Twinned and Entangled
For each of 10 possible pathways a quantum particle might follow, for example, there would exist a separate universe. Since the 's, Dr.
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John F. Clauser of the University of California at Berkeley, Dr. Alain Aspect at the Institut des Optics in Orsay, France, and others have been experimenting with pairs of entangled particles.
One way to create a pair of entangled twins is to start with a single photon of ultraviolet radiation and pass it through a peculiar artificial mineral called a ''down-conversion crystal. The crystal splits the photon in two, producing two new photons that continue on in somewhat different directions, and whose combined energy equals the energy of their parent photon.
View all New York Times newsletters. The special quality of such pairs, as shown both by theory and experiment, is that they are entangled quantum mechanically. This means that if the polarization or energy or timing of one of the particles is measured, its indefinite state is destroyed and it falls into a definite state. The astonishing consequence of this is that the particle's distant twin experiences exactly the same metamorphosis at the same moment, even though there is no physical link or signal between the two twins.
Far Apart, 2 Particles Respond Faster Than Light
In a famous paper by Albert Einstein, Boris Podolsky and Nathan Rosen challenged the quantum theory prediction that entangled particles could remain instantly in touch with each other. One of their objections was based on the speed limit imposed by Einstein's Special Theory of Relativity: nothing can travel faster than the speed of light. Einstein and his colleagues preferred a more intuitive explanation of the simultaneous correlation between entangled particles, based on the idea that the match between them is ordained by their identical antecedents.
The behavior of each particle, they argued, is the product of hidden ''local'' factors, not by spooky long-distance effects. But again and again in recent years, increasingly sensitive experiments have decisively proved that Einstein's explanation was wrong and quantum theory is correct. In Dr. Gisin's experiment, as in earlier ones, no signal of any kind was transmitted between the photons, but despite this, one of the photons ''knew'' what happened to its distant twin, and mimicked the twin's response.
This response took less than one ten-thousandth of the time a light beam would have needed to carry the news from one photon to the other at a speed of , miles per second. In fact, the correlation between the two particles was presumably instantaneous. The Swiss experiment merely set an upper limit on the time required for the response as about three ten-billionths of a second. Gisin's experiment made use of a system of paired interferometers developed by Dr. James D. Franson of Johns Hopkins University, who is also a leading investigator of quantum effects. Each interferometer, a device for separating and then recombining beams of light, consists of a complex arrangement of mirrors and ''beam splitters'' -- semi-opaque reflectors that randomly reflect some photons in one direction and transmit others in a different direction.
In an interview, Dr. Franson explained the system:. One goes one way and the other goes another way, both to identical interferometers. Entering its own interferometer, each photon must make a random decision as to whether it will travel a long pathway through the device or a short one. Then you look for a correlation between the pathways taken by the photons in their respective interferometers.
If the timing between the photons is exactly adjusted, each twin seems to know what the other is doing and matches its choice of pathway to coincide with that of its distant partner. Franson said of the correlation demonstrated over a seven-mile course by the Swiss experiment, ''It's pretty amazing. Whatever the nature of the connection between entangled particles may be, nearly all physicists agree that it cannot be used to transmit messages faster than the speed of light.
All it can do is assure that a random choice by one entangled particle is instantly echoed by its distant partner. This is not the same thing as transmitting information, the experts say, and therefore it does not violate relativity theory. But why is a numerical correlation between two particles different from information? Franson said, ''and I don't think anyone could give you a coherent answer. Quantum theory is confirmed by experiments, and so is relativity theory, which prevents us from sending messages faster than light.
I don't know that there's any intuitive explanation of what that means. Another deep quantum mystery for which physicists have no answer has to do with ''tunneling'' -- the bizarre ability of particles to sometimes penetrate impenetrable barriers. This effect is not only well demonstrated; it is the basis of tunnel diodes and similar devices vital to modern electronic systems. Tunneling is based on the fact that quantum theory is statistical in nature and deals with probabilities rather than specific predictions; there is no way to know in advance when a single radioactive atom will decay, for example.
The probabilistic nature of quantum events means that if a stream of particles encounters an obstacle, most of the particles will be stopped in their tracks but a few, conveyed by probability alone, will magically appear on the other side of the barrier. The process is called ''tunneling,'' although the word in itself explains nothing. Chiao's group at Berkeley, Dr. Aephraim M. Steinberg at the University of Toronto and others are investigating the strange properties of tunneling, which was one of the subjects explored last month by scientists attending the Nobel Symposium on quantum physics in Sweden.
