3/21

Agenda:
Big Bang introduction
Read: http://www.bbc.co.uk/science/0/20932483
Discuss in groups the following questions and write down answers:
a.  How do we know the universe is expanding?
Most of the light coming from galaxies is redshifted.  Redshifted means that the light is at a lower frequency, which tells us that it is moving away.  The inference (conclusion) that scientists draw from this evidence is that the universe is expanding.  

b.  What is the difference between light detected by a microwave telescope, and light detected by an optical telescope?   How do microwave telescopes help us see the afterglow of the Big Bang?
A microwave telescope detects CBR (Cosmic Background Radiation) which differs from "normal' light in that it has the same frequency no matter where it is in the universe.  We can deduce from this light's existence that it is the afterglow of a huge explosion and that all CBR comes from the same source (Big Bang).

c.  Distant gas clouds contain almost nothing besides hydrogen and helium.  How is this more evidence that supports the theory of the Big Bang?
By looking at gas clouds that are very far away, we are seeing as they were a long time ago, just after the Big Bang.  We observe that these gas clouds are composed of lithium, hydrogen, and helium.  This supports the assertion that after the Big Bang, there were only very simple elements.


d.  What happened before the Big Bang?