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K. Radhakrishnan
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Koppillil Radhakrishnan[2] (born 29 August 1949) is an Indian space scientist who headed the Indian Space Research Organisation (ISRO) between November 2009 and December 2014 as Chairman of Space Commission, Secretary of the Department of Space and Chairman of ISRO.[3][4][5] Prior to this, he was the Director of Vikram Sarabhai Space Centre (2007-2009) and Director of National Remote Sensing Agency (2005-2008) of the Department of Space. He had a brief stint of five years (2000-2005) in the Ministry of Earth Sciences as Director of Indian National Centre for Ocean Information Services (INCOIS).[6]

K Radhakrishnan
K-Radhakrishnan-2014.jpg
Radhakrishnan in 2014
Born
29 August 1949 (age 72)
Irinjalakuda, Travancore-Cochin, India
Alma mater
Government Engineering College, Thrissur (BE)
IIM Bangalore (MBA)
IIT Kharagpur (PhD)
Known for
Chandrayaan-1, Mangalyaan
Awards
Padma Bhushan (2014)[1]
Scientific career
Fields
Electrical Engineering
Space research
Institutions
VSSC, NRSA, INCOIS, ISRO, IITK
K. Radhakrishnan
Chairman, Indian Space Research Organisation
In office
30 October 2009 – 31 December 2014
Preceded by
G. Madhavan Nair
Succeeded by
Shailesh Nayak
Presently, he is the Chairperson of the Board of Governors of Indian Institute of Technology (IIT), Kanpur[7][8] and Chairman of the Standing Committee of the IIT Council besides being Honorary Distinguished Advisor in the Department of Space/ISRO.[9]

He is a Fellow of the Indian National Academy of Engineering; Fellow of the National Academy of Sciences, India; Honorary Life Fellow of the Institution of Engineers, India; Honorary Fellow of the Institution of Electronics and Telecommunication Engineers, India; Member of the International Academy of Astronautics; Fellow of the Andhra Pradesh Academy of Sciences; Honorary Fellow of the Kerala Academy of Sciences; Fellow of the Indian Society of Remote Sensing; and Fellow of the Indian Geophysical Union.[6] He is an accomplished vocalist (Carnatic music) and Kathakali artist.[10]

Penguin Random House India published his autobiography My Odyssey: Memoirs of the Man Behind the Mangalyaan Mission (ISBN 978-0-670-08906-2), co-authored by Radhakrishnan and Nilanjan Routh, in November 2016.[11]

Education and Personal Life
Indian Space Research Organisation
Ocean Observation and Information Services
Kathakali and Carnatic Music
Positions held
Major Awards and honours[9]
References
External links
Last edited 3 months ago by 202.164.139.132
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02/11/2021

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Apsara-U (Apsara- Upgraded) was successfully commissioned and its First Approach to Criticality (FAC) was achieved on 10th September 2018. Indigenously developed Low Enriched Uranium (LEU) fuel in Uranium Silicide form is used in the reactor. Hot water layer concept at the top of pool, which is first of a kind in India, is employed to minimize radiation dose. By virtue of higher neutron flux, Apsara-U will enhance indigenous production of radioisotopes for various societal applications. The reactor will also be used extensively for research in nuclear physics, material science and radiation shielding.

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01/11/2021

Abdul Qadeer Khan
Nuclear physicist and a metallurgical engineer, who founded the uranium enrichment program for Pakistan's atomic bomb project making research contributions to molecular morphology, the physics of marten site alloys, condensed matter physics, materials physics.
Awards: Hilal-i-Imtiaz, Nishan-e-Imtiaz.


