Introduction to Black Holes: Newbie Questions Answered

[turin]

Guy From Alberta,
I looked into the 4 types of BH's. This is what I've got so far:
Schwarzschild:
Is as I described. This is my default BH, so, if I am talking about a BH and I do not specify (or the context does not make the distinction obvious), then I am talking about the friendly Schwarzschild BH, or, more exactly, the associated metric/geometry. The only property that distinguishes one such BH from another is the mass. It is modeled as a singular point at the coordinate r = 0. There is one critical horizon, from r < such a particle cannot theoreticall escape.
Kerr:
This kind of BH has the additional identifying quality of angular momentum, L. Thus, whereas two BH's that both have mass = M are identical in the Schwarzschild case, they can be distinct in the Kerr case in their L's. This one is complicated (to me), so I will leave it to someone else to explain the finer points to you. From what I gathered, it seems that the Kerr BH has two horizons, but that will warrant further investigation.
Reissner-Nordstrom:
This kind of BH is the other extension of the Schwarzschild BH, but, instead of including L, it includes a charge, Q. I have read the justification that these are not expected to exist stably. I don't know if I agree, but, at any rate, their principle existence is not denied by anyone (from whom I have heard). These kinds of BH clearly have two horizons. I am still looking into the meaning.
Kerr-Newmann:
This kind of BH is believed to be the most general form possible in principle. I don't know anything about it.

Are you mentioning "causality" here in the context of "time axis;"

I don't know what you mean. I will define causality (as I understand the physicists to use the term) as the notion that all physical processes follow a common parameter in a monotonic sense, and that this sense is preserved for any transformation to a valid physical frame of reference. This parameter may or may not be the value of the projection on the time axis. One thing I feel I should point out about this notion/principle (and indeed about science in general) is that it is axiomatic and should not be endowed with any deeper meaning. There are good reasons for the postulate, but the reasons have never been (up to this point) absolutely conclusive.

how would we reconcile the phenomena or occurrence of "causality problems," (or exceptions)?

In general, there are two possibilities: 1) show that the problem/exception is merely ostensible, 2) eliminate the axiom that leads to the problem/exception. If you are referring to a specific case, let's hear it.

I know that S. Hawking's "chronology protection conjecture," states that the laws of physics do not allow time machines, for eg., and that "time travel," is only possible "microscopically," whatever that might mean.

If I detect a hint of cynicism here, then I would say that I am right there with you. I have heard/read/seen all kinds of crap (and by "crap" I mean reasoning for the inability to change the sense of one's time'parametrization wrt the rest of the physical system with which one is causally connected). This has been "disproven" on the micro-scopic level (to what I consider an acceptable degree of confidence), and even a mere description of decoherence into a causal mode of parametrization has yet to be clearly demonstrated (so far as I've seen). The basis of assertions of the "chronology protection conjecture" range from qutie convincing (albeit empirically devoid) billiard ball type situations to innane rhetoric such as "where are all the tourists." The resulting assertions have a stinkingly conjectural basis.

... a real paradox can occurr when some given particle moves faster than the speed of light...the "causality problem" happening from the fact that when 2 events, A and B, happen faster than the speed of light; (for a stationary frame of reference), then, accordingly, event B can happen before event A?

I think you've just about got it. Although, I would restate it:

"A real paradox could occur if some given particle moves faster than the speed of light...the 'causality problem' happening from the fact that when 2 events, A and B, happen in such a way that A is to cause B at a point in time much earlier than a light signal could arrive at B from A, ... then, according to the causal structure indicated by SR, event B could happen before event A, which is inconsistent with said causal structure."

A fellow named K. Thorne, has proposed that something called "wormholes" could be used as "time machines," but I don't understand how a human being could access a "wormhole," since, admittedly they are hypothetical.

It is not so much their hypothetical nature as it is the requirement of superluminal velocity, which is hypothetically impossible (is that an oxymoron?), in order to make use of them.

According to special relativity, from what I understand, traveling faster than light is equivalent to traveling backwards in time?

Not quite. In the frame of reference wrt which the velocity is faster than light, the object is still "moving forward through time." The issue is that, upon a Lorentz transformation, traveling faster than light in any inertial frame leads to inconsistent "direction of travel through time" in distinct inertial reference frames (which can result in "travelling backwards in time"). That, together with the principle of causality, is what prohibits superluminal velocity.

I guess all this is suggesting to me that perhaps, there may be a way we do have access to the future; as we consider "causality loops," where events of the future cause events of the past...

What is a "causality loop?" Do you mean a loop-hole in the theory re causality? SR provides no such loop-hole, and I am pretty certain that neither does GR. QM? Maybe. Reality? That's a totally different story.

