Faster Than Speed of Light

The inside of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider. Rochester physicists working at the detector have observed spin entanglement between top quarks and top antiquarks persisting at long distances and high speeds. Credit: CERN




Researchers have confirmed that quantum entanglement persists between top quarks, the heaviest known fundamental particles.

Physicists have demonstrated quantum entanglement in top quarks and their antimatter partners, a discovery made at CERN. This finding extends the behavior of entangled particles to distances beyond the reach of light-speed communication and opens new avenues for exploring quantum mechanics at high energies.

An experiment by a group of physicists led by University of Rochester physics professor Regina Demina has produced a significant result related to quantum entanglement—an effect that Albert Einstein called “spooky action at a distance.”

Entanglement concerns the coordinated behavior of minuscule particles that have interacted but then moved apart. Measuring properties—like position or momentum or spin—of one of the separated pair of particles instantaneously changes the results of the other particle, no matter how far the second particle has drifted from its twin. In effect, the state of one entangled particle, or qubit, is inseparable from the other.       READ MORE...

World's Most Powerful Laser

"Ready? Signal sent!" In the control room of a research center in Romania, engineer Antonia Toma activates the world's most powerful laser, which promises revolutionary advances in everything from the health sector to space.


The laser at the center, near the Romanian capital Bucharest, is operated by French company Thales, using Nobel prize-winning inventions.

France's Gerard Mourou and Donna Strickland of Canada won the 2018 Nobel Physics Prize for harnessing the power of lasers for advanced precision instruments in corrective eye surgery and in industry.

"The sharp beams of laser light have given us new opportunities for deepening our knowledge about the world and shaping it," said the Nobel Academy's citation.    READ MORE...

Fundamental Principle of Physics

A new study has overturned a fundamental principle of physics by demonstrating that similarly charged particles can attract each other in a solution, with the effect varying between positive and negative charges depending on the solvent. This discovery has significant implications for various scientific processes, including self-assembly and crystallization. 

The research reveals the importance of solvent structure at the interface in determining interparticle interactions, challenging long-held beliefs and indicating a need for a re-evaluation of our understanding of electromagnetic forces. Credit: Zhang Kang


“Opposites charges attract; like charges repel” is a fundamental principle of basic physics. However, a new study from Oxford University, recently published in the journal Nature Nanotechnology, has demonstrated that similarly charged particles in solution can, in fact, attract each other over long distances.

Just as surprisingly, the team found that the effect is different for positively and negatively charged particles, depending on the solvent.  READ MORE...

Uniting Gravity, Spacetime, and Quantum Theory

In a groundbreaking announcement, physicists from University College London (UCL) have presented a radical theory that unifies the realms of gravity and quantum mechanics while preserving the classical concept of spacetime, as outlined by Einstein.

This innovative approach, detailed in two simultaneously published papers, challenges over a century of scientific consensus and proposes a revolutionary perspective on the fundamental nature of our universe.

Dichotomy in modern physics
Modern physics rests on two contradictory pillars: quantum theory, which rules the microscopic world, and Einstein’s theory of general relativity, explaining gravity through spacetime curvature. These theories, despite their individual successes, have remained irreconcilable, creating a significant rift in our understanding of the universe.  READ MORE...

More Than Just Physics

Researchers have highlighted the importance of contextualizing physics education to reflect real-world energy issues. In a recent paper, they discuss how educators are incorporating case studies on power plants to teach students about the broader impacts of energy decisions. Their work emphasizes the need for a holistic approach that considers scientific, ethical, ecological, and cultural factors, encouraging students to participate in informed community decision-making.

Reframing power in terms of social and cultural dynamics enables students to actively participate in their communities.
Large-scale energy generation endeavors are influenced equally by economic and political factors as they are by the availability of natural resources and raw materials. The output of power plants encompasses more than just electricity; it also results in diverse scientific, ethical, ecological, and cultural consequences. These impacts are felt at various levels, from local communities to regional areas, and extend up to state, national, and global dimensions.

