Understanding Causal Set Theory and Its Implications for the Universe

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Discussion Overview

The discussion revolves around causal set theory, a framework suggesting that the universe can be understood as a collection of discrete events and their causal relationships. Participants explore its implications for quantum fields, the nature of events in spacetime, and the derivation of continuum from discrete elements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant introduces causal set theory and references their thesis on the Lagrangians of quantum fields.
  • Another participant inquires about the connection to Sorkin's work, to which a subsequent reply confirms Sorkin as the founder of the theory.
  • A question is posed regarding the definition of an "event" in the context of quantum fields.
  • A participant explains that, in their view, every point in spacetime is considered an event, and they assert that spacetime is inherently discrete, with events being densely packed points.
  • Another participant questions how a continuum can emerge from discrete elements, referencing a similar perspective by Xiao-Gang Wen about fundamental elements like spins or qubits.
  • A further inquiry is made about the implications of a discrete spacetime on the existence of a preferred frame, specifically in relation to Milne spacetime.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the nature of events in causal set theory and the implications of a discrete spacetime. The discussion includes questions and challenges, indicating that multiple competing views remain without consensus.

Contextual Notes

Some limitations include the ambiguity in defining "spaced so densely" and the assumptions regarding the continuity of spacetime from discrete points. The discussion also touches on the dependence of certain claims on specific theoretical frameworks.

Who May Find This Useful

Readers interested in theoretical physics, particularly in the foundations of quantum field theory and the implications of discrete models of spacetime.

causalset
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Anyone heard of causal set theory before? Basically, it is a concept that our universe should be viewed solely as set of discrete events and the causal relations between them. I wrote a thesis where I described the Lagrangians of quantum fields. Please let me know what you think: arXiv:0905.2263
 
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Is this related to Sorkin's work?
 
Yes, Sorkin founded it
 
What counts as an "event" (when you are describing quantum fields)?
 
Every point of space time is referred to as event. The only reason there are finitely many "events" is that I assume that there are only finitely many points in space time; they just are spaced so densely that they look continuous to us.

By the way, when I say "spaced so densely", it is not a well defined term since there is nothing "between" these points (after all, spacetime=points). So, according to causal set theory, spacetime, by its nature, is discrete, and its discrete elements are called events.
 
How is a continuum derived from discrete elements?

I've heard Xiao-Gang Wen say something similar, like the fundamental elements are spins or qbits with nothing between them. But I think when he talks about the low energy limit, that assumes some sort of fixed smooth background to define low energy.
 
Thinking of the Milne spacetime, it seems like it would be difficult for the density of a discrete spacetime not to produce a preferred frame?

(I'm not really disagreeing with the discrete approaches, just wondering if you could explain it a little more?)
 

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