Flamsteed Astronomy Society
The Big Questions: The Universe
Dr Stuart Clark
The 20 biggest cosmic mysteries made simple by Dr Stuart Clark
This lecture was presented by Dr Stuart Clark, Senior Editor for space science for the European Space Agency, and a contributor to the New Scientist, The Guardian, and The Times. Stuart has written several excellent books and this lecture was based upon his recent work, “The Big Questions: The Universe”. The book explores 20 fundamental questions in astronomy, physics, and cosmology. Rather bravely Stuart chose to touch on all 20, a very wide-ranging survey for a one-hour talk. Here are some aspects that stuck. If you think our report is a bit thin… you’re right! Read the book! You’ll enjoy it immensely.
What is the Universe?
Let’s start with something easy… er. It is everything; all space and all time. It is everything there ever has been, and will be. Trying to find a way of linking us with the wider universe can be explained by a few lines of mathematics. We can see the whole universe for the whole time in history.
How big / old is the Universe?
Stuart took a canter through the cosmic distance ladder: the scale of the solar system (the A.U.); parallax; Cepheid variables; type 1a supernovae; Hubble and redshift. The most distant object yet observed has a redshift of just over 8, converting into a distance of around 13 billion light years. Computer models based on the laws of general relativity suggest that the Universe has grown to over 95 billion light years across during that time. The latest estimates suggest it is around 13.7 billion years old.
What are stars made from?
Stuart gave a quick account of man’s faltering steps to understand the stars. As late as 1830 August Comte was writing that the composition of the stars was something we would never know because of their huge distance away from us. The discovery of spectroscopy changed all that, but our modern knowledge of stellar physics is very recent – a 20th Century work. The stars are predominantly hydrogen and helium and they shine because they release energy from nuclear fusion. Stars are born, live, and die with each new generation forming from the debris of the previous.
How did the Earth form, and why do planets stay in orbit?
The Earth formed at the same time as the Sun and the rest of the solar system about 4.6 billion years ago. The system condensed from a giant cloud of gas and dust left over from an exploding supernova. The force of gravity caused the condensation and keeps the planets in orbit. The planets are the left-over debris which did not make it into the central star.
Was Einstein right?
Yes! Newton described gravity as a force between masses which holds things in orbit in space. Einstein defined the space-time continuum and describes gravity as a warping of this 4-dimensional space by mass. Many experiments have confirmed Einstein’s description. One of its earliest successes was to describe accurately the orbit of Mercury.
What is a Black Hole?
We do not know! Black holes were predicted to form from the collapse of giant stars at the end of their lives, and we now also believe that most galaxies have huge black holes at their centre. The gravitational field of a black hole is so large that nothing can escape from it, not even light. Its escape velocity is higher than the speed of light. Our equations, the laws of physics, break down at the centre of a black hole – a ‘singularity’.
How did the Universe form? What were the first celestial objects?
There is evidence that the Universe formed in a ‘Big Bang’ almost 14 billion years ago, and expanded rapidly during a period called ‘cosmic inflation’. What triggered the big bang, and from what, and why inflation happened, are some of life’s great mysteries that create employment for many cosmologists. We really don’t know what formed first – galaxies, black holes, or megastars. Observational evidence is just beyond our present limit of capability to collect, which gives endless opportunity for theoretical speculation, and boundless optimism that the next huge telescope (probably in orbit) will resolve these questions, if only we had enough money.
What is Dark Matter?
Our present theories of galaxy formation and rotation require much more mass than we can observe or even possibly extrapolate. Something is gluing galaxies together which is not normal atomic matter…(either that, or our understanding of how gravity works is not completely correct) To explain all this, and rather than throw out Einstein and Newton, cosmologists have dreamt-up ‘dark matter’ which has mass but does not interact with light and is therefore very hard to detect. Particle physicists like this because thei