Implicate Order

It's been a long thread. What is evident is that time as a notion is very hard to pin down and reach consensus on. It's getting late and I thought I would add a metaphysical addition to the mix just as a way to put this into perspective from an observers viewpoint. Obviously each one of us have a sense of what time is. It represents a personal notion to each one of us of a 'moving now'. We have memories of a past through a trace of causative progression and we are confident that that past is real to us and that we have ridden upon the moving now from the past to this present point in time. I carry my own personal clock with me at all times as a device to measure how my 'moving now' relates to all your apparent 'now's' or to the 'nows' of other seperated things in space that carry their own clocks. To relate my time to yours I don't actually recognise that I am always looking into my past when dealing with you all. When I communicate with you I assume you share the same moment in time ("moving now") as me but that is just illusory. You actually all exist in my past light cone as you are all seperated in space from me and it takes time for me to see you. The reason for this of course is that 'c' is finite from each observers frame of reference and does not travel between different points in space from a particular frame of reference 'instantaneously'. This 'illusion' in our minds is not obvious to us as we assume when communicating with you all that we share the same moving now and the same causal history, but this is actually not the case at all. Different frames of reference that are causally connected will only share a portion of the other frame of reference's light cone (hubble volume). The information available in each overlapped region is less than the total information available within each observers entire light cone. The closer you are to the other frame in spacetime, the greater overlap of causal histories but they are never exactly equivalent unless the frames of reference are located at the exact same point in spacetime. While this illusion is not evident, we are aware of something strange going on in the way that I perceive your clocks time and also if you are not comoving in space with me inertially, then your tick seperation is also different to mine when viewed from my frame of reference. This is actually necessary for me to possess a notion of a causative past. If from my frame of reference your clocks didn't show a different time when we were spatially seperated, or tick differently if our frames of reference were relatively moving, then there would not be a causative past for me at all. The reason for this difference in perspectives is due to the reduced amount of information available in each overalapping light cone region. This results in me seeing only a fraction of your causative history that is available to you. Assume I wish to get peace of mind that we all share the same 'instantaneous' moving now. To initially get all our clocks on the same footing I gather all your personal clocks you are all carrying and bring them to me to synchronise first before I then pass these clocks back to you. But I can't pass these clocks to you all seperated in space away from me 'instantaneously'. If I did so, your clocks from my frame of reference would all show the same time as mine and if you were moving relatively to me, would tick at a different rate. The best I can do however is send these clocks to you (say by a very fast transport device) in my past as it takes time to get these clocks back to you. As the transport device gets these clocks back to you, I have already moved on with my moving now and you get the clocks in my causative past. You won't of course see it this way as you are all ahead of me. What is sacrificed however in you living in my past is that from 'my frame of reference' the time on your clock will differ to mine even though they were initially synchronised. The reason for this is because you are now spatially seperated from me. It is further compounded if you are relatively moving in space with respect to my frame of reference. The degree of causative lag into my past will directly influence the way I measure the time of your clock. I am assuming there is no lag to give peace of mind to me that you share the same moving now and therefore will all a common notion of simultaneous causative events. The reality is that each observer will have a different viewpoint on where and when an event occurred but you won't sense this. The illusion that you all share the same moving now as me keeps my world ordered and makes me believe that we all share the same notion of simultaneity. However to share a sense of the exact same causative path as you, something has to give as you really are in my past, What does give is that your clocks will show a different time to me when I view yours and vice versa. The only way to get your clocks to show the same time as me is for you to catch up to my moving now. If you did so however I wouldn't see you in a simultaneous moving now, as I look to you in my past as you are in a different place that is spatially seperate. Now note that it seemed logical that because you exist in my past I should be able to 'sense' this. I do not sense this however as this requires a self-referential judgement from the point of view of the observer. As Godel demonstrated in his incompleteness theorem, self-reference gets an observer into trouble. What I do sense however is that 'your clocks' tick at a different rate to mine. This is because by the process of measurement the information I am receiving is actually information drawn from my past. What time 'actually is in my opinion, is how an 'illusory' causative past is created by the delay in information received by an observer (or a frame of reference) from the external surrounds seperated in spacetime. We don't sense this however as we assume we are all on the same moving now. It is a frame dependent notion based on the information acquired from our external surrounds (our past) as a basis to interpret where we are located in spacetime. The causative history of information therefore creates a sense of time moving in one direction always forward on a 'moving now'. As our light cone expands, more and more information (causative history) is incorporated into our hubble volume to give the sense that we are moving forward. We as observers use a light cone emanating from our point in spacetime to interrogate the surroundings and the information we receive is only ever about our past, never our future. This is why IMO we 'sense' an arrow of time. ...and just to push things a bit further before I hit the sack....... I perceive the causative history of unfolding events of my time from my frame of reference in a different way you or other observers perceive their's. For massless things such as photons (the carriers of the information) they can access the entire information in each observers hubble volume instantaneously as they are timeless from their own frame of reference. What we perceive as causation, being a delay in the receipt of this information, is, from a photons frame of reference instantaneously available. This smacks of a greater illusion still in relation to time. What we need to recognise is that, like the photon, we can actually see our entire causal history at an instant. All things from their own frame of reference travel at 'c'. It is how we measure things external to this frame that the appearance of time and space emerge. Just look up to the stars at night to see your own entire causal history in an instant. What we measure however of things external to our frame 'lags' and is not received instantaneously attributed to spacetime seperation of the frames of reference we are measuring. In Quantum Mechanics, the collapse of the information contained in the light cone to provide a 'causative history' for us as observers is 'instantaneous' to the photon.However we would use a Schrodinger wave function to describe how that information state unfolds in our terms of time (from our frame of reference). Just look at Wheelers delayed choice experiment if you have any doubts on that.

