# Passage of time

1. Jun 18, 2004

### wespe

I've been thinking.. If time is what a clock measures, at what rate does time pass? By definition, the same rate as the clock's hand moves, but that's just circular. Then, there's also "everything is stationary wrt itself", so how does any change occur at all? It just dawned on me that it is related to memory. That is, passage of time or any change can be perceived, because we can compare the current status to the previous one in our memory. If we didn't remember a moment ago, we wouldn't have a concept of time, or life or anything for that matter. So it seems that memory (anything that can store information) must be very important, I didn't realize this before. Does anyone have some thoughts on this, or know of a web site where this line of thought is explored?

2. Jun 18, 2004

### loseyourname

Staff Emeritus
Everything is spatially stationary wrt itself. The same is not true of temporal movement. Unless frozen to absolute zero, there is always change of some sort and increasing entropy in closed systems. Time is the dimension through which this change (or movement, if you want to call it that) occurs.

3. Jun 18, 2004

### jcsd

How do you define any unit is the problem here? The simple answer is you define it by defining it; if two clocks 'tick' at the same rate (ignoring SR for a minute) they are essenmtially measuring the same thing, just as if two metre rules are the same length they are measuring the same thing.

4. Jun 18, 2004

### wespe

I'm becoming confused. Everything is spatially stationary because "here is here", and temporally stationary because "now is now". Isn't experienced proper time different than movement in time dimension?

5. Jun 18, 2004

### AWolf

Even though the two clocks produce the same result, they are not measuring the same thing.
Time is not an entity it is a perception directly related to an objects environment. Each clock is measuring its own time.

The difference would be infinitely small, but there would be a difference.

6. Jun 18, 2004

### jcsd

I said to ignore relativty, but in that case we simply refine it so that the clocks are local and at rest to each other.

7. Jun 20, 2004

### AWolf

Okay, so the clocks consist of exactly the same quantity of mass, are both at rest to each other and both have exactly the same gravitational force exerted on them - you take relativity out of the equation.

The clocks are still not measuring the same thing.
The movement of the mechanics/electronics of each clock is syncronised, but that is all.

The measurement of time is directly related to the components of the clock. Not the cogs and springs, not even the atoms, but the energy that comprises all the subatomic particles.

Even if one of the clocks is running slow, is measurement would be inacturate, but the clock would still preceive time the same as the other, it just wouldn't display it the same.

8. Jun 20, 2004

### ram1024

time = action

there's no other way to measure time except in the form of "something happening"

glad someone else besides me "gets" this, wespe :D

9. Jun 20, 2004

### jcsd

In that case they are essirtially measuring time on different scales, the only useful defintion of time is that which a 'clock measures'

10. Jun 20, 2004

### AWolf

That would imply that time is defined by the movement within a mechanical device.
Clocks provide you with a device that has a mechanical movement with a constant velocity. The amount of angular rotation of the cogs and hands at that velocity is how time is measured, but it is not a definition of time.

For a true definition of time you shouldn't ignore relativity, but rather use it.

A clock here on earth measures time at a different rate to one aboard an orbiting satelite. Why ?
The easiest answer is Relativity, but that doesn't tell you very much.

A true definition of time must be constant both here and in orbit.

If we take the simplest particle, the photon, and assume for a moment that rather than travelling through empty space that is being transmitted through a granular space, then the transmission of photon energy from one grain to the next would give you the basic definition of time.
The more compressed the grains (gravity well) the longer it will take for the photon to travel a set distance, but each grain is still transmitting the energy at the same rate, there's just more grains to be traversed.
The more dispersed the grains get (a satelite on orbit) the shorter it will take the photon to travel - less grains - same transmission rate.

Since the photon is unsigned energy, whatever rules it has to adhere to, so too all the subatomic particles.

This would give you the most fundemental definition of time, its value would be the same anywhere in the Universe.

11. Jun 20, 2004

### jcsd

A clock only measures it's proper time.

