Protons Are Probably Actually Smaller Than Long Thought (uni-bonn.de) 68
An anonymous reader shares a report from the University of Bonn in North Rhine-Westphalia, Germany: A few years ago, a novel measurement technique showed that protons are probably smaller than had been assumed since the 1990s. The discrepancy surprised the scientific community; some researchers even believed that the Standard Model of particle physics would have to be changed. Physicists at the University of Bonn and the Technical University of Darmstadt have now developed a method that allows them to analyze the results of older and more recent experiments much more comprehensively than before. This also results in a smaller proton radius from the older data. So there is probably no difference between the values -- no matter which measurement method they are based on. The study appeared in Physical Review Letters.
[...] Using this method, the physicists reanalyzed readings from older, as well as very recent, experiments -- including those that previously suggested a value of 0.88 femtometers. With their method, however, the researchers arrived at 0.84 femtometers; this is the radius that was also found in new measurements based on a completely different methodology. So the proton actually appears to be about 5 percent smaller than was assumed in the 1990s and 2000s. At the same time, the researchers' method also allows new insights into the fine structure of protons and their uncharged siblings, neutrons. So it's helping us to understand a little better the structure of the world around us -- the chair, the air, but also the stars in the night sky.
[...] Using this method, the physicists reanalyzed readings from older, as well as very recent, experiments -- including those that previously suggested a value of 0.88 femtometers. With their method, however, the researchers arrived at 0.84 femtometers; this is the radius that was also found in new measurements based on a completely different methodology. So the proton actually appears to be about 5 percent smaller than was assumed in the 1990s and 2000s. At the same time, the researchers' method also allows new insights into the fine structure of protons and their uncharged siblings, neutrons. So it's helping us to understand a little better the structure of the world around us -- the chair, the air, but also the stars in the night sky.
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That was a Monty Python meme for those that missed it. Good one AC!
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/. is reddit with shittier formating and edgier edgelords
Re:That reminds me of an old joke... (Score:5, Funny)
A neutron walks into a bar. The bartender replies, "For you, no charge."
Re:That reminds me of an old joke... (Score:5, Funny)
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Shore? Hey buuuddy.
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Re: That reminds me of an old joke... (Score:2)
A tachyon walks into Ten Forward.
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Probably Actually Smaller Than Long Thought? (Score:2)
A long thought can be minutes, so makes sense to me.
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Dark matter walks into a bar. The racist bartender says, "we don't interact with your kind here."
This will alter some constants (Score:5, Interesting)
It has to. Ony some of the forces follow an inverse square law 9the strong nuclear force is a weirdo and breaks the law when it can). In order for the forces to balance, you have to change the constants to match. It probably isn't a huge amount, but it'll be there. But that means that all other calculations using those constants must be redone. I'm sure they've done this, they aren't idiots, and most of the time it'll be a negligible shift. For pentaquarks, where you've got a metastable configuration, it's likely to alter things a lot.
Now, apparently, there are some new observations which fit the string theory model.
https://www.quantamagazine.org... [quantamagazine.org]
But a model is only as good as its predictions. At the levels string theory becomes important, the changes to the constants are likely very significant. So question 1 is whether the corrected corrections match a corrected string theory.
Heim theory (Score:2)
No theory we have can derive all the standard model particles masses from some smaller number of foundational constants.
Burkhard Heim proposed a theory [wikipedia.org] that deduces the masses for most particles from first principles.
Unfortunately, it deduced the masses of the particles measured at the time the theory was formulated. When the Tau was later measured, the theory didn't match [nextbigfuture.com], and so it is assumed that Heim theory has no validity.
It's considered a fringe theory, but interesting nonetheless
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Well, string theory necessitates supergravity and supersymmetry. I'm not sure if you can test supergravity (although if QLG is demonstrated, you would definitely falsify supergravity by necessity, as supergravity requires non-local gravity via a particle), but supersymmetry is definitely doable. We don't have to disprove all possible supersymmetries, the rule is that you should prefer the simplest model and the higher the order of supersymmetry the more complex the theory. So all you need do is falsify all
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It has to. Ony some of the forces follow an inverse square law 9the strong nuclear force is a weirdo and breaks the law when it can). In order for the forces to balance, you have to change the constants to match. It probably isn't a huge amount, but it'll be there. But that means that all other calculations using those constants must be redone. I'm sure they've done this, they aren't idiots, and most of the time it'll be a negligible shift. For pentaquarks, where you've got a metastable configuration, it's likely to alter things a lot.
It depends on whether the values of those constants are measured as a consequence of the size of the proton, or whether the size of the proton is being measured as a consequence of the value of those constants. If the measurement itself involved application of those constants, then the changes are already baked in.
Non-perturbative QCD (Score:2)
It has to.
No it does not. The reason being is that you cannot accurately calculate the radius of a proton from the underlying theory of QCD. The reason for this is that, at low energies such as quark bound states, QCD is non-perturbative. This makes the problem almost impossibly hard to calculate. There are approaches used by theorists to try and get around this but they rely on approximations or extrapolation of other measured quantities which add large uncertainties.
Lattice QCD is another approach that uses a v
Re:This will alter some constants (Score:5, Informative)
The proton is not a fundamental particle, it's composed of quarks bound together with gluons. Quark-gluon interactions (which control its radius) are incredibly difficult to calculate (damned near impossible, in fact). The radius of the proton is not actually very important anyways: it's not a terribly meaningful quantity to begin with, since protons aren't hard spheres but a fuzzy miasma of gluon-quark interactions. The "radius" is defined as the root-mean-square distribution of the charge, which only has a small contribution to the physical behavior of the proton. The more important physical quantities of the proton, such as the total charge or the residual strong force interactions (which are primarily responsible for its contribution to chemical and nuclear interactions, respectively) aren't a function of this radius, except for minor higher order corrections.
