IAS Gyan

Daily News Analysis


30th September, 2023 Science and Technology

Disclaimer: Copyright infringement not intended.


  • A long-standing dispute in physics has just been settled: how would antimatter, the counterpart of matter, behave under the influence of gravity?
  • Einstein’s general theory of relativity implied that antimatter would fall just like matter does, but some physicists have long been suggesting that it should rise upward.
  • Experiments at CERN have now demonstrated that antimatter falls, validating yet another aspect of the general theory.


Antimatter and Gravity

  • Antimatter is the counterpart of matter, with properties reversed, such as positively charged positrons instead of negatively charged electrons.
  • The general theory of relativity, proposed by Albert Einstein in 1915, treats all matter as identical, suggesting that both matter and antimatter should respond to gravitational forces in the same way.

The Experiment at CERN

  • CERN, the European Organization for Nuclear Research, conducted experiments to investigate how gravity affects antimatter.
  • The ALPHA collaboration at CERN has an Antimatter Factory where antihydrogen atoms are created and studied.
  • Antihydrogen atoms consist of a positron orbiting an antiproton nucleus, and they are confined to prevent contact with regular matter, as their annihilation would occur upon contact.

The Gravity Test

  • In the experiment, researchers switched off the magnetic field to allow antimatter annihilation.
  • An apparatus called ALPHA-g, commissioned in 2021, measured the vertical positions at which the annihilation occurred.
  • Groups of about 100 antihydrogen atoms were slowly released and compared to the results with "regular" matter under the same conditions

Experimental Results

  • Computer simulations predicted that 20% of matter atoms would exit through the top of the trap, and the remaining 80% would exit through the bottom due to gravity.
  • The experiment's results demonstrated that antimatter atoms exited through the top and bottom in the same proportion as predicted for matter atoms, indicating that antimatter falls under gravity, just like matter does.

Introduction to Antimatter

What is Antimatter?

  • Antimatter consists of particles that are the counterparts of normal matter particles, but with opposite electrical charge.
  • When matter and antimatter collide, they annihilate each other in a burst of energy.

Historical Overview and Discovery

  • The concept of antimatter was first introduced in the early 20th century by theoretical physicist Paul Dirac.
  • The first antiparticle, the positron (the antimatter counterpart of the electron), was discovered in 1932 by Carl D. Anderson.

Properties of Antimatter

  • Antiparticles: Antimatter has antiparticles for each type of matter particle. For example, the antiparticle of a proton is an antiproton, and the antiparticle of an electron is a positron.
  • Annihilation: When a particle encounters its corresponding antiparticle, they annihilate each other, releasing energy in the form of gamma rays.
  • Charge and Mass: Antiparticles have the same mass as their corresponding matter particles but carry opposite electrical charges.

Production of Antimatter

  • Particle Accelerators: Most antimatter is produced in particle accelerators, where high-energy collisions generate antiparticles.
  • Natural Sources: Cosmic rays and certain types of radioactive decay produce antimatter in small quantities.
  • Artificial Production: Researchers are continually developing more efficient methods for producing antimatter, as it is challenging and energy-intensive.

Antimatter in the Universe

  • Cosmic Rays: High-energy cosmic rays striking the Earth's atmosphere can produce antimatter particles.
  • Antimatter Galaxies: Some galaxies are believed to be composed primarily of antimatter, which could have profound implications for our understanding of the cosmos.
  • Cosmic Antimatter Distribution: Studying the distribution of cosmic antimatter can provide insights into the composition and history of the universe.

Applications of Antimatter

  • Medical Imaging and Cancer Treatment: Positron Emission Tomography (PET) relies on positron annihilation for medical imaging. Antimatter could also be used for precise cancer treatment.
  • Propulsion Systems: Antimatter propulsion systems have been proposed for future spacecraft, offering higher energy densities than conventional fuels.
  • Energy Generation: In theory, antimatter could be harnessed for power generation, but this is currently highly speculative.

Challenges and Limitations

  • Storage and Containment: Antimatter is notoriously difficult to store and contain due to its annihilative nature.
  • Production Costs: Producing antimatter is extremely energy-intensive, making it currently prohibitively expensive.
  • Ethical and Safety Concerns: The controlled use and transportation of antimatter would require robust safety protocols and international cooperation.

Theoretical Implications

  • Antimatter and the Big Bang: The abundance of matter over antimatter in the universe is a key question in cosmology related to the Big Bang.
  • Matter-Antimatter Asymmetry: The reason for the observed excess of matter over antimatter is still not fully understood.
  • Dark Matter and Antimatter: There are speculations about the possible connections between dark matter and antimatter.

Einstein's General Theory of Relativity

The Equivalence Principle

  • General Relativity starts with the Equivalence Principle, which posits that locally, in a freely falling elevator, there is no way to distinguish between gravity and acceleration.
  • This principle challenges the classical concept of gravity as a force and introduces the idea of curved spacetime.

Curved Spacetime

  • Einstein's theory proposes that massive objects warp the fabric of spacetime, causing other objects to move on curved paths.
  • The presence of mass-energy creates gravity by bending the geometry of the universe itself.

Einstein's Field Equations

  • General Relativity is mathematically described by Einstein's field equations, which connect the curvature of spacetime (Ricci tensor) with the distribution of matter and energy (the energy-momentum tensor).

Predictions of General Relativity

  • General Relativity predicts phenomena like gravitational time dilation, the bending of light by gravity (gravitational lensing), and the existence of black holes.


This discovery not only validates a prediction of Einstein's theory but also contributes to our knowledge of antimatter, which plays a crucial role in our understanding of the universe's early moments and fundamental physics.


Q. Einstein's General Theory of Relativity and the behavior of antimatter represent two distinct but interrelated realms of modern physics. Discuss the key principles of General Relativity and how they relate to the behavior of antimatter. Highlight the significance of recent experiments validating the behavior of antimatter under gravity and its broader implications in the field of physics and cosmology. (250 Words)