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What is dark energy and dark matter?

  • IAS NEXT, Lucknow
  • 24, Feb 2022
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Astronomical observations suggest that a significant part of the universe is made up of dark matter which interacts with the rest of the universe only through the gravitational pull.

  • Many large lab experiments have tried to detect elementary particles that could be candidates for dark matter. However, such dark matter particles have not been detected until now.

Assessing dark matter:

The researchers use the non-observation of the lensing signatures to assess what fraction of the dark matter could be made of black holes. Gravitational lensing is useful to cosmologists because it is directly sensitive to the amount and distribution of dark matter.

What is gravitational lensing? How does it work?

  • Gravitational lensing is an effect of Einstein’s theory of general relativity – simply put, mass bends light.
  • The gravitational field of a massive object will extend far into space, and cause light rays passing close to that object (and thus through its gravitational field) to be bent and refocused somewhere else.
  • The more massive the object, the stronger its gravitational field and hence the greater the bending of light rays – just like using denser materials to make optical lenses results in a greater amount of refraction.

What is Dark Energy?

More is unknown than is known. We know how much dark energy there is because we know how it affects the universe’s expansion. Other than that, it is a complete mystery. But it is an important mystery. It makes up about 68% of the universe.

Dark Energy is a hypothetical form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity.

  • It is causing the rate of expansion of our universe to accelerate over time, rather than to slow down. That’s contrary to what one might expect from a universe that began in a Big Bang.

How is dark energy different from dark matter?

Everything we see – the planets, moons, massive galaxies – makes up less than 5% of the universe. About 27% is dark matter and 68% is dark energy.

While dark matter attracts and holds galaxies together, dark energy repels and causes the expansion of our universe.

  • The existence of dark matter was suggested as early as the 1920s, while dark energy wasn’t discovered until 1998.

Did you know about the XENON1T experiment?

  • It is the world’s most sensitive dark matter experiment and was operated deep underground at the INFN Laboratori Nazionali del Gran Sasso in Italy.
  • It uses the dual-phase (liquid/gas) xenon technique and is located underground at the Laboratory Nazionali del Gran Sasso of INFN, Italy.

The theory of general relativity:

The leading theory, however, considers dark energy a property of space. Albert Einstein was the first to understand that space was not simply empty. He also understood that more space could continue to come into existence. In his theory of general relativity, Einstein included a cosmological constant to account for the stationary universe scientists thought existed.

  • After Hubble announced the expanding universe, Einstein called his constant his “biggest blunder.”
  • But Einstein’s blunder may be the best fit for dark energy. Predicting that empty space can have its own energy, the constant indicates that as more space emerges, more energy would be added to the universe, increasing its expansion.