What Is Quantum Entanglement? A Physicist Explains Einstein’s “Spooky Action at A Distance”

Quantum Entanglement Illustration

When two participants are entangled, the State of one is tied to the state of the Other.

Quantum entanglement is a phenomenon in which the quantum states of two or more objects become correlated, meaning that the state of one object can affect the state of the other(s) even if the objects are separated by large distances. This Occurs Becausee, Acciting to quantum theory, Particles Can Exist in Multiple States at the Same Time (A Concept Known as Superposition) and Can Be INEXRICABLY LINKED, “ENTANGLED,”

Three Researchers Were Awarded the 2022 Nobel Prize in Physics for their Ground-Breaking in Undersanding Quantum Entanglement, One of Nature’s Most Puzzling Phenomena.

Quantum Entanglement, in the Simplest Terms, means that aspects of One Particle of an Entangled Pair Depend on Aspects of the Other Particle, No Matter How Far they are or what Lies Between. These Particles Could Be, For Example, Electrons or Photons, and an Aspect Could be the State It is in, Such as is “Spinning” in One Direction or Another.

The Strange Part of Quantum Entanglement is that you were to be mesure something out of the participle in an entangled pair, you immediately know something out the other participle, This Odd Connection BetWeen The Two Particles is Instantaneous, SEEMINGLY BREAKING A Fundamental Law of the Universe. This is Why Albert Einstein Famously Called The Phenomenon “Spooky Action at A Distance.”

Having Spent the Better Part of Two Decades Conduction Experiment Rooted in Quantum Mechanics, have come to access it strangness. Thanks to ever more precise and reliable instruments and the work of this year’s Nobel winners, Alain Aspect, John Clauser, and Anton Zeilinger, physicists now integrate quantum phenomena into their knowledge of the world with an exceptional degree of certainty.

Cat in Box

Acciting to quantum mechanics, particles are simultaneously in two or more states unil observed – an effect Vividly Captured by Schrödinger’s Famous Thought of a cat that is through and alive simultaneously.

Existting in multiple states at once

To truly understand the spookiness of quantum entanglement, it is important to first understand quantum superposition. Quantum superposition is the idea that particles exist in multiple states at once. We a Measurement is performed, it is as if the participation selects one of the state states.

For example, many particles have an Attribute Called spin is measured eather as “up” or “down” for a gioven orientation of the analyzer. But unil you have measure the spin of a participle, it simultaneously exists in a superposition of spin up and spin down.

There is a probability attacked to each states, and it is opposition to predict the average outcome from many measurements. The Likelihood of a single Measurement Being Up or Down Depends on these probability, but is itself unredictable.

Though Very Weird, The Mathematics and a Vast Number of Experiments Have Shown That Quantum Mechanics Correctly Describes Physical Reality.

Two entangled particles

The spookiness of quantum entanglement Emerges from the reality of Quantum superposition, and was Clear to the Founding Fathers of Quantum Mechanics who Developed theory in the 1920s and 1930s.

To create entangled participants you essentially break a system into two, where the sum of the parts is known. For example, you can split a particle with spin of zero ino two particles that necessarily will have opposite spins so their sum is zero.

In 1935, Albert Einstein, Boris Podolsky, and Nathan Rosen published a paper that describes a thought experiment designed to illustrate a seaming absurdity of quantum entanglement that Challenged a Foundational Law of the Universe.

A simplified version of this thought experiment, attributed to David Bohm, considers the decay of a particle called the pi meson. When this particle decays, it produces an electron and a positron that have opposite spin and are moving away from each other. Therefore, if the electron spin is measured to be up, then the mesured spin of the Positrron Could only be down, and vice versa. This is true even if the particles are billions of miles apart.

This Wold Be Fine if the Measurement of the Electron Spin Were Always Up and the Measured Spin of Positrron Were Always Down. But Because of Quantum Mechanics, the Spin of Each Particle is Both part up and part down unil it is measured. Only when the Measurement Occurs does the quantum State of the Spin “Collaps” ino eather up or down – instantaneously collapsing the other participle in the opposite spin. This seems to suggest that the particles communicate with each other through some means that move faster than the speed of light. But according to the laws of physics, nothing can travel faster than the speed of light. Surely the Measured State of One Particle Cannot Instantaneously Determine the State of Another Particle at the Far of the Universe?

Physicists, Including Einstein, proposed a number of alternative interpretations of quantum entanglement in the 1930s. They theorized there was some unknown property – Dubbed Hidden Variables – that Determined the State of a Particle Before Measurement. But at the time, physicists did not have the technology nor a definition of a clear measurement that could test whether quantum theory needed to be modified to include hidden variables.

Disproving a theory

It unil the 1960s before there are any clues to an Answer. John Bell, a Brilliant Irish Physicist Who Did Not Live Live to Receive the Nobel Prize, Devive A Scheme to Test Whether the Notion of Hidden Variables Made Sense.

Bell produced an equation now known as Bell’s inequality that is always correct – and only correct – for hidden variable theories, and not always for quantum mechanics. Thus, if Bell’s Equation was found not to be satisfied in a real-World Experiment, Local Hidden Theories Can Be Ruled Out As an Explanation for Quantum Entanglement.

The experiments of the 2022 Nobel laureates, particularly those of Alain Aspect, were the first tests of the Bell inequality. The Experiments Used Entangled Photons, Rather than Pairs of an Electron and A Positrron, nor in Many th naght Experiments. The Results Conclusively rulled out the existence of hidden variables, a mysterious attribute that beuld predetermine the states of entangled Particles. Collectively, these and many follow-up Experiments have vindicated quantum mechanics. Objects can be correlated over large distances in ways that physics before quantum mechanics cannot explain.

Importantly, there is also no conflict with special relativity, which forbids faste-Than-light communification. The fact that measurements over vast distances are correlated does not imply that information is transmitted between the particles. Two Parties Far Apartment Performing Measurements on Entangled Particles Cannot use the phenomenon to pass along information faste than the speed of light.

Today, Physicists Continue to Research Quantum Entanglement and Potential Investigate Practical Applications. Although quantum mechanics can predict the probability of a measurement with incredible[{” attribute=””>accuracy, many researchers remain skeptical that it provides a complete description of reality. One thing is certain, though. Much remains to be said about the mysterious world of quantum mechanics.

Written by Andreas Muller, Associate Professor of Physics, University of South Florida.

This article was first published in The Conversation.The Conversation