# Conservation law: Wikis

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# Encyclopedia

In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves.

One particularly important physical result concerning conservation laws is Noether's Theorem, which states that there is a one-to-one correspondence between conservation laws and differentiable symmetries of physical systems. For example, the conservation of energy follows from the time-invariance of physical systems, and the fact that physical systems behave the same regardless of how they are oriented in space gives rise to the conservation of angular momentum.

A partial listing of conservation laws that are said to be exact laws, or more precisely have never been shown to be violated:

There are also approximate conservation laws. These are approximately true in particular situations, such as low speeds, short time scales, or certain interactions.

## References

• Victor J. Stenger, 2000. Timeless Reality: Symmetry, Simplicity, and Multiple Universes. Buffalo NY: Prometheus Books. Chpt. 12 is a gentle introduction to symmetry, invariance, and conservation laws.

# Simple English

A conservation law is a statement used in Physics that says that the amount of something does not change in time. That thing could be as simple as mass or charge, or something that has to be calculated, like energy, or angular momentum.

For example, the "law of conservation of mass" is the conservation law that says that the amount of mass is always conserved, even if it is changed into another form. This means that if the mass of the universe could be measured right now, its mass would be known tomorrow because it will not change.

## History

For a long time, people thought that these laws were true for the amount of mass and energy in the universe. Later on, Albert Einstein said that they were not completely true. He said that mass could change into energy (or the other way around). If this happened, it would be against the conservation laws because if mass was changed into energy, the total amount of mass goes down, and the total amount of energy goes up.

Einstein said that conservation laws could still be used if all the mass and all the energy were combined. He said that even though the mass changes or the energy changes, the sum when they are added together does not change. So now there is just one conservation law for mass and energy together.

### Problems

Of course, mass is measured in kilograms, and energy is measured in joules. They cannot be added together directly, but Einstein found a way to add them together. He created the equation $E=mc^2$. This equation means is that before adding the amount of mass to the amount of energy, the mass must be multiplied by the speed of light and then by the speed of light again.

## Purpose

Some of the things that are thought to be conserved are:

Conservation laws are helpful for people when they do problems in Physics. This is because if they know that a thing is conserved, it gives them more mathematical information about the thing they are doing the problem about.

Because science does not know where consciousness originally comes from, some mystic philosophers have guessed that there may also be a "law of conservation of consciousness" in the universe. That is to say, when something loses consciousness, or dies, that consciousness may not disappear, but may go into some kind of unseen pool of consciousness, according to this idea.

## Types of Conservation laws

Conservation laws can come in two types, global, or local.

### Global conservation

A global conservation law just says that the total amount of something in the universe does not change in time.

### Local conservation

A local conservation law says a little bit more than that. It says that if the amount of something changed in one place, it's because it moved in to or out of that place, and we can measure that movement.