It’s good now and then to let the imagination soar. Don Wilkins has been poking into the work of Carlo Rovelli at the Perimeter Institute, where the physicist and writer explores unusual ideas, though perhaps none so exotic as white holes. Do they exist, and are there ways to envision a future technology that can exploit them? A frequent contributor to Centauri Dreams, Don is an adjunct instructor of electronics at Washington University, St. Louis, where he continues to track research that may one day prove relevant to interstellar exploration. A white hole offers the prospect of even a human journey to another star, but turning these hypothesized objects into reality remains an exercise in mathematics, although as the essay explains, there are those exploring the possibilities even now.
by Don Wilkins
Among the many concepts for human interstellar travel, one of the more provocative is an offspring of Einstein’s theories, the bright twin of the black hole, the white hole. The existence of black holes (BH), the ultimate compression stage for aging stellar masses above three times the mass of our sun, is announced by theory and confirmed by observation. White holes, the matter spewing counterparts of BHs, escape observation but not the explorations of theorists.
Carlo Rovelli, an Italian theoretical physicist and writer, now the Distinguished Visiting Research Chair at the Perimeter Institute, discusses all this in a remarkably brief book called, simply, White Holes (Riverhead Books, 2023) wherein he travels in company with Dante Alighieri, another author with experience at descents into perilous places. Rovelli makes two remarkable assertions. [1]
1) Rovelli states that another scientist, Daniel Finkelstein, demonstrated that Einstein and other analysts are incorrect when they depict what occurs as one enters a black hole. From the Finkelstein paper (citation below):
The gravitational field of a spherical point particle is then seen not to be invariant under time reversal for any admissible choice of time coordinate. The Schwarzschild surface, r=2m is not a singularity but acts as a perfect unidirectional membrane: causal influences can cross it but only in one direction. [2]
In other words, no time dilation, no spaghettification of trespassers entering a black hole. Schwarzchild’s solution only applies to distant observers; it does not describe the observer crossing the event horizon of the black hole.
2) Rovelli believes in the existence of white holes. His white hole births when the black hole compresses its constituent parts into the realm of quantum mechanics. Rovelli speculates “… a black hole … quantum tunnels into a white one on the inside – and the outside can stay the same.”
In Figure 1 and Rovelli’s intuition, a quantum mesh separates the black hole and white hole. At these minute dimensions, quantum tunneling effects surge matter away from the black hole, into the mouth of the white hole and back into the Universe.
Figure 1. Relationship between a black hole and a white hole. Credit: C. Rovelli/Aix-Marseille University; adapted by APS/Alan Stonebraker.
The outside of a black hole and a white hole are geometrically identical regardless of the direction of time. The horizon is not reversible under the flow of time. As a result the interiors of the black hole and white hole are identical.
In a paper he co-authored with Hal Haggard, Rovelli writes:
We have constructed the metric of a black hole tunneling into a white hole by using the classical equations outside the quantum region, an order of magnitude estimate for the onset of quantum gravitational phenomena, and some indirect indications on the effects of quantum gravity. [3]
Haggard and Rovelli acknowledge that the calculations do not result from first principles. A full theory of quantum gravity would supply that requirement.
Figure 2: Artist rendering of the black-to-white-hole transition. Credit: F. Vidotto/University of the Basque Country. [9]
Efforts to design a stable wormhole require buttressing the entrance or mouth of the wormhole with prodigious amounts of a hypothesized material, negative matter. Although minute amounts have been claimed to form in the narrow confines of a Casimir device, ideas on how to manufacture planetary-sized masses of negative matter are elusive. [4]
According to recent research, the stability of the WH is dependent upon which of the two major families of matter, bosons or fermions, forms the WH. Bosons are subatomic particles which obey Bose-Einstein statistics and whose spin quantum number has an integer value (0, 1, 2, …). Photons, gluons, the Z neutral weak boson and the weakly charged bosons are bosons. The graviton, if it exists, is a boson. Theoretic analysis of stable traversable WHs founded on bosonic fields demonstrates a need for vast amounts of negative matter to hold open the mouth of a WH.
