Hundreds of books have been written on philosophical topics. However, for our purposes, the only important concept that we want to emphasize is the one that allows space and time to be interchanged with each other. What Einstein proposed, albeit implicitly, in his 1904 work was to link space and time together by means of a constant $c$. To emphasize this concept, we could say that the epistemological revolution introduced by Einstein in the conception of time and space was simply to consider time as equivalent to a spatial dimension, simply mediated by a proportionality constant, namely: $\Delta s \approx c \Delta t$.
The constant $c$ in question is represented by the speed of light, but it is important to specify that the relation imposed by Einstein transcends in some way the contingent case represented by light, to instead express a more general aspect. The reported equation, in fact, does not refer exclusively to the motion of light, but is a relation that, in Einstein's idea, directly links space and time together.
In a sense, we could summarize the concept that was the basis of Einstein's reasoning in a very simple way. If there exists a speed limit that cannot be exceeded, given that the concept of speed involves both space and time, then this limit on speed must inevitably translate into a constraint between space and time.
Without entering into the merits of Special Relativity, the Michelson-Morley ether wind experiments and the motivations that led Einstein to formulate this theory, what we want to emphasize at the moment is this simple formula that links space and time together making them in some way interchangeable.
For the physics that we will subsequently illustrate, every space is associated with a characteristic time and every time is associated with a space. The two concepts, for modern physics, are perfectly equivalent. In this perspective, therefore, we should not be surprised if immense spatial distances are measured with simple temporal indicators. Or if to observe distant realities in time, we are forced to scrutinize towards objects distant in space. In cosmology, space means time and time means space, and the law that links these two quantities is simply $\Delta s \approx c \Delta t$.
Causality, Mass and Energy
In 1874, in his Lectures on Divine-Humanity, the great Russian philosopher Vladimir Solovyov, ironizing on the fact that every philosophical theory is true in what it affirms and false in what it denies, said that the truths affirmed by materialism can be synthesized in two general maxims:
1. Everything that exists in the Universe consists of Energy and Matter
2. Everything that happens, happens according to irrevocable laws
In other words, the truth and fascination of materialistic theory would reside, according to Solovyov, in the demand for absolute causality. The Russian philosopher's point highlights and unites three concepts apparently very distant from each other, but which the physical investigation of the following century would finally bring to reconcile: Energy, Matter and Causality.
To introduce the concept of Energy synthetically, we could say that according to the description outlined by Physics, everything that exists in the Universe is nothing but space, time and capacity to act, that is, capacity to act in space and time. The quantity indicating this capacity to act is called Energy. Mass, on the other hand, is nothing but a particular expression of it. While the causal mechanism, by which this action is explained, is synthesized by what is called Physical Law.
Thus, with the theoretical-scientific advance of the 20th century, it appeared increasingly evident that Energy, Matter and Causality were intimately connected to each other, as if they were doubly linked to one another and their respective boundaries were nothing but simple sensory illusions.
Energy and Mass
In 1710, in his Treatise on the Principles of Human Knowledge, George Berkeley formulated his doctrine called immaterialism.
In his exposition, Berkeley formulated a principle that would have enormous fortune among Physicists of the first half of the twentieth century. According to Berkeley, "all the being of an object consists in its being perceived."
Since knowledge of every object is mediated by the interaction of one or more senses that receive its qualities. Man therefore, proceeding in this way, cannot know the object as it is, but only as it appears sensorially. The external object, ultimately, is only a cause of our perceptions and nothing else. From these reflections Berkeley derived that philosophical position, called by himself, immaterialism. Matter, according to Berkeley, does not exist as such, it is nothing but an idea perceived by man. Matter is nothing but a cause of sensations.
Berkeley's position and its revolutionary nature is difficult to understand today because of the scientific progress of recent centuries that has partially incorporated it as a dominant paradigm. With the progress of scientific investigation, man soon discovered that every perception of the external world, whether visual, auditory, tactile or otherwise, is the result of an elaboration of electrical forces that are perceived in a way...