9 ms·

Neutron Stars Hint at Another Dimension

192 points by dnetesn 2y ago

p_ing 2y ago
If anyone wants a super approachable lecture on Neutron stars, this was released just a couple of weeks ago - https://youtu.be/I12SQ7YOebY https://youtu.be/I12SQ7YOebY
- superjan 2y ago
  That was a great watch, thanks!
echelon 2y ago
To what degree are these Nautilus stories based off of the work of a single researcher or lab that does not have broader consensus amongst the research community? What's a good way for a layperson to tell if this is a new scientific consensus arrived at after hundreds of researchers come to the same conclusion or a breakthrough result that has shocked the entire research community?
- flufluflufluffy 2y ago
  > “In 1999, theoretical physicists Lisa Randall and Raman Sundrum proposed a wild restructuring of the cosmos” > “The brane-bulk model is a speculative idea for sure, but a fun one.” I feel like it’s communicated pretty clearly that it isn’t some breakthrough finding that everybody agrees on. You could google the mentioned researchers/theories and find out more information if you still weren’t sure.
  - patcon 2y ago
    Agreed. Yes, a bit roundabout, but it's pretty wild that we live in a spot in the universe where the distance we need to travel to "confirm plausibility" of a "deep truth of the universe we just heard about" is just to type a few glyphs into a magic box and decide if the person speaking the purported truth has a reputation in the relevant human thought-stuffs. The world we live in is crazy. To know such a thing so easily at an earlier time, would be unfathomable :)
- superjan 2y ago
  This is not consensus. There are lots of anomalies in what we observe in the cosmos. Here someone links two of those to a speculation about extra dimensions. It would get interesting if they have predictions that can be checked. A promising new theory should fit known observations, explain previously unexplained phenomenon, and predict something testable. That will be difficult to judge as a layperson.
- 20k 2y ago
  Virtually all reasonable alternatives to GR have been strongly ruled out, including theories with large extra dimensions in them. In general, these theories have a some kind of parameter which measures their deviation from GR, which is being squashed to zero. There's also just generally no reason to think there are extra dimensions at all This article brings up neutron stars being slightly larger than expected, but the reality is there's no real expected maximum mass for a neutron star - because the equation of state and physics for neutron star interiors is unknown. The spin, and magnetic field of a neutron star can also serve to increase the maximum mass of a neutron star, which are very hard to model as there are no analytic solutions to a spinning body (nor an oblate body) There are too many approximations in the paper to even come close to saying that the brane model explains this better than standard physics, and there's no reason to think that this event isn't explainable by standard physics
the__alchemist 2y ago
> Gravity, the thinking goes, can escape our brane and extend into the bulk. That explains why it’s so weak. All the other forces must play in only three spatial dimensions, while gravity can extend itself out to four, spreading itself much too thin in the process. Wouldn't this cause gravitational force to fall off with distance using something other than an inverse-square law? I think this explanation would be a better fit for the weak force than gravity for this reason. Thoughts? More broadly: inverse-square behavior (Gravity, EM etc) strikes me as an intrinsic property of 3D geometry; more so of a tell of dimensionality than the magnitude of the force. (I believe the article is inferring higher dimensionality from relative magnitude, vice distance falloff)
- ktrask 2y ago
  Yes, exactly. That is why we think the extra dimensions might be small, und the inverse square law is only violated at and below the size of the extra dimensions. This is also why we are using the Yukawa Potential to constrain that possibility, because it has a length scale and a strength of a potential deviation from the inverse square law. See also: https://en.wikipedia.org/wiki/Fifth_force https://en.wikipedia.org/wiki/Fifth_force
  - mnky9800n 2y ago
    Why does the extra dimension need to be small?
    - addaon 2y ago
      Because gravity will be observed to decay with distance cubed for distances on the scale of the extra dimension, and distance squared beyond that; and we have not found a scale where we see gravity decay faster than distance squared (but it gets harder and harder to measure at small scale, so the error bars grow).
    - ben_w 2y ago
      If it was big, you could see it. IIRC experimental gravity data rules out any compactified dimension bigger than 50μm, but a question I keep coming back to is "surely the pictures of atomic bonds taken by electron microscopes rules compactified dimensions larger than 1Å?"
whatever1 2y ago
Far from expert in the field, but assuming that gravity is acts in a 3+ND and we observe it in our 3D world, shouldn't we observe weird peculiarities with it rather that just its amplitude? Think that you live on a line, and you see projections of a 2d object doing circles on top of you. You would see the shade moving and changing sizes in a non-explainable manner to you.
- mystified5016 2y ago
