Entangled particles

[Gaylord]

I am not a physicist. I don't begin to have the math aptitude to become a physicist. But I think about it a lot, from a philosophical perspective.

 

I read in the news recently about a method for generating fairly large numbers of entangled particles. Here is a link to a New York Times article on the topic: Billions of entangled particles advance quantum computing.

 

 

Because the entanglement does not require that the particles be anywhere near each other, doesn't that make it possible to use entangled particles to transmit information instantaneously and therefore, faster than the speed of light?

[alpha2cen]

The problem is how to make a quantum entanglement state. How to make entangling at the quantum level? Distance is no problem, I know.

Edited June 15, 2012 by alpha2cen

[immortal]

 

Because the entanglement does not require that the particles be anywhere near each other, doesn't that make it possible to use entangled particles to transmit information instantaneously and therefore, faster than the speed of light?

 

 

Entanglement cannot be used to transmit information faster than the speed of light, quantum cryptography requires that a classical signal travelling at the speed of light must be sent between two communicating entities like Alice and Bob before they can communicate with each other.

[Aethelwulf]

I am not a physicist. I don't begin to have the math aptitude to become a physicist. But I think about it a lot, from a philosophical perspective.

 

I read in the news recently about a method for generating fairly large numbers of entangled particles. Here is a link to a New York Times article on the topic: Billions of entangled particles advance quantum computing.

 

 

Because the entanglement does not require that the particles be anywhere near each other, doesn't that make it possible to use entangled particles to transmit information instantaneously and therefore, faster than the speed of light?

 

Yes it makes it possible but this is not the general consensus.... but John Bell certainly realized that was a possibility.

[swansont]

Yes it makes it possible

 

No, it absolutely does not.

[elfmotat]

Imagine you have two balls: one red and one blue. The balls are, without you watching, put in separate boxes so that you can't tell which ball is in which box. Now, if you were to open one of the boxes and discover that the ball inside was red, you would immediately know what the color of the ball in the other box is. It doesn't matter how far apart you separate the boxes before you open one of them. That's sort of what entanglement is like. No information is transferred in this process.

[Aethelwulf]

No, it absolutely does not.

 

 

 

I am sorry, I misread him.

 

I realize he is wanting to talk about superluminal inference of information, when I thought he was arguing against it. This was why I mentioned John Bell, because he gave himself ways around that problem:

 

''There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be''

 

Of course, is is superdeterminism which is not the consensus. I've never heard anyone really talk about it other than John Bell.

 

Funnily, I actually had a dream on entanglement last night. The spin of two particles where always known at the moment of their creation. Which is kind of an odd thought, but would seem to agree with the John Bell example.

 

I obviously don't take dreams as facts though, was just a weird experience is all

[J.C.MacSwell]

Imagine you have two balls: one red and one blue. The balls are, without you watching, put in separate boxes so that you can't tell which ball is in which box. Now, if you were to open one of the boxes and discover that the ball inside was red, you would immediately know what the color of the ball in the other box is. It doesn't matter how far apart you separate the boxes before you open one of them. That's sort of what entanglement is like. No information is transferred in this process.

 

Now imagine doing that a million times, and finding out that opening the box from the top revealed a blue ball 60% of the time, and opening it from the bottom revealed a blue ball just 40% of the time...and you kept repeating this and finding the same results...so you conclude that their colours are not predetermined before opening.

 

So you then take a million matched sets of boxes a light year apart, and open half of them, all in one way, on xmas day. When the others a light year away are opened on boxing day, it would seem information could be gleaned from the results, knowing that the xmas balls were planned to be opened from the bottom only if it snowed that day...but this should not be possible, since a network of ball stations could relay the information back in such a way that the information was received the day before xmas, to help with the weather forecast.

[elfmotat]

So you then take a million matched sets of boxes a light year apart, and open half of them, all in one way, on xmas day. When the others a light year away are opened on boxing day, it would seem information could be gleaned from the results, knowing that the xmas balls were planned to be opened from the bottom only if it snowed that day...but this should not be possible, since a network of ball stations could relay the information back in such a way that the information was received the day before xmas, to help with the weather forecast.

