Tag: physics

Book review: Her Space, Her Time by Shohini Ghose

My next review is of Her Space, Her Time by Shohini Ghose. I picked this book up as a result of a review in New Scientist. It is in the spirit of Broad Band which covered the contributions of women to computing over the years – contributions which have historically been ignored. Her Space, Her Time does the same for women in physics, generally on the astrophysics and cosmology side of the subject.

The book is divided into seven chapters each covering an area of physics and a group of women who worked in those areas. The chapters cover star cataloguing (and rather more), the big bang, the space programme, radioactivity, nuclear fission, particle physics and dark matter/ beta decay. This results in a coverage which is approximately chronological.

There are some recurring themes in the book: women not allowed entry to universities for undergraduate and graduate studies, women not allowed employment in university departments and facilities (often the pretext is the lack of toilets for women), women not allowed employment at the same institution as their spouse (this seemed common in the US and its effect on the recruitment and promotion of women was noted as far back as 1966), being ignored by the Nobel Prize committee and (sometimes) their male collaborators. These women were frequently the only women in the room. Fleeing Nazi Germany (and Austria) is a theme too but that applies equally to men.

On a more positive note their work was often recognised and rewarded during their lifetimes by their scientific communities. In at least the case of Ernest Rutherford and Ernest Lawrence they had the support of senior scientists throughout their lives.

The Harvard Observatory features heavily in the first couple of chapters. Women originally became involved as “computers” analysing the stars in the photographic plates. They included Williamina Fleming, Annie Jump Cannon, Antonia Maury and Cecilia Payne-Gaposchkin with Anna Draper providing funding to the observatory via a bequest in the late 19th century. In they first instance they were analysing stars for brightness and then later for spectral features. A group of women were responsible for compiling the “Harvard” stellar classification scheme which classifies stars by temperature using the letters O, B, A, F, G, K, M (typically remembered by a sexist mnemonic). One of the women, Henrietta Swan Leavitt, discovered the relationship between brightness and period for stars which is central to measuring intergalactic (and shorter distances) and was key to understanding the scale of the galaxy and the universe. Over a very long period Harvard Observatory allowed women to be employed as astronomers, and finally become professors in astronomy. The transitions usually being the result of a change in observatory or university management.

The third chapter is a bit of an oddity, looking at women’s contributions to the space programme on the project management and rocketry side of things rather than physics as such.

The final four chapters are then an extended collection on nuclear physics starting with Marie Skłodowska-Curie, and the less well known Harriet Brooks who worked on the new subject of radioactivity in the late 19th century. Brooks worked with Rutherford, publishing in 1904 in Nature on their discovery of radon. Rutherford and Frederick Soddy would earn the Nobel Prize for the transmutation of elements whilst Brooks was left out. Rutherford and Brooks clearly had a long personal relationship, ending in 1933 on her death at the age of 56. Brooks had left physics research in 1907 when she married Frank Pitcher.

Chapter 5 largely concerns Lise Meitner who was involved in the discovery of nuclear fission with Otto Hahn with whom she worked closely for many years. Hahn received the Nobel Prize for their work on nuclear fission, whilst she did not – this has been seen as one of the more egregious omissions of the Nobel Prize Committee – Meitner was nominated for a Nobel Prize 48 times and was widely recognised as an expert in her field. Her position was made more difficult because she was Jewish, worked in Austria and with Hahn who despite protestations was a Nazi sympathiser at the very least.

Chapter 6 concerns cosmic rays and the photographic detection thereof. It starts with Bibha Chowdhuri who is from Ghose’s home city of Kolkata and was later to discover cosmic ray muons using this method. The focus of the chapter though is Marietta Blau and her student Hertha Wambacher who developed the method of photographic detection of cosmic rays. The Meitner/Hahn story is reprised here with Jewish Blau forced to leave Vienna in 1938 with her student Wambacher, a Nazi sympathiser, remaining to take credit. Elisa Frota-Pessoa, a Brazilian physicist, is mentioned somewhat incidentally towards the end of the chapter with Ghose stumbling on one of her (very prescient) publications whilst researching other work.