Re: This will alter some constants (Score:2)
You seem knowledgeable about this. Question: could the size of a proton change as a result of measurement?
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I would assume that the size is subject to quantum uncertainty, so it'll naturally vary but must average out at the size that has been observed and the variation must be bounded to be strictly less than the error bars in the calculation. However, this is an assumption and we must await the thoughts of those who know more.
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Sort of. The "size" of the proton depends on the positioning of the quarks that compose it, which is constantly changing. In fact the individual quarks don't usually have a well-defined position, they're spread out over some volume following a distribution (this is the "wave" part of "wave-particle duality" in quantum mechanics). This distribution is larger near the center of the proton, and falls off further out. The measurement in this story is about the average radius of this volume, i.e. we measure the
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I think that explains why I woke up in the middle of the night, wondering where I am. Uncertainty principle and things. I might also need to revise the circumference of my waist, which not a universal constant, as I thought when I bought my last pair of jeans.
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The biggest problem with String Theory is that nobody has been able to come up with any solutions that works in de Sitter space (a universe that is expanding at an accelerating rate - just like our own.), in-fact
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Well, that offers a theoretical way to falsify string theory that doesn't require observation, which is good -- if it can be shown De Sitter solutions do indeed sit in the "swampland" then string theory is impossible regardless of how it is formulated and with which supersymmetric particles. That's great, because it sounds like physics and maths are getting to the point where they can decide this issue once and for all. In the end, science is all about finding which solutions won't work.
But are you positive about this? (Score:3)
Muon measurements were unexpected (Score:5, Insightful)
Using muons was the novel measurement technique that kicked all of this off. The old radius had been measured using electrons, and it was expected that using muons would give the same radius, but it was 4% smaller. Shrunken Proton Baffles Scientists [scientificamerican.com] is an article from that time.
But it is still not compatible with the measurements taken by non-muonic techniques, says John Arrington, a nuclear physicist at Argonne National Laboratory in Lemont, Illinois. Errors in the muon-based measurements of the proton radius are unlikely to be to blame, Arrington says, and yet it seems equally unlikely that all the other measurements are wrong, too.
Now it turns out there is no new physics. The old values actually were incorrect.
Remember when humans had 48 chromosomes? (Score:2, Offtopic)
Then again, when I was young, there were nine
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24 pairs? There were even electron micrographs to prove it - I saw such science when I was in third grade. Then some yutz released a different picture and said we only have 23 pairs of chromosomes. When scientists (interested in disproving his work) went back to the old micrographs, they discovered that someone had miscounted years ago and nobody noticed. Sometime in the sixties, humanity went from 48 chromosomes to 46 chromosomes, and we didn't even notice!
Then again, when I was young, there were nine planets in the solar system.
The correct number of chromosomes was determined in 1956 so to be in third grade before the discovery you must be more than 75.
The story about the chromosome count [nature.com] is that it took the development of several laboratory methods to be able to count them accurately since only briefly during cell division (the metaphase) are they distinct and separate. Colchicine was needed to halt the cell division process, rapid fixation at just the right time is needed, specific techniques of preparation and staining are req
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I'm glad to hear that science had actually resolved this question even before I was born. I still clearly remember things as I have relayed them here - and I clearly remember being taught that we have 24 pairs of chromosomes.
Sorry you weren't there - you missed one heckuva sockaroo!
Re:Remember when humans had 48 chromosomes? (Score:4, Informative)
Now, get off my lawn, you insensitive clod.
There goes the experiment (Score:2)
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Thats what she said.
Shrinkage (Score:2)
What is a particle radius exactly in QM? (Score:2)
Does it together with the temperature give a probability of a collision? A kind of standard deviation?
Or is it really the minimum distance the particles can pass each other in a classical sense?
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Its impossible to target a single proton but you can do an experiment where you collide protons and electrons or muons at different energies, and look at the scattering.
it's not actually there is it ? (Score:1)
isn't it's probability function the thing that's "there", Schroedinger, Heisenberg and all that
so the radius is really a 1/2 power bandwidth or something ?
Read the label (Score:5, Funny)
I can't see an easy way to politicize this story (Score:1)
But I'll give it my best shot:
One side will approach this result with skepticism under the presumption that the discovery of a 5% bias in a tricky indirect measurement may imply there are other ways to cook the books that may lead to more refined estimates down the line.
The other side will dutifully scour their social media history, delete any posts referencing the old, heretical, value and proudly declare that the proton has *always* been known to be 5% smaller than you think it is. Follow the science.
Who is Long? (Score:2)
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Lazarus...
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Who is Long, and how big did he think a proton is anyway?
He was a rather corrupt governor and senator for the state of Louisiana. I've heard many things about him - but I didn't know he'd opined regarding the size of a proton.
Doesn't surprise me at all! (Score:2)
Happens to us all as we age (Score:1)
nuf sed
What is the radius of a fart? (Score:2)
One can measure its repulsive force, but that effect is dependent on the sensitivity of noses, and the social tolerance of rude smells. Tests indicate that there is an attractive component, where teenage boys are present. More research is clearly needed in this area, particularly because I get paid for writing stuff about it. My paper on the hand waving theory of knowledge has unfortunately not been accepted for publishing in a learned journal. I think they might be afraid I will give the game away.
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You can wave your hands as rapidly as you want to dissipate and attempt to increase the blame radius, however the act of fanning your butt itself is admission of guilt.
Repercussions at scale? (Score:1)
Were the previous measurements affecting other size constraints or measurements, such as the presumed radii of neutron stars? Maybe I'm conflating the metrics used but curious nonetheless!
sniffing gluons (Score:1)