The other family, the fermions, have odd half-integer (1/2, 3/2, etc.) spins. These particles, electrons, muons, neutrinos, and compound particles, obey the Pauli Exclusion Principle. It is this family that is employed by a team of researchers to describe a two fermion stable white hole [5]. Their configuration produces John Wheeler’s “charge without charge”, where an electric field is trapped within the structure without any physical electrical charge present. The opening in the white hole would be too small, a few hundred Planck lengths (a Planck length is 1.62 x 10-35 meters) to pass gamma rays.
Rovelli reenters the discussion here. [6] The James Webb Space Telescope has identified large numbers of black holes in the early Universe, more black holes than anticipated. Rovelli describes white holes forming from these black holes as Planck-length sized, chargeless entities, unable to interact with the matter except through gravity. In other words, the descendants of the early black holes manifest as the material we describe as dark matter. Rovelli is working on a quantum sensor to detect these white holes.
Once the white holes are detected, it might be possible to capture a white hole. John G. Cramer, professor emeritus of physics at the University of Washington in Seattle, Washington, suggests accelerating the wormhole to almost the speed of light. [7] Aimed at Tau Ceti, he predicts:
The arrival time as viewed through a wormhole is T’ = T/γ , where γ is the Lorentz factor [γ= (1- v/c)-½] and v is the wormhole-end velocity after acceleration. For reference, the maximum energy protons accelerated at CERN LHC have a Lorentz factor of 6,930. Thus, the arrival time at Tau Ceti of an LHC-accelerated wormhole-end would be 15 hours….Effectively, the accelerated wormhole becomes a time machine, connecting the present with an arrival far in the future.
Spraying accelerated electrons through the wormhole could expand the mouth to a size where it could be used as a sensor portal into another star system. The wormhole becomes a multi light-year long periscope, one that scientists could bend and twist to study up close and in detail the star and its companions. Perhaps the wormhole could be expanded enough to pass larger, physical bodies.
Constantin Aniculaesei and an international team of researchers may have overcome the need for an accelerator as large as the LHC to accelerate the white hole to useful size [8]. Developing a novel wakefield accelerator, wherein an intense laser pulse focused onto a plasma excites nonlinear plasma waves to trap electrons, the team’s machine produced 10 Giga electron Volt (GeV) electron bunches. The wakefield accelerator was only ten centimeters long, although a petawatt laser was needed to excite the wakefields.
Cramer hypothesizes that fermionic white holes formed immediately after the Big Bang and in cosmic rays. The gateways to the stars could be found in the cosmic ray bombardment of the Earth or possibly trapped in meteorites. The heavy particles, if ensnared on Earth, would probably sink to the center of the planet.
All that is needed to find a fermionic white hole, Cramer suggests, is a mass spectrometer. But let me quote him on this:
[Wormholes] might be a super-heavy components of cosmic rays….They might be trapped in rocks and minerals….In a mass spectrograph, they could in principle be pulled out of a vaporized sample by an electric potential but would be so heavy that they would move in an essentially undeflected straight line in the magnetic field. …wormholes might still be found in meteorites that formed in a gravity free environment.
The worm hole is essentially unaffected by a magnetic field. A mass detector would point to an invisible mass. The rest, as non-engineers like to say, is merely engineering.
If this line of reasoning is correct – a very large if – enlarged white holes could pass messages and matter through tunnels in the sky to distant stars.
References
1. Carlo Rovelli, translation by Simon Carnell, White Holes, Riverhead Books, USA, 2023
2. David Finkelstein, Past-Future Asymmetry of the Gravitational Field of a Point Particle, Physical Review, 110, 4, pages 965–967, May 1958, 10.1103/PhysRev.110.965
3. Hal M. Haggard and Carlo Rovelli, Black hole fireworks: quantum-gravity effects outside the horizon spark black to white hole tunneling, 4 July 2014, https://arxiv.org/pdf/1407.0989.pdf
4. Matt Visser, Traversable wormholes: Some simple examples, arXiv:0809.0907 [gr-qc], 4 September 2008.
5. Jose Luis Blázquez-Salcedo, Christian Knoll, and Eugen Radu, Traversable Wormholes in Einstein-Dirac-Maxwell theory, arXiv:2010.07317v2, 12 March 2022.
