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Category Archives: Quantum Physics
Posted: August 6, 2017 at 3:40 am
Major Grant From National Science Foundation Funds Dos Santos Study of Interacting Quantum Systems
How can transitions between different states of matterfor instance, liquids, gasses and solidsbe harnessed to create new kinds of matter for novel technologies? This is the focus of new research by Dr. Lea Ferreira dos Santos, professor of physics at Stern College for Women, whose project, Physics of Interacting Quantum Systems with Phase Transitions, has been funded by a three-year $190,000 grant from the National Science Foundations (NSF) Division of Materials Research.
Dr. Lea Ferreira dos Santos
We are all very well familiar with thermal phase transitions, said dos Santos. The best example is the transition from water to ice. In the liquid phase, the molecules move freely. As the water is cooled, the molecules slow down and begin to arrange themselves into a lattice structure, eventually resulting in the solid phase.
At absolute zero temperature, according to the laws of classical physics (that is, the laws that describe large objects, like human beings), molecules would stop moving and the phase transition would stabilize. However, at low temperatures, classical physics is no longer valid and quantum physics takes over. According to the laws of quantum physics, phase transitions can happen even at the absolute zero temperature. These are known as quantum phase transitions. This NSF grant will help in trying to identify and characterize these transitions.
Although seemingly esoteric, this research can have important real-world applications: For example, a specific phase may be associated with good or bad conduction of energy or electricity. New phases of matter are critical components of emerging technologies and may revolutionize how we use and produce energy, may lead to new electronic devices and may constitute the building blocks of quantum computers. The potential economic and social impact of the discovery of novel phases of matter is immense.
For dos Santos, this is part of what makes the study of physics endlessly intriguing. After so many years studying the subject, I am still fascinated by quantum mechanics. As Nobel Laureate Richard Feynman once said: Nobody understands it. However, over the years, we have been learning how to control and make use of its properties. Through this practical process, we may eventually unveil also its fundamental mysteries. I get a thrill every time I manage to put a couple of pieces of the big puzzle together.
Another welcome result is that this research, as stated in the proposals abstract, will also foster the participation of women in physics and improve the educational infrastructure at the Stern College for Women of Yeshiva University by offering new research opportunities and training in core areas of physics and in computational methods. In one of the projectsrelated to this research dos Santos will be working with three of her former students, who are now physics teachers in high schools for girls, to create a webpage designed for posting computer programs from courses and research findings that will contribute to the integration of teaching and research at other undergraduate institutions.
Posted: at 3:40 am
MORE than 20 years have passed since Pan Jianwei was first astonished by the quantum world. Pondering the strange micro world has carved deep lines in the quantum physicists forehead.
People still dont fully understand a phenomenon such as quantum superposition and quantum entanglement, but Pan is shining some light in the field, manipulating microscopic particles and applying the magical quantum characters to develop quantum cryptography and quantum computing.
The worlds first quantum satellite, Quantum Experiments at Space Scale, launched by China in 2016, has realized the distribution of entangled photon pairs over 1,200 kilometers. It has proved that quantum entanglement, described by Albert Einstein as a spooky action, still exists at such a distance.
As the satellites lead scientist, Pan has a greater goal: to test quantum entanglement between Earth and the moon at a distance over 300,000km, which may help research on gravity and the structure of spacetime.
Pan is a science legend. When his co-authored article about the first quantum teleportation was selected by academic journal Nature as one of the 21 classic papers for physics over the past century, he was only 29 years old. When he was appointed a professor of the University of Science and Technology of China, he was 31. When he was elected an academician of the Chinese Academy of Sciences, he was 41, the youngest academician at that time. When he won the first prize of National Natural Science, he was 45.
The star scientist and media celebrity says science should be in the spotlight rather than scientists.
Born on March 11, 1970 in Dongyang City, east Chinas Zhejiang Province, Pan was an excellent student and a playful boy. He went to study in the University of Science and Technology of China in Hefei City in 1987, where academic competition was fierce.
Wu Jian, Pans classmate in university and now a scientist in Chinas Dark Matter Particle Explorer Satellite project, recalls that he once gave Pan an ugly haircut, but he was not angry. Pan was happy-go-lucky.
In 1990, Pan first came into contact with quantum mechanics, which totally confused him. How can there be such a phenomenon as quantum superposition? Its like a person being in Shanghai and Beijing at the same time.
Pan almost failed in the midterm exam on quantum mechanics.
Desperately trying to figure it out, Pan chose quantum mechanics as his research direction and hes still entangled with it. He realized all the theories about quantum physics had to be tested in experiments. However, China lacked the conditions to do such experiments in the 1990s.
After graduation in 1996, Pan went to Austria to do his PhD at the University of Innsbruck, studying with Anton Zeilinger, a world-renowned quantum physicist.
When Pan came to me as a young student, he was a theoretical physicist. He had not done any experiments before. But I very soon realized he had the gift for doing experiments, Zeilinger said.
