Hey Chris, referring to non-zero cosmological constant 'lambda', yes, and also recent threads re Fraser and Pamelas 'shape of the universe' podcast, where we discussed, amongst other things curvature being closely related to density 'omega' - no one mentioned a temporal component, but I imagine it would be a small contribution to the total. I know Tommac is interested in this stuff generally.

By the way if anyone else was wondering what the hell is time reversal this might help!

And sorry for being thick, but what's MTW?

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

<wail>nooooooooohhhh!!!!</wail>

That page is talking about something completely different, which isn't even part of domain of the classical field theory, which is more related to the notion of a physical process which can in some sense briefly "reverse time".

Did we? Well, the trace reverse of the Ricci curvature tensor (the Einstein curvature tesnor) is directly proportional to the stress-energy tensor; equivalently, the Ricci tensor is directly proportional the trace-reverse of the stress-energy tensor, but gravitational radiation involves the Weyl curvature tensor (roughly speaking, "the other half" of the mathematical description of spacetime curvature).

Misner, Thorne, and Wheeler, Gravitation, Freeman, 1973, the first modern gtr textbook and IMO one of the great scientific books of all time. John Wheeler, the third author and the man most responsible for rendering respectable the notion of the concept of "black holes", died on Sunday at the age of 96. He was responsible for many of the fascinating ideas popsci authors love to discuss. To name just one example, the web page from the University of Oregon which you linked to above features a lovely visualization of "space-time foam", one of the icons of the search for quantum gravity.

My bad, I'll start another thread - at least I didn't link to wikipedia, I would have, but I didn't want to give you a coronary!


Not we, we, just the we that were there.

A life well lived. I'll get the book from the library. And some aspirin.

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

If black holes exist, then there is no question to whether white holes exist, since they are the time-reversed quantity of black holes.

I am not sure if that is true.

Well it stands to reason that if the arrow of time pointed backwards, which it probably will eventually, black holes will act analogous to white hole behavoiour. And white holes may well exist in nature, so long as black holes are there, and vice versa.

In a word, no. First, as I understand it, there are more than one arrows of time, and the only one that might reverse direction is the cosmological arrow of time, which points one way while the universe is expanding and points the opposite way if the universe contracts. Second, it is by no means certain or even probable that the universe will contract at any point in the future, so we really don't know if even this arrow of time will reverse its direction. Third, but not least, as the cosmological arrow of time is really just a fancy way of saying "the universe is expanding/contracting", even if the cosmological arrow of time reverses direction, it doesn't mean white holes and other time-reverse objects will magically pop into existence!

__________________
"It's over you head now. Time to get some professional help." - My fortune cookie from lunch

Ned Wright's Cosmology Tutorial

Usenet Physics FAQ

The cool part of the discussion about white holes is that a white hole really has to be also a black hole by definition ( I think ). If you time reverse crap falling into a black hole you will have crap popping out of a white hole ... however the effect of gravity remains constant. As stuff pops out of a white hole it decelerates the same way as when stuff falls into a black hole it accelerates. The gravitational force to decelerate the crap is equal to the gravitational force to accelerate the crap. gravity drops out of the equation of a time reversal.

One thing though ... if anything other than base energy was emmited out of the white hole ( I think ) the second law of thermo dynamics would be broken.

I think if a spaceship popped out of a white hole, in a time reversal of a space ship falling into a black hole does that break the laws regarding entropy? Because of its creation of ordered matter? Am I way off?


the other interesting thing is that stuff emmitted from a white hole has no past. Stuff entering a black hole has no future.

Not quite--- only the "eternal black hole". That is the physically implausible model which I mentioned. The physically plausible model is the OS collapsing dust ball model (described in the page mentioned by Codeslinger), which does not contain a white hole.

Correct.

I caution you again that there are several pitfalls here. First, I doubt you yet appreciate how "space" and "time" relate even in special relativity (since you haven't yet read the book I want to recommend). Second, unless you've studied the notion of coordinate charts you will surely fail to appreciate the distinction between coordinate derivatives and covariant derivaties.
Third, even in flat spacetimes there are multiple distinct but physically reasonable and operationally significant notions of "distance in the large", and thus of "velocity in the large", and thus of "acceleration in the large". Fourth, well never mind, there's much more but I think I've made my point.