 

How do you intend to transfer information by this effect? I.e. how would one group of people know when the other had opened their boxes?

[J.C.MacSwell]

How do you intend to transfer information by this effect? I.e. how would one group of people know when the other had opened their boxes?

 

They would know when because xmas day came and went, and by examining there own they would realize, not from checking a few but checking the whole million, that the others must have been opened from the bottom or top (or if the others forgot to open them on xmas day they should be able to recognize that as well)

 

Again this scheme could violate causality or relativity so something cannot be right, it should be impossible to send information faster than light speed...

[Gaylord]

I am pleased that this has generated some discussion from real physicists. I ask this because the possibility of faster than light information transmission should permit instantaneous communication with distant satellites and make unmanned interstellar exploration feasible. We still have to get the probe there and that would take time, but with entangled particles we could receive and transmit information instantaneously, with no loss of signal strength.

[swansont]

I am pleased that this has generated some discussion from real physicists. I ask this because the possibility of faster than light information transmission should permit instantaneous communication with distant satellites and make unmanned interstellar exploration feasible. We still have to get the probe there and that would take time, but with entangled particles we could receive and transmit information instantaneously, with no loss of signal strength.

 

No, we can't. There's been no discussion that supports this notion.

[Aethelwulf]

I am pleased that this has generated some discussion from real physicists. I ask this because the possibility of faster than light information transmission should permit instantaneous communication with distant satellites and make unmanned interstellar exploration feasible. We still have to get the probe there and that would take time, but with entangled particles we could receive and transmit information instantaneously, with no loss of signal strength.

 

Signals in the form of energy cannot exceed the speed of light. There might have to be some kind of radical change however to accommodate entanglement in physics. We don't know what causes it, so maybe not all information is made of physical things?

 

The idea itself borders almost on the metaphysical nature of a vacuum - is there some underlying property we cannot measure? Some which has a tweak of determinism about it? What if the vacuum is a busy sheet of ethereal information which is not bound by speed or location?

 

If we can't even measure such a thing what good does it do physics to speak of such a thing? We certainly don't and can't measure a superluminal signal in the form of energy.

[D H]

but with entangled particles we could receive and transmit information instantaneously.

No, you can't.

 

Bell's theorem says that there are no local hidden variables. This means any viable interpretation of quantum mechanics either has to throw out realism or locality. Realism: The Moon is still there when no one looks at it. Locality: No spooky action at a distance. So what if the "correct" interpretation of QM is to maintain realism? Wouldn't that imply that FTL communication might be possible?

 

The answer is no. There are a number of "no signaling" theorems that start from a basic set of assumptions to show that FTL communications cannot happen. Every viable interpretation of QM obeys those assumptions, even those that reject locality. So even if the universe truly is non-local, FTL communication still can't happen.

[Aethelwulf]

No, you can't.

 

Bell's theorem says that there are no local hidden variables. This means any viable interpretation of quantum mechanics either has to throw out realism or locality. Realism: The Moon is still there when no one looks at it. Locality: No spooky action at a distance. So what if the "correct" interpretation of QM is to maintain realism? Wouldn't that imply that FTL communication might be possible?

 

The answer is no. There are a number of "no signaling" theorems that start from a basic set of assumptions to show that FTL communications cannot happen. Every viable interpretation of QM obeys those assumptions, even those that reject locality. So even if the universe truly is non-local, FTL communication still can't happen.

 

There was an experiment recently which might solve this dichotomy... I'm currently looking for it. It involved entangled photons.

 

The short version (which only I can remember) is that particles when not being observed where showing up in places they shouldn't have been.

 

The moon is a macroscopic system - just as is Schrodinger's Cat. I don't believe the cat will show up in a different place nor the moon, but maybe realism should be cut up into microscopic realism and macroscopic realism - in which case, I'd throw out the microscopic realism.

 

found it:

 

http://www.economist.com/node/13226725

 

I read the paper a while back as well, it was quite technical.

 

I suppose if the realism strictly depends on whether the object is still ''there''.... or still ''exists'' is a big difference. If the object is not exactly ''there'' any more, but is in a different place, it puts a new slant on things. If the position of an object does not matter in realism, then long it lives.

