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.
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.
The maths of QM (Schrodinger equation, standard model) currently say that particles don't have gravity. But, they also imply that nothing has gravity - gravity doesn't exist at all according to the standard model. Obviously this is wrong, so we are searching for a theory of Quantum Gravity.
There are various pieces of math that do have gravity and are consistent with standard QM, but each of them has various other problems, so none is universally accepted, and they vary significantly in how they add gravity to the standard model.
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.
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.
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!
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. :-)
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.
I guess I get hung up on the quantum field part because I don't understand what exactly a quantum field is in a physical sense. I get that there's a mathematical concept of a quantum field, but does that map to something concrete? Is everything essentially made of nothing?
Whether they are directly describing reality or some kind of approximation remains an open question. I believe that some progress on the measurement problem, when it happens, could help point in this direction.
1. An account for how the world actually works are Newton's laws of motion - they describe how exactly objects interact and how it affects their movement. It is of course an approximation, and only works at certain scales and speeds, but it describes mathematically the phenomena that we can see happen.
2. An alternative account that gives the same values is Hamiltonian mechanics, which describes the system in terms of how its energy changes over time in certain coordinates. They both give the same predictions, and Hamiltonian mechanics is more suited for actually computing the motion of complex systems, but it is much more abstract and doesn't give a clear account of how the system actually works.