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The concept of the expanding universe is credited to:
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Answer: Option B — Edwin Hubble
Detailed Solution
Edwin Powell Hubble (1889-1953) was an American astronomer who worked at the Mount Wilson Observatory in California. He made two discoveries that changed our understanding of the universe.
First, in 1924-25, he showed that some of the fuzzy "spiral nebulae", such as Andromeda, were actually separate galaxies far outside our own Milky Way. This proved that the universe is much larger than previously thought and contains many galaxies.
Second, in 1929, by measuring the distances of galaxies and their redshifts (using earlier redshift measurements by Vesto Slipher), Hubble found that almost all galaxies are moving away from us, and that the farther away a galaxy is, the faster it is receding. This relationship is known as Hubble's law (now called the Hubble-Lemaître law):
v = H₀ × d
where v is the recession velocity of the galaxy, d is its distance, and H₀ is the Hubble constant. This showed that the universe is expanding.
Redshift: when a light source moves away from an observer, its light is stretched to longer (redder) wavelengths. This is similar to the Doppler effect in sound.
The Belgian priest and physicist Georges Lemaître had independently proposed the expansion of the universe in 1927 and suggested that the universe began from a "primeval atom". This led to the Big Bang theory, which says that the universe began about 13.8 billion years ago from an extremely hot and dense state and has been expanding ever since. The term "Big Bang" was coined, mockingly, by Fred Hoyle in 1949. Strong evidence for the Big Bang came in 1965, when Arno Penzias and Robert Wilson discovered the cosmic microwave background radiation, the faint afterglow of the Big Bang. In 1998, astronomers discovered that the expansion of the universe is accelerating, driven by "dark energy".
The Hubble Space Telescope, launched in 1990, is named in his honour.
Why not the other options?
- ✗Albert Einstein's general theory of relativity (1915) allowed for an expanding universe, but he initially added a "cosmological constant" to keep it static.
- ✗Isaac Newton gave the law of universal gravitation.
- ✗Stephen Hawking studied black holes and the origin of the universe.
Quick tip
Remember: Expanding universe = Edwin Hubble (1929, redshift, Hubble's law v = H₀d); Big Bang = Lemaître (1927), term by Fred Hoyle; cosmic background radiation = Penzias and Wilson (1965).
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Universe & Solar System — Preparation
This question tests your understanding of Universe & Solar System, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers the universe, galaxies and stars, the solar system and its planets, dwarf planets, moons, asteroids, comets and meteors, and the Earth's motions, including rotation, revolution, seasons, latitudes, longitudes and time zones. Common questions ask about the largest and smallest planets (Jupiter and Mercury), the hottest planet (Venus), the 'Red Planet' (Mars), and planets with the most moons. Other frequent questions cover solstices and equinoxes, the International Date Line, and Indian Standard Time, which is based on the 82.5 degree E meridian. Practise the universe and solar system questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.