A few questions about black holes

Factual Questions
1

Hello, i have a questions about black holes. Nobody could answer them till now.

First, why even bother with the singularities, as there are no black holes at all, and there NEVER will be one.

Confused?

Ok, lets call them frozen stars. Everywhere where a “black hole” is, there is actually a frozen Star(or a frozen galaxy-nucleus).

That is what the the Theory of Relativity says:

When a star collapses and gets near the event horizon, from our view it will get slower and slower as the gravitational forces get stronger and stronger, this is called time dilation. If a collapsing star would cross the event horizon, time would stop! This is equal to a spaceship actually reaching the speed of light - not possible. And why cant we see a frozen star? Its because all the radiadion will be redshifted so much, that no VISIBLE light can escape.

And how can scientists say that in about 10^500 Years even frozen stars would decay? From the view of the frozen star the whole 10^500 years are just the fraction of a second.
Its okay if they say that in about 10^32 years even the stable neutrons will decay, that is possible. But a “black hole”, that cant even exist?

Okay, small ones will “burn out” through Hawking-radiaton, but not the really big ones(can Hawking-radiation even exist, when there are no black holes? I dont know…)!

And whats up with the guys who say that black holes can be used as time machines if you form a wormhole?
First, there are no Black holes!
Second, when you fall into a black hole not only the gravitational forces will crush you, also the magnetic fields will twist your atoms to nothing, and all the radiation that will be created from now on (if you fall into a black hole you expirience quite the opposite of what i said above, you will see how everything goes faster and faster, you will see the galaxies spinning, new galaxies being created and old galaxies burn out, in fact you will see the WHOLE future of our universe, just blueshifted till infinity in about a second)
will burn you out of existence.

I´m confused.

I have more questions, but thats it for now. It would be great if someone could answer them!

greetings from Austria

ps.: I´m not that good at english, so please excuse me if i made some mistakes!

2

I have no clue but welcome to the board. Lots of interesting things a-happen here that you might enjoy.

3

While from some outside vantage point, any infalling object indeed suffers extreme time dilation on the horizon, from the point of view of some infalling observer, nothing special happens: if you fall into a black hole, you will cross the event horizon and hit the central singularity (after having been torn to bits by the gravitational tidal forces) in a finite amount of time. The same goes for collapsing matter: any sphere of matter will (if its gravity is not counterbalanced by other forces) collapse beyond its event horizon, forming a black hole.

4

You can find here (using the “Search” feature/pull-down above) a zillion threads on black holes. Go to Advanced and select Thread Titles (not Posts), and it will help slow the flood.

5

Thats right, but from our viewpoint there never will be any black holes in the universe. This missunderstanding is so widespread that even some scientists cant count 1+1 together and dont know that actually there are no black holes at all. Not to speak from people without knoledge about physics…

Everyone thinks that a black hole is a mystery, like the Big Bang singularity (that could be the reason why scientists are interested in the singularity!)

6

The o.p contains a number of misapprehensions about the basic mechanics and phenomonology associated with black holes. Rather than write the monograph-length post that would be required to even introduce the topic in depth, I would recommend that the o.p. read one or both of the following pop-sci books on the topic: *
Black Holes and Time Warps: Einstein’s Outrageous Legacy* by Kip Thorne (one of the topic experts in gravitation) or Black Holes, Wormholes and Time Machines by Jim al-Khalili (not an expert in gravitation, but a professor of physics as University of Surrey, formerly of University College London, and an excellent science writer. (I’ve recommended the latter’s *Quantum: A Guide for the Perplexed* to a number of people as a clear and correct explanation of the supposed “double slit paradox”.)

The time travel issue specifically comes from the ways that a rotating black hole can twist the space around it, which can create a Kerr metric with closed timelike curves (CTC). A black hole is not the only phenomenon that can create CTCs, but it is the only naturally appearing one (unless we discover actual evidence of cosmic strings or other topological defects in the spacetime manifold). There a reasons to believe that even if CTCs exist that it is not possible to leave such a path at a point in time prior to entering it, but that discussion is even more complex than the basic mechanics of black holes, and I would refer the o.p. back to the references about to gain a basic layman’s understanding of the topic.

Stranger

7

I know from another methot of creating CTCs, using a lot of neutron stars in a row
that are rotating Very fast, then you can find a path spiraling around the neutron stars to create a CTC.

