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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 experimen

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.
terryf 6y ago
I guess kind of a similar expecation was in place for light as well - if you dim your light source then it emits less light waves. Well, turns out if you go small enough then you see it's actually individual packets of light with certain amounts of energy where the amount of packets (photons) sent out decreases as you turn down the intensity. So, the total amount of energy outputted still matches the input, but the output is in discrete packets, where each packet can exceed the level of input energy at a specific time. So, on a large scale everything seems fine but as you go to very small energy levels it starts to look different. I guess the expectation with gravity is that going to very small masses, some different underlying mechanism will appear. Or it may not. So they're trying to find out.
tsimionescu 6y ago
The problem is that QM doesn't account for gravity so far - in QM as it exists today, particles have mass, but do not interact through gravity. This fits experiments, which is not surprising given that any theory of gravity we have today predicts that the gravitational attraction between two masses that low would be much smaller than what we can measure (remember for example that a kitchen magnet's electromagnetic force can oppose the gravitational pull of the entire earth, that's how weak gravity is compared to other forces). Still, obviously large masses have gravity, so everyone expects that, even if we can't measure it yet, and don't know how to compute it yet, there must be some attraction between particles. There are some theories about it (for example string theory has something that looks like gravity), but since they all predict values much lower than we could hope to measure for now, the problem remains wide open. However, simply applying Newton's or Einstein's theories of gravity to QM doesn't work. In QM, particles don't have a single position in space and time, each particle is more like a wave with peaks at different points in space at the same time. If you try to compute the gravitational field generated by all these peaks you get nonsense results. So, while we generally believe that there must be some gravitational attraction between particles with mass, we don't know how it would look like. I think there are also some theories that predict that elementary particles do NOT interact through gravity, that gravity is somehow an emergent phenomenon of a collection of many particles (just like an elementary particle doesn't have a temperature, but a collection of many many particles does have one). I believe this is a pretty fringe theory, but not quite "flat earth" land. Just including it for completeness.
- tumblewit 6y ago
  This is what I find interesting. Assuming two quantum particles exert forces on each other. Now they both have mass but the forces they exert on each other are so much more powerful that the gravitational force would be impossible to experiment. Sort of like a man at a distance exerting gravitational force on the Milky Way with instruments the size of galaxy clusters to measure that man or force. Beyond mathematics there would be no experimental way. But my question is if mathematics itself says quantum particles do not have gravity or is that just a limitation of current understanding.
  - 6y ago
ben_w 6y ago
> Question: Since mass exerts gravitation force, wouldn’t it mean that any mass of any size shape would do that? Yes. Absolutely everything should have a gravitational field. > What am I missing when they say quantum particles do not fit with gravity. Under Relativity, mass and energy are equivalent, therefore energy has a gravitational field. If you try to mathematically quantise the gravitational field the way the electromagnetic field was quantised (the latter giving you a photon, the former would be a graviton), then something goes wrong. This is where my grasp of the physics gets a bit hazy; I think you find any amount of gravity should produce more gravity, and this self-generation blows up to infinity rather than summing to a finite value. Or it might have something to do with the expected value of a corresponding zero-point gravity field? Or both? I’m not sure, I only do physics for fun. I keep thinking it’s a gravitational equivalent to the Ultraviolet Catastrophe, but if it was that simple someone would’ve already solved it.
- HPsquared 6y ago
  The Ultraviolet Catastrophe was solved by a complete rethink of the foundations (a shift from continuous to quantised energy). Perhaps the standard model needs a similar fundamental shift? (Though I have no idea what that would look like)
  - reasonabl_human 6y ago
    Anecdotally, I agree. When you look at the history of major breakthroughs in physics, mainstream understanding narrows down on some complex analytical theories (rotating shells above the earth controlling the movement of the heavenly bodies, crazy complex math) when in reality there was a fork in the road decades prior where mainstream physics took a wrong turn (heliocentric! orbits!). Things like this are obvious in retrospect, but radical for their time.. most of the physics I learned was elegant and well-understood, then particle physics just... didn’t really feel the same way. Tons of gotchas and edge cases, difficulty generalizing problems, and the obvious disconnect between the physics of the small and that of the large... In time we’ll look back at current iterations of the standard model and our understanding of the physics of the small and wonder how those Neanderthals didn’t just realize that xyz was the key to make everything much simpler and work in harmony... that’ll be a fun day!
oceanghost 6y ago
Any mass, as currently defined, distorts space-time. Interestingly enough, velocity contributes to mass. That is to say, if we imagined two toy tops, one at rest and one spinning, the spinning top would have more mass due to its additional energy. Gravity is something like 10^32 power smaller than the next meaningful force. The problem with gravity is this-- At that resolution, we can't distinguish between two theories-- that mass warps space-time, or that there is a particle that mediates the force of gravity (a "graviton"). That is to say, is gravity analog or is it digital? If gravity is digital, there is a particle that is extremely small that transmits its force. If gravity is analog, then it changes the space around us itself and acts exactly the same way. So we have a question for the ages-- we have 17 to 25 quantum fields (depending on how you count) and, one, analog field, gravity. So, is gravity analog, or is it impossibly small digital field? For gods sakes is there a physicist out there, please correct me if I'm wrong. :-)
- criddell 6y ago
  So how is mass defined? Matter, as I understand it, is excitations of a quantum field. Why should they attract each other?
  - stjohnswarts 6y ago
    Maybe it's centered around the particle's quantum density field aka the average position of the possible quantum positions?
  - tsimionescu 6y ago
    This is somewhat like saying 'mountains are just the greyish areas on a map, why should they be hard to climb?' We know that matter attracts other matter, at the macro level. As this article shows, we've been able to detect the gravitational pull of tiny masses (tiny by macro standards). Since the macro world is made out of the quantum world, QM must somehow explain how gravity arises for particles. Until it does, there is a fundamental piece missing from our understanding of the universe, so any conclusion we draw from QM or GR must be taken with a large grain of salt. You can't say 'matter is excitation in a quantum field, why should it attract', that is exactly the problem: we know it attracts, so if e citations in a quantum field don't attract, it must mean that matter is something else. Note: mass is generally defined by E=mc^2, where energy is defined by conservation laws.

