Physics in general always talks about energy conservation. We say that energy can nether be created nor destroyed but can only be transformed or transferred which elaborates the total to remain always be the same. But did you know that it sometimes does not match precisely? Yes in extreme cases such as cosmic time scale it is found so. Conservation of energy theory happens to be true most of the time but every theory has its limits. We humans would like to categorize or classify things in order to explain or study things much easier. However universe tends to create things that always breaks the rule.
1882-1935 (Image – Wikimedia)
Energy conservation laws emerge from profound and simple truths about the basis of reality or fundamental symmetries of the nature. The relationship of conservation law and symmetry is explained by a theory called Noether’s theorem. That was three years after the blossom of Einstein’s general theory of relativity.
Way back in 1915 Einstein’s general theory of relativity answered that the energy is not always to be conserved. On the other hand a phenomenon called the cosmological red shift happens to explains that when universe expands space and wave length tends to increase. As a result energy of each photon drops. Where had it gone?
Before the red shift concern was understood Emmy Noether found out that why the theory of conservation broke down on the theory of relativity. She realized that all conservation laws have much fundamental theory and it was named as Noether’s theory. It was summarized in a manner saying that every continues symmetry of the universe there exist a conserved quantity.
It is said that someone’s face is symmetry if the other half of the face looks the same at a mirror reflection. Snow flex symmetry lays in 60 degree rotation while playing cards got 180 degree rotation.
Actually speaking single flip by an axis or rotation by specific number all these comes under discreet symmetry. But Noether’s theory speaks about continues symmetries. Which means something will be continually symmetric if it remains the same for any size shift in a given coordinate. In another way it says all conserved quantities such as energy, charge or momentum are the result of some variance or symmetry in the universe.
A continually long flat road or a rotational sphere could be considered as perfectly symmetrical. If the road consists of ups and downs, the momentum of collision on two moving objects along this road is not conserved. That is because the momentum could vary according to the gravitational field due to the fact that the direction of the gravitational field changes with the direction of the ups and downs of the hill. It is not symmetric to translations along the road.
Time translation in variance tells that we get the same result no matter when we do it or how many times we do it. But for large time scales this will not be true.
Einstein’s in his theory of gravity explains that detentions of space and time could be dynamic. This means that they tend to very. If nature of space varies over time then the time continuous symmetry is broken. That’s what happens when the universe gets expanded. Energy could be lost because of the costmological red shift. Cosmic microwave background (CMB) is the light which existed in the early days of the universe. That particular light still happened to be travelling ever since and was energetic in the region of visible light initially. Since it was travelling even under the expansions of universe the characteristic of light later found to be shifted to the microwave region of the spectra of light which is found to be not visible any more but has reached the lower energies. That means it has lost its energy over time. The energy is considered as gone. In the mean time we know that the other major part of the universe constitutes to dark energy. So maybe it has to be there. But as the universe expands the dark energy also expands to maintain the energy density (energy for unit volume). If Energy (E)/Volume (V) equation is considered when volume increases the energy should also be increased. The interesting part of this is that it was found that the dark energy increases at a higher rate than cosmic microwave background loses its energy. So there is a net energy gain.
On the other hand even “Landau Lifshitz Pseudotensor” equations tries to save the energy conservation law by the entire universe’s gravitational potential energy to offset the gains and losses of dark energy and red shift. Although it is found to be controversial with its given application and interpretation.
Noether’s theorem applications allow physicists to gain powerful insights into any general theory in physics, by just analyzing the various transformations that would make the form of the laws involved invariant. The Noether charge is also used in calculating the entropy of stationary black holes.
So it is concluded with the laws of physics saying that the conservation theory could be applied only for a narrow time space but not for a large time space phenomena.
References
- Law of conservation of energy – https://energyeducation.ca/
- Simple applications of Noether’s first theorem in quantum mechanics and electromagnetism http://philsci-archive.pitt.edu/
- Symmetry, Structure and Spacetime – Sciencedirect.com
- https://www.britannica.com/science/cosmic-microwave-background/Isotropy-in-the-cosmic-background
