confused about the concept of time

[liam]

we measure time by the earth rotation around its axis and the sun but if it stand still for five minutes (i don't know how to word this properly) i have stopped but time its self keeps moving not time as in days hours and minutes but true time

 

so in the five minutes that i count some form of time has passed that i can not go back to what is this and how dose it move is there a speed to it?

 

hope that made scene

[DJBruce]

we measure time by the earth rotation around its axis and the sun but if it stand still for five minutes (i don't know how to word this properly) i have stopped but time its self keeps moving not time as in days hours and minutes but true time

 

so in the five minutes that i count some form of time has passed that i can not go back to what is this and how dose it move is there a speed to it?

 

hope that made scene

 

First of the official SI measurement of time is now based on the a certain number of radioactive emissions from cesium 133, so even if the Earth stopped moving there would be a measurement of time. Also the unit of time we use is completely arbitrary. For all intensive purposes I could measure time any unit I wished, it just so happened that the Earths rotation was easily measurable to the ancients.

 

I am not quite sure what the question is but hopefully this helped.

[liam]

what i mean is if i start at point A in time and move to point B in time i cant go back to point A we see it as time but what has actually just past

[swansont]

First of the official SI measurement of time is now based on the a certain number of radioactive emissions from cesium 133

 

Cs-133 isn't radioactive. The interaction is a low-energy atomic transition, specifically a spin-flip of the electron in the ground state.

[liam]

Anyone got a awser to this?

[swansont]

I'm not sure of the question. Time moves at 1 second per second in your frame, regardless of whether your clock is working. "What is time" is a metaphysical question, not a scientific one.

[liam]

so there is no scientific theory on how time as we see it actually moves from present to future?

[swansont]

so there is no scientific theory on how time as we see it actually moves from present to future?

 

There are scientific discussions on the asymmetry of time; these usually involve entropy.

 

http://preposterousuniverse.com/eternitytohere/

 

Note the included link "Blog posts on Cosmic Variance related to the book and to the arrow of time"

[Severian]

There are scientific discussions on the asymmetry of time; these usually involve entropy.

 

I have always really hated these "arrow of time" entropy discussions, since they just seem all wrong to me. Entropy is a property of large ensembles, while time must have a valid definition on a microscopic scale.

 

The usual argument is that if you have an ordered system it will tend to become disordered over time, so you can use the disorder (entropy) to distinguish which way time is flowing.

 

But what do we actually mean by 'ordered'? If I have N identical balls, say, bouncing about in a closed box, undergoing elastic collisions, I can specify the system with 6N numbers (a position and velocity for each ball) at any time t. It doesn't actually matter where the balls are, or what they are doing, every configuration is described by the same number of numbers, so in some sense they are all equivalent.

 

In the macroscopic sense, we then define 'order' as states where balls have like properties. For example, they have the same velocity or x-coordinate or somesuch, and disorder is then when there is no correlation between them. As time passes, this correlation is lost, so they become disordered.

 

The reason they become uncorrelated is that there are many many more configurations where they are uncorrelated than those where they are correlated (as defined by the original set-up), so it is much more likely that the balls will end up in an uncorrelated state. Technically, it is an opening up of 'phase-space'.

 

However, this opening up of phase-space has nothing to do with the arrow of time. It is only opening up as we move further from the boundary condition. We define order according to correlations we set when the balls start out their motion and then define disorder as being different from that. But in actuality, irrespective of what the balls are doing at the end, I could always write down their positions and velocities in a little book and declare that to be 'order' (they are correlations just the same). Then the original state is actually disordered (since it doesn't conform with the numbers in my book) and entropy has decreased with time (moved from a disordered state to an ordered one).

 

In terms of the more formal definitions of entropy, my above viewpoint also holds, since it uses a measure of all possible configurations available to the balls. If I take my boundary condition to be the end state of the balls (call that ordered) and ask what configurations of ball at some time in the past could lead to the 'ordered' configuration, I would find that the number of configurations in the past grew as I moved further into the past. Just as before, I am opening up my phase space.

