Photon question

Originally posted by danscan
We also have to remeber not to long ago many believed that you could not go faster then the speed of sound.

There's a difference between the 'unbreakability' of those two limits. The speed of sound was thought unbreakable because of practical problems. The speed of light is thought unbreakable because of theoretical impossibility. We see this impossibility everyday at supercolliders. You won't be able to get a particle with mass to the speed of light.

Originally posted by danscan
Two photons passing each other would make one photon seem as if it was going 2xSOL in accordance to the photons position.

Not necessarily. According to relativity, light travels at a constant 186,282 miles/sec. Even if you're traveling the same direction as the light, and moving at, say, 99% SOL, then as you observe the light, it's still travelling at 186,282 miles/sec faster than you.. So, then, conversely, if light was passing light in opposite directions, they would still seem, to each other, to be travelling at the constant 186,282, miles/sec.

Now, also according to relativity, photons, as particles, cannot have mass, because as any mass approaches the speed of light, it becomes more and more massive, and requires more and more energy to accelerate, until, just before the speed of light is reached, the object's mass becomes infinite, and the energy required also becomes infinite. So, then, it would be impossible for any object to actually reach the speed of light.

There are, however, scientists that theorize that the speed of light isn't the universal speed limit. There's a good article about that here.

Originally posted by Ouizel
So, then, conversely, if light was passing light in opposite directions, they would still seem, to each other, to be travelling at the constant 186,282, miles/sec.

Almost exactly correct, but you neglected to do the math. The Lorentz transformation for time elapsed for two events in a relative inertial frame is (sorry that it's poorly hand-drawn)



where t is the interval, v is the relative veloctiy of the inertial frame in question, and c is the speed of light, of course. This equation appears to approach infinity as v approaches c (sorry, I haven't figured it out because, let's face it, I'm lazy ), meaning that the observed time between any two events in the relatively moving frame would be infinite. Hence, to a photon, if (let's say) it experiences anything, no time passes at all in the outside universe as it travels, i.e. from the point of view of the photon, it is travelling infinitely fast in terms of "external events," or, to put it another way, if you could somehow ride a photon, you could travel an arbitrarily far distance, and arrive at your destination at the "same" "time" as you left (although of course you could never speed up or slow down, because then general relativity would kick in, and the narrator would be too lazy to figure out the equations)

The equation above is from p. 42 of Einstein's "Relativity: The Special and General Theory: A Clear Explanation that Anyone can Understand," per Wings Books, New York, 1961.

There's a reason, experimentally, that it appears that we can't go faster than the speed of light: The Michaelson-Morley experiment showed that the speed of light appears to be unaffected by direction and velocity of inertial travel, meaning that the speed of light appears to be the same for all reference frames.

That is to say, the speed of light appears to be a natural constant, innate somehow to the character of the Universe. Perhaps there will be some way, someday, to "travel" faster than light, but it won't be travel as we envision it (i.e. an object accelerating, moving inertially for a while, and decelerating), because that appears a priori impossible.

So, then, conversely, if light was passing light in opposite directions, they would still seem, to each other, to be travelling at the constant 186,282, miles/sec.

I think the result is that both appear to be standing still in regards to the other , I may be mistaken and this may be if things were traveling side by side

If you were to be moving at the speed of light , you would seem stationary in respect to yourself and the universe would move toward you .

The Michaelson-Morley experiment showed that the speed of light appears to be unaffected by direction and velocity of inertial travel, meaning that the speed of light appears to be the same for all reference frames .

I think this was to disprove the aether thru interferometry , and actually led to the Lorentz/Fitzgerald contraction and ratio formulas .

Where things get shorter in length , and heavier in mass as they approach the speed of light . The additional mass has been observed in accelerators , and is the reason physical items cannot reach the speed of light . They would be infinitely heavy , and need infinite acceleration to break the barrier . Just aint enough juice to kick them over the hump .

