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Comment by kmoser | Hacker News Reader

> A more reasonable upper limit might be to assume that every atom in the observable universe will get one ID (we assume atoms won’t be assigned multiple IDs throughout time, which is a concession). There are an estimated atoms in the universe. Using the same equation as above, we find that we need 532 bits to avoid (probabilistically) a collision up to that point.

This doesn't take into account that you will inevitably want to assign unique IDs to various groups of atoms (e.g. this microchip, that car, etc.). And don't even get me started on assigning unique IDs to each subatomic particle.

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> unique IDs to each subatomic particle

You only need one ID for each type of particle. Since the laws of physics dictate that the particles themselves are indistinguishable from each other.

Don't they have different x,y,z positions?

That's unclear https://en.wikipedia.org/wiki/One-electron_universe

Yes, but the issue is that they don't have identity. The idea of assigning unique identifiers to particles is doomed because, basically, "there are no particles, there are only fields" (https://arxiv.org/abs/1204.4616).

Particles are how quantized fields present themselves when probed by localized interactions. In general, they're also observer-dependent.

The idea of assigning an "ID" to an object reflects a macro-level notion of re-identifiable objects persisting through time. But at the quantum level, that kind of classical individuality - object identity - doesn't exist.

Just because a given particle is indistinguishable from another of the same type doesn't mean they are the same actual thing. If you are assigning IDs to each item in the universe for accounting/inventory purposes, you'll still want a separate ID for each particle.

Wouldn't the minimum discrete unit be something that is capable of recording the ID? Or, if not, space somewhere would need to identify that that atom has this ID, which would take at least as much space.

In other words, the act of 'assignment' presupposes some mechanism of assignment, and at a certain level of granularity the information needed for that mechanism to function is greater than the information the system can store.

It would be like assigning each byte in a stick of ram a 32 bit random access ID, and trying to store the assignments in the same memory space. Memory addressing only works because we assume a linear, unchanging order.

If we're talking reality, sure. But you can also consider it a Gedankenexperiment.

> This doesn't take into account that you will inevitably want to assign unique IDs to various groups of atoms (e.g. this microchip, that car, etc.).

Sure it does. Those are not going to add up to a single extra bit.

Even every possible permutation of every single subatomic element in the universe? Even if we just consider atoms, at 10^80 atoms in the entire universe, there are (10^80)! possible permutations, which is many, many, many orders of magnitude larger.

And this isn't even counting sets that include multiples of the same item; once you get into that territory, there really is no upper bound.

New atoms form all the time, either through fusion or fission. The latter is happening right now all around you- either from potassium in plants breaking down, to radon gas that sept up from the ground, to carbon itself. All of these have unstable isotopes with half lives short enough to have at least a little activity near you.

Given that constant change to the available combinations of sets, it would seem that a truly capable system would need to be practically infinite, no?

No, not every permutation. An atom gets to be in one larger object (recursively).

Definitely no multiples. What would that even mean, also you would need unbounded space for multiples of just two atoms.

> Definitely no multiples. What would that even mean, also you would need unbounded space for multiples of just two atoms.

I have a list and I want to assign a unique ID to each list item. Each list item itself contains one or more items:

  1. My umbrella [ID "a"] and my sunglasses [ID "b"]
  2. My umbrella ["a"], my sunglasses ["b"], and my umbrella ["a"]

List item 2 contains two references to my umbrella [ID "a"].

So in a physical sense of identifying things that's nonsense. And again if you allow that then lists of just one or two atoms can take up infinite storage space. That's a super obvious reject. It makes no sense to even try to accommodate it in an ID system.

>And don't even get me started on assigning unique IDs to each subatomic particle.

If a neutrino oscillates between flavors, does it get 3 IDs? Or does it get a new ID with each oscillation?

Thankfully, we only need one electron ID at all.

For the uninitiated: https://en.wikipedia.org/wiki/One-electron_universe

So UUIDv∞ will be at least 536 bit long?

And with group IDs, timestamp, etc. - 1024 bit long?

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