What is light?

[DerekSmith]

snip...

As for momentum, all particles carry momentum because they have energy, not neccessarily because they have mass. According to Newtonian physics, momentum is defined by an inertial mass, however Maxwell's equations show that electromagnetic radiation, and by extension photons, carry moment with them as well. Basically, when photons collide with a surface, they impart some of their energy to the surface in the form of kenetic energy.

Hope this helps.

Dangineer, I have never seen a description like this before. It suggests that photons are massless otherwise they could not travel at the speed of light, yet they have inertial mass capable of holding kinetic energy.

How much inertial mass does a photon carry? What does the inertial mass depend upon ?

Thanks
DerekSmith

 

[ArcCentral]

I hear that if you get light all wound up, it's tough to push around.

 

[MaxWithershins]

DerekSmith, I say again:

The photon might not be a strictly massless particle, in which case, it would not move at the exact speed of light. Relativity would be unaffected by this; the "speed of light" would then not be the actual speed at which light moves, but a constant of nature which is the maximum speed that any object could theoretically move. It would still be the speed of gravitons, but it would not be the speed of photons.

To wit; the best universally accepted upper limits on the photon charge and mass are 5×10−52 C (or 3×10−33 e) and 1.1×10−52 kg (6×10−17 eV/c2, or 1×10−22 me), respectively.

(I swear I don't make this stuff up!!)

There is so much we truly don't know, and so MUCH that we hypothesize ceaselessly about! Since a photon is never at rest, how can we possibly know if it's truly massless? Speculation and mathematics abound; the answer eludes.

It's really going to throw a wrench in the works of all the science fiction that's been written, to date, if it turns out "light speed" isn't actually "light speed." Somehow the phrase "jump to graviton speed" just doesn't have the same ring, you know? ;-D

 

[Oryan]

Light is the essence of Creation, it's the giver of Life...without it, we do not exist.

 

[DarwinLied]

Light is time, end of story.

 

[Kavrumbrun]

Just to clarify some incorrect points in previous posts:

- That PDF from 3dRelativity.org has probably not been peer-reviewed, and after a short skim, my impression is that the author is pretty much just making things up. (For example, claiming that proton-electron and electron-electron Coulomb interactions don't have the same space-time scale. WTH? Evidence? Measurements? Bueller?)

{ 30 minutes later }

Yeah, I was right. The papers in that PDF were rejected for publication. I wouldn't take anything in that as authoritative.

"A book is like a mirror: if a jackass peers into it, he can't expect a prophet to look back out." (Lichtenberger)

 

[zeestephen]

A question...

Since photons impart kinetic energy to a solid surface, what happens when two photons collide in space?

 

[Jerromy]

In my oppinion, light does not wave in 2 dimensions, it spirals in 3 dimensions. The light we see with our eyes just as every other wavelength of electromagnetic radiation, consists of not only a particle, but an anti-particle as well. These smallest individual particles of matter make up every atom in the universe. Every atom in the universe can be converted into its individual photons and is affected by collisions of every photon.

Light can be seen as "reflecting" but in all cases of observed reflection the actual photon that is released from an atom is not the same photon which collided with it. When a "black" object is observed the photons colliding with it cause molecular excitation instead of releasing another photon. The electrical energy which results are coupled photons attracted by the same force that attracts the photon and its antiphoton, otherwise known as an electron. When a photon collides with white matter it is absorbed in the same manner as a black object but another photon is released from the atom with which the photon had collided.

For a long time I have wondered how electricity knows the easiest path to follow to ground without being able to know where its energy is wanted the most. Since every atom desires to be complete, the perfect atom so to speak, it seeks to take charge from its adjacent atoms. This chain reaction reaches vast distances much faster than the speed of light, which is thought to be impossible, but is observed when a storm cloud releases a lightning bolt. The energy knows it will be recieved before it leaves. Gravity has the same impossible power. It pulls matter together across great distances against the desire of light to disperse evenly throughout an infinite void.

Light is the power of God, seeking to be free. Matter is the power of Satan, seeking to trap all the light.

 

[Jerromy]

When photons collide in space their energy of wavelength is transferred accordingly. Two photons colliding head on would create an electron as the impact would allow gravity to trap them in orbit of each other. Since every particle in the universe follows the same hexagonal "fabric" of space a "head-on" collision would be just that or a near miss. I believe this fabric of space is a constant grid which limits the speed a particle can travel from cell to cell otherwise known as light speed. I also believe this grid dictates the ultimate density of matter in the sense that only one photon can occupy a cell at a time.