I assigned him to do the experiment on teleportation with a group, a very complicated experiment. He accepted it and immediately got started.
He was full of enthusiasm. Soon he was the leading person in the experiment. When there was a problem, he was never discouraged. He always saw it as motivation to do something that had not been done before, Zeilinger says.
He was optimistic, always found solutions to problems, and always wanted to work to find something new, says Zeilinger.
He always got along with his colleagues. Now he is a global leader in the field of quantum physics. Im very proud of him, said Zeilinger. I encouraged him to go back to China. Because I could see there was a big opportunity for him in China.
After mastering advanced quantum technology, Pan returned to the University of Science and Technology of China in 2001 to establish a quantum physics and quantum information laboratory, hoping China could quickly catch up with the pace of development in the emerging field of quantum technology.
In order to make breakthroughs in quantum information research, the lab needed scientists with different academic backgrounds.
Pan sent his students to study in Germany, Britain, the United States, Switzerland and Austria to obtain the most advanced knowledge in specialties such as cold atoms, precision measurement and multiphoton entanglement manipulation.
So far, Pan and his team have published about 200 articles in authoritative academic journals including Science, Nature and Physical Review Letters, indicating that China is at the global forefront of quantum communication.
In experiments, there is inevitably frustration. But Pan says they need patience and the key is to have fun in the process. Pursuing the secrets of the quantum physics brings me calm and peace. Its like walking on the lawn in the spring sunshine, he said.
A fan of classical music, Pan says music and science both give him tranquility and happiness. In college, he read the essays of Einstein. For me, Einsteins essays are the most profound and beautiful sound of nature, he said.
The research of quantum physics has an impact on my personality and thoughts. Quantum mechanics tells me its very hard to define right and wrong, good and bad. It makes me tolerant.
He also takes part in many activities to promote science in China. Development driven by innovation is one of Chinas core strategies. Building an innovation-oriented country requires nurturing the publics interest in science, Pan said.
He believes China can catch up with Japan in about two decades in the field of science and technology, as long as the research funds are allocated and used by the best Chinese scientists properly.
The experiments on the QUESS satellite are the most important scientific research in my life, said Pan.
However, the quantum world remains mysterious. Will the spooky action that confused even Einstein extend in space without limit?
In theory, this bizarre connection can exist over any distance, but we think quantum entanglement might be affected by gravity. The different models need to be tested at a longer distance, and the boundary between quantum physics and the theory of relativity and study the structure of spacetime and gravity should be explored, Pan said.
Originally posted here:
Posted: July 17, 2017 at 4:40 am
Every time physicists find a new particle, the Standard Model gets one step closer to becoming a Super Model.
There’s always talk of whether the new arrival fits in, or stands out, or matches the model’s predictions. Everything gets related back to this “Bible of quantum physics”.
The Standard Model isn’t mystical, however. It’s purely, beautifully mathematical.
Yet for all its predictive power, it’s not perfect it can’t explain gravity, dark matter or dark energy. The real goal of particle-smashing physicists is to break it.
Only by finding new particles that weren’t predicted by the Standard Model, and can’t fit inside it, will we move to a new and improved model one that doesn’t have big gaps where gravity and the dark parts of physics should be.
Forty years ago scientists pulled everything they knew about quantum physics into one massive equation the Standard Model of particle physics.
If you can follow the maths, the Standard Model is a stunning piece of work. It’s like a how-to guide for the particles and forces that operate at the tiny quantum scale including all the atoms that makes up people, plants, planets and stars.
(Luckily for the non-physicists among us, it also comes in handy table form and our handy video above.)
The really big deal with the Standard Model is that it didn’t just describe particles that were already known, like the electron and quarks that make up atoms.
It did something much more important it predicted some new particles too, including the Higgs boson.
Testing predictions is at the heart of science, and every one of the particles that the Standard Model predicted has since been discovered. The Higgs was the last to be found, in 2012.
That ability to predict and explain every aspect of the quantum world makes the Standard Model a bit of a superstar.
But while it’s undeniably brilliant, no one has ever pretended the Standard Model is perfect.
The most obvious flaw in the Standard Model was there from the beginning it could never account for gravity, the force that rules at the macro scale. That’s not the Standard Model’s fault; quantum theory and Einstein’s gravitational theory just don’t work together.
But gravity’s not the only thing missing from the model.
The Standard Model can’t account for the dark matter and dark energy that make up a cool 95 per cent of the universe either.
And most bizarre of all, it comes right out and says that universe shouldn’t exist at least not the way it is. The Model predicts that matter and antimatter should have been produced in equal amounts at the birth of the universe and annihilated immediately thereafter, leaving one enormous sea of light.
Thankfully that hasn’t exactly gone to plan either; there’s matter all over the place, including little old you and me.
Some of the Standard Model’s other shortcomings are on a much less grand and galactic scale.