To understand gtr, another idea you would need to master is this: in gtr, those observers falling into a black hole are -not- accelerating. In gtr, the acceleration of an observer is simply the covariant derivative of the tangent vectors to his world line, taken along those tangent vectors. IOW, the "path curvature" of his world line (to understand this you need to study the differential geometry of curves in Riemannian and Lorentzian manifolds). Then, inertial observers feel no forces, which means that their world lines have vanishing path curvature (zero acceleration); they are geodesic curves. IOW, given two sufficiently nearby events on the world line, if you vary the segment of the timelike curve between those events from a timelike geodesic, the "length" (integrated proper time) will shorten.

For other readers: I was about to give up on tommac when he PM'd me to ask what book I wanted to recommend to him. I hope he doesn't mind my mentioning this (dunno why he would, since asking for recommended reading suggests a serious intent, which no doubt all BAUT expositors welcome). I had intended that he ask in public, and it seems worthwhile to divulge my recommendations here.

I suggest reading:

Edwin F. Taylor and John Archibald Wheeler,
Spacetime Physics
New York, W. H. Freeman and Co., Second edition 1992
ISBN:0-7167-2327-1.
Phone orders: 1-800-288-2131

New and used copies of this and many other books are readily available anywhere in the world from on-line booksellers, e.g.
http://www.amazon.com/Spacetime-Phys...dp/0716723271/

Many public libraries and most university libraries have searchable on-line catalogs. If your own local library does not have a copy of this book, you can inquire about interlibrary loan. This book should be in most college libraries. In fact, I just checked and found hundreds of libraries have it. To mention just a few examples from, oh, say, the vicinity of Pittsburgh:
a. Washington & Jefferson College (Washington, PA),
b. California University of Pennsylvania (California, PA),
c. Reeves Library (Greensburg, PA),
d. Geneva College (Beaver Falls, PA)
e. &c &c
(Hang on, there is a town in PA called California? Apparently so! I know it must be true because :-/ http://en.wikipedia.org/wiki/California%2C_PA Who knew?! And Beaver Falls, how ironic--- I wonder if they have The Origin of Species?)

Last but not least, see the home page of the living coauthor, Edwin F. Taylor, if you want to buy (I said buy!) some related software:
http://www.eftaylor.com/special.html

[EDIT: it seems that some BAUT posters pretend never to have heard of author royalties. Do we really need to say that we do not condone stealing books? Sheesh!]

If you (plural) like that, try these:

Geroch, General Relativity from A to B.

Weinberg, The First Three Minutes.

The first mostly uses only high school math; the second two are popular books. The book by Geroch does an superb job of conveying by pictures good intuition for light cones/tangent spaces in the simplest black hole model (Schwarzschild vacuum solution). The book by Weinberg does a superb job of describing the basic features of the Standard Hot Big Bang Theory.

I'd also recommend some excellent expository papers by Luminet which are available at the arXiv:

http://arxiv.org/abs/0704.3579

http://arxiv.org/abs/astro-ph/9801252

And two invaluable internet resources from Ned Wright for anyone interested in cosmology (regardless of background):

http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmology_faq.html

And from Andrew J. Hamilton, for anyone interested in black holes (regardless of background):

http://casa.colorado.edu/~ajsh/schw.shtml

Enjoy!

Huh? I am talking about a white hole having to be a black hole. I never mentioned anything about a black hole having to be a white hole.

Anyone have the torrent for these books?

Don't answer that, anyone! Tommac, ferchrissakes, just buy the darn book, already. A slightly used copy might cost the price of a few tubs of ice cream, and new copy costs roughly the price of six movies, eh? Or you can just borrow a copy from your local public library.

I forgot to say: as tommac suspected, that simply doesn't follow at all, at least in what I consider any reasonable interpretationof what Ghost meant.

I see you asked another question, tommac, but you misunderstood and now I really am done. Good luck.

What is the difference if I borrow it from my library or download it online?

The difference between leasing and stealing?

For at least three decades now, I've been aware that the expression,
"it stands to reason that..." is always and without exception followed
immediately by nonsense.

Just an observation.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

I dont think that it is stealing. Is it even against the law? I dont think so.

It is illegal to distribute copies of books without the copyright owner's
permission. Downloading the text of a book which has been illegally made
available for download would itself be illegal. You need to determine
whether the copyright owner has given permission for the download.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

-It stands to reason that... Lol., and yes. I agree.

