Why do people think Relativity predicts event horizons?

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Offline A Davis

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Re: Why do people think Relativity predicts event horizons?
« Reply #50 on: 12/12/2013 01:46:51 »
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #51 on: 15/12/2013 12:45:12 »
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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Offline Ethos_

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Re: Why do people think Relativity predicts event horizons?
« Reply #52 on: 18/12/2013 16:00:08 »
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............................
« Last Edit: 18/12/2013 16:02:56 by Ethos_ »
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Offline Bill S

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Re: Why do people think Relativity predicts event horizons?
« Reply #53 on: 19/12/2013 14:12:57 »
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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Offline Ethos_

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Re: Why do people think Relativity predicts event horizons?
« Reply #54 on: 19/12/2013 15:38:39 »
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.
« Last Edit: 19/12/2013 15:43:05 by Ethos_ »
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Offline Pmb

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Re: Why do people think Relativity predicts event horizons?
« Reply #55 on: 19/12/2013 15:42:10 »
Quote from: Bill S
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?

Quote from: Bill S
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #56 on: 22/12/2013 19:11:06 »
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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Offline Pmb

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Re: Why do people think Relativity predicts event horizons?
« Reply #57 on: 22/12/2013 20:32:07 »
Quote from: yor_on
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #58 on: 22/12/2013 22:34:02 »
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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Offline Pmb

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Re: Why do people think Relativity predicts event horizons?
« Reply #59 on: 23/12/2013 00:10:07 »
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #60 on: 23/12/2013 02:13:09 »
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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Offline Pmb

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Re: Why do people think Relativity predicts event horizons?
« Reply #61 on: 23/12/2013 05:58:44 »
Quote from: yor_on
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #62 on: 23/12/2013 13:13:31 »
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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Offline Pmb

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Re: Why do people think Relativity predicts event horizons?
« Reply #63 on: 23/12/2013 20:16:23 »
Quote from: yor_on
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #64 on: 25/12/2013 15:59:00 »
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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Re: Why do people think Relativity predicts event horizons?
« Reply #65 on: 31/12/2013 11:10:11 »
Quote from: Bill S
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?

Quote from: Bill S
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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Re: Why do people think Relativity predicts event horizons?
« Reply #66 on: 31/12/2013 11:14:47 »
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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Offline JP

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Re: Why do people think Relativity predicts event horizons?
« Reply #67 on: 31/12/2013 17:15:29 »
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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Offline Bill S

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Re: Why do people think Relativity predicts event horizons?
« Reply #68 on: 31/12/2013 23:27:00 »
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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Re: Why do people think Relativity predicts event horizons?
« Reply #69 on: 02/01/2014 01:11:49 »
Quote from: Bill S
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?

Quote from: Bill S
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #70 on: 02/01/2014 01:28:19 »
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.

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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Online jeffreyH

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Re: Why do people think Relativity predicts event horizons?
« Reply #71 on: 02/01/2014 02:14:49 »
Quote from: Bill S
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?

Quote from: Bill S
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #72 on: 02/01/2014 15:00:30 »
Sorry, that's not enough to define it. How do you get to a compression of a vacuum?
=

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?
« Last Edit: 02/01/2014 15:15:59 by yor_on »
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Re: Why do people think Relativity predicts event horizons?
« Reply #73 on: 02/01/2014 16:11:22 »
Sorry, that's not enough to define it. How do you get to a compression of a vacuum?
=

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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #74 on: 03/01/2014 12:58:54 »
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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Re: Why do people think Relativity predicts event horizons?
« Reply #75 on: 03/01/2014 20:20:41 »
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #76 on: 03/01/2014 22:20:14 »
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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Re: Why do people think Relativity predicts event horizons?
« Reply #77 on: 04/01/2014 01:01:56 »
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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Offline AndroidNeox

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Re: Why do people think Relativity predicts event horizons?
« Reply #78 on: 18/12/2014 00:24:16 »
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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Re: Why do people think Relativity predicts event horizons?
« Reply #79 on: 19/12/2014 20:45:34 »
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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Offline PmbPhy

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Re: Why do people think Relativity predicts event horizons?
« Reply #80 on: 19/12/2014 21:04:14 »
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
Quote
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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Offline yor_on

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Re: Why do people think Relativity predicts event horizons?
« Reply #81 on: 19/12/2014 23:24:44 »
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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Re: Why do people think Relativity predicts event horizons?
« Reply #82 on: 19/12/2014 23:41:29 »
 Well Hawking's paper was brief but very interesting.