Nima Arkani-Hamed - The end of Spacetime

I forgot to post this excellent layman's article in Quanta Magazine from last year, describing just how far Nima and friends have come in discovering a simple and primitive mathematical structure from which shared Experience emerges...


https://www.quantamagazine.org/physicist...-20240925/

" In the fall of 2022, a Princeton University graduate student named Carolina Figueiredo  stumbled onto a massive coincidence. She calculated that collisions involving three different types of subatomic particles would all produce the same wreckage. It was like laying a grid over maps of London, Tokyo and New York and seeing that all three cities had train stations at the same coordinates.

“They are very different [particle] theories. There’s no reason for them to be connected,” Figueiredo said.

The coincidence soon revealed itself to be a conspiracy: The theories describing the three types of particles were, when viewed from the right perspective, essentially one. The conspiracy, Figueiredo and her colleagues realized, stems from the existence of a hidden structure, one that could potentially simplify the complex business of understanding what’s going on at the base level of reality.

For nearly two decades, Figueiredo’s doctoral advisor, Nima Arkani-Hamed, has been leading a hunt for a new way of doing physics. Many physicists believe they’ve reached the end of the road when it comes to conceptualizing reality in terms of quantum events that play out in space and time. Such language can’t easily describe the beginning of the universe, for instance, when the space-time fabric likely didn’t exist in its current form. Arkani-Hamed therefore suspects that the usual notion of quantum particles moving and interacting in space-time is an approximation of deeper, more abstract concepts, which, if found, could serve as a better language for talking about quantum gravity and the origin of the universe.

A major development came in 2013, when Arkani-Hamed and his student at the time, Jaroslav Trnka, discovered a jewel-like geometric object that forecasts the outcome of certain particle interactions. They called the object the “amplituhedron.” However, the object didn’t apply to the particles of the real world. So Arkani-Hamed and his colleagues sought more such objects that would.

Now Figueiredo’s conspiracy is another manifestation of abstract geometric structure that seems to underlie particle physics... "

Your posts about Arkani-Hamed's work tend to be overlooked on this forum, so I’ll generously step in and share my thoughts.

While coming up with entirely novel ideas is precisely what science should strive for, there's also an enormous risk that the grand mathematical structure he's constructing will ultimately lead nowhere. A prime example is supersymmetry, which beautifully explains certain physical phenomena, as well as provided a candidate for darkmatter, with one minor inconvenience - there's zero experimental evidence. Those mathematically elegant super-partner particles stubbornly refuse to show up in reality.

Similarly, at present, there are numerous issues with Arkani-Hamed's current work, beyond the obvious lack of experimental validation. Two straightforward points highlighted in the article are so basic even a layperson can easily grasp them:

1. The theory currently can’t even account for why electrons have spin ±½h - a simple experimental fact that undergraduate physics students learn.

2. It lacks a non-perturbative description of gravity, making it incapable of explaining observed phenomena like gravitational waves.

Of course, there are additional, deeper obstacles, understandable perhaps only to the top-100 theoretical physicists globally.

Admittedly, after numerous theoretical breakthroughs, it's possible this framework could eventually become viable. But there's an equal chance it'll end up as just another theoretical dead-end. There's no doubt Arkani-Hamed could have made a superb used-car salesman had he not chosen the theoretical high-energy physics route. He certainly markets his theories impressively well, but personally, I’d suggest taking it all with a large grain of salt.

[Laird]

generously

Why not "magnanimously, out of my overflowing abundance of unsurpassed beneficence"?

The main reasons I didn't "like" your post were the "used-car salesman" dig at the end, and my lack of expertise in physics to assess how on-point your critique is. Otherwise, I do appreciate your comment.

On the subject of lack of responses to @Max_B's posts on this subject: yes, I've noticed that too, and I've tended to avoid even engaging because it looked very technical, and mostly required poring through lengthy videos, which I was reluctant to spend my time on. This was a much more accessible presentation of the work, and I finally have a bit of a handle on why Max is so excited about it. I do appreciate the share, Max. 👍

The main reasons I didn't "like" your post were the "used-car salesman" dig at the end, and my lack of expertise in physics to assess how on-point your critique is. Otherwise, I do appreciate your comment.

I had hoped the forum could handle a bit of lightheartedness. As I mentioned, new and unconventional ideas are absolutely necessary to move fundamental science forward, especially given the current stagnation.
But I want to clarify that my comment wasn’t meant as just a joke. I’m genuinely uneasy about how speculative theories often get elevated to the status of fundamental facts in the public sphere. For example, concepts like the universe’s origin or the inflationary epoch are sometimes presented as if they’re unassailable truths, rather than hypotheses with open questions.
I think scientists have a responsibility to be careful about how they communicate the broader, especially metaphysical, implications of their work when speaking to the public, outside of scientific journals. That kind of caution helps maintain a healthy distinction between what we know, what we hope, and what we’re still trying to figure out.

Your posts about Arkani-Hamed's work tend to be overlooked on this forum, so I’ll generously step in and share my thoughts.

While coming up with entirely novel ideas is precisely what science should strive for, there's also an enormous risk that the grand mathematical structure he's constructing will ultimately lead nowhere. A prime example is supersymmetry, which beautifully explains certain physical phenomena, as well as provided a candidate for darkmatter, with one minor inconvenience - there's zero experimental evidence. Those mathematically elegant super-partner particles stubbornly refuse to show up in reality.

Similarly, at present, there are numerous issues with Arkani-Hamed's current work, beyond the obvious lack of experimental validation. Two straightforward points highlighted in the article are so basic even a layperson can easily grasp them:

1. The theory currently can’t even account for why electrons have spin ±½h - a simple experimental fact that undergraduate physics students learn.

2. It lacks a non-perturbative description of gravity, making it incapable of explaining observed phenomena like gravitational waves.

Of course, there are additional, deeper obstacles, understandable perhaps only to the top-100 theoretical physicists globally.

Admittedly, after numerous theoretical breakthroughs, it's possible this framework could eventually become viable. But there's an equal chance it'll end up as just another theoretical dead-end. There's no doubt Arkani-Hamed could have made a superb used-car salesman had he not chosen the theoretical high-energy physics route. He certainly markets his theories impressively well, but personally, I’d suggest taking it all with a large grain of salt.

Thanks for those observations. I think my impression is that high energy physics and cosmology both suffer from the fact that theoretical speculations have outpaced experimental results.

I also find it unsettling that many 'facts' are built on towers of assumptions that may be false. For example, we can't measure the distance of astronomical objects beyond a certain distance without using Hubble's Law, which is not in fact a law at all. Our universe might be smaller than we think, or I suppose much larger. That would change a lot of cosmological ideas

In short, multiple theories fit the available facts, and are indeed 'sold' rather like used cars

Sabine Hossenfelder's videos are worth viewing in connection with this, and she is splendidly cynical about her field.

It is also worth remembering that as the relationship between mind and matter becomes better understood, many of these ideas may seem quite outdated.

David