12 ms·

Ultra-weak gravitational field detected

298 points by awb 6y ago

saagarjha 6y ago
Ok, we don’t know G all that well, but saying > Their estimate deviates from the internationally agreed value (see go.nature.com/2bwkrqz) by about 9% — a small amount, given that the experimental uncertainties of their system have not yet not been optimized for precise measurements of G. is just misleading. We’re pretty sure of the value of the gravitational constant to at least 4-5 significant figures. The experiment is cool but it’s not like it’s going to get us a more accurate value.
- s_gourichon 6y ago
  Getting a more accurate value was not the point. Measuring a gravitational force between those tiny spheres, distinguishing it from experimental noise was the point. Impressive experiment. Deducing a value for g that’s not wildly wrong was the icing on the cake.
  - saagarjha 6y ago
    Yep, I misread it.
- dnautics 6y ago
  Sorry, what's misleading about this statement?
  - saagarjha 6y ago
    Apparently it was misleading enough for me to misread it. I withdraw my claim.
- outsomnia 6y ago
  If they can improve precision, a somewhat different G might be very interesting for, eg, MOND vs Dark Matter question https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
  - isolli 6y ago
    Unless I'm mistaken, the difference between MOND and classical Newtonian gravity is not in the value of G, but in making the force proportional to distance (rather than distance squared) at very large distances.
    - deleted 6y ago
      [deleted]
    - d_tr 6y ago
      The point is that if you put the experimentally measured distance, masses, and force into Newton's inverse square law in a regime where it does not actually hold, you will get a different G and this is how you will know that modifications are needed. G will be variable in that regime.
z3t4 6y ago
Does something moving fast weight less? Would it get less G if it would spin really fast ? Or does speed only affect "speed of time" ?
- dogma1138 6y ago
  As objects move faster their (relativistic) mass increases*, the invariant mass however doesn’t change. *Relative to an external observer.
  - Zamicol 6y ago
    Are there any experimental tests of relativistic mass?
    - fsh 6y ago
      Yes, any particle accelerator has to account for the relativistic mass in order to function.
    - dogma1138 6y ago
      Yes, and pretty old ones at that https://en.wikipedia.org/wiki/Kaufmann%E2%80%93Bucherer%E2%80%93Neumann_experiments https://en.wikipedia.org/wiki/Kaufmann%E2%80%93Bucherer%E2%8... Special relativity is weird, but it's very much proven by countless experiments. https://en.wikipedia.org/wiki/Tests_of_special_relativity https://en.wikipedia.org/wiki/Tests_of_special_relativity
- elihu 6y ago
  My understanding which could be wrong is that the kinetic energy of an object can itself cause (tiny amounts) of gravity. So, for instance, a spinning object would weigh slightly more.
dvt 6y ago
Awesome experiment, and really cool findings, but I feel that... > The findings take us a step nearer to measuring gravitational fields that are so weak that they could enter the quantum regime. ...is overstated. There's a long way between 90 milligrams and quantum gravity.
- crubier 6y ago
  In terms of mass it takes us halfway there already, from 10^30kg to 10^-3kg, with quantum effects arriving around 10^-15kg. And in terms of force, the article states that the force involved in that experiment is equivalent to the force of earth gravity on a mass of 10^–15kg, which is probably even closer to the energy of a graviton.
  - penetraitor69 6y ago
    Depending on how you're cutting it, you could also call it 1/1000000000000 of the way there.
    - seanhunter 6y ago
      That's half (within some tolerance).
  - abdullahkhalids 6y ago
    Why do you say that quantum effects arise at 10^-15kg? The carbon atom is about 2x10^-26 kg. And I don't think we can put objects much larger than a few atom molecules into a superposition of two locations.
    - johncolanduoni 6y ago
      It depends on the nature of the quantization of the gravitational field. If we expect the gravitational field itself to be quantized in a manner somewhat similar to the electromagnetic field, we may be able to detect quantum effects without the objects being particularly small. A good analogue is the photoelectric effect, which involves no superposition at all and can be observed even with macro amounts of energy involved.
ajuc 6y ago
Wouldn't putting this device in a spherical container on Earth's orbit remove a lot of noise?
- WJW 6y ago
  Yes it would, but launching stuff into orbit is expensive and making ultrasensitive instruments launch-proof is trickier (and more expensive) than you'd think.
  - ajuc 6y ago
    I wonder if people on the ISS could make this device from components. Then you don't need to launch it.
