B Scientists may have discovered a new force of nature?

[Hacker Jack]

Thanks to BBC for making it readable for a layman

link to the article: https://www.bbc.com/news/56643677

 

[Borek]

"It has the potential to turn physics on its head."

Sigh, how I hate media. No, the everydays physics will not change at all. We will extend our description and understanding of minute details. Birds will still fly, cars will still drive, TVs will be still using the same old physics to transmit the same old dang.

 

[phinds]

And "the media" will continue to misunderstand and/or sensationalize science.

 

[pinball1970]

And "the media" will continue to misunderstand and/or sensationalize science.

Media aside what is it?
Anything at all?

 

[hmmm27]

There's an extant thread somewhere, in high energy...

here

 

[etotheipi]

"It has the potential to turn physics on its head."
Sigh, how I hate media. No, the everydays physics will not change at all. We will extend our description and understanding of minute details. Birds will still fly, cars will still drive, TVs will be still using the same old physics to transmit the same old dang.

And "the media" will continue to misunderstand and/or sensationalize science.

I do not like this take. The BBC is not writing for scientists, they are writing for people with only casual interest in Physics who would be completely turned off by an article littered with technicalities.

The titles tend to be a bit clickbait, sure, but at the end of the day if you want to make the average person excited about science then popular expositions play an important role. Silly example: when I called my mum earlier and she asked about the headline, I'm not going to turn around and say "Pffft, you fool! That's not real physics!"; I'm more just happy that she wanted to take an interest in a subject I'm passionate about.

So I say, sensationalise all you want (within reason ). It's just a bit of fun!

 

[hutchphd]

Issues surrounding Dark Stuff have to some degree "turned physics on its head". And that phrase can be interpreted many ways.
All in all the BBC article does a pretty good job IMHO.

 

[phinds]

... at the end of the day if you want to make the average person excited about science then popular expositions play an important role

Absolutely no argument there. The issue is that people THINK they are reading actual science and then they come here and we have to disabuse them of their "knowledge". This thread is a very minor example of that.

 

[david2]

How else to get funds from legislators? You have to make it spicy. I bet the media did not come to this conclusion by themselves.

 

[phinds]

How else to get funds from legislators? You have to make it spicy. I bet the media did not come to this conclusion by themselves.

I'll bet they did. Funding is not based on media reports and yes scientists do try to jazz up things in funding applications but they do not put out misleading stories because it makes them look foolish. For that kind of thing the media has Kaku and others.

 

[DaveC426913]

"It has the potential to turn physics on its head."
Sigh, how I hate media. No, the everydays physics will not change at all.

A fifth fundamental force would be pretty significant, if true.

In their defense, Einsteins' relativity and then quantum mechanics both "turned physics on its head" - even for (especially for) the layperson. It overturned how we see our universe.

 

[pinball1970]

So...what is it?
Something?
A hint of something?
or nothing?

 

[gleem]

New force, new physics? maybe not. A group known as the "Budapest-Marseille-Wuppertal Collaboration" has recomputed the magnetic moment and reduced the discrepancy between theory and experiment to 1.6 σ.

From ( The muon’s theory-defying magnetism is confirmed by new experiment – Physics World )

Alternative theory

Indeed, if a group of theorists going by the name of the Budapest-Marseille-Wuppertal Collaboration is correct, there may be no disparity between experiment and theory at all. In a new study in Nature, it shows how lattice-QCD simulations can boost the contribution of known virtual hadrons so that the predicted value of the muon’s anomalous moment gets much closer to the experimental ones. Collaboration member Zoltan Fodor of Pennsylvania State University in the US says that the disparity between the group’s calculation and the newly combined experimental result stands at just 1.6σ.

 

[f95toli]

I'll bet they did. Funding is not based on media reports and yes scientists do try to jazz up things in funding applications but they do not put out misleading stories because it makes them look foolish.

I so wish that was entirely true
Yes, media reports is not the only thing that matters and you need to convince your peers as well, but for "big science" where there is so much money involved that decisions about funding are actually taken by the government (or at least at government department level) a good media story is VERY helpful.

 

[PeroK]

So I say, sensationalise all you want (within reason ). It's just a bit of fun!

There is a risk that it undermines the public perception of established science. If fundamental physics can be "turned on its head", then why not the science of climate change, epidemiology, vaccinations and even the geological evidence against creationism?

The politically astute thing to do would be to play down the impact of new discoveries to established theories (which is often the technical reality in any case), and emphasise that this is something new that extends our knowledge - in this case, something to add to the standard model, rather than something that renders it obsolete.

 

[DaveC426913]

The politically astute thing to do ...

