New result out from Fermilab! The news dropped a couple days ago, but I thought to post it here. To set the table: The g-2 measurement characterizes the size of a particle's magnetic moment which...
Exemplary
New result out from Fermilab! The news dropped a couple days ago, but I thought to post it here. To set the table: The g-2 measurement characterizes the size of a particle's magnetic moment which is given by:
mu = g (e hbar/2m)
Particles like electrons and muons in addition to being charged, also act like bar magnets with a north and south pole (just like your everyday fridge magnet). The magnetic moment just tells you how strong it is. These particles also have a value of "g" very close to two, but not exactly two because of quantum vacuum polarization. Fancy words, this is where things like "virtual particles" are relevant. The value of g-2 then tells you the "anomaly" of the moment or how far away it is from two.
Physicists now have a brand-new measurement of a property of the muon called the anomalous magnetic moment that improves the precision of their previous result by a factor of 2.
This factor of two doesn't sound exciting, but famously there is a discrepancy in the measurement of the muon's magnetic moment where theory differed from experiment by a decent amount. This is called the "muon g-2 tension." This result tightens the experimental side of things to a much better degree and seems to resolve the tension to the disappointment of every head-in-the-clouds physicist hoping to find evidence for physics beyond the Standard Model.
The new experimental result, based on the first three years of data, announced by the Muon g-2 collaboration is:
g-2 = 0.002 331 841 10 +/- 0.000 000 000 43 (stat.) +/- 0.000 000 000 19 (syst.)
In comparison, our best theory calculation from 2020 is:
Yeah, we're really quibbling over those deep decimal places now. The pretty interesting part is the theory uncertainty is quite a bit bigger now than the experimental uncertainty. Another neat result is the aforementioned g-2 tension for the muon has sort of evaporated away with the better measurement now done by Fermilab. You can see the old best experimental measurement in the Fermilab news article above which clearly shows the apparent discrepancy. As a point of comparison, the muon's lighter brother, the electron, has a g-2 anomaly of:
which is probably the most precise measurement in all of science. You'll notice the electron value is several digits deeper than the muon.
Here's the /r/physics reddit thread on this news too which might be an interesting read. Some folks there point out that theory uncertainty has actually worsened since 2020 (which is the result I link to above) but I'm not familiar enough with the latest developments here to comment. This statement by the Theory Initiative goes into some details of why things are difficult. In short: Hadrons make everything murky and hard.
This always makes me wonder about the state of future developments. As physicists measure stuff more and more accurately its feels like it just reinforces existing models instead of challenging...
This result tightens the experimental side of things to a much better degree and seems to resolve the tension to the disappointment of every head-in-the-clouds physicist hoping to find evidence for physics beyond the Standard Model.
This always makes me wonder about the state of future developments. As physicists measure stuff more and more accurately its feels like it just reinforces existing models instead of challenging them. Current physics and maths very much beyond me so I don't know if this is a fair question, but is current theory approaching the end of our ability to advance it?
Regardless of all that, I really enjoy hearing about experimental scientists (in whatever field) measuring things with even more extreme accuracy. When I was a kid I wanted to do this kind of stuff but I'm glad I never did; I never would have kept up with the math and trying to control for whatever effect or error would drive me mental.
If you're only concerned with the Standard Model, it may seem this way, but there's definitely bright spots of fast movement in fundamental physics today. Cosmology and astrophysics have been...
Current physics and maths very much beyond me so I don't know if this is a fair question, but is current theory approaching the end of our ability to advance it?
If you're only concerned with the Standard Model, it may seem this way, but there's definitely bright spots of fast movement in fundamental physics today. Cosmology and astrophysics have been making leaps and bounds with new big discoveries coming every few years with theory struggling to keep up in many aspects. We've just begun the new field of gravitational wave astronomy and advances in neutrino physics may indeed "crack" the Standard Model open with new insights in the future. Neutrino masses are still not well understood and don't quite "fit" the Standard Model, so we know there has to be something more. Dark matter and dark energy are still huge mysteries as well.
On one hand it is a bit sad that the 'age of discovery' that the development of the Standard Model occurred in has somewhat past, but that's only because it's such a wonderful achievement. It's a really good theory. It might be sometime before technology advances enough for us to really stress it at ultra-high energies. There's a huge gulf between accessible energies today and where we expect Grand Unified Theories to reveal themselves for instance. That area of physics may very well be outside our current lifespan to probe.
Gotta be honest, I forgot that particle physics and and astrophysics were on different pages. I have been loosely following the gravitational wave stuff but I thought that was reinforcing existing...
Gotta be honest, I forgot that particle physics and and astrophysics were on different pages.
