The Big Bang and the Origin of the Cosmic Microwave Background

In 1923, astronomer Edwin Hubble made a groundbreaking discovery that shattered the perception of the universe. He revealed that the cosmos was not confined to the Milky Way alone but teemed with countless galaxies. However, his subsequent finding would prove even more astonishing – the realization that these galaxies were receding from us.

The electromagnetic emissions from distant galaxies appeared redder, a phenomenon known as redshift. This led Hubble to propose that the universe was expanding. But what did this mean for the origins of our vast cosmos? And how is the Cosmic Microwave Background related to that?

The Expanding Universe and the Big Bang

In 1948, physicist George Gamow presented an extraordinary theory that reshaped our comprehension of the universe’s beginnings – the Big Bang. According to Gamow’s audacious hypothesis, all the mass and energy of the cosmos were compressed into a minuscule space. This colossal explosion signified the genesis of the universe, leaving behind a remarkable remnant: the Cosmic Microwave Background (CMB).

Gamow proposed that the Cosmic Microwave Background, a “fossil” radiation, pervaded the entire expanse of the universe, providing a profound glimpse into its enigmatic origins. The significance of this discovery cannot be overstated, as subsequent research validated Gamow’s theory and revealed staggering insights into the nature of our existence.

Discovery of the Cosmic Microwave Background

In 1965, during their work on a microwave telecommunications antenna, Arno Penzias and Robert Wilson made a fortuitous finding. They picked up a faint background noise with astounding properties: isotropic radiation at a temperature of 2.7 degrees Kelvin and a frequency of 150 GHz.

This serendipitous discovery held immense significance—it was the long-sought evidence of the Cosmic Microwave Background, the residual echo of the universe’s primordial explosion. Penzias and Wilson had unwittingly captured the ancient reverberation of the universe’s profound “fiat lux” moment, providing a pivotal breakthrough in our understanding of cosmic origins. The detection of the CMB’s unique characteristics, such as its uniformity across the sky and the enormous scale of the radiation, firmly cemented its status as a paramount discovery in the field of astrophysics.

Understanding Cosmic Microwave Background Through General Relativity

According to Einstein’s General Relativity theory (1916), space and time are one single entity part of the four-dimensional space-time whose characteristics are regulated by matter.

A fundamental consequence of general relativity is that space-time does not respond to the Euclidean geometry rules, but it is an entity curved by the presence of mass. Only locally or in the case of small masses, it can be approximately treated with the Euclidean rules (in our solar system, space-time is almost everywhere Euclidean, apart from the immediate vicinity of the Sun).

If the matter is concentrated in a small volume, the space-time curves so much to trap everything in that region, even light. This is what occurs in a black hole, appearing to be completely black. According to the Big Bang theory, the entire mass (and energy) of the universe was initially condensed into a very small region of space, trapping everything there. When after the Big Bang the expansion of the universe began, the electromagnetic radiation produced by the initial explosion began to expand in space-time, gradually filling the entire universe.

The 2.7 Kelvin radiation is what is left of that big and amazing event, the last witness of one of the most important secrets of Modern Physics.

Modern Studies of the Cosmic Microwave Background

Modern studies of the Cosmic Microwave Background have provided invaluable insights into the early universe. Advanced instruments, such as the Planck satellite, have meticulously mapped the CMB’s temperature and polarization patterns with unprecedented precision.

By studying the statistical properties of these fluctuations, scientists have gained significant insights into the composition and evolution of the universe. One of the most remarkable findings is that the CMB anisotropies are consistent with the predictions of inflationary cosmology. This theory suggests that the universe underwent a rapid expansion phase in its early moments, smoothing out irregularities and imprinting the seeds of the structure we observe today.

Measurements of the CMB fluctuations have enabled scientists to determine the precise values of several cosmological parameters. For instance, the Planck satellite mission has provided a highly accurate estimate of the age of the universe, placing it at approximately 13.8 billion years. The observations also indicate that dark matter constitutes about 27% of the total energy density in the universe, while dark energy, responsible for accelerated expansion, makes up about 68%. The remaining 5% comprises ordinary matter, including atoms, stars, and galaxies.

Moreover, the CMB data has allowed scientists to infer the geometry of the universe. Currently, observations suggest that the universe is very close to being flat, implying that the angles of large triangles in space add up to 180 degrees, just as in Euclidean geometry. This finding aligns with the predictions of inflationary cosmology.

The exquisite precision of CMB measurements has also placed tight constraints on other cosmological parameters, such as the Hubble constant, which represents the present expansion rate of the universe. These measurements, in combination with other cosmological probes, have led to intriguing discrepancies, giving rise to ongoing debates and investigations to resolve the “Hubble tension.”

Conclusion

The discovery of the Cosmic Microwave Background has profoundly shaped our understanding of the universe’s origins. It offers a glimpse into the primordial era, when the entire cosmos was condensed into a tiny point, and guides us in unraveling the mysteries of the Big Bang.

As scientists continue to study and analyze the CMB, we move closer to a comprehensive understanding of the profound forces that shaped our existence. The journey of exploration and discovery in the realm of cosmology is far from over, promising even more remarkable revelations about our place in the vastness of the cosmos.