A Philosophical Introduction to Modern Physics
'In nature nothing remains constant. Everything is in a perpetual state of transformation, motion, and change. However, we discover that nothing simply surges up out of nothing without having antecedents that existed before. Likewise, nothing ever disappears without a trace, in the sense that it gives rise to absolutely nothing existing at later times… Everything comes from other things and gives rise to other things.
'This principle is not yet a statement of the existence of causality in nature. [Causality being the principle that everything has a cause, as opposed to randomness.] Indeed, it is even more fundamental than is causality, for it is at the foundation of the possibility of our understanding nature in a rational way.
'To come to causality, the next step is then to note that as we study processes taking place under a wide range of conditions, we discover that inside of all of the complexity of change and transformation there are relationships that remain effectively constant. Thus, objects released in mid-air under a wide range of conditions quite consistently fall to the ground. A closer study of the rate of fall shows that in so far as air resistance can be neglected, the acceleration is constant… Similarly, water put into a container quite invariably ‘seeks its own level’ in a wide range of conditions. Examples of this kind can be multiplied without limit. From the extreme generality of this type of behaviour, one begins to consider the possibility that in the processes by which one thing comes out of others, the constancy of certain relationships inside a wide variety of transformations and changes is no coincidence. Rather, we interpret this constancy as signifying that such relationships are necessary, in the sense that they could not be otherwise, because they are inherently and essential aspects of what things are. The necessary relationships between objects, events, conditions, or other things at a given time and those at later times are then termed ‘causal laws.’
'At this point, however, we meet a new problem. For the necessity of a causal law is never absolute. For example, let us consider the law that an object released in mid-air will fall. This in fact is usually what happens. But if the object is a piece of paper, and if ‘by chance’ there is a strong breeze blowing, it may rise. Thus we see that one must conceive of the law of nature as necessary only if one abstracts from contingencies [contingencies, meaning ‘possibilities’ that alter the the course of events]. Such contingencies lead to chance. Hence, we conceive of the necessity of a law of nature as conditional, since it applies only to the extent that these contingencies may be neglected…
'Now, here it may be objected that if one took into account everything in the universe, then the category of contingency would disappear, and all that happens would be seen to follow necessarily and inevitably. On the other hand, there is no known causal law that really does this. It is true that in any given problem we may, by broadening the context of the processes under consideration, even find the laws which govern some of the contingencies. Thus, in the case of the piece of paper being blown around by the wind, we could eventually study the laws which determine how the wind will blow. But here we will meet new contingencies. For the behaviour of the wind depends on the locations of the clouds, on the temperatures of bodies of water and land, and even as shown in some of the latest meteorological studies, on beams of electrons and ultraviolet rays which may be emitted with unusual intensity during sunspots. This means, however , that we must now go into the laws governing the formation of clouds, of land masses, of bodies of water, and of the processes in which the sunspots originate. Thus far, no evidence has been discovered that the possibility of tracing causal relationship in this way will ever end. In other words, every real causal relationship, which necessarily operates in a finite context, has been found to be subject to contingencies arising outside the context in question…
'In sum, then, we may say that the processes taking place in nature have been found to satisfy ‘laws of chance,’ and also laws which deal with the relationships between causality and chance. The general category of law, which includes the causal laws, the laws of change, and the laws relating these two classes of law, we shall call by the name of ‘laws of nature.’
- David Bohm, in 'Causality and Chance in Modern Physics.'
'This principle is not yet a statement of the existence of causality in nature. [Causality being the principle that everything has a cause, as opposed to randomness.] Indeed, it is even more fundamental than is causality, for it is at the foundation of the possibility of our understanding nature in a rational way.
'To come to causality, the next step is then to note that as we study processes taking place under a wide range of conditions, we discover that inside of all of the complexity of change and transformation there are relationships that remain effectively constant. Thus, objects released in mid-air under a wide range of conditions quite consistently fall to the ground. A closer study of the rate of fall shows that in so far as air resistance can be neglected, the acceleration is constant… Similarly, water put into a container quite invariably ‘seeks its own level’ in a wide range of conditions. Examples of this kind can be multiplied without limit. From the extreme generality of this type of behaviour, one begins to consider the possibility that in the processes by which one thing comes out of others, the constancy of certain relationships inside a wide variety of transformations and changes is no coincidence. Rather, we interpret this constancy as signifying that such relationships are necessary, in the sense that they could not be otherwise, because they are inherently and essential aspects of what things are. The necessary relationships between objects, events, conditions, or other things at a given time and those at later times are then termed ‘causal laws.’
'At this point, however, we meet a new problem. For the necessity of a causal law is never absolute. For example, let us consider the law that an object released in mid-air will fall. This in fact is usually what happens. But if the object is a piece of paper, and if ‘by chance’ there is a strong breeze blowing, it may rise. Thus we see that one must conceive of the law of nature as necessary only if one abstracts from contingencies [contingencies, meaning ‘possibilities’ that alter the the course of events]. Such contingencies lead to chance. Hence, we conceive of the necessity of a law of nature as conditional, since it applies only to the extent that these contingencies may be neglected…
'Now, here it may be objected that if one took into account everything in the universe, then the category of contingency would disappear, and all that happens would be seen to follow necessarily and inevitably. On the other hand, there is no known causal law that really does this. It is true that in any given problem we may, by broadening the context of the processes under consideration, even find the laws which govern some of the contingencies. Thus, in the case of the piece of paper being blown around by the wind, we could eventually study the laws which determine how the wind will blow. But here we will meet new contingencies. For the behaviour of the wind depends on the locations of the clouds, on the temperatures of bodies of water and land, and even as shown in some of the latest meteorological studies, on beams of electrons and ultraviolet rays which may be emitted with unusual intensity during sunspots. This means, however , that we must now go into the laws governing the formation of clouds, of land masses, of bodies of water, and of the processes in which the sunspots originate. Thus far, no evidence has been discovered that the possibility of tracing causal relationship in this way will ever end. In other words, every real causal relationship, which necessarily operates in a finite context, has been found to be subject to contingencies arising outside the context in question…
'In sum, then, we may say that the processes taking place in nature have been found to satisfy ‘laws of chance,’ and also laws which deal with the relationships between causality and chance. The general category of law, which includes the causal laws, the laws of change, and the laws relating these two classes of law, we shall call by the name of ‘laws of nature.’
- David Bohm, in 'Causality and Chance in Modern Physics.'