Question: what is a theoretical physicist ?

Jose Eliel Camargo Molina answered on 11 Mar 2019:

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Hi Grace2007_x and jermyn,

This is a great question. There are two very important steps in science, the first one is to look at nature, in other words, to make experiments. The second one is to build a model, a theory, for how nature works.

The word theory can be a bit misleading because in everyday language we associate it to the idea of something that is not “proven” or “true”. In science, it is almost the complete opposite. Let me explain.

Imagine for a second we have no idea why the sun goes up and you are a scientist trying to figure it out.

Let’s say you see that the sun comes up every morning. Armed with a watch, you go and write down for a week at what times the sun comes up and at what times it goes down again.

You have made an experiment.

Now, after making the experiment, you continue thinking and asking yourself the question “how”. How does the sun come up and down again? How does that work? You look at your notes, maybe do some math or drawings, just get down to think very hard about it.

You then come up with your theory: The earth is actually spinning! That might be it! so now, armed with your theory you can go back to the experiment to test whether you are right or not.

Based on your theory, namely that the earth spins, you make more measurements of the sunrise and sunset times. You calculate that it takes the Earth approximately 24 hours to do a full 360 degrees turn! now what?

Well, if your theory is right, now you have a superpower, you can make predictions!! and if your predictions are right, then your theory works!!!

So you go back to thinking, what can you predict with your theory? If Earth is rotating, are there any other consequences that we could measure?

Then you come up with a brilliant idea: If the Earth rotates, then the sun will go down at different times in different places provided you travel far enough to the east or west.

Not only that, because you know how long it takes to make a rotation, you can also predict the time difference between sunsets in different countries.

So you take a pen, paper, and with maths, you come up with your prediction:

-The sun will set in Rome 45 minutes before it sets in London!

So you take your phone and call a scientist friend in Rome, and she goes out and writes down when the sun goes down in Rome. You do the same in London and you compare the time difference.

And lo and behold, it is 45 minutes!!! OMG, now your theory has been successful in predicting how nature works!!

So to finally answer your question. In reality, the job of coming up with theories and the theory’s predictions and the job of performing the experiments are done by two closely related communities but that work somewhat separately: The theoretical physicists and the experimental physicists.

There are of course people that do both, but the skill-set and knowledge you need for being one or the other are very different. So in practice, most people decide which area they find most interesting and during their studies the specialize and learn what they need. Theoreticians learn a lot of advanced math and get really good at doing calculations and working out the formal side of theories, while experimentalists get really good at building and designing complicated machines, are wizards with data science and statistics and understand how to perform experiments and get the relevant data.