Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: AndroidNeox on 11/11/2013 21:58:47
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The current model of black holes depicts infalling objects appearing to slow to a virtual halt outside the event horizon and to never reach the event horizon in finite time. But, this is supposed to be an illusion and in reality matter passes through and on to the singularity.
What bothers me is that this violates Relativity which requires that observations from all frames be equally valid.
While I concede that event horizons might form in finite time and the contemporary model could be correct, it’s not possible to use Relativity to justify the model. Any model that violates one of the fundamental assumptions Einstein relied on to develop Relativity is inconsistent with Relativity and no conclusion that depends on such a violation can be valid, under Relativity.
I might not be good enough at math to solve the GR equations to describe this but I got an A in all my logic classes and I know that no logical argument is valid that depends upon violating one of its premises.
What I don’t understand is why people disregard the requirements of Relativity when using it to model physical systems. It wasn’t until about a decade after Einstein’s death that the general consensus changed from the “frozen star” model to one with event horizons and singularities but I’ve not been able to find a single justification for this belief.
Can anyone here explain why the accepted model changed?
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Why do people think Relativity predicts event horizons?
The laws of physics predicts them.
The current model of black holes depicts infalling objects appearing to slow to a virtual halt outside the event horizon and to never reach the event horizon in finite time. But, this is supposed to be an illusion and in reality matter passes through and on to the singularity.
It’s not an illusion. In relativity what is reckoned to happen depends on the observer. What each observer reckons is not an illusion.
What bothers me is that this violates Relativity which requires that observations from all frames be equally valid.
Relativity has no such requirement. Observations need not be the same for all observers. For example; one observer might be able to rightly say that that he reckoned a moving rod to be entirely inside a barn while another observer can also say that there was no time at which the rod was entirely inside the same barn. In another example one observer might reckon that a charged object is radiating EM waves while another observer might also reckon that at no time the same charged object never radiated EM waves. The list goes on. In fact that’s why it’s called relativity because what’s observed is observer dependant.
Can anyone here explain why the accepted model changed?
No accepted model changed. But what model is it that you are claiming changed and where in the above did you make this statement.
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One more thing -
I might not be good enough at math to solve the GR equations to describe this but I got an A in all my logic classes and I know that no logical argument is valid that depends upon violating one of its premises.
Where in your use of logic did you arrive at this assertion … Relativity which requires that observations from all frames be equally valid.
What do you think “observations from all frames” means and what does it mean to for them to be “equally valid” in your interpretation? I’ll tell you what it doesn’t mean. It doesn’t mean that all observations from all frames of reverence are identical.
Pleas use your skills in logic to go from the postulates of relativity to your assertion - … Relativity which requires that observations from all frames be equally valid.
Thanks
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The current model of black holes depicts infalling objects appearing to slow to a virtual halt outside the event horizon and to never reach the event horizon in finite time. But, this is supposed to be an illusion and in reality matter passes through and on to the singularity.
What we see at the event horizon is information left there in the form of electromagnetic radiation. Think about it like this: The images we see across vast distances of the universe, some coming to us from about 13.7 billion light years distant are actually events that occurred 13.7 billion years in the past. It's not exactly the same at the event horizon because gravitational energies have actually slowed the advance of time itself. But in both cases, the events we are seeing are real and not illusionary. Just because they appear to be current to our frame of reality does not mean that they are current to the process unfolding in that particular frame.
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What we see at the event horizon is information left there in the form of electromagnetic radiation. Think about it like this: The images we see across vast distances of the universe, some coming to us from about 13.7 billion light years distant are actually events that occurred 13.7 billion years in the past. It's not exactly the same at the event horizon because gravitational energies have actually slowed the advance of time itself. But in both cases, the events we are seeing are real and not illusionary. Just because they appear to be current to our frame of reality does not mean that they are current to the process unfolding in that particular frame.
Nice response! :)
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1) The requirement that Relativity requires causal consistency across all frames:
The “Principle of Relativity” requires that all frames of reference must exhibit the same rules. Observations of events in one frame must be compatible with any other frame. By compatible I mean that the observations from any frame can be translated to those of any other frame by using the equations of Relativity.
Another way of saying this is that, “no physical observable can depend on how you choose coordinates… And a lot of things you might detect are not frame invariant--- the energy of a photon for example” I use quotes because that’s the exact phrase used in a recent email to me by one of the physicists from Fermilab who was also involved in the LIGO gravity wave project.
2) “What we see at the event horizon is information left there in the form of electromagnetic radiation.”
Electromagnetic radiation doesn’t hang around. It always moves at the speed of light.
Regarding your comparison to the observable horizon… just as it’s not possible for any object to reach the observable horizon, because it moves away at the speed of light, nothing can fall to an event horizon because spacetime stretches without bound as the concentration of mass approaches the Schwarzschild radius (for the simplest black holes).
It might help with your confusion to consider that the time rate for an infalling object/observer is exponentially related to that of a distant, inertial observer. By the time the infalling object has run out of time and reached the event horizon, an infinite amount of time will have passed for the external observer.
If the idea of the object disappearing into an infinite redshift is bothering you, just imagine the infalling object to be a mirror and the radiation you use to see it to be from a light beam coming from the distant inertial observer. This way the gravitational redshift is eliminated from observations.
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Why do people think Relativity predicts event horizons?
The laws of physics predicts them.
No. General Relativity makes black holes inevitable but event horizons are impossible.
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A event horizon is where a observer find 'reflected light' from a object to cease to exist for him, as I think of it. You can take a look at https://en.wikipedia.org/wiki/Event_horizon for a description. There will be a real event horizon as defined relative a universe, and then apparent event horizons, as defined relative a observer.
"The definition of an absolute horizon is sometimes referred to as teleological, meaning that it cannot be known where the absolute horizon is without knowing the entire evolution of the universe, including the future. This is both an advantage and a disadvantage. The advantage is that this notion of a horizon is very geometrical, and does not depend on the observer, unlike apparent horizons, for example. The disadvantage is that it requires the full history (all the way into the future) of the spacetime to be known. In the case of numerical relativity, where a spacetime is simply being evolved into the future, only a finite portion of the spacetime can be known."
So what we see is apparent horizons, which on the other hand doesn't invalidate your observations of no light being reflected any more.
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Because infinities when we get to black holes arrrg relativity why do you fail us
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Now that depends on how you define relativity. Trying to define it versus a universe, is in a way a assumption of a container, containing us all. Defining it as a relation between the observer and the observed avoid this assumption. Using the last one relativity does not fail anywhere, it will always be about you, 'relative' another frame of reference, in where your definitions of time, distance, constants, principles, ad infinitum will define what time dilations, Lorentz contractions, etc etc you find. From that point of view an apparent event horizon is a real 'event horizon' ..... For you.
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Why do people think Relativity predicts event horizons?
The laws of physics predicts them.
No. General Relativity makes black holes inevitable but event horizons are impossible.
No, what would be impossible is not to have an event horizon. If a black hole exists, there must be some region from within which light can't escape to the rest of the universe. Outside that region, light can escape from the gravitational pull of the black hole. So clearly there's a boundary between those regions.
That boundary can't depend on the observer, either, since if one observer can view light escaping to the universe and the other can't, that's not only a huge paradox, but means that different observers see different laws of physics!
What we can't observer, from our perspective outside a black hole, is anything falling through the event horizon, but that's got nothing to do with whether it exists or not.
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Don't agree there JP. A apparent event horizon should be able to be defined as that 'boundary' you refer to, from where no light can be reflected as all light, from your measurements, is gone, into that black hole. And if I stop defining the universe as a 'objective container' observer dependencies are real. And they are, each time you measure them, as 'real' as can be, for you.
That is what we live by JP, our measurements.
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You need local constants and principles, shared by all frames of reference, to define such a 'universe'. And you need 'communication' between those frames of reference, resting/building on/from those constants and principles. And it should give you infinites when that 'communication' breaks down. It's not about the universe we see being an 'illusion', as much as it is about defining it from local principles, shared by all 'frames' possible to measure.
It creates a same universe as the one we measure on, but it defines it locally, thereby avoiding the discussion about what is 'more real' in two different measurements, getting different answers. From that point of view both are as real as they can become, from each observers frame of reference.
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Don't agree there JP. A apparent event horizon should be able to be defined as that 'boundary' you refer to, from where no light can be reflected as all light, from your measurements, is gone, into that black hole. And if I stop defining the universe as a 'objective container' observer dependencies are real. And they are, each time you measure them, as 'real' as can be, for you.
That is what we live by JP, our measurements.
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You need local constants and principles, shared by all frames of reference, to define such a 'universe'. And you need 'communication' between those frames of reference, resting/building on/from those constants and principles. And it should give you infinites when that 'communication' breaks down. It's not about the universe we see being an 'illusion', as much as it is about defining it from local principles, shared by all 'frames' possible to measure.
