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Author Topic: Event Horizons are Impossible: Any flaws in this thought experiment?  (Read 7078 times)

Offline AndroidNeox

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I have a thought experiment that I think is valid and correct and would be grateful if you would look it over.

Like Hawkingís black hole, BH, thought experiment, I have a platform (pictured below) fixed in space with respect to some Schwarzschild (zero charge & spin) BH. The platform is some sufficiently large distance from the BH so that relativistic gravitational effects are negligible.

On the platform is mounted a winch (or a wench, if sheís strong enough) that can raise and lower a rope, from which is suspended an ideal mirror (zero thickness) hanging horizontally above the black hole (Hawking used a box of light with perfect mirrors lining the boxÖ so, I just mostly use equipment he left behind).  On the platform is a laser that shines a beam down into the gravity well to reflect on the mirror and return to the platform where another device detects it. The wi/ench lowers the mirror, feeding out rope at a fixed rate.

Sitting on the mirror is a device that measures the wavelength of light being reflected and thereby calculates the current relative time flow rate on the platform WRT at the mirror. Also, it counts each light wave cycle and calculates the time on the platform when the light was transmitted.

Light reflected from the mirror is detected at the platform. Because it is returning to the same gravitational potential energy level as it began, relativistic effects are cancelled out and only the doppler shift from the mirrorís constant motion should be detectable.

Suppose the laser has a detector & wave counterÖ counting each phase cycle of the laserís beam. Before the mirror begins its descent, the counters are set up so that each wave sent by the laser increases the count and each received by the device decreases the count. Dividing by two will give the amount of rope the winch has payed out (in wavelengths).

When the mirror reaches the event horizon, the light it has reflected has been infinitely blue-shifted. This requires the laser to have sent infinitely many light wave cycles. The laser will have been sending out light long before it sent the light that reached the mirror, infinitely blue-shifted. Before an object moving at a constant rate, WRT external observers, reaches an event horizon, an infinite amount of time passes on the platform.

The argument extends to objects, e.g. mirrors, in free fall. The mirror will always be moving slower than light and so will be reflecting light infinitely blue shifted, WRT the platformís frame.

An event horizon can only form by swallowing matter. That is, matter must cross the event horizon from the perspective RF outside the event horizon. However, from the perspective of an observer (distant enough so that the black holeís gravity is insignificant) the infalling matter can never reach the event horizon.

Does it not bother GR physicists that formation of an event horizon would violate one of the assumptions of Relativity? i.e. All frames of reference are equally valid for the purposes of observation. When an argumentís conclusion violates one of its premises, that is proof that either the premises are inconsistent (i.e. the logical basis for Relativity is self-contradictory, which I cannot believe) or the argument is wrong. Those are the only two possibilities. Mathematics, being a subset of logic, is bound by this, too.

Itís not possible to use the equations of GR to show that matter can fall to an event horizon in finite time, from any frame of reference, because itís possible to prove that the matter cannot reach the event horizon in finite time for at least one frame of reference. Thatís all the proof thatís necessary, logically. Because crossing the event horizon is causally inconsistent with at least one frame of reference, it cannot be observed from any frame of reference.



 

Offline JP

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The idea that all reference frames have to agree on measurements is wrong.  They have to agree that the laws of physics hold, and in this case they do.  Seeing something never fall past the event horizon in one reference frame is entirely consistent with the laws of physics that say that from that object's reference frame, it does pass the event horizon.

This was pointed out by those who are better than I am with general relativity in your previous thread on the subject: http://www.thenakedscientists.com/forum/index.php?topic=49543.0


There is an information paradox that says that 1-way passage of information into the black hole cause information to be irrevocably destroyed if we believe General relativity alone.  This is not consistent with the other laws of physics (quantum mechanics) that state that information shouldn't be lost in this process.  This is where a lot of active research is going on, and it may be that event horizons don't exist in the sense of classical general relativity.
« Last Edit: 28/05/2014 15:52:13 by JP »
 

Offline Bored chemist

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I'd like an answer to a related question.
What happens if I sit on the mirror as it's winched past the event horizon and back?

Whenever I have asked that before I have been told "it's impossible- you can't pull something out of a black hole".
Two points:
If you build a long enough ladder, you can climb away from the Earth into space without ever reaching the escape velocity, so the fact that the escape velocity at the EH is C doesn't matter. I'm not trying to escape it ballistically like a rocket or photon would.

There was at one stage (a few decades ago) an idea in physics that the observable universe might actually be a black hole and we are inside it.
That idea was shown to be wrong, but the point remains, if you can't tell whether or not you are in a black hole, there can't be anything "special" at the border.

