Physicist Astrid Eichhorn is a leader in the field of asymptotic safety | Hacker News Reader

Physicist Astrid Eichhorn is a leader in the field of asymptotic safety

quantamagazine.org

137 pointstzury17 comments

Asymptotic Safety also predicted the higgs mass (126 GeV vs the measured value of 125 GeV). https://arxiv.org/abs/0912.0208

The trick is, at that time most of the possible mass range was excluded experimentally, so it is a bit less impressive. I'm not sure how much tuning went into it (possibly none)

The article is badly written. This has nothing to do with fractals, they are talking about the assumption that there is an UV fixed point for all physical laws, which can even be true and personally like. It means there are no ultraviolet divergences and that at some point quantum field theory becomes finite. Over a certain large mass scale (which still can be much smaller than the Plank scale) all the coupling constants freeze, there are no radiative corrections and all is simple and well behaved. The problem is, you need some extra fields to do that, with some symmetry cancelling the divergences over the mass scale (it does not have to be supersymmetry) and we lack a theory for that. Moreover, the low energy physics will be nearly independent from the high energy modifications, so the predictive power is low. Yes, they predicted the Higgs mass, but it could very well be a coincidence. If they could predict something really new, though, then it would become quite interesting.

Read on and see the retropredictions of top and bottom quark energies!

Even a retrodiction can be impressive and/or interesting if it is a sufficiently "nothing up my sleeve" [1] type of prediction. I don't know enough about this field and the article isn't informative enough for me to guess, but it's possible that they made a retrodiction where they didn't tune the parameters for it explicitly and got near the correct result directly. In that case, it would at least constitute some sort of clue, even if it isn't necessarily correct. Or they could have tuned the heck out of it and glossed over it in the article, I dunno.

[1]: https://en.wikipedia.org/wiki/Nothing-up-my-sleeve_number

Being able to predict such values from first principles is actually a very good sign for a theory.

I see a spacetime with no time, only mass and energy.

The headline feels off. Which, fair, headline.

But "seeing fractals" feels like a cheat of saying, things have a similarity as you change scale. This could be true even if you think things reduce to strings/loops/whatever. Such that contrasting fractals to strings feels off.

Still a neat and fun article.

If things have a similarity as you change scale and if things also reduce to strings, then we would expect to see strings at all scales, which we definitely don't.

That said, she makes the following observation at the end of the interview: "Asymptotic safety could be compatible with these other approaches. Perhaps at the fundamental scale there are strings or loops or something, but then as you zoom out you hit a realm where things change so slowly for a while that it looks as if you’re at a fixed point."

So while asymptotic safety is not fully compatible with string theory, the physical difference between them could be very small.

Agreed. And again, fair that I was critiquing the headline. I think I just balked at the use of fractals there implying that they were, themselves, somehow contrasted to other descriptions.

On things happening strangely at different scales, I confess I always thought this had to have some parallel to how basic scaling itself changes for values between zero and one. Fun to read more on it.

The fractals idea is less about the common popsci “zoom in or out and it looks the same” property that most people are familiar with.

What it’s really about is criticality(1), a point between chaos and order where all the interesting things happen.

(1) https://en.wikipedia.org/wiki/Self-organized_criticality

TL;DR: scientists are still pursuing science.

> Eichhorn and her colleagues are pursuing a different possibility. In 1976, Steven Weinberg, a theorist who would eventually earn a Nobel Prize, pointed out that if you zoomed in far enough, you might reach a place where the rules of physics would stop changing. New realms would stop appearing; the intensities of the forces would stabilize; and gravity would turn out to make perfect sense after all.

>TL;DR: scientists are still pursuing science.

if that is the entirety of what you took away from reading this (or, the entirety of what you think other people should take away), that is a shame.

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