Hi MigL I sense your frustration as I was facing a similar conundrum until recently. For over 8 years I have been swaying between the Loop Quantum Gravity camp and David Bohms hidden variables theory after being dissatisfied with String Theories multi-verse proposition (String theory's Landscape) and it's associated Anthropic principle, which to me (like you) appeared to be a neat cop-out. I have always sought a theory that at least could fully explain the classicality of this universe before entertaining the prospect of considering other universes. The multi-verse proposition did not offer that solution. As each landscape was causally disconnected, no mathematical findings applicable to other universes would necessarily help in understanding our own classical reality. String theory and it's eleventy billion alternatives appeared to be hopelessly drifting into a sea of mathematical obscurity........until recent events with the Holographic Principle and alternate conclusions drawn from String Theory when you treat this theory as frame-dependent...... and I will get to that. With regards to previously discussing LQG, this is in relation to my comments made in the thread "Quantum Entanglement Solar Flare Detection and Transmission" where I reported on the results of Fotini Markopoulou's work in the field of 'Causal Dynamical Triangulations' in post 81. In regards to background dependent or background independent theories, you are correct and my use was incorrect. My apologies. I frequently get this wrong in my head as unlike a pure GR advocate, due to my interest in QM and in particular the properties of vacuum space, I treat space-time as having physical properties, but this is a QM influence and not a GR one. So let's don't go down the old traditional aether debate as my interpretation is strictly QM. Consequently I see the dynamic nature of space-time (a constraint boundary) as a feature of LQG as the background geometry 'depends' on the contents. In my mind I see the traditional background independence of String Theory as a Newtonian description where the background is static in a framework that describes the contents. Your interpretation is more apt as it more faithfully describes GR in that there is no physical medium (space-time) and it is just about the relationships between things described in a coordinate framework coined space-time. ...but here I think lies the problem. I think we need to treat both spacetime and its contents as a physical medium but it is frame dependent. A GR advocate would say that space-time is not a physical manifestation and simply a co-ordinate reference system. I beg to differ. I furthermore think that it is not a correct assumption to extend GR to reflect global geometries as this necessitates that there is an external observer out there outside this universe looking in. There is enough suspicion in recent WMAP results to suggest that extending GR to a global definition may be inappropriate. GR I believe is a correct local tool to use and that is contingent on being applicable within the hubble volume (light cone) of a single observer. The conclusions drawn by an observer internal to the universe necessitates a relational perspective being taken with respect to the observations taken when compared to other frames of references. There is no external viewpoint that can actually see 'everything that is going on'. It is therefore incorrect to conclude a block universe as the 'be all and end all to the theory'. If a common frame of reference can be used for both QM and GR (being the extent of the light cone) then both theories can co-exist together and evolve together yet be indeterminate in nature. The local perspective between reference frames is linked by the information that can be derived from observations taken on those diferent frames by c. Shared observations require that each reference frame is causally connected....but I digress. LQG which has arisen from GR has previously been focussed on the geometrical properties of space time and has had very little to say about the nature of space-times contents which has always been string theorys strength. There is a possible way to reconcile the two approaches provided we avoid the multi-verse proposition. What is required however is to recognise that there is an abstract realm out there referred to as the quantum domain within which is embedded a classical 3D and 1T universe that can faithfully be described by both String Theory AND Loop Quantum Gravity. I personally see this is where it is all heading. Whether or not there is a multi-verse out there is actually not the point. What is the point is whether there is an alternate way to view the multi-verse proposition from a new angle which is fully embedded in a single 3D and 1T universe. This way we can get on the same footing between String Theory and Loop Quantum Gravity. Interestingly the change in tide to a frame of reference approach was promulgated by Hawking and Hertog in their ruthless condemning of cosmological approaches that are bottom-up in approach such as string theory. The problem with a bottom up approach is that you commence with a singularity and are immediately caught with the conundrum of trying to deduce which initial state you should commence from in building a cosmological history. You immediately start with an indeterminate number (infinity) and you can see why string theory is caught in a multi-verse proposition. Hawking and Hertog claim (and this is getting traction) that you should adopt a top-down approach from the frame of reference of an observer to determine a causal history. This top down approach from a single frame of reference avoids a singularity at the end. Furthermore, a correct relativistic approach would actually be to adopt a top down approach to determine the causal histories of all observers (points in space-time). Once this is done then in accordance to Feynmans sum of path histories, you can superimpose the wavefunctions of each causal history to obtain a Gods-eye view of space-time histories that are all causally connected provided each cosmological history shares the same causal patch. What is actually being done here is treating a multi-verse proposition as being equivalent to a many frames proposition in a classical 3D and 1T context. You can see that this approach is adopting an equivalent footing to Fotini Markopoulos LQG