What exactly is light? And why is "the speed of light" considered to be fastest anything can move?

[BigToque]

Whether or not light is a wave or a particle, what makes it any more special then any other type of wave or particle? Why is the speed that light moves at considered to be the ultimate limit of speed?

It just seems sort of strange to me that in a universe that appears to be infinite in space and time that objects/matter/anything would be restricted to a range of speeds (0 - C)

 

[djhuber82]

to move at the speed of light a particle must have zero mass, or it would take infinite energy to accelerate it. photons meet this crtiterea. i'm not aware of anything else that does.

 

[bobsmith1492]

Originally posted by: djhuber82
to move at the speed of light a particle must have zero mass, or it would take infinite energy to accelerate it. photons meet this crtiterea. i'm not aware of anything else that does.

Possibly gravitons, if there is such a thing...

 

[Cattlegod]

http://science.howstuffworks.com/relativity2.htm

read that page.

should answer most of your questions.

 

[sao123]

Originally posted by: sao123
I recommend you all read Brian Greens 2 books on this subject and more. He answers all of your questions in a laymans manner for all to understand.

The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory (Paperback)
The Fabric of the Cosmos : Space, Time, and the Texture of Reality (Vintage) (Paperback)

if you understand vectors, let me give you an oversimplified example.
Imagine you are moving at a constant velocity in a northerly direction. If you now begin to move in a easterly direction in addition to the northerly direction, but stay at a constant velocity... then your northerly speed magnitude must decrease.


Everything moves through spacetime(4d) at the speed of light. And this same property occurs. At complete rest, your entire vector magnitude, would be traveling though time (T) at the speed of light. As you begin moving in any of the otehr 3 directions (x,y,z), your motion through T, must decrease by that same amount. As an object reaches the speed of light, then its magnitude through T approaches zero. (time would stop at speeds of light.)

If a stationary body shoots a laser beam, the light will be traveling at C. If a moving body traveling at C/2 is traveling in the same direction as the laser, the light will also appear to be traveling at C. If you are able to travel at 1000C or 1000000000C, it will still appear to be traveling at C from the same, stationary source.

The reason this is so, is because of a mathematical limitations... watch.
As per above, something traveling at C in (X,Y,Z) travels through T at 0. Since speed is distance traveled divided by time, any distance in X,Y,Z traveled, divided by time = 0 (since time stops at velocity C) is undefined. Now you must read the books I posted to actually understand that which I have regurgitated to you from memory.

 

[spike spiegal]

So, we take an atom, and accelerate to, lets say, 90% C.

What happens to the electron cloud as it ocillates around the nuclei given in one vector it's approaching C while in the other vector it's slowing down? (at least relative to the baseball player who just knocked it into orbit).

I never solved the problem, but I heard one theoretical physicist type an interesting rant that strange things begin to occur near the speed of light that can't quite be predicted by we poor sublight citizens. Heisenberg Uncertainly Principle begins to gets weird, etc.

 

[iamaelephant]

To the OP, for the record light is both a wave and a particle. Weird yes, but experiments have confirmed it.

 

[RossGr]

It all started in the 1860s when Clerk Maxwell was able to formulate the accumulated knowledge of electromagnetism into a system of 4 equations, now known as Maxwell?s equations. He was the first one to manipulate his set of equations into the form of a 2nd order partial differential equation. The form of the PDE was what is known to be the ?wave equation? In the wave equation the speed of the waves represented appears in a very obvious manner. The combination of parameters which represent the speed of this electromagnetic wave were then, and are still, the basic constants of electromagnetism, the Permeability and Permittivity of free space. These numbers where well known to Maxwell. When he did the trivial calculation (the inverse of the square root of the product of the constants) he found himself looking at a number which was the then accepted experimental value for the speed of light. This became the first real proof that light was an electro magnetic phenomena. It also began the 40yr schism of physics, since the speed of light was a combination of constants there was no room for, or mention of, the velocity of the source, thus it did not obey the then thought to be universal law (Galilean Transforms) for addition of velocities.