It creates a same universe as the one we measure on, but it defines it locally, thereby avoiding the discussion about what is 'more real' in two different measurements, getting different answers. From that point of view both are as real as they can become, from the observers frame of reference.
The fact is, a point inside the black hole cannot send information to a distant star outside the black hole. This has to be true independent of your reference frame.
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Yes, that one must be true for all frames of reference, sharing those constants and principles. And that one I would define to the fact that there exist local constants, being equivalent for all frames of reference. Like a security net, keeping our universe together, but it also need some mean for communicating, and what that one should be? You have 'c' naturally, but then again, would that be a propagation from such a point of view? Or would it just be a limit of communication, as what it suggest is that my measurement is as good as the next persons, none lying. Meaning that it is the one that fit my universe, even if yours measurement states something different to you.
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The other point is that, assuming a black hole to exist, it have a presence even when defined as a singularity, impossible to measure on past that event horizon. There it won't matter what apparent event horizon I find, it will still be impossible to measure past it as I understands. And the presence of it, even when unable to measure, should then be able to be defined as it not sharing those local limits our 'commonly same universe' builds on. Meaning that something still can 'exist' for us, even though not sharing our local definitions? A weird thought, isn't it? We can pass a event horizon, but we can't get back.
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Like a bubble in a bubble somehow, as you as me JP, I think? Still expect the inside of it resting on the same physics we find outside it, that is if I remember it right?
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The universe we find us able to measure on is defined by 'two way communications'. It doesn't matter for this if your definition of a distance of propagation A to B differ from mine measurement. We can still define it as communicating both ways, and we can make it make sense using Lorentz transformations. As you point out, a black hole does not use a two way communication, unless we would refer to Hawking radiation, From our own time limited frames, it won't communicate though. And that becomes the 'surface' of that bubble. But if I assume that past it I would find the same physics as outside it I have two options. Using Hawking radiation it's no problem, it still 'communicates', even though not measurably for us. Using a 'time limited' definition though, it does not. The first places it inside our 'commonly same universe', even when impossible to measure on for us. The other?
In the first my 'bubble in a bubble' disappear, doesn't it?
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And that bring us to the concept of 'meaningful communication'. Is Hawking radiation a meaningful communication? If I define something meaningful as something able to decipher by the recipient (us). Would Hawking radiation tell us anything about the inside of that black hole? I don't think it would, but I'm willing to listen.
What you referred to JP, was, as I think :) just that concept, right? Like sending a radio transmission from inside a event horizon, describing that inside. And we wouldn't get it (outside that EH), ever.
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I'm afraid people aren't understanding the point of this thread. I'm not asking for the contemporary model of black holes. I know what it is and I agree with Einstein that it's wrong. What I asked is why people think event horizons can form.
People are just assuming they do, even though that violates general relativity by violating one of the assumptions GR is based on.
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The problem is that Einstein, in the end, did agree on black holes existing, I think he reversed his thoughts several times on that one. And if they do, there must be a point of no return for infalling mass and energy, as light. You can either define that point relative the full life of a universe, as described above, or you define it relative the observer in each case. In both cases the measurements you 'may be able to' make (the first case is very theoretical, and I can't see how you should construct a experiment there?) should give you the same answer though, no light (mass energy) reflected/returned from that point on. What exactly makes you doubt a event horizon? there are some mathematical hypothesis's over a black hole without a event horizon being possible but? That would be a very strange thing to me, as everything only should have one path, to its center, no matter how you turn it around. Anyway, here you go. See if it makes more sense to you. Destroying black holes with test bodies. (http://arxiv.org/abs/1006.1764)
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I think that question might depend on the physics of a black hole. I assume the same physics inside as 'outside its event horizon', but if there isn't? Then maybe you can make an assumption in where you can bypass the mass (gravity) by angular momentum for example? Quite strange idea. It's like one infinity meeting another, a infinite mass (or 'infinite gravity' might be better here?) meeting a infinite angular momentum, where the angular momentums 'infinity' then need to be of a greater magnitude than the mass? And if you use a 'one to one' correspondence to define what a infinity is, I find big problems imagining the possibility of defining one infinity as bigger than any other?
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The problem is that Einstein, in the end, did agree on black holes existing, I think he reversed his thoughts several times on that one.
I'm not familiar with his changing his opinion. That's surprising since until about a decade after his death the consensus in physics was that the "frozen star" model was correct. In The Trouble With Physics, Smolin claims Einstein always insisted that event horizons cannot form. I'd be interested to know if that's not correct.
But, despite my tremendous respect for Einstein, even if he did change his mind on the subject that wouldn't change anything since the reality of physics is independent of our opinions. My point, which I maintain, is that it's not possible to use Relativity to demonstrate the existence of event horizons. This is because if there is a point of no return then Relativity is wrong. Perhaps it is wrong under extreme circumstances but you can't use Relativity to prove an outcome that depends on Relativity being wrong unless Relativity itself is inconsistent.
If it has been demonstrated that G.R. is wrong regarding event horizons, that's a separate issue. I'd be fascinated to learn about that but I don't believe it to be the case.
And if they do, there must be a point of no return for infalling mass and energy, as light. You can either define that point relative the full life of a universe, as described above, or you define it relative the observer in each case. In both cases the measurements you 'may be able to' make (the first case is very theoretical, and I can't see how you should construct a experiment there?) should give you the same answer though, no light (mass energy) reflected/returned from that point on. What exactly makes you doubt a event horizon? there are some mathematical hypothesis's over a black hole without a event horizon being possible but? That would be a very strange thing to me, as everything only should have one path, to its center, no matter how you turn it around. Anyway, here you go. See if it makes more sense to you. Destroying black holes with test bodies. (http://arxiv.org/abs/1006.1764)
The important thing to remember is that the relationship between the total time experienced by an infalling observer as they fall into a black hole and the time experienced by an external inertial observer is exponential. Though the time remaining for the infalling observer will be finite and maybe even brief, that time will not elapse until an infinite amount of time has passed for the external observer. These two perspectives are mutually consistent.
Regarding how to construct the experiment: Drop a mirror into the black hole. Illuminate it with a light beam. If the contemporary model of black holes is correct, the mirror will appear to remain outside the event horizon forever even though it passes through the event horizon and stops reflecting light. At that point, Relativity would break down because not all frames would be consistent for observations.
I think that question might depend on the physics of a black hole. I assume the same physics inside as 'outside its event horizon', but if there isn't? Then maybe you can make an assumption in where you can bypass the mass (gravity) by angular momentum for example? Quite strange idea. It's like one infinity meeting another, a infinite mass (or 'infinite gravity' might be better here?) meeting a infinite angular momentum, where the angular momentums 'infinity' then need to be of a greater magnitude than the mass? And if you use a 'one to one' correspondence to define what a infinity is, I find big problems imagining the possibility of defining one infinity as bigger than any other?
The problem I see is that you are beginning with the assumption that event horizons exist when that is the question being considered. Relativity doesn't predict their existence so I'd be interested to know what physical theory you're using to arrive at (or, rather not arrive at but begin with). There are no problems with infinities unless the event horizon exists, in which case not only does causality get violated but infinite energies are involved... and infinite time passes within a finite period.
No, I can't accept that model. The contemporary model of black holes is nonsense. The frozen star model is self-consistent, entails no infinities, and doesn't violate causality... besides being the model required by Relativity.
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Got to admit that black holes are one of the most confusing as well as interesting ideas I know of. As for how Smolin defines it I don't know, would be nice to see the citation. But I know that Einstein changed his mind on Black holes. When it comes to a event horizon specifically? Well, I haven't seen any discussion about that one when it comes to Einstein and history, possibly Smolin is correct in arguing that Einstein didn't like that idea, as it could be read as relativity breaks down at a event horizon. But as far as I get it the event horizon has nothing to do with that, presuming that there is a center of 'infinite mass'.
"The simplest answer is that the curvature of space-time is a smoothly changing function of distance up to, and through, the event horizon. There is no indication from the curvature (Riemann's Curvature Tensor, or even Ricci's for that matter) that anything serious is happening just inside the event horizon. Einstein's 'equations' work just fine so long as the local curvature of space-time (the strength of the gravitational field) does not become singular. This does not happen just inside an event horizon, but only happens as you approach the 'r=0' singularity itself.
What all of this means is that the mathematical properties of spacetime that matter (its curvature) change smoothly through the event horizon, much like a ride in a sled down a snow-covered hill. Now, to prove that this is in fact the case will probably not be possible because we can never extract information from inside a black hole withough dying, or never being able to return! "
As for me I would expect the physics inside a Event Horizon to be the same as outside, I do not expect 'time' to become 'space' and 'space' become 'time' for a infalling observer. To the observer the local arrow should be 'as always', his ride toward the singularity's center taking a, for him, measurable time.
