Can we truly know the fate of objects in black holes?

[Jagella]

According to a recent published article, Physicist Leonard Susskind feels, along with Niels Bohr, that rather than try to come up with a mental picture of what objective reality is, scientists should limit themselves to creating hypotheses and testing them empirically. Susskind contends that a wariness about knowing reality is justified by some contradictions and paradoxes of modern physics.

One such paradox is the ambiguity about the fate of things that fall into a black hole. From the perspective of the object, it passes unaffected through the event horizon and is destroyed at the hole's center. An external observer, by contrast, sees the object incinerated as it passes the event horizon prior to reaching the center. Both viewpoints, although apparently irreconcilable, are considered by physicists to be valid. (1)

I'm wondering if anybody in this forum can explain this paradox. How sure are we that one of these interpretations are not wrong? If either one is wrong, then the paradox would be resolved.

Another question is one of epistemology: Do we really need to be sure we know what we think we know? Is physics properly a body of knowledge, or is it a methodology we can use for practical purposes?

I tend to lean a bit to the latter viewpoint. Rather than worry about how "right" modern physics is, I see physics as a way to solve problems. If it works for that purpose, then let questions of epistemology up to philosophers.

Jagella

(1) Peter Byrne, Bad Boy of Physics, Scientific American, July 2011, pp 80-81

 

[Nabeshin]

One such paradox is the ambiguity about the fate of things that fall into a black hole. From the perspective of the object, it passes unaffected through the event horizon and is destroyed at the hole's center. An external observer, by contrast, sees the object incinerated as it passes the event horizon prior to reaching the center. Both viewpoints, although apparently irreconcilable, are considered by physicists to be valid. (1)

The thing is, this isn't a paradox at all. What's wrong with the two observers coming to different conclusions about what they see? If the outside observer is smart, he can compute that for the guy who fell into the black hole, he was destroyed in a finite amount of proper time (he can say just how much!).

Here's a less black hole-y example:
http://en.wikipedia.org/wiki/Rindler_coordinates#The_Rindler_horizon

 

[Jagella]

What's wrong with the two observers coming to different conclusions about what they see?

Well, according to Special Relativity, sometimes observers do come to different conclusions about what they see. Length and time are relative to the frame of reference of the observer as I'm sure you know. Are there relativistic ramifications to what observers falling into a black hole might see versus what observers outside of the black hole might see?

If the outside observer is smart, he can compute that for the guy who fell into the black hole, he was destroyed in a finite amount of proper time (he can say just how much!).

I'm not sure how your scenario resolves the paradox. What is “proper time”?

The thing is, this isn't a paradox at all.

I'm thinking that our notion that something can only be destroyed in one place is simply wrong. If Susskind is right about the destruction of an object falling into a black hole, then obviously something can be destroyed in two different places. It may not make sense to us, but the world doesn't always make sense. Quantum mechanics offers a lot of evidence that our logic doesn't always apply to the “real world.” Common sense may be OK under common circumstances, but under circumstances that are very uncommon, like that of the proximity to a black hole or on the subatomic scale, we need to rethink our ideas of what makes sense.

It made sense to Aristotle that heavier objects fall faster than lighter objects, did it not?

Jagella

 

[DaveC426913]

What paradox?

Just because two people see different things does not mean there is a paradox.

Two people looking at a straw in a glass of water will "conclude" different things about how the straw is bent. Paradox? No.

To think so would be to assume that the light that reaches our eyes is a True and Bona Fide Account of Actual Reality. Which we know it isn't. Photons are not oracles of reality.

 

[jnorman]

inre: "Photons are not oracles of reality." i am not sure why you wrote this - photons are, indeed, the ultimate oracle of reality.

 

[Jagella]

What paradox?

Just because two people see different things does not mean there is a paradox.

Two people looking at a straw in a glass of water will "conclude" different things about how the straw is bent. Paradox? No.

To think so would be to assume that the light that reaches our eyes is a True and Bona Fide Account of Actual Reality. Which we know it isn't. Photons are not oracles of reality.

That's a very good point, Dave. Different people in different situations will often observe different things about an object. The key difference, though, is that we can readily explain the differences in the observed refraction of the light coming from an apparently bent straw because we understand the effects of parallax. But how do we explain the destruction of an object destroyed in two different parts of a black hole?

