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...
This is a bit of a technicality, but we don't live in a 4D world, we live in a 3+1D world - the 3 spacial dimensions are interchangeable, but the 1 time-related dimension is not interchangeable with the other three (the metric is not commutative).
I'm bringing this up because a lot of people seem to think that time and space are completely unified in modern physics, and this is very much not the case.
Equally, cause always precedes effect. If time were exactly like space, you could bypass a cause to get to an effect, which would break the fundamental laws of physics as we know them.
There's obviously a lot more, but that's a couple of examples to hopefully help someone.
Even worse, the weak force breaks another symmetry as well, parity symmetry (which basically means that moving backward in time, weak force particles "look" like their mirror image, instead of looking the same).
Why is a major question, but any understanding of our universe must assume this fact.
It seems like it would be hard to distinguish from the point of view of a 4D unit vector XYZT if T was massively larger. Is it distinguished because it's special or is it just distinguished just because the ratio to the other values is large.
Imagine if at the big bang there was stuff that went off in Z and XY and T were tiny in comparison? What would that look like? Part of me says relativity would say there's no difference, but I only have a slightly clever layman's grasp of relativity.
However, this is NOT the case in Special Relativity (or in QM or QFT). Instead, the distance between two points ("events") is (cT1-cT2)^2 - (X1-X2)^2 - (Y1-Y2)^2 - (Z1-Z2)^2. Note that this means that the distance between two different events can be positive, negative, or 0. These are typically called "time-like separated" (for example, two events with the same X,Y,Z coordinates but different T coordinates, such as events happening in the same place on different days); "space-like separated" (for example, two events with the same T coordinate but different X,Y,Z coordinates, such as events happening at the same time in two different places on Earth); or light-like separated (for example, if (cT1-cT2) = (X1 - X2), and Y, Z are the same; these are events that could be connected by a light beam). Here c is the maximum speed limit, what we typically call the speed of light.
This difference in metric has many mathematical consequences in how different points can interact, compared to a regular 4D space. But even beyond those, it makes it very clear that walking to the left or right is not the same as walking forwards or backwards in time.
Edit to add a small note: what I called "the distance" is not exactly that - it's a measure of the vector that connects the two points (specifically, it is the result of its scalar product with itself, v . v). Distance would be the square root of that, with special handling for the negative cases in 3+1D space, but I didn't want to go into these complications.
e.g. Dichronauts examines the 2+2D case which turns out to be very different from 4D or 3+1D.
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
It's not useless, though. String theory can be a fad (or "difficult to prove", per Witten) but some of the mathematics used in its research or "trying to prove it" have been used in other fields.
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.
https://www.youtube.com/watch?v=aO2dPIdEaR4
"But as Deepak Chopra taught us, quantum physics means anything can happen at any time for no reason. Also, eat plenty of oatmeal, and animals never had a war! Who's the real animals?" -Professor Hubert Farnsworth
You can only disprove.
The only way to prove a positive if there is a finite number of possibilities and you have disproven all but one. But even then, someone could conceivably come up with an alternate description that preserves the current understanding but makes additional predictions or is a simpler model making the same.
As Feyman said: "We can never know if we are right, we can only be certain if we are wrong".
For example:
Every continuous symmetry of action in a physical system with conservative forces has a corresponding conservation law. (Noether's Theorem)
There must be two antipodal points on Earth with exactly the same temperature and barometric pressure (as a result of the Borsuk-Ulam Theorem)
As far as I know these are absolutely proved positively because they are mathematical consequences of the properties of continuous functions etc. I'm not a scientist, but there are thousands of things like this where we are definitely absolutely certain we are right because of the possibility of a mathematical direct proof.
But otherwise, there is nothing special about positive or negative statements. You can express any positive statement as the negation of a negative statement, so to the extent that science can "disprove negatives", it can equivalently "prove positives".
> Still, the work is expected to launch a new era in matching the mathematical > elegance of string theory to the actual world we live in."
yeah, sounds real promising. string theory all over. nice maths but who cares if it doesnt map to reality, its nice maths!
Remember resources are limited. We cannot fund everyone who wants it. Society needs to make choices, we are generally okay with a bit of "interesting but unlikely to produce anything important", but most of what we fund needs a return on investment.
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 string theory be given up on at this point?
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?
https://www.youtube.com/watch?v=2p_Hlm6aCok&t=10m15s
This also references this podcast discussion between Leonard Susskind and Lawrence Krauss, where they discuss the same thing:
https://www.youtube.com/watch?v=qhszd_wqAgQ
Note that he still thinks that there is a way to produce some kind of similar theory, "a string theory" as opposed to "String Theory", could be the best answer.
According to this Reddit thread, he doesn't say it's "dead in the water" at all. It's just a version of string theory.
This is what I'm afraid of. People who aren't qualified spreading fake news on string theory.
I don't claim to be qualified. I just want to call out HN people who are extremely confident that string theory is dead but has no background in physics.
Now, if by "string theory is dead in the water" someone means that "working on a generalization of string theory is a bad idea", then they are wrong, Leonard Susskind doesn't believe that.
But if by "string theory is dead in the water" they mean "there is no point in studying String Theory deeper, with its general mathematical properties, maybe with a slight tweaks, as it is right now it can't describe the real world", then this is quite clearly professor Susskind's position.