said:
In my opinion, Einstein was pointing out the futility of positing an 'ether' with any physically quantifiable qualities. I interpret that as meaning it's irrelevant. I also think it's OK to disagree on that.
I don't think it's irrelevant. I think that the quantum vacuum (consisting of particle/antiparticle pairs that last for minimal times, in accordance with the Heisenberg uncertainty principle) can provide the Machian ether that Einstein envisioned without being "sensible" as a fixed background.

In later years (early 1950s) Dirac also made a case for the existence of an ether.

http://home.tiscali.nl/physis/HistoricPaper/Dirac/Dirac1951b.pdf
 
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  • #10
selfAdjoint said:
Virtual Photons, taking zero time en route as experienced by themselves and therefore unable to interact. Photons are not corpuscles.
Now I'm confused. If EM propagates as waves, not corpuscular entities traveling through empty space, how does EM propagate? Without a transmissive medium, waves go nowhere.
 
  • #11
Light waves do not obey the rules of classical mechanics. Maxwell's equations work perfectly without ascribing any properties to a 'transmissive media'. I think it is fair to say a media devoid of any physically quantifiable properties is the same as saying it is nonexistent [an occams razor thing]. I also think this is the point of Einstein's Leiden address. He was trying to put the issue in perspective and coax his audience into relinquishing their traditionally cherised concepts.
 
  • #12
Chronos said:
Light waves do not obey the rules of classical mechanics. Maxwell's equations work perfectly without ascribing any properties to a 'transmissive media'. I think it is fair to say a media devoid of any physically quantifiable properties is the same as saying it is nonexistent [an occams razor thing]. I also think this is the point of Einstein's Leiden address. He was trying to put the issue in perspective and coax his audience into relinquishing their traditionally cherised concepts.
Please read the address carefully. Einstein was not denouncing the ether - he was announcing his embrace of it and defining its role in physics, with historical references to its role in earlier physical models. He had come to realize that GR demanded the existence of an ether, else the properties of rotation and acceleration could not exist, except as Machian action-at-a-distance, which he would not accept. GR demanded that rotation and acceleration be expressed as changes relative to a LOCAL frame - the ether.

http://www.geocities.com/antonioferrigno/ether.html

Einstein at Leyden said:
To deny the ether is ultimately to assume that empty space has no physical qualities whatever.

The fundamental facts of mechanics do not harmonize with this view. For the mechanical behaviour of a corporeal system hovering freely in empty space depends not only on relative positions (distances) and relative velocities, but also on its state of rotation, which physically may be taken as a characteristic not appertaining to the system in itself.

In order to be able to look upon the rotation of the system, at least formally, as something real, Newton objectivises space.

Since he classes his absolute space together with real things, for him rotation relative to an absolute space is also something real. Newton might no less well have called his absolute space "Ether"; what is essential is merely that besides observable objects, another thing, which is not perceptible, must be looked upon as real, to enable acceleration or rotation to be looked upon as something real.

It is true that Mach tried to avoid having to accept as real something which is not observable by endeavouring to substitute in mechanics a mean acceleration with reference to the totality of the masses in the universe in place of an acceleration with reference to absolute space. But inertial resistance opposed to relative acceleration of distant masses presupposes action at a distance; and as the modern physicist does not believe that he may accept this action at a distance, he comes back once more, if he follows Mach, to the ether, which has to serve as medium for the effects of inertia. But this conception of the ether to which we are led by Mach's way of thinking differs essentially from the ether as conceived by Newton, by Fresnel, and by Lorentz. Mach's ether not only conditions the behaviour of inert masses, but is also conditioned in its state by them.

Mach's idea finds its full development in the ether of the general theory of relativity.
As for my original question, regarding the nature of the transmissive medium through which EM propagates in "empty" space :

Einstein at Leyden said:
Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether.

According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time.

The idea of motion may not be applied to it.
Einstein did not, as many imagine, kill the notion of an all-pervasive ether. To the contrary, he embraced the concept, stripped it to its bare essentials, and attempted to use it to unify gravitation and electromagnetism. He failed to accomplish this, but I firmly believe he was on the right track.