Researchers from the University of Washington Bothell and Seattle Pacific University discussed the importance of contextualizing physics principles. In The Physics Teacher, a journal co-published by AIP Publishing and the American Association of Physics Teachers, they outlined how teachers implemented case studies to teach about energy and the realities of power plants.  READ MORE...

Time Jumping Multiverse

“This retroactive idea. It has to be that,” says Nobel Prize-winning mathematical physicist Sir Roger Penrose (left), reflecting on a problem about the building blocks of reality that has dogged physics for nearly a century. “Any sensible physicist wouldn't be perturbed by this,” he adds. “However, I'm not a sensible physicist.”

If Penrose isn’t a sensible physicist it’s because the laws of physics aren’t making sense, at least not on the subatomic level where the smallest things in the universe play by different rules than everything we see around us. He has reason to believe this disconnect involves a fissure that divides two different kinds of reality. He also has reason to believe that the physical process that bridges these realities will unlock answers to the physics of consciousness: the mystery of our own existence.  READ MORE...

Quantum Physics Twisted Time

The 2022 physics Nobel prize was awarded for experimental work demonstrating fundamental breaks in our understanding of the quantum world, leading to discussions around “local realism” and how it could be refuted. Many theorists believe these experiments challenge either “locality” (the notion that distant objects require a physical mediator to interact) or “realism” (the idea that there’s an objective state of reality). However, a growing number of experts suggest an alternative approach, “retrocausality,” which posits that present actions can affect past events, thus preserving both locality and realism.

The 2022 Nobel Prize in physics highlighted the challenges quantum experiments pose to “local realism.” However, a growing body of experts propose “retrocausality” as a solution, suggesting that present actions can influence past events, thus preserving both locality and realism. 

This concept offers a novel approach to understanding causation and correlations in quantum mechanics, and despite some critics and confusion with “superdeterminism,” it is increasingly seen as a viable explanation for recent groundbreaking experiments, potentially safeguarding the core principles of special relativity.

In 2022, the physics Nobel prize was awarded for experimental work showing that the quantum world must break some of our fundamental intuitions about how the universe works.


Many look at those experiments and conclude that they challenge “locality” — the intuition that distant objects need a physical mediator to interact. And indeed, a mysterious connection between distant particles would be one way to explain these experimental results.


Others instead think the experiments challenge “realism” — the intuition that there’s an objective state of affairs underlying our experience. After all, the experiments are only difficult to explain if our measurements are thought to correspond to something real. Either way, many physicists agree about what’s been called “the death by experiment” of local realism.

But what if both of these intuitions can be saved, at the expense of a third? A growing group of experts think that we should abandon instead the assumption that present actions can’t affect past events. Called “retrocausality,” this option claims to rescue both locality and realism.  READ MORE...

Something is Created from Nothing

There are all sorts of conservation laws in the Universe: for energy, momentum, charge, and more. Many properties of all physical systems are conserved: where things cannot be created or destroyed.

We've learned how to create matter under specific, explicit conditions: by colliding two quanta together at high enough energies so that equal amounts of matter and antimatter can emerge, so long as E = mc² allows it to happen.

For the first time, we've managed to create particles without any collisions or precursor particles at all: through strong electromagnetic fields and the Schwinger effect. 

HERE's HOW...

Whoever said, “You can’t get something from nothing” must never have learned quantum physics. As long as you have empty space — the ultimate in physical nothingness — simply manipulating it in the right way will inevitably cause something to emerge. Collide two particles in the abyss of empty space, and sometimes additional particle-antiparticle pairs emerge. 

Take a meson and try to rip the quark away from the antiquark, and a new set of particle-antiparticle pairs will get pulled out of the empty space between them. And in theory, a strong enough electromagnetic field can rip particles and antiparticles out of the vacuum itself, even without any initial particles or antiparticles at all.

