13 replies to this topic

[Mind]

General Guidelines for this thread:

Please post new articles that relate to research and engineering in QM. Articles and papers that appear in science journals would be great, but also major news outlet reviews of QM lab achievements or business innovations are accepted. Links to audio and video clips are also welcome. Feel free to comment on why the article is important or what new light it sheds on the quantum world.

[Mind]

Here is an article of fantastic proportions. Forget calculating at light speed, how about instantaneously? Sounds far-fetched, but then again I am not a Quantum Mechanics expert. Still, it seems teleportation has some solid experimental backing.

Electricity teleportation

Technology Research News  February 9, 2004

Researchers from Leiden University in the Netherlands have devised a way to teleport electricity.

Teleportation is possible at the atomic scale, and was discovered a decade ago for photons in free space. The researchers' proposal works for electrons contained in conductors, and could eventually be used within computer circuits.

A major obstacle to quantum teleportation is that in a metal or semiconductor electrons exist in a crowd, dubbed the Fermi sea, making individual electrons difficult to isolate and manipulate.

When the two carriers of electrical current -- negatively charged electrons and positively charged holes -- meet, they cancel each other out. The researchers have postulated that an entangled electron, however, could continue its existence at a distant location.

Entangled electrons are connected in such a way that specific properties of the electrons remain synchronized regardless of the physical distance between them.

The method could eventually be used to instantly transport information between the quantum bits, or qubits, of a quantum computer if electrons could be transported over distances of around 100 microns. Quantum computers use the properties of particles like photons, electrons and atoms to compute and are theoretically very fast at certain large problems, including those that would render today's encryption-based security systems obsolete.

Laboratory demonstrations showing that the method could be used to transport electrons a few microns could happen within two to five years; practical applications are a decade or two away, according to the researchers. The work appeared in the December, 2003 issue of Physical Review Letters.

[Mind]

A full fledged Quantum computer continues to look more like a reality in the near future. The theoretical foundations are there....it is just an engineering problem now.

By John Carey in Gaithersburg, Md.

Physics: "Putting The Weirdness To Work" 
Scientists say quantum materials will be the basis for amazing devices, but when?


The world of the quantum stretches the limits of human imagination. Who could ever believe, for instance, that atoms -- the building blocks of our seemingly solid landscape -- are able to exist in different places at one time? That they can be "entangled" together such that an action on one atom or particle will affect another across considerable distances? Or that they are irrevocably altered simply by the act of being observed?

Yet that is what quantum laws tell us. Einstein himself was famously troubled by the implication that reality was actually just a collection of probabilities, where God not only played dice with the universe but also hid the dice. "To common sense, quantum mechanics is nonsensical," says Nobel prize-winning physicist William D. Phillips of the National Institute of Standards & Technology (NIST).

Nevertheless, developing quantum theory was "the crowning intellectual achievement of the last century," says California Institute of Technology physicist John Preskill. It's the underlying principle for many of today's devices, from lasers to magnetic resonance imaging machines. And these may prove to be just the low-hanging fruit. Many scientists foresee revolutionary technologies based on the truly strange properties of the quantum world.

For instance, there's a state of matter that scientists created less than a decade ago called the Bose-Einstein condensate, in which each of many millions of atoms act identically and are everywhere in the sample at once. Dozens of research groups around the world are experimenting with these condensates, whose properties portend a future we can barely glimpse. "Physicists relish the weirdness, but now we're starting to ask if we can put the weirdness to work," says Preskill.

Some of the theoretical possibilities boggle the mind. For example: the elusive but intensely desired quantum computer. The mathematical challenge of factoring a 400-digit number -- which would take 10 billion years on today's supercomputers -- might be cracked by a quantum computer in 30 seconds. While there are a number of approaches to building such a device, recent experiments with the Bose-Einstein condensates are opening up clever new paths.