!
source: wikipedia

01/11/2021

https://www.wionews.com/science/why-is-mysterious-dark-energy-leading-to-expansion-of-the-universe-425187

28/10/2021

IEEE.ORG
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TOPIC
New Optical Switch up to 1000x Faster Than Transistors“Optical accelerator” devices could one day soon turbocharge tailored applications
CHARLES Q. CHOI
15 OCT 2021
The Hybrid Photonics Labs at Skoltech where the new optical transistor was created.
The Hybrid Photonics Labs at the Skolkovo Institute of Science and Technology in Moscow, where the new optical switch was created.
SKOLTECH
A new optical switch is, at 1 trillion operations per second, between 100 and 1,000 times faster than today's leading commercial electronic transistors, research that may one day help lead to a new generation of computers based on light instead of electricity, say scientists in Russia and at IBM.

Computers typically represent data as ones and zeroes by switching transistors between one electric state and the other. Optical computers that replace conventional transistors with optical switches could theoretically operate more quickly than regular computers, as photons travel at the speed of light, while electrons, typically, don’t.

The new device relies on a 35-nanometer-wide organic semiconductor polymer film sandwiched between two highly reflective mirrors. The result is a microscopic cavity designed to keep incoming light trapped inside for as long as possible to help it couple with the cavity's material.

Two lasers help operate the device—a bright pump laser and a very weak seed laser. When the pump laser shines on the microcavity, its photons can couple strongly with excitons (electrons bound to their positively charged counterparts, holes) within the cavity's material. This can give rise to short-lived quasiparticles known as exciton-polaritons.

The cluster of exciton-polaritons can form so-called Bose-Einstein condensates, collections of particles that each behave like a single atom. The light from the seed beam could switch this condensate between two measurable states that serve as zero and one.

The new device not only can operate extraordinarily quickly, but it can switch using as little as one photon of input on average. In contrast, transistors generally needs dozens of times more energy to switch, while those that switch using single electrons are much slower.

"The most surprising finding was that we could trigger the optical switch with the smallest amount of light, a single photon," says study senior author Pavlos Lagoudakis, a physicist at the Skolkovo Institute of Science and Technology in Moscow.

Electronic transistors that are comparably switchable with just single electrons usually require bulky cooling equipment, which in turn consumes power and factors into their operating costs. In contrast, the new optical switch works at room temperature.

Lagoudakis cautions that all-optical computing likely lies far in the future. "It took 40 years for the first electronic transistor to enter a personal computer and the investment of many governments and companies and thousands of researchers and engineers," he says. "It is often misunderstood how long before a discovery in fundamental physics research takes to enter the market."

Still, Lagoudakis suggests their research could lead to "optical accelerators" one day relatively soon—optical computing devices that can perform specialized operations much faster than classical electronic computers. "These could be used to remove computational bottlenecks in supercomputers that usually rely on massive parallel processing," he notes.

Besides optical accelerators and all-optical computing, Lagoudakis says the super-sensitivity of the new optical switch to light suggests it could serve as a light detector that could find use in lidar scanners, such as those finding use in drones and autonomous vehicles.

The scientists detailed their findings in a recent issue of the journal Nature.

CHARLES Q. CHOI
is a science reporter who contributes regularly to IEEE Spectrum. He has written for Scientific American, The New York Times, Wired, and Science, among others.

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09/10/2021

Ramanujan always maintained that it was Namagari Thayar who 'placed equations on his tongue'Ramanujan always maintained that it was Namagari Thayar who 'placed equations on his tongue'
Culture
The Devi In Ramanujan's Dream: Because She Is 'The Mind Beyond Mind'
By Aravindan Neelakandan
October 07, 2021 at 2:29 PM
For Srinivasa Ramanujan, an equation "had no meaning unless it revealed the mind of god".

The 207th name of the goddess in Sri Lalitha Sahasranama is Manonmani, where she is the mind beyond the mind and the awakening that happens when awareness is raised to the highest possible state.

In the 2009 biopic of Charles Darwin, Creation, there is nothing mystical or mysterious. As Darwin uncovers one of the most fundamental processes of the universe, his psychological journey gets heavily infused with the conflict he has with the faith of his wife and the memories of his daughter.

Eventually though, it is his wife who gave him the final push to publish his famous On the Origin of Species. In a subtle, non-mystical way, the feminine plays a vital role in the movie adaptation of the book.

