Exploring the Limits of Light: Theories on Gravity and Black Holes

In summary: There's nothing weird about the use of the speed of light in equations. It's a universal constant, the same for all observers. We use it because it's there, not because we're fixated on it.In summary, the conversation discusses Albert Einstein's theories on motion, gravity, and space-time, with a focus on the speed of light. The question is raised about how black holes can exist in our dimension if nothing can travel faster than the speed of light. The conversation also explores the concept of gravitons and their potential to travel faster than light. The use of light in equations and its connection to gravity is also discussed. Overall, the conversation highlights the complexity and ongoing exploration of
  • #1
MajorComplex
19
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One of my greatest idols is Albert Einstein. He was obsessed by light and provided so much input into his theories on motion, gravity and even space time it's self because of it. When I think about it all though I find a lot of argument. One thing I think about a lot is how he said nothing can travel faster than the speed of light.

If nothing can travel faster than the speed of light, then how do black holes "exist" in our dimension? There's theories on the graviton right? Then shouldn't the graviton be traveling faster than the speed of light if it's strong enough to make light break it's own barrier? I don't understand how light could be the last barrier when things theoretically accell that speed.

I guess what I'm asking is, do you believe light is the final barrier or do you believe gravity could have a barrier of it's own?
 
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  • #2
I suggest you try asking this question in relativity forum, You might get some good answers there but here is what I know;

To answer this question you'll have to follow mathmatical equations provided by Einstein, Let's not forget that when an object is traveling with certain velocity it's mass increases where the increased mass is:

m = m0 / (1 - (v/c)^2)^0.5

where m = increased mass (somtimes called relativistic mass) m0 = mass at rest v=velocity of the object with mass m0 c=speed of light.

As you increase the velocity v for a fixed mass m0 you'll see that the value of m increases and as v aproches c, m aproches infinity.
And using the Energy mass equvalence its obvious that you'll need an infinite energy to keep an object of mass m0 traveling with the speed of light, hence its imposible.

SO HOW DOES PHOTONS TRAVEL WITH THE SPEED c?

Because photons have m0 = 0 as a result even if their velocity approach c their relativistic mass is zero hence no energy required.

Results: The only objects which can travel with the speed of light are the objects with zero mass when at rest.

hope its clear enough.
 
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  • #3
What reason do you have for saying that Einstein was "obsessed" with light? Einstein was working on problems related to electro-magnetism: of course he talked about light (actually as a term for general electromagnetic waves).

If nothing can travel faster than the speed of light, then how do black holes "exist" in our dimension?
What does the one have to do with the other?

There's theories on the graviton right? Then shouldn't the graviton be traveling faster than the speed of light if it's strong enough to make light break it's own barrier?
I'm sorry, why SHOULD the graviton be different from other "-tons"? Is there any reason to think that a graviton can " make light break it's own barrier"? Perhaps you are thinking that a photon increases its speed as it goes into a black hole in the same way a material object increases its speed as it falls into a gravitational "well". That's not true. A photon increases its energy in a situation like that by increasing wavelength, not its speed.

I don't understand how light could be the last barrier when things theoretically accell that speed.
What things are you referring to?

Actually, relativity does not say there can be no "things" going faster than light. It says that anything with positive mass must move, relative to any observer, slower than the speed of light. It is theoretically possible to have objects, called "tachyons", that move faster than the speed of light and can never move slower than the speed of light. Tachyons have never been observed (except on "StarTrek"!) and there is some reason to believe that if tachyons exist, it would be impossible for us "tardyon" folks to observe them (in which case, in what sense do they exist?).
 
  • #4
HallsofIvy said:
I'm sorry, why SHOULD the graviton be different from other "-tons"? Is there any reason to think that a graviton can " make light break it's own barrier"? Perhaps you are thinking that a photon increases its speed as it goes into a black hole in the same way a material object increases its speed as it falls into a gravitational "well". That's not true. A photon increases its energy in a situation like that by increasing wavelength, not its speed.


.

Photons are probably very different from gravitons. However, no one knows because no one has ever produced or directly observed one. One would only be guessing if one were to speculalte why gravitons could or could not exceed the speed of light. Gravitons could be composed of components that we are not even aware of or that have no mass 'at speed' or at rest. We just do not know.
 
  • #5
What does one have to do with the other? Well Einstein theorized that if you where to catch up to and go beyond light, you would be invisible. This would explain why light can't escape a black hole, other wise the light would be visible. If a black hole has the power to manipulate light, then shouldn't there be barriers beyond light? It's just weird how so many equations (i.e E=MC2) use the constant of light...
 
