q*c
发帖数: 9453 | 1 ou confused for a long time...
在QM 里面 有个双光子耦合试验，
不记的是不是EPR 试验了，
里面试验结果直接的说明了
那对光子就是知道对方的状态，
并且能够根据对方的状态来改变自己
的状态（自旋), 根本就不受任何速度限制...
那位大虾来给解释以下这个和相对论
以及因果律如何并存？
虽然这个试验还不能直接传送信息，
但是，只要存在这样一种途径，
信息能被超光速传递，我们就有
可能在将来直接利用啊，
那成什么样的世界了... | s**e
发帖数: 103 | 2
no, if you think carefully, no information has been propagated faster than
light. The person measured photon A knows the polarization of photon B
instantly, but for an observer at the position of photon B, he/she has no way
of knowing if A has make the measurement or not neither the result of it. QM
is consistant although I agree the interpretation is counter intuitive.
Please read the 1st chapter of Modern Quantum Mechanics by J.J.Sakurai if you
want to know more.
【在 q*c 的大作中提到】
: ou confused for a long time...
: 在QM 里面 有个双光子耦合试验，
: 不记的是不是EPR 试验了，
: 里面试验结果直接的说明了
: 那对光子就是知道对方的状态，
: 并且能够根据对方的状态来改变自己
: 的状态（自旋), 根本就不受任何速度限制...
: 那位大虾来给解释以下这个和相对论
: 以及因果律如何并存？
: 虽然这个试验还不能直接传送信息，
| c********s
发帖数: 123 | 3 he is talking about A, you are talking about B.
with your argument, information transfer speed cannot never exceed light
speed because A has to tell b what happens to B. But the thing is A knows
what happens to B once he knows A.
【在 s**e 的大作中提到】
:
: no, if you think carefully, no information has been propagated faster than
: light. The person measured photon A knows the polarization of photon B
: instantly, but for an observer at the position of photon B, he/she has no way
: of knowing if A has make the measurement or not neither the result of it. QM
: is consistant although I agree the interpretation is counter intuitive.
: Please read the 1st chapter of Modern Quantum Mechanics by J.J.Sakurai if you
: want to know more.
| f*******d
发帖数: 339 | 4
What you said is incorrect. A can not know what happens to B
(i.e. whether
B made an measurement, or in which direction did B made such
measurement).
He can only predict some behavior of B(i.e., if B made an
measurement
in the same direction as A does, he would found opposite
spin).
But this is not unique to quantum theory, even in classical
theory you
can make predictions of this kind, and it has nothing to do
with relativity.
This is the most common misconception about EPR I have seen.
【在 c********s 的大作中提到】
: he is talking about A, you are talking about B.
: with your argument, information transfer speed cannot never exceed light
: speed because A has to tell b what happens to B. But the thing is A knows
: what happens to B once he knows A.
| c********s
发帖数: 123 | 5 hehe, I was just reexpressing their ideas.
besides, you seem messed up with A and B.
【在 f*******d 的大作中提到】
:
: What you said is incorrect. A can not know what happens to B
: (i.e. whether
: B made an measurement, or in which direction did B made such
: measurement).
: He can only predict some behavior of B(i.e., if B made an
: measurement
: in the same direction as A does, he would found opposite
: spin).
: But this is not unique to quantum theory, even in classical
| s**e
发帖数: 103 | 6
agree with fisherdad. :-) knowing something about B is a prediction based on
your theory, there is no physical signal propagating.
【在 f*******d 的大作中提到】
:
: What you said is incorrect. A can not know what happens to B
: (i.e. whether
: B made an measurement, or in which direction did B made such
: measurement).
: He can only predict some behavior of B(i.e., if B made an
: measurement
: in the same direction as A does, he would found opposite
: spin).
: But this is not unique to quantum theory, even in classical
| q*c
发帖数: 9453 | 7 faint..., you guys know what I am talking?
A and B is not two PEOPLE!
they are two photons.
When People did the experiemnt, A and B are so far away from each other,
that, when A is meaured, and after time delta T, B is measured,
the delta T is so small, that nothing travelling slower than light
can communicate A and B.
So, A and B must not know each others state.
BUT! as far as you measured A, B instantly adjust itself spin to fit A.
First, you must know the idea that, no particle has a definite
【在 q*c 的大作中提到】
: ou confused for a long time...
: 在QM 里面 有个双光子耦合试验，
: 不记的是不是EPR 试验了，
: 里面试验结果直接的说明了
: 那对光子就是知道对方的状态，
: 并且能够根据对方的状态来改变自己
: 的状态（自旋), 根本就不受任何速度限制...
: 那位大虾来给解释以下这个和相对论
: 以及因果律如何并存？
: 虽然这个试验还不能直接传送信息，
| p*****g
发帖数: 38 | 8 this is too tricky... I feel like we are talking like pseudo-scientists,
too many pitfalls in the arguments.
but yes, there is this 'faster-than-light' effect embeded deep in the
classic QM fundermentals: when a state of a system collapses, it collapses
simultaneously at all spacepoint at once... this is instinctively so
controdictary to relativity, but actually the two are compatible, as we
already have a sucessful quantum field theory in which both are true.
within this framework, quantum effe
【在 q*c 的大作中提到】
: faint..., you guys know what I am talking?
: A and B is not two PEOPLE!
: they are two photons.
: When People did the experiemnt, A and B are so far away from each other,
: that, when A is meaured, and after time delta T, B is measured,
: the delta T is so small, that nothing travelling slower than light
: can communicate A and B.