The book finishes with the slightly odd pairing of Wu Chien Shiung who was instrumental in the discovery of parity violation which won her colleagues Tsung-Dao Lee and Chen-Ning Yang the 1957 Nobel Prize in Physics (they specifically mentioned her in their acceptance speech) and Vera Rubin who is credited with discovering dark matter by measuring the rotation curves of galaxies and observing that they flatten at large radii – an indicator of the presence of extra, unseen matter.

Reading back through my notes, women were at the heart of modern physics through the 20th century, often those women were the only ones in the room – it is clear they were exceedingly capable. The men around them collected a dozen Nobel Prizes whilst the only woman from this book to win the Nobel Prize for Physics was Marie Skłodowska-Curie. Maria Goeppert Mayer shared the Nobel Prize for Physics in 1963 she is the only other woman to win in the 20th century. She is not included in this book, perhaps because her Nobel Prize meant she was already well known.

In the past I thought the Nobel Prize committee were simply a bit careless in failing to award women but reading this book it seems they were rather purposeful – the physics community knew these women, and the significance of what they had done, and many were nominated for a Nobel Prize, often repeatedly.

As a result of this book I am now interested in a parallel volume of Indian scientists in the West!

Book review: The Pope of Physics by Gino Segrè and Bettina Hoerlin

fermiThe Pope of Physics by Gino Segrè and Bettina Hoerlin is the biography of Enrico Fermi. I haven’t read any scientific biography for a while and this book on Enrico Fermi was on my list. He is perhaps best known for leading the team that constructed the first artificial nuclear reactor as part of the Manhattan Project. As a lapsed chemical physicist I also know him for Fermi surfaces, Fermi-Dirac statistics, and the Fermi method. Looking on Wikipedia there is a whole page of physics related items named for him.

Fermi was born at the beginning of the 20th century, his parents were born before Italy was unified in 1870 when illiteracy was not uncommon and people typically stayed close to home since travel quickly involved crossing borders.

Fermi was identified as something of a prodigy whom a friend of his father, Adolfo Amidei, took under his wing and smoothed his path to Pisa Scuola Normale Superior. As I sit here in in a mild lockdown I was bemused to note that the entrance exams Fermi took were delayed by the 1918 Spanish Flu pandemic. At Pisa Fermi learned largely under his own steam, at the time physics was not an important subject – the Pisa Scuola had five professors in physics and only one in physics. Fermi graduated at the top of his class.

After Pisa Fermi fell into the path of Orso Mario Corbino, a physicist, politician and talented organiser who set about helping Fermi to build a career in physics. At the time a new quantum physics was growing, led primarily by young men such as Pauli, Dirac, Heisenberg and Schrödinger who was a little older. Fermi met them on a scholarship to Göttingen in Germany. He later went to Leiden on a scholarship where he met Ehrenfest, and Einstein who was very taken with him. This was preparation for building a new physics capability in Italy.

The fruits of this preparation were a period in the mid-1930s which saw Fermi and his research group at Rome University invent a theory of nuclear decay which revealed the weak nuclear force and postulated the existence of the neutrino (this theoretical work was Fermi’s alone). The wider research group studied the transmutation of elements by slow neutron bombardment. This work was to win Fermi the 1938 Nobel Prize for Physics.

This research led on directly to the discovery of nuclear fission and the chain reaction which became highly relevant as Fermi fled Italy to the US with his wife on the eve of the Second World War. Many of Fermi’s friends, including his wife Laura, were Jewish. Fermi steered clear of politics to a large degree, he benefitted from the patronage of Mussolini but was no fascist enthusiast. The Italian uses of chemical weapons in Ethopia and, ultimately, the racial laws of the late 1930s which expelled Jews from their positions drove him from the country. He had visited the US a number of times in the early 1930s and had little trouble finding a position at Columbia University.

The route to the atomic bomb was not quick and smooth in the early years of the war, a number of physicists had noted the possibility of the fission bomb and attempted to warn politicians of its potential. This all changed when the Americans joined the war, following the Japanese attack on Pearl Harbour.

