# １７　 Theory of Relativity（Albert Einstein）【What is the Universe？】Dialogue with the Universe

１７　 Theory of Relativity（Albert Einstein）【What is the Universe？】Dialogue with the Universe

○The universe is a four-dimensional space-time consisting of three-dimensional space and time, and the space-time can shrink or elongate. (Special relativity [1])
○ The speed of light(electromagnetic wave) traveling space-time is constant. (Special relativity)
○ You can write the relationship of energy and mass and speed of light with following equation. (Special relativity)
Ｅ＝ｍｃ＾２
※ｃ＾２：raise c to the 4 power

（Ｅ：energy（J）、ｍ：mass（ｇ）、ｃ：speed of light（ｍ／ｓ））
○If the mass of the object which exercises reaches speed of light, it will become infinite. (Special relativity)

○The space-time is distorted. (General relativity[2])
○ The universe is expanding. (General relativity)
○ Black hole exists. (General relativity)

※ In accordance with Special relativity and General relativity, it is called Theory of relativity.
※ According to theory of relativity, the phenomenon in which an error becomes large if Newtonian mechanics describes (movement near the speed of light and movement in a big gravitational field) , can be described correctly.

【Reference】
1. Special relativity（1905）
：The theory which dealt with the inertia system in the state where there is no gravity.
○The universe is the 4-dimensional world of time and space. The "space-time" seen from the watcher is a relative thing which is rectified by Lorentz transformation, and is extended or is shrunk.

○The length of a spacecraft is shrunk by a cross direction at a rate of.

(Ｖ: Motion speed, Ｃ：Light speed)
○At the system which exercises, compared with an external system, only is delayed in time.

2. General relativity
：Theory of gravity and space-time. （1915 - 1916）
○ Einstein’s equation: If you assign the mass of the material such as a star or energy in the right-hand side, it is possible to calculate the curvature of space-time around the star.

Ｇμν＋Λｇμν＝κＴμν

※ Left-hand side: Curvature of space-time (Geometrical quantity representing the bending of space-time)
※ Right-hand side: The distribution of the substance field (substance and light)

・Ｇμν：Einstein tensorTensor represents the distortion)
・Λｇμν ： The cosmological constant
・κ ：Einstein's constant of gravitation
（κ＝８πＧ／ｃ＾４ （π：pi、Ｇ：Gravitational constant、c ：Speed of light））
※ｃ＾４：raise c to the 4 power
・Ｔμν：energy-momentum tensor
・μ, ν: Identify the coordinates of space-time.