Where did I go wrong? Why is the night sky black?

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Olbers' Paradox

The Orion Nebula

One of the key definitions of a universe is that it is the only reality permissible for matter to exist in. Theories of Alternate Universes do exist, but they are just the same as various infinities in mathematics. In any mathematical (or) physical concept finite objects are used, and infinity is taken to something insurmountable and uniform.

Therefore by definition the Universe is considered to be infinite. 

This thought was thrown around for millennia both in astronomical and philosophical circles.

However random the star arrangement looks like in one bubble, the galaxies are depicted to be uniform. However random galactic structures are scattered they are symmetrically ordered in the cosmic web creating the Observable Universe.

From this point of view Heinrich Olbers wondered about the sky. In an infinite uniform universe there must be a symmetric arrangement of matter. So, the light coming from each star must reach Earth. Equally spaced stars with respect to the Earth must be seen at the same time, because the speed of light is fixed. The nearby stars are dimmer, but the distant ones are brighter.

Amounting all the light received from every single star he realised that the night sky should be brighter than the sun itself. This is a massive contradiction from the darkness of the night sky. This principle is known as Olbers' Paradox.

What is the reality then? One of our assumptions must be incorrect.

Scientists have proposed multiple solutions viz. Finite Age, Expansion and so on.

Finite Age of the Universe

One of the most strong evidences of the Finite Age (or) the Big Bang Theory is the presence of Cosmic Microwave Background Radiation (CMBR) which is the collective light recorded when the universe is in its formative stages. Calculations produces mark the event of the Big Bang at around 13.8 billion years ago.

If the universe had a beginning it isn't necessarily uniform. Therefore it is used as a solution to the Olbers' Paradox.

Since the universe was born and like anything known will die, researchers proposed many pathways for the future. Read Universe's Doom: Three Theories for more.

Expansion of the Universe

Apart from regular matter which makes us 5% of the observable matter an inert type of a new substance exists called Dark Matter detected only from its gravitational influence. This makes up 40% of the universe. The rest is an unknown kind of energy named Dark Energy. We are unable to produce this energy from existing sources. It is in kind known as the energy of pure empty space.

It is hypothesised that the expansion of the universe is accelerating due to this energy. We have no scientific proof of its intercoversion to the types of energies known to us.

Currently the math shows us that its quantity is the exact same as gravity. If any one of them loses the grip the universe may spiral into unforseen timelines.

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Whatever the universe is it is still an infinity to humans much like math. Examining the metaphysical nature of reality is doable but needs serious advancement in science, and probably philosophy as well. 

Till then, you may read How Far Did We Go? for other ideas thrown around in astronomical circles. You also can read the most trending article on this blog Extraterrestrial Life if you believe aliens are real. If you know about the recent Total Solar Eclipse, read The 2026 Eclipse: Update.

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Aditya VN Kadiyala