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Quantum Mechanics
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what is quantum entanglement
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from https://www.thoughtco.com/what-is-quantum-entanglement-2699355
Quantum entanglement is one of the central principles of quantum physics, though it is also highly misunderstood. In short, quantum entanglement means that multiple particles are linked together in a way such that the measurement of one particle's quantum state determines the possible quantum states of the other particles. This connection isn't depending on the location of the particles in space. Even if you separate entangled particles by billions of miles, changing one particle will induce a change in the other. Even though quantum entanglement appears to transmit information instantaneously, it doesn't actually violate the classical speed of light because there's no "movement" through space.
The Classic Quantum Entanglement Example
The classic example of quantum entanglement is called the EPR paradox. In a simplified version of this case, consider a particle with quantum spin 0 that decays into two new particles, Particle A and Particle B. Particle A and Particle B head off in opposite directions. However, the original particle had a quantum spin of 0. Each of the new particles has a quantum spin of 1/2, but because they have to add up to 0, one is +1/2 and one is -1/2.
This relationship means that the two particles are entangled. When you measure the spin of Particle A, that measurement has an impact on the possible results you could get when measuring the spin of Particle B. And this isn't just an interesting theoretical prediction ?but has been verified experimentally through tests of Bell's Theorem.
One important thing to remember is that in quantum physics, the original uncertainty about the particle's quantum state isn't just a lack of knowledge. A fundamental property of quantum theory is that prior to the act of measurement, the particle really doesn't have a definite state, but is in a superposition of all possible states. This is best modeled by the classic quantum physics thought experiment, Schrodinger's Cat, where a quantum mechanics approach results in an unobserved cat that is both alive and dead simultaneously.
The Wavefunction of the Universe
One way of interpreting things is to consider the entire universe as one single wavefunction. In this representation, this "wavefunction of the universe" would contain a term that defines the quantum state of each and every particle. It is this approach that leaves open the door for claims that "everything is connected," which often gets manipulated (either intentionally or through honest confusion) to end up with things like the physics errors in The Secret.
from https://www.scienceabc.com/pure-sciences/what-is-quantum-entanglement.html
This inexplicable phenomena came to be known as “Quantum entanglement”, a term originally coined by Erwin Schrödinger, another early adopter and theorist of the quantum world.
Given that nothing in the universe can move faster than the speed of light, and this “instantaneous” change of spin states revealed a transfer of information thousands of times faster than the “universal speed limit”, the greatest minds of the century were genuinely stumped.
Theoretically, even if these particles were separated by millions of light-years, they would still instantaneously counter one another’s movements, locked in their eternal connection across the cosmos. Thus far, the furthest distance two entangled particles have been is roughly 1.5 miles, but there are exciting plans to launch an entangled particle to the International Space Station (roughly 220 miles) and determine if its entangled particle partner back on Earth will continue this “spooky action at a distance”.
The entire concept has been bending minds for decades, because it breaks one of the most fundamental laws of the universe. The information transfer between the two particles cannot occur faster than the speed of light, and yet it does.
These tangled particles are not limited to pairs either; a study in 2014 artificially entangled approximately 500,000 particles, suggesting a particle cloud “group brain” that instantaneously reacts when any single component is measured or altered.
Taking this a step further, into the macrocosmic scale, let’s talk about the Big Bang, which was essentially the moment when the entire universe exploded from a single particle and began expanding (and hasn’t stopped since!). Given what we just learned about the strange nature of entangled particles, there could be entangled particles spread across the universe. Every single particle could be entangled with another, or a large group.
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