One of the best-known problems is that it predicts that one family of particles neutrinos should have zero mass. But as the recipients of the 2015 Nobel Prize in Physics can attest, these ridiculously small particles that travel at near light speed have very tiny, but not zero, masses.
Far from being considered a failure for its shortcomings, the Standard Model has always been appreciated by physicists for what it is: a great start to understanding and possibly unifying all of physics.
And in the decades since it appeared, theoretical physicists have thrown up a pile of possible additions to the Model, trying to account for the things it can’t explain.
These mostly involve new particles that are much heavier than the known quarks, leptons and bosons. In supersymmetry, the best known ‘upgrade’ to the model, every particle has a much heavier partner, called a sparticle, which helps patch the current gaps.
Theories are great, but if we want to find out which, if any, of the various upgrades to the Standard Model are right, we really need to find new particles. And that’s where particle accelerators come in.
The Higgs boson was found at the Large Hadron Collider in 2012. With higher energy collisions heavier particles could also be discovered.
The Higgs boson was found at the Large Hadron Collider in 2012. With higher energy collisions heavier particles could also be discovered.
Particle accelerators smash together tiny bits of matter everything from electrons to whole atoms at almost light speed. When that happens, the energy of the collision can be converted into matter. (Einstein’s E=mc2 tells us that mass and energy are two sides of the same deal).
And if there’s enough energy it can form a heavier particle than we’ve ever observed.
Heavy particles made in colliders are generally unstable they only exist for an incredibly short time before breaking down into lighter, more stable bits. But those telltale leftovers are exactly the thing physicists look for in particle accelerator experiments all over the world.
So far, new particles haven’t been able to ‘break’ the Standard Model; they just keep opening new chapters of it.
Knowing the mass and energy of these particles will favour some of the new theoretical additions, and knock others out of contention.
The more new particles we find, the narrower the field for refinements to the model.
Any new, heavy particles that are found will result in some new characters in the Standard Model equation, and the beginnings of an extra row or column in the accompanying table. This ‘Standard Model Plus’ could account for the mass of neutrinos, the antimatter/matter issue, dark matter and dark energy.
But accounting for gravity won’t happen without shifting to a new theory altogether one that accounts for all known particles and phenomena as well as the current model does, but that can work with gravity as well.
And theories of quantum gravity won’t be validated by particle accelerators any time soon. The energies required to test them are well beyond the range of even the very biggest atom smashers.
For now, a grand unified theory of the universe that ties in quantum and gravitational scales appears to be out of reach. If we ever find it, we’ll be in serious Super Model territory.
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Posted: at 4:40 am
July 12, 2017 The different spatial layout of the atoms in the iron lattice and in the nickel lattice is responsible for their different physical behaviour under extreme conditions. The coloured graphic shows the electronic dispersion of nickel in the region which is responsible for this behaviour. Credit: Michael Karolak
Without a magnetic field life on Earth would be rather uncomfortable: Cosmic particles would pass through our atmosphere in large quantities and damage the cells of all living beings. Technical systems would malfunction frequently and electronic components could be destroyed completely in some cases.
Despite its huge significance for life on our planet, it is still not fully known what creates the Earth’s magnetic field. There are various theories regarding its origin, but a lot of experts consider them to be insufficient or flawed. A discovery made by scientists from Wrzburg might provide a new explanatory angle. Their findings were published in the current issue of the journal Nature Communications. Accordingly, the key to the effect could be hidden in the special structure of the element nickel.
Contradiction between theory and reality
“The standard models for Earth’s magnetic field use values for the electric and thermal conductivity of the metals inside our planet’s core that cannot square with reality,” Giorgio Sangiovanni says; he is a professor at the Institute for Theoretical Physics and Astrophysics at the University of Wrzburg. Together with PhD student Andreas Hausoel and postdoc Michael Karolak, he is in charge of the international collaboration that was published recently. Among the participants are Alessandro Toschi and Karsten Held of TU Wien, who are long-term cooperation partners of Giorgio Sangiovanni, and scientists from Hamburg, Halle (Saale) and Yekaterinburg in Russia.
At Earth’s centre at a depth of about 6,400 km, there is a temperature of 6,300 degrees Celsius and a pressure of about 3.5 million bars. The predominant elements, iron and nickel, form a solid metal ball under these conditions which makes up the inner core of the Earth. This inner core is surrounded by the outer core, a fluid layer composed mostly of iron and nickel. Flowing of liquid metal in the outer core can intensify electric currents and create Earth’s magnetic field at least according to the common geodynamo theory. “But the theory is somewhat contradictory,” Giorgio Sangiovanni says.
Band-structure induced correlation effects
“This is because at room temperature iron differs significantly from common metals such as copper or gold due to its strong effective electron-electron interaction. It is strongly correlated,” he declares. But the effects of electron correlation are attenuated considerably at the extreme temperatures prevailing in Earth’s core so that conventional theories are applicable. These theories then predict a much too high thermal conductivity for iron which is at odds with the geodynamo theory.
