FRAMEWORK OF PHYSICS must somehow connect the exotica of quantum mechanics--its dead-and-alive cats, orbitals, oscillating ions and matter waves--with the more intuitive counterparts from classical physics: probabilities, planetary motions, pendulum swinging and double-slit, light-wave interference.
Image: DIGITAL COMPOSITION BY JEFF BRICE; WIGNER FUNCTION OF ATOMIC-MATTER WAVE THROUGH DOUBLE SLIT COURTESY OF MATTHIAS FREYBERGER, UNIVERSITY OF ULM
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Editor’s note (10/9/2012): We are making the text of this article freely available for 30 days because the article was cited by the Nobel Committee as a further reading in the announcement of the 2012 Nobel Prize in Physics. The full article with images, which originally appeared in the June 1997 issue, is available for purchase here.
“I am sorry that I ever had anything to do with quantum theory,” Erwin Schrödinger reportedly complained to a colleague. The Austrian physicist was not lamenting the fate of his now famous cat, which he figuratively placed in a box with a vial of poison in 1935. Rather he was commenting on the strange implications of quantum mechanics, the science behind electrons, atoms, photons and other things submicroscopic. With his feline, Schrödinger attempted to illustrate the problem: according to quantum mechanics, particles jump from point to point, occupy several places at once and seem to communicate faster than the speed of light. So why don’t cats—or baseballs or planets or people, for that matter—do the same things? After all, they are made of atoms. Instead they obey the predictable, classical laws quantified by Isaac Newton. When does the quantum world give way to the physics of everyday life? “That’s one of the $64,000 questions,” chuckles David Pritchard of the Massachusetts Institute of Technology.
Pritchard and other experimentalists have begun to peek at the boundary between quantum and classical realms. By cooling particles with laser beams or by moving them through special cavities, physicists have in the past year created small-scale Schrödinger’s cats. These “cats” were individual electrons and atoms made to reside in two places simultaneously, and electromagnetic fields excited to vibrate in two different ways at once. Not only do they show how readily the weird gives way to the familiar, but in dramatic fashion they illustrate a barrier to quantum computing—a technology, still largely speculative, that some researchers hope could solve problems that are now impossibly difficult.
The mystery about the quantum-classical transition stems from a crucial quality of quantum particles—they can undulate and travel like waves (and vice versa: light can bounce around as a particle called a photon). As such, they can be described by a wave function, which Schrödinger devised in 1926. A sort of quantum Social Security number, the wave function incorporates everything there is to know about a particle, summing up its range of all possible positions and movements.
Taken at face value, a wave function indicates that a particle resides in all those possibilities at once. Invariably, however, an observation reveals only one of those states. How or even why a particular result emerges after a measurement is the point of Schrödinger’s thought experiment: in addition to the cat and the poison, a radioactive atom goes into the box. Within an hour, the atom has an even chance of decaying; the decay would trigger a hammer that smashes open the vial of antifeline serum.
The Measurement Problem
According to quantum mechanics, the unobserved radioactive atom remains in a funny state of being decayed and not decayed. This state, called a superposition, is something quantum objects enter quite readily. Electrons can occupy several energy levels, or orbitals, simultaneously; a single photon, after passing through a beam splitter, appears to traverse two paths at the same time. Particles in a well-defined superposition are said to be coherent.
But what happens when quantum objects are coupled to a macroscopic one, like a cat? Extending quantum logic, the cat should also remain in a coherent superposition of states and be dead and alive simultaneously. Obviously, this is patently absurd: our senses tell us that cats are either dead or alive, not both or neither. In prosaic terms, the cat is really a measuring device, like a Geiger counter or a voltmeter. The question is, then, Shouldn’t measuring devices enter the same indefinite state that the quantum particles they are designed to detect do?
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Add CommentQuantum physics is so evident in our lives. Certain phenomenons aren't seen just because of the scales we use to evaluate them. It's like the earth moving with us. Do we feel it while on earth ? I would doubt. Or our milky way, moving so fast in its local group of galaxies.
Reply | Report Abuse | Link to thisInstead of introducing a mouse into the box, try a dog.
Reply | Report Abuse | Link to thisInside the box is a pregnant cat that eats mice and purrs oddly while on a rug. But if you bring the box to your quantum mechanic for repair, it never makes that odd purring sound.
