# １３　Expansion of the universe 【What is the Universe？】Dialogue with the Universe

１３　Expansion of the universe 【What is the Universe？】Dialogue with the Universe

１３−１　[1]
• Since the Big Bang, The universe has continued to expand.
・Everything is moving away from us, with a speed that is proportional to its distance. ：The Hubble Law [2]
・ For expansion of the universe is the expansion of space-time itself, so it is also possible to exceed the speed of light.
・The universe is the same everywhere.：Uniformity
・Currently, the observable universe is expanding at 3.5 times the speed of light.
・Expansion of the universe is described in the general theory of relativity.
・ Outside of the observable universe is not known whether infinite or finite.

⇒ Therefore, in order to escape from our universe, rather than fly, it is necessary to exceed the time and space.

１３−２　Standard candle −Observation of the size of the universe[3]
・Brighter Type Ia supernova is known to shine longer.・・・So, it is possible to know the specific brightness( absolute magnitude) of the star from the shining period.
・Thus, it is possible to determine the distance (D (kpc)) to the Type Ia supernova.

Ｄ＝0.2・10^（ｍ-Ｍ-10）

Kpc: kiloparsecs =3.26 light year
ｍ ：the apparent magnitude
Ｍ ：the absolute magnitude

・Supernova explosion is about once in a hundred years in one galaxy, but if you use a large enough telescope, you can see the 100,000 galaxies in the night sky of the size of the coin. And in every one of the galaxy, because it contains several billion of stars, in the order of magnitude of the coin, you can observe three explosions overnight. [4]
・By observation of the standard candle, it was possible to determine the Hubble constant with an error range less than 10%. As a result, the age of the universe could be estimated.

１３−３　The Moon Moving Away

・Because of tidal forces between earth and moon, earth's rotation would gradually slow.
•As a result, the moment of the Earth's rotation (rotational force) is reduced, and the moment of the moon around the Earth increases, and the moon away from Earth (3.8 cm per year).

【Reference】
[1] Wikipedia：宇宙(The universe/Japanese)
[2] edX/Cosmology/Section1 Space and Time/Lesson1/Referende Notes 1