Quantum weirdness also enables communications to be sent in unbreakable code. New companies, such as New York City's MagiQ Technologies and id Quantique of Geneva, are already turning these ideas into commercial products. At the same time, the exploration of quantum domains may shed more light on abiding scientific mysteries, such as how some substances conduct electricity with zero resistance -- a phenomenon called superconductivity. That could lead to the transmission of electricity across great distances with no loss. And a forthcoming paper from IBM researchers will show how quantum phenomena can be exploited to see molecules more clearly.

These uses may just scratch the surface of the possible. No one has ever been able to foresee transformations wrought by any revolutionary science. And the quantum world is no different. "We have not yet begun to figure out what the applications are," says NIST physicist Carl J. Williams. "But the risk is underestimating the impact."

Quantum computers and most other applications are decades away, if indeed they can be built at all. Still, the enormous potential has led to programs at companies like IBM (IBM ) and Hewlett-Packard Co. (HPQ ). The Pentagon's Defense Advanced Research Projects Agency is now beginning a major effort to construct a working quantum information processor. In all these efforts, "the goal is the control of quantum matter," says Immanuel Bloch of the Johannes Gutenberg University of Mainz. "It's a great challenge, but there are great rewards."

For a glimpse of this endeavor, drop by the lab of William Phillips and his team in Gaithersburg, Md. Sprawling over a giant lab bench is a maze of precision mirrors and lasers, all converging on a small glass vacuum chamber where the quantum world is being probed. Phillips won his Nobel in 1997 for a technique known as laser cooling, in which beams are used to slow atoms down. That chills the atoms until they are a fraction of a degree above absolute zero. Now, using rubidium atoms, Phillips is making them even colder by letting the warmer ones "evaporate."

PEAKS AND TROUGHS. Inside the glass chamber, he is creating the fragile Bose-Einstein condensate. The clump of atoms can be huge -- big enough to be visible to the naked eye. At that scale, you would expect the stolid laws of Newtonian physics to rule. Instead, the atoms obey the Heisenberg uncertainty principle, which specifies that an electron or atom can't be pinned down to any one location. Even though the clump is a tenth of a millimeter across and contains a million atoms, "every atom is everywhere -- that's what makes it so wonderful," says Williams.

This strange state of matter was predicted by Einstein, building on work by Indian physicist Satyendra Nath Bose, back in 1924. It was first created by Phillips' NIST colleague, Eric A. Cornell, and Carl E. Wieman of the University of Colorado, in 1995 -- a Nobel prize-winning achievement. Now, an estimated 50 groups around the world are experimenting with the strange stuff. "It can do some amazing things," says Phillips.

One of the most intriguing -- and potentially useful -- maneuvers in Phillips' lab involves putting the atoms into neat little rows. The trick is using precisely tuned laser light. Imagine dropping pebbles into a pond, sending waves across the water. Then drop pebbles at the opposite shore, dispatching waves in the other direction. Where the two groups of waves meet, they create so-called standing waves -- an unchanging collection of peaks and troughs, like a row of sand dunes in the desert.

Laser light is also a wave. So two intersecting beams similarly create peaks and valleys. Scientists call this an optical lattice. And when Phillips and other researchers shine intersecting laser beams though the Bose-Einstein clump of atoms, individual atoms almost magically go from being everywhere at once to nestling in the valleys. "It's a great gift of nature," says Phillips. "We've been lucky that things worked better than expected."

To information scientists, such a neat arrangement of atoms looks startlingly like the basis for a computer. It can be arranged that each atom is in one of two energy levels, separated by a small quantum jump. Thus, each atom could represent a 0 or a 1, like the bits in a regular computer.

But these are no ordinary bits. Because of quantum weirdness, an atom can be a 0 and a 1 at the same time. What's more, the different quantum bits, or "qubits," can be entangled with each other, even if there is no actual connection. "Because of the mystery of entanglement, the state of one atom will be dependent on the state of the other," explains Williams. "It's a much stronger relationship than marriage." As a result, for some calculations, the power of a quantum machine grows exponentially with the number of qubits -- twice the bits gives you four times the power. A 300-qubit machine could store more combinations than there are atoms in the entire universe, says Williams.........

