Saw this in another thread and made me think of something and wonder. Does anything else aside from light move at the speed of light? If not, could it be concluded from the above statement that Einstein determined that light is mass moving at a certain speed?

Can anything travel faster than the speed of light?

"No," is what Albert Einstein would likely say if he was alive today -- and he would be the man to ask, because scientists have been taking his word for it ever since the early 20th century.


According to Einstein's theory of special relativity, published in 1905, nothing can exceed the speed of light. That speed, explained Einstein, is a fundamental constant of nature: It appears the same to all observers anywhere in space.

The same theory says that objects gain mass as they speed up, and that speeding up requires energy. The more mass, the more energy is required. By the time an object reached the speed of light, Einstein calculated, its mass would be infinite, and so would the amount of energy required to increase its speed. To go beyond the infinite is impossible.

One hundred years of testing have only reinforced what Einstein wrote, said Donald Schneider, professor of astronomy and astrophysics at Penn State.

"There is no experiment that has contradicted special relativity. We have accelerated sub-atomic particles to well over 99 per cent of the speed of light, but not equal to or exceeding the speed of light.

"Theoretically, strange things happen when you exceed the speed of light," Schneider added. Time travel, for one thing, and a breakdown in cause and effect. Schneider uses an example of hitting a target with a gun that shoots bullets faster than the speed of light. "Some observers would see the bullet hit the target before they saw the shooter fire the gun," he said. "Since one of the guiding principles of relativity is that all physical laws are the same to all observers, this violation of causality would be a big problem."

Another oddity: tachyons. In 1967, Gerald Feinberg, a physicist at Columbia University, proposed the existence of these faster-than-light particles. In their mirror world above the light-speed barrier, tachyons would require infinite energy to slow down to the speed of light.

Other concepts that have popped up include "wormholes" -- shortcuts through space-time that would permit point-to-point travel faster than light -- and "warp drives," a kind of bubble created in space in which relativity wouldn't apply.

Although they have become staples of science fiction, tachyons, worm holes and warp drives remain speculation, and many physicists dismiss their significance. There is, however, at least one real-world example of superluminal (i.e., faster-than-light) travel. It occurs when light passes through water.

In this dense medium, Schneider explained, light is slowed to three-fourths of its speed in a vacuum. In a nuclear reactor, charged particles flying off the radioactive rods through the water they are submerged in exceed this reduced speed.

Because these particles contain an electric charge, they emit energy, called Cherenkov radiation. Any particles they bump into become radioactive, giving the water a characteristic blue glow.

"It's not at all exotic," Schneider said. "Every time you look at the water in a nuclear reactor, the bluish glow you see is radiation produced by charged particles moving faster than the speed of light in the water."

Still, slowing light down in order to beat it is cheating, Schneider conceded. And although he's not closing his mind to the possibility that relativity will one day be amended, for now, he said, Einstein's theory is the final word.

Um... no, last I read, light has momentum, but has no mass, it can be viewed as an oscillation in electric and magnetic fields, but I'm sure someone who more recently studied this has a better explanation for why light should not be viewed as 'mass' moving at a certain speed.

Oh, and its a common misconception that light always moves at exactly 'the speed of light.' Thats true in vacuum, but not in other media.

(last post out of sync, sorry)

How do photons move at the speed of light? Wouldn't they have an infinite mass?

I've not studied the subject matter in a LONG time, but as far as I remember, "photon" is just a name for light when *viewing it* as a particle. "Viewing it" as such being a key phrase. Photons have no mass.

Maybe a quick read of wikipedia might be helpful?

Well . . . I am not sure exactly what you mean here, but let me explain something and lets see how close we get.

Light has no rest mass. All of its energy is momentum.

All of lights movement is through space, and none of it is through time.

An object (I would assume made of matter) can never move at the speed of light through space.

This is becuase it would require infinite energy . .. which is not possible, infinity is not a quantity.
No "rest" mass. It has energy which has a specific energy density and thus a mass, just not rest mass.

Photons exhibit the properties of both a particle and a waveform. An ocean wave has no mass but it has energy. A photon is bent from it's path of a straight line by gravity, which indicates it has mass. Einstein equated mass and energy as the same thing but in different forms. Therefore the trick is to determine how much mass a photon would have if it was not moving. However, since photons always move at the speed of light (modified by medium), the actual calculation cannot be made. Here is a summary of the problem.

Begin Quote.

A New Limit on Photon Mass

A new limit on photon mass, less than 10-51 grams or 7 x 10-19 electron volts, has been established by an experiment in which light is aimed at a sensitive torsion balance; if light had mass, the rotating balance would suffer an additional tiny torque. This represents a 20-fold improvement over previous limits on photon mass.

Photon mass is expected to be zero by most physicists, but this is an assumption which must be checked experimentally. A nonzero mass would make trouble for special relativity, Maxwell's equations, and for Coulomb's inverse-square law for electrical attraction.

End Quote

Photons are tiny packets of energy which are equal to the change of state of an electron valence from one state to another. When you heat up an atom, the little electrons in the outer shell hop up to a higher energy state to absorb the energy. Since this is not their normal condition, they shed an energy packet equal to one photon to stabilize back to normal. The frequency of the photon runs the full spectrum of electromagnetic radiation.

Since E=M*C-squared, the mass would be E(dependant upon the frenquency) divided by the speed of light squared. Since the formula is based on dividing by the speed of light, if you set the speed at zero you are dividing by zero and the formula goes "kaput!".

Maybe you meant a light wave? An ocean wave most certainly has mass . . . H2O.

This should read that due to absorbing the energy the electrons move to a higher energy shell. Not that they move to that energy shell to absorb the energy. Energy is required to facilitate that movement, not its antecedent.

Exactly, and this is why it is not meaningful to even think of matter moving at the speed of light.


