Breaking the light barrier

[silverpig]

Okay, so we know that light is a purely electromagnetic phenomena. A photon is just an oscillation in the B and E fields of space. It makes sense that we can't go faster than light because we are made up of primarily electromagnetically charged particles.

What about glueballs? They haven't been detected (yet) but are theorized to be gluons that have attached themselves to each other and not to quarks, as they normally are. They are not electromagnetically charged at all, nor do they react electromagnetically (only strongly). Why should a glueball respect the speed of a photon in the EM field when it doesn't react with this field at all?

The only reason I can think of thus far is that there is a unification of forces at an energy where the glueballs would be approaching the speed of light. They would then have whatever speed limit is imposed by this singular super-force. This, however, seems to be hand-wavey just to say that this limit coincides with that of the speed of light.

 

[f95toli]

It doesn't work that way. The reason why nothing can go faster than light has nothing to do with "electromagnetically charged particles", even things like the effects of gravity is limited by the speed of light (that is, if the sun disaperad it would take a few minutes for the earth to leave its orbit, it takes time for the information to reach earth). Particles like the neotrino are not charged but are stull linited to speeds below c.

I usually think of c as the "speed limit of the universe", photons are travling as fast as possible, but the fact that a limit exists has nothing to do with photons.

So, the idea of glueballs does not work.

 

[silverpig]

The effects of gravity are supposed to be limited to light speed. We don't know for sure yet if they do. And neutrinos react weakly, which is an extension of the electromagnetic force.

 

[f95toli]

All particles are affected by some force (weak. strong, electromagnetic) and the standard model tells us that all of these forces are united into one if the energy is high enough.
So in a way they are all "extensions" of each other. So why would a glue ball be different?
I don't see the difference between a neutrino and a glueball in this case.

 

[silverpig]

Originally posted by: f95toli
All particles are affected by some force (weak. strong, electromagnetic) and the standard model tells us that all of these forces are united into one if the energy is high enough.
So in a way they are all "extensions" of each other. So why would a glue ball be different?
I don't see the difference between a neutrino and a glueball in this case.

Think of it this way: Space is permeated by an electromagnetic field (let's ignore gravity for now). Think of this field as a medium for waves of light to travel. Photons are just the little wave packets flying along in this medium. The EM field has a property called a coupling constant which describes the "tension" in this field and gives you the speed at which things interacting in this field can travel. Think of it sort of as a speed of sound in a medium type thing. If you change the coupling constant, you change the speed of light.

This coupling constant only appears in the equations for electromagnetism. Weak field theory and chromodynamics both have different coupling constants which are very different (chromodynamics' being very very much larger than EM and weak having some very odd vector/scalar mixing and parity stuff involved in it). So now in addition to having this EM medium permeating spaces, you also have a strong medium and a weak medium.

Particles that are affected by electromagnetism feel the EM coupling constant and are held to the properties of the medium they traverse. Same goes for the weak and the strong. However, purely strongly interacting particles don't have anything to do with the EM coupling constant. They just don't interact. It's like asking how fast can a fish swim through rock. It just doesn't work. All unification theories do is show that when travelling fast enough, the EM medium and the weak medium merge and become indistinguishable. It's kind of like how air seems to have no drag when you're moving very slowly, but when you're going very quickly it feels almost like water; or like how water can feel like concrete if you fall off a bridge into a river.

Approaching the speed of light is sort of similar to a sky diver approaching terminal velocity. Light speed is like the terminal velocity of the EM field.

Now, to continue my skydiving analogy let's have a skydiver jump from a plane to fall through the air and land in the ocean (no parachute! ). He falls at ~200 km/h or whatever terminal velocity is, and then smacks the water, slowing down drastically to say 5 km/h. His carcass interacts with both the air and the water. Now let's create a super-skydiver who doesn't react with water at all. He just reaches terminal velocity in the air, and then passes through the water as if it were air because he doesn't react with it. In the presence of water, the water-reacting guy is limited to 5 km/h whereas his lucky super-buddy doesn't have to obey any hydrodynamics.

