Jan 6, 2026 02:43 AM
https://www.templeton.org/news/a-univers...-spacetime
EXCERPTS: These are questions that philosophers of physics [...] tackle in their recent book Out of Nowhere. They discuss three of the best-known candidate theories that attempt to uncover the foundations of reality...
What might such building blocks of spacetime look like? The first possibility discussed by the authors is causal set theory, which conceives the seeds of reality to be “events”—points that we would understand as existing at a certain place in space and in time, but stripped of their temporal and spatial coordinates. These events can be drawn as dots on a diagram, with lines linking dots that have a causal relationship. If event A causes event B to happen, then dot A will be drawn lower on the diagram, with a line linking A to B. Thus, a few events can spawn a growing network, like branches on a tree, together generating space-time.
One major feather in casual set theory’s cap is that it predicted that our universe’s expansion should be speeding up, about ten years before astronomers discovered that this is indeed the case. This is because, in causal set theory, the volume of spacetime, growing from an ever-increasing number of events, fluctuates, creating an intrinsic energy that pushes its expansion outwards...
[...] Huggett and Wüthrich raise the slightest of eyebrows at the claim that dots defined by their causal relationships can truly be said to be entirely devoid of any concept of time, however. You might try an analogous trick, cutting up the frames of the Star Wars films, scattering them on the floor, and then ordering them in terms of cause and effect (the moment that Luke and Leia’s parents first meet must lie lower in the causal diagram than the twins’ births, for instance). It is true neither the individual frames nor their ordering contains a temporal flow, but they do contain an implicit sense of time.
On the flip side, the dots really do seem to lack spatial extent, making it tough for the theory to explain how a concept of space can emerge from the growing set of causal dots... Causal set theory, then, is still a work in progress, with no easy explanation for how space emerges from its dots.
[...] Not so for the next theory under consideration, loop quantum gravity, which claims that the fabric of spacetime is actually a net woven from quantum loops...
[...] Thanks to having distance built into its foundations, it’s much easier to accept that space, as we know it, could somehow emerge from quantum loops. What’s more confusing is how time arises from the network. This turns out to be a problem for all physicists who attempt to stick the equations of quantum theory together with those of relativity—in so doing, the time variable in both sets of equations cancels out, creating an equation of quantum gravity that describes a frozen universe that contains no time variable, and thus doesn’t seem to have any capacity to change.
Over the years, physicists have interpreted this “problem of time” to suggest that the equations of quantum gravity provide an external view of the universe, from a perspective outside of time. Within the cosmos, participants can experience the evolution of time, but only in relation to other objects in the universe, not against any external physical clock.
[,,,] The final portion of the book turns to probably the best-known candidate for a fundamental framework of reality: string theory, which posits that elementary particles and forces can all be described by tiny strings of energy... (MORE - missing details)
EXCERPTS: These are questions that philosophers of physics [...] tackle in their recent book Out of Nowhere. They discuss three of the best-known candidate theories that attempt to uncover the foundations of reality...
What might such building blocks of spacetime look like? The first possibility discussed by the authors is causal set theory, which conceives the seeds of reality to be “events”—points that we would understand as existing at a certain place in space and in time, but stripped of their temporal and spatial coordinates. These events can be drawn as dots on a diagram, with lines linking dots that have a causal relationship. If event A causes event B to happen, then dot A will be drawn lower on the diagram, with a line linking A to B. Thus, a few events can spawn a growing network, like branches on a tree, together generating space-time.
One major feather in casual set theory’s cap is that it predicted that our universe’s expansion should be speeding up, about ten years before astronomers discovered that this is indeed the case. This is because, in causal set theory, the volume of spacetime, growing from an ever-increasing number of events, fluctuates, creating an intrinsic energy that pushes its expansion outwards...
[...] Huggett and Wüthrich raise the slightest of eyebrows at the claim that dots defined by their causal relationships can truly be said to be entirely devoid of any concept of time, however. You might try an analogous trick, cutting up the frames of the Star Wars films, scattering them on the floor, and then ordering them in terms of cause and effect (the moment that Luke and Leia’s parents first meet must lie lower in the causal diagram than the twins’ births, for instance). It is true neither the individual frames nor their ordering contains a temporal flow, but they do contain an implicit sense of time.
On the flip side, the dots really do seem to lack spatial extent, making it tough for the theory to explain how a concept of space can emerge from the growing set of causal dots... Causal set theory, then, is still a work in progress, with no easy explanation for how space emerges from its dots.
[...] Not so for the next theory under consideration, loop quantum gravity, which claims that the fabric of spacetime is actually a net woven from quantum loops...
[...] Thanks to having distance built into its foundations, it’s much easier to accept that space, as we know it, could somehow emerge from quantum loops. What’s more confusing is how time arises from the network. This turns out to be a problem for all physicists who attempt to stick the equations of quantum theory together with those of relativity—in so doing, the time variable in both sets of equations cancels out, creating an equation of quantum gravity that describes a frozen universe that contains no time variable, and thus doesn’t seem to have any capacity to change.
Over the years, physicists have interpreted this “problem of time” to suggest that the equations of quantum gravity provide an external view of the universe, from a perspective outside of time. Within the cosmos, participants can experience the evolution of time, but only in relation to other objects in the universe, not against any external physical clock.
[,,,] The final portion of the book turns to probably the best-known candidate for a fundamental framework of reality: string theory, which posits that elementary particles and forces can all be described by tiny strings of energy... (MORE - missing details)
