# Time as a dimension

1. Nov 5, 2009

### mangaroosh

Just a quick question.

I know that it is pretty much taken to be axiomatic, but is time a testable dimension?

2. Nov 5, 2009

### Staff: Mentor

What is a "testable dimension?"

3. Nov 5, 2009

### mangaroosh

you'll have to forgive my lack of scientific understanding and therefore terms.

would measurable be a better way of stating it?

4. Nov 5, 2009

### A.T.

Time is measurable.

5. Nov 5, 2009

### mangaroosh

how is it measured?

6. Nov 5, 2009

### A.T.

With a clock.

7. Nov 5, 2009

### mangaroosh

is that not circular reasoning though?

8. Nov 5, 2009

### Fredrik

Staff Emeritus
9. Nov 5, 2009

### A.T.

Why?

10. Nov 5, 2009

### mangaroosh

is it not using time to prove that time exists?

11. Nov 5, 2009

### EvilTesla

Not really.

Becouse IF you are correct, and we are using time to prove that time exists. Then if time DIDN'T exist, then we wouldn't have it to prove that it exists.

If you see what I am saying.

Time undeniably exists. We measure it ever day. We experience it every day.

Take velocity, distence devided by time. If there is no time, there is no velocity.

Why time is so differnt from space, and what its underlying properties are is anouther matter.

12. Nov 5, 2009

### mangaroosh

I'm not saying time doesn't exist, rather trying to investigate certain claims or ideas that I have heard, in a manner that assumes very little.

the above however that if time didn't exist then we wouldn't measure it, just seems to be further circular reasoning, the opposite side of the same coin if you will. It could be that we misinterpret certain things in nature, attribute certain characteristics to it, and devise a measurement for it, based on a limited perspective, and then apply that en masse to everything.

the fact that we measure time could be more based on a subjective interpretation of reality, as opposed to an objective one. How though can we get beyond this subjectivity, if we consider that consensu isn't satisfactory.

13. Nov 5, 2009

### mangaroosh

14. Nov 5, 2009

### A.T.

No, it is using a clock measure time.

You asked if time is a measureble dimension, not to prove that time exists (whatever "exists" might mean). Physics is not about proving that something exists, but about defining how to measure and predicting what you will measure.

15. Nov 5, 2009

### mangaroosh

Ok, but before something can be measured does it not have to be shown to exist first?

with regard to existing, I would say that it is part of what goes to making up reality. Would physics then be about defining how to measure and predict reality, or those things that actually exist?

a clock essentially isn't really a measurement of time though is it? It is more a measurement of the earths rotation, with a year being a measurement of the earths orbit around the sun. Does this mean that time is an intrinsic function of these two things?

16. Nov 5, 2009

### James Leighe

No, a clock just measures time... and has nothing to do with the earth's rotation.

As a matter of fact, a second (as an example) is defined as 'the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.'. So we can define time using periodic events in elementary particles.

17. Nov 5, 2009

### Fredrik

Staff Emeritus
The concept of time (and any other measurable quantity really) has to be defined twice. You need to define it operationally, i.e. by describing the equipment you intend to use to measure it, and you need to define it mathematically so that you have something in your mathematical model that represents the real-world concept. By using the same word for both things, you're implicitly saying that theoretical results about "mathematical" time should be interpreted as statements about "actual" time in the real world.

So operational definitions should be thought of as axioms of the theory. They are the statements that tell you how to interpret the mathematics as predictions about the results of experiments.

However, I think this is a pretty awkward way to state the axioms of the theory. I prefer to be more explicit. For example, I would take one of the axioms of special relativity to be "A clock measures the proper time of the curve in Minkowski space that represents its motion". This is more explicit than just using the same word for two different things.

18. Nov 5, 2009

### A.T.

No, how would you show that anyway? In physics, if something can be measured it "exists", just like numbers "exists" in math.
Yes it is, per definition. A clock is defined as something that measures time.
You can use any process where measurable quantities change as a clock. Just a matter of conventions and practical considerations.

19. Nov 5, 2009

### mangaroosh

has that happened with the transition to the atomic clock?

It is still used to measure, perhaps more accurately, what was origianlly the length of "time" of the earth to revolve around its axis, no?

20. Nov 5, 2009

### mangaroosh

Ok, just with regard to stating the equipment that you are going to use. What equipment would be used to measure time? If we assume that it is to be a scientific test for the existence of time.