Speed of Light question

[Umbran]

Well, they may be testable one day.

*nod*. All I mean to say is that until that time, it's not a reliable source of descriptions of what is happening. Science education is in bad enough shape as it is, we shouldn't go using untested theories as education tools

There's no clear way of extending the theory to cover such situations, which is why most unified theories are particle/field theories (modeling the effects of gravity with gravitons rather than curved space-time).

Yep. And this is also why it is nearly impossible to compute anything useful in them. Differential theories are, mathematically, far more tractable.

 

[Umbran]

Actually, the models I mention here (coupled with relativity) led me to believe that, as one left an area of concentrated mass, the expansion of the universe would add apparent speed to one's motion.

Yes, I've seen models that describe it that way. But it is important to note that the normal gravitational mass of the matter is not sufficient to describe the slowing/bending. If that were the case, the bending of light by lenses would be merely a function of the physical density of the material, which is demonstrably not the case.

I find such theories to be excessive and inelegant, honestly. It's using a bazooka to kill a fly. The change of the speed of light in a medium can be more easily handled using standard QM/solid state physics - the EM fields of the propagating light interact with the EM fields that exist within the material, and that changes the effective speed one can move through the area.

 

[Harmon]

After a bit of research I am still confused

I find it pretty strange, a guy with my level of education, with my level of reading comprehension, asking questions about the Speed of Light (SoL).


http://archive.ncsa.uiuc.edu/Cyberia/NumRel/EinsteinTest.html

“The first prediction put to test was the apparent bending of light as it passes near a massive body. This effect was conclusively observed during the solar eclipse of 1919, when the Sun was silhouetted against the Hyades star cluster, for which the positions were well known.

“Sir Arthur Eddington stationed himself on an island off the western coast of Africa and sent another group of British scientists to Brazil. Their measurements of several of the stars in the cluster showed that the light from these stars was indeed bent as it grazed the Sun, by the exact amount of Einstein's predictions. Einstein became a celebrity overnight when the results were announced.

“The apparent displacement of light results from the warping of space in the vicinity of the massive object through which light travels. The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement o f light as gravitational lensing.

“But the Sun's gravity is relatively weak compared with what's out there in the depths of space. In the dramatic example of gravitational lensing below, the light from a quasar (a young, distant galaxy that emits prodigious amounts of radio energy) 8 billi on light years away is bent round by the gravity of a closer galaxy that's "only" 400 million light years distant from Earth.”


Here is another site- this one has a drawing about light being bent by gravity, am I miss understanding what you guys are saying about light and its bend-ability or am I miss understanding these sites?

http://www.uh.edu/engines/epi1765.htm


On the following site it kinda hits on something I was thinking about the exacts of the SoL. Heavier and lighter gravity areas in the universe would alter the speed of light. Am I reading this right?

http://www.grantchronicles.com/astro09.htm

“In the next parallel universe our laws of gravity and light would not work due faster velocities for the gravity and light particles. So a missing piece of the puzzle is that the concentration of Dark Matter not only determines the speed of light in our part of the universe, but the behavior of returning gravity particles.”


I really appreciate you guys taking the time to check out this thread. Personally I don’t think I understand this subject very well, but the logic of what I think and what I feel about it just seem so… well logical.

If I have not said it in a while- thank you for your time on this, its really killer that you would try to help me out. Thanks.

 

[the Jester]

I find it pretty strange, a guy with my level of education, with my level of reading comprehension, asking questions about the Speed of Light (SoL).

It's actually much more complex- and interesting- than you would think.

Re: light bending via gravity vs. traveling in a straight line- the light hasn't actually bent, the space it is traveling through has. The light continues in a straight line, but space deforms around it, so the straight line leads to a bent-looking course.

 

[Slife]

So, if light can't escape from a black hole, and nothing can go faster than light, how would gravitons escape?

 

[Harmon]

So, if light can't escape from a black hole, and nothing can go faster than light, how would gravitons escape?

One of the things that started me thinking about "faster then light" was that very question. Has to do with what is attractable and what is not- I will however step to the side and ask that someone more savy then I, speak up on the subject.