 

[Jeff7]

I had some ideas running around my head lately. Probably nearly meaningless, but here they are anyway. Stephen Hawking mentions "particle, anti-particle pairs." Going along with that - imagine this: Trace a point on a wheel as the wheel moves across your field of view. It looks sort of like a wave. Rotating particle-anti-particle pairs - satisfies both the wave theory and the particle theory.

Speed of light? Maybe that "ether" theory wasn't too far off - spacetime as a sort of fluid? Like trying to push through water - as you try to go faster, it takes more and more energy to accomplish. Same with spacetime. As you push through water, it curves down behind you - spacetime exhibits something similar: as you go faster, apparent mass (and thus gravitational attraction) also increases.

 

[CycloWizard]

Originally posted by: Jeff7
Speed of light? Maybe that "ether" theory wasn't too far off - spacetime as a sort of fluid? Like trying to push through water - as you try to go faster, it takes more and more energy to accomplish. Same with spacetime. As you push through water, it curves down behind you - spacetime exhibits something similar: as you go faster, apparent mass (and thus gravitational attraction) also increases.

Interesting idea, but not entirely correct. The resistance offered by a fluid (generalized by its viscosity) is dependent on the shear rate. The shear rate is a factor of geometry and velocity. So, for constant geometry (e.g. a boat), the shear rate increases with velocity. It is much more common for the viscosity of a fluid to decrease as shear rate increases (shear-thinning) than for the opposite to happen (shear-thickening). In the case of water, the viscosity is nearly independent of shear rate (Newtonian behavior), so the resisting force will increase just about linearly with velocity. So, if the 'ether' were a shear-thickening fluid, you might be right.

 

[Soccerman06]

Light is something called photons, which are emitted when electrons change their orbital distance (larger) from moving particles (or by energy). The brighter the things are, the more photons are emitted, not that they move faster, they cant afaik (one set speed). Speed of light is set as a universal constant because as objects move faster, they grow in mass, eventually reaching infinite mass and because you would need infinite energy to accelerate orbjects to/above C, its impossible with our tech. The only way around this would be to use gravity as a break in the spacetime (wormholes). You could build a warp engine, think star trek, which would create gratitational warps and push you along, allowing you to go faster than light (seeing how you could make yourself weightless with this tech).

 

[kotss]

My understanding is that a wormhole would not actually allow you to go faster than C, but give you the ability to achieve an average velocity greater than that of C.


Light from my understanding is the photon particle. This particle is considered to be the
mediator of the electromagnetic force. When energy needs to be transferred between
2 particles (there are other situations, I would suppose as well) a photon is generated from the energy release. (I do understand that light is also a wave.) Light will demonstrate the property you are looking for.

 

[Chiropteran]

Originally posted by: Jeff7
I had some ideas running around my head lately. Probably nearly meaningless, but here they are anyway. Stephen Hawking mentions "particle, anti-particle pairs." Going along with that - imagine this: Trace a point on a wheel as the wheel moves across your field of view. It looks sort of like a wave. Rotating particle-anti-particle pairs - satisfies both the wave theory and the particle theory.

Not really. Here is wierd thing about light. If you shine a light through a barrier with 2 slits, you will get an interference pattern of light and dark bands.

Now, the reason you get the light and dark bands is because the light waves comming from each slit interfere with each other, makes sense so far?

Now this is a creepy thing: Setup the same thing, but have the light emitting device only emit ONE photon of light per minute. You still get interference bands, as if a single photon simultaneously goes through both slits and interferes with itself.

And then one last thing to try... put a detector on each slit so you know which slit the photon went through, because if you know the photon went through 1 slit and not the other, it can't interfere with itself, can it?

If you have a detector setup, the interference bands go away. Turn it back off, and they come back.

Quantum mechanics is weird.

 

[f95toli]

Maybe someone should point out that there is no *real* paradox here.
Mathematically everything is consistent, you do not have to switch between a "wave" picture and a "particle" picture for light in the calculations, the so called wave/particle duality is just a natural consequence of quantum mechanics. We talk about this duality simply because we can not comprehend what light really IS, we have to resort to using familar familiar concepts from our everyday existence.

