11 ms·

An old theory of quantized gravity is gaining new life

110 points by bcaulfield 9y ago

dang 9y ago
Url changed from https://www.wired.com/story/why-an-old-theory-of-everything-is-gaining-new-life/ https://www.wired.com/story/why-an-old-theory-of-everything-..., which points to this.
goldenkey 9y ago
I think it is relevant to consider gravity from a more abstract standpoint as well by looking at Le Sage's theory and particularly Hyugens' comments. [1] Whether gravity is mediated by a graviton, and the intricacies that QM brings to bear, one interesting idea I took from the above hundreds of years of thought on the subject -- gravity may be a pushing force mediated by constant spherical wave emission (quantized as the graviton if necessary) from all mass/energy. Since every bit of mass-energy is releasing gravitons, the whole of space is rather isometrically filled with gravitons. The reason two objects would then appear to attract via Newton's inverse-square law is one of a shadowing effect. The graviton would apply a pushing force normally to any mass-energy it interacts with, and therefore any blockage/shadowing of one object by another, would end up looking like attraction. Le Sage's theory is more exacting and supposes gravitons are of similar substance to regular matter. I don't agree with most of these notions but what I said above is what I gained. 1] https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitation https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitat...
- simpsond 9y ago
  That’s a really interesting way of thinking about it. Gravity resists space.
- Florin_Andrei 9y ago
  This is one of the many kinetic theories of gravity. It's very old. No scientist nowadays believes that kinetic theories could really work in this realm. This is mostly of historic interest only.
  - goldenkey 9y ago
    I'm aware of that-- but no one is sure about how the graviton operates. So though the kinetic part might not be very realistic or all that relevant anymore, the other parts still are.
    - Retra 9y ago
      The 'non-kinetic' parts are just geometry, which we already understand and incorporate into general relativity.
      - goldenkey 9y ago
        Just as there is a huge difference between Maxwell's laws and QED -- the same gap lies with relativity and the graviton. Knowing the gravitational field as full fidelity partial differential equations based on the stress energy tensors is a great achievement. But it alone does not tell the full story as to how that field is mediated. Just as EM is mediated via virtual photons, we wish to know more..
        PuffinBlue 9y ago
        Not that i understood much of what you just said, but you're the first person I've seen say gravity is a push force, so i have a question. Does it me any sense to say mass repels spacetime? So imagine a spring on the surface of a massive sphere. Imagine that you compress the spring and release it. The spring would compress outwards, the sphere not moving (especially if an another antipodean spring was set up with a compression release cycle occurring at the same time). What if spacetime was like that spring, constantly being 'pushed' away or repelled from mass as it tries to return to an uncompressed state . The local effects would seemingly be the same, objects would travel the same curved paths through spacetime around the sphere as they would if mass was attractivly warping spacetime. Or perhaps we xould set up the conditions so that was so. Maybe ive misunderstood, but in most depictions of gravity its a point like a bottom of a well that's sort of stretched the 'rubber sheet' of spacetime. I know it's just an analogy but almost all layman explanations show spacetime elongating as it moves closer to the mass, the elongation depicting the 'warping' of spacetime. It's possible the real maths tells a more accurate story, but to me the more correct mental picture would be to think of circles around the mass spaced at distances where crossing between them takes time=1. For the outside observer it seems time slows as you draw nearer the mass, that would suggest the circles become 'closer' or you'd cross more space per unit time. It would also suggest the outside observer would see you eventually slow to a stop but locally you continue to accelerate along the curved spacetime, so it doesn't seem to violate special relativity. I'm not sure if mathematically space and time are treated separately, but if they're the same then thinking of mass as repelling spacetime 'outwards' from the surface of the mass seems to still work but might explain on larger scales where some of the expansion of space comes from - i.e. mass repels spacetime but the curvature this creates causes other mass to follow paths through spacetime that appear to make the two masses attract each other. I get that im no doubt wrong but ive not seen anyone adress this possibility (probably because it wrong!) but id be interested to hear where it breaks down, as i dont see it!
