Particles faster than light, for real...

Factual Questions
1

What would happen to a particle that was travelling close to the speed of light in an area of space-time which had a drop in vacuum energy density? Because this in turn decreases the speed of light, so would the particle continue travelling faster than the new (much slower) speed of light? or would time speed up and cause the particles velocity to decrease relative to the speed of light.

If it’s the latter answer then this raises some questions about different places in the universe having different speeds of time depending on their vacuum energy density etc.

2

I don’t know the subject, but I’ve heard that it’s something like:

Light (photons) ALWAYS travel at c. The local conditions change the apparent speed to the observer, but it never actually changes the speed.

But I have no idea what I’m talking about.

3

Nothing travels faster than light in a vaccum. However, there are ocassions when light can be slowed and other particles can travel faster than light.

Someone will be along to elaborate. …I hope.

4

Time changes, C is a constant by definition. I’m unclear what you are asking, but gather enough to assume this is the effect you are trying to investigate. Yue Han did a fine job explaining the effect in a recent GQ.

5

There is the theoretical open door for a particle known as the tachyon, which never slows down below the speed of light, but that’s about all I know about it. Perhaps one of our resident experts can elaborate.

6

Imaginary, i think this discussion could be more profitable if you shared with us your views on vacuum energy density.

7

The Lambda force is derived from the pressure of space-time, this pressure is caused by the energy within it, hence Vacuum Energy. When you severely reduce the density of matter in space then it causes a drop in the speed of light.

I am not saying that it accelerates past the speed of light, nor am I saying that it was travelling at the speed of light. I am saying if the particle were travelling through a bit of space in which the density of matter fell considerablily, when light becomes slower than the particle. What happens to the particle or time?

8

I’m not exactly sure what you are saying, but there are a couple of points here. First, light always locally travels at c, and second spacetime itself can expand faster than c (inflation.)

Light passing through a gravitational well (this can be cause by pressure) will take longer to cover a given distance, but nonetheless it’s still always traveling locally at c

9

No Ring light doesn’t always travel at a constant ‘c’ under the new theories involving Einstien’s Cosmological Constant and the new idea of Vacuum Energy. This has nothing to do with gravity wells. This has to do when a fundamental property such as the speed of light decreasing in the area of a particle moving though it at close to the speed of light, this causes the particle to be travelling at faster than the speed of light. What happens to the particle or time??

10

I hope you realize the above is gibberish.

A particle of light moving through light?? What are you talking about? Cerenkov radiation?

Are you talking about the fine structure constant changing over eons?

Are you talking about the expansion rate of the universe increasing via the cosmological constant?

Do you have any idea what you are talking about? I certainly don’t.

A photon always travels locally at c.

11

I don’t know what either of you are talking about… I just came to see the fight.

12

Ring, When I say particle I don’t mean a photon. I mean an electron for example. The electron is quite happily going along through space when the matter density decreases in that point (probabily because the universe expanded and dispersed into almost void) and the speed of light drops below the speed the electron was doing. So now the electron is moving faster than the speed of light. What happens to the electron or time in that area?

13

Imaginary, the action of the cosmological constant is to stretch space-time. There’s no true “cosmological force;” what happens is that if you have two non-interacting particles travelling along, initially moving in the same direction, they’ll gradually get farther apart as the space between them stretches out. This is not a new force.

Assuming we’re thinking about the same thing, what would happen is that as the electron moves into an area of low vacuum energy density, it starts to slow down, and it will always be moving at a speed less than c. Light will always be moving at c, it’s just that the distance it has to travel increases as it moves, and it looks like the light has slowed down, even though it hasn’t.

14

c is the speed of light in a vacuum. Period. When light (and therefore photons) travels through various media, its speed changes. Some things move faster in say, water, than light does. See this column of Cecil’s: http://www.straightdope.com/classics/a990430a.html .

15

Maybe none of you have caught a glimps of the new theory. All of you are clinging to the theory that the speed of light in a vacuum is constant. I’ll give you a couple of sites:

http://www.astro.ucla.edu/~wright/cosmo_constant.html

http://www.channel4.com/equinox/ein_transcript.html

Then we’ll let someone like Chronos answer the question.