Maybe, but consider: some citizens will benefit more from science news than others.

Even if 90% of the public are merely passive readers, but 10% are actively interested, it might still be advantageous to target the `10%.

Interested citizens get involved, get educated, invest, donate, pursue careers and join science forums - in the sciences.

(Ultimately, the 10% won't be led astray by clickbait articles, since their self-education will innoculate them from low quality information.)

 

[collinsmark]

Here's Dianna Cowern's (from Physics Girl) attempt to explain it in lay-people's terms:

 

[DennisN]

A fifth fundamental force would be pretty significant, if true.

So...what is it?
Something?
A hint of something?
or nothing?

I don't know. But if it's a force of nature, it's probably in some way related to Chuck Norris.

Edit:

Here's Dianna Cowern's (from Physics Girl) attempt to explain it in lay-people's terms:

Interesting. A deviation from expectations in the Standard Model is rather exciting, I think.

 

[Jarvis323]

There is a risk that it undermines the public perception of established science. If fundamental physics can be "turned on its head", then why not the science of climate change, epidemiology, vaccinations and even the geological evidence against creationism?

The politically astute thing to do would be to play down the impact of new discoveries to established theories (which is often the technical reality in any case), and emphasise that this is something new that extends our knowledge - in this case, something to add to the standard model, rather than something that renders it obsolete.

This does make sense. I often have read articles that have illegitimately caused loss of faith in a theory.

But then there is a loss of credibility when dogma is defended for the sake of keeping the masses faithfull.

Covid has been an extreme lesson on this, with many authorities having been constantly defending their old and now known to be wrong ideas: asymptomatic, masks, mutations, airborne, etc.

What makes me trust science is when there is an openness about uncertainty, a quickness to acknowledge mistakes.

Neil says science is right whether or not you believe in it. I don't agree with that or that we should tell the masses that for example.

 

[DaveC426913]

...a quickness to acknowledge mistakes.

I would alter that to say "...a quickness to acknowledge obsolescence".

 

[epenguin]

I have been reading articles in other journals to the same effect since a few days.
It does not seem to me fair to blame the journalists for what people are finding wrong – scientists seem to be feeding them, see the quotes.

I had been meaning to ask here just what is there about this experiment that a disagreement between its results and a theoretical calculation is necessarily some totally fundamental change of physics. (Also I'd always heard the Standard Model described as a useful thing to be going on with, even a bit ramshackle, is that right? not something perfect that it would be shocking to modify).

 

[Tom.G]

A rather more technical take on the experiment itself is this 12 minute, fast moving video:


Cheers,
Tom

 

[collinsmark]

New Sixty Symbols video. Professors Ed Copeland and Tony Padilla discuss latest results in particle physics from Fermilab and the Large Hadron Collider.

 

[mfb]

I had been meaning to ask here just what is there about this experiment that a disagreement between its results and a theoretical calculation is necessarily some totally fundamental change of physics. (Also I'd always heard the Standard Model described as a useful thing to be going on with, even a bit ramshackle, is that right? not something perfect that it would be shocking to modify).

If both theoretical prediction and measurements are robust then every deviation is revolutionary and will change fundamental physics a lot. We had a single clear deviation from the SM in the last decades - neutrino masses.

We already have a discussion here
There are two theory predictions, one agrees with the experiment. It's very likely that the other prediction is just incorrect. We already know that at least one of them must be off, and it's probably not the one that agrees with experiment.

 

[ohwilleke]

A fifth fundamental force would be pretty significant, if true.

In their defense, Einsteins' relativity and then quantum mechanics both "turned physics on its head" - even for (especially for) the layperson. It overturned how we see our universe.

Suppose that there really is a 4.2 sigma discrepancy and the BMW calculation is wrong.

One thing we can say with certainty is that a measurement that is 4.2 sigma from a theory prediction for muon g-2 does not tell us "what" is causing the discrepancy.

It only tells us "how big" the discrepancy is, and even then, only partially. A discrepancy could be due to a tiny tweak to something central to calculating muon g-2, or it could be a huge tweak to something that only makes a small contribution to the overall result, or it could be something in between, or a bit of all of those explanations.

But, since the calculation of muon g-2 receives contributions from all three Standard Model forces and most of the Standard Model fundamental particles (in addition to any new physics contributions), it is a very global measure of the consistency of the Standard Model with experiment.

Lots of plausible explanations wouldn't involve a "fifth force", just one or more new particles. For example, while no one is proposing this particular explanation of the muon g-2 anomaly, as proof of concept, if there were a fourth generation of Standard Model fermions (t', b', tau', tau neutrino'), this would change the value of muon g-2 a little, without changing any of the forces of the Standard Model.

