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Spooky action vs. spooky communication

Quantum reach
Credit: Pixabay/CC0 Public Domain

Is communication at faster than the speed of light possible – actual, instantaneous communication across vast distances using entangled (so-called) particles?

After a conversation with an acquaintance last June … He was reading Katie Mack’s book re cosmology, and said that entanglement permitted instantaneous communication. He referenced information theory. And that information requires no “embodiment.”

Anyway, Chad Orzel‘s 2015 article (below) explains the historical debunking of the notion.

And in another of my posts (“What the heck is quantum entanglement?“), there’s a point that “there can be correlation without communication.”

Orzel’s key point is about quantum randomness, indeterministic quantum states. Namely, that to encode a message you need to deterministically set the value of a “carrier” by measurement; but for an entangled particle that value is not predefined – the value you measure is probabilistic.

In order to send a message (e.g., a non-random bit sequence), the sender needs to pre-define the information and deterministically encode it – something which quantum state randomness defeats.

So, the values measured by the “receiver” – while the same as (correlated with) what the sender measures – are random. An incoherent message, eh.

So, is there a difference between saying “spooky action at a distance” and “spooky communication at a distance“?

The standard rebuttal to the claim – that “spooky action at a distance” allows spooky communication at a distance – is that such a claim violates the theory of relativity regarding the speed of light. And that Alice & Bob would need to confirm correlated information via standard light-speed means.

No physical object, message or field line can travel faster than the speed of light in a vacuum.

Such standard reasoning addresses the puzzle but begs for something deeper than a prohibition.

In a prior post, “How to create entangled photon pairs” (April 25, 2017), physicist Chad Orzel explains why “spooky communication at a distance” (transmitting information faster that light) is not an outcome of entanglement’s “spooky action at a distance.”

• Forbes > “How Quantum Randomness Saves Relativity” by Chad Orzel (Aug 11, 2015) – Why photon state correlation does not permit faster-than-light communication.

The notion that quantum particles do not have well-defined states prior to measurement was just too radical a departure from classical physics for Einstein to stomach …

Without that indeterminacy, quantum physics would allow the sending of messages faster than the speed of light, with disastrous consequences for the whole idea of causality, which is central to the operation of physics.

This [entanglement] might seem like it opens the possibility of faster-than light communication between Alice and Bob. They simply share entangled photons with each other, and then measure their polarizations, calling one outcome “0” and the other “1.” This lets them transmit messages in binary code, and violate the restriction from relativity that nothing can exceed the speed of light.

But this is where quantum randomness, … steps in to save the day. The simplest possible scheme you could imagine – Alice assigns a “1” to vertical polarization and a “0” to horizontal polarization – doesn’t work at all, because there’s no way to force a particular outcome. When Alice sets her polarization analyzer to vertical, there’s a 50% chance that her photon will turn out vertical, and a 50% probability that it turns out horizontal. Bob’s photons will be perfectly correlated with Alice’s, but all that means is that they each have the same totally random string of 0’s and 1’s. No information passes from Alice to Bob.

Orzel then considers another scheme between Alice & Bob, which also is compromised by quantum randomness. A photon cloning scheme also does not work: “an indeterminate state cannot be faithfully duplicated.”

In a 2018 articlePaul Sutter also explains why photon state correlation does not permit faster-than-light communication.

The resolution to Einstein’s question comes via an excruciatingly careful examination of who knows what and when. … while the process of disentanglement happens instantaneously, the revelation of it does not. We have to use good old-fashioned no-faster-than-light communication methods to piece together the correlations that quantum entanglement demands.

Looking for some useful visualizations … [1]


[1] Perhaps via Wigner function visualizations?

• Quora > “Can quantum entanglement be visualized

Mark John Fernee
20+ years as a physicist 4y [2018]
It depends on what you mean by visualized.

