What did Einstein mean by “Spooky Action at a Distance"?

Summary

In this video, the concept of 'spooky action at a distance' in quantum mechanics is explored, challenging the common belief that Einstein referred to entanglement. The script delves into Einstein's original context, suggesting he was concerned with the instantaneous wave-function collapse upon measurement, not entanglement itself. It explains quantum mechanics' probabilistic nature and how Einstein viewed quantum mechanics as incomplete, predicting a more direct description of reality would emerge. The video also promotes Brilliant's interactive courses for a deeper understanding of the subject.

Takeaways

• 🌌 Quantum mechanics is often described as 'weird' due to its non-intuitive phenomena like 'spooky action at a distance'.
• 🔍 The term 'spooky action at a distance' is commonly attributed to Einstein's critique of quantum mechanics, specifically entanglement, but the script suggests a deeper meaning.
• 💬 Einstein's original use of 'spooky action at a distance' came from a 1947 letter to Max Born, expressing his disbelief in quantum mechanics due to its incompatibility with a realistic representation of space and time.
• 📚 Quantum mechanics operates on the principle of a wave-function, from which probabilities for measurement outcomes are derived, but the wave-function itself is not directly observable.
• ⚡ The wave-function 'collapse' upon measurement is instantaneous and appears to occur faster than the speed of light, which troubled Einstein.
• 👣 In 1927, Einstein used the example of electron diffraction to illustrate the peculiar mechanism of action at a distance in quantum mechanics.
• 🧬 The EPR paper of 1935, co-authored by Einstein, Podolsky, and Rosen, examined entanglement as a way to demonstrate the 'spooky action' concept with two particles.
• 🤝 Entanglement is a form of correlation between particles, but it is not the action itself that is 'spooky'; rather, it's the instantaneous change in the wave-function upon measurement.
• 🧦 An analogy is made with two socks in envelopes to explain non-local correlations, which are not inherently problematic or 'spooky'.
• 🔮 Einstein was not against quantum mechanics but believed it to be incomplete, suggesting that a more comprehensive theory would eventually emerge.
• 🎓 The script encourages active engagement with quantum mechanics through interactive learning platforms like Brilliant, which offer courses on related topics.

Q & A

What did Einstein mean by 'spooky action at a distance'?

Einstein referred to the phenomenon where the measurement of a quantum system instantaneously affects its counterpart, regardless of the distance between them. He was concerned about the instantaneous 'update' of the wave-function upon measurement, which seemed to him to be incompatible with the requirement that physics should represent reality in space and time without such non-local influences.

What is the origin of the phrase 'spooky action at a distance'?

The phrase originated from a letter Einstein wrote to Max Born in March 1947, where he expressed his disbelief in quantum mechanics due to its incompatibility with the concept of local realism.

What is quantum entanglement?

Quantum entanglement is a phenomenon where two or more particles become linked in such a way that the state of one particle instantaneously influences the state of the other, no matter how far apart they are.

Why did Einstein, Podolsky, and Rosen write the EPR paper?

Einstein, Podolsky, and Rosen wrote the EPR paper to explore the implications of quantum mechanics on the concept of local realism. They considered a scenario involving two entangled particles to illustrate the paradoxical nature of 'spooky action at a distance'.

What is the difference between entanglement and 'spooky action at a distance' according to the script?

Entanglement is a type of correlation between particles that can be non-local, but it does not involve any 'action' at a distance. 'Spooky action at a distance', as Einstein referred to it, is the instantaneous update of the wave-function upon measurement, which affects the entangled particle regardless of distance.

How does the script explain the correlation between two socks as an analogy for entanglement?

The script uses the socks analogy to illustrate how knowing the color of one sock instantly tells you the color of the other sock, due to their correlated properties. This is similar to entanglement, where measuring one particle's property instantly determines the property of its entangled partner.

What was Einstein's view on quantum mechanics in relation to reality?

Einstein believed that quantum mechanics was an incomplete theory. He thought it was an indirect description of reality and that a more complete and direct description would eventually replace it.

What does the script suggest about the nature of reality in quantum mechanics?

The script suggests that reality in quantum mechanics is not predetermined but is instead influenced by the act of measurement. This is contrary to Einstein's belief in a reality that exists independently of observation.

How does the script differentiate between quantum correlations and classical correlations?

Quantum correlations, such as entanglement, can be stronger and more instantaneous than classical correlations, which are limited by the speed of light and do not involve 'spooky action at a distance'.

What was Einstein's concern regarding the measurement update in quantum mechanics?

Einstein was concerned that the measurement update in quantum mechanics implied a non-local 'physical intervention' that could not be reconciled with his understanding of space and time.

What is the role of Brilliant in the context of this script?