I must wonder if we may be reaching the limits of human understanding. Dogs evidently cannot understand classical mechanics. Humans may not be able to understand quantum mechanics.

Jagella

 

[Cosmo Novice]

They are the oracles of past reality not present reality, present reality doesn't exist as all as all perceptions are based on time.

Example; Look at the sun, we see approximately 8 mins back; Look at the stars further away and we look further back in time.

I thank what Dave is getting at is that we have to take into account the speed limit of the universe - apologies if I have misinterpreted you Dave.

 

[Cosmo Novice]

That's a very good point, Dave. Different people in different situations will often observe different things about an object. The key difference, though, is that we can readily explain the differences in the observed refraction of the light coming from an apparently bent straw because we understand the effects of parallax. But how do we explain the destruction of an object destroyed in two different parts of a black hole?

I must wonder if we may be reaching the limits of human understanding. Dogs evidently cannot understand classical mechanics. Humans may not be able to understand quantum mechanics.

Jagella

It is not destroyed in two different places. It is destroyed in a single spacetime with multiple frames of reference as I understood it.

 

[DaveC426913]

inre: "Photons are not oracles of reality." i am not sure why you wrote this -

Hm. I would have thought my point so obvious it would have been the last word on the subject...

photons are, indeed, the ultimate oracle of reality.

Really? So the straw in a glass of water is bent in reality?

Taken at face value, photons lie about their history. Photons do not make straight lines between their destination (our eyes) and their origin (the bottom tip of the straw). When we observe the straw underwater, we take into account the fact that our very observations are distorted. We must tease out of it what is really happening based on what we know about diffractive media and light. Photons are not oracles of reality. The straw is not bent.

This is perfectly analagous to the black hole example. Our observations are completely subject to the whims of the photons that deign to reach our eyes after whatever adventure they happen to go on. we know that the BH (or water) is mangling the paths/frequencies/etc. of the photons. Once you compensate, there's no paradox at all.

 

[DaveC426913]

That's a very good point, Dave. Different people in different situations will often observe different things about an object. The key difference, though, is that we can readily explain the differences in the observed refraction of the light coming from an apparently bent straw because we understand the effects of parallax. But how do we explain the destruction of an object destroyed in two different parts of a black hole?

We explain it by understanding that "the object" and "our image of the object" are not at all the same thing. Our image of the object is highly distorted in both space and time.

Seriously, I don't know why you guys are making a big deal of this.

Yes, observations near a black hole are highly distorted. No one is naive enough to think that, because we see the infalling object stop at the EH, that that is what really happens to it. Are they??

 

[Drakkith]

Why exactly would an outside observer see the object incinerated at the event horizon?

 

[DaveC426913]

Why exactly would an outside observer see the object incinerated at the event horizon?

An excellent question actually. Good catch. I chose to ignore it - probably shouldn't have.

It's possible that the OP thinks there's a paradox only because they misunderstand what is actually observed.

An outside observer would see an infalling object time dilated and red-shifted as they approached the EH. The object is asymptotically time-dilated and red-shifted to zero even while its image fades away as fewer and fewer photons climb out of the hole. (And only in principle at that. Those last few photons spread out over eternity don't really constitute much of an "image".)

Quite the opposite of an incineration actually, more like ... infreezeration...

 

[Cosmo Novice]

An excellent question actually. Good catch. I chose to ignore it - probably shouldn't have.

It's possible that the OP thinks there's a paradox only because they misunderstand what is actually observed.

An outside observer would see an infalling object time dilated and red-shifted as they approached the EH. The object is asymptotically time-dilated and red-shifted to zero even while its image fades away as fewer and fewer photons climb out of the hole. (And only in principle at that. Those last few photons spread out over eternity don't really constitute much of an "image".)

Quite the opposite of an incineration actually, more like ... infreezeration...

In my opinion, the misconception of the OP is that they cannot reconcile the frame of reference of the observer and of the infalling object;

For the external observer the infaller approaches the EH of the BH and becomes increasingly redshifted towards infinity. In our frame of reference this is totally valid.
For the infalling observer they approach and indeed cross the "boundary" of the EH and I use the term boundary loosely. Once they cannot escape the BH they proceed (in a finite time) to head towards the singularity or whatever other predicted mathematical model of quantum gravity would hold true. (I know this isn't known)
Both frames of reference are completely valid, and coexist. There is essentially no paradox; this is a mapping of a finite observer time to an infinite coordinate time.