What experiment are you referring to? Not the first example over a whole space-times history, right? That's the one I wouldn't know how to define. As for the one with a 'apparent event horizon'. The whole idea of that, is that it for the observer becomes his 'limit of observation'. Meaning that wherever he finds it to be, that also will be the place of 'no return' for his experiments, and as far as I understands it, no more reflections observed, from his frame of reference. That should mean that your mirror will 'disappear' for the observer at that point. And there will also be a 'dimming' of that mirror, due to the redshift of that reflected light as it propagates 'uphill', getting 'stretched out' by the Black holes gravity if described as waves. So it will probably just dim out and disappear as it falls in. To that you can add a time dilation, making it 'slow down' for the observer as it closes in on that event horizon.
As for why a event horizon is needed? It's just a place where all geodesics starts to lead to a same place, relative the observer, or a 'whole SpaceTime'. And that should be the center of its singularity. And light follows those geodesics. A reflection can only be seen if that geodesic leads back to you. A event horizon is defined from the way light, (energy), gravity and mass interacts. But a black hole is truly weird, as it do contain a infinity at some point, if the mathematics are correct. And there is no way to describe what happens there, as far as I know. And it's GR that describes a black hole. Karl Schwarzchild used Einstein's theory of general relativity to define a non spinning black hole 1916.
"An object whose radius is smaller than its Schwarzschild radius is called a black hole. The surface at the Schwarzschild radius acts as an event horizon in a non-rotating body (a rotating black hole operates slightly differently). Neither light nor particles can escape through this surface from the region inside, hence the name "black hole". The Schwarzschild radius of the (currently hypothesized) supermassive black hole at our Galactic Center would be approximately 13.3 million kilometres." from Schwarzschild radius. (https://en.wikipedia.org/wiki/Schwarzschild_radius)
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I wrote ' A event horizon is defined from the way light, (energy), gravity and mass interacts.' But I don't think you need to add 'time' to that. Time is to me locally invariant, its arrow of time always ticking at a same rate for you. And as I define it as equivalent to 'c', also a local invariant, I therefore will assume that this will hold true for accelerations/decelerations too. 'c' must be 'c' at all kinds of 'motion' for the equivalence to hold. And that goes for the inside of a black hole too.
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Got to admit that black holes are one of the most confusing as well as interesting ideas I know of. As for how Smolin defines it I don't know, would be nice to see the citation. But I know that Einstein changed his mind on Black holes. When it comes to a event horizon specifically? Well, I haven't seen any discussion about that one when it comes to Einstein and history, possibly Smolin is correct in arguing that Einstein didn't like that idea, as it could be read as relativity breaks down at a event horizon. But as far as I get it the event horizon has nothing to do with that, presuming that there is a center of 'infinite mass'.
The quote is something like, Einstein always insisted that event horizons cannot form and continues by saying but he was wrong. I think it's in chapter 1 of The Trouble With Physics.
"The simplest answer is that the curvature of space-time is a smoothly changing function of distance up to, and through, the event horizon. There is no indication from the curvature (Riemann's Curvature Tensor, or even Ricci's for that matter) that anything serious is happening just inside the event horizon. Einstein's 'equations' work just fine so long as the local curvature of space-time (the strength of the gravitational field) does not become singular. This does not happen just inside an event horizon, but only happens as you approach the 'r=0' singularity itself.
Spacetime is stretched by concentrations of mass. As the concentration approaches the Schwarzschild limit, the stretch approaches infinity. It is no more possible for matter (including light) to reach an event horizon than it is to accelerate a particle of non-zero rest mass to the speed of light.
What all of this means is that the mathematical properties of spacetime that matter (its curvature) change smoothly through the event horizon, much like a ride in a sled down a snow-covered hill. Now, to prove that this is in fact the case will probably not be possible because we can never extract information from inside a black hole withough dying, or never being able to return! "
It's simple to present a thought experiment to study the problem, though. The simplest is to drop a mirror into the black hole and shine a beam of light off of it and observe the reflection. Because the beam retraces its path into the gravity well, any gravitational redshift is eliminated. Perhaps you can describe what the contemporary model of black holes would predict. I know Einstein would say that the mirror will, from the perspective of the external observer, slow to a virtual halt and the light beam reflection could be observed forever.
Another thought experiment is based on the one Hawking used in calculating the thermodynamics of event horizons in which he lowers a box full of light via a rope down to the vicinity of the E.H. and then dumps the light in. Using the same setup, replacing the box with a mirror, lower the mirror toward the event horizon. Now, measure the distance down to the mirror as it's lowered by bouncing a laser beam off of it and feeding the return beam into an interferometer... counting each dark-light transition would give the distance in terms of wavelength of light. Before the mirror passes through the event horizon, an infinite number of such transitions will be counted, an infinite amount of rope would be payed out.
As for me I would expect the physics inside a Event Horizon to be the same as outside, I do not expect 'time' to become 'space' and 'space' become 'time' for a infalling observer. To the observer the local arrow should be 'as always', his ride toward the singularity's center taking a, for him, measurable time.
Since the path length from every point in spacetime to any event horizon is always infinite, the potential conditions inside the event horizon never arise. Not even the matter that initially collapsed to form the black hole can reach it.
I might have figured out where the problem is. People might be calculating the instantaneous path length to the event horizon instead of taking into account that spacetime continues to stretch indefinitely as the matter that has fallen into the black hole continues toward the unreachable Schwarzschild limit.
What experiment are you referring to? Not the first example over a whole space-times history, right? That's the one I wouldn't know how to define. As for the one with a 'apparent event horizon'. The whole idea of that, is that it for the observer becomes his 'limit of observation'. Meaning that wherever he finds it to be, that also will be the place of 'no return' for his experiments, and as far as I understands it, no more reflections observed, from his frame of reference. That should mean that your mirror will 'disappear' for the observer at that point. And there will also be a 'dimming' of that mirror, due to the redshift of that reflected light as it propagates 'uphill', getting 'stretched out' by the Black holes gravity if described as waves. So it will probably just dim out and disappear as it falls in. To that you can add a time dilation, making it 'slow down' for the observer as it closes in on that event horizon.
I think I've addressed these concerns in the experiment I describe, above, where gravitational redshift is cancelled out.
Relativity requires that observations made in any reference frame can be translated (via the equations of Relativity) to those of any other frame. The insurmountable problem is that, if there is an event horizon, if it's possible to do as Hawking suggests and have a reference frame that's in the E.H.'s vicinity, then it is impossible to reconcile observations of matter passing into the E.H. with observations of distant observers.
The error isn't in Relativity. The error is in misapplying it.
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I do not expect 'time' to become 'space' and 'space' become 'time' for a infalling observer.
Now, there’s an interesting thought! If space and time changed places, would we notice any difference? I think not.
What could it possibly mean?
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Oh dear it's controversy time. I do believe in the frozen star hypothesis and for this reason. The matter at the surface of a star that is collapsing towards the schwarzschild radius will itself undergo time dilation as it nears this point. The total gravitation below the surface will be increasing and must induce time dilation on matter nearer the surface. Otherwise time dilation just fails totally. As this matter at the surface approaches the horizon it to will take an ever longer time to get there. You can't have one rule for matter off the surface and another for the infalling surface itself. It too is effected by the gravitation from its own centre of gravity.
As an update, you can take this dilation all the way to the centre of the mass. If you take as your measurement half the radius of the collapsing mass then as this collapses internally it will also approach its own event horizon. As before the mass at its assumed surface will also take an infinite time to reach its own event horizon.
I have been asking questions such as what will fit inside a Planck volume to see if anyone else was thinking along these lines but few took that one up. There is usually a reason for the strange questions I ask.
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Since the path length from every point in spacetime to any event horizon is always infinite, the potential conditions inside the event horizon never arise. Not even the matter that initially collapsed to form the black hole can reach it.
Hopefully JP will not mind if I quote from another thread. Proves I took notice. :)
Infinity is used in physics as a stand-in for "very large," and it comes into play with "very small" (infinitesimally small) and we can use the mathematical tools for handling infinity in these cases to produce useful results, often with much less work than would be involved if we tried to plug in large or small numbers.
If this is right, the stretching of spacetime is not really infinite, it’s just so large that it is convenient to refer to it as infinite.
I would be the last to argue with anyone who maintained that it is impossible to reach a point that is infinitely far away, such would not be the case if the point were simply an unthinkably long way away.
Surely all we are saying when we talk of finite things going to infinity is that they reach a point where our finite calculations are unable to cope, whether those calculations involve relativity, or not.
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Oh dear it's controversy time. I do believe in the frozen star hypothesis and for this reason. The matter at the surface of a star that is collapsing towards the schwarzschild radius will itself undergo time dilation as it nears this point. The total gravitation below the surface will be increasing and must induce time dilation on matter nearer the surface. Otherwise time dilation just fails totally. As this matter at the surface approaches the horizon it to will take an ever longer time to get there. You can't have one rule for matter off the surface and another for the infalling surface itself. It too is effected by the gravitation from its own centre of gravity.
