News Todays 1

Newton’s law of universal gravitation (1687) was one of the most profound scientific breakthroughs in history, accurately describing:

• Planetary orbits
• Terrestrial gravity (g ≈ 9.8 m/s²)
• Tidal forces

But in light of Einstein’s general relativity (1915), we now understand Newton’s law has fundamental limitations:

Where Newton’s Law Fails

1. Extreme Gravity Regimes

• Near black holes (e.g., Mercury’s orbit requires GR corrections)
• At velocities approaching light speed (Newton assumes instantaneous action)

1. Gravitational Time Dilation

• Clocks run slower in strong gravitational fields (GPS satellites require GR adjustments)
• Newton’s theory predicts no time curvature

1. Gravitational Waves

• Merging black holes emit ripples in spacetime (first detected 2015 by LIGO)
• Newtonian gravity has no wave solutions

1. Light Bending

• Starlight curves around the Sun (confirmed 1919 Eddington expedition)
• Newton’s corpuscular theory predicts only half the observed deflection

The Mathematical Difference

Newton (1687)	Einstein (1915)
F = G(m₁m₂)/r²	Gᵤᵥ = 8πTᵤᵥ (field equations)
Instantaneous action	Propagates at light speed
Flat spacetime	Curved spacetime metric

Is Newton “Wrong”?

Not exactly – it’s a special case approximation:

• For weak fields (e.g., Earth’s surface) and low velocities (≪ c), Newton and Einstein agree within 0.0001%
• All NASA moon missions used Newtonian calculations (with minor GR tweaks)

Modern Status

• Engineering/Education: Still taught and used for most practical applications
• Fundamental Physics: Superseded by GR, but remains phenomenally accurate for:
• Building construction
• Spacecraft trajectories (except near compact objects)
• Basic astronomy education

Key References:

1. Will (2018) Theory and Experiment in Gravitational Physics
2. Misner, Thorne & Wheeler (1973) Gravitation
3. LIGO Collaboration (2016) Phys. Rev. Lett. 116, 061102

The truth is subtler than “true/false” – Newton’s law remains one of history’s most useful approximations, while GR gives the complete picture.