However I ask this:
Could it be argued that inside a BH; due to the immense relativistic time dilation (from the external observers FoR) that a singularity never occurs, that from our FoR zero volume and infinite density is never reached? How does this tie in with the FoR of the infalling object?

 

[DaveC426913]

However I ask this:
Could it be argued that inside a BH; due to the immense relativistic time dilation (from the external observers FoR) that a singularity never occurs, that from our FoR zero volume and infinite density is never reached?

It is meaningless to ask if something that we have no way of measuring "really" occurs.

Simply: under circumstances in which it can be determined whether it occurs, we would determine that indeed it occurs.

 

[Drakkith]

Dave, I love that word. Infreezeration. I think you should copyright it or something.

 

[Jagella]

We explain it by understanding that "the object" and "our image of the object" are not at all the same thing. Our image of the object is highly distorted in both space and time.

Seriously, I don't know why you guys are making a big deal of this.

Yes, observations near a black hole are highly distorted. No one is naive enough to think that, because we see the infalling object stop at the EH, that that is what really happens to it. Are they??

It should be helpful for me to quote directly from the Scientific American article I cited in my opening comments:

One thing that led Susskind to this conclusion is his principle of black hole complementarity, which holds that there is an inherent ambiguity in the fate of objects that fall into a black hole. From the point of view of the falling object itself, it passes without incident through the hole's perimeter, or horizon, and is destroyed when it reaches the hole's center, or singularity. But from the vantage point of an external observer, the falling object is incinerated at the horizon. So what really happens? The question, according to the principle of black hole complementarity, is meaningless: both interpretations are valid.

Leonard is not saying that observers merely see the object differently but that it suffers a different fate upon entering the black hole. Is he naive as you say? Either that or he may have cut physics' legs out from under it.

Is this issue a “big deal”? Again, I see physics more as a means to an end than an end in itself. It is obviously useful even if we do encounter some logical quandaries as we probe the more extreme and remote parts of the cosmos. The universe doesn't care what we think: It just goes on its merry way. It has defied theologians and philosophers for millenia. It evidently has no more respect for scientists.

Jagella

 

[DaveC426913]

Well, I've never before heard anyone suggest that anything gets incinerated at the EH.

That alone leads me to suspect the veracity of either the quote or, if accurate, the person being quoted.

 

[disregardthat]

Isn't it so that an observer (as a technical term) calculates its hypothetical observation according to the theory of relativity, and by that makes up for distortions caused by gravitational fields and redshifts? So to me it shouldn't really be an issue what one would actually measure, as the only thing in consideration is what one could calculate from the measurements.

I also have a question about an external observer watching an object falling into a black hole. Now I have read that the external observer will se the object falling closer and closer but never reaching the event horizon. But isn't this ignoring the fact that an observer actually would calculate that the object actually fell into the black hole from the measurements by taking into account the massive redshift? Though I can see how there might be some difficulty defining the event of falling into a black hole. This event doesn't really happen in any frame of reference, which leads me to the second question: Does it make sense to talk about an observer at the exact edge of a black hole horizon? Or rather, is this a valid inertial frame? It would seem to me as a valid of an inertial frame of reference as that of a photon (and thus not hypothetically capable of observing anything).

 

[DaveC426913]

I also have a question about an external observer watching an object falling into a black hole. Now I have read that the external observer will se the object falling closer and closer but never reaching the event horizon. But isn't this ignoring the fact that an observer actually would calculate that the object actually fell into the black hole from the measurements by taking into account the massive redshift?

It's not ignoring it, it's demonstrating that a physcial observation is different from a calculation to explain what is expected to happen. If your model and your calculation is correct, it agrees with the observation.

Just like the refraction of light in a glass of water.

 

[disregardthat]

It's not ignoring it, it's demonstrating that a physcial observation is different from a calculation to explain what is expected to happen. If your model and your calculation is correct, it agrees with the observation.

Just like the refraction of light in a glass of water.

You misunderstand, my point was that one should specify the distinction (which is crucial), and without doing so is leaving out half the story. (You should see that I am in my post making the exact same point as you just did.) I would like to hear your comments on my other questions.

 

[Drakkith]

When we say that "The observer would see" that is saying that we are observing it, not calculating it.

 

[Jagella]

Really? So the straw in a glass of water is bent in reality?

