Science Questions

What is quantum entanglement?

Tue, 16th Jun 2015

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Question

Will asked:

In Quantum Entanglement, exactly how are the objects linked together? What force or energy connects them?

Answer

We put this question to Dave Zobel, author of "The Science of TV's The Big Bang Theory: explanations even Penny would understand"

Dave Zobel - Quantum entanglement which Albert Einstein referred to as spooky Quantum computer ion trapaction at a distance or he actually used the German words for it which sounds like spooky action at a distance if you say it with a German accent is, this concept that we really can't tell why it happens.

We can say what happens. Itís a bit like some of the other things weíve spoken about in the show already. If you have two particles that are created at the same instance by the same process which can happen quite frequently, they can have certain properties that are identical but opposite.

One of them is a property called spin which has nothing to do with what we think of when we say the word spin, and that's why we call it spin!

If those two particles are moved very far apart but no one has measured their spin, then it's not just that they have spin that is unknown. They don't yet have any meaningful spin.

It's not that they have spin zero. They just have no spin that we can speak of. If you then measure the spin of one of the particles, you will find that whatever it is, when you measure the spin of the other particle, it's the exact opposite.

It's as if the two particles had spoken to each other and said, "Okay, heís about measure me. I'm going to have spin plus one. You have spin minus one, right?"

But, in fact, they can't communicate that way and so, we donít really know what's happening and that, I think, is why Einstein used the German word for spooky.

Chris - And I think Niels Bohr said, "If you're not baffled by quantum mechanics then you just didnít understand it!"

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Will asked the Naked Scientists:

In Quantum Entanglement, exactly how are the objects linked together? What force or energy connects them? How do they "communicate?"

What do you think? Will, Wed, 24th Sep 2008

This topic makes my brain spin....both up and down.... Evie, Wed, 24th Sep 2008

I don't think anyone actually knows the answer. It just happens, as do many things in quantum mechanics. DoctorBeaver, Thu, 25th Sep 2008

Classical physics says that when two objects are connected, they are connected by forces/energies/particles.  All of these classical connections are easy to think of because we see examples of them every day.

Quantum mechanics introduced an entirely new way to connect two objects: entanglement.  Entanglement is tough to explain because it doesn't depend on any classical ways of connecting things.  It's also not something intuitive, like forces, since we aren't used to seeing its effects. jpetruccelli, Thu, 25th Sep 2008



In other words no-one can explain it  DoctorBeaver, Thu, 25th Sep 2008

One the one hand, yeah.  It just is that way.  :)

On the other hand (on some level) you just have to accept that the forces that connect things just "exist."  We just happen to intuitively grasp them a lot easier, and we've studied them a lot longer.  jpetruccelli, Thu, 25th Sep 2008



And QFT seems to explain them quite nicely (except for gravity). Quantum Entanglement is very different in that respect. DoctorBeaver, Thu, 25th Sep 2008

To take this on more of a tangent, the odd thing to me is that forces are so obvious to think about, but so complicated when you get down to trying to figure out how they work on a quantum level.  Entanglement is so bizarre and abstract to picture, but it drops out of the equations of QM fairly painlessly. jpetruccelli, Fri, 26th Sep 2008

What I find strange is that scientists accept the existence of forces they can't explain, yet dismiss out of hand the possibility of forces such as psychokinesis or telepathy. Yes, I appreciate that the known forces have been demonstrated experimentally and that puts them on a more scientific footing. But to say something doesn't exists simply because it hasn't been successfully demonstrated under laboratory conditions seems a bit narrow-minded.

They can surmise dark matter to account for phenomena regarding galaxies & gravity - we can't see it, touch it, hear it, or anything else it. Yet when someone thinks of a person who subsequently phones or visits out of the blue, that's just coincidence. DoctorBeaver, Fri, 26th Sep 2008

I'm not saying that I actually believe this...