As an update, you can take this dilation all the way to the centre of the mass. If you take as your measurement half the radius of the collapsing mass then as this collapses internally it will also approach its own event horizon. As before the mass at its assumed surface will also take an infinite time to reach its own event horizon.
I have been asking questions such as what will fit inside a Planck volume to see if anyone else was thinking along these lines but few took that one up. There is usually a reason for the strange questions I ask.
Right. I imagine a neutron star on the verge of collapse to a black hole having that last little bit of matter dropped onto it like the straw that broke the camel's back. The nucleation point (where the collapse begins) will be at the surface, where gravity is most intense. As the matter begins falling together and approaches the Schwarzschild limit, spacetime stretching will hold it apart, almost frozen.
Can you explain more about your thinking regarding Planck scale?
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Infinity is used in physics as a stand-in for "very large," and it comes into play with "very small" (infinitesimally small) and we can use the mathematical tools for handling infinity in these cases to produce useful results, often with much less work than would be involved if we tried to plug in large or small numbers.
If this is right, the stretching of spacetime is not really infinite, it’s just so large that it is convenient to refer to it as infinite.
I would be the last to argue with anyone who maintained that it is impossible to reach a point that is infinitely far away, such would not be the case if the point were simply an unthinkably long way away.
Surely all we are saying when we talk of finite things going to infinity is that they reach a point where our finite calculations are unable to cope, whether those calculations involve relativity, or not.
Sometimes infinity really is infinity. Relativity has some. For example, if you apply some finite acceleration to an object with non-zero rest mass, like a bowling ball or a proton:
Question: How long will it take to accelerate the object to the speed of light?
Answer: Infinitely long
Question: How much energy will be required to accelerate the object to the speed of light?
Answer: Infinite energy
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Sometimes infinity really is infinity. Relativity has some. For example, if you apply some finite acceleration to an object with non-zero rest mass, like a bowling ball or a proton:
Question: How long will it take to accelerate the object to the speed of light?
Answer: Infinitely long
That position sounds all well and good but what about the inflationary period following the big bang? It is surmised that during this event, the speed of light was exceeded, and it didn't take eternity or infinitely long to reach.
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Oh dear it's controversy time. I do believe in the frozen star hypothesis and for this reason. The matter at the surface of a star that is collapsing towards the schwarzschild radius will itself undergo time dilation as it nears this point. The total gravitation below the surface will be increasing and must induce time dilation on matter nearer the surface. Otherwise time dilation just fails totally. As this matter at the surface approaches the horizon it to will take an ever longer time to get there. You can't have one rule for matter off the surface and another for the infalling surface itself. It too is effected by the gravitation from its own centre of gravity.
As an update, you can take this dilation all the way to the centre of the mass. If you take as your measurement half the radius of the collapsing mass then as this collapses internally it will also approach its own event horizon. As before the mass at its assumed surface will also take an infinite time to reach its own event horizon.
I have been asking questions such as what will fit inside a Planck volume to see if anyone else was thinking along these lines but few took that one up. There is usually a reason for the strange questions I ask.
Right. I imagine a neutron star on the verge of collapse to a black hole having that last little bit of matter dropped onto it like the straw that broke the camel's back. The nucleation point (where the collapse begins) will be at the surface, where gravity is most intense. As the matter begins falling together and approaches the Schwarzschild limit, spacetime stretching will hold it apart, almost frozen.
Can you explain more about your thinking regarding Planck scale?
Well the original question was too vague. The better one is at the surface of the earth under gravitation how many planck volumes would be needed to contain a proton? If we calculated this then from that we worked out say how many planck volumes would be needed to contain 1kg of a mass. If we then work out what the schwarzschild radius for the 1kg mass would be and calculated how many planck volumes would contain it we may find the absolute mass-energy density ratio. As this would be an absolute just as the speed of light and absolute zero are we would resolve the breakdown in relativity. This would also rid physics of the singularity. The big bang would then be simply caused by quantum fluctuations of the collapse of a previous universe to cause the expansion by simply ejecting enough mass over a very long period of time so that the mass expands away from its schwarzschild radius.
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Android, the thing about infalling past a event horizon is that it also is about frames of reference. If you have a far observer, as well as a observer falling past then the far observer will see what you speculate about. The infalling observer 'stopping' before it ever reach past that event horizon, alternatively 'fading out' for him as the redshift should quench the light, the redshift comes from the light paths having to propagate 'uphill', away from a black holes gravitation. If we turn it around the observer infalling might at some point, see a 'infinite blue shift', assuming him able to stay still (which actually means him 'accelerating') just before a event horizon, looking out at a universe. I'm not sure what you mean by writing "The simplest is to drop a mirror into the black hole and shine a beam of light off of it and observe the reflection. Because the beam retraces its path into the gravity well, any gravitational redshift is eliminated." The beam does not get the redshift eliminated by 'retracing itself' as far as I know, it's about gravity that one, and about a direction/vector/velocity relative that center of 'infinite mass'. There is no way it can retrace its light path either, as we have a dynamic SpaceTime, in where ones local arrow always 'moves', even if assuming everything else (matter and its motion) to be 'static/unmoving' in a SpaceTime. As for lowering anything to a event horizon? That one is tricky and I've seen a lot of takes on that one :) as have you I guess.
So two observers do not need to agree on a time taken, that is what relativity is about. The infalling observer will find light moving at, 'c' as will the far observer', and splitting 'c' you can get to a local arrow. That becomes a 'shared global background/constant' of time keeping as I see it, always locally defined though. And as the infalling observer find 'c' the universe acts as usual for him, his arrow of time ticking. What happens inside a event horizon with the room/time should be any-body's guess, it depends on mass, angular momentum, and what frame of reference you use/imagine to measure it by.
But locally there are no weird things happening, only when you start comparing your frame of reference to another will time dilations, Lorentz contractions (and expansions) become noticeable. So the infalling observer must pass that event horizon, locally defined.
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You may have spagettifications etc, naturally, caused by tidal forces, But what I mean is that there is nothing strange about any of it, they are perfectly explainable phenomena. And the infalling observer, inside a black box, ignoring tidal forces, will pass that event horizon, never noticing anything out of order locally.
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Try this one http://www.universetoday.com/1605/
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Question: How long will it take to accelerate the object to the speed of light?
Answer: Infinitely long
Question: How much energy will be required to accelerate the object to the speed of light?
Answer: Infinite energy
"Infinitely long" = you can't get there.
"Infinite energy" = you'll never have enough energy.
Infinity cannot be established by experiment; it is always a conjecture.
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Sometimes infinity really is infinity. Relativity has some. For example, if you apply some finite acceleration to an object with non-zero rest mass, like a bowling ball or a proton:
Question: How long will it take to accelerate the object to the speed of light?
Answer: Infinitely long
That position sounds all well and good but what about the inflationary period following the big bang? It is surmised that during this event, the speed of light was exceeded, and it didn't take eternity or infinitely long to reach.
The limitation of c is a matter of the geometry of spacetime. But, superluminal inflation is allowed by Relativity because nothing's moving through spacetime faster than c. Rather, spacetime itself is stretching and 'pulling' along the matter within it.
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Don't know why people keep arguing that ftl is relativity too? Relativity builds on 'c', nothing other. As soon as you discuss ftl you go away from relativity. It's like saying that as relativity builds on comparing frames of reference, from a 'inside' of a universe, it also state that there is a 'outside'. Relativity is defined from a inside, and has a limit of communication related the speed of light in a vacuum. FTL is something different, and also outside the borders of relativity.
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The expansion is a additive thing as I get it, over long empty stretches a 'accelerating expansion of a vacuum' will be able to expand faster than a light beam can propagate.
"The Hubble constant tells us that - for every megaparsec of distance between two galaxies-, - the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second -.
Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers). " http://curious.astro.cornell.edu/question.php?number=575
The speed of light is defined as a distance light propagate in a vacuum, relative a defined time. About 300.000 km per second. Light does not do FTL. An expansion is neither a 'thing' propagating ftl. It's a distance widening, consisting of nothing at all classically.
Easiest to see if you imagine a acceleratingly expanding vacuum, in where you is the only thing existing observing that 'expansion'. Feel free to show me how to do that.
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Don't know why people keep arguing that ftl is relativity too? Relativity builds on 'c', nothing other. As soon as you discuss ftl you go away from relativity.
You're right. I haven't responded sooner because I hadn't fully considered this. I've been intellectually sloppy and let the statements of others slide past without questioning. But, you're right. If there are any conditions under which something can exceed c, no matter the mechanism, relativity is violated.
