Relativity, black holes and gravitons
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07-01-2014, 01:07 AM (This post was last modified: 07-01-2014 03:54 AM by fredlc.)
Relativity, black holes and gravitons
Hello, guys.

Here's a question that that I've been throwing around since I begun reading about modern physics, such as the theory of elementary particles, string theory, etc...

I didn't know before reading new books recently that the forces of the universe are conveyed as particles, called messenger particles. A weird idea, but not weirder than extra dimensions, and other wild concepts of modern theories.

But I'm having trouble converging that notion with the central idea of general relativity that gravity is caused by warps in the fabric of space; I mean, it's simple to conceive the idea that such warps can cause "slides" that matter will follow in spacetime, but how the heck a shape can be communicated as particles is something none of the books I read confronted.

But at this point, I was taking this difficulty as a linguistic problem, as the inadequacy of rhetoric to explain what the warping of reality truly is. However, considering this difficulty, something came up that challenged all the understanding I was building, and again, that I didn't found confronted in the books I've read or the lectures I've watched on youtube:

Here's the problem - the core idea of special relativity, what lead Einstein to his amazing achievements, was the concept that no matter, no energy, no information or influence, can travel faster than the speed of light - therefore, the speed of gravity also could not exceed this limit.

If that is true, than how come the gravitons - the messenger particles for gravity - can transmit the monstrous force of a black hole? I mean, black holes are black because light-speed is not good enough as escape velocity; so, gravitons also shouldn't be able to reach escape velocity. All gravitons should be immediately crushed at the singularity.

It's easy to understand a black hole if you understand the concept of gravity as a deformation of the spacetime, but as an effect of constant exchanging of messenger particles, it seems to me that gravity would neutralize itself, making it impossible for the particles to escape it's own shackles.

It would be relatively easy to accommodate this if I thought that the particle escapes "only once" to cause the warping of space time, than later the already curved space would not need the trapped particles to exert influence. But this would create a gravitational influence that, once settled, is instantaneous across the space and not bound by the light-speed limit, flying in the face of the whole theory.

I do understand that the unified field theory is THE problem of modern physics, but AFAIK, both String Theory and Quantum Loop Gravity theory have laid unproven, but mathematically viable means to describe gravity in quanta terms... So there must be SOME description of this phenomenae that is consistent, even if unproven.

So, is there anyone here who is physics-prone who can enlighten the topic without getting overly mathematical?

Regards Smile.
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07-01-2014, 03:58 PM
RE: Relativity, black holes and gravitons
Hmmm... Guess this will go unanswered again.

Regards Smile.
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07-01-2014, 04:12 PM
RE: Relativity, black holes and gravitons
We have some scientists here who can speak to this and hopefully they will.

" Generally speaking, the errors in religion are dangerous; those in philosophy only ridiculous."
David Hume
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07-01-2014, 04:28 PM
RE: Relativity, black holes and gravitons
I think if I'm not mistaken. Gravity is one of the least understood forces by physics. If I'm not mistaken, gravitons are hypothetical and we're not sure if they even exist.

My 2 cents

“The reason people use a crucifix against vampires is because vampires are allergic to bullshit.” ― Richard Pryor
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07-01-2014, 04:34 PM
RE: Relativity, black holes and gravitons
Also, nothing travels faster than the speed of light in a vacuum (299 792 458 m / s), but gravity is known to bend light. It's possible that the theoretical light trying to escape the black hole is not traveling quite at 299 792 458 m/s which might allow for that phenomenon to happen.

“The reason people use a crucifix against vampires is because vampires are allergic to bullshit.” ― Richard Pryor
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07-01-2014, 08:17 PM (This post was last modified: 07-01-2014 08:40 PM by Physb.)
RE: Relativity, black holes and gravitons
We need to take into consideration that gravity is an attractive force. As one of our bothers mentioned: Gravitons are hypothetical particle that was/is used to explain certain phenomenon in the standard model.

M-theory suggest that gravity is a weak force do X number of dimensions. It's a spread out force.

Black holes has been a difficult concept to grast since first proposed(Frozen stars). To understand fully why a black hole can trap light but the light still always travels at constant velocity requires an understanding of the General Theory of Relativity, but the essential point is that the black hole curves spacetime back on itself, so that all paths in the interior of the black hole lead back to the singularity at the center, no matter which direction you go (an analogy in two dimensions is that no matter which direction you go on the surface of the Earth in a "straight line" (what mathematicians call a "geodesic" or a "great circle"), you never escape the Earth but instead return to the same point. Imagine extending that analogy to the 4 dimensions of spacetime and you have a rough explanation for why light travels at light speed, but cannot escape the interior of a black hole.

Also, see this may help.
http://arxiv.org/abs/hep-ph/0502005
http://curious.astro.cornell.edu/questio...number=264
http://www.physicsforums.com/showthread.php?t=65583

I was going to make analogies, but I'm a curious fellow. Its better to make them on your own with the provided information!

There are still many unsolved mysteries. This is one of the reasons why I have a profound passion for nature.
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08-01-2014, 05:21 AM (This post was last modified: 08-01-2014 05:26 AM by Stevil.)
RE: Relativity, black holes and gravitons
(07-01-2014 04:34 PM)djkamilo Wrote:  Also, nothing travels faster than the speed of light in a vacuum (299 792 458 m / s), but gravity is known to bend light. It's possible that the theoretical light trying to escape the black hole is not traveling quite at 299 792 458 m/s which might allow for that phenomenon to happen.
Gravity is not a force and light is not bent by gravity. Light must always travel exactly at the speed of light. It is impossible in the vacuum of space for light to travel slower than that.

The answer is perception.
Knowing that distance, time and mass are relative and that the velocity of light is the only given constant.

"light" is merely a massless particle. All massless particles travel at the speed of light through the vacuum of space from all perspectives. No massive particle can ever achieve the speed of light.

The straightest path anything can travel at is what light does. There is no straighter path. Thus from the perspective of light, light's path is straight, not bent.
It you think gravity bends the path of light then you are mistaken.

But even massive objects always travel in a straight line through the vacuum of space. Take the moon for instance. It is traveling in a straight line. I know it appears to travel in an elliptical orbit around the Earth but that is because we are mistakenly viewing space as if it has a 3 dimensional Euclidean geometry. Given the revelation of General Relativity, 3 dimensional Euclidean space is absurd.
But a beam of light, initially traveling at the same trajectory, same position as the moon, does not find itself caught in a never ending orbit around the Earth. This is because the path through space is dependent on the time taken to travel through space a.k.a the speed with which an object moves. Light is much faster than the moon, thus its velocity is quicker than its acceleration towards the Earth and thus it is able to escape Earth's orbit even though it experiences the same Space and the same Gravity that the moon is subject to.

What this means is that the shape of Space is non Euclidean (a.k.a. curved) and dependent on the time taken to travel through it. Thus we are to view the shape of Space from the perspective of SpaceTime rather than Space alone.

Since light is the fastest speed possible then we must say that the straightest Space gets is the path with which we observe light to travel through it. When compared to a hypothetical Euclidean geometry x,y,z axis then it is observed that light diverges from the Euclidean "straight" path. This can only mean that Euclidian geometry is unrealistic. Space cannot be seperated from SpaceTime and SpaceTime is curved. Curved by the presence of mass.

With regards to a black hole, SpaceTime is so bent that there is no possible path out of the event horizon even for massless particles.

Anyway, just my thoughts on the matter. It does do my head in trying to think about it.
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