Philosophical reflections in physics
What is destiny? Perhaps under the understanding of most people, fate is a person's future development and changes, what a person can achieve, and what events will be experienced.
Or what exactly does man's existence in the world look like?
Different people have different views on the discussion and trust of fate, and perhaps in the long journey of life, the older people may believe in fate more.
But in any case, the discussion of fate is actually the embodiment of human free will and its choices, believing in fate, then we can say that there is an arrangement in the dark.
Human activities and ideas
Not believing in fate, or rebelling against it, is another manifestation of human free will.
We don't believe in having an arranged life, and everything we do is a necessity in cause and effect that cannot be changed.
As long as it is through the will of man, it can certainly be changed by hard work.
Human beings always have all kinds of ideas in discussing the philosophical propositions of the self and the future, and even in the scientific community there are similar philosophical questions.
Of course, this is thought through rigorous mathematical inferences and physical experiments, for scientists:
The advent of quantum mechanics had to make them think once again about the possibility of fate, whether human free will really existed.
Are human thoughts really their own?
Perhaps the most classic of these is the words of Einstein, god does not roll dice.
Admittedly, Einstein held his faith firm in his thoughts about God, but his later controversy with Bohr changed the physical world's discussion of free will.
Einstein believed that the properties of matter were predetermined, had nothing to do with observation, and were not transferred by the will of man.
But Bohr argues that the properties of matter are not predetermined, but appear only when we observe them.
Einstein and Bohr
The discussion became a frequent contradiction in later quantum mechanics, and in 1935 Einstein, Podolsky, and Rosen published a thought experiment.
Through this experiment, they hope to reveal Copenhagen's revelation of quantum mechanics, violating the incompleteness of local causality at the microscopic scale of its description.
In the Copenhagen experimental view, the surveyor's choice of measurement has a direct effect on the observer's state.
But under the locality hypothesis, the operation of the Alice system in the experiment does not affect the "real" or "ontological" state of Bob's system.
Alice and Bob conjecture
The experimental concept of a "complete description" in physics was later formalized with suggestions for hidden variables.
The so-called hidden variable theory is a proposal to explain quantum mechanical phenomena by introducing unobservable hypothetical entities.
The introduction of hidden variables determines the statistics of the measurement results, but is not accessible to observers.
So in Einstein's question, can a complete description of quantum mechanics be given to locally hidden variables according to the "principle of local action".
Einstein's discussion of local hidden amounts rose to philosophy
The embodiment of the will
What makes quantum mechanics confusing and contradictory is the emergence of measurements and superpositions, and the double-slit experiment is an important experiment for scientists to explore quantum mechanics.
The experimental process is simple, just through a thin slit to let the photon through, this slit is small enough, so small that only the photon can pass through it.
However, the light after passing through the gap is no longer the original continuous light source effect, but an intermittent photon performance.
But the problem is that there is nothing else that can interfere with the activity of the photon except that the photon itself can pass through this gap, so what exactly is interfering with it?
The process of a double-slit experiment
The scientists found that the activity of photons interfered with itself, interfering with light rays in a superposition state and causing streaks in the light source.
However, when the scientists looked closely, the problem stopped happening, the pattern shown by the interference disappeared, and the light source became two simple beams of light.
The superposition of photons and the collapse of observer measurements have become problems that physicists have long wanted to figure out.
Whether measuring whether it will affect the motion of photons and how the superposition behaves has become a major problem in the physics community at that time.
Results of double-slit experiments
Going back to the thought experiments of Einstein and others mentioned earlier, several of the world's top physicists at the time believed that quantum mechanics's description of physical manifestations was incomplete.
Although the performance of the double-slit experimental photon is bizarre, the concept of "entangled state" is proposed as quantum mechanics deepens further.
Einstein, Podolsky, and Rosen pointed out that if an entangled particle measures the position of one of the particles, it can predict the position of the second particle and the measurement result.
If you measure the momentum of the first particle instead, you can measure the momentum result of the second particle.