 

[mojo1701]

So, if light can't escape from a black hole, and nothing can go faster than light, how would gravitons escape?

They don't escape, they are emitted.

 

[Umbran]

I find it pretty strange, a guy with my level of education, with my level of reading comprehension, asking questions about the Speed of Light (SoL).

What's strange? Curiosity comes at all levels of education.

On the following site it kinda hits on something I was thinking about the exacts of the SoL. Heavier and lighter gravity areas in the universe would alter the speed of light. Am I reading this right?

http://www.grantchronicles.com/astro09.htm

Whether you're reading it right or not is irrelevant. That website needs to be taken 'round back of the barn and shot, to put it out of its misery. That content is so poorly organized and presented that it is difficult to tell if they're technically correct.

I really appreciate you guys taking the time to check out this thread. Personally I don’t think I understand this subject very well, but the logic of what I think and what I feel about it just seem so… well logical.

Don't sweat it. Very few people actually understand the subject very well.

The problem is that what most folks refer to as logic doesn't necessarily apply. Everyday logic is based upon assumptions found in the everyday world, but out everyday world is only a small subset of the Universe. What really applies here is mathematical logic, that starts with only a few, well-stated assumptions.

 

[fuindordm]

“Sir Arthur Eddington stationed himself on an island off the western coast of Africa and sent another group of British scientists to Brazil. Their measurements of several of the stars in the cluster showed that the light from these stars was indeed bent as it grazed the Sun, by the exact amount of Einstein's predictions. Einstein became a celebrity overnight when the results were announced.

Note that the bending of light by gravity is also predicted by Newtonian gravitational theory. Einstein's prediction was that the degree of deflection would be exactly double the about predicted by Newton, and he was right! This was a pretty difficult measurement to make at the time, but a lot of his contemporaries thought his theory was unnecessarily complicated.

“The apparent displacement of light results from the warping of space in the vicinity of the massive object through which light travels. The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement o f light as gravitational lensing.

A phenomenon used extensively today to verify the existence of dark matter and map its distribution in the universe. Here's a dramatic example, where the images of very distant galaxies are stretched out into long arcs by the gravity of the galaxy cluster in the foreground.

http://antwrp.gsfc.nasa.gov/apod/ap011007.html

On the following site it kinda hits on something I was thinking about the exacts of the SoL. Heavier and lighter gravity areas in the universe would alter the speed of light. Am I reading this right?

http://www.grantchronicles.com/astro09.htm

This site is written by a crank. Their writing style is very distinctive. Lots of people are interested in the answers to the grand questions, and borrow the trappings of physics and mathematics without bothering to learn enough of the subject to be able to analyze their own ideas with any rigor. Instead, they assert the truth of their statements as self-evident or mystical revelation, and throw in a bit of math to make it seem as if they have done the work.

When I started my first postdoc, I received an unsolicited paper from a crank who had a new theory on the origins of the universe, something about a fundamental wave spawning other waves of ever-increasing complexity. None of it was comprehensible, but the paper attracted my attention because of the last line of his abstract:

"...and in addition, we rationalize pi."

Intrigued, I turned to the appendix. He started off by taking pi=22/7, wrote out the decimal version to something like twenty places, then did some arithmetic to prove that the result was a rational number.

It was good for a laugh, at least.

Ben

 

[fuindordm]

So, if light can't escape from a black hole, and nothing can go faster than light, how would gravitons escape?

That's a very good question, and you're right that it poses a problem for particle theories of gravity.

IIRC, the string theories that deal with this generally have 11 spatial dimensions, and gravitons are special because they can propagate along all of these--the other particles are confined to the three spatial dimensions of our usual experience. This has the advantage of explaining to some degree why gravity is so weak relative to the other fundamental forces--the gravitons are spread thinner than the other particles.

So that way you can end up with black holes that trap all particles except gravitons.

But I really know very little about string theory, and what I know is gleaned from popular science books like The Elegant Universe and others. I could well be wrong.

Ben