Daily Archives: July 25, 2021

"I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem."

The American physicist Richard Feynman said this about the notorious puzzles and paradoxes of quantum mechanics, the theory physicists use to describe the tiniest objects in the Universe. But he might as well have been talking about the equally knotty problem of consciousness.

Some scientists think we already understand what consciousness is, or that it is a mere illusion. But many others feel we have not grasped where consciousness comes from at all.

The perennial puzzle of consciousness has even led some researchers to invoke quantum physics to explain it. That notion has always been met with skepticism, which is not surprising: it does not sound wise to explain one mystery with another. But such ideas are not obviously absurd, and neither are they arbitrary.

For one thing, the mind seemed, to the great discomfort of physicists, to force its way into early quantum theory. What's more, quantum computers are predicted to be capable of accomplishing things ordinary computers cannot, which reminds us of how our brains can achieve things that are still beyond artificial intelligence. "Quantum consciousness" is widely derided as mystical woo, but it just will not go away.

Quantum mechanics is the best theory we have for describing the world at the nuts-and-bolts level of atoms and subatomic particles. Perhaps the most renowned of its mysteries is the fact that the outcome of a quantum experiment can change depending on whether or not we choose to measure some property of the particles involved.

When this "observer effect" was first noticed by the early pioneers of quantum theory, they were deeply troubled. It seemed to undermine the basic assumption behind all science: that there is an objective world out there, irrespective of us. If the way the world behaves depends on how or if we look at it, what can "reality" really mean?

The most famous intrusion of the mind into quantum mechanics comes in the "double-slit experiment"

Some of those researchers felt forced to conclude that objectivity was an illusion, and that consciousness has to be allowed an active role in quantum theory. To others, that did not make sense. Surely, Albert Einstein once complained, the Moon does not exist only when we look at it!

Today some physicists suspect that, whether or not consciousness influences quantum mechanics, it might in fact arise because of it. They think that quantum theory might be needed to fully understand how the brain works.

Might it be that, just as quantum objects can apparently be in two places at once, so a quantum brain can hold onto two mutually-exclusive ideas at the same time?

These ideas are speculative, and it may turn out that quantum physics has no fundamental role either for or in the workings of the mind. But if nothing else, these possibilities show just how strangely quantum theory forces us to think.

The most famous intrusion of the mind into quantum mechanics comes in the "double-slit experiment". Imagine shining a beam of light at a screen that contains two closely-spaced parallel slits. Some of the light passes through the slits, whereupon it strikes another screen.

Light can be thought of as a kind of wave, and when waves emerge from two slits like this they can interfere with each other. If their peaks coincide, they reinforce each other, whereas if a peak and a trough coincide, they cancel out. This wave interference is called diffraction, and it produces a series of alternating bright and dark stripes on the back screen, where the light waves are either reinforced or cancelled out.

The implication seems to be that each particle passes simultaneously through both slits

This experiment was understood to be a characteristic of wave behaviour over 200 years ago, well before quantum theory existed.

The double slit experiment can also be performed with quantum particles like electrons; tiny charged particles that are components of atoms. In a counter-intuitive twist, these particles can behave like waves. That means they can undergo diffraction when a stream of them passes through the two slits, producing an interference pattern.

Now suppose that the quantum particles are sent through the slits one by one, and their arrival at the screen is likewise seen one by one. Now there is apparently nothing for each particle to interfere with along its route yet nevertheless the pattern of particle impacts that builds up over time reveals interference bands.

The implication seems to be that each particle passes simultaneously through both slits and interferes with itself. This combination of "both paths at once" is known as a superposition state.

But here is the really odd thing.

If we place a detector inside or just behind one slit, we can find out whether any given particle goes through it or not. In that case, however, the interference vanishes. Simply by observing a particle's path even if that observation should not disturb the particle's motion we change the outcome.

The physicist Pascual Jordan, who worked with quantum guru Niels Bohr in Copenhagen in the 1920s, put it like this: "observations not only disturb what has to be measured, they produce it We compel [a quantum particle] to assume a definite position." In other words, Jordan said, "we ourselves produce the results of measurements."

If that is so, objective reality seems to go out of the window.

And it gets even stranger.

If nature seems to be changing its behaviour depending on whether we "look" or not, we could try to trick it into showing its hand. To do so, we could measure which path a particle took through the double slits, but only after it has passed through them. By then, it ought to have "decided" whether to take one path or both.

The sheer act of noticing, rather than any physical disturbance caused by measuring, can cause the collapse

An experiment for doing this was proposed in the 1970s by the American physicist John Wheeler, and this "delayed choice" experiment was performed in the following decade. It uses clever techniques to make measurements on the paths of quantum particles (generally, particles of light, called photons) after they should have chosen whether to take one path or a superposition of two.

It turns out that, just as Bohr confidently predicted, it makes no difference whether we delay the measurement or not. As long as we measure the photon's path before its arrival at a detector is finally registered, we lose all interference.

It is as if nature "knows" not just if we are looking, but if we are planning to look.

Whenever, in these experiments, we discover the path of a quantum particle, its cloud of possible routes "collapses" into a single well-defined state. What's more, the delayed-choice experiment implies that the sheer act of noticing, rather than any physical disturbance caused by measuring, can cause the collapse. But does this mean that true collapse has only happened when the result of a measurement impinges on our consciousness?

It is hard to avoid the implication that consciousness and quantum mechanics are somehow linked

That possibility was admitted in the 1930s by the Hungarian physicist Eugene Wigner. "It follows that the quantum description of objects is influenced by impressions entering my consciousness," he wrote. "Solipsism may be logically consistent with present quantum mechanics."

Wheeler even entertained the thought that the presence of living beings, which are capable of "noticing", has transformed what was previously a multitude of possible quantum pasts into one concrete history. In this sense, Wheeler said, we become participants in the evolution of the Universe since its very beginning. In his words, we live in a "participatory universe."

To this day, physicists do not agree on the best way to interpret these quantum experiments, and to some extent what you make of them is (at the moment) up to you. But one way or another, it is hard to avoid the implication that consciousness and quantum mechanics are somehow linked.

Beginning in the 1980s, the British physicist Roger Penrose suggested that the link might work in the other direction. Whether or not consciousness can affect quantum mechanics, he said, perhaps quantum mechanics is involved in consciousness.

What if, Penrose asked, there are molecular structures in our brains that are able to alter their state in response to a single quantum event. Could not these structures then adopt a superposition state, just like the particles in the double slit experiment? And might those quantum superpositions then show up in the ways neurons are triggered to communicate via electrical signals?

Maybe, says Penrose, our ability to sustain seemingly incompatible mental states is no quirk of perception, but a real quantum effect.

Perhaps quantum mechanics is involved in consciousness

After all, the human brain seems able to handle cognitive processes that still far exceed the capabilities of digital computers. Perhaps we can even carry out computational tasks that are impossible on ordinary computers, which use classical digital logic.

Penrose first proposed that quantum effects feature in human cognition in his 1989 book The Emperor's New Mind. The idea is called Orch-OR, which is short for "orchestrated objective reduction". The phrase "objective reduction" means that, as Penrose believes, the collapse of quantum interference and superposition is a real, physical process, like the bursting of a bubble.

Orch-OR draws on Penrose's suggestion that gravity is responsible for the fact that everyday objects, such as chairs and planets, do not display quantum effects. Penrose believes that quantum superpositions become impossible for objects much larger than atoms, because their gravitational effects would then force two incompatible versions of space-time to coexist.

