A Level Physics


Kit Betts-Masters


Space exploration presents a lot of problems.  We, as humans, haven't gone very far really... I mean the moon is far, but it's just around the corner when compared to other astronomical distances.  Even at the speed of light it would take eight minutes to get to the sun, or forty two years to our next nearest star.


So most of this topic will be about how we take measurements of our universe without actually going there.  We use trigonometric parallax to measure distances to nearby stars.  (You can probably take a good stab at the meaning of that as you'll have come across both words before in your studies.)  We use standard candles for more distant stars.  We analyse the light that comes from these stars and from that we can make conclusions about the temperature and mass of these stars.  Hence we can get an idea of the temperature of the planets around them, hence we can see if there are likely to be any planets in that exclusive "Goldilocks" zone; not too hot, not too cold, for liquid water, and therefore life!


But really all this is an aside to what is really interesting, the process of stellar-evolution.  We can plot a star's journey from nebula to white-dwarf on what we call a Hertzprung-Russell diagram.  A REALLY interesting graph.


Finally, for this topic, and for this course, is the question of where, when and how did it all begin?  And where, when and how will it all end?  Hubble analysed the red-shift of distant galaxies and came up with a graph whose gradient is inverse the age of the Universe.   We call this gradient the Hubble constant or H0.  It has been refined experimentally and we are currently thinking the Universe is about 14 billion years old.


So that's the beginning sorted.  The end of the Universe has been debated a lot recently, is the universe, open, closed, flat?  Will it expand forever or come back together in a kind of "big crunch"?  Latest evidence is that it is none of the above, but that it is actually accelerating!  It is expanding, yes, it will go on expanding, yes, but it is actually expanding at an accelerating rate.  This is evidence for the existence of a dark energy, and dark matter; stuff that we cannot see as it seems not to interact with light at all.  And this stuff, which we cannot see, which doesn't seem to interact with anything at all, which we know nothing about at all, comprises about 95% of the universe.


And this is where we are at with Physics today; we know a lot!  We have a huge number of Laws, theories and models which explain much of what we see and can do.  But this knowledge is only about 5% of the story.  Only about 5% of what there is to know.  I hope very much that you want to be a part of that story of discovery.