Surprising as it may be to most non-scientists and even to some scientists, Albert Einstein concluded in his later years that the past, present, and future all exist simultaneously. In 1952, in his book Relativity, in discussing Minkowski's Space World interpretation of his theory of relativity, Einstein writes:
Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence.
Einstein's belief in an undivided solid reality was clear to him, so much so that he completely rejected the separation we experience as the moment of now. He believed there is no true division between past and future, there is rather a single existence. His most descriptive testimony to this faith came when his lifelong friend Besso died. Einstein wrote a letter to Besso's family, saying that although Besso had preceded him in death it was of no consequence, "...for us physicists believe the separation between past, present, and future is only an illusion, although a convincing one."
Most everyone knows that Einstein proved that time is relative, not absolute as Newton claimed. With the proper technology, such as a very fast spaceship, one person is able to experience several days while another person simultaneously experiences only a few hours or minutes. The same two people can meet up again, one having experienced days or even years while the other has only experienced minutes. The person in the spaceship only needs to travel near to the speed of light. The faster they travel, the slower their time will pass relative to someone planted firmly on the Earth. If they were able to travel at the speed of light, their time would cease completely and they would only exist trapped in timelessness. Einstein could hardly believe there were physicists who didn’t believe in timelessness, and yet the wisdom of Einstein's convictions had very little impact on cosmology or science in general. The majority of physicists have been slow to give up the ordinary assumptions we make about time.
The two most highly recognized physicists since Einstein made similar conclusions and even made dramatic advances toward a timeless perspective of the universe, yet they also were unable to change the temporal mentality ingrained in the mainstream of physics and society. Einstein was followed in history by the colorful and brilliant Richard Feynman. Feynman developed the most effective and explanatory interpretation of quantum mechanics that had yet been developed, known today as Sum over Histories.
Just as Einstein's own Relativity Theory led Einstein to reject time, Feynman’s Sum over Histories theory led him to describe time simply as a direction in space. Feynman’s theory states that the probability of an event is determined by summing together all the possible histories of that event. For example, for a particle moving from point A to B we imagine the particle traveling every possible path, curved paths, oscillating paths, squiggly paths, even backward in time and forward in time paths. Each path has an amplitude, and when summed the vast majority of all these amplitudes add up to zero, and all that remains is the comparably few histories that abide by the laws and forces of nature. Sum over histories indicates the direction of our ordinary clock time is simply a path in space which is more probable than the more exotic directions time might have taken otherwise.
Other worlds are just other directions in space, some less probable, some equally as probable as the one direction we experience. And some times our world represents the unlikely path. Feynman's summing of all possible histories could be described as the first timeless description of a multitude of space-time worlds all existing simultaneously. In a recent paper entitled Cosmology From the Top Down, Professor Stephen Hawking of Cambridge writes; “Some people make a great mystery of the multi universe, or the Many-Worlds interpretation of quantum theory, but to me, these are just different expressions of the Feynman path integral.”
Also check out CASE 237 - The laws of physics
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