The essence of it is captured in the first verse of “Dem Bones“:
Toe bone connected to the foot bone
Foot bone connected to the heel bone
Heel bone connected to the ankle bone
Ankle bone connected to the shin bone
Shin bone connected to the knee bone
Knee bone connected to the thigh bone
Thigh bone connected to the hip bone
Hip bone connected to the back bone
Back bone connected to the shoulder bone
Shoulder bone connected to the neck bone
Neck bone connected to the head bone …
The final line gets to the bottom of it (if you are a deist or theist):
… Now hear the word of the Lord.
But belief in the connectedness of everything in the universe doesn’t depend on one’s cosmological views. In fact, a strict materialist who holds that the universe “just is” will be obliged to believe in universal connectedness because everything is merely physical (or electromagnetic), and one thing touches other things, which touch other things, ad infinitum. (The “touching” may be done by light.)
Connectedness isn’t necessarily causality; it can be mere observation. Though observation — which involves the electromagnetic spectrum — is thought to be causal with respect to sub-atomic particles. As I put it here:
There’s no question that [a] particle exists independently of observation (knowledge of the particle’s existence), but its specific characteristic (quantum state) is determined by the act of observation. Does this mean that existence of a specific kind depends on knowledge? No. It means that observation determines the state of the particle, which can then be known.
I should have been clear about the meaning of “determine”, as used above. In my view it isn’t that observation causes the quantum state that is observed. Rather, observation measures (determines) the quantum state at the instant of measurement. Here’s an illustration of what I mean:
A die is rolled. Its “quantum state” is determined (measured) when it stops rolling and is readily observed. But the quantum state isn’t caused by the act of observation. In fact, the quantum state can be observed (determined, measured) — but not caused — at any point while the die is rolling by viewing it, sufficiently magnified, with the aid of a high-speed camera.
Connectedness can also involve causality, of course. The difficult problem — addressed at the two links in the opening paragraph — is sorting out causal relationships given so much connectedness. Another term for the problem is “causal density“, which leads to spurious findings:
When there are many factors that have an impact on a system, statistical analysis yields unreliable results. Computer simulations give you exquisitely precise unreliable results. Those who run such simulations and call what they do “science” are deceiving themselves.
Is it any wonder that “scientists” tell us that one thing or another is bad for us, only to tell us at a later date that it isn’t bad for us and may even be good for us? This is a widely noted phenomenon (though insufficiently documented). But its implications for believing in, say, anthropogenic global warming seem to be widely ignored — most unfortunately.