Which of the following is/are cited by the scientists as evidence/evidences for the continued expansion of universe? 1. Detection of microwaves in space 2. Observation of redshift phenomenon in space 3. Movement of asteroids in space 4. Occurrence of supernova explosion in space Select the correct answer using the codes given below:
Contents17
- A1 and 2
- B2 only
- C1, 3 and 4
- DNone of the above can be cited as evidence
Show answer
Answer: (A) 1 and 2
Two key pieces of evidence for the expanding universe:
Detection of microwaves (statement 1) — the Cosmic Microwave Background Radiation (CMBR), discovered in 1965, is the 'afterglow' of the Big Bang and supports the expansion theory.
Redshift (statement 2) — when galaxies move away from us, their light shifts toward the red end of the spectrum (Hubble's Law). This is the most direct evidence of expansion.
Statement 3 is wrong — asteroid movement within our solar system doesn't prove universal expansion.
Statement 4 is wrong — supernovae occur for various reasons; their mere occurrence doesn't prove expansion (though Type Ia supernovae ARE used to measure expansion rate, the question says 'occurrence' generally).
Answer: 1 and 2.
The expanding universe theory is fundamental to modern cosmology, supported by two major discoveries: cosmic microwave background radiation (the afterglow of the Big Bang) and redshift observations showing galaxies moving away from us.
UPSC tests whether students can distinguish between phenomena that occur within our solar system (like asteroid movement) versus cosmic-scale evidence that proves the entire universe is expanding.
Cosmic Microwave Background Radiation
Science And Technology microwaves in space Detection of microwaves
Cosmic Microwave Background Radiation: The Universe's Afterglow
CMBR is leftover radiation from the Big Bang, discovered in 1965
Fills entire universe as microwave radiation at 2.7 Kelvin
Provides direct evidence for expanding universe theory
Discovery earned 1978 Nobel Prize to Penzias and Wilson
CMBR is the faint microwave radiation that permeates the entire universe — essentially the 'echo' of the Big Bang still detectable today.
Key Properties
Temperature: 2.7 Kelvin (almost absolute zero)
Frequency: Microwave range of electromagnetic spectrum
Distribution: Nearly uniform across all directions in space
Age: Radiation has been traveling for 13.8 billion years
Source: Hot, dense state of early universe 380,000 years after Big Bang
Discovery Context
In 1965, Arno Penzias and Robert Wilson accidentally discovered this radiation while working on satellite communications. They initially thought it was equipment noise until realizing it came from space itself.
Trap: Don't confuse microwaves in space (CMBR) with radio waves from pulsars
Trap: CMBR is uniform background radiation, not emissions from specific objects like stars
Trap: Discovery was accidental in 1965, not a planned search for Big Bang evidence
Redshift Phenomenon & Hubble's Law
Science And Technology redshift phenomenon Observation of redshift
Redshift: Direct Evidence of Universal Expansion
Redshift shows galaxies moving away from us due to universal expansion
Light wavelength stretches as galaxies recede, shifting toward red end
Hubble's Law: farther galaxies recede faster (v = H₀d)
Most direct and convincing evidence for expanding universe
Redshift occurs when light from distant galaxies gets stretched to longer (redder) wavelengths as those galaxies move away from us — similar to how an ambulance siren sounds lower-pitched as it drives away.
How Redshift Works
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Galaxy emits light**
Star emits light at specific wavelengths`"]
s2["`**Space expands**
Universe expansion stretches space between us and galaxy`"]
s3["`**Light wavelength stretches**
Photons get 'stretched' to longer wavelengths`"]
s4["`**We observe redshift**
Light appears shifted toward red end of spectrum`"]
s5["`**Calculate recession velocity**
Greater redshift = faster recession = farther distance`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Types of Redshift
Type | Cause | Scale | Example |
|---|---|---|---|
Doppler Redshift | Galaxy motion through space | Local | Andromeda galaxy (actually blueshifted) |
Cosmological Redshift | Expansion of space itself | Universal | Distant galaxies, quasars |
Gravitational Redshift | Light escaping strong gravity | Stellar | Light from neutron stars |
Hubble's Discovery
Edwin Hubble (1929) found farther galaxies recede faster
Hubble's Law: v = H₀d (velocity = Hubble constant × distance)
Hubble constant: ~70 km/s/Mpc (rate of universal expansion)
Proved universe is expanding uniformly in all directions
Trap: Cosmological redshift (space expansion) ≠ Doppler redshift (object motion)
Trap: All distant galaxies show redshift, not just some — this proves uniform expansion
Trap: Redshift measures recession velocity, not rotational or random motion
Asteroids & Solar System Dynamics
Science And Technology asteroids in space Movement of asteroids
Asteroid Movement: Local Motion vs Universal Expansion
Asteroids orbit the Sun within our solar system — this is local motion
Asteroid movement does NOT prove universal expansion — wrong scale entirely
Universal expansion evidence requires intergalactic observations, not solar system
Most asteroids located in asteroid belt between Mars and Jupiter
Asteroids are rocky objects that orbit the Sun, mostly concentrated in the asteroid belt between Mars and Jupiter. Their movement is governed by solar gravity, not universal expansion.
