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I don't understand what you mean by conservation of gravity. Do you mean conservation of mass? There is literally nothing else than mass and some universal cons

I don't understand what you mean by conservation of gravity. Do you mean conservation of mass? There is literally nothing else than mass and some universal constants that determine the gravitational force. As for "no magnetic monopoles" - this one isn't actually a law, there's nothing in any of our physical theories that says you cannot have magnetic monopoles, it's just that experimentally nobody's ever found one (and we've looked pretty hard). It's important to note about magnetic monopoles that the magnets we know are not made up of magnetic monopoles, they are made up of magnetic dipoles. No matter how small pieces you break a magnet into, even going down towards atom-sized bits, the pieces still have a north and a south pole.

titanomachy 8y ago
Isn't divB=0 one of Maxwell's equations? That seems to be "one of our physical theories" claiming the impossibility of magnetic monopoles.
- semi-extrinsic 8y ago
  Ah, but this is indeed just us saying "hey, we don't see any monopoles anywhere, so let's simplify the equations to divB=0". The "full" equations have a divB={stuff that's perfectly symmetric to divE RHS}, and also a modified curlE term to make the "full" set of equations completely symmetric for electricity and magnetism. You can see these equations at https://en.wikipedia.org/wiki/Magnetic_monopole https://en.wikipedia.org/wiki/Magnetic_monopole
  - titanomachy 8y ago
    Interesting! I guess I've never learned much physics more recent than 1904.
- jeffwass 8y ago
  It’s perfectly possible to modify Maxwell’s equations to include magnetic monopoles. Doing so makes Maxwell’s equations more symmetric between electric and magnetic fields. The reason we have equation ∇·B=0 is due to empirical observation. https://en.m.wikipedia.org/wiki/Magnetic_monopole https://en.m.wikipedia.org/wiki/Magnetic_monopole
ars 8y ago
> I don't understand what you mean by conservation of gravity. Do you mean conservation of mass? I don't. Say you suddenly open a wormhole and gravitational force pours though. This would violate conservation of gravity since now there is gravity when before there wasn't. i.e. such a wormhole would be impossible. Or some kind of gravity shield that blocks any gravity from passing. Again, violates this rule. (It would have to deflect the gravity instead, so the total force doesn't change.) > there's nothing in any of our physical theories that says you cannot have magnetic monopoles It's not about having the monopole, it's about creating just one of them, and not creating both at once. I believe there is a conservation of magnetism law that would prevent that, analogous to conservation of charge (you can not create just one charge, both a plus and minus need to be created together).
- semi-extrinsic 8y ago
  > Say you suddenly open a wormhole and gravitational force pours though. This would violate conservation of gravity since now there is gravity when before there wasn't. Note that you can replace "open a wormhole" by "suddenly introduce a mass" and this statement is the same. In practice, both "introducing a mass" and "opening a wormhole" cannot be done instantly unless you violate conservation of energy, and as Einstein told us, energy also introduces gravitational force. So as you're turning the wormhole on, you would see the gravitational field increasing slowly and in accordance with conservation of mass and energy. There's no additional "conservation of gravity". > It's not about having the monopole, it's about creating just one of them, and not creating both at once. Ah, but this is conservation of magnetic charge. In a world where magnetic monopoles exist, this follows directly from the "full" Maxwell's equations, just like electric charge conservation does. See https://en.wikipedia.org/wiki/Maxwell's_equations#Charge_conservation https://en.wikipedia.org/wiki/Maxwell's_equations#Charge_con... But the point is, we can't even create two magnetic monopoles in a way that conserves total magnetic charge. We literally need a new fundamental particle for this to happen.

titanomachy 8y ago

Isn't divB=0 one of Maxwell's equations? That seems to be "one of our physical theories" claiming the impossibility of magnetic monopoles.

semi-extrinsic 8y ago
Ah, but this is indeed just us saying "hey, we don't see any monopoles anywhere, so let's simplify the equations to divB=0". The "full" equations have a divB={stuff that's perfectly symmetric to divE RHS}, and also a modified curlE term to make the "full" set of equations completely symmetric for electricity and magnetism. You can see these equations at https://en.wikipedia.org/wiki/Magnetic_monopole https://en.wikipedia.org/wiki/Magnetic_monopole
- titanomachy 8y ago
  Interesting! I guess I've never learned much physics more recent than 1904.
jeffwass 8y ago
It’s perfectly possible to modify Maxwell’s equations to include magnetic monopoles. Doing so makes Maxwell’s equations more symmetric between electric and magnetic fields. The reason we have equation ∇·B=0 is due to empirical observation. https://en.m.wikipedia.org/wiki/Magnetic_monopole https://en.m.wikipedia.org/wiki/Magnetic_monopole

ars 8y ago

> I don't understand what you mean by conservation of gravity. Do you mean conservation of mass? I don't. Say you suddenly open a wormhole and gravitational force pours though. This would violate conservation of gravity since now there is gravity when before there wasn't. i.e. such a wormhole would be impossible. Or some kind of gravity shield that blocks any gravity from passing. Again, violates this rule. (It would have to deflect the gravity instead, so the total force doesn't change.) > there's nothing in any of our physical theories that says you cannot have magnetic monopoles It's not about having the monopole, it's about creating just one of them, and not creating both at once. I believe there is a conservation of magnetism law that would prevent that, analogous to conservation of charge (you can not create just one charge, both a plus and minus need to be created together).

semi-extrinsic 8y ago
> Say you suddenly open a wormhole and gravitational force pours though. This would violate conservation of gravity since now there is gravity when before there wasn't. Note that you can replace "open a wormhole" by "suddenly introduce a mass" and this statement is the same. In practice, both "introducing a mass" and "opening a wormhole" cannot be done instantly unless you violate conservation of energy, and as Einstein told us, energy also introduces gravitational force. So as you're turning the wormhole on, you would see the gravitational field increasing slowly and in accordance with conservation of mass and energy. There's no additional "conservation of gravity". > It's not about having the monopole, it's about creating just one of them, and not creating both at once. Ah, but this is conservation of magnetic charge. In a world where magnetic monopoles exist, this follows directly from the "full" Maxwell's equations, just like electric charge conservation does. See https://en.wikipedia.org/wiki/Maxwell's_equations#Charge_conservation https://en.wikipedia.org/wiki/Maxwell's_equations#Charge_con... But the point is, we can't even create two magnetic monopoles in a way that conserves total magnetic charge. We literally need a new fundamental particle for this to happen.