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Why do people think Relativity predicts event horizons?

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.

Can anyone here explain why the accepted model changed?

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 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.

Quote from: AndroidNeoxWhy do people think Relativity predicts event horizons?The laws of physics predicts them.

Quote from: Pmb on 12/11/2013 00:22:03Quote from: AndroidNeoxWhy 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.

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.==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 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. ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

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?

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.

I do not expect 'time' to become 'space' and 'space' become 'time' for a infalling observer.

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.

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.

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.

Quote from: JP 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

Quote from: jeffreyH on 20/11/2013 01:37:43Oh 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?

Question: How long will it take to accelerate the object to the speed of light?Answer: Infinitely longQuestion: How much energy will be required to accelerate the object to the speed of light?Answer: Infinite energy

Quote from: AndroidNeox on 20/11/2013 02:38:20Sometimes 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 longThat 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.

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.

But, you're right. If there are any conditions under which something can exceed c, no matter the mechanism, relativity is violated.

Thank you for your posting. You make a very good point.

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.

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.

FTL is something different, and also outside the borders of relativity.

"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). " ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

I've been considering the excellent point you make, that not even spacetime expansion allows for FTL, ..

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, …

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.

And how do I define any speed, without a arrow?

Did Einstein really consider tachyons?

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."

Well, if the physics community thinks it to exist I don't.

How do you get to the "magnitude of the velocity vector." without a arrow?=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.

Quote from: AndroidNeoxI'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?"

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.

Quote from: AndroidNeoxNo 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 ...sorry, you cannot view external links. To see them, please REGISTER or LOGINQuoteQuestion: 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.

Comoving distances have no real justification in science and certainly not in Relativity.

While it might have value as a way of speculating how things might work, it's unobservable and has no real physical consequence.

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.

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.

Quote from: AndroidNeoxComoving 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.