Say white holes do exist. ( dont want the "we havent found one" argument )

If a white hole spit out stuff at the speed of light ( It would need to in order to escape the event horizon )

Stuff being expelled near the white hole would exist in a very condensed space-time as they are effected by the white holes extreme gravity. As they get farther from the white hole they slow ( with decreasing force as it leavels the gravity well of the white hole ) ( would it ? ) but at the same time their space-time would grow. Their space-time would be expanding quickly from a VERY SLOW very condensed near stopped pace.

The things that got shot out ahead of them would appear to be getting farther from them because of the warping of time space. ( Note: how does the escape velocity come into play? )

The things emitted behind them would seem to be getting farther away as we are speeding up leaving everything in the very limited past behind.


OK this is where I am going with this:

Would everything appear redshifted to an observer that was emmited from a white hole?

If so ... how is that different than our big bang? COuld the big bang just be a continuous flow out of a white hole?


Relatively how long would it take for something to be emmited from a white hole from event horizon ( or even from its singularity ) to outside its massive gravitational pull? What would be the expansion of stuff being emmited? By expansion I mean that stuff coming out would be very small but as time-space expanded it would become very large, how much of a difference could there be proportionally???

Well, first you need a Swartzchild wormhole, which is itself unstable, disconnecting the moment it connects. Second, white holes themselves violate the second law of thermodynamics. Third, quasars and active galactic nucleii spew out jets formed from the accretion disk via magnetic fields which warps the matter towards the poles. Forth, some researchers are now theorizing that when a black hole forms, it creates a new universe which spews the matter out in sort of a "cosmological white hole." But this isn't a point source. Rather, they theorize that it's all throughout the universe, or only at the outer bounday.

Thus, there may never have actually been a Big Bang. Everything we see might just be the result of a supermassive black hole in another universe, perhaps one where time runs backwards compared to us.

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No, that's not right. White holes (if they existed, which they probably don't) wouldn't spit 'stuff' out at the speed of light. Nothing with mass can go that fast. Only light and other massless particles can travel at light speed.

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If this could happen could that happen;...? NO !

and for the reason you stated. There are none. There is little point making what if proposals based on a myth.
Yes also to ejecting mater at light speed. Not a possible act unless the space itself was doing the expanding thing... and its not. In this case.
In this nonexistent white hole... How would there be a event Harrison?
You can not mix this sort of half truth with science fact and expect us to agree... we do not know your rules. Do better to move away from science fiction and onto science fact. Its easer

If they did exist. At the event horizon they would need to be travelling at exactly the speed of light. If they werent, they would not travel fast enough to escape the gravitational pull of the whitehole itself. At the event horizon of a white hole gravity pulls back space-time at exactly the speed of light.

Maybe what gets spit out of a white hole is energy / or light ( hawkings radiation? ?? ) so lets say a photon of light is emmited

would all other photons of light red shift relative to that one? photons that were emitted previously would be moving away relativistically and ones that were emitted after would redshift because I was moving away from them relativistically.

Right?

I was referring to theoretical white holese :
http://en.wikipedia.org/wiki/White_hole#Origin
Basically just a time reversal of a black hole.

OK lets call them blackholes then. let me ask the same question about black holes.


In addition ... I dont quite understand what the difference between a white hole / black hole would be vs the big bang. To me they sound very similar.

In fact wouldnt the same argument around the second law of thermodynamics be the same for white hole vs big bang?

In some equations, a white hole is "permitted" to exist, but just because the math allows for it doesn't mean it actually does exist.
There are other observations and math that severely reduce the liklihood of a white hole, including the speed limit of c and that matter cannot travel at c.

As to red shifting light photons... If they are all escaping at light speed, then no red shift would be seen. There is no velocity difference. For the sake of this thought I do not think A White Hole has a event horizon. By definition its the opposite of a Black Hole. I can not see one of these things existing for more than a nanosecond. Leading me to questions like; Does a supper massive black hole ever reach a point where it just overcomes its own gravity mass and explodes in a most spectacular energy eruption.?

Just a slight correction. A white hole is not by definition the opposite of a black hole. In fact white holes and black holes may be the same thing.

A white hole has the same gravitational pull as a black hole so by that fact alone I would find it hard to distiguish between the two as stuff would be sucked into a white hole in the same way they are sucked into a black hole.

I believe the definition is that a white hole is a time reversal of a black hole. Which using that definition would clearly show that it has a gravitational effect exactly equal to a black hole.

Although there would be no velocity difference wouldnt there be a red shift? Because one is deeper inside the gravity well and fighting against a compressing space time, similar in some ways to something travelling close to the speed of light ( at least in the sense that its space time is compressed ) so even though two beams of light are travelling at c doesnt mean that they are not redshifted right?

