Debate

[steevey]

So this is a long topic, but it started out someone I know asking how something could react instantaneously, and my friend said there's nothing we currently know of that does that. So then, I introduced entanglement theory, saying that when particles are also waves of existence and the atomic and subatomic level, and when they come into close enough proximity with each other, their wave functions become entangled in a way that the properties of one is dependent on the other. I also stated that it's been proven that distance does not cause the wave functions of either particle to collapse, so long as the entangled particles are separated carefully. I went on to say that because of this entanglement thing, scientist are beginning to develop it for a number of technologies, such as computers, cryptography, and communications in the future.

My friend went on to say that this entanglement system doesn't allow the transmission of "information", which is what the light barrier is about, but I said that scientists could use this for information because instead of using photons, they could use electrons or protons in their spin states in specific patterns which to form specific letters, much like Morse code (forgot where I learned about that). In explaining this, I said that scientists can figure out the spins of electrons and other particles without destroying the entanglement. This is what we're mainly having a bigger debate about, because I said that they couldn't know what the spins are randomly, they've done experiments where two particles are entangled, but they can somehow know what the spin is, there has to be some way they know what the spin is without destroying entanglement. My friend then brought up wave function collapse which I already knew about, saying that if the system is measured in any way, the particles disentangle. I kept saying there has to be some way for them to know what the spin is. I brought up the double slit experiment, because that proves you can observe the effects of the wave function, but not the wave function itself as its happening. But, he stated that quantum teleportation requires a classical communications channel to "transmit" any information from point A to point B. I think (someone correct me if I'm wrong) that this type of communication would be useful because it would allow for nearly unlimited bandwith, but it certainly doesn't allow for faster-than-light communications.

Here's what I said around the same time

" Two particles, usually photons since it's easier to deal with as their initial velocity carries them apart, have a wave function. A wave function is part of the particle, so every elementary particle we think of, and light, is both a particle and a wave. The wave function is a wave of existence itself. However, like all waves, is has a frequency. The places where a particle is most likely to show up, are the polar coordinates where the wave crest is maximum/minimum in the wave function. And where the wave hardly moves at all (on a graph or sound analyzer thing I forgot the name of), a particle usually doesn't show up. At this level, size matters a lot. If a particle is bigger, it has a less probable places that it can show up, or occupies a smaller amount of probable space. If a particle is smaller, like an electron, it can occupy grater areas of probability, or more space. When two particles come close enough to each other, their wave functions interact. They become entangled, to the point where the properties of some are dependent on the other. When you do something to one, the other reacts instantly. You can set up an experiment to emit electrons in pairs, so that their wave functions are entangled. Both have spins flip-flopping up and down, and they both respond to each other's spin. However, when an observer measures any particular particle, the system disentangles instantly. Scientists say this wave function collapses. However, when scientists shot single electrons in their double slit experiment, the electrons still had a wave function, and occasionally passed through both slits of a metal board at the end, and left markings on the back panel, proving you can see indirects effects of entanglement without destroying entanglement. It's only when they decided to measure the electrons themselves before they had any impact that their wave functions collapse. "

To which he said

"This is incorrect. The spins aren't "flip-flopping", they exist as a superposistion of all possible quantumn states, which we tend to think of as a probability distribution (something that can't be directly observed). Wave function collapse isn't some unfortunate side effect of entanglement that can be avoided, it's actually a phenomenon that allows quantumn teleportation to work in the first place. I'm not sure what point you're trying to make here. The fact is that classical information can not (as of yet, and likely very far into the future) be transmitted at faster than light speeds. Particles don't have size. All particles are point particles in quantum mechanics. The associated wave function has a size of a sort, in that you can find the boundary surface within which the particle is found X% of the time, and call that the "size" of the wavefunction, but the X is arbitrary. Entanglement has nothing to do with them coming "close enough". It has to do them interacting in a way such that conservation laws impose requirements on the total state. For example, when a free neutron decays into a proton, electron, and electron antineutrino, because of conservation of angular momentum, the spins of the electron and the neutrino have to be the same (they have to total to 1 because the W boson they came from had 1 spin). Their spins are entangled. When you measure the spin of one of them, the wavefunction for the other collapses to the same singlet state."

What are either of us wrong and right about? If scientists can figure out the spin of a particle in a quantum mechanical system of entangled particles, how do they do it without destroying the entanglement? What's the deal with "classical" information not being carried through entanglement instantly, but properties are, as my friends state?

 

 

 

[swansont]

"When you do something to one, the other reacts instantly" is wrong, though it is commonly presented this way in the pop-sci press.

