"The statement in [Genesis] 1:1 not only identifies the Creator, it also explains the origin of the world. According to the sense of 1:1 (see Notes), the narrative states that God created all that exists in the universe. As it stands, the statement is an affirmation that God alone is eternal and that all else owes its origin and existence to him. The influence of this verse is reflected throughout the work of later biblical writers (e.g., Ps 33:6; John 1:3; Heb 11:3)."
Also: "In opening the account of Creation with the phrase 'in the beginning' (BERESIT), the author has marked Creation as the starting point of a period of time."
Here's what Keil-Delitzsch say:
"'In the beginning God created the heaven and the earth.'" - Heaven and earth have not existed from all eternity, but had a beginning; nor did they arise by emanation from an absolute substance, but were created by God. This sentence, which stands at the head of the records of revelation, is not a mere heading, nor a summary of the history of the creation, but a declaration of the primeval act of God, by which the universe was called into being. That this verse is not a heading merely, is evident from the fact that the following account of the course of the creation commences with w (and), which connects the different acts of creation with the fact expressed in Genesis 1:1, as the primary foundation upon which they rest. בּרשׁיח (in the beginning) is used absolutely, like ἐν ἀρχῇ in John 1:1, and מראשׁיח in Isaiah 46:10. The following clause cannot be treated as subordinate, either by rendering it, 'in the beginning when God created ..., the earth was,' etc., or 'in the beginning when God created...(but the earth was then a chaos, etc.), God said, Let there be light' (Ewald and Bunsen)."
David S. Oderberg argues for a cosmic beginning as he refutes Adolf Grünbaum in the article "Adolf Grünbaum and the Beginning of the Universe," Philosophia Naturalis Band 36 (1999):187-94.
Robert Jastrow (agnostic astronomer) famously wrote:
Recent developments in astronomy have implications that may go beyond their contribution to science itself. In a nutshell, astronomers, studying the Universe through their telescopes, have been forced to the conclusion that the world began suddenly, in a moment of creation, as the product of unknown forces.
The first scientific indication of an abrupt beginning for the world appeared about fifty years ago. At that time American astronomers, studying the great clusters of stars called galaxies, stumbled on evidence that the entire Universe is blowing up before our eyes. According to their observations, all the galaxies in the Universe are moving away from us and from one another at very high speeds, and the most distant are receding at the extraordinary speed of hundreds of millions of miles an hour.
This discovery led directly to the picture of a sudden beginning for the Universe; for if we retrace the movements of the moving galaxies backward in time, we find that at an earlier time they must have been closer together than they are today; at a still earlier time, they must have been still closer together; and if we go back far enough in time, we find that at a certain critical moment in the past all the galaxies in the Universe were packed together into one dense mass at an enormous density, pressure and temperature. Reacting to this pressure, the dense, hot matter must have exploded with incredible violence. The instant of the explosion marked the birth of the Universe.