Humanity has not found a fifth force of nature. This is a warning to the media at large. Please do not tell people muon g-2 found a fifth force of nature or make any other such claims.  There are a few serious issues to consider with how the recent muon g-2 experiment results are being reported on.

Theoretical Calculations Do Not Agree.

Now as I did not do these calculations by my own hand, I will not act like I fully understand them.  In fact, no physicist would act like they fully understand them because they are that hard.  I like the description given on Twitter by @astrokatie.  Paraphrasing Katie Mack, this is a calculation that requires computing every possible way that every particle that exist in the standard model will interact with a muon.  This has been done two different ways one of which agrees with the experiment the other disagrees.  

It is this disagreement between theory and experiment that suggest there might be new physics to find.

However, given that it takes such a complex calculation to make the prediction, and that the calculations disagree, it is quite possible that a calculation error could account for all the discrepancy.  

Dark Energy Would Be A “Fifth Force”.

As the BBC reported it. Muons: 'Strong' evidence found for a new force of nature. As I write this fifth force of nature will bring up so many results on Google.

The thing is if there has been a true fifth force of nature it lay in an effect which we have known about for a while, Dark Energy.   This force causes the expansion of the universe to increase the father apart two points are.  This expansion is not an expansion in space but an expansion of space itself.   

We have no solid theoretical idea what causes the dark energy.  Dark energy is so well observed in astronomy and cosmology that we can consider it to be almost as much of a fact as gravity. 


If there is a fifth force it would be whatever is responsible for the well observed dark energy which effects the whole of the universe.  If the discrepancy between theory and experiment is not just a miscalculation on the theoretical side, then it would hint at a possible fifth force. 

The most important conclusion is that one can do interesting physics without having a larger or more powerful super collider.  Although a muon accelerator would be a great idea.   I would even be all for having a particle accelerator dug right around the whole circumference of the planet.  However, the real win for science here is that it does not need to be big and huge to be impactful.

Media should think of this as.  Scientist have found a discrepancy between two complex theoretical calculations and experiment.  That everyone needs to double check everything twice and gather more data.  

That is my two cents.

My colleague Tommasso Dorigo has a much more detailed take on this.  I am but a humble theoretical astrophysicist and not an expert on particles. He knows a lot more than me.