“I am a phd-student in neuroscience and I often get the impression that in physics "everything is better". E.g. they replicate their stuff, they care about precision, etc. I've always wondered to what extend that is actually true, as I obviously don't know much about physics (as a science). I've also heard (but to a far lesser extent than physics being praised) that in theoretical physics you can make up anything bc there is no way of testing it. Is that true? Sorry if that sounds ignorant, as I said, I don't know much about it.”This question was put forward to me by Amoral Atheist at Neuroskeptic’s blog.
Dear Amoral Atheist:
I appreciate your interest because it gives me an opportunity to lay out the relation of physics to other fields of science.
About the first part of your question. The uncertainty in data is very much tied to the objects of study. Physics is such a precise science because it deals with objects whose properties are pretty much the same regardless of where or when you test them. The more you take apart stuff, the simpler it gets, because to our best present knowledge we are made of only a handful of elementary particles, and these few particles are all alike – the electrons in my body behave exactly the same way as the electrons in your body.
If the objects of study get larger, there are more ways the particles can be combined and therefore more variation in the objects. As you go from elementary particle physics to nuclear and atomic physics to condensed matter physics, then chemistry and biology and neuroscience, the variety in construction become increasingly important. It is more difficult to reproduce a crystal than it is to reproduce a Hydrogen atom, and it is even more difficult to reproduce cell cultures or tissue. As variety increases, expectations for precision and reproducibility go down. This is the case already in physics: Condensed matter physics isn’t as precise as elementary particle physics.
Once you move past a certain size, where the messy regime of human society lies, things become easier again. Planets, stars, or galaxies as a whole, can be described with high precision too because for them the details (of, say, organisms populating the planets) don’t matter much.
And so the standards for precision and reproducibility in physics are much higher than in any other science not because physicists are smarter or more ambitious, but because the standards can be higher. Lower standards for statistical significance in other fields is nothing that researchers should be blamed for, it comes with their data.
It is also the case though that since physicists have been dealing with statistics and experimental uncertainty at such high precision since hundreds of years, they sometimes roll eyes about erroneous handling of data in other sciences. It is for example a really bad idea to only choose a way to analyze data after you have seen the results, and you should never try several methods until you find a result that crosses whatever level of significance is standard in your field. In that respect I suppose it is true that in physics “everything is better” because the training in statistical methodology is more rigorous. In other words, one is lead to suspect that the trouble with reproducibility in other fields of science is partly due to preventable problems.
About the second part of your question. The relation between theoretical physics and experimental physics goes both ways. Sometimes experimentalists have data that needs a theory by which they can be explained. And sometimes theorists have come up with a theory that they need new experimental tests for. This way, theory and experiment evolves hand in hand. Physics, as any other science, is all about describing nature. If you make up a theory that cannot be tested, you’re just not doing very interesting research, and you’re not likely to get a grant or find a job.
Theoretical physicists, as they “make up theories” are not free to just do whatever they like. The standards in physics are high, both in experiment and in theory, because there are so many data that are known so precisely. New theories have to be consistent with all the high precision data that we have accumulated in hundreds of years, and theories in physics must be cast in the form of mathematics; this is an unwritten rule, but one that is rigorously enforced. If you come up with an idea and are not able to formulate it in mathematical terms, nobody will take you seriously and you will not get published. This is for good reasons: Mathematics has proved to be an enormously powerful way to ensure logical coherence and prevent humans from fooling themselves by wishful thinking. A theory lacking a mathematical framework is today considered very low standard in physics.
The requirement that new theories both be in agreement with all existing data and be mathematically consistent – ie do not lead to internal disagreements or ambiguities – are not easy requirements to fulfil. Just how hard it is to come up with a theory that improves on the existing ones and meets these requirements is almost always underestimated by people outside the field.
There is for example very little that you can change about Einstein’s theory of General Relativity without ruining it altogether. Almost everything that you can imagine doing to its mathematical framework has dire consequences that lead to either mathematical nonsense or to crude conflict with data. Something as seemingly innocuous as giving a tiny mass to the normally massless carrier field of gravity can entirely spoil the theory.
Of course there are certain tricks you can learn that help you invent new theories that are not in conflict with data and are internally consistent. If you want to invent a new particle for example, as a rule of thumb you better make it very heavy or make it very weakly interacting, or both. And make sure you respect all known symmetries and conservation laws. You also better start with a theory that is known to work already and just twiddle it a little bit. In other words, you have to learn the rules before you break them. Still, it is hard and new theories don’t come easily.
Dark matter is a case in point. Dark matter has first been spotted in the 1930s. 80 years later, after the work of tens of thousands of physicists, we have but a dozen possible explanations for what it may be that are now subject to further experimental test. If it was true that in theoretical physics you “can make up anything” we’d have hundreds of thousands of theories for dark matter! It turns out though most ideas don’t meet the standards and so they are discarded of very quickly.
Sometimes it is very difficult to test a new theory in physics, and it can take a lot of time to find out how to do it. Pauli for example invented a particle, now called the “neutrino,” to explain some experiments that physicists were confused about in the 1930s, but it took almost three decades to actually find a way to measure this particle. Again this is a consequence of just how much physicists know already. The more we know, the more difficult it becomes to find unexplored tests for new ideas.
It is certainly true that some theories that have been proposed by physicists are so hard to test they are almost untestable, like for example parallel universes. These are extreme outliers though and, as I have complained earlier, that they are featured so prominently in the press is extremely misleading. There are few physicists working on this and the topic is very controversial. The vast majority of physicists work in down-to-earth fields like plasma physics or astroparticle physics, and have no business with the multiverse or parallel universes (see my earlier post “What do most physicists work on?”). These are thought-stimulating topics, and I find it interesting to discuss them, but one shouldn’t mistake them for being central to physics.
Another confusion that often comes up is the relevance of physics to other fields of science, and the discussion at Neurosceptic’s blogpost is a sad example. It is perfectly okay for physicists to ignore biology in their experiments, but it is not okay for biologists to ignore physics. This isn’t so because physicists are arrogant, it is because physics studies objects in their simplest form when their more complicated behavior doesn’t play a role. But the opposite is not the case: The simple laws of physics don’t just go way when you get to more complicated objects, they still remain important.
For this reason you cannot just go and proclaim that human brains somehow exchange signals and store memory in some “cloud” because there is no mechanism, no interaction, by which this could happen that we wouldn’t already have seen. No, I'm not narrowminded, I just know how hard it is to find an unexplored niche in the known laws of nature to hide some entirely new effect that has never been observed. Just try yourself to formulate a theory that realizes this idea, a theory which is both mathematically consistent and consistent with all known observations, and you will quickly see that it can’t be done. It is only when you discard the high standard requirements of physics that you really can “make up anything.”
Thanks for an interesting question!