Live data from Hacker News

Physicists finally nail the proton’s size, eliminating an anomaly

quantamagazine.org

101–110 of 115 posts

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#101

Earlier quoted context omitted.

One thing that's always interested me is that the recent history of breakthroughs doesn't tell you when the next one will arrive. For instance reconciling quantum mechanics and gravity, we don't know if we're within 11 years, 110 years, or even 1100 years!

It seems people like newton or Einstein come around every few hundred years. So another huge leap may take a while.

Seems like a good reason to make sure everyone is given the opportunity to achieve their fullest potential. The more we keep ourselves as a species oppressed by one another, the less likely we are to experience the Newtons and Einsteins condemned to rice fields and coal mines.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#102

Earlier quoted context omitted.

Please. Millions of dollars are spent every year researching alternative theories and modifications to GR that eliminate the need for Dark Matter and Dark Energy. The problem is, and has always been, that these alternative theories are never as accurate or precise as GR and their observational evidence is never as good as what we have for DM and DE. It's not a conspiracy that scientific consensus is that they both ex…

It's not a conspiracy per se, but it fits into a realm where virtually every single documentary about space these days are making overt or not-so-overt claims that it's absolutely real and we're not even considering other possibilities. Of course we are, but that's not how it gets presented by the vast majority of "television physicists" and I find most documentaries about space completely unwatchable these days. Usu…

DE and DM are not assumptions, there's strong indirect evidence of their existence. You don't have to see a thing directly to deduce it's there. The problem isn't the shows, the problem is you think you know more than the people who actually know and you're bothered by their confidence in something you wrongly think is just an assumption.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#104

I wish a physicist could explain here how the very notion of "diameter" has any meaning for an object whose size (IIUC) belong entirely to the quantum realm. Is the hydrogen atom two hard little balls of matter orbiting one another, as we were taught in primary school, or are they a probabilistic soup with various, vaguely localized extrema? If the latter, how do you even define the notion of diameter?

This is a surprisingly hard question to answer! An orthodox point of view says "diameter" is just a word for a physical quantity which can be measured by experiment and plugged into a formula to predict the result of other experiments. In my personal opinion, theoretical physics is not currently capable of providing a satisfactory answer, but if we knew more about the relationship between quantum field theory and general relativity it would probably be possible to say more.

There are plenty of ways to wave your hands about it, and I have been doing this for a long time and could give 100 different explanations. At the end of the day what do I see in my head when I think about the "diameter" of the proton? Basically a probabilistic soup which is confined to a small area.

The "wave function" of a quantum particle can tell you where it is but is not the same as the particle itself. Standard QM assumes particles are infinitesimal points, in QFT this leads to infinities which can be resolved if you assume particles have a "smeared out" radius. This "smeared out" radius is what the proton diameter should be related to when the more complete quantum and gravity theory is discovered.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#105
post #64

Earlier quoted context omitted.

Authors don't always have a final say on what the headline will be. Sometimes they don't have any say at all.

The original headline is much more positive: http://yfile.news.yorku.ca/2019/09/06/just-how-big-is-a-prot... I'd say the writer has a tendency to write gloomy headlines: https://www.quantamagazine.org/famous-experiment-dooms-pilot...

It's not a case of an "original headline": this is an entirely separate article, not a regurgitation of the press release. Wolchover is a very serious writer.

It's pretty sickening to watch the (sadly predictable) HN sneering and mockery around the topic of someone's (anyone's) mental health. It's such a cruel, distorted and completely non-constructive conversation. Do you guys really not have anything more interesting to say?

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#106
post #10

I think in some areas of physics, such as high-energy physics, there is not much left to discover. The Standard Model works. What branches of physics are likely to see progress?

Someone please help correct my intuition here: the harder it is to find flaws in the Standard Model, the harder it would be to use such new physics in engineering. Basically I'm curious whether continuing failures to find new physics can be taken as evidence that, if and when we find the new physics, it will be very difficult to apply. I'm not against science for its own sake, however. Just more of an engineer than a…

If the effects require an accelerator the size of a small country to show up, then it's unlikely they'll be useful in anything small.

I think people have been misled by science fiction. Stories posit all sorts of interesting and exciting physics not because that's plausible, but because it makes interesting stories.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#107

I wish a physicist could explain here how the very notion of "diameter" has any meaning for an object whose size (IIUC) belong entirely to the quantum realm. Is the hydrogen atom two hard little balls of matter orbiting one another, as we were taught in primary school, or are they a probabilistic soup with various, vaguely localized extrema? If the latter, how do you even define the notion of diameter?

