## Schrodinger 3 years ago For s&g/the sake of knowing: If the universe, for some crazy reason, was completely devoid of gravity, would we able to find the mass of anything? I'm aware that we can measure the mass of objects in a massless environment by using a spring and looking at T=2(pi)(sqrt(m/k)), but that's based on the fact that we know the spring constant, as far as i'm aware, from experiments utilizing gravity on earth.

1. Schrodinger

(i.e. So what would happen if we didn't know the spring constant beforehand, and we couldn't, at least through gravity.)

2. Algebraic!

inertia, things have mass independent of a local gravity field.

3. Schrodinger

? Could you explain some more? :/

4. Schrodinger

(I'm aware they still have mass, but I don't know if we could measure it.)

5. Algebraic!

imagine an electron and a proton in deep space far away from any g field. the exert a force on each other. based on that force they accelerate according to F=ma.

6. Schrodinger

Okay. So, inertia based on electrical properties? So, question on top of that, without electrical properties, would there be any way?

7. Algebraic!

it's mass: the 'resistance' to change in velocity

8. Schrodinger

Not sure what the implications were of you just said.

9. Algebraic!

mass is intrinsic to particles. you don't need the* force of gravity to measure it. there are 4 forces, any of them will do.

10. Schrodinger

Okay, so would it to be accurate to say that within the realm of classical mechanics, disavowing nuclear forces (I should've prefaced this with me saying that the experiment you would do to find out something's mass would be macroscopic, and relatively "intuitive" as opposed to quantum mechanics), EM and Gravity are the only ways you could find something's mass?

11. Algebraic!

a collision would probably do the trick too. collisions are problems involving mass and velocity that you can solve...

12. Schrodinger

Could you give me a physical example of this (and relate the math to it, i'm guessing (blatantly assuming) you're talking about \[1/2mv ^{2} _{(1)} + 1/2mv ^{2} _{(2)} = E\] or something very closely related? The reason I ask is I think, and again, this is just a thought, that most of the variables involved in elastic collisions are somehow derived through mass or dependent on mass. I'm also just taking a second. \[v = d/t\] Okay, so you can determine velocity without mass. That could account for the velocities of both objects. So from here what could you do, using this equation, (assuming that what you would do) to figure out an object's mass?

13. Schrodinger

(By the way, thanks for this. I don't mean to be a bother by making this a super long thread or anything.)

14. Algebraic!

momentum and energy are conserved in ideal collisions, so you could find mass if you measured velocities before and after the collision.

15. Schrodinger

So, using: \[1/2mv ^{2} _{(x1)} + 1/2mv^{2} _{(y1)} = 1/2mv ^{2} _{(x2} + 1/2mv ^{2} _{(y2)}\]Mass could be determined. Just being totally clear.

16. Algebraic!

that's conservation of energy, momentum is conserved also. in fact momentum is conserved in any collision, KE is just conserved in elastic collisions.

17. Algebraic!

it's all interrelated anyway, you can't really get away from any one part of it. a particle is an excitation of 5 fields, it's a resonant excitation, it's stable and propagates. because only certain resonances can be stable, it couples very precisely to fields based on a charge. coupling to the EM field gives the traditional notion of charge: electric charge, coupling to the strong field gives 'color' charge, coupling to the Higg's field gives mass 'charge' (it's a little different than the charges of the other four fields). it's really just a bundle of coupling constants, and each constant defines a set of properties. coupling to the higg's field defines its mass.

18. Algebraic!

the fields make up space, (the exist even when there are no particles around), the way the space (fields) are bent by mass (the coupling to the higg's field) makes the gravitational force...

19. Schrodinger

O.O I'm not at Higgs-field/Higgs Boson level stuff other than a very basic conceptual understanding. All I know at this point in the convo is that while the Higgs Field is likely, it's still hypothetical and is at odds with SUSY regarding explaining dark matter.

20. Schrodinger

(Despite this summer and CERN.)

21. Algebraic!

well, they found the boson, and honestly, not much would work without the higg's field, mass would just be a random weird thing, two identical electrons could have wildly different masses for no particular reason...

22. Algebraic!

or no mass at all...

23. Schrodinger

They likely found the Boson, last I heard. It's overwhelmingly likely that they did, but it's not definite. I have to ask, do you know any of this stuff through your career/major/what you generally dedicate your life to, or are you just really good at Physics? lol.

24. Algebraic!

armchair physicist / electrical engineer

25. Schrodinger

YES that's exactly my double major! But i'm a freshman so I don't know what i'm doing yet, XD. Well, anyways, thank you for a very thought provoking convo and all, That gave me a pretty solid answer of my question until it got into stuff I don't understand yet.

26. Algebraic!

here's something you might not know that's related. the schrodinger wave equation, the one that describes a particle's probability to be in certain distribution or propagate... it's actually an expression of F=ma: it's the space derivative of energy = the time derivative of momentum: potential = -constant*ma !

27. Schrodinger

Well, again, thank you very much! (And yeah, I didn't know that.)