Brilliant is mentioned as a sponsor of the video and is described as a platform offering interactive courses on various scientific and mathematical topics, including quantum mechanics, to help viewers actively engage with and understand the subject matter.

Outlines

00:00

🌌 Quantum Mechanics and 'Spooky Action'

This paragraph delves into the concept of 'spooky action at a distance' within the realm of quantum mechanics, a term popularly attributed to Albert Einstein. It challenges the common belief that Einstein was referring to entanglement when he used the phrase. Instead, the script suggests that Einstein was actually concerned with the instantaneous update of the wave-function upon measurement, which he viewed as incompatible with a realistic representation of physics in space and time. The paragraph also provides a brief explanation of how quantum mechanics operates with wave-functions and the calculation of probabilities from them, emphasizing the non-observable nature of the wave-function itself and the instantaneous nature of measurement outcomes.

05:04

🧦 Understanding Correlations and Entanglement

The second paragraph explores the nature of correlations and entanglement in quantum mechanics, using the analogy of two socks with correlated colors to illustrate the concept. It argues that entanglement, while a strong form of correlation, does not inherently involve 'spooky action at a distance'. The script explains that entanglement is simply a correlation that can exist over large distances, similar to the momentum conservation when a ball bounces off a wall. The paragraph further discusses Einstein's concerns about the implications of quantum mechanics, particularly the instantaneous change in wave-function upon measurement, which he believed indicated an incomplete understanding of reality. The script defends Einstein's position, suggesting that his critique was not about quantum mechanics being wrong, but rather that it was an incomplete theory.

10:10

📚 Learning Quantum Mechanics with Brilliant

The final paragraph shifts focus to the educational platform Brilliant, which offers interactive courses on various scientific and mathematical topics, including quantum mechanics. The script encourages active engagement with the subject matter through problem-solving and learning, suggesting that watching videos alone is not sufficient to truly understand quantum mechanics. The paragraph promotes Brilliant's courses on linear algebra and quantum objects as valuable resources for deepening one's understanding of the subject. It also mentions a special offer for viewers of the video, providing a link and a discount for the first 200 subscribers who sign up for the annual premium subscription.

Keywords

💡Quantum Mechanics

Quantum mechanics is a fundamental theory in physics that describes the physical properties of nature at the scale of atoms and subatomic particles. It is the main theme of the video, as it delves into the peculiarities of quantum phenomena. The script discusses how quantum mechanics is often deemed 'weird' due to its non-intuitive predictions, such as 'spooky action at a distance'.

💡Spooky Action at a Distance

This term, famously attributed to Albert Einstein, refers to the phenomenon in quantum mechanics where the state of one particle instantly affects the state of another particle, regardless of the distance separating them. It is central to the video's exploration of Einstein's skepticism about certain aspects of quantum mechanics, as he believed in a physics that represented reality in space and time without such instantaneous 'spooky' interactions.

💡Entanglement

Entanglement is a quantum mechanical phenomenon where pairs or groups of particles interact in such a way that the quantum state of each particle cannot be described independently of the state of the others, even when the particles are separated by a large distance. The script challenges the common interpretation that Einstein's 'spooky action' was referring to entanglement, suggesting instead it was about the instantaneous update of the wave-function upon measurement.

💡Wave-function

In quantum mechanics, the wave-function is a mathematical description of the quantum state of a system. It is used to calculate the probabilities of different outcomes when measurements are made. The script explains that the wave-function is not directly observable but is crucial for understanding the 'spooky action' Einstein was concerned with, as its 'update' upon measurement is instantaneous.

💡Measurement

Measurement in quantum mechanics refers to the process of gaining information about the state of a quantum system. The script emphasizes the role of measurement in the 'spooky action' debate, as it is the act of measurement that collapses the wave-function and seemingly causes instantaneous changes at a distance.

💡Reality

The concept of reality in the context of the video pertains to the philosophical and scientific debate about what constitutes the true state of the world, independent of observation. Einstein believed that quantum mechanics was an incomplete description of reality, as it did not account for the instantaneous effects observed in 'spooky action at a distance'.

💡Einstein's EPR Paper

The EPR paper, co-authored by Einstein, Podolsky, and Rosen, is a foundational work in quantum mechanics that challenged the completeness of quantum theory by proposing a thought experiment involving entangled particles. The script mentions the EPR paper as a key reference point in the discussion of 'spooky action at a distance', even though the term was not used in the paper itself.

💡Correlation

Correlation in the script is used to describe the relationship between two variables or events. It is important in understanding entanglement, as the script argues that entanglement is a form of correlation that does not imply 'spooky action'. Instead, it is a statistical relationship that can exist without any direct interaction between the correlated entities.