approach where she inserts light cones at each point in the lattice of quantum space. GR is not simply about the geometric properties of space time. The Einstein equation demonstrates that geometry (Einstein tensor) represents one-side of the equation and it is equivalent to talk in terms of the mass-energy distribution of space-time (its contents given by the stress-energy tensor). Given that LQG seeks to determine how things can arise from the vacuum due to their relationships with quantised space-time then it is helpful to talk in terms of boundary constraints or the contents contained within those boundaries. Wheeler had an expression that the boundary of a boundary is zero. He showed that he equations of GR follow this principle in that the local curvature of space time cancels out the energy and momentum of the mass thats present there. This only occurs however when the boundary is closed. What this is saying is that everything you need to know about what was going on in the interior of some region of space-time is fully described by the boundary. So black holes and their boundaries may be an ideal candidate to use in searching for clues in how unite both String Theory and Loop Quantum Gravity. ..anyway about recent events. Whilst we can generically talk about the string theory camp as advocating the String theory landscape, some in the field disagree with this approach and are seeking a 3D and 1T alternative. It is Raphael Bousso himself, the originator of the string theory landscape idea with Joe Polchinski , who sees deep flaws in the multi-verse proposition and argues vehemently with multi-verse advocates such as Linde. Susskind with his debate with Stephen Hawking that 'won the black hole wars' is turning the tide in he String Theory camp away from irreconcilable multi-verses towards a 'frame-dependent viewpoint in a 3D and 1T context with the complementarity principle. In dealing with black holes and their horizons, the battle lines between Hawking and Susskind were drawn. Either QM needed to give, or GR needed to give. This actually was a battle between String Theory or LQG. The only way to preserve both positions was in how to treat the dilemma faced between two different frames of reference and the results of their conclusions about whether or not information was contained on the event horizon or whether or not information was lost into the black hole. For very large black holes, an inertial observer (riding an in-falling elephant) would simply follow the geodesic in free fall and should not experience anything 'different' when passing through the event horizon. They would not be aware of any horizon at all and according to GR they just will be free-falling (no forces) in vacuum space. Once past this 'hidden boundary' information is lost from the external region. For the accelerated observer outside the black hole that watches the elephant as it makes it's way towards the event horizon, they will observe an event horizon with associated entropy. They will see the elephant get stretched from trunk to tail and slow down as it approaches to be ultimately torched by the entropy of the event horizon. We have a paradox here for both GR and QM. In one interpretation the elephant is dead and smeared over the event horizon and with the other the elephant is alive and well inside the event horizon. In one interpretation information about the state of the elephant is lost to the external system and in the other, information is spread across the event horizon. The only way out of this conundrum to avoid a breakdown of both QM or GR was to adopt the Complementarity Principle. That is to say that either one interpretation OR the other interpretation were correct and that one interpretation AND the other interpretation were NOT correct. This was achieved by ensuring that each interpretation had to be frame dependent and this was the huge break-through that has shaken up the String Theory Camp, put questions on the multi-verse proposition and forced relativism into its picture. Both interpretations are right but in one interpretation we see things emerge from the vacuum such as a boundary with entropy, particles and heat while from the other frame of reference, these features do not emerge. The observer is simply following the geodesic in empty space. What this has done is bring the holographic principle into fully fledged form in the string theory camp and provided it is frame dependent, you do not need a multi-verse description. Leonard Susskind despite being an advicate of the multi-verse is now questioning this notion and recognising the importance of frame-dependence. A De-Sitter universe can be explained in terms of either the boundary of the universe or its contents dependent on the frame of reference of the observer. With space-time accelerating expansion, unlike black holes, it is the inertial observer who sees the boundary and it is the accelerating observer who does not. I hope MigL that this explains why I see that both camps are actually significantly contributing to unification as opposed to travelling their separate paths. You can see recent discussions on this bt the proponents themselves on Edge.org. To nail the point home we have had an approach called String Theory starting with defining things from bottom-up and ending up with boundary descriptions, while we have had LQG starting from top down commencing with boundary constraints and ending up with things described with light cones embedded in the lattice of quantum space. We have then made String theory frame dependent with the Complementarity Principle and furthermore flipped the theory to be a top down approach like LQG. We still have the 10D and 1T dimensioins of string theory to deal with but we could possible extract the 7 microscopic dimensions and shuffle them off to Hilbert space and then we will appear to be now on the same footing where both approaches are different interpretations of the same universe but both aproaches are embedded in a higher abstract mathematical geometry. PS. Once again thanks to Amanda Gefter for helping me see the light as this interpretation is not my own but an interpretation arising from discussions held between Amanda Geftner, her father and the swathe of physicists from both camps that she has interviewed. I urge anyone that is interested to look at her book "Trespassing on Einstein's Lawn".

