Chapter 8 - THEORIES IN PHYSICS

Dr. Roy A. Clouser

 Next to mathematics, the science most often thought to be independent of religious belief is physics. It is not hard to show, however, that in physics,  just as in math, there are competing theories whose conflicts can be traced   to different perspectives on the nature of reality which, in turn, presuppose different beliefs about what is divine.

 

8.1            SOME MISUNDERSTANDINGS TO AVOID

Before proceeding to that task I want to point out some possible misunderstandings of the meaning of the term “physical.” In ordinary speech we often speak of something as physical, meaning that it is real rather than imaginary. That is not the meaning it has in physics, however,  and it is not how I will   be using the term here. In this chapter we will be concerned with the physical aspect displayed by the things and events of our ordinary, pre-scientific experience. Thus, in keeping with our earlier definition of an aspect, I will be using the term “physical” to refer to a specific kind of properties and laws, the kind that delineates the field of the science of physics in all its branches. Included in this kind are such properties as mass, weight, density, specific gravity, charge, etc. And laws which hold between properties of this kind include Pascal’s law, Boyle’s law, universal gravitation, and the laws of dynamics, as well as Einstein’s famous E=mc². As in the case of the qualifying adjectives of all the other aspects, it is not possible to give a precise definition of “physical.” But in keeping with the (provisional) list of aspects given earlier, we may circumscribe the physical as that kind of properties and laws which have temporal, numerical, and spatial prerequisites but are not those that would be actively possessed by a biotically living thing only if it were alive, and which thus distinguish a living being from a being incapable of life.¹

Another way the term “physical” can be misunderstood is when it occurs in the expression “physical object.” This should not be taken to mean that the object so designated is only physical. For while there are theories which propose that there are purely physical objects, we never experience anything in that way. Thus in ordinary speech the expression never means that. For example, while a tree is surely physical, we experience it to have properties of many other aspectual kinds, and to be subject to many more kinds of laws than just the physical. Every tree displays qualities and exhibits conformity to laws that we experience as quantitative, spatial, biological, sensory, logical, aesthetical, and so on. Just as with other pre-scientifically experienced objects, we experience a tree to be a multi-aspectual thing. It is true, of course, that working  in the physical sciences requires the physical aspect of things to be abstracted and focused upon, allowing the remaining (nonphysical) aspects of things to fall from the center of attention. But this fact about scientific procedure does not show that anything has only that aspect. From the standpoint of describing our immediate experience, it is simply false that there are things experienced as solely physical, so that it is likewise false to suppose that it is purely physical things which are the subject matter of physics. Rather, physics, like so many other sciences, starts with the multi-aspectual objects of our ordinary experience and abstracts a specific aspect of them as its special field of investigation. In sum, physics is not about a limited set of purely physical things, but about the physical aspect of all things.

I have belabored this point here because, as was noted earlier, many prominent thinkers take the view that physics does indeed deal with exclusively physical objects. As we review their opinions, therefore, it must be kept in mind that regarding the domain of physics this way is itself the result of a perspectival view of the nature of reality, a view that needs to be defended if they are to be entitled to it.

With these points of clarification out of the way, we will now look at a  few important theories of physics to see whether disagreements among them really do arise because physicists presuppose different views of the essential nature of reality, which in turn presuppose different divinity beliefs. To see that this is so, we need only examine the most widely accepted theory in all of physics, the atomic theory. Roughly, atomic theory holds that the objects of our everyday experience are made up of parts (atoms and sub-atomic particles) so small that they cannot be directly observed. But here, too, a reminder is   in order: please continue to keep in mind that the religious regulation of a theory doesn’t mean that inventing it depended on holding a particular religious belief. I am not suggesting that someone would have to be a materialist or a rationalist or whatever in order to have thought of the hypothesis “there are atoms.” Rather, I said that religious regulation consists of the ways divinity beliefs control how the nature of a theory’s postulates gets interpreted. So, too, for atomic theory. We have to know what kind of things we’re talking about; we have to specify the nature of atoms, etc., in order to know how they are supposed to explain those features of the world they were invented to explain. But the fact is that physicists disagree over the essential nature of atoms and particles, and thus they also differ over just how they explain the data they’re supposed to explain. To illustrate such differences we need consider only the three most recent interpretations of atomic theory, those that dominated the twentieth century.