 

If you flip a coin and it comes up heads, you instantly know the other side is tails. Even if the coin is a light-minute thick. There is no violation of relativity here, because all of the information about both sides of the coin is given to you — you already knew that one side is heads and the other side is tails. Similarly, two entangled particles share some trait because of a conservation law — if you know the spin or polarization of one, you instantly know the value of the other. The other particle doesn't react, just as the coin faces didn't react. Because they are entangled, you have to treat it as a single system.

 

What is different is that the coin is a classical system — you could, in principle, know the starting conditions and oscillation frequency and determine which way the head and tail are pointing at all times. That's not possible for a quantum system, and where the analogy doesn't apply.

[steevey]

So are saying completely confidently, that it's scientific fact that when the properties of one entangled particle changes, that the properties of the other particle don't change instantaneously, which means information somehow automatically travels through all solid matter and space to get to the exact point of the other particle responding to it at the speed of light or below? Cause when I refer to the instantaneousness in entangled particles, I'm not referring to when they measure it during when the experiment is happening. I'm referring to when they have timers which count the same, get some entangled particles, separate them by over 100km, and find out that the exact time they tried to change the property of one, that the other changed instantly. I get what your saying with the measurement thing, and how it would be mistaken for instantaneousness, but then how could you "keep" changing the properties, because otherwise in your analogy with the coin, you'd have to measure one of the particles.

 

Your saying they know what the spins of entangled particles are at one specific point, because after that point, the entanglement collapses and the properties become determined. I'm talking about multiple times, a continuous bases of one entanglement, that the spin is changing and the other particle reacts.

Edited November 17, 2010 by steevey

[swansont]

They don't change the property of one particle, that's another turd laid by the pop-sci press. You do a measurement in which you determine what state the particles are in. After that, the particles are no longer entangled.

[steevey]

They don't change the property of one particle, that's another turd laid by the pop-sci press. You do a measurement in which you determine what state the particles are in. After that, the particles are no longer entangled.

 

 

Why would so many sources and actual scientists get this wrong? Even the discovery channel said something similar to this. I've looked it up in books, youtube, google, and they all say this instantaneous thing works in a similar way to how I described it. But then, how do the scientists know that the spin states keep changing during entanglement, if when you measure it, the properties become determined?

 

 

Also what about the mass thing? Was I right about how mass and probability correspond at a quantum level?

Edited November 17, 2010 by steevey

[swansont]

Why would so many sources and actual scientists get this wrong? Even the discovery channel said something similar to this. I've looked it up in books, youtube, google, and they all say this instantaneous thing works in a similar way to how I described it. But then, how do the scientists know that the spin states keep changing during entanglement, if when you measure it, the properties become determined?

 

I don;t know why scientists get it wrong. Journalists, however, are usually not scientists, so I think it's a translation issue as they try and recast what the scientist said in terms they think their readers will understand. Like a game of "telephone," the meaning changes. Purple monkey dishwasher.

 

Also what about the mass thing? Was I right about how mass and probability correspond at a quantum level?

 

I don't see where you discussed that.

[steevey]

At this level, size matters a lot. If a particle is bigger, it has a less probable places that it can show up, or occupies a smaller amount of probable space. If a particle is smaller, like an electron, it can occupy grater areas of probability, or more space.

Is what I said,

I don't think its exactly right, but I know that it explains why an electron occupies probable spaces which are much greater than that of the nuclei's.

[swansont]

It's probably best not to equate size and mass, since they are different properties.

 

The Heisenberg Uncertainty Principle and deBroglie wavelength tell you that a low-mass particle, which will generally have a small momentum (all else being equal), will have a larger wavelength, which corresponds to a larger uncertainty in its position.

[steevey]

"When you do something to one, the other reacts instantly" is wrong, though it is commonly presented this way in the pop-sci press.

 

If you flip a coin and it comes up heads, you instantly know the other side is tails. Even if the coin is a light-minute thick. There is no violation of relativity here, because all of the information about both sides of the coin is given to you — you already knew that one side is heads and the other side is tails. Similarly, two entangled particles share some trait because of a conservation law — if you know the spin or polarization of one, you instantly know the value of the other. The other particle doesn't react, just as the coin faces didn't react. Because they are entangled, you have to treat it as a single system.

 

What is different is that the coin is a classical system — you could, in principle, know the starting conditions and oscillation frequency and determine which way the head and tail are pointing at all times. That's not possible for a quantum system, and where the analogy doesn't apply.

 

So, just be clear:

When you have two particles that are entangled, and a property like the spin changes, the spin of the article does't respond instantaneously to have the opposite spin?

[swansont]

So, just be clear:

When you have two particles that are entangled, and a property like the spin changes, the spin of the article does't respond instantaneously to have the opposite spin?

 

No, it doesn't. If the particles are entangled because of their spins, you don't know what the spin of either particle is. If you know, they aren't entangled.