The intuitive component of our psyche is always feminine. The deeper we delve into our intuitive realms, the more sacred the feminine becomes. In societies where the divine feminine is not suppressed by cultures and dogmas, it manifests as the agency that delivers the genius his song or his equation.

In India, we have a long tradition of the goddesses appearing in the dreams or in a luminal experience of geniuses.

A well-attested tradition is that of Thiru Gnana Sambandar, who was given the milk of wisdom by Goddess Parvati. The songs with their supra-human mathematical precision of rhythm and meaning — entire poems written in the form of palindromes — show that Sambandar was a genius. Tradition, of course, attributes it to the divine milk.

In oral traditions about Kalidasa in northern India and Kalamega Kavi in the south, we see the goddess appearing in a subliminal realm that exists between dream and reality. She either writes the pranava mantra on the tongue, as in the Kalidasa story, or spits betel leaf juice into the mouth of the poet as in the case of poet Kalamega.

While Kalidasa is virtually the national poet of India, Kavi Kalamegam, known for his songs that are filled with extraordinary pun, satire, caustic humour and creativity par excellence, is well known in Tamil.

The same goes for the great humorist Tenali Raman. One should remember that Tenali Raman, despite the popular imagery of him being a clever court jester, was also a great composer of philosophical works.

Can we consider them all as myths of pre-modern times? Or is there a deeper, psychological-spiritual phenomenon involved here?

A recent phenomenon that still has implications for mathematics and theoretical physics should actually make us further investigate the event so consistently mentioned in Hindu traditions.

Srinivasa Ramanujan!

The discoveries of Srinivasa Ramanujan help theoretical physicists even today. In his dreams, Namagiri Thayar, the divine consort of Maha Vishnu in the temple at Namakkal — would appear and make him ‘see’ the equations and he would later commit them to paper.

One should remember that Ramanujan himself was a mathematical genius. He would struggle in his own unorthodox ways with theorems he taught himself. And as he would fall asleep, the goddess would appear and give him the intuitive push. So was it his own intuitive abilities which were taking the form of the goddess he knew so well because of his cultural conditioning?

There is more to it — some deeper resonances.

Physicist Michio Kaku has pointed out that Ramanujan's function also appears in string theory ‘miraculously’. This seems to have some kind of archetypal connection with ancient Sankhya Darshana. In an earlier essay, this connection has been explored. So, the number 24 appearing in Ramanujan’s papers and its deeper relation to certain approaches to the fundamental problems of the universe — make us pause and reconsider the intuition taking the form of the goddess.

What is at play may be something more fundamental than intuition. From Thiru Gnana Sambandar through Kalidasa, Kalamegam to Srinivasa Ramanujan, from Parvati to Kali to Namagiri Thayar — the phenomenon may be a doorway for us to get a glimpse into the incredible universe of the divine feminine — who perhaps may be the very substratum of all that exists in the phenomenal world of space and time, and names and forms of infinite variety.

Perhaps, we may get some more clues in the yogic-tantric psychology of Thirumoolar, a mystic of Shaiva Siddhanta tradition.

In the fourth ta**ra of his work Thirumanthiram — auspicious mantra — in the 1,107th verse, he states that Manonmani comes to one who is in divine slumber and pulls him close to her by her hand wearing beautiful, enchanting bangles, and then transfers her spittle into the person’s mouth, not asking them not to sleep anymore, thus performing a miracle.

Thirumanthiram further describes Manonmani, the form of the goddess who appears in the divine slumber of the seeker, in a later verse, as the one who is beyond words and mind and yet surrounded by the diversity of the devilish and ghoulish forms. To Shiva, she is at once his mother, daughter and wife. This is because in the primordial timeless time, Shakti brings forth Shiva — and becomes his mother. Shiva brings forth Shakti and she becomes his daughter and then Shakti and Shiva are in dynamic union in all existence and hence, she is his consort.

