The essence of quantum entanglement is quantum relativity.
Then why is quantum entanglement? What is its essence?
To understand this, it is necessary to mention the theory of relativity. As we all know, contemporary physics has two foundations-relativity and quantum mechanics. These two theories have undergone many rigorous experiments since they were put forward, and their correctness is beyond doubt.
At present, the fundamental conflict between the two theories is that quantum field theory is a particle field of fundamental force based on the flat space-time of general relativity. If we want to quantize the gravitational field through this same model, the main problem is that under the curved space-time framework of general relativity, we can't realize the quantization description through renormalization mathematical skills as before, and we can't get meaningful finite values through mathematical skills.
In contrast, for example, in the description of photons in quantum electrodynamics, although there are some infinite values, they can rarely be eliminated by renormalization, and measurable and meaningful finite values can be obtained.
So the correction direction of general relativity is these two points:
1, the cause of gravity is not curved in time and space. The space-time background of general relativity is curved space-time, but it is not the cause of gravity.
The origin of gravity is time and space. Moreover, when describing the quantization of gravity, we must use "differential" thinking to solve the embarrassment of space-time bending. But gravity is not caused by the bending of time and space. Gravity can be said to be a space-time property. And then it will affect the construction of time and space. The action of gravity travels at the speed of light.
So does the discussion of "superluminal" caused by quantum entanglement pose a challenge to relativity? The answer is no again!
Don't forget that the two pillars of quantum mechanics complement each other. Waves and particles are mutually exclusive at the same time, but they are unified at a higher level. The uncertainty principle shows that the position and momentum of particles cannot be determined at the same time.
Therefore, in quantum mechanics, microscopic particles are not clearly defined, but a "probability cloud" with strange functions. These particles will not only exist in one place, nor will they just arrive from one route to another. We generally use wave functions to describe the behavior and characteristics of these particles. Between two microscopic particles from the same source, as long as one particle changes, the other will also change. This change happens immediately, which is quantum entanglement.
Have you noticed that the mechanism of quantum entanglement is limited? It doesn't mean that any two particles are n kilometers apart, and quantum entanglement can occur. For example, it is impossible for a particle on the earth to have quantum entanglement with a particle 100 light years away.
Quantum entanglement between two or more particles must be in a system, and the particles have a common source.
"Two-photon system" For example, the photon field generated by the same laser is split by dual polarization. Because it is a coherent state generated by the same laser, the two photon systems generated by splitting belong to a coherent entangled state. Then when we measure a physical parameter of a photon state, we will find that the physical parameter corresponding to another photon will change at the same time, so we say that the' two-photon coherent system' is a quantum entangled state for this physical parameter!
Quantum entanglement indicates that there is a strong quantum correlation between two or more stable particles. For example, in the two-photon entangled state, the photon moving to the left (or right) is neither left-handed nor right-handed, and has neither X polarization nor Y polarization. In fact, before the measurement, neither the spin nor its projection existed. The two particle states are inseparable without measurement.
Then it is not difficult to understand the cause of quantum entangled States. In fact, as long as we think that the two-photon system before and after splitting is a whole, the quantum entanglement effect is easy to understand, but is it really like this? Some people will say that the photon space is divided into two parts, how can it still be a whole? The emphasis is on the preconditions of quantum entangled states. The two-photon system is a correlated state, and it is a whole before it is disassociated!
Quantum mechanics is a non-localized theory, which has been predicted by Bell inequality. Any localized hidden variable theory cannot repeat all the statistical predictions of quantum mechanics. Therefore, quantum mechanics shows many counter-intuitive effects. In quantum mechanics, states that cannot be expressed as direct products are called entangled states.
The correlation between entangled states cannot be explained classically. The so-called quantum entanglement refers to the existence of non-local and non-classical strong correlation between two or more quantum systems. Quantum entanglement involves the basic problems of quantum mechanics such as realism, localization, hidden variables and measurement theory, and plays an important role in the research of quantum computing and quantum communication.
The most common form of multi-system quantum state is entangled state, and the non-entangled state which can be expressed as direct product is only a very special quantum state. The concept of entangled state first appeared in 1935 Schrodinger's paper on "cat state".
In fact, it can be seen from the system of quantum entanglement itself that it is closely related to the principle of complementary uncertainty. The uncertainty principle embodies "connection", that is, the connection between position and momentum. The principle of complementarity embodies that the inevitable result of the combination of "contradiction and unity" is "entanglement". Moreover, Bell inequality is permanently established and cannot appear as Einstein thought. That is, the theory of hidden variables can completely explain the evolution behavior of all observable measurements in physical systems, thus avoiding any uncertainty or randomness.
Moreover, when the quantum entanglement is disturbed, the quantum entangled state will be eliminated immediately, that is to say, the description of this related state function is over.
This also shows the "locality" of quantum entanglement. It won't be "wide area" like gravity. But the global nonlocality of quantum mechanics is actually a "wide area", and quantum entanglement exists in it according to certain laws.
In a more popular way, we can understand that the quantum entangled state of two or more particles is the same thing, which is described by a wave function and has nothing to do with distance. It's like two people sitting on the seesaw When A and B sit on it, there is a connection. If a goes down, b will inevitably come up; On the contrary, B goes down and A comes up at once. But it can't be said that this connection is beyond the distance, that is, the change between A and B is completed at superluminal speed. You know, this has nothing to do with the direct distance between A and B, but with the connection state between them.