What is the reason for mass defect in a nuclide?

[maline]

No offence but being 'slightly' patronising is more likely to scare people away and I think people expect answers to be of a high standard if they ask them. I appreciate what you're saying but frankly, any help is gratefully received. Just because he put some maths in there doesn't make it a demanding answer, proton numbers and atomic mass numbers are not new and a concise formula can be quite enlightening.

I stand corrected and apologize.

Also, perhaps my answer seems less patronising now that I wrote the actual post. I had accidentally clicked "post reply" after only writing the p.s. :-)

 

[maline]

Zero energy, as far as General Relativity is concerned, is a patch of flat Minkowski space.

Doesn't that demonstrate my point? Einstein wrote one of the greatest equations in history, describing how curvature depends on energy/momentum/stress. But ask "is the energy zero, positive, or negative?" and the best available answer is "check whether the spacetime is flat"! Can we really be satisfied that we have a concept of energy?

 

[Anonymous Vegetable]

Zero energy, as far as General Relativity is concerned, is a patch of flat Minkowski space.

You've made your point hahaha.

 

[Anonymous Vegetable]

I stand corrected and apologize.

Also, perhaps my answer seems less patronising now that I wrote the actual post. I had accidentally clicked "post reply" after only writing the p.s. :-)

And I too apologise if I sounded a bit defensive there. I appreciate you taking the time to answer and sorry for any misunderstanding.

 

[vanhees71]

p.s Vanhees91, with all due respect, I think you could be a bit gentler on a high-school kid. The main result of a detailed answer full of unfamiliar terms will be to scare kids away from the forum...

Ehm, if what I wrote is unfamiliar to high school students, I'm really even more worried about the state of our schools (world wide) than I was before. So what's supposed to be unfamiliar?

 

[maline]

On rereading, your post is much lighter than I thought. I apologize. The discussion of lattice-QCD could be a bit scary though, depending on the reader's attitude.

 

[nikkkom]

Doesn't that demonstrate my point? Einstein wrote one of the greatest equations in history, describing how curvature depends on energy/momentum/stress. But ask "is the energy zero, positive, or negative?" and the best available answer is "check whether the spacetime is flat"! Can we really be satisfied that we have a concept of energy?

Don't know about you, but for me this answer is acceptable. GR says that region of zero energy must be flat (and thus, necessarily empty) Minkowski space. It does not require any stretch of imagination to declare that empty space has zero energy.

 

[maline]

It does not require any stretch of imagination to declare that empty space has zero energy.

Certainly, empty space has zero (local) energy. But is that the only possible situation with zero energy? If so, why?

 

[vanhees71]

Well, gravitational waves are solutions of the source-free Einstein equations, i.e., a spacetime with zero energy. See, e.g.,

http://www.itp.kit.edu/~schreck/general_relativity_seminar/Gravitational_waves_in_general_relativity_exact_plane_waves.pdf

 

[maline]

Well, gravitational waves are solutions of the source-free Einstein equations, i.e., a spacetime with zero energy.

That's why I mentioned local energy- to avoid the complications of "gravitational energy". I am more interested here in how the energy density- the (0,0) element of the Stress-Energy Tensor- can be defined without reference to gravity or to particular examples. Also whether this density can ever be negative, because to me, that is a determining factor in whether energy can be thought of as a "substance".

 

[Vanadium 50]

Uh, everyone, this thread is marked "B". Maybe we don't need to go down the GR rabbit hole?

 

[maline]

Yes, I suppose the question about defining energy should really be a separate thread. I will start it now.

 

[Anonymous Vegetable]

Yes, I suppose the question about defining energy should really be a separate thread. I will start it now.

Thanks for the help everyone anyway and enjoy your rabbit hole hahaha.

 

[vanhees71]

Uh, everyone, this thread is marked "B". Maybe we don't need to go down the GR rabbit hole?

Well, how do you want to discuss gravitational waves without GR? It's like asking to discuss electromagnetic waves without reference to Maxwell ;-)). SCNR.