What Does Quantum Theory Actually Tell Us about Reality?

Nearly a century after its founding, physicists and philosophers still don’t know—but they’re working on it

• By Anil Ananthaswamy on September 3, 2018
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Credit: Alexandre Gondran Wikimedia (CC BY-SA 4.0)

For a demonstration that overturned the great Isaac Newton’s ideas about the nature of light, it was staggeringly simple. It “may be repeated with great ease, wherever the sun shines,” the English physicist Thomas Young told the members of the Royal Society in London in November 1803, describing what is now known as a double-slit experiment, and Young wasn’t being overly melodramatic. He had come up with an elegant and decidedly homespun experiment to show light’s wavelike nature, and in doing so refuted Newton’s theory that light is made of corpuscles, or particles.

But the birth of quantum physics in the early 1900s made it clear that light is made of tiny, indivisible units, or quanta, of energy, which we call photons. Young’s experiment, when done with single photons or even single particles of matter, such as electrons and neutrons, is a conundrum to behold, raising fundamental questions about the very nature of reality. Some have even used it to argue that the quantum world is influenced by human consciousness, giving our minds an agency and a place in the ontology of the universe. But does the simple experiment really make such a case?

In the modern quantum form, Young’s experiment involves beaming individual particles of light or matter at two slits or openings cut into an otherwise opaque barrier. On the other side of the barrier is a screen that records the arrival of the particles (say, a photographic plate in the case of photons). Common sense leads us to expect that photons should go through one slit or the other and pile up behind each slit. 

They don’t. Rather, they go to certain parts of the screen and avoid others, creating alternating bands of light and dark. These so-called interference fringes, the kind you get when two sets of waves overlap. When the crests of one wave line up with the crests of another, you get constructive interference (bright bands), and when the crests align with troughs you get destructive interference (darkness).

But there’s only one photon going through the apparatus at any one time. It’s as ifeach photon is going through both slits at once and interfering with itself. This doesn’t make classical sense.

Mathematically speaking, however, what goes through both slits is not a physical particle or a physical wave but something called a wave function—an abstract mathematical function that represents the photon’s state (in this case its position). The wave function behaves like a wave. It hits the two slits, and new waves emanate from each slit on the other side, spread and eventually interfere with each other. The combined wave function can be used to work out the probabilities of where one might find the photon.

The photon has a high probability of being found where the two wave functions constructively interfere and is unlikely to be found in regions of destructive interference. The measurement—in this case the interaction of the wave function with the photographic plate—is said to “collapse” the wave function. It goes from being spread out before measurement to peaking at one of those places where the photon materializes upon measurement. 

This apparent measurement-induced collapse of the wave function is the source of many conceptual difficulties in quantum mechanics. Before the collapse, there’s no way to tell with certainty where the photon will land; it can appear at any one of the places of non-zero probability. There’s no way to chart the photon’s trajectory from the source to the detector. The photon is not real in the sense that a plane flying from San Francisco to New York is real.

Werner Heisenberg, among others, interpreted the mathematics to mean that reality doesn’t exist until observed. “The idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them ... is impossible,” he wrote. John Wheeler, too, used a variant of the double-slit experiment to argue that “no elementary quantum phenomenon is a phenomenon until it is a registered (‘observed,’ ‘indelibly recorded’) phenomenon.”

But quantum theory is entirely unclear about what constitutes a “measurement.” It simply postulates that the measuring device must be classical, without defining where such a boundary between the classical and quantum lies, thus leaving the door open for those who think that human consciousness needs to be invoked for collapse. Last May, Henry Stapp and colleagues argued, in this forum, that the double-slit experiment and its modern variants provide evidence that “a conscious observer may be indispensable” to make sense of the quantum realm and that a transpersonal mind underlies the material world.

But these experiments don’t constitute empirical evidence for such claims. In the double-slit experiment done with single photons, all one can do is verify the probabilistic predictions of the mathematics. If the probabilities are borne out over the course of sending tens of thousands of identical photons through the double slit, the theory claims that each photon’s wave function collapsed—thanks to an ill-defined process called measurement. That’s all.

Also, there are other ways of interpreting the double-slit experiment. Take the de Broglie-Bohm theory, which says that reality is both wave and particle. A photon heads towards the double slit with a definite position at all times and goes through one slit or the other; so each photon has a trajectory. It’s riding a pilot wave, which goes through both slits, interferes and then guides the photon to a location of constructive interference.

