What did Einstein mean by “Spooky Action at a Distance"?
Summary
TLDRIn 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
🌌 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.
🧦 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.
📚 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.
Mindmap
Keywords
💡Quantum Mechanics
💡Spooky Action at a Distance
💡Entanglement
💡Wave-function
💡Measurement
💡Reality
💡Einstein's EPR Paper
💡Correlation
💡Locality
💡Incompleteness
💡Brilliant
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.
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