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Or is it, because physics! you can model mutation on top of values and in fact immutable systems do this
by dustingetz 7y ago
Or is it, because physics!
you can model mutation on top of values and in fact immutable systems do this
- Geee 7y agoThe world (space-time state) is immutable. World space state is a pure function of time. If you call World(time) you always get the same answer.
- tachyonbeam 7y agoExcept that there is no such thing as World(time). We don't live in a Newtonian world, we live in a relativistic universe. Time doesn't elapse at the same rate in every location, it depends on gravity and the speed you're moving at. I'd argue that since time is a local phenomena, the mutable universe interpretation makes a lot more sense.
- bollu 7y agoJust because the universe is relativistic doesn't mean that we can't model it. Mathematics is inherently immutable --- this is why describing programming language semantics requires the introduction of something "extra" (a state monad, hiding the mutability inside the operational / denotational semantics, whatever). We _do_ have a mathematical model of the universe --- the differential equations that govern space-time evolution describe the universe in a pure fashion: universe(t+1) = f(universe(t)).
- dnautics 7y agoNo, you're missing the point. There is no such thing as world(time), but there is world(location, time). If you don't respect that, you'll wind up with unsustainable system designs like using atomic clocks to guarantee consistency.
- k__ 7y agoI think the problem here is the definition of "time". You are talking about a relativistic time and they are talking about an absolute global time. I don't know if it makes sense in some kind of way to talk about something abstract as a global time in any way. If the global absolute time goes on for 1 second, some peoples relativistic time went on more or less than a second. Can we measure this abstract concept of time? Even if it made some kind of philosophical sense?
- dnautics 7y agoRelativistic time is a real thing in distributed systems, even without worrying about einsteinian relativity; the premise of physics relativity is that perfect synchronization is impossible and that is highly analogous to the impossibility to perfectly synchronize nodes in a distributed system.
- senderista 7y agoThere is a nice analogy between causal relations in special relativity and in asynchronous distributed systems, but it is no more than an analogy. Synchronized clocks are a physically feasible possibility in every realistic distributed system I’ve seen. The difficulties are merely of a technical nature.
- dTal 7y agoThe effects of relativity are non-negligible in GPS, which is essentially nothing but a distributed system on synchronized clocks.
- dnautics 7y agoSure, you can get sufficiently close, and at what cost in terms of developer effort and physical infrastructure? Not everyone is Google, and in most cases if you explicitly have code that doesn't assume synchronicity you will avoid footguns that inexperienced devs will make.
- 7y ago
- LASR 7y agoRelativity doesn’t change anything.
- Geee 7y agoWe can pick a reference time and place such as Unix time on Earth and relative to that frame of reference, the world is immutable.
- senderista 7y agoAt the largest (cosmological) scale, given a metric such as FLRW, you can define a global family of comoving observers, with a corresponding notion of global time: https://en.wikipedia.org/wiki/Cosmic_time https://en.wikipedia.org/wiki/Cosmic_time. This is less applicable at smaller scales, of course, where other solutions of GR (e.g. the Schwarzschild solution) more accurately model the system under study.
- emn13 7y agoBy that not so very useful definition, mutable systems are immutable, since they're in the same state at any specific moment.