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

91–100 of 159 posts

Re: Cosmologically Unique IDs

#91

Post by jquery »

UltraSane wrote: post #76
u1hcw9nx wrote: post #35

Earlier quoted context omitted.

If you go far beyond nanoseconds, energy becomes a limiting factor. You can only achieve ultra-fast processing if you dedicate vast amounts of matter to heat dissipation and energy generation. Think on a galactic scale: you cannot have even have molecular reaction speeds occurring at femtosecond or attosecond speeds constantly and everywhere without overheating everything.

If you have a black hole as an infinite heat sink this helps a great deal.

Black holes have a maximum growth rate

Re: Cosmologically Unique IDs

#92

Post by linuxhansl »

Heh. I once had to make an argument that 256 bit randomly assigned identifiers are good enough without explicit collision checking. People wanted me to add complex and expensive collision checks.

My argument was the 2^256 actually approaches the number of atom in the observable universe (within 1 to 3 orders of magnitude), and that collisions are so unlikely that we'll have millions of datacenter meltdowns first (all assuming we have a good source of random numbers, of course). In the end I convinced everybody that even 128 bits are good enough, without any collision checking required.

I thought my arguments was clever, but this is so much better. :)

Re: Cosmologically Unique IDs

#93

Post by itishappy »

frikit wrote: post #32
Sharlin wrote: post #23

Earlier quoted context omitted.

If protons decay. There isn't really any reason to believe they're not stable.

Protons can decay because the distinction between matter and energy isn't permanent. Two quarks inside the proton interact via a massive messenger particle. This exchange flips their identity, turning the proton into a positron and a neutral pion. The pion then immediately converts into gamma rays. Proton decayed!

This destroys a baryon, an operation which is prohibited by the standard model.

Re: Cosmologically Unique IDs

#94

Post by itishappy »

lisper wrote: post #27
Etheryte wrote: post #22

Earlier quoted context omitted.

That's such an odd way to use units. Why would you do 10^56 * 10^-9 seconds?

This was my thought. Nanoseconds are an eternity. You want to be using Planck units for your worst-case analysis.

Planck units are a mathematical convenience, not a physical limit. For instance, the Planck mass is on the order of an eyelash or grain of sand.

Re: Cosmologically Unique IDs

#95

Post by lisper »

itishappy wrote: post #94
lisper wrote: post #27

Earlier quoted context omitted.

This was my thought. Nanoseconds are an eternity. You want to be using Planck units for your worst-case analysis.

Planck units are a mathematical convenience, not a physical limit. For instance, the Planck mass is on the order of an eyelash or grain of sand.

Planck units are physical limits. The Planck mass is the limit of the mass of an elementary particle before it would form a black hole.

Re: Cosmologically Unique IDs

#96

Post by itishappy »

lisper wrote: post #95
itishappy wrote: post #94

Earlier quoted context omitted.

Planck units are a mathematical convenience, not a physical limit. For instance, the Planck mass is on the order of an eyelash or grain of sand.

Planck units are physical limits. The Planck mass is the limit of the mass of an elementary particle before it would form a black hole.

"Plank units are not physical limits on reality itself" is what I should have said. We can obviously have larger or smaller masses.

The plank time is a limit on a measurement process, not the smallest unit of time.

Re: Cosmologically Unique IDs

#97

Post by lisper »

itishappy wrote: post #96
lisper wrote: post #95

Earlier quoted context omitted.

Planck units are physical limits. The Planck mass is the limit of the mass of an elementary particle before it would form a black hole.

"Plank units are not physical limits on reality itself" is what I should have said. We can obviously have larger or smaller masses. The plank time is a limit on a measurement process, not the smallest unit of time.

> Plank units are not physical limits on reality itself

We don't actually know that. They might be. Planck units are what happens when GR meets QM and we just don't know yet what happens there.

But as a heuristic, they probably put pretty good bounds on what we can reasonably expect to be technologically achievable before humans go extinct.

Re: Cosmologically Unique IDs

#98

Post by kelseyfrog »

The Dewey section and Elias omega encoding was fun, but it reminded me of Project Xanadu's tumblers[1] - a variable length dotted notion where each segment is unbounded.

Tumblers are modeled using transfinite numbers which makes me wonder: what are the similarities and differences between transfinite numbers and Elias omega encoding? I'm not well versed in either, so I expect it's either a question from ignorance or I may have a lot to learn. :)

1. https://www.artandpopularculture.com/Tumbler_%28Project_Xana...

Re: Cosmologically Unique IDs

#99

Post by da_chicken »

linuxhansl wrote: post #92

Heh. I once had to make an argument that 256 bit randomly assigned identifiers are good enough without explicit collision checking. People wanted me to add complex and expensive collision checks. My argument was the 2^256 actually approaches the number of atom in the observable universe (within 1 to 3 orders of magnitude), and that collisions are so unlikely that we'll have millions of datacenter meltdowns first (all…

Nah, it's much easier than that.

The total amount of computer data across all of humanity is less that 1 yottabyte. We're expected to reach 1 yottabyte within the next decade, and will probably do so before 2030. That's all data, everywhere, including nation-states.

The birthday paradox says that you'll reach a 50% chance of at least one collision (as a conservative first order approximation) at the square root of the domain size. sqrt(2^256) is 2^128.

Now, a 256 bit identifier takes up 32 bytes of storage. 2^128 * 32 bytes = 10^16 yottabytes. That's 10 quadrillion yottabytes just to store the keys. And it's even odds whether you'll have a collision or not.

And if the 50% number scares them, well, you'll have a 1% chance of a collision at around... 2^128 * 0.1. Yeah, so you don't reach a 1% over the whole life of the system until you get to a quadrillion yottabytes.

Because you're never getting anywhere near the square root of the size, the chances of any collision occurring are flatly astronomical.

Re: Cosmologically Unique IDs

#100

Post by adityaathalye »

pavel_lishin wrote: post #13
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.

You should check out Vernor Vinge's A Fire Upon The Deep for more fun examples of how intra-galactic communication would be labeled, with routes & such.

In fact, it is right here in my stack of to-reads! Picking it up now due to your recommendation. Cheers!
Post reply on HN