    - fsh 6y ago
      The ISS is actually a pretty bad microgravity environment. Human occupants and their life-support systems lead to rather strong system vibrations. Also the low orbit required for efficient supply flights causes a significant amount of atmospheric drag. Space stations are mainly there for show, the actual science is better done somewhere else.
      - ben_w 6y ago
        Surely how good it is for an experiment depends on the experiment? Microgravity effects on biology don’t need anything close to the same precision as the test in the link.
      - ajuc 6y ago
        I meant: - send components to ISS - assemble - subtly nudge the container to a different orbit - wait for it to do the experiment and catch when the orbits meet again. Or if that's too hard just wait for results to be transmitted
  - Fordec 6y ago
    Once we have a proper suite of in-orbit manufacturing (not just 3d printing a plastic part) it's going to be a straight up Cambrian explosion event for what technology we can design for a space environment by letting go of vibration tolerances, G force tolerances and rocket dimension constraints. The new ways to manufacture are cool, but the dropping of existing constraints is a dream for a potential new wave of creativity for both new problems to fix in a new environment, with orders of magnitude operational scale (Everything is still basically bespoke one offs, bar a number of companies I can count on my fingers) and how to create solutions for all that new scale entails.
tumblewit 6y ago
Question: Since mass exerts gravitation force, wouldn’t it mean that any mass of any size shape would do that? Just because we don’t have a scientific experiment to measure gravitational forces at small scales doesn’t mean they don’t exist mathematically right? What am I missing when they say quantum particles do not fit with gravity.
- brg 6y ago
  Highly over simplified, but the idea is that the curvature of space-time is smooth but quantum mechanics is discrete.
  - tsimionescu 6y ago
    Quantum mechanics is not discrete in regards to space and time. The problem has much more to do with the fact that particles can be in multiple places at once, and what that means for their gravitational pull / space-time curvature.
- drbw 6y ago
  Try this episode of PBS SpaceTime which goes into the dichotomy between GR and QM: https://www.youtube.com/watch?v=YNEBhwimJWs https://www.youtube.com/watch?v=YNEBhwimJWs.
- TheGallopedHigh 6y ago
  Yep any size particle should. But gravity is described by classical physics through general relativity. When you have situations of very small quantum scales and large gravitational fields both general relativity and quantum field theory don’t work well together. This is a big problem in physics. See here for more details https://en.m.wikipedia.org/wiki/Quantum_gravity https://en.m.wikipedia.org/wiki/Quantum_gravity
- osamagirl69 6y ago
  >Just because we don’t have a scientific experiment to measure gravitational forces at small scales doesn’t mean they don’t exist mathematically right? That is correct--it has been expected (since, you know, Newton...) but not yet measured at this scale. That is why the headline says "detected" as opposed to theorized. >What am I missing when they say quantum particles do not fit with gravity. Quantum mechanics predicts that Newtons description of gravity will break down under certain conditions. We currently do not have the ability to measure this effect, so it is all theoretical at this point.
Hani1337 6y ago
How many more decades until scientists realize chemical bonding is molecular scale gravity? I've claimed for years galaxies and molecules operate with the same logic only with a different scale. The laws of physics are dependent on scale, it's stupid to try and find rules anchored in answers figured out with absolute math because it's all fucking relative.
- banachtarski 6y ago
  Is this... serious? Your theory is on the surface impossible because electromagnetic forced would dominate your “gravity”, forcing protons apart among other things. If what you’re suggesting is that at a certain scale, gravity just acts differently all of the sudden, how is this any different than modeling the interaction with a different type of force, aside from a naming convention?
  - Hani1337 6y ago