Edited June 18, 2012 by Aethelwulf

[Widdekind]

Requesting "all the room in the envelope" for FTL communication...

 

Is it not true, that entangled photons embody a pluri-potentiality, of multiple possibilities, latent in those photons ("H" or "V" polarization, say); and, which "smorgasbord" of possibilities were pre-encoded, into said signals, at time of entanglement-and-transmission ? If so, then as long as you limited yourself, to choosing from "food on the smorgasbord" ("H" or "V" polarization, say); then any decision, which had been pre-encoded today, could be actualized tomorrow, without violating Causality. For, the decision selected, had been possible the entire time.

 

Therefore, could you not imagine, exploiting QE, to manifest instantaneous communication, across vast distances, as long as the communicated information, had been "pre-loaded" into the entangled signal, at time of entanglement-and-transmission ? In simplistic terms, perhaps you could exploit the pluri-potentiality of the "smorgasbord" quantum state, to "pre-command" multiple maneuvers of some remote probe (say); then, that "program of pre-encoded potential commands" could be propagated to the probe; and, hours later (say), the probe receives those signals, briefly becomes entangled with them, and then influenced by them, upon wave function "collapse". As long as you chose "food from the smorgasbord" to "feed the probe", then perhaps you could transmit information to the probe, instantaneously, FTL, from amongst the suite of pre-encoded possible commands ? That would not violate Causality -- what you wound up choosing to do, had been possible, the entire time (like a photon propagating around an entire galaxy, later deciding, in an earth telescope, to "have gone left / right the entire time", per Wheeler's galactic double slit experiment). As the signals were propagating towards the probe, they would "ambiguously embody" both "go forward" and "go backward". Once they reached the probe, perhaps you could then-and-there choose to actualize one or the other command; you would not violate Causality. What you chose to wind up saying, had been possible, for you to have been saying, the entire time.

 

In baseball analogy, you throw a fastball & a curve ball at the probe. Later, you actualize "fastball". Causality would be preserved -- you had been throwing a fastball the entire time. Accepting such pre-defined limitations, perhaps FTL communication, thusly prescribed, might be possible?

 

Requesting "all the room in the envelope" for FTL communication...

 

Is it not true, that entangled photons embody a pluri-potentiality, of multiple possibilities, latent in those photons ("H" or "V" polarization, say); and, which "smorgasbord" of possibilities were pre-encoded, into said signals, at time of entanglement-and-transmission ? If so, then as long as you limited yourself, to choosing from "food on the smorgasbord" ("H" or "V" polarization, say); then any decision, which had been pre-encoded today, could be actualized tomorrow, without violating Causality. For, the decision selected, had been possible the entire time.

 

Therefore, could you not imagine, exploiting QE, to manifest instantaneous communication, across vast distances, as long as the communicated information, had been "pre-loaded" into the entangled signal, at time of entanglement-and-transmission ? In simplistic terms, perhaps you could exploit the pluri-potentiality of the "smorgasbord" quantum state, to "pre-command" multiple maneuvers of some remote probe (say); then, that "program of pre-encoded potential commands" could be propagated to the probe; and, hours later (say), the probe receives those signals, briefly becomes entangled with them, and then influenced by them, upon wave function "collapse". As long as you chose "food from the smorgasbord" to "feed the probe", then perhaps you could transmit information to the probe, instantaneously, FTL, from amongst the suite of pre-encoded possible commands ? That would not violate Causality -- what you wound up choosing to do, had been possible, the entire time (like a photon propagating around an entire galaxy, later deciding, in an earth telescope, to "have gone left / right the entire time", per Wheeler's galactic double slit experiment). As the signals were propagating towards the probe, they would "ambiguously embody" both "go forward" and "go backward". Once they reached the probe, perhaps you could then-and-there choose to actualize one or the other command; you would not violate Causality. What you chose to wind up saying, had been possible, for you to have been saying, the entire time.

 

In baseball analogy, you throw a fastball & a curve ball at the probe. Later, you actualize "fastball". Causality would be preserved -- you had been throwing a fastball the entire time. Accepting such pre-defined limitations, perhaps FTL communication, thusly prescribed, might be possible?