Previously, it was thought that the highest particle energies of all would be needed to produce these effects: the kind only obtainable at high-energy particle physics experiments or in extreme astrophysical environments. But in early 2022, strong enough electric fields were created in a simple laboratory setup leveraging the unique properties of graphene, enabling the spontaneous creation of particle-antiparticle pairs from nothing at all. 

The prediction that this should be possible is 70 years old: dating back to one of the founders of quantum field theory, Julian Schwinger. The Schwinger effect is now verified, and teaches us how the Universe truly makes something from nothing.  READ MORE...

Our Understanding of Distance

The researchers discovered that a new theoretical framework to unify Hermitian and 

non-Hermitian physics is established by the duality between non-Hermiticity and curved spaces.

According to traditional thinking, distorting a flat space by bending it or stretching it is necessary to create a curved space. A group of scientists at Purdue University has developed a new technique for making curved spaces that also provides the answer to a physics mystery. 

The team has developed a method using non-Hermiticity, which occurs in all systems coupled to environments, to build a hyperbolic surface and a number of other prototypical curved spaces without causing any physical distortions of physical systems.

“Our work may revolutionize the general public’s understanding of curvatures and distance,” says Qi Zhou, Professor of Physics and Astronomy.

“It has also answered long-standing questions in non-Hermitian quantum mechanics by bridging non-Hermitian physics and curved spaces. These two subjects were assumed to be completely disconnected. 

The extraordinary behaviors of non-Hermitian systems, which have puzzled physicists for decades, become no longer mysterious if we recognize that the space has been curved. 

In other words, non-Hermiticity and curved spaces are dual to each other, being the two sides of the same coin.”

The team’s results were published in the journal Nature Communications in an article titled “Curving the Space by Non-Hermiticity.” Most of the team’s members are employed at Purdue University’s West Lafayette campus. 

The Purdue team is made up of Professor Qi Zhou, Zhengzheng Zhai, a postdoctoral researcher, with graduate student Chenwei Lv serving as the primary author. Professor Ren Zhang from Xi’an Jiaotong University, who is a co-first author of the paper, was a visiting scholar at Purdue when the study was originally started.  READ MORE...

Time Does Not Exist (?)

Does time exist? The answer to this question may seem obvious: Of course it does! Just look at a calendar or a clock.

But developments in physics suggest the non-existence of time is an open possibility, and one that we should take seriously.

How can that be, and what would it mean? It'll take a little while to explain, but don't worry: Even if time doesn't exist, our lives will go on as usual.

A crisis in physics
Physics is in crisis. For the past century or so, we have explained the Universe with two wildly successful physical theories: general relativity and quantum mechanics.

Quantum mechanics describes how things work in the incredibly tiny world of particles and particle interactions. General relativity describes the big picture of gravity and how objects move.

Both theories work extremely well in their own right, but the two are thought to conflict with one another. Though the exact nature of the conflict is controversial, scientists generally agree both theories need to be replaced with a new, more general theory.

Physicists want to produce a theory of "quantum gravity" that replaces general relativity and quantum mechanics, while capturing the extraordinary success of both. Such a theory would explain how gravity's big picture works at the miniature scale of particles.

Time in quantum gravity
It turns out that producing a theory of quantum gravity is extraordinarily difficult.

One attempt to overcome the conflict between the two theories is string theory. String theory replaces particles with strings vibrating in as many as 11 dimensions.  READ MORE...

Backwards in Time

A wild new theory suggests there may be another "anti-universe," running backward in time prior to the Big Bang.  The idea assumes that the early universe was small, hot and dense — and so uniform that time looks symmetric going backward and forward.

If true, the new theory means that dark matter isn't so mysterious; it's just a new flavor of a ghostly particle called a neutrino that can only exist in this kind of universe. And the theory implies there would be no need for a period of "inflation" that rapidly expanded the size of the young cosmos soon after the Big Bang.

If true, then future experiments to hunt for gravitational waves, or to pin down the mass of neutrinos, could answer once and for all whether this mirror anti-universe exists.