    I think my point, even if I'm not well educated to formulate it in scientist language, is that measuring everything in absolutes is fucking up with science's accuracy. Speed is a human construct to triangulate distance over time. Light doesn't have speed. Light is a constant that defines speed. A lot of things we think we know and take for granted is actually slightly inaccurate when the scale shifts drastically. That's because we focus on absolutes instead of relative values. Numbers are a human construct, scientists have forgotten that. Because our brain can easily add 2+2 doesn't mean it's a technique that scales infinitely and remains true. Do we have proof of numbers stability through scale or do we just say there's an "infinite" amount of them to make it easier on the explaining? ps: pi is another of these constants that rule the laws of the universe. We can't really explain why but it does. It's the same principle as for light. Constants are true not matter the scope, because everything is relative. Our numbers can't truly represent that because additions are inherently flawed when the scale shifts. Everything that adds recursively is actually a multiplication array, and thinking of it as an addition is inaccurate. tldr: our math needs to evolve to follow an OoP logic instead of being stuck at a human scale perspective.
- marcorentap 6y ago
jcims 6y ago
I’ve often wondered if it would be possible to make a type of gravitational radar. Imagine a large array of this type of detector spread over an area of a few square km. Combine the force vectors of each toward any specific point and it seems you should be able to monitor the masses at that point. Edit: measuring the force of the ISS passing over head would require femtonewton precision for a mass of 100kg. Might be a bit tricky lol
- Gravityloss 6y ago
  https://grace.jpl.nasa.gov/mission/grace/ https://grace.jpl.nasa.gov/mission/grace/
- deleted 6y ago
  [deleted]
- rocqua 6y ago
  This is an amazing idea for sci-fi! Spread the masses out over orbit, measure net gravity on those (by orbit deviations?), and you should be able to detect changes in gravity from distant objects. With enough spread maaaaybe you could do something with parallax to detect distance too. Imagine a system like this in 'the expanse' to detect the stealth asteroids hurled towards earth. Or, in general, to detect massive ships that are 'on the float'.
- hugh-avherald 6y ago
  https://en.wikipedia.org/wiki/Cavendish_experiment https://en.wikipedia.org/wiki/Cavendish_experiment
choeger 6y ago
Maybe I am missing something, but how could a quantum theory of gravity explain curvature of spacetime? If a photon follows a curve around a large mass, it does so because that curve is the shortest path through spacetime, if I am not mistaken. But how would a theoretical graviton explain this effect? Would it interact with the photon to carry over a force? And if so, how would it "know" the direction of said force (wouldn't it be itself subject to gravity?). Or would it interact with space itself?
- irjustin 6y ago
  All good questions. Fast answer: we have no clue. Until we have a good quantum theory of gravity, we can't explain how it affects the curvature of spacetime at the quantum level. All the current quantum gravity theories, i.e. loop quantum gravity, string theory, etc... work if you squint just right, otherwise they fall apart really fast. Spacetime has a bunch of episodes on going theories. A very large elephant in the room is, a lot of these ideas don't have a method of testing. And sure, a lot of theories start out without a practical method until decades later where technology can catch up, but we don't even have a theoretical test to start with! Spacetime recently did an episode touching on some of your thoughts at the classical level and even then it's... relative[0]. [0] https://www.youtube.com/watch?v=OHdV9aO6jaE https://www.youtube.com/watch?v=OHdV9aO6jaE
  - ArtWomb 6y ago
    >>> we don't even have a theoretical test to start with Every quantum computing calculation, is a desktop quantum experiment ;) Non-Gaussianity as a signature of a quantum theory of gravity https://arxiv.org/abs/2004.01189 https://arxiv.org/abs/2004.01189 Another cool aspect of the optomechanical tabletop device research was that it wasn't entirely fruitless at all. Although the original mission of finding gravity in quantum space may have failed. The behavior exhibited was so extremely non-classical that an explosion of waveguide manipulating metamaterials was born!
- contravariant 6y ago
  The idea is that it would be similar to the way that photons mediate the effect of the electromagnetic field. Though I've personally always thought that this description wasn't too good at explaining large gradual changes in the electromagnetic field, similar to how gravitons are a bit of weird model for the large gradual curvature of spacetime (it's not that it can be done but it is a bit awkward). Anyway the most straightforward way to implement gravitons in this sense doesn't pan out mathematically so we're not even sure if this model is at all accurate.
k_sze 6y ago
Please correct me if I'm wrong, but the second sentence of the first paragraph already seems weird: > The gravitational force is the weakest of these four. Isn't that distance dependent? At macroscopic distances, the weak and strong interactions are even weaker, no?
- irjustin 6y ago