With nickel things are different. “We found nickel to exhibit a distinct anomaly at very high temperatures,” the physicist explains. “Nickel is also a strongly correlated metal. Unlike iron, this is not due to the electron-electron interaction alone, but is mainly caused by the special band structure of nickel. We baptised the effect ‘band-structure induced correlation’.” The band structure of a solid is only determined by the geometric layout of the atoms in the lattice and by the atom type.
Iron and nickel in Earth’s core
“At room temperature, iron atoms will arrange in a way that the corresponding atoms are located at the corners of an imaginary cube with one central atom at the centre of the cube, forming a so-called bcc lattice structure,” Andreas Hausoel adds. But as temperature and pressure increase, this structure changes: The atoms move together more closely and form a hexagonal lattice, which physicists refer to as an hcp lattice. As a result, iron looses most of its correlated properties.
But not so with nickel: “In this metal, the atoms are as densely packed as possible in the cube structure already in the normal state. They keep this layout even when temperature and pressure become very large,” Hausoel explains. The unusual physical behaviour of nickel under extreme conditions can only be explained by the interaction of this geometric stability and the electron correlations originating from this geometry. Despite the fact that scientists have neglected nickel so far, it seems to play a major role in Earth’s magnetic field.
Decisive hint from geophysics
The goings-on inside Earth’s core are not the actual focus of research at the Departments of Theoretical Solid-state Physics of the University of Wrzburg. Rather Sangiovanni, Hausoel and their colleagues concentrate on the properties of strongly correlated electrons at low temperatures. They study quantum effects and so-called multi-particle effects which are interesting for the next generation of data processing and energy storage devices. Superconductors and quantum computers are the keywords in this context.
Data from experiments are not used in this kind of research. “We take the known properties of atoms as input, include the insights from quantum mechanics and try to calculate the behaviour of large clusters of atoms with this,” Hausoel says. Because such calculations are highly complex, the scientists have to rely on external support such as the SUPERMUC supercomputer at the Leibniz Supercomputing Centre (LRZ) in Garching.
And what’s the Earth’s core got to do with this? “We wanted to see how stable the novel magnetic properties of nickel are and found them to survive even very high temperatures,” Hausoel says. Discussions with geophysicists and further studies of iron-nickel alloys have shown that these discoveries could be relevant for what is happening inside Earth’s core.
Explore further: Splitting water for the cost of a nickel
More information: A. Hausoel et al. Local magnetic moments in iron and nickel at ambient and Earth’s core conditions, Nature Communications (2017). DOI: 10.1038/ncomms16062
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Posted: July 14, 2017 at 5:43 am
Of the five electric guitars owned by experimental quantum physicist David Reilly, he likes this one the best. Themustard-yellow Fender Telecaster has two pickups, a maple fretboard and country-rock twang. When he’s not in the laboratory pondering the mysteries of life, the universe and everything, he likes to lay down tracks on his axe at home, alone. “It’s a fantastic way of switching off.”
Electric guitar and quantum science are surprisingly similar, he says. To start with, neither pursuit presents an inherentlystable career path. “There are many scientists I know who drive taxis because it’s not easy to get a job, like musicians,” he says.
Professor Reilly directs the quantum nanoscience laboratory at the University of Sydney and spends timecogitating”spooky” questions, such as: “What does the world look like when I am not observing it?” and “What is the ’80s sound?” He’s intoJohn Mayer and quantum entanglement. Steely Dan and cryogenic electronics.
Music and quantum physics are quite alikemathematically, he says. “The physics of sound and the construction of tonal systems, such as the way in which a guitar is laid out, captures a lot of the essence of what quantum physics is,” he says. “Quantum physics tells us the world is made up of vibrations or waves, just like the waves when you pluck a guitar string.”
The rockstar scientist in blue jeans and brown suede shoes who is left-handed but usesregular right-handedguitars will discuss such parallels while playing on stage at the City Recital Hall on August 14, as part of the This Sounds Like Sciencefree lunchtime series.
“There’s an enormous amount of electronics and instrumentation and experimental physics wrapped up in music,” he says. “It’s total nerd heaven.”
Professor Reilly started playing guitar at the age of nine and practised every day until his late teens, when he had to choose between the lotof a musician or a scientist. Do you ever wish you were a professional rock guitarist, I ask. “At certain times I flirt with that idea,” he says.
But quantumphysics and guitar riffs can feed off each other, he adds. “Science is very much like music, it’s about thinking outside the box. Somehow, tapping other parts of your brain musically opens up different thought processes.
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“A lot of people talk about having ideas in the shower. I would say that playing guitar gives me scientific ideas.”
He has played in various bands over the years, at wedding receptionsand in pubs. The 1238-seat City Recital Hall, in Angel Place, will be his largest gigby far. He has something special planned for the show. “My hope is that I can tune the configuration of the guitar strings to match that of the hydrogen atom,” he says.
