# Some black holes erase your past

In the real world, your past uniquely determines your future. If a physicist knows how the universe starts out, she can calculate its future for all time and all space.

But a UC Berkeley mathematician has found some types of black holes in which this law breaks down. If someone were to venture into one of these relatively benign black holes, they could survive, but their past would be obliterated and they could have an infinite number of possible futures.

Such claims have been made in the past, and physicists have invoked "strong cosmic censorship" to explain it away. That is, something catastrophic – typically a horrible death – would prevent observers from actually entering a region of spacetime where their future was not uniquely determined. This principle, first proposed 40 years ago by physicist Roger Penrose, keeps sacrosanct an idea – determinism – key to any physical theory. That is, given the past and present, the physical laws of the universe do not allow more than one possible future.

But, says UC Berkeley postdoctoral fellow Peter Hintz, mathematical calculations show that for some specific types of black holes in a universe like ours, which is expanding at an accelerating rate, it is possible to survive the passage from a deterministic world into a non-deterministic black hole.

What life would be like in a space where the future was unpredictable is unclear. But the finding does not mean that Einstein's equations of general relativity, which so far perfectly describe the evolution of the cosmos, are wrong, said Hintz, a Clay Research Fellow.

"No physicist is going to travel into a black hole and measure it. This is a math question. But from that point of view, this makes Einstein's equations mathematically more interesting," he said. "This is a question one can really only study mathematically, but it has physical, almost philosophical implications, which makes it very cool."

"This … conclusion corresponds to a severe failure of determinism in general relativity that cannot be taken lightly in view of the importance in modern cosmology" of accelerating expansion, said his colleagues at the University of Lisbon in Portugal, Vitor Cardoso, João Costa and Kyriakos Destounis, and at Utrecht University, Aron Jansen.

As quoted by *Physics World*, Gary Horowitz of UC Santa Barbara, who was not involved in the research, said that the study provides "the best evidence I know for a violation of strong cosmic censorship in a theory of gravity and electromagnetism."

Hintz and his colleagues published a paper describing these unusual black holes last month in the journal *Physical Review Letters*.

**Beyond the event horizon**

Black holes are bizarre objects that get their name from the fact that nothing can escape their gravity, not even light. If you venture too close and cross the so-called event horizon, you'll never escape.

For small black holes, you'd never survive such a close approach anyway. The tidal forces close to the event horizon are enough to spaghettify anything: that is, stretch it until it's a string of atoms.

But for large black holes, like the supermassive objects at the cores of galaxies like the Milky Way, which weigh tens of millions if not billions of times the mass of a star, crossing the event horizon would be, well, uneventful.

Because it should be possible to survive the transition from our world to the black hole world, physicists and mathematicians have long wondered what that world would look like, and have turned to Einstein's equations of general relativity to predict the world inside a black hole. These equations work well until an observer reaches the center or singularity, where in theoretical calculations the curvature of spacetime becomes infinite.

Even before reaching the center, however, a black hole explorer – who would never be able to communicate what she found to the outside world – could encounter some weird and deadly milestones. Hintz studies a specific type of black hole – a standard, non-rotating black hole with an electrical charge – and such an object has a so-called Cauchy horizon within the event horizon.

The Cauchy horizon is the spot where determinism breaks down, where the past no longer determines the future. Physicists, including Penrose, have argued that no observer could ever pass through the Cauchy horizon point because they would be annihilated.

As the argument goes, as an observer approaches the horizon, time slows down, since clocks tick slower in a strong gravitational field. As light, gravitational waves and anything else encountering the black hole fall inevitably toward the Cauchy horizon, an observer also falling inward would eventually see all this energy barreling in at the same time. In effect, all the energy the black hole sees over the lifetime of the universe hits the Cauchy horizon at the same time, blasting into oblivion any observer who gets that far.

**You can't see forever in an expanding universe**

Hintz realized, however, that this may not apply in an expanding universe that is accelerating, such as our own. Because spacetime is being increasingly pulled apart, much of the distant universe will not affect the black hole at all, since that energy can't travel faster than the speed of light.

In fact, the energy available to fall into the black hole is only that contained within the observable horizon: the volume of the universe that the black hole can expect to see over the course of its existence. For us, for example, the observable horizon is bigger than the 13.8 billion light years we can see into the past, because it includes everything that we will see forever into the future. The accelerating expansion of the universe will prevent us from seeing beyond a horizon of about 46.5 billion light years.