  Technically yes, but usually this statement is assumed at the quantum level/distances.
- _Nat_ 6y ago
  Yeah, there're qualifications behind it. [This PDF](http://web.mit.edu/sahughes/www/8.022/lec01.pdf http://web.mit.edu/sahughes/www/8.022/lec01.pdf) starts with some potentially helpful context. Usually this claim is discussed in connection to the so-called ["hierarchy problem"](https://en.wikipedia.org/wiki/Hierarchy_problem https://en.wikipedia.org/wiki/Hierarchy_problem).
- cbkeller 6y ago
  Not exactly: if you had a kg of free protons and a kg of free electrons, the electromagnetic forces between them would dwarf the gravitational forces between them even at macroscopic distances. By a lot, as Feynman liked to note in his Lectures [0,1]. It’s just hard to get a kg of free protons exactly because the forces involved are so large. So charges tend to pair up and screen [2], which just camouflages the true strength of the force. For the strong force the situation is the same in a sense, if you had a kg each of quarks of different colors — except you literally can’t have that, because the energy involved in separating a pair of quarks is so large that it actually causes two new quarks to snap into existence and pair off with the two you were trying to separate before you can separate them on anything approaching macroscopic scales [3]. So the strong force is obligatorily screened (camouflaged) at long distances, but only because it is so strong. The kg-of-protons experiment on the other hand you could do in principle, it would just probably be better if you didn’t. [0] https://www.feynmanlectures.caltech.edu/II_01.html https://www.feynmanlectures.caltech.edu/II_01.html [1] https://sieste.wordpress.com/2012/04/22/feynmans-electric-force-analogy/ https://sieste.wordpress.com/2012/04/22/feynmans-electric-fo... [2] https://en.wikipedia.org/wiki/Electric-field_screening https://en.wikipedia.org/wiki/Electric-field_screening [3] https://en.wikipedia.org/wiki/Color_confinement https://en.wikipedia.org/wiki/Color_confinement
tezza 6y ago
It appears they used Frequency Modulation to prove the connection. Radio over Gravity !
kristianp 6y ago
Interesting statement in the article that measurements of the gravitational constant, G, haven't converged on a number like other constants have. Anyone here know anything about this?
sriku 6y ago
The article ends with a stated goal of measuring the gravity of masses of the order of 10^-8 kg or about 10 micrograms. This reminded me of a calculation involving known fundamental constants - h, G, c - to derive dimensionless units for mass, length and time by setting these constants to unity. Setting c=1 is common among general relativists. When you do that for all three constants, you get (iirc) a unit of mass to be 10^-8kg = 1 and of time to be 10^-43secs = 1 and 10^-35m = 1 (only stating orders of magnitude). The latter two are Planck time and Planck length and the first is Planck mass ... and we may indeed expect quantum effects to manifest at that scale. I've also read on the occasion that 10micrograms is around the scale at which quantum superpositions may be sustainable before decoherence becomes unstoppable.
- Iwan-Zotow 6y ago
  >you get (iirc) a unit of mass to be 10^-8kg = 1 Sure, this is Plank mass, 2 \times 10^-8 kg. Length unit would be obviously PLank length, ditto for Plank time > 10micrograms is around the scale at which quantum superpositions may be sustainable before decoherence becomes unstoppable that doesn't make sense
- sandworm101 6y ago
  If they can actually measure such tiny blips then they can build particle detectors that might answer all sorts of fundamental problems. Such detectors would be exponentially smaller (read cheaper) than those in LHC-class colliders. There are no double many Nobel prizes up for grabs to anyone who can measure the gravity of particle flux.
  - qubex 6y ago
    > There are no double many Noble prizes There are no doubt many Noble prizes?
mrfusion 6y ago
If we can get this sensitive I think it would be cool to measure under all sorts of conditions. High magnetic field, high electric field, just to see if there are any tiny effects.
morpheos137 6y ago
I think maybe we are looking at it backwards. In order to understand what gravity is first we may need to understand what distance is. Gravity is essentially the effect of information at different distances. Matter or energy is localised information. Something here, nothing there. Gravity acts at a great distance compared to the other fundamental forces so perhaps it is not like them, not amenable to a quantum theory. Perhaps gravity is meta information about space. Space contains certain clusters or concentrations of information at different distances.The ensemble of these clusters is also information. A certain level information density may extert a pull on matter that we call the gravitational force.

