@paulbalduf

> #causalSetTheory [...] assumes ST is fundamentally discrete, not like a lattice, but more like a random #graph edges representing causal relations

Btw.: can labelling events be understood e.g. such that (causally connected and ordered) events with the same label are specifically chronologically connected; being visited by the same identifiable participant?

> [...] surprisingly hard [...] order emerges dynamically, can change during the simulation. [...] random [...] random [...] Poisson sprinklings [...] The difficulty: edges must represent consistent order relations in the poset. Say I want to generate a random poset by adding one edge at a time at random. [...] quite costly to do even a single update.

The #causalSetTheory problem that occupies me is quite the opposite of "random" (and thus perhaps rather simple to solve), namely:

Would the causal sets community please provide an _explicit example_ of a graph which is

(1) consistent with ("can be exctly embedded in", "necessarily occurs in") any suitably extended region of 3+1-dim (conformally) _flat_ spacetime, and ideally also

(2) inconsistent with ("can not be exactly embedded in") any suitably extended region of 3+1-dim uniform (conformally) _non-flat_ spacetime, and ideally also

(3) with at least some of its chronological ordered subgraphs being subsets of the timelike worldlines of constituents of an inertial frame (in Rindler's sense, and thus indeed very much like a lattice -- e.g. an octet-truss #PingCoincidenceLattice)

?

(If that's really not as easily done as I envision, and indeed providing instances of "well-stitchedness" ( https://arxiv.org/abs/2302.12209 ) then I'd like to learn about remaining difficulties.)

How to detect the spacetime curvature without rulers and clocks

We demonstrate how one can distinguish a curved 4-dimensional spacetime from a flat one, when it is possible, relying only on the causality relations between events. It is known that it is possible only for spacetimes that are not conformally flat. We prove that if a spacetime is not conformally flat, then its non-flatness can be verified by only a few (sixteen) measurements of causal relations. Therefore the results of this paper clarify what can be said about flatness or non-flatness of the spacetime after a finite number of measurements of causal relations.

arXiv.org

"The path to quantum gravity with causal sets"

A two day conference on recent developments in the causal set approach to quantum gravity.

Where? Manchester, UK
When? 07 - 08 September 2026
Organised by Stav Zalel and Yasaman Yazdi, hosted by the Royal Society

You may still request an invitation on their website.

https://royalsociety.org/science-events-and-lectures/2026/09/path-to-quantum-gravity/

#quantumgravity #causalsettheory #causalset

A while ago I shared a #paperOfTheDay about #causalSetTheory , a combinatorial approach to #quantum #gravity , that caught some interest. For researchers interested to learn more or even collaborate, there is now a #scientificConference in September 2026, organized by @ykyazdi . It takes place in-person in Manchester, UK, free of charge, and registration is open now (and manually approved by the organizers, as usual for this type of specialized meetings). #mathematics #physics #causet
https://royalsociety.org/science-events-and-lectures/2026/09/path-to-quantum-gravity/
I had not made the connection before, but #Causal-Set-Theory has several profound connections to a resonant #spacetime metric, which of course is its own 'fine tuning' (& just so problems). 1 that jumped out in this video was the relegation to number to a minor role, compared to order (causality).

RE: https://bsky.app/profile/did:plc:i3kkr4gz3lj4sxvjb6mgxa2w/post/3mj653atzys2l
@paraw I've only been following #causalSetTheory from the sidelines, so don't quote me on this. However, my understanding is that
1. This is a partially ordered set, so there are pairs of vertices without either being in the future of the other (in physics, they would be "spacelike separated", i.e. not causally connected). Also I think it is allowed that pairs of distinct vertices are equivalent in terms of relations, i.e. 2 vertices have all the same future and past relations, but being distinct. I'm not sure if a situation like that would perhaps been penalized from imposing a physically motivated weighting function (maybe, this situation would correspond to some piece of spacetime "existing twice", which, however, might be fine on very small quantum scales)
2. The simulation paper I shared used labelled vertices, which makes the simulation simpler. In my understanding, in the original physical theory the vertices are not necessarily labelled and the order emerges dynamically, and can change during the simulation.
Under these conditions, a large uniform random partially ordered set most likely consists of 3 layers only. This is why one wants to impose some non-uniform weighting function in order to produce "longer" partially ordered sets which can sensibly be interpreted as a space time.
As is well known, the Einstein-Hilbert action of general #relativity, i.e. Einstein #Gravity, can not be "simply" turned into a #quantumFieldTheory in the usual perturbative way. Over the decades, this has given rise to dozens of proposed solutions, either by modifying the Einstein-Hilbert action (e.g. introducing a fourth derivative term), or by modifying quantum field theory (e.g. replace it by #stringTheory ), or by examining the possibility for fully non-perturbative quantum field theory (e.g. #asymptoticSafety studies via functional renormalization).
One of the approaches that somehow combines the first and second viewpoint is #causalSetTheory . There, one assumes that spacetime is fundamentally discrete, not like a lattice, but more like a random #graph and the edges in this graph represent causal relations (i.e. being in the future or past light cone). Viewed from afar, this might look like a 4-dimensional spacetime, but looked closely, there is only discrete structure. The edges (causal connections) do not only join nearest neighbours, but can reach far along the lightcone, this gives rise to non-trivial effects, and it makes it surprisingly hard to simulate such a causal set (I've tried that once, but without much success).
The causal sets community has produced a 1 hour video to explain these concepts to a general audience interested in #physics
https://www.youtube.com/watch?v=5EoZE1rOHAo
Causal Sets : The quantum theory that predicted dark energy

YouTube

"Ob der Weg zu einer möglichen Theorie der #Quantengravitation gerade sein wird, oder sprunghaft, wird sich erst weisen"

Spannend, aktuell und erstaunlich gut erklärt von Reinhard #Kleindl

#Relativitätstheorie #RicciKrümmung #CausalSetTheory #Raumzeit

https://www.derstandard.at/story/3000000280264/luecke-in-einsteins-relativitaetstheorie-wird-nach-ueber-100-jahren-geschlossen

Lücke in Einsteins Relativitätstheorie wird nach über 100 Jahren geschlossen

Die allgemeine Relativitätstheorie versagt bisher bei Brüchen in Raum und Zeit. Zwei Wiener Forscher kitten nun die Risse und ebnen so den Weg zur Quantengravitation

DER STANDARD