Universe: how big can it possibly be?
People struggle to realize how big the universe. The reason is that everything here on Earth, and even the Earth itself, is very small while associated to the enormous measure of the universe.
Hence let's think about it a dissimilar way, by using something we see and interrelate with every day like light.
However we imagine light to be instant, photons of light actually take time to travel from one side of the room to the other. For instance, a photon of light leaving the Sun has travelled about 10 million kilometers comparable to travelling around the Earth 250 times.
Light that leaves our second nearest star, Proxima Centauri, takes just over four years to reach Earth and consequently we can define it as four light years away.
Therefore, if we look at Proxima Centauri, we would not be seeing the star as it is right now, but how it 'was' 4 years ago!
We see everything in the universe as they were in the past, whether they're on the other side of the galaxy or on the other side of the room.
To take this thought advance, the nearest large galaxy for us is Andromeda which is so big and close that you can see it in the night sky with your bare eyes.
Certainly we are seeing is 1,000's of billions of stars in a conformation equally to our Milky Way. Though, entirely those stars are about 2.5 million light years away, which means we are seeing Andromeda as it was 2.5 million years ago.
The whole universe is overwhelmed with galaxies just alike the Milky Way and Andromeda, as well as using our utmost powerful telescopes we can see light from galaxies that have taken more than 13 billion years to reach us!
Meanwhile a photon of light left one of these galaxies, life flashed into reality and progressed. Dinosaurs ruled the Earth. Humans seemed, advanced tools, art, science and technology, made the Hubble Space Telescope, placed it into orbit and lastly stopped that lowly photon on its 13 billion year excursion!
The universe is about 13.8 billion years old, hence any light we see has to have been travelling for 13.8 billion years or less and we call this the 'observable universe'.
However, the detachment to the edge of the observable universe is about 46 billion light years since the universe is escalating every time.
Whereas that Photon has been travelling over space, the universe has extended. We have moved away from the point where the light was released, and it has moved away from us as well.
Yet, the light might have only travelled for 13.8 billion years, the detachment from us to the point it came from is, at present, 46 billion light years!
Accordingly how big is our Universe? Fine we don't actually know, and then it is gigantic. So gigantic that even light hasn't had time to cross it in almost 14 billion years! Plus it is still becoming bigger all of the time.