In 1979, Chris Dewdney and colleagues at Birkbeck College, London, simulated the theory’s prediction for the trajectories of particles going through the double slit. In the past decade, experimentalists have verified that such trajectories exist, albeit by using a controversial technique called weak measurements. The controversy notwithstanding, the experiments show that the de Broglie-Bohm theory remains in the running as an explanation for the behavior of the quantum world.

Crucially, the theory does not need observers or measurements or a non-material consciousness.

Neither do so-called collapse theories, which argue that wave functions collapse randomly: the more the number of particles in the quantum system, the more likely the collapse. Observers merely discover the outcome. Markus Arndt’s team at the University of Vienna in Austria has been testing these theories by sending larger and larger molecules through the double slit.

Collapse theories predict that when particles of matter become more massive than some threshold, they cannot remain in a quantum superposition of going through both slits at once, and this will destroy the interference pattern. Arndt’s team has sent a molecule with more than 800 atoms through the double slit, and they still see interference. The search for the threshold continues. 

Roger Penrose has his own version of a collapse theory, in which the more massive the mass of the object in superposition, the faster it’ll collapse to one state or the other, because of gravitational instabilities. Again, it’s an observer-independent theory. No consciousness needed. Dirk Bouwmeester at the University of California, Santa Barbara, is testing Penrose’s idea with a version of the double-slit experiment. 

Conceptually, the idea is to not just put a photon into a superposition of going through two slits at once, but to also put one of the slits in a superposition of being in two locations at once. According to Penrose, the displaced slit will either stay in superposition or collapse while the photon is in flight, leading to different types of interference patterns. The collapse will depend on the mass of the slits. Bouwmeester has been at work on this experiment for a decade and may soon be able to verify or refute Penrose’s claims.

If nothing else, these experiments are showing that we cannot yet make any claims about the nature of reality, even if the claims are well-motivated mathematically or philosophically. And given that neuroscientists and philosophers of mind don’t agree on the nature of consciousness, claims that it collapses wave functions are premature at best and misleading and wrong at worst.

ABOUT THE AUTHOR(S)

Anil Ananthaswamy

Anil Ananthaswamy is the author of The Edge of Physics, The Man Who Wasn't There and, most recently, Through Two Doors at Once: The Elegant Experiment That Captures the Enigma of Our Quantum Reality.

SOURCE:

Scientific American Space & Physics

 7 SEPT. 2018

A Neuroscientist Explores the "Sanskrit Effect"

MRI scans show that memorizing ancient mantras increases the size of brain regions associated with cognitive function 

• By James Hartzell on January 2, 2018

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Manjuvajramandala with 43 deities, from Tibet. Credit: Google Cultural Institute Wikimedia

A hundred dhoti-clad young men sat cross-legged on the floor in facing rows, chatting amongst themselves. At a sign from their teacher the hall went quiet. Then they began the recitation. Without pause or error, entirely from memory, one side of the room intoned one line of the text, then the other side of the room answered with the next line. Bass and baritone voices filled the hall with sonorous prosody, every word distinctly heard, their right arms moving together to mark pitch and accent. The effect was hypnotic, ancient sound reverberating through the room, saturating brain and body. After 20 minutes they halted, in unison. It was just a demonstration. The full recitation of one of India´s most ancient Sanskrit texts, the Shukla Yajurveda, takes six hours.

I spent many years studying and translating Sanskrit, and became fascinated by its apparent impact on mind and memory. In India's ancient learning methods textual memorization is standard: traditional scholars, or pandits, master many different types of Sanskrit poetry and prose texts; and the tradition holds that exactly memorizing and reciting the ancient words and phrases, known as mantras, enhances both memory and thinking.

I had also noticed that the more Sanskrit I studied and translated, the better my verbal memory seemed to become. Fellow students and teachers often remarked on my ability to exactly repeat lecturers’ own sentences when asking them questions in class. Other translators of Sanskrit told me of similar cognitive shifts. So I was curious: was there actually a language-specific “Sanskrit effect” as claimed by the tradition?

When I entered the cognitive neuroscience doctoral program at the University of Trento (Italy) in 2011, I had the opportunity to start investigating this question. India's Vedic Sanskrit pandits train for years to orally memorize and exactly recite 3,000-year old oral texts ranging from 40,000 to over 100,000 words. We wanted to find out how such intense verbal memory training affects the physical structure of their brains.