Nice considered case Swansont and I agree with your sentiments. My post was directed at less considered viewpoints particularly from those apparent professionals out there whose hostile stance actually discourages enquiry from the lay audience.

Nice post Ophiolite. While there is a stigma attached with pop-sci books in many science forums I have frequented, for those avid readers of pop-science it becomes patently obvious through the analogies given by many of the ardent critics, that they themselves are utilising pop-science contributions in their forum contributions. To a well read enthusiast it stands out like proverbial hanging bits on canines. To the cynics amongst us, this reads to us as perhaps an ardent critic who does not wish to come clean where all there wordly knowledge has been drawn from. How many times do we have to hear the trampoline being pulled out onto the lawn to describe gravitation from those that perhaps should know better. How many expanding balloon analogies do we need to hear to explain space-time expansion, how many Einstein's biggest blunder remarks do we have to hear from the authoritative camps.....and it goes on and on thanks to the regurgitative use in pop-science. I don't see these analogies for example coming from peer reviewed papers but then again, I don't see better analogies coming from the scientists themselves. Furthermore to the pop-sci reader (dare I say it) who actually may have some inclination about the science involved from their readings, it also stands out when a supposed expert writes a few lines of dribble in an attempt to profess a statement about their very special knowledge that they are unwilling to divulge to the forum community. In a Science Forum (or perhaps a pop-science forum such as this) it would be healthy to discuss science in a way that has general appeal for all the community as opposed to leaving bits of morse code as posts that offer nothing to discussion with the false perception that the mystical post somehow adds value to the discussion. More openness and transparency in forums such as these adds to dialogue and increases membership. Please note that while this post is directed at many forums, it is my experience that this forum is actually one of the better ones. That's why I am here for example, as I enjoy discussion with all forms of contributor. It is far more tolerant than many others where peer pressure turns them into pseudo fundamentalist camps for science enthusiasts of a particular leaning. Unfortunately, while the critics might not want to admit it, it is the pop-sci books which give us the tools to be able to discuss things on a science forum such as this so that the discussions can be held across a wide audience. What scientists have to realise is that it is essential that there ideas can be relayed to the masses in a coherent and understandable way, for their very funding depends on it. Not only that, but the material contained in these pop-sci books may actually spark and interest from a scientists heavily involved in a related or disparate field to 'new ideas' that may spark a new approach in their methodology. The pop-sci books also have probably made a significant contribution to encouraging a greater interest in science and also in inspiring the lay-person to join the ranks of the scientific elite. If we can climb down from our high horses for a second, then perhaps we can appreciate the contributions a large number of eminent scientists have made to popular science including the likes of Hawking, Smolin, Greene, Kaku, Susskind, Penrose, Stenger, Fritszch, Livio, Atkins, Reiss, Carroll, Gleick, Gould, Dawkins, Krauss, Barrow, Gribbin, Feynman, Hofstadter, Stewart, Tegmark....etc., etc. etc.. I don't think all these contributions are worthless. There might actually be some science in them despite their *apparent* mass appeal and simplicity. Furthermore where do you draw the line between pop-sci and authoritative works. Do we dispatch all of Dawkins works to the pop-sci trash can?