But you miss the point, there are actually no black holes there. Or i´m wrong with this? just a plian yes-no question.

I think i have more than layman knowledge about black holes, but if i am trying to combine them with relativity there the problems arise.

And thanks for your answers.

8

Is the OP asking if singularities don’t “exist” in a sense because we can never observe one? I’d like to know the answer to that myself.

9

What I think we have here is a failure to differentiate between what is seen and what is observed. You seem to be saying “when we look at the star, we’ll always see a little bit of light that it was emitting as it was collapsing. Therefore, the star is still there, just frozen.” The first sentence is perfectly fine as a statement about what you see, but the second sentence makes an extrapolation to what you’re observing, by which I mean “what you infer to be the current state of affairs.”

A simpler example: Suppose that tomorrow we see Eta Carinae, a star 7500 light years away, blow up in a supernova. Would you say that Eta Carinae still existed today? I would suspect not; because of the light travel time, you’d say that it exploded 7500 years ago, and that the star didn’t exist after 5487 BC.[sup]1[/sup] When we go from what we see to what we observe, we have to take the light travel time into account; the star isn’t necessarily still there just because we’re still observing light from it.

Going back to the case of the black hole, then: it’s true that we never see the star disappear, since some light is always reaching us. But the photons we’re receiving at a given time were emitted closer & closer to the event horizon of the black hole as time goes on. At one particular time (call it t = 0), we might see photons that were emitted when the surface of the star was 1 km outside the event horizon. At t = 1 hour, we would be seeing photons emitted when the star’s surface was 0.1 km outside the event horizon. At t = 10 hours, we would see photons emitted when the surface was 0.01 km outside the event horizon. And so forth.[sup]2[/sup] As time goes on, the photons reaching us were emitted when the surface was getting closer and closer to the event horizon, Zeno-like, but never quite reaching it.

But here’s the thing: if we traced all of these photons back to the time they were emitted, not received by our eye, we would find that their emission times also got closer and closer to a particular time in the past. In the above example, for example, we might find that the first batch of photons was emitted at t = -1 hour, the second at t = -0.1 hour, and the third at -0.01 hour, and so forth. As the surface of the star gets closer to the eventual event horizon, the light rays take longer & longer & longer to reach us; even though we continue to receive light for an arbitrarily long time, it’s because the light rays take longer & longer to reach us and not because the star actually stays outside the black hole for an arbitrarily long time. So it wouldn’t be accurate to say that the star still existed outside the event horizon after t = 0; no light rays reach us that were emitted by the star after that time.

In summary: yes, light continues to reach us for an arbitrarily long time after the star starts to collapse. But that doesn’t mean that the star still exists in any meaningful sense, since the light travel time gets completely messed up due to the strong gravity of the collapsing star.

I hope this helps. If this explanation was too basic for you, let me know and I can point you towards the boring mathematics.

[sup]1[/sup]Note to special relativists: Nitpick noted. Now hush.
[sup]2[/sup]I haven’t done the exact calculations here about travel times and such, so take these numbers for illustrative purposes only.

10

Black holes are inherently a prediction of general relativity, so we can only examine the problem in general relativity or in an extension of that theory.

The big problem with your idea is that the ‘frozen surface’ (called technically a trapped null surface) of a black hole which you say shows that a true black hole never forms, cannot form (under reasonable assumptions) in general relativity unless the spacetime is singular (i.e. there exists a singularity)

11

Which is a configuration that we have essentially no expectation to occur naturally. Similarly, we don’t expect Tipler cylinders, Gödel lambdadust, or other conditions to create CTCs to occur in nature.

I don’t understand the last statement. A black hole is an inherently relativistic phenomenon, and in fact their properties are predicted by particular solutions of the Einstein field equations.

As for whether there really are black holes, we have not directly observed a black hole in the sense of watching matter and light fall into the event horizon and disappear, as the closest presumed black hole (V616 Monocerotis) is about 3,000 ly from Earth. We do, however, have a considerable body of experimental evidence that is consistent with theoretical predictions of black hole phenomena.

