No, simply because white holes cannot exist. They are a misunderstanding of an early, incorrect analysis of an oversimplified theory of the nature of black holes.

Early on, to make the math simpler, certain simplifying assumptions were made about the nature of black holes. That led (in a multi-dimensional space-time diagram) to a perfectly symmetrical structure, with two entrances in opposite directions from the singularity at the center of the black hole. Questions then arose about whether it would be possible, if the black hole were rotating, for the point in the center to turn into a sort of tight funnel, allowing things to go in one side, past the singularity, and out the other side. The passage through the middle came to be called a "wormhole", and the supposed exit on the other side, a "white hole". But...

(1) If the "exit" on the other side had existed, it would not have been an exit, but simply another entrance, so that anything that somehow managed to avoid the singularity could not have escaped on the other side, but would have simply been pulled into the singularity from the other direction, and

(2) Once the simplifying assumptions were removed, so that real black holes could be modeled, all that remained was the entrance on one side of the multi-dimensional space-time diagram, and the singularity in the center. So not only did the nonexistent "wormhole" idea never really exist, neither did the so-called but completely misunderstood "white hole".

That doesn't mean that the idea of those things disappeared. Science fiction writers love the idea, so you still hear about white holes and wormholes, though neither have ever existed or will ever exist. As currently used they are merely the stuff of fairy-tales, and since they have no reality, there is no way that you could use one for any purpose, any more than you can use a pinch of fairy dust.

Courtney Seligman If white holes cannot exist, is because they brake a law or various laws in physhics right? If not, why shouldnt they? And if so, which laws? As far as I know, white holes are solutions to Einsteins GR equations, a time-reversed black hole.

Addiotionally, we cannot rule out their existence if their non-existence is not proven. We have never observed or develop any experiment inside a black hole... so there could be something as weird as a white hole inside (the gravitational singularity predicted is already very weird). I think is very impulsive to arbitrarily say that they have no reality, remember that back in the days when the Schwarzschild solution was obtained, no body (not even Einstein) thought that black holes were real entities out there. And now we know they are.

Either way, my question was about the Penrose process, which is already very theoretical, so I suggested a theoretical approach to the hypotheses of the white holes.

"if their non-existence is not proven"

The non-existence of anything cannot be proven by observation, or by the lack of observation of something that does not exist. All observations can prove is the existence of things, or the lack of observations that prove their existence; actual non-existence cannot be proven by observation.

My statement that white holes cannot exist is therefore not based on observational evidence, since the previous paragraph explains that such proof cannot exist. Instead, my statement that they cannot exist as described in anything I've ever read is based on the fact that their supposed existence was based on a false interpretation of an incorrect theory of black holes. If something similar to a white hole can exist, its origin and properties lie beyond the bounds of current physical knowledge, and those properties are undoubtedly completely different from anything like white holes as originally described, since they would simply be an alternate entry to a black hole.

In any event, it is possible to extract energy from the rotating disk of material surrounding a black hole, and in fact when a small black hole absorbs a stellar mass, as much as 70% of the rest-mass energy of the infalling material is radiated away before what's left enters the black hole's event horizon (which is 100 times more than the energy produced by the most efficient nuclear fusion known, the conversion of hydrogen into helium). That's where the energy radiated by quasars comes from, and where high-energy polar jets emitted from the accretion disks of material falling into a black hole get their energy from. So you don't need a white hole to get energy; any black hole will do just as good or better a job of doing that for you, if you have the technology to toss a star into one. Which, if you're trying to get energy out of a rotating white hole, is a good thing, since even if you ignore the theory of black holes, white holes probably still do not exist.

You are correct, and thanks for clarifying that you didn't state that because of their non observable evidence.

I again must repeat that arent white holes just time reversed black holes? You only described the maximally extended solution to black holes by, for example, kruskal szekeres coordinates or the full penrose diagram for black holes, in which white holes appear.

In relation to the extraction of rotational energy, I was refering to the penrose process rather than what you described of obtaining energy by radiated material falling into the black hole. The penrose process for a rotational black hole implies that a a particle (or mass) is divided into two in a particular way in the ergosphere. One scapes the black hole, and another enters it, extracting energy from the black hole. That occurs because the rotational energy is not localized inside the event horizon but in the ergoshepere.

But for the case of a white hole, no particles or masses can enter the event horizon, and thats my question. How do you apply then the penrose process to a white hole?

Wight hole is the result of collapse of the object whose gravitational field is a field of repulsion. For example, this situation is applicable to de Sitter bubble: its gravitational field is the field of repulsion where gravitational force of repulsion is F^1 = c^2r/a^2, where a is the radius of bubble, r is the distance from the center. This exact solution is obtained as result of collapse of liquid homogeneous sphere obtained by Schwarzschield. Note, Schwarzschield has considered in detail only regular part of his solution, because he has applied it for description of the Sun as a regular star. If ignore these assumption we obtain the object in the state of collapse. Note, gravitational radius of this collapsar equals to r_g = a = 2GM/c^2, but this object possesses gravitational force of repulsion. It is possible, this force is linked with gravitational energy of repulsion. This consideration is applicable and to rotating and non-rotating objects. Applying this solution to the Universe we find F^1 = c^2/a = H^2a, where H = c/a is Hubble constant. This model is applicable to neutron stars.