- whatshisface 9y ago
  There's no particular need for a special explanation of how particle exchange could produce an attractive force: as unlikely as it seems in classicical physics, it's how the forces (electromagnetic) arise in QED. The exchange of virtual photons can transport momentum any way you like.
  - effie 9y ago
    'Exchange of virtual photons' is a metaphorical expression used to describe artifacts of perturbation theory, it is not necessarily a real process. There is no widely accepted model of what really happens on microscopic scales, we only have equations and those are often replaced by simpler perturbation scheme. So, explanations of attractive force are welcome, Le Sage - type models including.
    - whatshisface 9y ago
      >There is no widely accepted model of what really happens on microscopic scales, There's no experimental reason to come up with one - virtual photons work, which means anything else is at this point a matter of philosophy. That's not to cast off philosophy, of course.
      - effie 9y ago
        Virtual photons work in a very limited way (metaphorical language describing perturbation theory). Physics outside of applicability of perturbation QED (bound systems of charged particles, gravity) is not a matter of philosophy.
- Taniwha 9y ago
  Dumb question: how do you exchange gravitons with a black hole?
  - ars 9y ago
    A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity. It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change). It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.) But that means it can't interact in a way that is detectable, other than gravity. Because you can not give it energy, you can also never create it artificially. If you did, you would be creating gravitational force out of nothing, which is impossible because it violates conservation of energy, and you can not pay for that violation because you can not give it energy. It's pretty much the ultimate impossible to study particle.
    - Florin_Andrei 9y ago
      > A graviton would have to be both massless and energyless. However, gravitational waves do carry energy. Gravitons, whatever they are, must be some very tricky things.
    - auntienomen 9y ago
      This comment is almost completely wrong. It muddles together classical and quantum reasoning in any incoherent way. Gravitons are best understood as the quanta of the effective qft governed by the Einstein Hilbert action. This mathematical model is the universal low energy approximation to any quantum theory that reduces to general relativity. Gravitons need to be massless. They need not be zero energy. They can indeed be associated with frequency. They do couple to gravitational backgrounds and to other gravitons. You can crate them just like any other field quanta. The barrier to studying gravitons the way we do photons is that they couple very weakly to other systems.
      - ars 9y ago
ars 9y ago
> "In other words, gravity would be asymptotically safe if the theory at high energies remains equally well behaved as the theory at low energies. In and of itself, this is not much of an insight. The insight comes from realizing that this good behavior does not necessarily contradict what we already know about the theory at low energies (from the early works of DeWitt and Feynman)." But what are the actual expected changes at high energy that would differ from what is seen at low energy? I kept waiting for her to explain what differences would be observed if this theory is correct, but she never did.
- T-A 9y ago
  You would observe the theory not blowing up. :) The key feature she never names is known as a "UV fixed point". UV = UltraViolet, which in this context simply stands for "high energy". Fixed point... for that you need to know that the effective values of coupling "constants" aren't actually constant in quantum field theory; they depend on the interaction energy (i.e. how hard you bang your particles together). So they are called "running" coupling constants. Yes, it's contradictory. That dependence on interaction energy is described by differential equations (known as the renormalization group flow equations, which may sound impressive but is actually a misnomer), which you can integrate to see how a coupling measured in the lab at low energy will change when your descendants finally get enough funding for a larger accelerator. One interesting behavior is the coupling going to zero when you increase the energy