 

[DarwinLied]

"Light is the power of God, seeking to be free. Matter is the power of Satan, seeking to trap all the light."


where did that one come from? some book of fairy tales?

Satan is a completely made up word with a made up description. That is pure fear mongering.

 

[Jerromy]

"Light is the power of God, seeking to be free. Matter is the power of Satan, seeking to trap all the light."


where did that one come from? some book of fairy tales?

Satan is a completely made up word with a made up description. That is pure fear mongering.

Quantum, atom, space, universe... all made up words meant to represent something. Satan is an angel that was cast out of Heaven who represents the opposite of God. If God were a star shining brightly Satan would be a black hole consuming all light. Fear the total absence of light, not some made up word.

 

[drwayne]

*Moderator hat on*

This is a physics forum, so discussions about religious issues are not on-topic here.
Discussions of religious topics (within reason) should fall in the "Unexplained" group.

*Moderator hat off*

Wayne

 

[csmyth3025]

This is a very interesting thread. The most common answer here to the question "What is light?" seems to be that light is a form of energy (electromagnetic radiation) which is one of the four known [or, at least, widely accepted] fundamental forces of nature - along with the strong nuclear force, the weak nuclear force, and gravity.
I wonder if in the original post "1waffle 1" had a more subtle question in mind. The comment "It's not matter." in that post seems to indicate that the questioner already knows that there's a distinction between matter and energy - and that light falls into the latter category. If this is, in fact, the case then I would ask "1waffle 1": Do you mean "What is energy?"? I would also ask: "Are you looking for a conceptual description or a technical explanation?" I suspect that a layman's explanation - if such a thing is possible - would be preferred.
I mention all this because the question "What is energy?" is one that puzzles me as well as, perhaps, "1waffle 1". I understand that the Standard Model predicts that in the first moments after the "Big Bang", temperature were so extreme that for all intents and purposes only high energy photons could exist. These photons continually crashed into one another, creating matter/anti-matter particle pairs. These pairs almost immediately annihilated each other or neighboring particles, creating high energy photons again. If my understanding of the Standard Model in this scenario is incorrect please feel free to comment.
This brings us back to "What is light?" which is, in the era described above, synonymous with the question "What is energy?". I've read the technical explanations and I have a rudimentary understanding of the mathematical treatment given by the equations of Maxwell and others. Still, I'm left struggling to conceptualize what it is.
Unfortunately, I have nothing to offer "1waffle 1" - or myself, for that matter - on this question.
Chris

 

[dangineer]

"What is energy" is a very interesting question and I think warrents discussion in this thread. From my study of physics I've seen that energy is usually defined based on the situation; kenetic energy, potential energy, EMR, etc. all have different definitions depending on what they "do." I've come to the conclusion that the most general definition of energy is that it is the potential that one particular region or point in the universe has to affect another point in some physical way. This is a very broad and vague definition and probably requires a lot of explanation. Just for some definitions, I mean physical as some property that can, at least in theory, be measured or observed. So affecting would mean changing the properties.

For example, when we say something has kenetic energy (i.e. it is moving in space), this means nothing unless compared to something else (from relativity). This way we can measure its velocity. The idea of kenetic energy only becomes important, though, if it affects something else (i.e. a collision). Or a particles rest mass can be considered the amount of potential that particle has to do other things like decay into other particles or turn into gamma rays through anhilation, etc.

I guess in this sense, energy is a construct humans made in order to explain how things interact in the universe. Energy seems to be the currency of the universe.

 

[csmyth3025]

There's no doubt in the mind of any one of us that there are forms of energy that are easily recognizable and observable. The workman who drops a heavy tool on his (her) toe instinctively understands the concept of potential and kinetic energy. The idea that this simple (but painful) act ultimately results in the conversion of potential energy to kinetic energy to thermal energy (electromagnetic radiation - aka light) is one that's a bit more difficult to comprehend.
The notion that if all the "stuff" in the world were to fall together into a big blob (or black hole, to be more scientifically realistic), it would release a lot of thermal radiation that would flit about the universe unimpeded forever stretches the imagination even farther.
The thought that all of the "stuff" of the universe - now squashed into its final resting place - once came from the collision of high energy photons is simply mystifying.
What is this light? It can make "stuff" which, by various means, can make light or even be transformed back into light. Is electromagnetic radiation the only real constant in our world? Is everything else just the result of photons sticking together in the right combination of energies to produce hadrons and leptons?
I suppose that, for now, I'll have to be content with the scientific descriptions of how light acts. Understanding what light is seems beyond my ability.
Chris

 

[origin]

How much inertial mass does a photon carry? What does the inertial mass depend upon ?