Through the India-Trento Partnership for Advanced Research (ITPAR), we recruited professional Vedic pandits from several government-sponsored schools in the Delhi region; then we used structural magnetic resonance imaging (MRI) at India’s National Brain Research Center to scan the brains of pandits and controls matched for age, gender, handedness, eye-dominance and multilingualism.

What we discovered from the structural MRI scanning was remarkable. Numerous regions in the brains of the pandits were dramatically larger than those of controls, with over 10 percent more grey matter across both cerebral hemispheres, and substantial increases in cortical thickness. Although the exact cellular underpinnings of gray matter and cortical thickness measures are still under investigation, increases in these metrics consistently correlate with enhanced cognitive function.

Most interestingly for verbal memory was that the pandits' right hippocampus—a region of the brain that plays a vital role in both short and long-term memory—had more gray matter than controls across nearly 75 percent of this subcortical structure. Our brains have two hippocampi, one on the left and one on the right, and without them we cannot record any new information. Many memory functions are shared by the two hippocampi. The right is, however, more specialized for patterns, whether sound, spatial or visual, so the large gray matter increases we found in the pandits’ right hippocampus made sense: accurate recitation requires highly precise sound pattern encoding and reproduction. The pandits also showed substantially thickening of right temporal cortex regions that are associated with speech prosody and voice identity.

Our study was a first foray into imaging the brains of professionally trained Sanskrit pandits in India. Although this initial research, focused on intergroup comparison of brain structure, could not directly address the Sanskrit effect question (that requires detailed functional studies with cross-language memorization comparisons, for which we are currently seeking funding), we found something specific about intensive verbal memory training.

Does the pandits’ substantial increase in the gray matter of critical verbal memory organs mean they are less prone to devastating memory pathologies such as Alzheimer's? We don't know yet, though anecdotal reports from India's Ayurvedic doctors suggest this may be the case. If so, this raises the possibility that verbal memory “exercising ‘or training might help elderly people at risk of mild cognitive impairment retard or, even more radically, prevent its onset.

If so, the training might need to be exact. One day I was filming four senior pandit teachers demonstrating the different recitation speeds. Partway into one session all four suddenly stopped. “What’s wrong? ‘ I asked. “One of us made a slight error," came the response. "I don’t mind," I said. "Yes, but we do," and they restarted the entire recitation from the beginning. 

Author's note: Senior personnel responsible for this project were not involved in the conception or writing of the blog text; it was not presented to them for approval; any opinions or conclusions expressed in the blog are Dr. Hartzell's alone.

This post was written by a graduate of the online course Share Your Science: Blogging for Magazines, Newspapers and More, offered by Scientific American and the Alan Alda Center for Communicating Science at Stony Brook University, with sponsorship from the Kavli Foundation.

The views expressed are those of the author(s) and are not necessarily those of Scientific American.

ABOUT THE AUTHOR(S)

James Hartzell

James Hartzell is a postdoctoral researcher at the Basque Center on Cognition, Brain and Language, in Spain; a Guest Researcher at the Center for Mind/Brain Sciences at University of Trento, in Italy, and a Consultant for the Center for Buddhist Studies at Columbia University, in New York.

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MIND & BRAIN

January 10, 2018

A Physicist’s Physicist Ponders the Nature of Reality

Edward Witten reflects on the meaning of dualities in physics and math, emergent space-time, and the pursuit of a complete description of nature.

Natalie Wolchover

Senior Writer

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November 28 2017

Among the brilliant theorists cloistered in the quiet woodside campus of the Institute for Advanced Study in Princeton, New Jersey, Edward Witten stands out as a kind of high priest. The sole physicist ever to win the Fields Medal, mathematics’ premier prize, Witten is also known for discovering M-theory, the leading candidate for a unified physical “theory of everything.” A genius’s genius, Witten is tall and rectangular, with hazy eyes and an air of being only one-quarter tuned in to reality until someone draws him back from more abstract thoughts.

During a visit this fall, I spotted Witten on the Institute’s central lawn and requested an interview; in his quick, alto voice, he said he couldn’t promise to be able to answer my questions but would try. Later, when I passed him on the stone paths, he often didn’t seem to see me.