To get back to the original question: what is the nature of the transmissive medium through which EM propagates?
 
  • #13
Yes, and his ether was the dynamic metric field of spacetime gemoetry. He spent the rest of his life trying to tweak that metric field so it would support EM, but he died before fully achieving that. I don't see what his opinion forces on us today.

It is clear that EM by itself, while perfectly usable within its proper energy/scale envelope, cannot predict the detailed spectra or behavior of charged particles such as electrons. There are further effective theories: Dirac's. QED. and the Standard Model, which do that much more accurately. So trying to unify "light waves" with gravity at this late date is like putting elliptical epicycles into Ptolemy.
 
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  • #14
selfAdjoint said:
Yes, and his ether was the dynamic metric field of spacetime gemoetry. He spent the rest of his life trying to tweak that metric field so it would support EM, but he died before fully achieving that. I don't see what his opinion forces on us today.
His opinion forces nothing on us; however it might be wise to reconsider his opinion periodically, especially in the light of things that came to be better-understood later.

The properties of the vacuum were poorly understood when Einstein was at his most productive, and Einstein was not too fond of quantum theory anyway. Today (and for some time actually) we have demonstrable proof that the quantum vacuum exists (Casimir effect, Lamb effect, etc). It is the baseline of our universe, and as such, it is practically insensible. It is pervasive and universal, and Sakharov believed that interaction of matter with this vacuum field endowed the matter with mass, inertia, and gravitation. Does not this sound suspiciously like the Machian ether described by Einstein in his Leyden address?

Again, does the quantum vacuum act as a transmissive medium for EM waves? If not, what is the nature of the field upon which EM waves travel in "empty" space?
 
  • #15
turbo-1 said:
His opinion forces nothing on us; however it might be wise to reconsider his opinion periodically, especially in the light of things that came to be better-understood later.

The properties of the vacuum were poorly understood when Einstein was at his most productive, and Einstein was not too fond of quantum theory anyway. Today (and for some time actually) we have demonstrable proof that the quantum vacuum exists (Casimir effect, Lamb effect, etc). It is the baseline of our universe, and as such, it is practically insensible. It is pervasive and universal, and Sakharov believed that interaction of matter with this vacuum field endowed the matter with mass, inertia, and gravitation. Does not this sound suspiciously like the Machian ether described by Einstein in his Leyden address?

Again, does the quantum vacuum act as a transmissive medium for EM waves? If not, what is the nature of the field upon which EM waves travel in "empty" space?

First Einstein and now Sakharov! You can't build physics by cherry-picking quotations from famous dead men. The quantum vacuum as it exists in actual physics is the ground state of a quantum field. In order to talk about gravitation and quantum vacuum meaningfully you have to quantize gravitation. When you have done that come back and we'll talk about whether the quantum vacuum you derive from your quantized gravity theory does or does not support EM in such a way as to be sensibly called an ether.
 
  • #16
selfAdjoint said:
First Einstein and now Sakharov! You can't build physics by cherry-picking quotations from famous dead men.
I think you would find it very difficult to do real physics without studying the problems that have stumped the great minds. Understanding and breaking down these problems lead to paradigm shifts. It is called epistemology, and Einstein was a great fan of that process. Case in point: Mach's concept that inertia arose from a body's acceleration relative to the entirety of the universe. Einstein's distaste for this action-at-a-distance concept was central to his view that the ether is real and local.
selfAdjoint said:
The quantum vacuum as it exists in actual physics is the ground state of a quantum field. In order to talk about gravitation and quantum vacuum meaningfully you have to quantize gravitation. When you have done that come back and we'll talk about whether the quantum vacuum you derive from your quantized gravity theory does or does not support EM in such a way as to be sensibly called an ether.
I think that it is a bit much to demand that I develop a full-blown theory of quantum gravity before you will condescend to answer a simple question:

Through what transmissive medium does EM propagate in "empty" space?