When Samuel Johnson was throwing a hissy fit and kicking stones in his refutation he unfortunately was not adorned with the devices that need Quantum Mechanics to explain their workings such as GPS tracking devices. He was also not aware that the reality he was kicking was an electromagnetic field as opposed to a solid object. When it comes to a question of whether or not the universe is real, we need to appreciate that the 'reality' may be totally different to our intuitive notion of what the reality should be. Provided you can draw a line between an observer and a region external to the observer, then that probably is the safest definition to use in dealing with any possible 'reality' out there. If not, then perhaps it is all in the mind. If that is the case you then have to query how the observer got there in the first place. For this reason I seek solace in the notion that an observer and an external reality exists but I would reason that both observer and any external reality are fundamentally derived from the same 'thing'. A 'thing' as opposed to a 'nothing'. This philosophical stance would denounce that our universe arose from the 'absence of a thing', which is the traditional definition of 'nothing' (being the absence of things), and propose that our universe and it's observers at least sprang from a state (termed nothing) due to its homogenous and timeless/spaceless nature. That way, a classical universe and its observers can at least be derived from a transition of this preceding state to the classical state through transofrmations of the state. When dealing then with an observer and the external context, we can derive clues from cognitive sciences regarding those definitions of 'consciousness' being related to notions of 'self-awareness'. The foundational principle of 'self' arising from the process of measurement, namely deriving information from an external state and comparing that state from the frame of reference of an observer. What we need for a measurement to occur is the use of a contrived wavefunction used by a particular frame of reference designed to extract information from the surrounding wavefunction that relates the frame of reference of the observed to the frame of reference of the observer. The information derived from their interrogation however will relate to the causality of things in their light cone. Each observers light cone will be different. Those observers however that share the same opinion of any classical reality will share the same patches of my light cone. What seperates an observer from their context is a boundary and that boundary is the information that is causally arranged in that light cone. Each frame of reference occupies a different point in spacetime. A measurement entails extracting information from a different frame of reference and measuring how that information 'relates' to the frame of reference from where the measurement originated. Using that foundational principle of 'the act of measurement' amplified billions of times through evolution and the development of advanced brains to process that information and project the observers reality of that external wavefunction in their own frame of reference I think allows us to question the notion of reality today. Provided other observers share patches of the same causality, they will all agree on that interpretation. Those that refute it thus such as Samuel Johnson therefore share parts of my hubble volume.

The assumption of universal homogeneity and isotropy has always struck me as a controversial assumption. Even WMAP results clearly show anomalies that many conveniently forget to mention such as the Axis of Evil and the Great Void of Erodanus which is indicative of some 'dark flow' and that the universe is not as smooth and featureless as once believed. Still the standard model of Cosmology and inflation lives on. If a theory is to come crashing down, I think the Standard Model is the one to take the hit. There is one big assumption with the Standard Cosmological Model and that is that the universe extends significantly or infinitely beyond the hubble volume as the treatment has always been that the boundary of the observable universe is simply an observational restriction as opposed to a possible 'physical' boundary condition associated with a boundary being inserted in vacuum space. One of the controversial areas from WMAP which is shaking the Standard Cosmological Model and more importantly the inflation model is the 'Low CMB Quadrupole' argument which is the observation from WMAP that there are no temperature fluctuations at scales larger than 60 degrees. This is suggestive that the universe is finite and more importantly puts a limit of the universe to coincide with the hubble volume itself. It certainly does not appear to be a glitch in WMAP data as it is also seen in the COBE data as well. In a De Sitter universe it is possible that the hubble volume actually is a geometric boundary condition like an 'event horizon' of a black hole which, unlike the black hole event horizon is dependent on the frame of reference of an inertial observer from within the universe, as opposed to a black hole horizon which appears to be from the frame of reference of an external accelerating observer of a gravitationally compact object. If this is the case, then we do not need to conjecture what may exist beyond the horizon in classical terms but just recognise that a boundary is, or is not present dependent on the viewpoint of the observer. Namely a 'local phenomenon'. We do not need inflation within the Standard Cosmological Model in this interpretation. The anomalies recorded with WMAP are simply the anomalies to be expected from asymmetrical collapse which is a feature of either environmental decoherence associated with shared frames of reference or singular wavefunction collapse associated from the perspective of a measurement undertaken from a single frame of reference. The notion of 'global' in this context being the universal state agreed on by all frames of reference is an unnecessary viewpoint.