[Mind]

Originally Posted By alex83

The concept of transferring info faster then the speed of light was the solution to the EPR paradox, in which EPR (Einstein, Padolsky and Rosen if I recall correctly) suggested in the 30-ies that quantum mechanical description is not full, in the following way:

Imagine you could excite an atom so it emits two photons, EPR claimed that if you measure the spin polarity of one of them (vertical for example) you can immediately know the spin polarity of the other (horizontal). You didn't made any measurements on the other photon but you know his polarity, which is not allowed by the wave description. Hence they assumed the wave description is incomplete.

The solution to the paradox is that the polarity of the other photon not defined before the measurement, the measurement made on one of the photons immediately sets the other photons state (independently of the distance between the photons). This was confirmed by an experiment (in 1983, if I recall correctly), I can tell about the experiment but it won't be understandable if you don't know quantum mechanics.

This is the “not locality” principle (i.e. one can determine particles property (collapse its wave function) immediately by performing measurement on another particle in other place).

Buy the way, to say something is simultaneously in different places is delusive. According to quantum mechanics there is curtain probabilities to measure something in different places, you won't measure something in tow places at once. Moreover you won't even measure tow fermions (electrons, protons etc = differential spin. not photons, gravitons etc = integral spin) in the same place...

[Mind]

Originally posted by Lazarus Long

Here is an interesting application. Unbreakable encryption?

http://www.newscient...p?id=ns99994914

Entangled photons secure money transfer
17:10 22 April 04
NewScientist.com news service

An electronic money transaction has been carried out in at a bank in Austria using entangled photons to create an unbreakable communications code.

Although of commercial quantum cryptography products already exist, none of these use entangled photons to guarantee secure communications.

The link was used to transfer money between Vienna City Hall and Bank Austria Creditanstalt on Wednesday. The cryptographic system was developed by Anton Zeilinger and colleagues from the University of Vienna and the Austrian company ARC Seibersdorf Research.

Entangled photons obey the strange principles of quantum physics, whereby disturbing the state of one will instantly disturb the other, no matter how much distance there is in between them.

The pairs of entangled photons used were generated by firing a laser through a crystal to effectively split single photons into two. One photon from each entangled pair was then sent from the bank to the city hall via optic fibre.


Key creation

When these photons arrived at their destination, their state of polarisation was observed. This provided both ends of the link with the same data, either a one or a zero. In this way, it is possible to build a cryptographic key with which to secure the full financial transaction.

Quantum entanglement ensures the security of communications because any attempt to intercept the photons in transit to determine the key would be immediately obvious to those monitoring the state of the other photons in each pair.
(excerpt)

[Mind]

Originally posted by Lazarus Long

This link is to a NOVA series on String Theory, Relativity, and Quantum Mechanics. It requires sound and probably a broadband connection to enjoy it best but if you have these and a desire to view a well organized and "fun" basic primer of advanced physics here it is.

The Elegant Universe
(3 hours)
To view any part of this three-hour mini-series, choose an episode from one of the three columns.
Each hour-long episode is divided into eight chapters. These programs are not available for downloading due to rights reasons.
http://www.pbs.org/w...nt/program.html

********
Please everyone as you find high quality Video Lecture series like these post the links so that all subsequent seekers can share the wealth of knowledge we are gathering here.

[Mind]

Originally posted by Lazarus Long

I am also going to cross link this thread to the one on the lecture series started independently by Kevin and the one on String Theory where Jay posted the same link. This is because I am applying a unification principle of my own and encouraging the discussion to review the important information available in those threads.

String Theory
http://www.imminst.o...9&t=2909&hl=&s=

The Elegant Universe
http://www.imminst.o...9&t=2208&hl=&s=

[chubtoad]

http://www.umich.edu...4/Apr04/r043004

Physics researchers find striking quantum spin behavior

ANN ARBOR, Mich.—A University of Michigan physics professor and his team recently found striking behavior when, for the first time, they manipulated tiny spinning particles called “bosons”; then they used quantum mechanics to derive a new formula that exactly described the bosons’ unexpected spin behavior.