Let's start there.
 
  • #17
turbo-1 said:
Through what transmissive medium does EM propagate in "empty" space?

Assuming that the teachings of QED and the electroweak theory survive the quantization of gravity, light is carried by real photons, which do not interact with the quantum vacuum. The photons are not corpuscles as you well know, and it is disingenuous to suggest they are. They may on occasion be observed as plane waves when traveling from one star to another. But those are not waves that change the state of any circumambient medium.
 
  • #18
I think the point is lost in semantics. The quantum vacuum does have properties, specifically, it produces measurable effects in the presence of matter [e.g., casimir effect]. But it does not exhibit properties consistent with those of a transmissive media in classical mechanics. There is nothing suggesting the quantum vacuum interacts with EM fields. Thus the contextual meaning of this statement by Einstein:

"...we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether..."

But, the more important point Einstein made is, IMO:

"... But this ether may not be thought of as endowed with the quality characteristic of ponderable media..."

Which is to say, IMO, it is not endowed with any of the properties typical of a classical transmissive media [e.g., viscosity, mass, rigidity, etc.] Does that make any sense?

Hence, the central argument of the great ether controversy is, does empty space behave consistent with classical mechanics? Einstein's answer is no.
 
  • #19
by Cronos, Which is to say, IMO, it is not endowed with any of the properties typical of a classical transmissive media [e.g., viscosity, mass, rigidity, etc.] Does that make any sense?
I think people do give the medium properties, i remember Marcus told me that
ST rings like a bell, How else can gravity waves propagate?
 
  • #20
Casimir, at least, thought of the virtual particles as having wave lengths; that was how he worked out his "effect".
 
  • #21
selfAdjoint said:
Casimir, at least, thought of the virtual particles as having wave lengths; that was how he worked out his "effect".
Yes, that is key to the concept of supression of the EM wavelengths that demonstrated the reality of the energy of the vacuum.

Again, through what media does EM propagate through "empty" space? It there is no field ("ether", in the case of Einstein's 1920 Leyden address),there can be no propagation of EM waves through space. This is not a trick question, boys and girls! Is there an answer that is acceptible by adherents of the concordance model?
 
  • #22
What properties of your 'ether' contribute to the propogation of EM waves? Would you agree the only relevant properties are what is usually called permissivity and permeability? How do those relate to your concept of a 'transmissive medium'? Perhaps a quantified definition of what constitutes a 'transmissive medium' would clarify matters.
 
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  • #23
Chronos said:
What properties of your 'ether' contribute to the propogation of EM waves? Would you agree the only relevant properties are what is usually called permissivity and permeability? How do those relate to your concept of a 'transmissive medium'? Perhaps a quantified definition of what constitutes a 'transmissive medium' would clarify matters.
I already have a very concrete concept of what that transmisive medium is, and why it behaves the way it does, and if I explain it here, this thread will be locked and the discussion will stop.

I ask again, to all the adherents of the standard model:

Please explain how EM traverses "empty" space. If, like Einstein, you believe that EM waves need a medium through which to propagate, please describe the medium. If you believe that EM waves can propagate without a medium, please explain your reasoning.
 
  • #24
We've all done that and you just ignore us and repeat your question. Maybe you don't want to hear the answer?
 
  • #25
turbo-1 said:
If there is no field ("ether", in the case of Einstein's 1920 Leyden address),there can be no propagation of EM waves through space.

EM waves without an ether?! That's like...like...the universe without a creator!

Don't force your preconceived notions on the universe. You can make a theory that predicts an ether, but it will have to conform to the experimental limits already in place.
 
  • #26
SpaceTiger said:
EM waves without an ether?! That's like...like...the universe without a creator!

Don't force your preconceived notions on the universe. You can make a theory that predicts an ether, but it will have to conform to the experimental limits already in place.
Einstein called it an ether - you can call it an EM field or whatever you like, but can EM waves propagate in the absence of a field?
 