A collapsing star (collapsar) is not “frozen” at the event horizon as you suggest, because it forms the horizon as it collapses, and the mass that forms the hole is already well within the horizon once it achieves the density to become a black hole. Nor does infalling matter and energy stop at the event horizon, or indeed, even notice the passing except that all possible future trajectories are now “downward”. Whether the mass actually forms a singularity is in question; general relativity suggests that it does, and this is the way it is treated mathematically. However, this causes problems with quantum mechanics. Because there is no working quantum field theory incorporating gravity analagous to quantum electrodynamics or quantum chromodynamics this is currently an irresolvable problem with black hole physics (and general relativity in general at those scales). However, the impact on overall behavior of basic gravitational effects would remain essentially the same whether the mass is truly compacted into a singularity or to a minmum allowable condensate.

Stranger

12

Well, we know something is there. The laws of physics as we know it tells us what it is even though we can’t experience it directly up to a point… the very point of singularity. Then the math breaks down. And it is at that point there can be only guesses.

However, there is nothing to support a frozen star as a correct guess.

13

I know, but aren´t photons travelling at the speed of light, seen from every inertial system possible? They get red- or blueshifted, but i thought they will not slow down?

And you are saying that in own inertial system we can trace down the exact time when the collapsing star actually crossed the event horizon with kind of taking a limes?

But would that not be equivalent to a starship reaching the speed of light, again from our own inertial system?

If you have a link to the mathematics, post it and i dive in!

14

Sorry, i was too late.

The problem comes when i try to combine general relativity with special relativity.
(If this makes sense)

By the way, something i find cool with black holes is that their surface area equates entropy, if two of the same size collide, the resulting black hole has double the diameter of the originals.

15

Sorry about the mass of posts, my browser logs me out everytime i do anything, so i cant edit my posts.

What i wanted to ask:
Is there actually a theory besides m-theory that combines the electroweak force with QCD?

16

Special relativity is a special case of general relativity (hence, the term) in which a “flat” Minkowski space (one in which gravity is not present and mass is essentially independent of other field properties) is used to represent the spacetime topology. This simplifies problems such that they can generally be represented by simple vectors and trigonometry. General relativity requires treating spacetime as a complex metric consisting of a pseudo-Rienmannian manifold distorted by a stress-energy-momentum field, which is a generalization of all forces acting on spacetime (of which gravity dominates at everyday scales). These are represented by tensors of partial differential equations that make up the Einstein field equations, and are very, very difficult to solve for all but the most trivial conditions; most cannot be solved in closed form at all.

The previously cited books on black holes will explain all of this clearly in terms a layman can understand. Trying to look at the Einstein field equations and make sense of them will not aid your comprehension; the full equations are not even generally presented to physics students until final undergraduate or graduate level coursework, and actually learning to solve them is a series of courses, each of which focuses on classes of solutions or techniques. Chronos, who actually works in this field of research, can elucidate on what it takes to become even marginally competent in general reelativity.

Stranger

17

Well, the biggie is tensor analysis. Lots of fields of physics and engineering use tensors, but for some reason most of them make it a lot harder than they need to. The tensors used in GR are a bit more complicated, in that they’re four-dimensional instead of three, and the metric has that odd minus sign on the time component, but it’s not fundamentally all that different.

18

Here’s an interesting factoid:

When studying a black holes, unless your particularly interested in the collapse process, the collapse is usually ignored. This is for several good reasons: firstly it has been shown that black holes quickly settle down in to the highly symmetrical objects we all know and love (this is the famous no hairs theorem), so they are pretty much the same objects governed by a small set of parameters regardless of how they formed; secondly it vastly simplifies the spacetime under study to a highly-symmetric and stationary one. When you ignore collapse you study a black hole as an object that has existed for all time i.e. an eternal black hole.

Now what happens when you trace the path of test particles, such as light rays, travelling radially outwards from the event horizion an eternal black hole back in time (assuming they have always been travelling radially outwards)? To an observer in the exterior region of the black hole they seem to have been travelling outwards for all time, but this does not actually give you the maximal extension of their paths back in time. If you take the maximal extension, you actually find that they originate from inside the event horizon of a white hole and (if applicable) they take finite amount of proper time (i.e.time from their own perspective) to travel from the white hole interior region to the black hole exterior region.

19

Yes, the various grand unified theories, which are much better understood than M-theory. Essentially, the aim of string-/M-theory is to unify all the forces, i.e. include gravity, as well, which GUT’s don’t attempt to do, and which is generally understood to be a much harder task.

As for the black holes, if you’re still not convinced they exist, you can just try jumping into one. That should eliminate all remaining doubt. :wink:

20

How will he let us know?