6. What is a white hole? – with Carlo Rovelli, The Royal Institution, https://www.youtube.com/watch?v=9VSz-hiuW9U
7. John G. Cramer, Fermionic Traversable Wormholes, Analog Science Fiction & Fact, January/February 2022.
8. Constantin Aniculaesei, Thanh Ha, Samuel Yoffe, et al, The Acceleration of a High-Charge Electron Bunch to 10 GeV in a 10-cm Nanoparticle-Assisted Wakefield Accelerator, Matter and Radiation at Extremes, 9, 014001 (2024), https://doi.org/10.1063/5.0161687
9). Rovelli, “Black Hole Evolution Traced Out with Loop Quantum Gravity,” Physics 11, 127 (December 10, 2018).
https://physics.aps.org/articles/v11/127
Questions:
1. The text suggests that white holes have not been observed. However, they may be generating dark matter. If so, does that mean that normal matter is being consumed and converted to dark matter?
2. If dark matter is being created, shouldn’t the ratio of normal to dark matter be observable as we peer back in time?
3. If the universe started with a “big bang”, can we infer what role white holes and dark matter could have played in the inflation?
4. Is dark energy pushing matter apart counteracting any process to create more BHs and thence dark matter?
1. The implication is there (see below).
2. This is an important point. The DM (really, cold DM) distribution that we observe could only come about if it was there from the beginning. Distribution of matter and DM evolved together, by gravitation only, so it is no surprise that the DM is bound to galaxies.
3. Were WH or BH there from the start, that is, primordial? There is no evidence for either.
4. It’s possible that DE is “operationally” acting in opposition to gravitation, but if so it is only at cosmological scales. It has no effect of gravitational bound objects and that certainly includes stars and BH.
On a more general observation, the authors state that their derivation of WH and their behavior is *not* based on fundamentals. It’s really a wild speculation. That these WH are essentially widespread, evenly distributed (?) and infinitesimal appears to be nothing more than an appeal based on a lack of evidence that they exist. An easy counter-argument is (2) above.
I always understood the universe’s energy budget as being very close to zero—so any overage is enough to spark creation in a budding off of a new cosmos—that might be what a white hole is–another universe’s big bang perhaps.
All that is needed is that infinite compression only a collapsar can provide.
In short—the multiverse is diesel. ;)
If correct, Rovelli’s wormhole telescope would make SETI’s electromagnetic searching rather moot. A civilisation would spend but a relatively short time mucking about with radio.
SETI focused on radio searches in its early days for several reasons: Radio astronomy was a fairly new science when Frank Drake conducted Project Ozma in 1960; radio is a relatively easy and inexpensive way to communicate across interstellar distances; and it was assumed most technical civilizations would at least go through a radio phase before moving on to more sophisticated communications methods.
Regarding that last statement above, this is also an indicator of how early SETI project and their participants were largely focused on finding beings who at least thought and acted like humanity. Note how they also often targeted Sol-types stars and assumed anyone in such systems conducting their version of METI would be done from the surface of an Earthlike world and done out of scientific altruism. They genuinely tended to steer away from any unfamiliar possibilities for alien intelligences, which of course has limited SETI for decades. Only now are we finally getting outside that paradigm and slowly improving our chances of success.
BTW, radio is still a good medium to search in, for the reasons I listed at the beginning of my comment.
RE: “The outside of a black hole and a white hole are geometrically identical regardless of the direction of time. The horizon is not reversible under the flow of time. As a result the interiors of the black hole and white hole are identical.”
Does this mean we should find the white equivalent of supermassive black holes in the observable universe? If that inference is correct, shouldn’t radiating white holes of this size/magnitude be easily observable?
