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Comment by trimethylpurine | Hacker News Reader

Is it creepy when you throw a ball up and it magically falls back into your hand? It moves back into your hand specifically because time on the ground is moving slower. The ball, like everything else, moves towards the slower moving timeline (a lesser inertial state). That's actually not creepy at all. It would be creepy if the ball went the other way for no apparent reason like a poltergeist.

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The fact that there exist consistent structured phenomena, instead of everything being pure noise, is actually creepy.

Yes, it is creepy. And now that you mention it, Fermat's principle (the principle of least time) is creepy too. Why is physics so weird? It's like everything is choosing things all the time! And it gets worse with quantum effects, since apparently there is hidden computational machinery that happily computes superposition of essentially infinite wave forms - and that scales exponentially - without slow-down or effort.

The comprehensibility of the world is an illusion. Humans don't explain, we describe, and we give ourselves credit for undoing the confusion of some superficial effects that turned out to have a simple description. The mystery and awe of what the universe is doing and how remains poignant.

Sure, that's true. My comment is expanding on your claim that you accept gravity as a simple force in contrast to the mystery of creepy spacetime concepts of the universe. You accept gravity which is the same force as time dilation. It sounds like if I change the name it's less creepy for you.

Upon further reflection the idea of inanimate objects "wanting things" is what I find most creepy. It's enough to make a person consider monadism seriously. The notion of inanimate objects modifying spacetime just by existing is secondarily creepy - it's destructive to the notion of "introduce a coordinate system" because now the phenomena you're describing messes with the coordinate system you picked to describe it! And yes renaming things does help. I don't like thunderstorms, I find them legitimately scary, and understanding their physics didn't help but calling them "unicorn farts" did.

Its not that the ball wants things. Its own gravity and its behavior toward the gravity of other objects is just a result of what it is: a cluster of protons and neutrons and electrons in a given radius.

I'm being a bit cheeky; I have a physics degree. And I love Feynman's take on magnetism if you look up that video. He makes a strong distinction between "why" and "how" noting that physics doesn't really know why. It's a needed dose of humility for those who need to be reminded that humans are NOT the masters of the universe, and our understanding of physics has profound limits (and is poorly distributed throughout the human population). Why is the principle of least action a thing? Why does entropy only ever increase? What is actually doing all that computation behind quantum effects? No-one knows.

About Hamilton's stationary action (which you refer to as 'least action').

I have created an educational resource in which I address the question of how it comes about that F=ma can be recovered from Hamilton's stationary action. This resource gives a two-pronged approach: the concepts are illustrated with interactive diagrams, and parallel to that a full presentation of the mathematics.

I start with a discussion of the nature of Calculus of Variations. I use the problem of a soap film stretching between two parallel concentric rings as motivating example. This leads to a derivation of the Euler-Lagrange equation.

Then I move to the Catenary problem. Interestingly, with the catenary problem both approaches are possible; you can solve for the catenary with differential calculus (as Leibniz did) or you can apply calculus of variations. What that means is that the catenary problem can serve as a Rosetta stone, offering a bridge between differential calculus and calculus of variations.

http://cleonis.nl/physics/phys256/calculus_variations.php

The discussion specifically for Hamilton's stationary action is in an article of its own:

http://cleonis.nl/physics/phys256/energy_position_equation.p...

> it's destructive to the notion of "introduce a coordinate system" because now the phenomena you're describing messes with the coordinate system you picked to describe it!

That's the whole point of GR - coordinate systems aren't physically meaningful.

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