Talk:General Relativity

Comment

This article is a redirect from General Relativity (capital R) to General relativity (lower case r).--Dthomsen8 (talk) 02:27, 31 May 2019 (UTC)

A 5 minutes explanation of Relativity

Abstract: A very simple explanation of Relativity is presented.

1. Introduction

1.1 Galileo Galilei

According to Galileo Galilei, the Father of modern science, the knowledge must be tested with quantitative experiments and results should be described mathematically. He formulated 2 principles* of inertia and of relativity:

1. Objects retain their velocity unless a force acts upon them.

2. Any two observers moving with constant velocity relative to each other will obtain the same results for all mechanical experiments.

Galileo assumed that a body can move by inertia not only uniformly in a straight line.

1.2 Sir Isaac Newton

Sir Isaac Newton discovered the three fundamental laws of classical mechanics, the first one was Galileo's Principle of Inertia. In Newton's model time and space are independent and absolute.

1. Every body remains in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

2. The rate of change of the momentum of a body equals the force $\mathbf {F}$ acting on the body, $d\mathbf {p} /dt=\mathbf {F}$.

3. To every action there is always opposed an equal reaction.

1.3 Albert Einstein

Albert Einstein used two postulates to build his Special Theory of Relativity; the first one was the generalized Galileo's principle of relativity:

1. All the laws of nature are the same in all inertial reference frames.

2. The speed of light in vacuum is the same in all inertial reference frames.

In Einstein's model time and space separately are not absolute, but the united four-dimensional time-space is absolute.

2. Essence of Relativity

It is accepted that Special Relativity is built on two postulates. In both of them the term inertial reference frames is used and the principle of inertia defines it. There is only one essential difference between Special Relativity and Newtonian mechanics and it is kinematical. This is the postulate of the constancy of the speed of light in vacuum - c. The velocity is kinematical term and it is defined by some geometry. The principle of the invariance of the speed of light defines the use of pseudo-Euclidian geometry. There is no difference between the dynamical part of Special Relativity and the Newtonian dynamics; the principle of inertia is the same in both. The second law of Newton $d\mathbf {p} /dt=\mathbf {F}$ remains valid but can be generalized to four dimensional invariant. The laws of conservation of mass, energy and momentum are united in a general law of conservation by the momentum four-vector. The equivalence between rest energy and mass, $E_{0}=m$, is a special case of more general equivalence between the mass and magnitude of the momentum four-vector, $|\mathbf {p} |=m$ !

There is another essential dynamical difference between General Relativity and Newtonian mechanics. The principle of inertia can be generalized: the physical objects conserve their state of motion, if they do not interact with other objects. This quality of conservation of state of motion is inertia, and quantitatively is characterized by a set of conservative quantities - momentum $\mathbf {p}$, angular momentum $\mathbf {L}$, energy $E$ and mass $m$. The momentum four-vector is preserved if there is no interaction ($\mathbf {p=const} ,d\mathbf {p} /d\tau \ =\mathbf {\nabla _{u}p=0}$), and the motion of objects is along extreme line. Dynamics of General Relativity defines pseudo-Riemannian geometry.

Is a 5 minutes explanation of Relativity possible? Yes, it is, if we use the time relativity (time dilation).

More:

[1].Marinchev, E., Universality, http://universality.hit.bg/

[2]. Marinchev, E., Universality, LANL e-print: physics/0211106

[2a]. http://en.wikipedia.org/wiki/Talk:Inertia

[2b]. http://adsabs.harvard.edu, bibcode=2002physics..11106M

[3]. http://www.33beat.com/moment%20of%20inertia.html

[4]. http://www.mauspfeil.net/inertia.html

[5]. http://math.ucr.edu/home/baez/gr/gr.html

[6]. http://xxx.lanl.gov/abs/physics/0408077

• PRINCIPLE: A fundamental truth from which others are derived or on which others are founded and that is tested many times experimentally.

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BetacommandBot 01:29, 24 July 2007 (UTC)