"Matter tells space how to curve, and space tells matter how to move." – Physicist John Wheeler
The big bang, widely accepted in a variety of forms by most physical scientists today, was first put forward in rudimentary form by a Belgian priest-astronomer, Georges LeMaître, in 1927. LeMaître’s concept of an expanding universe (not yet as a consequence of a 'big bang') was stimulated by the earlier discoveries of American astronomer Edwin Hubble and others that galaxies were in motion at high speeds and the work of the Soviet mathematician Alexandr Friedmann, who showed that an expanding universe was a possible mathematical consequence of Einstein’s 1915 general theory of relativity. Astronomical observations established that the properties of the universe were essentially the same everywhere, independent of the position in the universe. Further work by Hubble showed that galaxies were moving away from each other at speeds related to the distance.
In 1931, LeMaître reasoned that if one traced time backward, it was possible to conclude that the universe originated in the explosion of a primeval atom that contained all the matter of the universe, which he also described as 'the Cosmic Egg exploding at the moment of the creation.' LeMaître’s hypothesis was dubbed derisively 'big bang' by British astronomer Fred Hoyle. The name became less derisive as it acquired increasing acceptance with mounting experimental evidence for the universe’s expansion.
A theoretically predictable consequence of the big bang theory was that the temperature of the universe as measured by the distribution of the frequencies of background electromagnetic waves throughout space should prove to be now only a few degrees above absolute zero. Just as the temperature of a gas drops as it is allowed to expand in volume (the principle on which most refrigerators work), the temperature of the universe should also drop as the energy is distributed over a greater volume. When this temperature was measured in 1964/65 by Robert Wilson and Arno Penzias, the results confirmed the prediction. Subsequent measurements of this temperature established the age of the universe as 13.7 billion years.
In LeMaître’s 1931 theory, the 'cosmic egg' at the moment of creation was a point mass (called a 'singularity' in mathematical physics) that contained all the matter of the universe in raw form. As the explosion proceeded, the volume of the matter increased; the raw matter differentiated in form, ultimately arriving at the system of galaxies with which we are familiar today.
The model of the big bang beginning with a singularity – that is, at a point of zero size containing a huge but finite amount of raw matter – was attractive mathematically as well as religiously to those who saw it as evidence of a creation. Most physical scientists, however, are consciously or unconsciously committed to a materialist outlook, so that alternative models were sought. Indeed, although a very small minority of cosmologists reject the big bang theory in general, hardly anyone holds the view that the big bang started from a point, rather than from a small size. The latter idea leaves open the path for the question of how the universe had arrived at that small size.
One of the world’s leading cosmologists, Stephen Hawking, not philosophically committed to a materialist outlook, has alternated between the singularity and nonsingularity approaches, but no longer accepts the former. In A Brief History of Time, he relates an amusing account of his audience with the Pope at the end of a conference on cosmology organized by Jesuits in the Vatican in 1981: He told us that it was all right to study the evolution of the universe after the big bang, but we should not inquire into the big bang itself because that was the moment of Creation and therefore the work of God. I was glad then that he did not know the subject of the talk I had just given at the conference – the possibility that space-time was finite but had no boundary, which means that it had no beginning, no moment of Creation. I had no desire to share the fate of Galileo, with whom I feel a strong sense of identity, partly because of the coincidence of having been born exactly 300 years after his death.
The process following the big bang should not be considered to be that of a sphere containing a huge quantity of matter expanding into the void. Rather, space and matter form a dialectical unity of form and content, whereby it is the space itself – with its historically conditioned various forms of matter distributed more or less evenly throughout it – that is expanding. When Newton formulated the laws of motion that form the basis of what is known as classical mechanics, he assumed the existence of absolute space and time. Although these notions were retained in physics essentially up to the time of Einstein, alternate views were being put forth on the basis of the examination of dialectical interconnections among the philosophical categories of matter, motion, space, and time. Thus Engels cites Hegel’s comment in the early 1800s that the essence of motion is the immediate unity of space and time. . . . It is the concept of space itself that creates its existence in matter. Often a beginning has been made with matter, and then space and time regarded as forms of matter. . . . Just as there is no motion without matter, so also there is no matter without motion. The physical properties of three-dimensional space do not allow us to form a mental image of a space of finite size with no space outside it, although we are able to represent its properties mathematically. Nevertheless, the following analogies will allow us to understand its principal features.