Originally posted by oddtodd

The Michaelson-Morley experiment showed that the speed of light appears to be unaffected by direction and velocity of inertial travel, meaning that the speed of light appears to be the same for all reference frames .

I think this was to disprove the aether thru interferometry , and actually led to the Lorentz/Fitzgerald contraction and ratio formulas .

The experiment was actually done not to disprove the existence of the aether, but to check what the aether's motion was relative to the Earth.

But the original purpose of the experiment is irrelevant. The fact of the matter is that the experiment showed that the speed of light in a vacuum was a natural constant for any inertial frame, regardless of its relative velocity.

The bit about a particle needing too much juice to accelerate is a good explanation, but there are other reasons for this fact than simply the energy needed... you may have already stated this... forgive me, it is late and I am tired.

Ok, AlexKennedy, you are correct. I did not do the math. Since you seem to be conversant on the issue, I'd like to ask you your thoughts on this?

It seems interesting, to me, to find that something can travel faster than what was, until recently, thought to be the universal speed limit.

Originally posted by Ouizel
Since you seem to be conversant on the issue, I'd like to ask you your thoughts on this?

Oh, I'm not conversant at all... merely an interested amateur. As a former Microbiologist and High School Science teacher in training, my education doesn't really cover this (I took a grand total of one course on relativity )

Anyway, the thing about that link is that it's not to a scientific paper, merely to some breathless reporter's description of a scientific paper. It's not really clear what was actually done, and what the results actually were. If cesium vapour can actually make light travel faster than "the speed of light" we have a lot more problems than an inconvenience with theory: the whole ediface of modern physics has been torn down for situations that are fairly normal (i.e. no black holes involved, speeds pretty ordinary, etc., etc.)

Now, I can't and won't say either way what's going on, because I haven't read the original paper, but I will hazard a guess that what we have here is an over-eager reporter with a less-than-firm grasp on the science involved.

There are some things, however, which seem to "move" faster than light, such as the theoretical Tachyon and the "information" about spin in the EPR Paradox, although I prefer the cooler name "Spooky Action at a Distance" Tachyons appear not to exist, however, and what's happening in the EPR Paradox is not actually "motion."

I, too, am an interested amatuer. Now, I have noticed several studies that seem to shake relativity's foundations. I've also not read the published paper on the experiment, but I'm very interested to see if what was reported was true. Here is PhysicsWeb's article on the acceleration and deceleration of light. Again, it's just an article on it, and not the paper, but it's not CNN, so the "reporter effect" is minimized. I'll keep looking for their paper, and if I find it I'll u2u you the link.

Also, the concepts of entanglement and non-locality fascinate me.



[edit on 18-6-2004 by Ouizel]

Originally posted by Ouizel
Here is PhysicsWeb's article on the acceleration and deceleration of light.

Well, quite, but in the leader to the article is the explicit statement that "these findings do not contradict special relativity." Essentially, a brief overview seemed to say to me that what was happening was that light was travelling through a substance faster than one would think possible, given the refractive index of that substance. This was due to some kind of quantum effect. Actually, it seems this experiment doesn't have anything specific to do with relativity, but if they label it as relating to relativity, they'll get more readers

Certainly, they'd get more readers if they imply that general relativity has been proven to be incorrect. It certainly caught my attention. I think that it's indeed possible that general relativity could have problems, but, the theory, because of it's subject matter, is notoriously difficult to either prove, or disprove. And, the nature of theories is that they're considered to be correct, until proven false. I'm not saying that I have empirical data that disproves relativity, but, we're getting closer to proof either way, and I think that it bears watching.

I like your post except the following:

Originally posted by Ouizel
And, the nature of theories is that they're considered to be correct, until proven false.

That's not exactly true. A "theory" is usually considered to be a scientific hypothesis that has been borne out by experimentation. If we follow the Popperian view of science (which most modern scientists do), then a single experiment can disprove any theory.

The Theory of Reliativity has actually been confirmed by several experiments... it's not just a priori thinking.

And you're correct, of course.