298 points by awb 6y ago

Ok, we don’t know G all that well, but saying > Their estimate deviates from the internationally agreed value (see go.nature.com/2bwkrqz) by about 9% — a small amount, given that the experimental uncertainties of their system have not yet not been optimized for precise measurements of G. is just misleading. We’re pretty sure of the value of the gravitational constant to at least 4-5 significant figures. The experiment is cool but it’s not like it’s going to get us a more accurate value.

s_gourichon 6y ago
Getting a more accurate value was not the point. Measuring a gravitational force between those tiny spheres, distinguishing it from experimental noise was the point. Impressive experiment. Deducing a value for g that’s not wildly wrong was the icing on the cake.
- saagarjha 6y ago
  Yep, I misread it.
dnautics 6y ago
Sorry, what's misleading about this statement?
- saagarjha 6y ago
  Apparently it was misleading enough for me to misread it. I withdraw my claim.
outsomnia 6y ago
If they can improve precision, a somewhat different G might be very interesting for, eg, MOND vs Dark Matter question https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
- isolli 6y ago
  Unless I'm mistaken, the difference between MOND and classical Newtonian gravity is not in the value of G, but in making the force proportional to distance (rather than distance squared) at very large distances.
  - deleted 6y ago
    [deleted]
  - d_tr 6y ago
    The point is that if you put the experimentally measured distance, masses, and force into Newton's inverse square law in a regime where it does not actually hold, you will get a different G and this is how you will know that modifications are needed. G will be variable in that regime.

z3t4 6y ago

Does something moving fast weight less? Would it get less G if it would spin really fast ? Or does speed only affect "speed of time" ?

dogma1138 6y ago
As objects move faster their (relativistic) mass increases*, the invariant mass however doesn’t change. *Relative to an external observer.
- Zamicol 6y ago
  Are there any experimental tests of relativistic mass?
  - fsh 6y ago
    Yes, any particle accelerator has to account for the relativistic mass in order to function.
  - dogma1138 6y ago
    Yes, and pretty old ones at that https://en.wikipedia.org/wiki/Kaufmann%E2%80%93Bucherer%E2%80%93Neumann_experiments https://en.wikipedia.org/wiki/Kaufmann%E2%80%93Bucherer%E2%8... Special relativity is weird, but it's very much proven by countless experiments. https://en.wikipedia.org/wiki/Tests_of_special_relativity https://en.wikipedia.org/wiki/Tests_of_special_relativity
elihu 6y ago
My understanding which could be wrong is that the kinetic energy of an object can itself cause (tiny amounts) of gravity. So, for instance, a spinning object would weigh slightly more.

dvt 6y ago

Awesome experiment, and really cool findings, but I feel that... > The findings take us a step nearer to measuring gravitational fields that are so weak that they could enter the quantum regime. ...is overstated. There's a long way between 90 milligrams and quantum gravity.

crubier 6y ago
In terms of mass it takes us halfway there already, from 10^30kg to 10^-3kg, with quantum effects arriving around 10^-15kg. And in terms of force, the article states that the force involved in that experiment is equivalent to the force of earth gravity on a mass of 10^–15kg, which is probably even closer to the energy of a graviton.
- penetraitor69 6y ago
  Depending on how you're cutting it, you could also call it 1/1000000000000 of the way there.
  - seanhunter 6y ago
    That's half (within some tolerance).
- abdullahkhalids 6y ago
  Why do you say that quantum effects arise at 10^-15kg? The carbon atom is about 2x10^-26 kg. And I don't think we can put objects much larger than a few atom molecules into a superposition of two locations.
  - johncolanduoni 6y ago
    It depends on the nature of the quantization of the gravitational field. If we expect the gravitational field itself to be quantized in a manner somewhat similar to the electromagnetic field, we may be able to detect quantum effects without the objects being particularly small. A good analogue is the photoelectric effect, which involves no superposition at all and can be observed even with macro amounts of energy involved.

ajuc 6y ago

Wouldn't putting this device in a spherical container on Earth's orbit remove a lot of noise?

