Do black holes really exist in the real world or are they just virtual objects

Where are you getting these numbers? If the theoretical EH of Cygnus X-1 is 50km in diameter, then my "Dark Star" description of it would be a mass of highly compressed material on the brink of gravitational collapse with a diameter just above 50km.

 

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Welcome to geodesics and singularities. Perhaps you can appreciate why I made the claim that they do not exist "today".

 

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Here. Read.

 

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It took 10 seconds to read the qualifiers that you apparently skipped over.

You cannot win this argument because it is involves inferences, definitions, semantics and a bit of philosophy. Meanwhile, you giving references only proves that you were mistaken to take such a hard-line stance, and unfortunately pointing at a dark region in space proves nothing.

 

http://en.wikipedia.org/wiki/Cygnus_X-1

Again:
1. If it was a million km in diameter and is now 50, how can you say that it didn't collapse? Or alternately, what would you call the process that made its size change?
2. Please state at least one externally observable difference between a "dark star" and a "black hole". I'll give you a hint: the first theory that proposed the existence of black holes predicts they only have two identifiable properties: mass and event horizon diameter. http://en.wikipedia.org/wiki/Schwarzschild_metric

Now even if we can establish a difference between a "dark star" and a "black hole", there is a still a linguistic and historical problem that "black hole" got there first. I just wanted to make you aware so you don't think I'm blind-siding you with that, but we can set it aside for now.

So you punt. Fair enough. I'll drop it, but it doesn't make the contradiction go away if you refuse to explain it.

Just a quick point of clarification:
You asserted/acknowledged that Cygnus X-1 does in fact exist and that it is a "dark star" - a term presumably that you just made up on the spot. So you're already down that path further than that attempt at hedge will allow. The object needs a name, whether it is "dark star" or "black hole". Scientists agree that it is a black hole. Wiki is a decent source, but not a perfect one: the quote you quoted is both incomplete and the source is misquoted. The source says repeatedly that Cygnus X-1 is a black hole based on Hawking's conceding of the bet.
http://astronomy.swin.edu.au/sao/astronomynews/astronews2004s1.xml

 

deleted - consolidating

 

deleted - consolidating

 

1) Where does that link reference a diameter of one million km? I don't question gravitational collapse, only collapse beyond the neutron star density (or whatever other form of matter that precedes the formation of the singularity, event horizon, etc). The irony here is that I'm not refuting GR, I'm REFERENCING it from a philosophical stand point!

2) I'm not sure I can, actually. Forces coming from Newton's Shell are, from an external observation, identical to a situation where all of the mass was concentrated at its center. A "dark star" would have a given mass asymptotically approaching the diameter of its event horizon without ever actually passing the threshold; there would be at best a theoretically small difference which was practically impossible to ever measure. If your point is that we cannot ever practically detect the difference and therefore conflating reality with the mathematical theory is inconsequential...I disagree. The reason I disagree is not because I'm saying the math is wrong; it's because I'm saying our interpretation of the math is wrong! The math actually suggests that no black holes exist* today, period.


*and so, we go in circles, which is why I pointed out that a rigorous definition of "exist" must be agreed upon in my very first post in this thread

 

Hi Russ, moving forward I would actually rather you DIDN'T consolidate your posts. That way I can respond to them as I see them with the comfort that they won't change or be added to by the time I post a response.

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Anyway, you might find this interesting.

 

But whether it is a Newtonian concept Dark Star, or whether it is the GR BH, there is no "externally observable difference" in either of them.

I would also note that the gravitational field is the biggest giveaway of a Dark Star/BH, and the gravitational field of either is of course a fossil field anyway, originating from the Star from whence it was formed.


Also I would reference this.........

The spacetime of a black hole is curved in such a way as to cause the future light cones to tip inward. At a specific distance from the black hole, the light cones are so tipped-over that the "outgoing edge" of each light cone is vertical in the diagram below. These "edges" form a surface (drawn as a cylinder in the diagram). This surface (called the event horizon) is the characteristic feature of a black hole.

more at....

http://www.phy.syr.edu/courses/modules/LIGHTCONE/schwarzschild.html

 

Nice try at diversion, I was pointing out the the fallacy of your claim that "you have to travel to the black hole to prove that it is a black hole". Black hole tests are all remote tests. They fall in one of the categories:
-light bending (gravitational lensing)
-Shapiro delay
-detection of gravitational waves
-accretion of matter

Err, the "argument" was your refusal to accept the value of the Schwarzschild radius of about 50km (more precisely, 44km). Please stop the desperate diversions and try learning. This is your third thread on denying the existence of black holes, you should have learned by now.

 

Didn't you already have a thread about this?

"Exist" does not have a precise or rigorous definition in physics for the simple and sensible reason that there has never been any need for one. Applied to black holes, the reason for this is that GR black hole solutions already define very precisely in what sense black holes "exist" according to GR and what their implications are. Starting a committee and legislation on the correct use of the word "exist" is not going to lead to new insights about black holes among people who already understand the models. If you need precision, the best candidate for that is the language and concepts of relativistic spacetime and Riemannian geometry that are already used for that purpose.

Compare with your New Year's Eve example. New Year's Eves and the ensuing celebrations happen periodically, every year. At the time of writing, the last one was just over ten months ago, while the next one, New Year's Eve 2013, will occur in a couple of months. New Year's Eve is not happening now. Can New Year's Eve reasonably be said to "exist"? Honestly, I don't give a damn, because whatever answer you come up with isn't going to tell me anything about New Year's Eve that I don't already know or change how seriously I take the event.