  • #27
selfAdjoint said:
We've all done that and you just ignore us and repeat your question. Maybe you don't want to hear the answer?
I think your most succinct answer (correct me if I'm wrong) was:
selfAdjoint said:
...light is carried by real photons, which do not interact with the quantum vacuum.
I have seen no research to back up that assertion. In fact, if the Scharnhorst effect is real, light MUST interact with the EM field of the quantum vacuum.

I am not trying to be disengenuous or abtuse, as you have suggested. Is there is an EM field suffusing all of space through which EM waves can propagate, and if so, what is the nature of that field? Can that field be subject to densification, rarification, polarization, etc? What are the properties of the field through which EM propagates in "empty" space?
 
  • #28
It is not enough to assert a transmissive medium is required for EM waves without quantifying the relevant properties. According to accepted theory, the only relevant properties are P&P, as already mentioned. Those properties bear no resemblance to the 19th century concept of an 'ether'. Furthermore, Einstein stated his version of 'ether' was "not endowed with the quality characteristic of a ponderable media." Which is the basis of my objection to this argument:
Turbo-1 said:
... Can that field be subject to densification, rarification, polarization, etc? ...
Does that not appear to conflict with Einstein's comment?
 
  • #30
A vibrating point extended through space geometrically constitutes a wave . Since vibrating points i.e. electrons are the source of EM radiation. You don't need a medium, all you need is for the vibrating point to be extended by its relative motion through space or by the expansion of space itself .This would also explain why there is a fixed speed in a vacuum since the wave is in a sense not 'pushed' out from its source but rather 'pulled' at a fixed rate . As the photon/EM wave has a different relation to time than matter does (ie no time passes for it ) this is consistent with the notion that it is in a sense standing still in time while the space in which it exists is drawing out giving it its characteristic wave form .
 
  • #31
Am moving this to Quantum Physics. Other than that the 'astronomical' or 'cosmological' domain may be where some of the (important) tests of concepts, theories, and ideas related to the OP are conducted, I feel the content of this thread has far more to do with quantum physics than GA&C (as ST pointed out, very early on).
 
  • #32
turbo-1 said:
have seen no research to back up that assertion. In fact, if the Scharnhorst effect is real, light MUST interact with the EM field of the quantum vacuum.

I apologize, I did not know about the Scharnhorst effect. The photon does interact with the quantum vacuum by sometimes creating virtual electron-positron pairs. After their brief candle is out it procedes as a photon till it creates another pair. It cannot create real ones because that would violate conservation of energy and momentum, but it can create virtual ones, "off the mass shell". No names, no pack drill.

But far from supporting the radiation this quantum process slows it down! It is precisely the point of Scharnhorst's theory that by intervening with plates a la Casimir we can cause fewer of these transitions and hence increase the speed of the photon above ordinarily measured c. So invoking Scharnhorst, and the active QED vacuum generally, as a "modern ether" is exactly in the wrong direction.
 
  • #33
turbo-1 said:
Now I'm confused. If EM propagates as waves, not corpuscular entities traveling through empty space, how does EM propagate? Without a transmissive medium, waves go nowhere.

Think at the ocean and at some waves propagating at the surface of it; it is not always the water that moves, but the ondulation of the surface going up and down without any lateral motion that give us the sensation of a "propagation". Can we not imagine a similar picture for EM waves and vacuum? Or going further can we not imagine that infinitesimal variations of the metric are only giving us the illusion that something is propagating ?
 
  • #34
selfAdjoint said:
I apologize, I did not know about the Scharnhorst effect. The photon does interact with the quantum vacuum by sometimes creating virtual electron-positron pairs. After their brief candle is out it procedes as a photon till it creates another pair. It cannot create real ones because that would violate conservation of energy and momentum, but it can create virtual ones, "off the mass shell". No names, no pack drill.
Do not apologize. Nobody can be familiar with all the research done by everyone in physics. In fact, I had been trying to determine the optical properties of the quantum vacuum for nearly a year when one of the most prominent researchers in that field tipped me off to the Scharnhorst effect in an email. I was coming at this from the viewpoint of an optician and was not as familiar with the theoretical/experimental work in quantum physics as I could have been.

