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What is the Speed of Light, Dark Matter?

  1. Jul 28, 2004 #1
    Why does light have a speed? Why does Gravity (Gravitons) have a speed? There is nothing to slow them down... (Or is there!?) E.g. Sounds in water have a speed because of the matter they travel through. Light traveling through different materials will be effected on how fast it can travel through the material. (Sometimes faster). Just like when you drive your car, if there was no resistance (air) you would be able to travel much faster. That is why I believe light has a resistance to a substance ("stuff") we cannot detect. Is that what dark matter is btw?....

    My theory on this is, no vacuum is empty. It is impossible to have "empty" space. We simply cannot detect "what" is there because of the state of existence. Anything there would not be effected by time from what I guess. (Not sure on this yet). This "stuff" that occupies this empty space effects the speed of light and possibly gravity.

    Unless there is some connection between light/gravity & time. Maybe it's a loop where light and gravity travel at instant speeds but we only see the maximum and they are cut at the maximum time would allow, maybe not stopped but put back through time (re-injected into the beginning) where the loop of time begins. Gravity plays a big role in time. Without it we would not exist. Maybe that's how the 2nd time frame gets it's light and gravity except it's all backwards and ours is forward.

    One example I've tried to come up with. Lets say you had 2 stars in "space". (And nothing else, no universe).

    1. How far apart would these 2 stars be?
    (My theory on this is, if there is nothing in space then the distance would equal the most outer part of the star, they would be beside each other).

    There is no way for these 2 stars to be further apart unless there was some kind of "stuff" occupying the space in between them.

    Now lets say for argument sake you say "Sure" they can be further apart and there is nothingness in between them. (let's put them 1000 light years apart)

    How long would it take gravity to travel from one star to another?
    My answer would be instant. If there was "nothingness in space". Maybe then the gravitons occupy the space and effect the speed of light, then distance would be 1000 light years. But I don't think that's possible.

    This stuff that occupies the spaces we cannot detect i believe is in some way related to other states of existence and "time". As our universe is in a state of existence there are possibilities of other universes existing in the same "space" as us but in another state. Similar to how we cannot see certain spectrums of light we cannot see this universe. Hawking says there's 11 different dimensions and 2 different time frames, I'm still trying to figure that one out. Why 11?
  2. jcsd
  3. Jul 29, 2004 #2
    Call me a skeptic.

    You're right about one thing, a complete vacuum is impossible as it's forbidden by quantum mechanics. Fluctuations in energy must occur, thereby violating the definition of a complete vacuum. However, the speed of light has a constant speed not because something resists its motion but because of conditions in the universe that can be traced back to the big bang. Right now, we are travelling through time. The speed at which we travel through time cannot be infinite or else we wouldn't perceive the passage of time as the time of our existence would be reduced to 0. Therefore, we have a finite velocity through time. In the big bang scenario our passage through time has something to do with an sort of winding up much like you wind up a clock, perhaps to do immensely high entropy. Furthermore, even before Einstein and relativity, the fact that only relative motion matters was a part of physics. The conclusion drawn from certain though experiments as well as observations is that every object in the universe is always moving at the same velocity through spacetime: the speed of light, c. This makes sense, if from your perspective you're at rest (again, only relative motion matters) you would conclude from my previous remarks that you're travelling through time at a set velocity and not at all through space. Now if this velocity is dictated by the winding up from the big bang, then we can't simply accelerate through spacetime, the total energy of the universe is set, we can't simply get more. Therefore, if you start moving relative to me through space, I would conclude that since your velocity through spacetime is constant, your velocity through time must decrease. It's this idea, that all objects travel through space and time at a set rate that Einstein's theory of relativity is built on. According to his equations, which are just built on what I have already said, time doesn't pass for something travelling at c through space relative to us, namely light. Therefore it's spatial velocity about 300,000km/s and it's temporal velocity is 0. Therefore, due to the constant speed idea, we would conclude that an object at rest relative to us is travelling at 300,000km/s through time (the units are the same, they are just functions of distance really, which is applicable to both space and time) and 0km/s through space. So, we're back to my statement that all objects travel at c. As you increase your object through space, you must divert some of your velocity through time. Light travelling at about 300,000km/s through space must be travelling at 0m/s from our perspective. If it were to go any faster, it's time would be negative which is impossible. Not that the negative passage of time is is impossible in any hypothetical universe, just that again duehe situation at the big bang (the case of high entropy comes back), it's impossible- at least wer'e pretty sure- for it to happen in our universe. Therefore, whether or not something is opposing it, photons (and gravitons) cannot travel faster than c due to the limitations of the universe, and they cannot travel slower since Maxwell's equations for electromagnetism, carried over into general relativity, do not give a reference for the motion of light, therefore the velocity the equations predict, c, must be relative to everything, so even if we try and chase a beam of light it must still travel at the same speed. The effects that allow for this to happen are explained in special relativity. The final conclusion then, is that light cannot travel faster or slower than c, resistance or not.

