Expanding Universe Background: Before 1917, many scientists thought the universe always existed. But Einstein’s revolutionary theory of gravity changed all the rules. It opened up the mind-boggling possibility that space itself the permanence of which had never been questioned-might actually be expanding. If space is expanding, the universe we inhabit today could once have been infinitely smaller.  In 1929, astronomer Edwin Hubble made the amazing discovery that distant galaxies are speeding away from us. This means that the galaxies we see today were once much closer together –originating from a tiny region of space. The origin of the universe remains one of the greatest questions in science. Current scientific evidence supports the Big Bang theory, which states that 12 to 15 billion years ago, the entire universe began expanding from a very hot, very dense state. This sudden expansion is known as the Big Bang. What does it mean to say the universe is expanding? The Big Bang was an expansion of space itself. Every part of space participated in it. Space is not simply emptiness; it’s a real, stretchable, flexible thing. Galaxies are moving away from us because space is expanding. Galaxies are moving with space, not through space! The models in this activity demonstrate how the motions of the galaxies reveal the continuing expansion of the universe. In the 1920s, Edwin Hubble measured the motion of galaxies. By measuring a galaxy’s distance from us and how fast that galaxy is receding (its recession velocity), he found a simple relationship: double the distance, double the velocity; triple the distance, triple the velocity. This is Hubble’s Law. In equation form, it is written: V = H0 x d Recession velocity  = Hubble’s constant x distance from us The slope of the graph of the distance vs. velocity represents the Hubble Constant for the universe. The Hubble Constant describes how fast the universe is expanding. By measuring the rate of expansion, the size and age of the universe can be calculated. Interpreting recent observational results from space-borne and ground-based telescopes, scientists have determined different values of Hubble’s constant. Determining the precise value of the Hubble constant is key to understanding the origin of the universe, and there are several factors that affect this determination. For example, the universe may not have been expanding at the same rate throughout time; that is, the expansion itself may be accelerating. Questions like these make the age of the universe a hot topic – one of the most controversial in the study of cosmology. 

Reading Questions (from reading)

What is the Big Bang Theory?

Why are galaxies moving away from us?

If galaxies are moving away from each other now, what does that say about the distance of these same galaxies in the past?

Describe the relationship of Hubble’s Law?

What is the equation for Hubble’s Law?

 What is recession velocity?

What does the Hubble Constant describe?

Why is Hubble’s Constant important in determining the age of the universe?