  We do observe really weird gravitational effects. Dark matter, for instance. Under Newtonian and Einsteinian physics, galaxies shouldn't be able to form in the way we observe. The way galaxies and their contents move makes no sense with our present understanding of gravity-- unless we assume there's a lot more mass. So we invented dark matter as a sort of placeholder variable to make the math make sense. More anomalies: simply being near a large gravitational field alters the flow of time. Frame dragging around black holes (spacetime itself twists into a rotating spiral). The final parsec problem (co-orbiting black holes bleeding energy as gravitational waves). And don't forget the gravitational singularity of a black hole. But perhaps the most important thing to know is that we've only just gained the ability to examine gravitational waves. Once we build more detectors (especially LISA), we'll probably discover a lot more is wrong with our understanding of gravity.
  - nathan_compton 2y ago
    > More anomalies: simply being near a large gravitational field alters the flow of time. Frame dragging around black holes (spacetime itself twists into a rotating spiral). The final parsec problem (co-orbiting black holes bleeding energy as gravitational waves). And don't forget the gravitational singularity of a black hole. These are not really anomalies per se - they are predicted by the relatively well tested theory of GR and (except for the singularity part) also experimentally observable. They are weird from our point of view, but not weird to contemporary physics.
    - mrkstu 2y ago
      From recent discussion though it seems as though the time dilation effects or that time itself moves differently in different patches of spacetime- that could remove the need altogether for dark energy/dark matter: https://www.theguardian.com/science/2024/mar/09/controversial-new-theory-of-gravity-rules-out-need-for-dark-matter https://www.theguardian.com/science/2024/mar/09/controversia...
MrMcCall 2y ago
[flagged]
- idiotsecant 2y ago
  [flagged]
- mnky9800n 2y ago
  The problem is most of what you say is unmeasurable. So it’s not really something physics can comment on and those immeasurable quantities cannot really be commented on by physics. So maybe your thoughts are enjoyable to you or others but they don’t really have anything to do with how dynamics in the universe play out, which is all that physics has to say about things.
  - MrMcCall 2y ago
    It took many years before Einstein's ToR was confirmed by pictures of light bending around our sun during an eclipse. Paul Dirac predicted antiparticles purely by mathematical intuition. It wasn't until later that the theory proved true, and he was recognized to be the genius that he was. First comes the theory, then experiments are devised. Then physics gets updated. I merely suggest these things, not because I have the math to understand how it would affect GR or QED, or even what experiments would be needed to verify them, but merely to plant the seeds of how things work to stimulate those who can do those things to think about what their ramifications might be. That no one understands how these things can even be known, much less that they are true, is already known by me, but the truth is never beholden to the naysayers. I'm not a Boltzmann who was (sadly) bullied into suicide by the fools of his era. I don't really care if anyone believes what I say. I say these things because I love you all and maybe a few people will be stimulated to contemplate other avenues that may explain the as yet inexplicable. And, really, y'all are out of ideas as to what or where dark matter or energy are anyway, so there is nothing for anyone to lose. Put another way, Einstein knew what would happen to light that passed close to the sun (even though his calculations were off), but the naysayers were irrelevant, right? They, too, thought they already knew it all.
deleted 2y ago
[deleted]
Ygg2 2y ago
> The force of gravity is weak. And not just a little bit weak. It’s so much weaker than the other three fundamental forces—electromagnetism and the strong and weak nuclear forces—that it’s almost impossible to provide analogies. Nothing in nature prevents gravity from just being super weak. Some forces could just be super weak. The unspoken premise of gravity being weaker than other forces is that all forces were unified at some point. So iff you assume all forces in nature were once one force, then gravity being weak is an anomaly.
- eggn00dles 2y ago
  if you use planck units instead of anthropocentric ones gravity isnt weak. its the mass of the proton that is much less than its charge. but why should those two values be equivalent to begin with?
  - Ygg2 2y ago
    Strength is relative. It will always be a rounding error in particle interactions.
deadbabe 2y ago
If you could orient something along a higher dimension in the correct way could we conceivably create some kind of anti gravity or artificial gravity?
pk-protect-ai 2y ago
God, so many words to cover only one phrase with a "possible hint" at an extra mass coming from imaginary source ...
codingdave 2y ago
I'm ignorant when it comes to physics, admittedly, so please forgive me if my question has an obvious answer... But when I read articles like this, in particular when they mention branes, I want to ask: How do we know that dark matter is not just some interaction coming from the "bulk"?
- stormbeard 2y ago
  We don't know! But we also can't feasibly test for something like that.
EvgeniyZh 2y ago
No they don't
amai 2y ago
Extra dimensions are always a desperate measure. If you add them to your theory you open up a huge parameter space, because you have no clue about the number, size and topology of the extra dimensions. What is missing is a real physical symmetry or reason that would enforce the existence of extra dimensions and on the other side restricts its geometry and topology. Just adding more parameters to your theory will allow you to overfit the data better, but that does not mean you understand more about nature.
johnea 2y ago
Where are the flaggers? Come on, you're slacking off. Neutron Stars? Other Dimensions? This has GOT to be woke, right? The level of flagging on HN lately is totally out of control. And they complained that the woke were cancelling people...