Ta Schneibster.

Your secret is safe. No more mention of the job from me Herr Schneibster

Good to see you are getting your health back......but I don't like the trade-off that's occurring with the job. I am working out the 'death' thing at the moment. After that I suppose I have to look at the 'tax' thing, but a monastery is looking good at the moment. Some polytechnic somewhere in the Alps has a certain appeal.

Well I may be fibbing a bit. I am constantly cross-referring between books as when I come across something it reminds me to have a re-read of an earlier book to get a different perspective on the matter. Things like food, sleep, kids, wife, dog, cat and other classical emergent phenomena don't seem to get a look-in at the moment.

LOL. Your lounge sounds like mine. The only problem is I am finding it hard to get the books into the library. Each book is taking about 2 to 3 reads each as I am shifting between relativity, quantum mechanics, thermodynamics, complexity theory, information theory, genetics and cognitive sciences......... and I am sufferring from a growing backlog and acute anxiety /TIC.

Looks like I have a bit of reading to do on the 'Fluctuation Theorem'. Thanks for the heads-up. It sounds interesting. So many different system approaches arriving at similar conclusions. It is quite exciting.

I think we do know what M-theory stands for now. Witten was asked directly at Harvard and his response was that it was up to the interpretation of the user but he actually initially coined it to refer to the term "Membrane". I am getting a bit fed up with the plethora of pop-sci books that have recently come up that talk about the irreconcilable nature of the two most popular approaches (being string theory and loop quantum gravity). It appears to me at least that both theories are fast-tracking towards a unification of approaches as opposed to going in different directions towards mathematical obscurity. The rationale given in these books is that ST and LQG have started from two different commencement points (namely String theory as commencing as a background independent approach from QM whereas LQG commencing as a background dependent approach from GR. ). The assumption is from the pessimists that the gap between the two approaches is getting progressively wider but this is not actually the case. It just takes a good project manager to be familiar with the two approaches to see this in action. No one has bothered to take the time partly due to the fact that the two approaches are mathematically daunting, but also because once again our blinkers come on and we assume that it must be one or the other and not just perhaps two different interpretations of the same thing. String theory has had 2 great revolutions in it's progression that has shifted it's stance towards a fully relational approach and it looks like the 3rd revolution is underway now with the holographic principle. It appears obvious to me that both approaches are now getting onto a similar background dependent solid footing. Namely we have two types of relativistic expression taken from two different frames of reference. That of a frame of reference dealing with a boundary condition (string theories holographic principle) and that of an observers frame of reference dealing with the contents (LQG Causal Dynamic Triangulation). I have already discussed LQG elsewhere so now I will just focus on String Theory. The folowing information has been derived from discussions and work derived with notable string theorists (Joe Polchinski, Leonard Susskind, Juan Malcadena, Raphael Busso, Ed Witten) and is found in Amanda Geftner's book "Trespassing on Einstein's Law". If we want to talk about a pop-sci book with guts then this is a great read. I site the book as it is important to note that the discussion below is not emanating from my head, but the heads of theoretical physicists who are deeply immersed in the subject. String theory has come a long way since the 90's (Revolution 1) of 10 dimensions where the descriptions were all about vibrating strings and in particular closed strings. Closed strings had much interest due to implications that arose from T-duality and how this feature explained HUP. In T-duality, closed strings receive their energy from two energy forms. Namely vibrational energy (kinetic energy) from the string's vibration and winding energy (potential energy) that arises from the increased PE arising from a closed string winding themselves around tiny curled up compact dimensions of space. When you vary the size of the compact dimension there is a trade off between a strings vibrational energy (KE) and its winding energy (PE). Increase the radial dimension of the space (stretch the spring) and you increase the winding energy and lower the vibrational energy. Increase PE and decrease KE and you get HUP in relation to specifying a strings position or momentum. The smaller the dimension (lower PE and higher KE), the more localised the strings position and the more vibrational energy of the string and the more erratic or uncertain is the momentum and vice versa. What T-duality was showing was the direct relationship between closed strings and space-time geometry. For example assume we have a string in a box (geometric constraint applied to how that string vibrates). In this interpretation we are talking about a 'thing' inside