 

8.2            THE THEORY OF MACH

The first interpretation of atomic theory we will discuss is that of Ernst Mach. Most people have heard of Mach’s name without realizing it, because to honor his work his colleagues named the speed of sound “Mach 1,” and double the speed of sound “Mach 2,” and so on. Another fact most people do not realize about Mach is that he did not believe that atoms exist! Nor was Mach alone in holding such a view. During his lifetime a large number of very distinguished scientists and philosophers came to agree with him, so that he became the founder of a distinct movement in science which was enormously influential throughout the first two-thirds of the twentieth century. But despite Mach’s rejection of the reality of atoms and other particles, he still insisted that atomic theory is not to be discarded; it is far too successful for that. Instead he held that it is to be accepted the way Dewey accepted talk about numbers and the procedures of mathematics — as a useful way of explaining what we experience, even though its statements are not true because the entities it refers to are not real. So Mach called atoms and subatomic particles “useful fictions.” This was the result of the fact that Mach and his disciples adopted a perspectival hypothesis about the nature of reality which sees all the aspects of our experience as collapsed to the sensory aspect. You may recall that on this same basis Mill took the position that the formulae of mathematics are nothing more than generalizations about sensations. Mach applied this view of reality to the science of physics in detail. The result was that he, too, rejected the existence of anything other than sensory perceptions and feelings.

In order to understand his reasons for this view, and its far-reaching consequences for physics, it may be helpful to fill in the background of this philosophical perspective a bit more. The theory of reality which maintains that all things have an exclusively sensory nature has its roots in the early seventeenth century, when the belief arose that the human mind works much like an eye or a camera. According to this view, we must distinguish the reality which is outside our minds from the copy of it which is inside our minds, just as the world of things outside an eye or camera is distinct from the images which appear on a retina or film. Thus the mind came to be thought of as the retina or film on which the sensations of sight, touch, smell, sound, and taste impressed representations of the things which are external to the mind.

In the eighteenth century, such thinkers as George Berkeley and David Hume showed convincingly that if this picture of the mind is correct then all we can truly know are the purely sensory images inside our minds, so that it is impossible to know that they do copy anything outside the mind. In other words, if your mind is the camera and all you know is what is on your “film,” you could never tell whether the world outside your mind is really like what is on your film, or even be sure there is a real world outside your camera at all. For all you know, what is on your film might be an internally generated virtual reality show!

This bizarre conclusion is very close to what Berkeley, Hume, Mill, and Mach ended up accepting. They concluded that so far as we can ever know from our experience, reality is made of sensations. According to them, when we observe a tree in a field, we ought not to suppose that what we are seeing is physical either in the sense that it possesses distinctly physical properties or in the sense that it exists externally to the perceiver. What we are seeing is actually a bundle of sensory properties comprising a perception that registers in our mind. Consequently, they believed that all we can ever know of the nature of a tree is that it is a collection of all the possible sensations we could ever get from it. The tree (or any other object) is an arrangement of color patches, touch-feels, sound-impressions, tastes, and smells. And though it may be natural to want to argue that there must be a real tree outside our minds causing our tree-sensations, they pointed out that there is no way we could ever find that out. It was on the basis of this perspective on the nature of reality, the perspective that assigned exclusive reality to the sensory aspect, that Mach and many other physicists came to believe that we cannot know that there is anything other than our own perceptions. In fact, so convincing did their arguments seem that even thinkers who disagreed with their conclusion did so while admitting that it is at best a theory (an educated guess) that there are really objects external to us!

Earlier I made the point that from the standpoint of our immediate experience there are no good reasons to suppose that any objects are exclusively physical, since in our experience everything appears to be multi-aspectual. So you may be wondering why I made that point, and have now gone on to talk about the theories of Berkeley, Hume, Mill, and Mach, which claim not that everything is exclusively physical, but that everything we directly experience is exclusively sensory. The reason is that my point applies equally to both theories, and each provokes the other as a response.² Thinkers who took the position that objects outside our minds are exclusively physical (like Galileo and Descartes) also held that the sensations inside our minds are purely sensory, not physical. The problem was that it then had to be explained how we can know the sensations in our minds are faithful copies of objects outside them. That is what Berkeley and Hume showed could not be done. So they, like Mill and Mach after them, regarded the existence of external (purely) physical objects as a theory which it is impossible to confirm. It was on this ground that Mach dismissed the existence of objects that are both external to perceivers and that possess distinctly physical properties as an unscientific theory, and proceeded to try to show how physics could be conducted without it. As he says:

