
How Renormalization Saved Particle Physics - theafh
https://www.quantamagazine.org/how-renormalization-saved-particle-physics-20200917/
======
ssivark
The concept underlying renormalization/invariance as we now understand it, is
a fundamental and profoundly beautiful idea about the very nature of what it
means to make a model for a phenomenon. Essentially:

 _A theory is nothing but a way to turn (a finite number of) measurements into
predictions_.

The number of degrees of freedom in some putative model might be infinite, but
all/most of them will be common between the observed context and the
prediction context; it’s only the difference between those two that matters.
And renormalization theory provides certain bookkeeping tools to track &
ensure that, which then makes tractable the task of predicting.

~~~
clickok
> A theory is nothing but a way to turn (a finite number of) measurements into
> predictions.

That's a very nice way of putting it. Is there a particular book, lecture, or
other resource you could recommend for this interpretation of theorizing?

~~~
ssivark
That particular statement is something I made up once I finally understood
what was going on; I’ve not seen any references which explain it quite that
way. If there are any specific leading questions, I might try to unwrap that
intuition here; otherwise it’s a little difficult and I’ll need to think
harder to cook up a nice motivating example :-)

That said, Simon Dedeo has a relatively accessible set of online lectures
which explain the concepts behind renormalization and broader connections to
ideas in computing and other fields, without needing as much heavy machinery
as a typical theoretical physics treatment. I haven’t watched it, but in
general I appreciate his pedagogy, so here’s the playlist:
[https://www.youtube.com/playlist?list=PLF0b3ThojznTzAA7bfLWh...](https://www.youtube.com/playlist?list=PLF0b3ThojznTzAA7bfLWh4RKzRrwNF4L0)

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ternaus
Renormalization is a beautiful hack, but it is a hack.

Let's take infinity, subtract other infinitites add a bit of alchemy and here
is our prediction. <\- from mathematical perspective this is a very sketchy
business.

But it works. And it works in other fields. For example in the theory of phase
transitions (I have PhD on the topic :))

And it is pretty common in Physics to work with sketchy constructions for
decades before mathematicians catch up.

I love the example of "Generalized Functions" (examples are Delta function and
Step Function) that were widely in Physics decades before a consistent
mathematical theory was developed.

I hope, at some point we will have a similar story with Renormalization
theory.

~~~
improbable22
Well, that's how this was discovered, as a clever hack that worked. In the
1940s.

But it was subsequently understood much better, in the 70s. There are no
infinities involved in thinking about renormalisation group flow.

That progress seems like exactly the story the article is trying to tell.

It's indeed not so different from the story of calculus. You don't even need
Dirac, the very basic idea of calculus is a hack for dividing zero by zero
without getting confused, which later got nicely cleaned up to became
respectable mathematics.

------
acqq
Following the links in the article, it seems it's about:

[https://ncatlab.org/nlab/show/Schwinger-Tomonaga-Feynman-
Dys...](https://ncatlab.org/nlab/show/Schwinger-Tomonaga-Feynman-Dyson)

leading to:

[https://ncatlab.org/nlab/show/perturbative+algebraic+quantum...](https://ncatlab.org/nlab/show/perturbative+algebraic+quantum+field+theory)

~~~
spekcular
The first link is indeed relevant, but the second is emphatically _not_ what
physicists talk about when they talk about QFT. (It is generally true that
nLab usually lacks perspective, to put it mildly, and the corresponding
Wikipedia articles are likely more information.)

For a description of the differences, I suggest this paper (link is to a
preprint version): [http://philsci-
archive.pitt.edu/8890/1/critique_sep10.pdf](http://philsci-
archive.pitt.edu/8890/1/critique_sep10.pdf). The author also gave a talk on it
which was recorded and put on YouTube.

~~~
acqq
> the second is emphatically not what physicists talk about when they talk
> about QFT

Thanks many times. It looked weird to me too, but I've thought "well, some
fringe theoretical physicists -- metaphysics topics".

"Quantum" attracts everything.

------
Florin_Andrei
> _renormalization’s hostility to microscopic details works against the
> efforts of modern physicists who are hungry for signs of the next realm
> down_

No, it doesn't. It simply says "your tools are good down to about here; beyond
this point, you must use different tools." That's all.

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senderista
Ken Wilson wrote a beautiful popular article on the renormalization group for
SciAm in 1979.

[https://websites.pmc.ucsc.edu/~wrs/Project/2014-summer%20sem...](https://websites.pmc.ucsc.edu/~wrs/Project/2014-summer%20seminar/Renorm/Wilson-
many%20scales-Sci%20Am-79.pdf)

------
Koshkin
So, the need for the renormalization group could be seen as Nature's answer to
reductionism. Emergent phenomena can (and perhaps should) be treated
independently.

------
Shoop
@dang: Could we get a title change to "How Renormalization Saved Particle
Physics"?

~~~
lacker
It's interesting, you can see in the URL that at some point the article was
named "How Renormalization Saved Particle Physics". My guess is that an editor
changed it to make it more comprehensible / clickbaity.

~~~
davidkuhta
I found it less click-baity and more a sly reference to the perception of the
theory by its contemporaries (particularly Feynman in his QED book):

"…is technically called ‘renormalization.’ But no matter how clever the word,
it is what I would call a dippy process! Having to resort to such hocus-pocus
has prevented us from proving that the theory [...][...] is self-consistent.
It’s surprising that the theory still hasn’t been proved self-consistent one
way or the other by now; [...][...] What is certain is that we do not have a
good mathematical way to describe the theory of quantum electrodynamics: such
a bunch of words…" \- Feynman, QED 1985

kudos to /u/acqq for the links in their comment.

