Let's get this straight right away: I don't really understand general relativity.
I've read a lot of explanations about it. Briefly I'll feel like I grasp what general relativity is all about in a non-mathematical sense.
A few days later, or even sooner, that understanding has slipped away and I'm basically as clueless as I was before. Which is strange, because usually I can conceptually grasp scientific truths much more fully.
So there's something weird for me about general relativity. Which probably is best explained by the fact that almost everybody feels the same way.
Spend two minutes watching this video of Neil deGrasse Tyson trying to explain gravity, which is the centerpiece of Einstein's theory of general relativity. Even Tyson starts off his explanation in a quizzical fashion.
Now, while Tyson says that Einstein said the following, actually it was theoretical physicist John Archibald Wheeler.
Spacetime tells matter how to move;
Matter tells spacetime how to curve.
It doesn't matter who was the source of this quote. As Tyson's interviewer says, that's poetic. It's my favorite explanation of general relativity, because I can grasp these two sentences even as I don't understand them.
A recent special issue of Scientific American is devoted to "100 Years of General Relativity." Here's a passage from one of the articles in the issue that says much the same thing.
Einstein's goal as he pursued his general theory of relativity was to find the mathematical equations describing two interwoven processes: how a gravitational field acts on matter, telling it how to move, and how matter generates gravitational fields in spacetime, telling spacetime how to curve.
So even though I don't begin to grasp the mathematics of general relativity, I have an, um, general conceptual feeling for it -- at least as it pertains to gravity.
It's that word, "interwoven," that seems key here. We're used to hierarchies, since human life and culture is full of them. This rules that. This causes that. This is above that.
Yet nature rarely, if ever, works that way.
Like gravity in general relativity, this causes that and that causes this. Interwoven loops abound. Nature is much more of a circle than a straight line. Everything is interconnected, even though we humans do our best to break things apart and view them as discrete entities.
This is one reason why the concept of God no longer appeals to me. Like most religiously-minded people, I used to look upon God as The Big Man Upstairs, the cosmos' CEO who occupies the coolest office on the top floor.
But this doesn't mesh with either common sense or scientific understanding.
For example, if God created the cosmos and now rules over it, who or what created God? If the supposed answer is no one, because God has always existed, then why can't the cosmos always have existed without a God?
An interwoven cosmos, or universe, seems considerably more likely than a hierarchical one. I've talked about this sort of thing before in posts such as:
I'm obviously not capable of capturing the essence of the cosmos in a few pithy sentences, as Wheeler did with gravity. About the best I can do is...
The universe causes me to do things; the things I do change the universe.