The latest in Ph-word: April ’21

April had it all: some big news in particle physics, some exciting news in space exploration and some beautiful news in avant-garde astronomy.

Something’s (still) funny with muons

The month started with a long-awaited blast. Long-awaited, that is, for those who happen to be particle physicists. At any rate, the Muon g-2 experiment gave additional verification to the most important difference between experiment and theory of elementary particles that we have so far.

So, what exactl did said experiment find, why is it important and what does it mean? Also, how certain are we about it? Glad you asked.

Muon g-2 found that muons (particles that are a lot like good old electrons only much heavier) behave slightly differently than the theory predicts. The difference concerns the tiny magnetic field that surrounds the tiny muons, and it appears only at several decimal digits down the line.

Still, any difference between experiments and the theory of the Standard Model, which describes what happens with the smallest building blocks of nature is big news: it gives physicists much-needed clues about where to look for the next big thing.

Now, here comes the most important part: this discrepancy in the muon’s magnetic field was “long-awaited” because it was actually first seen two decades ago at a different experiment, at the Brookhaven lab at New York. The new experiment, at the Fermilab lab outside Chicago, was built specifically with the goal to cross-check the previous surprising finding. And now its first results are in agreement with Brookhaven’s (which removes a major headache from its directors who would have to explain a few things to politicians otherwise).

But what does this discrepancy between the data and the theoretical prediction about the muon’s magnetic field mean? Well, nobody knows, but if it is indeed new physics then it most probably means that there are particles that we don’t know of yet. Explaining why would need a few more pages and I’m literally writing this in the subway because this is the only free time I found, so if you want the explanation you can head over to this much more pleasant comic by Jorge Cham.

And now for the venomous question: how certain are we about this results? Tbh, not tremendously much. The most possible explanation for the discrepancy is that the theoretical calculations about the muon’s magnetic field are wrong. Well, not wrong in the sense that they have mistakes. But these specific calculations involve many assumptions and approximations and many of them are still an open issue; so naturally it is expected that they are the weakest link in this story. (If you feel like reading about this in a little more detail, I recommend one of my favourite blogs – but only the first half of the post.)

The 25-word summary: this is the biggest news in elementary particle physics in the last decade, but still nobody is sure yet that it’ll turn out to be true.

Things are getting serious on the red and pink planet

If that felt like a letdown, let’s look at things that nobody doubts. (Well, unless you believe martian landings actually take place in a Hollywood studio.) Yes, they involve Mars. They involve helicopters and they involve oxygen.

The cute helicopter Ingenuity made the first flight ever on another planet! In fact it went on to make several more. Apart from doing it because it can, the main purpose was to showcase that flight can happen in Mars’s thin atmosphere.

And talking of Mars’s atmosphere, Perseverance, the rover that brought Ingenuity along, succeeded in making oxygen out of the planet’s carbon monoxide! It did so by electrolysis and made only a few grams. Also here, the goal was to check how easy or hard this is, with an eye towards creating the oxygen needed for having kitties as pets on Mars. Yeah, the actual outlook is human colonies, but we all know that everything is eventually done for the cats.

Zooming out of a black hole

The other of the exactly four beautiful news of the month in any field was about the first black hole that was photographed two years ago. It now turns out that at the time that the Event Horizon Telescope took its picture, 19 other telescopes were turned towards it as well.

Those telescopes scan the sky for whole different types of light, from visible light to infrared to X-rays. The reason they were orchestrated is that black holes change in time; and the Event Horizon Telescope wanted to make sure that as much info about the hole as possible was gathered in one specific stretch of time, so that it is all combined for maximum impact.

The processing of the info will probably take some more time, but in the meantime the telescopes came together to give us this video and images which are not bad at all.

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