I foolishly sat in 8.821 [0] while at MIT thinking I could make sense out of quantum gravity. Most of the math went over my head, but the way I understand this paper, it’s basically a cosmic engineering fix for a geometry problem. Please correct me if necessary.
String theory usually prefers universes that want to crunch inwards (Anti-de Sitter space). Our universe, however, is accelerating outwards (Dark Energy).
To fix this, the authors are essentially creating a force balance. They have magnetic flux pushing the universe's extra dimensions outward (like inflating a tire), and they use the Casimir effect (quantum vacuum pressure) to pull them back inward.
When you balance those two opposing pressures, you get a stable system with a tiny bit of leftover energy. That "leftover" is the Dark Energy we observe.
You start with 11 dimensions (M-theory) and roll up 6 of them to get this 5D model. It sounds abstract, but for my engineer brain, it's helpful to think of that extra 5th dimension not as a "place" you can visit, but as a hidden control loop. The forces fighting it out inside that 5th dimension are what generate the energy potential we perceive as Dark Energy in our 4D world. The authors stop at 5D here, but getting that control loop stable is the hardest part
The big observatiom here is that this balance isn't static -- it suggests Dark Energy gets weaker over time ("quintessence"). If the recent DESI data holds up, this specific string theory solution might actually fit the observational curve better than the standard model.
I don't know who wrote the title for this submission, but adding a question mark that is not in the linked article seems like a terrible editorial decision.
Here is the latest and in my opinion the best interview with Ed Witten [1]
Things he talks about go mostly over my head. What disappointed me a little bit is that he seems to be a materialist. But that is pretty common position among physicists anyway, so not that surprising.
If materialists disappoint you, then you should check out Deepak Chopra, for all your self affirming quantum woo needs and desires. He will make your dreams come true! Just buy lots of his books, and you both will be very happy.
Side note, there’s been a few recent publications showing that dark energy may not be needed to explain what we are seeing.
1. Inhomogeneity backreaction (Moffat 2025)
Large-scale cosmic inhomogeneities such as voids and dense regions can create an effective expansion history that mimics evolving dark energy when averaged using standard homogeneous assumptions.
https://arxiv.org/abs/2503.20912
2. Timescape cosmology (Wiltshire)
Because cosmic voids expand faster than dense regions and dominate volume at late times, observers may infer acceleration from redshift data even if the universe is not globally accelerating.
https://www.livescience.com/physics-mathematics/dark-energy/...
3. Local giant void hypothesis
If the Milky Way resides inside a large underdense region, locally measured redshifts and distances can bias expansion measurements and partially explain apparent acceleration and Hubble tension.
https://www.livescience.com/space/cosmology/echoes-from-the-...
4. Void universe models (LTB cosmologies)
Placing the observer near the center of a large cosmic void can reproduce supernova redshift–distance relations without dark energy, though such models struggle with other cosmological constraints.
https://arxiv.org/abs/0807.1443
5. Structure formation and virialisation effects
The growth of cosmic structure and entropy production alters averaged expansion rates, potentially generating an apparent dark-energy-like signal without introducing a new energy component.
https://www.aanda.org/articles/aa/full_html/2024/09/aa50818-...
6. Redshift drift as a discriminator
Measuring how cosmological redshifts change over time can distinguish true cosmic acceleration from redshift effects caused by voids or inhomogeneous expansion.
https://arxiv.org/abs/1010.0091
Hm, string theory can describe a lot of things, but it's not testable with current technology. I'm pretty sure that other mathematical constructs exist that could also describe a similar set of properties, but we just happened to stumble upon string theory first, and got enamored with some of the nice properties it had initially.
Only in universe with 5 dimensions. Shouldn't string theory be given up on at this point? This theory has existed for over 50 years and hasn't produced any results. Even the predictions made by it such as e.g. supersymmetry have not been confirmed despite searching for them at particle colliders.
If you want to bash badly-spent potential look at people doing cutting edge ad research and optimization, or HFT. This is at least good base research that others can build on.
Fair point, but waste in one domain should not be used to excuse waste elsewhere. Unless your argument is that it's generally hard for human societies to know where to best invest their scientific talent without the benefit of hindsight.
