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Review:

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**This is the story of the tree of gravitation that grew up from the seed of Newton's apple of knowledge. Celebrating the 100th anniversary of Albert Einstein's Theory of General Relativity (GR), it pretends to put in context more than ten theoretical branches developed between 1905 and 2015.**

The gravity apple tree is a conceptual network that relates fundamental principles and theories of gravity, following also a temporal logic. The time line is indicated by gray lines which have their base in two axis that point towards the theory of Special Relativity. Experiments and observations are located in the time-line space. Proponents for theories and dates for main published articles are colored in green. Links to online Pdf's files are included. Principles followed by theories are written in the middle of branches or colored in purple. Main theories are in red, models in yellow and alternative formulations of GR in orange. Approaches to quantum gravity are in blue. Branches represent theories. Apples would represent the knowledge brought by following a particular path.

A quick tour has been designed, but a manual navigation is recommended for further exploration of the tree. Some other useful references and bibliography is included in the Gravity Apple Tree. Enjoy!

The gravity apple tree is a conceptual network that relates fundamental principles and theories of gravity, following also a temporal logic. The time line is indicated by gray lines which have their base in two axis that point towards the theory of Special Relativity. Experiments and observations are located in the time-line space. Proponents for theories and dates for main published articles are colored in green. Links to online Pdf's files are included. Principles followed by theories are written in the middle of branches or colored in purple. Main theories are in red, models in yellow and alternative formulations of GR in orange. Approaches to quantum gravity are in blue. Branches represent theories. Apples would represent the knowledge brought by following a particular path.

A quick tour has been designed, but a manual navigation is recommended for further exploration of the tree. Some other useful references and bibliography is included in the Gravity Apple Tree. Enjoy!

**All theories rest on some previous knowledge, like logic, semantics, algebra, analysis, general systems theory... which we normally don't question. Here, we look at the core of the fundamental principles in theories of gravity. Some of them, like the absolute space and time of newtonian theory are hypothesis. Others are empirical laws and and measurements, such as Kepler's laws or the value of G, measured by Cavendish.**

Newton's universal law of gravitation remains at the core of the Gravity Apple Tree as a limit for low velocity, weak field, high acceleration regime.

For more than 200 years, Newton-Poisson theory of gravitation grew as a robust tree with small setbacks, until the beginning of the XXth century...

Newton's universal law of gravitation remains at the core of the Gravity Apple Tree as a limit for low velocity, weak field, high acceleration regime.

For more than 200 years, Newton-Poisson theory of gravitation grew as a robust tree with small setbacks, until the beginning of the XXth century...

**Thank you!**

Special thanks to Shahen Hacyan, Sergio Mendoza, Xavier Hernández, Oliver López, Universidad Nacional Autónoma de México, CONACyT 357910.

Mario Casanueva, Hernán Miguel, Diego Méndez and the seminar of Representation and Modelization of the Universidad Autónoma Metropolitana-Cuajimalpa,

CONACyT CB-2012/182084

Fredrick Hehl, Allan Heiblum, and all my friends that have inspired and supported my work.

Pictures and graphs taken from the web, special thanks to all creators.

México, D.F., nov. 2015.

Special thanks to Shahen Hacyan, Sergio Mendoza, Xavier Hernández, Oliver López, Universidad Nacional Autónoma de México, CONACyT 357910.

Mario Casanueva, Hernán Miguel, Diego Méndez and the seminar of Representation and Modelization of the Universidad Autónoma Metropolitana-Cuajimalpa,

CONACyT CB-2012/182084

Fredrick Hehl, Allan Heiblum, and all my friends that have inspired and supported my work.

Pictures and graphs taken from the web, special thanks to all creators.

México, D.F., nov. 2015.

**Some reflections...**

The gravity apple tree is a guide for further discussion about plurality of theories, nature of ramifications, thickness or "popularity" of branches, citation lineages, interconnection between theories, the role of experiments constraining or promoting the growth of branches, and about the structure of theories. We do not pretend to give the answer to these questions, but to give a new and perhaps useful interactive perspective into the matter.

The temporal logic of the gravity apple tree gives a different configuration than those of similar trees, where the upper level nodes represent concepts of wither domains.

Research continues as it gives a basic data base that can generate new visualizations, in a circular feedback workflow. The tree is alive, it keeps growing and better defining its shape.

The gravity apple tree is a guide for further discussion about plurality of theories, nature of ramifications, thickness or "popularity" of branches, citation lineages, interconnection between theories, the role of experiments constraining or promoting the growth of branches, and about the structure of theories. We do not pretend to give the answer to these questions, but to give a new and perhaps useful interactive perspective into the matter.

The temporal logic of the gravity apple tree gives a different configuration than those of similar trees, where the upper level nodes represent concepts of wither domains.

Research continues as it gives a basic data base that can generate new visualizations, in a circular feedback workflow. The tree is alive, it keeps growing and better defining its shape.

http://goo.gl/RPZL1r

https://goo.gl/kVjXj3

G ∞ 1/t

2

M

∞ t

**http://goo.gl/pM0Vel**

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Fredrick Hehl

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