    Now I'm not saying dark matter doesn't exist. It could, I don't know. However, if it exists it's not for the reason you said. Dark matter would not cause an otherwise infinite speed to become finite. You see, there is no such thing as resistance against light. Why? Because the speed of light must be constant like I said. Photons still travel at c even in a material. It's just that when it hits an atom, the atom absorbs it a short time later emits a new photon travelling in the same direction as the original, travelling at c. When this photon encounters an atom, the process repeats. So light doesn't really slow down in a medium, it's just that the interval between when it enters and exists is increased do to some time the photons spend in limbo in the atoms. So, a material like dark matter wouldn't resists light's motion, thereby making an infinite speed finite, it would just increase the interval. But if you say the speed of light is infinite, than the interval is infintely small to start with! If the interval is infinite in the small direction, increasing it will still leave with an infinitely small interval so the speed of light would still be infinite. Therefore, the speed of light must have a finite speed as previously shown. Again, I'm not saying dark matter doesn't exist. I think it's unlikely and at the moment it's little more than a curiosity.

    Now for the dimensions. Your referring to string theory, or more generally, M-theory, the supposed "theory of everthing" (which incidentally is built on special relativity among other things, which would be invalidated if the speed of light was actually infinte, so if you insist on continuing your arguement then I'm afraid you can't really reference the hidden dimensions). The extra dimensions are required by the math (in response to your question, there's 11 because allowing strings to vibrate in 10 spatial dimensions-the 11th is time-because it gets rid of nasty negative probabilities), and more over do a neat job of explaining the four fundamental forces. They are entirely possible as demonstrated by Franz Kaluza. I'm not entirely sure what you mean by 2 time dimensions, as far as I know, M-theory requires 10 spatial dimensions and 1 time dimension, for a total of 11. If you would like to learn more about string theory and extra dimensions, I would suggest reading "The Elegant Universe" by Brian Greene. Now, the problem with using them for your argument. Due to the definition of a dimension, resistance to motion in one dimension can only affect motion in Ithatdimension, none of the others. Also, In order for them to escape our detection, they must be "curled-up". It's hard to explain, again I would recommend the book. In their curled up state, they are quite tiny, about the size of the Planck length in fact. It's important to note that in the many dimensions scenario we too are 11-dimensional, it's the those extra dimensions are small that our extent in them goes unnoticed. As we travel through the 10 dimensions of space, our motion through the extra space dimensions is extremely due to their curled up nature. They're like loops and we traverse the dimension and return to our starting point in it in almost no time at all. Therefore, since the dimensions are curled up, as they must be to escape notice, our motion through them is miniscule compared to our motion through familiar 3 dimensional space. So, while dark matter in these curled dimensions up dimensions would retard light's motion through them, the relatively tiny motion through them in the first place would cause this to go unnoticed, meanwhile it would have no effect on motion through the other three spatial dimensions. Now all this was also based on the idea that the speed of light is infinite and something slows it down, an incorrect assumption, however it's just a way of showing that if you're determined to disregard everything I've already said, the dark matter must exist in the familiar three spatial dimensions along with the extra dimensions.

    As a final remark, Einstein first introduced something like dark matter into his general relativity equations, calling it the cosmological constant, because the original equations predicted the universe was expanding and Einstein refused to let go of his notion of a static universe. It was, in his own words, the biggest blunder of his scientific career as several decades later Edwin Hubble showed that the universe is expanding. Einstein sadly returned to his equaitions and erased the cosmological constant, wondering what would have happened if he had trusted his own equations and waited for confirmation of an expanding universe. While their is some genuine scientific interest in dark matter today, variations of it have often been used as a "fudge factor", something added when we can't find a solid explanation for something. The luminiferous aether, the cosmological constant, so many easy ways out. If we're going to reintroduce dark matter, we'd better have one heck of a reason.
    Last edited: Jul 31, 2004
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