Comment by oceanghost | Hacker News Reader

Comment by oceanghost | Hacker News Reader

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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. :-)

I'm not really a physicist, but I can suggest better terms than "analog" vs "digital." The words you're actually looking for are "continuous" vs "quantized."

So how is mass defined? Matter, as I understand it, is excitations of a quantum field. Why should they attract each other?

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.

Thanks for taking my question seriously.

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?

I'm pretty sure we are not yet equipped to answer this question. In the end, QFT and QM are extraordinarily successful mathematical models that predict to extreme precision the behaviors of small numbers of particles interacting.

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.

Note: when I'm comparing "describing reality" vs "approximation", I'm thinking of the following examples:

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.

Maybe it's centered around the particle's quantum density field aka the average position of the possible quantum positions?

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