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TheHeraclitus
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- TL;DR Summary
- Does CDT involve gravitons? How many dimensions? Presentism, Eternalism or Agnosticism about time?
It treats space and time differently which Einstein thought us not to do.
It means that space and time are not treated on an equal footing. In other words, it's not manifestly relativistic covariant.TheHeraclitus said:Also, what does Sabine mean in this video by the sentence:
So it denies the reality of Spacetime?Demystifier said:It means that space and time are not treated on an equal footing. In other words, it's not manifestly relativistic covariant.
According to Sabine, yes.TheHeraclitus said:So it denies the reality of Spacetime?
Interesting, that would make sense since Wikipedia says CDT is related to Hořava gravity where space and time are treated differently too.Demystifier said:According to Sabine, yes.
Causal Dynamical Triangulation (CDT) is a theoretical framework used in quantum gravity to model the structure of spacetime. It involves discretizing spacetime into simplexes (triangles in 2D, tetrahedra in 3D, etc.) and then summing over all possible configurations to study the quantum properties of the universe. The "causal" aspect ensures that these configurations respect causality, meaning the sequence of events is consistent with the flow of time.
CDT differs from other approaches to quantum gravity, such as Loop Quantum Gravity and String Theory, primarily in its use of discrete building blocks to model spacetime and its emphasis on maintaining causality. Unlike approaches that use continuous mathematical structures, CDT uses a discrete lattice of simplexes. This method aims to provide a non-perturbative and background-independent formulation of quantum gravity.
Causality is a fundamental aspect of CDT, ensuring that the order of events adheres to the cause-and-effect relationship inherent in our understanding of time. This constraint is crucial for maintaining the physical realism of the model, as it prevents configurations that would imply backward time travel or other non-causal phenomena. By enforcing causality, CDT aims to produce more physically meaningful and realistic models of quantum spacetime.
One of the main successes of CDT has been its ability to produce a universe that resembles our own at large scales when simulated on a computer. This includes the emergence of a four-dimensional spacetime from the theory's fundamental principles. Additionally, CDT has provided insights into the nature of spacetime at the Planck scale, suggesting that spacetime may have a fractal-like structure at extremely small scales.
Current challenges for CDT include understanding the detailed dynamics at the Planck scale and integrating matter fields into the framework. Additionally, researchers are working on improving computational methods to handle larger and more complex simulations. Future directions involve exploring the connections between CDT and other quantum gravity approaches, as well as investigating potential observational consequences that could be tested experimentally or astrophysically.