I think I have a model that would both satisfy this most conservative interpretation of relativity and the observed smoothness of the cosmos but I need another day or so to think about it.
Thank you for your posting. You make a very good point.
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Don't know why people keep arguing that ftl is relativity too? Relativity builds on 'c', nothing other. As soon as you discuss ftl you go away from relativity.
That's incorrect. Particles which can travel faster than the speed of light can exist and is consistent with special relativity.
The type of particles that can travel FTL are called tachyons. These are particles that are created moving faster than the speed of light. What SR says can’t happen is that a particle with real and finite proper mass cannot be accelerated from v < c to a speed v > c. Otherwise there's nothing wrong with particles (aka tachyons) being created which are moving faster than the speed of light. G. Feinberg showed this to be true and called that class of particles tachyons.
The original article which postulates the existence of FTL particles and which coins the term tachyon is Possibility of Faster-Than-Light Particles, Feinberg, G. (1967), Physical Review, 159 (5): 1089–1105. You can download and read the article from here -- http://www.relativitycalculator.com/images/superluminal_velocities/possibility_faster_than_light.pdf
The abstract reads (from http://prola.aps.org/abstract/PR/v159/i5/p1089_1)
We consider the possibility of describing, within the special theory of relativity, particles with spacelike four-momentum, which therefore have velocities greater than that of light in vacuum. The usual objections to such particles are discussed, and they are found to be unconvincing within the framework of relativistic quantum theory. A quantum field theory of noninteracting, spinless, faster-than-light particles is described. The field theory is Lorentz-invariant, but must be quantized with Fermi statistics. The associated particle theory has the property that the particle number is not Lorentz-invariant, and the no-particle state is not Lorentz-invariant either. Nevertheless, the principle of relativity is satisfied. The Lorentz invariance implies a relation between emission and absorption processes, in contradiction to the usual case. Some comments are made about the problem of introducing interactions into the field theory. The limiting velocity is c, but a limit has two sides.
Please note the important part in that abstract – The usual objections to such particles are discussed, and they are found to be unconvincing within the framework of relativistic quantum theory.
See also http://en.wikipedia.org/wiki/Tachyon
But, you're right. If there are any conditions under which something can exceed c, no matter the mechanism, relativity is violated.
That is incorrect. It’s a not uncommon error based on a misunderstanding of special relativity.
Thank you for your posting. You make a very good point.
Nope. He’s normally spot on but on this point he’s quite wrong.
Here’s a much more recent paper on the subject of tachyons. Faster-than-light speeds, tachyons, and the possibility of tachyonic neutrinos by Robert Ehrlich, Am. J. Phys., 71(11), Now. (2003)
Faster-than-light speeds and hypothetical FTL particles known as tachyons are exciting subjects for students, given their speculative and controversial nature. This article presents an overview of these subjects and their role in special relativity and examines the possibility that one or more of the three neutrinos is a tachyon. The paper also describes several low tech demonstrations useful for teaching about faster-than-light speeds and tachyons in intermediate and advanced introductory college-level physics courses.
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Don't know why people keep arguing that ftl is relativity too?
Because the existance of particles which always move faster than the speed of light (known as a tachyon) is not inconsistent with special relativity (SR). All SR says is that you can't accelerate a particle (with real, non-zero proper mass) from a speed less than the speed of light to a speed equal to or greater than the speed of light. It doesn't say that a tachyon can't exist or that it's inconsistent with their existance. Where did you get the idea otherwise?
Relativity builds on 'c', nothing other. As soon as you discuss ftl you go away from relativity.
Nope.
FTL is something different, and also outside the borders of relativity.
Nope.
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"The Hubble constant tells us that - for every megaparsec of distance between two galaxies-, - the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second -.
Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers). " http://curious.astro.cornell.edu/question.php?number=575
This distance works out to be the radius of the observable universe, 13.8 billion light years.
I've been considering the excellent point you make, that not even spacetime expansion allows for FTL, and how that relates to cosmological models based on rapid (FTL) inflation of space in the early universe. Rather than take this thread off-topic it might be more appropriate to start a different thread. Because it's my own theory, I've put it in the Theories forum under the Lighter section: Causality, the Big Bang, and the Shape of the Cosmos.
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I've been considering the excellent point you make, that not even spacetime expansion allows for FTL, ..
Since when? Two galaxies can be traveling away from each other faster than the speed of light as a result of the epxasion of space. What are you referring to?
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It's not relativity Pete, not as I think of it. It may be consistent with an assumption of what may exist outside 'c', but it's a mathematical hypothesis to me. 'c' is relativity to me, with the equivalence principle becoming its extension to gravity. I suspect I will continue to argue that 'c', as a limit, is correct for all frames of reference, as long as we do not involve weird definitions of ftl, as defining a expansion as being ftl. Or lights propagation in matter proving ftl. You can define both without involving ftl as I think.
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I have a different take on it as I expect 'c' and a arrow of time to be locally equivalent. Using scales and that definition a arrow seems to disappear under Planck scale. And how do I define any speed, without a arrow?
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Did Einstein really consider tachyons?
Not as I get it? Did he?
https://en.wikipedia.org/wiki/Tachyon
As far as I get it this is a term created by "Gerald Feinberg (27 May 1933, New York City – 21 April 1992, New York City)" and he thought of it in terms of analyzing their quantum field properties. "In the 1967 paper that coined the term, Feinberg proposed that tachyonic particles could be quanta of a quantum field with negative squared mass. However, it was soon realized that excitations of such imaginary mass fields do not in fact propagate faster than light, and instead represent an instability known as tachyon condensation. Nevertheless, negative squared mass fields are commonly referred to as "tachyons", and in fact have come to play an important role in modern physics."
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It's not relativity Pete, not as I think of it.
Actually it is relativity as the physics community thinks of it.
It may be consistent with an assumption of what may exist outside 'c', but it's a mathematical hypothesis to me.
Here you've taken a tangent to the conversation. What are you talking about when you say exist outside 'c'? Also, there are no mathematical hypotheses in SR, only physical ones.
'c' is relativity to me, …
That’s fine but irrelevant since we’re not talking about particles moving at the speed of light here. And even if we were we all know that SR let’s particles move at the speed of light. A particle that always moves at the speed of light is called a Luxon.
I suspect I will continue to argue that 'c', as a limit, is correct for all frames of reference, as long as we do not involve weird definitions of ftl, as defining a expansion as being ftl.
I simply don’t understand why you brought “c”: into this discussion? Why? Where does it fit into it?
And how do I define any speed, without a arrow?
Only velocity requires an “arrow,” not speed since speed is the magnitude of the velocity vector.
Did Einstein really consider tachyons?
No. However relativity isn’t defined strictly by the applications he mentioned in that article.
As far as I get it this is a term created by "Gerald Feinberg (27 May 1933, New York City – 21 April 1992, New York City)" and he thought of it in terms of analyzing their quantum field properties. "In the 1967 paper that coined the term, Feinberg proposed that tachyonic particles could be quanta of a quantum field with negative squared mass. However, it was soon realized that excitations of such imaginary mass fields do not in fact propagate faster than light, and instead represent an instability known as tachyon condensation. Nevertheless, negative squared mass fields are commonly referred to as "tachyons", and in fact have come to play an important role in modern physics."
I don’t know what …that excitations of such imaginary mass fields do not in fact propagate faster than light[/quote] means since its conceivable that tachyons exist and if they do their mass will be imaginary.
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Then you can direct me to where Einstein discuss tachyons? I looked for it but couldn't find it Pete. As far as I can see it seems to be a later addition to relativity? Ahh, okay. Saw you write he didn't. Well, if the physics community thinks it to exist :) I don't.
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How do you get to the "magnitude of the velocity vector." without a arrow?
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As for why I don't think about it that way (ftl existing) has a lot to do with how I think of indeterminacy, instead of virtual particles (of such short 'time sequences' that they doesn't 'exist') too. It's something not having to do with how we define as a speed at all, to me that is. A indeterministic property that you can use statistics and probability for, but not a speed.
I've wondered about the definition of 'virtual particles before Pete. In Are virtual particles exclusively virtual, or do some exist in reality too? (http://www.thenakedscientists.com/forum/index.php?topic=45847.0)
And the link I have there is still good, as I think. http://www.mat.univie.ac.at/~neum/physfaq/topics/virtual
I can put it this way too, as a reason. Scaling something down we meet statistics and probability, quantum entanglements and lights duality. But I can't see how it would change the measurements we make macroscopically, scaling a universe up instead of down, from where we find ourselves at a daily basis. It's when scaling down I meet those 'new' QM phenomena, as far as I know that is. Scaling up 'c' will be 'c', scaling down we meet Planck scale.