Chiao said, ''that a barrier placed in the path of a tunneling particle does not slow it down. In fact, we detect particles on the other side of the barrier that have made the trip in less time than it would take the particle to traverse an equal distance without a barrier -- in other words, the tunneling speed apparently greatly exceeds the speed of light.
Moreover, if you increase the thickness of the barrier the tunneling speed increases, as high as you please. Most physicists and engineers set aside the contemplation of quantum mysteries and are content to exploit the innumerable applications quantum physics has found in technology, including lasers, solid-state electronics and much more. But the sense of mystery has never been entirely suppressed.
The late Rockefeller University physicist Heinz Pagels, like many other theorists, believed that quantum physics is a kind of code that interconnects everything in the universe, including the physical basis of life itself. In his book ''The Cosmic Code,'' Dr.
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Pagels, an ardent mountain climber, wrote:. Such dreams are commonplace to the ambitious or those who climb mountains. Lately I dreamed I was clutching at the face of a rock, but it would not hold. Gravel gave way. I grasped for a shrub, but it pulled loose, and in cold terror I fell into the abyss. This is the subtlety I wanted to avoid in the post. The last link in the post does talk about it in detail although, looking at it again, it helps a lot to have read chapters 2 and 3 already, and to have a little back ground in quantum mech.
Thus, it is possible to determine whether the particle is entangled.
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Suppose we have a right a left slit in a double slit experiment. If we send some photons towards the slits, we might call going through the left slit 0 and the right slit 1. Allowing the particle to be detected on a screen beyond the slits acts in much the same way as our example unitary transformation.
We see interference on the screen, which is analogous to always measuring 0. So long as the detector has perfect information — as long as L and R are orthogonal — we no longer see interference at the screen. This is how measurement destroy interference. In regards to the previous comment by Mark Eichenlaub I would love to know the physicists response to his ideas about the collapse of the wave function in the double slit experiment and if it is in fact the particle entangling with the measuring device?
I know entanglement takes very specific situations to take place, but could this be an explanation for the collapse of the wave function? If the detector is not there, then the photon can go through both slits and act like a wave. Once you put the detector there then the photon should still act the same, unless you have retrocausality taking place whereby the photon goes through both slits, is measured and then entangles itself with the detector and then goes back to acting like a wave. How can the photon KNOW to act differently?
Why not to assume that the entangled particles are actually physically connected like 2 balls on either side of a stick? The Physicist, delving a bit into hypotheticals for a moment, if you wouldnt mind. There are theoretical uses for entanglement, for this question, long rang instant communication. Could you use a so called Q-phone I had to make a pun somewhere, forgive me to observe conditions on the opposite side of the event horizon? As I understand black holes which I may be woefully misinformed about particles do not simply cease to exist past the event horizon.
Is this incorrect? What do our theories say on this hypothetical situation? I understand that the idea itself may violate causality, but please, humor me. Am I incorrect in stating that position and forces do not influence the entanglement of a particle assuming shielding from decoherence , in the sense that no classical force can disrupt it?
It might be that gravity cold be explains with some entanglement also.. Now we know about Highs and the gravity could be a phenomenon in that field… Than layers of universe and it is time for fuzzy logic. I assume that several particles can be entangled? From what I could gather the answer was yes but correct me if wrong. Then as each instance is used in different ways it evolves individually through its life cycle, not to mention biological influences nature vs nurture. In summary, could a massive structure of particles, containing some entangled particles, create new entanglement relations from non entangled particles that belong to that same structure and sub structure?
There's a book! It's a collection of over fifty of my favorite articles, revised and updated. It's interesting. It's good. You should buy it. Click the photo for a link to the amazon page, or this link for the ebook. Email Address. Skip to content. Home About Faq. Would any change take place? And does centrifugal force have an effect on gravity? Q: Two entangled particles approach a black hole, one falls in and the other escapes.
Do they remain entangled? What about after the black hole evaporates? Posted on December 28, by The Physicist. Email Print Facebook Reddit Twitter. Bookmark the permalink. Crosse says:. December 29, at am. The Physicist says:. Luke says:.