Perhaps they are emited as neutrinos which rarely interact with matter or even perhaps the more elusive graviton. I personally am very sceptical about white holes as the BH would seen to be reducing in size over time on a substantial scale.
Figure 1 implies that matter flows through the BH-WH pair. If so, how do BHs grow if they lose the matter that forms them?
What does this theory imply for Hawking radiation?
The event horizon is a effectively a one-way membrane with respect to the flow of time outside the BH. If we could observe a clock as it falls into the BH its ticks would come farther apart until the ticks would stop entirely. This is one reason why at one time BH were known as “frozen stars”.
The implication is that anything that passes the EH is cut off from our spacetime. No matter where it goes (singularity, WH, or whatever) cannot be seen. If it were to tunnel out via a speculative WH into our observable spacetime, the matter in our universe would increase! That is, counted twice. That is unlikely.
That is why it has been speculated that if WH exist, they must be in a disconnected spacetime (or universe), with the BH acting as a tunnel to it. But this is nothing more than fanciful speculation.
The only known way to “escape” a BH is via Hawking radiation, and that requires no speculative physics.
The white whole idea was supposed to be only used with a singularity. I won’t deny I am biased against the idea of the universe starting with a singularity because how would we be able to free the matter from it? One would need an antimatter singularity to turn it into energy. Also Einstein rejected the idea of black holes, but one could still use general relativity to prove them.
It’s general relativity and Newton’s law of universal gravitation and inverse square law where the strength of gravity falls of inversely proportional to the distance that completely invalidates the worm hole idea. Space can be made shorter, but only locally, but not over many light years. Also like an equation that must be balanced it is impossible to make the space much shorter inside the wormhole without making the space on the outside shorter as well. Space can’t be made shorter over long distances. We might move stars and bodies closer, but the space can only be warped locally. Further more, it is the space that expands and contracts based on the energy density, the energy we add to empty space. Einstein’s general relativity states that matter and energy warp space time and that warp we call gravity.
There is the idea that gravitons are their own anti particles with exactly the same properties. The graviton has a spin of 2 and zero mass which would be the same for the anti graviton. I assume that the spin of the anti graviton would have to be reversed in order to give the anti gravity effect.
Just going off from memory here, didn’t Stephen Hawking become famous for determining that particles CAN escape from black holes. This would lead to their eventual evaporation, by which was meant a massive explosion. Perhaps that is how the Universe could have come from a singularity.
No, he fully developed another’s idea that BH have a temperature and therefore radiate. The radiation is not composed of particles that previously entered the BH. However, that radiation reduces the BH mass (energy and mass are two heads of the same coin). Larger BH are colder than small ones. If that lost mass isn’t replaced, the BH will eventually(!) reach a point where the temperature gets quite high, the mass loss rapidly increases and the event horizon vanishes. What comes out at that point is debatable, but it would likely do so explosively.
None of the theory is empirically confirmed. If correct, every BH is gaining mass and will do so for a very very long time. That’s because their temperatures are far lower than the CMBR.
While both are completely hypothetical, worm holes are not the same as a white holes. This article seems to conflates the two.
I don’t think it’s a conflation, but since one requires the other they must both exist and be closely associated in some way. At least according to the speculation.
Cosmic strings seem to be a viable idea, and are described as topological defects with something other than 360 degrees around the string. In my ignorance I have to wonder: is it conceivable to have a loop of cosmic string which has exactly 720 degrees of rotation around the string at any point, so that you could look through the loop and see strange stars? Would such a loop of string end up being the same as a wormhole, or could it be some other sort of putative “Star Gate”?
I’ve always thought that “white holes” are a fantasy inspired by nomenclature. If we used the older term “black star” or the Russian “frozen star” I doubt anyone would be writing papers about their converses. But a “hole” implies an opening to someplace else, so naturally curious humans start to wonder about what’s inside that hole, or where it goes.
Good points. I also have to wonder why astronomers did not go with the term collapsar for a black hole, considering how popular the terms quasars and pulsars were and are.
You have history reversed. The BH term came first. The name itself was controversial for a time.
