0.1 What is physics?  (Page 2/2)

Simplification and unification

Simplification and unification have emerged as the basic trait of physics. There are only a few laws to define a wide variety of natural phenomena – a fact that underlines the simplification of governing laws in physics.On the other hand, unification of physical quantities and concepts is also prevalent. Take the example of matter and energy. They are now considered equivalent. The Special Theory of Relativity establishes the equivalence of these two quantities as $E=m{c}^2$ . Further, this dual nature of matter highlights the wave (E energy) nature of particles (m mass), which underlies the concept of mass-energy equivalence. Similarly, the treatment of magnetism in terms of electrical charge is an example of unification of physical concepts.

Simplification can also be seen in the laws governing gravitation and electrostatics.Gravitational and electrical forces are conservative forces, determined by inverse square laws. The similarity of the forms ofmathematical expressions is no coincidence, but a sure indication of the underlying nature of the universe, which emphasizessimplification :

$$\begin{array}{cc}{F}_{\mathrm{G}}=\frac{G{m}_1{m}_2}{4\pi r^2}& \text{.......... Gravitation Force}\end{array}$$

$$\begin{array}{cc}{F}_E=\frac{q_1{q}_2}{4\pi {\varepsilon }_0{r}^2}& \text{.......... Electrostatic Force}\end{array}$$

Simplification and unification of physical quantities, concepts and laws are remarkable, suggesting more such cases – which are yet to be discovered. Consider the physical quantities: “mass” and “charge”. There is as yet no relationship connecting these two fundamental quantities of physics. Similarly, the two major categories of forces known as nuclear and weak forces are not yet fully understood. Scientists are working to examine these unknown territories.

Scientific validation and experimental verification

The fundamental laws of physics are set against either too big or too small quantities, presenting apeculiar problem in establishing direct validation of basic theories in physics. Even today, there is not a single experimentalset up which could directly verify Einstein’s theory of relativity. For example, mass of an electron moving at two – third of the speedof light can not be measured directly. As we do not see the atom and its constituents, theories based on them are also not directlyverifiable. We can not even verify Newton’s first law of motion, which states that an object in the absence of net external forceshall keep moving! We have seen all objects come to rest in the earth's frame of reference, when left unaided. This peculiarity, however, does not mean that these laws have not beenvalidated as required for scientific studies.

It should be amply clear that scientific method for validation also includes inferences based on indirectmeasurements. In that sense, Einstein’s special theory of relativity has been tested and verified by results obtained from the experimentsinvolving motions of charged particles at great speed. Surprising is the exactness and accuracy of the results obtained. In the samecontext, accuracy of predications involving solar systems, satellites etc. have validated laws of gravitation.

Recasting and revalidating laws in the light of new revelations

Studies and experiments continue to bring new details and dimensions to our understanding of natural phenomena.New revelations recast old facts, hypotheses and theories. The relativity theory propounded by Albert Einstein, for example,revealed that Newton’s laws of motions are basically a subset of more general theory. Similarly, Newton’s hypothesis regardingvelocity of sound was recast by Laplace, arguing that propagation of sound is adiabatic and not isothermal process as considered by Newton.His assertion was based on the experimental result and was correct. There are many such occasions when an incomplete or erroneousunderstanding of natural event is recast or validated when new facts are analyzed.

Domains of physical laws

There is an irresistible perception that physical phenomena are governed by a universal law - a fundamental law, which is valid at all dimensions and at all speeds. As against this historically evasive natural conjecture, our understanding and formulation are limited to domains of applicability. Newton’s law works fine in our world, where dimensions are bigger than atomic size and speed is not exceeding 0.17c (speed of light, “c”). If the speed of an object exceeds this limit, the relativistic effects can not be ignored.

Consequently, we are currently left with a set of laws, which are domain specific. One law resigns in favor of other as we switch from one domain to another. The plot below approximately defines the domains of four major physical laws in terms of dimension and speed. Though, there are further subdivisions proposed, but this broader classification of applicability of natural laws is a good approximation of our current understanding about natural phenomena.

The reduction of the special theory of relativity into classical mechanics at smaller speeds gives an indication that there may be a law which is the most general and, therefore, universal. At present, however, there is no such clear cut “deducibility” among other domain specific laws, which involves “quantum mechanics” or “general relativity”. Unquestionably, unification of physical laws is the most fundamental question eluding all scientific investigation to this date.

There is a long way to go

Our knowledge about nature is improving progressively with every passing day. Yet our so called understanding at any point of time is subject to new revelation and meaning. Most of the time, we come to realize that our understanding is mostly limited to our surrounding and the context of application. It may sound bizarre but it is a fact that we have yet not fully understood even the basic concepts like distance, mass and time. Theory of relativity attached new meaning to these terms. It may not be totally brazen to think that even relativistic improvisations be ultimately incomplete and inaccurate. Who knows ?