: So, A and B must not know each others state.
: BUT! as far as you measured A, B instantly adjust itself spin to fit A.
: First, you must know the idea that, no particle has a definite
| s**e
发帖数: 103 | 9
QM is consistant because it claims nothing is physical until you measure
it. when you measure A, you can predict what you will get if you measure
B. But, until you measure B, nothing is physical about the spin of B. So
physical signal propagation is defined by the informational gained by
measurement of A and B. Unless when A is measured, the person that is going
to measure B instantly know the result of measurement, no physical signal is
propagating faster than light.
This is the wieldest thing
【在 q*c 的大作中提到】
: faint..., you guys know what I am talking?
: A and B is not two PEOPLE!
: they are two photons.
: When People did the experiemnt, A and B are so far away from each other,
: that, when A is meaured, and after time delta T, B is measured,
: the delta T is so small, that nothing travelling slower than light
: can communicate A and B.
: So, A and B must not know each others state.
: BUT! as far as you measured A, B instantly adjust itself spin to fit A.
: First, you must know the idea that, no particle has a definite
| f*******d
发帖数: 339 | 10
Yeah, we know, but just for a short hand...
agree above
That is not quite true. After seperating the two particles,
their state
is of the form (a |Aup, Bdown>+ b |Adown Bup>), so when you
measure A
you know the spin of B. Of course, it is changed (for
example to |Aup Bdown>,
I do not deny that, but this change is not directly
measurable in a single
experiment, as I explained in pose "quantum paradox".
Only people "know" something, it is not the particle know
anything.
At this point we are still
【在 q*c 的大作中提到】
: faint..., you guys know what I am talking?
: A and B is not two PEOPLE!
: they are two photons.
: When People did the experiemnt, A and B are so far away from each other,
: that, when A is meaured, and after time delta T, B is measured,
: the delta T is so small, that nothing travelling slower than light
: can communicate A and B.
: So, A and B must not know each others state.
: BUT! as far as you measured A, B instantly adjust itself spin to fit A.
: First, you must know the idea that, no particle has a definite
| | | q*c
发帖数: 9453 | 11 not quite understood and reasonable if "reality" has a clear definition.
BUt...if reality did not have a clear definition... it is also
hard to understand, so I'd better go back to Buddism, which
claim the world is illusion, and you can do it yourself...,
hehe, recently I meet people who claim world and time is just a illusion
and they can jump back to past or future...., I like it. :)
【在 f*******d 的大作中提到】
:
: Yeah, we know, but just for a short hand...
: agree above
: That is not quite true. After seperating the two particles,
: their state
: is of the form (a |Aup, Bdown>+ b |Adown Bup>), so when you
: measure A
: you know the spin of B. Of course, it is changed (for
: example to |Aup Bdown>,
: I do not deny that, but this change is not directly
| f*******d
发帖数: 339 | 12
Once David Mermin said QM shows that the moon does not exist
when no one
is looking at it:-) Of course, refuted by He Zuo Xiu:-)
【在 q*c 的大作中提到】
: not quite understood and reasonable if "reality" has a clear definition.
: BUt...if reality did not have a clear definition... it is also
: hard to understand, so I'd better go back to Buddism, which
: claim the world is illusion, and you can do it yourself...,
: hehe, recently I meet people who claim world and time is just a illusion
: and they can jump back to past or future...., I like it. :)
| l******r
发帖数: 4 | 13 谁能把EPR关联清楚地讲一讲
呵呵,俺真的有了兴趣 | q*c
发帖数: 9453 | 14 Never mention He..., I really
do not think he is a big guy.
he may be big only in CHINA.
【在 f*******d 的大作中提到】
:
: Once David Mermin said QM shows that the moon does not exist
: when no one
: is looking at it:-) Of course, refuted by He Zuo Xiu:-)
| q*c
发帖数: 9453 | 15 it is a litte long.
when you generate two photons simutaneously,
they have to meet the momentum conservation law.
so, when toy measure one, you will know the other.
BUT, QM does not permit you know one thing definitely
before you measure it. in fact, the particle did not
have a definite state before you measure it.
so, when you measure A, you in fact change B instantly.
people designed experiement,they do it one way that,
they measurement bwtween A and B is so close in time and
far away in space
【在 l******r 的大作中提到】
: 谁能把EPR关联清楚地讲一讲
: 呵呵,俺真的有了兴趣
| c********s
发帖数: 123 | 16 faint, what a blow to Wei-Wu-Zhu-Yi-Zhe.
hehe
【在 f*******d 的大作中提到】
:
: Once David Mermin said QM shows that the moon does not exist
: when no one
: is looking at it:-) Of course, refuted by He Zuo Xiu:-)
| l******r
发帖数: 4 | 17 而明白了,
量子力学的系统问题,
超距作用,
非相对论量子力学是承认的么
同志们,
没什么大惊小怪的么!
理论要靠实践来检验的.
【在 q*c 的大作中提到】
: it is a litte long.
: when you generate two photons simutaneously,
: they have to meet the momentum conservation law.
: so, when toy measure one, you will know the other.
: BUT, QM does not permit you know one thing definitely
: before you measure it. in fact, the particle did not
: have a definite state before you measure it.
: so, when you measure A, you in fact change B instantly.
: people designed experiement,they do it one way that,
: they measurement bwtween A and B is so close in time and
|
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