I just published "Gravity", first part of a series of 4 articles about Bitcoin's PoW, its properties and its efficiency.
TL/DR (full Galilei mode): https://translate.google.co.uk/#auto/en/Eppur%20diventa%20pi%C3%B9%20efficiente
I do quite like 'digital gravity' as an analogy.
However, don't you think 'digital inertia' would be more accurate (and would also tie in with the quote at the top of the article, the first law)?
(We'll ignore for a moment einstein's revelation about the equivalence principle :) )
In the past, I've tended to think about it as 'solidity'.
Another word I like to describe what PoW is doing is 'reification'.
(For third-party readers; the above is just some near-random thoughts; Laurent's article itself is very interesting)
The funny thing is that when I started to work on this model, I knew the 2 properties of Bitcoin's PoW but I didn't think to this analogy. After several iterations I came up with the BDS model and at some point I noticed that it had a lot of similarities with a momentum (what Newton called the res viva). That led me to the first law and I started to wonder what would be the "forces" existing in the "bitcoin universe" and able to modify the state of an utxo.
At this point, I realized that there were 2 types of forces (txs spending the utxos and PoW) and that these 2 "forces" had an important difference: a tx is local while PoW is global. And this is how I came to the analogy between PoW and gravity.
I tend to be cautious with metaphors and analogies so I'm not sure how far we can use this one but it's certainly correct to say that PoW acts like a homogeneous field. And this property should be reflected in metrics measuring PoW efficiency.
OK ... Isn't what we're talking about here fundamentally the resistance of a utxo to changes of state?
I didn't quite understand why inertia isn't a better analogy. External forces would be whatever is trying to change the state.
I think the biggest problem with physical analogies is the lack of an analog to one-way trapdoor functions, which are so fundamental to modern crypto.
Inertia is definitely a part of the analogy/intuition. If an utxo was a moving particle, rewriting its history would require that you apply a "force" (PoW) driving its "speed" to 0.
Another metaphor would be to imagine an utxo as a particle trapped in a potential well. Rewriting its history would require that you apply enough energy to "push" it from level Eu to level E0 (see my crappy schema ;)
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!