# Is there any need to introduce time as a parameter?

• sanjibghosh
In summary, Russ is saying that time is necessary because we need to measure changes, and motion is necessary because we need to measure positions.f

#### sanjibghosh

is there any need to introduce time as a parameter?
is there any meaning of time, without any velocity?
time is because of some change and that change can be measure by position only. so why is there an unnecessary extra parameter (time).is there any need to measure a rate of change with some non-physical quantity (like time)?

The questions really don't make a lot of sense to me. It almost seems like you are thinking about it backwards: there is no such thing as "velocity" without time, but time most ceratainly can exist without velocity. I'm sitting on my couch right now, experiencing time without velocity!

I think he is saying that instead of saying X happened for a Y time interval, we should say X happened while Y happened Z times.

Which is how it is currently right? I mean we have to use some physical yardstick as a standard for us to all agree on how long 1 second is.

The first is correct. Just because we use motion to measure time, that does not mean that time requires motion.

So Russ, have you been sitting (motionless) on your couch for ten minutes or twenty? How do you know?

One should also note that we use time to measure distances or space, per Special Relativity. The fact that "c" is defined using both time and space imply that you can't have one without the other, either explicitly or implicitly.

The whole question of the OP is also puzzling. To prove that one doesn't NEED anything, try describing something without any use of it. So try describing the dynamics of a system without using something. That you have shown that that something isn't needed.

I don't see how one can eliminate time from the Hamiltonian of a system. Until I see that, I consider the argument that time isn't needed as being false.

Zz.

A couple of month ago, I stumbled over this article:

http://www.chronos.msu.ru/EREPORTS/rovelli_time.pdf [Broken]

Is this complete hogwash? I found it interresting.

I was really intrigued and started thinking a lot about time. The same question as the OP popped up. What is most fundamental? Time or motion (change)?

When Russ sits on his couch, how does he experience time? One answer could be that he does because things are changing. no? His thoughts are evolving, heart beating, a fly flies by, etc.

I know that SR basically says 'Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows', but I'm still not convinced that time even is neccessary.

Would it be psossible to remove time altogether and invent some new concept of change with some new unit? I don't know if this even makes sense, but I'm still thinking about it ;)

/Frederic

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is there any need to introduce time as a parameter?
is there any meaning of time, without any velocity?
time is because of some change and that change can be measure by position only. so why is there an unnecessary extra parameter (time).is there any need to measure a rate of change with some non-physical quantity (like time)?
Why do neutrons scattering off of nuclei obey the "1/v cross section dependence", i.e., the one-over-velocity dependence of neutrons scattering on nuclei?

To describe a single state, like a photograph, you do not need time. To make a prediction of a future state or to describe any change from a previuos state, time, as a dimension is required.

Is the question whether time is constant or variable?

From my understanding of SR, time is always constant for a single observer. Its when you have multiple, diversly located observers, using duplicate time measurement devices, that time is variable.

Although, thinking out-of-the-box, I could imagine replacing space/time with space/distance. You would need all observers to use a centrally located time measurement device. The variable is the amount of space that needs to be traveled for a given distance. So it could take you more or less time to travel a given distance depending on how much space there was in that distance.

"To describe a single state, like a photograph, you do not need time. To make a prediction of a future state or to describe any change from a previuos state, time, as a dimension is required."

Actually, that is false. Time is still required for photographs. Show me a camera with a 0 second exposure time and I'll show you some pretty dull pictures.

The questions are actually good questions.

What if there were a demon who could cause everything in the universe to stop moving, and then start everything back up moving again exactly as it had been before. We would not have the slightest clue that the demon had done the deed... no time would pass if nothing was moving.

Time and motion are inherently linked.

Actually, that is false. Time is still required for photographs. Show me a camera with a 0 second exposure time and I'll show you some pretty dull pictures.

That is why I used "like". The photograph analogy wasn't meant to be literal and account for the exposure time.

What if there were a demon who could cause everything in the universe to stop moving, and then start everything back up moving again exactly as it had been before. We would not have the slightest clue that the demon had done the deed... no time would pass if nothing was moving.

Since you're in the literal mood ;), wouldn't the demon also be affected and not be able to start time again? Unless you are suggesting this demon could choose what is affected by the stoppage of time. In that case you could say that stopping a single particle's momentum is stopping time for that particle. So ceasing all movement and stopping time are the same (not linked).

to all,
I think one can replace time by entropy. A lot of problems are there but still one could think about it(as I think).I don't know whether it is more difficult or easy for calculation, but it has a great physical meaning.
This is one of the possibilities.In some sense it is equivalent to the time as a parameter,but problem is that time has no physical sense like entropy or other physical quantity.
as lachelimbo said to describe a single state I don't need any 'time',similarly to describe a periodic motion you don't need any time, all physical quantities can be written in the form of position only. after calculating all these quantities we have seen that they are just independent of time, so is it not enough to think.
I am not saying that there is some mistake in SR or any thing else.What i am saying is that, SR or any thing else are developed in the view point of time as a continuous parameter, is there any chance to think 'dynamics' without time.
I don't know what is the meaning of time without any motion. one could experience time without any physical motion ('I'm sitting on my couch right now, experiencing time without velocity!') but what about his motion of realization (he realize 'time' by some motion like motion of a clock).