Preserving symmetry
Physicists have identified a set of fundamental symmetries in nature. The three most important symmetries are: charge (if you flip the charges of all the particles involved in an interaction to their opposite charge, you'll get the same interaction); parity (if you look at the mirror image of an interaction, you get the same result); and time (if you run an interaction backward in time, it looks the same).

Physical interactions obey most of these symmetries most of the time, which means that there are sometimes violations. But physicists have never observed a violation of a combination of all three symmetries at the same time. If you take every single interaction observed in nature and flip the charges, take the mirror image, and run it backward in time, those interactions behave exactly the same.

This fundamental symmetry is given a name: CPT symmetry, for charge (C), parity (P) and time (T).

In a new paper recently accepted for publication in the journal Annals of Physics, scientists propose extending this combined symmetry. Usually this symmetry only applies to interactions — the forces and fields that make up the physics of the cosmos. But perhaps, if this is such an incredibly important symmetry, it applies to the whole entire universe itself. In other words, this idea extends this symmetry from applying to just the "actors" of the universe (forces and fields) to the "stage" itself, the entire physical object of the universe.

Creating dark matter
We live in an expanding universe. This universe is filled with lots of particles doing lots of interesting things, and the evolution of the universe moves forward in time. If we extend the concept of CPT symmetry to our entire cosmos, then our view of the universe can't be the entire picture.

Instead, there must be more. To preserve the CPT symmetry throughout the cosmos, there must be a mirror-image cosmos that balances out our own. This cosmos would have all opposite charges than we have, be flipped in the mirror, and run backward in time. Our universe is just one of a twin. Taken together, the two universes obey CPT symmetry.

The study researchers next asked what the consequences of such a universe would be.  They found many wonderful things.  READ MORE...

Lost in Spacetime

Einstein’s forgotten twisted universe

There’s a kind of inevitability about the fact that, if you write a regular newsletter about fundamental physics, you’ll regularly find yourself banging on about Albert Einstein. As much as it comes with the job, I also make no apology for it: he is a towering figure in the history of not just fundamental physics, but science generally.

A point that historians of science sometimes make about his most monumental achievement, the general theory of relativity, is that, pretty much uniquely, it was a theory that didn’t have to be. When you look at the origins of something like Charles Darwin’s theory of evolution by natural selection, for example – not to diminish his magisterial accomplishment in any way – you’ll find that other people had been scratching around similar ideas surrounding the origin and change of species for some time as a response to the burgeoning fossil record, among other discoveries.


Even Einstein’s special relativity, the precursor to general relativity that first introduced the idea of warping space and time, responded to a clear need (first distinctly identified with the advent of James Clerk Maxwell’s laws of electromagnetism in the 1860s) to explain why the speed of light appeared to be an absolute constant.

When Einstein presented general relativity to the world in 1915, there was nothing like that. We had a perfectly good working theory of gravity, the one developed by Isaac Newton more than two centuries earlier. True, there was a tiny problem in that it couldn’t explain some small wobbles in the orbit of Mercury, but they weren’t of the size that demanded we tear up our whole understanding of space, time, matter and the relationship between them. But pretty much everything we know (and don’t know) about the wider universe today stems from general relativity: the expanding big bang universe and the standard model of cosmology, dark matter and energy, black holes, gravitational waves, you name it.

So why am I banging on about this? Principally because, boy, do we need a new idea in cosmology now – and in a weird twist of history, it might just be Einstein who supplies it. I’m talking about an intriguing feature by astrophysicist Paul M. Sutter in the magazine last month . It deals with perhaps general relativity’s greatest (perceived, at least) weakness – the way it doesn’t mesh with other bits of physics, which are all explained by quantum theory these days. The mismatch exercised Einstein a great deal, and he spent much of his later years engaged in a fruitless quest to unify all of physics.  READ MORE...