Your example of using a beam splitter does not create an entangled state. For a single photon, a beam splitter creates a superposition of two possible paths. An entangled state requires at least two or more quantum objects (photons, electrons or something more exotic). In fact specific properties can be entangled such as spin, polarisation and so on. In that sense, an entangled particle pair usually refers to some specific property of the pair.

Entanglement shows up in correlated measurement outcomes for the entangled particle pair such that the measurement of one part of the pair is enough to know the measurement of the other.

As for a visualisation, well that can be done using a phase space representation known as a Wigner function. A recent study has used the IBM’s 5 qubit quantum computer to determine the Wigner functions for a range of different entangled states, here Simple procedure for phase-space measurement and entanglement validation. Be warned that this is a technical paper and not really suited to conveying concepts to a more general audience. You will notice a number of 3D plots that visualise the entangled states. However, their interpretation would take some time and effort. What’s really cool about this is they used an IBM quantum computer to calculate the results. It’s really just about the Wow factor …

2 thoughts on “Spooky action vs. spooky communication

  1. Here’s an excellent video visualization (includes clips from popular sci-fi films) which recaps why superluminal (FTL) communication via a “quantum entanglement communicator” is far-fetched. Alice & Bob examples. There’s already over a 1000 comments.

    (quote) … entanglement is really just a special case of a superposition, and one that involves two or more particles, but rather than being a generic superposition, it’s a superposition of correlated measurement outcomes, such that the measurement of one particle is associated with a definite measurement outcome for the other.

    • YouTube > Cool Worlds > “Does Quantum Entanglement Allow for Faster-Than-Light Communication?” (Sep 9, 2022) – In relativity, the speed of light isn’t just the speed of a photon, it truly represents the speed of causality.

    (Description) Quantum entanglement allows particles to affect one another faster than the speed of light. So does this mean we could one day build a device to exploit this and enable superluminal communication? A popular trope in sci-fi for sure, but today let’s look at the science.

    Presented by Prof David Kipping (Columbia). Special thanks to Prof. Ehud Altman (Berkeley), Prof Tim Byrnes (NYU) & Prof. Raquel Queiroz (Columbia) for fact checking our script.

    [See description also for further references on this topic, as well as the list of film/TV clips used.]

    00:00 The FTL Dream
    02:10 Relativistic FTL?
    03:41 Quantum FTL?
    06:27 Quantum 101
    09:01 FTL Action at Distance
    10:33 How to Exploit?
    12:23 Idea 1: Repeat Measurements
    14:16 Idea 2: Double Slits
    18:04 Idea 3: XY Switching
    22:20 Where From Here?
    28:11 Outro & Credits

    (from transscript) The concept of a quantum entanglement communicator, let’s just call it QEC for short, has been popular in science fiction for years.

    The primary fact that QEC proponents highlight is that the effects of entanglement have been clearly established to travel faster than the speed of light. Now, that statement on its own isn’t quite the same thing as saying, therefore, FTL communication is allowed, but naively, it seems like indeed it should make it possible.

    In short, because Bob can’t force an entangled particle to adopt a particular spin, there’s no way to actually use this to transmit any information.

    Now, some of you might still be stubbornly clinging onto hope here because after all, we just need to find some way, any way that Bob can influence the state of their particle. And then the entanglement would cause that information to be transmitted FTL.

    … it makes no difference what Bob does to what Alice gets. Either way, Alice is left with a random sequence, just like we had before.

    In fact, physicists have even gone a step further and shown that if the fundamental assumptions of quantum mechanics are taken as true, then one can rigorously show that such communication is impossible, known as the no-communication theorem.

    And when we think in terms of causality, we see that action at a distance isn’t in violation. It may be non-local, but it’s not non-causal.

    Video screenshot

  2. A quantum physics foundational question – regarding quantum randomness, indeterminate quantum states. Back to quantum basics … as noted above in Chad Orzel’s 2015 article:

    (quote) The notion that quantum particles do not have well-defined states prior to measurement was just too radical a departure from classical physics for Einstein to stomach …

    In this article (below), Ethan Siegel discusses the source of quantum randomness (which I prefer as a foundational label rather than the term uncertainty). He recaps some seminal experiments. But his premise appears to be that quantum properties are intrinsic rather than relational [1]. A classical tone [2]. So that “hidden variable” theories might find something intrinsic at a deeper level.