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look at : Aharonov, Y.; Komar, A.; Susskind, L. (1969). "Superluminal Behavior, Causality, and Instability". Phys. Rev. (American Physical Society) 182 ({5},): 1400–1403. Bibcode:1969PhRv..182.1400A. doi:10.1103/PhysRev.182.1400 for "However, it was soon realized that excitations of such imaginary mass fields do not in fact propagate faster than light." You can find direct links to it in https://en.wikipedia.org/wiki/Tachyon
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Well, if the physics community thinks it to exist :) I don't.
Yes. We know that you don’t think so. Therefore you don’t have to keep repeating it.
Also, nobody said that the physics community thinks tachyons exists. That article I quoted only states that they haven’t ruled out one of he neutrinos as being a tachyon. All that I said was that the physics community knows that the existence of a tachyon does not contradict the principles of relativity.
Tell you what. To demonstrate this I recommend that you attempt to prove that the existence of tachyons proves SR is wrong. You’ll find that it’s impossible to do so.
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How do you get to the "magnitude of the velocity vector." without a arrow?
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As for why I don't think about it that way (ftl existing) has a lot to do with how I think of indeterminacy, instead of virtual particles (of such short 'time sequences' that they doesn't 'exist') too. It's something not having to do with how we define as a speed at all, to me that is. A indeterministic property that you can use statistics and probability for, but not a speed.
They have nothing to do with each other.
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Sometimes infinity really is infinity. Relativity has some. For example, if you apply some finite acceleration to an object with non-zero rest mass, like a bowling ball or a proton:
Question: How long will it take to accelerate the object to the speed of light?
Answer: Infinitely long
That position sounds all well and good but what about the inflationary period following the big bang? It is surmised that during this event, the speed of light was exceeded, and it didn't take eternity or infinitely long to reach.
The only justification for the idea that the cosmos underwent a period of superluminal inflation immediately after the Big Bang is the homogeneity of matter through space. That's it. It's just a means to explain uniformity.
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I've been considering the excellent point you make, that not even spacetime expansion allows for FTL, ..
Since when? Two galaxies can be traveling away from each other faster than the speed of light as a result of the epxasion of space. What are you referring to?
No such thing is observable. To quote a phrase, "What are you referring to?"
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No such thing is observable. To quote a phrase, "What are you referring to?"
A well known and widely accepted part of the Big Bang theory is that some galaxies recede from us faster than the speed of light due to what is known as universal expansion. See http://en.wikipedia.org/wiki/Faster-than-light#Universal_expansion
The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies.
See also http://www.universetoday.com/13808/how-can-galaxies-recede-faster-than-the-speed-of-light/
Question: How Can Galaxies Move Away Faster Than Speed of Light?
Answer: Einstein’s Theory of Relativity says that the speed of light – 300,000 km/s – is the maximum speed that anything can travel in the Universe. It requires more and more energy to approach the speed of light. You could use up all the energy in the Universe and still not be traveling at light speed.
As you know, most of the galaxies in the Universe are expanding away from us because of the Big Bang, and the subsequent effects of dark energy, which is providing an additional accelerating force on the expansion of the Universe.
Galaxies, like our own Milky Way are carried along by the expansion of the Universe, and will move apart from every other galaxy, unless they’re close enough to hold together with gravity.
As you look at galaxies further and further away, they appear to be moving faster and faster away from us. And it is possible that they could eventually appear to be moving away from us faster than light. At that point, light leaving the distant galaxy would never reach us.
Such rapidly moving galaxies are said to have a high value of cosmological redshift. z . If z is large enough then that galaxy is moving FTL as reckoned by observers at rest in one of the two galaxies.
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No such thing is observable. To quote a phrase, "What are you referring to?"
A well known and widely accepted part of the Big Bang theory is that some galaxies recede from us faster than the speed of light due to what is known as universal expansion. See http://en.wikipedia.org/wiki/Faster-than-light#Universal_expansion
The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies.
Using the Hubble "constant", the recession rate of matter at the observable horizon is the speed of light. Everything in our universe seems to be within this bubble of space.
Comoving distances have no real justification in science and certainly not in Relativity. The comoving distance is a value based on a godlike perspective outside of spacetime. While it might have value as a way of speculating how things might work, it's unobservable and has no real physical consequence.
See also http://www.universetoday.com/13808/how-can-galaxies-recede-faster-than-the-speed-of-light/
Question: How Can Galaxies Move Away Faster Than Speed of Light?
Answer: Einstein’s Theory of Relativity says that the speed of light – 300,000 km/s – is the maximum speed that anything can travel in the Universe. It requires more and more energy to approach the speed of light. You could use up all the energy in the Universe and still not be traveling at light speed.
As you know, most of the galaxies in the Universe are expanding away from us because of the Big Bang, and the subsequent effects of dark energy, which is providing an additional accelerating force on the expansion of the Universe.
Galaxies, like our own Milky Way are carried along by the expansion of the Universe, and will move apart from every other galaxy, unless they’re close enough to hold together with gravity.
As you look at galaxies further and further away, they appear to be moving faster and faster away from us. And it is possible that they could eventually appear to be moving away from us faster than light. At that point, light leaving the distant galaxy would never reach us.
Such rapidly moving galaxies are said to have a high value of cosmological redshift. z . If z is large enough then that galaxy is moving FTL as reckoned by observers at rest in one of the two galaxies.
The current interpretation of Relativity is that nothing can exceed c within spacetime but that spacetime can be deformed or stretched at any rate. Maybe, maybe not. I only noted that yor_on had made a valid point, that no matter what the mechanism, no superluminal effects can be observed.
Again, the only justification for suggesting a period of rapid inflation immediately after the Big Bang is the uniformity of the distribution of matter throughout the observable universe.
I think it's much more likely that we are NOT in a unique period in the history of the cosmos. It seems more likely to me that most of the facts discounted as coincidences are in fact consequences of rules we don't fully appreciate.
For example, anything emitted at time = zero and travelling at the speed of light would be within our observable horizon. Since matter was probably dense and hot enough to be opaque then, we couldn't receive light from there/then. But, we should still receive light from the surface of last scattering. Contemporary thought has it that accelerating spacetime inflation will push that outside of our observable horizon. Maybe, but there are other possibilities.
The instantaneous appearance of the observable universe satisfies (to within 3%) the requirements for a Schwarzschild black hole: zero spin, zero charge, and radius/mass = 2G/c2. If this is a requirement and not a coincidence then one requirement would be that matter would accelerate apart at an increasing rate. This is because the radius and mass would be directly proportional but, because the observable universe is a spherical volume, the mass density would have to drop off in proportion to (age of universe)2.
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The idea behind a inflation is not a 'speed' per se, not to me at least. If I want to give a inflation a speed I first have to define some origin from where I can use a clock and ruler to measure that 'speed' with. Inside a vacuum, without reference points, that should be a impossibility as I think. Also it is so that if there is no center to a universe, neither it should be to inflation or a expansion, meaning that inflation should be in all 'points', to make sense to me. to call it ftl presumes a ruler and a clock to measure it by, with reference points.
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So, using my own arguments here, you might be able to call a accelerating expansion for 'ftl' :) but a 'ftl' is defined by a locally measured 'infinite blueshift' (and redshift depending on 'motion') at least as we move uniformly relativistically close to light, relative some reference point . Earth should also be doing 'ftl', or just under then, depending on what possible reference star we want to use to measure that 'speed' relative. Do we find a local infinite blueshift in some direction? And a infinite redshift in the opposite?
And one also have to remember that we can pick any reference point (as a star) we want, to get to different uniform 'speeds', depending on the distance measured between our reference points. The only measurable way to relate a speed to a uniform motion is relative some other object, as a star, or the CBR, or just measure incoming light. But it's all dependent on your reference points as it seems to me.
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Comoving distances have no real justification in science and certainly not in Relativity.
Wow! Where did this from? Nobody mentioned them in this thread I can see so I don’t understand why you raised the subject? Please explain.
By the way, there’s no such thing as a commoving distance. I was talking about commoving coordinate. The justification in relativistic cosmology is their usage. That usagage is as an identifier of the location of the galaxy, i.e. as a sort of “address” of the galaxy.
The comoving distance is a value based on a godlike perspective outside of spacetime.
[//quote]
The same can be said of your house.
While it might have value as a way of speculating how things might work, it's unobservable and has no real physical consequence.
Their physical reality is their use as a way to locate a galaxy in the cosmos relative to the established coordinate system.
The current interpretation of Relativity is that nothing can exceed c within spacetime but that spacetime can be deformed or stretched at any rate. Maybe, maybe not.
In the wonderful world of physics, in this case the branch known as relativistic cosmology, it’s the way it is according to current theory and as verified by observation. Outside that theory I have no interest in discussing. First publish it and then I’ll talk to you about it. I don’t do “new theory” here.
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The idea behind a inflation is not a 'speed' per se, not to me at least. If I want to give a inflation a speed I first have to define some origin from where I can use a clock and ruler to measure that 'speed' with.