So I guess I have a double edged question here: Why does a non-water reacting super skydiver (glueball) have to respect hydrodynamics (speed of light) when he doesn't react with water (EM field), and if he does, then why is it the speed of light that is the limit and why is it not the coupling constant for one of the other forces which determines the maximum velocity of a particle?

 

[Drayvn]

Actually u can go faster than light, i remember some experiment was done to see how much u could slow the speed of light down and they slowed it down to like 30mph or something in this long glass rectangle with different gases and stuff, so if u did that and ran at 31mph u could go fast than light

 

[Geniere]

Drayvn ? Actually light does not slow down, speed up, or stop, never has, never will. Light always propagates at exactly C. Legitimate experimenters have succeeded in slowing or stopping the group velocity of a light beam. Science writers/reporters mistakenly report this as a change in the speed of light.

 

[silverpig]

Originally posted by: Geniere
Drayvn ? Actually light does not slow down, speed up, or stop, never has, never will. Light always propagates at exactly C. Legitimate experimenters have succeeded in slowing or stopping the group velocity of a light beam. Science writers/reporters mistakenly report this as a change in the speed of light.

^

What he said

 

[Fandu]

I remember reading about a similar experiment where they were able to "teleport" light across a medium, however the information that was encoded in the light still arrived as if it was 'only' traveling at C. Figure that one!

 

[f95toli]

Silverping: It seems to me you are considering second quantization of the EM field but in a simplified way.
My main objection is that the special- and general theories of releativity predict that c is the maximum speed you can trabel without invoking secnd quantization at all, the nature of the interaction is not relevant.
Now. since we do not yet know know to unite GR and QM there is of course a chance that FTL speeds are possible, but for now GR seems to hold.
I know that in string theory they use the speed of light to check their theories, a a particle is allowed to trabel at speeds>c there is something wrong with the theory (temember tachyons?).

Another problem is that AFAIK glueballs can be described using the standard model, hence it should not be possible to exceed c since that limit is built into the model.

 

[everman]

Originally posted by: Fandu
I remember reading about a similar experiment where they were able to "teleport" light across a medium, however the information that was encoded in the light still arrived as if it was 'only' traveling at C. Figure that one!

I think you are referring to quantum entanglement which seems to somehow transfer information faster than light. It's some kind of relationship between 2 particles, which happens to be capable of being used in teleportation. But I believe the original object, such as a photon, is destroyed in the process isn't it? I don't really know what I'm talking about

 

[bwanaaa]

Originally posted by: Geniere
Drayvn ? Actually light does not slow down, speed up, or stop, never has, never will. Light always propagates at exactly C. Legitimate experimenters have succeeded in slowing or stopping the group velocity of a light beam. Science writers/reporters mistakenly report this as a change in the speed of light.

please clarify. If the speed of light in air is slower than in a vacuum, and the speed of light in water is slower than in air, how are these measurements taken? what is the group velocity and is it different from the 'speed of light'?

 

[silverpig]

Originally posted by: bwanaaa

Originally posted by: Geniere
Drayvn ? Actually light does not slow down, speed up, or stop, never has, never will. Light always propagates at exactly C. Legitimate experimenters have succeeded in slowing or stopping the group velocity of a light beam. Science writers/reporters mistakenly report this as a change in the speed of light.

please clarify. If the speed of light in air is slower than in a vacuum, and the speed of light in water is slower than in air, how are these measurements taken? what is the group velocity and is it different from the 'speed of light'?

Air is just a vacuum with little particles in it. The light travels in this vacuum at c, but interacts with the particles as well causing it to slow down.

Throw two rocks into a pond very close to each other. You'll see the pond ripple. You'll notice that there is an outer edge to this ripple that moves at a speed v away from where the rocks were dropped. This is the group velocity. If you look at the ripples inside this ring though you may see them seemingly moving faster than the outer ring. A ripple will start off, speed up to the outer ring, and then disappear. This ripple travels with the phase velocity of the waveform. This phase velocity is the velocity of the waves which are the result of the addition and subtraction of the separate waveforms of the two rocks. This phase velocity may be much faster or much slower than the group velocity depending on how the waves add.

