16.41 Physics, chemistry and biology


“Physics World” is a magazine for members of the UK’s Institute of Physics. The September 2016 issue contained a very interesting letter about science teaching in schools, and especially about encouraging girls to study physics.

However, the writer was concerned that many of her pupils can’t tell the difference between physics, chemistry and biology. They’re not alone – I can’t clearly distinguish between these “separate sciences” either.

I know that someone who discovers new particles at the Large Hadron Collider is a physicist. I know that someone who makes new compounds (see posts 16.30 and 16.33) that might, for example, have the potential to prevent tumour growth is a chemist. And I know that someone who classifies different species of snails is a biologist.

But it isn’t usually that simple. I’m not sure how I would classify many of the research topics that I’ve worked on: some could be considered as either engineering or physics or physical chemistry or medicine.

Let’s think about some of the posts in this blog. The concept of “energy” (post 16.21) is fundamental to all of physics and chemistry and many topics in biology (for example, nutrition). The ideas about energy levels in atoms (post 16.29) seem to belong to physics but they are fundamental to understanding the formation of molecules (post 16.30), which is chemistry. Ideas about the behaviour of electrons in molecules (post 16.31) are usually considered to belong to chemistry but they are very similar to ideas about electrons in metals and semiconductors, which is usually considered as physics.

The idea of “entropy” was developed from the concept of “temperature” (post 16.34) – physics. In post 16.38 the relationship between entropy and disorder is explored by looking at interacting discs. If these discs are what we see when we look down at atoms lying on a the surface of a catalyst (see post 16.33), then we are talking about chemistry. In a comment on post 16.18, Professor Peter Purslow used the concept of entropy to consider what we mean by “life”; this seems to be about biology, since biology is the science of living things.

To make things even more complicated – I don’t believe there is a clear distinction between living and non-living things (post 16.18). So how do we decide where physics and chemistry end and biology begins?

Some people seem to think that biology is not mathematical – unlike physics and physical chemistry. However, if you want to really understand how populations of predators and prey (like the foxes and rabbits of post 16.8) interact, you will need to understand about coupled ordinary differential equations. I suspect that some physicists and many chemists have never met equations of this kind. In post 16.5 I used the growth of a colony of bacteria to describe “exponential growth”.

The concept of “scientific laws” (post 16.2), the role of experiments (post 16.3) and the distinction between “association” and “cause and effect” (post 16.10) are common to physics, chemistry and biology. Physicists, chemists and biologists are all familiar with “precision” (post 16.24), the normal distribution (post 16.26) and “significant differences” (post 16.28). They should all think very carefully before making predictions (post 16.8).

Physics, chemistry and biology all try not to be subjective (post 16.22) and their ability to solve problems may have financial constraints (post 16.32).

I suppose that it greatly simplifies teaching science by considering physics, chemistry and biology as separate subjects – but let’s not pretend that they are completely independent. Most of the problems that scientists have to solve are a consequence of what is happening in the world around us and so don’t fit neatly into one of these categories.

Related posts

16.36 Good and bad
16.32 Faith in science
16.22 Science can’t explain everything
16.18 What is life?
16.15 Science education
16.11 Giving a scientist a job

Follow-up posts

17.14 Confusion



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