Sometimes I wonder where I come up with some of this stuff.

Yes, I know that relativity has been been bourne out by experimentation. Someone else in this thread noted that workers at accelerators deal with the light speed limit, and the mass gain on a daily basis, further emphasizing relativity. However, it seems that we've managed to fling light even faster than light, thereby causing the appearance of it travelling backward in time, as the theoretical tachyon is supposed to do. I did find a link to a PhysicsWeb article about speeding up light. It's here

Let us not forget that C is the speed of light through a vacuum...
As such, this is not a vacuum. The only thing this experiment shows is that there is a medium in which light can travel faster than in a vacuum, if my understanding of the results are correct..

I think one of the reasons my theory on Light resistance is so easily dismissed is based upon preconeived notions. So don't think of it terms that Realitivity is a law. Lets assume something is missing.

Would not light resistance like air resistance build up over a period of acceleration? Would this not make an object seem as though it had a greater mass then it really does? We assume a vacuum is a true vacuum but what if light is acting like air.

The whole thing about an object increasing in mass while accelerating towards the speed of light is based off of the assumption that without any other force acting upon the only other reason for the increase in energy needed to accelerate the object must be that its mass is increasing.

This same effect happens in sports cars. Two identical cars in terms of shape and mass. One with 100hp and one with 200hp. Assuming that the gearing is exactly the same. In a vaccum the 200hp should accelarate twice as fast as the one with 100hp. But it does not. It is a percentage there of. Or more precisly it should be able to go twice as fast but it can not. Why air resistance. For along time in human history air resistance was unknown. So lets assume that those theories are from a day when light resistance was unknown.

I wonder if some one could do a formula inwhich we give a photon an amount of mass. Then do a computer model of an object moving through this light. Would the results work out the same? Would the object need more and more energy(expontially) as it moved faster and faster? As it fought against more and more waves of photons. As its speed increased more and more photons began acting against it. and not for it.

I just see a stricking resemeblence between the acceleration of objects through air as acceleration of objects as they approach the Speed of Light.

Perhaps this whole aether thing was not as far off as first thought. But it is the photons which are the aether.

Well, a couple of things.

First of all, the existence of Aether was disproven about as thoroughly disproven as something can be by the Michaelson-Morley experiment: two beams of light travelling in orthagonal directions, one the same as the direction of motion of the Earth and one at right angles, were found to travel at exactly the same speed. If there was an Aether, then the speed of light would be dependant on the velocity of travel relative to the Aether. But it's obvious that you can't have the same velocity of travel in two orthogonal directions unless the net relative vector is either zero or moving along the 45-degree line.

If the net relative vector is zero, that would mean that the Aether was moving at exactly the same speed and in the same direction as the Earth. This is unlikely, to say the least. This would be geocentrist of the highest order, and distant light effects would of course not be the same in every direction... so, we can discount this theory.

I the Aether is moving on a vector offest by 45 degrees from the motion of the Earth, we run into the same problem -- distant light effects would not look the same in every direction. Plus, again, the movement of the Aether would have to change as the Earth moves.

As for photons "being" the Aether, I don't know what this means. Electro-magnetic waves are self-maintaining, yes, because the magnetic "portion" of the wave acts at right angles to the electric "portion," so in a sense, yes, a photon "waves" itself, but it is unclear to me how changing the terms we use helps us progress in knowledge.

As for the idea of resistance to acceleration being due to a counter-acting pressure, in a sense you're right because inertia acts kind of like such a pressure. But in a more important sense you are incorrect. The infinite energy required to accelerate an object to the speed of light is entirely accounted for by the equivalence of mass and energy. I.e., as an object is accelerated, it seems to the observer to gain mass proportional to the energy "input." This gain in mass means that further acceleration is energetically more difficult. Acceleration, sadly, is not relativistic in the same way that inertial motion is... i.e., if you observe your friend accelerating, he will observe himself accelerating, not you. That's why the twin paradox is possible.