well there is evidence that the speed of light (i guess in a vacuum) has changed slightly over the course of the existence of the universe. i can't remember the term but something like the "fine structure constant" or something structure something or whatever has changed slightly and that has something to do with many things, including the speed of light. but i've never heard about light being different speeds in the different parts of our universe.
Smartass. How else to explain the growing rate of expansion? That's all I'm really curious about. Relativity should dictate that it would be slowing, not accelerating. (you've got to admit that over great distances, a nonconstant speed of light would explain that phenomenon)
OK, think of it this way: do photons have mass? They must have an infitesimal amount of mass. No, we cannot weigh it, but it must be there. It exists, and it is not a vacuum. Anything that has mass is going to interact with the space-time continuum. Photons have for some reason always been left out of this interaction. But if they have even a tiny amount of mass, will they not impact it? Anything with any mass must impact it, if even on a miniscule scale. Consider that you pushed a marble along a ruler's edge. Say it got from 0 to 12 inches in one second.. Now, consider that you just ate a taco and pushed that marble along the ruler's edge. It gets there 1/1000th of a billionth seconds faster. Do you notice the difference? Of course not. But stretch that ruler out 1 to the sixth power length, and you will certainly notice the difference. If the speed of light is constant, then the marble will get there at the same time every time. If it is variable it will not. I'm not even saying that it's variable. I think the speed of light degrades over long distances because photons must have mass somewhere... Just like how a marble would slow down over time (because of gravity, density, and the earth's mass), a photon must slow down (because of gravity, density, and the universe's mass). It slows because another force is acting upon it. Gravity. (Which no one really understands)
photons have zero mass according to this article, typing a lot for hyperlinks also found to be fun And here is how photons interact with gravity apparently. The energy-momentum 4-vector of a particle, rather than its mass, is the gravitational analogue of electric charge. The corresponding analogue of electric current is the energy-momentum stress tensor which appears in the gravitational field equations of general relativity. A massless particle can have energy E and momentum p because mass is related to these by the equation m2 = E2/c4 - p2/c2 which is zero for a photon because E = pc for massless radiation. The energy and momentum of light also generates curvature of space-time so according to theory it can attract objects gravitationally. This effect is far too weak to have been measured. The gravitational effect of photons does not have any cosmological effects either (except perhaps in the first instant after the big bang). There are far too few with too little energy to make up any noticeable proportion of dark matter And treeman are you saying that the expansion is increasing or just exploring the possibilities if it happens to be.
F4P: I don't think there's any such thing as "massless radiation". Everything I know about radiation suggests that it is intricately connected to gravity equations. Black holes could not exist without radiation having mass (in theory). Everything that is not a part of the vacuum must have some mass. Energy must have mass. In immeasurable (at present) amounts, but it still must have mass. Do not equate "immeasurable" with "nonexistent". Not the same thing, especially where quantum physics are concerned. Photon mass is still the only variable that I can think of that explains the gap of light transverse as it relates to universal expansion acceleration. Personally, I think it's impossible to explain gravity without admitting that energy (photons) have mass. And vice versa (it's impossible to explain energy without including gravity in the explanation)... Again, no one really nows what "gravity" is. No one really knows what "energy" is, for that matter... I think they both need to be explained.
Here's a link to a picture from Hubble giving evidence to the expansion of the universe. It also discusses the most widely suggested reason. Here's a question that helps me to put the concept of gravity and 'gravitons' into perspective: Imagine a black hole. Black holes have something called an event horizon, a point at which nothing with mass is able to escape. No energies, either. Well, if gravity is a particle with mass, or gravity is a energy wave, how do these particles or waves escape the inescapeable event horizon? Also, I recently saw some research that suggested that the supposed constant nature of the speed of light in a vaccum may not be as constant as originaly thought. Here's one reference to the changing speed of light. and here's another. Back to the original question, it is truly mindblowing and impossible to really grasp the number of stars that we can see in the universe. The estimated number is 1,000,000,000,000,000,000,000 stars. I don't know about you, but that number is so vast I just can't believe that, despite the fact that it seems that life may be difficult to start, it has to have happened more than once given that many chances.
The same way that velocity that so many classical mechanics equations seem to fail at relativistic speeds, the same is true of calculating the energy of a photon at relativistic speeds. At classical speeds, the momentum of an object is usually defined by : p (momentum) = m (mass) * v (velocity) So how the heck can something with no mass have energy? Was Einstein puffin' the relativistic bong?! The answer is simple : at relativistic speeds, energy can be defined by momentum. But at relativistic speeds, momentum is defined as : p = h (Planck's constant) * f (frequency)/c (speed of light in a vacuum). but... E = hf, so : p = E/c. therefore... E (energy) = p (momentum) / c (speed of light in a vacuum). So yes, you can have a massless particle that has momentum but no mass, which means you can have energy without mass. Also, the question of why black holes can affect something supposedly massless like a photon is best answered by thinking in 4-dimensional space. Photons are affected by black holes because they are affected by the curvature of space caused by the black hole's presence (I think... it's been a while, so somebody correct me). This curvature of space and the photon's behavior really have nothing to do with whether or not it has a mass or not.
The most interesting theory I've heard about gravity involves n-brains, and the supposed 13 or so dimensions, most of which have curved back in on themselves to a size smaller than the Planck-length. The concept was that one of these dimensions was perhaps pulled away from the others, and it's weak perturbations in the distance of it's pulling away cause gravity by affecting the strings in the 3 more common dimensions. Of course, I couldn't even begin to understand the math. Visualizing objects in four dimensions is IMO one of the easiest examples of how the human brain simply cannot conceive some things on a very real level. People's brains are developed at an early age for hunting prey in 3-d. (N+3)-d is simply useless evolutionarily for a hunter's very specialized and complex visual cortex. Maybe if you could start someone thinking that way when they were like, 1 or 2, perhaps... I think a lot of Physicists, going back to some of the people who pioneered the concepts, consider photons, gravitons, gluons, and the other so-called "virtual particles", consider them to simply be convenient explanations for explaining the way these things work, without actually representing a true picture of how they interact in reality.
My theory is that the universe is replicating, not expanding, and thus is what you would call life. Next question.
