What is inside a black hole?

[solkoe]

A black hole is a condensed star so a black hole must be made of condensed matter. In what form is that matter contained? Is it neutrons? In that case, what a distinguishes a black hole from a neutron star?

[Whack-a-Mole]

Well unfortunately if you peek inside one you'll never be able to tell anyone outside what is in there.

Nevermind what the matter was before entering a black hole. On the way in the matter is stripped to its most basic constituents (basically quarks) and then squished into an infinitely dense point. Doesn't matter if it was a star or a cheese sandwich. All the same inside a black hole.

What does that infinitely dense point looks like? Nobody knows. Physics falls apart at the singularity.

One thing I have never reconciled is that for anyone falling in to the Black Hole the singularity is always in their future. To me that sounds like in a manner of speaking they never quite reach the singularity. But if they cannot reach the singularity then how can there be a singularity (i.e. nothing ever gets there to squish together)?

::head explodes::

[Napier]

Thirty years ago the prevailing theory was called "black holes have no hair", meaning that there are very few details about them. Not that few were known, but that fundamentally black holes had to be very simple. They have a mass, an angular momentum, and a net charge. None of these things can be created or destroyed, so they must stay constant from the stuff that formed the hole to the hole itself.

The current issue of Scientific American has an article on Naked Singularities that paints a much more complicated picture.

[ProfessorX]

Yeah, that's the thing, nobody knows. It must be a different kind of matter though because of the force of the black hole doesn't behave like anything else that we have witnessed.

[Q.E.D.]

Originally Posted by Whack-a-Mole

On the way in the matter is stripped to its most basic constituents (basically quarks) and then squished into an infinitely dense point.

The fact is we don't know, and probably will never know, what's going on in there. However, knowing what we know about how things behave, it's probably reasonably safe to assume it's neither infinitely dense nor a point. It likely has some spatial extent, albeit very small and therefore some finite density, albeit very large. Generally when your math spits out infinites, you know something's not exactly quite right. Nevertheless, black holes is plenty weird.

[yanceylebeef]

You might want to pick up Death from the Skies!, the latest book by Phil Plait (Bad Astronomer).


Among the other ways we could die, he discusses black holes, and what happens when you are pulled into one.


It's an amazing look at our galaxy, as well.

[Q.E.D.]

Originally Posted by ProfessorX

Yeah, that's the thing, nobody knows. It must be a different kind of matter though because of the force of the black hole doesn't behave like anything else that we have witnessed.

I don't know what this means. Gravitationally, they look like any other object of similar mass. If the Sun were to turn iinto a black hole right now, it would certainly go dark, but the Earth's orbit (and those of all the other planets and cosmic junk) would remain unchanged.

[sweeteviljesus]

Doesn't string theory say something about matter being incompressible beyond the Planck length?

Thanks,
Rob

[Tom Tildrum]

So, conceivably, they could have hair on the inside?

[ralph124c]

How do Black holes evaporate? what happens to their mass., plus-enerby that falls into a BH-what happens to it?
There was some peculation years ago, that the analogue to Blakholes (White Holes) existed-has anyone ever found one?

[MikeS]

Originally Posted by Whack-a-Mole

One thing I have never reconciled is that for anyone falling in to the Black Hole the singularity is always in their future. To me that sounds like in a manner of speaking they never quite reach the singularity.

When people say that the singularity is always in the future if they're inside a black hole, what they means is that anyone who's inside a black hole will run into the singularity, guaranteed, no matter what they do. However, this doesn't mean that it takes an infinite amount of time (as measured by an observer) to get to the singularity; in fact, you can show that the amount of time elapsed before you hit the singularity is always finite.

[Stranger On A Train]

Here are a couple of old threads that might be of interest to the o.p.:
How is the "size" of a black hole defined?
The Universe, Black Holes and Entropy

Neutron stars (and other exotic hypothetical celestial bodies like quark stars) are still theoretical. Because of the tendency of unbound neutrons to decay it is unclear how such a body would behave or exactly what type of matter it would be composed of. Mass inside of a singularity, compressed by the curvature of space into an unimaginably small point, much denser than even quarks pressed "edge to edge". We can't really say what form mass takes in that form; indeed, a black hole can in many ways be considered a giant composite quantum particle.

Originally Posted by Whack-a-Mole

One thing I have never reconciled is that for anyone falling in to the Black Hole the singularity is always in their future. To me that sounds like in a manner of speaking they never quite reach the singularity. But if they cannot reach the singularity then how can there be a singularity (i.e. nothing ever gets there to squish together)?

