Riddle by Matt D

I am running, always running, never tired

I never go anywhere, but I’m always running

Sometimes I am empty, sometimes I am full

I am always cold, yet they are comfortable in their skin

I watch them come, I watch them go

I hear their laughter and their prayers

The center of their universe, I nourish them as if I was their mother

Whose stomach can be empty but never hungry?

I am silent, but open to anyone

No one can live without me.