What is your definition of reality, and how do we know what reality is?

In the bent-straw example, what makes the straight straw any more real than then bent straw?Observing the straw out of the water it looks straight, and partially in the water, it looks bent. Which situation is "real" and which is not?

Another example is that of our solar system. We see Copernicus as being "right" when he posited that the Earth orbits the sun rather than the sun orbiting the earth. Why not just see the Earth as the center of the cosmos? True, it's simpler to assume that the Earth orbits the sun, but is a simpler view any more real than a more complex viewpoint? Einstein posited that space is not absolute. There is no universal spatial point of reference that all objects move in relation to. If Einstein is right, then we may arbitrarily choose any location as a point of reference which objects move relative to. The Earth can be that point of reference.

Subjectivity is something we just cannot get away from. An "objective reality" may exist, but we may never know what it is.

Jagella

 

[DaveC426913]

What is your definition of reality, and how do we know what reality is?

In the bent-straw example, what makes the straight straw any more real than then bent straw?Observing the straw out of the water it looks straight, and partially in the water, it looks bent. Which situation is "real" and which is not?

Uh. The straw is not bent; it is straight. Pretty much no question here about what's real and what's an optical illusion.

(But for your own edification, try sticking a darning needle down the length of the straw.)

This is kind of a silly place to play the "what is real" game.

 

[Jagella]

Uh. The straw is not bent; it is straight. Pretty much no question here about what's real and what's an optical illusion.

Actually, I agree with you. If a straw looks straight and feels straight, then we can be sure that it is straight. Much like you, I normally won't worry too much about certainty, and I operate under the assumption that there are real things in the world and with some effort on my part I can have some real understanding about those real things. We physicists evidently need to operate under such an assumption, or our work would be impossible.

(But for your own edification, try sticking a darning needle down the length of the straw.)

Assuming that the needle is straight, then it's safe to assume that it will fit into a straw with a sufficiently large cross-section.

This is kind of a silly place to play the "what is real" game.

I wouldn't be so quick to dismiss the work of Leonard Susskind. He's a Stanford University physicist He co-founded string theory and helped to develop the idea of parallel universes. I suppose he just goes to show that the difference between a silly idea and a great discovery is that the latter is successfully tested and eventually gains acceptance in the scientific community.

Good day!

Jagella

 

[DaveC426913]

I wouldn't be so quick to dismiss the work of Leonard Susskind.

I am not doing so.

I pointed out that I've never heard of anything being "incinerated" at the EH of a BH.

If he did not say that then the OP is simply a paraphrase. I'm doubting the accuracy of the paraphrasing. If "incineration" was mangled in translation, what else has been?

 

[Jagella]

I pointed out that I've never heard of anything being "incinerated" at the EH of a BH.

If he did not say that then the OP is simply a paraphrase. I'm doubting the accuracy of the paraphrasing.

Here's the direct quotation (again).

One thing that led Susskind to this conclusion is his principle of black hole complementarity, which holds that there is an inherent ambiguity in the fate of objects that fall into a black hole. From the point of view of the falling object itself, it passes without incident through the hole's perimeter, or horizon, and is destroyed when it reaches the hole's center, or singularity. But from the vantage point of an external observer, the falling object is incinerated at the horizon. So what really happens? The question, according to the principle of black hole complementarity, is meaningless: both interpretations are valid.

(Emphasis mine)

As you can see, the Scientific American article uses the word “incinerated.” Why is that word a problem for you?

If "incineration" was mangled in translation, what else has been?

I'd recommend that you read the article, Bad Boy of Physics, in the July 2011 issue of Scientific American. It's a very interesting interview.

Jagella

 

[Christopher G]

Publications about science for non-scientists (nearly) always misrepresent the facts to make things sound more exiting.

But the reality of it is, nothing special happens at the event horizon from the frame of a person falling in.

Also, a person outside the black hole would simply see his friend get darker until he could not see him any longer. Hardly an incineration by most standards. Simply that light cannot escape the gravity any longer so you can't see him! There never was a paradox.

To emphasis another point: The straw is not bent, it's the light's trajectory that's being bent... You really think that when you look into a fun-house mirror your being changed somehow? No, the light is being reflected at different angles. It's really very simple.

==EDIT==
A relevant example of misrepresenting facts is the whole 'parallel universes' thing. String theory can be 'configured' differently by curling up the extra dimensions in different ways. That's it. That's where the 'parallel universes' thing comes from. It's not even scientific.

