The basic truth about space that Albert Einstein taught us is that it is not a state of ‘nothingness’. Instead, it is a bendable, stretchable medium that we occupy, much like water is for fish.
Each form of energy tells the universe how to expand in its own way.
This is much like how you can inflate a balloon with air, water or sand, and in each case it will have a characteristic look and feel.
Since dark energy dominates the energy budget of the universe, it also dictates the rate at which space expands.
We can reverse-engineer this fact to estimate how much dark energy is present in any volume
of space, by considering the size and age of the universe.
Add too much positive energy and the cosmos would expand too fast.
Galaxies would fly away from us faster than light, so that only the regions of the universe nearest to us will be visible.
Effectively, this “observable universe” would appear to shrink.
Add too much negative energy and the universe would actually shrink to a tiny point.
The greater this negative energy, the sooner this event.
Everyone can agree that the universe is larger than India and older than the Indus Valley Civilisation.
These facts alone restrict the density of dark energy to the caloric content of a pinch of sugar in a cubic metre.
In reality, the universe is wider than billions of lightyears and older than 10 billion years, so the dark energy is actually as dilute as one sugar crystal in a cubic kilometre.
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