This primordial consciousness, both dynamic and the basic substratum, emerges in the awareness that is between the real and the dream state and reveals its secrets — poetic, mathematical, aesthetic and mystic.

In Sri Lalitha Sahasranama the 207th name of the goddess is Manonmani. She is variedly described. She is the mind beyond the mind. She is the awakening that happens when the awareness is raised to the highest possible state.

For Srinivasa Ramanujan, mathematics was not just a knowledge domain. He famously said that for him an equation has no meaning unless it reveals the mind of god.

In the Sri Vaishnava tradition from which he hailed, the god is of course Vishnu and seated in his heart is Lakshmi. The mind of god is the goddess. So, she visited him in his dream.

She revealed to him the equations — the thoughts, the vimarsa waves that arise in the luminous ocean of Brahman. This is, of course, mystic speculation. But if some day the yogic psychology becomes a serious tool to explore our inner realms, we, or others, will continue with this exploration.

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NOBEL PRIZE
My PhD supervisor just won the Nobel prize in physics. Here’s how his research changed science
The prize for Giorgio Parisi, Syukuro Manabe and Klaus Hasselmann is an amazing recognition of an entire research area of complex systems in physics.
Paolo Barucca, The Conversation
Oct 06, 2021 · 11:30 pm

Giorgio Parisi’s work has helped us tease predictable patterns from complexity. | Sapienza Università di Roma/flickr, CC BY-NC-SA
The Nobel Prize in Physics for 2021 has been jointly awarded to Italy’s Giorgio Parisi, Japan’s Syukuro Manabe and Germany’s Klaus Hasselmann for their “groundbreaking contributions to our understanding of complex systems”.

Pleasant surprise
When I heard the news, I could hardly believe it. I studied for my master’s thesis and my PhD in theoretical physics under Professor Parisi at Sapienza University in Rome.

When I say I was in disbelief, do not misunderstand me. Of all the people I have ever met in my research experience – perhaps in my life – he is, without doubt, the most ingenious. So I was not surprised about the Nobel Prize committee’s decision to name him as a Laureate. Rather, it was their decision to recognise his “contributions to our understanding of complex systems” that piqued my interest.

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This prize for Professor Parisi, split with trail-blazing meteorologists Professor Manabe and Professor Hasselmann, is an amazing recognition of an entire research area – perhaps a little less glamorous than the likes of general relativity or string theory – that attempts to understand and model what we in physics call “complex systems”.

These include things like climate ecosystems, financial systems and biological phenomena, to name a few. The sheer variety of complex systems – represented in fluctuating markets and flocking starlings – makes it very hard to derive any sort of universal rules for them. Parisi’s work has allowed us to derive unprecedented conclusions about such systems that, on the surface, look random, unpredictable and impossible to model theoretically.

Unlike some other physics models, complex systems are not a collection of identical particles, regularly interacting in a way that is consistent and predictable. Instead, complex systems are systems of elements, potentially different from each other, interacting in different and seemingly unpredictable ways while exposed to varying external conditions.

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A stepping stone for modelling complex systems is the theory of “disordered systems”. These are essentially systems in which different pairs of elements experience different, potentially conflicting forces that can lead the elements to become “frustrated”.

A way of illustrating this is to imagine a party (a closed social system), where Alice may want to chat with Bob, and Bob may want to chat with Charlie, but Charlie may not want to chat with Alice. There is frustration here – so what should they do?

In this example, one corner of the triangle is frustrated. Photo credit: Johan Jarnestad/The Royal Swedish Academy of Sciences, CC BY-NC
Professor Parisi’s research clarified what happens when frustration occurs in disordered and complex systems. He identified that complex systems are able to remember their trajectories over time, and can get stuck in sub-optimal states for a long time.

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In our party example, imagine Alice, Bob, Charlie and other guests irregularly changing conversational groups and partners, hoping to find the best group of people to chat with – yet potentially never finding it. That is the sub-optimal state complex systems can get stuck in.