...but an alternative way of looking at the instantaneous communication of state between two separated Quantum Entangled particles is to view them as just a single particle that happens to be in two places at the same time.  Just as weird, of course:) LeeE, Fri, 26th Sep 2008



I'm not convinced. They could have different directions of motion, different velocities, etc.. How could that be if they were 1 and the same particle? You would have to do some very strange things to spacetime for it to work. DoctorBeaver, Fri, 26th Sep 2008

It's not something I believe - it's just a logical possibility.

It would be something akin to a torus intersecting a plane (with the torus looping above and below the plane - not aligned across the plane's surface)  You'd then have a single object that appears to be in two places on the plane.  Moreover, you'd be seeing different parts of the same object at the two locations and on top of that, the object itself could be changing over time.

It's an extra-dimensional solution, of course, but then QE can't be explained in the context of our four-dimensional space-time anyway, which in turn suggests an extra-dimensional solution. LeeE, Sat, 27th Sep 2008


I think there is a huge difference between the two. Science experiments can be repeated and repeated, yielding consistent results. Even the variability involved with quantum effects follows are reliable pattern. The forces are suggested as reasons for certain effects which can be repeated.
Has anyone ever demonstrated that sort of reliability in fringe non-Science such as telekinesis? lyner, Sat, 27th Sep 2008

Quantum entagnlement isn't all that mysterious once you're getting used to the way quantum mechanics describes our world. First of all you need to know that both classical and quantum mechanics describes our world in terms of "states". There are two main differences between classical and quantum states:

1] Unlike in classical physics, in quantum physics an object doesn't need to be in one particular state but can also be in a "superposition" of states. Such a superposition is not a statistical mix of two states, but it is a pure state all by itself.

2] In any given quantum state some observed quantities may not be measurable with infinite precision as a matter of principle. Most wellknown is the fact that momentum and position are not simultaneously measurable with infinite precision. This is not due to a lack of measuring accuracy, rather quantum states, are in some sense, structurally incapable of "storing" all the information needed to allow such double infinite precision.

If we discus a system consisting of multiple objects, A, B, C, ..., one way to describe them quantum mechanically is by assigning a seperate state S(A), S(B), S(C)_,..., to each object. The system as a whole can then be described by a state which is the "product" of the seperate states S(whole) = S(A)S(B)S(C)...
However, superpositions of such states are also allowed. And some superpositions cannot be written as a single product of states. These superpositions are called "entangled states" and the object A, B, C, ... are said to be "entagled". It essentially means that the objects lose aspects of their individuality in the description of the whole. DarthTutor, Sat, 27th Sep 2008


I think there is a huge difference between the two. Science experiments can be repeated and repeated, yielding consistent results. Even the variability involved with quantum effects follows are reliable pattern. The forces are suggested as reasons for certain effects which can be repeated.
Has anyone ever demonstrated that sort of reliability in fringe non-Science such as telekinesis?


Maybe not reliability; but there are enough examples to make some scientists think that something is going on that they can't explain. DoctorBeaver, Sat, 27th Sep 2008

The answer may be that the particles appear to be independent individuals but are in fact connected, in a way that we are not currently able to discern.

One admittedly incomplete example:  Imagine that we are a water bug.  We know only the surface of the pond, and can move freely on that large surface.  Then, we see two individual eyes separated by 10 inches, each right on the surface of the water.  They don't appear connected to us but in reality they are connected underwater, to the face of an alligator.

To me, quantum entanglement is strongly suggestive of there being additional spatial dimensions that we have yet to discern how to sense and observe.  It may be only a matter of time before we find a way to do so, and what waits for us there could be astonishing beyond belief.

For example, we could learn that all living things are in fact connected.  We could also learn that our consciousness in this dimension is a small outgrowth of our true selves, which exist differently.  This other dimension could be the place where most or all intelligent life goes when it reaches "maturity." 