So, can anyone explain to me why I can't take a ride down "into" a black hole and back?

(I'm assuming the black hole is very big so the rate of change of gravity with distance isn't big over distances like the length of the winch cable. This avoids the spaghettification issue.)
 

Offline JP

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BC, first a disclaimer: I'm a trained physicist, but not by any means an expert in general relativity. 

As I understand it, the difference between the case of trying to escape a black hole's event horizon and the earth's gravity is fundamentally different.  Why?  In the case of the earth, even though I can climb the ladder slower than the escape velocity, I'm aided in that climb by the forces holding the ladder together, which are communicated at faster than escape velocity.  Technically if you drill down far enough, it's mostly electromagnetism which moves at the speed of light. 

The problem with the case of an event horizon is that to build a ladder that you could climb out, the ladder itself would have to be rigid from points inside the event horizon to points outside of it.  For a point inside to communicate with a point outside and thus maintain the rigidity of the ladder, we'd need the force-carrier to travel faster than the speed of light.  Therefore, the ladder itself isn't going to stay together if we try to yank it out of the black hole. 

It's not necessarily going to be torn apart crossing the event horizon (that depends on the tidal forces there), but it does mean that if I try to pull it out, there is no force strong enough to do so because such a force would have to be communicated superluminally across the event horizon.
 

Offline yor_on

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Damn Jp, You're a pleasure to have with us :)
Whatever comes.
 

Offline Bored chemist

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In the case of the earth, even though I can climb the ladder slower than the escape velocity, I'm aided in that climb by the forces holding the ladder together, which are communicated at faster than escape velocity. 

Thanks for taking the time to think about it but, that information doesn't travel through the ladder at the speed of light; it travels at the speed of sound in timber.
That's a lot less than the escape velocity from the Earth, so that can't be the explanation.
 

Offline yor_on

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Think it is the last one that builds your argument AndroidNeox?


"Because crossing the event horizon is causally inconsistent with at least one frame of reference, it cannot be observed from any frame of reference."

And what I think you're saying there is that it must be a symmetry?
 

Offline yor_on

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It's a really interesting point actually. Is the universe a symmetry?
 

Offline yor_on

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 And yes BC. If you built that latter I see no immediate reason why it wouldn't hold, and giving the person time enough i see no reason why he wouldn't be able to climb 'out'. The idea, as I see it, isn't about some place becoming a closed environment. It's just adapted to the local time perspective,
 

Offline yor_on

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The idea here will be that from one one point to another we will assume that there is no incredibly forceful 'tidal force' getting into creation. that way your ladder should hold, I think? :)
 

Offline yor_on

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In fact, it's in reality a question what geometry means, in relativity
 

Offline yor_on

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To simplify it. A straight line, will it hold?
 

Offline JP

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In the case of the earth, even though I can climb the ladder slower than the escape velocity, I'm aided in that climb by the forces holding the ladder together, which are communicated at faster than escape velocity. 

Thanks for taking the time to think about it but, that information doesn't travel through the ladder at the speed of light; it travels at the speed of sound in timber.
That's a lot less than the escape velocity from the Earth, so that can't be the explanation.

The speed of sound is the macroscopic rate of communication through some chunk of material.  The speed of light is the limit on the particle-to-particle communication that holds the material together and it's what matters fundamentally when trying to pull something out of the black hole.
 

Offline Bored chemist

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Ah well, I seem to have found the answer.
"For the case of the horizon around a black hole, observers stationary with respect to a distant object will all agree on where the horizon is. While this seems to allow an observer lowered towards the hole on a rope (or rod) to contact the horizon, in practice this cannot be done. The proper distance to the horizon is finite, so the length of rope needed would be finite as well, but if the rope were lowered slowly (so that each point on the rope was approximately at rest inSchwarzschild coordinate), the proper acceleration (G-force) experienced by points on the rope closer and closer to the horizon would approach infinity, so the rope would be torn apart. If the rope is lowered quickly (perhaps even in freefall), then indeed the observer at the bottom of the rope can touch and even cross the event horizon. But once this happens it is impossible to pull the bottom of rope back out of the event horizon, since if the rope is pulled taut, the forces along the rope increase without bound as they approach the event horizon and at some point the rope must break. Furthermore, the break must occur not at the event horizon, but at a point where the second observer can observe it."
from
http://en.wikipedia.org/wiki/Event_horizon
« Last Edit: 31/05/2014 11:19:10 by Bored chemist »
 