Using A Drunkard's Walk

(Image credit: Adrienne Bresnahan/Getty Images)

A physics problem that has plagued science since the days of Isaac Newton is closer to being solved, say a pair of Israeli researchers. The duo used "the drunkard's walk" to calculate the outcome of a cosmic dance between three massive objects, or the so-called three-body problem.

For physicists, predicting the motion of two massive objects, like a pair of stars, is a piece of cake. But when a third object enters the picture, the problem becomes unsolvable. That's because when two massive objects get close to each other, their gravitational attraction influences the paths they take in a way that can be described by a simple mathematical formula. But adding a third object isn't so simple: Suddenly, the interactions between the three objects become chaotic. 

Instead of following a predictable path defined by a mathematical formula, the behavior of the three objects becomes sensitive to what scientists call "initial conditions" — that is, whatever speed and position they were in previously. Any slight difference in those initial conditions changes their future behavior drastically, and because there's always some uncertainty in what we know about those conditions, their behavior is impossible to calculate far out into the future. 

In one scenario, two of the objects might orbit each other closely while the third is flung into a wide orbit; in another, the third object might be ejected from the other two, never to return, and so on.

In a paper published in the journal Physical Review X, scientists used the frustrating unpredictability of the three-body problem to their advantage.

"[The three-body problem] depends very, very sensitively on initial conditions, so essentially it means that the outcome is basically random," said Yonadav Barry Ginat, a doctoral student at Technion-Israel Institute of Technology who co-authored the paper with Hagai Perets, a physicist at the same university. "But that doesn't mean that we cannot calculate what probability each outcome has."

To do that, they relied on the theory of random walks — also known as "the drunkard's walk." The idea is that a drunkard walks in random directions, with the same chance of taking a step to the right as taking a step to the left. If you know those chances, you can calculate the probability of the drunkard ending up in any given spot at some later point in time.

So in the new study, Ginat and Perets looked at systems of three bodies, where the third object approaches a pair of objects in orbit. In their solution, each of the drunkard's "steps" corresponds to the velocity of the third object relative to the other two.

"One can calculate what the probabilities for each of those possible speeds of the third body is, and then you can compose all those steps and all those probabilities to find the final probability of what's going to happen to the three-body system in a long time from now," meaning whether the third object will be flung out for good, or whether it might come back, for instance, Ginat said.  READ MORE...

Quantum Spin Liquid

A solid is made of atoms that are, more or less, locked in an ordered structure. A liquid, on the other hand, is made of atoms that can flow freely around and past each other. But imagine atoms that stay unfrozen, like those in a liquid–but which are in a constantly changing magnetic mess.

What you have then is a never-before-seen state of matter, a state of quantum weirdness called a quantum spin liquid. Now, by carefully manipulating atoms, researchers have managed to create this state in the laboratory. The researchers published their work in the journal Science on December 2.

Scientists had discussed theories about spin liquids for years. “But we really got very interested in this when these theorists, here at Harvard, finally found a way to actually generate the quantum spin liquids,” says Giulia Semeghini, a physicist and postdoc at Harvard University, who coordinated the research project and was one of the paper authors.

Under extreme conditions not typically found on Earth, the rules of quantum mechanics can twist atoms into all sorts of exotica. Take, for instance, degenerate matter, found in the hearts of dead stars like white dwarfs or neutron stars, where extreme pressures cook atoms into slurries of subatomic particles. Or, for another, the Bose-Einstein condensate, in which multiple atoms at very low temperatures sort of merge together to act as one (its creation won the 2001 Nobel Prize in Physics).  READ MORE...

A Conscious Universe

(Image credit: NASA/Shutterstock)

As humans, we know we are conscious because we experience and feel things. Yet scientists and great thinkers are unable to explain what consciousness is and they are equally baffled about where it comes from.

"Consciousness — or better, conscious experience — is obviously a part of reality," said Johannes Kleiner, a mathematician and theoretical physicist at the Munich Center For Mathematical Philosophy, Germany. "We're all having it but without understanding how it relates to the known physics, our understanding of the universe is incomplete."

