Big Bang Evidence: All About Cosmic Microwave Background Radiation

How did the discovery of the Cosmic Microwave Background lead scientists to unravel the mysteries of the Big Bang and trace the origins of our universe?

I recall vividly learning about the Big Bang idea as a child. The concept that our entire cosmos arose from a single minuscule concentrated point approximately 14 billion years ago astounded me.

Our own existence seemed to be dependent on solving the mysteries of those early cosmic moments. Scientific discoveries have unveiled important new chapters understanding the origins of space and time in the decades after my childhood exposure to cosmology.

Yet many fundamental mysteries persist from the beginning of time, waiting to be decoded inside ancient signals such as cosmic microwave background radiation. Unravelling their meaning holds the potential of revealing our true place in this big cosmic drama.

The Revelation of an Expanding Universe

When visionary astronomer Edwin Hubble analysed light from distant galaxies in the 1920s, our understanding of the universe was irrevocably altered. He became aware that they were swiftly receding from us, with velocities proportional to their distances – a relationship now known as “Hubble’s law” [1].

This revealed that, on cosmic scales, space-time itself is extending apart [2]. Backward extrapolation of cosmic expansion implies that all observable matter and energy started from an exceedingly tiny, dense, and hot primordial state – the “Big Bang” notion [3].

Hubble calculated the expansion rate to be 500 km/s per megaparsec at first. This indicates that a galaxy two megaparsecs (Mpc) away recedes at 1000 km/s, but one four Mpc away recedes at 2000 km/s. Today’s expansion rate is 67.4 km/s per Mpc, according to more recent observations using type 1a supernovae and the cosmic microwave background [4]. This improved value has helped constrain other critical cosmological parameters governing the makeup and ultimate fate of our cosmos.

Glimpsing the Echo of Creation

George Gamow, a famous scientist, brought Hubble’s observations to a logical conclusion in 1948. Extrapolating backwards, the hot, dense early universe should have radiated the universe strongly. Despite being redshifted and diluted by expansion, Gamow predicted that the leftover glow would pervade the universe as microwaves, forming the “cosmic microwave background” (CMB) [3].

As early as 380,000 years after the Big Bang, this ancient signal afforded an unprecedented look into fundamental conditions [5]. However, technologies at the time lacked the ability to detect such a subtle, ubiquitous hiss from creation itself. The search for solid evidence for what Gamow dubbed the “Big Bang” model [3] continued at a period when its main rival was the Steady State theory, which postulated an infinite universe [6].

Discovery of the Cosmic Microwave Background

Arno Penzias and Robert Wilson were working at Bell Laboratories in 1964, designing ultra-sensitive microwave receivers for early satellite communications. When they tested one of these horn antennas, they discovered a strange background interference – a pervasive low-level noise at a temperature of 2.7 degrees Kelvin and a frequency of 150 GHz that was equally powerful day and night, summer and winter, and seemed to come from all directions [7].

“When we looked at the sky we saw the noise was isotropic…it was the same wherever you looked…that noise, we figured was coming from the antenna looking at the sky.”

– Robert Wilson

The strange signal persisted even after they took efforts to remove potential sources, at one point even speculating if bird waste inside their antenna caused anomalies!

“We did not know…pigeons sometimes roosted there, leaving…deposits which caused the excess antenna noise”

– Arno Penzias

Their crucial insight came upon learning that Princeton physicists had predicted radiation left over from an explosive Big Bang origin should permeate all space as microwave photons cooled by cosmological expansion.

Penzias and Wilson had already serendipitously discovered the sought-after signal [7].

The Ideal Cosmic Cryogen

Detailed investigations revealed that the temperature of the CMB matched equilibrium conditions in an early hot dense cosmos on a scale comparable to today, exactly as anticipated by Big Bang theories. Its incredible isotropy surpasses even the most advanced projections, revealing origins in the distant cosmic past [8].


The newborn universe shone at about 10 billion K shortly after the Big Bang, compared to the Sun’s 5800K surface – hot enough to totally ionise primordial plasma [9]! Due to cosmic expansion, those once-scorching photons have now cooled to only 2.7 degrees above absolute zero. As a result, the CMB is the most perfect natural cryogen known, blanketing the entire universe [5].

Their surprising discovery provided conclusive evidence in favour of Hot Big Bang cosmology over rival models lacking a dynamic expanding genesis [6][10]. News spread fast about Penzias and Wilson tuning into the lingering “noise” from creation itself!

Decoding the Blueprints to Existence

Since its discovery, increasingly precise satellite observations have helped to characterise CMB features [7][8]. The COBE mission of NASA demonstrated for the first time that this relic light preserves minor temperature variations matching to early cosmic density fluctuations.

Analyses of these intricate patterns in the CMB yield precise estimates of critical factors regulating cosmic evolution [9]. For example, we now know that normal stuff accounts for only 4.9% of the universe’s energy budget. 68.3% is made up of an even more enigmatic component known as “dark energy,” which accelerates cosmic expansion, while 26.8% is made up of non-luminous “dark matter” [10].

Cosmic Microwave Background

The CMB also hints at our universe’s ultimate fate: its extraordinary uniformity predicts a flat spacetime geometry, which is consistent with predictions of infinite cosmic expansion [11].


When I show students photographs of the CMB, I tell them that hidden among its brilliant multi-colored patches is the fading thunder from creation’s cataclysm. Since Penzias and Wilson first witnessed its primordial fire in 1964, the cosmic microwave background has exposed key moments in our universe’s birth tale.

Despite this, many profound mysteries dating back to the dawn of time continue to reverberate through its swirling patterns.

What fresh mysteries can be revealed as we continue to decipher the message hidden within this primaeval gleam? The past, present, and future of our cosmos collide in one magnificent relic glow.


  1. [1] Hubble, Edwin (1929). A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae.
  2. [2] NASA (2022). Hubble’s Law and the Expanding Universe.
  3. [3] NASA Science (2022). The Big Bang Theory.
    [4] Wu, Katherine J. (2019). When Did the Universe Become Transparent?
  4. [5] Penzias, A. A.; Wilson, R. W. (1965). A Measurement of Excess Antenna Temperature at 4080 Mc/s.
  5. [6] Peebles, P.J.E. et al. (1991). The case for the relativistic hot Big Bang cosmology.
  6. [7] Smoot Group (2022). Cosmic Microwave Background.
  7. [8] Bennett, C.L. et al. (2013). Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations.
  8. [9] Planck Collaboration (2020). Planck 2018 results. VI. Cosmological parameters.
  9. [10] NASA (2021). Pie Chart of the Universe.
  10. [11] NASA WMAP (2010). Geometry of Space.

Quantum Soul
Quantum Soul

Science evangelist, Art lover

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