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Great read...and a small query

October 30, 2015

Author:       Sarthak Delete  Reply  IP  
I have a small query regarding the tidal effects in general relativity.
According to the explanation of tidal effects in the book, these are the consequence of height dependent time in General relativity. Could you please give an intuition for this reason or some references where I can read it?

CS: In general relativity, the change of time with height is due to the gravitational potential phi. The gravitational potential of a compact mass, in turn, is responsible for tides.

More precisely, the 00 component of the metric g is related to the potential, if everything behaves slowly and nicely: g_00= 1−2 phi /c^2.

Any updates soon?

October 19, 2015

Author:       Ian Bourke Delete  Reply  IP  
I've been anticipating an update for over a year now. Do you feel the need for one at this time or have there not been enough significant discoveries to warrant changes? Thanks!

CS: Many small changes are accumulating. A new edition will appear, but I do not know when yet. If you have a favorite topic, let me know!

October 16, 2015

Author:       Maruf Hasan Delete  Reply  IP  

A new world

October 9, 2015

Author:       Tarcisio Delete  Reply  IP  
Christoph, thank you for your books. They told me many things about nature that I did not know before. I am telling all my friends to read them.

CS: Thank you - I hope your friends and you enjoy it!

Energy Universe

June 26, 2015

Author:       Atlas Delete  Reply  IP
Energy is every DIFFERENCE in time - space according to time - space itself.

CS: Dear Atlas, sorry, but what you wrote makes no sense. Energy is measured in Joule, and time in seconds.

Great read.

June 3, 2015

Author:       C. Sarge Delete  Reply  IP  
I really appreciate this overview of physics, but I just have one question. Why such an anti-Newton bias? He is widely regarded as the greatest scientist of all time, but you seem to regard him as almost inconsequential. Does history regard him to highly?

CS: C., I do not know anybody who thinks that Newton is the greatest scientist of all time. Such fairy tales are only told by bad teachers. (Greater than Democritus, Hippocrates, Euclid, Galileo, Einstein, Pasteur, Koch, Liebig? What does "greatest" means anyway?) On the other hand, he surely was one of the most important alchemists of all times. He spent a much larger part of his life doing alchemy than doing physics. He spent most of his life looking for the philosopher's stone. But alchemy is not science. Even theology was more important to him than physics. The myth about Newton is very different from the real person. The book tries to give an objective account of his life.

Nice SR book (but...)

May 6, 2015

Author:       Pete Brown Delete  Reply  IP  
I took a look through the relativity text and found it to be a very nice text. There's one mistake in it that people make all too often and that's the belief that Einstein never used or believed in using relativistic mass (RM). This is incorrect. RM, m, is defined as momentum, p, over speed, v. I.e. m = p/v. If the object is a particle which moves slower than light then the RM can be written as m = gamma*m_0 where m_0 is the particles proper mass. If the particle is moving in a gravitational field and is moving slowly then m does not equal m_0. m is a function of the gravitational potential. This can be found in Moller's text. I've derived it and placed it on my website at:

Einstein used this in his text "The Meaning of Relativity" on page 102.

In his GR paper of 1916 he wrote that mass and energy are essentially the same thing and is fully described by the "energy tensor" which we now refer to as the "stress-energy-momentum tensor". He also assigned a mass density to EM energy density in one of his papers. So asserting that he never used RM is quite misleading. Actually he had to depend on it in his argument regarding Mach's principle.
Einstein also

CS: Dear Pete, in the book you mention, Einstein uses m to mean "rest mass", what you call m_0 ! In fact, he always did so, as far as I know. There is no paper where he used both m_0 for rest mass and m for relativistic mass. Also in the book you cite, Einstein does not use "relativistic mass" at all. And on page 102, there is nothing of what you are claiming. Furthermore, in the 1916 paper you mention, Einstein just says in §16 that "träge Masse nichts anderes ist als Energie", but not that relativistic mass should be used. In fact, the statement means "Inertial mass is nothing else than energy"! Of course, E/c^2 is a mass value, and that is what the statement expresses; but most researchers agree that is not useful to give it a special name. (By the way, your statement on Mach's principle is mistaken. The quantity m does not depend on the gravitational potential, whatever you may mean by "m".) But a fact remains: "Relativistic mass" was never used by Einstein; it is a concept only used by tabloids and by grandstanding authors.

A great idea- free physics

January 2, 2015

Author:       Tomctutor Delete  Reply  IP  
It's so refreshing to see this textbook provided free of charge for the whole student community worldwide as such traditional paperbooks in physics are typically very expensive, with some undergraduate volumes near $200 each to purchase.
The author will definitely have a place on my website here in Scotland. Thankyou Christoph

CS: Tom, thank you! The book is written both for enjoyment and learning.


November 15, 2014

Author:       Michael Dube Delete  Reply  IP  
Dear Christoph
Physics was a mystery to me in high school. It was intimidating; a struggle to get through. Over the last 40 years I continued to take a poke at understanding at least the basics. Now I find MotionMountain Physics - and understanding increases with every page. Thank you for this wonderful work. Students will be better for it; I know I am!

CS: Thank you for your message - I am happy that you like the book! If you have questions, email me.

October 11, 2014

Author:       Oliver Delete  Reply  IP  
Your work gives an new and unique perspective of Physics. Motion Mountain is my favourite among the hundreds of Physics ebooks I've explored. It's awesome, thank you!

CS: Thank you - enjoy it!

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