Patterns from disorder
One of the many theoretical tools Professor Parisi has used to establish his theory is the so-called “replica trick” – a mathematical method that takes a disordered system, replicates it multiple times, and compares how different replicas of the system behave. You can do this, for instance, by compressing marbles in a box, which will form a different configuration each time you make the compression. Over many repetitions, Parisi knew, telling patterns might emerge.

The replica trick can be conducted by compressing balls in a box. Photo credit: Johan Jarnestad/The Royal Swedish Academy of Sciences, CC BY-NC
This method is now one of the few theoretical pillars for the development of the whole theory of complex systems as we know it today. Professor Parisi’s theory has been shown to give reliable predictions on the statistical properties of complex systems ranging from supercooled liquids (liquids below their solidification temperature), frozen liquids, amorphous solids such as glass and even flocks of starlings.

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The theory of disordered systems allows us to make sense of the beautiful emergence of coherent flight patterns within tight flocks of birds – who manage to stick together and form vast groupings despite adverse conditions.

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Parisi has studied how starling flocks behave under predation by peregrine falcons.

The same framework has been used to make sense of Earth’s climate. The meteorologists who share the Nobel prize with Professor Parisi will have relied upon breakthroughs in theoretical physics to produce the models we now use to reliably demonstrate global warming.

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I had the chance to discuss these topics with Professor Parisi in Rome, while his experiments with flocks of birds were taking place and during his computer simulations on the behaviour of glass. Knowing a little of his mind, I am not at all surprised he has been awarded the Nobel prize in physics.

But I am pleasantly surprised that the field of complex systems, which is quietly pushing at the frontier of theoretical research in physics, has been given this exposure. This Nobel award has delivered new legitimacy – and, we can hope, new minds – to this fascinating area of contemporary physics.

Paolo Barucca is a Lecturer, Department of Computer Science at University College London.

This article first appeared on The Conversation.

Support our journalism by contributing to Scroll Ground Reporting Fund. We welcome your comments at [email protected].
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06/10/2021

Interesting Engineering

SCIENCE
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SCIENCE
Black Holes Might Conceal a Huge Wall of Fire. But We May Never See Them
And anything that crosses will face a 'seething maelstrom of particles'.

By John Loeffler
Oct 05, 2021

Black Holes Might Conceal a Huge Wall of Fire. But We May Never See Them
Event Horizon Telescope collaboration et al / via NASA
Alice and Bob are two of the most famous explorers you've probably never heard of. If there is a quantum experiment being discussed, Alice and Bob are usually involved, and they've been through a lot together. But in the last 50 years, classical physics and quantum mechanics have come into a direct conflict at the bleeding edge of the most extreme objects in the universe, black holes, and things have not turned out great for Alice.

See, Alice is a sub-atomic particle, and she's been everywhere from hanging out with Schrodinger's Cat to performing immensely complex computations in a quantum computer. But, if a recent theory about an especially thorny physics paradox is correct, Alice just might end her intrepid travels for good by falling past the event horizon of a black hole, only to be immediately incinerated by a massive wall of intense energy that runs all along the entire event horizon, forever beyond our ability to ever see it.

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This black hole firewall, as it's become known, was immediately dismissed as ludicrous, and even insulting, when it was initially proposed in 2012, but nearly a decade later, scientists are still struggling to refute it, and the controversy could have profound implications for physics as we know it.

A Brief History of Black Holes
Before we can wrangle with the mysterious interior of a black hole, we should start by describing what we know about black holes.

Black holes were first predicted by a humble English rector John Michell in 1783, who used Newtonian mechanics to posit the existence of "Dark Stars" whose gravity was stronger than a particle of light's capacity to escape it. However, the concept of black holes we are more familiar with arose from Albert Einstein and his theory of relativity in 1915.

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Karl Schwarzschild, a German physicist and astronomer, read Einstein's 1905 paper on special relativity a few months and produced the first exact solution to Einstein's general gravitational equations, which impressed even Einstein himself. "I had not expected that one could formulate the exact solution of the problem in such a simple way," he wrote to Schwarzchild in 1916.