Reply | Report Abuse | Link to thisI have to wonder about your use of the word "evident". Yes, quantum physics is necessary for the production of microchips that run our everyday lives, just as relativity is necessary for the operation of GPS satellites that many people rely on.
Reply | Report Abuse | Link to thisI wouldn't say, though, that either quantum physics or relativity is "evident". The reason that investigations into the quantum/classical boundary are so interesting is that the quantum mechanical laws underlying everything are /not/ obvious or intuitive.
By the way, I wish all SciAm articles were of the same quality as this long article by Haroche. Maybe it's because it was written by a Nobel Prize winner? Or maybe he's a Nobel winner precisely /because/ he can provide a clear and inspiring introduction to complicated topics.
http://www.scientificamerican.com/article.cfm?id=cavity-quantum-electrodynamics
Had we human beings or our measuring instruments been also of the size of quantum scales, will superposition still collapse since in that case boundary between quantum and classical will vanish? A question arises: what triggers the collapse of superposition -- measurement or difference in scale? Even more basic issue is why nature at small scales demonstrate quantum fuziness? Atoms and electrons may be quantum with respect our scales in which we or our instruments reside but if instruments are also of the size of atomic scale, both can be treated quantum or classical. In that case, measuring instrument should also show quantum fuziness. When measuring instruments and objects to be measured are of the comparable scales, the distinction between quantum and classical disappear.
Reply | Report Abuse | Link to thisIf measurement irrespective of scale difference collapses the superposition then this is really mysterious and difficult to explain. However, if scale difference between measuring instruments and object to be measured introduces de-coherence, it implies quantum superposition is all pervading in universe. This is even more mysterious. A cat may also be in superposition position w.r.t a measuring instrument of the size of a galaxy.
It appears true to its nature, understanding of quantum world may also remain in state of fuziness
Article does not seem to touch this issue. Any reader if he/she could address the issue.
I still have some questions of my own, but there's some good discussion in the SciAm article written by one of those recent Nobel Prize winners.
Reply | Report Abuse | Link to thisThe journal articles being described in it aren't all that new, so I was able to Google the list of authors for each study and find almost all of the texts published online. In the comments, I linked to a slide-show version of one of the papers it talks about the good agreement between theory and reality on how fast a given case of decoherence will happen.
http://www.scientificamerican.com/article.cfm?id=cavity-quantum-electrodynamics
Ref.5: Mr.Vinodkumarsehgal .the below topic will be of profound importance to your thoughts,it has been taken from a Bangladesh newspaper, -" The daily Star "
Reply | Report Abuse | Link to thisOne of the unsolved mysteries of contemporary science is how highly organized structures can emerge from the random motion of particles. This applies to many situations ranging from astrophysical objects that extend over millions of light years to the birth of life on Earth.
The surprising discovery of self-organized electromagnetic fields in counter-streaming ionized gases (also known as plasmas) will give scientists a new way to explore how order emerges from chaos in the cosmos. This breakthrough finding was published online in the journal, Nature Physics on Sept. 30.
"We've created a model for exploring how electromagnetic fields help organize ionized gas or plasma in astrophysical settings, such as in the plasma flows that emerge from young stars," said lead author Nathan Kugland, a postdoctoral researcher in the High Energy Density Science Group at Lawrence Livermore National Laboratory (LLNL). "These fields help shape the flows, and likely play a supporting role alongside gravity in the formation of solar systems, which can eventually lead to the creation of planets like the Earth."
"This observation was completely unexpected, since the plasmas move so quickly that they should freely stream past each other," explained Hye-Sook Park, team leader and staff physicist at LLNL. Park added that "laser-driven plasma experiments can study the microphysics of plasma interaction and structure formation under controlled conditions."
Studying astrophysics with laboratory experiments can help answer questions about astrophysical objects that are far beyond the reach of direct measurements. This research is being carried out as part of a large international collaboration, Astrophysical Collisionless Shock Experiments with Lasers (ACSEL), led by LLNL, Princeton University, Osaka University and Oxford University, with many other universities participating.
This work was performed at the OMEGA EP laser by the Lawrence Livermore National Laboratory.
I am explaining your missed inquiry Ref.21-Mr Vinodkumarsehgal's previous( Ultimo), Blog post, which is related to the above blog "7" Article.
Reply | Report Abuse | Link to thisAt physical level, when space expands, "what is that?" constituents of space which expands? In other words, whether fabric of space comprises of some physical building blocks or space is purely vacuum implying "nothing".
