If time did not exist, things could NOT happen in the "same moment" because even a single "moment" is a part of time. If there was no such thing as time, I don't think there would even be life for that matter because there would literally be no time, which means nothing can be done because things happen in accord with time.
Time is what separates things that have happened, from things that are happening, from things that WILL happen.
Without space, there is no separation between me and you, here and there. It is all the same.
Without time, there is no separation between what has happened, what will happen, or what is happening. It all just happens. Together. At once. Without order, and without progression.
Without time. Earth exists as Pangaea. Our current configuration, and the remaining husk that is left after our sun goes super nova... all together in the same existence.
Everything IS.
Technically, I would same time doesn't PHYSICALLY exist. But I take the word "physical" to mean fathomable\touchable. Time is simply time.
We measure it just as we measure time - we have slapped a label on "time" and have formulated a way to measure it for our convenience.
Same reason we measure miles. Distance still exists.
This is one question I've never been able to understand HOW\WHY people could possibly believe that time was NOT linear.
If time branches off - what makes us only live\see one of those branches? I have heard the argument that there are the infinite different branches of time representing every small decision that we make. Using our own free-will, is how we chose which branch to take.
If this is the reasoning, then this brings in the whole debate on free will.
How/Why is simple.
If we are able to change the past, does the future no longer exist, or do you simply branch to a different future.
If the future was destroyed, then you would not have gone back in time, and you would not have destroyed that future, hence the very event of traveling back in time would create a paradox that eventually destroyed all of time, past present and future.
Think of it like a feedback loop.
Going back in time destroys the future, which prevents you from going back in time, which restored the future, which allows you to go back in time, which destroys the future, which prevents you from going back in time, which restores the future.
Eventually the gravitons and Higgs Boson particles disintegrate which results in no more universe. Ever.
So, if time travel is possible, time would almost certainly need to be something other than linear.
Then, if you go back in time, you can never return to the future from which you left. The very act of being present in the past means that you are branched from the actual past of the future you came from, and can only return to a new future.