Scientists sometimes want to orient particles’ spins in a single direction in order to study the effect of spin on the scattering process, which in turn reveals a sort of medical scan of the particles' interior. The boson research was started at Indiana University's 0.5 GeV Cooler Storage Ring and continued at the Research Center Julich's 3 GeV COSY Storage Ring in Germany.

The team used beams of heavy hydrogen nuclei called deuterons. Because their spin value is exactly twice that of the more familiar elementary particles called protons and electrons, the deuterons are called bosons.

The behavior of spinning bosons is different from that of spinning electrons and protons, which can be fully described by their vector polarization. Describing spinning bosons also requires a tensor polarization which has one more dimension than a vector polarization, just as a sheet of paper has one more dimension than a string. 

A speculative, but perhaps possible, application of this research comes from the spinning bosons’ extra dimension. This might make the still-speculative but promising quantum computers more effective, because much more information could be stored in the extra dimension—a lake can hold much more water than a narrow stream, said Alan Krisch, U-M physics professor.

However, the main result of this basic research is the demonstration of yet another phenomenon that can only be explained by the elegant but hard-to-believe theory called quantum mechanics, and by the still-mysterious quantity called spin, which apparently can only have values of exactly one, two, three or four times the electron’s and proton’s exactly equal single-spin-values, Krisch said.

The new COSY data will be presented at the May meeting of the American Physical Society in Denver in a preliminary report prepared by graduate student Vasily Morozov and Krisch, who led the team of researchers from U-M, Illinois Tech, and Bonn University and the Research Center Julich in Germany. Most of the team are now carrying out yet another spin experiment at COSY; its timing conflicts with the May 1-4, 2004 APS meeting in Denver; thus, U-M graduate student Charles Peters will present the data.

The striking behavior was first seen at the Indiana Cooler Ring in 2002, but publication was delayed because the behavior could not be explained by any known formula. Then in late 2003, soon after a Michigan seminar by Wisconsin professor and deuteron expert, Willy Haeberli, the team derived a formula, from the quantum mechanics for bosons, which exactly explained the behavior. The paper was then quickly published in Physical Review Letters in November 2003. In December, the experiment was repeated at the COSY Storage Ring; this higher energy experiment confirmed the striking behavior found at the Indiana Cooler Ring, as will be reported at the Denver APS meeting. 

[Clifford Greenblatt]

Here is an article of fantastic proportions. Forget calculating at light speed, how about instantaneously?

Entangled electrons are connected in such a way that specific properties of the electrons remain synchronized regardless of the physical distance between them.

Laboratory demonstrations showing that the method could be used to transport electrons a few microns could happen within two to five years;

The electrons are synchronised over a distance, but are they synchronised at superluminal speeds? Objects that are mechanically linked to each other are mechanically synchronised, but not at superluminal speeds.

OTOH, an electron can exist in several places at the same time, but quantum-mechanical time travel does not carry information.

[chubtoad]

The electrons are synchronised over a distance, but are they synchronised at superluminal speeds?

Yes it is instantaneous. Its not like gravity where if the sun disappeared it would take time for the earth to realize it. This is one of the things that makes entanglement so weird.

[jasonmog]

is this legit or not? it's been around for some quite some time and having joined this forum, thought i should share it with all. it used to be accessible by searching teleportation in google but not anymore >.> MIT Teleportation

i also wanted to bring up these interesting questions that may or may not arouse some discussion:

- in the article it says it took 17 seconds i believe the number was for the mice to "reanimate" after teleportation. if this is relative to the mass and/or complexity of the object being teleported, then humans could take hours.. maybe days to reanimate!