If this accelerating expanding universe catches up with and reverses that what is ('Forces Unknown') pulling it out. Stops.
Then... Begins to fall ever inward. Why do you think that would reverse time? It would not.
We might not notice for a very long time. Let me guess...13.7 billion years, maybe. Time and our observation of distance across space would not become any different than it is now. Our perception of time would not change... Other than the obvious blue shift.. and ...
and I have no regard for the list of copyright owners who's books I will never read...They may be wrong...O:

$61 for a BOOK???? Are books only for the rich these days? Who can afford $61 for a book ...

<chuckle> Some text books see $100 well into their rearview mirror

The value of the book is determined by what's inside it.

Fortunately for the rest of us, there also exists public libraries, which Chris recommended right after the section you quoted.

__________________
"It's over you head now. Time to get some professional help." - My fortune cookie from lunch

Ned Wright's Cosmology Tutorial

Usenet Physics FAQ

Done with what? BTW I BOUGHT the book.

__________________
http://www.whatisorganicliving.com
http://www.cancerfightforums.com/forum/
http://www.nycbrownies.com
"Banned by BAUT" Alumni (2008)

I would have to say that since we understand that gravity is not really a "force" in the sense that is is not a fundamental model force like the week force or the strong or magnetism.

I would have to speculate that a White Hole would have a gravitational attraction just like a black hole. (since gravity is a phenomena of a geometric space)

and since Mass and energy are interchangable, (meaning they are the same thing). I would presume that a White hole would put out "stuff" at the speed of light in the form of energy.

Wait...
don't stars do that?

case closed.

__________________

-work in progress--

the problem with time,

it is exactly like quantum superposition, where the future is is the combination of all the possible states of a system and like the Copenhagen interpretation of quantum mechanics which implies that the superposition only undergoes collapse into a definite state at the exact moment of quantum measurement. when the present happens, the superposition of time collapses and the event that is observed becomes its final state. The past is nothing more than a condensate of the future and the present is where the observation collapses superposition of the system.

__________________

-work in progress--

The difference is where this stuff would come from. Remember that the white hole would still have curved space so that light could not escape. Thus the dilemma.

Actually I think the deal is that a white hole and a black hole are really the same thing.

__________________
http://www.whatisorganicliving.com
http://www.cancerfightforums.com/forum/
http://www.nycbrownies.com
"Banned by BAUT" Alumni (2008)

Tommac, oas i understood is more / less like this...

Both black and white holes are somewhat linked, so one is opposite of the other, so while space is "compressed" in the blacky, space is expanding in the white one, and there should not been any trouble with a massive WH, anyways because it will never be massive enough to counter the space dilatation (since it lose mass constantly)

White holes became popular in cosmology because Mr. Hawking did not have a real answer for the information paradox, so he came with this stuff adding some other nice star trek things, another patch for the cosmology... (but seems it was fixed later, althought dont know how)

There are several doubts about if the singularities actually exist.....so this debate could be meaningless

By definition a white hole is the time reversal of a black hole ... so white holes have the same gravitational pull as a black hole.

__________________
http://www.whatisorganicliving.com
http://www.cancerfightforums.com/forum/
http://www.nycbrownies.com
"Banned by BAUT" Alumni (2008)

This is correct, if we are taking the position that SMBH's are 'real' 'physical' entities *which we are if we are discussing Black Holes*, with event horizons, as boundary conditions, where once anything goes below this event horizon, it can never return back up through 'this same event horizon'.

Tommac...Understand, once and for all, that the 'jets' of a SMBH CANNOT be a 'White Hole'...period. That concept came from a "Gross" misunderstanding of what is happening 'below the event horizon!!!

The "White Hole" is at the "Other End" of the SMBH...

Now,,,

Here is a very simple question for everyone...

IF, there is "ONE" SMBH in that "Other Universe"...shouldn't there be MANY SMBH's in that universe, just like there are in Our Universe?

SO, where would those MANY (Kerr) SMBH's, come "Into Our Universe"???

Once you get this, I will cover the time reversing.

__________________
RussT
________________________________
Everything is, as it should be, otherwise, it wouldn't be!

I am saying at the EH. the emitted needs to be at the speed of light.

__________________
http://www.whatisorganicliving.com
http://www.cancerfightforums.com/forum/
http://www.nycbrownies.com
"Banned by BAUT" Alumni (2008)