Unacceptable--- time reversal has no scientific basis. It can not happen. A black hole is never a white hole. Time being reversed is not possible.

I might be wrong?

Go on..... show me an example of this?

Again it may be impossible for a white hole to exist ... actually they are not likely to exist ... but the definition of a white hole is a time reversal of a black hole. That is its mathmatical definition.

So is Zero Multiplied by infinity.

Mathematics is a representation we use.

Ummmmm I didnt make this up. I think it is valid mathmatically ... at least as valid as a black hole.

The big proof against them from what little I understand is that they break the second law of thermodynamics, I belive by the creation of matter out of nothing. Personally I feel that could be explained but that seems to be the concensous.

I'm sorry, I'm well aware you are not inventing things or making stuff up.

The math allows for the existance of white holes in some areas. But not all.

No problem I was just referring to astomarks comment:

My point was that mathmatically a white hole is a time reversal of a black hole. That is the definition of a white hole, it would neither exist or not exist if it was not defined and that is the definition.

Ok, but my point (And I think Astromarks) is that the mathematics is not the complete picture. The math is GREAT, don't get me wrong, but there is more to the picture than just one facet.
The mathematics can allow for a white hole in some ways. But that still is not the complete picture.

From Curious About Astronomy:

(bold mine)

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OK where I really wanted to go with all of this is :

Drum roll please ...
Why is a white hole not possible but the big bang is almost taken as fact.

Really they dont seem that much different?
What is the piece that makes the BB real and white holes imagination?

See Codeslinger above...

(Hints at "matter")

Again why would that be different for the big bang?

Did you see the bolded part about how once there is any amount of matter in the nearby spacetime, the mathematical solution that yields white holes no longer works? My understanding is that the BB singularity, on the other hand, is under no such restriction. I believe this is one of the many differences that separates the BB singularity and white holes.

tommac, you appear to have great curiosity and a good grasp of certain basic concepts. But you seem to have rather significant gaps to fill as well, and speculating and asking questions on internet fora are no substitute for reading and studying on your own. I suggest starting a thread (or two) in Q&A to solicit recommendations for books on topics that interest you the most.

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If a "white hole" has gravity like that of a black hole, then anything
emitted from inside its event horizon would need to be moving faster
than the speed of light as it crosses that horizon in order to escape
ballistically. Alternativey, it could be emitted by some repulsive force
which causes it to accelerate as it rises.

If the gravity of a white hole is like that of a black hole, and the stuff
being emitted from it is any kind of matter or radiation we know of, and
there is no magical repulsive force causing the stuff to accelerate, then
the stuff will slow down as it leaves, and will get closer together, not
farther apart. Same for black holes as for white. Light from particles
which emerged from the hole earlier would appear blueshifted, not
redshifted, to a particle which emerged later.

I can try to clarify something about Hawking radiation:

Hawking radiation is caused by a combination of two things:

1) Pairs of virtual particles are constantly being created and destroyed
everywhere. They are mostly virtual photons, but include particles of
all kinds. The length of time they can exist normally depends on their
energy, and is described mathematically by the principle of uncertainty.

2) The black hole's extreme gravitational gradient. The gradient causes
some pairs of virtual particles to split up after they form and before they
can be destroyed. One particle goes into the black hole, and the other
escapes. This can only happen very close to the event horizon. A pair
of virtual particles which forms inside the event horizon will both remain
inside the black hole, and nothing special happens. A pair of virtual
particles which forms far outside the event horizon will both escape,
and again nothing special will happen. If one particle falls in while the
other escapes permanently, some of the black hole's mass-energy will
be carried away by the escaping particle. The strength of the gravity
gradient determines how frequently this happens. It happens far, far
more frequently with small black holes than large ones, so small black
holes would have high temperature and evaporate rapidly, while large
black holes would have very low temperature and evaporate very, very
slowly.

-- Jeff, in Minneapolis

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Is it worth reflecting that perhaps the big bang singularity is itself far from well understood?

Big Bang cosmology plays the 'video tape' of expansion of the universe backwards so we find all the matter, space and time of our observeable universe compressed into a 'singularity' of infinite density and heat at time=zero seconds.

Fair enough, but the singularity itself is not directly observeable (I've put up a prior modest post about the phenomenon of nature constructing event horizons around singularities, with a link to an interesting web page at the University of Oregon, here) and our best theories, relativity and quantum mechanics, are incompatible at t=10^-43. Science does seem to have a good handle on events after that, but even then relies on inflation which is less well understood than the rest of the standard cosmology.

