Answer to Question #113193 in Classical Mechanics for Lizwi

Question

Which statement best describes the relationship between matter and energy in the universe?
1 : Changes of mass to energy and energy to mass are observable in all chemical reactions.
2 : The sum of mass and energy in the universe is increasing over time
3 : Matter and energy can be converted from one to the other, but their sum stays constant.
4 : The sum of mass and energy in the universe is decreasing over time

Answer 1

As per the given statement in the question over the relationship between matter and energy in the universe

1. In the chemical reaction, no mass added or taken away from the system. So total mass of the chemical elements always stay same. In any chemical reaction, mass of the reactant is getting convert into the product of the reaction so it is changing form one form to another form hence statement is not describing the true relation.

2. The total energy of the universe is increasing such that the energy inherent of space-time is kept constant as the universe expands. It is like, in order to build an extra cubic kilometer of space-time you need this quanta of energy. No more and no less. This energy has to come from somewhere.

3.The total energy of the universe is remain constant, it can change from one form to another form but as per the first law of thermodynamics, energy neither can be produce nor can be destroy, it can change one form to another but it will always remain constant.Hence it is describing the true relation.

4.As per the third statement, energy of the universe always be conserve. hence the statement 4 is incorrect.