As I noted earlier, Mach accepted both our ordinary talk about matter and the atomic theory as playing a role in physics very like the role Dewey gave to numerals in mathematics.⁶ That is, although the terms and symbols of atomic theory do not stand for realities, they are still useful in dealing with the perceived world because they help us make predictions from one set of experiences to another. As the quote above shows, it is not just atoms and subatomic particles that Mach’s perspective rules out of reality, but all objects whatever that are supposed to possess physical properties. In his book Knowledge and Error, Mach specifically extended his view to the laws of physics, regarding them as merely our own psychological projections. He said they are nothing more than “the product of our mental need to find our way about in nature,” and (following Hume) that they are “subjective prescriptions for an observer’s expectations.”⁷ At the same time, however, he wanted to keep them in the theories of physics because “within certain limits” they lead us to right expectations (about future perceptions) and so should not be abandoned.

 

8.3            THE THEORY OF EINSTEIN

Not all physicists agreed with Mach. Some, like Einstein, maintained that our sensations really are caused by objects that are unperceivable because exclusively physical, and are external to our minds. But even so, he felt compelled to admit that this belief was only a theory. In affirming it against Mach, Einstein wrote:

In this quote we can see that Einstein’s view of reality begins by agreeing with Mach. Like Mach, he accepts the perspectival theory which holds that the objects we directly experience are of a purely sensory nature. So he, too, accepts that the test for whether something can be directly known to be real is whether it is sensorily perceived. All else must be hypothesis. Thus he admits that he cannot be sure there are really external “bodily” objects. Nevertheless he disagreed with Mach in other ways. One is that he believed that there do exist physical things external to our perception. He does so for the reason that the theory which proposes them lends so much rational understanding to our sense perceptions that we are entitled to believe it is true. This, then, was the chief difference between them: Einstein believed that we are entitled to say there are (purely) physical objects outside our minds which cause our sensations, while Mach denied it.

Einstein defended this disagreement with Mach by emphasizing that our minds possess the capacity for logical and mathematical reasoning in addition to perceiving and feeling. What is more, he held that logical and mathematical properties and laws are as real as the sensory properties and laws, so that rational thought can form concepts which are independent of perception. He says:

Because he attributed independent reality to the logical and mathematical properties and laws, Einstein maintained that rational thinking, as well as perception, may be taken as a rule for what counts as real. Notice that at the end of the first section quoted from him, he said that believing “bodily objects” have “real existence” is justified by the way that belief helps us understand the “labyrinth of sense impressions.” In other words, because the theory that there are physical objects makes rational sense, physical objects as well as sensory perceptions should be accepted as real. Thus, the belief in physical objects, like all other entity hypotheses, may be viewed as indicative of reality provided it comprises “a conceptual system . . . firmly enough connected with sensory experiences” and shows “as much unity and [economy] as possible” in its task of “ordering and surveying sense experience.”¹⁰

This perspective, which takes the logical/mathematical in addition to the sensory as the rule for what counts as the nature of reality, stands in a long tradition which comes to us from the work of the seventeenth-century mathematician and philosopher René Descartes, who proposed that the rule for both philosophy and physics be that all things which, generally speaking, are comprehended in the object of pure mathematics, are truly to be recognized as external objects.¹¹

 At the heart of this proposal is the assumption that the laws of mathematics and logic govern all reality and not just our thinking, and do so in such a  way as to guarantee a correspondence between reality and our thought. This assumption has often been expressed as the belief that whatever is rational (i.e., logical or mathematically calculable) is real. Einstein admits, however, that his confidence that nature is rational in this sense cannot be demonstrated. It is, he says, “a matter of faith that nature — as she is perceptible to the five senses — takes the character of such a well-formulated puzzle.” But, he adds, the successes of science “give a certain encouragement for this faith.”¹² This faith that the essential nature of reality is, in part, rational is precisely what Mach denied because he thought reality to be exclusively sensory in nature.

This led to some very sharp disagreements between the physicists who followed Mach and those who followed Einstein. For one thing, Mach’s denial requires adopting an attitude toward theories which assumes that they are never anything more than our inventions and serve only as devices to predict what we can expect if we do such and such. This means that in an important sense theories do not ever discover anything about the world we live in. They are kept and used because they succeed in predicting future experience, but all the while it is the greatest mystery why some predict successfully and some do not. In this way, Mach’s perspective lends a different meaning to the entire enterprise of physics; it requires a different interpretation not only of the nature of the entities proposed by physics, but of what physics is.

