Re: L'ing. Keshe sta facendo il possibile...
Inviato da Lord9600XT il 27/1/2013 11:44:20
Se la vostra ricerca fosse stata un attimo più approfondita, avreste scoperto che tramite il fenomeno dell'entanglement quantistico non è possibile inviare alcuna informazione a velocità superiore della luce.
Il punto cruciale della questione è che il collasso della funzione d'onda dello stato entangled è sì istantaneo, ma la funzione d'onda non è un osservabile, quindi questa istantaneità non è misurabile: ecco spiegato il motivo fisico per cui non è affatto possibile usare il collasso della funzione d'onda per inviare istantaneamente informazioni.
Visto che mi limiterei soltanto a ripetere gli stessi concetti, cito testualmente un trafiletto trovato in rete (tra l'altro, nella prima pagina di ricerca di Google alla voce "entanglement speed light") che spiega estremamente bene la situazione:
"Suppose that we have two spin 1/2 particles (if you don't know what that is, think of them as coins that have a "heads" side that can be either up or down). They are in an entangled state such that 50% of the time particle A is found to be spin up (heads up) and particle B is spin down (heads down, i.e. tails), and the other 50% of the time A is found to be spin down and B is spin up. This is called a maximally entangled bell state and can be written
|ψ> = 1/sqrt(2) (|up>A*|down>B + |down>A*|up>B)
in Dirac notation. Now, the important point about this entanglement is that it can never happen that A and B are found with both spins up or both spins down, so if we measure A and find that it is spin up, then we already know that B MUST be spin down, even before we measure it.
At this point you might object, "But you just said we know the state of particle B even before we measure it, so if it's like a million light years away, doesn't that mean we just got information faster than the speed of light?" The answer is no, not really. We only know what state B is in because we already knew the quantum state of the system made up of A and B at the beginning and we know the outcome of the measurement on A. The true test of whether information is sent is whether we're able to use this to send some sort of message to someone who is measuring particle B.
Ok, so let's say that Alice has particle A here on earth, and Cooper is light years away in deep space with particle B. They want to use their entangled pair to send a signal. Well, if Alice measures A, she can't control which outcome she gets, so she can't control which outcome Cooper gets. That makes it hard to send any message. Well, what if Alice and Cooper have agreed that at noon Alice will measure A if she want him to come back and she won't if she doesn't want him back. So instead of using the outcome of the measurement to carry a message, Alice would send a message based on whether or not she measured the state. Unfortunately, this doesn't work either, because if Alice measures, 50% of the time she gets up and 50% of the time she gets down. That means that when Cooper measures his afterward, 50% of the time he will get down (corresponding to Alice's up) and 50% of the time he will get up (corresponding to Alice's down). The problem is that those are the same probabilities as in the case that Alice hasn't measured at all. So it seems this scheme just isn't going to work.
Now you could get trickier than Alice and Cooper. For one thing you could first do things (introduce interactions) to particle A or particle B in order to change the entangled state and then measure them. In the end, though, this doesn't work either, but I'll leave that to my examination of the general case for those who are more expert in the field [nota: ho omesso la parte tecnica successiva]. Suffice it to say that no matter how tricky you try to get, the situation is always essentially the same as the preceding example. Now, it is true that something changed faster than light, the wave function (or state vector). The thing is that the wave function is not directly observable and this change has no consequence accessible to people observing either particle individually, which is why we couldn't use it to transmit information. The change in the state is only directly observable when you compare the two measurements, which can only be done at speeds less than or equal to light (unless you have some other faster than light communication technology)."
Anche per quanto riguarda la storia del teletrasporto quantistico, la zuppa è sempre quella: il tizio A che vuole teletrasportare l'informazione al tizio B, deve comunque comunicare l'esito della sua misura (comunicazione che non può essere istantanea) a B affinché questo possa "duplicare" lo stato quantistico.
Quindi...
@fefochip: la mettiamo che l'entanglement non può essere usato per la trasmissione istantanea di informazioni.
@Fabrizio70: le daranno anche a 15 anni, ma almeno il quindicenne è capace di fare una ricerca approfondita (e non superficiale) rispetto ad altri. Mi dispiace, ritenta, sarai più fortunato in futuro.
