# Q & A: Time-Dependency

Q:
Generally in Physics we consider time as independent quantity, really time is an independen quantity? what exactly is the defn of time? If time is a measure of change, it depends surely on our perception and also the change will not be constant always.It varies from one’s perception to other’s perception,if this is the case every individual will have his own defn of time.. how physics can explain the ambiguity of time? We always feel the time is moving forward, is there anything really moving forward or it is just our feeling? If time is moving then definately it would have started at one particular undefined variable(or constant ) like Time(we can’t say it as time, because we don’t know what it is), can our human mind is able to define that variable? Whatever we see in the physical world is our individual perception even then why physics has not given importance to the term perception? this perception is again controlled by our mind, is there anything beyond mind where we can define everything absolutely..??
- Sai Ram (age 24)
A:
Sai -

These are wonderful questions and your own observations are excellent.

I guess the practical reason that we consider time to be an independent quantity is because our perception is that we have no control over it. Our understanding of quantities we deal with in everyday live certainly has this as an implicit assumption. As a simple example, take velocity... velocity is the change in position over the change time, with time as the independent variable. If time were actually a dependent quantity, then velocity could no longer be described in such a simple fashion.

But yes, we certainly could describe time as being dependent. Perhaps you're right and it is just a figment of our perception. But this would imply that all of the other rules of the universe are significantly more complex than we currently view them as being. And since we know of nothing else on which to suggest that time depends, we follow Occam's Razor, which says that the simplest explanation must be the true one.

As a more general statement, we base our scientific progress on the assumption that we can draw conclusions about the world around us beyond just our perception. This is because we have seen that in the past, the things that we have observed could be predicted according to certain rules. Then we use these rules to predict what will happen in the future. Certainly, we can not be 100% confident that the future will continue to follow the rules of the past. But in the end, we have two possibilities: either the future does not obey the rules established by the past, in which case modeling them would be useless but not harmful, or the future will continue to obey the rules established by the past, in which case our assumptions will have practical benefit.

-Tamara

(published on 10/22/2007)