What they do when they "stop" light is they set up a gas of atoms with some very clever energy levels in the electron cloud. They basically make the gas perfectly transparent at one very narrow energy level, and virtually opaque (ie: there are electrons at the energy levels around the narrow gap which will absorb incoming photons) around the gap. They then pass light through within a limited energy range centered on the energy of this gap. The result is an addition and subtraction of the waves which leads to a very very slow moving resultant wave of light.

 

[Geniere]

Oops- Silverpig beat me to it but anyhow here's my spin.

There have been many threads in this forum re: the speed of light. It seems that much confusion stems from high school physics teachers telling students that light travels slower in glass, water, etc. A light beam consists of many photons. When the beam hits a piece of glass all the photons comprising the beam interact with the electrons in the glass, whether bound to the glass molecules or not; whether reflected or transmitted. None of the photons that exit on the other side of the glass are the photons that entered. The exit photons are those that have been re-emitted by the electrons interacting with the entrance beam. The exit photon may have been the result of millions of such interactions. Since most mediums such as glass are homogeneous, each exit photon will have the probability of having undergone the same number of interactions within the glass as any other photon, but some will have had more interactions, some will have had less. Each interaction takes a very brief time. The phase relationship of the all the EM fields combine to smear the exit beam in time, determining the group velocity and the ?index of refraction? of the medium. Similarly, when electricity flows in a wire each individual electron moves very slowly and very quickly becomes bound to another atom in the wire. But when you flick on a light switch, the light comes on almost instantaneously. How is that possible when the electrons only move at a snails pace for very short distances? When an electron is set in motion by a voltage it produces an EM field. The EM field is a composite field of all the electrons set in motion. It is the group velocity of the EM fields that propagates very rapidly along the wire setting other electrons in motion as it goes.

Imagine sitting by a pond and throwing pebbles. If you are very precise in accuracy and timing you can cause a large wave to occur by the smaller waves adding to it. This same process causes the smaller waves to become smaller and almost invisible. Some of the near invisible small waves will arrive at the shore before the large wave. The large wave could be said to represent the group velocity if the small waves were made to disappear completely.

 

[silverpig]

Originally posted by: Geniere
Oops- Silverpig beat me to it but anyhow here's my spin.

There have been many threads in this forum re: the speed of light. It seems that much confusion stems from high school physics teachers telling students that light travels slower in glass, water, etc. A light beam consists of many photons. When the beam hits a piece of glass all the photons comprising the beam interact with the electrons in the glass, whether bound to the glass molecules or not; whether reflected or transmitted. None of the photons that exit on the other side of the glass are the photons that entered. The exit photons are those that have been re-emitted by the electrons interacting with the entrance beam. The exit photon may have been the result of millions of such interactions. Since most mediums such as glass are homogeneous, each exit photon will have the probability of having undergone the same number of interactions within the glass as any other photon, but some will have had more interactions, some will have had less. Each interaction takes a very brief time. The phase relationship of the all the EM fields combine to smear the exit beam in time, determining the group velocity and the ?index of refraction? of the medium. Similarly, when electricity flows in a wire each individual electron moves very slowly and very quickly becomes bound to another atom in the wire. But when you flick on a light switch, the light comes on almost instantaneously. How is that possible when the electrons only move at a snails pace for very short distances? When an electron is set in motion by a voltage it produces an EM field. The EM field is a composite field of all the electrons set in motion. It is the group velocity of the EM fields that propagates very rapidly along the wire setting other electrons in motion as it goes.

Imagine sitting by a pond and throwing pebbles. If you are very precise in accuracy and timing you can cause a large wave to occur by the smaller waves adding to it. This same process causes the smaller waves to become smaller and almost invisible. Some of the near invisible small waves will arrive at the shore before the large wave. The large wave could be said to represent the group velocity if the small waves were made to disappear completely.

Actually, many of the photons that exit are the same ones that enter. And it's not because they are absorbed and re-emitted by the electrons at all. Absorbtion occurs at discrete energy levels, as does re-emission (lyman alpha line in hydrogen for example). Furthermore, re-emission occurs in a random direction, so any beam coming in would be diffused randomly. It's actually much more complex than simple absorbtion and re-emission and requires very careful manipulation of the energy levels of electrons in a gas.