How do we know the real size of the space in the Universe? Is it finite or infinite?

[Dandav]

Unfortunately, I couldn't find real answer for this question.

After long thinking, there is a possibility that the answer was always there Infront of our eyes.

That answer is called CMBR.

https://en.wikipedia.org/wiki/Cosmic_microwave_background

The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe

So, it is all about Microwave radiation.

What is Microwave?

https://en.wikipedia.org/wiki/Microwave

Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz and 300 GHz, 

Microwaves are non-ionizing radiation, which means that microwave photons do not contain sufficient energy to ionize molecules or break chemical bonds, or cause DNA damage, as ionizing radiation such as x-rays or ultraviolet can.^[25] The word "radiation" refers to energy radiating from a source and not to radioactivity. The main effect of absorption of microwaves is to heat materials;

All warm objects emit low level microwave black-body radiation, depending on their temperature, so in meteorology and remote sensing, microwave radiometers are used to measure the temperature of objects or terrain.^[17] The sun^[18] and other astronomical radio sources such as Cassiopeia A emit low level microwave radiation which carries information about their makeup,

Hence, All warm objects (including any star, warm Pulsar, BH, planet and moon) emit low level microwave black-body radiation

There are billions of objects just in our MW galaxy. 

Each object emits low level microwave black-body radiation

If we could set the MW galaxy in a some sort of a giant oven, that microwave black-body radiation could stay there and eventually heat the entire giant oven while keeping the black body radiation.

In the same token, we could set any nearby galaxy in a similar oven and get also there a black-body radiation in its CMBR.

There is no limitation for the oven size.

Therefore, we can set each nearby galaxy in an oven so their external walls would touch our galaxy' oven.

Let's assume that we have 9 ovens in the same size touching each other.

If we will eliminate the internal walls of those ovens, we would get a 9 times bigger oven while keeping the black-body radiation in the CMBR.

There are billions of galaxies in the observable universe. Hence, if we could keep all of them in a single oven it will still keep the black-body radiation in the CMBR.

However, once we eliminate the oven, we would lose the black-body radiation in the CMBR.

Now, let's assume that the space in the universe has only three real dimensions and it is infinite, while the number of the galaxies is finite.

In this case, as the number of the galaxies is limited and therefore, there is a limit for the size of the oven.

Hence, once we eliminate the oven (around all the finite galaxies in the Infinite space universe), there won't be a black-body radiation in its CMBR.

However, if the number of the galaxies is also infinite and they are located in the whole infinite space universe, then it is clear that even without placing it in an oven it would still keep the black-body radiation in the CMBR.

We currently estimate that "The CMB is landmark evidence of the Big Bang theory for the origin of the universe. "

However, in this case, there must be some sort of curvature in the universe. In other words, the space in this kind of universe must be limited or finite and therefore, there is no need for infinite galaxies to fill all of that finite space. A finite number of galaxies could still keep the black-body radiation in the CMBR (In a finite space universe - without an oven) .

conclusions:

There are two possibilities to maintain the black-body radiation in the CMBR:

1.  Finite space Universe - There must be a curvature in the Universe and therefore it has a limited / finite space. In this case finite no. of galaxies should be good enough to maintain the black-body radiation in the CMBR (without a need to place them all in an oven)

2. Infinite space Universe - There is no curvature in the Universe and therefore its space is infinite. In this case, the number of the galaxies must also be infinite to maintain the black-body radiation in the CMBR ((without a need to place them all in an oven).

If I understand it correctly, so far, we didn't observe any sort of curvature in our Universe.

Therefore, could it be that the second choice might be the correct one?

Edited 2 hours ago by Dandav