Offline yor_on

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It's sort of weird. Just for my imagination :) let's say that I'm inside a singularity, unaffected by tidal forces, able to build that ladder going to a (my definition of a) event horizon? JP, you relate it to where all roads point inward, if I get you right. But is it so that I can consider that event horizon as equivalent to speed of light? Isn't it so that in a free fall there will be no point where I find myself disintegrating due to (my) particles inability of communication. And a event horizon, isn't that just a result of a distorted Space Time? I think the idea seems to be that at a event horizon becomes equivalent to the speed of light here as any added motion (yanking that rope/ladder away) somehow would lead to it breaking? I know I've wondered before if you would reach the speed of light passing that (observer dependent) event horizon, but on logical grounds it seems that should countermand any idea of anything ever reaching a singularity, unless we assume that the event horizons 'end' is the singularity? And even then I'm unsure how such a transition would be possible, as we're discussing matter.

Building that ladder step by step you should be able to in some infinite time reach a event horizon, I still think, maybe :) ? But, what happens there?
=

I think I could argue against myself on ground of geodesics, and the energy you need to spend to break them, and 'break through' that event horizon, though? so no, the ladder can be built but it would need a really infinite time (and energy), never ending I suspect, to even come close.

Maybe :)
« Last Edit: 31/05/2014 22:54:47 by yor_on »
 

Offline yor_on

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The point with passing a event horizon is that it is a singularity. You do not get any information back from it. You shouldn't be able to reach a infinite blue shift from that mirror unless it has, from your observation, passed that event horizon. And if it has, the communication between the mirrors frame, and yours, is gone. Up to that point you must be able to Lorentz transform between those frames to get a consistent logic. And that, I think, is what I got as your idea of there needed to be a symmetry, right?

But I don't think the inside of a singularity is a part of this symmetry, even though we expect it to exist.
==

Ahh it's me thinking wrong. The gravity, as you come really close to a singularity(event horizon) rises to infinity. The reason why we still can survive a free fall, is that you're moving with the stream, meaning that you're in a geodesic. You're 'at rest' with whatever gravitational potential there might be. And so the rope must break, as it can not be at rest with that 'infinite gravity' when you yank it up. But what about that ladder? Well, it can't be at rest as with that 'free fall', can it? So it must break too. But I'm still wondering if there is some sort of equivalence between the speed of light and a event horizon?

(This is a gross over simplification really, there is 'spagettification' too, to consider. You getting elongated/stretched as you fall into the event horizon. Maybe a simpler definition of why things break?)
=

I don't think the correct expression there is being 'at rest' really (with a gravitational potential, as I certainly would expect Pete to point out:) . When you're in a 'free fall' you're rather 'transforming away' gravity, defined from your frame of reference not there at all. And I find that one very interesting, as it opens for how one want to define this universe? If you exist in some definable sort of 'container', can gravity be transformed away? And, if it's not a 'container'? What is gravity a result of? Somehow gravity becomes a description of constant free fall, although hindered. As if all of this universe consist of a free fall toward some 'center' :) gravity coming into play when geodesics gets broken or changed, by matter, energy, etc. That's a pretty weird thought, isn't it? And is it a motion, or a force? One perfectly spherical body of a even matter density in a empty (flat) space, which way points gravity? And where is its motion?
« Last Edit: 01/06/2014 01:30:53 by yor_on »
 

Offline yor_on

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And no, I can't find a equivalence for the speed of light as compared to gravity? A 'photon' has a momentum, dependent on its energy. It doesn't try to leave anything, captured inside a event horizon. The path it find is decided by the least, (as in no), expenditure of energy, all as I think of it. And that means gravity define the geodesics. Those geodesics must exist everywhere we expect light propagating. So we have to assume that they exist inside a event horizon too.

If now gravity was a force? Shouldn't there be a equivalence between somewhere near a infinity of gravity and lights speed in a vacuum? Because if I define gravity as a force, then it must 'force' that photons geodesic, mustn't it?. And if it does, how can those photon paths be without loss of energy? To it one can add that the minimum lifetime of a propagating photon seems to be a billion billion years, as calculated by black body radiation from the birth of the universe. http://www.nature.com/news/big-bang-light-reveals-minimum-lifetime-of-photons-1.13474

« Last Edit: 01/06/2014 01:22:41 by yor_on »
 

Offline dlorde

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The point with passing a event horizon is that it is a singularity.
The event horizon isn't a singularity; the singularity is the notional point that causes the gravitational field of which the event horizon is a feature. At the event horizon, the escape velocity is c, the gravity doesn't become infinite at the event horizon, nor do the tidal forces. For a very large (e.g. galactic) black hole, the tidal forces might not even be noticeable to a human at the EH.
 