8.4            THE THEORY OF HEISENBERG

Werner Heisenberg disagreed with both Mach and Einstein. For Heisenberg, the elementary atomic particles are not to be thought of as realities in the way observable objects are real, but neither are they outright fictions as Mach thought. Instead, he holds the view that they are essentially mathematical possibilities. In explaining this, Heisenberg asserts not only that elementary particles lack any sensory qualities, but that it is not even accurate to say they have being. He says:

This does not mean that the essential nature of reality is only mathematical, however. Heisenberg goes on to make it clear that reality has a dual nature: there is energy, which is “the primary substance of the world,” and there are the mathematical laws which make possible the specific forms which energy can take. So he confidently predicts that

In fact, Heisenberg conceives of elementary atomic particles as so thoroughly mathematical that there can be nothing about them that is not mathematically explicable. So he says that

This view of reality as essentially mathematically explicable is behind Heisenberg’s famous interpretation of what are called “uncertainty relations,” the relations which exist between finding the momentum of a subatomic particle and finding its position. The uncertainty arises because the way to find out the location of a particle is to have it hit something massive enough to stop it. In that case we know where it is, but we can no longer find out how fast it was going. On the other hand, the way to find out a particle’s momentum is to have it collide with something which is not massive enough to stop it. Then, provided we already know the mass of whatever the particle strikes, we can calculate the particle’s velocity by how far it moves the object it hit. Once the particle has collided with the other object, however, its location is not knowable because it bounces off at such high speed. For this reason, finding out the position and momentum of a particle simultaneously is impossible; whichever of the two we discover prevents us from discovering the other.

This sort of uncertainty is not such a strange thing. There are many uncertainty relations in our everyday experience. Earlier I used the example of the uncertainty that arises when we try to ascertain the temperature of water in a glass by inserting a thermometer into it. Doing that changes the temperature of the water. Thus the very action taken to find that information precludes our getting it, creating an uncertainty relation between that action and what we want to know.

But the view Heisenberg held of the nature of atoms and other particles required him to take a very special interpretation of the uncertainty between the momentum and location of particles — one that has come to be known as the “Copenhagen interpretation.” Since he was committed to the view that reality is mathematically calculable “in every detail,” and since we cannot calculate both the position and momentum of a particle, Heisenberg said that particles must not have both speed and location. This means that any particle for which we choose to measure either momentum or location only ever had whichever one of those properties we chose to measure! That is, if we find a particle’s velocity, then it never had location; while if we find its location, then it never had velocity. Heisenberg admits this is a bizarre thing to say:

 He goes on to comment, however, that we should be prepared to give up our ordinary, “classical” concepts when we deal with the world of subatomic entities.¹⁷

Einstein rejected this view, holding that the uncertainty between a particle’s velocity and its location is a limit not to reality itself but to our ability to calculate and discover subatomic events — in the same way putting a thermometer in water limits us to discovering what its temperature now is rather than what it was before we put the thermometer in it. The difference between these two physicists is the different status they gave to the mathematical aspect in relation to all the other aspects. We have already seen that in opposition to Mach,

Einstein took the mathematical aspect of our experience and thought to be equally as real as the sensory aspect, so that the explanatory successes of math warrant us in believing in the existence of the entities physics proposes. But he does not take his esteem of math so far as to say that anything not mathematically calculable is therefore unreal. Against Heisenberg’s more exalted view of math, Einstein once quipped: “Not everything that can be counted counts, and not everything that counts can be counted.”

 

8.5            WHAT DIFFERENCE DO SUCH THEORIES MAKE?

We have now briefly examined some very different conceptions of reality which led to very different interpretations of atomic theory. For example, on Mach’s view it would make no sense to attempt to confirm the existence of entities such as atoms and subatomic particles. Since they are all fictions, conducting experiments to confirm their reality would make no more sense than inspecting the roof on Christmas morning for reindeer hoof prints. On the other hand, physicists who reject Mach’s perspective have engaged in extensive efforts to discover whether the entities proposed by their theories really exist.

