Can we change the past?

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Can we change the past?

Who has no regrets about what has been done in the past? Somehow, wouldn’t it be nice if we could go back and adjust some bad decisions?

This sounds (we’ll see, in a way) like science fiction.

The laws of physics are forbidden to go back in time for many reasons. If we do go back in time and change the course of events, we will change the course of history. An oft-cited example is grandfather paradox: if you go back to the past and when he was a high school student killed your grandfather and his grandmother wouldn’t have met you and your father, you don’t exist.

One popular example of this is the glamorous Canadian TV show “traveler” : in the distant future, the earth is in chaos. Human beings are controlled by benevolent artificial intelligence, which discovers a way of projecting people’s consciousness into the 21st century without knowing the host. The idea is that future travelers will take over the minds of people in the 21st century before they die. There are some vague discussions about the quantum entanglement of consciousness between travelers and their owners, but this is secondary. The point of the show is that travelers go back and try to change the course of history – so that the future looks better.

Does the scientific community even have something like this to put humanity or consciousness back in place for the time being? Surprisingly, yes. In quantum particles (we are talking about a single photon, elementary particles or individual atoms) level, there are some called wheeler delayed choice experiment, shows that behavior can affect the past now.

These experiments used a wave particle duality called light and matter, in fact the physical properties of a quantum object are uncertain before being measured. In other words, this means that particles of light or matter can be represented as waves (spread out in space, represented by interference) or as particles (together as a bundle), depending on the measuring device. Long and ongoing discussions about the nature of quantum physics are still trying to figure out what this actually means. Does our mind determine the nature of material reality? Interested readers can see the more detailed content I have written in “the island of knowledge: the limits of science and the search for meaning”.

But experimentally – they don’t ask questions. If he had seen the results, the physicist John wheeler, who proposed the experiment in the 1970s, would have been surprised. It seems, now, that it can affect the past, at least on the level of quantum objects.

In the double-slit experiment, imagine that after the photon passes through the slit, set – or no screen – determines. This is what the arrow in the diagram represents, the possibility that the screen exists or does not exist.

The picture on the right explains the story. Imagine the origin of a photon (or other small quantum particle). A photon can go through a double slit. There is a screen behind the double slit. If the photons hit the screen, the experimenter would observe the pattern of the interference pattern of the typical wave’s light and dark stripes. If the screen is not there, and the photon counter is aligned with the slit, the photon will bump into one or the other, just like a small bullet (or particle). So far, this is a typical setup for double-slit experiments.

The “mystery” of the two-sewed physicist Richard feynman’s famous comment is that the person who performs the experiment determines the physical properties of the particle — whether it is a wave or a particle. And, with wheeler, the mystery deepens.

Imagine setting – with or without a screen – after the photon passes through the slit. This is what the arrows in the diagram represent, the possibility that the screen exists or does not exist. In 2007, a team in France did exactly that, allowing a photon to pass through a double slit and then, after passing, a random number generator to select whether the screen was tested there. As wheeler wrote: “therefore, it is decided that the photon will come through a route or two routes after the journey has been completed.” Since then, many other groups, such as here, have refined versions of the experiment, confirming wheeler’s intuition.

An important detail is that the detection device’s switch must be faster than photons must be sent to the detector. In this way, the photon cannot “know” what to do. (in any case, if a photon knows anything). Experiments in October extended the range of photon travel to about 2,200 miles, and the photons always seemed to choose the path that was consistent with the delay. As McCray wrote in this scientific warning, “even after the horse has run 2,200 miles from the outside, it can still wait for the finish line to decide which game to run.” That is, the path to the finish line.

Of course, photons are not human and it is very difficult to maintain quantum superposition, especially as the size of the object increases. Nevertheless, there is something surprising and mysterious about this behavior, which is that the spatial path occupied by objects seems to be unaffected by time. It’s like two choices (particles or waves; One or two are suspended and only implemented after the spatial arrangement is determined. It is no wonder that wheeler likes to refer to this idea as the “pared-universe” directive, that is, our minds are connected to a universe of space and time. After all, the selection of equipment can be done by a random number generator, but the interpretation of the equipment and data requires our intent and design.

Food for the future. Or maybe it was?

Unfortunately, these experiments have little to say about how we interfere with events related to human scale. It’s best to think carefully about decisions, rather than trying to solve them.

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