192 points by dnetesn 2y ago

If anyone wants a super approachable lecture on Neutron stars, this was released just a couple of weeks ago - https://youtu.be/I12SQ7YOebY https://youtu.be/I12SQ7YOebY

superjan 2y ago
That was a great watch, thanks!

echelon 2y ago

To what degree are these Nautilus stories based off of the work of a single researcher or lab that does not have broader consensus amongst the research community? What's a good way for a layperson to tell if this is a new scientific consensus arrived at after hundreds of researchers come to the same conclusion or a breakthrough result that has shocked the entire research community?

flufluflufluffy 2y ago
> “In 1999, theoretical physicists Lisa Randall and Raman Sundrum proposed a wild restructuring of the cosmos” > “The brane-bulk model is a speculative idea for sure, but a fun one.” I feel like it’s communicated pretty clearly that it isn’t some breakthrough finding that everybody agrees on. You could google the mentioned researchers/theories and find out more information if you still weren’t sure.
- patcon 2y ago
  Agreed. Yes, a bit roundabout, but it's pretty wild that we live in a spot in the universe where the distance we need to travel to "confirm plausibility" of a "deep truth of the universe we just heard about" is just to type a few glyphs into a magic box and decide if the person speaking the purported truth has a reputation in the relevant human thought-stuffs. The world we live in is crazy. To know such a thing so easily at an earlier time, would be unfathomable :)
superjan 2y ago
This is not consensus. There are lots of anomalies in what we observe in the cosmos. Here someone links two of those to a speculation about extra dimensions. It would get interesting if they have predictions that can be checked. A promising new theory should fit known observations, explain previously unexplained phenomenon, and predict something testable. That will be difficult to judge as a layperson.
20k 2y ago
Virtually all reasonable alternatives to GR have been strongly ruled out, including theories with large extra dimensions in them. In general, these theories have a some kind of parameter which measures their deviation from GR, which is being squashed to zero. There's also just generally no reason to think there are extra dimensions at all This article brings up neutron stars being slightly larger than expected, but the reality is there's no real expected maximum mass for a neutron star - because the equation of state and physics for neutron star interiors is unknown. The spin, and magnetic field of a neutron star can also serve to increase the maximum mass of a neutron star, which are very hard to model as there are no analytic solutions to a spinning body (nor an oblate body) There are too many approximations in the paper to even come close to saying that the brane model explains this better than standard physics, and there's no reason to think that this event isn't explainable by standard physics

