The Cosmic Scale

n  Now that we know the few elementary particles and forces let’s see how their ‘Universality’ applies at different scales.

n  We will start with the Universe and its various contents. At this scale only ‘Gravity’ is the relevant force.

n  Remember: what Newton realized seeing the falling apple is not that gravity exists, which is trivial, but that it is a universal force, i.e. the same force that makes the apple fall, also keeps the planets go around the Sun, millions of stars spinning around the center of a galaxy etc.

The Cosmic Scale Menu

•  Big Bang Cosmology

•  Gravitation – Planetary Motion – Kepler laws – Satellites/Orbits – Escape Velocity

•  Black holes

Our Universe

• how big is it?

• how did it begin?

• how will it end?

• what is it doing in the meantime?

Does it go forever?

• Olbers’ paradox. –  He asked a simple question:

•  “Why is the night sky dark?” – It should be as bright as day!!!!??

•  If Universe is infinite, whole sky should be as bright as the sun!

•  No matter where you look, you would see a star. Where the stars are further away, there are more of them!

Olbers’ Paradox

But…the night sky IS dark

•  So, maybe, the stars do not go on forever

• Maybe, the Universe is finite! It ends somewhere!!

– As we said earlier, do not ask ‘what lies beyond’…wrong question !!!

A Universe of Galaxies

•  Play movie ‘Deep Space’

•  Play movie ‘GALAXY EVOLUTION’

The Milky Way is a disk-shaped galaxy, a collection of dust, planets, and billions of stars, including our Sun and solar system. The force that binds it or any other galaxy together is the same force that holds the Moon in orbit and you on Earth

GRAVITY

KENT!

Today’s (9/4/2014) news. The Milky Way is part of Local Cluster of Galaxies which, in turn, is part of a Supercluster of Galaxies called ‘Laniakea, Hawaiian for “Immeasurable Heaven.” It appears that all Galaxies in the cluster move towards a ‘Great Attractor” under the force of

GRAVITY

http://www.space.com/27016-galaxy-supercluster-laniakea-milky-way-home.html?cmpid=558267

•  Play movie ‘Laniakea’movie

https://www.youtube.com/watch?v=rENyyRwxpHo

But…this is not all

•  Not only the Universe appears to be finite but it also appears to be expanding

•  Stars (and galaxies) are moving away from each other –  the further a galaxy is from us, the faster it is

moving away •  What is going on?