UPSC Prelims 2018 Q62: Science & Technology – Physics
- (a) 1 and 2 only
- (b) 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Albert Einstein's General Theory of Relativity (1915) - Predictions
| Phenomenon | Predicted by General Relativity? | Detail |
|---|---|---|
| 1. Light is affected by gravity | YES | Gravitational bending of light around massive objects. Confirmed by Arthur Eddington's 1919 solar eclipse observation. Also predicts gravitational lensing. |
| 2. Universe is constantly expanding | YES | Einstein's field equations led to the discovery of expanding universe solutions (by Friedmann, Lemaitre). Einstein himself initially added a 'cosmological constant' to keep it static, later called it his 'biggest blunder' when Hubble (1929) confirmed expansion. |
| 3. Matter warps surrounding space-time | YES | This is the central insight of General Relativity - mass-energy curves the geometry of space-time, and this curvature IS gravity. |
Answer: (d) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Statement 3 (matter warping space-time) is THE central insight of General Relativity.
- (b) Incorrect. All three phenomena are predictions of General Relativity, not just space-time warping.
- (c) Incorrect. Expansion of the universe (Statement 2) is also a Relativity-derived prediction (Friedmann-Lemaitre).
- (d) CORRECT. All three phenomena - gravitational effect on light, cosmic expansion, and space-time warping by mass - are predictions of General Relativity.
Key point
General Relativity (1915) predictions: Light bending by gravity (verified 1919), gravitational time dilation, precession of Mercury's perihelion, gravitational waves (LIGO 2015), black holes, expanding universe (Friedmann-Lemaitre), gravitational lensing.
Remember
Einstein's General Theory of Relativity (1915) predicts that light is bent by gravity (confirmed in Eddington's 1919 solar eclipse experiment), that mass and energy warp the surrounding fabric of space-time (the theory's central insight), and that the universe is expanding (via the Friedmann-Lemaitre solutions to Einstein's equations, confirmed by Hubble in 1929).
Common mistakes
- Confusing General Relativity (1915, gravity + space-time) with Special Relativity (1905, no gravity, E=mc^2).
- Assuming Einstein predicted expansion - he initially resisted it by adding cosmological constant; expansion was confirmed by Hubble (1929).
- Missing that all three predictions have been experimentally confirmed - GR is one of the most tested theories in physics.
Exam tip
GR predictions confirmed: Mercury's perihelion, light bending (1919 eclipse), gravitational redshift (Pound-Rebka 1959), GPS clock corrections, gravitational waves (LIGO 2015), black hole imaging (EHT 2019).
Sources
- NCERT Class XI Physics — Gravitation
- Charles W. Misner, Kip S. Thorne and John A. Wheeler — Gravitation (W. H. Freeman, 1973)