the__alchemist 2y ago

> Gravity, the thinking goes, can escape our brane and extend into the bulk. That explains why it’s so weak. All the other forces must play in only three spatial dimensions, while gravity can extend itself out to four, spreading itself much too thin in the process. Wouldn't this cause gravitational force to fall off with distance using something other than an inverse-square law? I think this explanation would be a better fit for the weak force than gravity for this reason. Thoughts? More broadly: inverse-square behavior (Gravity, EM etc) strikes me as an intrinsic property of 3D geometry; more so of a tell of dimensionality than the magnitude of the force. (I believe the article is inferring higher dimensionality from relative magnitude, vice distance falloff)

ktrask 2y ago
Yes, exactly. That is why we think the extra dimensions might be small, und the inverse square law is only violated at and below the size of the extra dimensions. This is also why we are using the Yukawa Potential to constrain that possibility, because it has a length scale and a strength of a potential deviation from the inverse square law. See also: https://en.wikipedia.org/wiki/Fifth_force https://en.wikipedia.org/wiki/Fifth_force
- mnky9800n 2y ago
  Why does the extra dimension need to be small?
  - addaon 2y ago
    Because gravity will be observed to decay with distance cubed for distances on the scale of the extra dimension, and distance squared beyond that; and we have not found a scale where we see gravity decay faster than distance squared (but it gets harder and harder to measure at small scale, so the error bars grow).
  - ben_w 2y ago
    If it was big, you could see it. IIRC experimental gravity data rules out any compactified dimension bigger than 50μm, but a question I keep coming back to is "surely the pictures of atomic bonds taken by electron microscopes rules compactified dimensions larger than 1Å?"

whatever1 2y ago

Far from expert in the field, but assuming that gravity is acts in a 3+ND and we observe it in our 3D world, shouldn't we observe weird peculiarities with it rather that just its amplitude? Think that you live on a line, and you see projections of a 2d object doing circles on top of you. You would see the shade moving and changing sizes in a non-explainable manner to you.

mystified5016 2y ago
We do observe really weird gravitational effects. Dark matter, for instance. Under Newtonian and Einsteinian physics, galaxies shouldn't be able to form in the way we observe. The way galaxies and their contents move makes no sense with our present understanding of gravity-- unless we assume there's a lot more mass. So we invented dark matter as a sort of placeholder variable to make the math make sense. More anomalies: simply being near a large gravitational field alters the flow of time. Frame dragging around black holes (spacetime itself twists into a rotating spiral). The final parsec problem (co-orbiting black holes bleeding energy as gravitational waves). And don't forget the gravitational singularity of a black hole. But perhaps the most important thing to know is that we've only just gained the ability to examine gravitational waves. Once we build more detectors (especially LISA), we'll probably discover a lot more is wrong with our understanding of gravity.
- nathan_compton 2y ago
  > More anomalies: simply being near a large gravitational field alters the flow of time. Frame dragging around black holes (spacetime itself twists into a rotating spiral). The final parsec problem (co-orbiting black holes bleeding energy as gravitational waves). And don't forget the gravitational singularity of a black hole. These are not really anomalies per se - they are predicted by the relatively well tested theory of GR and (except for the singularity part) also experimentally observable. They are weird from our point of view, but not weird to contemporary physics.
  - mrkstu 2y ago
    From recent discussion though it seems as though the time dilation effects or that time itself moves differently in different patches of spacetime- that could remove the need altogether for dark energy/dark matter: https://www.theguardian.com/science/2024/mar/09/controversial-new-theory-of-gravity-rules-out-need-for-dark-matter https://www.theguardian.com/science/2024/mar/09/controversia...