Motion Scale Comparison
Motion Type | Scale | Cause | Relevance to Expansion |
|---|---|---|---|
Asteroid orbits | Solar system | Sun's gravity | None — local motion only |
Galaxy recession | Intergalactic | Space expansion | Direct evidence |
Planetary motion | Solar system | Sun's gravity | None — bound system |
Star movement | Within galaxy | Galactic gravity | None — internal motion |
Why Asteroid Motion Irrelevant
Solar system is gravitationally bound — expansion doesn't affect it
Asteroid motion is orbital around Sun, not recession from us
Universal expansion only detectable at megaparsec distances
Need observations of other galaxies, not solar system objects
Trap: Local motions (asteroids, planets) don't prove universal expansion
Trap: Expansion affects unbound systems (galaxies), not bound systems (solar system)
Trap: Don't confuse orbital motion with recession motion
Supernovae Types & Cosmological Uses
Science And Technology supernova explosion Occurrence of supernova
Supernovae: Stellar Death vs Cosmological Tools
Supernova occurrence alone does NOT prove universal expansion
Type Ia supernovae are used as standard candles to measure expansion
Supernovae occur due to stellar death, not because universe expands
1998 Nobel discovery: Type Ia showed accelerating expansion (dark energy)
Supernovae are explosive stellar deaths that occur for internal stellar reasons. While Type Ia supernovae serve as excellent distance measuring tools, their mere occurrence doesn't prove expansion.
Supernova Types
Type | Cause | Brightness | Cosmological Use |
|---|---|---|---|
Type Ia | White dwarf exceeds 1.4 solar masses | Always same peak brightness | Standard candle for distance |
Type II | Massive star (>8 solar masses) core collapse | Variable brightness | Limited cosmological use |
Hypernova | Extremely massive star collapse | Ultra-bright | Early universe studies |
Cosmological Applications
Type Ia supernovae: uniform peak brightness makes them 'standard candles'
Compare apparent vs absolute brightness to calculate distance
1998 discovery: distant Type Ia were dimmer than expected
Conclusion: expansion is accelerating due to dark energy
Nobel Prize 2011 awarded for this dark energy discovery
Question Context
The question asks about supernova occurrence as evidence. Supernovae occur because stars die, not because the universe expands. However, measuring Type Ia supernovae distances does provide expansion evidence.
Trap: Supernova occurrence ≠ evidence for expansion (they happen due to stellar evolution)
Trap: Type Ia measurements DO prove expansion, but question asks about occurrence
Trap: Don't confuse why supernovae happen with how we use them as distance tools
Expanding Universe Theory
Science And Technology expansion of universe continued expansion
Expanding Universe: Theory & Evidence Overview
Universe has been expanding since Big Bang 13.8 billion years ago
Two main evidences: CMBR detection and redshift observations
Expansion is accelerating due to mysterious dark energy
Space itself expands — galaxies aren't moving through space
The expanding universe theory states that space itself is continuously stretching, carrying galaxies away from each other. This isn't galaxies flying apart through space — it's space expansion.
Evidence Categories
Evidence Type | What It Shows | Discovery | Significance |
|---|---|---|---|
CMBR detection | Universe had hot, dense beginning | 1965 | Proves Big Bang theory |
Galactic redshift | Galaxies receding uniformly | 1929 | Direct expansion measurement |
Type Ia supernovae | Expansion is accelerating | 1998 | Revealed dark energy |
Primordial nucleosynthesis | Light element abundances match theory | 1940s-70s | Confirms early universe conditions |
Modern Cosmological Model
# Expanding Universe
## **Components**
- **Dark Energy** (68%)
- **Dark Matter** (27%)
- **Normal Matter** (5%)
## **Timeline**
- **Big Bang** (t=0)
- **Inflation** (first second)
- **CMBR release** (380,000 yrs)
- **Today** (13.8 billion yrs)
## **Key Evidence**
- **Hubble's Law**
- **CMBR**
- **Type Ia SNe**
- **Element abundances**Trap: Local motions (within solar system/galaxy) don't prove universal expansion
Trap: Space expands — galaxies aren't flying through space like explosion fragments
Trap: Need cosmological distance observations, not local astronomical phenomena