What Is Quantum Mechanics Probability
In quantum mechanics, a probability amplitude is a complex number used in describing the behaviour of systems. … These probabilistic concepts, namely the probability density and quantum measurements, were vigorously contested at the time by the original physicists working on the theory, such as Schrödinger and Einstein.
Quantum Physics: Our Study Suggests Objective Reality Doesn’t Exist
by Alessandro Fedrizzi and Massimiliano Proietti, The Conversation
Alternative facts are spreading like a virus across society. Now it seems they have even infected scienceat least the quantum realm. This may seem counter intuitive. The scientific method is after all founded on the reliable notions of observation, measurement and repeatability. A fact, as established by a measurement, should be objective, such that all observers can agree with it.
But in a paper recently published in Science Advances, we show that in the micro-world of atoms and particles that is governed by the strange rules of quantum mechanics, two different observers are entitled to their own facts. In other words, according to our best theory of the building blocks of nature itself, facts can actually be subjective.
Observers are powerful players in the quantum world. According to the theory, particles can be in several places or states at oncethis is called a superposition. But oddly, this is only the case when they aren’t observed. The second you observe a quantum system, it picks a specific location or statebreaking the superposition. The fact that nature behaves this way has been proven multiple times in the labfor example, in the famous double slit experiment .
When Wigner and the friend compare notes later on, the friend will insist they saw definite outcomes for each coin toss. Wigner, however, will disagree whenever he observed friend and coin in a superposition.
Bell’s Theorem And Its Implications
Adding a further wrinkle to the nature of quantum reality, Herbert presents the EPR paradox, and its resolution in the form of Bell’s theorem. The EPR paradox, resting on the long-held assumption of locality, suggests the existence of “elements of reality”unmeasured quantum attributes which are nonetheless realwhich are not predicted by quantum theory. Bell’s theorem resolves this paradox by proving that locality is ruled out by observationthat any model of reality consistent with observation must allow for non-local interaction. However, Herbert is careful to note, Bell’s theorem does not entail any prediction of experimentally observable non-local phenomena, nor does it allow for superluminal communication.:211231
Herbert then re-evaluates the aforementioned interpretations of quantum reality in light of Bell’s theorem:
Herbert concludes that, although Bell’s theorem does not preclude any of the aforementioned interpretations of quantum mechanics, it insists that any valid interpretation must allow for non-local interaction.:245
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Ii What Is The Difference Between Classical Mechanics And Quantum Physics
Science & Wisdom LIVE recently hosted several events on quantum theory and its interpretations. But how does quantum theory differ from classical physics? What is the difference between these two descriptions of reality, and why does it matter?
Classical mechanics was mainly built out of concepts formed via our everyday intuition. When we look at the world, we see many separate objects that exist out there, separate from us. We experience them as independent from the mental processes needed to perceive them. If we see an apple falling from a tree, we clearly see that there is a tree, on the one hand, and an apple, on the other. Those two objects appear to exist completely independent of each other. Never mind that the apple needed the tree for it to come into existence and the tree was born from an apples seed. Moreover, we tend to assume that trees and apples exist exactly as we humans perceive them.
Classical mechanics sought to explain what we see in day-to-day life in terms of the so-called fundamental particles and their interactions. In doing so, classical mechanics projected on these concepts some of our everyday intuitions. In other words, such fundamental particles and their interactions were not unlike the collection of objects described above: here you have a particle, there you have another, in between you have an interaction, and none of these has anything to do with the process of observation.
An Obscure Idea In Quantum Physics Says Yes
Wheeler called it the Participatory Anthropic Principle. It goes something like this. The answers we get from posing questions to Nature depend very much on the questions we ask. Without any questions, nothing would be answered hence we are participants in the bringing about of events. His most quotable quip was the following.
No phenomenon is a real phenomenon until it is an observed phenomenon.
Law Without Law
John Wheeler was one of the most interesting characters of the 20th century. If youre familiar with the idea of space as a seething boil of virtual particles popping in and out of existence, or if youve heard the words wormhole or black hole, then youve been in some way influenced by Wheeler. His story is ripe with legacy, which is why you can find it in manyotherplaces and also why I wont retell it here. Besides, I wouldnt do it justice, and I really only wanted to talk about one of his many ideas.
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How Many Dimensions Are There
The world as we know it has three dimensions of spacelength, width and depthand one dimension of time. But theres the mind-bending possibility that many more dimensions exist out there. According to string theory, one of the leading physics model of the last half century, the universe operates with 10 dimensions.
A Quantum Experiment Suggests Theres No Such Thing As Objective Reality
Back in 1961, the Nobel Prizewinning physicist Eugene Wigner outlined a thought experiment that demonstrated one of the lesser-known paradoxes of quantum mechanics. The experiment shows how the strange nature of the universe allows two observerssay, Wigner and Wigners friendto experience different realities.