Imagine an ant whose world is restricted by being confined to a circular wire with specks of food dispersed over the entire circumference. Assume further that the sensual apparatus of the ant is limited to events along the wire. If it had a human consciousness, the ant could become aware of the finite size of its universe by counting the number of steps needed to cover the circular path. The space is limited (closed) but unbounded in the direction of the wire. The furthest distance between two points along the wire can be used as a measure of the size of its space. If the radius of the circle increases, the distance between any two specks of food will increase.
Now consider the same 'intelligent' ant confined to the surface of a sphere, with the specks of food dispersed over the entire surface. Assume that its sensual apparatus is limited to the two dimensions of the surface. It can follow various circular paths and obtain knowledge of the geometrical characteristics of the spherical surface, just as humans, by following circular paths at various latitudes on Earth, can obtain such corresponding knowledge. The maximum distance between any two points along the 'great circles' is physically measurable. In this two-dimensional world, the space is unbounded but limited (closed). The furthest distance along the surface between two points can be used as a measure of its size. If the radius of the sphere increases, the distance between the specks of food increases.
We can consider the three-dimensional space of our universe in an analogous manner. In this case, however, we cannot form a visual image, since our spatial sensations are limited to three dimensions, just as in the first and second examples the sense-world of the ant was limited to one and two dimensions respectively. At the time of the big bang, the size of this space was very small – that is, the maximum distance between any two material objects was minuscule (in some theories even less than a millimeter) compared with today. We cannot with any certainty say how small, since there are many unverified theoretical models about the form of matter and its spatial dimensions at the time, 13.7 billion years ago, that the expansion began. Moreover, we cannot view this space as a miniature model of our current space. Since Einstein formulated his general theory of relativity (several principal conclusions of which were subsequently confirmed experimentally), we have come to understand in what way space and time are properties of matter. For example, there is no universal geometry that can be applied to the entire universe; spatial relations vary with the density and concentration of matter. Euclidean geometry, according to which the sum of the internal angles of a triangle formed by three intersecting straight lines is 180 degrees, works well on Earth. According to the general theory of relativity, Euclid’s conclusions have a precision that is high enough for our practical needs, but they cannot be considered to be absolutely true. The higher the concentration of matter in a given region, the greater will be the departure from Euclid’s theorem. There are no criteria for a line’s being straight that are not associated with the local distribution of matter.
Scientists who philosophically reject the concept of the big bang generally share Immanuel Kant’s view of space and time. They consider space and time and the logic from which their properties are derived to be independent of and prior to the material universe to which they are applied. Kant considered God to be the source of these a priori concepts, although once these concepts had been created, Kant did not need God again in this connection. These a priori concepts, including the logic, are considered to have had an eternal existence.
Dialectical materialism maintains, as do most physicists and astrophysicists today, that the properties of space and time are inseparably connected with matter. Some scientists use the term energy interchangeably with the term matter, although a dialectical materialist distinguishes between them by considering energy to be a measure of the capacity of a physical system to undergo transformation from one form or level of integration and organization of matter to another.
As a consequence of the huge energy released in the material transformations that accompanied the big bang, the resulting matter in its variety of forms spreads out in the ever-growing spatial volume that arises in the process.
An additional complication arises in the meaning of 13.7 billion years as the age of the universe. We think of time flowing evenly, like the steady ticking of a clock. But the general theory of relativity also predicts that time intervals associated with the same physical processes also depend on the local concentration of matter. Einstein’s projections were again borne out when it was confirmed that identical atomic clocks at two different heights above the surface of the earth yield different times. Calculations involving space probes have to take these matters into to consideration.
Physical scientists need not be consciously committed to the dialectical-materialist worldview to obtain correct and meaningful results. A conscious awareness of the scientific way in which this worldview seeks to understand the world about us, however, has proved to be useful for avoiding the traps of speculative philosophy.
A specific influence of Marxist thought on the way the subject matter of physics has been viewed during the past quarter century is that modern textbooks now present physics as the science of changes in the physical world rather than the previous formulation that physics was the study of the invariances in nature.
