Expanding Universe 

Robert NemiroffMichigan Tech U.

Physics X: About This Course

• Officially "Extraordinary Concepts in Physics"• Being taught for credit at Michigan Tech

o Light on math, heavy on concepts o Anyone anywhere is welcome

• No textbook requiredo Wikipedia, web links, and lectures onlyo Find all the lectures with Google at:

"Starship Asterisk" then "Physics X"  o http://bb.nightskylive.net/asterisk/viewforum.php?f=39

Considering Our Universe as a Whole

• The Cosmological Principleo Universe Homogeneous & Isotropic

• Homogeneouso Smooth when averaged outo Example: jello, even fruity jello

• Isotropico Same in every directiono Example: room with the lights out

The Expanding Universe: Hubble’s Law

• Our Universe is expanding!• Discovered by Edwin Hubble in 1930s• More distant galaxies are moving away

faster• Hubble’s Law: v = Ho d

o v is galaxy velocity, d is galaxy distance and Ho is Hubble’s constant

Expanding Universe

            What is our universe expanding into?

1.  Empty space.2.  An extra spatial dimension.3.  An extra time dimension.4.  General Relativity only says that objects can move apart.

Expanding Universe

           4.  General Relativity only says that objects can move apart.

There are theories that use other spatial dimensions, but Einstein's General Relativity (GR), by itself, isn't one of them.  GR only says that the entire universe could be expanding.  GR does not include a larger "empty space" that it could be expanding into.  In GR, matter and energy is everywhere.  Observations indicate that matter is diluting everywhere.  

http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html

Center of the Universe

        

Toward which direction is the center of the universe?

1.  The Sun.2.  The center of our Milky Way Galaxy.3.  The dipole hotspot on the microwave background.4.  No direction.

The Expanding Universe: Where is the center?

In General Relativistic Cosmology:

• There is no center.• There is no “Big Bang National Park”.• The Universe is not an exploding golf ball.• Every point can be considered the center.• The expansion looks the same from every point.

http://www.hk-phy.org/articles/univexpand/univexpand.jpg

(Courtesy of SLAC and Nicolle Rager)http://www.interactions.org/imagebank/search_detail.php?image_no=SL0062

The Expanding Universe: What is expanding?

• Newtonian cosmology does have a centero Would result in strange unseen forces

• You and I do not expando Anything held together does not expand

• The average space between galaxies expands – almost drifts -- apart