  • #6
MajorComplex said:
What does one have to do with the other? Well Einstein theorized that if you where to catch up to and go beyond light, you would be invisible.
He did? When?
This would explain why light can't escape a black hole, other wise the light would be visible.
No. If an object is moving faster than the speed of sound, can you still hear it?
If a black hole has the power to manipulate light, then shouldn't there be barriers beyond light?
No.

I'm not sure why this is in philosophy, but the basic problem here is that you are speculating about things that you have no actual knowledge of. The basic concepts here aren't that difficult to understand, and you'd be able to avoid a lot of spinning your wheels if you would try to learn them instead of making it up as you go along.
 
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  • #7
Why don't you stop posting like a wise ass and tell me then? That is the whole point in the thread... If I knew these things I wouldn't be here...

As for the invisible thing... Einstein was once trying to think what it would look like if you caught up to light. He imagined he was traveling along side the speed of light and had a mirror infront of him. What he came up with was that since you're traveling at the speed of light, the light never leaves your eyes to bounce off the mirror, thus making you appear invisible.
 
  • #8
MajorComplex said:
Why don't you stop posting like a wise ass and tell me then? That is the whole point in the thread... If I knew these things I wouldn't be here...
I'm trying to make you think. You're philosophizing about things that aren't philosophy and speculating about things that are already known. That isn't a good way to approach learning.

Consider an airplane traveling twice the speed of sound (the speed of sound is 1100 feet per second). It is 1100 feet from you. It emits a very loud noise. Will you hear the noise and if so, when?
As for the invisible thing... Einstein was once trying to think what it would look like if you caught up to light. He imagined he was traveling along side the speed of light and had a mirror infront of him. What he came up with was that since you're traveling at the speed of light, the light never leaves your eyes to bounce off the mirror, thus making you appear invisible.
If light doesn't hit your eyes, you won't see anything, but that does not mean that light can't still bounce off you (or be created by you) to be seen by someone else. You're not invisible. Also, the only light you won't see is light traveling directly behind you (or in a cone shape behind you if you are going much faster than light). Someone can still stand next to you and shine a flashlight on you when you go by, no matter what speed you are going.
 
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  • #9
I just like to add, he's trying to help and he's not posting like a wise ass. And he's a mentor, don't talk sh*t to him lol.
 
  • #10
Gib Z said:
I just like to add, he's trying to help and he's not posting like a wise ass. And he's a mentor, don't talk sh*t to him lol.
And moderator status means what exactly?

Yeah thanks, I kind of get the idea now. It really just shows how little information casual science references actually give you...

So, do all "tons" (neutons, protons, electrons) have zero mass? Or only some of them like photons? It kind of makes sense now how zero mass objects can travel so fast because they have no value to increase at progressive speeds. I guess thinking about it logically is the hard part...
 
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  • #11
MajorComplex said:
And moderator status means what exactly?
He didn't say moderator, he said mentor. On physicsforums, mentors are appointed to help others grasp, understand and apply concepts that they need help with.

Yeah thanks, I kind of get the idea now. It really just shows how little information casual science references actually give you...
If by casual science, you mean your casual approach to understanding it, yes. Physics is an empirical science using the rigorous language of mathematics as a method of quantifying and describing material reality. To deeply understand and grasp Einstein's General Theory of Relativity, it takes years of mathematics and physics. Russ is trying to help you understand the conceptual physics using visually descriptive thought simulations and I don't think he is trying to sound condescending if that's how you percieve his dialogue.

So, do all "tons" (neutons, protons, electrons) have zero mass? Or only some of them like photons? It kind of makes sense now how zero mass objects can travel so fast because they have no value to increase at progressive speeds. I guess thinking about it logically is the hard part...

In modern quantum mechanics, particles of matter called fermions possesses mass, however, particles of force called bosons do not possesses mass. Read up on Quantum Electrodynamics and Qunatum Chromodynamics for more information.
 
  • #12
Its actually just photons when concerned with light, The tons (as you define) do have a mass.
 
  • #13
Is there any specific reason that the gravitational force from the black hole is so strong that it would take years for light to even reach a nanometer? The light would most likely be bent towards the surface of the black hole, even though the point in the middle is not a singularity. Just wild guessing. The objects that passes through the black hole even horizon...is there any specific reason we know they exceed the speed of light?
 
  • #14
HallsofIvy said:
Actually, relativity does not say there can be no "things" going faster than light. It says that anything with positive mass must move, relative to any observer, slower than the speed of light.
I'm not completely sure about this. What I think SR says is that given the postulate of <<light's speed independent on the inertial frame reference>>, then we can show that light's speed is the maximum possible speed. So, if, somwhere, light's speed is not independent on the inertial frame reference, then it's not the maximum possible speed. Example: inside glass.

