Black Holes, Singularities, Confusion

Thanks Kuresu! Bit busy at the moment, but will be back later...

Well, I need a bit more than that... it's a big subject Was it the wormhole aspect of Black Holes you wanted to explore, or singularities, or something else?Just to start: the usual wormhole mentioned wrt black holes is the Einstein-Rosen Bridge, which is not really a wormhole at all. It is simply the observation that a mathematically pure black hole (not the type that results from collapse of a star for example) is actually a connector that joins two infinite spaces or "universes". Unfortunately, as much as it is a connector, it is also a restrictor, in that it restricts any communication and/or travel between the two universes, unless you can travel FTL, which sort of defeats the point! We call it a wormhole because if you take a cross-sectional (spatial) slice of the black hole, it looks like a wormhole despite its total impracticality.The fun begins when you take a black hole that is rotating and/or charged. The Einstein-Rosen Bridge is still there, connecting the two mutually-inaccessible universes, but there are also an infinite number of Bridges, sequentially stacked along a corridor of time, each with a pair of "universes" that can be accessed once inside the black-hole. It's sort of like the corridor of doors from Matrix-Reloaded and other fantasy works.

Here's some Penrose diagrams (Carter-Penrose for the pedants) of what I have been talking about -Schwarzschild Black Hole (uncharged, non-rotating) is top left. Space is left-right and time is up-down. If you don't move, you trace a line vertically up the diagram as time passes. Speed tips your line over to a maximum of 45 degrees, which is the speed of light. You can see how if your line crosses the event horizon, you are doomed to hit the singularity, as you cannot tip your line more than 45 degrees. You can see some possible astronaut "world-lines" on the right hand diagram.You can see how "our universe" and "other universe" are just regions within one "total universe", connected by the "black hole".The rotating and/or charged balck hole is shown on the right. You can see the "corrdior" stretching off into the future, but it also stretches into the infinite past, with an inifnite number of pairs of "universes" attached.Note that each "universe" is an infinite universe in its own right, both spatially and temporally. So this is an infinity of infinite universes Edited by cavediver, : No reason given.Edited by Admin, : Narrow the diagram.

Hi Phat, Yes, if you check out the diagrams above, you'll see the singularities as jagged lines. Yes, the Big Bang starts in a singularity. Sort of. There is a great problem with this common view of "everything", as if all the atoms and stars and rocks and things were all squished together at the BB. The universe isn't like that. There aren't "things" that live or exist in the universe, just aspects of the universe. The aspects that we call "things": stars, cars, footballs weren't in evidence at the BB, nor for long long afterwards. Think of the universe as the ocean, and "things" as various formations of waves on the ocean. At the BB the ocean was very flat... Perhaps, or maybe we are God observing the universe Not necessrily. Infinite aspects can leave finite signatures.

Yes and no. There are definitely objects that meet the criteria for being black holes, but as for whether they are black holes inside the event horizon- in the sense of General Relativity - that remains open. But given how phenomenally successful GR has been so far, it would be hard to understand how they could not. If it falls towards the singularity, yes. In the Schwarzschild this is unavoidable. But in the charged and/or rotating case, the singularities can be avoided. I wish I knew The issue is with a microscopic black hole that is evaporating rapidly via Hawking Radiation. Theer comes a point where it is evaporated its entire mass away. The horizon shrinks to zero size, so what happens to the singularity? Does it remain as a "naked singularity"? Or does it wink out of existence with a bang? It has long been thought that some gamma ray bursters could be endpoints of Hawking Radiation - black holes going pop...

Matter is created and destroyed all of the time. Two photons (not matter) can stimulate the creation of an electron (matter) and a positron (anti-matter). Conversely, an electron and a positron can annihilate giving off two photons.There is certainly conservation of "mass-energy", but not matter.

Yes, you could say space-time is a fabric. Black-holes ARE space-time, curved in a particular way. Think of a knot tied into the fabric. In fact, if you think of all particles as different kinds of little knots in the fabric, you are not too far from how we view things. This concept gets you away from the eroneous idea of space-time being an arena for "things" to live in. No, "energy" is a derived concept. You cannot describe space-time in physical terms. Only mathematics suffices at this level.