- if you are destroyed and a 'copy' of you is made elsewhere instantaneously, isn't that death? would there be a clone walking around with all of your memories and personality walking around not knowing the difference nor others knowing either? scary eh? you'd no longer exist and some clone would be with your wife, raise your children, and be you. no one can know for sure, but after all there are completely different atoms arranged the same way as your own. what do you guys think? maybe i'd come out on the other side being...me?

- matter can neither be created nor destroyed... so what happens to the matter in the space your destination body takes up? as you are pieced back together, do your atoms move the oxygen, carbon dioxide, etc out of the way or what... it can't simply replace it :\ and how can the source body just be "destroyed"?

i don't expect anyone to know definite answers but who knows what you'll all think up

[alex83]

The article about teleportation was meant as an April Fools joke, look at: http://dgl.com/msg/v...pic=5&forum=5

Edited by alex83, 12 August 2004 - 11:41 PM.

[Lazarus Long]

I came across this discussion of the Uncertainty Principle and issues of Quantum theory. I thought it nicely laid out the areas of focus and it also includes numerous highly useful links on the source page. I hope this helps many of you integrate what you know with what you suspect and also what is generally understood.

http://story.news.ya...taintyprinciple




Quantum Astronomy: The Heisenberg Uncertainty Principle

Fri Nov 19,11:29 AM ET Science - Space.com

Laurance R. Doyle
Astronomer, SETI Institute
SPACE.com

This is the second article in a series of four articles each with a separate explanation of different quantum phenomena. Each article is a piece of a mosaic, so every one is needed to understand the final explanation of the quantum astronomy experiment we propose, possibly using the Allen Array Telescope and the narrow-band radio-wave detectors being build by the SETI Institute and the University of California, Berkeley.

In the first article, we discussed the double-slit experiment and how a quantum particle of light (a photon) can be thought of as a wave of probability until it is actually detected. In this article we shall examine another feature of quantum physics that places fundamental constraints on what can actually be measured, a basic property first discovered by Werner Heisenberg, the simplest form known as the "Heisenberg Uncertainty Principle."

In scientific circles we are perhaps used to thinking of the word "principle" as "order", "certainty", or "a law of the universe". So the term "uncertainty principle" may strike us as something akin to the terms "jumbo shrimp" or "guest host" in the sense of juxtaposing opposites. However, the uncertainty principle is a fundamental property of quantum physics initially discovered through somewhat classical reasoning -- a classically based logic that is still used by many physics teachers to explain the uncertainty principle today. This classical approach is that if one looks at an elementary particle using light to see it, the very act of hitting the particle with light (even just one photon) should knock it out of the way so that one can no longer tell where the particle actually is located -- just that it is no longer where it was.

Smaller wavelength light (blue, for example, which is more energetic) imparts more energy to the particle than longer wavelength light (red, for example, which is less energetic). So using a smaller (more precise) "yardstick" of light to measure position means that one "messes up" the possible position of the particle more by "hitting" it with more energy. While his sponsor, Nehls Bohr (who successfully argued with Einstein on many of these matters), was on travel, Werner Heisenberg first published his Uncertainty Principle Paper using this more-or-less classical reasoning just given. (The deviation from classical notion was the idea of light comes in little packets or quantities, known as "quanta," as discussed in article one). However the uncertainty principle was to turn out to be much more fundamental than even Heisenberg imagined in his first paper.

Momentum is a fundamental concept in physics. It is classically defined as the mass of a particle multiplied by its velocity. We can picture a baseball thrown at us at 100 miles per hour having a similar effect as a bat being thrown at us at ten miles per hour; they would both have about the same momentum although they have quite different masses. The Heisenberg Uncertainty Principle basically stated that if one starts to know the change in the momentum of an elementary particle very well (that is usually, what the change in a particle's velocity is) then one begins to lose knowledge of the change in the position of the particle, that is, where the particle is actually located. Another way of stating this principle, using relativity in the formulation, turns out to be that one gets another version of the uncertainty principle. This relativistic version states that as one gets to know the energy of an elementary particle very well, one cannot at the same time know (i.e., measure) very accurately at what time it actually had that energy. So we have, in quantum physics, what are called "complimentary pairs." (If you'd really like to impress your friends, you can also call them "non-commuting observables.")

