What is a Particle?: Some Answers

Environmental & Science Education, STEM, Nature of Science, History of Science

Ed Hessler

Those of you familiar with the Next Generation Science Standards/A Framework for Science K-12 Science Education know that the writing teams focused not only on practices of science and engineering, but also on crosscutting concepts, and core ideas. The two documents may be examined, read, even printed for free except for the cost to you on-line.

One of the crosscutting concepts is Structure and Function which is defined as "The way in which an object or living thing is shaped and it substructure determine many of its properties and functions." This short entry has little, no nothing to do with schooling except at the advanced research level but I was reminded of this concept when I read a splendid essay by Quanta's science editor/writer Natalie Wolcher posed the following question: Just what are those "particles" in quantum mechanics. No claim is made that I understood all of it!

Much is known about their functional side but little about the "particles," the structures themselves. So she asked a dozen particle physics and found that "they gave remarkably diverse descriptions."

Before moving on I want to say a couple of things about definitions. Several years (or longer) I read an Amazon description of one of the basic texts for AP biology. The student reviewer described the book he and his class were using as a "damned dictionary." Rodger Bybee described several definitions of scientific literacy, a literacy that develops over a lifetime. They are illiteracy, nominal (in name only; the term is scientific), functional scientific and technological literacy (able to use the term say on a test or in reading a newspaper), conceptual and procedural literacy (how the concepts relate to the discipline and are used), and multidimensional scientific and techological literacy (understanding the essential structures/features that help complete it, including the relationship to the whole of science and technology and to society.)

Definitions have their use but are not by any means the whole of science: the emphasis is on understanding and this was expressed in the reform preceding NGSS (Project 2061) and the NGSS. Limit the vocabulary; increase human understanding. The aim is a theory supported by evidence which makes predictions that can be tested. This is what the following ideas are driving at--theory, one that is encompassing (although some theoreticians suggest that there is no reason Nature had this in mind). Perhaps one theory is not enough, the so-called theory of everything.

The list is short but includes illustrated which help provide you an idea of what theoretical physicists who work with these particle daily (mostly on chalkboards and paper) are dealing with and thinking about and how they think about this problem.

Wolcher first draws attention to two typical and unsatisfying answers although one is a non-answer 1). "The easy answer quickly shows itself to be unsatisfying. Namely, electrons, photons, quarks and other 'fundamental' particles supposedly lack substructure or physical extent.  2). We say they are ‘fundamental,’ said Xiao-Gang Wen, a theoretical physicist at the Massachusetts Institute of Technology. 'But that’s just a [way to say] to students, ‘Don’t ask! I don’t know the answer. It’s fundamental; don’t ask anymore.’” 

A particle is--don't let the arcana drive you away. Take a look, perhaps just one you have heard about.You will find references to patterns and their potential usefulness in making observations, frustrations of beginning students, things so small they can't be detected, the use of bits that can be stored--think of bits (0's and 1's) in transistors, and the role of mathematics in all this. None of this is easy but you might want to take a look anyway. The attempt is admirable and one of the best "popular" accounts I've seen.

--a collapsed wave function. 

--a quantum excitation of a field.

--an irreducible  representation of a group.

--I'll put this one as a particle is a many layered thing (particles have so many layers).

--might be vibrating strings.

--deformation of the Qubit ocean.

--what we measure in a detector.

Here is the definition I like best. Netta Englehart, a particle physicist at MIT said to Wolcher, "'We don't know' is the short answer.'" This is not to be taken as a claim that these building blocks of nature are not unknowable but they are not known for the time being.

For information about the magazine, Quanta see here.