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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17269
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revolution
Borsuc wrote:
Entanglement is not communication. Entanglement is only valid if you look AT BOTH of them. And looking at both of them REQUIRES information travel, light travel communication.

It is like encryption. Suppose you generate a random seed, and share it with me ("entangle" the two seeds). You and me will then have this key and go on different ends of the Universe.

I run the seed once and predict that after X number of usage (random function), the seed will be 0. (if it's a pseudo-random function that changes seed on usage)

I know that after Y number of usage in YOUR seed, the seed will also be 0. Hence I know your outcome.

Is this FTL? Not kinda.

It really isn't that weird, as far as I understood it at least. Suppose you have "quantum states" instead of "random seed", which are entangled. Then we go to opposite ends of the Universe. This 'state' is random and has a 50% chance to be in A and 50% to be in B (this is for simplification purposes).

I then examine it and it falls on A. Then, I know that in YOUR case, it will 100% fall on A, not 50%. But you don't know that, because you haven't communicated with me, which requires light-speed communications.
You explanation misses an important point. The analogy above suggest that the photons have already decided what value to have before the measurement is made. This is not the way it is stated to work in QM. Unlike the PRNG sequence - which is predictable - the photon state is not predictable. The important difference is that with a PRNG you can both independently run the sequence at any time without affecting the outcome of the other person, entanglement is different in that only when one person measures their photon, does the other photon then "decide" which state to take on. If that seems paradoxical, then that is good, even proponents in the field say it is a weird behaviour. QM is like that, I still have hard time accepting some of the claims. But I don't now enough to say whether it is wrong or right. Tests like the delayed choice quantum eraser have tried to discover if this behaviour is correct.
Post 11 May 2009, 04:23
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Madis731



Joined: 25 Sep 2003
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Location: Estonia
Madis731
Actually its not that simple, Borsuc, with quantum mechanics envolved. Why they are talking about measuring and communications in the same sentence is because (from what I've read) you can't measure a particle without affecting it. Thus you measure and you automatically change its state some way. The other particle (which is entangled) will share the same knowledge, but it is not light-travel.
As I understand it, they are (on quantum level) "magnetically linked" (closest term I could conceive) and when you take a parallel approach with two magnets on a stick able to rotate ( "+"T"-" ), you will rotate one magnet and the other will follow.
But in quantum-mechanics it happens almost instantly (as we know it).

I'm always glad to hear corrections if you may!
EDIT: And the corrections start coming in: "(classical teleportation) has also been formally shown to be impossible. (See the no teleportation theorem.) This is another way to say that quantum information cannot be measured reliably." from http://en.wikipedia.org/wiki/Quantum_teleportation and related articles.

EDIT2: I just remembered this: http://xkcd.com/465/

EDIT3: I found this to be interesting
Post 11 May 2009, 06:34
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Borsuc



Joined: 29 Dec 2005
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Location: Bucharest, Romania
Borsuc
Madis731 wrote:
Actually its not that simple, Borsuc, with quantum mechanics envolved. Why they are talking about measuring and communications in the same sentence is because (from what I've read) you can't measure a particle without affecting it. Thus you measure and you automatically change its state some way.
This is the problem. The other person must measure it too, and change it because of that. If the PRNG gives you '5' the first time which has a 10% chance (from probability), the other person is not aware of that situation. When he/she measures it, it also gets a '5'. You KNOW that he/she will measure '5' with 100% certainty instead of 10% as before. Does that mean you affected the output instantly? Not kinda. And unless you communicate this to him/her, he/she will think it's 10%. And communication requires at most light travel.

Imagine what would happen if the entanglement was really 'communication' travel instantly. Our whole experiments would be pointless -- what if aliens were fooling around with the atoms that we used in our experiments? Or not aliens but rather the Universe fooling around with entangled particles? It means our experiments would surely not be predictable at all.

But it's at least the way I understood it from some texts (try to google why entanglement doesn't transfer information and see a lot of them Confused).

@revolution: the problem is that measuring AFFECTS the output. If you want to see that 2 entangled photons affect each other, you have to measure them, which will modify them, which means: moot point. That is why it seems weird, but I really don't think it is. Just that we're not omniscient Wink

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Post 11 May 2009, 17:28
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Madis731



Joined: 25 Sep 2003
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Madis731
With the link I posted with my 3rd edit in my last post I try to defend that teleportation indeed is possible. http://www.signandsight.com/features/614.html
second paragraph under his picture he starts his answer to "What are you doing?":
Anton Zeilinger wrote:

Transferring the properties of light particles over certain distances onto other light particles, with no time delay.
Post 11 May 2009, 18:51
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Borsuc



Joined: 29 Dec 2005
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Borsuc
Anton Zeilinger wrote:
Theoretically yes. The effect has so far been proved across a distance of a hundred kilometres. The amazing thing is that there can be no exchange of information between the two particles. They react absolutely in synch, although they could could never know anything of each other's existence. You can think of it as two dice far away from each other that always land on the same number, without there being any kind of mechanism which connects them. Absurd!
'teleportation', as far as my definition is concerned, must teleport information.

Of course quantum tunneling is already such a thing. But not of teleportation of information for large distances.
Post 11 May 2009, 19:03
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Madis731



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Madis731
Hmm, my mind is blown up Smile I have no more counter-arguments.
Post 12 May 2009, 05:59
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Borsuc



Joined: 29 Dec 2005
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Borsuc
For sure it is weird, but in my opinion, quantum tunneling is a much better candidate if properly understood for teleportation than entanglement Smile
Post 12 May 2009, 19:13
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edfed



Joined: 20 Feb 2006
Posts: 4237
Location: 2018
edfed
everything is gears.
if something moves somewhere, something else will move elsewhere just because of GEAR effect.

but it cannot be instataneous because of PROPAGATION.
even in a perfect mechanism, there will be propagation and then, time to transmit the movment (information).
even with perfect materials there will be propagation speed because matter is not only matter, it is full of vaccum too, and this vaccum gives elasticity to matter.

:s
Post 14 May 2009, 22:38
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