Thanks
DerekSmith

The momentum of a photon is directly proportional to it's frequency.

 

[James_Hawk_III]

Just to clarify some incorrect points in previous posts:

- That PDF from 3dRelativity.org has probably not been peer-reviewed, and after a short skim, my impression is that the author is pretty much just making things up. (For example, claiming that proton-electron and electron-electron Coulomb interactions don't have the same space-time scale. WTH? Evidence? Measurements? Bueller?)

{ 30 minutes later }

Yeah, I was right. The papers in that PDF were rejected for publication. I wouldn't take anything in that as authoritative.

"A book is like a mirror: if a jackass peers into it, he can't expect a prophet to look back out." (Lichtenberger)

Hey, if you have numbers, present numbers. If you have experimental proof, provide it. If you don't, you can't argue the authenticity of your claims. The papers were rejected for publication because they were too speculative, and you state that yourself in your own work. What's your problem with facts? If you're unhappy that I used the colloquial "making things up" as opposed to "speculated," then I apologize. Allow me to correct my earlier statement: ladies and gentlemen, my impression is that the author is engaging in too much speculation. (I am not the first to have said so. I merely repeat what the author himself has revealed.)

Furthermore, your private message accusing me of slander is nothing short of ridiculous. Unless your claims are published and undergo peer review, they simply can't be regarded as authoritative in any sense of the word. That's part of the process in science. (I have been trained in science, in case you didn't know, as has my wife, who has a Ph.D. in the physical sciences just like you do.) You also submitted some of the articles in the PDF to someone on whose work you based some of your speculations; that individual declined to participate. (Again, I'm simply quoting content you published yourself.) To me that suggests that published, career physicists (and science journal editors) have enough problems with your work to deem it not worthy of serious consideration at this time. I'm sure that doesn't make you happy--but repeating it here is not slander. It's simply transmission of fact. My statement that your hypothesis cannot be construed as authoritative follows logically from what precedes it--the facts.

I'm not attacking you, I'm saying that based on various facts already in evidence, the hypotheses you present cannot be taken as authoritative in light of current research. I'm expressing an opinion based on an unbiased evaluation of the evidence. (I don't know you. I've never met you. I can hardly, therefore, be biased against you, or have any agenda other than warning anyone less educated in the sciences than you or I that they should tread lightly. For all I know, you could be right, but the scientific community currently disagrees. I even researched your Coulomb interaction space-time scale claim, and didn't find anything supporting it. It's entirely possible I missed something, but wouldn't the journal editors have done the same research, and done a better job than I had time to do?)

Get the paper(s) published in a decent scientific journal and this entire issue goes away. Until then, the facts are the facts, and stating them isn't slander.

 

[rubicondsrv]

Just to clarify some incorrect points in previous posts:

- That PDF from 3dRelativity.org has probably not been peer-reviewed, and after a short skim, my impression is that the author is pretty much just making things up. (For example, claiming that proton-electron and electron-electron Coulomb interactions don't have the same space-time scale. WTH? Evidence? Measurements? Bueller?)

{ 30 minutes later }

Yeah, I was right. The papers in that PDF were rejected for publication. I wouldn't take anything in that as authoritative.

"A book is like a mirror: if a jackass peers into it, he can't expect a prophet to look back out." (Lichtenberger)

Hey, if you have numbers, present numbers. If you have experimental proof, provide it. If you don't, you can't argue the authenticity of your claims. The papers were rejected for publication because they were too speculative, and you state that yourself in your own work. What's your problem with facts? If you're unhappy that I used the colloquial "making things up" as opposed to "speculated," then I apologize. Allow me to correct my earlier statement: ladies and gentlemen, my impression is that the author is engaging in too much speculation. (I am not the first to have said so. I merely repeat what the author himself has revealed.)

Furthermore, your private message accusing me of slander is nothing short of ridiculous. Unless your claims are published and undergo peer review, they simply can't be regarded as authoritative in any sense of the word. That's part of the process in science.
Get the paper(s) published in a decent scientific journal and this entire issue goes away. Until then, the facts are the facts, and stating them isn't slander.

