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Author Topic:   Age of the Universe
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 91 of 103 (63525)
10-30-2003 9:17 PM
Reply to: Message 90 by Percy
10-30-2003 5:40 PM


Percipient,
So how is it that we can use the Bell experiment to serve as a detection system for encryption? Is that not information?
------------------
Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 90 by Percy, posted 10-30-2003 5:40 PM Percy has replied

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JustinC
Member (Idle past 4844 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 92 of 103 (63555)
10-31-2003 12:45 AM


I was thinking more along the lines of this: The photons have indeterminate polarities until one is observed. Once one is observed, the other photon has to somehow "know" this. So wouldn't the fact that the one photon is observed be transmitted instantaneously across the distance between the two photons?
JustinC

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 93 of 103 (63595)
10-31-2003 8:50 AM
Reply to: Message 92 by JustinC
10-31-2003 12:45 AM


JustinCy writes:
I was thinking more along the lines of this: The photons have indeterminate polarities until one is observed. Once one is observed, the other photon has to somehow "know" this. So wouldn't the fact that the one photon is observed be transmitted instantaneously across the distance between the two photons?
To reexpress this in terms of my stock market example, let's say you want your partner to sell stock upon your command. You entangle some photons and and give your partner one, telling your partner that when she detects that you've observed your photon she should sell the stock.
How does she know you've observed your photon? She can't keep checking her photon, because the first time she checks it it will collapse to a specific polarity, collapsing yours simultaneously, which wasn't what you intended to happen. This problem calls attention to a key facet of these quantum experiments that is rarely mentioned - that time synchronization between the two observers is strictly maintained by some means. You and your partner have to agree upon the specific time that you will be observing your photon, you have to maintain strict synchrony between your clocks, and then your partner has to observe her photon an instant after the time you said you would observe it.
Naturally if you have to preagree upon a time of observation then there's no way that your approach could be used to communicate that time. In fact, let us say you sleep in and fail to observe your photon at the agreed upon time. Your partner would observe her photon at that time but would have no way of knowing that you didn't. At least not until you call her later by regular speed-of-light telephone and sheepishly admit that you'd screwed up.
--Percy

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 94 of 103 (63598)
10-31-2003 8:59 AM
Reply to: Message 91 by Rrhain
10-30-2003 9:17 PM


Rrhain writes:
So how is it that we can use the Bell experiment to serve as a detection system for encryption? Is that not information?
Unbreakable encryption is a practical application of entanglement, while faster-than-light communication using entanglement is not thought possible in the context of current theory.
--Percy

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JustinC
Member (Idle past 4844 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 95 of 103 (63658)
10-31-2003 1:12 PM


Does information have to have a practical use for the conscious observer to be considered info? I think I'm working with too broad of a definition.
What would we say is happening? Say we only have two angles of polarity. Then collapsing of one photon causes the causes the other sphoton to have a hundred percent chance of being polarized at a certain angle if it collapsed. So somehow an event caused an instantaneous effect light years away. Doesn't the other photon somehow have to "know" the other one is beign observed?
JustinC
[This message has been edited by JustinCy, 10-31-2003]

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sidelined
Member (Idle past 5908 days)
Posts: 3435
From: Edmonton Alberta Canada
Joined: 08-30-2003


Message 96 of 103 (63669)
10-31-2003 2:03 PM
Reply to: Message 95 by JustinC
10-31-2003 1:12 PM


It is rare that further study of quantum mechanics makes things clearer but you might take a look at this interpretation of entanglement. http://www.quantum.univie.ac.at/links/newscientist/bit.html

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 97 of 103 (63671)
10-31-2003 2:33 PM
Reply to: Message 95 by JustinC
10-31-2003 1:12 PM


JustinCy writes:
Does information have to have a practical use for the conscious observer to be considered info? I think I'm working with too broad of a definition.
Information need have no practical use, and it need not originate with an intelligence. Indeed, for the purposes of information theory, a random bit stream contains more information than anything else. This is because the information density of a stream of bits is a function of the probability that the receiver can't predict the next bit.
The common use of the word "information" is not the same as in an information theory context. "Information" in information theory is often confused with knowledge. But in information theory, information is a mathematical concept. The maximum information content of any bit stream is proportional to the log2 of the number of bits.
What would we say is happening? Say we only have two angles of polarity. Then collapsing of one photon causes the causes the other sphoton to have a hundred percent chance of being polarized at a certain angle if it collapsed. So somehow an event caused an instantaneous effect light years away. Doesn't the other photon somehow have to "know" the other one is beign observed?
I don't think I know whether it "knows" immediately upon the other photon being observed, or whether it only "knows" after it is observed. But for the sake of this discussion, let us assume that it "knows" immediately upon the other photon being observed. How is it going to communicate the information that the other photon has been observed to the local observer? It can't ring a bell. And when the local observer looks at it, it's not possible for her to know whether she or her partner with the other entangled photon was the first to observe, not without exchanging some additional speed-of-light information.
--Percy

