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Comment by jose_mr | Hacker News Reader

But when exactly did it stop being the same car?

An easy way to say would be when it's still 50% original, but I think an interesting way to look at it is that it becomes a whole new thing after every major change.

First it's his new car, then it becomes his new car with new tires, and then his car with new windshield wipers, and finally his old car with all new parts and some old ones. None of them are the same car.

I think in cases where it' a major rebuild, like turning a WW2 Minesweeper first into a ferry, and finally into Cousteau's research ship Calypso this outlook is more obvious. Are these ships all the same despite getting almost a full refit at each stage? I would say none of them are the same ship, but completely separate "things" with some old and some new parts.

When you changed the VIN :)

And what if you took the other parts and built a separate car from them?

You've just answered your own question, haven't you? If it's a separate car then it can't be the original by definition.

If you completely disassemble a car then reassemble it, is it the same car?

What if you disassemble all of the car except the wheels and reassemble it but with new wheels?

How about if you also exclude the seats too.

At what point does the answer change? That’s the whole point of the ship of theseus.

Fun fact, on average most (not all though) of the cells in your body are brand new after 7 years. When do you stop being you and take a new name?

At least we're not going around saying "diggan says the only original part of his person is likely the body/chassi"

This kind of thing is repeated often, but I don't think it's true. For one thing, how would tattoos last so long then?

More relevantly, I don't think neurons are replaced. There must be some material churn in the atoms and molecules that make them up, but even then different for different molecules - e.g. I don't know how much of our DNA molecules get replaced over a lifespan from the repair or other mechanisms.

The "on average" is doing an awful lot of work. Some cells are never replaced, some organs are replaced every few years or even partially over decades, some organs are replaced every few months (one of which is the skin).

Tattoos however, IIUC, sort of "float" between cells, and as those cells are replaced one-by-one the ink is kept in place by the surrounding cells that are still there.

I suppose tattoo ink isn’t all in the cells. I’d guess the ink within intracellular spaces is never removed by the body (or very, very slowly).

> how would tattoos last so long

Answered by Kurzgesagt: https://www.youtube.com/watch?v=nGggU-Cxhv0

It hasn’t, the law decided a car is it’s shell and that’s it.

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