Is energy of universe constant?

Question

First of all please do not flag this question as duplicate(I have read all the others like this one, this one and this one is just talking about observable universe. none of them talked in this context) read it completely.

There is not any proof that energy remains constant for universe just evidence for a observable scale

Then why does thermodynamics and conservation laws states that energy of our universe remains constant. As there might be some other phenomenon that remains unobserved (I have an Idea for one but noone is ready to listen. You can comment if you want to).

And why aren't we trying to focus on some experiment that can calculate if energy of our universe is constant or remains same or not constant. (If there is already an experiment going on then please do tell)

Edit-

There were some users who have already asked this question but they are simply asking why but I am thinking that if we take conservation laws into account for our universe and there should be two outcomes

1. If energy is constant then we should leave the thoughts about parallel universe but if

2. the energy is not constant(increasing or decreasing) then we can think of enrgy being drained or sucked by our universe from some other universe(MOST PROBABLY).

Answer 1

"Then why does thermodynamics and conservation laws states that energy of our universe remains constant?"

Because this refers only to any local region of the universe for a period of time small relative to the age of the universe, rather than to the universe as a whole during its entire lifetime. The dynamics of the expanding universe prevents conservation of energy within the whole universe as one single collection of stuff. This is the case even if the universe is finite.

Answer 2

surely if we do an experiment and if the consequence comes out that the energy is constant

We do experiments in the laboratory, which can be a few meters long or even two laboratories thousand of kilometers away from each other, but still the dimensions are the dimensions of the earth. With these experiments conservation of energy is always shown to be true , so we have made it a law in our theories. Laws are extra axioms imposed on the mathematical model to chose solutions of equations with that describe natural phenomena and , very important, predict new.

then the thoughts about the parallel universe will have almost no chances but for the case the energy is not constant.

To really understand the mathematics of the models for parallel universes needs a lot of study, and it depends on the model .

As I read an article that the temperature of the universe is increasing

That article is using a different definition of temperature of the universe than the cosmological models you try to discuss.

then we can talk about the existence of parallel universe or antiuniverse. And the (most accepted theory of origin of our universe. The big Bang that had an ambiguity of who kept the mass at point of

All these models depend on very formal mathematical theories which maybe you will study in the future. At the moment it suffices to say that there exist at present different models, some expressed well with mathematical theories fitting observations , and some, like the many worlds one being mathematical games at present because there are no testable predictions.

At the size of the universe the law of conservation of energy with General Relativity is no longer a law, so it is not possible to extrapolate from earth like systems to the whole universe.

One uses general relativity and quantum mechanics in order to build models that describe astrophysical observations, the Big Bang being the dominant model. When the models succeed in describing existing data, one can extrapolate the mathematics for regions that are not observable now, but might become observable in the future, allowing to distinguish between models.