To give a more "real" example, one of the big differences between the prediction that says there is a 4.2 sigma distinction between experiment and prediction, and the one that says that there is only a 1.6 sigma distinction, is that the second prediction treats up and down quarks as having different masses, while the first one uses only the average mass of the up and down quarks. This slight tweak in the assumed masses of two Standard Model quarks makes a quite significant impact on the predicted discrepancy between theory and experiment, even though both the up quark and down quark masses are tiny (about 2.5% and 5% respectively, of the muon mass).

Also, keep in mind that the discrepancy, even if it is highly statistically significant, is still tiny. It is on the order of 2 parts per billion.

The same can be said of other anomalies that are out there.

For example, there are several kinds of decays of B mesons (composite particles with a valence quark and anti-quark, one of which is a b quark or anti-b quark) which seem to produce decays that generate more electrons than muons for reasons beyond those attributable to their mass differences even though in the Standard Model, this shouldn't happen. This isn't seen in any other kind of decay process.

But guess what. There are almost no processes of engineering importance, or importance in the post-Big Bang natural world, even in extreme circumstances like the inner structure of neutron stars and supernova, in which the ratio of lepton flavors produced in B meson decays play an important part. It is intellectually interesting and could even lead to a tweak of the Standard Model, but it is not important in any practical sense. Nobody even predicted that b-quarks existed until 1973 and no one in the entire history of life on Earth had knowingly observed one until 1977. B mesons are so ephemeral that they have a mean lifetime on the order of a trillionth of a second, and have only ever been produced in the lab in a handful high energy particle colliders.

So, while there may be a crack or two in the Standard Model that doesn't yet have a full explanation, it is still an incredibly precise and accurate description of the real world, and the cracks that are present are either tiny, or in highly exotic phenomena produced only in the most rarified laboratory conditions.

 

[nolxiii]

There are two theory predictions, one agrees with the experiment. It's very likely that the other prediction is just incorrect. We already know that at least one of them must be off, and it's probably not the one that agrees with experiment.

Ya but the other one is still 1.6 sigma off right? Still new physics until it isn't.

 

[ohwilleke]

Ya but the other one is still 1.6 sigma off right? Still new physics until it isn't.

The universally accepted practice in physics experiments (and almost all other disciplines as well) is to consider any result within two sigma of the prediction to be "consistent" with the prediction and statistically insignificant (which means that the discrepancy has more than a 5% chance of being due to random statistical flukes).

If your estimated uncertainty is perfectly determined, and your predicted value is exactly right, the expected average difference between experiment and prediction, simply due to random chance, is 1 sigma.

If your results are consistently showing less than a 1 sigma difference between prediction and experiment, it means that you have overestimated the uncertainty in your measurement.

Physicists consider "new physics" to be discovered when there is a 5 sigma difference, the result has been replicated, and there is some plausible scientifically motivated theory to explain why there is a difference.

When there is a discrepancy that is more than 2 sigma and less than 5 sigma, physicists call that a "tension" between theory and experiment, which is considered a "weak tension" if it is just a little more than 2 sigma, and a "strong tension" if it is close to 5 sigma.

In real life, because margins of error are routinely underestimated and systemic errors (as opposed to sample size based errors) usually have "fat tails" that make big errors more likely than they would be if they were simply due to a small sample size, discrepancies of 3 sigma and less end up going away over time about half of the time.

The requirements of replication and a scientifically motivated theory to consider "new physics" to be discovered is there to guard against systemic errors in either the experiment or the theoretical calculation that the original people to find the discrepancy had no idea were present, like the faulty cable at the Opera Experiment that seems to show that neutrinos were traveling faster than the speed of light.

The first scientists to 5 sigma are considered to have discovered "new physics" but only retroactively once their results are replicated and confirmed. Experiments like the Large Hadron Collider and Tevatron were set up with two independent groups of scientists for each main part of the experiment that share the equipment, in order to allow results to be replicated, even though it means that each independent group gets less statistically significant results as a result.

 

[mfb]

Ya but the other one is still 1.6 sigma off right?

1.3 sigma including a more recent hadronic light by light scattering calculation, but it doesn't matter.
That's at the level of getting 3 "heads" when flipping a coin 10 times. Sure, it's not most likely result, but would you assume the coin is biased seeing that?

Still new physics until it isn't.

You can never reach infinite precision with measurements or theory. There is always some uncertainty, and we don't expect the values to match exactly. Being compatible within the uncertainties is the best (or worst?) outcome, and 1.3- 1.6 sigma is certainly within what we expect from statistical fluctuations.

