# Question of Time

1. Oct 19, 2015

### pnorris2000

My question is: do we know that time stays consistant throughout all the universe. We know that time and space are intertwined, and that time is relative depending on mass, such as near an event horizon. Does the absence of any mass, out in the voids of space, between galaxies, also affect time's consistancy? If not, would light pass though these areas at a different rate comparatively?

2. Oct 19, 2015

### phinds

There is no reason to believe otherwise.

yes, they are part of the same thing
No, we don't "know" that, since it's not true as regards the event horizon of a black hole. What is true is that observations from far away from an event horizon show an appearance of time slowing down but we know that the time for the object AT the event horizon is not affected at all by the event horizon (which isn't even a physical thing, just a coordinate).

What is also true is that if you were to approach such an event horizon and then return to a starting point far away from the BH, you would have experienced a different amount of time's passage than would someone who had just stayed at your starting point. Both of you, however, would see no difference in the rate of time flow. It flows at one second per second for both of you but you have taken different paths through space-time and so have experience different numbers of seconds.
There is no reason to believe so.
Not clear what this even means. Light travels at c in a vacuum regardless of any nearby mass but the amount of time it can take to get from point A to point B can depend on the path that it takes through space-time so the light in an Einstein Ring, for example, will have taken longer to get to us than it would have had there been no intervening mass that "bent" the light back towards us and the light had just come directly towards us.

3. Oct 19, 2015

### Staff: Mentor

What does "time stays consistent" mean? How would you test to see whether time "stays consistent" or not?

What does "time is relative depending on mass" mean? How does it show up in experiments?

The point of my questions is to get you to think in terms of actual specific observations. I think that will help you to better focus your questions.

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