Redshift. Identify the spectrum of some common element, like hydrogen, and look for it redshifted.
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Comoving distances have no real justification in science and certainly not in Relativity.
Wow! Where did this from? Nobody mentioned them in this thread I can see so I don’t understand why you raised the subject? Please explain.
You added it to the thread. Check out your post of 04/12/2013 02:32:55.
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Don't know current theory on the event horizon where is it's position around a black hole.
Inside it.
At it's surface.
Or outside it.
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Depends on type of black hole, and what 'frame of reference' you will use, measuring it. A non rotating black hole can from its inside be measured, theoretically, as we can't communicate with that inside, as having a greater volume than what you would find measuring its circumference, orbiting it from outside a event horizon. Weird, isn't it? :)
From the outside you will still find all sorts of definitions of what a event horizon might be, depending on types.
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Depends on type of black hole, and what 'frame of reference' you will use, measuring it. A non rotating black hole can from its inside be measured, theoretically, as we can't communicate with that inside,
Using current theory, this statement is very true. There is one possibility however that may give us opportunity to communicate with the inside. Because gravity's influence can be felt outside the event horizon, we may someday be able to discover details about conditions lying inside using gravitational energies as the message carrier. Just a thought............................
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Two questions come to mind.
How strong is the evidence for non-rotating black holes?
If gravity is a distortion of spacetime, would gravity ever be able to tell us more than the mass of the object in question?
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Two questions come to mind.
How strong is the evidence for non-rotating black holes?
If gravity is a distortion of spacetime, would gravity ever be able to tell us more than the mass of the object in question?
Probably only if we become technologically able to detect perturbations in the gravity field itself will we be able to extract information about what's going on inside.
We know that neutron stars rotate with exceedingly great velocities. This fact makes the likelihood for black hole rotation notable. I don't think we have irrefutable evidence yet because physically locating these objects is quite difficult even though it is proposed that one lies at the center of just about every galaxy. One possible evidence for this phenomenon are the observed polar jets of energy coming from distant quasars. This suggests the presence of a rotating black hole at their centers but is not conclusive proof for that proposition even though it remains a strong hypothesis.
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How strong is the evidence for non-rotating black holes?
I don't understand this question. Are you asking if there's any evidence that black holes exist or are you asking of there is any evidence that black holes whare aren't rotating exist? If it's the later then that's like asking me for evidence that planets exist that aren't rotating. How would you answer such a question?
If gravity is a distortion of spacetime, ...
Which it's not. Tidal forces are a curvature in spacetime. Please define the term distortion of spacetime for me.
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Don't think there are any evidence for non rotating black holes? Then again, maybe it can exist some semi stable solution in a universe?? But I don't think personally, that they can exist 'for ever', non rotating, in a dynamically (gravitationally) updated universe through 'c'? I'm not sure though, just a guess.
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Don't think there are any evidence for non rotating black holes?
Do you think that there's any evidence of neutron starts that rotate once every 1.0437482340840813408237402384501384023872380237489327059817 seconds?
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Well Pete, do you have evidence for non rotating black holes?
Feel free to present them, I have not seen any myself?
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Well Pete, do you have evidence for non rotating black holes?
Feel free to present them, I have not seen any myself?
I don't understand why you expect me to answer your question when you won't answer mine which was asked to make a very serious point. If you answer my question then I'll answer yours.
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Are you arguing that a neutron star must lose angular momentum to debris etc, and at some point stop rotating? And that the same then should be for a rotating black hole? Why not argue that gravity, as its reach is infinite, then also must transfer angular momentum to neutron stars?
You can see it, angular momentum, in binary stars, and also 'gravitational waves', but if you have a isolated neutron star? As for a black hole I still have seen no evidence for non rotating black holes? And that was what I asked if you had?
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Are you arguing that a neutron star must lose angular momentum to debris etc, and at some point stop rotating?
There you go again. Asking me another question expecting me to answer it and yet refusing to answer the question I asked you first. Why do you expect me to answer your question when you refuse to answer mine?
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Ok, fair is fair, yes, there should be all sorts of spin so it's a possibility. Not that I get what you are referring to there? We were discussing if a non rotating black hole could exist, and personally I don't think it does, I know no evidence of it anyway? So I presume your point to be about that?
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Ok, fair is fair, yes, there should be all sorts of spin so it's a possibility.
And the same thing is true with black holes because zero spin is just one example of a rotating black hole.
If you have two rotating black holes with the same magnitude of angular momentum but opposite direction and they collided then the new black hole which formed as a result would be non-rotating. There’s nothing in nature that says that non-rotating black holes can’t exist. I can’t even imagine why you’d claim otherwise. What’s your argument to justify such an assertion?
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Simply that they are nowhere to be seen, as far as I know? Also assuming, now ignoring the possibility you put forward, that black holes must get a increased angular momentum while compressing. I used to think of non rotating as a possibility, but the more time pass without astronomical proofs, the more I wonder.
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How strong is the evidence for non-rotating black holes?
I don't understand this question. Are you asking if there's any evidence that black holes exist or are you asking of there is any evidence that black holes whare aren't rotating exist? If it's the later then that's like asking me for evidence that planets exist that aren't rotating. How would you answer such a question?
If gravity is a distortion of spacetime, ...
Which it's not. Tidal forces are a curvature in spacetime. Please define the term distortion of spacetime for me.
Curvature is a very misleading term and I hate that early physicists chose it to describe the effect. It is a compression of spacetime. Curvature has nothing to do with it at all. The flat plane diagrams used to depict gravity wells were only a device to make the concept somewhat understandable.
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Two questions come to mind.
How strong is the evidence for non-rotating black holes?
If gravity is a distortion of spacetime, would gravity ever be able to tell us more than the mass of the object in question?
Probably only if we become technologically able to detect perturbations in the gravity field itself will we be able to extract information about what's going on inside.
We know that neutron stars rotate with exceedingly great velocities. This fact makes the likelihood for black hole rotation notable. I don't think we have irrefutable evidence yet because physically locating these objects is quite difficult even though it is proposed that one lies at the center of just about every galaxy. One possible evidence for this phenomenon are the observed polar jets of energy coming from distant quasars. This suggests the presence of a rotating black hole at their centers but is not conclusive proof for that proposition even though it remains a strong hypothesis.
The high velocities of rotation for neutron stars is a puzzle. Under compression time dilation should go up. This seems to suggest that the mass generating the gravitation is itself immune from the dilation.
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Two questions come to mind.
How strong is the evidence for non-rotating black holes?
If gravity is a distortion of spacetime, would gravity ever be able to tell us more than the mass of the object in question?
There seem to be a few posts taking off from this point, Bill, so pardon me for digging it up, please. :)
Regarding your first question, a non-rotating black hole is probably about as uncommon as a non-rotating star or planet--i.e. extremely unlikely to appear. This isn't due to fundamental physics: a non-rotating black hole isn't particularly special. It's due to the fact that there are many, many, many more ways for something to rotate than the one way for it to not rotate. So the odds of a black hole forming naturally with zero rotation is quite likely to be near-infinitesimal.
Now, for your second question gravity is a result of curved space-time, and this curvature results from two things: energy and momentum and their flows in space and time. Mass is one component of energy, which is why mass creates gravity, but a rotating object has angular momentum which can also curve space-time. This is why rotating black holes should look different than non-rotating black holes. Black holes also should emit electromagnetism if they are charged. The classical explanation for this is that a black hole looks like a "frozen star" in the sense that the time it takes light to reach us outside the black hole increases to infinity as the source of the light approaches the event horizon. In-falling charged matter will therefore appear to us to be close to the event horizon and emitting electromagnetic fields.
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Thanks JP, it's good to get an answer to a question "as asked", rather than "as interpreted". :)
Happy New Year. (That's for everyone, not just JP).
I'm going before the scotch cuts in.
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How strong is the evidence for non-rotating black holes?
I don't understand this question. Are you asking if there's any evidence that black holes exist or are you asking of there is any evidence that black holes whare aren't rotating exist? If it's the later then that's like asking me for evidence that planets exist that aren't rotating. How would you answer such a question?
If gravity is a distortion of spacetime, ...
Which it's not. Tidal forces are a curvature in spacetime. Please define the term distortion of spacetime for me.
Curvature is a very misleading term and I hate that early physicists chose it to describe the effect. It is a compression of spacetime. Curvature has nothing to do with it at all. The flat plane diagrams used to depict gravity wells were only a device to make the concept somewhat understandable.
Sorry Jeffery but I don't see how you get to a 'compression' of a vacuum? And a geodesic passing a sun is assumed to be curved, theoretically as we can't follow a light path any other way. We could use 'weak experiments' measuring identical paths by identical photons at different positions, but for a single 'photon' it only can be defined by its origins recoil, and at the 'photons' annihilation. In reality we only can measure a photon once, annihilating.