MrMcCall 2y ago

[flagged]

idiotsecant 2y ago
[flagged]
mnky9800n 2y ago
The problem is most of what you say is unmeasurable. So it’s not really something physics can comment on and those immeasurable quantities cannot really be commented on by physics. So maybe your thoughts are enjoyable to you or others but they don’t really have anything to do with how dynamics in the universe play out, which is all that physics has to say about things.
- MrMcCall 2y ago
  It took many years before Einstein's ToR was confirmed by pictures of light bending around our sun during an eclipse. Paul Dirac predicted antiparticles purely by mathematical intuition. It wasn't until later that the theory proved true, and he was recognized to be the genius that he was. First comes the theory, then experiments are devised. Then physics gets updated. I merely suggest these things, not because I have the math to understand how it would affect GR or QED, or even what experiments would be needed to verify them, but merely to plant the seeds of how things work to stimulate those who can do those things to think about what their ramifications might be. That no one understands how these things can even be known, much less that they are true, is already known by me, but the truth is never beholden to the naysayers. I'm not a Boltzmann who was (sadly) bullied into suicide by the fools of his era. I don't really care if anyone believes what I say. I say these things because I love you all and maybe a few people will be stimulated to contemplate other avenues that may explain the as yet inexplicable. And, really, y'all are out of ideas as to what or where dark matter or energy are anyway, so there is nothing for anyone to lose. Put another way, Einstein knew what would happen to light that passed close to the sun (even though his calculations were off), but the naysayers were irrelevant, right? They, too, thought they already knew it all.

deleted 2y ago

[deleted]

Ygg2 2y ago

> The force of gravity is weak. And not just a little bit weak. It’s so much weaker than the other three fundamental forces—electromagnetism and the strong and weak nuclear forces—that it’s almost impossible to provide analogies. Nothing in nature prevents gravity from just being super weak. Some forces could just be super weak. The unspoken premise of gravity being weaker than other forces is that all forces were unified at some point. So iff you assume all forces in nature were once one force, then gravity being weak is an anomaly.

eggn00dles 2y ago
if you use planck units instead of anthropocentric ones gravity isnt weak. its the mass of the proton that is much less than its charge. but why should those two values be equivalent to begin with?
- Ygg2 2y ago
  Strength is relative. It will always be a rounding error in particle interactions.

deadbabe 2y ago

If you could orient something along a higher dimension in the correct way could we conceivably create some kind of anti gravity or artificial gravity?

pk-protect-ai 2y ago

God, so many words to cover only one phrase with a "possible hint" at an extra mass coming from imaginary source ...

codingdave 2y ago

I'm ignorant when it comes to physics, admittedly, so please forgive me if my question has an obvious answer... But when I read articles like this, in particular when they mention branes, I want to ask: How do we know that dark matter is not just some interaction coming from the "bulk"?

stormbeard 2y ago
We don't know! But we also can't feasibly test for something like that.

EvgeniyZh 2y ago

No they don't

amai 2y ago

Extra dimensions are always a desperate measure. If you add them to your theory you open up a huge parameter space, because you have no clue about the number, size and topology of the extra dimensions. What is missing is a real physical symmetry or reason that would enforce the existence of extra dimensions and on the other side restricts its geometry and topology. Just adding more parameters to your theory will allow you to overfit the data better, but that does not mean you understand more about nature.

johnea 2y ago

Where are the flaggers? Come on, you're slacking off. Neutron Stars? Other Dimensions? This has GOT to be woke, right? The level of flagging on HN lately is totally out of control. And they complained that the woke were cancelling people...