Like black holes, white holes emerge from general relativity. However, there isn’t any observational evidence for white holes. BHs occur when a singularity is project forward in time and WHs backwards in time. This description may make a physicist’s head explode but I believe it is essentially right. No one knows if a WH can exist in the universe. They might immediately collapse into a BH or we may be living inside one.
When the authors of this paper state that their hypothesis isn’t based on fundamentals, do they may mean GR?!?
I watched his recent RI lecture (1 hour) on his theory. I gather that it takes a long time for the matter to pass through the event horizon, become squeezed to the point of quantum effects, and then emerge in the future as a Plank length-sized white hole in the speculated form of dark matter. The time of emergence depends on the size and age of the BH – the larger and older, the longer the time to emergence. What is not clear is how this allows for Hawking radiation as these quantum effects happen deep inside a distorted space-time BH, and not near the event horizon, nor is it clear to me why any matter can escape from the WH – perhaps it doesn’t.
Adopting a purely “mechanistic” point of view, if we consider black hole/white hole parity and the idea of matter/energy conservation – a kind of input-output: what could be the function of these objects in the universe ? Could they be regulating matter in the universe, like a valve ?
OT
Interesting new spacecraft, many have thought along these lines, looks promising.
https://phys.org/news/2024-01-nasa-invests-nuclear-rocket-concept.html
With the alpha particles being emitted at 5% of c, that offers interesting performance, although the mass loss is a small fraction of the total Thorium mass, let alone the sail structure. It will be interesting to see how it fares with the NIAC 1 study and whether it progresses to NIAC 2 or not. The claim is very high velocities, but this can be modeled with assumptions about the sail structure and payload.
@Ron S.
I appreciate your many comments on this post.
Rovelli suggests [in the RI lecture] that inside the BH time still moves forward after “freezing” at the event horizon and that space is stretched out as the radius declines. The WH appears at the quantum level once the radius reaches Plank-lengths. The WH appears sometime in the [far] future, some distance from the BH. It is a pity no questions were allowed in the lecture as I am sure there might have been some lively ones from physicists and astronomers in the audience.
I am unclear whether this distance is random and cosmos-sized, so that WHs will be like the CMB spread out across space or closer to BHs. His claim that WH == DM in some way would seem to suggest that DM increases as normal matter decreases over time as the BH emits DM in the future. (If so, I note the conceptual similarity to Cixin Liu’s last book of the Three Body trilogy, Death’s End, where the universe is being progressively reduced to 2 dimensions.)
[In the RI lecture, he treats Dante Alighieri’s poetic journey through hell into paradise as a metaphor for his exploration of BHs and WHs, although I don’t know whether he sees himself as Dante or Virgil. My only interest is Gustave Doré’s gorgeous illustrations.]
Alex, I lot of the decay products have low boiling points so will more than likely evaporate out over time reducing their parasitic mass. Hope the idea has traction as it looks to have.
Alex, you might want to review the WP article on Penrose diagrams since it is very helpful to understand what happens outside, at and inside the event horizon of a BH:
https://en.wikipedia.org/wiki/Penrose_diagram
In brief, although the clock (as I previously described) appears to slow and stop as it falls toward the BH, due to spacetime curvature, the clock itself is unaffected: proper time of the clock (or a person falling in) continues normally. A free fall is no different than any other free fall toward any body, including Earth. You only notice that it’s different when the tidal forces become significant. Also, infalling photons, which are of course moving faster, get blue shifted and can eventually cause harm.
No particles can survive the tidal forces deep within — everything gets torn apart eventually. Then, as Rovelli says, we are in a quantum regime that is outside of current physical theories, quantum or classical. We do not know what happens. If there is a singularity (and there need not be — Roy Kerr has a recent paper about this), you will always reach it.
I have not watched the RI lecture. My only source is the paper in Don’s reference [3], which I read through before commenting on this article. So I don’t know how he argues the DM aspect of the conjecture. And it is a conjecture. As I commented earlier, his conjecture that DM comes out of a vast number of widely dispersed “white holes”, lacks evidence or theoretical justification. An interesting conjecture, but that’s all it is.
