Dark Energy and Dark Matter – UPSC IAS

In this article, You will read Dark Energy and Dark Matter for UPSC IAS.

Matter is anything that has mass and takes space. But apart from the ‘normal’ matter, there are different other forms of hypothesized matter. A few examples include Dark Matter, Anti Matter, and Negative Matter.

You by now know that matter and energy are interconvertible; so there is Dark Energy, Anti Energy, and Negative Energy too.

Now let’s see what each of these terms signify.

Dark Energy and Dark Matter

The term ‘dark’ is used to denote the unknown. 

  • Dark energy is an unknown form of energy that is hypothesized to permeate (spread throughout) all of space, tending to accelerate the expansion of the universe.
  • Dark matter works like an attractive force — a kind of cosmic cement that holds our universe together. This is because dark matter does interact with gravity, but it doesn’t reflect, absorb or emit light.
  • Meanwhile, dark energy is a repulsive forcea sort of anti-gravity — that drives the universe’s everaccelerating expansion.
  • Dark energy is the far more dominant force of the two, accounting for roughly 68 percent of the universe’s total mass and energy.
  • Dark matter makes up 27 percent.
  • And the rest – a measly 5 percent is all the regular matter we see and interact with every day.
  • The velocity of rotation for spiral galaxies depends on the amount of mass contained in them, But the outer arms of the Milky Way are rotating much too fast to be consistent with the amount of matter that we know exists in them.
  • Such fast rotation is possible only when there is more mass, and that extra mass is believed to come from dark matter.
  • Dark matter is a hypothetical form of matter. The majority of dark matter is thought to be composed of some as-yet-undiscovered subatomic particles.
  • The name dark matter refers to the fact that it does not appear to interact with observable electromagnetic radiation, such as light.
  • It is thus invisible (or ‘dark’) to the entire electromagnetic spectrum, making it extremely difficult to detect.
  • Dark matter interacts with the rest of the universe only through its gravity (that’s how we know it exists).
  • The material is considered to be a ‘matter’ since it has gravitational attraction and it is ‘dark’ because it does not seem to interact with light (or any part of the electromagnetic spectrum).
Dark Energy and Dark Matter
Are Black Holes Dark Matter?

Black holes could be considered as a dark matter for the reasons mentioned below:

  1. Almost collision-less.
  2. They are stable (if sufficiently massive)
  3. They have non-relativistic velocities.
  4. They formed very early in the history of the universe.

In March 2016, 3 groups of researchers proposed that Black Holes had a primordial origin. Results from 2 groups are consistent with the scenario that almost all dark matter is made of primordial black holes. 3rd group concluded that black holes contributed to only less than 1% of total dark matter.

Anti-Matter and Anti Energy

  • Anti’ means the opposite. So anti-matter has some properties opposite with respect to the usual matter. 
    • For example, the electron has as its antiparticle the antielectron. The electron and the antielectron have exactly the same masses, but they have exactly opposite electrical charges.
  • It is hypothesized that every elementary particle in the Universe has a partner particle, known as an ‘antiparticle’.
  • The particle and its antiparticle share many similar characteristics, but many other properties are the exact opposite.
  • The electron, for example, has as its antiparticle the antielectron. They both have the same masses, but they have exactly opposite electrical charges.
  • Most of the human understanding of anti-matter comes from high-energy accelerator experiments.
  • When a matter particle meets its antimatter particle, they destroy each other completely (i.e. annihilation), releasing the energy equivalent of their rest masses (following Einstein’s E = mc2).
  • For instance, when an electron meets an antielectron, the two annihilate and produce a burst of light which produces a corresponding energy level equivalent to the masses of the two particles.

Negative Matter and Negative Energy

  • Negative matter is a hypothetical type of matter which if it exists will have negative mass and negative energy.  
  • It will in essence have a negative gravitational charge and repel normal matter.  Yet it will interact just like any other matter in every other way.
  • Hope you remember that matter and anti-matter will attract each other resulting in annihilation. But matter and the negative matter will repel each other under gravity.

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