In the world that we live in, it is a well-known fact that causality forms sequences of events in nature. Indeed, for every effect there is a cause, and without a cause there is no effect. In our daily experience, related events are formed in a casual sequence.
In the beginning of the last century with the advent of Einstein’s special theory of relativity, the question of whether time orders sequence of an event received a definite clear yes and no answer.
There are certain events that have nothing to do with each other, meaning that there is no cause and effect relationship between them. The sequence of events can be clearly defined only if there is a cause and effect relationship between two events.
But this connection can apply only if one event exchanges energy with the other event. In physical terms, a relation of cause and effect between two events implies that energy or signals can travel from the first event to the second while the reverse being impossible.
Einstein’s theory posed the argument that should the speed of light be somehow surpassed, then the causality principle can be violated and the future can change the past!
But our daily experience rules out this argument owing to experimental tests that the speed of light is maximal. It means that travel to the past is impossible and the causality principle seems to be the preferred rule in nature.
However, with the introduction of quantum physics with its deep concepts about the structure of the universe and matter the situation changed. Indeed, recent experiments suggest a violation of causality principle, at least in the sub-particle world.
In its April 22 edition of Nature Magazine, it was reported that a group of researchers at the Institute for Quantum Optics and Quantum Information at the University of Vienna managed to entangle light quanta in a way that a future decision could affect the past state of particles!
This may seem quite bizarre, but indeed for the first time, scientists succeeded to entangle particles while they could longer exist!!
The experiment was carried out with two pairs of light quanta, named photons, in a complicated arrangement that, according to Anton Zeilinger, led to an amazing result that the decision to entangle photons was made virtually after they no longer existed.
This experiment as was mentioned in Nature magazine was first proposed by physicist Asher Peres in 2000, but it was not carried out until this year.
Such experiments at the quantum level pave the way for further research aimed at giving a definite answer to the old question of whether the future can affect the past.
Should such an idea turn out to be true, then it will lead to a drastic change to our understanding of the physical concept of time as well as strange implications such as the old idea that for every effect there corresponds a cause at an earlier time.
For more information about quantum entanglement you may refer to: