Treasures of modern physics

Last Saturday morning I dropped into Boobooks, Armidale's wonderful second-hand bookshop, and came away with two classics of modern physics: Louis de Broglie's Wave Mechanics (1930 - translated from the French original) and Paul Dirac's The Principles of Quantum Mechanics (3rd edition 1947, first published 1930). These two authors made fundamental contributions to their respective branches of physics, de Broglie winning the Nobel Prize for Physics in 1929, and Dirac sharing the prize with Erwin Schrödinger in 1933.

The flyleaf of de Broglie’s Wave Mechanics showed it to have been the property of “R.H. Healey B.Sc., Physics IV 1932”.

Imagine my delight on subsequently discovering on another flyleaf that it once belonged to my physics professor, J.M. (Jack) Somerville, who was also my first year tutor (those were the days!). Jack Somerville was one of the four original staff members of the New England University College, teaching the full University of Sydney Physics and Mathematics curriculum, and became the first Professor of Physics at UNE. Sadly, he died suddenly in 1964, while I was working as a research assistant in the Department, a great shock to the University community as a whole.

I already have a copy of a more modern text on quantum mechanics (David Beard’s Quantum Mechanics), sent to him by a publisher, which he gave to me in 1963, inviting me as he did so me to give him my opinion of it (which was highly favourable). I am very happy to have fortuitously acquired this additional link with such an admirable man.

On looking to see who R.H. Healey might be, I find that he was a student at Sydney University who shared with physicist, radio astronomer and school teacher Ruby Payne-Scott (1912-1981) the Deas Thomson and Walter Burfitt scholarships for physics.

As for Dirac’s Quantum Mechanics, that belonged to one N.W. Taylor. That will be Nathaniel Wesley Taylor, an outstanding mathematician who was one of the first two recipients of a University of New England Ph.D., at the Graduation Ceremony in 1958, and who was in the Mathematics Department when I was a student.

I think I will go back to Boobooks and see what other treasures I can find amongst the mathematics and physics texts.

Paul Dirac’s PhD thesis

I cannot resist posting this link to Paul Dirac’s handwritten notes for his PhD thesis – the first ever written on quantum mechanics: http://academia.edu/323246/PhD_Thesis_of_Paul_Dirac .

It was launched into the twittersphere by Dirac’s biographer Graham Farmelo (@grahamfarmelo).

Paul Dirac was one of the great physicists of the twentieth century and this thesis was one of his great contributions.  The Dirac Equation is one of the building blocks of modern physics and leads directly to prediction of the existence of antimatter. In 1933, aged only thirty-one, Dirac shared the Nobel Prize for Physics with Erwin Schroëdinger “for the discovery of new productive forms of atomic theory”.

He was an interesting character: the Wikipedia entry on him is worth a read.

Radiation Dose Chart

The news from Fukushima and the continuing drama about whether the six reactors can successfully be brought to a safe and stable condition has, quite understandably, got people all over the world worrying about the hazards of nuclear radiation. 

The hazards from an uncontrolled event are very real. There is no safe dose, and no-one should fall for the silly and irresponsible material that has been circulating on the web and in the twittersphere to the effect that small amounts of radiation are good for you. They are not.

On the other hand, we are exposed to ionising radiation every moment of our lives, and the modest risks associated with low doses or with infrequent higher doses under controlled conditions are something we all need to live with. In a wide range of medical circumstances the risks of exposure to ionising radiation are the better part of the risks of failing to make a timely diagnosis.

Most people are aware that medical radiation can be harmful, but very few are aware of the small doses we receive every day of our lives, or the relativities of the different sources of radiation.

The Radiation Dose Chart at http://xkcd.com/radiation/ sets it out very nicely. There are many things to be discovered here; I will point out just a few. By way of background, the standard unit for absorbed dose is the sievert (Sv), hopefully measured in millionths of a sievert (microsieverts μSv) or thousands of a sievert (millisieverts mSv).

Now for some comparisons. According to the data painstakingly compiled on the chart:

-  Living for a year within 50 miles of a nuclear power plant for a year (0.09 μSv) involves just under twice the exposure you get from sleeping next to someone (0.05 μSv), and slightly less than you get from eating a banana (0.1 μSv)

-  If you live within 50 miles of a coal fired power station for a year you will absorb 0.3 μSv, more than three times the exposure  of someone who lives within 50 miles of a nuclear power station for a year (0.09 μSv)

-  That in turn is less than a third of what you would receive from an arm X-ray or using a CRT monitor for a year (1 μSv)

-  These in turn are only a tenth of the dose from background radiation received by an average person on a normal day (10 μSv)

-  Which is only a quarter of what you would receive taking a single flight from New York to Los Angeles (40 μSv)

- Living in a stone, brick or concrete building for a year involves higher exposure again (70 μSv)

-  All of which pale into insignificance alongside a single mammogram (3 mSv, i.e., 3000 μSv), which is roughly comparable to the normal yearly background dose (about 3.65 mSv)

The fact is that just about everything is radioactive to some degree.

Physics: Dark energy - does it really exist?

The April 2009 edition of Scientific American contains an article by Oxford cosmologists Timothy Clifton and Pedro G. Ferreira that addresses the question of whether “dark energy” exists.

The question of whether this baffling form of energy exists arose in the wake of the discovery 11 years ago, due to measured anomalies in the red shifts of light from supernova explosions, that the expansion of the universe is accelerating. This flies in the face of our expectation that the gravitational pull of all the matter in the universe should be causing the expansion of the universe following the “Big Bang” to slow, leading ultimately to a massive collapse.

The fact that there is something that we cannot detect (dark energy) pushing the universe along rather than causing it to slow is so puzzling that some cosmologists are revisiting the fundamental postulates that led them to deduce its existence in the first place.

Of these the most fundamental is the Copernican assumption that we live in an ordinary neighbourhood of space, that there is nothing special about our part of the universe. This revolutionary (in the 16^th century) principle, so seemingly mundane, is a very powerful one for cosmologists: it means that they can work on the basis that the universe has a uniform density and looks the same in every direction. We can therefore extrapolate from what we see in our own region to the universe at large. There is a huge amount of evidence to support this idea.

A possible alternative explanation which would not require the existence of dark energy involves postulating that we live in a massive region in which the density of the universe is only half or a third of the density elsewhere. With that assumption it is possible to construct a chain of reasoning that says that the anomalous red shifts of supernova explosions that make it look as though the expansion of the universe is accelerating is in fact due to the fact that the light we see from the explosion travels at different speeds as it passes through more and less dense regions.

Whichever of these explanations turns out to be the more supportable, this conundrum is a huge challenge for modern physics. Both explanations strike cosmologists as extremely unlikely. Fortunately the cosmic void idea does not exactly mimic dark energy, so there are some ideas for very sophisticated observations that would help us to distinguish between the two.

Read the full article here.

Physics: Naked singularities

The February edition of Scientific American contains an article by Professor Pankaj S. Ghoshi of the Tata Institute of Fundamental Research, Mumbai, which addresses the issue of whether so-called “naked singularities” could be formed when a large star collapses.

The two possible outcomes of the collapse of a dying massive star are the formation of black holes and the formation of naked singularities. In either case we see the formation of a singularity – a wad of matter so dense that the laws of physics break down and we need new laws to describe it. Anything that hits the singularity is destroyed.

In the case of a black hole, the singularity is “clothed”, that is, surrounded by a boundary that hides it. This boundary is called the event horizon. Nothing that falls through this surface can ever get back out, and no information can get out.

A naked singularity has no such boundary. It is visible to outside observers, and objects that fall toward the singularity can in principle reverse course right up to the moment of impact.

Conventional wisdom has it that a large star eventually collapses to a black hole, but some theoretical models suggest that it might instead become a naked singularity. Sorting out what happens is one of the most important unresolved problems in astrophysics.

The Editors of Scientific American observe that discovery of naked singularities would transform the search for a unified theory of physics, not least by providing direct observational tests of such a theory.

This material is not light reading but it is written to be accessible to the lay reader and goes to the heart of what makes the universe tick, so is worth the effort. It may be accessed here on the Scientific American website.