Is Light the Ultimate Barrier to Understanding Black Holes and Gravity?

[lightarrow]

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.

 

[chroot]

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

 

[quantum123]

The fact that light travels at c is because of how we define the metre.

 

[Tzemach]

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?

 

[chroot]

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

 

[marlon]

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?

Sorry for bumping in but i don't understand what this has to do with c being an universal constant, which is the crux of what chroot is saying ?


marlon

 

[marlon]

The fact that light travels at c is because of how we define the metre.

Untrue, very much UNTRUE ! c is DEFINED as a constant at the very beginning of special relativity. This entire theory is built upon c being universally constant. The fact that special relativity allows us to make correct predictions within the appropriate physical regime, only shows us that the "c definition" is correct.

marlon

 

[marlon]

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.

You are talking about black holes which are described by general relativity. I urge you to look how "velocity" is defined in general relativity. You are making the mistake of using a classical physics definition within a general relativity framework. This will not work, as you will find out yourself.

marlon

 

[lightarrow]

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.

Sorry, I didn't use the correct way to express the concept in english: I was intended to mean nothing can "surpass" the speed of light, that is, something that starts from v<c and that cannot go beyond v = c.

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.

Defined how?

 

[Marco_84]

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.

REALLLLLLLLLLLLY BIG MISTAKE, there are vector bosons that have mass.
Have u ever heard something about Z0 W+ W-, they are the mediators particles for weak forces. Weak currents charged and not were discovered in 1983 by CARLO RUBBIA at CERN GINEVRA. He got the Nobel prize for that.
DON'T use words that you cannot understand, I'm only 22 and know beginning studying all this things, after 3 years of many hamiltonian system deep relativity Hard Quantum mechanics calculus, tensor algebra, groups theory and so on.
SO PLEASE it is better that you go back to read some books.

ANd for everybody: I suggest you all to read some books, don't take you information only from wiki...

 

[Schrodinger's Dog]

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.

Probably although not to us for obvious reasons.

OK I didn't post this just to make a very bad joke.

Major, I suggest you do a bit of reading into special and general relativity. Once you've done this many of your questions will answer themselves.

Here's a few websites:-

General relativity
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GenRelativity.html
http://astro.physics.sc.edu/selfpacedunits/Unit57.html

Special Relativity
http://www.howstuffworks.com/relativity.htm
http://casa.colorado.edu/~ajsh/sr/sr.shtml

 

[Aether]

The fact that special relativity allows us to make correct predictions within the appropriate physical regime, only shows us that the "c definition" is correct.

marlon, it is also possible to make all of the same correct predictions using completely different assumptions about c. The standard formulation of special relativity has both a conventional and a non-conventional content. It is not possible to prove that the "c definition" is correct (e.g., the conventional content of the theory) without disproving the non-conventional content of the theory. Any claim that empirical evidence tends to show that the "c definition of special relativity is correct" actually amounts to a claim (inadvertently) that the non-conventional content of the theory is falsified.

 

[marlon]

marlon, it is also possible to make all of the same correct predictions using completely different assumptions about c.

How ?

The standard formulation of special relativity has both a conventional and a non-conventional content.

I don't even know what that means but isn't the very basis of SR that c is an universal constant ? In SR c is the only velocity which will be the same for each and every observer. Now, in what "theory or version" of SR is this denied ?

It is not possible to prove that the "c definition" is correct (e.g., the conventional content of the theory) without disproving the non-conventional content of the theory.

I don't understand. SR works, so the c definition is "correct", what is the problem ?

Any claim that empirical evidence tends to show that the "c definition of special relativity is correct" actually amounts to a claim (inadvertently) that the non-conventional content of the theory is falsified.

Again, i don't understand what you mean by this "non-conventional content of the theory "

marlon

 

[pervect]

How ?

We've had this argument (with Aether) here in the relativity forums before.

It's only possible by changing the conventions of how one measures velocity - specifically by how one synchronizes clocks. The fundamental issue is isotropy - SR is based on an isotropic clock synchronization.

The resulting theory with anisotropic clock synchronization isn't actually any different than SR, if appllied correctly (which seems to be somewhat rare). The proponents, on the one hand, argue that clock synchronization is "just a manner of convention". On the other hand, they then try to argue that changing a convention makes a theory a "different theory".

This short summary doesn't really explain very well how unpleasant anisotropic clock synchronization is. A short, concise explanation would be this. Rapidity is an alternate to velocity, where one uses a single onboard clock to measure elapsed time for a trip, rather than a pair of synchronized lab clocks. An isotropic clock synchronization as used in relativity is the only way to make objects traveling a marked course (say a racetrack) which have the same rapidity have the same velocity. In short, an isotropic clock synchronization is a "fair' clock synchronization. So if you go west-east over the course in one second by your onboard clock, and you go east-west over the same course in one second by your onboard clock, the Einstein clock synchronization is the only clock synchronization that makes your velocity east-west the same as your velocity west-east.

 

[Aether]

How ?

Please see these two papers:
1. J.A. Winnie, Special Relativity without One-Way Velocity Assumptions: Part-I, Philosophy of Science, Vol. 37, No. 1. (Mar., 1970), pp. 81-99.

