Question: In the following sentence I want to understand the meaning of the bolded part:

> 
> The light from most stars takes millions of years to reach us, so not only the present existence of these stars debatable, but so are ***the very concepts of the "present" and "existence".***
> 
> 
> 

What does it mean?

Answer: 
It refers to the fact that *stars* have been existing for millions of years, and their light takes millions of years to reach us, to be visible to us. So, when we see theirs light, are the stars form which the light is sent still in existence? If not, can we say that they still exist because we see their light at present?
> 
> The light from most stars takes millions of years to reach us, so not only the present existence of these stars debatable, **but so are the very concepts of the "present" and "existence".**
> 
> 
> 

Einstein's Special Relativity showed that anything that is far away in space is also distant in time. That is counterintuitive, but it seems to have held up in experiments. So the idea of "the present" meaning "at this same moment" now only works for something that is also "present" in the other sense, meaning "here."

I also so not understand how the concept of existence is made debatable by the distance and by relativity. Maybe the author claimed a little too much?