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.

terryf 6y ago

I guess kind of a similar expecation was in place for light as well - if you dim your light source then it emits less light waves. Well, turns out if you go small enough then you see it's actually individual packets of light with certain amounts of energy where the amount of packets (photons) sent out decreases as you turn down the intensity. So, the total amount of energy outputted still matches the input, but the output is in discrete packets, where each packet can exceed the level of input energy at a specific time. So, on a large scale everything seems fine but as you go to very small energy levels it starts to look different. I guess the expectation with gravity is that going to very small masses, some different underlying mechanism will appear. Or it may not. So they're trying to find out.

tsimionescu 6y ago

The problem is that QM doesn't account for gravity so far - in QM as it exists today, particles have mass, but do not interact through gravity. This fits experiments, which is not surprising given that any theory of gravity we have today predicts that the gravitational attraction between two masses that low would be much smaller than what we can measure (remember for example that a kitchen magnet's electromagnetic force can oppose the gravitational pull of the entire earth, that's how weak gravity is compared to other forces). Still, obviously large masses have gravity, so everyone expects that, even if we can't measure it yet, and don't know how to compute it yet, there must be some attraction between particles. There are some theories about it (for example string theory has something that looks like gravity), but since they all predict values much lower than we could hope to measure for now, the problem remains wide open. However, simply applying Newton's or Einstein's theories of gravity to QM doesn't work. In QM, particles don't have a single position in space and time, each particle is more like a wave with peaks at different points in space at the same time. If you try to compute the gravitational field generated by all these peaks you get nonsense results. So, while we generally believe that there must be some gravitational attraction between particles with mass, we don't know how it would look like. I think there are also some theories that predict that elementary particles do NOT interact through gravity, that gravity is somehow an emergent phenomenon of a collection of many particles (just like an elementary particle doesn't have a temperature, but a collection of many many particles does have one). I believe this is a pretty fringe theory, but not quite "flat earth" land. Just including it for completeness.