“Can you tune your guitar to hydrogen or helium or lithium? I am not sure how good that is going to sound.”
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Posted: at 5:43 am
Earths magnetic field does way more than guide our compasses and cause occasional worry. Its part of the reason theres life at all on this planetit protects us from harmful solar radiation that might otherwise blow our ozone layer away.
But theres still a lot about the magnetic field scientists dont understand. Most importantly, theyre having trouble figuring out why its so strong. One team decided to take a closer look at the role of the individual elements inside the planet that are thought to influence the field. Turns out, the way nickel behaves at the smallest scales might help explain the magnetic fields strength, to the point that some existing models would need to be rethought. And understanding the Earths magnetic field has implications for everything that relies on it, including activities that require drilling underground.
This is a new idea put into the geophysics research line that nickel has been neglected for the explanation of the geodynamo, the mechanism for creating the magnetic field, study author Giorgio Sangiovanni from the Institute for Theoretical Physics and Astrophysics at the University of Wrzburg in Germany told Gizmodo.
At its most basic level, the Earth probably gets its magnetic field from temperature gradients in the outer core causing metal to convectthis is more or less the way water moves around in a pot of boiling water. Metals can conduct electricity. So, moving metals combined with Earths rotation could create tubes of electric current that point to the poles. Loops of electric current generate magnetic fields through them, so the entire Earth ends up looking like a magnet where the poles align with the tops and bottoms of the tubes.
The problem, which people have been talking about for a while now, is that theres another way for heat to transfer between elements around the core, conduction, that doesnt require metals to physically move. In that case, the energy just gets passed between the atoms as they bump into one another, like how heat travels down the handle of the pot of water youre boiling. But if the outer core loses too much heat through conduction, then theres not enough energy to drive the convection creating the magnetic field. Scientists think that might be the case, and are looking for a source of extra energy that could generate the magnetic field they observe.
Sangiovanni and his colleagues decided to make calculations about the metals in the inner core, to see if they could find some of the missing energy. But unlike the outer core, which is mostly iron, the inner core is 20 percent nickel. The team decided to examine how nickel and irons specific quantum mechanical properties in the Earths solid core impact the magnetic field.
These properties arent fundamental enough to require you to bend over backward imagining Schrdingers cat. They describe the structure of nickel and iron atoms at high temperatures, how electrons interact in collections of these atoms, and how these elements behaviors change at high pressures. It turns out that nickels shape in a solid slows its electrons down. The electrons also interact and scatter off of each other, preventing nickel from being a good conductor of heat, according to the paper published yesterday in Nature Communications. Iron, meanwhile, has a high conductivity at the temperatures and pressures found in the inner core.
In short, the researchers think nickel could reduce the overall conductivity of the core, causing it to retain extra energy that drives convection. And this new insight might have a large enough effect that models of the Earths magnetic field need some reconsidering.
But the researchers findings cant be taken as fact yetthey still need to calculate other properties relating to how nickel conducts heat. But it is promising, said Sangiovanni. Well see after we calculate other important observables, like the thermal and electrical conductivity.
Sangiovanni said that others he spoke to were surprisedmany folks are looking at how lighter elements like silicon influence the physics of Earths core. I would say that people for a long time have discussed the possible presence of nickel in the Earths core, Dario Alf, physics professor at University College, London told Gizmodo, but no one has really discussed it in the way Giorgios paper points out, the effect of nickel on the conductivity of the core.
All that being said, just take solace in the fact that if you dont think you understand the Earths magnetic field, scientists arent completely sure how it works, either.
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Posted: at 5:43 am
One of the most well-accepted physical theories makes no logical sense. Quantum mechanics, the theory that governs the smallest possible spaces, forces our human brains to accept some really wacky, uncomfortable realities. Maybe we live in a world where certain observations can force our universe to branch into multiple ones. Or maybe actions in the present influence things earlier in time.
A team of physicists did some thinking, and realized this latter idea, called retrocausality, is a consequence of certain interpretations of quantum mechanics, and therefore, certain interpretations of the nature of reality. Their new paper is more of a what-if, an initial look at how to make some of those quantum mechanical interpretations work. Some people I asked thought the work was important, some thought it didnt matter. Others felt their own interpretation of quantum mechanics avoids the problems posed by the new paper. But no matter what, quantum mechanics will force us to make some uncomfortable conclusions about the world.
The foundations of quantum theory are very controversial. We all agree how to use the theory but theres no consensus about the reality it gives us, study author Matthew Leifer from Chapman University told Gizmodo. This is an unusual situation for a theory in physics, since other theories are mostly based on intuitive things we can see and test. Quantum mechanics math, and its predictions, describe the world perfectly, but its sort of impossible to fully grasp whats actually happening beyond the equations.