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Why do neutrons scattering off of nuclei obey the "1/v cross section dependence", i.e., the one-over-velocity dependence of neutrons scattering on nuclei?
it is not only for neutrons scattering, the all physics depend on the time, because we have already set the picture in that way.

So Russ, have you been sitting (motionless) on your couch for ten minutes or twenty? How do you know?
My watch doesn't require me to be moving in order to report the time to me.

Would it be psossible to remove time altogether and invent some new concept of change with some new unit? I don't know if this even makes sense, but I'm still thinking about it ;)
Sure, let's call it the "Watters concept of change" and call the units "Russ"... of course, a unit of "Russ" would be referenced to a second and the "Watters concept of change" would be indistinguishable from what we now call "time"...

To describe a single state, like a photograph, you do not need time.
Yes you do. When you use such a description, there is an implicit time coordinate (or range) to it. Think about your address. Is that address for you valid for all times or just now and over a certain range? A million years from now, will I find you at that address?

to all,
I think one can replace time by entropy. A lot of problems are there but still one could think about it(as I think).I don't know whether it is more difficult or easy for calculation, but it has a great physical meaning.
This is one of the possibilities.In some sense it is equivalent to the time as a parameter,but problem is that time has no physical sense like entropy or other physical quantity.
as lachelimbo said to describe a single state I don't need any 'time',similarly to describe a periodic motion you don't need any time, all physical quantities can be written in the form of position only. after calculating all these quantities we have seen that they are just independent of time, so is it not enough to think.
I am not saying that there is some mistake in SR or any thing else.What i am saying is that, SR or any thing else are developed in the view point of time as a continuous parameter, is there any chance to think 'dynamics' without time.
I don't know what is the meaning of time without any motion. one could experience time without any physical motion ('I'm sitting on my couch right now, experiencing time without velocity!') but what about his motion of realization (he realize 'time' by some motion like motion of a clock).
That's mostly just gibberish. The fact that mass doesn't require time doesn't in any way imply that time (or length!) doesn't exist. Entropy can be used to discern the arrow of time, but it doesn't describe the same thing as time and thus can't be a replacement for time. You can't describe periodic motion without time because without time, there is no motion. And my clock's motion is not *my* motion.

You asked the question in the OP, so why don't you see if you can answer (prove) it yourself. See if you can describe the concept of velocity without time! If you can do that, then just maybe you're on to something...

to all,
I think one can replace time by entropy.

All you have done so far is make unverified speculation.

Fine, replace time with entropy. Now solve for the equation of motion of a simple pendulum and show me you get the same thing.

Zz.

Yes you do. When you use such a description, there is an implicit time coordinate (or range) to it. Think about your address. Is that address for you valid for all times or just now and over a certain range? A million years from now, will I find you at that address?

Maybe it is just semantics but I disagree. I can describe a yellow box without a time coordinate. I don't have to describe what it was before or whether it will be there a million years from now. That is making a prediction, which requires a time coordinate. The same applies to my address.

Yes, but to take a picture of anything, you have to look at it over a range of times.

Instants in time don't exist. They are used as thought experiments involving limiting processes when we're trying to understand things that happen so quickly it's like they never happen at all.

Every single thing in the entire universe either exists for a finite, non-zero interval of time, or it doesn't really exist at all.

Maybe it is just semantics but I disagree. I can describe a yellow box without a time coordinate. I don't have to describe what it was before or whether it will be there a million years from now. That is making a prediction, which requires a time coordinate. The same applies to my address.

No you can't. You would need time in order to describe the yellow box.

The way I see it is that time is dependent on motion, and therefore energy/mass, whereas motion is only dependent on time because of the need for a parameter to describe the motion of the universe (because we made the choice to "set the picture" as such). As Ernst Mach said,

"The goal which it [physical science] has set itself is the simplest and most economical abstract expression of facts. When the human mind, with its limited powers, attempts to mirror in itself the rich life of the world, of which it itself is only a small part, and which it can never hope to exhaust, it has every reason for proceeding economically."

For this reason I feel that this concept of space-distance (lachelimbo) is a great speculation, and we may find some truth in such ideas in future...

We can observe motion without grasping a universal notion of the interval of time which the event occurred within, and if we measure that interval, there will be minute discrepancies for each observer experiencing a unique quantity of motion (SR). But imagine time without any instance of motion. How would anything be able to perceive the persistence of time? If all motion was to "stop," there would not be any feasible method of predicting what time interval elapsed during the motionless period. The concept of time would become meaningless.

I am a fairly new member and a naive high school student, and realize that my understanding of the topic may be quite misguided...