2. J.A. Winnie, Special Relativity without One-Way Velocity Assumptions: Part-II, Philosophy of Science, Vol. 37, No. 2. (Jun., 1970), pp. 223-238.

I don't even know what that means but isn't the very basis of SR that c is an universal constant ?

No, this is only assumed in the standard formulation of SR. This assumption amounts to the selection of a convenient coordinate system.

In SR c is the only velocity which will be the same for each and every observer. Now, in what "theory or version" of SR is this denied ?

You can do a search of this forum for previous discussions of Lorentz ether theory (LET aka GGT). This "theory" is empirically equivalent to the standard formulation of special relativity, but maintains absolute simultaneity. It is presented only as a counter-example to the coordinate system used in the standard formulation of special relativity, and not as a competing "theory"'; these two coordinate systems actually make all of the same empirical predictions.

I don't understand. SR works, so the c definition is "correct", what is the problem ?

It doesn't make sense to say "my coordinate system works, so therefore it is correct", especially if you are implying by this that other coordinate systems must not be correct.

Again, i don't understand what you mean by this "non-conventional content of the theory "

Please see the bottom of page 1 of ref. 1 above:

According to the CS thesis [the conventionality of simultaneity], this situation reveals a structural feature of the Special Theory, and thereby of the universe it purports to characterize, which not only makes the one-way speed of light indeterminate, but reveals that its unique determination could only be at the expense of contradicting the nonconventional content of the Special Theory.

 

[Aether]

On the other hand, they then try to argue that changing a convention makes a theory a "different theory".

My apologies if I ever implied such a thing here. I do not try to argue this.

 

[marlon]

The resulting theory with anisotropic clock synchronization isn't actually any different than SR, if appllied correctly (which seems to be somewhat rare).

So but has c a different value in this theory ? I would find that hard to believe since light travels at c because of the zero restmass. If c had a different value, how does light still travel at c then ?


marlon

 

[DaveC426913]

So but has c a different value in this theory ? I would find that hard to believe since light travels at c because of the zero restmass. If c had a different value, how does light still travel at c then ?
marlon

Photons are not like tiny rockets speeding to catch up to c. They go as fast as the universe allows.

It is said that if you could render the inertia of an object zero, the object would fly off at the speed of light. There's nothing to hold them still.

So, look at it this way. Objects in the universe move at c - unless they have mass, which causes them to slow down (presumably via interaction with the Higgs field).

 

[DaveC426913]

You know this leads me to the wild speculation that c is the natural state of the universe, and that only certain exotic particles in the universe - namely those with mass - behave oddly.

I wonder what the universe would look like if we turned it on its head - where c is the natural "rest velocity" and that what we call "rest" is the extreme, where rules break down...

 

[Aether]

You know this leads me to the wild speculation that c is the natural state of the universe, and that only certain exotic particles in the universe - namely those with mass - behave oddly.

I wonder what the universe would look like if we turned it on its head - where c is the natural "rest velocity" and that what we call "rest" is the extreme, where rules break down...

What we call "rest" is only observed as an average velocity through an appreciable time interval:

...we can conclude that a measurement of a component of the velocity of a free electron is certain to lead to the result \pm c...Since electrons are observed in practice to have velocities considerably less than that of light, it would seem that we have here a contradiction with expriment. The contradiction is not real, though, since the theoretical velocity in the above conclusion is the velocity at one instant of time while observed velocities are always average velocities through appreciable time intervals. We shall find upon further examination of the equations of motion that the velocity is not at all constant, but oscillates rapidly about a mean value which agrees with the observed value. --- P.A.M. Dirac, Quantum Mechanics - Fourth Edition, p.262, 1958.

 

[marlon]

Photons are not like tiny rockets speeding to catch up to c. They go as fast as the universe allows.

Huh ? When did i say that photons needed to be accelerated ? Or when did i claim they were tiny rockets ?

So, look at it this way. Objects in the universe move at c - unless they have mass, which causes them to slow down (presumably via interaction with the Higgs field).

I said photons travel at c because they have zero (rest)mass. There is nothing wrong with saying that. Point final. Also, i don't agree with what you say above. Because you seem to imply that two objects with equal mass would always travel with the same speed. Why ?

Finally, what does this have to do with my original question to Pervect ?

greets
marlon

 

[DaveC426913]

Huh ? When did i say that photons needed to be accelerated ? Or when did i claim they were tiny rockets ?

I may have underestimated your knowledge of the subject, and was attempting to address what I thought was a misunderstanding on your part. I confess I went a little too far into analogy.

If c had a different value, how does light still travel at c then ?

This statement seemed to imply that if c changed, light would not, as if light had its own preferred speed, independent of c.

I concede the conversation to those more directly involved in it.

 

[Chris Hillman]

Hi all,

This thread has gotten rather confused. Way back at the initial post

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 noticed that the problem is the same misconception discussed in http://www.math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html and "How does gravity escape from a black hole?" at http://www.math.ucr.edu/home/baez/RelWWW/group.html , but assumed others would point this out, so I didn't speak up. Maybe that was a mistake...

MajorComplex, does reading the above cited FAQ entry or my own archived sci.physics.relativity post on the same topic help?