# Time as non-fundamental physical quantity

1. Jul 13, 2012

### Nemanja989

I have a little confusion in my head when I want to imagine time. Time is a bit more abstract then space dimensions for me. So I began from definition of time, and it is defined through motion of electrons in Cs atom.
Therefore, I thought if the Universe was so simple, such that there are only two particles (without any internal constituents), weather described with quantum or classical mechanics. And if we have motion of those two particles we could define time in that way. But in case that those two particles stand still, there is no motion in that Universe, so my question would be: what happens with time in that case? Does it pass? Or stand still?

My opinion is that time is artificially introduced concept, and that it doesn't really exist. I think that it is simply consequence of motion of particles and therefore I would say that velocity is more fundamental than time.

With this thinking, there is no possibility of time travelling because everywhere exist only now (if that is correct choice of words).

Last edited: Jul 13, 2012
2. Jul 13, 2012

### Staff: Mentor

First, let me warn you that there have been several threads about time in the past month or so here on PF, and each one ends up being locked because they get flooded with nonsense.

Now, I can almost guarantee you that the next sentence will be just about the best, most accurate way of describing time that you will ever hear.

Time is what a clock measures.

That's it. That's what time is. Think about distance. What is it? It is what a ruler or other measuring device measures. That's it. We use this to build models of space and time and put coordinate systems in these models where we can say that X moves 5 meters to this point or whatever, but it all depends on our measurements of these distances in time and space.

3. Jul 13, 2012

### ZapperZ

Staff Emeritus
Ooookay! As an exercise in futility, here are some points to counter your arguments:

1. Relativity puts "time" and "space" on equal footing. If you don't think time is "fundamental", then neither is space, and we are left with nothing.

2. If you have done Lagrangian mechanics, you'll know that q (representing the spatial coordinates) and dq/dt (the temporal dynamics) are the only two quantities that really matters. There's "time" in there!

3. A ton of phenomena are described via the broken time-reversal symmetry principle (example: superconductivity).

It is extremely strange for something that is such an important and necessary ingredient is considered to not exist and not fundamental.

Zz.

4. Jul 13, 2012

### DragonPetter

Not trying to argue, because I think the definition is a valid way to think about time, but I don't think that definition could ever satisfy physics. Perhaps that is one of the best definition we can give now, but I don't think that will be the end of the story (not trying to suggest anything other than our understanding might be a little deeper eventually). Also, an instant in time is not measured by a clock, but rather the progression of time (a clock has a reference point), just as a ruler does not measure a point in space or what space is, but a distance in space.

Would I say "charge is what an electrometer measures" is the best definition for charge? Of course it is accurate, but it is not satisfying and does not give very useful information about charge. Or would we say, "distance is what a ruler measures"?

There are also more detailed definitions that probably give more, correct, essence to the meaning of time, although it might be just as unsatisfying to what the OP might want to hear.

Edit: perhaps I am wrong in what I considered time. The "second" unit implies a progression of time, or time with reference, rather than an unreferenced point "instance" of time.

Last edited: Jul 13, 2012
5. Jul 13, 2012

### Nemanja989

I am totally aware of think that this discussion can go in wrong direction, but the only thing what I want to know is your opinion for this question (nothing more than that):

If by any chance happens that somehow everything simply stops (there is nothing that moves), do you think that in that case time would pass or not? I am interested only in answer to this question, nothing more.

6. Jul 13, 2012

### Nemanja989

@ZapperZ

On your second argument you say that the only two quantities that matter are q and dq/dt, where dq/dt represents motion, and I am not in contrary with that at all.

I started this discussion only because of curiosity, nothing more (I am not some kind of person who thinks that has revealed something)..

7. Jul 13, 2012

### ZapperZ

Staff Emeritus
And considering that the Lagrangian needs that to describe completely the dynamics of the system, how then can you still proclaim what you wrote in the original post? It makes no sense IF you actually already understood all this.

And what about Point #1 and #3?

Zz.

8. Jul 13, 2012

### Nemanja989

If by any chance happens that somehow everything simply stops (there is nothing that moves), do you think that in that case time would pass or not?

9. Jul 13, 2012

### ZapperZ

Staff Emeritus
Why not? Just because use measure time using motion, doesn't mean that we DEFINE it that way! That's like saying if I lose all of my rulers, space doesn't exists!

So now it is my turn to ask you. When will you be addressing the rest of the points that I brought up?

Zz.

10. Jul 13, 2012

### arul_k

You need some sort of change to a system in order to measure time. If you define time as the change itself then i guess you could say that if there is no change there is no time. On the other hand one could argue that just because you can't measure time it dosen't mean that time does no exist.

11. Jul 13, 2012

### Mesmer8

The one thing you can't do in SpaceTime is not travel. Even if we all stood still and didn't metabolize, it would have to be for a certain amount of... Time, for as long as we occupy Space...! *\* We are only able to travel through / on / with / against SpaceTime. No standing Time still, since that's where non-existence lives. See you, later? (I've heard that before....)

12. Jul 13, 2012

### jbriggs444

If all the clocks stop at ten o'clock and nothing moves further then there is no experimental grounds for thinking that it ever becomes eleven o'clock.

Whether this means that "time" stops is not a physical question.

13. Jul 13, 2012

### Mesmer8

If all the clocks stop (such as when the power goes out), there is no experimental grounds for thinking that Time, itself, has also stopped. Rather, after the power is restored, one must set his clock forward by the amount of time the power was out. As another example, when the speedometer stops showing your speed, you can't guarantee from this fact, alone, that your motion has stopped.

Similarly, while clocks measure time, they can't be blamed for creating the time they measure. Surely, time existed before clocks - even before Sun dials. Time was, you could not tell the difference between light and gravity. We can jam sync to the flow of time - it doesn't have to be GMT or bust. We can add a second to June and not end up with broken cities. We just give the Common Present a new name. But it knows its own name. Too bad it can't tell Us, even though we can tell time.

Contrary to the quip, Time doesn't really keep everything from happening at once. Time doesn't care how the deal goes down. It mocks intention.

Time exists wherever you have Space. Without Time, Space actually takes up no space.

- Mesmer8

14. Jul 14, 2012

### Staff: Mentor

Please, let's keep "what if's" out of the thread. These kinds of things are what gets other threads discussing time locked. If it isn't believed to be possible please don't mention it.
I highly recommend everyone stick to the following when discussing time:

1. How we measure it.
2. How we use it in current theories and models.
3. What it means in regards to the above 2.

The following things WILL get the thread locked:

1. Time travel discussion.
2. Wild speculation.
3. Nonstandard theories and models.
4. Personal opinions that have nothing to do with real science.

This may make for a boring discussion, but it's either that or no discussion at all.

15. Jul 14, 2012

### Nemanja989

I just want to point out that I asked you this question like I would ask some other questions to my parents or my professors on faculty.

@ZapperZ
Unfortunately I can't give you an answer to your questions, but I would like to discuss a little more.
I am aware of fact that mine kind of reasoning is probably bad. While reading chapter on time dilatation in the Feynman lectures I found that it is more easily for me to understand dilatation as being consequence of light being able to travel only at one speed regardless of reference system. And time dilatation is explained through slower ticking of the clock that is moving, and that ticking is slowed because of the light is slowed in direction of ticking (which is perpendicular to the direction of motion).
That made me thinking that time is consequence of motion.

Also, I red that direction of time is determined with entropy (+t associated with increasing entropy). Could you then say that positions of all particles determines what time it is, if we consider a box with particles?

And also, how would you define time if there is no motion at all?

16. Jul 14, 2012