# Aside from Noether's theorem, what other concepts would explain energy conservation?

Energy is defined more in the mathematical sense, and tends to show true with observations in the physical world.

But why is energy conserved aside from "Noether's theorem"?

In a closed system that has an energy $E$, we know that system will always have this much energy, but why?

In the cosmological scale I heard that energy is not conserved, why?

Is the universe creating more energy?

OR

Is the expansion of the universe due to the energy at the beginning that caused it's creation?

Could anyone explain their point in layman terms? Without using difficult Mathematics, I'm not as "qualified" to understand such rigorous equations yet.

Energy is defined more in the mathematical sense, and tends to show true with observations in the physical world.

You are putting the cart before the horse in the above statement. Conservation of energy is an experimental fact, as is conservation of momentum. The mathematics came in order to model this experimental fact, and Noether's theorem is the most elegant form

But why is energy conserved aside from "Noether's theorem"?

Energy is conserved in local sense because it is an experimental fact, once special relativity solved the nuclear problem. In a sense we have defined energy so that it is conserved, have found mathematics that describe the situation, and the mathematical theory is validated continually with all the data and the new observations.

In a closed system that has an energy E, we know that system will always have this much energy, but why?

It is an experimental fact, having formulated all the types of energy, potential, internal, chemical, nuclear so tat the statement is true and can be fitted by the theories that have been developed.

In the cosmological scale I heard that energy is not conserved, why?

This is true in some cases because conservation requires a unique definition of time (quantities are conserved in time), and general relativity introduces deformations in time. When looking at local environments, the observations of energy conservation still hold.

Is the universe creating more energy?

As with all other conundrums when experimentally energy seemingly was not conserved, new energy forms were postulated, ( as with nuclear energy and the special relativity frameworkd) a new form of energy ( mass as energy) was defined that helped in keeping conservation of energy strict and true. In the cosmological scene the job is taken up by what is called "dark energy", but as I said the concept of energy is still under discussion in proposals for different cosmological models and boundary conditions.

OR

Is the expansion of the universe due to the energy at the beginning that caused it's creation?

Well, dark energy and inflation are tied up together in the current Big Bang model. It is still a main point of research in astrophysics.

• Very nice and comprehensive answer. +1! – Neuneck Jun 12 '14 at 8:09
• What about variables being a function of time? For example: Velocity of an object being a function of time, or electric current being a function of time due to Noether's theorem we know that energy is conserved. What confuses me, even if we have a function of time, how can time and symmetry relate to conservation of energy here is where I struggle to understand. – Pupil Jun 12 '14 at 15:29
• When you start using complicated systems, as for example systems with friction where the velocity changes with time, you introduce differential changes in time that will pick up the slack. For friction it is heat that is generated and has to be added to the budget, which will be constant if summed up over all forms. Energy is not only kinetic energy. – anna v Jun 12 '14 at 16:46
• Basically any positive force applied over a distance that is +work there follows a negative force that does -work? That makes more sense than ever. When we do work, there has to be an opposing force, yet if there is "ever" a +force adding to that +work, its another energy source, what if a + force exited that just makes no sense, and that is considered "impossible". – Pupil Jun 12 '14 at 21:15
• Things are considered impossible because we have never seen/measured them and the mathematical models we have developed to fit and predict our measurements are never falsified. If we ever have an excess in the energy budget that falsified energy conservation, we would change the mathematical models to include a new form of energy in the mathematical framework, if at all possible. This method has worked up to now. – anna v Jun 13 '14 at 3:17