Quantum mechanics starts with the observation that at the smallest scale, stuff, whether it be light or a piece of an atom, can act simultaneously like a wave and a particle. That means that scientists deal with some level of probability when it comes to tiny things. Send one electron through a pair of parallel slits in a barrier, and youll see it hit the wall behind the barrier like a dot. But if you send many electrons, youll see a striped pattern as if they traveled like a light wave. You cant predict exactly where one electron will hit, but you can create a list of the most likely spots.
Trouble is, describing particles with probabilities leads to some messy stuff. If you have two particles interacting and ones innate physical properties relies on the others, then their associated probabilities, and therefore their identities, are intertwined. As an example, lets say there are two bags, and each has one of two balls, red or green. You give a bag to your friend. Quantum mechanics only gives the probabilities that your bag contains either ball color, and thats all you know before making the observation. At human scales, each bag already contains a red or green ball. But on the particle scale, quantum mechanics says both balls are red and green at the same timeuntil you look.
Thats weird on its own, but it gets worse. If you look at your ball, the other ball automatically takes on the other color. How does the other ball know that you looked? Maybe there is hidden physics, or faster-than-light travel that allows the information to be communicated. One popular interpretation is that we live in a multiverse. In that case, the probabilities dont say anything about the ball, but about which universe we live in. Seeing a certain ball color just means that youre in the universe where your bag had the green ball. In the other universe, you saw a red ball.
Quantum mechanics is weird as hell, where the rules of the world you experience dont apply. Even
So, researchers want to know which of these interpretations is correct. In their new paper, they specifically tackled cases where observing the first ball directly influences the ball in the other bag, through some form of communication. At first glance, this requires information to travel faster than the speed of light. And that sucks, because theres already a theory that says nothing can travel faster than light. But thats okay, say the researchers, if things can influence other things back in time. Forwards in time, Id look at my red ball, then your bag would mysteriously contain a green ball. The retrocausality case says that backwards in time, we already know both ball colors, and my ball must be red because you already knew your ball was green. Then, the balls go hidden into the bag where they become red and green simultaneously. Basically, in this case, you cant run an experiment where you can control for the effects the future has on the past.
This idea of events in the present influencing things in the past is a mathematical consequence of a pair of the authors assumptions. The first assumption is that quantum mechanics should satisfy their definition of time-symmetry, like lots of other physics theories. That means that particles should behave the same way both forward and played in reversea billiard ball hitting a stationary ball looks the same no matter how you play the tape. The theory should also be real, as Leifer says. This means that the particles are more than a list of numbers, but are instead actual things that behave the same yesterday as they will tomorrow, and have properties that are innate, whether or not the experimenter is able to observe them.
Add the math, and according to the new paper published in Proceedings of the Royal Society A this past week, boom. If you want your theory to be time symmetric, and work the same every day, retrocausality is required.
Most would say this is horrible, of course. If things can influence other things in the past, then who cares about all of science? Why test something at all if the result could be causing the cause? Leifer does offer a solutiona sort of block universe, where events in space and time dont cause one another, but instead fit together like a jigsaw puzzle. But this idea hasnt been developed into a mathematical theory, yet.
Basically, if retrocausality is true, then cause-and-effect is an illusion due to the fact that humans only see things in one direction. The paper is only dealing in what-ifs here, and doesnt get into the specifics of how this effect would manifest, aside from in experiments. But the effect would be built into the very fabric of the universe.
Some physicists didnt find this idea compelling. Christopher Fuchs from the University of Massachusetts, Boston told me that these so-called block universes are neither living nor forced nor momentous for me. He takes these terms from the philosopher William James, and means that the hypothesis doesnt sound like a genuine possibility. It doesnt force him to make a decision one way or the other, and essentially, it isnt groundbreaking. In my mind a far more viable path has already been blazed through very different considerations, treating the observer of the universe as the most important agent, and sort of avoiding the impossible-to-observe.
Physicist Sean Carroll from CalTech thought the new paper was interesting, but he happens to like the already-strange many worlds theory, that says different results manifest in different universes described under the same probabilistic description. Thats the one where, in the red/green ball case, there are actually two universes, one where I saw the red ball and one where I saw the green ball. It is perfectly time-symmetric and reversible under the conventional definitions, he said. And it certainly doesnt require retrocausality. So as usual, if you are willing to take seriously the many worlds inside the wave function… much less weirdness is implied by quantum mechanics in other ways. Essentially, hes willing to trade the weirdness of retrocausality for the weirdness of many worlds.
But another expert I spoke with was far more forgiving, and instead thought of this work as an important go/no-go idea for this line of thinking. This paper makes a mathematical statement around retrocausality, said Renato Renner from ETH Zurich in Switzerland. It says maybe we need it if we want time symmetry, a theory that still works if you play the physics in reverse.He thought this paper was one of the first pieces of research make such a well-defined statement about that concept.