Building an atomic bomb presented a number of scientific challenges which Fermi was well-placed to address, primary amongst these was building “Critical Pile 1” the first system to undergo a self-sustaining nuclear chain reaction. It was constructed, slightly surreptitiously, in a squash court at Chicago University. It was built there as a result of a dispute with the contractor who was due to build it a little outside Chicago, at Argonne.

The “critical pile” demonstrated two things: firstly that chain reactions existed, and secondly it provided a route to producing the nuclear isotopes required to produce a bomb. It still left the question of how to purify the isotopes, and the question of how to produce a critical mass fast enough to cause a worthwhile explosion.

Fermi would go on to help in the Manhattan Project at Hanford and then Los Alamos where he held a position combining both universal scientific consultancy and administration, or at least organisation.

It is difficult to talk about Fermi’s strengths as a physicist – he had so many – he is almost unique in being both a top flight experimentalist, and theoretician. This is the great divide in physics, and people who are talented in both fields are rare. He was also clearly an excellent teacher, as well as undergraduate teaching and writing a high school physics book he supervised 7 students who would go on to earn Nobel Prizes in physics. Alongside this he was clearly personable.

Fermi died in November 1954 a little after his 53rd birthday, leaving in his wake a large number of prizes, buildings and discoveries as a memorial.

I found The Pope of Physics highly readable, the chapters are quite short but focused.

Book review: Lost in Math by Sabine Hossenfelder

lost_in_mathIt is physics for my next read, although my background is in physics and chemistry I don’t read much physics. Lost in Math by Sabine Hossenfelder is a journey through modern fundamental physics and how it has lost its way over the last few years in a quest for beauty rather than relevance.

My background is actually in a different part of physics, the physics of squishy things like plastics, proteins and plants. I stopped being an academic physicist nearly twenty years ago but even at that time there was a definite feeling that some area of physics felt themselves superior to others. Experimental soft matter physicists, like myself, were at the bottom of the pile.

This background does mean that I’ve talked to actually string theorists about string theory, and been intrigued that when you asked them where the extra (20 or so) dimensions the theory requires were the fall back answer was always “curled up very small” – they were unable to express it differently. 

The problem in fundamental physics is that theory is running well ahead of what can be experimentally confirmed. The Higgs boson found at CERN in 2012 was predicted in the early sixties, some 50 years previously. Gravitational waves, first observed in 2016, were predicted by Einstein 100 years previously. Theories today are generating hypotheses which may never be experimentally accessible, on current technology they require accelerators the size of galaxies and and Jupiter sized detectors.

With theory running so far ahead of experiment, how does one decide whether a theory is correct, an accurate model of the universe? The answer of choice for a number of years has been beauty, and naturalness. Distinctly unphysical concepts. Defining beauty is a difficult business, in physics as well as elsewhere. For physicists it means beautiful maths. I wonder whether there is a a link with music here, the Westerners have trained their ears to find particular note combinations harmonious or beautiful but in other traditions different combinations are considered beautiful. Naturalness is a related idea, which has a technical meaning, naturalness abhors taking one very large number from another very large number to leave a number of just the right size. What are the chances of that happening?

Hossenfelder embarks on a world tour to address these issues, talking to scientists across the US and Europe. The style of her writing is journalistic and confessional. This is refreshing to see in a book about physics.

An interesting point raised is that the point of a Kuhnian revolution is as much that our perception of beauty shifts when there is a paradigm shift, as anything else.

The pain for particle physicists is that there is this zoo of 25 particles from which all the matter we can see is constructed but they seem so arbitrary, there is no rhyme or reason to their masses or deep reason for their number. Really, particle physicists want an equation from which these features simply appear rather than find themselves in the position of having to set the values of masses and so forth. This is why physicists are physicists and not biologists or chemists. Chemists revel in mess, biologists are even worse.

The hope was that the LHC at CERN would reveal new particles after the Higgs boson, which would confirm that there was something beyond the Standard Model, this would provide some meat for them to gnaw at and the prospect of planning the next big facility to find out more. But so far there has been nothing, leaving particle physics at a loss.

Cosmology is suffering from a similar problem, although the problem in cosmology is linking up general relativity which explains black holes and the like with quantum mechanics. No one really knows what quantum mechanics means, just that it allows you to explain the values measured in certain experiments really well for reasons best not inspected too closely.