I hope we find out soon. Bart, Mon, 27th Jul 2009



There's no scientific evidence suggesting the existence of such things at all. There are plenty of unverifiable anecdotes and there's lots of innuendo, but no scientific evidence. exton, Mon, 27th Jul 2009



That's my thought on the subject. DoctorBeaver, Sun, 9th Aug 2009



There's no scientific evidence suggesting the existence of such things at all. There are plenty of unverifiable anecdotes and there's lots of innuendo, but no scientific evidence.


I fully appreciate that there is no scientific evidence for such phenomena, but having experienced it personally on quite a number of occasions I cannot deny that it exists. Absence of evidence is not evidence of absence. It could be that there are so many factors involved that we haven't yet scientifically created the precise conditions required. DoctorBeaver, Sun, 9th Aug 2009



That's my thought on the subject.


I'm not sure there's scope for an additional spatial dimension, or at least one that can't be summed with our three known spatial dimensions.

The phenomenon of relativistic time-dilation seems to tell us a lot about how many dimensions we seem to be dealing with in practice.  If you plot the normalised rate of time against the summed and normalised speed through space you end up with a circular quadrant of constant radius, which appears to show that the sum of the rates of movement through time and space is constant and equal to 'c'.

Now if there was an additional dimension, which couldn't be summed with one or other of the other two, you'd have to raise the plot from a 2D circular quadrant to a spherical 3D surface instead and, if the radius of the sphere remained constant in three dimensions, we should see variations in the radius of the 2D circle as the radius lifts up into the third axis and so foreshortens in the other two axis.  We don't seem to see this though. LeeE, Sun, 9th Aug 2009

LeeE - what about dimensional compactification? The extra dimension would be so tiny it wouldn't have any noticeable effect on time dilation; at least, not over distances that we can measure accurately enough. DoctorBeaver, Sun, 9th Aug 2009

Do you mean so that the radius could only lift up from the 2D plane by just a very small amount?  That would mean that the compactified dimension could only accommodate a very small range of values and couldn't allow a normalised 0-1 range.  The only values it could accommodate would be either a small range of values from 0 or from 1, but couldn't ever include 0.5, from either start value.

A bit weird, but it doesn't seem to be intrinsically impossible.  Instead of a complete spherical 3D surface you'd have an open/truncated spheroid, but you would need an additional factor, or law, to control the truncation and its depth, whereas a complete spherical surface still needs only its radius to loft from a 2D plane to a 3D surface.  Basically, this comes down to finding an explanation and reason, or factor, for why some particular dimensions are compactified when others are not.  It's the introduction of that additional factor, where it would be held or stored and how it acts, that bothers me about that solution though.  You would seem to need to add even more to make the addition work, and so on... LeeE, Mon, 10th Aug 2009

Space is very bendable...
So for a stretch  perhaps two particles connected by Quantum Entanglement are really the same particle on an overlapping plane of space.

Laughable- yes. Conceivable- oh... wait a minute. Stefanb, Tue, 11th Aug 2009

Quantum entangement is one of the most mysterious things about our universe and seems to suggest that our universe is simultaneously very large (as we see it) and very small (as the entangled particles see it).  This is as yet unexplained but I feel that eventually we will come up with a model that explains how this happens.

The string theorists have some ideas how this might happen but have too many theories to work through at the moment.  I have suggested an attractive analysable and simpler approach that could be proved right or wrong using current knowledge and technology in the new theories topic  "evolutionary cosmolgy" Soul Surfer, Tue, 11th Aug 2009

could our universe be a hologram? lonequark, Fri, 21st Aug 2009

at what point do quantum and classical physics cross lonequark, Fri, 21st Aug 2009



Things tend to obey classical mechanics when you deal with large masses or energies (where large is in comparison to the single particles of quantum mechanics).  jpetruccelli, Fri, 21st Aug 2009

Some questions to help me understand:

Is this QE always between 2 particles? Never 3 or more?
Is QE between particles constant? Or does it occur at random moments like on/off? Nizzle, Fri, 21st Aug 2009

Extra dimensions beyond the four we experience seem inexcapable. For instance, subatomic particles do not travel through an infinite number of points going from A to B.  Instead, they seem to jump from place to place according to plank time and distance. It seems to me they jump in and out of another dimension.

