### The most frequently asked questions about TGD 2014 . The headlines:

- Why TGD? (pdf-article)
- How can TGD help to solve the problems of recent day theoretical physics?
- What are the basic principles of TGD?
- What are the basic guidelines in the construction of TGD?

Standard model summarize the recent understanding of physics. The attempts to extrapolate physics beyond standard model are often based on naive length scale reductionism and have produced Grand Unified Theories (GUTs), supersymmetric gauge theories (SUSYs). The attempts to include gravitation under the same theoretical umbrella with electroweak and strong interactions has led to superstring models and M-theory. These programs have not been successful, and the recent dead end culminating in the landscape problem (criticality lost?) of superstring theories and M-theory could have its origins in the basic ontological assumptions about the nature of space-time and quantum.

**The question requires an overall view about the recent state of theoretical physics.**

1. Why TGD?

1. Why TGD?

- Thermodynamics, special relativity, and general relativity involve also postulates, which can be questioned, as in thermodynamics second law in its recent form, and the assumption about fixed arrow of thermodynamical time, since it is hard to understand biological evolution in this framework.

- In general relativity the symmetries of special relativity are in principle lost and with Noether's theorem this means also the loss of classical conservation laws, even the definitions of energy and momentum are in principle lost.

- In quantum physics the basic problem is that the nondeterminism of quantum measurement theory conflicts with the determinism of Schrödinger equation.

**2. How can TGD help?**The view about space-time as 4-D surface in fixed 8-D space-time is the starting point.

**motivated by the energy problem of general relativity****fusion of the basic ideas of special and general relativities (a TOE).**

- dark matter as
- extension of physics in p-adic number fields assumed to describe correlates of cognition and intentionality,
- zero energy ontology (ZEO) - quantum states
are identified as counterparts of physical events (two times required).

These new elements generalize considerably the view about space-time and quantum + give possibility to understand living systems and consciousness in physics.

**3. TGD as a mathematical theory, basic principles.**

A generalization of Einstein's geometrization program from space-time level to the level of "world of classical Worlds" as space of 4-surfaces.

The infinite-dimensional geometry fixes it uniquely.

It is the modes of the classical imbedding space spinor fields - eigenstates of four-momentum and standard model quantum numbers - that define the ground states of the super-conformal representations. It is these modes that correspond to the 4-D spinor modes of QFT limit.

+TGD as a generalized number theory with three separate threads.

It is not yet clear if both visions (geometrization and number theory) are needed. In any case their combination has provided a lot of insights about quantum TGD.

**4. Guidelines in the construction of TGD.**The construction of physical theories is nowadays to a high degree guesses about the symmetries and deduction of consequences. The very notion of symmetry has been generalized in this process. Super-conformal symmetries play even more powerful role in TGD than in superstring models and the gigantic symmetries of WCW is a powerful 'proof'.

In TGD context string like objects are not something emerging at Planck length scale but in scales of elementary particle physics. The irony is that although TGD is not string theory, string like objects and genuine string world sheets emerge naturally from TGD in all length scales.

Even TGD view about nuclear physics predicts string like objects.

The most important guidelines:

A kernel of WCW = a conjecture.

M

^{4}× CP

_{2}as choice for the imbedding space

Number Theoretical Universality

'Quantum classical correspondence' where classical theory is no approximation but an exact part of quantum theory.

And more technical guidelines:

- Strong form of General Coordinate invariance (GCI) is a very strong assumption, that gives the assumption that Kähler function is Kähler action for a preferred extremal as a counterpart of Bohr orbit. Strict determinism not required. Strong form of GCI requires that the light-like 3-surfaces represent partonic orbits and space-like 3-surfaces at the ends of causal diamonds are physically equivalents as effective 2-D states. The intersections of these two kinds of 3-surfaces and 4-D tangent space data at them code for quantum states.
- Quantum criticality means that Universe is analogous to a critical system with maximal structural richness. Universe is at the boundary line between chaos and order. Quantum criticality fixes the basic coupling constant dictating quantum Dynamics.
- Finite measurement resolution using von Neumann algebras. Usually the measurement problem is a messy, ugly duckling in theoretical physics.
- Strong form of holography from strong form of GCI and TGD reduces to an almost topological QFT= a conjecture. Weak form of electric-magnetic duality is a TGD version of electric-magnetic duality discovered by Olive and Montonen.
- Generalized Feynman diagrams. TGD leads to a realization of counterparts of Feynman diagrams at the level of space-time geometry and topology. The highly non-trivial challenge is to give them precise mathematical content. Twistor revolution has made possible a considerable progress in this respect and led to a vision about twistor Grassmannian description of stringy variants of Feynman diagrams.
- The localization of spinor modes at string world sheets. There are three reasons for the modes of the induced spinor fields to be localized to 2-D string world sheets and partonic 2-surfaces - or to the boundaries of string world sheets at them defining fermionic world lines.

