Mass/Energy Creation and Conservation

  • Context: Undergrad 
  • Thread starter Thread starter Nugso
  • Start date Start date
  • Tags Tags
    Conservation Creation
Click For Summary

Discussion Overview

The discussion revolves around the concepts of mass and energy conservation, particularly in the context of their origins and the implications of various physical theories, including relativistic and non-relativistic mechanics, as well as cosmological models. Participants explore questions about the creation of energy, the conservation of mass in chemical reactions, and the nuances of energy conservation in general relativity.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants question how energy was created at the beginning of the universe, particularly in relation to the Big Bang.
  • There is a discussion on whether mass is conserved in closed systems, with references to chemical reactions and particle annihilation.
  • One participant notes that while energy is conserved in both relativistic and non-relativistic mechanics, mass conservation applies only in non-relativistic contexts.
  • Another participant mentions that mass is not conserved during processes like electron-positron annihilation, although energy and momentum are conserved.
  • There is a reference to the lack of a global energy conservation principle in expanding cosmological models within general relativity, emphasizing local conservation instead.
  • Some participants express uncertainty about the implications of these concepts and the nature of energy in cosmological contexts.

Areas of Agreement / Disagreement

Participants generally agree that energy conservation is a fundamental principle, but there is disagreement regarding the conservation of mass, especially in the context of particle interactions and cosmological models. The discussion remains unresolved regarding the origins of energy and the implications of mass conservation in various scenarios.

Contextual Notes

Limitations include the dependence on definitions of mass and energy, the unresolved nature of cosmological models, and the complexities surrounding the concept of energy conservation in general relativity.

Nugso
Gold Member
Messages
170
Reaction score
10
Hello everyone. First of all, I should like to apologize if the question I'm going to ask looks so ridiculous. As far as I know, energy can't be destroyed or created. It only changes forms. So far so good, but how in the beginning did it occur? How was it created? Where/How did the first energy come?


My second question is about the conservation of mass. Is mass really conserved? In closed systems? I don't think it really is converted. ( Speaking in terms of the today's matter explanation) Basically, what I've learned in high school is that it's conserved.( Like in C + O2 -> CO2) Is mass conserved in that? Or by saying mass is conserved, are we talking about mass-energy is conserved? ( Electron + Positron -> Photon)
 
Space news on Phys.org
Nugso said:
Hello everyone. First of all, I should like to apologize if the question I'm going to ask looks so ridiculous. As far as I know, energy can't be destroyed or created. It only changes forms. So far so good, but how in the beginning did it occur? How was it created? Where/How did the first energy come?


My second question is about the conservation of mass. Is mass really conserved? In closed systems? I don't think it really is converted. ( Speaking in terms of the today's matter explanation) Basically, what I've learned in high school is that it's conserved.( Like in C + O2 -> CO2) Is mass conserved in that? Or by saying mass is conserved, are we talking about mass-energy is conserved? ( Electron + Positron -> Photon)

While energy is conserved in both relativistic and non-relativistic mechanics, mass is only conserved in non-relativistic mechanics. This includes chemical transformations as the speed of the valence electrons is low compared with the speed of light, but not electron positron anihilation.
 
  • Like
Likes   Reactions: 1 person
DrDu said:
While energy is conserved in both relativistic and non-relativistic mechanics, mass is only conserved in non-relativistic mechanics. This includes chemical transformations as the speed of the valence electrons is low compared with the speed of light, but not electron positron anihilation.

Thanks, DrDu. So in non-relativistic mechanics such as closed or open systems, mass are conserved.

By the by, where/how did the first energy come from? We say it cannot be destroyed or created, but in fact at some point when the universe was created( Big Bang), it also came into play, but how?
 
Nugso said:
So far so good, but how in the beginning did it occur? How was it created? Where/How did the first energy come?

Drumroll! You have unlocked the next level in the game. Welcome to open questions in cosmology. There are different hypotheses (note: hypotheses) beyond the Big Bang - you can have a look at this section as an introduction.

Nugso said:
My second question is about the conservation of mass. Is mass really conserved?

Like DrDu mentioned, mass is not conserved in annihilation and pair production (but energy and momentum is conserved).

Nugso said:
First of all, I should like to apologize if the question I'm going to ask looks so ridiculous.

No, it's not ridiculous, these are good questions IMO. But if I could answer what happened at (or, hypothetically, before) the Big Bang, you should award me a Nobel Prize :smile:.
 
Last edited:
  • Like
Likes   Reactions: 1 person
DennisN said:
Drumroll! You have unlocked the next level in the game. Welcome to open questions in cosmology. There are different hypotheses (note: hypotheses) beyond the Big Bang - you can have a look at this section as an introduction.

Thanks for the link DennisN! Though I don't think I'll ever be able to answer those questions, they're really worth reading and thinking about.





DennisN said:
Like DrDu mentioned, mass is not conserved in annihilation and pair production (but energy and momentum is conserved).

So, the law of conservation of mass is like the laws of Newtons. They're correct to some extent.


DennisN said:
No, it's not ridiculous, these are good questions IMO. But if I could answer what happened at (or, hypothetically, before) the Big Bang, you should award me a Nobel Prize :smile:.

Who knows, maybe you'll one day win!

Thanks for the answer by the way. :biggrin:
 
There is no notion of global energy conservation for expanding cosmological models (e.g. Friedmann models) in general relativity. In order to even define a physically meaningful notion of the total energy of a space-time you need asymptotic flatness, which the Friedmann models don't have. Energy is only conserved locally in general.
 
  • Like
Likes   Reactions: 1 person
Hi WannaBeNewton, thanks for the answer, but what did you mean by "conserved locally in general"?
 
What I mean is that we always have a differential conservation of energy (to put it loosely, one that holds in arbitrarily small regions) even for expanding cosmological models but only a special class of space-times (of which expanding cosmological models do not belong to) have a physically meaningful notion of total energy and global energy conservation (global in the sense that it includes everything-it is an integral relationship over all of space).
 
  • Like
Likes   Reactions: 1 person
Oh, okay! Thanks for the explanation.
 

Similar threads

Undergrad "Energy is not conserved" vs. energy is conserved: Friedmann Equations
  • · Replies 17 ·
Replies
17
Views
6K
High School Conflict between the conservation of matter and the rapid expansion of our universe
  • · Replies 18 ·
Replies
18
Views
2K
Undergrad Is energy conserved during the formation of local systems?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Conservation of energy in quasar outflows?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Conservation of energy in cosmology
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Conservation of energy in an expanding universe
  • · Replies 10 ·
Replies
10
Views
2K
High School Red shifted tired light doubts
  • · Replies 10 ·
Replies
10
Views
2K
Undergrad Dark energy and conservation of energy
  • · Replies 20 ·
Replies
20
Views
3K
High School Questions about Noether's theorem -- Conservation of Energy and Mass
  • · Replies 9 ·
Replies
9
Views
1K
Undergrad Does mass conservation correspond to a pseudo-symmetry?
  • · Replies 6 ·
Replies
6
Views
2K