If there is a problem with PM exchanges please report it to the moderators by PM instead of mentioning it in a thread.

 

[emperor_of_localgroup]

When matter loses energy through various means, that energy loss is emitted via electromagnetic radiation. This includes light. This energy propagates via electromagnetic waves. These waves carry the energy and momentum. It is one of the four known fundamental forces of nature. The other three are the strong and weak force as seen in nuclear physics and, the most familiar, gravity.

What happens it that these photon interact with matter in the sun (electrons) on their journey towards your eyes. During these interactions with electrons the photons lose energy and eventually fall to energy levels (frequencies) that your eyes can detect.

Another good interpretation (also accepted) of light as only waves. In this case, is light energy stored in electric and magnetic fileds? But both fields become zero at the same point many times, depending on the frequency. Where is the energy at those points where electric and magnetic fields are both zero?

My other question may sound ridiculous. Do photons exist? To put it in another way, 'Are photons really particles'? Beginning physics students in their textbooks are given the impression photons are real particles. Let me explain what I have in my mind.

When light interacts with matter it delivers all or part of its energy to the matter. But our thoughts of energyor energy as we know it are always associated with particles (objects), that may be a reason we treat light as photon particles and it fits our model of particles very well. Note that when light delivers partial energy to matter, all light does is loses frequency. Which again can be interpreted as 'a particle lost some of its energy'.

What I'm trying to ask is, we can model light as a photon particle, but is it really a particle?? Or a photon is the only 'visible energy' in the universe?

 

[centsworth_II]

... a photon is the only 'visible energy' in the universe?

Anything that stimulates a signal in the optic nerve will be "seen" by the brain. A cosmic ray or a smack with a bat for example. But these events are, hopefully, rare. Neutrinos and 'gravitons' don't interact enough to stimulate the nerve. I suppose that if you looked into a beam of electrons, neutrons, or protons, you would see flashes (if the beam did not fry your retina outright).

 

[drwayne]

As I mumbled earlier in the thread, the classical theory of light, derived from Maxwell's equations basically
leads to the following dance:

A time varying electric field leads to the generation of a time varying magnetic field

and

A time varying magnetic field leads to the creation of a time varying electric field

...

With respect to the engnergy content of the wave, our friend is the Poynting vector

Wayne

 

[DarwinLied]

ok you got me there, it's too bad you cant refer to god as "steven" and satan as " the ***** that sucked the life out of him"

but like the mod said those references do not belong in this forum

"Light is the power of God, seeking to be free. Matter is the power of Satan, seeking to trap all the light."


where did that one come from? some book of fairy tales?

Satan is a completely made up word with a made up description. That is pure fear mongering.

Quantum, atom, space, universe... all made up words meant to represent something. Satan is an angel that was cast out of Heaven who represents the opposite of God. If God were a star shining brightly Satan would be a black hole consuming all light. Fear the total absence of light, not some made up word.

 

[dryson]

Correct answer probably is 'we don't know'. This is my take on light.

It's a tiny bit of energy, whose physical nature is unknown (some one can fill in here), travels through space in straight line. When it travels it creates electric and magnetic fields around its path, these fields are wave-shaped. Every wave has a wavelength/frequency, that's where light gets its wavelength, and the name electromagnetic wave.

I'd love to hear other interpretations of light.

Is it a separate dimension? or does it travel in a separate dimension? Current science says 'no'. But I won't rule out anything because there's something strange about light.

But wouldn't also make light a particle as well? If light emits a visible field of energy then it would also have to be a particle
maybe even a particle wave where both function of each operation is occurring at the same time.

 

[Jerromy]

I have a bit of a puzzle in my mind thinking of this. If a photon is like every other photon and travels at the speed of every other photon, how could the frequency of the wavelength of the photon cause such dramatic changes in momentum? It seems to be like saying "a pair of projectiles fired together with a short cord have more momentum than a pair of projectiles with a long cord." They should still have the same relativistic mass and therefore carry the same kinetic energy but gamma rays are far more energetic than optical light. Does anyone have any inspired insight as to why this might be?

 

[dryson]

But light has mass, otherwise light wouldnt be effected by gravity unless gravity and light are within the same family of energy, light might be the weaker force, with gravity being the stronger force, otherwise if light was the stronger force, then gravity would not effect light in the manner that it does.