towards infinity. That happens in QCD: counterintuitively, the harder you bang quarks together, the less they affect each other (via QCD, that is; they also have other kinds of interactions which behave differently). So QCD is called "asymptotically free": in the limit of infinite interaction energy, as far as QCD is concerned, quarks are free particles, completely unaffected by each other's presence. In asymptotic safety, as opposed to freedom, the coupling does not go to zero as you increase the energy; instead, the rate at which it changes goes to zero, and it does so at some finite value of interaction energy. So, as you crank up the interaction energy toward that value, the coupling constant "runs" slower and slower, and once you get there, it stops "running" altogether. From there on, you can raise the interaction energy all you want, and the coupling constant stays... constant. And that is a UV fixed point.
  - deleted 9y ago
pixl97 9y ago
I'm not a particle physicists by any means, but doesn't any theory of gravity have to deal with 'real' infinities at high energies from the physics we already know? We have some idea that black holes are a type of singularity (something that could possibly called an infinity). With E=MC2 we have an idea that if you apply enough energy to a particle it can become massive enough that it becomes a singularity itself.
- Florin_Andrei 9y ago
  A singularity popping out of the math is almost always an indication that something else is going on. According to general relativity, at the center of a black hole there might be some kind of "singularity" - but in reality what that means is GR is probably inadequate, when used alone, to describe the center of a BH. "Singularity" really means "your math broke and you need to fix it" by bringing in another theory that can fill in the gaps - or, rather, extending the current theory in a way that eliminates the division by zero.
- pmiller2 9y ago
  No, not really. A singularity in a quantized theory would simply be a place where gravity is strong enough that you can't move more than a Plank distance away from it.
- RuggeroAltair 9y ago
  The issue is not only about mass. Any mass could form a black hole, the main point is about mass density, and that's not trivial to obtain. That aside, real infinities is a vague concept. What's important is that any theory of gravity has to deal with the fact that the current understanding of classical gravity and quantum field theory make (when you combine them) a theory that has problems at the Planck scale. Those are problems that any theory of quantum gravity or every theory of everything have to deal with. But it doesn't mean that those potential theories would have any infinities. Such a theory, though, has been very elusive. With the exception of string theory, which is the leading theory in terms of its success, most theories tend to have fundamental problems. String theory research is certainly not complete, but it's in my opinion currently the best shot we have. Online, and in academia, you can find lots of very opinionated discussions about it, which include aspects of testability, predictivity, etc. which means that some people really dislike string theory and prefer other approaches.
jpeg_hero 9y ago
> The theory called asymptotically (as-em-TOT-ick-lee) safe gravity was proposed in 1978 by Steven Weinberg. Would a person interested in an article about quantum gravity not be familiar with the term asymptotically?
- laretluval 9y ago
  Moreover knowing the pronunciation doesn't give you any help if you don't know the meaning.
  - intrasight 9y ago
    That bothered me as well (pronouncing rather than defining)
    - sago 9y ago
      Particularly as the pronunciation is strange. Strange place to break syllables, and I'm not sure the second vowel is a 'e' in most pronunciations. /a-sim-TOT-i-klee/
      - gnulinux 9y ago
        This is how I pronounce it in IPA: /a.sim'to:.ti.kli:/ Why is TOT one syllable?
        jsmthrowaway 9y ago
        The weird thing about IPA is that the non-IPA pronunciation you’re replying to seems easier to understand.
        InternetOfStuff 9y ago
        Only to you. I feel exactly the opposite way. <Rant> I wish people would use the IPA instead of their absurd ad-hoc systems. I learned IPA at school, and it has served me well. All the pronunciation systems based on some other language are unreliable and idiosyncratic. And English, with its near-absence of reliable pronunciation/spelling rules, is particularly ill-suited. </Rant>
blackrock 9y ago
