I recently read the book “Concepts of Simultaneity” by Max Jammer where Jammer presents the history of concepts of simultaneity. Primarily he starts with the Greek philosophers and works through to the modern age—with philosophers and physicists. The book outlines that in regards to the concept of simultaneity the most significant developments occurred in the past 110 years, starting with Albert Einstein when he published his famous paper on Special Relativity in 1905.
Time is intrinsically linked with simultaneity. Simultaneity involves how we might synchronise distant clocks with our own local clocks. This issue then has an enormous bearing on some significant philosophical questions. How do we measure the speed of light coming from the distant cosmos? How old is the universe? How do we know how old the universe is?
We accept as fact, even consider it as empirical fact, something that is actually not fact at all but conventional. I explain below. But an incorrectly held notion has led to the idea that we can definitively know how old the universe is. Since we know the speed of light is finite (not infinite) and the universe is enormously large, then it is concluded that it must have taken light billions of years to travel to Earth from the distant cosmos. From that it follows that both theist and atheist have incorrectly concluded that the biblical timeline cannot be correct. The atheists even use this as an argument against the existence of the Creator.
In classical (Newtonian) physics, up to several hundred years before Einstein and any measurement of the speed of light, a distant event was considered simultaneous with a local event if the local observer saw them occur at the same time, as measured by his local clock. This is because the speed of light was assumed to be infinite. There was no delay between the light leaving its source and its reception at the observer. But that all changed.