16

I have not heard anything about the vacuum energy density having any effect on the speed of light. On perusing the two links in Imaginary’s post, there, the first one seems to be a fairly accurate summary of what is known about the cosmological constant (presumed to be a sort of vacuum energy), but on a quick perusal, I couldn’t find anything about the speed of light changing in it. The second link is from a non-scientific news source, and doesn’t say anything about the qualifications of the parties involved, or the details of the theory, so I’m rather skeptical of it. It also seems to have a strong current of “Einstein was WRONG!”, which is usually the mark of a crackpot. Yes, we’re all clinging to the idea that “The speed of light in a vacuum is constant”, because all observations anyone has ever made are 100% consistent with that idea.

Now, setting that aside for a moment, there are situations where the bulk speed of light can be changed. In vacuum, light travels at exactly c. In any medium, it’ll travel slower on average, at about .75 c in water, for instance. Note that it’s c that’s the limit, not whatever the “speed of light” may happen to be in a material. It’s quite possible, for instance, for an electron to travel through water at, say, .8 c, and thus be faster than the speed of light in water. When this happens, you get something called Cherenkov radiation, which is similar to a sonic boom or the wake behind a boat. Presumably, if vacuum energy is capable of affecting the speed of light (doubtful, as that would imply that the vacuum energy has a preferred rest frame), then it would presumably cause a similar effect.

17

O’well I like their theory better so I’ll email them the question.

18

I recently read an article about this issue. It concerned the “glow of radioactive particles in water” or something like that. Anyway, the point of the article was a) light slows down in water and b)the glow comes from particles moving close to the speed of light hitting the water and slowing down and emitting photons.

Eric

19

Imaginary, you are causeing us all to make huge assumptions about what you are talking about here. vacuum energy density is a very new line of thinking, and no one knows if it is even correct yet. the only way anyone can answer this is in terms of what you believe about the theory, which is why i asked earlier that you explain that. but instead, you only defined what this energy density is, which helps nothing.

but since you haven’t specified your beliefs, i’ll assume you believe that there is a constant (with slight fluctuations) and positive amount of energy density in the vacuum of space, and you’re thinking about the hypothetical idea of there being an area where the energy has been dampened for some reason. i’m fairly certain that we can all agree that c is a constant and time is not (which, may i add, still holds true for this new theory. the speed of light does not change, it is only our idea of the vacuum of space that has changed). now traveling at the speed of light causes time to stop, correct? so if a lesser amount of energy in that particular area caused light to appear to be slowing down, it would mean that time is being stretched. but for another particle to surpass the speed of the light moving through this area, you would have to assume that the loss of energy density is not affecting the speed of that particle, and we don’t have enough knowledge about what vacuum energy density is, if it exists, or what it is contained in to be able to assume that.

so, in short, your question cannot be answered in terms of science or fact, only opinion. specify your opinion, and maybe we can help you.

20

Given the definite article in the conclusion of Wright’s discussion,

I’d have to say that any change in the VED would be experienced universe-wide. In other words, even if the VED is greater than zero, there simply won’t be the kind of local “shortages” of VED that the OP is asking about. The VED has some value, either zero or not, for the entire universe.

I’m no expert on this, but it seems to me that if VED could change at a local level, then, given the tremendous amount of space we can see, we would be able to observe the universe expanding at different rates in different places. After all, it would be probable that the overall, or average, VED between galaxies X and Y could be different from the average VED between galaxies X and Z, or galaxies A and B, for that matter. A locally-varying VED would make quite the mess of things.

The final paragraph of the second cite speaks volumes. Joao Magueijo believes he both is and is not contradicting relativity, a contradiction in itself. He’s trying to find a test which will tell him whether the theory is right or wrong, meaning that it’s all speculation at this point.

On the other hand, nothing I read in that page (and I’ll admit to skimming) which suggests that Magueijo believes that the VED can change locally, either. The impression I got was that he believes the VED has changed exactly once for the observable universe we live in now.

His theory appears to say that after the speed of light slowed down (why it changed doesn’t seem to be in evidence), the VED had to change to compensate. And if the VED made that particular change, there’d be a lot of energy generated. Where would that energy go? Into mass and radiation. Thus, at one point in time, c dropped suddenly, the VED compensated, and the Big Bang happened as a result.

This would appear, to me at least, to be completely unverifiable, and therefore a question science cannot even begin to answer.