You could say: "but we are talking about light's speed in the void". Ok, but I don't think it's really so important. What if we lived in a universe made of glass?
Not realistic, of course, but, what would happen in a region of void if, hypotetically, the constants mu_0 and epsilon_0 where different?
Would it be possible? Maybe, if the density of virtual particles where different. I don't see the void, in principle, very much different from any other medium with specific electromagnetical properties, from this point of view.
 
  • #15
So why are black holes black? Why can't we actually see the matter that's inside of them? Or photons for that matter...
 
  • #16
Jarle said:
Is there any specific reason that the gravitational force from the black hole is so strong that it would take years for light to even reach a nanometer? The light would most likely be bent towards the surface of the black hole, even though the point in the middle is not a singularity. Just wild guessing. The objects that passes through the black hole even horizon...is there any specific reason we know they exceed the speed of light?
Reason? You can calculate it. I'm not sure what you are asking...
 
  • #17
lightarrow said:
what would happen in a region of void if, hypotetically, the constants mu_0 and epsilon_0 where different?
Would it be possible? Maybe, if the density of virtual particles where different. I don't see the void, in principle, very much different from any other medium with specific electromagnetical properties, from this point of view.
It is a void. How can there be different voids? Isn't that like saying there is more than one value of "0"?
 
  • #18
MajorComplex said:
So why are black holes black? Why can't we actually see the matter that's inside of them? Or photons for that matter...
The escape velocity of a black hole is greater than the speed of light, therefore light does not escape.
 
  • #19
russ_watters said:
The escape velocity of a black hole is greater than the speed of light, therefore light does not escape.
Then why can't the light be seen? Wouldn't that suggest it would be invisible to the eye? To an outside observer? This is what confuses me...
 
  • #20
I'm not following. The only light we see is light that reaches our eyes. If light does not escape a black hole, it never reaches our eyes and thus cannot be seen.
 
  • #21
lightarrow said:
I'm not completely sure about this. What I think SR says is that given the postulate of <<light's speed independent on the inertial frame reference>>, then we can show that light's speed is the maximum possible speed. So, if, somwhere, light's speed is not independent on the inertial frame reference, then it's not the maximum possible speed. Example: inside glass.

This is false. Relativity says nothing at all about c being the "maximum possible speed." Relativity simply says that c is the only velocity that every observer will agree upon, regardless of that observer's own motion.

In fact, people have long theorized about particles called tachyons, which would be confined to always travel at velocities greater than c. Such particles, if they exist, would require an infinite amount of energy to slow down to c, in the same way that normal particles would require an infinite amount of energy to speed up to c.

- Warren
 
  • #22
MajorComplex said:
Then why can't the light be seen? Wouldn't that suggest it would be invisible to the eye? To an outside observer? This is what confuses me...

You can't "see" black holes, since they do not emit light*. You don't observe their light directly. Instead, you observe their gravitational effect on nearby objects, which do emit light, and can be seen with telescopes.

*there is a small, but irrelevant caveat called Hawking radiation.

- Warren
 
  • #23
It would be hitting objects near the eye though wouldn't it?
 
  • #24
MajorComplex said:
It would be hitting objects near the eye though wouldn't it?

What are you talking about? Please explain your questions more thoroughly so that we can attempt to answer them.

- Warren
 
  • #25
Light wouldn't be hitting any objects outside the event horizon, since light can't even get out of the black hole.

Imagine being in a completely dark room. Inside that room, on a table, is a strong box. Nothing can get out of that box. Not even light.

Someone turns on a light inside that box. What do you see? Nothing... the light can't touch anything outside the box because it can't get out.

Now, the box is actually spherical. And it isn't really a tangible box--just an area of space that nothing can get out of, once it's in there. And the reason things can't get out of it is that space is actually curved too steeply for that. It isn't that you slam your head into the wall of the box. It's just that no matter how hard you're running, you never find yourself closer to the wall!
 
  • #26
Ahh, so the light never actually leaves the black hole to hit my eyes? Makes perfect sense, thanks a lot, especially for your 3rd post...

So I guess to my other question, is there another "barrier" beyond light? I mean, the conversion of mass to energy is squared by the speed of light, but why that specific number? What's so significant about the speed of light? Is the speed of sound significant?
 
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  • #27
MajorComplex said:
If nothing can travel faster than the speed of light, then how do black holes "exist" in our dimension? There's theories on the graviton right? Then shouldn't the graviton be traveling faster than the speed of light if it's strong enough to make light break it's own barrier? I don't understand how light could be the last barrier when things theoretically accell that speed.

