Whether it’s science fiction or science fiction movies, the coolest concept is traveling through time and space. Because based on common sense, everything is always developing towards the future, and no matter how fast or slow the passage of time, there is only one direction.
As sci-fi fans, many people dream of being able to travel through time and space, some hope to travel to the past, and some to the future.
The future is uncertain, and it is theoretically feasible to travel to the future. If we can drive a spacecraft to fly at a speed close to the speed of light, or orbit a black hole at a close distance, and by these two methods, we can delay the passage of time in our space-time region, and theoretically we can travel to the future.
The past has already happened, and if we can really travel to the past on the same timeline, then it is possible to change the present. The most famous is the grandmother paradox. If you go back to the past and accidentally harm your young grandmother, your father will not be born, so how did you come and travel back to the past to cause the accident? Wouldn’t that be a contradiction! The act of traveling back into the past breaks the law of causality.
However, parallel universes can solve this contradiction. According to the idea of parallel universes, if you travel back in time and accidentally kill your young grandmother, that change will create a new branch of time, splitting off a parallel universe from that point in time. With the concept of a parallel universe, there is no need to worry about changing the past and affecting the future during the travel process, because this change will only generate new time branches, and the old timeline will not be affected.
According to this assumption, not long after the birth of the universe, there will be almost infinite parallel universes.
When it comes to parallel universes, the concept was born not from the time travel paradox, but from quantum mechanics. This goes back to a cat more than 80 years ago. The owner of this cat is the famous physicist Schrödinger, so this cat is also called “Schrödinger’s cat”.
Schrödinger, as the founder of wave mechanics in quantum mechanics, proposed the thought experiment “Schrödinger’s cat” in 1935. The purpose is to make people feel how weird the Copenhagen interpretation of quantum mechanics is, so as to attack the incompleteness of the Copenhagen interpretation.
The Copenhagen School believes that the quantum world is inherently uncertain, and that the properties of the system can only be described by probabilities, and the measurement behavior will have an impact on the system, and the set of probabilities is reduced to one of all possibilities. Scientists use wave functions to describe the properties of quantum systems, so this situation is also known as wave function collapse.
Schrödinger said that if a cat is kept in an airtight container containing a small amount of radium and the highly toxic cyanide, there is a chance that the radium decays and controls an electronic switch. If the radium decayed, it would trigger the mechanism to break the bottle containing the cyanide, and the cat would die; if the radium did not decay, the cat would still be alive.
According to quantum mechanics, radioactive radium is in a superposition of both decayed and non-decayed states. According to this principle, the cat in the airtight container should also be in a superimposed state of dead cat and live cat, which is the “Schrödinger’s cat” that is both dead and alive. The cat’s life and death status is determined only when we open the container.
For traditional physicists, this is inconceivable, and living and dying defies logic. They argue that the cat’s outcome is doomed before the container is opened: life or death. Just because the container wasn’t opened for observation, we’re not sure about the cat’s life or death.
It is well known that microscopic matter has wave-particle duality, and before observation, particle and wave properties are in a superposition state. According to the Copenhagen School of Quantum Mechanics, before opening the container, Schrödinger’s cat is in a state of superposition of life and death. Once the observation behavior is involved, this superposition state will be disturbed and manifested as one of the eigenstates.
This thought experiment cleverly moved the quantum phenomena in the microscopic world to the macroscopic world with a cat. It is one of the very classic thought experiments in the history of science. In fact, the reason for this bizarre result is that quantum superposition states are not suitable for macroscopic large objects.
Since the cat’s state of life is unknown before the container is opened, and there are two states, then perhaps there should also be two different worlds, one where the cat is alive and the other where the cat is dead . Based on this idea, the concept of parallel universes was derived.
In the 1950s, physicist Hugh Everett proposed the many-worlds interpretation of quantum mechanics and believed that there is no wave function collapse at all, and that cats and dead cats actually exist in two parallel universes.
According to this theory, everything that could have happened in the past and in the future either actually happened or will happen, but they all happened in other universes and have nothing to do with our universe. If there are really many parallel universes, then there must be another me in some parallel universes, but their lives are different.
All things have a beginning and an end. Physicists believe that there must be a proto-universe, and other parallel universes are constantly differentiated on this basis. These parallel universes coexist, and there will be no connection between the newly differentiated parallel universe and the original parallel universe, and they exist independently of each other.
Thinking about that cat gave birth to perhaps the most daring conjecture in the field of physics-parallel universe. Just for its existence, scientists can only discuss it from a theoretical level. However, there is a big problem with this theory. Will the universe really make such a big change for the life and death of a cat?
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