selfAdjoint said:
But far from supporting the radiation this quantum process slows it down! It is precisely the point of Scharnhorst's theory that by intervening with plates a la Casimir we can cause fewer of these transitions and hence increase the speed of the photon above ordinarily measured c. So invoking Scharnhorst, and the active QED vacuum generally, as a "modern ether" is exactly in the wrong direction.
No, it's exactly the right direction for my purposes. Now let's think through the implications of this: If the Sharnhorst effect is real, and the quantum vacuum is the dynamical gravitational ether envisioned by Einstein, we have something to work with. The gravitational densification/polarization of the vacuum field would cause an increase in these reactions, resulting in a slowing of the propagation speed of light, while rarification/relaxation of this field would result in faster propagation of light (a la the Scharnhorst effect between the plates of a Casimir device). This is a real mechanical explanation of "gravitational lensing" that makes sense in classical optics.

I am trained as an optician and have been studying the quantum vacuum field as if it were a refractive medium. If the Scharnhorst effect is confirmed, then the quantum vacuum is definitely a refractive medium, and optical effects will give us powerful probes into the qualities of the vacuum fields around galaxies and clusters.
 
  • #35
The gravitational densification/polarization of the vacuum field would cause an increase in these reactions, resulting in a slowing of the propagation speed of light, while rarification/relaxation of this field would result in faster propagation of light (a la the Scharnhorst effect between the plates of a Casimir device)

Quantum polarization is not densification. The optical consequences of the Scharnhorst effect were shown by Visser to be unobservable. The quantum vacuum as a medium does nothing but resist and slow the photon, it did not create it and does not support its momentum.
 
<h2>1. What is the medium through which EM waves propagate in empty space?</h2><p>The medium through which EM waves propagate in empty space is known as the "electromagnetic field". This field is made up of electric and magnetic components that are perpendicular to each other and oscillate in a perpendicular direction to the direction of propagation.</p><h2>2. Is empty space truly "empty" or is there something that allows EM waves to propagate?</h2><p>Empty space is not completely empty. It contains a small amount of energy known as the "vacuum energy" or "zero-point energy". This energy allows for the propagation of EM waves in empty space.</p><h2>3. How do EM waves travel through empty space without a medium?</h2><p>EM waves do not require a medium to travel through empty space. This is because they are self-propagating and do not rely on physical particles to carry their energy. Instead, they are made up of oscillating electric and magnetic fields that can travel through the vacuum of space.</p><h2>4. Can EM waves travel through any type of medium?</h2><p>Yes, EM waves can travel through a variety of different media, including air, water, and solids. However, they do not require a medium to travel through empty space.</p><h2>5. How fast do EM waves travel through empty space?</h2><p>In a vacuum, EM waves travel at the speed of light, which is approximately 299,792,458 meters per second. This is the fastest speed at which anything can travel in the universe.</p>

1. What is the medium through which EM waves propagate in empty space?

The medium through which EM waves propagate in empty space is known as the "electromagnetic field". This field is made up of electric and magnetic components that are perpendicular to each other and oscillate in a perpendicular direction to the direction of propagation.

2. Is empty space truly "empty" or is there something that allows EM waves to propagate?

Empty space is not completely empty. It contains a small amount of energy known as the "vacuum energy" or "zero-point energy". This energy allows for the propagation of EM waves in empty space.

3. How do EM waves travel through empty space without a medium?

EM waves do not require a medium to travel through empty space. This is because they are self-propagating and do not rely on physical particles to carry their energy. Instead, they are made up of oscillating electric and magnetic fields that can travel through the vacuum of space.

4. Can EM waves travel through any type of medium?

Yes, EM waves can travel through a variety of different media, including air, water, and solids. However, they do not require a medium to travel through empty space.

5. How fast do EM waves travel through empty space?

In a vacuum, EM waves travel at the speed of light, which is approximately 299,792,458 meters per second. This is the fastest speed at which anything can travel in the universe.

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