Total number of beings in the entire space as we know is constant? Increases? Decreases? I am a being. So are you. According to Buddhism there is not soul and maybe there is nothing called myself which makes this a very tough question to ask. I am living my sansara. A never ending thought processes taking different forms (Human, Deva etc). This thought process or sansara does not overlap with any others or does not branch out. My theory is that the total number of beings (may not be the best word to use) or sansaras of different thought processes (again maybe wrong use of terminology but I hope you get the picture) does not change unless someone attains nibbhana/ becomes an arahath. Is this correct? or can it reduce without it being due to the passing of an arahath? Can it by any chance increase?
In DN 9, the Buddha advised not to speculate on certain types of questions:

“Potthapada, I haven’t expounded that the cosmos is eternal, that only this is true and anything otherwise is worthless.”
“Then is it the case that the cosmos is not eternal, that only this is true and anything otherwise is worthless?”
“Potthapada, I haven’t expounded that the cosmos is not eternal, that only this is true and anything otherwise is worthless.”
“Then is it the case that the cosmos is finite … the cosmos is infinite … the soul &amp; the body are the same … the soul is one thing and the body another … after death a Tathagata exists … after death a Tathagata does not exist … after death a Tathagata both exists &amp; does not exist … after death a Tathagata neither exists nor does not exist, that only this is true and anything otherwise is worthless?”
“Potthapada, I haven’t expounded that after death a Tathagata neither exists nor does not exist, that only this is true and anything otherwise is worthless.”
“But why hasn’t the Blessed One expounded these things?”
“Because they are not conducive to the goal, are not conducive to the Dhamma, are not basic to the holy life. They don’t lead to disenchantment, to dispassion, to cessation, to calm, to direct knowledge, to self-awakening, to Unbinding. That’s why I haven’t expounded them.”
“And what has the Blessed One expounded?”
“I have expounded that, ‘This is stress’ … ‘This is the origination of stress’ … ‘This is the cessation of stress’ … ‘This is the path of practice leading to the cessation of stress.’
“And why has the Blessed One expounded these things?”
“Because they are conducive to the goal, conducive to the Dhamma, and basic to the holy life. They lead to disenchantment, to dispassion, to cessation, to calm, to direct knowledge, to self-awakening, to Unbinding. That’s why I have expounded them.”