Saturday, 17 March 2018

Stephen Hawking RIP

Most of the readers of this blog will be saddened by the death of Stephen Hawking earlier last week a good obituary by his first colleague Roger Penrose can be found here

https://www.theguardian.com/science/2018/mar/14/stephen-hawking-obituary

Also his Adams Prize essay which deals with his earlier (and in my mind most significant work ) where he along with Penrose established the fact that Classical General relativity had to have inevitable singularities associated with it. Penrose had established this for black holes and stellar collapse, Hawking along with a coworker Ellis was able to establish this for cosmology.


An introduction to the essay is given here

https://www.epj.org/images/stories/news/2014/10.1140--epjh--e2014-50014-x.pdf

And the actual essay itself is here

https://www.epj.org/images/stories/news/2014/10.1140--epjh--e2014-50013-6.pdf

The essay was later extended into a book

https://www.amazon.co.uk/Structure-Space-Time-Cambridge-Monographs-Mathematical/dp/0521099064

Whilst the work is undoubtedly important most physicists and cosmologists  will probably find this approach totally alien to their background as it assumes a knowledge of topology and coordinate free differential geometry. I fall into this category myself. and whilst I bought the book have never really understood it. It along with Von Neumann's book on the Foundations of quantum mechanics must deserve the title of one of the most incomprehensible books on physics ever written.


It unfortunately does not seem that easy to get the requisite background either. As the pure mathematicians way of thinking proof lemma proof does not lend itself easily to those who want to get stuck in and calculate say the Riemann tensor for a given geometry and solve the resulting equations.

At least the essay does not seem as intimidating as the book, but it would take a long time to get the necessary background to understand it. I don't as yet have the pre-requisites to understand the pre-requistes :). Who knows one day I might get this background but it's a long way off and I want to concentrate on more accessible calculations.



Anyway despite not being in a position to understand Hawking's or even Penrose's work one cannot but feel sad that Hawking is no longer with us. I would add at the risk of being churlish, the claim in the media that Hawking is the greatest physicist since Einstein is typical of unjustified hype. Feynman for example is surely greater. One could make a case that Hawking and Penrose and all the people such as Ed Witten working on superstrings, whilst udoubtedly great mathematicians are not physicists in that they have not actually established a new fact about nature. In that respect the developers of the Standard model of particle physics such as Weinberg, Salam, t'Hooft and Veltmann have achieved more from a physics point of view, than all the mathematicians working on quantum gravity will ever do. Of course given the nature of quantum gravity, it is highly unlikely that any empirical fact will emerge from it that one can measure. It is highly unlikely that quantum gravitational corrections to say the decay rate of the neutron or the magnetic moment will ever lead to anything measurable. Thus by choosing to concentrate on a subject in which it is highly unlikely that any empirical evidence will arise to verify the claims, then it must be said that Hawking was not really a physicist.

Having said that of course there is still room for understanding the underlying mathematical structure of a subject and it would appear that Hawking did this brilliantly with General Relativity it is such a shame however that his ideas will probably only be understood by a select few individuals. Anyway with the death of Hawking we have lost one of the major players in the field and the world is a poorer place without him. At least he will now know how the universe works ๐Ÿ˜ƒit just a pity he wont be able to tell us.

Added 3rd April 2018 

There is in fact an overview of Hawking and Penroses work on singularities which was a set of lectures that the two gave in the 1990's. Hawkings lectures are contained here

https://arxiv.org/abs/hep-th/9409195


And the full set is here

https://press.princeton.edu/titles/9165.html

This is certainly more informative than Hawkings popular books such his notorious 'Brief History of Time' or his later one 'The Grand Design'

Anyway reading the lectures and the book should give the average physicist who knows a smattering of General relativity a bit of an idea of the singularities associated with General relativity but it still would not be a substitute for the Adams Prize Essay or the actual book itself.