With that in mind, Kleiner is hoping math will enable him to precisely define consciousness. Working with colleague Sean Tull, a mathematician at the University of Oxford, U.K., the pair are being driven, to some degree, by a philosophical point of view called panpsychism.

This claims consciousness is inherent in even the tiniest pieces of matter — an idea that suggests the fundamental building blocks of reality have conscious experience. Crucially, it implies consciousness could be found throughout the universe.  READ MORE...

Constructor Theory

Constructor Theory is a new approach to formulating fundamental laws in physics. Instead of describing the world in terms of trajectories, initial conditions and dynamical laws, in constructor theory laws are about which physical transformations are possible and which are impossible, and why. 

This powerful switch has the potential to bring all sorts of interesting fields, currently regarded as inherently approximative, into fundamental physics. These include the theories of information, knowledge, thermodynamics, and life.

Physics Mystery Solved

Technion researchers have found an effective solution to the famous age-old, three-body problem in physics.

The three-body problem is one of the oldest problems in physics: it concerns the motions of systems of three bodies – like the Sun, Earth, and the Moon – and how their orbits change and evolve due to their mutual gravity. The three-body problem has been a focus of scientific inquiry ever since Newton.

When one massive object comes close to another, their relative motion follows a trajectory dictated by their mutual gravitational attraction, but as they move along, and change their positions along their trajectories, the forces between them, which depend on their mutual positions, also change, which, in turn, affects their trajectory et cetera. For two bodies (e.g. like Earth moving around the Sun without the influence of other bodies), the orbit of the Earth would continue to follow a very specific curve, which can be accurately described mathematically (an ellipse).

However, once one adds another object, the complex interactions lead to the three-body problem, namely, the system becomes chaotic and unpredictable, and one cannot simply specify the system evolution over long time-scales. Indeed, while this phenomenon has been known for over 400 years, ever since Newton and Kepler, a neat mathematical description for the three-body problem is still lacking.

Star orbits in a three-body system. Credit: Technion

In the past, physicists – including Newton himself – have tried to solve this so-called three-body problem; in 1889, King Oscar II of Sweden even offered a prize, in commemoration of his 60th birthday, to anybody who could provide a general solution. In the end, it was the French mathematician Henri Poincaré who won the competition. He ruined any hope for a full solution by proving that such interactions are chaotic, in the sense that the final outcome is essentially random; in fact, his finding opened a new scientific field of research, termed chaos theory.  READ MORE...

Was Einstein Wrong?

As in history, revolutions are the lifeblood of science. Bubbling undercurrents of disquiet boil over until a new regime emerges to seize power. Then everyone's attention turns to toppling their new ruler. The king is dead, long live the king.

This has happened many times in the history of physics and astronomy. First, we thought Earth was at the center of the solar system — an idea that stood for over 1,000 years. Then Copernicus stuck his neck out to say that the whole system would be a lot simpler if we are just another planet orbiting the sun. Despite much initial opposition, the old geocentric picture eventually buckled under the weight of evidence from the newly invented telescope.

Then Newton came along to explain that gravity is why the planets orbit the sun. He said all objects with mass have a gravitational attraction towards each other. According to his ideas we orbit the sun because it is pulling on us, the moon orbits Earth because we are pulling on it. 

Newton ruled for two-and-a-half centuries before Albert Einstein turned up in 1915 to usurp him with his General Theory of Relativity. This new picture neatly explained inconsistencies in Mercury's orbit, and was famously confirmed by observations of a solar eclipse off the coast of Africa in 1919.  TO READ MORE, CLICK HERE...

Hawking's Black Holes Paradox

Netta Engelhardt puzzles over the fates of black holes in her office at 

the Massachusetts Institute of Technology.

In 1974, Stephen Hawking calculated that black holes’ secrets die with them. Random quantum jitter on the spherical outer boundary, or “event horizon,” of a black hole will cause the hole to radiate particles and slowly shrink to nothing. Any record of the star whose violent contraction formed the black hole — and whatever else got swallowed up after — then seemed to be permanently lost.