[steevey]

No, it doesn't. If the particles are entangled because of their spins, you don't know what the spin of either particle is. If you know, they aren't entangled.

 

I'm not saying they are entangled "because" of spins, I'm saying the properties of their individual spins are dependent on each other once they get entangled. Couldn't they easily prove that distance doesn't effect entanglement this way by simply getting some really good timers, which count at the same time, separating them and two entangled particles, and measure them only exactly when a person on one end changes the spin on purpose, or something like that? So your saying that "because" they measure the entanglement, that it can't happen faster than light, which doesn't make sense. So, why not just, they can see for a fact that entanglement happens instantaneously, but once they do see it, the system becomes disentangled after that?

 

So you have two electrons which are entangled, rather than photons. Both have spins which are now co-dependent on each other. You separate them, then you measure one, and find that it's spin up. So your thinking that the other must be spin down, but according to all the information your given to me, if the two electrons are no longer entangled, then at the very moment the scientists measure the spins, both the spins have a chance of being the same, but as far as I know, that's never been the case.

Edited November 22, 2010 by steevey

[swansont]

When I said entangled because of spins I meant that spin is the entangled property. If this is the case, then you don't know what the individual spins are until you measure them. At that point, one will be spin up and the other spin down (assuming they were entangled as a spin zero system). Once the measurement has occurred, changing the spin of one of them will not affect the other; they are no longer entangled.

 

Before the measurement, "changing the spin on purpose" means some kind of an interaction, which breaks the entanglement.

[steevey]

When I said entangled because of spins I meant that spin is the entangled property. If this is the case, then you don't know what the individual spins are until you measure them. At that point, one will be spin up and the other spin down (assuming they were entangled as a spin zero system). Once the measurement has occurred, changing the spin of one of them will not affect the other; they are no longer entangled.

 

Before the measurement, "changing the spin on purpose" means some kind of an interaction, which breaks the entanglement.

 

But before the measurement, the spins respond instantaneously?

[immortal]

When one say that we have to treat the entangled photons as a single system it means that the polarization of the pair of photons (for example - photons passed through a HV polarizer) will appear randomly as either H and V or as V and H on both sides of the measurement. They just appear that way because it is the allowed values of the quantum system. One photon's polarization value does not determine the value of the other photon they just appear randomly as it is the case in every quantum measurement.

 

for example if you pass a photon through a HV polarizer there is a equal probability for the photon to appear randomly as either H polarized or as V polarized. Now extending this case to the entangled photons they can randomly appear as either H and V or as V and H.

 

(H-horizontal, V-vertical)

 

steevey asked

But before the measurement, the spins respond instantaneously?

 

Well the copenhagen interpretation of QM tells me that it is wrong to describe a quantum system when it is not being observed. So without doing a measurement we can not know what the spins are doing.

Edited November 23, 2010 by immortal

[swansont]

But before the measurement, the spins respond instantaneously?

 

The question doesn't make sense, quantum mechanically. Before the measurement, you aren't doing anything to the particles. There's no response, since there's no interaction.

[steevey]

Well, during entanglement, the the properties of spins are dependent on each other. If spins can change by them selves without us, then it would still happen instantaneously that either one changes because of the other. You said then once you measure one, you automatically know the spin of the other one, but that could only be true if the information was carried faster than it would take light to travel the same distance.. Otherwise, you'd need to calculate how long it would take light, then after you determine that, you could determine that the spin is opposite.

 

Well, during entanglement, the the properties of spins are dependent on each other. If spins can change by them selves without us, then it would still happen instantaneously that either one changes because of the other. You said then once you measure one, you automatically know the spin of the other one, but that could only be true if the information was carried faster than it would take light to travel the same distance.. Otherwise, you'd need to calculate how long it would take light, then after you determine that, you could determine that the spin is opposite.

 

Well, during entanglement, the the properties of spins are dependent on each other. If spins can change by them selves without us, then it would still happen instantaneously that either one changes because of the other. You said then once you measure one, you automatically know the spin of the other one, but that could only be true if the information was carried faster than it would take light to travel the same distance.. Otherwise, you'd need to calculate how long it would take light, then after you determine that, you could determine that the spin is opposite.

 

Well, during entanglement, the the properties of spins are dependent on each other. If spins can change by them selves without us, then it would still happen instantaneously that either one changes because of the other. You said then once you measure one, you automatically know the spin of the other one, but that could only be true if the information was carried faster than it would take light to travel the same distance.. Otherwise, you'd need to calculate how long it would take light, then after you determine that, you could determine that the spin is opposite.