Offline yor_on

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Yes, that's true. There are several ideas of what happens when you pass a event horizon though. Myself I used to think of it as if its inside had a center, observer dependent or not, and that was (I think? Been a very long time since I wondered about that one) where I also wondered if you would reach the speed of light, at least getting infinitesimally close to it. But then, later, I've seen other definitions in where everything inside that event horizon become a 'center' too? Black holes are on the whole a very weird expression of the universe. And the last part you wrote about was what I was thinking of arguing about no tidal forces inside it.

What I can't pass though is a strange feeling of that there should be something binding together absolutes, as a 'infinite gravity' and a 'absolute speed limit of light'. Then again, it sort of depends on how you define a propagation, doesn't it? Without a propagation, if we now assume some field with excitations instead, I believe we can get to the same logic that we use describing a propagation, and limits. But I still can't shake away the feeling that there should be something binding those together, using propagation. It's also a little like a 'translation' of one logic to another, propagation or no propagation. If you do it you still will find limits? And what you define as a limit from one type of description should then have its representation/equivalence in that other type of logic, somehow everything comes down to symmetries for me :) Even this.
 

Offline yor_on

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It's in a way about semantics too. Let's assume that a infinite gravity should give you a infinite speed, as per its gravity 'accelerating' you infinitely :) And as we define both to information carriers telling the universe to behave in a logical way, we then should be able to define both to 'c'. Anything outside of that definition then becomes a singularity of its own, as tachyons, unmeasurable, solely theoretical. But using this logic, then defining it such as the event horizon is the place from where all ways point into a singularity, the event horizon also becomes my barrier between what is known physics, and what is unknown. And then anything inside this point of no return also should be a center, by a same reason as light have no way out.
=

There are so many ways to think about it Dlorde :) It can drive one nuts actually. I prefer to look at the universe from constants, using them to define the machinery, nuts and bolts :) of it. Then what isn't inside that logic becomes singularities. Doesn't matter how a tachyon sees the universe, or if it even would exist for such a entity. We exist anyway, and we define our universe. All ideas of propagation leads to imponderable conclusions, from what a 'photon' would see, to ??

Easier to look at it from a reasoning in where waves is a description over frames of reference, 'photons' a description of locality. And a field is okay to me, what's not okay is not asking oneself from where it comes, what its 'limits' are. Either we have a 'container model' in where we find this field, or the 'field' is what defines a container. Because the logic we use normally define motions, accelerations, and propagation, existing inside a 'room & time'. All of them able to be questioned, from relativity as well as from quantum mechanics.
==

One very simple description is Astronomy, and that link I gave earlier. It goes out from measuring on a existing room, from that and what we know of black body radiation defining a minimal life time to a photon. Dimensions also builds on a assumption of them being something primeval to me? Although I'm not sure how strings and loops really consider that, they all seem to presume at least one dimension to have to exist for them to have a existence. Maybe, just maybe, all of those assumptions are wrong. Maybe :) what gives us any sheet, or plane, to build a room from, initially is without dimensions? And that would then be a 'field' defining itself, as measured from the inside. Pure speculation naturally.
« Last Edit: 01/06/2014 14:43:19 by yor_on »
 

Offline yor_on

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"Itís not possible to use the equations of GR to show that matter can fall to an event horizon in finite time, from any frame of reference, because itís possible to prove that the matter cannot reach the event horizon in finite time for at least one frame of reference."

A 'finite time' is your local time Android, the one you measure with your wrist watch. Assuming that you can pass a event horizon without tidal forces and spagettification it will run out for you, same as it will eventually for us all. But relativity does not state that this local time measuring is a illusion. Instead it define this type of time keeping as your 'proper time'.

When Einstein referred to time as an illusion he did not refer to the fact that we all live a while, to then die. Instead he was referring to a measuring on a whole universe in where we find time dilations. From that 'eye of a God' time seems an illusion, but for you locally it will keep you centered to a same life cycle as it holds us all.

It's what I call the 'container idea', and how you may want to define that container.

There is nothing stopping you to pass a event horizon, but what you will meet inside it depends on how you define its physics. If you expect the same physics as outside you can define different types of black holes, some in where you might survive, most that you won't. If you think of it as a singularity, no information let out? How will we ever know the physics inside them?
==

If you consider Hawking radiation his ideas, as far as I get them, also goes out from a container definition in where singularities is a part of a common cosmos, universe. That's how those virtual particle pairs can become real, as well as 'split' the one surviving being in a entanglement containing the same information as its annihilated twin inside, or at, the event horizon.

Most of our ideas presumes preexisting dimensions and commonly shared containers.

« Last Edit: 01/06/2014 15:41:06 by yor_on »
 

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