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This one is nice, as always :)
"A ray of starlight grazing the sun would be bent as the light fell into the sun's gravitational field. This bending would be manifested as a displacement of the star's apparent position in the sky and this displacement would be visible at the time of solar eclipse.
In 1907, Einstein had predicted the gravitational bending of light. But he did not realize that it might actually be tested at the time of a solar eclipse. After his 1907 Jahrbuch article, Einstein's efforts were redirected towards the puzzle of the quantum. In 1911, however, he returned to theorize about gravity. He realized then that his prediction of the gravitational bending of light could be tested at a solar eclipse. He wrote another paper developing this idea and also other aspects of his theory." By John D Norton. (http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/general_relativity_pathway/)
But Einstein built it on a idea of a bent light path. "For the physicist accelerating with the box, however, the light will be judged to fall, just like everything else in the box. As a result, the physicist will find the light's path to be bent downward by the gravitational field." More often described as a elevator thought experiment if I remember right. Although the same restrictions goes for that one as for any other light path one see. It's only the annihilations we observe.
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How strong is the evidence for non-rotating black holes?
I don't understand this question. Are you asking if there's any evidence that black holes exist or are you asking of there is any evidence that black holes whare aren't rotating exist? If it's the later then that's like asking me for evidence that planets exist that aren't rotating. How would you answer such a question?
If gravity is a distortion of spacetime, ...
Which it's not. Tidal forces are a curvature in spacetime. Please define the term distortion of spacetime for me.
Curvature is a very misleading term and I hate that early physicists chose it to describe the effect. It is a compression of spacetime. Curvature has nothing to do with it at all. The flat plane diagrams used to depict gravity wells were only a device to make the concept somewhat understandable.
Sorry Jeffery but I don't see how you get to a 'compression' of a vacuum? And a geodesic passing a sun is assumed to be curved, theoretically as we can't follow a light path any other way. We could use 'weak experiments' measuring identical paths by identical photons at different positions, but for a single 'photon' it only can be defined by its origins recoil, and at the 'photons' annihilation. In reality we only can measure a photon once, annihilating.
What do you think space is? It is a vacuum. You do not need an atmosphere around a celestial body or any particles at all for the gravitation to bend light. So what else is being effected? Every electron in the whole universe has to have a different energy state to every other electron. Although this is always an infinitesimal difference that is what quantum theory states. Also an electron has to be thought of as following every possible path to get to its destination. The universe contains a lot of what we think of as nothing so what does this imply? This is the spooky action at a distance that Einstein disliked so much and follows from the Pauli exclusion principle. So when you tell me that the vacuum cannot be compressed think of the expansion of the universe where the vacuum is pushing galaxies apart.
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Sorry, that's not enough to define it. How do you get to a compression of a vacuum?
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One could consider using 'Casimir force', two plates, almost touching, assuming a energy (neutral) existing in a perfect vacuum. That one is from that perspective mostly defined by waves, some fitting between the plates, others unable to as the distance between plates shrink, so creating a imbalance in the local vacuum, drawing plates together. But that's no compression to me. (If anything one might consider such an idea a 'local suction' :)
I do not know how to compress a vacuum Jeffrey?
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Sorry, that's not enough to define it. How do you get to a compression of a vacuum?
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One could consider using 'Casimir force', two plates, almost touching, assuming a energy (neutral) existing in a perfect vacuum. That one is from that perspective mostly defined by waves, some fitting between the plates, others unable to as the distance between plates shrink, so creating a imbalance in the local vacuum, drawing plates together. But that's no compression to me. (If anything one might consider such an idea a 'local suction' :)
I do not know how to compress a vacuum Jeffrey?
Consider the celestial body to be very large. We assume that gravitation with include a length contraction element and will have an effect on not only an orbiting body but also light. If the surroundings of the body contain no material matter other than 1 orbiting body then that body will undergo contraction and light will be effected. If light leaves the orbitting body it is travelling through a length contraction. So what exactly is contracted? It is travelling through a vacuum so there is no mass to contract.
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Jeffrey, either one define a universe constricted, that represent a 'fish bowl'. In such a universe a Lorentz contraction still will be observer dependent though, meaning that as we have a fish bowl to go out from I can make smaller fish bowls in it, 'systems' that I limit by some mean. In my 'system' I can define as many observers I like. Each observer having a different motion relative all other observers. I can also let each observer inside that 'system' represent a different mass. Each one of those observers inside my 'system' will measure a different time dilation, and defining a Lorentz contraction as a complementary description to a time dilation, depending on frame of reference you use for your observation, there also will be differently Lorentz contracted 'fishbowls', all locally defined.
Either that is a illusion, or it is true. If it is true then using a 'fish bowl' perspective becomes very tricky, as the system you defined is observer dependent, and also as there is no frame of reference more right than any other, including the one you used defining that 'system'. One also need to acknowledge that a Lorentz contraction makes no difference between a vacuum and 'mass', for example looking in the direction one travel at a relativistic speed.
It is observer dependent.
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Jeffrey, either one define a universe constricted, that represent a 'fish bowl'. In such a universe a Lorentz contraction still will be observer dependent though, meaning that as we have a fish bowl to go out from I can make smaller fish bowls in it, 'systems' that I limit by some mean. In my 'system' I can define as many observers I like. Each observer having a different motion relative all other observers. I can also let each observer inside that 'system' represent a different mass. Each one of those observers inside my 'system' will measure a different time dilation, and defining a Lorentz contraction as a complementary description to a time dilation, depending on frame of reference you use for your observation, there also will be differently Lorentz contracted 'fishbowls', all locally defined.
Either that is a illusion, or it is true. If it is true then using a 'fish bowl' perspective becomes very tricky, as the system you defined is observer dependent, and also as there is no frame of reference more right than any other, including the one you used defining that 'system'. One also need to acknowledge that a Lorentz contraction makes no difference between a vacuum and 'mass', for example looking in the direction one travel at a relativistic speed.
It is observer dependent.
You do realize of course that the vacuum you propose according to quantum physics is seething with Higgs bosons and elementary particles popping into and out of existence all the time.
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The vacuum 'system' I describe is from Einsteins definitions Jeffrey. And QM is not relativity, although most of us, you and me too, would like for them to join together, into one description making sense. Time dilations and Lorentz contractions are existent everywhere, gravitationally and motion wise. And they are proved to exist by NIST, as well as by others, experimentally.
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The vacuum 'system' I describe is from Einsteins definitions Jeffrey. And QM is not relativity, although most of us, you and me too, would like for them to join together, into one description making sense. Time dilations and Lorentz contractions are existent everywhere, gravitationally and motion wise. And they are proved to exist by NIST, as well as by others, experimentally.
I would agree with all of that.
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The October issue of Astronomy magazine presents an excellent explanation of why black holes cannot have event horizons. Looks like Einstein was right.
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Think there was an idea using a definition in where no matter ever reached past that event horizon using time dilation. But a time dilation is observer dependent, several observers of a same object might give it different 'clocks', 'simultaneously'. The only case in where you prove a time dilation to exist indefinitely after is the one in where you arrange a twin experiment, as far as I can see, practically that is.
If you split 'c', using it as your local clock. Then to get to a situation in where you don't pass the event horizon, you will have to change your local measurement of 'c'. And 'c' is 'c'. That's what I understand SR to build on, that and Maxwell's equations. Can you see how I think there? To say that I can't pass that event horizon is the same as telling me that 'c' won't be 'c'. That local clock never stops, and according to that and displacements, you will pass.
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The October issue of Astronomy magazine presents an excellent explanation of why black holes cannot have event horizons. Looks like Einstein was right.
Thanks for bringing this to my attention. I know that such claims like "there are no black holes" etc. more often than not come from crackpots and cranks. But in this case the assertion came from Steven Hawking and in Nature magazine! See: http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583
Most physicists foolhardy enough to write a paper claiming that “there are no black holes” — at least not in the sense we usually imagine — would probably be dismissed as cranks. But when the call to redefine these cosmic crunchers comes from Stephen Hawking, it’s worth taking notice. In a paper posted online, the physicist, based at the University of Cambridge, UK, and one of the creators of modern black-hole theory, does away with the notion of an event horizon, the invisible boundary thought to shroud every black hole, beyond which nothing, not even light, can escape.
The paper which he wrote about this is at http://arxiv.org/abs/1401.5761
Event horizons are funny things. I've always been unsure about them because they can't be observed.
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Maybe you read this one Pete? Alternatives, linked by Dlorde, As for which one is most close to reality I don't know, but I find Bees approach to it, as being a paradox that logically fails, interesting. I just can't make me believe in the idea of a 'firewall', https://medium.com/starts-with-a-bang/yes-virginia-black-holes-exist-df0a131d7b95
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Well Hawking's paper was brief but very interesting.