WJW 6y ago
Yes it would, but launching stuff into orbit is expensive and making ultrasensitive instruments launch-proof is trickier (and more expensive) than you'd think.
- ajuc 6y ago
  I wonder if people on the ISS could make this device from components. Then you don't need to launch it.
  - fsh 6y ago
    The ISS is actually a pretty bad microgravity environment. Human occupants and their life-support systems lead to rather strong system vibrations. Also the low orbit required for efficient supply flights causes a significant amount of atmospheric drag. Space stations are mainly there for show, the actual science is better done somewhere else.
    - ben_w 6y ago
      Surely how good it is for an experiment depends on the experiment? Microgravity effects on biology don’t need anything close to the same precision as the test in the link.
    - ajuc 6y ago
      I meant: - send components to ISS - assemble - subtly nudge the container to a different orbit - wait for it to do the experiment and catch when the orbits meet again. Or if that's too hard just wait for results to be transmitted
- Fordec 6y ago
  Once we have a proper suite of in-orbit manufacturing (not just 3d printing a plastic part) it's going to be a straight up Cambrian explosion event for what technology we can design for a space environment by letting go of vibration tolerances, G force tolerances and rocket dimension constraints. The new ways to manufacture are cool, but the dropping of existing constraints is a dream for a potential new wave of creativity for both new problems to fix in a new environment, with orders of magnitude operational scale (Everything is still basically bespoke one offs, bar a number of companies I can count on my fingers) and how to create solutions for all that new scale entails.

tumblewit 6y ago

Question: Since mass exerts gravitation force, wouldn’t it mean that any mass of any size shape would do that? Just because we don’t have a scientific experiment to measure gravitational forces at small scales doesn’t mean they don’t exist mathematically right? What am I missing when they say quantum particles do not fit with gravity.

brg 6y ago
Highly over simplified, but the idea is that the curvature of space-time is smooth but quantum mechanics is discrete.
- tsimionescu 6y ago
  Quantum mechanics is not discrete in regards to space and time. The problem has much more to do with the fact that particles can be in multiple places at once, and what that means for their gravitational pull / space-time curvature.
drbw 6y ago
Try this episode of PBS SpaceTime which goes into the dichotomy between GR and QM: https://www.youtube.com/watch?v=YNEBhwimJWs https://www.youtube.com/watch?v=YNEBhwimJWs.
TheGallopedHigh 6y ago
Yep any size particle should. But gravity is described by classical physics through general relativity. When you have situations of very small quantum scales and large gravitational fields both general relativity and quantum field theory don’t work well together. This is a big problem in physics. See here for more details https://en.m.wikipedia.org/wiki/Quantum_gravity https://en.m.wikipedia.org/wiki/Quantum_gravity
osamagirl69 6y ago
>Just because we don’t have a scientific experiment to measure gravitational forces at small scales doesn’t mean they don’t exist mathematically right? That is correct--it has been expected (since, you know, Newton...) but not yet measured at this scale. That is why the headline says "detected" as opposed to theorized. >What am I missing when they say quantum particles do not fit with gravity. Quantum mechanics predicts that Newtons description of gravity will break down under certain conditions. We currently do not have the ability to measure this effect, so it is all theoretical at this point.

Hani1337 6y ago

How many more decades until scientists realize chemical bonding is molecular scale gravity? I've claimed for years galaxies and molecules operate with the same logic only with a different scale. The laws of physics are dependent on scale, it's stupid to try and find rules anchored in answers figured out with absolute math because it's all fucking relative.

banachtarski 6y ago
Is this... serious? Your theory is on the surface impossible because electromagnetic forced would dominate your “gravity”, forcing protons apart among other things. If what you’re suggesting is that at a certain scale, gravity just acts differently all of the sudden, how is this any different than modeling the interaction with a different type of force, aside from a naming convention?
- Hani1337 6y ago
  I think my point, even if I'm not well educated to formulate it in scientist language, is that measuring everything in absolutes is fucking up with science's accuracy. Speed is a human construct to triangulate distance over time. Light doesn't have speed. Light is a constant that defines speed. A lot of things we think we know and take for granted is actually slightly inaccurate when the scale shifts drastically. That's because we focus on absolutes instead of relative values. Numbers are a human construct, scientists have forgotten that. Because our brain can easily add 2+2 doesn't mean it's a technique that scales infinitely and remains true. Do we have proof of numbers stability through scale or do we just say there's an "infinite" amount of them to make it easier on the explaining? ps: pi is another of these constants that rule the laws of the universe. We can't really explain why but it does. It's the same principle as for light. Constants are true not matter the scope, because everything is relative. Our numbers can't truly represent that because additions are inherently flawed when the scale shifts. Everything that adds recursively is actually a multiplication array, and thinking of it as an addition is inaccurate. tldr: our math needs to evolve to follow an OoP logic instead of being stuck at a human scale perspective.
marcorentap 6y ago