Imagination of quantum entangled states
That is, observing the activity of one particle leads to the outcome of another, and there is a clear causal relationship between the two.
And Einstein et al. also believe that any action on one of the particles does not immediately affect the other.
Because it is impossible for particles to transmit information faster than the speed of light, this is forbidden by the theory of relativity.
But Bohr, who was studying quantum mechanics at the time, believed that the theory of Einstein and others was wrong.
Because the measurements of position and momentum are complementary, choosing to measure the change in one of the particles necessarily excludes the possibility of the other.
Particles should not behave faster than the speed of light
In quantum mechanics, entangled particles have some unmeasurable properties that predetermine the final quantum state before they separate.
Therefore, if locality is considered, quantum mechanics must be incomplete and cannot fully describe the true physical properties of particles.
It was the unpredictability and uncertainty of this part that made quantum measurements undeterminable, and later became known as hidden variables.
Therefore, in Bohr's view, entangled quanta cannot be actually measured.
Bell's inequality
At that time, the discussion of the relevant theory was only at the academic level, because there was no experimental equipment that met the conditions at that time, and no one could verify whether the theory was correct.
But then Bell came up with a new idea, and it needs to be explained that Bell himself affirms the theory of Einstein and others, that one side of the measurement must know the other.
He further elaborated on Einstein's theory, arguing that if two separated particles entangled were measured independently, the outcome would depend on the hidden variables in each half.
If hidden variables do not exist, then particle activity in the entangled state cannot be explained by classical theory.
Bell is teaching
The ideas and discussions put forward by Bell came to be known as Bell's inequality, so that the hypothesis of Einstein and others was supported by scientific theories and only needed to be proved experimentally.
It wasn't until the 1970s that scientists empirically tested whether the pseudo-Bell inequality and the assumptions of Einstein and others were correct.
Early experiments with Bell's inequality proved that local hidden variables do not exist, that is, there are no hidden variables to interfere with particle activity, and the assumptions in Bell's formula and quantum mechanics were proved.
About local hidden variables
But at the time, it was believed that two particles were too close together, which gave them the opportunity to influence the activity of another particle in some form faster than the speed of light.
So later this experiment was constantly upgraded.
In the 1980s, Alain Pace and his team at The Paris Orsay improved the experimental protocol.
Particle detection has a higher frequency detector and increases the distance between particles.
In addition, they even designed a device that can change the detection direction, even the particles can change the detection direction at the moment of being emitted, so that more rigorous experimental data can be obtained.
The category of discussion of Bell's inequality
It turns out that Bell's inequality still does not hold.
In many experiments since then, scientists have successively upgraded the experimental configuration requirements and become more and more stringent, after all, the fewer loopholes, the more accurate the experimental results.
Even in 2015, scientists developed a "flawless" version of Bell's experiment that proved that Bell's inequality does not hold.
It seems that the answer to the question was solved, but soon scientists came up with the idea that the experiment was not rigorous enough.
Because the random generator used in the experiment is not really random, to some extent, every random arrangement is a necessary result.
Bell inequality experiment
So in 2018, scientists decided to add human free will by recruiting 100,000 volunteers to add random data to the experiment.
The random data is played by volunteers in online mini-games developed by European laboratories, and then the player's choices are transmitted to European data centers.
This would solve the random problem, and eventually the experiment showed that Bell's inequality does not hold.
However, things are obviously not so simple, online games from play to data transmission, volunteer response time will also be delayed due to network and physiological activities.
Although this delay is small, it is also a local hidden variable at the physical level.
The Bell experiment carried out by scientists
It seems that we have obtained random results, but why are there hidden variables that affect human choices?
In other words, even if human free will is added, perhaps the outcome is decided in the first place.
The final discussion of the problem verified Bell's inequality with the help of experiments, but perhaps we can't really know how things will change in the future, and the problem once again becomes a philosophical speculation.
The authenticity of the world seems exact to Bell's inequality, but is it really so?