Since then, physicists have used the Wigners Friend thought experiment to explore the nature of measurement and to argue over whether objective facts can exist. Thats important because scientists carry out experiments to establish objective facts. But if they experience different realities, the argument goes, how can they agree on what these facts might be?
Thats provided some entertaining fodder for after-dinner conversation, but Wigners thought experiment has never been more than thatjust a thought experiment.
Last year, however, physicists noticed that recent advances in quantum technologies have made it possible to reproduce the Wigners Friend test in a real experiment. In other words, it ought to be possible to create different realities and compare them in the lab to find out whether they can be reconciled.
Wigner imagined a friend in a different lab measuring the state of this photon and storing the result, while Wigner observed from afar. Wigner has no information about his friends measurement and so is forced to assume that the photon and the measurement of it are in a superposition of all possible outcomes of the experiment.
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What Is Quantum Physics In Simple Terms
What is quantum physics? Put simply, its the physics that explains how everything works: the best description we have of the nature of the particles that make up matter and the forces with which they interact. Quantum physics underlies how atoms work, and so why chemistry and biology work as they do.
What Does It All Mean
Although a conclusive test may be decades away, if the quantum mechanical predictions continue to hold, this has strong implications for our understanding of reality even more so than the Bell correlations. For one, the correlations we discovered cannot be explained just by saying that physical properties dont exist until they are measured.
Now the absolute reality of measurement outcomes themselves is called into question.
Our results force physicists to deal with the measurement problem head on: either our experiment doesnt scale up, and quantum mechanics gives way to a so-called objective collapse theory, or one of our three common-sense assumptions must be rejected.
There are theories, like de Broglie-Bohm, that postulate action at a distance, in which actions can have instantaneous effects elsewhere in the universe. However, this is in direct conflict with Einsteins theory of relativity.
Another way to resolve the conflict could be to make Einsteins theory even more relative. For Einstein, different observers could disagree about when or where something happens but what happens was an absolute fact.
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The Battle For Reality
Quantum mechanics works extremely well to describe the behaviour of tiny objects, such as atoms or particles of light . But that behaviour is very odd.
In many cases, quantum theory doesnt give definite answers to questions such as where is this particle right now? Instead, it only provides probabilities for where the particle might be found when it is observed.
For Niels Bohr, one of the founders of the theory a century ago, thats not because we lack information, but because physical properties like position dont actually exist until they are measured.
And whats more, because some properties of a particle cant be perfectly observed simultaneously such as position and velocity they cant be real simultaneously.
No less a figure than Albert Einstein found this idea untenable. In a 1935 article with fellow theorists Boris Podolsky and Nathan Rosen, he argued there must be more to reality than what quantum mechanics could describe.
The article considered a pair of distant particles in a special state now known as an entangled state. When the same property is measured on both entangled particles, the result will be random but there will be a correlation between the results from each particle.
However, in 1964 Northern Irish physicist John Bell found Einsteins argument broke down if you carried out a more complicated combination of different measurements on the two particles.
Does Reality Need An Observer
Does reality need an observer?
What makes something an observer? Observer is a special person which does not obey the usual laws of quantum mechanics. While it is much easier to define observer from a philosophical point of view, the mathematical answer is that the observer is a system which manifests subjective decoherence when observed.
What does quantum mechanics say about reality? An odd space experiment has confirmed that, as quantum mechanics says, reality is what you choose it to be. Physicists have long known that a quantum of light, or photon, will behave like a particle or a wave depending on how they measure it.
Do electrons know they being observed? In other words, the electron does not understand that it is being observed it is so very tiny that any force that interacts with it such that you can determine its position, will change its behavior, unlike common macroscopic objects which are so very massive that bouncing photons off of them has no discernible
War Of The Many Worlds
One criticism of the many worlds interpretation is that while it offers a colorful way to think about the world, it doesnt deliver any new insights into how nature works. It is completely content-less, says physicist Christopher Fuchs of the University of Massachusetts, Boston.
Fuchs favors an alternative called Quantum Bayesianism, which offers a path back to an old-fashioned single reality. He argues that the universe changes when you look at it not because you are creating new worlds but simply because observation requires interacting with your surroundings. No coffee dates, no other lives for you. In this way, measurement is demoted from being something mystical to being about things as mundane as walking across a busy street: Its an action I can take that clearly has consequences for me, he says.
Multiple Splits Multiple Worlds
Even to seasoned scientists, its odd to think that the universe splits apart depending on whether a molecule bounces this way or that way. Its odder still to realize that a similar splitting could occur for every interaction taking place in the quantum world.