Physics luminaries since Albert Einstein, who lived out his days in the same intellectual haven, have sought to unify gravity with the other forces of nature by finding a more fundamental quantum theory to replace Einstein’s approximate picture of gravity as curves in the geometry of space-time. M-theory, which Witten proposed in 1995, could conceivably offer this deeper description, but only some aspects of the theory are known. M-theory incorporates within a single mathematical structure all five versions of string theory, which renders the elements of nature as minuscule vibrating strings. These five string theories connect to each other through “dualities,” or mathematical equivalences. Over the past 30 years, Witten and others have learned that the string theories are also mathematically dual to quantum field theories — descriptions of particles moving through electromagnetic and other fields that serve as the language of the reigning “Standard Model” of particle physics. While he’s best known as a string theorist, Witten has discovered many new quantum field theories and explored how all these different descriptions are connected. His physical insights have led time and again to deep mathematical discoveries.

That’s extremely strange, that the world is based so much on a mathematical structure that’s so difficult.

Researchers pore over his work and hope he’ll take an interest in theirs. But for all his scholarly influence, Witten, who is 66, does not often broadcast his views on the implications of modern theoretical discoveries. Even his close colleagues eagerly suggested questions they wanted me to ask him.

When I arrived at his office at the appointed hour on a summery Thursday last month, Witten wasn’t there. His door was ajar. Papers covered his coffee table and desk — not stacks, but floods: text oriented every which way, some pages close to spilling onto the floor. (Research papers get lost in the maelstrom as he finishes with them, he later explained, and every so often he throws the heaps away.) Two girls smiled out from a framed photo on a shelf; children’s artwork decorated the walls, one celebrating Grandparents’ Day. When Witten arrived minutes later, we spoke for an hour and a half about the meaning of dualities in physics and math, the current prospects of M-theory, what he’s reading, what he’s looking for, and the nature of reality. The interview has been condensed and edited for clarity.

Physicists are talking more than ever lately about dualities, but you’ve been studying them for decades. Why does the subject interest you?

People keep finding new facets of dualities. Dualities are interesting because they frequently answer questions that are otherwise out of reach. For example, you might have spent years pondering a quantum theory and you understand what happens when the quantum effects are small, but textbooks don’t tell you what you do if the quantum effects are big; you’re generally in trouble if you want to know that. Frequently dualities answer such questions. They give you another description, and the questions you can answer in one description are different than the questions you can answer in a different description.

What are some of these newfound facets of dualities?

It’s open-ended because there are so many different kinds of dualities. There are dualities between a gauge theory [a theory, such as a quantum field theory, that respects certain symmetries] and another gauge theory, or between a string theory for weak coupling [describing strings that move almost independently from one another] and a string theory for strong coupling. Then there’s AdS/CFT duality, between a gauge theory and a gravitational description. That duality was discovered 20 years ago, and it’s amazing to what extent it’s still fruitful. And that’s largely because around 10 years ago, new ideas were introduced that rejuvenated it. People had new insights about entropy in quantum field theory — the whole story about “it from qubit.”

The AdS/CFT duality connects a theory of gravity in a space-time region called anti-de Sitter space (which curves differently than our universe) to an equivalent quantum field theory describing that region’s gravity-free boundary. Everything there is to know about AdS space — often called the “bulk” since it’s the higher-dimensional region — is encoded, like in a hologram, in quantum interactions between particles on the lower-dimensional boundary. Thus, AdS/CFT gives physicists a “holographic” understanding of the quantum nature of gravity.

That’s the idea that space-time and everything in it emerges like a hologram out of information stored in the entangled quantum states of particles.

Yes. Then there are dualities in math, which can sometimes be interpreted physically as consequences of dualities between two quantum field theories. There are so many ways these things are interconnected that any simple statement I try to make on the fly, as soon as I’ve said it I realize it didn’t capture the whole reality. You have to imagine a web of different relationships, where the same physics has different descriptions, revealing different properties. In the simplest case, there are only two important descriptions, and that might be enough. If you ask me about a more complicated example, there might be many, many different ones.

Given this web of relationships and the issue of how hard it is to characterize all duality, do you feel that this reflects a lack of understanding of the structure, or is it that we’re seeing the structure, only it’s very complicated? 

I’m not certain what we should hope for. Traditionally, quantum field theory was constructed by starting with the classical picture [of a smooth field] and then quantizing it. Now we’ve learned that there are a lot of things that happen that that description doesn’t do justice to. And the same quantum theory can come from different classical theories. Now, Nati Seiberg [a theoretical physicist who works down the hall] would possibly tell you that he has faith that there’s a better formulation of quantum field theory that we don’t know about that would make everything clearer. I’m not sure how much you should expect that to exist. That would be a dream, but it might be too much to hope for; I really don’t know.

