Quizzes & Puzzles11 mins ago
Fao Jim (Or Anyone Else With An Understanding!) Ref Khandro's "speed Of Light" Thread Below....
14 Answers
Jim, can you help me here please. According to the article photons from the 2 electrons were induced to meet midway between them to activate QE. So is that all that is needed for QE? if so QE must be naturally occurring all the time everywhere. a) is that correct. b) what effects would that give day to day, I mean are Quatum effects having a large effect on the macro world? thanks.
Answers
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I'm afraid that's a detail that is really tricky to explain -- partly because I don't understand the steps myself, and I'd have to work through it first. But in terms of your question, the particles (ab) remain entangled at least in part so that one can't be separated from the other, even after the further step of entangling with (c), so that the full description...
21:34 Sun 01st Nov 2015
My guess is that the effects of quantum entanglement in the macro world would be difficult to notice if they exist at all. The way of these quantum events is that the average of what could happen inevitably tends to result in what we predict in the macro world anyway. So umpteen things are tangled for a time, I can't see that being noticeable but await an informed opinion with interest.
OK, here goes.
a) yes;
b) sort of, but not really.
* * * * *
I'll start with a, mainly with a proper definition of entanglement. To do this I will have to introduce a bit of (rough) notation. the state of a quantum system, a, will be labelled as (a) -- note the brackets as they are really important here.
Entanglement works like this: take two particles, a and b, whose individual quantum states are called (a) and (b). The total system ab will have a quantum state (ab). For the system to be entangled, the following has to hold:
(ab) is not equal to (a)(b)
That is to say, you cannot pretend that your two-particle state is really just two separate one-particle states. The whole, in a sense, is greater than the sum of the parts (or, more accurately, the product, but let's not split hairs too much; this is meant as a very rough description).
Intuitively you might expect that, most of the time, (a)(b) is the same as (ab), but in fact it's almost always the other way round and quantum systems with multiple particles are usually entangled to some extent.So entanglement does occur (naturally) all over the place, and is fairly easy to set up, although not everything is entangled with everything else. Also, in experiments you want an entangled system to have a few useful properties: it has to be a well-defined type of entanglement, so that you can make useful predictions and measurements; and ideally the system should also stay entangled for long enough that you can do something with it. The last two aren't always true in "natural" entangled states, that are often hideously complicated or rather unstable.
But the short answer is yes: quantum entanglement effects occur all over the place in nature.
I'll answer (b) in a separate post a bit later, as it almost deserves a whole essay -- in the meantime, do please let me know if my answer to (a)'s clear/ helpful.
a) yes;
b) sort of, but not really.
* * * * *
I'll start with a, mainly with a proper definition of entanglement. To do this I will have to introduce a bit of (rough) notation. the state of a quantum system, a, will be labelled as (a) -- note the brackets as they are really important here.
Entanglement works like this: take two particles, a and b, whose individual quantum states are called (a) and (b). The total system ab will have a quantum state (ab). For the system to be entangled, the following has to hold:
(ab) is not equal to (a)(b)
That is to say, you cannot pretend that your two-particle state is really just two separate one-particle states. The whole, in a sense, is greater than the sum of the parts (or, more accurately, the product, but let's not split hairs too much; this is meant as a very rough description).
Intuitively you might expect that, most of the time, (a)(b) is the same as (ab), but in fact it's almost always the other way round and quantum systems with multiple particles are usually entangled to some extent.So entanglement does occur (naturally) all over the place, and is fairly easy to set up, although not everything is entangled with everything else. Also, in experiments you want an entangled system to have a few useful properties: it has to be a well-defined type of entanglement, so that you can make useful predictions and measurements; and ideally the system should also stay entangled for long enough that you can do something with it. The last two aren't always true in "natural" entangled states, that are often hideously complicated or rather unstable.
But the short answer is yes: quantum entanglement effects occur all over the place in nature.
I'll answer (b) in a separate post a bit later, as it almost deserves a whole essay -- in the meantime, do please let me know if my answer to (a)'s clear/ helpful.