jcims 6y ago

I’ve often wondered if it would be possible to make a type of gravitational radar. Imagine a large array of this type of detector spread over an area of a few square km. Combine the force vectors of each toward any specific point and it seems you should be able to monitor the masses at that point. Edit: measuring the force of the ISS passing over head would require femtonewton precision for a mass of 100kg. Might be a bit tricky lol

Gravityloss 6y ago
https://grace.jpl.nasa.gov/mission/grace/ https://grace.jpl.nasa.gov/mission/grace/
deleted 6y ago
[deleted]
rocqua 6y ago
This is an amazing idea for sci-fi! Spread the masses out over orbit, measure net gravity on those (by orbit deviations?), and you should be able to detect changes in gravity from distant objects. With enough spread maaaaybe you could do something with parallax to detect distance too. Imagine a system like this in 'the expanse' to detect the stealth asteroids hurled towards earth. Or, in general, to detect massive ships that are 'on the float'.
hugh-avherald 6y ago
https://en.wikipedia.org/wiki/Cavendish_experiment https://en.wikipedia.org/wiki/Cavendish_experiment

choeger 6y ago

Maybe I am missing something, but how could a quantum theory of gravity explain curvature of spacetime? If a photon follows a curve around a large mass, it does so because that curve is the shortest path through spacetime, if I am not mistaken. But how would a theoretical graviton explain this effect? Would it interact with the photon to carry over a force? And if so, how would it "know" the direction of said force (wouldn't it be itself subject to gravity?). Or would it interact with space itself?

irjustin 6y ago
All good questions. Fast answer: we have no clue. Until we have a good quantum theory of gravity, we can't explain how it affects the curvature of spacetime at the quantum level. All the current quantum gravity theories, i.e. loop quantum gravity, string theory, etc... work if you squint just right, otherwise they fall apart really fast. Spacetime has a bunch of episodes on going theories. A very large elephant in the room is, a lot of these ideas don't have a method of testing. And sure, a lot of theories start out without a practical method until decades later where technology can catch up, but we don't even have a theoretical test to start with! Spacetime recently did an episode touching on some of your thoughts at the classical level and even then it's... relative[0]. [0] https://www.youtube.com/watch?v=OHdV9aO6jaE https://www.youtube.com/watch?v=OHdV9aO6jaE
- ArtWomb 6y ago
  >>> we don't even have a theoretical test to start with Every quantum computing calculation, is a desktop quantum experiment ;) Non-Gaussianity as a signature of a quantum theory of gravity https://arxiv.org/abs/2004.01189 https://arxiv.org/abs/2004.01189 Another cool aspect of the optomechanical tabletop device research was that it wasn't entirely fruitless at all. Although the original mission of finding gravity in quantum space may have failed. The behavior exhibited was so extremely non-classical that an explosion of waveguide manipulating metamaterials was born!
contravariant 6y ago
The idea is that it would be similar to the way that photons mediate the effect of the electromagnetic field. Though I've personally always thought that this description wasn't too good at explaining large gradual changes in the electromagnetic field, similar to how gravitons are a bit of weird model for the large gradual curvature of spacetime (it's not that it can be done but it is a bit awkward). Anyway the most straightforward way to implement gravitons in this sense doesn't pan out mathematically so we're not even sure if this model is at all accurate.

k_sze 6y ago

Please correct me if I'm wrong, but the second sentence of the first paragraph already seems weird: > The gravitational force is the weakest of these four. Isn't that distance dependent? At macroscopic distances, the weak and strong interactions are even weaker, no?