a boundary constraint. If we reduce the size of the box there comes a point when the box gets smaller than the string. T-duality shows that there is another way to look at this interpretation, and that is by removing the energy contents (the string) and talking in terms of the energy of the box provided the box get's bigger to preserve the Law of Conservation of Energy. Now in string theory the energy of the box is referred to as a boundary constraint (sub-manifold) or a 'brane'. This is the first glimpse we get in String Theory of the dynamic nature between space-time and particle properties. It is suggestive that space-time is not fundamental but is simply a different way of looking at the same underlying process - it is a duality. There is a fundamental difference in a theory of point particles and a theory of strings as point particles do not have any winding energy. Strings see geometry differently to point particles. Open strings on the other hand do not have winding energy and they are free to roam through space unimpeded by constraints. Their energy is defined purely from vibrational energy. If you shrink the geometry down to zero it never has an impact on the geometry. What you find is that you can reduce the geometry (described in 9 spatial dimensions and 1T dimension) to 8 spatial and 1T dimension to describe the open string. But how can you have different space-time’s without throwing relativity out in the process? String theorists needed a new way to describe the open string in a closed string geometry. This was achieved by introducing a D-brane to allow for a dynamic geometry and allow for an object (described as an open string) to move in a 9D and 1T geometry. The D-brane was an object in it's own right and you could stack D-branes together. Importantly by allowing D-branes to freely move you could preserve the democracy of reference frames and allow for both open strings and closed strings to exist in the same universe. The duality still remained. What looked like empty space looked from another reference frame as an object (a boundary). For example, what appeared to be background space between strings could also be a vase from another frame of reference. What has been found with D-branes is that the duality of string theory and gauge theory are really the same theory. Both are frame of reference dependent. Both lead to the emergence of classicalism such as particles, fields, forces, the vacuum and space-time geometries. What this is strongly suggesting is that GR and QM are two ways of looking at the same thing but what is changing here is the nature of space-time. As space-time is no longer fundamental, quantum mechanics actually wins the battle. We have an equivalence a the plank boundary between the two theories but below this boundary, we have the quantum domain to deal with if we search further for fundamental causes. Revolution 2 - This kicked off in 1995 when Ed Witten suggested that all the five alternate string theory descriptions of the day were simply different interpretations of the same underlying theory (M-Theory) or Membrane Theory by adding a further dimension to 10D and 1T. This assumption needed D-branes to prove it. In achieving this, Witten needed to turn string theory into a 'local' symmetrical theory rather than a 'global' symmetrical theory and he introduced super-symmetry into the framework. Super-symmetry is the symmetry that allows an observer to shift their reference frame to swap fermions for bosons but in doing so recognising that 'c' ensures this swap cannot occur everywhere at once. Just like gauge symmetry, the misalignment that occurs with phase shift associated with the finite speed of light requires fictitious forces to patch up the differences (and restore the symmetry). Interestingly the 'force' that restores the super-symmetry in this occasion is gravity. It is gravity that restores the mismatched symmetry between inertial and accelerated observers on M-theory. Through this revolution the notion of 'string's' withered away to be replaced with membranes in 10D and 1T yet these membranes are not fundamental in themselves and are reference frame dependent. Strings were important to commence the theory but now with M-theory it was all about membranes. Strings became regarded as simply 'one classical limit'. It is not correct to think of the universe as being made of strings. In fact it is better not to conclude that he universe is made of anything. Each of the 5 different string theories created 5 different sets of particles but what is an elementary particle on one of the versions is composite in another. Thanks to the dualities all 5 theories are equally true. M-theory concludes that there are no basic ingredients. They appear as 'real ingredients' dependent on your perspective. But are there 'branes'? M-theory gets to a point where local objects appear dynamically. The theory is very non-local in nature. It is dependent on the frame of reference of the observer and the notion of boundaries (branes) or stuff inside the boundaries is frame of reference dependent. Now M-theory is starting to be replaced by the Holographic Principle and it appears that the Holographic Principle will be the 3rd great revolution of String theory. On this footing there appears to be significant scope for the merging String Theory and Loop Quantum Gravity camps.