Hi Holmes, glad you're still with us despite your rather disturbing news. All the best to you and your partner in resolving the situation.First off, subatomic particle physics research and SR are utterly intertwined. SR is not theoretcial in the sense that every moment of every day a particle lab somewhere in the world will be confirming SR to the nth degree via its particle experiments. Ensuring that two particles circling a cyclotron in opposite directons at essentially c have a chance of colliding, requires making extremely accurate corrections to the guiding magnets based on relativistic calculations. Were SR not correct to our limits of detectability, these experiements just would not work. Furthermore, our entire study of particle physics is actually based upon the combination of quantum maechanics and SR - the study of quantum field theory (qft).Ok, back to some of your earlier points. What is hard to convey (even to other professional physicists outside the arena of fundemental phsyics) is how we have no underlying reality anymore other than mathematics. The only way of understanding the concepts is through mathematics - there has been a total disconnect with principles that we would call "physical". We don't model the physical systems with mathematics, because there are no physical systems to model. We look for consistent mathematical constructs that give rise to emergent physical properties. GR was the first full-scale example of this, although Maxwell's equations can be viewed this way in hindsight. This is not well portrayed by popular science, for the simple reason that popular science actively translates this work into physical, tangible analogies that are digestible by the layman. But there are no "particles", "things", "objects" anymore. The Universe, it appears, is a far better pure mathematician than any of us!Energy is very much related to time. "Energy" is a consequence of the time-translation-symmetry of the undelying space-time "fabric". "Momentum" is the same concept but related to the space-translation-symmetry. Given time is 1d and space is 3d, you can see how energy is a scaler and momentum is a 3-vector. Actually, there is a unified 4d quantity known as 4-momentum that combines the two. Oh, we have angular momentum becasue of the rotational symmetry of the 3d space. Thus energy is no more and no less fundemental than momentum and angular momentum.The wonder of SR is its simplicity. Everything within it can be broken down to considering rotations and translations in four dimensions, where instead of the 4d space being Euclidean, it has a twist that distinguishes one of the dimensions from the other three. For example, Pythagoras on this space is h^2 = x^2 + y^2 + z^2 - t^2 instead of h^2 = x^2 + y^2 + z^2 + t^2. That is all there is to it. In 3d, we have rotations and translations. In this twisted 4d, we have (x, y, and z) rotations and translation as normal, but we also have rotations between (x, y, or z) and t. We call these rotations velocity.If you have a competing theory, first off measure the complexity of your ideas aganist this. Oh, and make sure you can beat the record that SR holds for being the most successfully (accurately) tested physical thoery in history This is has been the wonder of 20th C funde physics - its unbelievable simplicty (once you've managed to shrug off the manacles of "common-sense" and "everyday-experience")

Nice explanation - just one caveat: SR deals with acceleration and deceleration without any problems. The Twin's Paradox can be a purely SR subject.

Yeah, new thread time I think. I haven't really dived in to the depths of this while here at EvC though I have often touched upon it. Not long after discovering EvC I got into discussions over this issue but I didn't make a good job of presenting the subject - I hadn't before discussed this stuff at an academic-ish level away from practioners of the field and I was surprised by the lack of familiarity and the resistance to the ideas. When you have been immersed in a field for so long it is difficult to appreciate how little of the realities of that field make it out to the general academic public, including physicists and mathematicians. This has been how funde physics has progressed for the past 100 years so it's not really new! And we don't work on this basis because we like mathematics (though most of us do ), but becasue it works and works better than phsyics has ever worked in any other area. But we can talk all about this in another thread.One thing to remember is that "equations" are our representations of the mathematics. By mathematics, I am talking about pattern and symmetry, as expressed through areas such as geometry and topology. Yep, that's how I'd put it. Not dumb. It is very similar, though the SE is non-relativistic. In its relativistic cousins (Dirac Eqn, Klein Gordon Eqn) that's exactly how it appears. To the relativist or quantum theoretician, you may as well talk about your attachment to creationism

No problem, but to be just given the remit "explain black holes in layman's terms" is a little daunting given my limited time and the size of the subject! Questions are always well received

Ok, here's the one I came up with when I was eight. It's a bit embaressing that it took me so long, as I'd been reading about black holes for four years by then

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just because the gravity of an object increases to the point that light cannot escape, why should that invoke tales of wormholes, other universes and time-travel? Why could it not just be a super-dense object (maybe crushed to a point) and the event horizon simply be the region within which light cannot escape?

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Try that one...

Spot on. I was actually going to present exactly the same scenario to explain my position, but you have saved me the effort and made a better job of it.

Hi Greg, welcome to EvC Good question, but some difficult concepts on their way! It is a little appreciated fact that the speed of light limit is actually only for external observers, in the sense that you as a traveller can travel as quickly as you like, up to infinite speed! That is, if you define speed as known distance to your destination divided by the time it takes you to reach that destination. So for example, as you accelerate towards Alpha Centauri (4.3 ly away), you start to notice that you are getting closer to Alpha C far more quickly than expected, so much so that soon you are far exceeding the speed of light. How? Well, we are used to talking about time-dilation on such a trip but often fail to realise what this means in respect of our perceived velocity. There is also the effect of Lorentz Contraction: lengths shrink at relativistic speeds - the most important length is that between you and your destination! At the speed of light itself, your perceived distance to Alpha C becomes 0, and so the time to reach Alpha C is 0! So you have actually travelled 4.3 yrs in 0 time > infinite velocity.Ok, so what about "space-like" travel, which would be lines greater than 45 degrees on the diagrams. Well, hopefully you can appreciate that these no longer conform to our ideas of "speed" and "travel". If at c, it takes your zero time to travel any distance, what can "faster" than this mean??? Time doesn't "tick" along these space-like paths, so you could never be conscious of such a path. There is no definiton of future and past on these paths. You can teleport or wormhole from one point on this space-like path to another, but this isn't what we usually mean by travelling faster than c. This is cheating However, any time you cheat, you are also creating a time-machine because of this lack of distinction between future and past.Don't worry if the above is too confusing and/or generates ten more questions. Ask away And before anyone says anything, yes this is intimately connected with black holes and needs to be appreciated.

I'd certainly recommend it, Brad. I'm sure you'll love it. Hawking's 'Brief History...' and 'Universe in a Nutshell' are both well worth a good read, as in Brian Greene's book. If fancy some maths (and I mean reall maths!), try Penrose's 'road to reality'.Have fun!