Think of it as a playground for the exercise and training of a pool of minds that will one day either make the glove fit or kick the sand castle over replacing it with a better mousetrap.
Too many metaphors? Hmmm, maybe fold in some dimensional reduction somehow.
I agree plus ST takes a person who would have researched somewhere else. The Googler or Jane Street or guy who decides to travel the world in the canoe have different reasons and probably would need way more persuading to be in academia.
Shouldn't string theory be given up on at this point?
Has anti string theory propaganda taken over HN? Sabine Hossenfelder succeeded?
Anyone who is anti string theory actually qualified to make statements saying string theory is wrong or not worth more investment from researchers?
Are these anti string theory posts on HN mostly just laymen hearing how string theory can’t be tested and we wasted a lot of resources on it so it needs to be repeated on every string theory post here?
String theory usually prefers universes that want to crunch inwards (Anti-de Sitter space). Our universe, however, is accelerating outwards (Dark Energy).
To fix this, the authors are essentially creating a force balance. They have magnetic flux pushing the universe's extra dimensions outward (like inflating a tire), and they use the Casimir effect (quantum vacuum pressure) to pull them back inward.
When you balance those two opposing pressures, you get a stable system with a tiny bit of leftover energy. That "leftover" is the Dark Energy we observe.
You start with 11 dimensions (M-theory) and roll up 6 of them to get this 5D model. It sounds abstract, but for my engineer brain, it's helpful to think of that extra 5th dimension not as a "place" you can visit, but as a hidden control loop. The forces fighting it out inside that 5th dimension are what generate the energy potential we perceive as Dark Energy in our 4D world. The authors stop at 5D here, but getting that control loop stable is the hardest part
The big observatiom here is that this balance isn't static -- it suggests Dark Energy gets weaker over time ("quintessence"). If the recent DESI data holds up, this specific string theory solution might actually fit the observational curve better than the standard model.
[0] https://ocw.mit.edu/courses/8-821-string-theory-and-holograp...
Things he talks about go mostly over my head. What disappointed me a little bit is that he seems to be a materialist. But that is pretty common position among physicists anyway, so not that surprising.
[1] - https://www.youtube.com/watch?v=sAbP0magTVY
1. Inhomogeneity backreaction (Moffat 2025) Large-scale cosmic inhomogeneities such as voids and dense regions can create an effective expansion history that mimics evolving dark energy when averaged using standard homogeneous assumptions. https://arxiv.org/abs/2503.20912
2. Timescape cosmology (Wiltshire) Because cosmic voids expand faster than dense regions and dominate volume at late times, observers may infer acceleration from redshift data even if the universe is not globally accelerating. https://www.livescience.com/physics-mathematics/dark-energy/...
3. Local giant void hypothesis If the Milky Way resides inside a large underdense region, locally measured redshifts and distances can bias expansion measurements and partially explain apparent acceleration and Hubble tension. https://www.livescience.com/space/cosmology/echoes-from-the-...
4. Void universe models (LTB cosmologies) Placing the observer near the center of a large cosmic void can reproduce supernova redshift–distance relations without dark energy, though such models struggle with other cosmological constraints. https://arxiv.org/abs/0807.1443
5. Structure formation and virialisation effects The growth of cosmic structure and entropy production alters averaged expansion rates, potentially generating an apparent dark-energy-like signal without introducing a new energy component. https://www.aanda.org/articles/aa/full_html/2024/09/aa50818-...
6. Redshift drift as a discriminator Measuring how cosmological redshifts change over time can distinguish true cosmic acceleration from redshift effects caused by voids or inhomogeneous expansion. https://arxiv.org/abs/1010.0091
I personally have no practical application, so it does me no good to learn this stuff that will be obsolete sooner or later.
Too many metaphors? Hmmm, maybe fold in some dimensional reduction somehow.
shouldn't* decide
Anyone who is anti string theory actually qualified to make statements saying string theory is wrong or not worth more investment from researchers?
Are these anti string theory posts on HN mostly just laymen hearing how string theory can’t be tested and we wasted a lot of resources on it so it needs to be repeated on every string theory post here?