It is sometimes thought that scientists collect loads of data and then come up with a theory that explains it all, this hasn’t been the case in physics for a long time. For the best part of the last 400 years physics has been about coming up with plausible theories and checking to see if they are correct.

Hossenfelder finishes with some thoughts on other types of cognitive and social bias, and even provides an appendix of remedies to address them.

Lost in Math has the air of a disenchanted author making a final tour of the topic she loves before leaving for a job in industry, so it is heartening to find Hossenfelder still in fundamental physics. It seems to me that this level of introspection and the personal touch is something that is needed in academic research.

Fortunately for British readers the phrase “lost in math” is scarcely used in the text.

The Periodic Table

Understanding the Periodic Table is very much like making love to a beautiful woman, there’s no point rote-learning the location of the different elements if you don’t know what they do… langtry_girl*

The Periodic Table of the Elements is a presentation of the known elements which provides information on the relationships between those elements in terms of their chemical and physical properties. An element is a type of atom: iron, helium, sulphur, aluminium are all examples of elements. Elements cannot be broken down chemically into other elements, but elements can change. An atom is comprised of electrons, protons and neutrons.

This is all very nice, but if you look around you: at the wallpaper, the computer screen, the table – very little of what you see is made from pure elements. They’re made from molecules (pure elements joined together), and the molecules are arranged in different ways which may be completely invisible. So in a sense the periodic table represents the bottom of the tree of knowledge for people interested in materials, other scientists may be more interested in what makes up the elements.

The periodic table, approximately as it is seen today, was discovered by Dmitri Mendeleev in 1869, he designed it based on the properties of the elements known at that time. For a scientist the Periodic Table is pleasing, it says of the elements: “this many and no more”. It also stands as one of the great scientific predictions: Mendeleev proposed new elements based on his table constructed from the known elements and ,behold, they appeared with roughly the properties he expected.
Mendeleev’s periodic table was a work of organisation, it later turned out through the discovery of quantum mechanics that the periodicity and order found in the table can be derived from the behaviour of electrons in atoms.
To reverse a little, there is scope for more elements in the periodic table, they appear tacked on at the end of the table and are made artificially. The experimental scheme to achieve this is to fire atoms of existing elements into each other in the in the hope that they’ll fuse, occasionally they do, but the resulting atoms have a fleeting existence. They are rarely found in any number and vanish in fractions of a second, they are not elements of which you can grab hold. This has always struck me as being akin to flinging the components of a car off a cliff and claiming you have made a car when momentarily the pieces look like a car as they plummet to the ground.
I had a struggle here deciding whether to describe the periodic table as being designed, invented, or discovered. I stuck with discovered, because discovering is what scientists do, inventing is for inventors and designing is for designers ;-) It does raise an interesting philosophical question which has no doubt been repeatedly discussed down through the ages.

As a design, shown above, the periodic table is a cultural icon which everyone knows. Even if they don’t understand what it means, they know what it stands for – it stands for science. How to make sure people know your scene is set in a lab or your character is a scientist? Bung in a periodic table. It has been purloined to organise other sorts of information, such as Crispian Jago’s rather fine “Periodic Table of Irrational Nonsense“, some more examples here. There is a song.

At various times in my life I’ve been able to name and correctly locate all the elements in the periodic table, normally takes a bit of effort and some mnemonics to help. Increasingly now, I can remember the mnemonics but not the elements they refer to.

Different parts of the periodic table are important to different sorts of scientists. To organic chemists carbon (C), hydrogen (H), oxygen (O), nitrogen (N) hold the majority of their interest with walk on parts for some of the transition metals (the pink ones in a block in the middle) which act as catalysts. Inorganic chemists are more wide ranging, only really forbidden from the Noble Gases (helium (He), neon(Ne), argon (Ar), krypton (Kr), xenon (Xe)) which refuse to react with anything. Semi-conductor physicists are after the odd “semi-metals”: silicon (Si), indium (In), gallium (Ga), germanium (Ge), arsenic (As). For magnets there’s iron (Fe), cobalt (Co), nickel (Ni) along with other transition metals and the Lanthanides. The actinides are for nuclear physicists, radiation scientists and atomic bomb makers. Hydrogen is for cosmologists. In this view, as a soft condensed matter physicist, I am closest to the organic chemists.

