# B Photons bending

#### itallcomestoenergy

Are photons vibration or is vibration the transport medium for light? In what kind of medium are photons more transferrable?

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#### Dale

Mentor
Are photons vibration or is vibration the transport medium for light?
I would not say vibration has anything to do with it. The word vibration brings a concept of a medium and there is no medium for light.

#### HallsofIvy

Homework Helper
First, in regard to you title, "Photons bending": photons don't bend- their paths bend in a gravitational field. The medium for light is the electro-magnetic field that pervades the universe.

#### itallcomestoenergy

First, in regard to you title, "Photons bending": photons don't bend- their paths bend in a gravitational field. The medium for light is the electro-magnetic field that pervades the universe.
ESL. In the visible spectrum (some hundreds nm) There are vibrations included, right? Where does this come in? Every mediums transport includes some form of vibration, is my form of perception

#### itallcomestoenergy

I would not say vibration has anything to do with it. The word vibration brings a concept of a medium and there is no medium for light.
But photons need some kind of matter to travel thru. Is there a different kind of frequency for the different kind of matter the photons travel thru? Does blue and green operate in a different frequency in different mediums?

#### HallsofIvy

Homework Helper
Am I missing something here? The original post asked in what medium "light" is vibrations. I answered that light consist of vibrations in the electro-magnetic field. Now you are saying "But photons need some kind of matter to travel thru." NO! They don't! Where did you get that idea? Light, photons, from stars thousands of light years from earth travel through empty space, not "through matter"!

Perhaps you are using the word "matter" in a very stange way. Exactly what do you mean by "matter"?

#### itallcomestoenergy

Am I missing something here? The original post asked in what medium "light" is vibrations. I answered that light consist of vibrations in the electro-magnetic field. Now you are saying "But photons need some kind of matter to travel thru." NO! They don't! Where did you get that idea? Light, photons, from stars thousands of light years from earth travel through empty space, not "through matter"!
Your are not missing anything. My point is that there are some kind of transport-medium in space, right? It is not totally empty out there. What about gravitational waves, their energy travels thru something before they affect matter

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#### HallsofIvy

Homework Helper
The "transport medium" for light, as I said before, is the electro-magnet field. That is definitely NOT "matter".

#### itallcomestoenergy

The "transport medium" for light, as I said before, is the electro-magnet field. That is definitely NOT "matter".
Than what is it? Do we have a name for it? The electro-magnetic field is not every where in space? There are lots of light in space, but nothing to attach it to. A paradox, right?

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#### davenn

Gold Member
Than what is it?
Again … a propagating EM wave does not need a physical medium, as sound waves do

Do we have a name for it?
You were just told and you even quoted it ....

The "transport medium" for light, as I said before, is the electro-magnet field

The electro-magnetic field is not every where in space?
again, you were just told that it was everywhere

The medium for light is the electro-magnetic field that pervades the universe.

There are lots of light in space, but nothing to attach it to.
that is meaningless

Do you know/understand that photons are not little particles of mass shooting through
space etc like bullets ?

#### Dale

Mentor
But photons need some kind of matter to travel thru
No, they don’t. They travel through vacuum just fine. This is well established by two facts. First, there are vacuum solutions to Maxwell’s equations. Second, there has never been a successful detection of a luminiferous aether despite many sophisticated tests to do so.

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#### itallcomestoenergy

No, they don’t. They travel through vacuum just fine. This is well established by two facts. First, there are vacuum solutions to Maxwell’s equations. Second, there has never been a successful detection of a luminiferous aether despite many sophisticated tests to do so.
Ok, but in vacuum we can detect particles that appear an dissapear, right? Snd inthe vacuum of space there are also atoms, right?

#### Nugatory

Mentor
Ok, but in vacuum we can detect particles that appear an dissapear, right?
No. You may have been misled by non-technical descriptions of "vacuum flucuations" and "virtual particles" - these are a (generally well-intentioned) best effort at a math-free explanation of concepts that cannot be properly explained without math, so are often seriously misleading.

We have a number of Insights articles on this subject, and there's really no substitute for a serious quantum field theory textbook.... but the quick summary is: Vacuum really is vacuum with nothing there, and that doesn't stop electromagnetic and gravitational fields from propagating through it.

#### DennisN

Snd inthe vacuum of space there are also atoms, right?
In space there are comparatively very few atoms, that is low density, compared to e.g. the atmosphere of Earth. And those atoms are not arranged in any orderly fashion like a grid.
By the way, here is a page about the Michelson-Morley experiment and the idea of an ether as a propagating medium for light:
http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/mmhist.html

#### vanhees71

Gold Member
I think it's harder for a beginner to understand what light is than one thinks when having thought about it some years of physics education.

First of all at this level of understanding, forget anything you heard about photons. Photons are a quite complicated concept which cannot be understood without relativistic quantum field theory. Any attempt to explain what photons are without the necessary and quite abstract mathematical formalism of QED is doomed to provide wrong concepts.