Things get downright bizarre when you realize that all those subatomic splits would also apply to bigger things, including ourselves. Maybe theres a world in which a version of you split off and bought a winning lottery ticket. Or maybe in another, you tripped at the top of a cliff and fell to your death oops.
It’s absolutely possible that there are multiple worlds where you made different decisions. We’re just obeying the laws of physics, says Sean Carroll, a theoretical physicist at the California Institute of Technology and the author of a new book on many worlds titled “Something Deeply Hidden.” Just how many versions of you might there be? We don’t know whether the number of worlds is finite or infinite, but it’s certainly a very large number,” Carroll says. “Theres no way its, like, five.
Carroll is aware that the many worlds interpretation sounds like something plucked from a science fiction movie. And like a Hollywood blockbuster, the many worlds interpretation attracts both passionate fans and scathing critics.
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Exceptional Fossil Preservation Suggests That Discovering Dinosaur Dna May Not Be Impossible
In the classical, macroscopic world, theres no such thing as a measurement problem. If you take any object that you like a jet, a car, a tennis ball, a pebble, or even a mote of dust you can not only measure any of its properties that you want to, but based on the laws of physics that we know, we can extrapolate what those properties will be arbitrarily far into the future. All of Newtons, Einsteins, and Maxwells equations are fully deterministic if you can tell me the locations and motions of every particle in your system or even your Universe, I can tell you precisely where they will be and how theyll be moving at any point in the future. The only uncertainties well have are set by the limits of the equipment were using to take our measurements.
But in the quantum world, this is no longer true. There is an inherent uncertainty to how well, simultaneously, you can know a wide variety of properties together. If you try to measure, for example a particles:
- position and momentum,
- spin in any two perpendicular directions,
- or its angular position and angular momentum,
youll find that theres a limit to how well you can simultaneously know both quantities: the product of both of them can be no smaller than some fundamental value, proportional to Plancks constant.
Theresa Knott / Tatoute of Wikimedia CommonsClara-Kate Jones/ MJasK of Wikimedia CommonsNASA/CXC/M.WeissR. Bach et al., New Journal of Physics, Volume 15, March 2013
Heres where it gets weird, though.
What Is Quantum Spirituality
Quantum mysticism is a set of metaphysical beliefs and associated practices that seek to relate consciousness, intelligence, spirituality, or mystical worldviews to the ideas of quantum mechanics and its interpretations. Quantum mysticism is considered by most scientists to be pseudoscience or quackery.
Is Criminology An Empirical Science
Science. Contemporary criminology self-identifies as a science. Its emphasis is on empirical research and scientific methodology. … The use of scientific method to study crime and criminal behavior developed in the late nineteenth century with the emergence of the positive school of criminology.
Are We As Human Beings Capable Of Understanding The World What Does The Scientist And What Does The Philosopher Say
This is a very deep question. Niels Bohr once answered to that question, with regard to quantum physics: Yes, we will understand, but we will also learn anew what understanding means. When I first read his statement as a student, it made me wonder, but at the same time, it encouraged me to keep on studying the miracles of quantum physics. I personally regard Bohr’s remark as probably the most important general philosophical insight we can gain from quantum physics: That due to its weirdness, quantum physics forces us to start thinking about what understanding actually means, and how limited our human imagination is. Quantum physics, like no other scientific theory ever devised, pushes us to the point where we have to accept that we cannot find any kind of visualization of what happens in nature anymore. We can devise models for one phenomenon or another, but these models will certainly fail in different circumstances.
And when you start thinking about why our mind is not able to imagine microscopic processes, you easily reach the conclusion that it is like that because evolution has not made us this way. Never in the history of our ancestors have microscopic phenomena been part of their sensory environment. So there has never been any need to develop structures of consciousness that would enable us to better understand the quantum world.
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Have We Been Interpreting Quantum Mechanics Wrong This Whole Time
For nearly a century, reality has been a murky concept. The laws of quantum physics seem to suggest that particles spend much of their time in a ghostly state, lacking even basic properties such as a definite location and instead existing everywhere and nowhere at once. Only when a particle is measured does it suddenly materialize, appearing to pick its position as if by a roll of the dice.
Original story reprinted with permission fromQuanta Magazine, an editorially independent division ofSimonsFoundation.org *whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.*This idea that nature is inherently probabilistic that particles have no hard properties, only likelihoods, until they are observed is directly implied by the standard equations of quantum mechanics. But now a set of surprising experiments with fluids has revived old skepticism about that worldview. The bizarre results are fueling interest in an almost forgotten version of quantum mechanics, one that never gave up the idea of a single, concrete reality.
A Quantum Drop
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Harris et al., PRL