Further, various particles seem to jump in and out at varying rates, depending upon their relative velocity. IMHO, the more energy imparted to a particle, the more mass it has, and the longer is stays in the other dimension. That accounts for relativistic effects . The fast moving particle gets spit out in the proper place according to its mass/velocity, but has been held outside of time longer then slower moving particles.

Two Cents of Speculation


litespeed, Fri, 21st Aug 2009

Thought Experiment

The speed of electromagnetic radiation, including light, is not constant. It varies depending upon how much mass it encounters. For instance, a prizm splits light because various energies of light travel faster or slower through the glass depending on their wavelength.

Further, a light beam that passes near a massive sun bends around the sun due to mass bending space time. The light travels at the same speed through space, but gets here later since it travelled further due to the curve it traversed.

The Michalson/Morely experiment attemted to discover whether light traveled through an 'either' in much the same way sound travels through air. On earth, vehicles can outrun sound waves, but MM determined the speed of light was the same in all directions, and could not be outrun; interestingly, however, even though light could not be outrun, it COULD be red or blue shifted.

That is to say, even if every light wave comes to you at the same velocity, you can overtake the frequency of that wave. If you speed fast enough away from the source, you will see red shift, even if the velocity of that red light is the same as before you took off in front of it.

In space you CAN put distance between you and subsequent wave formation. This has two effects. First, the energy you used to obtain velocity has resulted in a lower energy ecounterd by the wave that catches up to you even though the wave that caught you did so at the speed of light.

The mind boggles at the implications. litespeed, Fri, 21st Aug 2009

That is one of the possibilities and recent results on noise in gravitiational wave detectors suggest that tis may well be so. Soul Surfer, Sun, 23rd Aug 2009


Your thought experiment indicates that the light is really reaching you at a slower speed. It is your measuring equipment that has distorted due to your speed. So everything you can detect indicates that light speed is still the same.

So if we had not abandoned the Lorentz version of relativity phenomena we would not have the light speed mind boggling problem. Vern, Sun, 23rd Aug 2009



Hi.

Somehow that made me think of fractals, if you move one bit then its instantly mirrored in the rest. But that would mean a fractal universe or a new fractal dimension.

Food for thought maybe.

Hi vern.

Didn't Lorentz also promote the aether idea? that mad man, Sun, 23rd Aug 2009

Yes I think so; but there need not be physical stuff that makes up space. We seem to be moving to an even worse situation than aether filled space. We have space that is expanding. We have space that is distorting when something moves in it. If it can stretch and be distorted, how can space simply be nothingness?

Vern, Sun, 23rd Aug 2009

No one has suggested that space is "nothingness" for years. lyner, Sun, 23rd Aug 2009

litespeed

The interaction that slows down the light is an electromagnetic one - not particularly because of the mass. If it were due to the mass, how would the dispersion characteristic tie in with the energy levels in the glass? Diamond has very low density but a high refractive index plus a high dispersion. lyner, Sun, 23rd Aug 2009


Then it must be that we simply changed the name of aether to space Of course we realize that light does not swim in it or be dragged along with it.

Edit: Oops; no we can't say that; expanding space does drag light along with it Vern, Mon, 24th Aug 2009

I was drawn to this thread because it asks "What is quantum entanglement?". I don't think we've answered that yet. I know that in quantum theory, it is a superposition of two or more states that are only determined when they are observed. The question is then, do the entangled states exist as they will be determined, from the time that they were created? Or do they take on the determined states only when observed?

I do not know of an experiment that can answer that. Vern, Mon, 24th Aug 2009


Then it must be that we simply changed the name of aether to space Of course we realize that light does not swim in it or be dragged along with it.