Moreover, we need to be carefull when we talk about photons. A photon is NOT a regular particle, what we call a photon is mathematically just a single mode of a quantized EM field. Experimentally you can for example have a situation where you have a single photon trapped in a high-Q cavity, but this photon is then distributed throughout the whole volume, i.e. you can't think of the photon as a "ball" of light bouncing around in the cavity.

The photon concept is very "deep" and more or less impossible to truly understand unless you have studied quantum mechanics (and quantum optics in particular) for a few years.

 

[imported_Seer]

Information can travel faster than light. The wave form resulting from interference of two EM waves can travel faster than light.

 

[herm0016]

Originally posted by: Seer
Information can travel faster than light. The wave form resulting from interference of two EM waves can travel faster than light.

no, it cant. and if you still think it can prove it to us with some evidence.

you should also look up the "2 slit " experement. where a single photon is shot into a solid that has 2 slits very close together. convention says the photon will go through one of them, but in reality it travels through both and you get a possion bright spot on the screen on the opposit side.
also think about this: atoms and light and cows all have wave lengths and wave functions. we just dont have technology that has a resolution below the wavelength of the em spectrem. the wave function tells you that the atom has the probablity of being found in a spot. stuff only decides where to be when it is measered (or is interfered with by another partical because measerment is like saying interfering with) also you are only able to know one property of a partical at a time, because in the process of measureing that property you will have alterd the rest of the properties. i.e "shroders cat"

Originally posted by: f95toli
Moreover, we need to be carefull when we talk about photons. A photon is NOT a regular particle, what we call a photon is mathematically just a single mode of a quantized EM field. Experimentally you can for example have a situation where you have a single photon trapped in a high-Q cavity, but this photon is then distributed throughout the whole volume, i.e. you can't think of the photon as a "ball" of light bouncing around in the cavity.

so actually you cant think of a partical in the classical way either, it is also a wave function like a photon before you measure it.

 

[f95toli]

Originally posted by: herm0016
[
so actually you cant think of a partical in the classical way either, it is also a wave function like a photon before you measure it.

True, but the difference is that for ordinary particles such as electrons and protons we can usually succesfully use the "particle approximation" when we calculate e.g the equation of motion and we can do so using classical physics (with relativistic corrections if we need accurate results), it is only when interference effects become important that we need to use the full quantum mechanical hamiltonian.
Photons are always fully "quantum mechanical" objects and in many cases semi-classical approximations are used instead where the electromagnetic field is just treated like a classical (unquantized) field. This often works surprisingly well.

 

[Born2bwire]

Originally posted by: Jeff7
I had some ideas running around my head lately. Probably nearly meaningless, but here they are anyway. Stephen Hawking mentions "particle, anti-particle pairs." Going along with that - imagine this: Trace a point on a wheel as the wheel moves across your field of view. It looks sort of like a wave. Rotating particle-anti-particle pairs - satisfies both the wave theory and the particle theory.

Speed of light? Maybe that "ether" theory wasn't too far off - spacetime as a sort of fluid? Like trying to push through water - as you try to go faster, it takes more and more energy to accomplish. Same with spacetime. As you push through water, it curves down behind you - spacetime exhibits something similar: as you go faster, apparent mass (and thus gravitational attraction) also increases.

One of the fundamental flaws of ether is the fact that it requires a rest state. The ether itself will have a relative velocity with your emitters and detectors and as such, the motion of light relative to the motion of your ether should impact it's velocity. But the fact that this does not happen in real life, as demonstrated in the famed Michelson-Morley experiment, is the real major blow against the idea of an ether. The watchword of the day is that with anything electromagnetics, avoid the use of the word ether like the plague.

Information can travel faster than light. The wave form resulting from interference of two EM waves can travel faster than light.

One thing to keep in mind is what is information. In electromagnetic waves, the information is encapsulated in the energy of the wave or a combination of an embedded amplitude and phase modulation. In certain modes of propagation, like in waveguides, different aspects of the wave can propagate faster than the speed of light. The guide phase velocity of the wave in a waveguide can be faster than the speed of light. However, the information does not propagate with the guide phase velocity but rather with the group velocity, which is always less than the speed of light.

