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Author Topic: Why can't quantum teleportation transmit information faster than light?  (Read 2589 times)

Offline Expectant_Philosopher

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From what I see published about quantum teleportation and quantum entanglement scientist adhere to the notion that information cannot be transmitted faster than light.  However they at the same time tell us for entangled particles that if you change the state of one entangled particle the other entangled particle in the pair immediately changes state no matter how far apart they are.  To me the ability to induce a change at one end and to see the change in state of the entangled particle at the far end is the basis for a digital transmission system.  With current digital communications systems we arbitrarily measure low voltages as a digital zero and high voltages as a digital 1 and the modulation of these states to transfer information.  With quantum entanglement if we arbitrarily established that the digital zero would be represented by two simultaneous quantum state changes and the digital one as three simultaneous quantum state changes with the null state change as the character separator we could, it seems to me to transmit information digitally between far flung places, faster than the speed of light.


 

Offline PmbPhy

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Quote from: Expectant_Philosopher
From what I see published about quantum teleportation and quantum entanglement scientist adhere to the notion that information cannot be transmitted faster than light.
I donít know much about quantum teleportation but I do this; because it depends on classical communication, which can proceed no faster than the speed of light, it cannot be used for superluminal transport or communication.
Entanglement canít be used simply because no information can be sent using entanglement.
Quote from: Expectant_Philosopher
However they at the same time tell us for entangled particles that if you change the state of one entangled particle the other entangled particle in the pair immediately changes state no matter how far apart they are.
All that can be done is to make a measurement of a system. Once the measurement is made the system collapses into one of say two states. For example; if the spin of one particle is measured to be up then all that can be said is that the spin of the other particle will be down. No information is transmitted in such a process.
Quote from: Expectant_Philosopher
To me the ability to induce a change at one end and to see the change in state of the entangled particle at the far end is the basis for a digital transmission system.
The problem is that you canít control which state the system collapses into when a measurement is made. Therefore you have no idea whatís going on with one particle merely by measuring properties of the other particle.
 

Offline Expectant_Philosopher

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If the spin states are exactly opposite then you know the state of the far particle without looking at it, merely knowing the spin state of the near particle. Can you arbitrarily induce spin state in the near particle thereby controlling the spin state at the opposite end?
 

Offline PmbPhy

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Quote from: Expectant_Philosopher
If the spin states are exactly opposite then you know the state of the far particle without looking at it, merely knowing the spin state of the near particle.
That's correct. However that isn't sending information or anything like that.

Quote from: Expectant_Philosopher
Can you arbitrarily induce spin state in the near particle thereby controlling the spin state at the opposite end?
Unfortunately, no. If that were possible then it'd be possible to send information FTL.
 

Offline jeffreyH

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If the spin states are exactly opposite then you know the state of the far particle without looking at it, merely knowing the spin state of the near particle. Can you arbitrarily induce spin state in the near particle thereby controlling the spin state at the opposite end?

Say you have two participants in an experiment 300 million metres apart. one starts the entanglement transmission and you detect one entangled particle. The sender would have to trap his particle in order to measure its state and send a confirmation. So even with a one second gap you are only guessing until confirmation arrives. Consider the two participants at 1 million times greater the distance. You then cannot even guarantee that the entanglement remains unaffected in its journey and the confirmation time is even worse. The send and receive times are worse. In this case the signal round trip is 22 days. Not exactly FTL.

How would you ever have error correction without confirmation?
« Last Edit: 31/07/2014 02:07:41 by jeffreyH »
 

Offline Expectant_Philosopher

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Why couldn't the message itself without standard error correction be the check?  If you have an outgoing transmission system and an incoming transmission system, and the outgoing sends a serial code say 12345678 and the incoming system receives the proper next serial code of 12345679 then you'd know a proper and expected transmission took place.
 

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