From the subjective viewpoint of an infalling black-hole-diver, external time will slow as he or she is accelerated asymptotically to c when approaching the singularity "surface". Note that the singularity is where the curvature of spacetime becomes infinite, or at least larger than can be measured down to quantum scales (Planck length). The singularity for a rotating black hole (and we can readily assume that all naturally created black holes will have some amount of rotational momentum conserved from the original matter it condensed from) is actually a ring rather than a point, though the size of the ring for a stellar mass black hole is immeasurably tiny, and the diver falling into such a hole would be torn to component atoms by the tidal shearing forces long before.

It is tempting to say that the outside observer would see the hole-diver as reaching the singularity surface in a finite (and actually very short) time, but as the observer will never see anything that occurs within the Schwarzschild radius, as escape speed now exceeds c. (This also means that the hole-diver will not see what goes on in his past, as the light cone now folds in on itself.) Although we can mathematically determine, given the initial momentum properties, when a mass falling into a black hole will contact the singularity, for all practical purposes it is "gone" from our universe once it passes the Schwarzschild radius, and is now a part of the "no hair" region that is the intimate core of the black hole.

It is possible to enter the ergosphere (the area of space that is distorted by frame dragging) of a very massive, quickly rotating black hole and exit out again; one can even plot paths that go backwards in time, though in order to escape without falling in you'll have to turn around and come forward to at least your entry time. You can also fall into an orbit somewhere outside the Schwarzschild radius (3 Schwarzchild radii is the minimum radius for a stable circular orbit) which will keep you in a permanent and inescapable orbit, such that your personal future is bounded by some energy "surface" that you have insufficient ability to achieve.

Stranger

[mlees]

In reading Wikipedia about black holes, I read this article on the largest (mass-wise) one we know of: OJ287

http://en.wikipedia.org/wiki/OJ_287

Originally Posted by wiki

The optical light curve shows that OJ 287 has a periodic variation of 11-12 years with a narrow double peak at maximum brightness. This kind of variation suggests that an engine is a binary supermassive black hole where a smaller black hole with a mass of only 100 million MSun orbits the larger one with an observed 11-12 year orbital period. The maximum brightness is obtained when the minor component moves through the accretion disk of the supermassive component at perinigricon.

<snip>

The companion's orbit is decaying via the emission of gravitational radiation and it is expected to merge with the central black hole within approximately 10,000 years.

A different wiki article says:

As of November 2008, another binary pair, in OJ 287, contains the most massive black hole known, with a mass estimated at 18 billion solar masses.

So. Will the "merge" of this pair be spetacular?

[mlees]

*spectacular :doh:

Respectfully request spellchecker

[Stranger On A Train]

Originally Posted by ralph124c

How do Black holes evaporate? what happens to their mass., plus-enerby that falls into a BH-what happens to it?
There was some peculation years ago, that the analogue to Blakholes (White Holes) existed-has anyone ever found one?

Very small rotating black holes evaporate (Bekenstein-Hawking radiation) due to virtual particle pair creation near the Schwarzschild radius; one member of a pair is absorbed but another flies off, taking with it a large amount of kinetic energy (in comparison to total rotational kinetic energy of the black hole). This energy loss reduces the mass of the black hole, and eventually the mass disappears (or is at least too small to form a measurable curvature of space). The size of black hole we're talking about here is very small and incapable of being formed by the normal gravitational collapse, and instead must be due to some kind of quantum effects (hence why they are often called "quantum black holes"). Once the mass to surface area ratio of a black hole becomes too large the quantum effect no longer dominate, and while such a black hole will continue to radiate the amount of mass-energy loss is insignificant. Note that no one has ever observed Bekenstein-Hawking radiation, as it would be vastly less than the amount of normal radiation (due to interactions from infalling material) coming from any observable black hole, but the concept is widely accepted in the astrophysics community and is consistent with black hole thermodynamics as we know it.

The concept of "white holes" spewing matter and energy out is problematic; for one, a black hole is an area of space that contains maximal entropy within the event horizon, which cannot radiate away. Once matter goes into such a region, it cannot emerge back into our universe, or at least, not in any area of it we could observe without seriously interfering with causality and thermodynamics as currently accepted. It may be that the material enters some new region, isolated from our universe, and indeed, the expansion of our universe appears in many ways to be a black hole running in reverse, or at least, cockeyed.