In that scenario, the expansion of the universe counteracts the amplification caused by time dilation inside the black hole, and for certain situations, cancels it entirely. In those cases – specifically, smooth, non-rotating black holes with a large electrical charge, so-called Reissner-Nordström-de Sitter black holes – an observer could survive passing through the Cauchy horizon and into a non-deterministic world.

"There are some exact solutions of Einstein's equations that are perfectly smooth, with no kinks, no tidal forces going to infinity, where everything is perfectly well behaved up to this Cauchy horizon and beyond," he said, noting that the passage through the horizon would be painful but brief. "After that, all bets are off; in some cases, such as a Reissner-Nordström-de Sitter black hole, one can avoid the central singularity altogether and live forever in a universe unknown."

Admittedly, he said, charged black holes are unlikely to exist, since they'd attract oppositely charged matter until they became neutral. However, the mathematical solutions for charged black holes are used as proxies for what would happen inside rotating black holes, which are probably the norm. Hintz argues that smooth, rotating black holes, called Kerr-Newman-de Sitter black holes, would behave the same way.

"That is upsetting, the idea that you could set out with an electrically charged star that undergoes collapse to a black hole, and then Alice travels inside this black hole and if the black hole parameters are sufficiently extremal, it could be that she can just cross the Cauchy horizon, survives that and reaches a region of the universe where knowing the complete initial state of the star, she will not be able to say what is going to happen," Hintz said. "It is no longer uniquely determined by full knowledge of the initial conditions. That is why it's very troublesome."

He discovered these types of black holes by teaming up with Cardoso and his colleagues, who calculated how a black hole rings when struck by gravitational waves, and which of its tones and overtones lasted the longest. In some cases, even the longest surviving frequency decayed fast enough to prevent the amplification from turning the Cauchy horizon into a dead zone.

Hintz's paper has already sparked other papers, one of which purports to show that most well-behaved black holes will not violate determinism. But Hintz insists that one instance of violation is one too many.

"People had been complacent for some 20 years, since the mid '90s, that strong cosmological censorship is always verified," he said. "We challenge that point of view."

Explore further

**More information:**Vitor Cardoso et al. Quasinormal Modes and Strong Cosmic Censorship,

*Physical Review Letters*(2018). DOI: 10.1103/PhysRevLett.120.031103 , On

*Arxiv*: https://arxiv.org/abs/1711.10502]

**Citation**: Some black holes erase your past (2018, February 21) retrieved 18 September 2019 from https://phys.org/news/2018-02-black-holes-erase.html

## User comments

sirdumpalotantialias_physorgThis is not how atoms work (what you are thinking of is the Bor model of an atom, which is an oversimplification of what really happens in an atom).

Electrons are found within a certain probability distribution around the nucleus in quantized orbitals (so they can't really move away or closer...at best they can jump from one orbital to another). Note that 'orbital' does not mean a circular orbit.

https://en.wikipe..._orbital

Note also that the electron isn't a 'hard ball-like point' that has a defined place and momentum at each point in time within its orbital. It's a distributed waveform (as can be demonstrated with a double slit experiment)

antialias_physorgQM constructs are probability distributions.

Well...even worse: their *square* are probability densities. What the (unsquared) waveform really signifies is still up for debate.

If you model something like an atom or nucleons as things that are held together by the exchange of gluons and W/Z-bosons then things become tricky, as these would have to travel at superluminal speeds to keep an atom stable inside the event horizon. Whether tunneling is a way around this I don't know (but my gut feeling is that it's not).

EyeNSteinHowever if Dr Robert Spekkens of the Perimeter Institute is correct: There may be an underlying causal reality after all:- https://www.youtu...5m3UMer4

(He interprets psi as 'knowledge' rather than 'reality' and illuminates the inconsistencies of the various QM interpretations. He encompasses Bell's Inequality and may be a couple of mathematical leaps away from a consistent reality)

But then anything may be better than the fudged up holy cow of the Copenhagen interpretation.

cantdrive85This is pure unadulterated bullshit! The audacity of the Acolytes of the Church of the standard theory is beyond the religionists. What a pathetic display!

sirdumpalot'Energy can neither be created nor destroyed, it can only change forms', is what the fear of the destruction of information is tied to.

BenniOn a Stationary System With Spherical Symmetry Consisting of Many Gravitating Masses

Author(s): Albert Einstein Reviewed work(s): Source: The Annals of Mathematics, Second Series, Vol. 40, No. 4 (Oct., 1939), pp. 922-936 Published by: Annals of Mathematics Stable URL:

http://www.cscamm...hild.pdf

The essential result of this investigation is a clear understanding as to why the "Schwarzschild singularities" do not exist in physical reality. Although the theory given here treats only clusters whose particles move along circular paths it does not seem to be subject to reasonable doubt that most general cases will have analogous results. The "Schwarzschild singularity" does not appear for the reason that matter cannot be concentrated arbitrarily. And this is due to the fact that otherwise the constituting particles would reach the velocity of light.

