Steady State Theory vs Big Bang Theory
Introduction & Conceptual Foundation
In the mid-20th century, cosmology was divided into two competing schools of thought regarding the origin and nature of the universe: the Big Bang Theory and the Steady State Theory.
The Steady State Theory
Proposed in 1948 by British scientists Fred Hoyle, Hermann Bondi, and Thomas Gold, the Steady State Theory was formulated as an alternative to the Big Bang model. Its core foundation relies on the Perfect Cosmological Principle, which states that the universe is homogeneous, isotropic, and unchanging in its overall appearance when viewed from any place at any time.
Key postulates of the Steady State Theory include:
- Infinite Age: The universe has no beginning and no end. It has always existed in a state similar to what we observe today.
- Constant Density: Although the universe is expanding (as demonstrated by Edwin Hubble's observations of redshift), its overall density remains constant over time.
- Continuous Creation of Matter: To maintain a constant density as galaxies drift apart, new matter is continuously and spontaneously created in the empty spaces between galaxies at a very slow rate (approximately one hydrogen atom per cubic meter per billion years).
- No Ultimate Fate: Unlike the Big Bang, which suggests an ultimate end (such as a Big Crunch, Big Freeze, or Big Rip), the Steady State universe is eternal and permanent.
Contrast with the Big Bang Theory
The Big Bang Theory, on the other hand, operates under the standard Cosmological Principle (the universe is homogeneous and isotropic in space, but not static in time). It argues that the universe is dynamic, has a finite age (13.8 billion years), and its density decreases as space expands because no new matter is created to fill the void.
UPSC Prelims Perspective
For the Civil Services Preliminary Examination, candidates must understand the core parameters of distinction between the two theories and the key scientific terms involved.
Comparison Table: Big Bang vs. Steady State
| Feature | Big Bang Theory | Steady State Theory |
|---|---|---|
| Proponents | Georges Lemaître (1927) | Fred Hoyle, Hermann Bondi, Thomas Gold (1948) |
| Age of Universe | Finite (~13.8 billion years) | Infinite (Eternal, no beginning or end) |
| Density | Decreases continuously as the universe expands | Remains constant over time despite expansion |
| Matter Creation | All matter was created at the instant of the Big Bang | Continuous, spontaneous creation of new matter in empty space |
| Cosmological Principle | Applies to space (homogeneous & isotropic) | Perfect Cosmological Principle (applies to space and time) |
| Leftover Radiation | Predicts uniform background radiation (CMBR) | Cannot naturally explain uniform background radiation |
| Ultimate Fate | Big Crunch, Big Freeze, or Big Rip | No end; remains in a steady state eternally |
Key Terminology to Know
- Perfect Cosmological Principle: The philosophical assumption that the universe looks the same from any point, in any direction, at any time in history.
- C-Field (Creation Field): A theoretical concept introduced by Fred Hoyle to mathematically explain the continuous creation of matter and the driving force behind the universe's expansion without a singular origin point.
UPSC Mains Perspective
Multi-Dimensional Analysis & Why Steady State Was Discarded
In UPSC Mains, questions may ask for a comparative evaluation or the reasons behind the transition of cosmology from the Steady State model to the Big Bang model.
Reasons for the Scientific Rejection of Steady State Theory
The Steady State Theory was highly popular in the 1950s because it avoided the philosophical and physical problems associated with a "beginning" (the singularity). However, by the late 1960s, a series of observational discoveries completely discredited the theory:
- Discovery of Cosmic Microwave Background Radiation (CMBR) (1965):
- The Big Bang model predicted that the early universe was hot and dense, and a remnant thermal radiation should be visible today as a uniform glow in the microwave spectrum.
- The discovery of CMBR by Penzias and Wilson showed a highly uniform blackbody radiation of 2.73 K. The Steady State Theory could not explain this radiation without invoking ad hoc, highly complex, and unproven mechanisms (such as starlight scattered by cosmic dust).
- Evolution of Cosmic Structures (Quasars):
- In the 1960s, astronomers discovered Quasars (extremely bright, active galactic nuclei powered by supermassive black holes).
- Observations showed that quasars only exist at immense distances, which means they existed only in the distant past (billions of years ago).
- Under the Steady State model, the universe should look the same at all times; hence, quasars should be found nearby as well. Their absence in the local/recent universe proved that the universe has evolved over time.
- Abundance of Light Elements:
- Steady State theory assumed that all helium was created inside stars via stellar nucleosynthesis.
- However, the observed ratio of Helium (about 25% of the universe's baryonic mass) is far too high to have been produced solely by stars since the universe's stars haven't burned long enough. Only the Big Bang nucleosynthesis model could accurately account for this abundance.
Practice Questions
Prelims Practice Question
Q. Which of the following observations directly led to the abandonment of the Steady State Theory of the universe?
- The detection of Cosmic Microwave Background Radiation (CMBR) by Penzias and Wilson.
- The observation of Quasars only at high redshifts (immense distances).
- The discovery of gravitational waves from merging black holes.
Select the correct answer using the code given below:
(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2 and 3
Correct Answer: (b) 1 and 2 only
Explanation:
- Statement 1 is correct: The discovery of the CMBR in 1965 was the primary blow to the Steady State Theory. The CMBR represents the thermal relic of a hot, dense early universe, which the Steady State theory could not explain.
- Statement 2 is correct: Quasars are only found at high redshifts (which correspond to the distant past). This showed that the universe was structurally different in the past compared to the present, violating the Perfect Cosmological Principle of the Steady State Theory.
- Statement 3 is incorrect: The discovery of gravitational waves (in 2015) confirmed Einstein's General Theory of Relativity but was not a factor in discarding the Steady State Theory, which had already been abandoned by the late 1960s.
Mains Practice Question
Q. Contrast the Steady State Theory with the Big Bang Theory of the origin of the universe. Analyze the key observational discoveries that led to the universal acceptance of the Big Bang model over its competitor. (15 Marks, 250 Words)
Approach/Answer Framework:
- Introduction: Introduce both theories by mentioning their key proponents (Georges Lemaître for Big Bang; Hoyle, Bondi, and Gold for Steady State) and their basic premises (finite dynamic universe vs. infinite steady universe).
- Body:
- Core Differences (use a structured comparison or bullet points): Contrast the concepts of the beginning of time, conservation of matter vs. continuous matter creation, and changes in density over time.
- Observational milestones that discarded Steady State:
- CMBR Discovery (1965): Explain why the uniform 2.73 K radiation supports a hot, dense past.
- Quasar Distribution: Explain how the presence of quasars only in the early universe proves cosmic evolution.
- Light Element Abundances: Detail why helium levels could only be explained by early universe nucleosynthesis.
- Conclusion: Summarize that while the Steady State Theory was elegant and avoided the singularity paradox, empirical evidence is the ultimate test in cosmology, leading to the triumph of the Big Bang model.