One can illustrate the basic results of the uncertainty principle with a not-quite-filled balloon. On one side we could write "delta-E" to represent our uncertainty in the value of the energy of a particle, and on the other side of the balloon write "delta-t" which would stands for our uncertainty in the time the particle had that energy. If we squeeze the delta-E side (constrain the energy so that it fits into our hand, for example) we can see that the delta-t side of the balloon would get larger. Similarly, if we decide to make the delta-t side fit within our hand, the delta-E side would get larger. But the total value of air in the balloon would not change; it would just shift. The total value of air in the balloon in our analogy is one quantity, or one "quanta," the smallest unit of energy possible in quantum physics. You can add more quanta-air to the balloon (making all the values larger, both in delta-E and delta-t) but you can never take more than one quanta-air out of the balloon in our analogy. Thus "quantum balloons" do not come in packets any smaller than one quanta, or photon. (It is interesting that the term "quantum leap" has come to mean a large, rather than the smallest possible, change in something, and the order of the dictionary definitions of "quantum leap" have now switched, with the popular usage first and the opposite, physics usage second. If you say to your boss, "We've made a quantum leap in progress today" this can still, however, be considered an honest statement of making absolutely no progress at all.)

When quantum physics was still young, Albert Einstein (and colleagues) would challenge Nehls Bohr (and colleagues) with many strange quantum puzzles. Some of these included effects that seemed to imply that elementary particles, through quantum effects, could communicate faster than light. Einstein was known to then imply that we really could not be understanding physics correctly for such effects to be allowed to take place for, among other things, such faster-than-light connectedness would deny the speed-of-light limit set by relativity. Einstein came up with several such self-evidently absurd thought experiments one could perform, the most famous being the EPR (Einstein, Podolski, Rosen) paradox, named after the three authors of this paper, which showed that faster-than-light communication would appear to be the result from certain quantum experiments and therefore argued that quantum physics was not complete-that some factors had to be, as yet, undiscovered. This led Nehls Bohr and his associates to formulate the "Copenhagen Interpretation" of quantum physics reality. This interpretation, (overly simplified in a nutshell), is that it makes no sense to talk about an elementary particle until it is observed because it really doesn't exist unless it is observed. In other words, elementary particles might be thought of not just as being made up of forces, but that some constituents of it that must be taken into account are the observer or measurer as well, and that the observer can never really be separated from the observation.

Using the wave equations formulated for quantum particles by Erwin Schrödinger, Max Born was the first to make the suggestion that these elementary particle waves were not made up of anything but probabilities! So the constituents of everything we see are made up of what one might call "tendencies to exist" which are made into particles by adding the essential ingredient of "looking." Looking as an ingredient itself, it must be noted, took some getting used to! There were other possible interpretations we could follow, but it can be said that none of them was consistent with any sort of objective reality as Victorian physics had known it before. The wildest theories could fit the data equally well, but none of them allowed the particles making up the universe to consist of anything without either an underlying faster-than-light communication (theory of David Bohm), another parallel universe branching off ours every time there is a minute decision to be made (many worlds interpretation), or the "old" favorite, the observer creates the reality when he looks (the Copenhagen Interpretation).

Inspired by all these theories, a physicist at CERN (news - web sites) in Switzerland named John Bell came up with an experiment that could perhaps test some of these theories and certainly test how far quantum physics was from classical physics. By now (1964) quantum physics was old enough to have distinguished itself from all previous physics to the point that physics before 1900 was dubbed "classical physics" and physics discovered after 1900 (mainly quantum physics) was dubbed "modern physics." So, in a sense, the history of science in broken up into the first 46 centuries (if one starts with Imhotep who built the first pyramid as the first historical scientist) and the last century, with quantum physics. So, we can see that we are quite young in the age of modern physics, this new fundamental view of science. It might even be fair to say that most people are not even aware, even after a century, of the great change that has been taking place in the fundamental basis of the scientific endeavor and interpretations of reality.

