I have read Lee Smolin’s latest book “Einstein’s Unfinished Revolution“. I highly recommend it. In this post I wanted to contrast his ideas to other speculations regarding space and time.

**Note 1:** Scientists strive to find theories (models) of Reality that are simple, explanatory and predictive. The goal is to produce models with minimum number of free parameters. The simplest and the most efficient (yielding to calculations) model with the smallest number of free parameters that can explain the widest range of observations will be accepted as the most worthy. **This is a tall order**. Natural philosophers or physicists out there who are thinking on their alternative fundamental physics theories are facing huge challenges. It is not so easy to demonstrate that your theory is the simplest, most efficient, most predictive and explanatory. My goal is not to compete with physicists. My goal is to provide complementary models to deepen our understanding. I share my half-baked (sometimes raw) thoughts with the hope that they trigger ideas in others.

**Note 2**: There are thousands of books and papers on space and time. It is impossible for me to cover all ideas in this blogpost. I tried to summarize the ones that attracted my attention.

Lee Smolin: **time is fundamental, space is emergent**.

*“Time, in the sense of causation, is fundamental. This means the process by which future events are produced from present events, called causation, is fundamental.” *[1]

*“Time is irreversible. The process by which future events are created from present events can’t go backward. Once an event has happened, it can’t be made to un-happen.” *[1]

*“Space is emergent. There is no space, fundamentally. There are events and they cause other events, so there are causal relations. These events make up a network of relationships. Space arises as a coarse-grained and approximate description of the network of relationships between events.”* [1]

James Hartle – Stephen Hawking: **space is fundamental, time is emergent**.

This is one way to interpret the Hartle-Hawking “no boundary” hypothesis. Please see Natalie Wolchover’s article at the Quanta Magazine for a nice explanation of the Hartle-Hawking “no boundary” hypothesis, especially the parts where she mentions **pure space**: *“Hawking and Hartle were thus led to ponder the possibility that the universe began as pure space, rather than dynamical space-time.”*

Qubit network perspective: **primordial entangled qubits are fundamental**.

According to this perspective the fabric of the universe is a network of primordial qubits connected to each other by quantum entanglement. Space and time emerges from this qubit network. The ontological status of the primordial qubit is not known. This is my summary based on [2],[3],[4],[5]

John Preskill predicts that physicists will be able to create spacetimes that did not exist before by creating highly entangled quantum systems in tabletop experiments in the future.

Nature article: There is a Nature article by Ron Cowen titled “The quantum source of space-time“. This is the story of Mark Van Raamsdonk and his 2010 paper “Building up spacetime with quantum entanglement“. In his Nature article Ron Cowen talks about the role of quantum entanglement in a wider scope. Very good article! The diagrams are very informative also.

Nima Arkani-Hamed: I recommend the article he wrote in 2012 titled “The Future of Fundamental Physics” where he articulates his ideas about the emergence of space and time among other things. You can also listen to his lecture he gave at PSW titled “The Doom of spacetime: Why it must dissolve into more fundamental structures“. His intuition is that space and time as well as the rules of Quantum Mechanics emerge from underlying principles which may be geometrical or combinatorial in character.

Shahn Majid: **quantum spacetime**

The book titled “On Space and Time” edited by Shahn Majid is an important book. Majid’s long essay in that book is very substantive.

*“I think that spacetime is fundamentally not a smooth continuum at the pre-subatomic level due to quantum-gravity effects and why a better although still not final picture is one where there are no points, where everything is done by algebra as in quantum mechanics, what I therefore call ‘quantum spacetime'”. *[6]

*“The search for a fundamental theory of physics is the search for self-dual structures in a representation-theoretic sense.”* [6]

Roger Penrose: **spin networks and twistor theory**

Roger Penrose is the source of many ideas regarding space and time. It is not necessarily a good thing to have many ideas 🙂 We, the students of Penrose, get confused. So, I will use this quote and urge readers to dive deeper into Penrose’s ideas.

*“Twistor theory does not claim to be an approach to a quantum-gravity theory, as such, but provides a different outlook on spacetime, where nonlocal features arise at a fundamental level, and where the notion of ‘spacetime point’ (or event) is regarded as a secondary construct, the light ray (or, more correctly, the history of a massless entity with spin) provides something closer to the primitive element of the theory. Many aspects of physics, both classical and quantum, find neat descriptions in terms of complex-manifold geometry in twistor theory, but the scheme is not completely wedded to the conventional formalism of quantum mechanics, there being some scope for generalization to non-linear scheme in which quantum state reduction might find some dynamical description.”* [6]

My view:

Space and time cannot be understood without the knowledge of the vacuum (internal space). Remember that the current crises in String Theory is due to the realization that the theory allows infinite number of vacuua. In other words, String Theory allows too many possibilities for the characterization of the vacuum. All physicists realize the importance of the vacuum. They express their intuition in different ways. It is also obvious that quantum entanglement cannot be understood without the knowledge of the vacuum either.

In my conceptual world, the dualities “cognitive/creative” and “confinement/liberation” play a central role. I see the interplay between cognitive and creative aspects of Reality as fundamental. I speculate that at some stage the cognitive/creative duality transforms into the confinement/liberation duality. We are talking about an interplay between two aspects with many modalities. How many modalities are there? Can we describe the modalities? At a later stage the confinement/liberation interplay transforms into an interplay between “cognitive cores” and “interaction”. How do we get space and time from cognitive cores and interaction? Can this approach be useful in other areas of physics? I am thinking on these questions.

Whatever the deeper structure is, focusing on space-time-matter, my intuition is that the progression order is like this:

space time matter

This means that I am closer to “*space is fundamental, time is emergent*” view in the sense that I also speculate that vacuum (internal space) activity develops as a reaction to the expansion of the external space. Vacuum fluctuations start as soon as the external space emerges. Particle fields and their quanta are created out of the vacuum fluctuations. This implies that the emergence of (physical) time is related to the emergence of vacuum fluctuations.

Lee Smolin’s definition of time is different. He is talking about the causal order of events. In that case one can ask the question: “*what is an event*“? Also, to those who claim fundamental status for quantum entanglement we can ask the question: “*what is quantum entanglement?*” And I fully expect that you ask “What is confinement/liberation?” Fair questions!

**Divine Time, Causal Time, Physical Time**

In this 2013 blog post I put together all the views – that I was aware of at that time – about the concept of “time”. In that post I included some interesting quotes also. Clearly there are different kinds of “time”?

**Other ideas**

Few more ideas are listed in my 2015 blog post titled “Proposals for space-time extensions“.

**References**

[1] Lee Smolin, “Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum” , page 236

[2] https://www.quantamagazine.org/20161129-verlinde-gravity-dark-matter/

[3] https://www.quantamagazine.org/20161201-quantum-gravitys-time-problem/

[4] https://arxiv.org/abs/1611.02269

[5] https://www.quantamagazine.org/20150428-how-quantum-pairs-stitch-space-time/

[6] “On Space and Time”, by Shahn Majid Eds. (Alain Connes, Michael Keller, Roger Penrose, John Polkinghorne, Andrew Taylor), Cambridge University Press (2008), 052188926X / 9780521889261