 

So, in my view, entropy increases as we move away from our boundary condition. It is irrespective whether that is forward in time or backwards. We only consider it as increasing with time because of our propensity to set boundary conditions and watch a system evolve, rather than asking what configurations could have led to a final boundary condition. I therefore come to the conclusion that, as far as entropy is concerned, there is no asymmetry in time, other than one of perception.

[swansont]

I have always really hated these "arrow of time" entropy discussions, since they just seem all wrong to me. Entropy is a property of large ensembles, while time must have a valid definition on a microscopic scale.

 

The usual argument is that if you have an ordered system it will tend to become disordered over time, so you can use the disorder (entropy) to distinguish which way time is flowing.

 

But what do we actually mean by 'ordered'? If I have N identical balls, say, bouncing about in a closed box, undergoing elastic collisions, I can specify the system with 6N numbers (a position and velocity for each ball) at any time t. It doesn't actually matter where the balls are, or what they are doing, every configuration is described by the same number of numbers, so in some sense they are all equivalent.

 

In the macroscopic sense, we then define 'order' as states where balls have like properties. For example, they have the same velocity or x-coordinate or somesuch, and disorder is then when there is no correlation between them. As time passes, this correlation is lost, so they become disordered.

 

The reason they become uncorrelated is that there are many many more configurations where they are uncorrelated than those where they are correlated (as defined by the original set-up), so it is much more likely that the balls will end up in an uncorrelated state. Technically, it is an opening up of 'phase-space'.

 

However, this opening up of phase-space has nothing to do with the arrow of time. It is only opening up as we move further from the boundary condition. We define order according to correlations we set when the balls start out their motion and then define disorder as being different from that. But in actuality, irrespective of what the balls are doing at the end, I could always write down their positions and velocities in a little book and declare that to be 'order' (they are correlations just the same). Then the original state is actually disordered (since it doesn't conform with the numbers in my book) and entropy has decreased with time (moved from a disordered state to an ordered one).

 

In terms of the more formal definitions of entropy, my above viewpoint also holds, since it uses a measure of all possible configurations available to the balls. If I take my boundary condition to be the end state of the balls (call that ordered) and ask what configurations of ball at some time in the past could lead to the 'ordered' configuration, I would find that the number of configurations in the past grew as I moved further into the past. Just as before, I am opening up my phase space.

 

So, in my view, entropy increases as we move away from our boundary condition. It is irrespective whether that is forward in time or backwards. We only consider it as increasing with time because of our propensity to set boundary conditions and watch a system evolve, rather than asking what configurations could have led to a final boundary condition. I therefore come to the conclusion that, as far as entropy is concerned, there is no asymmetry in time, other than one of perception.

 

But there are configurations in which you can start without increasing entropy over time — a Maxwell-Boltzmann distribution of speeds, i.e. thermal equilibrium. We always tend towards this distribution; the final boundary condition is always the same. The decision of "order" isn't arbitrary, it follows kln(N)

[Severian]

We always tend towards this distribution; the final boundary condition is always the same.

 

That is only in a statistical sense with lots of ensembles. If you only have one, then you always end up with a single entry from somewhere in the distribution.

 

Also, the same thing would happen backwards. If I had lots of ensembles, all of which end in the same configuration, evolving backwards in time, I would find the ensembles would also develop into a Maxwell-Boltzmann distribution.

[phyti]

liam,

post 3

what i mean is if i start at point A in time and move to point B in time i cant go back to point A we see it as time but what has actually just past

 

There are no points in time, and nothing passes, unless you're a poet.

 

Your comment is a common misconception trying to objectify time, but it's

not a thing, it's a relationship, just like a spatial measurement. Length is

expressed in terms of a unit of measure, i.e. a number.

You are measuring activity (events) using a standard rate of activity (clock).

A clock has to produce a uniform periodic event. The precision of the uniformity depends on the purpose, from the sun for daily social activities, to atomic vibrations for scientific experiments. Once you record the times, you have an ordered sequence of events for historical study or prediction purposes.

The only motion is from A to B in space. Of course you can't go back because

the dynamic universe has changed to a different configuration, and will not

repeat itself.