Penrose developed this idea further with American physician Stuart Hameroff. In his 1994 book Shadows of the Mind, he suggested that the structures involved in this quantum cognition might be protein strands called microtubules. These are found in most of our cells, including the neurons in our brains. Penrose and Hameroff argue that vibrations of microtubules can adopt a quantum superposition.

But there is no evidence that such a thing is remotely feasible.

It has been suggested that the idea of quantum superpositions in microtubules is supported by experiments described in 2013, but in fact those studies made no mention of quantum effects.

Besides, most researchers think that the Orch-OR idea was ruled out by a study published in 2000. Physicist Max Tegmark calculated that quantum superpositions of the molecules involved in neural signaling could not survive for even a fraction of the time needed for such a signal to get anywhere.

Other researchers have found evidence for quantum effects in living beings

Quantum effects such as superposition are easily destroyed, because of a process called decoherence. This is caused by the interactions of a quantum object with its surrounding environment, through which the "quantumness" leaks away.

Decoherence is expected to be extremely rapid in warm and wet environments like living cells.

Nerve signals are electrical pulses, caused by the passage of electrically-charged atoms across the walls of nerve cells. If one of these atoms was in a superposition and then collided with a neuron, Tegmark showed that the superposition should decay in less than one billion billionth of a second. It takes at least ten thousand trillion times as long for a neuron to discharge a signal.

As a result, ideas about quantum effects in the brain are viewed with great skepticism.

However, Penrose is unmoved by those arguments and stands by the Orch-OR hypothesis. And despite Tegmark's prediction of ultra-fast decoherence in cells, other researchers have found evidence for quantum effects in living beings. Some argue that quantum mechanics is harnessed by migratory birds that use magnetic navigation, and by green plants when they use sunlight to make sugars in photosynthesis.

Besides, the idea that the brain might employ quantum tricks shows no sign of going away. For there is now another, quite different argument for it.

In a study published in 2015, physicist Matthew Fisher of the University of California at Santa Barbara argued that the brain might contain molecules capable of sustaining more robust quantum superpositions. Specifically, he thinks that the nuclei of phosphorus atoms may have this ability.

Phosphorus atoms are everywhere in living cells. They often take the form of phosphate ions, in which one phosphorus atom joins up with four oxygen atoms.

Such ions are the basic unit of energy within cells. Much of the cell's energy is stored in molecules called ATP, which contain a string of three phosphate groups joined to an organic molecule. When one of the phosphates is cut free, energy is released for the cell to use.

Cells have molecular machinery for assembling phosphate ions into groups and cleaving them off again. Fisher suggested a scheme in which two phosphate ions might be placed in a special kind of superposition called an "entangled state".

Phosphorus spins could resist decoherence for a day or so, even in living cells

The phosphorus nuclei have a quantum property called spin, which makes them rather like little magnets with poles pointing in particular directions. In an entangled state, the spin of one phosphorus nucleus depends on that of the other.

Put another way, entangled states are really superposition states involving more than one quantum particle.

Fisher says that the quantum-mechanical behaviour of these nuclear spins could plausibly resist decoherence on human timescales. He agrees with Tegmark that quantum vibrations, like those postulated by Penrose and Hameroff, will be strongly affected by their surroundings "and will decohere almost immediately". But nuclear spins do not interact very strongly with their surroundings.

All the same, quantum behaviour in the phosphorus nuclear spins would have to be "protected" from decoherence.

This might happen, Fisher says, if the phosphorus atoms are incorporated into larger objects called "Posner molecules". These are clusters of six phosphate ions, combined with nine calcium ions. There is some evidence that they can exist in living cells, though this is currently far from conclusive.

I decided... to explore how on earth the lithium ion could have such a dramatic effect in treating mental conditions

In Posner molecules, Fisher argues, phosphorus spins could resist decoherence for a day or so, even in living cells. That means they could influence how the brain works.

The idea is that Posner molecules can be swallowed up by neurons. Once inside, the Posner molecules could trigger the firing of a signal to another neuron, by falling apart and releasing their calcium ions.

Because of entanglement in Posner molecules, two such signals might thus in turn become entangled: a kind of quantum superposition of a "thought", you might say. "If quantum processing with nuclear spins is in fact present in the brain, it would be an extremely common occurrence, happening pretty much all the time," Fisher says.

He first got this idea when he started thinking about mental illness.

"My entry into the biochemistry of the brain started when I decided three or four years ago to explore how on earth the lithium ion could have such a dramatic effect in treating mental conditions," Fisher says.

At this point, Fisher's proposal is no more than an intriguing idea

Lithium drugs are widely used for treating bipolar disorder. They work, but nobody really knows how.

"I wasn't looking for a quantum explanation," Fisher says. But then he came across a paper reporting that lithium drugs had different effects on the behaviour of rats, depending on what form or "isotope" of lithium was used.

On the face of it, that was extremely puzzling. In chemical terms, different isotopes behave almost identically, so if the lithium worked like a conventional drug the isotopes should all have had the same effect.

But Fisher realised that the nuclei of the atoms of different lithium isotopes can have different spins. This quantum property might affect the way lithium drugs act. For example, if lithium substitutes for calcium in Posner molecules, the lithium spins might "feel" and influence those of phosphorus atoms, and so interfere with their entanglement.

We do not even know what consciousness is

If this is true, it would help to explain why lithium can treat bipolar disorder.

At this point, Fisher's proposal is no more than an intriguing idea. But there are several ways in which its plausibility can be tested, starting with the idea that phosphorus spins in Posner molecules can keep their quantum coherence for long periods. That is what Fisher aims to do next.

All the same, he is wary of being associated with the earlier ideas about "quantum consciousness", which he sees as highly speculative at best.

Physicists are not terribly comfortable with finding themselves inside their theories. Most hope that consciousness and the brain can be kept out of quantum theory, and perhaps vice versa. After all, we do not even know what consciousness is, let alone have a theory to describe it.

We all know what red is like, but we have no way to communicate the sensation

It does not help that there is now a New Age cottage industry devoted to notions of "quantum consciousness", claiming that quantum mechanics offers plausible rationales for such things as telepathy and telekinesis.

As a result, physicists are often embarrassed to even mention the words "quantum" and "consciousness" in the same sentence.

But setting that aside, the idea has a long history. Ever since the "observer effect" and the mind first insinuated themselves into quantum theory in the early days, it has been devilishly hard to kick them out. A few researchers think we might never manage to do so.

In 2016, Adrian Kent of the University of Cambridge in the UK, one of the most respected "quantum philosophers", speculated that consciousness might alter the behaviour of quantum systems in subtle but detectable ways.

Kent is very cautious about this idea. "There is no compelling reason of principle to believe that quantum theory is the right theory in which to try to formulate a theory of consciousness, or that the problems of quantum theory must have anything to do with the problem of consciousness," he admits.

Every line of thought on the relationship of consciousness to physics runs into deep trouble

But he says that it is hard to see how a description of consciousness based purely on pre-quantum physics can account for all the features it seems to have.

One particularly puzzling question is how our conscious minds can experience unique sensations, such as the colour red or the smell of frying bacon. With the exception of people with visual impairments, we all know what red is like, but we have no way to communicate the sensation and there is nothing in physics that tells us what it should be like.

Sensations like this are called "qualia". We perceive them as unified properties of the outside world, but in fact they are products of our consciousness and that is hard to explain. Indeed, in 1995 philosopher David Chalmers dubbed it "the hard problem" of consciousness.

