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Introduction

Scientific realism is the view according to which scientific theories provide us with the descriptions that are true or approximately true. But the important thing is that we know exactly which of the things described in this world are "real things." In this vein, it is important to consider what are fundamentals, such that they provide the "fundamental basis" for other things of the world, in principle, and if there are fundamental things, how we can the analysis of the things of the world be done more fundamentally? That is to say, we want to know whether after going through some stages we come to the final fundamental things, and this division ends or continues indefinitely, or the relation of the fundamental affairs is a two-way dependence which can be regarded as a closed-loop (McKenzie, 2014) and (Tahko, 2018) there is a difference.

We can call "real things" in physical theories "physical reality"; now the above questions are about "physical reality." This article aims to determine one of the main characteristics of physical reality by turning to theories of contemporary physics.

In contemporary physics, one of the most important principles on the basis of which physical reality can be determined is the principle of symmetry. In fact, it is not an exaggeration to say that new physics is based on the principles of symmetry. These principles are used in both the major fields of modern physics, the field of quantum theories, and the field of relativity (although these principles are also present in previous theories, such as Galileo's symmetry in Newtonian mechanics). The principles of contemporary physics are symmetry principles.

In this paper, an attempt is made to state the conditions for physical reality and real physical state, or in general the condition of objectivity, which expresses the strong intuitions that exist in contemporary physics about physical reality and the real physical state, and in fact, it is based on symmetry principles. Also, according to the three definitions of scientific realism, stated in (Masoumi, 2017a), we will determine the relation of these conditions with the definitions. 

In the second part, the problem arises from the various formulations, interpretations, and idealizations in physical theories for realizing things. We will show that what is the same in the formulations, interpretations and different idealizations are "the symmetry features of a theory". Thus, this problem does not arise in the case of "the symmetry features of a theory". In the third section, we will explain the gauge quantities, the gauge transformations, and the conditions of real physical quantities and real physical description. Explanations are also given about the general covariance and symmetry of a theory. In the fourth section, we look at the relationship between the concept of physical reality and the concept of absolute from Friedman's point of view. Finally, the sixth section summarizes and concludes.

The requirements of physical reality

Here we need to make an important distinction. This is the distinction between "physical quantity" and "physical description" expressed by field equations and equations of motion, which are, in fact, relationships between physical quantities. In changing frameworks or changing observers, both can change. For example, in Newtonian mechanics, when we go from an inertial frame to a rotational frame, the mass of a particle does not change as a physical quantity, but the acceleration changes, and is not equal in the two frames.

Based on what has been said, we can state the conditions for physical to be real, for physical quantity and the physical description, respectively as follows.

(Physical reality feature)

Physical reality is something that is independent of an observer; that is, it does not depend on a coordinate system.

Because we are dealing with space-time theories, space-time theories quantities (space-time fields, and material fields), and their descriptions, in this case, we can deal with the above statement in detail. Let's say more with the following principles.

Condition 1 (real quantity feature)

The real space-time context and physical quantity is the quantity that is independent of an observer; that is, it does not depend on a reference framework or coordinate system.

Condition 2 (real description feature)

The real description is the description of a physical condition that is independent of an observer; that is, the real description does not depend on a reference frame, calling mathematically by the concept of substantive general covariance.

The real thing as the absolute thing (the Friedman's division)

In this section, we examine the concept of absolute and the relation between this concept and the concept of physical reality, which seems to be closely related to it. In the literature of the philosophy of science, the most important field in which the concept of absolute is discussed in the field of space-time theories. One of the divisions that exist about the absolute is the division that Friedman (1983: 62-64) has made, seeming to be useful in clarifying the feature of being real as absolute. The division is based on what is in the literature (Friedman, 1983: 62).

Absolute versus relational

Friedman divides the main issue into two parts. The first part of the issue is about space-time theories. The question can be posed (taking into account a four-dimensional space-time) as to whether space-time theories, when presented by a four-dimensional object, have a domain in which physical events take place (substantivalism) or, in fact, this domain is nothing but a collection of physical events (relationalism).

The second part is whether space-time relations or properties, as defined in space-time theories, can be reduced to more fundamental relationships and properties (such as the causal relationship between material identities (relationalism) or, conversely, are defined independently of material relations and properties and have an independent existence (substantivalism)

Absolute versus relative

In this viewpoint, the elements of space-time structures are absolute that is not dependent on a coordinate system and can be defined independently of the coordinates; in the other words, they can be intrinsically defined on manifold.

Absolute versus dynamical

This is a distinction that Anderson-Friedman makes to show the difference between relativity theory and other theories such as Newtonian mechanics and special relativity (Friedman, 1983, Ch. 2), (Anderson, 1967). In this view, geometric objects are divided into two kinds: dynamic objects and absolute objects. Thus, the difference between theories such as the theory of general relativity and other theories such as special relativity or Newtonian theory is that the first kind lacks an absolute object, but in the second kind, there are absolute objects such as Minkowski metric of special relativity.

Conclusion

Given the above, it seems that the principles we have stated for "physical reality" and "real description" both satisfy our intuition that real things are independent of the observation of an observer, and it is also an important feature to be real in contemporary physics. We have tried to introduce the above intuitive concept in detail in the principles introduced. We also saw that in the second sense of the absolute concept in Friedman's view, "physical reality" and "real description" are absolute.

References

- Ladyman, J. (2002). Understanding Philosophy of Science, London, and New York: Routledge.

- Ladyman, J., and Ross, D., et al. (2007). Every Thing Must Go: Metaphysics Naturalized, Oxford: Oxford University Press.

- Maidens, A. (1998). Symmetry groups, absolute objects and action principles in general relativity. Studies in the History and Philosophy of Modern Physics, 29, 245.

- Mandl, F. & Shaw, G. (2010). Quantum Field Theory, (2nd ed.), New York: Wiley.

- McKenzie, K. (2014). Priority and Particle Physics: Ontic Structural Realism as a Fundamentality Thesis, British Journal for the Philosophy of Science, 65: 353-80.

- Psillos, S. (1999). Scientific Realism: How Science Tracks Truth, London, and New York: Routledge.