I Spy

So many things in our wee world
Are actually not on show ,
And when we think a little bit
There's not much we really know;
Of a trillion billion galaxies
We can see but five
And to see the last you have to squint
And tilt your head to the side.
We still don't know what gravity's for
Though it's a fundamental power
And we can never see it
Though it keeps on Earth for hours.
We completely change each seven years,
Our cells completely renewed ,
So when we look in the mirror our true selves
Are invisible too.
Can't see dark matter, electricity,
Or sometimes even light,
Anything we look at too much
Disappears into Earth's might.
We don't even know why we're here
In this unusual lifelong chore
So the wise say it's to help others, but then
Well, what are the Others for?