"Every line of thought on the relationship of consciousness to physics runs into deep trouble," says Kent.

This has prompted him to suggest that "we could make some progress on understanding the problem of the evolution of consciousness if we supposed that consciousnesses alters (albeit perhaps very slightly and subtly) quantum probabilities."

"Quantum consciousness" is widely derided as mystical woo, but it just will not go away

In other words, the mind could genuinely affect the outcomes of measurements.

It does not, in this view, exactly determine "what is real". But it might affect the chance that each of the possible actualities permitted by quantum mechanics is the one we do in fact observe, in a way that quantum theory itself cannot predict. Kent says that we might look for such effects experimentally.

He even bravely estimates the chances of finding them. "I would give credence of perhaps 15% that something specifically to do with consciousness causes deviations from quantum theory, with perhaps 3% credence that this will be experimentally detectable within the next 50 years," he says.

If that happens, it would transform our ideas about both physics and the mind. That seems a chance worth exploring.

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The strange link between the human mind and quantum physics

The history of quantum mechanics is a fundamental part of the history of modern physics. Quantum mechanics' history, as it interlaces with the history of quantum chemistry, began essentially with a number of different scientific discoveries: the 1838 discovery of cathode rays by Michael Faraday; the 185960 winter statement of the black-body radiation problem by Gustav Kirchhoff; the 1877 suggestion by Ludwig Boltzmann that the energy states of a physical system could be discrete; the discovery of the photoelectric effect by Heinrich Hertz in 1887; and the 1900 quantum hypothesis by Max Planck that any energy-radiating atomic system can theoretically be divided into a number of discrete "energy elements" (Greek letter epsilon) such that each of these energy elements is proportional to the frequency with which each of them individually radiate energy, as defined by the following formula:

where h is a numerical value called Planck's constant.

Then, Albert Einstein in 1905, in order to explain the photoelectric effect previously reported by Heinrich Hertz in 1887, postulated consistently with Max Planck's quantum hypothesis that light itself is made of individual quantum particles, which in 1926 came to be called photons by Gilbert N. Lewis. The photoelectric effect was observed upon shining light of particular wavelengths on certain materials, such as metals, which caused electrons to be ejected from those materials only if the light quantum energy was greater than the work function of the metal's surface.

The phrase "quantum mechanics" was coined (in German, Quantenmechanik) by the group of physicists including Max Born, Werner Heisenberg, and Wolfgang Pauli, at the University of Gttingen in the early 1920s, and was first used in Born's 1924 paper "Zur Quantenmechanik".[1] In the years to follow, this theoretical basis slowly began to be applied to chemical structure, reactivity, and bonding.

Ludwig Boltzmann suggested in 1877 that the energy levels of a physical system, such as a molecule, could be discrete (as opposed to continuous). He was a founder of the Austrian Mathematical Society, together with the mathematicians Gustav von Escherich and Emil Mller. Boltzmann's rationale for the presence of discrete energy levels in molecules such as those of iodine gas had its origins in his statistical thermodynamics and statistical mechanics theories and was backed up by mathematical arguments, as would also be the case twenty years later with the first quantum theory put forward by Max Planck.

In 1900, the German physicist Max Planck reluctantly introduced the idea that energy is quantized in order to derive a formula for the observed frequency dependence of the energy emitted by a black body, called Planck's law, that included a Boltzmann distribution (applicable in the classical limit). Planck's law[2] can be stated as follows: I ( , T ) = 2 h 3 c 2 1 e h k T 1 , {displaystyle I(nu ,T)={frac {2hnu ^{3}}{c^{2}}}{frac {1}{e^{frac {hnu }{kT}}-1}},} where:

The earlier Wien approximation may be derived from Planck's law by assuming h k T {displaystyle hnu gg kT} .

Moreover, the application of Planck's quantum theory to the electron allowed tefan Procopiu in 19111913, and subsequently Niels Bohr in 1913, to calculate the magnetic moment of the electron, which was later called the "magneton;" similar quantum computations, but with numerically quite different values, were subsequently made possible for both the magnetic moments of the proton and the neutron that are three orders of magnitude smaller than that of the electron.

In 1905, Albert Einstein explained the photoelectric effect by postulating that light, or more generally all electromagnetic radiation, can be divided into a finite number of "energy quanta" that are localized points in space. From the introduction section of his March 1905 quantum paper, "On a heuristic viewpoint concerning the emission and transformation of light", Einstein states:

"According to the assumption to be contemplated here, when a light ray is spreading from a point, the energy is not distributed continuously over ever-increasing spaces, but consists of a finite number of 'energy quanta' that are localized in points in space, move without dividing, and can be absorbed or generated only as a whole."

This statement has been called the most revolutionary sentence written by a physicist of the twentieth century.[3] These energy quanta later came to be called "photons", a term introduced by Gilbert N. Lewis in 1926. The idea that each photon had to consist of energy in terms of quanta was a remarkable achievement; it effectively solved the problem of black-body radiation attaining infinite energy, which occurred in theory if light were to be explained only in terms of waves. In 1913, Bohr explained the spectral lines of the hydrogen atom, again by using quantization, in his paper of July 1913 On the Constitution of Atoms and Molecules.

These theories, though successful, were strictly phenomenological: during this time, there was no rigorous justification for quantization, aside, perhaps, from Henri Poincar's discussion of Planck's theory in his 1912 paper Sur la thorie des quanta.[4][5] They are collectively known as the old quantum theory.

The phrase "quantum physics" was first used in Johnston's Planck's Universe in Light of Modern Physics (1931).

In 1923, the French physicist Louis de Broglie put forward his theory of matter waves by stating that particles can exhibit wave characteristics and vice versa. This theory was for a single particle and derived from special relativity theory. Building on de Broglie's approach, modern quantum mechanics was born in 1925, when the German physicists Werner Heisenberg, Max Born, and Pascual Jordan[6][7] developed matrix mechanics and the Austrian physicist Erwin Schrdinger invented wave mechanics and the non-relativistic Schrdinger equation as an approximation of the generalised case of de Broglie's theory.[8] Schrdinger subsequently showed that the two approaches were equivalent.

Heisenberg formulated his uncertainty principle in 1927, and the Copenhagen interpretation started to take shape at about the same time. Starting around 1927, Paul Dirac began the process of unifying quantum mechanics with special relativity by proposing the Dirac equation for the electron. The Dirac equation achieves the relativistic description of the wavefunction of an electron that Schrdinger failed to obtain. It predicts electron spin and led Dirac to predict the existence of the positron. He also pioneered the use of operator theory, including the influential braket notation, as described in his famous 1930 textbook. During the same period, Hungarian polymath John von Neumann formulated the rigorous mathematical basis for quantum mechanics as the theory of linear operators on Hilbert spaces, as described in his likewise famous 1932 textbook. These, like many other works from the founding period, still stand, and remain widely used.

The field of quantum chemistry was pioneered by physicists Walter Heitler and Fritz London, who published a study of the covalent bond of the hydrogen molecule in 1927. Quantum chemistry was subsequently developed by a large number of workers, including the American theoretical chemist Linus Pauling at Caltech, and John C. Slater into various theories such as Molecular Orbital Theory or Valence Theory.