Stranger

[Jake]

"18 billion solar masses!" I can't get my mind around this. Will anyone describe what this would look like?

[Q.E.D.]

Like this: .

[Whack-a-Mole]

Originally Posted by Jake

"18 billion solar masses!" I can't get my mind around this. Will anyone describe what this would look like?

Sure. Like this --> .

Except a lot bigger

ETA: Argh...beaten to it! Curse you! ::shakes fist::

[Half Man Half Wit]

Originally Posted by ralph124c

How do Black holes evaporate? what happens to their mass., plus-enerby that falls into a BH-what happens to it?
There was some peculation years ago, that the analogue to Blakholes (White Holes) existed-has anyone ever found one?

Black holes evaporate via a process called Hawking radiation; for a somewhat intuitive picture, think of it like this: in quantum mechanics, there is no such thing as 'empty space' -- the Heisenberg uncertainty principle allows for spontaneous generation of particle/antiparticle pairs, provided they annihilate again after some short time (basically, they live on borrowed energy, and borrowed energy, in this case, means also borrowed time). Now, if such a process happens just on the edge of a black hole horizon, it might just happen that one of the pair falls right into the black hole, while the other manages a narrow escape; however, then, the two can obviously never recombine and return their borrowed energy, in blatant (or so it would appear) disregard of fundamental physical principles and common decency.

But, if one looks at the whole process a little closer, one finds that for this to be allowed to happen, the particle that fell into the black hole must actually have had negative total energy, and thus its falling into the event horizon has effectively reduced the black hole's total energy -- by just the amount that's now being carried away by the other particle!
So, at the end of the day, the cosmic account keeper has nicely balanced books, at the cost of things looking for all the world like the black hole just spit out something in stark contrast to its usual, sucky nature.

As for white holes, no, there have never been any observed, and they're mostly thought to be mathematically sound, yet unphysical solutions to the equations of general relativity.

ETA: Yes, well, or what Stranger said better.

[Anne Neville]

Originally Posted by yanceylebeef

You might want to pick up Death from the Skies!, the latest book by Phil Plait (Bad Astronomer).


Among the other ways we could die, he discusses black holes, and what happens when you are pulled into one.

I want this book. So badly I can taste it (It tastes like chicken). Today's my birthday, and I'm hoping it is waiting at home for me...

Originally Posted by Tom Tildrum

So, conceivably, they could have hair on the inside?

Yes, also socks that get lost in the dryer, pens that my cats have gotten hold of, and the pair of glasses that mysteriously vanished from my purse in 1997. But I'm not going in there to check.

[Napier]

>Gravitationally, they look like any other object of similar mass.

A nitpick, and a minor one at that: Gravitationally, items of the same mass give gravitational fields that are similar at a given distance only to a first order or approximation. Gravitational fields have various details to them, though. For example, recall that spacecraft orbiting planets or moons demonstrate dynamic behavior that let us deduce details of the overall and local structure of those planets or moons.

The hardest homework problem I ever succeeded in doing involved comparing different level analyses of the gravitational field of an almost but not quite uniformly dense, almost but not quite spherical, body.

I bet swapping a same-mass black hole with the Earth would make the Moon behave noticeably differently within a human lifetime. Whether doing that with the Sun would make Earth behave noticeably differently, I don't want to guess.

The only way I can think of that the force of a black hole doesn't behave like other things we have witnessed, would be that black holes should impose way impressive tidal forces on objects that get too close to them. You could get your feet half as far from a black hole as your head, which you can't do with a planet. While it lasted, the pull along the length of your body would be spectacular. But that's just because a black hole is compact enough to let you position yourself this way. And, we never witness such extreme things, because we don't do this painful experiment.

There are, though, ways to use gravitational fields to distinguish between the natures of some of these animals.

[Frylock]

Whack-a-Mole suggested that from the point of view of an object falling into a black hole's singularity, it takes an infinite amount of time to reach that singularity. (Incidentally, I recall having read this somewhere as well. If I had to bet, I would bet I read it in the book Stephen Hawking's Universe long long ago.)

MikeS said this is not true--that "the singularity is always in the future" just means the singularity is inescapable.

But Stranger on a Train also addressed Whack-A-Mole's comment, and seemed to be agreeing that it is true--that "the singularity is always in the future" in the sense that the meeting with it is never in the present.

Which is it, then? Or did I misread someone?

