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.
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.
To expand on this a little for those interested, time has properties space doesn't. For example, you can turn left to swap your forward direction for sideways in space. You cannot turn though, in a way that swaps your forward (as it were) direction in space for a backward direction in time.
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.
Can you expand on this? I’m guessing that it’s something to do with preservation of mass & energy? Like mass doesn’t have to be preserved over a spatial dimension (eg rotating an object) but does over time.
How is the difference between them characterised in physics?
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.
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.
Agree, its editorialising and not allowed under the guidelines here (unless it was in the original and that was changed), but given the uselessness of the field you could argue that any "String Theory" claim in any title should have an automatic question mark (or perhaps several) attached afterwards.
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.
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
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.
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.
String theory does not work with de-Sitter spaces, only with anti de-Sitter spaces. Science has proved we are living in a de-Sitter space. String theory cannot be true.
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".
This is just sleight of hand. It's true that science can never be certain about anything, not to the same level as mathematics.
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".
I don't think that's true regardless of whether you or Feynman or anyone else says it.
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.
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.
The issue isn't string theory yes or no (there are reasons physicists went this way and other alternatives aren't so much better), but the difficulty in getting data and testable predictions. It's very likely the most effective way to help particle physics is getting way more data at high energies, not a new theory.
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?
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.
[0] https://ocw.mit.edu/courses/8-821-string-theory-and-holograp...
> we perceive as Dark Energy in our 4D world
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.
To expand on this a little for those interested, time has properties space doesn't. For example, you can turn left to swap your forward direction for sideways in space. You cannot turn though, in a way that swaps your forward (as it were) direction in space for a backward direction in time.
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.
5 replies →
Can you expand on this? I’m guessing that it’s something to do with preservation of mass & energy? Like mass doesn’t have to be preserved over a spatial dimension (eg rotating an object) but does over time.
1 reply →
How is the difference between them characterised in physics?
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.
2 replies →
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.
Agree, its editorialising and not allowed under the guidelines here (unless it was in the original and that was changed), but given the uselessness of the field you could argue that any "String Theory" claim in any title should have an automatic question mark (or perhaps several) attached afterwards.
> given the uselessness of the field
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.
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
The prediction is just 105 orders of magnitude (and an extra dimension) away, but ok.
Only about 2 orders of orders of magnitude - not bad for string theory.
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.
[1] - https://www.youtube.com/watch?v=sAbP0magTVY
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.
I'm sad to discover that wisdomofchopra is no more.
3 replies →
You are clearly very philosophically inclined.
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.
Sounds like overfitting.
Yeah I am awaiting the Copernican Revolution of quantum mechanics before I care about this stuff.
I personally have no practical application, so it does me no good to learn this stuff that will be obsolete sooner or later.
Just few extra dimensions and you can handle anything.
String theory does not work with de-Sitter spaces, only with anti de-Sitter spaces. Science has proved we are living in a de-Sitter space. String theory cannot be true.
That is literally what this article is about.
> “What they have found is a 5D de Sitter solution, and we don’t live in 5D,” said > Antonio Padilla(opens a new tab) of the University of Nottingham.
> 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!
1 reply →
Science never proves a positive.
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".
This is just sleight of hand. It's true that science can never be certain about anything, not to the same level as mathematics.
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".
I don't think that's true regardless of whether you or Feynman or anyone else says it.
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.
3 replies →
but you can use that exact logic to say the inverse; that nothing can be disproved, because you can never be sure youve disproved every alternative
They had to keep the theory alive somehow.
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.
As I understand it, it's still our best candidate for a unified theory of everything. Not for lack of effort in researching alternatives, either.
The issue isn't string theory yes or no (there are reasons physicists went this way and other alternatives aren't so much better), but the difficulty in getting data and testable predictions. It's very likely the most effective way to help particle physics is getting way more data at high energies, not a new theory.
It has produced some good math though. That's something.
At what opportunity cost?
12 replies →
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?
Susskind himself said its dead in the water. We dont live in an anti de-Sitter space, the basis of string theory.
4 replies →
Yes. Like Python can describe any turing machine.
Related:
The string theory hype machine will never die
https://news.ycombinator.com/item?id=46621518