I’m rather fond the periodic table, it is the scientist’s badge, but I’m scared of fluorine.

*To be fair to langtry_girl, I pondered on twitter “Trying to finish the sentence: “Understanding the Periodic Table is very much like making love to a beautiful woman…” and I think hers was the best reply. It is, of course, a reference to Swiss Toni.

What kind of scientist am I?

Following on from my earlier blog post on the tree of life, this post is about the taxonomy of my area of science: physics. I should point out now that I’m not too keen on the division science in this way. These divisions are relatively recent, as an example: the Cavendish Laboratory, the department of physics at Cambridge University, was only founded in 1874.

I am an experimental soft-matter physicist.

So taking the first word: experimental. This is one of the three great kingdoms of physics, the others being  computer simulation and the theory. “Experimental” means I spend a large part of my time trying to do actually experiments on objects in the real world, this may involve substantial computational work to process the output data and should generally involve some comparison to theory when published, although serious development of theory tends to end up in the hands of specialists. Computer simulation is distinct from from theory: simulation is like doing an experiment in a computer – give a set of entities some rules to live by and set them at it, measure results after some time. Theory on the other hand attempts to model the measurements without the fuss of explicitly modelling each entity in the collection.

Next to the physicist bit: In a sense theory is the essence of what physics is about: building an accurate model of the world. The important thing with physics is abstraction, to take an example I’m interested in granular materials; from a physics point of view this means I’m looking for a model that covers piles of ball bearings, avalanches, sand dunes, grain in silos, cereals in a box and possibly even mayonnaise all in a single framework.

And so to the final division: soft-matter. Physical Review Letters, which is the global house journal for physics, has the following subdivisions (in italics):

  • General Physics: Statistical and Quantum Mechanics, Quantum Information, etc; Domain of Schrödingers cat, Alice and Bob exchanging secure messages, and Bose-Einstein condensates.
  • Gravitation and Astrophysics; Physicists go large. Stephen Hawking lives here – black holes, the big bang.
  • Elementary Particles and Fields; down to the bottom, with things very small studied by things very large (like the Large Hadron Collider at CERN). Here be Prof Brian Cox.
  • Nuclear Physics; The properties of the atomic nucleus, including radioactivity, fission and fusion. This is Jim Al-Khalili‘s field. 
  • Atomic, Molecular, and Optical Physics; Stuff where single atoms and molecules are important, things like spectroscopy, fluorescence and luminescence go here.
  • Nonlinear Dynamics, Fluid Dynamics, Classical Optics, etc; Pendulums attached to pendulums, splashes and invisibility cloaks!
  • Plasma and Beam Physics; Matter in extreme conditions of temperature: fusion power goes here.
  • Condensed Matter: Structure, etc; Condensed matter is stuff which isn’t a gas – i.e. liquids and solids, and is acting in a reasonable size lump. 
  • Condensed Matter: Electronic Properties, etc; This is where your semiconductors, from which computer chips are made, live. 
  • Soft Matter, Biological, and Interdisciplinary Physics; Soft-matter refers to various squishy things, plastics, big stringy molecules in solution (polymers), little particles (colloids, like emulsion paint or mayonnaise), liquid crystals, and also granular materials (gravel, grain, sand and so forth).

So there I am in the last division, studying squishy things.

Since I’ve provided a means to wind up most sorts of scientist in previous blog posts, I thought I could provide a few here for me. Theoreticians can wind me up by assuming that experiments, and the analysis of the resulting data, are trivially easy to do and if they don’t fit their theory then I need to try again. Simulators I have a bit more sympathy with, simulations are experiments on a computer, however when you’re writing a paper perhaps you should say in the title you ran a simulation, rather than did a  proper experiment like a real man ;-)

Update: I made this post into a podcast: http://bit.ly/6EA17H – it’s on Posterous because uploading of audio is easier. I used a basic Logitech headset microphone, Audacity to do the capture and editing with the Lame plugin for MP3 export.  I’m not sure I’ll do it again but it was fun to try!