-FrL-

[Half Man Half Wit]

If you fall into the singularity, you -- or rather, whatever tidal forces have turned your constituent particles into -- do encounter the singularity after a finite amount of time; that the singularity is always in your future only means that there exists no path that does not meet it beyond the event horizon.

The often-repeated 'it takes forever to fall into a black hole' only is true from the point of view of external observers -- to those, due to gravitational time dilatation, an object approaching the event horizon seems to asymptotically slow down to a standstill just before actually encountering it (of course, its light will also be redshifted beyond visibility, so you couldn't look at a black hole and see all the stuff that ever fell in just kinda hang around at the event horizon). However, the object falling in knows nothing of this -- in fact, it can't even tell when it crosses the horizon.

[Frylock]

Originally Posted by Half Man Half Wit

The often-repeated 'it takes forever to fall into a black hole' only is true from the point of view of external observers -- to those, due to gravitational time dilatation, an object approaching the event horizon seems to asymptotically slow down to a standstill just before actually encountering it (of course, its light will also be redshifted beyond visibility, so you couldn't look at a black hole and see all the stuff that ever fell in just kinda hang around at the event horizon). However, the object falling in knows nothing of this -- in fact, it can't even tell when it crosses the horizon.

Actually, that's what I was remembering, I think. I got my frames of reference mixed up.

-FrL-

[Ring]

Originally Posted by Half Man Half Wit

But, if one looks at the whole process a little closer, one finds that for this to be allowed to happen, the particle that fell into the black hole must actually have had negative total energy, and thus its falling into the event horizon has effectively reduced the black hole's total energy -- by just the amount that's now being carried away by the other particle!

What Half Man Half Wit said is absolutely correct, however a couple of other points.

Even though the total energy of the infalling particle is negative the energy of the particle itself is still positive.

And another way to look at is that the hole via its tidal gravity has expended enough energy to create two real particles (from the virtual particle pair) but only gets the energy of one particle back. Effectively radiating a particle.

[Altair33]

Has anyone ever figured out the minimum IQ you need to have to be able to understand stuff like general relativity and particle physics? I like to think I'm a pretty smart guy and I have a law degree from a good school, but this stuff goes way over my head. Oh sure, I can parrot back the stuff I've read like "massive objects warp spacetime" but I don't really understand, for example, how space and time can be the same thing. It's fascinating stuff as long as you are content with only understanding every few sentences you read.

[Ring]

Originally Posted by Altair33

Has anyone ever figured out the minimum IQ you need to have to be able to understand stuff like general relativity and particle physics? I like to think I'm a pretty smart guy and I have a law degree from a good school, but this stuff goes way over my head. Oh sure, I can parrot back the stuff I've read like "massive objects warp spacetime" but I don't really understand, for example, how space and time can be the same thing. It's fascinating stuff as long as you are content with only understanding every few sentences you read.

You'll have to judge for yourself how reputable this site is.

According to these tables, the average IQ of a physics PhD student is about 130. For comparison, english/literature PhD students average about 120 and sociology PhD students only 115. (115 is the average for college students in general, so the typical sociology TA is no smarter than the students in his or her class ;-) Amazingly, the average grad student in education (109) is below the average for college students!

http://infoproc.blogspot.com/2005/12...s-them-in.html

[Exapno Mapcase]

Originally Posted by Altair33

Has anyone ever figured out the minimum IQ you need to have to be able to understand stuff like general relativity and particle physics? I like to think I'm a pretty smart guy and I have a law degree from a good school, but this stuff goes way over my head. Oh sure, I can parrot back the stuff I've read like "massive objects warp spacetime" but I don't really understand, for example, how space and time can be the same thing. It's fascinating stuff as long as you are content with only understanding every few sentences you read.

I guarantee you most physicists couldn't get through a court opinion without specialized help. I've had the misfortune to read hundreds of medical journal articles and they are often incomprehensible. Interest, aptitude, and prolonged study are the key in almost every field.

I grok most concepts in advanced physics without an advanced degree. I can't explain them the way the physicists do but I've read about each advance over the past 40 years and I've read all the good popular books explaining the concepts by going back to the beginning and leading me through the logic. I'm not coming at it suddenly from the outside and trying to let it sink in by deep end immersion.

Law is no different. How many threads have there been in which Gfactor quotes yards of law jargon and people have to ask for a simple explanation. Anybody else's jargon is impenetrable until you can find the time to hack a pathway through it with the aid of a good translator. That doesn't make you less smart.