Beginning in 1927, researchers attempted to apply quantum mechanics to fields instead of single particles, resulting in quantum field theories. Early workers in this area include P.A.M. Dirac, W. Pauli, V. Weisskopf, and P. Jordan. This area of research culminated in the formulation of quantum electrodynamics by R.P. Feynman, F. Dyson, J. Schwinger, and S. Tomonaga during the 1940s. Quantum electrodynamics describes a quantum theory of electrons, positrons, and the electromagnetic field, and served as a model for subsequent quantum field theories.[6][7][9]

The theory of quantum chromodynamics was formulated beginning in the early 1960s. The theory as we know it today was formulated by Politzer, Gross and Wilczek in 1975.

Building on pioneering work by Schwinger, Higgs and Goldstone, the physicists Glashow, Weinberg and Salam independently showed how the weak nuclear force and quantum electrodynamics could be merged into a single electroweak force, for which they received the 1979 Nobel Prize in Physics.

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History of quantum mechanics - Wikipedia

Quantum theory is the theoretical basis of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level.The nature and behavior of matter and energy at that level is sometimes referred to as quantum physics and quantum mechanics. Organizations in several countries have devoted significant resources to the development of quantum computing, which uses quantum theory to drastically improve computing capabilities beyond what is possible using today's classical computers.

In 1900, physicist Max Planck presented his quantum theory to the German Physical Society. Planck had sought to discover the reason that radiation from a glowing body changes in color from red, to orange, and, finally, to blue as its temperature rises. He found that by making the assumption that energy existed in individual units in the same way that matter does, rather than just as a constant electromagnetic wave - as had been formerly assumed - and was therefore quantifiable, he could find the answer to his question. The existence of these units became the first assumption of quantum theory.

Planck wrote a mathematical equation involving a figure to represent these individual units of energy, which he called quanta. The equation explained the phenomenon very well; Planck found that at certain discrete temperature levels (exact multiples of a basic minimum value), energy from a glowing body will occupy different areas of the color spectrum. Planck assumed there was a theory yet to emerge from the discovery of quanta, but, in fact, their very existence implied a completely new and fundamental understanding of the laws of nature. Planck won the Nobel Prize in Physics for his theory in 1918, but developments by various scientists over a thirty-year period all contributed to the modern understanding of quantum theory.

The two major interpretations of quantum theory's implications for the nature of reality are the Copenhagen interpretation and the many-worlds theory. Niels Bohr proposed the Copenhagen interpretation of quantum theory, which asserts that a particle is whatever it is measured to be (for example, a wave or a particle), but that it cannot be assumed to have specific properties, or even to exist, until it is measured. In short, Bohr was saying that objective reality does not exist. This translates to a principle called superposition that claims that while we do not know what the state of any object is, it is actually in all possible states simultaneously, as long as we don't look to check.

To illustrate this theory, we can use the famous and somewhat cruel analogy of Schrodinger's Cat. First, we have a living cat and place it in a thick lead box. At this stage, there is no question that the cat is alive. We then throw in a vial of cyanide and seal the box. We do not know if the cat is alive or if the cyanide capsule has broken and the cat has died. Since we do not know, the cat is both dead and alive, according to quantum law - in a superposition of states. It is only when we break open the box and see what condition the cat is that the superposition is lost, and the cat must be either alive or dead.

The second interpretation of quantum theory is the many-worlds (or multiverse theory. It holds that as soon as a potential exists for any object to be in any state, the universe of that object transmutes into a series of parallel universes equal to the number of possible states in which that the object can exist, with each universe containing a unique single possible state of that object. Furthermore, there is a mechanism for interaction between these universes that somehow permits all states to be accessible in some way and for all possible states to be affected in some manner. Stephen Hawking and the late Richard Feynman are among the scientists who have expressed a preference for the many-worlds theory.

Although scientists throughout the past century have balked at the implications of quantum theory - Planck and Einstein among them - the theory's principles have repeatedly been supported by experimentation, even when the scientists were trying to disprove them. Quantum theory and Einstein's theory of relativity form the basis for modern physics. The principles of quantum physics are being applied in an increasing number of areas, including quantum optics, quantum chemistry, quantum computing, and quantum cryptography.

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What is quantum theory? - Definition from WhatIs.com

One of the most important open questions in science is how our consciousness is established. In the 1990s, long before winning the 2020 Nobel Prize in Physics for his prediction of black holes, physicist Roger Penrose teamed up with anaesthesiologist Stuart Hameroff to propose an ambitious answer.

They claimed that the brains neuronal system forms an intricate network and that the consciousness this produces should obey the rules of quantum mechanics the theory that determines how tiny particles like electrons move around. This, they argue, could explain the mysterious complexity of human consciousness.

Penrose and Hameroff were met with incredulity. Quantum mechanical laws are usually only found to apply at very low temperatures. Quantum computers, for example, currently operate at around -272C. At higher temperatures, classical mechanics takes over. Since our body works at room temperature, you would expect it to be governed by the classical laws of physics. For this reason, the quantum consciousness theory has been dismissed outright by many scientists though others are persuaded supporters.

Instead of entering into this debate, I decided to join forces with colleagues from China, led by Professor Xian-Min Jin at Shanghai Jiaotong University, to test some of the principles underpinning the quantum theory of consciousness.

In our new paper, weve investigated how quantum particles could move in a complex structure like the brain but in a lab setting. If our findings can one day be compared with activity measured in the brain, we may come one step closer to validating or dismissing Penrose and Hameroffs controversial theory.

Our brains are composed of cells called neurons, and their combined activity is believed to generate consciousness. Each neuron contains microtubules, which transport substances to different parts of the cell. The Penrose-Hameroff theory of quantum consciousness argues that microtubules are structured in a fractal pattern which would enable quantum processes to occur.

Fractals are structures that are neither two-dimensional nor three-dimensional, but are instead some fractional value in between. In mathematics, fractals emerge as beautiful patterns that repeat themselves infinitely, generating what is seemingly impossible: a structure that has a finite area, but an infinite perimeter.

Read more: Explainer: what are fractals?

This might sound impossible to visualise, but fractals actually occur frequently in nature. If you look closely at the florets of a cauliflower or the branches of a fern, youll see that theyre both made up of the same basic shape repeating itself over and over again, but at smaller and smaller scales. Thats a key characteristic of fractals.

The same happens if you look inside your own body: the structure of your lungs, for instance, is fractal, as are the blood vessels in your circulatory system. Fractals also feature in the enchanting repeating artworks of MC Escher and Jackson Pollock, and theyve been used for decades in technology, such as in the design of antennas. These are all examples of classical fractals fractals that abide by the laws of classical physics rather than quantum physics.

Its easy to see why fractals have been used to explain the complexity of human consciousness. Because theyre infinitely intricate, allowing complexity to emerge from simple repeated patterns, they could be the structures that support the mysterious depths of our minds.

But if this is the case, it could only be happening on the quantum level, with tiny particles moving in fractal patterns within the brains neurons. Thats why Penrose and Hameroffs proposal is called a theory of quantum consciousness.

Were not yet able to measure the behaviour of quantum fractals in the brain if they exist at all. But advanced technology means we can now measure quantum fractals in the lab. In recent research involving a scanning tunnelling microscope (STM), my colleagues at Utrecht and I carefully arranged electrons in a fractal pattern, creating a quantum fractal.

When we then measured the wave function of the electrons, which describes their quantum state, we found that they too lived at the fractal dimension dictated by the physical pattern wed made. In this case, the pattern we used on the quantum scale was the Sierpiski triangle, which is a shape thats somewhere between one-dimensional and two-dimensional.