We know that there is no global defitnion of time as it would not be Lorentz invariant.

12. Jun 20, 2004

### wespe

This is what I meant in post #4. A clock doesn't measure movement in time dimension.

Jcsd, do you think the following statement is okay?
Everything is spatially stationary wrt itself because "here is here",
and temporally stationary wrt itself because "now is now"

Actually my emphasis in this thread was: if we didn't remember a momement ago, we couldn't compare it to now, and we wouldn't perceive a passage of time. More like philosophy than physics.

Last edited: Jun 20, 2004
13. Jun 22, 2004

### geistkiesel

There are three basic states of time.
1. The Past.
2. The Future.
3. The Here and Now.

14. Jun 22, 2004

### wespe

Am I supposed to extract anything useful out of that? What do you mean by "state of time"? If these are the basic ones, what are the more complex "states of time"? Why do you include "Here" with now?

15. Jun 22, 2004

### AWolf

There is only one state of time and that is NOW

Everything else is a measurement of elapsed time.
• Past -> positive elapsed time
• Future -> Negative elapsed time

16. Jun 24, 2004

### Opethian

I see a clock as being nothing more than a device which relates numbers to time in such a way as to make it easy for the general population to understand a difficult to explain phenomenon.

Clocks, and calenders too for that matter, are nothing more than number based systems which makes the average Joe's life easier and more productive. For example; if you had no idea what year you were born you could not possibly know how old you are. Thanks to the calender, average Joe knows he's 35 years old, or whatever the case may be.

Similarly we can use an egg timer to cook an egg for 7 minutes, but wtf is 7 minutes besides 7 full rotations of the second hand on the clock?

17. Jun 24, 2004

### Prometheus

What do you mean by state of time. Perhaps that is where you lose me. What does this statement mean?

You seem hung up on the word measurement. How Newtonian of you. Time is more than its measurement by mankind.

I agree with geistkiesel. The most fundament awareness of time is the present. This is followed by the past and then the future. There are more complex states of time, but you seem not ready for them yet, as you seem hung up on measuring time.

The universe is not all at the same time. Time does not flow at constant speed, and no two entities move at the same rate through time. I have no idea what you mean by there is only one state of time, now. What do you mean?

You use the word elapsed. Elapsed is a verb expressed in the past tense. The past tense refers to time that has occurred in the past. Yet, you would speak of past time in the future, and use the word negative to do that. I challenge this. What do you mean?

18. Jun 24, 2004

### Prometheus

This is a Newtonain concept. In Einsteinian physics, time is much more than what a clock measures. Are you not aware of this? Are you not aware of space-time? I recommend that you investigate this.

19. Jun 24, 2004

### Antonio Lao

No physical theory can answer this question. Time flows uniformly even in the theory of relativity but there is a component of spacetime that can be curved as warping of time but this warpage of time is linked to the warpage of space. The two warpages cannot be separated into rate of time and rate of space.

This is the time's arrow. And theoretically, there are four arrows. And nobody can answer these mysteries of one directional arrows.

1. Thermodynamics arrow - heat flows from hot to cool. The 2nd law. The increase of entropy.

2. Electromagnetic arrow - EM radiation always emanates outward from the source never inward.

3. Cosmology arrow - The expansion of the universe. The domination of redshifts over blueshifts.

4. Psychology arrow - We remember the past but not the future.

20. Jun 24, 2004

### wespe

well if my clock measures different values than your clock (they are identical, but due SR effects), then my time is different than your time, which means time is relative. that's what I understand from time is what clock measures.

I am aware of spacetime but in spacetime diagrams there's a formula like sqrt(dx^2-dt^2) to find the elapsed proper time, so you don't just use dt as elapsed time, so I don't know why the 4th dimension is labelled time.

Actually I don't know what I'm talking about so feel free to embarras me.

I was trying to relate passage of time with memory but no one was interested so let the thread die..