John Bell proposed an experiment that could measure if a given elementary particle could "communicate" with another elementary particle farther away faster than any light could have traveled between them. In 1984 a team led by Alain Aspect in Paris did this experiment and indeed, this was undeniably the apparent result. The experiment had to do with polarized light. For illustrative purposes, let's say that you have a container of light, and the light is waving all over the place and -- if the container is coated with a reflective substance, except for the ends -- the light is bouncing off the walls. (One might picture a can of spaghetti with noodles at all orientations as the directions of random light waves.) At the ends we place polarizing filters. This means that only light with a given orientation (say like noodles that are oriented up-and-down) can get out, while back-and-forth light waves (noodles) cannot get out. If we rotate the polarizers at both ends by 90 degrees we would then let out back-and-forth light waves, but now not up-and-down light.

It turns out that if we were to rotate the ends so that they were at an angle of 30 degrees to each other, about half of the total light could get out of the container -- one-fourth from one side of the bottle and one-fourth through the other side. This is (close enough to) what John Bell proposed and Alain Aspect demonstrated. When the "bottle" was rotated at one end, making a 30-degree angle with the other side so that only half the light could escape, a surprising thing happened. Before any light could have had time to travel from the rotated side of the "bottle" (actually a long tube) to the other side, the light coming out of the opposite side from the one that was rotated changed to one-fourth instantaneously (or as close to instantaneous as anyone could measure). Somehow that side of the "bottle" had gotten the message that the other side had been rotated faster than the speed of light. Since then this experiment has been confirmed many times.

John Bell's formulation of the fundamental ideas in this experiment have been called "Bell's Theorem" and can be stated most succinctly in his own words; "Reality is non-local." In other words, not only do the elementary particles that make up the things we see around us not exist until they are observed (Copenhagen Interpretation), but they are not, at the most essential level, even identifiably separable from other such particles arbitrarily far away. John Muir, the 19th Century naturalist once said, "When we try to pick out anything by itself, we find it hitched to everything else in the universe." Well he might have been surprised how literally -- in physics as well as in ecology -- this turned out to be true.

In the next essay we will combine the uncertainty principle with the results of Bell's Theorem and increase the scale of the double slit experiment to cosmic proportions with what Einstein's colleague, John Wheeler, has called "The Participatory Universe." This will involve juggling what is knowable and what is unknowable in the universe at the same time.


---------------------------


For more information:

Werner Heisenberg: http://www.aip.org/history/heisenberg/

Nehls Bohr: http://en.wikipedia....wiki/Niels_Bohr

Albert Einstein: http://scienceworld....y/Einstein.html

John Bell: http://physicsweb.or...s/world/11/12/8

Erwin Schrödinger: http://scienceworld....hroedinger.html

Max Born: http://en.wikipedia.org/wiki/Max_Born

[jaydfox]

Here's an interesting article, comparing the decoherence process with natural selection. The most likely/stable states are most likely to decohere the same for each observer, making them "objective". Survival of the fittest/most stable quantum states. Quantum Darwinism. Et cetera...

http://www.nature.co.../041220-12.html



Published online: 23 December 2004; | doi:10.1038/news041220-12

Natural selection acts on the quantum world

Philip Ball

Objective reality may owe its existence to a 'darwinian' process that advertises certain quantum states.

A team of US physicists has proved a theorem that explains how our objective, common reality emerges from the subtle and sensitive quantum world.

If, as quantum mechanics says, observing the world tends to change it, how is it that we can agree on anything at all? Why doesn't each person leave a slightly different version of the world for the next person to find?

Because, say the researchers, certain special states of a system are promoted above others by a quantum form of natural selection, which they call quantum darwinism. Information about these states proliferates and gets imprinted on the environment. So observers coming along and looking at the environment in order to get a picture of the world tend to see the same 'preferred' states.