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JustinC
Member (Idle past 4844 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 98 of 103 (63796)
11-01-2003 10:47 AM


Let's say we put an electron in a box, then divide the box in half. The probability wave is now in both halfs, and each has a 50/50 chance of having the electron. Each box is given to a person. Each person is sent in opposite directions, identically accelerated to a constant velocity. Before they left, they synchronized their atomic clocks and the one agreed to begin to observe whats in the box at time x and the other at time x+1. Wouldn't the observer at x+1 recieve "information" about what the observer at x is observing? Or am I equivocating information and knowledge?
JustinC

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Taco
Inactive Member


Message 99 of 103 (63827)
11-01-2003 4:58 PM
Reply to: Message 98 by JustinC
11-01-2003 10:47 AM


JustinC,
I don't think it works that way. Fundamentally, there is no way of knowing if the wavefunction has collapsed because of observer A or observer B.

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 100 of 103 (63828)
11-01-2003 4:58 PM
Reply to: Message 98 by JustinC
11-01-2003 10:47 AM


Hi JustinCy,
Wouldn't the observer at x+1 recieve "information" about what the observer at x is observing?
Well, sort of, but only in retrospect. The observer at time x+1 cannot know for certain that at time x her partner observed his box. All she can know is that *if* he did as he said he would, then she knows faster than the speed of light what he observed. Of course, she can't know this for certain until they carry out some much slower speed-of-light communications.
The speed-of-light communication problem is key. We can set up a Schroedinger's cat kind of scenario. The observers pledge that whoever finds an electron in their box will commit suicide. The observers travel a few light years apart, and then they look in their boxes. The one who finds the electron presumably commits suicide as agreed. The other observer finds no electron and knows, faster than the speed of light, that their partner is dead. Saddened, our observer returns home expecting that their partner would have been buried several years before, but is instead surprised and delighted to be greeted by their partner, who reveals that they just couldn't go through with the suicide. And this information could only be communicated no faster than the speed of light.
You can spend endless hours developing scenarios where it appears that information is transmitted faster than light, and many, many people have done this, but in the end you find you've only made more difficult discovering the flaw in the scenario, and that faster-than-light communication of information is truly impossible.
--Percy

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JustinC
Member (Idle past 4844 days)
Posts: 624
From: Pittsburgh, PA, USA
Joined: 07-21-2003


Message 101 of 103 (63836)
11-01-2003 7:08 PM


quote:
Well, sort of, but only in retrospect. The observer at time x+1 cannot know for certain that at time x her partner observed his box. All she can know is that *if* he did as he said he would, then she knows faster than the speed of light what he observed. Of course, she can't know this for certain until they carry out some much slower speed-of-light communications
Thanks, I think I understand now. You have to assume information in order to obtain any, and that assumption cannot be known except by through information that traveled less than the speed of light.
Would my scenerio really be any different than two kids travelling apart in different directions, and the one agrees to jump at time x. So when time x comes around, you "know" he jumped?
JustinC

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BobAliceEve
Member (Idle past 5395 days)
Posts: 107
From: Seattle, WA, USA
Joined: 02-03-2004


Message 102 of 103 (82511)
02-03-2004 7:00 AM
Reply to: Message 101 by JustinC
11-01-2003 7:08 PM


What is an observation?
I have not been able to locate a description of a valid observer. Is it:
1. A human who will tell the truth about the observation.
2. A human who will lie about it.
3. An honest person traveling at 2/3 the speed of light and only gets a tiny glimpse of the box.
4. My well trained, fully aware cat at 2:00 AM.
5. My well trained, lazy cat at 2:00 PM.
6. An electron which happens to drift past the observable.
Thanks in advance,
Bob, Alice, and Eve

This message is a reply to:
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BobAliceEve
Member (Idle past 5395 days)
Posts: 107
From: Seattle, WA, USA
Joined: 02-03-2004


Message 103 of 103 (85703)
02-12-2004 6:53 AM
Reply to: Message 101 by JustinC
11-01-2003 7:08 PM


I see better now
On further reading, I think I have a better understanding of this. I took literally statements like "The universe sees itself unfolding through our eyes" and thought there had to be an observer. Then I came across articles that explained technically that when the wave travels into matter it "declares an attribute" Is that more correct?
Thanks,
Bob, Alice, and Eve
P.S. I am interested, possibly obviously, in cryptography from the quantum side.

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