Take, for example, the hypothesis of the neutrino proposed by Wolfgang Pauli. His invention was intended to make sense of a number of observations and also to preserve the law of conservation of energy. It did those jobs very well, and later on solved other explanatory gaps in atomic theory as well. But it still bothered physicists that the neutrino would have to be so small as to  be undetectable; they were concerned that it might only be an invention. For according to the theory, neutrinos are so tiny that they could be expected to collide with another object only rarely. In fact, one scientist estimated that to collide with even the nucleus of an atom, a single neutrino would have to “pass through the equivalent of 50 light years of solid lead,” and that a “shielding wall capable of thinning out a beam of neutrinos would have to be as thick  as 100,000,000 stars.”¹⁸ That is why so many scientists initially thought the neutrino would always remain impossible to detect.

This seemingly impossible task was finally accomplished, however, in 1956.¹⁹ But getting the evidence took a tremendous amount of ingenuity, equipment, time, and money. The great expense and effort highlights the motive which drove the physicists involved. Clearly, the motive was the belief that theories are attempts to know reality; that is, theories try to discover what exists and to know its nature. My point is that this belief presupposes a philosophical perspective which would have to accept (minimally) the logical, mathematical, spatial, physical, and sensory aspects of experience as (at least part of) the nature of reality. So whether that view was consciously adopted by those thinkers or not, it is the sort of perspective on reality that science needs. It needs, and is most benefited by, a view of reality that openly accepts its multi-faceted nature. Perhaps it is now clear why even though all these thinkers claimed to accept the atomic theory, they mean something very different by it — so different that it is fair to say that the twentieth century has actually produced three atomic theories, not minor differences within one and the same theory. For Mach, atomic theory meant inventing a system of micro-entities that is useful though populated with fictions. For Einstein, it meant postulating purely physical objects which we never experience. For Heisenberg it meant postulating micro-entities that comprise reality and that, while composed of physical energy, are essentially mathematical in nature. These sharp disagreements over the nature of atoms and particles mirror their disagreements over the nature of reality, views which rest on different priority assignments among the various aspects of experience. And these, in turn, rest upon different views of what is divine.

 

8.6            THE ROLE OF RELIGION IN THESE THEORIES

By now it should be fairly obvious why the theories just reviewed do, in fact, reflect divinity beliefs. But rather than make that claim as though it’s an accusation I need to justify, let’s allow these thinkers to speak for themselves. For example, in a comment similar to the one quoted earlier from Mill, Mach said of sensation that:

 This quote assigns to the sensory aspect the status we found to be the defining characteristic of divinity. Moreover, Mach gives no argument for this crucial point. So, just as in the case of Mill, I find Mach’s declaration to be the confession of his creed; it states the religious belief that regulated and guided his theorizing.

On the other hand, Einstein differs by insisting that the logical and/or mathematical aspects are also essential to the nature of reality. In fact, he ended up regarding our sensations as caused by the inter-action of physical objects with our minds, so that what is sensory is denied independent existence altogether. Thus even though Einstein agreed with Mach that the objects of our direct experience are purely sensory, it is not they which have independent, divine, existence but matter and the principles of rational thought which are divine. This makes sense of the rest of his view. He bases acceptance of a hypothesis on the belief that whatever is rational is real. Thus human rationality (rather than perception) is the rule for belief about what exists. And his faith in human reason is based, in turn, on the belief that the laws of logic and mathematics apply to all reality because they are the governing principles which make possible all the forms matter can take. Thus they (as well as matter) are self-existent and divine. Einstein says as much himself:

 Finally, we have seen that Heisenberg accords a special status to mathematical concepts, and explicitly says so in terms very similar to the quote given earlier from Descartes.²² He says that while all our other concepts are doubtful and “we do not know how far they will help us to find our way in the world,”²³ the concepts of math are immune from doubt of any kind and reflect the nature of all reality in such a way that not only what they can calculate is real, but whatever they cannot calculate is not real. The presupposition to this rule is the belief that mathematical laws are the self-existent principles which make all else possible. This makes the mathematical aspect divine, so that the basic presupposition of Heisenberg’s theory is also a religious belief. But I need not argue this point, however, since Heisenberg made it himself:

 In sum: the postulates of these theories are assigned different natures because those natures are assigned under the control of whatever their advocates find to be the basic nature of reality as a whole. And the aspects taken to be the nature of reality as a whole are given their (alleged) priority over all the other aspects on the ground that they also identify the nature of whatever is unconditionally self-existent and makes all else possible and actual. Thus the theories ultimately differ relative to what their advocates take to be divine.