This was an exciting finding, but STM techniques cannot probe how quantum particles move which would tell us more about how quantum processes might occur in the brain. So in our latest research, my colleagues at Shanghai Jiaotong University and I went one step further. Using state-of-the-art photonics experiments, we were able to reveal the quantum motion that takes place within fractals in unprecedented detail.

We achieved this by injecting photons (particles of light) into an artificial chip that was painstakingly engineered into a tiny Sierpiski triangle. We injected photons at the tip of the triangle and watched how they spread throughout its fractal structure in a process called quantum transport. We then repeated this experiment on two different fractal structures, both shaped as squares rather than triangles. And in each of these structures we conducted hundreds of experiments.

Our observations from these experiments reveal that quantum fractals actually behave in a different way to classical ones. Specifically, we found that the spread of light across a fractal is governed by different laws in the quantum case compared to the classical case.

This new knowledge of quantum fractals could provide the foundations for scientists to experimentally test the theory of quantum consciousness. If quantum measurements are one day taken from the human brain, they could be compared against our results to definitely decide whether consciousness is a classical or a quantum phenomenon.

Our work could also have profound implications across scientific fields. By investigating quantum transport in our artificially designed fractal structures, we may have taken the first tiny steps towards the unification of physics, mathematics and biology, which could greatly enrich our understanding of the world around us as well as the world that exists in our heads.

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Can consciousness be explained by quantum physics? My research takes us a step closer to finding out - The Conversation UK

We take for granted that an event in one part of the world cannot instantly affect what happens far away. This principle, which physicists call locality, was long regarded as a bedrock assumption about the laws of physics. So when Albert Einstein and two colleagues showed in 1935 that quantum mechanics permits spooky action at a distance, as Einstein put it, this feature of the theory seemed highly suspect. Physicists wondered whether quantum mechanics was missing something.

Then in 1964, with the stroke of a pen, the Northern Irish physicist John Stewart Bell demoted locality from a cherished principle to a testable hypothesis. Bell proved that quantum mechanics predicted stronger statistical correlations in the outcomes of certain far-apart measurements than any local theory possibly could. In the years since, experiments have vindicated quantum mechanics again and again.

Bells theorem upended one of our most deeply held intuitions about physics, and prompted physicists to explore how quantum mechanics might enable tasks unimaginable in a classical world. The quantum revolution thats happening now, and all these quantum technologies thats 100% thanks to Bells theorem, says Krister Shalm, a quantum physicist at the National Institute of Standards and Technology.

Heres how Bells theorem showed that spooky action at a distance is real.

The spooky action that bothered Einstein involves a quantum phenomenon known as entanglement, in which two particles that we would normally think of as distinct entities lose their independence. Famously, in quantum mechanics a particles location, polarization and other properties can be indefinite until the moment they are measured. Yet measuring the properties of entangled particles yields results that are strongly correlated, even when the particles are far apart and measured nearly simultaneously. The unpredictable outcome of one measurement appears to instantly affect the outcome of the other, regardless of the distance between them a gross violation of locality.

To understand entanglement more precisely, consider a property of electrons and most other quantum particles called spin. Particles with spin behave somewhat like tiny magnets. When, for instance, an electron passes through a magnetic field created by a pair of north and south magnetic poles, it gets deflected by a fixed amount toward one pole or the other. This shows that the electrons spin is a quantity that can have only one of two values: up for an electron deflected toward the north pole, and down for an electron deflected toward the south pole.

Imagine an electron passing through a region with the north pole directly above it and the south pole directly below. Measuring its deflection will reveal whether the electrons spin is up or down along the vertical axis. Now rotate the axis between the magnet poles away from vertical, and measure deflection along this new axis. Again, the electron will always deflect by the same amount toward one of the poles. Youll always measure a binary spin value either up or down along any axis.

It turns out its not possible to build any detector that can measure a particles spin along multiple axes at the same time. Quantum theory asserts that this property of spin detectors is actually a property of spin itself: If an electron has a definite spin along one axis, its spin along any other axis is undefined.

Armed with this understanding of spin, we can devise a thought experiment that we can use to prove Bells theorem. Consider a specific example of an entangled state: a pair of electrons whose total spin is zero, meaning measurements of their spins along any given axis will always yield opposite results. Whats remarkable about this entangled state is that, although the total spin has this definite value along all axes, each electrons individual spin is indefinite.

Suppose these entangled electrons are separated and transported to distant laboratories, and that teams of scientists in these labs can rotate the magnets of their respective detectors any way they like when performing spin measurements.

When both teams measure along the same axis, they obtain opposite results 100% of the time. But is this evidence of nonlocality? Not necessarily.

Alternatively, Einstein proposed, each pair of electrons could come with an associated set of hidden variables specifying the particles spins along all axes simultaneously. These hidden variables are absent from the quantum description of the entangled state, but quantum mechanics may not be telling the whole story.

Hidden variable theories can explain why same-axis measurements always yield opposite results without any violation of locality: A measurement of one electron doesnt affect the other but merely reveals the preexisting value of a hidden variable.

Bell proved that you could rule out local hidden variable theories, and indeed rule out locality altogether, by measuring entangled particles spins along different axes.

Suppose, for starters, that one team of scientists happens to rotate its detector relative to the other labs by 180 degrees. This is equivalent to swapping its north and south poles, so an up result for one electron would never be accompanied by a down result for the other. The scientists could also choose to rotate it an in-between amount 60 degrees, say. Depending on the relative orientation of the magnets in the two labs, the probability of opposite results can range anywhere between 0% and 100%.

Without specifying any particular orientations, suppose that the two teams agree on a set of three possible measurement axes, which we can label A, B and C. For every electron pair, each lab measures the spin of one of the electrons along one of these three axes chosen at random.

Lets now assume the world is described by a local hidden variable theory, rather than quantum mechanics. In that case, each electron has its own spin value in each of the three directions. That leads to eight possible sets of values for the hidden variables, which we can label in the following way:

The set of spin values labeled 5, for instance, dictates that the result of a measurement along axis A in the first lab will be up, while measurements along axes B and C will be down; the second electrons spin values will be opposite.

For any electron pair possessing spin values labeled 1 or 8, measurements in the two labs will always yield opposite results, regardless of which axes the scientists choose to measure along. The other six sets of spin values all yield opposite results in 33% of different-axis measurements. (For instance, for the spin values labeled 5, the labs will obtain opposite results when one measures along axis B while the other measures along C; this represents one-third of the possible choices.)

Thus the labs will obtain opposite results when measuring along different axes at least 33% of the time; equivalently, they will obtain the same result at most 67% of the time. This result an upper bound on the correlations allowed by local hidden variable theories is the inequality at the heart of Bells theorem.

Now, what about quantum mechanics?Were interested in the probability of both labs obtaining the same result when measuring the electrons spins along different axes. The equations of quantum theory provide a formula for this probability as a function of the angles between the measurement axes.

According to the formula, when the three axes are all as far apart as possible that is, all 120 degrees apart, as in the Mercedes logo both labs will obtain the same result 75% of the time. This exceeds Bells upper bound of 67%.

Thats the essence of Bells theorem: If locality holds and a measurement of one particle cannot instantly affect the outcome of another measurement far away, then the results in a certain experimental setup can be no more than 67% correlated. If, on the other hand, the fates of entangled particles are inextricably linked even across vast distances, as in quantum mechanics, the results of certain measurements will exhibit stronger correlations.

