The difference between an engineer and a physicist

As a researcher who has recently published an article in the elegantly-named journal ‘Biomedical Physics and Engineering Express’ (in other words, biology, medicine, physics, engineering all in one) it’s clear to me that the boundaries that we often like to use to define ourselves are rather blurry. I am a physicist (yes!) but also, at times, I have to drift into being an engineer, biologist, mathematician, computer scientist and so forth. Indeed, many of humanity’s best scientific advances have been made at the fringes of disciplines, where different scientists have come together with different perspectives on the same problem and come up with something wonderful as a consequence.

That said, I shall now have a moan about a piece of software (no names mentioned) that has clearly been written by engineers not physicists.

You don’t need to understand what my problem is to understand the point of the post, but for those that want some idea, I’m wanting to model the induced electric field due to the rapidly changing magnetic field (Faraday’s Law) resulting from providing a time-varying current to a coil of wire.

There are two very well used pieces of commercial software for doing electromagnetic modelling – and I’ll call them “A” and “B” to protect the guilty. Now, software “A”  will solve the problem (I’ve used it before), but due to its outrageous price we haven’t renewed our licence for it. Will software “B” solve the problem instead? The advertising material is a little bit coy as to whether it does this or not. But we’ve given it a go.

After much frustrating effort, grappling with the not-very-helpful ‘Help’ facility, and the not-very-helpful on-line user forums, and the not-very-helpful hard-copy documentation for the software, I’ve reached the conclusion that ‘yes’, this software will do what we want, but we have to cheat.

The sticking point is  software “B” does not model the electric field in a vacuum. We can model electric fields in other objects, but, in a vacuum, no. And, buried in the documentation, I finally discover why – the assumption is that no-one is interested in the electric field in a vacuum. In one way this makes perfect sense – an electric field is only going to do something if you put something in the field for it to do something on – and then it’s not a vacuum any more.  Essentially, the software says, in a vacuum, the electric currents flowing are zero (since there is nothing to flow) and so who cares what the electric fields are – so it doesn’t bother calculating them.

That’s an engineer’s answer.  Pragmatic but infuriating.

As a physicist, I do care what the electric fields are, not because I want to know the electric currents (there aren’t any of course), but because by using a vacuum I can look more systematically at the effects of changing the shape of my current-carrying coil without worrying what objects we put in the vicinity of the coil.

Put it another way,  I want to make my problem simpler, not make my solution simpler. Unfortunately, the developers of “B” have decided in advance that what I want isn’t interesting. I’ll be the judge of what is interesting to me, thank you.

But, as it turns out, we can use software “B”-  we just have to cheat a bit and make sure our vacuum isn’t quite a vacuum. Give it a teeny-weeny bit of electrical conductivity and then the software decides it is interesting calculating the electric field after all. It just takes longer to do it.



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