Gravity is measurement of the distortion of space, caused by mass. It is an emergent property. The more massive something is, the more its gravity will distort the space around it. So, a small piece of rock that you can hold in your hand, will cause a gravitational ripple in the space surrounding it. This is similar to how the Earth causes a gravitational ripple in the space around it, and it keeps us grounded to the ground. But, the Earth causes a much bigger gravitational ripple, than a small rock. And we as humans, are grounded to the Earth, as if we are at the bottom of this massive and invisible whirlpool. We cannot see it, but this whirlpool is rotating all around us, and we cannot get out. It is easy for us to move around horizontally, but it is very difficult for us to move vertically. Unless we can move horizontally so fast, that we can reach escape velocity, and then, we orbit the Earth. That said. What is gravity? Why does mass cause a ripple in the space around it? I wonder if gravity is just some type of neutral electro-magnetic force. Kind of like the magnetic field lines that you see with the North pole and South pole. But instead of being magnetically charged, it is neutrally charged, and it affects everything around it equally. Or, instead of being magnetically charged like the North or South pole, it is gravitationally-charged, and the direction points in only one way, into the center of your massive object. And unless you are moving faster than that massive object's escape velocity, then you will always be stuck in that object's gravitational ripple. If we can truly understand what is gravity, then I wonder if we can create a counter gravity. Like, in your spaceship, if you can create a negative mass above you, then it would cause your spaceship to act buoyant in the planet's atmosphere. And you can use thrusters to move around vertically, as easy as you can move around horizontally. Or, maybe you can create a temporary blackhole above your spaceship, and instead of your spaceship falling into the gravitational ripple caused by the Earth, then it becomes attracted to the gravitational ripple caused by your blackhole. And this causes your spaceship to rise, and defy the Earth's gravity. Anyways. I'm not a gravitational physicist. Maybe I should take this idea, and write a novel. There has been much worse Sci-Fi ideas created, like Time Travel, or the ridiculous many-worlds-interpretation theory of quantum mechanics.
- RuggeroAltair 9y ago
  From a physics perspective, the many-world, as ridiculous as it sounds, is a more sound theory (believed to be correct by some top physicists) than negative gravity. The explanation of why gravity is only positive is a complex one, but physicists believe it's almost axiomatic. This doesn't mean that you can't have repulsive type of effects, similar to one of the contributions that's believed to make the universe expand more quickly than with the simple 4 fources (often called fifth force, maybe related to dark energy, and to the rate of the universe expansion acceleration). PS. There are a number of Sci-Fi stories that use this idea, including a famous one from Asimov, in which if I recall correctly the normal gravitational force was working negatively when traveling in FTL speed. Obviously that seemed fishy but the book was cool (Nemesis).
perpetualcrayon 9y ago
Has anyone (sane) ever theorized that the ripples in spacetime in some cases may have existed before the masses of particles (ie. planets / stars) arrived at those locations?
auntienomen 9y ago
I'm not sure I see any real change in the status of asymptotic safety. It's a hypothesis. Proving it directly is next to impossible. (Except in spacetime dimension <= 3, when the theory is topological, making the assertion a triviality.) Testing it experimentally is unlikely; the constraints it implies are pretty weak. Nonetheless there are some people working on it, and while their ideas have some merit, they haven't yet caused the physics world to pay drastically more attention. Also, it's unwarranted hype to call asymptotic safety 'an old theory of everything'. It's explicitly not a theory of everything. It's only about gravity. Couple it to the Standard Model, and you still have a theory which breaks down at the hypercharge and Higgs Landau poles.
deleted 9y ago
[deleted]
esahione 9y ago
I think the author completely glosses over the fact that Loop Quantum Gravity actually does make predictions, and could provide the explanation for fast radio bursts. Also, the theory is so intuitive and follows such a straightforward logical path from Quantum Mechanics and Relativity, that I would be incredibly surprised if it wasn't the theory closest to actual reality.
- thicknavyrain 9y ago
  By any chance, we’re you ALSO in Carlo Rovelli’s lecture a few days ago? ;)
  - esahione 9y ago
    I've literally watched every lecture he has out there lol :)