What Schwarzchild is perhaps best known for, however, is applying the math of Einstein's relativity and deriving the possible existence of black holes based on the escape velocity of light (much as Michell had done with Newtonian mechanics). Schwarzschild himself didn't believe that black holes actually existed, but his work provided the mathematical basis on which our modern understanding of black holes was built.

The key feature of the black holes he described was an event horizon, a boundary located a predictable distance from the center of the black hole's mass which represented the gravitational threshold where the escape velocity from the black hole exceeds the speed of light. On the outside of the event horizon, escape was possible, but once you passed that boundary, relativity meant you could never leave, since nothing can travel faster than light.

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There have been some major developments in our understanding of black holes since Schwarzchild, but these basic features have stayed more or less the same since he first proposed them.

Some Fundamental Features of Quantum Mechanics
Black Holes Might Conceal a Huge Wall of Fire. But We May Never See Them
Source: Pixabay
Stepping away from the macroscale for a moment, we now need to dive below the level of the atom and discuss subatomic particles.

Subatomic matter does not behave in the same way as matter at the macroscale level. Instead, at the quantum level, the universe is governed by a strange world of probabilities and physics-defying features like quantum entanglement.

This feature of quantum entanglement, where two subatomic particles interact with one another and in the process become inextricably linked so that they behave as if they were a single object, seems to pay no mind to relativity, happily transmitting information between two entangled particles instantaneously over distances so vast that this information can be said to be traveling faster, sometimes exponentially faster, than light.

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Einstein and other noted physicists in the first half of the 20th century were so bothered by some of the peculiarities of quantum mechanics, particularly quantum entanglement, that they went to great lengths to try to refute its results, but its math has held up sound and some of the fundamental laws have proved to be as unassailable as Relativity. Quantum entanglement isn't just predictable, it's become the bedrock of actual working technology like quantum computing.

Quantum mechanics isn't constructed using the same kind of math as classical physics, though. Classical physics relies on predictable mathematical techniques like calculus, while quantum mechanics is built largely on probabilities, the math of the card game, and the craps table.

The probabilities that form the basis of quantum mechanics, however, rely on an important principle that cannot be violated: the preservation of information.

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If you roll a six-sided die, you have an equal one-in-six chance of rolling any of its values, but the probability that you will role a result is 1, which is the sum of adding up all the individual probabilities for all possible outcomes (in the case of the die, rolling a 1, 2, 3, 4, 5, or 6 all have one-sixth probability, so add all six one-sixths together and you get six-sixths, which is equal to 1). This summing up of probabilities in quantum mechanics is known as the principle of unitarity.

This predictive quality of probability relies on an even more fundamental rule, though, which is that knowing the current quantum state of a particle is predictive of its future state and also allows you to wind the particle back to its previous state.

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Theoretically, if you had perfect knowledge of how a die was rolled, as well as the result, you could move back in time to identify which side was facing up when it was in your hand.

In order for this to work, though, that information about a previous quantum state must be preserved somehow in the universe. If it were to suddenly disappear, it would be like taking one of the die faces off the die and leaving nothing in its place.

When that die is rolled again, its five remaining sides still have a one in six probability, but now those sides add up to five-sixths rather than 1. So destroying information, like removing one of those die faces, breaks the quantum probabilities of that die roll.

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This sort of transgression in quantum mechanics can't be allowed, since the information being destroyed directly leads to us not even being able to tell how many die faces we started out with originally and, thus, we couldn't actually know the true probabilities for anything.

Quantum mechanics as we know it would no longer work if quantum information is somehow destroyed.

What's more, there is also a principle in quantum mechanics known as monogamous quantum entanglement. Essentially, a particle can only be maximally entangled with one other particle, to the exclusion of all others, and this is key to how information in a quantum system is preserved.

There is a lot more to quantum mechanics than just these principles, but these are the essential ones to understanding how a black hole's event horizon could really be a gigantic, invisible shell of blazing hot energy.