irjustin 6y ago
Technically yes, but usually this statement is assumed at the quantum level/distances.
_Nat_ 6y ago
Yeah, there're qualifications behind it. [This PDF](http://web.mit.edu/sahughes/www/8.022/lec01.pdf http://web.mit.edu/sahughes/www/8.022/lec01.pdf) starts with some potentially helpful context. Usually this claim is discussed in connection to the so-called ["hierarchy problem"](https://en.wikipedia.org/wiki/Hierarchy_problem https://en.wikipedia.org/wiki/Hierarchy_problem).
cbkeller 6y ago
Not exactly: if you had a kg of free protons and a kg of free electrons, the electromagnetic forces between them would dwarf the gravitational forces between them even at macroscopic distances. By a lot, as Feynman liked to note in his Lectures [0,1]. It’s just hard to get a kg of free protons exactly because the forces involved are so large. So charges tend to pair up and screen [2], which just camouflages the true strength of the force. For the strong force the situation is the same in a sense, if you had a kg each of quarks of different colors — except you literally can’t have that, because the energy involved in separating a pair of quarks is so large that it actually causes two new quarks to snap into existence and pair off with the two you were trying to separate before you can separate them on anything approaching macroscopic scales [3]. So the strong force is obligatorily screened (camouflaged) at long distances, but only because it is so strong. The kg-of-protons experiment on the other hand you could do in principle, it would just probably be better if you didn’t. [0] https://www.feynmanlectures.caltech.edu/II_01.html https://www.feynmanlectures.caltech.edu/II_01.html [1] https://sieste.wordpress.com/2012/04/22/feynmans-electric-force-analogy/ https://sieste.wordpress.com/2012/04/22/feynmans-electric-fo... [2] https://en.wikipedia.org/wiki/Electric-field_screening https://en.wikipedia.org/wiki/Electric-field_screening [3] https://en.wikipedia.org/wiki/Color_confinement https://en.wikipedia.org/wiki/Color_confinement

tezza 6y ago

It appears they used Frequency Modulation to prove the connection. Radio over Gravity !

kristianp 6y ago

Interesting statement in the article that measurements of the gravitational constant, G, haven't converged on a number like other constants have. Anyone here know anything about this?

sriku 6y ago

The article ends with a stated goal of measuring the gravity of masses of the order of 10^-8 kg or about 10 micrograms. This reminded me of a calculation involving known fundamental constants - h, G, c - to derive dimensionless units for mass, length and time by setting these constants to unity. Setting c=1 is common among general relativists. When you do that for all three constants, you get (iirc) a unit of mass to be 10^-8kg = 1 and of time to be 10^-43secs = 1 and 10^-35m = 1 (only stating orders of magnitude). The latter two are Planck time and Planck length and the first is Planck mass ... and we may indeed expect quantum effects to manifest at that scale. I've also read on the occasion that 10micrograms is around the scale at which quantum superpositions may be sustainable before decoherence becomes unstoppable.

Iwan-Zotow 6y ago
>you get (iirc) a unit of mass to be 10^-8kg = 1 Sure, this is Plank mass, 2 \times 10^-8 kg. Length unit would be obviously PLank length, ditto for Plank time > 10micrograms is around the scale at which quantum superpositions may be sustainable before decoherence becomes unstoppable that doesn't make sense
sandworm101 6y ago
If they can actually measure such tiny blips then they can build particle detectors that might answer all sorts of fundamental problems. Such detectors would be exponentially smaller (read cheaper) than those in LHC-class colliders. There are no double many Nobel prizes up for grabs to anyone who can measure the gravity of particle flux.
- qubex 6y ago
  > There are no double many Noble prizes There are no doubt many Noble prizes?

mrfusion 6y ago

If we can get this sensitive I think it would be cool to measure under all sorts of conditions. High magnetic field, high electric field, just to see if there are any tiny effects.

morpheos137 6y ago

I think maybe we are looking at it backwards. In order to understand what gravity is first we may need to understand what distance is. Gravity is essentially the effect of information at different distances. Matter or energy is localised information. Something here, nothing there. Gravity acts at a great distance compared to the other fundamental forces so perhaps it is not like them, not amenable to a quantum theory. Perhaps gravity is meta information about space. Space contains certain clusters or concentrations of information at different distances.The ensemble of these clusters is also information. A certain level information density may extert a pull on matter that we call the gravitational force.