110 points by bcaulfield 9y ago

dang 9y ago

Url changed from https://www.wired.com/story/why-an-old-theory-of-everything-is-gaining-new-life/ https://www.wired.com/story/why-an-old-theory-of-everything-..., which points to this.

goldenkey 9y ago

I think it is relevant to consider gravity from a more abstract standpoint as well by looking at Le Sage's theory and particularly Hyugens' comments. [1] Whether gravity is mediated by a graviton, and the intricacies that QM brings to bear, one interesting idea I took from the above hundreds of years of thought on the subject -- gravity may be a pushing force mediated by constant spherical wave emission (quantized as the graviton if necessary) from all mass/energy. Since every bit of mass-energy is releasing gravitons, the whole of space is rather isometrically filled with gravitons. The reason two objects would then appear to attract via Newton's inverse-square law is one of a shadowing effect. The graviton would apply a pushing force normally to any mass-energy it interacts with, and therefore any blockage/shadowing of one object by another, would end up looking like attraction. Le Sage's theory is more exacting and supposes gravitons are of similar substance to regular matter. I don't agree with most of these notions but what I said above is what I gained. 1] https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitation https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitat...

simpsond 9y ago
That’s a really interesting way of thinking about it. Gravity resists space.
Florin_Andrei 9y ago
This is one of the many kinetic theories of gravity. It's very old. No scientist nowadays believes that kinetic theories could really work in this realm. This is mostly of historic interest only.
- goldenkey 9y ago
  I'm aware of that-- but no one is sure about how the graviton operates. So though the kinetic part might not be very realistic or all that relevant anymore, the other parts still are.
  - Retra 9y ago
    The 'non-kinetic' parts are just geometry, which we already understand and incorporate into general relativity.
    - goldenkey 9y ago
      Just as there is a huge difference between Maxwell's laws and QED -- the same gap lies with relativity and the graviton. Knowing the gravitational field as full fidelity partial differential equations based on the stress energy tensors is a great achievement. But it alone does not tell the full story as to how that field is mediated. Just as EM is mediated via virtual photons, we wish to know more..
      - PuffinBlue 9y ago
        Not that i understood much of what you just said, but you're the first person I've seen say gravity is a push force, so i have a question. Does it me any sense to say mass repels spacetime? So imagine a spring on the surface of a massive sphere. Imagine that you compress the spring and release it. The spring would compress outwards, the sphere not moving (especially if an another antipodean spring was set up with a compression release cycle occurring at the same time). What if spacetime was like that spring, constantly being 'pushed' away or repelled from mass as it tries to return to an uncompressed state . The local effects would seemingly be the same, objects would travel the same curved paths through spacetime around the sphere as they would if mass was attractivly warping spacetime. Or perhaps we xould set up the conditions so that was so. Maybe ive misunderstood, but in most depictions of gravity its a point like a bottom of a well that's sort of stretched the 'rubber sheet' of spacetime. I know it's just an analogy but almost all layman explanations show spacetime elongating as it moves closer to the mass, the elongation depicting the 'warping' of spacetime. It's possible the real maths tells a more accurate story, but to me the more correct mental picture would be to think of circles around the mass spaced at distances where crossing between them takes time=1. For the outside observer it seems time slows as you draw nearer the mass, that would suggest the circles become 'closer' or you'd cross more space per unit time. It would also suggest the outside observer would see you eventually slow to a stop but locally you continue to accelerate along the curved spacetime, so it doesn't seem to violate special relativity. I'm not sure if mathematically space and time are treated separately, but if they're the same then thinking of mass as repelling spacetime 'outwards' from the surface of the mass seems to still work but might explain on larger scales where some of the expansion of space comes from - i.e. mass repels spacetime but the curvature this creates causes other mass to follow paths through spacetime that appear to make the two masses attract each other. I get that im no doubt wrong but ive not seen anyone adress this possibility (probably because it wrong!) but id be interested to hear where it breaks down, as i dont see it!
whatshisface 9y ago
There's no particular need for a special explanation of how particle exchange could produce an attractive force: as unlikely as it seems in classicical physics, it's how the forces (electromagnetic) arise in QED. The exchange of virtual photons can transport momentum any way you like.
- effie 9y ago
  'Exchange of virtual photons' is a metaphorical expression used to describe artifacts of perturbation theory, it is not necessarily a real process. There is no widely accepted model of what really happens on microscopic scales, we only have equations and those are often replaced by simpler perturbation scheme. So, explanations of attractive force are welcome, Le Sage - type models including.
  - whatshisface 9y ago
    >There is no widely accepted model of what really happens on microscopic scales, There's no experimental reason to come up with one - virtual photons work, which means anything else is at this point a matter of philosophy. That's not to cast off philosophy, of course.
    - effie 9y ago
      Virtual photons work in a very limited way (metaphorical language describing perturbation theory). Physics outside of applicability of perturbation QED (bound systems of charged particles, gravity) is not a matter of philosophy.
Taniwha 9y ago
Dumb question: how do you exchange gravitons with a black hole?
- ars 9y ago
  A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity. It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change). It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.) But that means it can't interact in a way that is detectable, other than gravity. Because you can not give it energy, you can also never create it artificially. If you did, you would be creating gravitational force out of nothing, which is impossible because it violates conservation of energy, and you can not pay for that violation because you can not give it energy. It's pretty much the ultimate impossible to study particle.
  - Florin_Andrei 9y ago
    > A graviton would have to be both massless and energyless. However, gravitational waves do carry energy. Gravitons, whatever they are, must be some very tricky things.
  - auntienomen 9y ago
    This comment is almost completely wrong. It muddles together classical and quantum reasoning in any incoherent way. Gravitons are best understood as the quanta of the effective qft governed by the Einstein Hilbert action. This mathematical model is the universal low energy approximation to any quantum theory that reduces to general relativity. Gravitons need to be massless. They need not be zero energy. They can indeed be associated with frequency. They do couple to gravitational backgrounds and to other gravitons. You can crate them just like any other field quanta. The barrier to studying gravitons the way we do photons is that they couple very weakly to other systems.
    - ars 9y ago

ars 9y ago

> "In other words, gravity would be asymptotically safe if the theory at high energies remains equally well behaved as the theory at low energies. In and of itself, this is not much of an insight. The insight comes from realizing that this good behavior does not necessarily contradict what we already know about the theory at low energies (from the early works of DeWitt and Feynman)." But what are the actual expected changes at high energy that would differ from what is seen at low energy? I kept waiting for her to explain what differences would be observed if this theory is correct, but she never did.