💡Locality

Locality refers to the principle that physical processes occurring at one location do not depend on the properties of objects at other locations. The script uses the concept of locality to discuss the paradox of 'spooky action at a distance', questioning whether quantum mechanics violates this principle.

💡Incompleteness

The term 'incompleteness' in the script refers to Einstein's belief that quantum mechanics does not provide a complete picture of physical reality. He suggested that there must be additional, yet undiscovered, variables or principles that would provide a more complete and direct description of reality.

💡Brilliant

Brilliant is an educational platform mentioned in the script that offers interactive courses on various scientific and mathematical topics, including quantum mechanics. The script suggests that to truly understand quantum mechanics, one should actively engage with the subject, and Brilliant is presented as a resource for such engagement.

Highlights

Quantum mechanics is often described as 'weird' due to its non-intuitive phenomena.

Einstein's term 'spooky action at a distance' is commonly misattributed to entanglement.

Einstein's actual use of 'spooky action at a distance' originated from a 1947 letter to Max Born.

Einstein's skepticism was rooted in quantum mechanics' incompatibility with local realism.

Quantum mechanics operates through complex-valued wave-functions and probability calculations.

Wave-function 'collapse' upon measurement is instantaneous and appears to exceed the speed of light.

Einstein's 1927 Solvay conference example illustrated the peculiar mechanism of action at a distance.

Entanglement involves measurement effects on one particle influencing another, regardless of distance.

Correlations in entanglement are non-local but do not constitute 'action at a distance'.

A simple analogy of socks in envelopes demonstrates non-local correlations without 'spooky action'.

Conservation laws, like momentum transfer, create natural correlations without requiring 'spooky action'.

Einstein, Podolsky, and Rosen's 1935 EPR paper examined entangled particles to explore 'spooky action'.

Einstein's concern was with the wave-function update upon measurement, not entanglement itself.

Einstein believed quantum mechanics was incomplete, not incorrect, and would be replaced by a more complete theory.

The video argues for a nuanced understanding of Einstein's views on quantum mechanics, challenging common misconceptions.

The video was sponsored by Brilliant, an educational platform offering interactive courses in science and mathematics.

The video encourages active engagement with quantum mechanics through problem-solving and understanding.

Transcripts

Quantum mechanics is weird – I am  sure you’ve read that somewhere.  

And why is it weird? Oh, it’s because it’s  got that “spooky action at a distance”,  

doesn’t it? Einstein said that. Yes, that  guy again. But what is spooky at a distance?  

What did Einstein really say? And what does  it mean? That’s what we’ll talk about today.

The vast majority of sources on the internet claim  that Einstein’s “spooky action at a distance”  

referred to entanglement. Wikipedia for example.  And here is an example from Science Magazine.  

You will also find lots of videos on YouTube  that say the same thing: Einstein’s spooky  

action at a distance was entanglement. But  I do not think that’s what Einstein meant.

Let’s look at what Einstein actually said.  

The origin of the phrase “spooky action at  a distance” is a letter that Einstein wrote  

to Max Born in March nineteen 47. In this  letter, Einstein explains to Born why he  

does not believe that quantum mechanics  really describes how the world works.

He begins by assuring Born that he knows perfectly  well that quantum mechanics is very successful:  

“I understand of course that the statistical  formalism which you pioneered captures a  

significant truth.” But then he goes on  to explain his problem. Einstein writes:

“I cannot seriously believe [in quantum  mechanics] because the theory is incompatible  

with the requirement that physics should  represent reality in space and time  

without spooky action at a distance…”

There it is, the spooky action at a distance.  But just exactly what was Einstein referring to?  

Before we get into this, I have to quickly  remind you how quantum mechanics works. 

In quantum mechanics, everything is described by  a complex-valued wave-function usually denoted  

Psi. From the wave-function we calculate  probabilities for measurement outcomes,  

for example the probability to find a particle  at a particular place. We do this by taking  

the absolute square of the wave-function. But we cannot observe the wave-function itself.  

We only observe the outcome of the measurement.  This means most importantly that if we make a  

measurement for which the outcome was not  one hundred percent certain, then we have to  

suddenly „update” the wave-function. That’s  because the moment we measure the particle,  

we know it’s either there or it isn’t. And this  update is instantaneous. It happens at the same  

time everywhere, seemingly faster than the speed  of light. And I think *that’s what Einstein  

was worried about because he had explained  that already twenty years earlier, in the  

discussion of the nineteen 27 Solvay conference. In nineteen 27, Einstein used the following  

example. Suppose you direct a beam of electrons  at a screen with a tiny hole and ask what happens  

with a single electron. The wave-function of the  electron will diffract on the hole, which means it  

will spread symmetrically into all directions.  Then you measure it at a certain distance from  

the hole. The electron has the same probability to  have gone in any direction. But if you measure it,  

you will suddenly find it in one particular point. Einstein argues: “The interpretation, according to  

which [the square of the wave-function] expresses  the probability that this particle is found  

at a given point, assumes an entirely peculiar  mechanism of action at a distance, which prevents  

the wave continuously distributed in space from  producing an action in two places on the screen.”