I guess what I'm asking is, do you believe light is the final barrier or do you believe gravity could have a barrier of it's own?

An electrically charged black hole will attract/repel charged objects outside of the event horizon. How can this be, since photons are the particles that mediate an electrical field and photons cannot escape a black hole? The answer is that the speed of light is not a barrier to the exchange of virtual photons.

Gravitons are hypothetical particles. There is no theory regarding gravitons. However, gravitons mediating a static gravitational field should interact in a way similar to how photons mediate a static electrical field: by virtual exchange of field-mediating particles.
 
  • #28
D H said:
An electrically charged black hole will attract/repel charged objects outside of the event horizon. How can this be, since photons are the particles that mediate an electrical field and photons cannot escape a black hole? The answer is that the speed of light is not a barrier to the exchange of virtual photons.

Since gtr is a classical field theory, one should be able to give a classical answer. And we can: it is basically the same answer as offered in the FAQ essay http://www.math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html and an old usenet post my myself, "How does Gravity Escape from a Black Hole?", which is archived at http://www.math.ucr.edu/home/baez/RelWWW/group.html [Broken], only with the electromagnetic field replacing the gravitational field.
 
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  • #29
MajorComplex said:
It really just shows how little information casual science references actually give you...
It's sad, really. "Pop" science is at least partially harmful to science.
 
  • #30
russ_watters said:
It is a void. How can there be different voids? Isn't that like saying there is more than one value of "0"?
Not exactly. Virtual particles do really exist (even if they are called virtual). Inside two very close metal plates there are less virtual particles, and for this reason the plates are attracted one to another (Casimir effect).

So, when light propagates in the void, it must interact with virtual particles; what exactly would happen in a region of space with a lower density of them I don't know, but maybe light's speed increase:
http://en.wikipedia.org/wiki/Scharnhorst_effect
 
  • #31
chroot said:
Originally Posted by lightarrow

I'm not completely sure about this. What I think SR says is that given the postulate of <<light's speed independent on the inertial frame reference>>, then we can show that light's speed is the maximum possible speed. So, if, somwhere, light's speed is not independent on the inertial frame reference, then it's not the maximum possible speed. Example: inside glass.
This is false. Relativity says nothing at all about c being the "maximum possible speed." Relativity simply says that c is the only velocity that every observer will agree upon, regardless of that observer's own motion.
Ok, but saying that "c is the only velocity that every observer will agree upon, regardless of that observer's own motion" or <<light's speed is independent on the inertial frame reference>> is equivalent, given the relativity principle, to say that light's speed cannot be exceeded.

So, what really counts is to have something which propagates to a speed which is invariant for every inertial observer in that region of space. It doesn't really matter if this "something" is light or anything else.
 
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  • #32
lightarrow said:
Ok, but saying that "c is the only velocity that every observer will agree upon, regardless of that observer's own motion" or <<light's speed is independent on the inertial frame reference>> is equivalent, given the relativity principle, to say that light's speed cannot be exceeded.

No, it's not equivalent, and I have no idea why you think it is. Special relativity says absolutely nothing about c being the maximum possible speed, nor does it forbid tachyons. Special relativity quite happily admits particles that travel faster than light, with some consequences, such that their mass is imaginary, etc. Tachyons may be unphysical, and almost certainly don't really exist -- but the mathematics of special relativity does not forbid them.

So, what really counts is to have something which propagates to a speed which is invariant for every inertial observer in that region of space. It doesn't really matter if this "something" is light or anything else.

In its barest form, c doesn't even have anything to do with light. c is just a velocity, and it has the special status of being the only velocity that every observer will always agree upon. The fact that light travels at c is a consequence of its zero rest-mass. even if light did not exist, c would still be a meaningful velocity.

- Warren
 
  • #33
The fact that light travels at c is because of how we define the metre.
 
  • #34
chroot said:
In its barest form, c doesn't even have anything to do with light. c is just a velocity, and it has the special status of being the only velocity that every observer will always agree upon. The fact that light travels at c is a consequence of its zero rest-mass. even if light did not exist, c would still be a meaningful velocity.

- Warren

We should also remember that velocity is calculated V=d/t so that to agree on velocity we must also be using similar measures of distance and time. Small variations express themselves as variations in wavelength etc but it is sometimes interesting to think about large variations for instance if you were so near a black hole that time had slowed to the point that a second was equal to two seconds, how would you perceive incoming light? Try going the other way if a second was only equal to 0.5 of a normal second, how would the universe appear to you?
 
  • #35
quantum123 said:
The fact that light travels at c is because of how we define the metre.

c is a constant, it has no dependence on units whatsoever. You might as well call c = 1, as astrophysicists typically do.

- Warren
 

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