 

Well, during entanglement, the the properties of spins are dependent on each other. If spins can change by them selves without us, then it would still happen instantaneously that either one changes because of the other. You said then once you measure one, you automatically know the spin of the other one, but that could only be true if the information was carried faster than it would take light to travel the same distance.. Otherwise, you'd need to calculate how long it would take light, then after you determine that, you could determine that the spin is opposite.

 

Well, during entanglement, the the properties of spins are dependent on each other. If spins can change by them selves without us, then it would still happen instantaneously that either one changes because of the other. You said then once you measure one, you automatically know the spin of the other one, but that could only be true if the information was carried faster than it would take light to travel the same distance.. Otherwise, you'd need to calculate how long it would take light, then after you determine that, you could determine that the spin is opposite.

[swansont]

Well, during entanglement, the the properties of spins are dependent on each other. If spins can change by them selves without us, then it would still happen instantaneously that either one changes because of the other. You said then once you measure one, you automatically know the spin of the other one, but that could only be true if the information was carried faster than it would take light to travel the same distance.. Otherwise, you'd need to calculate how long it would take light, then after you determine that, you could determine that the spin is opposite.

 

 

To say that the spins change by themselves implies they have a known spin, which isn't the case. The individual spin state is undetermined until measured. And the information doesn't have to travel faster than c to get to you, since the spins of both particles is given to you when you make the measurement. And you can't get independent information about the other particle faster than c via another communication channel, so there is no violation of relativity.

[steevey]

To say that the spins change by themselves implies they have a known spin, which isn't the case. The individual spin state is undetermined until measured. And the information doesn't have to travel faster than c to get to you, since the spins of both particles is given to you when you make the measurement. And you can't get independent information about the other particle faster than c via another communication channel, so there is no violation of relativity.

 

Ok, so two electrons are entangled and separated at opposite ends of the galaxy. It takes light 100,000 years for light t travel from one of of the galaxy to the other. Now, all of a sudden, without any prior knowledge of what the spin of either electron was at any time, I measure one, and find that it's spin up. Therefore, the other HAS to be spin down. But, how could you automatically know what the other one is if you know one like you said? Well, in this case, it would have to happen faster than it would take light to make the same distance. I'm not saying qubits of information are being transfered, I'm just saying the spins are dependent on each other no matter what the distance is.

[swansont]

Ok, so two electrons are entangled and separated at opposite ends of the galaxy. It takes light 100,000 years for light t travel from one of of the galaxy to the other. Now, all of a sudden, without any prior knowledge of what the spin of either electron was at any time, I measure one, and find that it's spin up. Therefore, the other HAS to be spin down. But, how could you automatically know what the other one is if you know one like you said? Well, in this case, it would have to happen faster than it would take light to make the same distance. I'm not saying qubits of information are being transfered, I'm just saying the spins are dependent on each other no matter what the distance is.

 

Yes, you know both spins instantly, but the information about the spins in encoded in both electrons — it's one system, not two separate ones. You can't use this effect to send any information faster than c.

[steevey]

Yes, you know both spins instantly, but the information about the spins in encoded in both electrons — it's one system, not two separate ones. You can't use this effect to send any information faster than c.

 

So in other words, because its one system you aren't gaining any knowledge? But isn't it only mathematically "treated" as one system? Because why couldn't you have two electrons which have properties dependent on each other but not have all quantum numbers be the same, therefore not causing the wave functions to cancel out?

[swansont]

The wave functions don't cancel out in an entangled system, it's that the wave function describes two particles instead of one.

[steevey]

The wave functions don't cancel out in an entangled system, it's that the wave function describes two particles instead of one.

 

Right, but I'm saying your right about how it works, but I'm wondering if it works that way because if you had two different electrons with all the same quantum numbers, wouldn't they cancel each other out? Let's say you have a wave on a line, like one of those spectrometers. It's going up and down once a second. Then, you introduce another wave that acts exactly the same as that wave, but at opposite times. So, if you counted it as two systems, then both probable spots on the wave would be equidistant from the line they are resonating on, except one is negative and positive, which means if you added any of the same points on the same vertical line together, you'd get 0.

Edited November 27, 2010 by steevey

[swansont]

No; because they are fermions, having the same quantum numbers means they can't occupy the same space. They don't cancel and can't cancel, because that would violate a bunch of conservation laws.

[steevey]

No; because they are fermions, having the same quantum numbers means they can't occupy the same space. They don't cancel and can't cancel, because that would violate a bunch of conservation laws.

 

If I have two electrons in the ground state though, and all electrons in the universe are identical, what's the difference between those two? Shouldn't they be violating impenetrability since they are both waves and particles? Otherwise the only other option for them is to cancel out.

[swansont]

Two electrons in the ground state (e.g. He) will have opposite spins. This is the Pauli Exclusion principle. Two Fermions can't occupy the same state.