We don't really know where the universe came from...

just my $0.02

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Hi Jeff

Why do small black holes evaporate faster?

For a moment I thought perhaps because gravity is stronger for a large black hole so fewer particles would escape, but that would seem to balance out with a steeper gradient, so more pairs would 'split', presumably?

Then I recalled reading that because the 'area' of an event horizon increases more slowly than the 'volume' (squared vs cubed?) the density of some of the largest black holes is not much more than water? So is it the case larger black holes have 'weaker' gravity?

Or am I up the creek without a paddle?

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The gravity gradient at the event horizon of a small, low-mass black hole
is much greater than the gradient at the event horizon of a large, very
massive black hole. The smaller the black hole, the stronger the tidal
force at the event horizon.

So pairs of virtual particles are often pulled apart by the gravitational
tide near the surface of a small black hole, but very rarely pulled apart
by the tide near the surface of a large black hole. Thus, small black
holes emit particles from just above the event horizon at a high rate,
while large black holes emit particles at an extremely low rate.

-- Jeff, in Minneapolis

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point of rockets is to explore them!" -- Kai Yeves

Nice, thanks Jeff.

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No, that's incorrect.

According to gtr, a "white hole" is simply a time reversed black hole. It follows that:

1. the "eternal" version of the Schwarzschild vacuum solution is both a while hole and a black hole,

2. since an observer can (must) fall into a black hole at less than the speed of light (think of light cones; even at the event horizon itself such an observer is not falling "faster than light"), an observer can (must) emerge from a white hole at less than the speed of light.

These points will probably seem unclear. That is because you need to know about Carter-Penrose conformal diagrams.

Would you read a (semi-popular) book if I recommended it, tommac?

No such concept in gtr, but it is possible that you might be struggling toward trying to envision one of the key concepts in interpreting Carter-Penrose diagrams, namely nested "concentric" two spheres formed into a "timelike sheet", a three-dimensional submanifold of our four-dimensional spacetime.

To repeat: you can't get very far in learning about gtr without recognizing that there are multiple distinct but operationally significant notions of "distance in the large", and therefore "speed in the large", over and above the usual stuff about velocity vectors and orthogonal three-forms from special relativity.

Because the physical experience of an observer emerging from a white hole's event horizon is simply the time reversed history of an observer falling into a black hole's event horizon, this is almost the same thing as answering the question: what is the optical experience of an observer who falls into a black hole? I have discussed that in detail in many places on many previous occasions.

This is about the fifth time I've tried to tell you this: no. See http://www.math.ucr.edu/home/baez/ph.../universe.html and then reread what I told you before, contrasting models of isolated massive objects with models of homogeneous isotropic expanding (and/or contracting) universes.

All of those claims are incorrect.

You can envision photons or ordinary matter emerging from a white hole, but since Hawking radiation is emitted from the event horizon of black hole... (complete the sentence, based upon what I said above).

To repeat, all assertions about frequency shift involve a pair of world lines (of an emitter and of an observer), so you need to refine your question by specifying these world lines, which must be timelike curves (the world line of a "photon" is a null geodesic).

Ah, good, progress. I lost track of what this "same question" is, but maybe I answered it above.

See the FAQ essay and then reread what I wrote in another thread you started, contrasting models of isolated massive objects (these involve an asymptotically flat spacetime which is neither homogeneous nor isotropic) with FRW models (and related cosmological models), which are homogeneous and isotropic. But to really understand this, you'd need to learn about Carter-Penrose diagrams. Would you read a book if I recommended one?

This is a good example of the pitfalls of acting as if one can discuss subtle notions concerning curved Lorentzian manifolds using only ambiguous and imprecise verbal formulas. You can't.

Carter-Penrose diagrams would sure help. Would you be willing to try to learn to interpret them? (First, you'd need to back up and read a book about the geometry of "spacetime" as used in special relativity, though.)

The local versus global distinction strikes again! That's a fundamental concept in the theory of manifolds, usually discussed in graduate level mathematics courses on differerential geometry or gtr. You can see the problem faced by expositors of gtr when talking to a popular audience--- you can't avoid "committing lies of omission". And these tend to be whoppers. When some bright young person sees he wasn't told the whole truth, two reactions are possible: (1) "I just gotta learn the math!", or (2) "all scientists are liars" [sic]. I recommend the first option.

You happen to be right about that, but it worries me that you cited, not a printed textbook, but a Wikipedia article. Wikipedia is not suitable as an information resource, except perhaps in order to list key words which you can search for in your public library catalog. Would you be willing to read a book if I recommended one?

