Quantum Nature of Gravity

Important Facts for Prelims

Quantum Nature of Gravity

Why is it in the news?

Scientists are conducting experiments with nanocrystals to investigate whether gravity adheres to quantum principles.

This research aims to reconcile General Relativity, which explains gravity on macroscopic scales, with Quantum Mechanics, which governs atomic and subatomic interactions. As these theories are fundamentally incompatible, this effort contributes to the search for a unified theory of quantum gravity.

What is the Proposed Experiment to Test Gravity's Quantum Nature?

• About the Experiment: Scientists propose using quantum superposition, where particles exist in multiple states until observed.
• Nanocrystal Test: The experiment will involve placing a test mass crystal in superposition (existing in two locations simultaneously) while another mass interacts with it through gravity.
• Measurement Process: After observing the second crystal, researchers will check whether gravity causes the test mass to collapse into a definite state, which could indicate that gravity follows quantum principles.

Significance:

If successful, this experiment could demonstrate that gravity is not merely a classical force, but also exhibits quantum characteristics, as current theories suggest gravity should show quantum effects. Unlike other quantum gravity tests, which typically rely on strong gravity (e.g., black holes), this experiment focuses on weak gravity near small objects, making it more feasible to test.

Challenges:
The experiment requires extreme precision, as even minor disturbances (like air molecules or seismic activity) could interfere with the results. It will also require a near-perfect vacuum, and measurements will need to be taken very quickly. The technology needed to carry out the experiment is still under development.

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

What are Quantum Mechanics and General Relativity?

• Quantum Mechanics:

  • About: Quantum mechanics explains the behavior of subatomic particles, like electrons and photons, which can behave both as particles and as waves— a concept known as wave-particle duality.
  • Key Principles:
    • Wave-particle Duality: Particles can act as both waves and particles.
    • Superposition: A particle can exist in multiple states until it is measured.
    • Entanglement: Two particles can become correlated so that the state of one affects the other, even across vast distances.
    • Uncertainty Principle: The position and momentum of a particle cannot both be precisely determined at the same time.

• General Relativity:

  • About: General relativity, proposed by Albert Einstein in 1915, extends Newton’s law of universal gravitation and 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 passes more slowly in stronger gravitational fields (e.g., near black holes).
    • Equivalence Principle: In a closed system, acceleration and gravitational forces are indistinguishable.

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)

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