In his remarkable Reith Lectures, Stephen Hawking said, “In space, no one can hear you scream; in a black hole, no can see you disappear“. The boundaries of what’s knowable about a black hole spirals into a void of uncertainty in the singularity it houses. Singularity, of course, being the great enigma of our time, where the gravitational field becomes infinite. Anyone who gets past a Black Hole’s event horizon is drawn into the eventuality of the singularity, much like Robert Herrick’s poem on the inifnite, eternal,
O years! and age! farewell:
Behold I go,
Where I do know
Infinity to dwell.And these mine eyes shall see
All times, how they
Are lost i’ th’ sea
Of vast eternity: –
But to an observer outside, watching a person inch past a black hole is just not possible. We’d see the person frozen in time, taking forever to cross the event horizon. This is not a paradox, though- it is merely two observers seeing an “event” from their field of view. Something as strange as the singularity is bound to bring some paradoxes, though. After all, there’s infinitude involved. We’ve all heard of the famous dictum that some infinities are bigger than other infinities. The paradox of infinity was well put by Emily Dickinson, who when her mother died, was unconsolable:
Mother’s dying almost stunned my spirit… She slipped from our fingers like a flake gathered by the wind, and is now part of the drift called “the infinite.” We don’t know where she is, though so many tell us.
The Chinese words that refer to infinity are: “wuji” meaning “boundless”, and “wuqiong” meaning “endless,”. The Chinese believe in the harmony of the opposite and believe that the infinite can be approximated to nothingness. The singularity, the infinity it houses, and the myriad of pardoxes it brings aren’t what Hawking’s Balck Hole paradox refers to. This great cosmologist who worked at the intersection of general relativity and quantum mechanics formulated “the black hole information paradox”.
Image: NASA
Defining information to make a better sense of the paradox
To a lay person information is typically a measure of what is visible to naked eye: whether an apple is red, whether the Earth is round, whether the varnish glistens. But physics is more concerned with defining information in terms of quantum constituents: What is the position, spin, and velocity of an apple, the Earth, and the varnish? And what is the total quantum information of all the particles that exist in our cosmos? After all, all objects in the universe are composed of particles having a unique set of quantum properties.
One of the most pivotal laws of physics states that “the total amount of quantum information in the Universe must be conserved“. Even if you destroy an object (say, a forest) beyond recognition (by starting a wildfire), its quantum information is never permanently deleted. And theoretically, if we were to know the quantum information about the state of the ashen remains of the forest, one could reconstruct the forest in its original form.
Image:NASA
Conservation of information is a mathematical necessity, a quintessential foundational block of modern science is built. But around black holes, those foundations get shaken. When a forest of particle enters a black hole, what remains of it? After all, for us, the outside observers, all information seems to be frozen in time, while the objects are sphagettified or pancake detonated, and head towards the singularity. It seems as though all information is lost. Big Think explained this paradox in the following manner:
“If you throw a book into a black hole, that book contains all sorts of information: the order of the pages, the text contained on them, the quantum properties (like baryon number and lepton number) of the particles making up the pages and the cover, etc. That information goes into the black hole, adding to its mass/energy and increasing the size and surface area of the black hole’s event horizon. Much later, when the black hole decays via Hawking radiation, that energy comes back out, but the information encoded in that radiation is predicted to be totally random: it’s as though the book’s information has been erased.”
Information might be out of sight, not out of hand
It might be wrong to presuppose that the quantum information related to any object entering a black hole is permanently deleted. For all practical purposes, the quantum information may be out of sight, but it might still exist within the black hole.
Theories also suggest that information related to any object entering a black hole is encoded on the surface layer of the black hole i.e., its event horizon. When a black hole guzzles down any object, the surface area of the event horizon increases as well. Perhaps the increase in the surface area allows for the possibility of quantum information in the event horizon.
If we were to expand the idea of this holographic principle, that the 2D surface of an event horizon can store quantum information, it would lead us to the suggestion that the very boundary of the observable universe is also a 2D surface encoded with information about real, 3D objects. If this is true, it’s possible that reality as we know it is just a holographic projection of that information.
However, there’s a slight leakage that we haven’t taken into consideration.
Leaking particle by particle: Hawking radiation
Stephen Hawking showed that black holes evaporate over incredibly long periods of time, as they shed particles away. Italian astrophysicist Fabio Pacucci suggested that the “evaporating particles are unrelated to the information the black hole encodes– suggesting that a black hole and all the quantum information it contains could be completely erased“. If information is indeed destroyed, it would force a complete rewriting of the laws of physics.
Image: NASA
As a result, a couple of solutions around this conundrum have been proposed:
- Information is encoded in the escaping (Hawking) radiation, and we’ll have to learn more how to unravel the information in the radiation.
- The information paradox is just a product of our inability to reconcile quantum mechanics and general relativity in a meaningful way.
Scientists have found combining General Relativity and Quantum Mechanics almost impossible. A “unified theory of everything” is expected to get rid of paradoxes like Hawking’s Black Hole Information paradox.
Here are a few other possibilities of resolving this paradox, as explained by comologist John Stutter:
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Maybe somehow the information stuck to the surface of the black hole does end up threading its way into the emitted radiation.
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Maybe Hawking’s original analysis was too simple, and by careful observations of the radiation we could painstakingly reconstruct the books and cats and spaceships that fell in.
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Perhaps information doesn’t get stuck to the surface, but instead is left behind in some sort of crunchy nugget just as the black hole finishes evaporating.