Cosmic Microwave Background

The Cosmic Microwave Background (CMB) is a sea of radiation, a vital piece of evidence supporting the Big Bang theory. This theory posits that the universe began with rapid inflation, expansion, and cooling, leaving behind the CMB as residual heat from the Big Bang. Scientists view it as a “shockwave” from this monumental event.

In 1916, Albert Einstein used general relativity to develop a cosmic model, incorporating the then-prevailing belief of a static universe. To support this idea, he introduced the cosmological constant into his equations. However, he later regarded this as his “greatest blunder,” prompted by Edwin Hubble’s observations in the 1920s. Hubble noted that light from distant galaxies shifts to longer wavelengths, suggesting they are moving away from us. This discovery led to the development of models for an expanding universe, forming the foundation of today’s standard cosmological model.

In the 1920s, Belgian priest Georges Lemaître introduced the Big Bang theory, suggesting the universe originated from a singular point. This concept was further detailed in the 1940s by physicists George Gamow, Ralph Alpher, and Robert Herman. They asserted that the universe, right after its explosive beginning, was both extremely dense and hot. During this high-temperature phase, most of the universe’s contents existed as intense light (or radiation) rather than matter.

As the universe expanded, light and matter spread across an ever-growing space, leading to a decrease in their density. The expansion stretched the light’s waves, reducing its energy more rapidly than matter’s density. As a result, the universe transitioned from being dominated by radiation to matter, its current state.

The three scientists theorized that the Big Bang’s radiant energy should still permeate the universe today, albeit at a much lower intensity due to space expansion. However, they did not attempt to find it, possibly assuming the necessary technology did not exist yet.

The proof of the Big Bang theory came accidentally in 1964 when Arno Penzias and Robert Wilson, telecommunications engineers, encountered persistent microwave static with their equipment while working on early mobile phone technology. 

This static, unchanged regardless of the antenna’s direction or time, was initially unexplainable. Their investigation, which even considered pigeon droppings in the antenna, led to the discovery of the first observational evidence supporting the Big Bang theory. This background static represented the Big Bang’s “shockwave,” detectable as a subtle “wallpaper” behind galaxies and other cosmic structures. Penzias and Wilson earned the 1978 Nobel Prize in Physics for this discovery.

The cosmic microwave background is the universe’s oldest and most distant light detectable by telescopes. It dates back to about 380,000 years after the Big Bang when cooling allowed the first atoms to form and photons to travel freely. Recent probes like ESA’s Planck mission (2009-2013) have meticulously mapped this light, revealing insights into the universe’s earliest years and current composition. These findings affirm the standard cosmological model, which includes the enigmatic dark matter and energy.

Planck’s findings refined the universe’s expansion rate (the Hubble constant), indicating a galaxy about 1 million light-years away is moving at 20.59 kilometers per second, slower than previously thought. This revision suggests the universe is about 13.82 billion years old, around 80 million years older than earlier estimates.

Yet, cosmologists still face numerous mysteries as Planck’s map supported the existence of the “axis of evil,” an unusual alignment in the universe previously identified by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP).

The CMB is generally expected to be isotropic, meaning it should be uniform in all directions. However, some analyses of the CMB data, particularly those from the Planck spacecraft, have revealed certain large-scale patterns that appear to be aligned across the sky. These patterns seem to be oriented in a particular direction, forming what is colloquially known as the “axis of evil.” Some scientists dismiss this as a figment of imagination, while others suggest it could challenge standard cosmological theories and our understanding of the structure of the universe.

Moreover, Planck’s observations have confirmed a large, unexplained cold spot in the CMB. Some cosmologists believe that this indicates the existence of other universes, as suggested by the eternal inflation model, where new universes continuously emerge and expand. Such expansion could lead to a collision with our universe, creating observable effects like a “bruise” or cold spot.

These discoveries fuel continuing debates in cosmology. Meanwhile, the CMB provides astronomers with the closest possible view of the Big Bang, standing as one of the most valuable tools for understanding the origin and evolution of our universe.