So now, researchers have sat and wracked their brains about a solution to a problem that only arises if they assume certain things about the worldin other words, its a new idea, its only a requirement of the universe if you assume certain other things, and its kind of fringe. But as of now, no matter how you want to understand the fabric of the universe, youre going to need to accept something that feels ridiculous, be it a multiverse, faster-than-light communication, or maybe even a world where the future influences the past.
Theres a substantial group of people trying to understand the question of whats really going on, and can we construct a theory based on stuff that really exists out there, said Leifer. The more different approaches we can think of and try out the better.
[Proceedings of the Royal Society A]
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Posted: at 5:43 am
Scientists have successfully teleported something into space for the first time ever.
The experiment saw Chinese scientists send a photon up away from Earth, further than ever before.
Teleportation of this kind uses the bizarre effects of quantum entanglement, rather than physically hurlingthe object itself over distances. Instead it transfers the information about a photon to another point in space creating a faithful replication of the object.
It marks the first ever time that effect has been tested over long distances. The success could bring with it a whole range of uses including a quantum internet that connects different parts of the world atseemingly impossible speed.
Until now, experiments had been restricted to short distances because of problems with the wires or signals that would carry the information.
But the new test saw scientists teleport up to a satellite. That is likely to be the way that such teleportation will work in practice sending objects up to space and then back down again to wherever they are needed, since it means there arerelatively clear paths between all of the different points.
Teleportation has become fairly common on the Earth, where scientists can instantly shoot information about photonsover small distances. But the new study moves towards making that effect more practically useful.
“This work establishes the first ground-to-satellite up-link for faithful and ultra-long-distance quantum teleportation, an essential step toward global-scale quantum internet,” the scientists write in their paper, which has been published online.
The satellite itself named Micius after an ancient Chinese philosopher was sent up from the Gobidesert last year, by the team in charge of the project. It dropped off the rocket that carried it to space and it has been in orbit above the Earth ever since.
Micius itself canreceive photons and is sensitive enough to catch and spot them;the team on the ground had kit that could send those photons up into space. Together, that kit could allow the scientists to test how the team on Earth were able to interact with photons floating way above our planet.
It works by harnessing the strange effects of quantum entanglement, which Einstein described as “spooky action at a distance”. The effect describes the behaviour where particles seem to act on each other instantly and in bizarre ways.
That entanglement is notconstrained by distances, meaning that two particles can interact despite being a very long way apart. Scientists hope to be able to use that effect for their own ends,includingsending messages that are received far more quickly than using traditional means, for example.
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Posted: at 5:43 am
Quantum physics has spawned its share of strange ideas and hard-to-grasp concepts – from Einsteins spooky action at a distance to the adventures of Shroedingers cat. Now a new study lends support to another mind-bender – the idea of retrocausality, which basically proposes that the future can influence the past and the effect, in essence, happens before the cause.
At this point, retrocausality does not mean that you get to send signals from the future to the past – rather that an experimenters measurement of a particle can influence the properties of that particle in the past, even before making their choice.
The new paper argues that retrocausality could be a part of quantum theory. The scientists expound on the more traditionally accepted concept of time symmetry and show that if that is true, then so should be retrocausality. Time symmetry says that physical processes can run forward and backwards in time while being subject to the same physical laws.
The scientists describe an experiment where time symmetry would require processes to have the same probabilities, whether they go backwards or forward in time. But that would cause a contradiction if there was no retrocausality, as it requires these processes to have different probabilities. What the paper shows is that you cant have both concepts be true at the same time.
Eliminating time symmetry would also get rid of some other sticky problems of quantum physics, like Einsteins discomfort with entanglement which he described as spooky action at a distance. He saw challenges to quantum theory in the idea that entangled or connected particles could instantly affect each other even at large distances. In fact, accepting retrocausality could allow for a reinterpretation of Bell tests that were used to show evidence of spooky action. Instead, the tests could be supporting retrocausailty.
The paper, published in the Proceedings of the Royal Society A, was authored by Matthew S. Leifer at Chapman University in California and Matthew F. Pusey at the Perimeter Institute for Theoretical Physics in Ontario. The scientists hope their work can lead towards a fuller understanding of quantum theory.
“The reason I think that retrocausality is worth investigating is that we now have a slew of no-go results about realist interpretations of quantum theory, including Bell’s theorem, Kochen-Specker, and recent proofs of the reality of the quantum state,” said Leifer to Phys.org. “These say that any interpretation that fits into the standard framework for realist interpretations must have features that I would regard as undesirable. Therefore, the only options seem to be to abandon realism or to break out of the standard realist framework.
Are we going to have time travel as a result of this? In one idea proposed by Richard Feynman,existence of retrocausality could mean that positrons,antimatter counterparts of electrons, would move backwards in time so that they could have a positive charge. If this was proven to be true, time travel could involve simply changing the direction of moving particles in the single dimension of time.