Hawking Radiation
Black Holes Might Conceal a Huge Wall of Fire. But We May Never See Them
Source: Kerr Newman/Wikimedia Commons
When Steven Hawking did his most important work on black holes in the 1970s, he wasn't setting out to lay the foundation for a black hole firewall that annihilates anything unfortunate enough to fall into it, but may be what he did when he proposed the existence of Hawking radiation in 1974.

In even the emptiest of space, there is a roiling boil of quantum activity. It is thought that, spontaneously, virtual quantum particle and anti-particle pairs entangled together are constantly materializing and annihilating each other, drawing energy from the universe to create themselves and returning that same energy when they destroy each other.

Hawking realized, though, that if a pair of virtual particles materialize along the edge of a black hole's event horizon, though, one particle could fall into the black hole while its entangled partner on the outside is able to break free of the black hole and escape, producing what is now known as Hawking radiation.

The problem is that, according to the first law of thermodynamics, energy in a closed system must be conserved. If two virtual particles draw from the energy of the universe to materialize but don't immediately annihilate each other, then energy has been drawn from the universe without crediting it back. The only way something like this can happen is that the infalling particle must have negative energy in equal absolute value to the positive energy of the escaping particle.

But black holes, while immensely massive and energetic, aren't infinite — they have a defined mass, and any infalling, negative-energy particle subtracts an infinitesimally small amount of that black hole's mass when it enters. If the black hole doesn't accrete any additional material to add more mass, these tiny substractions due to Hawking radiation start to add up, and as more mass gets evaporated away, the evaporation of the black hole accelerates.

Eventually, enough Hawking radiation is emitted that the largest black holes shrink to nothing and simply wink out of existence.

The Information Paradox

The challenge presented by Hawking radiation is that even if spacetime becomes infinitely warped at a black hole's singularity, it is held that whatever quantum information enters a black hole is still somehow preserved and therefore, theoretically, retrievable.

If nothing else, all that information hangs out at the black hole's infinite singularity and can at least still factor into any quantum probabilities so everything continues to add up to 1.

Critically, Hawking said that this radiation, even as it is still entangled with its infalling anti-particle, contains no encoded information about the black hole or its contents.

This means that all of the information that falls into a black hole never leaves it and would presumably evaporate into nothing, along with the black hole, due to Hawking radiation. This would take all of that information out of the overall quantum equation and the probabilities would suddenly stop adding up correctly.

Other physicists, like John Preskill of the California Institute of Technology, have argued that Hawking radiation actually becomes entangled with the area immediately outside the event horizon where the quantum information from infalling particles must be encoded. So long as the infalling particle and the outside particle do not share this information between them, quantum information need not be destroyed.

This was a tangled knot to begin with, but in 2012, a group of University of California, Santa Barbara, physicists proposed a solution to the information paradox that only seemed to make everything more contentious.

The Great Black Hole Firewall Controversy
Black Holes Might Conceal a Huge Wall of Fire. But We May Never See Them
Source: Jeremy Schnittman/Wikimedia Commons
When attempting to wrestle with the information paradox in 2012, Ahmed Almheiri, Donald Marolf, Joseph Polchinski, and James Sully — collectively known as AMPS — published a paper in the Journal of High Energy Physics arguing that along the edge of a black hole's event horizon was a swirling wall of energy so intense that it completely incinerated anything that touched it.

This was the result, AMPS argued, of the entanglement responsible for Hawking radiation being effectively severed by the event horizon, releasing an enormous amount of energy in the process. And since Hawking radiation is a constant process all along the edge of the event horizon, this energy is also being released constantly all across the event horizon.

What makes this theory so controversial is that this would violate another pillar of modern physics: the principle of equivalence. According to General Relativity, gravitational and inertial forces have a similar nature and are often indistinguishable. So, you would not be able to tell the difference between being in a stationary elevator in a gravitational field and an accelerating elevator in free space. This means that, if an observer were to pass the event horizon of a black hole, they should not notice anything amiss — at least not immediately — because it is still entangled to the observer outside the event horizon.

