Physics We Can All Understand - Part 3: Quantum Entanglement

Hi, I'm John Skieswanne, and this post is part 3 of a series on physics. In this series I will explain a few pillars of modern physics. I won't be using any complex maths. It is my hope that this series will introduce some of you brilliant, curious-minded laymen out there to the inner circles of Physics.
So, sit back and enjoy.


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Quantum Entanglement.

At the subatomic level, particles are represented with probability wave functions - their properties are blured into a cloud of probabilities. This is a direct result of the Uncertainty Principle, in which one cannot measure a particle's property without affecting other of its properties. Wave functions are rather good models for guessing the most likely properties of a particle. When two particles share the exact same properties, they may be both represented with the exact same wave function. Only one wave function will be enough to predict the properties of both particles, since they are exactly identical in nature. These two particles are "entangled".

Now, if you were to measure the property of one of these twin particles, you'd be knowing exaclty one of its properties. You would have collapsed its wave function (that is, you would have eliminated all other possibilities down to zero). The fascinating thing is, this means that you also now know the property of the other twin particle (it's the same that the one you just observed) without having to measure it - no matter how far this other particle is located. It could be at the end of the Universe, it won't matter: as soon as you know one particle's property, you also know the other's. Both particles are modelled with the same wave function; as soon as the latter collapses, both particles get to have their property known, no matter how far apart they are.
An analogy to explain the phenomenon:

Imagine you have two coins, and a table covered with ink. You put both coins "heads"-up, and you glue them side by side. You flip the coins, but as they land on the ink, you don't look. You just separate them, and seal them in two individual envelopes (envelope A and envelope B). You send Envelope B to Bob, your friend on Mars.



Once Envelope B reaches Mars, you finally venture and open your own envelope. Until now you never checked on which side your coin (and your friend's) landed after you have flipped them. What you do know, is that since you glued both of them together, they'll have both landed on the same side (either heads for you and heads for Bob, or tails for you and tails for Bob). But until now you didn't know which side the coin chose, it could be heads or tails, with 50/50 chances.
As you open your envelope, you discover that there's ink on, say, the "tails" side of your coin. Instantly, you know which side has ink on Envelope B's coin, even though Envelope B is now in the hands of Bob some 60,000,000 kilometres away (or over three minutes at the speed of light). The second you saw your coin, and as you knew that Bob's was identical, then you knew that Bob's coin had ink on its "tails" side, just like yours. Thus this effect enables information to apparently "travel" at speeds way, way higher than the speed of light.





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Can an useful communication be transmitted using entanglement? After all, since upon opening his own envelope, Bob will also know which side of your coin has ink on it, then doesn't this mean one can send faster-than-light messages that way?

Well, the thing is, not only do you have to send an entangled particle (or coin) to your friend in the first place (and the delivery truck cannot go faster than the speed of light). But also, even if you could send an entangled particle (or coin) in a matter of seconds, the outcome of the entanglement is unpredictable. Remember that until you observe it, the coin has 50/50 chances of being on either sides. Which mean you won't know the message you sent before sending it in the first place. If you and Bob agree that "ink on tails side" means "Hello mate", and "ink on heads side" means "You are despicable", Then Bob has 50 percent chances of receiving "You are despicable" even though you really meant him to receive "Hello mate" (and vice-versa).
The chance of him receiving the correct message is just as good as pure random chance.



You might be tempted to simply dip the tails side of Bob's coin in ink so to make sure he receives "Hello mate", but then you'd already know the properties of the coin before sending it - defeating the whole point of entanglement in the first place, since you already collapsed the wave function - might as well send him an actual call, with actual radio waves which already travel at light speed (and can carry way more meaningful messages).


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I hope you enjoyed this read; Part 4 will be coming soon, and will deal about the Standard Model of Particle Physics - a very popular aspect of modern physics.


Swan


Other parts of the series:

-Part 1: the Uncertainty Principle
-Part 2: the Special Theory of Relativity

6 flags, but still no replies...

Then what is it that New Agers talk about when they talk about Entangled Mind? Is it scientifically possible, or just another speudo-science myth, like the observation principle?

a reply to: starheart

More or less. Some New Agers have absolutely no idea what true entanglement is, and assume that it means telepathy. In truth the whole of Entanglement can be explained using pure and formal materialism.

a reply to: swanne

I love these, thanks for all the effort.

I do have one question on the two entangled particles. Forgive me, I am not a physicist.

How do we know with all the zillions of particles out there, which one is entangled with which one? How do the pair decide who their mate is?

Very good questions.

originally posted by: ABNARTY
How do we know with all the zillions of particles out there, which one is entangled with which one?

Long answer simple... we don't.

To make sure two particles are entangled, we have to make them ourselves. Otherwise we just can't know for sure if two random particles are or are not entangled (most probably aren't).

How do the pair decide who their mate is?

We decide for them. To make sure two particles are entangled, they are produced that way in a laboratory. Like twins, they will be produced from the same "mother" atom and thus will share common traits.