Your above para requires your careful analysis,the edict word -"Nothing ", is not applicable in Experimental Physics,mathematics and Space Time Cosmologies of Nature Bounds---as the pure vacuum of space always keeps topping up, with 1/2 SPIN PARTICLES,& as yet unknown Negative Mass Particles' that flit and fro, in the so called erroneous word, which misguides the factual entity and meaning of the word used as, "VACUUM IN PHYSICS."
KEEP IN MIND THAT LIGHT --confirms-that light speed appears "Constant in" any "Inertial Frame" ,
"TIME FREEZES IN CONICITY TRIANGULATION UNDER DYNAMIC INERTIA GRAVITY "
The metaphor of Schrodinger's cat certainly has its merits. It is rather disappointing however that it is still misused to drag consciousness into the discussion and to see quantum physics as scientific evidence in the context of dualism and the 'mind-matter' issue.
Reply | Report Abuse | Link to thisAs for the cat, lifting the lid, light reaching the eye and processing by the mind are all irrelevant considerations here but reappearing stubornly over and over again.
It has been proven experimentally for several decades that it is not 'observation' but rather 'observability' that determines whether superposition occurs or not. Superposition occurs only if no 'which-way' information remains, to be observed or not. The observer does not kill the cat.
The article correctly cites "Quantum rules forbid 'which-way' information and interference from coexisting" and "Decoherence does away with any special need for a consciousness or new physical forces". It balances these insights however with metaphysical considerations that contribute little to our understanding.
True, decoherence doesn't select a particular outcome, and many aspects of the collapse remain unexplained. I do not see any relation with consciousness however. Not in the old sense of "the observer killing the cat". Neither in more recent metaphysical considerations such as "how a conscious mind perceives an outcome" or what quantum physics has to do with "a better understanding of how brain and mind are related".
You are speaking of oft repeated Casmeir effect. Casmeir effect mentions of popping "in and out" of quantum particles from vacuum but does not describes about the stuff of space. Do you want to state that stuff of space comprises of these particles?
Reply | Report Abuse | Link to thisWhat is meant by "observability'? Does it amounts to the notion that when some quantum particle is observed, it is the limitation of observing instrument that it can not detect superposition and we interpret this as creation of decoherence but at ground level superposition still remains alive?
Reply | Report Abuse | Link to thisIn quantum mechanics, the most powerful principle is principle of superposition. Every state of everything is superposition of rest of all states. Schrodinger cat is dead and alive both at the same time before the observation. Observed cat is either dead or alive. observation collapses on state. This year, Nobel Prize is awarded to Dr. Haroche and Dr. Wineland for developing experimental technique to study individual quantum system in a particular quantum state.
Reply | Report Abuse | Link to thisS. N. Tiwary
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The problem is the theoretical and practical domain. in the recent years, many perspectives have been developed in the theoretical domain which have hypothesized many explanations for the phenomenon in the realm of physics. quantum theory is one such attempt. the coherence of the particles so to speak is beginning to border on absurdity. there are also some philosophical views that subscribe to such hypotheses. the result of the marriage between quantum physics and philosophy is the hypothesis of the existence of Multivers. It may be true that particles' coherence results in the simultaneity of presence in two spaces at once, but the important fact is also the decoherence of the event when a viewer sees it. it is no longer present in two possible spaces. As far as I know, what matters is the observer not the reality backstage since reality is what we perceive not what we think there is, detached from us. what does it mean that there is a multiverse but as soon as we perceive it, it becomes one? so it is one anyway. does it exist outside of us? it may, but what does it do when it is detached from our reality. it is also said that there is a link between the observer and observee. it means that the phenomena of observation is not detached from the phenomena of the observee. for us, reality is what effect us, what we see, what we end up with, what we have encoded in our formulas and so on and so forth. Do I care if in another world far beyond our reach, 1+1 =3 ? if this is the possibility, then let's just say that anything else even our wildest dreams and our most outrageous fictions can also be a possibility. when we can't set the boundary of what can be right and what can't be and where we have to stop getting absurd, science will turn into a joke and a circus. Then I can put some basic knowledge together and claim that I am not one. I have millions of clones like me filling every inch worth of space in an unknown galactic system, but can I ? what will be the practical aspect of such a wild
Reply | Report Abuse | Link to thisapocryphal claim?