Which scientist thought of the concept of steady state of the universe?

The correct answer is Fred Hoyle.

Fred Hoyle (1915–2001) was a renowned British astronomer and cosmologist who is most famously associated with the Steady State Theory of the universe. He proposed this theory in 1948 along with his colleagues Thomas Gold and Hermann Bondi.

What is the Steady State Theory?

The Steady State Theory proposed that the universe has no beginning and no end — it looks the same at all times and in all places. Even though the universe is expanding (as Edwin Hubble's observations showed), Hoyle argued that new matter is continuously created to fill in the gaps left by galaxies moving apart, keeping the overall density and appearance of the universe constant (in a "steady state").

Key ideas of the Steady State Theory:

• The universe is infinite in age — it had no special creation moment.
• Matter is continuously created at a very slow rate to maintain a uniform density.
• The universe obeys the Perfect Cosmological Principle — it appears the same to all observers, at all times and all places.

Why the other options are incorrect:

• Harold Jeffreys — A British geophysicist and astronomer, known for work on Earth's interior and probability theory, not the Steady State concept.
• Edwin Hubble — Discovered the expansion of the universe and classified galaxies, but did not propose the Steady State Theory.
• Pierre-Simon Laplace — An 18th–19th century French mathematician and astronomer known for classical mechanics and probability; lived long before modern cosmological theories were developed.

An Interesting Historical Note:

Ironically, it was Fred Hoyle himself who coined the term "Big Bang" — a phrase he used dismissively to mock the competing theory of a universe born from a singular explosive event. Despite this, the Big Bang Theory eventually gained dominance, especially after the discovery of the Cosmic Microwave Background Radiation in 1965 by Penzias and Wilson, which the Steady State Theory could not adequately explain.

Therefore, Fred Hoyle is the scientist credited with the concept of the Steady State universe.