I'll take Einstein's work over this author's.

MerritSpaced out EngineerWithout an ontology of relational theory, it is worth the investigation. A complete theory would have both outcomes. It is by trying everything is made possible.

Who needs to survive, if close enough representational content could be approximately cloned?

Could we run a program, such as the Halting problem, Godel's Incompleteness theorem, or ourselves on Malament–Hogarth spacetime? After all you can only run it once.

We are finding, what we once thought we astronomical theories, in local substrates.

We can experimentally verify the same mirroring of low dimensialty.

Clearly science is sustained by surprise. So at least Shannon had it right.

julianpenrodPerlmutter's "method" is flawed

He said they found a galaxy determined to be 5 billion light years away, by comparing the Hubble Constant with its red shift. But, then, they claim to have found a Type Ia supernova that, at maximum, was dimmer than expected which "means" it had to be further away than 5 billion light years. But that means it must have a larger red shift than something 5 billion light years away or the Hubble Constant is different. If the galaxy is going faster than expected, why does it still have a relatively low red shift?

But, also, consider, if acceleration began five billion years ago, then it's continuing now. Which means the Hubble Constant would not be Constant nearby, but it is.

julianpenrodThis is important, since so many are determined to ignore the meaning of a formula and, instead,make physical predictions based solely on it.

If you toss a ball outward and upward from the edge of a cliff, the parabolic formula will indicate that it goes into negative measured space. But it doesn't. It goes below the level of the cliff. And it will not continue forever, it will hit the ground and bounce.

The same is true of the formula they try to say equates matter and energy. Using "relativistic" formulas for the kinetic energy of a moving mass, you get a formula which subtracts the mass times speed of light squared from a total mass like formula. This only means that mass times speed of light squared is the zero starting point for measuring by the formula, not that the mass is energy.

philecrawfordHyperfuzzyrrwillsjWhere all the improbabilities are possible.

And all the impossibilities are probable.

And all us hyper-hypotheticaters, are way out in the midst of a vast forest. We all have our faces firmly planted against the trunk of a single tree. With our noses pressed into a knothole. Loudly asserting that what we can see, is all of reality!

granville583762The black hole can go no smaller than the escape velocity radius of gravity where the escape velocity is the velocity that gravity travels at, the speed of light. Black holes with their quasars eject matter out their spin axis into the two Fermi bubbles above and below the black hole where stars form from the matter the black hole takes in and ejects out is spin axis. Gravity is compressing matter to its escape velocity radius the speed of light R=2GM/C*. The matter in the black hole goes right its escape velocity radius where the gravity is zero at it its centre of mass, exactly the same as hole through the centre of earth where falling mass is weightless at the earth's core The mass the black hole takes in is broken down to exactly the same constituency as the black hole star of creation. What memory the matter had before, when it passed through the light radius any reminisces of memory is lost.

AllStBobNo, it is based on the operator solution in Quantum Mechanics (and Classical mechanics) being Unitary and hence invertible.

TheGhostofOtto1923... mystic.

"Quantum mysticism is a set of metaphysical beliefs and associated practices that seek to relate consciousness, intelligence, spirituality, or mystical world-views to the ideas of quantum mechanics and its interpretations."

"Although Oxford mathematician Roger Penrose shared with Stephen Hawking the Wolf Prize for Physics in 1988, Hawking has vigorously opposed the attempts of Penrose to develop an explanation for consciousness from quantum physics (as has also noted physicist and atheist Victor Stenger and philosopher Daniel Dennett)."

idjyitCool diagram though 8-)

Nonlin_orgWasn't the universe just after the Big Bang a Black Hole? If so, how come it started to expand?

sirdumpalotHow can an atom have a probability distribution for an electron orbital that is behind the nucleus, or in front of the nucleus? The issue becomes that the nucleus and the electron have only one directional communication. I wonder what the relational interpretation of QM says about this.

idjyitSo for particles to form and persist you have to achieve a T=0 state, after which it will persist indefinitely and can slow down, exchange energy, exhibit gravity, form structures etc etc etc.

At T=0, the past is no longer applicable. All previous energy exchanges are effectively reset because they have been converted into mass.

Varade1) If nothing else not even light can escape from black hole then why it is interacting with outside word with gravity (provided gravity speed=light speed)?