Not a physicist, but I spent some time on this, exploring the possibility of a "teach scale down to nuclei, then nuclei up to matter" learning progression for primary school.

Nuclei are quasi-classical little balls. It's electrons that are wacky quantum weirdness.

Which makes the current pedagogical emphasis on electrons, rather nuclei, as a foundation for understanding atoms... perhaps miss some opportunities for greater clarity. And that's even before getting to state standards that require teaching both "atoms are conserved in chemical reactions" and "atoms are electrically neutral, so if charged, they are no longer atoms, but ions". Sigh.

Nucleons overlap (not orbit), but nuclei aren't homogeneous, especially light ones. Light nuclei are well described as clusters of alpha particles, heavier ones as liquid drops. Ground states are generally more or less spherical. Though Neon looks like an old-style wine bottle, with a tetrahedron of alphas in the bowl, and a fifth making a neck. Non-ground states for lights are mostly rearranged alphas, for heavies, variously distorted balls. Fission is droplets stretching and necking apart.

A proton is a mix of odd shapes, but directly measurable properties are spherical. It's just a ball.

Nuclear mass and charge density are, to a good first approximation, colocated. You don't have mass concentrated one place and charge somewhere else. No surprises.

Electrons are a peak with exponential falloff, making choosing a radius quite arbitrary. What's the diameter of a cartoon volcano, that blends seamlessly into plains? Wacky, wacky electrons.

Nuclei have a flat-ish density plateau, then a steep slope, and only then a tiny exponential footlands (Woods–Saxon potential). So it's just a ball with a fuzzy edge, rather than a wacky exponential cloud thing.

Note the narrow range of sizes being discussed. No one is suggesting 10 femtometers, or 0.1 femtometers, or even 1.0 fm or 0.8 fm. "GEOID-Next committee tables discussion and heads to a bar, unable to agree on the shape of the Earth!!! News at 11!!!" But for most everyone, primary school up, that's "a femtometer ball".

A superball can be bounced, and crushed, and burned. You need polymer physics to understand just why it behaves as it does. But you can describe that behavior to a Kindergartener. They don't need polymer physics. Nuclei are just little balls.

Now look at the giant hairy mess of this thread. It's like, we teach "4/3 pi r^3, 4 pi r^2", but not "the volume and area of a ball are half of its box". But dialed way way up. Science education, variously distracted, failing to provide a coherent briefing on the physical world.

If anyone has ideas on how to describe this point, I'd appreciate them, as I've never come up with something nice.

Here's a tiny Neon pic. I just think Neon is cute. https://arxiv.org/abs/1406.2473 page 4. There's a nicer one somewhere...

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#108

One has to wonder why the original "muon" paper, which produced such controversial results, did not include the control of measuring with the same methods conventional ("electron") hydrogen. Doing the control would have cleared things up a lot sooner.

It took Eric Hessel's group eight years of hard work to do the measurement in electronic hydrogen. The experiments are completely different.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#109

Earlier quoted context omitted.

The original headline is much more positive: http://yfile.news.yorku.ca/2019/09/06/just-how-big-is-a-prot... I'd say the writer has a tendency to write gloomy headlines: https://www.quantamagazine.org/famous-experiment-dooms-pilot...

It's not a case of an "original headline": this is an entirely separate article, not a regurgitation of the press release. Wolchover is a very serious writer. It's pretty sickening to watch the (sadly predictable) HN sneering and mockery around the topic of someone's (anyone's) mental health. It's such a cruel, distorted and completely non-constructive conversation. Do you guys really not have anything more interesti…

sneering

mockery

cruel

distorted

non-constructive

You get all this from "make sure they're doing ok?".

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#110
post #3

so, a failure in measurement sparked a mystery which went on for decades. i wonder how often that happens in science ;P

All the time! People propose hypotheses, supported by some preliminary data, and then they need to be tested. Some problems are easy, some take years or decades to be overturned. It's messy sometimes, but that's how science is supposed to work!

You're really stretching that 'supposed'.

I think if we were closer to ideal science, we'd work harder to verify numbers as a first step. More replication means stronger foundations and less wasted work.

There will always be some bad results that stick around for a long time before being overturned. But the median lifetime of bad results can change based on how we prioritize research. That statistic might currently be far from optimal.

Post reply on HN