The division of physics, by akin themes or by the type of activity, let to study and to deal with physics efficiently. For instance the themes: Deposition of thin films, surface conductivity, doping effects, physical phenomena of interfaces, etc. are under the same area: Surface physics. For the specialist the advantages of dividing the physics into areas are very clear; the division facilitates the communication between the professionals and the dissemination of new results. For the tyro those advantages are not clear; for the novice, the physics put into fragments, appears as a collection of disarticulated areas; without relation; disconnected.
The themes of physics appear so disconnected, that, for the type of activity, it appears that there are two physics: One theoretical and another experimental. The physicists speak in those terms. Besides, the official courses of physics, by tradition, are separated into theoretical and experimental. The student ends the official studies believing that there are two physics. One experimental and another theoretical; without any relation between one and the other.
For that structure, the connection between physics and tangible world is lost. For the student that ends the official studies, the physics has almost nothing to do with the external world. For that student there is no relation between physics and external world.
However the reality is not that. The physics is unique. The physics is an experimental science. That does not mean that the experimental labor is more important than the theoretical labor, but that the theoretical labor must be based on experimental evidences. The experimental labor and the theoretical labor feed back each other. One causes the advances of the other in the general objective of physics: The description and interpretation of the external world.
If the division of the physics facilitates the study and growth of physics, that division has no other purpose or justification. The physics must be treated as an integral discipline. And must be presented as that. The nature is unique, therefore the physics is unique. Without divisions.
The student can obtain by himself, or by herself, the general objective of physics examining the pioneer works, and checking the obtained results by the authors of those works. Let us introduce some examples:
The object of all science, whether natural science or psychology, is to co-ordinate our experiences and to bring them into a logical system. A. Einstein wrote in the introduction of his celebrated book The meaning of relativity.
And with respect to the advances of the general theory of relativity, in the same book he wrote:
Since the first edition of this little book some advances have been made in the theory of relativity. Some of these we shall mention here only briefly:
The first step forward is the conclusive demonstration of the existence of the red shift of the
spectral lines by the (negative) gravitational potential of the place of origin. This demonstration
was made possible by the discovery of so-called "dwarf stars" whose average density exceeds that
of water by a factor of the order 
. For such star (e.g. the faint companion of Sirius), whose mass
and radius can be determined, this red shift was expected, by the theory, to be about 20
times as large as for the sun, and indeed it was demonstrated to be within the expected range.
A. Einstein discusses about the purpose of the science and about the experimental confirmation of his theory, in the above paragraphs. Einstein took care about putting clearly, and with very simple words, his science and scientific position. The student must conclude, after meditating about the words of Einstein.
Another master of physics was E. Fermi. In the introduction of his book Thermodynamics he wrote:
We know today that the actual basis for the equivalence of heat and dynamical energy is to be sought in the kinetic interpretation, which reduces all thermal phenomena to the disordered motions of atoms and molecules. From this point of view, the study of heat must be considered as a special branch of mechanics: the mechanics of an ensemble of such an enormous number of particles (atoms or molecules) that the detailed description of the state and the motion loses importance and only average properties of large number of particles are to be considered. This branch of mechanics, called statistical mechanics, which has been developed mainly through the work of Maxwell, Boltzmann, and Gibbs, has lead to a very satisfactory understanding of the fundamental thermodynamics laws.
But the approach in pure thermodynamics is different. Here the fundamental laws are assumed as postulates based on experimental evidence, and conclusions are drawn from them without entering into the kinetic mechanism of the phenomena. This procedure has the advantage of being independent, to great extend, of the simplifying assumptions that are often made in statistical mechanical considerations.
In these paragraphs, E. Fermi discusses about different approximations of the science to the same problem. And put in clear that the bases of physics must be supported by experimental evidences. The student must conclude, after thinking very deep in the above passage.
The above two examples illustrate the position of two fathers of physics. The two men describe physical phenomena in their theories. The two men based their theories on experimental evidences. And the two men search for the experimental confirmation of the consequences of their theories. For these two men the external world is the object of study. And in spite of that they are speaking about very different branches of physics, the approximation and the method that they are following are the same. The experimental evidence has a preponderant place in the theory. That is the method of the physics.
In this way, the physics deals with the description and interpretation of the external world. This is the very general objective, and at the same time very particular objective, of physics. From this point of view, the fragmentation of physics is artificial.
The physics reveals all its potential when we see it in the above form. Because the physicist when knows and understands the laws of the nature can manipulate the nature for multiple purposes. For the raw pleasure -like the majority of the physicists do-, for commercial purposes -like the majority of scientists and engineers, that look for the creation of new satisfactories that increase the people level of life- do.
Hence, we will illustrate, in the following pages, the two facets of physics that we just mentioned above. We use the high energy physics to present this illustration, however we could use any other branch or area of the physics to identical purposes. In the way, we will show the high energy physics.