Are the related questions tacked on manually, or something?
Nothing showing below this one yet, so here's a crosslink back to the thread with the news article in it.
http://
Nothing showing below this one yet, so here's a crosslink back to the thread with the news article in it.
http://
It depends on the details of the system but basically some entangled states are stable (ie last for pretty much ever), and these are the ones that can be/ are used in such experiments.
Still thinking a bit about part (b), it's a far more significant question, but I'll get to it this evening I think.
Also I wanted to take the opportunity to point out a powerful implication of entanglement, namely that quantum teleportation is possible. The principle being that you create an entangled state of two particles, and then entangle this state further with the actual particle you want to teleport, and then second one of the first two particles off elsewhere. A measurement of what is left will end up "telling" the distant particle to be in a quantum state related to the state of the particle you wanted to teleport. This evades problems of measurement collapsing the system, or running into the Uncertainty principle, because the final state isn't actually measured. A bit weird and tricky to explain, but it's been successfully realised in experiment already and the principle can be scaled up arbitrarily in theory at least.
Still thinking a bit about part (b), it's a far more significant question, but I'll get to it this evening I think.
Also I wanted to take the opportunity to point out a powerful implication of entanglement, namely that quantum teleportation is possible. The principle being that you create an entangled state of two particles, and then entangle this state further with the actual particle you want to teleport, and then second one of the first two particles off elsewhere. A measurement of what is left will end up "telling" the distant particle to be in a quantum state related to the state of the particle you wanted to teleport. This evades problems of measurement collapsing the system, or running into the Uncertainty principle, because the final state isn't actually measured. A bit weird and tricky to explain, but it's been successfully realised in experiment already and the principle can be scaled up arbitrarily in theory at least.
I'm afraid that's a detail that is really tricky to explain -- partly because I don't understand the steps myself, and I'd have to work through it first. But in terms of your question, the particles (ab) remain entangled at least in part so that one can't be separated from the other, even after the further step of entangling with (c), so that the full description has to be (abc) rather than (a)(bc) or something like that.
* * * * * *
So, to your second OP question.
Yes, quantum effect are having an effect on the macro world. They have to, because the quantum world is real and is indeed a far closer description of reality than the non-quantum world. On the other hand, quantum effects seem to effectively stop mattering after a while. It's not really easy to pin down why this is, although the best way of looking at it is as a scale thing. Most -- if not all -- quantum effects are measured in terms of a scale characterised by the Planck Constant h, which is roughly 10^-34 Joule seconds. The transition point between "classical", or macro-world, physics and quantum physics can be simply defined as the point where it starts to matter that the Planck constant is not actually zero.
For example:
-- the Uncertainty Principle states that, if x is a position measurement and p a momentum measurement, then the uncertainty in x times the uncertainty in p will be roughly equal to h. If you can say h = zero, then there is no uncertainty (so that position and momentum can be precisely known at the same time).
-- the property of quantum particles known as spin is quantised in units of h: this means that classically spin doesn't even exist (this is a little hand-wavy but is essentially a correct statement).
-- there is an important technique used in quantum physics called the "path-integral formalism", that amounts to working out how a particle travels between two points. when the quantum physics matters, the formalism can be interpreted as telling you that you have to consider, and sum over, all possible paths between the two points. (Whether the particle actually takes all paths is another matter.) But in the h=0 (classical) limit, the sum over all possible paths collapses into effectively just a single path that actually matters, which is the classical/ actual route taken.
In all of these the precise details are very fiddly, but the overall story is that quantum effects are too small-scale on the macro world to be of much importance in any practical calculations. They tend to cancel out, or smooth over, or just be too tiny to notice. So the macro world is the quantum world at large scales, but by accident or design this turns out not to matter. Most of the time.
I don't know if that's any use or not, but it's really hard to explain. In part because I don't think anyone really knows where the actual threshold between caring and not caring is. The "h=0 limit" is a useful way of expressing it mathematically but it is a little hand-wavy. Sorry I can't be more precise, but if you have any more questions I'll try to answer.
* * * * * *
So, to your second OP question.