Since the 1970s, physicists have made increasingly precise experimental tests of Bells theorem. Each one has confirmed the strong correlations of quantum mechanics. In the past five years, various loopholes have been closed. Locality that long-held assumption about physical law is not a feature of our world.

Editors note: The author is currently a postdoctoral researcher at JILA in Boulder, Colorado.

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How Bell's Theorem Proved 'Spooky Action at a Distance' Is Real - Quanta Magazine

In therecent Nature study, Basov and his colleagues recreated Fizeaus experiments on a speck of graphene made up of a single layer of carbon atoms. Hooking up the graphene to a battery, they created an electrical current reminiscent of Fizeaus water streaming through a pipe. But instead of shining light on the moving water and measuring its speed in both directions, as Fizeau did, they generated an electromagnetic wave with a compressed wavelengtha polaritonby focusing infrared light on a gold nub in the graphene. The activated stream of polaritons look like light but are physically more compact due to their short wavelengths.

The researchers clocked the polaritons speed in both directions. When they traveled with the flow of the electrical current, they maintained their original speed. But when launched against the current, they slowed by a few percentage points.

We were surprised when we saw it, saidstudy co-author Denis Bandurin, a physics researcher at MIT. First, the device was still alive, despite the heavy current we passed through itit hadnt blown up. Then we noticed the one-way effect, which was different from Fizeaus original experiments.

The researchers repeated the experiments over and over, led by the studys first-author, Yinan Dong, a Columbia graduate student. Finally, it dawned on them. Graphene is a material that turns electrons into relativistic particles, Dong said. We needed to account for their spectrum.

A group at Berkeley Lab founda similar result, published in the same issue of Nature. Beyond reproducing the Fizeau effect in graphene, both studies have practical applications. Most natural systems are symmetric, but here, researchers found an intriguing exception. Basov said he hopes to slow down, and ultimately, cut off the flow of polaritons in one direction. Its not an easy task, but it could hold big rewards.

Engineering a system with a one-way flow of light is very difficult to achieve, saidMilan Delor, a physical chemist working on light-matter interactions at Columbia who was not involved in the research. As soon as you can control the speed and direction of polaritons, you can transmit information in nanoscale circuits on ultrafast timescales. Its one of the ingredients currently missing in photon-based circuits.

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Physicists Show That a Quantum Particle Made of Light and Matter Can Be Dragged by a Current of Electrons - Columbia University

11:00 am12:00 pm

Please join us:

Christian Ferkos PhDThesisDefense

Monday July 26, 2021 at 11 am CDT

SUPERSYMMETRY AND IRRELEVANT DEFORMATIONS

This The T bar{T} operator provides a universal irrelevant deformation of two-dimensional quantum field theories with remarkable properties, including connections to both string theory and holography beyond AdS spacetimes. In particular, it appears that a T bar{T}- deformed theory is a kind of new structure, which is neither a local quantum field theory nor a full-fledged string theory, but which is nonetheless under some analytic control. On the other hand, supersymmetry is a beautiful extension of Poincare symmetry which relates bosonic and fermionic degrees of freedom. The extra computational power provided by supersymmetry renders many calculations more tractable. It is natural to ask what one can learn about irrelevant deformations in supersymmetric quantum field theories.

In this talk, I will describe a presentation of the T bar{T} deformation in manifestly supersymmetric settings. I define a ``supercurrent-squared'' operator, which is closely related to T bar{T}, in any two-dimensional theory with (0, 1), (1, 1), or (2, 2) supersymmetry. This deformation generates a flow equation for the superspace Lagrangian of the theory, which therefore makes the supersymmetry manifest. In certain examples, the deformed theories produced by supercurrent-squared are related to superstring and brane actions, and some of these theories possess extra non-linearly realized supersymmetries. Finally, I will show that Tbar{T} defines a new theory of both abelian and non-abelian gauge fields coupled to charged matter, which includes models compatible with maximal supersymmetry. In analogy with the

Dirac-Born-Infeld (DBI) theory, which defines a non-linear extension of Maxwell electrodynamics, these models possess a critical value for the electric field.

Committee members:

Savdeep Sethi (Chair)

Jeffrey Harvey

Robert Wald

Mark Oreglia

Christian will be starting a postdoc at UC Davis in the Center for Quantum Mathematics and

Physics (QMAP).

Thesis Defense

Read more here:

Christian Ferko's PhD Thesis Defense | Department of Physics | The University of Chicago - UChicago News

Stephen Hawking was one of the greatest theoretical physicists of the modern age. Best known for his appearances in popular media and his lifelong battle against debilitating illness, his true impact on posterity comes from his brilliant five-decade career in science. Beginning with his doctoral thesis in 1966, his groundbreaking work continued nonstop right up to his final paper in 2018, completed just days before his death at the age of 76.

Hawking worked at the intellectual cutting edge of physics, and his theories often seemed bizarrely far-out at the time he formulated them. Yet they're slowly being accepted into the scientific mainstream, with new supporting evidence coming in all the time. From his mind-blowing views of black holes to his explanation for the universes humble beginnings, here are some of his theories that were vindicated and some that are still up in the air.

Hawking got off to a flying start with his doctoral thesis, written at a critical time when there was heated debate between two rival cosmological theories: the Big Bang and the Steady State. Both theories accepted that the universe is expanding, but in the first it expands from an ultra-compact, super-dense state at a finite time in the past, while the second assumes the universe has been expanding forever, with new matter constantly being created to maintain a constant density. In his thesis, Hawking showed that the Steady State theory is mathematically self-contradictory. He argued instead that the universe began as an infinitely small, infinitely dense point called a singularity. Today, Hawking's description is almost universally accepted among scientists.

More than anything else, Hawking's name is associated with black holes another kind of singularity, formed when a star undergoes complete collapse under its own gravity. These mathematical curiosities arose from Einstein's theory of general relativity, and they had been debated for decades when Hawking turned his attention to them in the early 1970s.

According to an article in Nature, his stroke of genius was to combine Einstein's equations with those of quantum mechanics, turning what had previously been a theoretical abstraction into something that looked like it might actually exist in the universe. The final proof that Hawking was correct came in 2019, when the Event Horizon Telescope obtained a direct image of the supermassive black hole lurking in the center of giant galaxy Messier 87.

Black holes got their name because their gravity is so strong that photons, or particles of light, shouldn't be able to escape from them. But in his early work on the subject, Hawking argued that the truth is more subtle than this monochrome picture.

By applying quantum theory specifically, the idea that pairs of "virtual photons" can spontaneously be created out of nothing he realized that some of these photons would appear to be radiated from the black hole. Now referred to as Hawking radiation, the theory was recently confirmed in a laboratory experiment at the Technion-Israel Institute of Technology, Israel. In place of a real black hole, the researchers used an acoustic analog a "sonic black hole" from which sound waves cannot escape. They detected the equivalent of Hawking radiation exactly in accordance with the physicist's predictions.

In classical physics, entropy, or the disorder of a system that can only ever increase with time, never decreases. Together with Jacob Bekenstein, Hawking proposed that the entropy of a black hole is measured by the surface area of its surrounding event horizon.

The recent discovery of gravitational waves emitted by merging pairs of black holes shows that Hawking was right again. As Hawking told the BBC after the first such event in 2016, "the observed properties of the system are consistent with predictions about black holes that I made in 1970 ... the area of the final black hole is greater than the sum of the areas of the initial black holes." More recent observations have provided further confirmation of Hawking's "area theorem."