tumblewit 6y ago
This is what I find interesting. Assuming two quantum particles exert forces on each other. Now they both have mass but the forces they exert on each other are so much more powerful that the gravitational force would be impossible to experiment. Sort of like a man at a distance exerting gravitational force on the Milky Way with instruments the size of galaxy clusters to measure that man or force. Beyond mathematics there would be no experimental way. But my question is if mathematics itself says quantum particles do not have gravity or is that just a limitation of current understanding.
- 6y ago

ben_w 6y ago

> Question: Since mass exerts gravitation force, wouldn’t it mean that any mass of any size shape would do that? Yes. Absolutely everything should have a gravitational field. > What am I missing when they say quantum particles do not fit with gravity. Under Relativity, mass and energy are equivalent, therefore energy has a gravitational field. If you try to mathematically quantise the gravitational field the way the electromagnetic field was quantised (the latter giving you a photon, the former would be a graviton), then something goes wrong. This is where my grasp of the physics gets a bit hazy; I think you find any amount of gravity should produce more gravity, and this self-generation blows up to infinity rather than summing to a finite value. Or it might have something to do with the expected value of a corresponding zero-point gravity field? Or both? I’m not sure, I only do physics for fun. I keep thinking it’s a gravitational equivalent to the Ultraviolet Catastrophe, but if it was that simple someone would’ve already solved it.

HPsquared 6y ago
The Ultraviolet Catastrophe was solved by a complete rethink of the foundations (a shift from continuous to quantised energy). Perhaps the standard model needs a similar fundamental shift? (Though I have no idea what that would look like)
- reasonabl_human 6y ago
  Anecdotally, I agree. When you look at the history of major breakthroughs in physics, mainstream understanding narrows down on some complex analytical theories (rotating shells above the earth controlling the movement of the heavenly bodies, crazy complex math) when in reality there was a fork in the road decades prior where mainstream physics took a wrong turn (heliocentric! orbits!). Things like this are obvious in retrospect, but radical for their time.. most of the physics I learned was elegant and well-understood, then particle physics just... didn’t really feel the same way. Tons of gotchas and edge cases, difficulty generalizing problems, and the obvious disconnect between the physics of the small and that of the large... In time we’ll look back at current iterations of the standard model and our understanding of the physics of the small and wonder how those Neanderthals didn’t just realize that xyz was the key to make everything much simpler and work in harmony... that’ll be a fun day!

oceanghost 6y ago

Any mass, as currently defined, distorts space-time. Interestingly enough, velocity contributes to mass. That is to say, if we imagined two toy tops, one at rest and one spinning, the spinning top would have more mass due to its additional energy. Gravity is something like 10^32 power smaller than the next meaningful force. The problem with gravity is this-- At that resolution, we can't distinguish between two theories-- that mass warps space-time, or that there is a particle that mediates the force of gravity (a "graviton"). That is to say, is gravity analog or is it digital? If gravity is digital, there is a particle that is extremely small that transmits its force. If gravity is analog, then it changes the space around us itself and acts exactly the same way. So we have a question for the ages-- we have 17 to 25 quantum fields (depending on how you count) and, one, analog field, gravity. So, is gravity analog, or is it impossibly small digital field? For gods sakes is there a physicist out there, please correct me if I'm wrong. :-)

criddell 6y ago
So how is mass defined? Matter, as I understand it, is excitations of a quantum field. Why should they attract each other?
- stjohnswarts 6y ago
  Maybe it's centered around the particle's quantum density field aka the average position of the possible quantum positions?
- tsimionescu 6y ago
  This is somewhat like saying 'mountains are just the greyish areas on a map, why should they be hard to climb?' We know that matter attracts other matter, at the macro level. As this article shows, we've been able to detect the gravitational pull of tiny masses (tiny by macro standards). Since the macro world is made out of the quantum world, QM must somehow explain how gravity arises for particles. Until it does, there is a fundamental piece missing from our understanding of the universe, so any conclusion we draw from QM or GR must be taken with a large grain of salt. You can't say 'matter is excitation in a quantum field, why should it attract', that is exactly the problem: we know it attracts, so if e citations in a quantum field don't attract, it must mean that matter is something else. Note: mass is generally defined by E=mc^2, where energy is defined by conservation laws.