 

[Guy From Alberta]

Hi Turin

I agree with, and see your points re "causality." I actually do not intend to insinuate any exceptions to "causality" here; but bear with me a few days till I figure out what I do mean by that. I uncovered "causality loop" somewhere in my recent studies; and need to figure out where. I agree, that everything needs to be governed by definite laws of physics. And perhaps, other "laws." Your philosophical question re conscience is one I will defintely get back to as well. Very interesting.

I wonder though...is it possible for anything to travel faster than light? If so; what are some examples?

 

[turin]

I agree with, and see your points re "causality." I actually do not intend to insinuate any exceptions to "causality" here; but bear with me a few days till I figure out what I do mean by that.

I appologize if my responses seemed like an affront. My style may be a little obstreperous sometimes. You may have a better definition than I; I merely wanted to rigorously indicate the definition that I have in my mind when the term causality is used in the context of relativity.

I agree, that everything needs to be governed by definite laws of physics. And perhaps, other "laws."

Well, I'm not so sure that I strictly agree with that. Perhaps there are physical laws; but, perhaps they are mental constructs that enable the human beast to cope with its existence in an orgainzed way that promotes evolution. Introspectively, I cannot rule out the latter. Furthermore, in my own mind, I cannot comprehend of a set of laws, no matter how fundamental, without a "legislature," nor can I comprehend of every object in the universe adhering to these laws without an immense "bureaucracy."

Your philosophical question re conscience is one I will defintely get back to as well.

Just keep in mind that I in no way claim to know the answer. One reason why I posed the question was to seed the distinction between the rigorous relativistic definition of time, and your personal phenomenology of time.

...is it possible for anything to travel faster than light? If so; what are some examples?

Of course, if you allow for a loose definition of "anything" and "travel." The most immediate example that comes to mind is phase velocity.

Imagine a wave (in the ocean) that is coming into shore at a slight angle. Associate the speed of the wave with the velocity of light. Then, from some perdendicular distance from the shore, d, the wave will take some time to arrive at the shore, t. d/t is less than the velocity of the wave, so it can be associated with less than the velocity of light. Now consider the incidence. The wave hits some point at one end of the shore, and, as the wave continues to move in, that point slides down to the other end. This sliding of the point of incidence happens extremely quickly, in fact, much more quickly than the speed of the wave. You can associate this speed with the phase velocity along the shore.

The phase velocity does not causally connect events. The event of the wave hitting the shore at one end has no influence on the wave hitting the shore at the other end. Both events had some exterior cause out in the distant ocean. This is one model that people have used to justify the phenomenon of entanglement (of course, with matter waves rather than ocean waves).

 

[Guy From Alberta]

Quote by Turin

What does this have to do with the r-axis being timelike? Simply this: inside a BH, the r coordinate of a particle cannot increase. It is doomed to decrease monotonically. Thus, any physical process (I use the term freely) inside a BH can be parametrized according to its distance from the center, or r coordinate. Thus, this parameter, the r coordinate, can be
isomorphically transformed into time, and is therefore timelike.

If it's philosophy that you're after, then here's a thought (not an answer, but a thought): Physical processes must have a monotonic variation in their timelike parameter. Is consciousness so intimitely connected to physical process that it too must follow such a parameter, or is it possible to survive a conscious eternity within a BH? I suppose this could give some indirect insight into the nature of consciousness.

This is just another quick question - I find myself wondering how/if this "nature of consciousness" would be affected when we consider whether or not the person is kind and loving; or whether they are mean and wicked? How might personality affect this monotonic variation; when we consider the nature of consciousness?

Also, perhaps more in the philosophy realm; is another question sort of related to "time;" and the "monotonic variation" it may have is the concept of "forever;" and related terms. Some of our studies make me wonder what "forever" might really be. That is, does "time" ever end?

I will be back likely on the week end.

 

[turin]

Be careful not to get too philosophical in here. I request that we please try to stick to the physics. I know that I'm the one who brought it up, and I appologize. I just know that these philosophical discussions tend to irritate a lot of posters here (including myself, usually). If you would like to keep talking about this issue, then PM me, or maybe you could start another thread about it (I think there's a philosophy board somewhere around here) and then give me the link.

 

[Guy From Alberta]

Be careful not to get too philosophical in here. I request that we please try to stick to the physics. I know that I'm the one who brought it up, and I appologize. I just know that these philosophical discussions tend to irritate a lot of posters here (including myself, usually). If you would like to keep talking about this issue, then PM me, or maybe you could start another thread about it (I think there's a philosophy board somewhere around here) and then give me the link.

Hi Turin

I understand your request in the last post above; no problems here on my end. I was more or less just responding to your one comment above. I am sorry for taking so long to get back here; but in the nicer weather, plus with my studies; I will have to be away from time to time. I will be back later tonight, or tomorrow with some more physics questions/comments.