Tag Archive: physics

May 12 2019

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.

Jul 22 2010

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.

Dec 23 2009

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!

Oct 20 2009

Twitter, rumours and physics

The twittersphere avoided making a bit of a mistake this morning. Wikileaks had obtained a new version of the BNP membership list, which they released (the BNP claim this list is a fake). Prior to release it was claimed that a peer of the realm was on the list and immediately post release that peer was named. Only it turns out it wasn’t him, someone who styled himself Lord with a very similar name was the man on the list. Fortunately the released list was detailed enough that this could be checked, someone had the wit to check before blindly repeating the name. Once they’d done this they started correcting the false rumour (in what looks like quite a vigorous manual effort). It’s worth noting here that the fact-checker appears to be a trained journalist.

But it could so easily have been very different. It could have been very difficult to establish the rumour was false, it could have been that the diligent fact checker stopped to finish his cup of tea before tweeting his correction, the rumour could have been re-tweeted by someone with many followers. All of these things could have happened but didn’t, will this be true the next time?

On the plus side, twitter rumours do appear to be traceable back to source and it’s very easy to find the individual rumour-mongers and put them right. This is certainly true for non-malicious rumourmongering (that’s to say where people have not made a special effort to propagate a rumour, nor hide their tracks).

There is a scientific link here, modelling of all sorts of networks has long been a respectable scientific field. For example, there’s Per Bak’s forest fire model and work that follows on from there. More recently there’s been work focussing more explicitly on computer networks and social networks. To a physicist Twitter represents an example of a simple system which has nodes (with ingoing and outgoing links) and messages that are propagated between the nodes. The nodes could be trees in a forest and the thing passed could be fire, or the nodes could be computers in a network with the message being network traffic; the nodes could be scientific papers with the messages citations of other papers. The physics doesn’t care about the detail of these things, it cares about a small number of parameters in the system: how many links in and out of a node? What’s the probability of a message being transmitted from one node to the next?

So there’s an interesting bit of network analysis to do here. How fast can a rumour propagate on Twitter? What fraction of people refrain from tweeting a false rumour to stop it propagating? What’s the best way to squash a false rumour?

Having watched the no doubt frenzied activities involved in squashing today’s rumour. One useful tool would be an automated rumour-quashing robot. It would search for tweets containing the rumour (probably based on a manually selected keyword) and tweet the originator with a rebuttal.

Think before you tweet!