I have been loosely following the gravitational wave stuff but I thought that was reinforcing existing theory? Regardless, it is pretty exciting stuff and its fun to follow since the idea of gravity waves and the methods for measuring them are pretty easy to grasp.
Yes and no. There's no evidence that anything beyond normal Einstein's General Relativity is going on, but the mergers themselves are challenging our understanding of the formation of the universe...
I have been loosely following the gravitational wave stuff but I thought that was reinforcing existing theory?
Yes and no. There's no evidence that anything beyond normal Einstein's General Relativity is going on, but the mergers themselves are challenging our understanding of the formation of the universe because of their sizes and frequency. Additionally, the latest result from pulsar timing indicating that there is a "cosmic gravitational wave background" is incredibly surprising as it's unexpectantly measurable and we have no confident idea what makes it. Cosmology and astrophysics is popping at the moment.
New result out from Fermilab! The news dropped a couple days ago, but I thought to post it here. To set the table: The g-2 measurement characterizes the size of a particle's magnetic moment which is given by:
Particles like electrons and muons in addition to being charged, also act like bar magnets with a north and south pole (just like your everyday fridge magnet). The magnetic moment just tells you how strong it is. These particles also have a value of "g" very close to two, but not exactly two because of quantum vacuum polarization. Fancy words, this is where things like "virtual particles" are relevant. The value of g-2 then tells you the "anomaly" of the moment or how far away it is from two.
This factor of two doesn't sound exciting, but famously there is a discrepancy in the measurement of the muon's magnetic moment where theory differed from experiment by a decent amount. This is called the "muon g-2 tension." This result tightens the experimental side of things to a much better degree and seems to resolve the tension to the disappointment of every head-in-the-clouds physicist hoping to find evidence for physics beyond the Standard Model.
In comparison, our best theory calculation from 2020 is:
Yeah, we're really quibbling over those deep decimal places now. The pretty interesting part is the theory uncertainty is quite a bit bigger now than the experimental uncertainty. Another neat result is the aforementioned g-2 tension for the muon has sort of evaporated away with the better measurement now done by Fermilab. You can see the old best experimental measurement in the Fermilab news article above which clearly shows the apparent discrepancy. As a point of comparison, the muon's lighter brother, the electron, has a g-2 anomaly of:
which is probably the most precise measurement in all of science. You'll notice the electron value is several digits deeper than the muon.
Here's the /r/physics reddit thread on this news too which might be an interesting read. Some folks there point out that theory uncertainty has actually worsened since 2020 (which is the result I link to above) but I'm not familiar enough with the latest developments here to comment. This statement by the Theory Initiative goes into some details of why things are difficult. In short: Hadrons make everything murky and hard.
This always makes me wonder about the state of future developments. As physicists measure stuff more and more accurately its feels like it just reinforces existing models instead of challenging them. Current physics and maths very much beyond me so I don't know if this is a fair question, but is current theory approaching the end of our ability to advance it?
Regardless of all that, I really enjoy hearing about experimental scientists (in whatever field) measuring things with even more extreme accuracy. When I was a kid I wanted to do this kind of stuff but I'm glad I never did; I never would have kept up with the math and trying to control for whatever effect or error would drive me mental.
If you're only concerned with the Standard Model, it may seem this way, but there's definitely bright spots of fast movement in fundamental physics today. Cosmology and astrophysics have been making leaps and bounds with new big discoveries coming every few years with theory struggling to keep up in many aspects. We've just begun the new field of gravitational wave astronomy and advances in neutrino physics may indeed "crack" the Standard Model open with new insights in the future. Neutrino masses are still not well understood and don't quite "fit" the Standard Model, so we know there has to be something more. Dark matter and dark energy are still huge mysteries as well.
On one hand it is a bit sad that the 'age of discovery' that the development of the Standard Model occurred in has somewhat past, but that's only because it's such a wonderful achievement. It's a really good theory. It might be sometime before technology advances enough for us to really stress it at ultra-high energies. There's a huge gulf between accessible energies today and where we expect Grand Unified Theories to reveal themselves for instance. That area of physics may very well be outside our current lifespan to probe.
Gotta be honest, I forgot that particle physics and and astrophysics were on different pages.
I have been loosely following the gravitational wave stuff but I thought that was reinforcing existing theory? Regardless, it is pretty exciting stuff and its fun to follow since the idea of gravity waves and the methods for measuring them are pretty easy to grasp.
Yes and no. There's no evidence that anything beyond normal Einstein's General Relativity is going on, but the mergers themselves are challenging our understanding of the formation of the universe because of their sizes and frequency. Additionally, the latest result from pulsar timing indicating that there is a "cosmic gravitational wave background" is incredibly surprising as it's unexpectantly measurable and we have no confident idea what makes it. Cosmology and astrophysics is popping at the moment.