Edit: Oops; no we can't say that; expanding space does drag light along with it

I think there is an essential difference between Space and Aether.
The idea of an Aether assumed, perhaps implicitly, that there is some sort of grid in which all objects move. Michelson Morely showed that things don't behave like that. That is not what was mean by Space, subsequently. Space is just what fills in between 'things' with mass. It is defined by the things 'in it'. As the (or a) universe expands or contracts, it does not expand 'into' space, like an exploding grenade nor does it leave Space behind it as it contracts. What you are referring to as 'Nothing' is really 'not space'. Your 'nothing' is outside space - but that 'outside' is not part of space nor does it have any meaning or relevance to the Universe, in terms of what we can observe; it's just 'not universe'. (And I reckon that includes time as well - so 'before' the BB is just as meaningless as 'outside the Universe')

lyner, Mon, 24th Aug 2009

As for quantum entanglement - I could imagine an excellent betting scam based on entanglement.
You have a coin, with its heads or tails state defined by the quantum state of one of a pair of entangled particles.
This coin is somewhere remote, say on a Moon of Jupiter. No one else knows that you have the other member of the pair in your pocket. You then gamble on the state of the coin. You look at the state of your local, entangled system and that tells you, instantly, the state of the remote coin. You go into the bookmakers and place your bet and, lo and behold, when the message about the remote coin comes in over the radio waves, minutes later, you have won your bet. Until William Hill know about your sneaky quantum link, they will just have to keep paying out on your correct bets. Neat.
You haven't violated anything and you haven't actually SENT any information faster than light. lyner, Mon, 24th Aug 2009

Nizzle, Tue, 25th Aug 2009

i read some books said the entanglement is the way the two electrons in the EPR experiment 'linked', once one of the electron is being observed, we can know another electron 's spin immediately, so even the 2 electrons are separated apart from few light yrs, the information 'traveled' faster than light year. But this didnt' obey Einstein 's theory because it is faster than light speed, and some scientists explained this entanglement didnt' carry anything so it is okay for faster than light speed johnson039, Tue, 25th Aug 2009


And you also have not determined whether the entangled states existed in their observed state from the time the entanglement occurred.
Vern, Tue, 25th Aug 2009

You mean that you can't be sure that they're still entangled after you've taken one of them out of the Lab?
That seems reasonable - even if it's a bit or a bore as far as my scam goes. lyner, Tue, 25th Aug 2009

No; I mean that we have no experimental way to determine whether entangled states assume their observed state at the time of observation, or whether they assumed their observed state when they were created.

For example, in pair production, one will be spin up, the other spin down. They may have taken on those states the instant of creation. Vern, Tue, 25th Aug 2009


Any disturbance in the environment can cause entangled particles to "decohere". Researchers would love to store entangled states for even 1ms at room temperature (like the early silicon Dynamic RAM chips).

Most experiments with entangled states take place in cryogenically-cooled apparatus, shielded from light and external magnetic fields.

You don't know whether a particular particle is still entangled when it gets to the destination. When you measure many particles, you can determine whether most, none or some of them are still entangled - after you have compared notes with the "far" end (presumably at less than the speed of light). evan_au, Tue, 16th Jun 2015

Conversation about forces or energy between linked objects has no meaning in the Neils Bohr interpretation. There are no objects and there is no force between them ( I realize that this is a simplified statement).

The Initial incident only generates an abstract, mathematical, probability field that contains all of the probabilities for the future particles or photons. Because they are all part of the same quantum field their probabilities are linked.

When an interaction occurs that actualizes one of the members, all of the other members are simultaneously actualized. In some interpretations the actualized particle or photon is still a mathematical abstraction but with a reduce set of probabilities.

Exton's comment that there is no scientific evidence for such a thing is very true and important. I started a tread some time ago titled " Is remote entanglement not proven".  I could probably start a new thread based on current research titled has remote entanglement been disproved.

Have a look at an article in the New Scientist September 2012 issue, New Maths Triggers a Call to Ironout quantum world.  sciconoclast, Tue, 16th Jun 2015

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