There’s another curious fact that you might want to consider, which is that quantum field theory is very central to physics, and it’s actually also clearly very important for math. But it’s extremely difficult for mathematicians to study; the way physicists define it is very hard for mathematicians to follow with a rigorous theory. That’s extremely strange, that the world is based so much on a mathematical structure that’s so difficult.

What do you see as the relationship between math and physics?

I prefer not to give you a cosmic answer but to comment on where we are now. Physics in quantum field theory and string theory somehow has a lot of mathematical secrets in it, which we don’t know how to extract in a systematic way. Physicists are able to come up with things that surprise the mathematicians. Because it’s hard to describe mathematically in the known formulation, the things you learn about quantum field theory you have to learn from physics.

I find it hard to believe there’s a new formulation that’s universal. I think it’s too much to hope for. I could point to theories where the standard approach really seems inadequate, so at least for those classes of quantum field theories, you could hope for a new formulation. But I really can’t imagine what it would be.

You can’t imagine it at all? 

No, I can’t. Traditionally it was thought that interacting quantum field theory couldn’t exist above four dimensions, and there was the interesting fact that that’s the dimension we live in. But one of the offshoots of the string dualities of the 1990s was that it was discovered that quantum field theories actually exist in five and six dimensions. And it’s amazing how much is known about their properties. 

If there’s a radically different dual description of the real world, maybe some things physicists worry about would be clearer, but the dual description might be one in which everyday life would be hard to describe.

I’ve heard about the mysterious (2,0) theory, a quantum field theory describing particles in six dimensions, which is dual to M-theory describing strings and gravity in seven-dimensional AdS space. Does this (2,0) theory play an important role in the web of dualities?

Yes, that’s the pinnacle. In terms of conventional quantum field theory without gravity, there is nothing quite like it above six dimensions. From the (2,0) theory’s existence and main properties, you can deduce an incredible amount about what happens in lower dimensions. An awful lot of important dualities in four and fewer dimensions follow from this six-dimensional theory and its properties. However, whereas what we know about quantum field theory is normally from quantizing a classical field theory, there’s no reasonable classical starting point of the (2,0) theory. The (2,0) theory has properties [such as combinations of symmetries] that sound impossible when you first hear about them. So you can ask why dualities exist, but you can also ask why is there a 6-D theory with such and such properties? This seems to me a more fundamental restatement. 

Dualities sometimes make it hard to maintain a sense of what’s real in the world, given that there are radically different ways you can describe a single system. How would you describe what’s real or fundamental?

What aspect of what’s real are you interested in? What does it mean that we exist? Or how do we fit into our mathematical descriptions?

The latter.

Well, one thing I’ll tell you is that in general, when you have dualities, things that are easy to see in one description can be hard to see in the other description. So you and I, for example, are fairly simple to describe in the usual approach to physics as developed by Newton and his successors. But if there’s a radically different dual description of the real world, maybe some things physicists worry about would be clearer, but the dual description might be one in which everyday life would be hard to describe.

What would you say about the prospect of an even more optimistic idea that there could be one single quantum gravity description that really does help you in every case in the real world?

Well, unfortunately, even if it’s correct I can’t guarantee it would help. Part of what makes it difficult to help is that the description we have now, even though it’s not complete, does explain an awful lot. And so it’s a little hard to say, even if you had a truly better description or a more complete description, whether it would help in practice.

Are you speaking of M-theory?

M-theory is the candidate for the better description.

You proposed M-theory 22 years ago. What are its prospects today?

Personally, I thought it was extremely clear it existed 22 years ago, but the level of confidence has got to be much higher today because AdS/CFT has given us precise definitions, at least in AdS space-time geometries. I think our understanding of what it is, though, is still very hazy. AdS/CFT and whatever’s come from it is the main new perspective compared to 22 years ago, but I think it’s perfectly possible that AdS/CFT is only one side of a multifaceted story. There might be other equally important facets.

What’s an example of something else we might need?

Maybe a bulk description of the quantum properties of space-time itself, rather than a holographic boundary description. There hasn’t been much progress in a long time in getting a better bulk description. And I think that might be because the answer is of a different kind than anything we’re used to. That would be my guess.

Are you willing to speculate about how it would be different?