Leifer doesnt go as far as time travel in his explanation, but speculates that if retrocausality does exist in the universe, then there could be evidence of it in the cosmological data, saying that there are certain eras, perhaps near the big bang, in which there is not a definite arrow of causality.
Is this idea ready for the big time? It is supported by Huw Price, a philosophy professor at the University of Cambridge who focuses on the physics of time and is a leading advocate of retrocausality. Leifer and Pusey are taking things in stride, however, realizing that much more work needs to be done.
“There is not, to my knowledge, a generally agreed upon interpretation of quantum theory that recovers the whole theory and exploits this idea. It is more of an idea for an interpretation at the moment, so I think that other physicists are rightly skeptical, and the onus is on us to flesh out the idea, said Leifer.
There are no experiments underway by the physicists to test their theory, but they hope this work will question the assumptions of quantum mechanics and lead to new discoveries down the line.
You can read the study here.
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Posted: July 9, 2017 at 12:44 pm
Milo Faust, 1, looks at a book from the Baby University series. Courtesy of Amber Faust hide caption
Milo Faust, 1, looks at a book from the Baby University series.
When Kelly Barrales-Saylor was a new mom, she got a lot of children’s books as gifts. Most were simple books about shapes, colors and letters. There were none about science or math.
“My editorial brain lit up and said there must be a need for this,” says Barrales-Saylor, who works as an editor for a publishing company outside Chicago.
Halfway across the world, Chris Ferrie was similarly unsatisfied.
When reading to his kids, Ferrie noticed that most books used animals to introduce new words. In today’s world, that just didn’t make sense to him.
“We’re not surrounded by animals anymore,” says Ferrie, a physicist and mathematician at a university in Sydney, Australia. “We’re surrounded by technology.” So he created some math and science books for his own children and self-published them online.
That’s where Barrales-Saylor found them. And together, they designed a series of books aimed at toddlers and babies.
The books introduce subjects like rocket science, quantum physics and general relativity with bright colors, simple shapes and thick board pages perfect for teething toddlers. The books make up the Baby University series and each one begins with the same sentence and picture This is a ball and then expands on the titular concept.
In the case of general relativity: This ball has mass.
But some of the topics Ferrie covers are tough for even grown-ups to comprehend. (I mean, quantum physics? Come on.)
A firm grasp of rocket science isn’t really the point, Barrales-Saylor says.
“We know toddlers aren’t going to pick up the exact high-level concepts we’re explaining,” she says. “We’re trying to introduce the small seeds of information meant for them to remember years later.”
Some parents hope a happy primer to a complex subject will yield results later on. Take Amber Faust, 33, who lives in South Carolina.
Physics never came easily to her she got a “C” in her college class but that hasn’t stopped her from introducing the science to her kids.
She reads Ferrie’s Baby University series with sons Oliver, 2, and Milo, 1. Then, they “act it out.”
“We make funny noises and run through the house,” Faust says. “The 2-year-old is a crazy active baby, so anything we read we have to act out.”
Connecting the books to the real world is the best thing parents can do, says Jeff Winokur, an early education and elementary science instructor at Wheelock College in Boston.
“It’s important to give kids physical experiences and a chance to talk about them,” says Winokur, who remembers learning to dislike science by reading about it.
According to Winokur, what kids and parents need is to accompany their reading with an experiment. It could be as simple as asking the question: “What happens when I roll this ball down a hill?” he says.
Children would do better to engage with physical objects rather than static pictures on a page that way, they bring the subjects to life.
And the idea that physics is incomprehensible to small children? Let’s just say, the babies may know more than we think.
“Infants come into the world equipped with expectations that accord very closely to what we consider Newtonian physics,” says Kristy vanMarle, who has been researching children’s “intuitive physics” at the University of Missouri.
Children as young as 2 months comprehend that objects unsupported will fall and objects hidden will not cease to be, according to vanMarle’s study.
“Of course, they can’t talk about it, or explain it, but the knowledge in the form of expectations seems to be in place,” vanMarle says.
As the children grow, so does their understanding. They learn the language to describe the phenomena they have experienced all their life
In Washington, D.C., Rosie Nathanson is trying to make Ferrie’s physics books work for her two younger children.
At her home on Capitol Hill, Nathanson sits on the couch with Henry, 6, and Sylvie, 2 1/2, and reads Rocket Science for Babies:
“This is a ball. This ball is moving.”
Henry has been learning about this concept flight in school.
Nathanson continues: “Air can’t go through it.”
” ‘Cause it’s aerodynamic,” Henry responds. He’s excited to hear words he understands.
But while Henry plunges through the books, his little sister grows restless. “I need water,” says Sylvie, who’s having a hard time grasping this intro to rocket science.
Her mom thinks she might be more interested in the books a year from now. Henry, meanwhile, gives the books a qualified endorsement.
“I like it half and I didn’t like it half,” says Henry. The half he didn’t like? It’s “for babies.”