Hawking’s calculation posed a paradox — the infamous “black hole information paradox” — that has motivated research in fundamental physics ever since. On the one hand, quantum mechanics, the rulebook for particles, says that information about particles’ past states gets carried forward as they evolve — a bedrock principle called “unitarity.” 

But black holes take their cues from general relativity, the theory that space and time form a bendy fabric and gravity is the fabric’s curves. Hawking had tried to apply quantum mechanics to particles near a black hole’s periphery, and saw unitarity break down.

So do evaporating black holes really destroy information, meaning unitarity is not a true principle of nature? Or does information escape as a black hole evaporates? Solving the information paradox quickly came to be seen as a route to discovering the true, quantum theory of gravity, which general relativity approximates well everywhere except black holes.

In the past two years, a network of quantum gravity theorists, mostly millennials, has made enormous progress on Hawking’s paradox. One of the leading researchers is Netta Engelhardt, a 32-year-old theoretical physicist at the Massachusetts Institute of Technology. 

She and her colleagues have completed a new calculation that corrects Hawking’s 1974 formula; theirs indicates that information does, in fact, escape black holes via their radiation. She and Aron Wall identified an invisible surface that lies inside a black hole’s event horizon, called the “quantum extremal surface.” 

In 2019, Engelhardt and others showed that this surface seems to encode the amount of information that has radiated away from the black hole, evolving over the hole’s lifetime exactly as expected if information escapes.  READ MORE

Quantum Entanglement

 

Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently of the others, even when the particles are separated by a large distance—instead, a quantum state must be described for the system as a whole.

Measurements of physical properties such as position, momentum, spin, and polarization, performed on entangled particles are found to be appropriately correlated. For example, if a pair of particles are generated in such a way that their total spin is known to be zero, and one particle is found to have clockwise spin on a certain axis, the spin of the other particle, measured on the same axis, will be found to be counterclockwise, as to be expected due to their entanglement. However, this behavior gives rise to paradoxical effects: any measurement of a property of a particle can be seen as acting on that particle (e.g., by collapsing a number of superposed states) and will change the original quantum property by some unknown amount; and in the case of entangled particles, such a measurement will be on the entangled system as a whole. It thus appears that one particle of an entangled pair “knows” what measurement has been performed on the other, and with what outcome, even though there is no known means for such information to be communicated between the particles, which at the time of measurement may be separated by arbitrarily large distances.


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Such phenomena were the subject of a 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen, and several papers by Erwin Schrödinger shortly thereafter, describing what came to be known as the EPR paradox.

The EPR thought experiment, performed with electron–positron pairs. A source (center) sends particles toward two observers, electrons to Alice (left) and positrons to Bob (right), who can perform spin measurements.


Einstein and others considered such behavior to be impossible, as it violated the local realist view of causality (Einstein referring to it as “spooky action at a distance”) and argued that the accepted formulation of quantum mechanics must therefore be incomplete. Later, however, the counterintuitive predictions of quantum mechanics were verified experimentally.


Experiments have been performed involving measuring the polarization or spin of entangled particles in different directions, which—by producing violations of Bell’s inequality—demonstrate statistically that the local realist view cannot be correct. This has been shown to occur even when the measurements are performed more quickly than light could travel between the sites of measurement: there is no lightspeed or slower influence that can pass between the entangled particles. Recent experiments have measured entangled particles within less than one hundredth of a percent of the travel time of light between them. According to the formalism of quantum theory, the effect of measurement happens instantly.It is not possible, however, to use this effect to transmit classical information at faster-than-light speeds.

Quantum entanglement is an area of extremely active research by the physics community, and its effects have been demonstrated experimentally with photons, neutrinos, electrons, molecules the size of buckyballs, and even small diamonds. Research is also focused on the utilization of entanglement effects in communication and computation.