Yes, quantum effect are having an effect on the macro world. They have to, because the quantum world is real and is indeed a far closer description of reality than the non-quantum world. On the other hand, quantum effects seem to effectively stop mattering after a while. It's not really easy to pin down why this is, although the best way of looking at it is as a scale thing. Most -- if not all -- quantum effects are measured in terms of a scale characterised by the Planck Constant h, which is roughly 10^-34 Joule seconds. The transition point between "classical", or macro-world, physics and quantum physics can be simply defined as the point where it starts to matter that the Planck constant is not actually zero.
For example:
-- the Uncertainty Principle states that, if x is a position measurement and p a momentum measurement, then the uncertainty in x times the uncertainty in p will be roughly equal to h. If you can say h = zero, then there is no uncertainty (so that position and momentum can be precisely known at the same time).
-- the property of quantum particles known as spin is quantised in units of h: this means that classically spin doesn't even exist (this is a little hand-wavy but is essentially a correct statement).
-- there is an important technique used in quantum physics called the "path-integral formalism", that amounts to working out how a particle travels between two points. when the quantum physics matters, the formalism can be interpreted as telling you that you have to consider, and sum over, all possible paths between the two points. (Whether the particle actually takes all paths is another matter.) But in the h=0 (classical) limit, the sum over all possible paths collapses into effectively just a single path that actually matters, which is the classical/ actual route taken.
In all of these the precise details are very fiddly, but the overall story is that quantum effects are too small-scale on the macro world to be of much importance in any practical calculations. They tend to cancel out, or smooth over, or just be too tiny to notice. So the macro world is the quantum world at large scales, but by accident or design this turns out not to matter. Most of the time.
I don't know if that's any use or not, but it's really hard to explain. In part because I don't think anyone really knows where the actual threshold between caring and not caring is. The "h=0 limit" is a useful way of expressing it mathematically but it is a little hand-wavy. Sorry I can't be more precise, but if you have any more questions I'll try to answer.
I think that's a Neils Bohr quote. Glad to be of help -- the main problem is that I'm trying to translate mathematical expressions of basically not really real things into words and avoiding maths entirely. I don't think that is ever going to be more than partly successful.
Still, thanks for asking.
Still, thanks for asking.
@jim360
and there was I, thinking there was a subtle dig, embedded in the question of whether the quantum world has any measurable effect (relevance, to put it bluntly) in the real world. What a cynic I am!
I'm not going to accuse it of being the counting of angels on pinheads, in the literal sense but, figuratively, it is at a similar remove from the daily lives of the general public.
Wait until the mystic types get hold of it though, assuming they grasp the whole "interconnectedness of all things" aspect. We'll not hear the end of it.
and there was I, thinking there was a subtle dig, embedded in the question of whether the quantum world has any measurable effect (relevance, to put it bluntly) in the real world. What a cynic I am!
I'm not going to accuse it of being the counting of angels on pinheads, in the literal sense but, figuratively, it is at a similar remove from the daily lives of the general public.
Wait until the mystic types get hold of it though, assuming they grasp the whole "interconnectedness of all things" aspect. We'll not hear the end of it.
You'd have to ask TTT if that was what he meant. If so, then the answer is that it has loads of relevance including the huge potential benefits of quantum computing, that while still very much stuck in the lab remains a very promising field making progress almost daily. More tangible benefits include lasers, ultra-precise atomic clocks, semiconductors (ie all modern computing), certain medical applications including MRI scanners, etc etc. The modern world is heavily built on the quantum -- although, in some instances, it isn't strictly necessary to know that this was the case. Apparently even light bulbs rely heavily on quantum phenomena in order to work -- which is both a surprise to me and not a surprise at the same time (a superposition of surprise states, you could say!)
Also, mystics have already jumped all over quantum mechanics for ages. They're all wrong in what they say, but that's never stopped anyone from abusing scientific concepts before.
Also, mystics have already jumped all over quantum mechanics for ages. They're all wrong in what they say, but that's never stopped anyone from abusing scientific concepts before.
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