 

[collinsmark]

Here's Lawrence Krauss's take on the subject, complete with a at least a little bit of mathematics*. I found it rather insightful.

Part 1:


Part 2:


*I assume that since you're reading this on PF, you're probably not one to run away at the first sign of a math equation.

 

[epenguin]

Rovelli today Guardian
https://www.theguardian.com/comment...-discovery-physicists-headline-announcements?

 

[ohwilleke]

Rovelli today Guardian
https://www.theguardian.com/comment...-discovery-physicists-headline-announcements?

Shorter Rovelli. Don't freak, it is probably just a fluke.

 

[artis]

@ohwilleke in your post #25 you mention the masses of up and down quarks and how they are used to calculate the sigma of the muon experiment ,

To give a more "real" example, one of the big differences between the prediction that says there is a 4.2 sigma distinction between experiment and prediction, and the one that says that there is only a 1.6 sigma distinction, is that the second prediction treats up and down quarks as having different masses, while the first one uses only the average mass of the up and down quarks. This slight tweak in the assumed masses of two Standard Model quarks makes a quite significant impact on the predicted discrepancy between theory and experiment, even though both the up quark and down quark masses are tiny (about 2.5% and 5% respectively, of the muon mass).

Pardon if this comes across as lazy but don't we know the mass of those quarks with certainty that we can use different numbers for different approaches?

 

[mfb]

Up and down quarks never appear in isolation, which makes it difficult to define what their mass is, and you get different answers (and large uncertainties) with different methods. Many calculations get much simpler if you neglect the small masses of up and down, or at least neglect their difference. But that's not what lead to the deviating theory predictions here. They used completely different approaches.

 

[DennisN]

A rather more technical take on the experiment itself is this 12 minute, fast moving video:

New Sixty Symbols video. Professors Ed Copeland and Tony Padilla discuss latest results in particle physics from Fermilab and the Large Hadron Collider.

Very interesting. Thanks for posting!

 

[ohwilleke]

But that's not what lead to the deviating theory predictions here. They used completely different approaches.

The approaches aren't completely different. Almost all of the difference comes from HVP and there are about five main differences between the two approaches. Using a 1+1+1+1 Lattice approach rather than a 2+1+1 Lattice approach is one of the significant differences.

 

[mfb]

I thought you were comparing it to the reference value that leads to a large discrepancy, not another lattice calculation. The sigma values suggested that.

 

[collinsmark]

A few words of caution about potential, new physics discoveries. Some historical examples are given. (The video leads up to the new anomalies discussed in this thread.)

 

[phinds]

Nice, informative discussion. Thanks for posting.

 

[CGandC]

If one wants to read quality scientific news with technicalities ( assuming the reader has BSc in physics ) , what kind of media can you recommend?

 

[weirdoguy]

https://arxiv.org/

 

[ohwilleke]

Blogs by credentialed physicists (Twitter feeds too).

 

[ChrisVer]

A few words of caution about potential, new physics discoveries. Some historical examples are given. (The video leads up to the new anomalies discussed in this thread.)

I really liked seeing the historical examples in her videos. I find it interesting that these are not talked about much, while most of the public discussion weight goes on the "holy grail" of 5σ... But these examples are a proof that what shines is not necessarily gold... So, it made me thinking:
What is the approach one would take after observing a 5 or even a 6σ deviation from the SM expectation? Wouldn't it be called it a discovery right away? I suppose, these are set by the collaborations or the analysists beforehand (the 5σ of HEP would put most of other sciences' null hypotheses results indestructible), but the point is that their claims would directly affect the theory community worldwide (they would have an indirect verification in hand that there is BSM).

For example FNAL said during their conferences that after unblinding, whatever their result would be, that's what would be published. So, supposing they had observed a 5σ deviation to Δαμ, would that be called an "observation of LFV" right away?
The latest example from particle physics was the Higgs discovery (OK and several other bound states that are observed by LHCb every now or then). For the Higgs, it looks like the case was to call it a discovery right away, but it could be because it's a special occasion (it appeared in different decay channels and in 2 "independent" experiments at the same time).

 

[mfb]

A deviation in g-2 doesn't have to be LFV. It can be anything.
Keep in mind that systematic uncertainties and theory uncertainties are not Gaussian - they have long tails. A 5 sigma systematics/theory error is far more likely than a 5 sigma statistical fluctuation. I would have expected a careful phrasing of the result. It's not like the discovery of the Higgs boson, which was dominated by statistical uncertainties that are well understood, and of course seen by two experiments that both had ~5 sigma.