Why didn't quantum entanglement at FTL violate Einstein's theory of relativity?

2020-06-20

Under the leadership of Pan Jianwei and other scientists, China has achieved a breakthrough in the field of quantum communication technology and is in an international leading position. The concept of quantum entanglement has also caught fire.

Einstein's theory of narrow relativity holds that the speed of light cannot be surpassed and that no object can move faster than the speed of light in a vacuum. As of now, no physical phenomenon that violates the theory of relativity has been found. The speed of induction between two particles in an entangled state is faster than the speed of light, but this does not violate the theory of relativity. What's going on here, let's take a closer look.

What is quantum entanglement?

Quantum entanglement is a quantum effect that occurs on photons and electrons, the fundamental particles that make up matter. According to the scale, the world is divided into macroscopic and microscopic, quantum effects occur mainly in the microscopic world at the atomic and subatomic scale. The concept of quantum entanglement was named by Schrödinger, the founder of wave dynamics.

When we talk about quantum entanglement, we must first talk about the quantum. Observations and experiments have shown that the motion of atomic and subatomic particles is discontinuous, or that the variation in the motion of these particles is discrete. We use physical quantities to describe the changes in the motion of these particles, and if we fill the number axes with the changing values of a physical quantity, the number axes cannot be Fill, exist intervals, and the number axis is divided into one by these intervals, and these intervals correspond to changes in physical quantities, and There is always a minimum interval, which is the quantization of a physical quantity, and the minimum interval, or unit of change, is the quantum.

This change is described by quantum mechanics, which differs from classical mechanics, which describes the motion of matter in the macroscopic world, in which physical quantities are The change of the quantum world is continuous, or the amount of change can be infinitely small, and there is no smallest unit of change. The biggest feature of the quantum world is the uncertainty and randomness of particle motion, and this is where the volatility of particles comes from. This is precisely this reason, scientists can only use statistics and probability to describe the movement of particles. The position and velocity of a particle, for example, are uncertain until they are observed, and they cannot be measured precisely at the same time. "Schrödinger's cat" best illustrates this uncertainty.

The electron cloud model of the atomic structure is a clear illustration of the problem, as shown in the diagram below, where the electrons do not have a defined orbit like planets around a star.

Different particles have different quantum states, and when several particles interact, their quantum states are superimposed on each other. Several particles are in an entangled state. There is a special connection between the particles in the entangled state, and two particles are in different places, even if they are 1 light year apart. When the state of one particle changes, the state of the other particle changes correspondingly. This connection is independent of the distance between the particles, and the whole process is instantaneous, also known as overdistance action.

When we measure a particle that is in an entangled state, the quantum state in a superposition state collapses, creating a A deterministic quantum state, no matter how far apart, another particle will also sense this measurement behavior and collapse to a deterministic state. This collapsing process is also random. And before the measurement, we only know the state of the entire quantum system, not the state of individual particles.

Although Einstein was the main founder of quantum mechanics, he also questioned the role of supergiants in quantum entanglement, and, along with Rosen and Podolski co-proposed the EPR thought experiment in 1935, and in 1964, John Bell proposed the Bell inequality , and the ERP thought experiment has become feint. Wheeler was the first to propose an experiment to verify the entangled state of photons, and since then, scientists have successfully implemented the experiment, generating mutual Entangled Photon Pairs.

The following figure shows the principle of generation of entangled photon pairs

Quantum entanglement phenomena are independent of distance, time

Quantum entanglement is a ghostly connection that is independent of distance. Two particles in an entangled state, even if separated by billions of light-years, will be telepathically linked to each other. However, this telepathic process is mainly reflected in the moment when the entanglement state is lifted, one particle is disturbed, the other particle Immediately a corresponding change will be made and the entangled state will then be released. If there is no interference, the entangled state will remain.

Scientists have done many experiments and have not found a time delay in the collapse of entangled particle pairs. It is therefore generally accepted that the process involves no time difference, or takes 0. The velocity is equal to the distance divided by the time, no matter how far away. How do you determine the speed when the time is always 0? For the phenomenon of quantum entanglement, neither 100 times the speed of light, nor 10,000 times the speed of light, is of any practical significance. You could also argue that the speed of quantum entanglement is infinite.

As for why this connection is made, scientists are not too sure about the deeper reasons behind it. To be sure, quantum entanglement is an objective physical phenomenon.

The existence of FTL does not mean that it violates relativity.

Einstein, in his theory of special relativity, argued that the fastest speed in the universe is the speed of light in a vacuum, which is the limit of the speed at which all objects move. No object can move faster than the speed of light, and no object with mass can reach the speed of light. Light is an electromagnetic wave, which can also be regarded as a photon, and since photons have no rest mass, light travels at the speed of light from its inception. The reason why an object with mass cannot reach the speed of light is that, as the object moves, its mass increases with its speed. And it increases exponentially. This means that the closer the velocity is to the speed of light, the more energy is required to accelerate the object, and the more mass an object has, the more energy is required to accelerate it. There is also more energy.

It is known that there are three main types of superluminal phenomena in the universe, one is what this paper calls quantum entanglement, one is the expansion of cosmic space at superluminal speeds, and one is in the medium.

The speed of light propagating in a vacuum is 300,000 kilometers per second, while the speed of light propagating in a medium will be smaller than the speed of light propagating in a vacuum. Sometimes the speed of other particles in the medium can exceed the speed of light propagation in the medium, which does not exceed the speed of light in the vacuum and does not count! True FTL.

The universe was born in one big bang, and the galaxies seemed to be distributed on the surface of a balloon, and as the universe expanded, which is to say, the balloons Any two points on it are moving away from each other, and the further apart they are, the faster they move away from each other. The expansion of space is like the expansion of a balloon; the further away a galaxy is from Earth relative to the Earth, the faster it moves away from the Earth! . More than 14 billion light-years away from Earth, space is already expanding faster than the speed of light, but the speed of matter movement in space-time It does not exceed the speed of light.

Quantum entanglement is a manifestation of the uncertainty of the quantum world, and the collapse of quantum superposition states, while appearing to exceed the speed of light in terms of time and distance limit, but the whole process does not involve the superluminal motion of matter. The entire process of collapsing the superposition state is random, and quantum entanglement does not transmit any information or energy. What we call quantum communication technology is strictly speaking a technique that uses quantum entanglement to encrypt the communication process, and the information goes The still traditional channel.

Matter is a carrier of information and energy, we now use light or radio waves to transmit information and they are essentially matter as well. Neither quantum entanglement, nor the superluminal expansion of cosmic space, involve the motion of matter, and therefore are not subject to narrow relativity. The limitations. Trying to use quantum entanglement to achieve instantaneous transfer in science fiction is currently impossible.

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