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Comment by hprotagonist | Hacker News Reader

“a model that completely describes the system is about as useful as a map at 1:1 scale” — a quote from my advisor in grad school.

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One of my profs was fond of the saying "with enough money, anyone can design a bridge that will stand up. Only an engineer can design a bridge that will just stay up".

I think the same is true of simulation and modeling: it requires a domain expert to include the useful stuff in your model while skirting or abstracting away the extraneous bits.

The second year civil engineers at my university had a project where they had to design a bridge that could support 2 people, but would break under the weight of 3, to teach that exact lesson.

People vary in weight by more than 50%. I don't see that the spec is possible.

The three people are known to you in advance (it’s your group). It was common to game this a little by saving the biggest person as the third one that had to break the bridge.

Woosh..

That's the point!

To quote Ulam

Knowing what is big and what is small is more important than being able to solve partial differential equations.

Well a 1:1 map is super useful. This is another use-case of VR. You can visit appartments or wander the World in Google Earth. I also used this recently for renovation work, my wife created the model of how the studio would look in the future, I imported it in Unity and we visited it in VR before starting the groundwork.

The trick is that the map itself is 1:1 but your moving around in the map is not constrained by the same limitations as in the real world.

Arguably the trick is it's not a physical map, which isn't a detail that would have needed to be specified when the saying first came into use.

Even a physical 1:1 map can have utility, since it ostensibly has more portability. That is, as long as it's a map and not a 3d model. Even then, though, a 3d model can have uses, such as tailoring when the customer cannot physically be there. That is, as long as it's a 3d model and not a clone. Then again, a clone has their uses...

Whoever came up with that saying just wasn't very imaginative.

Physical 1:1 maps are still useful. They have numerous military applications, and in general allow you to become familiar with an area without having to physically be in that area, if being there or getting there is difficult for any reason.

Do you have any example of a Physical 1:1 map ? I truly believed that such a thing is (physically) impossible.

Maybe Exercise Tiger[0] w which was a rehearsal for the D-Day Normandy landings, where they created a replica of the beach landscape that would be encountered. Or there's Sindh Kalay[1] which is an Afghan village created in Norfolk, UK.

0. https://en.wikipedia.org/wiki/Exercise_Tiger

1. https://www.independent.co.uk/news/uk/this-britain/welcome-t...

I would imagine soldiers train for urban combat in actual houses or whatever landscape they need.

I would also say, that a "complete model" is not a model anymore, but a copy of the thing itself.

A model is always an incomplete simulation of something, keeping some relevant aspect but discarding less relevant ones while remaining useful.

But that's completely untrue when the implementation does not match.

Suppose one day we manage to create brain uploads. They're not brains but would have additional or different capabilities despite being 1:1 maps - being possible to restore the original from them. This is because they could be ran on different hardware.

Likewise, consider lossless compression. It is an accurate model of the data in shorter form.

This is a good example where overloading the meaning of a word decreases its usefulness. There might be a better word for "an effective copy of the same underlying thing but with a different substrate/implementation"; perhaps "homomorphisms", perhaps make up a new word.

We have the word already in art, it's a sketch or diorama - something known to not be an accurate representation.

Or just call it a simplification instead of a model. It's a subset of all models. Alternatively, an explanation of it captures all the detail.

Model is combined with another interesting word, essence as in essential, which is what it's supposed to capture, for given purpose.

If the purpose of the model is explanatory power and accuracy, these two do not necessarily form a one dimensional trade-off.

I think it would be easier to just accept that "model" already means "simplified description" (source https://en.oxforddictionaries.com/definition/model) and use another word to refer to the superset you're mentioning.

That's because language is mostly useful for communication between people, here and now. Treating a natural language as a construct to refine until it reaches a mathematical beauty where nice and short words mean what they "should mean" often causes so much grief and wasted energy.

Implementation is an aspect though, possibly the non-relevant one for your usecase.

A braindump would keep some aspects, like the neuron configuration etc, but discard others, like vascular properties, exact positional information of neurons etc. You could even go as deep as exact positioning of all contained atoms in the original brain.

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