Usually atoms produce one photon as their electron drops to ground, but some atoms may be prepared so that they produce two photons instead. Since these photons share the same wavelength and other properties, they get to be entangled with each other.

two things: firstly we do not understand entanglement to the degree i would be definitive on any of it. for example recent peer reviewed articles say that the mechanism through which entanglement may work is quantum level wormholes. in addition separate articles state that gravity may also propagated via the same mechanism. this latter development means that there *IS* some actual communication or energy exchange going on and moves it from pseudo interaction to a real transaction.

e.g;

www.scientificamerican.com...



secondly the uncertainty principle is at least a little less uncertain. there have been devised a means of observing both conditions via weak interactions. while it is true that you still cannot determine both of a set of properties to no uncertainty you can observe both with precision such that the uncertainty is reduced to the point of insignificance. still one value will inevitable still be less certain than the other. the uncertainty principle still holds but is greatly modified.

originally posted by: stormbringer1701
this latter development means that there *IS* some actual communication or energy exchange going on and moves it from pseudo interaction to a real transaction.

Isn't this in contradiction with the No-Communication Theorem?

the no-communication theorem is a no-go theorem from quantum information theory, which states that, during measurement of an entangled quantum state, it is not possible for one observer, making a measurement of a subsystem of the total state, to communicate information to another observer. The theorem is important because, in quantum mechanics, quantum entanglement is an effect by which certain widely separated events can be correlated in ways that suggest the possibility of instantaneous communication. The no-communication theorem gives conditions under which such transfer of information between two observers is impossible. These results can be applied to understand the so-called paradoxes in quantum mechanics, such as the EPR paradox, or violations of local realism

source: en.wikipedia.org...

The no-communication theorem makes it possible to solve the EPR paradox. If the N-CT is false, then it means the EPR paradox becomes unresolved once again.

secondly the uncertainty principle is at least a little less uncertain. there have been devised a means of observing both conditions via weak interactions.

Weak interaction? Hm, this is rather intriguing. Any source I can check out?

a reply to: swanne

OK, so I am tracking:

1. If we "make" the particles, they can be entangled.

2. Outside of number 1, currently there is no way to know which particles are entangled "in the wild".

3. The only way we can say particles "in the wild" are entangled is extrapolation out from experiments.

Again no expert here, could what we are seeing in these experiments simply be the tip of a much more complex iceberg ? Why only two particles?

This thread has some more on it. I guess I am not the only one scratching their head

www.abovetopsecret.com...

a reply to: swanne


You just did ATS a service imho Sir Swanne. Honestly I thought I knew how entanglement worked and I was more or less right, however when FTL info got brought up then I would actually get a little confused. Not everyone here is a NASA scientist or has a Doctorate in theoretical physics.

So being a layman who is extremely interested in these kinds of universal mechanisms or functions if you will, but only grasped part of the concept I say thank you. Between posters like you and jade star and even.... phage (don't tell his ego I said that ) you guys make understanding and participating in these threads is more worth while . Its beats the typical response generally heard. Thanks for an informative thread.

Top credit to the poster and this confilms what I have been saying for a while now.

"Quantum Entanglement" is nothing but a hoax and spinning particles as pairs and sending each one to the other side of the universe is just the same as sending a left or right shoe hidden in a box to your mate up the road.

I hope the double slit exsperiment does not turn out to be another hoax with the part about recording the information but not reading the results.

People also need to understand that you can only learn so much from crashing snooker balls into each other at cern and looking at how the balls shatter using the biggest and most exspensive machine in the world.

The glass jar is also empty and does not contain black mass, black energy or fairy dust that pops into exsistance and vanishes before anyone can see it but photon's off light passing throught the jar can created a solar wind that makes two bits of gold leaf come togeather inside the jar.

I understand more than most on this subject after weeks of research and have come to the conclusion that when I see the word "Quantum" I always start out thinking that it's a hoax.

originally posted by: ABNARTY
Again no expert here, could what we are seeing in these experiments simply be the tip of a much more complex iceberg ? Why only two particles?

In an entanglement, you can, actually, have more than just two particles. It's technically possible to have three or even a hundred of entangled particles. As long as all these particles all share the exact same properties, then yes, they may be modelled with the one and only wave function - or, in other words, entangled.

The problem is that once again, if these many entangled particles are running in the wild, then it comes back to your Point 2: currently there is no way to know which particles are entangled "in the wild".

And, finally, although hundred of entangled particles is theoretically permitted by the Quantum Model, in practice, preparing an atom which can produce hundred of entangled photons in one go is nearly impossible. Most of these atoms usually manage to produce only one photon as their electron drops back to ground. Two photons requires alot of special preparation. A hundred is currently un-achievable.

a reply to: CitizenJack

a reply to: VirusGuard

when I see the word "Quantum" I always start out thinking that it's a hoax.

This "hoax" is incredibly successful at describing the mechanism behind electron's orbit around a charged nucleon. According to any classical model, the electron's orbit would quickly have decayed and collided into the nucleon, preventing the atom from exhibiting many observed properties such as spectral lines. The quantum model is the only one which was able to solve this problem, by stating that there exist wave functions and electrons may not be located in the zones of least-probability of these said wave functions, although exception may occur (the non-zero edges of the wave) and thus would give rise to quantum tunnelling, another observed phenomena.

I too am divided on the philosophical aspect behind Bohr's theories, but I do think that we should be fair and give credit where credit is due.

Part 4: the Standard Model

a reply to: swanne

Nice writing! I really like the way you put all your info together!

a reply to: Quantum12

Plenty more where that comes from!

a reply to: swanne

All I can add is you really know 100% what you are talking about.

Unlike another thread...you know what I mean?