So the world is gradually catching up with Stephen Hawking's amazing predictions. But there are still quite a few that have yet to be proven one way or the other:

The existence of Hawking radiation creates a serious problem for theoreticians. It seems to be the only process in physics that deletes information from the universe.

The basic properties of the material that went into making the black hole appear to be lost forever; the radiation that comes out tells us nothing about them. This is the so-called information paradox that scientists have been trying to solve for decades. Hawking's own take on the mystery, which was published in 2016, is that the information isn't truly lost. It's stored in a cloud of zero-energy particles surrounding the black hole, which he dubbed "soft hair." But Hawking's hairy black hole theorem is only one of several hypotheses that have been put forward, and to date no one knows the true answer.

Black holes are created from the gravitational collapse of pre-existing matter such as stars. But it's also possible that some were created spontaneously in the very early universe, soon after the Big Bang.

Hawking was the first person to explore the theory behind such primordial black holes in depth. It turns out they could have virtually any mass whatsoever, from very light to very heavy though the really tiny ones would have "evaporated" into nothing by now due to Hawking radiation. One intriguing possibility considered by Hawking is that primordial black holes might make up the mysterious dark matter that astronomers believe permeates the universe. However, as LiveScience previously reported, current observational evidence indicates that this is unlikely. Either way, we currently don't have observational tools to detect primordial black holes or to say whether they make up dark matter.

One of the topics Hawking tinkered with toward the end of his life was the multiverse theory the idea that our universe, with its beginning in the Big Bang, is just one of an infinite number of coexisting bubble universes.

Hawking wasn't happy with the suggestion, made by some scientists, that any ludicrous situation you can imagine must be happening right now somewhere in that infinite ensemble. So, in his very last paper in 2018, Hawking sought, in his own words, to "try to tame the multiverse." He proposed a novel mathematical framework that, while not dispensing with the multiverse altogether, rendered it finite rather than infinite. But as with any speculation concerning parallel universes, we have no idea if his ideas are right. And it seems unlikely that scientists will be able to test his idea any time soon.

Surprising as it may sound, the laws of physics as we understand them today don't prohibit time travel. The solutions to Einstein's equations of general relativity include "closed time-like curves," which would effectively allow you to travel back into your own past. Hawking was bothered by this, because he felt that backward travel in time raised logical paradoxes that simply shouldn't be possible.

So he suggested that some currently unknown law of physics prevents closed timelike curves from occurring his so-called "chronology protection conjecture." But "conjecture" is just science-speak for "guess," and we really don't know whether time travel is possible or not.

One of the questions cosmologists get asked most often is "what happened before the Big Bang?" Hawking's own view was that the question is meaningless. To all intents and purposes, time itself as well as the universe and everything in it began at the Big Bang.

"For me, this means that there is no possibility of a creator," he said, and as LiveScience previously reported, "because there is no time for a creator to have existed in." That's an opinion many people will disagree with, but one that Hawking expressed on numerous occasions throughout his life. It almost certainly falls in the "will never be resolved one way or the other" category.

In his later years, Hawking made a series of bleak prophecies concerning the future of humanity that he may or may not have been totally serious about, BBC reported

These range from the suggestion that the elusive Higgs boson, or "God particle," might trigger a vacuum bubble that would gobble up the universe to hostile alien invasions and artificial intelligence (AI) takeovers. Although Stephen Hawking was right about so many things, we'll just have to hope he was wrong about these.

Originally published on Live Science.

Originally posted here:

4 bizarre Stephen Hawking theories that turned out to be right (and 6 we're not sure about) - Livescience.com

Back in the plague year of 1665-1666, Isaac Newton changed the scientific world, discovering the universal law of gravity and the mathematics of calculus. Now, in the plague year of 2020-2021, is history about to repeat itself?

Stephen Wolfram thinks so. The British-born scientist, who lives in the US, claims he has found a route to a fundamental theory of physics that answers some of the biggest questions, such as what is space? What is time? And why does the Universe exist?

To be fair, a lot of the work was done in 2019 and we were about to start speaking about it in March 2020, but everything locked down for COVID, says Wolfram. But it is true to say that we have made more progress towards finding a fundamental theory of physics than I dared believe was possible.

Wolframs starting point was to ask: What is space? Physicists dont often ask this question, he says. They merely think of space as the backdrop against which the events of the Universe play out.

According to Wolfram, space is made of a network of nodes, which are connected to each other. The nature of the connections how each node is linked to nearby and faraway nodes can create a space of any dimension. So if the number of nodes increases as the square of the distance from any given node like the surface area of a sphere the network has the properties of familiar 3D space.

Read more theories of the Universe:

I actually believe the Universe started out with infinitely many dimensions and gradually cooled down to the three we have today, says Wolfram. But I dont yet know why there are precisely three.

Wolfram is interested in what is the minimal stuff needed to create the Universe. And in addition to the network of nodes the atoms of space there is another ingredient, the rules that change the network. So, for instance, a rule will say: wherever there is a particular pattern of nodes, replace it with another particular pattern of nodes.

It is the application of such rules, over and over again the continual updating of the space network that knits together space, says Wolfram. The miracle is that this process can also create all the matter in the Universe and all laws of physics we have discovered over the past 350 years.

Stephen Wolfram Wolfram Research Inc/Tom Straw

Before examining this remarkable claim, it is worth considering how Wolfram got to this point. Born in London in 1959, he was publishing physics papers at the age of 15. As a graduate student at the California Institute of Technology in Pasadena, he worked with Richard Feynman, arguably the most notable post-war US physicist. But a crucial event for Wolfram was a discovery he made in 1981 when he used a computer to investigate the consequences of simple computer programs ones whose output is repeatedly fed back in as their input, like a snake eating its own tail.

The simplest computer programs he could think of at the time were cellular automata. These are one-dimensional lines of squares, each of which can be empty or filled. A rule is applied that replaces a certain pattern of squares with another. In this way, a new line of squares is created. And another new line. And so on.

Most of the time Wolfram found that nothing interesting happened. In some cases, however, there were persistent features that moved across the evolving cellular grid, reminiscent of subatomic particles in the real world. But the big surprise was that there were a few rules that created never-ending novelty and complexity.

This was a light bulb moment for Wolfram. Usually, simple programs have simple outputs and complex programs have complex outputs. But Wolfram had discovered simple programs with complex outputs. His immediate thought was, Is this how the Universe creates a rose or a newborn baby or a galaxy? Is it merely applying a simple program over and over again?

In 2002, Wolfram published A New Kind Of Science, a 1,200-page tome with 1,000 black-and-white pictures and half a million words. In it, among other things, he explored the consequences of all 256 possible rules for one-dimensional cellular automata, among which was Rule 30, which generated unlimited complexity. The book was met with hostility from the physics community. Partly, it was because he had published it himself without going through the usual peer review process. But another reason was that other physicists could not see how to use his ideas to predict anything useful.

They had a point. Basically, Wolfram was saying that most of what the Universe is doing is computationally irreducible that is, the outcome can be discovered only by running the computer program for the 13.82 billion years the Universe has been in existence. To many other physicists that was a fat lot of good.

But Wolfram was also saying that, within the Universe-generating computation, there are computationally reducible islands, where it is possible to deduce the outcome without actually running the program. These shortcuts are none other than the laws of physics we have discovered, says Wolfram.