If it wasn't for quantum darwinism, the researchers suggest in Physical Review Letters1, the world would be very unpredictable: different people might see very different versions of it. Life itself would then be hard to conduct, because we would not be able to obtain reliable information about our surroundings... it would typically conflict with what others were experiencing.

Taking Stock

The difficulty arises because directly finding out something about a quantum system by making a measurement inevitably disturbs it. "After a measurement," say Wojciech Zurek and his colleagues at Los Alamos National Laboratory in New Mexico, "the state will be what the observer finds out it is, but not, in general, what it was before."

Because, as Zurek says, "the Universe is quantum to the core," this property seems to undermine the notion of an objective reality. In this type of situation, every tourist who gazed at Buckingham Palace would change the arrangement of the building's windows, say, merely by the act of looking, so that subsequent tourists would see something slightly different.

Yet that clearly isn't what happens. This sensitivity to observation at the quantum level (which Albert Einstein famously compared to God constructing the quantum world by throwing dice to decide its state) seems to go away at the everyday, macroscopic level. "God plays dice on a quantum level quite willingly," says Zurek, "but, somehow, when the bets become macroscopic he is more reluctant to gamble." How does that happen?

Quantum mush

The Los Alamos team define a property of a system as 'objective', if that property is simultaneously evident to many observers who can find out about it without knowing exactly what they are looking for and without agreeing in advance how they'll look for it.

Physicists agree that the macroscopic or classical world (which seems to have a single, 'objective' state) emerges from the quantum world of many possible states through a phenomenon called decoherence, according to which interactions between the quantum states of the system of interest and its environment serve to 'collapse' those states into a single outcome. But this process of decoherence still isn't fully understood.

"Decoherence selects out of the quantum 'mush' states that are stable, that can withstand the scrutiny of the environment without getting perturbed," says Zurek. These special states are called 'pointer states', and although they are still quantum states, they turn out to look like classical ones. For example, objects in pointer states seem to occupy a well-defined position, rather than being smeared out in space.

The traditional approach to decoherence, says Zurek, was based on the idea that the perturbation of a quantum system by the environment eliminates all but the stable pointer states, which an observer can then probe directly. But he and his colleagues point out that we typically find out about a system indirectly, that is, we look at the system's effect on some small part of its environment. For example, when we look at a tree, in effect we measure the effect of the leaves and branches on the visible sunlight that is bouncing off them.

But it was not obvious that this kind of indirect measurement would reveal the robust, decoherence-resistant pointer states. If it does not, the robustness of these states won't help you to construct an objective reality.

Now, Zurek and colleagues have proved a mathematical theorem that shows the pointer states do actually coincide with the states probed by indirect measurements of a system's environment. "The environment is modified so that it contains an imprint of the pointer state," he says.

All together now

Yet this process alone, which the researchers call 'environment-induced superselection' or einselection2, isn't enough to guarantee an objective reality. It is not sufficient for a pointer state merely to make its imprint on the environment: there must be many such imprints, so that many different observers can see the same thing.

Happily, this tends to happen automatically, because each individual's observation is based on only a tiny part of the environmental imprint. For example, we're never in danger of 'using up' all the photons bouncing off a tree, no matter how many people we assemble to look at it.

This multiplicity of imprints of the pointer states happens precisely because those states are robust: making one imprint does not preclude making another. This is a Darwin-like selection process. "One might say that pointer states are most 'fit'," says Zurek. "They survive monitoring by the environment to leave 'descendants' that inherit their properties."

"Our work shows that the environment is not just finding out the state of the system and keeping it to itself", he adds. "Rather, it is advertising it throughout the environment, so that many observers can find it out simultaneously and independently."


References

1. Ollivier H., Poulin D. & Zurek W. H. Phys. Rev. Lett., 93. 220401 (2004). | Article | PubMed | ChemPort |
2. Zurek W. H. Arxiv, Preprint http://www.arxiv.org...uant-ph/0105127 (2004).
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