T-A 9y ago
You would observe the theory not blowing up. :) The key feature she never names is known as a "UV fixed point". UV = UltraViolet, which in this context simply stands for "high energy". Fixed point... for that you need to know that the effective values of coupling "constants" aren't actually constant in quantum field theory; they depend on the interaction energy (i.e. how hard you bang your particles together). So they are called "running" coupling constants. Yes, it's contradictory. That dependence on interaction energy is described by differential equations (known as the renormalization group flow equations, which may sound impressive but is actually a misnomer), which you can integrate to see how a coupling measured in the lab at low energy will change when your descendants finally get enough funding for a larger accelerator. One interesting behavior is the coupling going to zero when you increase the energy towards infinity. That happens in QCD: counterintuitively, the harder you bang quarks together, the less they affect each other (via QCD, that is; they also have other kinds of interactions which behave differently). So QCD is called "asymptotically free": in the limit of infinite interaction energy, as far as QCD is concerned, quarks are free particles, completely unaffected by each other's presence. In asymptotic safety, as opposed to freedom, the coupling does not go to zero as you increase the energy; instead, the rate at which it changes goes to zero, and it does so at some finite value of interaction energy. So, as you crank up the interaction energy toward that value, the coupling constant "runs" slower and slower, and once you get there, it stops "running" altogether. From there on, you can raise the interaction energy all you want, and the coupling constant stays... constant. And that is a UV fixed point.
- deleted 9y ago

pixl97 9y ago

I'm not a particle physicists by any means, but doesn't any theory of gravity have to deal with 'real' infinities at high energies from the physics we already know? We have some idea that black holes are a type of singularity (something that could possibly called an infinity). With E=MC2 we have an idea that if you apply enough energy to a particle it can become massive enough that it becomes a singularity itself.

Florin_Andrei 9y ago
A singularity popping out of the math is almost always an indication that something else is going on. According to general relativity, at the center of a black hole there might be some kind of "singularity" - but in reality what that means is GR is probably inadequate, when used alone, to describe the center of a BH. "Singularity" really means "your math broke and you need to fix it" by bringing in another theory that can fill in the gaps - or, rather, extending the current theory in a way that eliminates the division by zero.
pmiller2 9y ago
No, not really. A singularity in a quantized theory would simply be a place where gravity is strong enough that you can't move more than a Plank distance away from it.
RuggeroAltair 9y ago
The issue is not only about mass. Any mass could form a black hole, the main point is about mass density, and that's not trivial to obtain. That aside, real infinities is a vague concept. What's important is that any theory of gravity has to deal with the fact that the current understanding of classical gravity and quantum field theory make (when you combine them) a theory that has problems at the Planck scale. Those are problems that any theory of quantum gravity or every theory of everything have to deal with. But it doesn't mean that those potential theories would have any infinities. Such a theory, though, has been very elusive. With the exception of string theory, which is the leading theory in terms of its success, most theories tend to have fundamental problems. String theory research is certainly not complete, but it's in my opinion currently the best shot we have. Online, and in academia, you can find lots of very opinionated discussions about it, which include aspects of testability, predictivity, etc. which means that some people really dislike string theory and prefer other approaches.

jpeg_hero 9y ago

> The theory called asymptotically (as-em-TOT-ick-lee) safe gravity was proposed in 1978 by Steven Weinberg. Would a person interested in an article about quantum gravity not be familiar with the term asymptotically?

laretluval 9y ago
Moreover knowing the pronunciation doesn't give you any help if you don't know the meaning.
- intrasight 9y ago
  That bothered me as well (pronouncing rather than defining)
  - sago 9y ago
    Particularly as the pronunciation is strange. Strange place to break syllables, and I'm not sure the second vowel is a 'e' in most pronunciations. /a-sim-TOT-i-klee/
    - gnulinux 9y ago
      This is how I pronounce it in IPA: /a.sim'to:.ti.kli:/ Why is TOT one syllable?
      - jsmthrowaway 9y ago
        The weird thing about IPA is that the non-IPA pronunciation you’re replying to seems easier to understand.
        InternetOfStuff 9y ago
        Only to you. I feel exactly the opposite way. <Rant> I wish people would use the IPA instead of their absurd ad-hoc systems. I learned IPA at school, and it has served me well. All the pronunciation systems based on some other language are unreliable and idiosyncratic. And English, with its near-absence of reliable pronunciation/spelling rules, is particularly ill-suited. </Rant>