I really doubt I can say anything useful. I guess I suspect that there’s an extra layer of abstractness compared to what we’re used to. I tend to think that there isn’t a precise quantum description of space-time — except in the types of situations where we know that there is, such as in AdS space. I tend to think, otherwise, things are a little bit murkier than an exact quantum description. But I can’t say anything useful.

The other night I was reading an old essay by the 20th-century Princeton physicist John Wheeler. He was a visionary, certainly. If you take what he says literally, it’s hopelessly vague. And therefore, if I had read this essay when it came out 30 years ago, which I may have done, I would have rejected it as being so vague that you couldn’t work on it, even if he was on the right track.

You’re referring to Information, Physics, Quantum, Wheeler’s 1989 essay propounding the idea that the physical universe arises from information, which he dubbed “it from bit.” Why were you reading it? 

I’m trying to learn about what people are trying to say with the phrase “it from qubit.” Wheeler talked about “it from bit,” but you have to remember that this essay was written probably before the term “qubit” was coined and certainly before it was in wide currency. Reading it, I really think he was talking about qubits, not bits, so “it from qubit” is actually just a modern translation.

I tend to assume that space-time and everything in it are in some sense emergent.

Don’t expect me to be able to tell you anything useful about it — about whether he was right. When I was a beginning grad student, they had a series of lectures by faculty members to the new students about theoretical research, and one of the people who gave such a lecture was Wheeler. He drew a picture on the blackboard of the universe visualized as an eye looking at itself. I had no idea what he was talking about. It’s obvious to me in hindsight that he was explaining what it meant to talk about quantum mechanics when the observer is part of the quantum system. I imagine there is something we don’t understand about that.

Observing a quantum system irreversibly changes it, creating a distinction between past and future. So the observer issue seems possibly related to the question of time, which we also don’t understand. With the AdS/CFT duality, we’ve learned that new spatial dimensions can pop up like a hologram from quantum information on the boundary. Do you think time is also emergent — that it arises from a timeless complete description?

I tend to assume that space-time and everything in it are in some sense emergent. By the way, you’ll certainly find that that’s what Wheeler expected in his essay. As you’ll read, he thought the continuum was wrong in both physics and math. He did not think one’s microscopic description of space-time should use a continuum of any kind — neither a continuum of space nor a continuum of time, nor even a continuum of real numbers. On the space and time, I’m sympathetic to that. On the real numbers, I’ve got to plead ignorance or agnosticism. It is something I wonder about, but I’ve tried to imagine what it could mean to not use the continuum of real numbers, and the one logician I tried discussing it with didn’t help me.

Do you consider Wheeler a hero?

I wouldn’t call him a hero, necessarily, no. Really I just became curious what he meant by “it from bit,” and what he was saying. He definitely had visionary ideas, but they were too far ahead of their time. I think I was more patient in reading a vague but inspirational essay than I might have been 20 years ago. He’s also got roughly 100 interesting-sounding references in that essay. If you decided to read them all, you’d have to spend weeks doing it. I might decide to look at a few of them.

Why do you have more patience for such things now?

I think when I was younger I always thought the next thing I did might be the best thing in my life. But at this point in life I’m less persuaded of that. If I waste a little time reading somebody’s essay, it doesn’t seem that bad.

Do you ever take your mind off physics and math?

My favorite pastime is tennis. I am a very average but enthusiastic tennis player.

In contrast to Wheeler, it seems like your working style is to come to the insights through the calculations, rather than chasing a vague vision. 

In my career I’ve only been able to take small jumps. Relatively small jumps. What Wheeler was talking about was an enormous jump. And he does say at the beginning of the essay that he has no idea if this will take 10, 100 or 1,000 years.

And he was talking about explaining how physics arises from information.

Yes. The way he phrases it is broader: He wants to explain the meaning of existence. That was actually why I thought you were asking if I wanted to explain the meaning of existence.

I see. Does he have any hypotheses?

No. He only talks about things you shouldn’t do and things you should do in trying to arrive at a more fundamental description of physics.

Do you have any ideas about the meaning of existence?

No. [Laughs.]

Correction: This article was updated on Nov. 29, 2017, to clarify that M-theory is the leading candidate for a unified theory of everything. Other ideas have been proposed that also claim to unify the fundamental forces.

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4.     The Strange Second Life of String Theory

SOURCE: Quanta Magazine Quanta@simonsfoundation.org

Note:The original have photos from Jean Sweep for Quanta Magazine