Not correct, since parts of a black hole, including its singularity, can be contained in an external observer's causal present. Black holes are not exclusively constrained to the causal future of outside observers. (Also, I find it weak to base theoretical arguments only on the point of view of outside observers. GR certainly has things to say about what you'll experience if you fall into a black hole. It's just up to you to decide if you're willing to risk the predicted impending doom if you're ever presented with the opportunity to test them for yourself.)

 

Two more, to be exact. See the bottom of the page. He's on the third "black holes do not exist"

 

paddoboy: thanks for the link

tach: you don't get it

przyk: I was answering the OP's question by pointing out that "exist" isn't as simple as he/she presumably thinks; don't forget I'm a philosopher at heart. I was recently exploring this idea, in fact, so the timing was fortunate.

 

I do, you are on your third trolling thread on the subject.

 

It actually doesn't - but our sun is more than a million km in diameter and is well below the size of the star Cygnus X-1 is believed to have formed from (that last part is in the link).

Arright, then please stop with the word games. You said before "on the brink of gravitational collapse" (meaning gravitational collapse hasn't happened yet) and "AH!... It has not already collapsed..." Looks to me like you are just playing games; ducking and diving and forcing me to back you into a corner before you are willing to acknowledge things you already know instead of discussing this with maturity.

[edit] You even said in a thread four years ago "collapse from a neutron star". Games are so immature and ultimately pointless. Why bother?

1. According to the link, Cygnus X-1 is too dense to be a neutron star. Please explain this discrepancy if it hasn't collapsed beyond neutron star density. [edit: You said four years ago that they collapsed beyond neutron star density. So if you want, I'll let you gracefully retract or move on from that claim you already know is wrong.]
2. Are you saying that you do not accept that Cygnus X-1 even has an event horizon? Now you're going beyond arguing that we can't see what is in side the car and now saying we can't even see the outside of the car! That is quite definitely false.

Yeah, that's part of why this argument of yours is so problematic: scientists don't deal in philosophy, they deal in...science.

So if from an external point of view there is no difference between a black hole and a "dark star", then what good is this name you invented? It offers no advantage over the name "black hole" -- and frankly, implies a greater similarity to stars than actually exists.

This has nothing to do with practicality, it has to do with what is at or behind the event horizon. Since you acknowledge that either way we don't know (again with the games: previously you said they were different, now you acknowledge they are not), the difference has no bearing on whether we can say that black holes exist.

What you are calling a "dark star" is actually just your name for a particular idea about what the internal structure of a black hole might look like. And that makes this a good time to bring in that caveat I made earlier: what a black hole is is not required to be fixed. It is not required to be exact. It isn't even required to be correct for the name "black hole" to be useful. The name "planet", for example, has been used for millennia and for most of its use was very wrong, but the name has still persisted. Why? Why bother changing it? As our understanding has improved, we just update the definition.

So too with black holes. Black holes exist. Our understanding of what, exactly they look like exactly at the event horizon or inside may or may not be right, but that is not an issue that necessitates the abandonment of the name "black hole".

I've had no argument with your apparent definition of "exist", so I don't know why you would bring it up now except if you want to add additional obfuscations. Your argument style here seems intended to prevent reaching understandings. But by all means, if you want to complain about that too, go ahead and say what your issue is.

 

Fair enough.

I actually hadn't heard of that. Is that what you intended with your use of the term? Are you aware that Newton's theory of gravity predicts the wrong amount of gravitational deflection of light, experimentally verified, and has therefore been falsified?

 

I think it can be a headache partly for some dumb reasons that have nothing to do with science or philosophy, like the term having multiple meanings depending on context and generally not being used consistently or even restricted to reality (e.g., as you already know, saying black holes "exist" in the context of GR is not the same as saying they "exist" in reality).

Making up definitions for the sake of making up definitions isn't philosophy. Also, you seem to be introducing a convention for when the present tense of the verb "to exist" should be used, rather than a definition of the verb itself.

On the fundamental level that actually really puzzles people ("existence" in the sense of "having objective reality"), I seriously doubt "existence" is meaningfully definable at all.

 

Sometimes I just like to say 'it exists as real natural phenomena'. Based on the evidence I'm going to say that about black holes. They exist as real natural phenomena. There's direct and indirect evidence for black holes in this universe. I'm glad the universe is different from what I first imagined it to be.

 

Russ: What I said was that I don't question gravitational collapse...how could anyone? However, certain types of compact stars (caused by gravitational collapse) exist today, while I'm suggesting that black holes do not. Not sure what I said four years ago; I try to stay logically consistent over the ages but that doesn't mean my thoughts can't change. Also, this isn't a game in that I'm trying to "trap you in a corner" (don't flatter yourself, I don't know you and don't care what you believe). I'm just pointing out that the OP's question in this thread is not immediately obvious because of the word EXIST.

Exploring concepts is the heart of philosophy. If you'd like to take a stab at what it means to exist I'd love to see it. Also, you have a good point about delineating between defining exist and defining when to use present tense, because we can consult the dictionary for both terms.

EXIST: to have real being whether material or spiritual

PRESENT TENSE: the tense of a verb that expresses action or state in the present time and is used of what occurs or is true at the time of speaking

So, to the OP's question:

Black holes would need to have "real material being in the present time or at the time of speaking". Black holes do not qualify under this definition. Do you disagree?