blackrock 9y ago

Gravity is measurement of the distortion of space, caused by mass. It is an emergent property. The more massive something is, the more its gravity will distort the space around it. So, a small piece of rock that you can hold in your hand, will cause a gravitational ripple in the space surrounding it. This is similar to how the Earth causes a gravitational ripple in the space around it, and it keeps us grounded to the ground. But, the Earth causes a much bigger gravitational ripple, than a small rock. And we as humans, are grounded to the Earth, as if we are at the bottom of this massive and invisible whirlpool. We cannot see it, but this whirlpool is rotating all around us, and we cannot get out. It is easy for us to move around horizontally, but it is very difficult for us to move vertically. Unless we can move horizontally so fast, that we can reach escape velocity, and then, we orbit the Earth. That said. What is gravity? Why does mass cause a ripple in the space around it? I wonder if gravity is just some type of neutral electro-magnetic force. Kind of like the magnetic field lines that you see with the North pole and South pole. But instead of being magnetically charged, it is neutrally charged, and it affects everything around it equally. Or, instead of being magnetically charged like the North or South pole, it is gravitationally-charged, and the direction points in only one way, into the center of your massive object. And unless you are moving faster than that massive object's escape velocity, then you will always be stuck in that object's gravitational ripple. If we can truly understand what is gravity, then I wonder if we can create a counter gravity. Like, in your spaceship, if you can create a negative mass above you, then it would cause your spaceship to act buoyant in the planet's atmosphere. And you can use thrusters to move around vertically, as easy as you can move around horizontally. Or, maybe you can create a temporary blackhole above your spaceship, and instead of your spaceship falling into the gravitational ripple caused by the Earth, then it becomes attracted to the gravitational ripple caused by your blackhole. And this causes your spaceship to rise, and defy the Earth's gravity. Anyways. I'm not a gravitational physicist. Maybe I should take this idea, and write a novel. There has been much worse Sci-Fi ideas created, like Time Travel, or the ridiculous many-worlds-interpretation theory of quantum mechanics.

RuggeroAltair 9y ago
From a physics perspective, the many-world, as ridiculous as it sounds, is a more sound theory (believed to be correct by some top physicists) than negative gravity. The explanation of why gravity is only positive is a complex one, but physicists believe it's almost axiomatic. This doesn't mean that you can't have repulsive type of effects, similar to one of the contributions that's believed to make the universe expand more quickly than with the simple 4 fources (often called fifth force, maybe related to dark energy, and to the rate of the universe expansion acceleration). PS. There are a number of Sci-Fi stories that use this idea, including a famous one from Asimov, in which if I recall correctly the normal gravitational force was working negatively when traveling in FTL speed. Obviously that seemed fishy but the book was cool (Nemesis).

perpetualcrayon 9y ago

Has anyone (sane) ever theorized that the ripples in spacetime in some cases may have existed before the masses of particles (ie. planets / stars) arrived at those locations?

auntienomen 9y ago

I'm not sure I see any real change in the status of asymptotic safety. It's a hypothesis. Proving it directly is next to impossible. (Except in spacetime dimension <= 3, when the theory is topological, making the assertion a triviality.) Testing it experimentally is unlikely; the constraints it implies are pretty weak. Nonetheless there are some people working on it, and while their ideas have some merit, they haven't yet caused the physics world to pay drastically more attention. Also, it's unwarranted hype to call asymptotic safety 'an old theory of everything'. It's explicitly not a theory of everything. It's only about gravity. Couple it to the Standard Model, and you still have a theory which breaks down at the hypercharge and Higgs Landau poles.

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esahione 9y ago

I think the author completely glosses over the fact that Loop Quantum Gravity actually does make predictions, and could provide the explanation for fast radio bursts. Also, the theory is so intuitive and follows such a straightforward logical path from Quantum Mechanics and Relativity, that I would be incredibly surprised if it wasn't the theory closest to actual reality.

thicknavyrain 9y ago
By any chance, we’re you ALSO in Carlo Rovelli’s lecture a few days ago? ;)
- esahione 9y ago
  I've literally watched every lecture he has out there lol :)