The abstract of the three lectures will be as follows.

Lecture 1
This lecture will begin by laying down the generally accepted criteria for a scientific theory, namely that  (1) it makes testable, and possibly disprovable, assertions; (2) it explores uncharted territory by speculations provided clear-cut methods are specified for testing those ideas and (3) the theory should be tested not just once but repeatedly and in as many different circumstances as possible. Theories by Pythagoreans on the Earth going round a central fire or by Aristotle, followed by Hipparchus and Ptolemy  on the cosmos revolving round a fixed earth are examples of theories that did not work out.  Coming to modern cosmology, examples will be given of how the inputs of facts gradually removed wrong ideas and convictions.  Nevertheless, it will be argued that the subject has been driven by strongly held notions, that have not received any independent support.

Lecture 2

The second lecture will first describe the modern big bang cosmology which began with Hubble’s discovery of the velocity-distance relation and Einstein’s theory of relativity. The simplest models led to the notion of big bang origin. The entire universe is supposed to have been created in a singular explosive event, which generated outward motion.  This model has recently undergone a modification invoking an extra repulsive force that makes the universe accelerate. The thrust of present effort is directed towards understanding what went on shortly after the big bang.

The relic radiation background recalling the early existence of very high energy radiation comes in the way, however, if one wishes to peer through it to very early epochs. Thomson scattering intervenes to stop and scatter the radiation from travelling far undisturbed. The closer one goes into the past the stronger this effect. It begins at a redshift of 1000 or so.  That is, it prevents any coherent imaging of the universe prior to the epoch when the universe was approximately a thousandth part of its present linear size. Thus what happened prior to this epoch has to rest not on solid observed facts but inferred indirect effects of those early epochs that we cannot see. Some consequences of this speculative approach will be discussed.

Lecture 3

The last lecture will examine the present work on the very early universe. Starting with the premise that the epochs closer and closer to the big bang would be dominated by particles of higher and higher energies, there has developed close collaboration between cosmologists and high energy particle physicists. Known as astro-particle physics, this field has generated lot of interest in recent times.
However, most of it depends on speculative physics, i.e., on physics not tested in the laboratory. These speculations are coupled with cosmological speculations (which, as we saw earlier are not observable directly). The results are interesting but can hardly be considered credible as a scientific theory. In fact the level and type of speculation reminds one of the Pythagorean speculation described in Lecture 1. Finally, one also realizes that the sequence of events describing the history of the universe is non-repeatable and so does not satisfy the third criterion of a scientific theory.

Taking these aspects one may find it hard today to ascribe credibility to modern cosmology as a scientific theory.