So let's use classical physics to get a first understanding of what light is. Since Maxwell (1865) we know that all the phenomena we can observed with regard to light is that it's a freely propagating electromagnetic field. It is not possible to explain what an electromagnetic field is than to explain which phenomena it describes. It's one of the most fundamental concepts of physics and thus cannot be explained in more simple terms.

The electromagnetic field is described as two vector fields $\vec{E}(t,\vec{x})$ and $\vec{B}(t,\vec{x})$ called the electric and magnetic field (components). It's a function of time and position, i.e., at any time and at any point in space there are these two vectors. As I said, it's a fundamental entity of physics. I cannot explain it simpler, and we are aware of its existence through the consequences of the presence of these two vectors at every point in space and any time.

Another fundamental quantity we need in this context is electric charge. It's also an fundamental quantity that cannot be described simpler than just noting that it's needed to describe certain phenomena. Take a small piece of matter that you can describe in good approximation as a "point particle". If it's located at place $\vec{r}$ at time $t$ moving with velocity $\vec{v}$ and it carries the electric charge $q$, then due to the presence of the electromagnetic field at the location of the particle, a force acts on this particle given by
$$\vec{F}=q [\vec{E}(t,\vec{r})+\vec{v} \times \vec{B}(t,\vec{r})].$$
That's it. I cannot describe it simpler, but that's how we know that there are electric charges and an electromagnetic field in nature.

Of course, what one has to know too is how the electromagnet field behaves with time and how it is created by other charges. This is the gread achievement of Maxwell: He discovered the field equations describing how the electromagnetic field changes with time in dependence of the distribution of electric charge and current distributions. These equations told him that the electromagnetic field is present everywhere, also in regions where no matter and thus also no charges and currents are present. The electromagnetic field is there due to some charges and currents at other places and it spreads like waves, and the propagation speed of these waves turned out to be quite accurately the known speed of light in a vacuum. That's why Maxwell concluded that light might be described as electromagnetic waves traveling in a vacuum, and it turned out that the math gave precisely the right properties of light. The direct experimental proof that electromagnetic waves are created by moving (accelerated) charges is due to Heinrich Hertz's experiments (1888), though these were radio waves of much lower frequency than light.

Since before the physicists only knew wave phenomena related with mechanics like water waves or sound waves in air, liquids and solid, i.e., waves of moving continuous media they indeed first thought that there must be some other kind of matter, not yet known at the time, which mediated electromagnetic waves, including light. As it turned out however, the more they thought about the properties of such a medium, called "lumineferous aether", the weirder it got! Finally all ideas about experimentally finding the aether failed and assuming its existence even lead to contradictions with observations. If something kills wrong ideas in the natural sciences it's experimentally disproving predictions, and that's what happened with the aether. Finally the solution of these riddles was the discovery of what's today called the Special Relativity Theory by Einstein (based also on earlier attempts by Lorentz, FitzGerald, Heaviside, and Poincare): There's no need for an aether. There's just the electromagnetic field itself which spreads in empty space from charge-current as its sources.

#### Dale

Mentor
Snd inthe vacuum of space there are also atoms, right?
Yes, and there are very large (meters) gaps between them. Light can travel in the empty space between the atoms just fine. Light has no need for a material through which to propagate.

#### itallcomestoenergy

that is meaningless

Do you know/understand that photons are not little particles of mass shooting through
space etc like bullets ?
If there is no light in space, than how do we have light on this planet?

#### DennisN

If there is no light in space, than how do we have light on this planet?
There is light in space, but there is no material medium (e.g. ether) through which light propagates.

#### Dale

Mentor
If there is no light in space, than how do we have light on this planet?
There is light in space.

Staff Emeritus
This is well established by two facts
Three. We can see the stars.

#### itallcomestoenergy

There is light in space, but there is no material medium (e.g. ether) through which light propagates.
Okey, so the medium is vacuum. With hints of atoms(?) What about sound waves? They operate in a lower frequency, but they are not transferrible in vacuum? Do I get this right? The reason I ask is because of illustrations of lights frequency spectrum.

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#### itallcomestoenergy

No, they don’t. They travel through vacuum just fine. This is well established by two facts. First, there are vacuum solutions to Maxwell’s equations. Second, there has never been a successful detection of a luminiferous aether despite many sophisticated tests to do so.
So gravity affects the receptive issue of photons. Then where does sound waves come in? I have this picture that everything is vibration. Vibration in the lower sector causes sound, and in the higher sector causes visable light. Am I far out? And if so, where can I find understandable information about this subject?

#### itallcomestoenergy

There is light in space, but there is no material medium (e.g. ether) through which light propagates.
This I dont get, and pardon my knowledge. Is it like if you are very far away from a light source (stars) there is total blackness?

#### itallcomestoenergy

No. You may have been misled by non-technical descriptions of "vacuum flucuations" and "virtual particles" - these are a (generally well-intentioned) best effort at a math-free explanation of concepts that cannot be properly explained without math, so are often seriously misleading.

We have a number of Insights articles on this subject, and there's really no substitute for a serious quantum field theory textbook.... but the quick summary is: Vacuum really is vacuum with nothing there, and that doesn't stop electromagnetic and gravitational fields from propagating through it.
Can you send me a basic understandable insight article?

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