This audiobook is narrated by a digital voice.

The story of modern cosmology begins with one of the most profound insights in scientific history: the universe had a beginning. This revolutionary understanding emerged from a convergence of theoretical physics and astronomical observations in the early twentieth century, fundamentally transforming our conception of space, time, and existence itself. The Big Bang theory, now the prevailing model for cosmic evolution, describes a universe that emerged from an extremely hot, dense initial state approximately 13.8 billion years ago and has been expanding and cooling ever since.

The theoretical foundation for the Big Bang emerged from Albert Einstein's General Theory of Relativity, published in 1915. Einstein's equations revealed that space and time are not fixed backdrops for cosmic events but rather dynamic entities that can stretch, compress, and curve in response to matter and energy. Initially, Einstein himself resisted the implications of his own equations, which suggested that the universe must be either expanding or contracting. The notion of a static, eternal cosmos was so deeply ingrained in scientific thinking that Einstein introduced the cosmological constant, a repulsive force that would counteract gravitational contraction and maintain cosmic equilibrium.

The first observational evidence for cosmic expansion came from Edwin Hubble's careful measurements of distant galaxies in the 1920s. Using the newly constructed Mount Wilson telescope, Hubble discovered that virtually all galaxies are moving away from us, with more distant galaxies receding at higher velocities. This relationship, now known as Hubble's Law, provided the first concrete evidence that the universe is expanding uniformly in all directions. If the universe is expanding now, logic dictated that it must have been smaller and denser in the past, ultimately suggesting a moment of cosmic birth.