Have Scientists Really Discovered a New FORCE? Muon g-2 Experiment EXPLAINED by Parth G

hey everyone parth here and yes in today's video we do have a slightly different background more on that in a future video but today i want to quickly discuss a rather exciting development in the world of physics now there have been reports recently that scientists have found strong evidence for the existence of a new fundamental force of nature up until recently all of the forces that we know of could be sorted into one of four kinds gravitational forces electromagnetic strong nuclear and weak nuclear these were and currently still are technically known as the four fundamental forces of nature but is that about to change to understand a little bit more about this new potential fundamental force of nature as well as whether or not it actually exists let's begin by talking about this particle here a muon a muon is very similar to an electron same charge same spin same everything except its mass the mass of a muon is larger than the mass of an electron scientists have been studying the behavior of these muons when they're placed in a magnetic field and they've been comparing the behavior that we expect to see based on all of the current physics that we know and the behavior that we actually do see the idea is that if our experiments show behavior that is quite far from what we expect from our theoretical understanding of physics then perhaps the theory needs to be changed in order to reflect reality and we'll also discuss in this video exactly how far the experimental result needs to be from the theoretical prediction in order for us to justify changing our theories now when we take a muon and we place it in a magnetic field the spin of the muon causes it to interact with the magnetic field in some interesting ways by the way if you're not familiar with spin then please do check out this video i made a little while ago but this interaction between the spin of our muon and the magnetic field allows us to define a quantity known as the spin magnetic dipole moment of the muon now in classical physics a magnetic dipole moment is simply a measure of the strength of a magnetic dipole like a bar magnet usually the stronger the bar magnet the larger the magnetic dipole moment that it has and mathematically we can relate to the dipole moment of our muon our little particle to its spin using this equation here s is the spin of the muon which is exactly the same as that of an electron and so you might be familiar that electrons have spin half this particular value doesn't really matter here what actually matters is some of the other quantities in this equation specifically we see the mass of the muon here in the denominator and we also see the charge of the electron which again happens to be the same as the charge of the muon and hence that's why we find it in this equation but the most interesting quantity is this one here it's known as the g factor of the muon the easiest way to think about this is a constant of proportionality between the spin of our muon and its magnetic dipole moment now when we use some basic principles of quantum mechanics the g factor for a muon is expected to be exactly two but it turns out that in real life the magnetic dipole moment of the muon is not exactly two it's slightly larger than two if we account for not just basic quantum mechanics which is where we got g is equal to 2 from but all of the physics that we know in all of the standard model as it's known then the predicted value of the g factor for muon is slightly larger than 2. we can quantify this difference because it's so very small by considering what's known as the anomalous magnetic dipole moment which is essentially defined like this as we can see the anomalous magnetic dipole moment just measures the difference between the actual g-factor value based on all of our theoretical calculations and two which is what we expected based on just basic quantum mechanics and then for some reason we divide it by two probably just to make the mathematics easier but that doesn't really matter we could always multiply it by two at any time when we need to but here's the problem when we account for all of the physics that we do know and we calculate what the value of g should be that's still slightly different to what we find the value of g to be when we actually measure it experimentally with our muons we're still missing a chunk even after accounting for everything that we know in terms of what the value of g should be and this is true even with our most precise theoretical calculations they still don't account for a small chunk of the actual value of g that we observe when we do an experiment what this means is that there may be another fundamental force of nature that is not accounted for in our standard model in our complete understanding of physics complete understanding that may be causing the actual g value to be slightly larger than what we expected so exactly how different do these two values need to be the experimentally measured value and our theoretical expectation based on all of the physics that we know in order for us to say hang on these values look quite different maybe they look different enough that there's some physics we haven't accounted for well with every experimentally measured value scientists also have to give a range in which this value could reasonably fall this is calculated based on all the possible sources of error in the experiment itself as well as any other sources of error in other experimentally measured quantities that are used in our calculations now you can also find a similar range for the theoretical calculations as well but for our purposes let's just focus on the experimental one this quantity the range within which our experimental value can reasonably lie either higher than what we calculated or lower than what we calculated is known as a standard deviation and a standard deviation is labeled with the greek letter sigma in order for scientists to claim that they have discovered something new some new science perhaps the general convention is that the theoretical prediction and the experimentally measured value have to be five sigma apart this indicates just a one in 3.5 million chance that the experimental value was just a fluke or a coincidence in other words when scientists are so sure that the values are different enough that the experiment could only be a fluke in one in three and a half million possible experiments then that's when they say that this is a new scientific discovery now currently the scientists working on this muon experiment are finding a discrepancy of 4.2 sigma pretty close to the five sigma threshold but not quite there yet and the way to push this over the five sigma threshold is to either conduct more experiments or improve the original experiment in such a way that the errors are reduced the scientists become more certain of the range in which the experimentally measured value actually lies in other words we're reducing the value of sigma and therefore the theoretical prediction and the experimentally measured value will eventually be more than five sigma apart now as it turns out the recent experiment on this whole thing conducted by fermilab is in fact a successor to a much older experiment conducted in brookhaven about 20 years ago the result that they found was quite peculiar they found that the experimentally measured value of g for a muon was quite far away from the theoretical expectation and so the fermilab experiment was essentially designed to either confirm this or refute that and it turns out it seems to be confirming that the original experiment had it correct combining these two experiments is what's currently giving us a 4.2 sigma difference between the theoretical prediction and the experimental measurement and scientists are now working towards getting that five sigma level of confidence either that or they'll find that both these experiments have gone horrendously wrong and we don't need to worry about thinking about any new physics at all but if and when this five segment threshold is reached we'll have very very strong evidence to suggest that the standard model is incomplete perhaps we seriously need to consider that fifth fundamental force of nature perhaps there's some other solution but either way this is really exciting because there is probably some new physics to be found now i've seen lots of popular science articles bringing up dark matter and dark energy alongside this almost discovery that is so exciting because maybe this new fifth fundamental force will be able to explain why all of the matter known to us in the universe only accounts for a very small proportion of the mass that we see out there but who knows at this point the fact of the matter is that there is new signs to be discovered quite likely and that is something that we should be very very excited about so tldr the spin magnetic dipole moment of a muon is slightly larger than expected if we account for all of the physics that we currently know the discrepancy between the theoretical prediction and the experimental measurement is 4.2 sigma as of when i'm making this video and if scientists manage to push it over the five sigma threshold then they'll be able to call this a brand new scientific discovery that would suggest that the standard model is incomplete and perhaps there's a fifth fundamental force of nature that we don't know anything about yet that we'd need to add to the standard model and with all of that being said i'm going to finish up here thank you so much for watching if you enjoyed this video please do hit the thumbs up button and subscribe for more fun physics content hit that bell button if you'd like to be notified when i upload and please do check out my patreon page if you'd like to support me on there thank you so much for watching and i will see you very soon [Music] you

Channel: Parth G

Views: 80,850

Keywords: fundamental force, muon, muon g-2, fermilab, fermilab experiment, new physics, new science, parth g, physics, fundamental force of nature, standard model, standard model of particle physics, anomalous magnetic dipole moment, spin magnetic dipole moment, magnetic dipole moment, g factor, brookhaven, standard deviation, 5 sigma, 4.2 sigma

Id: xHEjh5fXuW4

Length: 9min 5sec (545 seconds)

Published: Tue Apr 13 2021