White holes, although allowed by the time reversal symmetry of the formation of black holes (BHs) in general relativity, are actually unstable. That is, a tiny perturbation to an emerging white hole (WH) can make the latter collapse into a BH. Even if a WH is discovered, it would be explosive in nature and itself would lead to production of energy, Penrose process notwithstanding.

What about the cases in which white holes are considered to exist only at the other side of the black hole (on the interior).

yes

Yes. Gravitational energy of white hole is energy of repulsion^: it is directed from white hole. Considering white hole as de Sitter Bubble in the state of inflation (p = - rho c^2) we obtain the expression for gravitational force F = c^2r/a^2, where r is the distance from white hole, a is its radius. We see, it is centrifugal force, therefore it radiates gravitational energy of repulsion. In other words, white hole rotates with the angular frequency c/a. Thus its energy of rotation is directed to outer space. This model is applicable to pulsars, neutron stars, the Universe. It means that we use the energy of the Universe. The expression c/a is the Hubble constant. So, we use the energy of the Univw=erse and neutron stars. Usual stars, galaxies, ... possess gravitational energy of attraction of Newton kind. These object can form only black holes whose gravitational energy of attraction is directed inside these objects.

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We live in the Universe where the Earth is its part. We extract the energy of the Earth --- the part of the Universe. If we accept the idea that the Universe is a fractal we must accept the existence of energetic exchanges between another fractals (fragments fractal "Universe". This fractal is not a picture constructed by scientists) as a result of some mathematical formulas. Fractal "Universe" is a creation of Nature, therefore the Universe is a living subject. We live in correspond to the Laws of the Universe. We construct different pictures of the living Universe taking into account the dates of observations. The model of the Universe as inflation de Sitter bubble in the state of collapse of special type (bubble is simultaneously in the states of gravitational and inflation collapse) is only the mathematical construction. It is represented with the aim --- to show that the observed dates can be explained not in frames of expanding Universe. Friedman's model cannot correspond with model of the fractal Universe. Scientists must take into account contemporary results of observations and experiments. Shnoll experiments demonstrate fractal structure of Time. Kozyrev's observations prove the existence of momentary transfer of signals from distant objects. Astronomers observe the changes of flow of time near horizon of events. It follows that energy of the Universe is extracted by us (if we see phenomena near horizon of events, we feel the energy of the Universe. Einstein theory (GR) is not an absolute construction, it is only one step, demonstrating the role of Time: if experimental dates shows new results we must investigate new horizons but not refuse from new knowledge. The next step is investigation of Time as the Energy which construct our world. Really, we extract the Time and transform it to our life.

Rotation of white hole is materialization of its energy --- non-material ((energetic) substation called the Time. That to understand the nature of some phenomena it is necessary to consider seriously the concept of energetic world as a substation which creates non-material world. Black and white holes are collapsed objects. It means that they possess surfaces where the observed time is stopped (see Landay, Theory of the field). If the observed time is stopped for observer it means that white (black) hole and the observer are in the same moment of the observed time. It means that observer receives the energy of this hole. This energy changes its consciousness and he begin to think about obtaining this energy. That to use this energy practically it is necessary to study the physical structure of Time. This helps us to understand the nature of the Time and to use new methodes of interaction with Cosmos. That to fly to stars it is necessary to understand the nature of stellar energy. The light of stars is one of manifestation of Tme in th form of electromagnetic radiation. But this energy spreads slowly for us if we want to fly to stars. We must think by another methods. Because we can observe holes (black and white) we feel theirs states at the moment of observation. That to continue experiments with the Time it is necessary to study not only different holes, because the Time creates all material objects and phenomena. Kozyrev made many experiments with usual material --- water, biological objects etc. I repeated some experiments with flows of different flows of the Time as Kozyrev. These flows exist really and act on detector. It is necessary only to allow that the Time is the same substance which creates our world and us --- its parts.

Energy of white hole is similar with energy of centrifugal force. We know from the school that centrifugal energy is analogical to the Newtonian gravitational energy because their contradiction creates the state of weightlessness: GM/r^2 = v^2. This condition is obtained in flat -space, where all clocks show the same time. The notion "white hole" is obtained in space-time where white hole is collapsed sphere consisting from homogeneous liquid with constant density (for simplification). Collapse this sphere (star) is realized by the condition r_g = 2GM/c^2 = a (radius of white hole). Thus we obtain naked white hole radiating centrifugal energy, where gravitational force is F = c^2r/a^2, where c/a is the angular velocity. This model is applicable to neutron stars, pulsars, quasars. Because the radius of white hole a = 10 km approximately, we find the value of angular velocity of rotation c/a = 30000 Hz. This value is also the own frequency of the star emitted to the surrounding space: so extraction of energy is realized

in the Nature. If we want to understand this process, we must study rotational motion by different methods. Rotation of energetic flows takes the place in the Nature: rotation of material body is materialization of processes in energetic world. So, the rotation of celestial bodies is the result of transmission of non-material energy between the bodies. Our Galaxy rotates around this axis and this rotation gives energy stars, planet, people, ... It is impossible to think that only material worls exists. We see that conditions at the Earth change with acceleration. This process is linked immediately with the motion of Milky Way which comes to intergalactic medium with more high density. Because our Universe is a fractal, we must feel these changes. Conclusion: it is necessary consider our world in more spread frames.

Larissa Borissova This is going far away from my question. Im just asking if the Penrose process can be applied to a white hole, because it requires mass crossing the event horizon and that cant happend for a white hole. That's the point of discuss.