The only group that really is smarter than everybody else is writers.

[Ring]

Exapno I don't doubt you grok the concepts, but that's the easy part. Until you grok the Mathematics you don't really understand why you don't understand it.

So.

How are you at groking the math?

Actually I found that groking the math wasn't as difficult as groking the notation, especially indicial notation. That shit almost killed me.

And the real physicists here are still so far out my league that I need a telescope to even see them.

[Stranger On A Train]

Originally Posted by Ring

Exapno I don't doubt you grok the concepts, but that's the easy part. Until you grok the Mathematics you don't really understand why you don't understand it.

So.

How are you at groking the math?

Actually I found that groking the math wasn't as difficult as groking the notation, especially indicial notation. That shit almost killed me.

Or as the old saw attributed to Thomas Edison goes, genius is 1% inspiration and 99% perspiration. The primary characteristic of most "geniuses" is that they're wonks; that is, that they are able to focus in and study the intimate details of some field (or subfield) in such detail and depth that their knowledge of it is intimate and vastly exceeding that which any dilettante could hope to approach. This is not to say that it doesn't take a modicum of intelligence to understand the mathematics behind general relativity, but once you get past the notation (which, as Ring notes, is fiendishly difficult to interpret) the math is relatively straightforward...just very, very, very tedious to work through for any significant problem. And at least GR gives answers that are more or less intuitive (once you accept the underlying premises of the theory). This places it in contrast with quantum mechanics, where you just have to accept that the math just because it happens to work, not because it makes any kind of sense.

Of course, an understanding of advanced physics based upon analogized explanations is just that; comprehension based on comparative similarity. A practical mastery of the material comes when you can concoct a scenario, develop a predictive model, and match your answers to reality.

Stranger

[Rigamarole]

What I don't understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now?

[Der Trihs]

Originally Posted by Rigamarole

What I don't understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now?

The inverse square law, and orbits. Gravity becomes weaker with distance; so once everything nearby has been pulled in ( or thrown away ) only objects that drift nearby are significantly tugged on by the hole. And in order to actually be pulled in, an object has to hit the hole. Just as planets can orbit the Sun without being "sucked in" and immolated, objects can orbit or just fly by a black hole.

Originally Posted by mlees

So. Will the "merge" of this pair be spetacular?

From what I recall, and from my googling while an enormous amount of energy is released, it's almost all in the form of invisible gravity waves.

[Frylock]

Originally Posted by Rigamarole

What I don't understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now?

Because not everything is within some black hole's "surroundings," so to speak.

As long as you stay away from the event horizon of a black hole, you're good to go. Everything that hasn't been captured by a black hole by now, then, is all the stuff that hasn't come within the event horizon of a black hole. It's not suprising that there's so much stuff left, since the volume bound by event horizons of black holes is a tiny fraction of the volume of space in the universe.

-FrL-

[Anne Neville]

Originally Posted by Anne Neville

I want this book. So badly I can taste it (It tastes like chicken). Today's my birthday, and I'm hoping it is waiting at home for me...

It was! I'm enjoying it immensely.

Originally Posted by Stranger on a Train

Or as the old saw attributed to Thomas Edison goes, genius is 1% inspiration and 99% perspiration.

I can tell you that this is true of majoring in physics. You really do a lot of slogging through problem sets, or at least I did when I was getting my undergrad degree in physics. And then there are the labs. I would say that "being willing and able to put in a lot of time doing the work for your classes" is at least as important as raw intelligence for a physics major. It really isn't a matter of reading something like "space and time are the same thing" and immediately and intuitively understanding what that means- it's doing a lot of problems where you have to treat space and time the same way.

[Q.E.D.]

Originally Posted by Rigamarole

What I don't understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now?

This was explained waaaaay back in post #7.

[billfish678]

Originally Posted by Anne Neville

It was! I'm enjoying it immensely.



I can tell you that this is true of majoring in physics. You really do a lot of slogging through problem sets, or at least I did when I was getting my undergrad degree in physics. And then there are the labs. I would say that "being willing and able to put in a lot of time doing the work for your classes" is at least as important as raw intelligence for a physics major. It really isn't a matter of reading something like "space and time are the same thing" and immediately and intuitively understanding what that means- it's doing a lot of problems where you have to treat space and time the same way.

In my graduate school, there was a minimum they required on the standardized tests (the math ones). It wasnt a HARD rule to be admitted, if you could convince them some other way that you could grok the math at the required level, they would consider that.