2) Are we implementing Lorentz transformation hypothesis (and not Einstein one) properly into theory?

3) How we can measure charge inside black hole (not asking about event horizon)? If two charges interacting with virtual photons (speed=c) falling in black hole. As virtual photon will interact with black hole more, the interaction/force between charges should be poor. Is it so? Is charge parity maintained in the black hole?

If we get answer these questions, then we can understand black hole much better.

antialias_physorgNo. Right at the big bang there was no matter. That came later.

Good question. Short answer: Nobody knows (yet). Stuff that affects spacetime is still very much a subject being researched. The label under which this area of research goes in science is 'dark energy'.

What do you mean by 'behind'?

Why?( Hint: If time would stop then you could not have something like decay. )

antialias_physorgBecause gravity is a spacetime effect. It is (probably) not conveyed by particles....(though a graviton is postulated). Gravity does not interact with gravity - it superposes. Light moves along the curvature of spacetime. Gravity IS the curvature of spacetime.

idjyitBase particles don't decay they may lose energy but the prime particle in invariant.

Energy exchange is a product of a T=0 particle interacting with other T=0 particles.

idjyitantialias_physorgEvery measurement we've done so far says otherwise. If it's a choice between what you say and actual measurement, I'll believe actual measurement every time.

Antimatter annihilation produces photons. The word 'annihilation' might also be a clue that you're wrong...just sayin'.

Mark ThomasSo while I am far from an expert on time travel paradoxes, it seems that if you are erased from the past, you would be otherwise free to travel to the past without creating paradoxes. For example, no such thing as the Grandfather Paradox because once you cross the Cauchy horizon of a Reissner-Nordström-de Sitter black hole you did not exist in the past and don't have a grandfather. Some people think it is the paradoxes that prevent time travel to the past and this idea may remove that obstacle.

The whole thing is pretty tough to swallow, but it is interesting to think about.

Spaced out EngineerDoes this still hold for a frustration free identity? Ex. A more apt to exit middle-out quantum gravitational perturbation theory. Spacetime operators groundstate of space, but spacetime as nothingness, whose flux is what is observed rather than a unitary identity of nothing (hence frustration free).

I guess this still does not explain compactification, nor why the offset from the groundstate is more probable.

Superdeterminism, all positive and negative pressure fracturings. of symmetry occur

The question is just which noncausal "locally connected" null geodesicy fracture are we a part of. What is curious is, I am not sure if such a theory excludes pythagorean, platonic accounts or picks a side. It takes a pop and push for this. D-9 brane astronaut conserved in a noisy channel.

idjyitYeah right M8!

The Universe would be a giant black hole if that were true.

The maths doesn't add up.

humyOh dear. Even with a totally realist interpretation of quantum physics of the deterministic kind that Einstein would have approved of, that simply couldn't be more wrong. This author of the above comment obviously doesn't know the first thing about modern quantum physics and should be put right.

humySomething can be both totally deterministic and yet STILL be impossible to predict in practice.

Predictability requires deterministic but deterministic doesn't require predictability.

AlfvenArpIn the real world it is what you do in the present, not the past, that determines your future. Living in the present is what provides infinite possible futures, not a type of black holes. Perhaps this mathematician is unhappy being a mathematician and is hoping to find this kind of black hole to reset his life. I hope he finds it.

milnikmilnikmilnikYou do not even know the order of the process of formation of particles or celestial bodies. Black holes are "tombs" of matter, where matter returns to the form of substance AETHER, from which it is formed by the natural laws determined by the Creator everything in the observer of the universe, that is, the MEEU, which is the material energy entity of the universe, your body.

milnikDoes any of you in these discussions know anything about your existence and about your abilities and how you are and from whom, everything got and how and when you will lose it all.? ENJOY THE TRUTH AND DO NOT REDE FROM THE LOVE OF ANIMALS OF ANIMALS RETURNING TO THE INSTITUTE LEVEL, DO YOU DO NOT KNOW WHAT IS CREATOR, AND THAT ALL IT IS ALLOWED WITH EVERYTHING, EXCEPT THROUGH REPEATING, WHAT THE CONTAMINATORS OF OUR COVERAGE RECOGNIZED !!

SKULLTRAPgranville583762You can not violate general relativity because Albert Einstein was modifying and rewriting his theories as he mellowed with age and all his theories were mainly constructed when he worked in the patent office because by definition by Albert Einstein changing his own theories he was violating general relativity, common sense says you cannot violate your own theories.

postfutureThank you, mackita, for pointing that out. Much simpler and even very trivial things can 'disintegrate' the 'past', as well as the 'present' and the 'future' ;)

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