Note: this topic is from July 17, 2002.
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Posted on 07/17/2002 3:47:40 PM PDT by gcruse
Here's how... Let's say two entangled photons are "frozen", they still keep their entangled properties, even if they don't move, am I wrong about that or do we not know yet? One photon is taken on a spaceship to alpha centauri. By manipulating the photon on earth, the one on the spaceship reacts. One type of reaction could be a DOT, the other a DASH. Presto, morse code, or even bits and bytes.
As in statistics, correlation is not causality. When you measure the polarization states of two entangled photons, you can no more say that event A caused event B than you can say that event B caused event A. For events with a "spacelike" separation (i.e., events with an invariant interval that is negative, which means that FTL communication is needed for a causal connection between them) the time ordering of the events is frame-dependent.
Suppose I keep two photons that are entangled. They resulted from the decay of a pi0 meson, and I've managed to catch each one in a box that is mirrored inside. The photons will bounce around inside indefinitely. At some point, Alice opens her box and measures the polarization state of her photon. Note that she can't choose the polarization state; all she can do is set up a filter which will either stop the photon or allow it to pass.
Bob opens his box at some other time (it doesn't really matter when, as long as Bob and Alice are far enough apart, because the time ordering of the events will be different for different observers). He measures the polarization state of his photon.
Later, Alice and Bob can compare notes, and see that the polarization states of the photons were correlated. If their filters were parallel, either both photons were absorbed or both were not; if their filters were perpendicular, one photon was absorbed and one was not; at intermediate angles, the correlation changes in a characteristic, angle-dependent way. But at no point was there any opportunity for Alice and Bob to send information to each other. There is no way either can divine the orientation of the other's polarization filter; the probability of any photon making it through the filter is 50%, regardless of orientation.
Go ahead an dash my dreams on this physie, just as I may have done to you on the "WE WILL FIND ET" thread.
You mean the probability argument? I still maintain that until you can enumerate all the ways in which life could have arisen, there is no way you can calculate how likely it was to have occurred.
Good old quantum mechanics. There's only so much information in a wave function. If you start with a single pi0 meson, for example, it only has one polarization state. That single state might not be an eigenstate of the system, however: the single state might be a 50% superposition of two eigenstates, for example, so if you go to measure it, it will collapse into one of those eigenstates. If nothing perturbs the system, it will not collapse into an eigenstate; it will be happy in its superposed state. If it decays into two photons, they will inherit that superposition, but there is still no more information than you started out with: the polarization states of the photons can't be independent of each other.
Now, you might say that, OK, the polarization state of the pi0 meson collapsed into an eigenstate upon its decay; the polarizations of the photons are correlated, of course, but they were decided when the decay occurred; I can do just as well by preparing two independent photons with the same polarization, and putting them into the mirror boxes instead. You could say that, but you'd be wrong. The photons you prepare that way will satisfy Bell's Inequality when you look at an ensemble of correlations, whereas an ensemble of photons from pi0 decay will violate it. The collapse of the polarization state of the long-defunct pi0 doesn't occur until the first of the boxes is opened (even though the order of the openings is ambiguous).
The problem with this feat is that it violates Einstein's long-held tenet that no communication can travel faster than the speed of light. Since traveling faster than the speed of light is tantamount to breaking the time barrier, this daunting prospect has caused some physicists to try to come up with elaborate ways to explain away Aspect's findings.
Codswallop. A lot of mysticism has arisen around the Aspect experiment, but all it did was to confirm the quantum mechanics of the 1920's. More specifically, it verified that nature violates Bell's Inequality, an implication of QM that was first noticed by John Bell in the 1960's. There is no need to "explain away" Aspect's findings; indeed, if they'd been otherwise, it would have been a serious problem for physics.
The correlations do not require any violation of special relativity. What they show is that nature is not locally causal. This was Einstein's main objection to quantum mechanics, its "spooky action-at-a-distance", to use his phrase. (We now know that Einstein was wrong about this.) But QM achieves this correlation without postulating any kind of a signal, so why do we need to introduce one? Just because nature isn't locally causal, it doesn't mean we have to throw out causality. We can simply throw out the notion of locality. Some information in the universe isn't tied to a specific location, that's all.
That's not to say that you can't construct, as Bohm did, a consistent interpretation wherein the correlations are mediated by a faster-than-light signal (which nonetheless cannot be used to communicate, an important point about Bohm's pilot wave). But the primary value in Bohm's work is to demonstrate that multiple metaphysical interpretations can coexist for the same epistemological model. There is no testable consequence of Bohm's interpretation that won't fit the Copenhagen interpretation equally well.
Hey,
You might enjoy the following article, if QE really interests you.
http://www.joot.com/dave/writings/articles/entanglement/
Ciao!
T
What entangled webs we weave!
Thanks!
Note: this topic is from 7/17/2002. Thanks gcruse.
So they pass through a metal barrier, and the entanglement remains? Why is that a surprise? I dont think that whatever the entanglement “is”, it does not go through our normal space.
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