In the end, Wolfram did not pursue the ideas he had laid out in A New Kind Of Science. On the one hand, he says, there was no demand from physicists. And on the other hand, there was demand for his software such as the computer language Mathematica and the intelligent search engine WolframAlpha, which had made him a billionaire. He therefore spent the next two decades developing them instead.

But in 2019, he met some young physicists who encouraged him to continue his search for a fundamental, computational theory of physics. And, at the age of 60, it was now or never.

From order there was chaos: Wolframs Rule 30 found that even a simple rule that determines the colour of cells in a row can generate complexity Richard Ling/Wikipedia

The problem with cellular automata is that they run on a pre-existing grid. Wolfram realised quickly that he needed something simpler, even more basic. This is how he hit on the idea of a self-updating space network. There are persistent features in the networks, rather like vortices in water, and these are matter. Ultimately, then, everything arises from space. There is nothing else. Actually, that is not entirely true. There is one other thing. Time, which everyone since Einstein has thought is the same as space, isnt, says Wolfram. Time is actually the process of step-by-step computation.

One of the problems with Wolframs earlier approach was that, if he found the program that is generating the Universe and he believed it might be no longer than four lines of code in his own computer language, Mathematica the question would then arise, why this program and not another? Wolfram therefore hit on the idea that the Universe is being generated byall possible programs running simultaneously.

At first sight it seems unbelievably messy. How can anything useful come out of this? he says. But the miracle is that everything does, including the twin pillars of modern physics: Einsteins theory of gravity [General Relativity] and quantum theory.

The key thing is to realise that we are not observing the Universe from outside. That is impossible. Instead, we are pieces of self-updating space network within the overall self-updating space network of the Universe. Not only are we limited in the amount of computation we can do and so unable to perceive most of the irreducible computation going on all around us but we are also limited by our biology, which causes us to impose a single thread of time on what we see. Despite the fact that all possible rules are actually operating, our sampling will reveal a single rule generating the Universe, says Wolfram.

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Crucially, our fundamental limitations do not permit us to see the atoms of space. Instead, we see them linked together to make a smooth continuum a continuum, furthermore, that is described by General Relativity. In Einsteins theory, masses like planets follow the shortest path, or geodesic, through space-time. Space-time is in turn warped by the presence of energy (strictly speaking, energy-momentum). According to Wolfram, energy in his picture is nothing more than the amount of activity going on at any location in the network, and it is this computation that ultimately bends the geodesics of massive bodies.

Quantum theory, in contrast, describes the microscopic realm of atoms and their constituents, and is notorious for appearing fundamentally incompatible with General Relativity. Specifically, there is no such thing as a unique path through space. Atoms can follow multiple paths, each with an associated probability. According to Wolfram, this multiple history is built into his framework because, each time a piece of space network is updated, it can be updated by not just one rule but multiple possible rules, leading to multiple histories. Quantum theory is not a bolt-on, as in standard physics, he says.

Wolfram goes further. He imagines a branchial space that encapsulates all these multiple histories. And this requires the tools of Mathematica to visualise, which is one reason why other physicists, not just mere mortals, find it hard to follow Wolfram. However, the key thing Wolfram claims is that General Relativity, with its geodesics bent by energy-momentum in normal space, is exactly the same as quantum theory with its geodesics bent by energy-momentum in branchial space. General Relativity and quantum theory are basically the same theory! he says. I never expected to discover such a lovely result.

This is indeed an astonishing result. In mainstream physics, only string theory provides a framework that unites General Relativity and quantum theory, and it has big problems, not least the fact that it leads not to a single Universe but to a multiverse of about 10,500 universes. There is a strong hint, however, known as the holographic principle, that quantum theory and General Relativity are intimately connected and that quantum theory manifests itself as General Relativity in a higher dimensional space. Wolfram sees his work as confirming this connection.

Carlo Rovelli at Aix-Marseilles University works on loop quantum gravity, a rival of string theory, which attempts to show that space-time, down at the impossibly small Planck scale, is made of finite loops woven together into a complex shifting network. Is there any connection between Wolframs work and loop quantum gravity? Indeed, I have been curious about the same question! says Rovelli.

Others find Wolframs work fascinating. One is Gregory Chaitin, the Argentinian-American who invented a field of mathematics algorithmic information theory when he was 15. I personally think his new work is very interesting, he says. And, yes, something like General Relativity and like quantum mechanics emerges rather naturally.

Chaitin likes the originality of Wolframs approach. What is fun is that this is completely orthogonal [distinct] to what everyone else is doing. Up to now, string theory has been the only game in town that attempts to operate at this level. Now there is another game.

Artists impression of the Universe, with galaxy clusters concentrated at nodes Science Photo Library

Wolfram is encouraged by the response to his latest work, which is very different to the response he experienced in 2002. He says lots of the young physicists are attending his seminars, and older physicists are sending their students. He is live-streaming a lot of the development on the web so people can see what he is doing. I have been surprised at how few people have said this cant possibly work, says Wolfram. Its been more like I cant understand this or tell us what phenomena we can look for.

Wolfram is also not alone, as he was in 2002. He now has a handful of other physicists working with him. Chaitin thinks this is significant. Unusually for Stephen, he even gives co-author credit to some, he says. But one of the major differences between now and 2002 is the idea that information-processing is at the heart of the Universe is far more mainstream than it was two decades ago. In a way, nothing Wolfram is doing is contradicting accepted physics. He is merely attempting to go beneath the bonnet of the car to reveal the computation that both generates the Universe and the laws of physics that we observe.

One consequence of Wolframs picture is that aliens with different biologies and different senses may see different parts of the Universe-generating computation and therefore deduce different laws from quantum theory and General Relativity. In fact, they may forever be invisible to us, existing in parts of the space network our senses are simply not sampling. Our view is limited by our size of about a metre in height and our insistence on seeing a single thread of time, says Wolfram. But creatures the size of the planet and without this insistence would see something entirely different.

In the end, it will be predictions of new phenomena that will confirm or refute Wolframs computational universe. And at the moment these are lacking. However, Wolfram sees places that may be fruitful in yielding observational predictions. For instance, he believes there could be domains of our Universe with different numbers of dimensions. And, in particular, he suspects the black holes may be able to spin faster than permitted by standard physics and, in doing so, whole chunks of space-time may break off, something which is impossible in General Relativity.

Read more about the Universe:

The big question remains, why is there a Universe? And here Wolfram thinks the Universe may exist in the much the same sense that mathematics exists. Mathematics consists of a set of givens, or axioms, and the consequences, or theorems, that can be deduced from them by applying the rules of logic. Similarly, the Universe is merely the logical consequence of applying all possible rules to a network of disembodied nodes. It is inevitable that it exists, in the same way it is inevitable that 1+1=2, he says.

We, of course, experience the Universe as a solid thing, not an abstract thing like the edifice of mathematics. However, since we are also made of the same stuff as the Universe like virtual creatures in a virtual reality everything appears solidly real to us.

Whether or not Wolfram turns out to be the new Newton, the plague year has definitely played to Wolframs strengths. I have always worked remotely from my company, he says. This last year has suited me. He admits there is still a long way to go in getting a fundamental theory of physics. But I am amazed how far things have progressed in a short time, he says. I never imagined it would work this well.

Stephen Wolfram is a computer scientist and physicist. He is the author ofA New Kind of Science and created the programming software Mathematica and the computational knowledge engine WolframAlpha.

Continue reading here:

Inside the simple computer program that could explain why the Universe exists at all - BBC Science Focus Magazine