Back to the spacetime disconnection inside the BH. There is no reasonable argument at present for the conjectured exit of matter via a WH back into our spacetime). There is no evidence that DM is increasing; maybe it is, but there is no good reason to expect it. Distribution of primordial DM is pretty well explained at this point, as I mentioned in a previous comment.
His is an entertaining conjecture, but little more. BH are increasing in mass, not decreasing, and Hawking radiation (which has never and cannot be observed for all known masses of BH) is a separate issue. That radiation is not due to the exit of the matter that fell into and comprises the BH.
What happens inside a BH is an ongoing theoretical question, and it will not be answered anytime soon! You might also find it interesting to read about the BH information loss problem.
How do you reconcile Penrose diagrams with Hawking radiation? Each diagonal cell on the diagram represents an infinite amount of time from top to bottom – but every black hole will decay, at a time a very distant from the present but surely more distant from infinity. Most typically, I think, people interpret that matter entering the black hole “returns” to our universe, such as by quantum tunneling from the singularity to the event horizon. If the event horizon is expected to move, such as to expand and eventually to disappear entirely, it is not actually a 45-degree line on the diagram. Matter said to be escaping through a ring singularity to some other universe nonetheless must leave its mass behind as Hawking radiation in this universe. How can anything on these diagrams be meaningful?
Reconcile? What do you want? As I already stated in an earlier comment, Hawking radiation is *not* matter or radiation tunneling or leaking out of the BH in whatever fashion. This is a common misconception that seems difficult to dispel despite a lot of excellent explanatory information available at our fingertips.
Second, a singularity. There is no good reason to expect that there must be a singularity inside. Again, as I stated in an earlier comment, Kerr (of the Kerr metric for rotating BH) has a recent paper giving good reasons why there is unlikely to be a singularity inside real astrophysical BH. Many have come to the same conclusion over the decades by other routes.
Third, WH and wormholes remain speculative even though they are not proscribed by the mathematics of GR. But we know that neither GR nor QM are the final word, and even a workable quantum gravity theory may not answer these questions.
I suggest further reading on Penrose diagrams and Hawking radiation.
I should clarify I hadn’t taken any position in the larger conversation, and was only questioning whether Penrose diagrams make any sense. I agree that the quantum tunneling explanation seems odd when we consider that Hawking radiation is just a type of Unruh effect, but maybe “where Unruh radiation tunnels from?” has a really interesting answer? A 2023 paper ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10241825/ ) was studying the Hawking tunneling model with ” a chain of superconducting transmon qubits”, so I doubt the point is settled.
The Roy Kerr paper is indeed interesting. “…there will be a region between the event shell and the central body where an eagle can fly if it flaps its wings hard enough.” Not what I’ve been led to expect! I suppose due to radiation the life forms native to black holes may be a bit more exotic, and alas they’re not good candidates for SETI, but still: a welcome addition to the Realm of Possibilities!
I perhaps should have given the link to Kerr’s paper, but at the time of my comment I didn’t think that you’d be interested. I see that you found it. For the benefit of others, here it is: https://arxiv.org/pdf/2312.00841.pdf
Unruh radiation is a solid prediction but not yet observed, and some dispute its existence. I have nothing to add to that discussion. Unfortunately, it and Hawking radiation are testable predictions that are very difficult to actual observe. Time will tell. Unruh radiation will likely be the first to be definitively tested since we have no sufficiently small and near BH to measure.
Hi All
There’s some confusion about black holes vs white holes vs wormholes. Whiteholes are in essence time-reversed black holes – they can only emit mass-energy, not absorb it. They can only get bigger, else they collapse behind an event horizon. Wormholes, unlike either black or white holes, don’t have event horizons and mass-energy flow is both ways. In fact a wormhole – the Einstein-Rosen Bridge – forms between the black hole-white hole dyad as space-time evolves inwards during collapse. Of course it’s quite temporary.