 

[byosys]

Originally posted by: djhuber82
to move at the speed of light a particle must have zero mass,

Based on what I understand of Einstein's theory, I'd have to disagree with you on this point. Einstein's theory said you can't accelerate a particle to c or faster than c. It made no mention of particles that spend their entire "lives" at speeds greater than that of c. Ie, Einstein left open the possibility that there are undiscovered particles that always travel faster than the speed of light.

Note: the above I have considered based on what I know of Einstein's theory. Below I'm just kinda thinking out loud. If there are other theories that address particles always traveling faster than c, please either explain or link me to some reference materials on them as I am quite interested in this branch of physics.

I suppose that some force could act on thoes particles (the ones that travel faster than c) and slow them down to c or less than c, but I'm not sure if we would be able to tell if they ever traveled at speeds greater than c or if we could tell if they traveled > c, what properties they had while traveling > c or how to harnes their special properties (mainly traveling > c). Basically, I'm considering what we could/couldn't find out about particles traveling faster than the speed of light and with my limited knowledge, I really am just guessing.

 

[DrPizza]

Originally posted by: byosys

Originally posted by: djhuber82
to move at the speed of light a particle must have zero mass,

Based on what I understand of Einstein's theory, I'd have to disagree with you on this point. Einstein's theory said you can't accelerate a particle to c or faster than c. It made no mention of particles that spend their entire "lives" at speeds greater than that of c. Ie, Einstein left open the possibility that there are undiscovered particles that always travel faster than the speed of light.

Note: the above I have considered based on what I know of Einstein's theory. Below I'm just kinda thinking out loud. If there are other theories that address particles always traveling faster than c, please either explain or link me to some reference materials on them as I am quite interested in this branch of physics.

I suppose that some force could act on thoes particles (the ones that travel faster than c) and slow them down to c or less than c, but I'm not sure if we would be able to tell if they ever traveled at speeds greater than c or if we could tell if they traveled > c, what properties they had while traveling > c or how to harnes their special properties (mainly traveling > c). Basically, I'm considering what we could/couldn't find out about particles traveling faster than the speed of light and with my limited knowledge, I really am just guessing.

It's a decent guess. Yes, there are theoretical particles that would travel faster than the speed of light (tachyons.) (Here's a place to begin reading. However, the speed of light serves as a barrier in both directions. If you have any math background, consider this analogy.. look at the graph of y=tanx. Note the asymptotes. Follow the curve from the left and you never quite make it to 90 degrees (Pi/2 radians). Follow the curve from the right of 90 degrees (Pi/2 radians) and you never quite make it back down to 90 degrees either.

edit: I should have used 1 / x^2. After all, we're generally dealing with positive values.

 

[byosys]

Interesting read on the wiki link. I guess the next question would be how to detect thoe particles and use them for pratical purposes which is no doubt quite problematic seeing as these aprticles have an imiganary mass (still haven't gotten my head around that part yet). Nor have I gotten my head around the fact that by taking energy away from the particle, you actually speed it up, the exact opposite of what happens in Newtonian physics. Also interesting to consider is how these particles interact with black holes. We all know that light can't escape a black hole, but the properties of these particles suggests to me that a black hole would have no effect on the travel of these tachyons if they exist. This assumes that gravity can't act on a praticle with imiganary mass, which at my current level of understanding is just a guess.

On a side note, I have a question about Einstein's theory. Did it say that it would be impossible to accelerate a particle to or faster than the speed of light? I know it seems like arguing semantics, but I would think that the answer has a very real impact on what happens on tachyons. If Einstein said that particles can be accelerated to the speed of light but not faster, could light (as we see it) simply be tachyons that have been slowed down to c by the addition of some energy from an unknown source? If Einstein said that it was impossilbe to accelerate any particle to c, then this question obviously has no meaning.

 

[msparish]

Can't accelerate to c.

 

[Alastria]

Originally posted by: Seer
Information can travel faster than light....

Are you perhaps thinking of the "seamless whole", or Einstein's "spooky action at a distance"? If so, then that's kind of like information moving faster than C (in a 3-dimensional way).

 

[asearchforreason]

Yeah, he must be referring to quantum entanglement. I'm not a physicist but as far as I'm aware even using entanglement information cannot be transmitted faster than light.