Codeslinger quoted something from [url=http://curious.astro.cornell.edu/question.php?number=108]. To see why this does not contradict what I've said above, you need to appreciate the local versus global distinction. In this case, the Cornell page is talking about something like the Oppenheimer-Snyder collapsing dust ball model of the formation of a black hole via the gravitational collapse of a massive object. The OS model is the simplest physically reasonable model of the formation of a black hole via gravitational collapse of a massive object (which is the way astronomers think the natural objects which they call "stellar mass black holes" formed). The "eternal black hole", the model which is both a white hole and a black hole, is OTH not considered to be physically reasonable, because the "boundary conditions" appear unreasonable.

The reasons why are related to a thought experiment suggested by Feynman: imagine wiggling an isolated electrical charge. According to the theory of electromagnetism, this creates an EM wave with roughly spherical and concentric wavefronts which expand at the speed of light. Now time reverse this; we have an EM wave with roughly spherical and concentric wavefronts which shrink at the speed of light, focusing on our charge, which obediently wiggles. The first scenario is mundane; the second is extremely implausible.

If you want to play word games: "I've seen a drawing of a horse, and I've seen a drawing of a unicorn, and I can hardly tell the difference! So why is the existence of unicorns disputed by mainstream naturalists, even though the existence of horses is universally accepted?"

If you are serious: I and others have tried repeatedly to tell you that white (or black) hole models are not really analogous at all to cosmological models featuring a Big Bang type strong scalar curvature singularity.

You're generating misstatements at a very rapid clip, and I'm still not sure whether you intend anyone to take what you say seriously, or to try to help you learn about physics and cosmology. Would you read a book if I recommended one?

That's correct, and this refers to the maximal analytic extension of the Schwarzschild vacuum solution, aka the "eternal black hole".

Do I hear jeers from the back of the hall? "Oh come now! How can this eternally static spacetime model contain a dynamic and in fact unstable phenomenon?" Well, it can, and again, Carter-Penrose diagrams are very useful for understanding why. Part of the answer has to do with this: the external part of the eternal black hole (actually, one of two "external universes" in this physically implausible model!) is indeed static, but the internal part (actually, the "future interior" or "past interior") is dynamic.

BTW, mugalien, it's Schwarz-schild ("black shield").

To prevent possible misunderstanding: "time reversed black hole" doesn't mean we imagine any physical process which "reverses time", it means that we apply the transformation t -> -t to the Schwarzschild solution, so that "forward pointing timelike vectors" and "past pointing timelike vectors" switch roles.

from the Baez link:

...nice, I didn't know that! (My bold.)

Does it also hold that accelerating expansion confers curvature to space-time in our current universe, I've only seen references to density in my reading up till now?

(Of course, a certain amount flies over my radar!)

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You mean the FAQ essay by Phil Gibbs, part of the UseNet Physics FAQ, which is mirrored on the website of John Baez. (Phil, John, and I are among several authors of various of these essays.)

My first independent discovery in gtr (of course, I later learned I had merely rediscovered something noticed by Painleve in 1921!) was this: in a Schwarzschild vacuum solution, consider the timelike geodesic congruence formed by the world lines of the "Lemaitre observers" (observers who fall radially inward "from rest at spatial infinity"). This congruence has vanishing vorticity, so it defines a family of spatial hyperslices, everywhere orthogonal to the Lemaitre congruence, which are all isometric to one another. "My" discovery was that these slices are locally isometric to ordinary flat euclidean space. The interesting thing about this story is that I didn't even know anything about calculus when I figured it out--- but I had figured out Minkowskian trigonometry, which is what you need here.

(This is actually "obvious", once you have learned to recognize such things, from the form of the line element in an "infalling" Painleve chart; see for example http://arxiv.org/abs/gr-qc/0502040)

Or again: the expanding FRW model with E^3 hyperslices gets its name because the world lines of the dust particles form a vorticity-free timelike geodesic cogruence, such that the family of spatial hyperslices everywhere othogonal to the world lines of the dust particles is locally isometric to E^3.

Speaking of the local versus global distinction, there are possibly viable models built from standard FRW models by taking "discrete quotients", so that one has for example spatial hyperslices which are all (metrically flat) three toruses.

Are you asking about FRW models with nonzero "cosmological constant terms" now? The modern way to think about them is to put that term on the RHS of the EFE, considering Lambda just another term in the stress-energy tensor. If you consider such a term in isolation, then it produces spacetime curvature in accordance with the EFE, yes. It has nothing to do with what we were just talking about, that I can see. Right now I can't figure out what Phil was thinking of when he wrote "The curvature can come from the temporal parts of the space-time metric which measures the deceleration of the expansion of the universe", but if nothing occurs to me bye and bye I can ask him to clarify.