What is infinity

 Long ago, when I heard about infinity first in school, I asked mom what is infinity - the symbol that looks something similar to a horizontal 8. She said it is something very large. The homework question in the book was - what is infinity + 1. Everyone (including that textbook) said infinity.  My first thought on hearing this was "what non-sense". 

A google search gives conflicting answers. Something very large is just not satisfactory enough as an answer. I will attempt to answer my own question - what is infinity ? 

To understand abstract concepts such as infinity, we must use logic as well as feel what it means. We often forget that a highly intellectual mind cannot absorb concepts correctly. Luckily, two tools can help us here - imagination and visualization. Visualization is not the same as hallucination. Visualization is a conscious process that involves effort.  

You might have come across this as a visualization exercise elsewhere, but it is very useful to understand what we will discuss. I came across this some time back in a book called the "gita" that is famous for the dialogue between Krishna and Arjuna. 

 From earth, the sun appears as a tiny circle. Close your eyes, imagine the sun to be a tiny circle. Now, without opening the eyes keep expanding the size of the sun. Can you completely fill up all the empty space ? 

You will notice that there are parts in the field of your closed eyes that will keep expanding, and there is no end. That is infinity.