The tidal force of the singularity's incredible gravity would eventually tear the observer apart into a very long string of atoms, but depending on the size of the black hole, an observer could continue to float down toward the black hole's singularity for anywhere from a few microseconds to possibly a few decades before this spaghettification occurs.

If the black hole firewall theory is correct though, the infalling observer would not even make it past the event horizon, since the outside particle becomes Hawking radiation when its entangled counterpart falls into the black hole. In order for the quantum information inside the black hole to be preserved, the new Hawking radiation must become entangled with the area outside the event horizon.

Quantum mechanics forbids this kind of dual-entanglement. Either Hawking radiation does not entangle with the region along the event horizon, meaning that quantum information is lost for good, or its entanglement with the infalling particle must be severed at the event horizon, meaning equivalence breaks down, which inexorably gives rise to the black hole firewall.

This did not go over well with physicists, since undoing the equivalence principle would pull the entire foundation of spacetime out from under Einstein's relativity, which simply couldn't be possible given how regularly relativity has been validated through experimentation. If equivalence didn't hold, then all of those experiments had to have been a 90-plus-year series of flukes that happened to confirm a false idea by pure chance.

This wasn't lost on AMPS, who pointed out that if everyone wanted to keep equivalence, then they had no choice but to sacrifice the preservation of information or completely rewrite what we knew about quantum field theory.

Attempts to Scale the Black Hole Firewall
Steve Giddings, a quantum physicist at the University of California, Santa Barbara, said the paper produced “a crisis in the foundations of physics that may need a revolution to resolve”.

When Raphael Bousso, a string theorist at the University of California, Berkeley, first read the AMPS paper, he thought the theory preposterous and believed it would be quickly shot down. "A firewall simply can’t appear in empty space, any more than a brick wall can suddenly appear in an empty field and smack you in the face," he said.

But as the years dragged on, no one has really been able to offer a satisfying rebuttal to put the controversy to rest. Bousso told a gathering of black hole experts who'd come to CERN in 2013 to discuss the black hole firewall that the theory, "shakes the foundations of what most of us believed about black holes... It essentially pits quantum mechanics against general relativity, without giving us any clues as to which direction to go next."

The controversy has produced some interesting counter theories though. Giddings proposed in 2013 that if Hawking radiation were to make it some short distance from the event horizon before its entanglement with the infalling particle is broken, the release of energy would be muted enough to preserve Einstein's equivalence principle. This has its own cost, though, as it would still require rewriting some of the rules of quantum mechanics.

Preskill, meanwhile, famously bet Hawking in 1997 that information was not lost in a black hole and soon after a theory was put forward by Havard University's Juan Maldacena argued that "holograms" could encode 3D information in a 2D space where gravity had no influence, allowing information to find its way out of the black hole after all.

This argument proved persuasive enough for Hawking, who conceded to Preskill that information could be saved after all. With this history, Preskill makes an odd champion for the idea that information loss is actually the least offensive solution to the black hole firewall, but that was the argument he put forward in the 2013 conference. Quantum mechanics might need a page-one rewrite if information is lost, he said, but it wasn't out of the question. "Look in the mirror and ask yourself: Would I bet my life on unitarity?" he asked attendees.

Another possible solution to the black hole firewall problem was proposed by Maldacena and Stanford University's Leonard Susskind in 2013: wormholes.

In Maldacena and Susskind's proposal, quantum entanglement and Einstein-Rosen bridges are both intimately connected and could be two ways of describing the same phenomenon. If wormholes from inside the black hole were able to connect the infalling particles to their outside partners, then a form of entanglement could be maintained that did not require breaking entanglement at the event horizon, thus sidestepping the need for a firewall.

For all their inventiveness though, no one seems to be totally satisfied with the answers, even if they are enjoying the excitement of the debate itself.

“This is probably the most exciting thing that’s happened to me since I entered physics,” Bousso said. “It’s certainly the nicest paradox that’s come my way, and I’m excited to be working on it.”

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