Il punto cruciale della questione è che il collasso della funzione d'onda dello stato entangled è sì istantaneo, ma la funzione d'onda non è un osservabile, quindi questa istantaneità non è misurabile: ecco spiegato il motivo fisico per cui non è affatto possibile usare il collasso della funzione d'onda per inviare istantaneamente informazioni.
Visto che mi limiterei soltanto a ripetere gli stessi concetti, cito testualmente un trafiletto trovato in rete (tra l'altro, nella prima pagina di ricerca di Google alla voce "entanglement speed light") che spiega estremamente bene la situazione:
"Suppose that we have two spin 1/2 particles (if you don't know what that is, think of them as coins that have a "heads" side that can be either up or down). They are in an entangled state such that 50% of the time particle A is found to be spin up (heads up) and particle B is spin down (heads down, i.e. tails), and the other 50% of the time A is found to be spin down and B is spin up. This is called a maximally entangled bell state and can be written
|ψ> = 1/sqrt(2) (|up>A*|down>B + |down>A*|up>B)
in Dirac notation. Now, the important point about this entanglement is that it can never happen that A and B are found with both spins up or both spins down, so if we measure A and find that it is spin up, then we already know that B MUST be spin down, even before we measure it.
At this point you might object, "But you just said we know the state of particle B even before we measure it, so if it's like a million light years away, doesn't that mean we just got information faster than the speed of light?" The answer is no, not really. We only know what state B is in because we already knew the quantum state of the system made up of A and B at the beginning and we know the outcome of the measurement on A. The true test of whether information is sent is whether we're able to use this to send some sort of message to someone who is measuring particle B.
Ok, so let's say that Alice has particle A here on earth, and Cooper is light years away in deep space with particle B. They want to use their entangled pair to send a signal. Well, if Alice measures A, she can't control which outcome she gets, so she can't control which outcome Cooper gets. That makes it hard to send any message. Well, what if Alice and Cooper have agreed that at noon Alice will measure A if she want him to come back and she won't if she doesn't want him back. So instead of using the outcome of the measurement to carry a message, Alice would send a message based on whether or not she measured the state. Unfortunately, this doesn't work either, because if Alice measures, 50% of the time she gets up and 50% of the time she gets down. That means that when Cooper measures his afterward, 50% of the time he will get down (corresponding to Alice's up) and 50% of the time he will get up (corresponding to Alice's down). The problem is that those are the same probabilities as in the case that Alice hasn't measured at all. So it seems this scheme just isn't going to work.
Now you could get trickier than Alice and Cooper. For one thing you could first do things (introduce interactions) to particle A or particle B in order to change the entangled state and then measure them. In the end, though, this doesn't work either, but I'll leave that to my examination of the general case for those who are more expert in the field [nota: ho omesso la parte tecnica successiva]. Suffice it to say that no matter how tricky you try to get, the situation is always essentially the same as the preceding example. Now, it is true that something changed faster than light, the wave function (or state vector). The thing is that the wave function is not directly observable and this change has no consequence accessible to people observing either particle individually, which is why we couldn't use it to transmit information. The change in the state is only directly observable when you compare the two measurements, which can only be done at speeds less than or equal to light (unless you have some other faster than light communication technology)."
Anche per quanto riguarda la storia del teletrasporto quantistico, la zuppa è sempre quella: il tizio A che vuole teletrasportare l'informazione al tizio B, deve comunque comunicare l'esito della sua misura (comunicazione che non può essere istantanea) a B affinché questo possa "duplicare" lo stato quantistico.
Quindi...
@fefochip: la mettiamo che l'entanglement non può essere usato per la trasmissione istantanea di informazioni.
@Fabrizio70: le daranno anche a 15 anni, ma almeno il quindicenne è capace di fare una ricerca approfondita (e non superficiale) rispetto ad altri. Mi dispiace, ritenta, sarai più fortunato in futuro.
Messaggio orinale: https://old.luogocomune.net/site/newbb/viewtopic.php?forum=54&topic_id=7208&post_id=229597