But, having said that, years of experience had shown them that statistically speaking, if you didnt test at some fairly above average math level, you just werent going to be able to cut it in the program.

And these professors seemed to be the nice ones that WANTED more folks in the program, not some elitist snobs looking for any reason to keep folks out.

For what its worth.

[billfish678]

Originally Posted by Stranger On A Train

Neutron stars (and other exotic hypothetical celestial bodies like quark stars) are still theoretical. Because of the tendency of unbound neutrons to decay it is unclear how such a body would behave or exactly what type of matter it would be composed of. Mass inside of a singularity, compressed by the curvature of space into an unimaginably small point, much denser than even quarks pressed "edge to edge". We can't really say what form mass takes in that form; indeed, a black hole can in many ways be considered a giant composite quantum particle.


Stranger

I thought neutron stars (like black holes) were fairly well confirmed observationally ? As to how they work detail wise (like black holes), thats a whole nuther issue .

[Anne Neville]

[quote=billfish678;10763138]In my graduate school, there was a minimum they required on the standardized tests (the math ones). It wasnt a HARD rule to be admitted, if you could convince them some other way that you could grok the math at the required level, they would consider that.[quote]

I went to grad school in astronomy, not physics. Maybe there was some minimum score on the math GRE, but nobody ever talked about it. I remember the math section of the GRE being really easy, though- supposedly, it's easier than the math SAT.

We did also have to take the physics GRE, which was definitely not easy. It's not an IQ test, though. It's a physics test, and supposedly scores vary quite a bit based on where you did your undergrad degree.

Originally Posted by Exapno Mapcase

I grok most concepts in advanced physics without an advanced degree. I can't explain them the way the physicists do

There are lots of physicists who aren't very good at explaining things, too.

[martu]

Do Black Holes grow?

[Whack-a-Mole]

Originally Posted by martu

Do Black Holes grow?

Sure. If the Black Hole has something to "feed" off of it will grow.

For instance, occasionally there is a star orbiting a black hole and the black hole is siphoning off material from the star. Since the black hole is gaining mass it is growing. Eventually the BH will completely consume the star (or the companion star, if of the right size, may form into a black hole too...eventually the two black holes would merge making one bigger one).

[Chronos]

Assorted nitpicks:

Quoth Stranger on a Train:

We can't really say what form mass takes in that form; indeed, a black hole can in many ways be considered a giant composite quantum particle.

A giant fundamental particle. Composite particles have hair.

The singularity for a rotating black hole (and we can readily assume that all naturally created black holes will have some amount of rotational momentum conserved from the original matter it condensed from) is actually a ring rather than a point, though the size of the ring for a stellar mass black hole is immeasurably tiny, and the diver falling into such a hole would be torn to component atoms by the tidal shearing forces long before.

Actually, if the hole is maximally rotating (believed to be a good approximation for almost all astrophysical black holes), then the ring is of order a kilometer in diameter, and there are geodesics which pass cleanly through it. You're still going to hit it if you fall in, though: Any nonzero test mass will, as it's falling, perturb the hole in such a way as to close up the ring just in time for the test mass to hit it.

Quoth Ring:

Actually I found that groking the math wasn't as difficult as groking the notation, especially indicial notation. That shit almost killed me.

I suspect that you didn't have a very good teacher. Taught well, the index notation makes tensor problems far, far easier. I always cringe when I see engineers (who haven't learned the Einstein summation convention) doing tensor problems the hard way.

On white holes, meanwhile, there's nothing in the laws of physics that says that they can't exist, but they can't form. So for a white hole to exist, it would have to have existed since the beginning of the Universe. Since our Universe apparently started without any white holes, without white holes it shall remain.

[billfish678]

Originally Posted by Chronos

On white holes, meanwhile, there's nothing in the laws of physics that says that they can't exist, but they can't form. So for a white hole to exist, it would have to have existed since the beginning of the Universe. Since our Universe apparently started without any white holes, without white holes it shall remain.

Could you expand on that without making most of our heads explode?

[Lemur866]

Or you could say that one white hole has existed since the beginning of the universe: the universe.

[Ring]

Chronos wrote:

I suspect that you didn't have a very good teacher.

I have an electrical engineering degree and an MBA. Over the years I bought about a zillion dollars worth of physics and math texts and taught myself.

So I can guarantee you that I didn't have a very good teacher. In fact he sucked canal water. If it weren't for sci.physics and the internet he and I would still be sucking it.