I have dabbled with the multi-verse but a real shakeabout in my thoughts occurred only recently with research by Fotini Markopoulou in regards to Causal Dynamical Triangulations. In a nutshell it refers to a background independent quantum gravity approach where rather than talking in terms of multi-verses talks in terms of multiple reference frames in a classical 3D and 1T universe. The approach recognises that to put General Relativity and Quantum mechanics on the same footing to be able to unite the two frameworks we need to ensure the frames of references applied to both theories are similarily on the same footing. Namely when both theories are applied to the frame of reference of an observer embedded in the system. CFD assumes like GR that the definition of the universe is 'all that exists'. In that context it is impossible to have a frame of reference interpreting this universe from the outside. Interpretations must be done from within the universe. General relativity has always been a theory examining the universe as a system from the inside. By superimposing the different frames of reference applicable to different frames of reference we then develop a 'block universe' description of the classical reality. Quantum Mechanics until CFD however always assessed a system from the frame of reference of an observer located outside the system. To be equivalent to GR, the frame of reference of the quantum observer needs to be embedded in the system they are interrogating. This makes sense to me. CFD therefore inserts causal light cones onto the quantum lattice grid of spacetime and defines wavefunctions by the content of information contained within each light cone. Given this new approach both theories then are assessed therefore from the frame of reference of any observer located at any point in spacetime or in any state of relative motion and their associated scope of the system (the laboratory within which they conduct experiments) is defined by the light cone (or hubble volume) surrounding the observer. Provided the light cones are all causally connected then the same physics should be applicable in each light cone from both a QM and GR perspective. This approach can then use gauge symmetries to then determine how different points of view can see frame dependent attributes of 'classicalism' emerge such as spacetime, forces, particles, boundaries etc. emerge with the classical universe. The result is a multi-frame of reference viewpoint in 3D and 1T as opposed to a traditional quantum multi-verse occupying seperate universes. By superimposing the different wavefunctions associated with the information contained in each observers light cone, you can then see how a 'shared classical universe arises' where every frame of reference that shares a portion of causality with each other will agree on the classical reality that emerges. This approach is giving me so much joy as it is insisting that before we entertain the possibilities of a multi-verse, it's first best to check whether or not our classical reality which can actually be observed and verified can be understood through a theory operating within the 3D and 1T context. It appears to me that CFD and also the Holographic principle from the string theory camp are getting extremely close to a 'Theory of the Classical Universe'. After that, then we can entertain the notion of wondering whether other universes may or may not be described.

I like you am a relativist. I say dispatch local realism to the sin bin. What science has consistently demonstrated is that what once was regarded as 'invariant' inevitably turns out to be 'co-variant' in nature thanks to symmetry. As Emmy Noether concluded, spacetime symmetries lead to Conservation Laws. The fewer symmetries involved leads to fewer Conservation Laws. You need to peel the onion skin again and again to seach for any possible fundamental invariants. At the bottom of the classical ladder is 'c', the Planck scale quantised definition of spacetime and an ordered high entropy state to get the classical ball rolling. All other classical 'things' such as temperature, pressure, seperate space or seperate time, forces, spacetime curvature, particles/fields etc. have dissolved away as 'classical illusions' at this stage. I think we can go further in our extension of relativism than what has been achieved by GR and QM which to me represent alternate expressions (co-variant expressions) of a 'classical reality'. QM in this context is the classical expression of quantum phenomena that arises from the planck boundary. At a more fundamental level itself is the quantum domain itself which can only be described through abstract mathematics (hilbert spaces). The problem with theoretical constructions from the bottom up is that we need to comence with an infinite array of classical commencement states for our construction (reflected by the singularity). The infinite array leaves us uncertain which approach is the valid approach that describes our classical universe. I think we need to flip the way we construct a theory to a top down approach and at least recognise we need to start with the here and now (what is classically observed) and then construct our theories backwards to their initial commencement state. I think these constructions need to be information theoretic in nature in that we need to describe all the possible states that can be 'classically described' by different observers and then work backwards following causal routes backwards that commence from that 'now state' to ultimately describe the 'first cause' fundamental information unit/s from that particular frame of reference. Once we have achieved that, we then superimpose the causal histories from each possible classical frame of reference to explain the classical singularity and the uncertainty associated with the initial classical commencement point.