11 Summary of Week 4

This week you’ve learned how our view of the universe is affected by the speed of light – looking out into space means looking back in time – and how the age of the universe limits the size of the observable universe. No knowledge of objects at greater distances is possible, as their light hasn’t had time to reach us.

The effective boundary of the observable universe is the cosmic background radiation which originated about 380 000 years after the Big Bang. It covers the whole sky like a fog, preventing us from seeing any further. Observations of galaxies within the observable universe show not only that the whole universe is expanding, but that the expansion is accelerating. Einstein’s theory of general relativity tells us that such a universe will expand forever.

General relativity has been fabulously successful, not only in modelling the universe, but in many other areas of astronomy and physics. But it cannot explain everything. Next week will probe the limits of the theory, starting by considering what it says about time, and then by exploring a place where this all gets broken apart.

You are now halfway through the course. The Open University would really appreciate your feedback and suggestions for future improvement in our optional end-of-course survey [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] , which you will also have an opportunity to complete at the end of Session 8. Participation will be completely confidential and we will not pass on your details to others.

You can now move on to Week 5.