What he is saying is that somehow the  wave-function on the left side of the screen  

must know that the particle was actually  detected on the other side of the screen.  

In 1927, he did not call this  action at a distance “spooky”  

but “peculiar” but I think he  was referring to the same thing.

However, in Einstein’s electron argument  it’s rather unclear what is acting on what.  

Because there is only one particle. This  is why, Einstein together with Podolsky and  

Rosen later looked at the measurement  for two particles that are entangled,  

which led to their famous 1935 EPR paper. So  this is why entanglement comes in: Because  

you need at least two particles to show that  the measurement on one particle can act on  

the other particle. But entanglement itself is  unproblematic. It’s just a type of correlation,  

and correlations can be non-local without  there being any “action” at a distance.

To see what I mean, forget all about quantum  mechanics for a moment. Suppose I have two socks  

that are identical, except the one is red and  the other one blue. I put them in two identical  

envelopes and ship one to you. The moment you  open the envelope and see that your sock is red,  

you know that my sock is blue. That’s  because the information about the color  

in the envelopes is correlated, and this  correlation can span over large distances. 

There isn’t any spooky action going on though  because that correlation was created locally.  

Such correlations exist everywhere and are  created all the time. Imagine for example  

you bounce a ball off a wall and it comes  back. That transfers momentum to the wall.  

You can’t see how much, but you know  that the total momentum is conserved,  

so the momentum of the wall is now  correlated with that of the ball.

Entanglement is a correlation like this, it’s  just that you can only create it with quantum  

particles. Suppose you have a particle with  total spin zero that decays in two particles  

that can have spin either plus or minus one.  One particle goes left, the other one right.  

You don’t know which particle has which spin,  but you know that the total spin is conserved.  

So either the particle going to the right had  spin plus one and the one going left minus one  

or the other way round. According to quantum mechanics,  

before you have measured one of the particles,  both possibilities exist. You can then measure the  

correlations between the spins of both particles  with two detectors on the left and right side.  

It turns out that the entanglement  correlations can in certain circumstances  

be stronger than non-quantum correlations. That’s  what makes them so interesting. But there’s no  

spooky action in the correlation themselves.  These correlations were created locally.  

What Einstein worried about instead  is that once you measure the particle  

on one side, the wave-function for the  particle on the other side changes.

But isn’t this the same with the two socks? Before  you open the envelope the probability was 50-50  

and then when you open it, it jumps to 100:0. But  there’s no spooky action going on there. It’s just  

that the probability was a statement about what  you knew, and not about what really was the case.  

Really, which sock was in which envelope  was already decided the time I sent them. 

Yes, that explains the case for the socks. But in  quantum mechanics, that explanation does not work.  

If you think that really it was decided already  which spin went into which direction when they  

were emitted, that will not create sufficiently  strong correlations. It’s just incompatible  

with observations. Einstein did not know that.  These experiments were done only after he died.  

But he knew that using entangled states you can  demonstrate whether spooky action is real, or not.

I will admit that I’m a little defensive of  good, old Albert Einstein because I feel that  

a lot of people too cheerfully declare that  Einstein was wrong about quantum mechanics.  

But if you read what Einstein actually  wrote, he was exceedingly careful  

in expressing himself and yet most physicists  dismissed his concerns. In April nineteen 48,  

he repeats his argument to Born. He writes that  a measurement on one part of the wave-function is  

a „physical intervention” and that “such an  intervention cannot immediately influence  

the physically reality in a distant  part of space.” Einstein concludes:

“For this reason I tend to believe that  quantum mechanics is an incomplete and  

indirect description of reality which will  later be replaced by a complete and direct one.”

So, Einstein did not think that quantum  mechanics was wrong. He thought it was  

incomplete, that something fundamental  was missing in it. And in my reading,  

the term “spooky action at a distance” referred  to the measurement update, not to entanglement.

This video was sponsored by Brilliant  which is a website and app that offers  

interactive courses on a large variety  of topics in science and mathematics.  

Watching videos is fun and gives you an  idea what quantum mechanics is all about,  

but if you really want to understand how quantum  mechanics works, you have to actively engage with  

the subject and challenge yourself by answering  questions. Brilliant is a great place to do that.  

For this video, for example, I recommend their  courses on linear algebra and quantum objects.

To support this channel and  learn more about Brilliant,  

go to Brilliant dot org slash Sabine and  sign up for free. The first 200 subscribers  

using this link will get 20 percent  off the annual premium subscription.

Thanks for watching, see you next week.