You MUST take these things with a heap of salt, unless you know the math, you don't know the physics. Don't mistake someones rough description of it as factual, you will find that your almost always misinformed.

 

[disregardthat]

But the reality of it is, nothing special happens at the event horizon from the frame of a person falling in.

But is there even such a thing as the frame of reference of an object falling into a black hole? I would say, even assuming accelerating frames, that the event of falling into the black hole horizon is not an event in any frame of reference.

 

[Christopher G]

But is there even such a thing as the frame of reference of an object falling into a black hole?

Yes, and for super-massive black holes you can fall far passed the event horizon before being 'spaghettified'. If you were to fall into one (please never let this happen! be careful when playing with black holes), you would agree that the event indeed did happen.

More scientifically, you can lorentz boost any frame into the frame of the person falling in. It exists.

==EDIT==
I now feel a bit uncomfortable having posted that, take it with a grain of salt. I might look more into it later.

But for some fun (for those who haven't already seen it):
http://jila.colorado.edu/~ajsh/insidebh/schw.html

What it looks like to fall into a black hole!

 

[DaveC426913]

As you can see, the Scientific American article uses the word “incinerated.” Why is that word a problem for you?

OK, so it's a quote from the article, not susskind. Yes, they nearly always dumb things down.

But that's simply apocryphal. Shame on them.

Either that, or I have some serious reading to do. But it won't be from Sci Am.

 

[DaveC426913]

But is there even such a thing as the frame of reference of an object falling into a black hole? I would say, even assuming accelerating frames, that the event of falling into the black hole horizon is not an event in any frame of reference.

Of course it has a valid frame of reference. Why on Earth would it not??

 

[Dale]

But is there even such a thing as the frame of reference of an object falling into a black hole? I would say, even assuming accelerating frames, that the event of falling into the black hole horizon is not an event in any frame of reference.

Sure. The event horizon is just a coordinate singularity, not a real singularity. It can be removed simply by a coordinate transformation. An object falling in has a perfectly valid frame of reference, and may not even notice anything unusual on crossing the horizon, particularly if the black hole is super-massive.

 

[phinds]

But is there even such a thing as the frame of reference of an object falling into a black hole? I would say, even assuming accelerating frames, that the event of falling into the black hole horizon is not an event in any frame of reference.

It strikes me that this is exactly equivalent to saying that when I drive down the highway and pass the 14 mile marker, you now get to say that I don't have a valid frame of reference because I have passed the 14 mile marker. It clearly doesn't make sense.

The event horizon is utterly irrelevant to a person falling into a black hole as he falls in, it's just a place where he no longer has the option of getting back out again. What's relevant is spaghettification and that that does not have anything to do with the EH. For big BH's it will happen inside the EH and for small ones outside.

 

[Jagella]

You really think that when you look into a fun-house mirror your being changed somehow? No, the light is being reflected at different angles. It's really very simple.

Well, no. I work under the assumption that I can differentiate the real from the unreal. Even more, I assume that there is something real—a “reality” that exists objectively and exists independently from myself. That way I can study the physics of the world.

Please note though that I'm making an assumption that there is an objective, independent reality. I know of no way to prove that that reality exists. Physics is an incomplete body of knowledge because you cannot prove within physics that its basis, the physical world, exists. You would need to go beyond physics to prove that reality exists. To do so may be impossible.

You MUST take these things with a heap of salt, unless you know the math, you don't know the physics. Don't mistake someones rough description of it as factual, you will find that your almost always misinformed.

With all due respect, Christopher, why should I believe you rather than Scientific American?

Good day!

Jagella

 

[Christopher G]

With all due respect, Christopher, why should I believe you rather than Scientific American?

Because of what I said in the first line of my first post.

"Publications about science for non-scientists (nearly) always misrepresent the facts to make things sound more exiting."

But you don't have to take my word for it! Study physics yourself! It's fascinating, but you have to start with the boring stuff unfortunately.Also, it's outside of the scope of physics to prove that reality, whatever that may be, 'exists'.

Here is a quote from Stephen Hawking:
"I don’t demand that a theory corresponds to reality, because I don’t know what it is. Reality is not a quality you can test with a litmus paper. All I’m concerned about is that the theory should predict the results of measurement."