    My take is that considering superposition and entanglement (as a particular case of a superposition) might be useful. And superposition as the common rather than rare thing. To paraphrase, the fault, dear Ethan, is not in elusive states but in our notion that quantum states can be described independently of the state of others. A different take on wave-packet spreading, perhaps. As John Preskill might say, the information is not stored in individual states [3].

    (quote) … entanglement between quantum systems arises naturally … In practice, unentangled (independent) states are rare exceptions, for whenever systems interact, the interaction creates correlations between them. – “Entanglement Made Simple” by Frank Wilczek (Quanta Magazine, April 28, 2016)

    • Big Think > “Ask Ethan: Where does quantum uncertainty come from?” by Ethan Siegel (September 16, 2022) – Why do certain quantum properties always possess an inherent uncertainty?

    You can easily imagine, based on the fact that there are quantum fields permeating all of space, even completely empty space, that these underlying fields themselves are the source of all of it [uncertainty, indeterminism]. The uncertainty that we’re seeing, perhaps, arises as a consequence of the quantum vacuum.

    [But, the Stern-Gerlach experiment makes it] hard to make sense of this under the assumption that the quantum vacuum itself is responsible for the whole of quantum uncertainty.

    It’s the interactions (or lack thereof) that a quantum system experiences which dictate how quantum uncertainty rears its head, not any property inherent to the fields permeating all of space.

    [Does] quantum uncertainty exist for gravitation as well …


    Hidden variables assumption / theories
    Conjugate variables
    Heisenberg uncertainty principle
    Trajectories of a particle in a box (aka an infinite square well)
    Wave-packet spreading
    Electromagnetic spectrum
    reduced Planck constant
    Zero-point (or vacuum) energy
    Stern-Gerlach experiment
    Double-slit experiment
    Electric potential and free electric charge


    [1] For lack of a better term, relational quantum theory. A more contextual (literally, “woven together”) quantum field theory. In an entangled landscape. As noted in prior posts which cite physicists Lee Smolin and Carlo Rovelli.

    Smolin: “An object’s properties are not intrinsic to it — rather they reflect the relationships or interactions that object has with other objects.”

    • My post re Rovelli’s book: Helgoland? – escape from quantum island

    • Wiki > Relational quantum mechanics > Rovelli

    Quantum reality, quantum worlds – the section on a July 10, 2018, podcast interview with Carlo Rovelli.

    So, Carroll talks about the measurment problem. And Rovelli’s Relational quantum mechanics replaces measurement with interaction as the way to remain a “realist about the wave function.” That is, a “property becomes concrete when two systems interact.”

    Swaying quantum vacuum energy vs compelling charge – the section in Note #5 about what Lee Smolin says about a relational model.

    How stiff is space-time? – the section in my November 2, 2021 at 9:44 AM comment on Relational theory à la Smolin, and relational quantum mechanics à la Rovelli.

    [2] As he also still uses the term particle in an equivocal manner. Versus at least indicating physicists understand that talking about “particles” is shorthand for localized field excitations. And perhaps that all such particles actually may be quasi-particles.

    [3] See References in my post “What the heck is quantum entanglement?” which cites this video in which Preskill uses the analogy of a quantum book.

    • YouTube > Caltech Science Exchange > “How Do Scientists Explain Quantum Entanglement?” (Oct 11, 2021)

    (quote) so that’s the way i look at it – the essence of quantum entanglement – that you can have a quantum system which stores a lot of information; but when you look at the parts of the system one at a time, you can’t see the information at all [because it’s an emergent relational group property].

    Conjugate variables x and p
    Credit: Maschen/Wikimedia Commons

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