To answer the question, No we have found no particle that is not light that moves at light speed.

There are theories as yet untested that hope to find gravity particles . . which would then be another piece of stuff that moves at the speed of light.

However many physicists think that gravity itself is a side effect of the higs boson, not a particle itself.

It all gets very technical and I can honestly say I do not know. I can honestly say also that leading physicist are not really sure either, but they do have a clearer picture then this third year student.

I thought MetalWing meant the wave itself, not the material which is waved. Sure, water has mass. But you can argue that the wave is a process, and that the wave process itself has no mass (in the sense that I was using the word earlier).

(Just to confuse matters: Or does it, in the sense that you are using it? Don't ocean waves have momentum, which can be imparted, say, to an unanchored boat? Could that momentum/energy be viewed as mass (but not rest mass))?

Bushido, I understand and agree that your use of terminology is valid, but I think it creates confusion. The 'mass' that light can be said to have exists only in the context of momentum and energy, which, I think, is completely different then what 99% of english speaking people normally mean by the word mass.

You got it right.

I agree completely, this is an issue between a scientific term and colloquial term.

So I was mistakenly thinking of the colloquial term for wave, and you are referring to the colloquial usage of mass. I agree waves are processes in science.

To have this kind of conversation we all need to make sure we are on the same boat, and I think we now are.
These terms do mean both things . .. just not at the same time and in the same context.
So in the context of this conversation you are right I am mistaken on the usage of wave. Meh bad.
In the context of this conversation the difference between rest mass, and energy mass is very important.


The big difference between waves of water, and waves of light is that the wave of water is made of matter which has lots of rest mass.

We don't find waves of water traveling at C.

So while it may be true that its the water doing the waving, not the actual wave it is important what the medium is that the wave traverses. (Im being captain obvious only for the sake of explaining my view whilst I stuck my foot deeply in my mouth)

There is a particle that has been theorized to exist that may also have no rest mass, however may not travel at the speed of light . . .

Can anyone guess?!!??

Perhaps a neutrino? Some call them ghost particles.

It is said they can reach up to the speed of light.

Then there is the Tachyron. I hope I spelled that right.

second guess got it.

Neutrino's have mass, and so cannot go the speed of light.

99.99999% does not count . . . hehe.


____

Tachyons are theorized to be particles that cannot move slower then the speed of light and thus move backward through time.

Now that is some mind bending shat,

That is very interesting Jeremy. Thankyou for sharing that. I suck in physics(which is probably ironic for a German) but it is never too late to learn what I can each and every day even if I will never need it for any particular reason later on. If anything I can relay what limited knowledge I have to my daughter when she has it in high school.

When you have completed your college in physics what do you plan to do with that degree? What interest do you have? Will you become a scientist for a specific field?

I dont know yet. I was thinking of Nano tech. Every day is a struggle right now, Calc II is kicking my @ss.

Right now I work for a Radiological software development company, and medical field is certainly interesting, not sure I want to be a physicist in this industry tho . . sigh not sure.

I am tempted to switch majors to music and become a sax bum.
I would have come full circle, theater and performing arts, to physics, to music hahahah.

A beautiful instrument the saxophone. I don't blame you if your heart reaches out to this instrument.

Nano tech is some complicated stuff I could imagine, yet I bet highly interesting if one knows what is talked about. The closest I will ever get to nano tech is on a science fiction roleplaying computer game like Galactic Civilization - the Dreadlords.

If I can give any advice, I would say never give up. You might discover something new to contribute to the science world or maybe even add to it. That would be an amazing feat indeed. I know what you post in here is very educational and I thankyou for doing this.

I think in his Relativity book for the layman, he said that information cannot go faster than light, so perhaps that is something that also goes at that speed.

And I've heard Susskind say something like "photons have energy, but no mass," on his very good youtube lectures on special relativity through Stanford University's channel. I recommend watching that and his general relativity lectures as well. He teaches the minimum you need, so it is good for a general science-interested audience.

I've wondered about these concepts near the important number c is considered, and have always thought that there is something fishy about light having energy (and hence technically mass, as they are conversion units) but not behaving like a mass. I don't think that the proposition that light travels at c is maintained in gr.

Moreso, The momentum factors into why something can't go at v=c. It's pretty much like this. A heavy body is accelerated up to about 75% lightspeed about normally, like Newtows gig that is quite familiar. But then the body gains the kinetic energy that was transfered from the source providing the acceleration pull or push that started the body going. So the body is then more massive, and has more momentum, and then it takes even more accelerating force, which makes it more massive, and so on... The result of the momentum formula in sr is such that a body just can't seem to get enough E to match c. I think it has something to do with how the 4-momentum behaves theoretically, and this momentum limit sets a certain velocity.

I know what you're saying though, a photon with mass (E), traveling at lightspeed. I've heard of the idea that light speed is not the ideal, but is actually a slightly bit slower than the real speed limit, and I took this to mean that the little bit of mass that a photon has limits it to some speed just below the ideal c. Such thinking hasn't born anything out theory wise that I've read, at least. But one would think that different light energies would then have different speeds, but I'm not sure that that is reflected experimentally. Gravity redshift might be a good spot to check for this, so that a different redshift rate could be based on energy requirements of light. But this is fishing for differences without a base for which they emerge.



What seems the most intersting when thinking about those 'why' questions with light is that it is true to say that light speed is the speed reached by a particle if (idealized) it is accelerated at the expansion rate of the universe for the time frame of the universe, all of those darker billions. So that offers the possibility that light is different value at earlier, or futher removed in the future, epochs. This would not be surprising granted that I think it technically already can vary slightly in gr around massive gravitating bodies. It also says that the expansion rate of the uni has something to do with the behavoir of matter in it. So that is about all I can say about this post topic.