> 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)
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
Fun fact: Newton attributed the inverse square law to Pythagoras. It’s esoteric, but it relates to harmony of the spheres and the fact that the weight/tension of a string has an inverse square relation to tone. More here, in this Royal Society article: https://www.researchgate.net/publication/250902005_Newton_an...
I wonder if a higher dimension could also be the explanation for extra mass in the universe instead of dark matter. It's outside our perceptible space, but it still exists as mass, poking through into black holes or gently resting on the skin of our 3d volume.
The weird thing about it though is that whatever the dark matter is it has to be spread out. It couldn’t be little planets or brown dwarfs or burned out stars (in a hidden dimension or not) because we’d see more gravitational lensing events than we do
I thought dark matter was only observed through movements of matter within galaxies. Outer layers of spiral galaxies are observed to move faster than they should, so there has to be additional gravity and therefore mass that binds them on their (fast) orbits around the center.
Perhaps there is a negative gravity outside of galaxies where space seems to bubble out of nowhere anyway and the universe is expanding.
This seems as an attempt to combine gravity with the standard model again, which in my very amateurish understanding comes with multiple extra dimensions anyway. Isn't the higgs field basically a recently discovered additional dimension already? Among the other forms of particles that can be seen as an excitation of fields that compose these dimensions.
But for extreme cases like neutron stars or black holes, we probably do need to combine these theories since gravity is a main reason these objects exist in the first place. And also isn't a curvature of space not already be an additional dimension as well? It would be mathematically as I understand it.
> 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.
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?
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.
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.
> 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.
I thought the final parsec problem is that co orbiting black holes can't have accretion discs which makes GW the only way for them to inspiral, and that's way too slow for us to have seen any.
The more distance along your 4th dimension you allow, the more strange geometric effects you will observe. If you let a 4th dimension be very, very, very small (imagine a 2d universe that actually has a third dimension, it's just subatomic in scale) the geometric effects are negligible.A 3d volume can exist in that 2d + 1 tiny dimension, in the technical sense, but not in any macroscopic sense. Your 3rd dimension curls around to where it started nearly immediately.
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.
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?
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.
> “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.
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 :)
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
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"?
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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)
https://en.wikipedia.org/wiki/MACHO_Project
Perhaps there is a negative gravity outside of galaxies where space seems to bubble out of nowhere anyway and the universe is expanding.
This seems as an attempt to combine gravity with the standard model again, which in my very amateurish understanding comes with multiple extra dimensions anyway. Isn't the higgs field basically a recently discovered additional dimension already? Among the other forms of particles that can be seen as an excitation of fields that compose these dimensions.
But for extreme cases like neutron stars or black holes, we probably do need to combine these theories since gravity is a main reason these objects exist in the first place. And also isn't a curvature of space not already be an additional dimension as well? It would be mathematically as I understand it.
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.
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.
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.
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.
Explain for a layman? I don't know what it means for movement to not make sense.
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.
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?
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.
> “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.
The world we live in is crazy. To know such a thing so easily at an earlier time, would be unfathomable :)
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