Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Cosmologically Unique IDs

jasonfantl.com

Post reply on HN
Print view View original

141–150 of 159 posts

Re: Cosmologically Unique IDs

#141

Post by kmoser »

wavemode wrote: post #115
kmoser wrote: post #101

> 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 inevita…

> 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.

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.

Re: Cosmologically Unique IDs

#142

Post by kmoser »

Dylan16807 wrote: post #121
kmoser wrote: post #108

Earlier quoted context omitted.

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.

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"].

Re: Cosmologically Unique IDs

#143

Post by chamomeal »

exfalso wrote: post #128
lisper wrote: post #7

This analysis is not quite fair. It takes into account locality (i.e. the speed of light) when designing UUID schemes but not when computing the odds of a collision. Collisions only matter if the colliding UUIDs actually come into causal contact with each other after being generated. So just as you have to take locality into account when designing UUID trees, you also have to take it into account when computing the o…

There's a fun hypothesis I've read about somewhere, goes something like this: As the universe expands the gap between galaxies widens until they start "disappearing" as no information can travel anymore between them. Therefore, if we assume that intelligent lifeforms exist out there, it is likely that these will slowly converge to the place in the universe with the highest mass density for survival. IIRC we even know…

I think I sense a strange Battle Royale type game…

Re: Cosmologically Unique IDs

#145

Post by adityaathalye »

Octoth0rpe wrote: post #6
adityaathalye wrote: post #2

Just past page 281 of Becky Chambers's delightful "the galaxy, and the ground within" . Received Message Encryption: 0 From: GC Transit Authority --- Gora System (path: 487-45411-479-4) To: Ooli Oht Ouloo (path: 5787-598-66) Subject: URGENT UPDATE Man I love the series. Looks like this multispecies universe has centrally-agreed-upon path addressing system.

From this book in particular, I love the scene with everyone sitting around talking about how horrifying the concept of cheese is. The rest of the quartet is wonderful, with the second book (A Closed and Common Orbit) being the MVP IMO.

Before replying, I waited for a moment to re-read those couple of pages once more. Cracked up again... Oh the utter incomprehension. And I can relate to the bit about eating the enzyme so that one can eat the cheese without getting sick. Cheese is horrifyingly great.

Re: Cosmologically Unique IDs

#146

Post by exfalso »

wat10000 wrote: post #140
zimzam wrote: post #136

Earlier quoted context omitted.

I think I missed something: how do galaxies getting further away (divergence) imply that intelligent species will converge anywhere? It isn’t like one galaxy getting out of range of another on the other side of the universe is going to affect things in a meaningful way… A galaxy has enough resources to be self-reliant, there’s no need for a species to escape one that is getting too far away from another one.

You'll run out of resources eventually. Moving to the place with the most mass gives you the most time before you run out.

Yes that's the idea. The expansion simply means that the window of migration will close. Once it's closed, your galaxy is cut off and will run out of fuel sooner than the high-density area.

Re: Cosmologically Unique IDs

#147

Post by antonvs »

Drakim wrote: post #118
wavemode wrote: post #115

Earlier quoted context omitted.

> 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?

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.

Re: Cosmologically Unique IDs

#148

Post by paulddraper »

zimzam wrote: post #136
exfalso wrote: post #128

Earlier quoted context omitted.

There's a fun hypothesis I've read about somewhere, goes something like this: As the universe expands the gap between galaxies widens until they start "disappearing" as no information can travel anymore between them. Therefore, if we assume that intelligent lifeforms exist out there, it is likely that these will slowly converge to the place in the universe with the highest mass density for survival. IIRC we even know…

I think I missed something: how do galaxies getting further away (divergence) imply that intelligent species will converge anywhere? It isn’t like one galaxy getting out of range of another on the other side of the universe is going to affect things in a meaningful way… A galaxy has enough resources to be self-reliant, there’s no need for a species to escape one that is getting too far away from another one.

Well eventually there are no galaxies just a bunch of cosmic rays. Some clusters of matter will last longer.

I think for this to work, either life would have to plentiful near the end, or you’d need FTL travel.

Re: Cosmologically Unique IDs

#149

Post by antonvs »

rbanffy wrote: post #30
antonvs wrote: post #25

Earlier quoted context omitted.

We don't "make" universes in the MWI. The universal wavefunction evolves to include all reachable quantum states. It's deterministic, because it encompasses all allowed possibilities.

Humpf… You just had to collapse my wave function here…

That's Copenhagen, not MWI! :P

Re: Cosmologically Unique IDs

#150

Post by zamalek »

jobigoud wrote: post #138
exfalso wrote: post #128

Earlier quoted context omitted.

There's a fun hypothesis I've read about somewhere, goes something like this: As the universe expands the gap between galaxies widens until they start "disappearing" as no information can travel anymore between them. Therefore, if we assume that intelligent lifeforms exist out there, it is likely that these will slowly converge to the place in the universe with the highest mass density for survival. IIRC we even know…

It is counter intuitive but information can still travel between places that are so distant that expansion between them is faster than the speed of light. It's just extremely slow (so I still vote for going to the party at the highest density place). We do see light from galaxies that are receding away from us faster than c. At first the photons going in our direction are moving away from us but as the universe expan…

That's not exactly it. Light gets redshifted instead of slowing down, because light will be measured to be the same speed in all frames of reference. So even though we can't actually observe it yet, light traveling towards us still moves at c.

It's a different story entirely for matter. Causal and reachable are two different things.

Regardless, such extreme redshifting would make communication virtually impossible - but maybe the folks at Blargon 5 have that figured out.

Post reply on HN