Who gave the first evidence of the Big-Bang theory?

The Big Bang Theory, also known as the expanding universe hypothesis, posits that the universe originated from a singular point and has been expanding ever since [4]. American astronomer Edwin Hubble provided the first observational evidence for this theory in the 1920s [4]. By observing the redshift phenomenon, Hubble demonstrated that galaxies are moving away from us, with their recession velocity being proportional to their distance—a relationship now known as Hubble's Law [2]. This galactic redshift indicates that the universe is not static but is continuously expanding [3]. While Albert Einstein's general relativity provided the theoretical framework, he initially favored a static universe. S. Chandrasekhar is noted for his work on stellar structure (Chandrasekhar limit), and Stephen Hawking for singularity theorems and black holes. Thus, Hubble's 1929 observations remain the foundational evidence for the Big Bang [4].

Sources

1. [4] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 1: Geography as a Discipline > Origin of the Universe > p. 13
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > Doppler-Shift or Redshift and Blueshift > p. 3
3. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > Importance of Gravitational Waves > p. 5
4. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > UPSC Prelims 2012] Which of the following is/are cited by the scientists as evidence(s) for the continued expansion of the universe? > p. 6