Thanks to holography fermions behave like pointlike particles, which are massless in 8-D sense. General relativity emerges as an approximation due to frustration.

- gives em-charge as eigenstates. Spinor modes can have have well-defined electromagnetic charges - the induced classical W boson fields and perhaps also Z field vanish at string world sheets so that only em field and possibly Z field remain.

- acts as spacetime 'genes'.

- sign problems with partition, not necessary positive always. This is avoided in the 2D World sheet of TGD (many sheeted spacetime).

This is a very compressed text about TGD. Go to the sources for better info.

Why TGD and What TGD is? 2018 (with spinor part), 49 pp.

A very short summary, a brief summary about TGD, 2018, 3 pp.

Topological Geometro-Dynamics(TGD) is a unified theory of fundamental interactions. Quantum classical correspondence [by dimensional reduction] has been one of the guiding principles.A different thinking in many questions is very much charachteristic of TGD. Matti himself says that TGD is an oldfashioned quantum hadron model (as instance described by Björken), and the dimensions are emergent from microcosmos and gauge Lorentz invariance with its roots in the vacuum or zero point field. See also The model for hadron masses revisited.

The basic differencies of TGD in relation to other main theories:

The basic objection against TGD is acc. to Matti, that induced metrics for space-time surfaces in M^4 × CP_2 form an extremely limited set in the space of all space-time metrics appearing in the path integral formulation of General Relativity. Even special metrics like the metric of a rotating black hole fail to be imbeddable as an induced metric. For instance, one can argue that TGD cannot reproduce the post-Newtonian approximation to General Relativity because it involves linear superposition of gravitational fields of massive objects. Holger B. Nielsen made this objection for at least two decades ago. Perhaps the strong objection against TGD is that linear superposition for classical fields is lost.

The linear superposition is however central

starting point of field theories. Many-sheeted space-time circumvent this argument.The replacement of linear superposition of fields with the superposition of their effecs meaning that sum is replaced with set theoretic union for space-time sheets.This simple observation has far reaching consequences: it becomes possible to replace the dynamics for a multitude of fields with the dynamics of space-time surfaces with only 4 imbedding space coordinates as primary dynamical variables. See also Standing waves in TGD.The continuityhas also been an obstacle in a world where even the quantum fraction is geometric.Discrete vs continuous controversy in physics - discrete and continuous features coexist in any natural phenomenon,

depending on the scales of observation.I quote from the TGD Intro (2007) about the main differencies from mainstream:

TGD was originally an attempt to construct a Poincare invariant theory of gravitation. Spacetime,

rather than being an abstract manifold endowed with a pseudo-Riemannian structure, is regarded as a 4-surface in the 8-dimensional space.The size of CP_2 which is about 10^4 Planck lengths replaces Planck length as a fundamental length scale in TGD Universe.The identification of

the spacetimes as a submanifolds leads to Poincare invariancebroken only in cosmological scales and solves the conceptual difficulties related to the definition of the energy-momentum in General Relativity. Even more, sub-manifold geometry, being considerably richer in structure than the abstract manifold geometry behind General Relativity, leads to a geometrization of all basic interactions and elementary particle quantum numbers. In particular, classical electroweak gauge fields are obtained by inducing the spinor curvature of CP_2 to the spacetime surface.Fig. 1. a) Future light cone of Minkowski space. b) CP_2 is obtained by identifying all points of C^3, space having 3 complex dimensions, which differ by a complex scaling \Lambda: z is identified with \Lambda x z.

This forces a generalization of the conventional spacetime concept to what might be called manysheeted spacetime or 'topological condensate'. The topologically trivial 3-space of General Relativity is replaced with a 'topological condensate' containing matter as particle like 3-surfaces "glued" to the topologically trivial background spacetime sheet by extremely tiny connected sum (wormhole) contacts having CP_2 size connecting the spacetime sheets. End quote.

The criticality.One big problem in physics is the criticality, how a classic world can come from the quantum uncertainty. This problem does not differ so much from M-theory, but the solution does very much.

TGD can be seen as a model giving rise to GR as a simple 'mirror image', and also there is a double mirror. Time dimension also have this 'mirror image', and magnetism, em-'force' can be vanishing? See How to perform WCW integrations in generalized Feynman diagrams? and "The relationship between TGD and GRT". He writes (from the GRT abstract, and I have filled in other links):