Quantum Nature of Gravity

• 01 Mar 2025

Source: TH 

Why in News?

 

Scientists are conducting experiments with nanocrystals to explore if gravity follows quantum principles.  

• This effort aims to bridge the gap between General Relativity (explains gravity at macroscopic scales) and Quantum Mechanics (governs atomic and subatomic interactions). 
  • Since these theories are fundamentally incompatible, the research contributes to the pursuit of a unified theory of quantum gravity. 

What is the Experiment Proposed to Test the Quantumness of Gravity? 

• About Experiment: Scientists propose an experiment using quantum superposition, where particles exist in multiple states until measured.  
  • Nanocrystals will test if gravity follows quantum mechanics.  
  • A test mass crystal will be placed in superposition (existing in two places at once) while another mass interacts with it via gravity.  
  • After measuring the second crystal, scientists will check if gravity causes the test mass to collapse into a definite state, potentially indicating that gravity follows quantum principles. 
• Significance: 
  • If successful, the experiment may prove that gravity is not just a classical force but also exhibits quantum properties, as current theories suggest that gravity should show quantum effects. 
  • Most quantum gravity tests rely on strong gravity (e.g., black holes), which is impractical to test.  
    • This experiment proposes studying weak gravity near small objects, making quantum gravity testing more feasible. 
• Challenges: 
  • The experiment requires extreme precision since even small disturbances (like air molecules or seismic activity) can affect the results. 
  • Scientists need to create a near-perfect vacuum and measure the results very quickly. 
  • The technology to perform this experiment is still being developed. 

Read More: What are the Key Features of Quantum Mechanics? 

What is Quantum Mechanics and General Relativity? 

• Quantum Mechanics: 
  • About: 
    • Quantum mechanics is the branch of physics that explains how sub-atomic particles, like electrons and photons, can behave both as particles (small bits of matter) and waves (energy disturbances).  
    • This concept is known as wave-particle duality and is a fundamental principle of quantum physics. 
  • Key Principles: 
    • Wave-particle Duality: Particles can behave both as waves and particles. 
    • Superposition: A particle can exist in multiple states until measured. 
    • Entanglement: Two particles can be correlated in such a way that the state of one instantly affects the other, even across vast distances. 
    • Uncertainty Principle: The position and momentum of a particle cannot both be precisely measured at the same time. 
• General Relativity: 
  • About: It is the modern theory of gravity proposed by Albert Einstein in 1915 as an extension of Newton’s law of universal gravitation. 
    • It describes gravity not as a force, but as the curvature of spacetime caused by mass and energy. 
  • Key Principles: 
    • Space-time curvature: Massive objects like the Sun bend space-time, causing planets to orbit. 
    • Time Dilation: Time moves slower in stronger gravitational fields (e.g., near black holes). 
    • Equivalence Principle: Acceleration and gravitational forces are indistinguishable in a closed system.

UPSC Civil Services Examination, Previous Year Question (PYQ) 

Q. Consider the following phenomena: (2018)

1. Light is affected by gravity. 
2. The Universe is constantly expanding. 
3. Matter warps its surrounding space-time. 

Which of the above is/are the prediction/predictions of Albert Einstein’s General Theory of Relativity, often discussed in media? 

(a) 1 and 2 only 
(b) 3 only 
(c) 1 and 3 only 
(d) 1, 2 and 3 

Ans: (d)