Time's arrow, or what universal property is asymmetric, anyway?

[Loren Booda]

"Time's arrow, or what universal property is asymmetric, anyway?"

A lot has been made of time's arrow not appearing in the equations of Newton, statistical mechanics, relativity and quantum mechanics - none preferring that past precedes the future or vice versa. Some very specific particle processes do seem to follow an asymmetry of time, but they are the far greater exception for interactions in general.

We ask if time as a universal property has a preferred direction. I ask if any cosmological phenomenon has been shown to obey an overall physical vector.

 

[BasketDaN]

That's like asking whether or not centimeters have a preferred direction. Time does not exist , just as centimeters do not exist .

 

[Loren Booda]

Can we then conclude that physics does not exist, or just that vectors ultimately have no global meaning?

 

[Deeviant]

Originally posted by BasketDaN
That's like asking whether or not centimeters have a preferred direction. Time does not exist , just as centimeters do not exist .

Actually, time really does exist. There is a reason why we use the term "spacetime"

Time is a element of the universe, just as our 3 physical dimentions.

 

[BasketDaN]

Originally posted by Deeviant
Actually, time really does exist. There is a reason why we use the term "spacetime"

Time is a element of the universe, just as our 3 physical dimentions.

That's what some people think, but I really don't believe it at all. Time is something humans invented, just like any measurement system.

 

[Loren Booda]

Think quick! The Temporal Conspiracy has been uncovered!

 

[john 8]

Can we then conclude that physics does not exist, or just that vectors ultimately have no global meaning?

What are you saying? If BasketDaN thinks that time or centimeters do not exist, than don't you think that giving evidence that these things have physical existence as independent units that exist on their own would be a more appropriate response?

What you did say really did not clear up the issue. Don't you agree.

As for the existence of time, I too agree with BasketDaN. Time is not a physical thing, it is a human concept.


Every measurement of time is based on what man decided that measurement to mean. Seconds, minutes, hours and so on are all man made. Time did not come pre-packaged in these units, man agreed on what to call these durations. Clocks measure how much of a pre-determined man made unit passed for a given motion. If something takes a minute of time, then that activity lasted for what man determined to be a minute. Time is the concept of man.

If you disagree with this please feel free to provide evidence of the physical nature of time.

Some observation or scientific reference that provides proof beyond a reasonable doubt that time is a physical thing would be nice.

Thank You.

 

[john 8]

Actually, time really does exist..

Exists in what form?

Time is a element of the universe, just as our 3 physical dimentions.

When you say time is an element of the universe do you mean time is one of the chemical elements? Can you be more specific in what you mean by element.

As for dimensions, are you saying that these too are chemical elements?

 

[LogicalTime]

The one thing people will agree on is that most current theories use time or space-time somehow. Now time/space/space-time may exist or may not, but nonetheless these are useful in these models. This is all we really can agree on at this time.

If you have an idea like "time does not exist" check out the consequences of that hypothesis and form a testable theory (the term "Testable theory" is a bit redundant I suppose).

 

[cesiumfrog]

A lot has been made of time's arrow not appearing in the equations of [..] statistical mechanics

That's incorrect. A random variation is statistically more likely to produce a less ordered state rather than a more ordered state. This can be proven mathematically, and from it the third law of thermodynamics (the arrow of time) follows. (The remaining mystery is only why the universe should have been destined for so improbable a state at what we call its beginning, since it seems a much less improbable one would have sufficed to produce agents such as us.)

 

[Phrak]

A lot has been made of time's arrow not appearing in the equations of Newton, statistical mechanics, relativity and quantum mechanics ...

It does appear in statistical mechanics as entropy. It also seems to make an implicit appearance in quantum mechanics. Edit: btw, I left out CPT symmetry.

As for the rest of these posts, existence is a philosophics topic, and as argued here, one in need of symmantical help.

 

[Loren Booda]

John 8,

Remember your Planck units, of which Planck time (=1.616... x 10^-33 cm) is one. It is not man made as much as a massless, radiative, natural measurement.
_________

For you statistical mechanics, time as you describe it would seem not absolute, but according to Clausius have a nonzero (albeit diametrically unequal) probability of either going "forward" or "backward." At least that's how I interpret it.
__________

Phrak,

What is the take on CPT asymmetry, anyway? Is it a local or global property?

How about this time asymmetry in quantum mechanics you mention?

 

[john 8]

John 8,

Remember your Planck units, of which Planck time (=1.616... x 10^-33 cm) is one. It is not man made as much as a massless, radiative, natural measurement.
_________

For you statistical mechanics, time as you describe it would seem not absolute, but according to Clausius have a nonzero (albeit diametrically unequal) probability of either going "forward" or "backward." At least that's how I interpret it.
__________

Phrak,

What is the take on CPT asymmetry, anyway? Is it a local or global property?

How about this time asymmetry in quantum mechanics you mention?

Max Planck was a man. This man established a measurement. Planck time would be man made.

Do you think time is a physical thing of some sort?

 

[lol1986]

If time is not exist, how can it will be twin paradox phenomena? Gravity can changes times, so why shouldn't time is physical?

 

[OAQfirst]

I don't see much discussion following the original question.

Can any cosmological phenomenon be shown to obey an overall physical vector?

 

[Coldcall]

Going back to the OP:

I think time's apparent asymmetric nature was locked in at the moment of the big bang, and therefore; time is not reversible. To turn the clock back one would have to somehow overcome the force and direction to which symmetry broke at the BB. However i don't think time exists in any objective form other than it being a "sense" of our reality. To me it appears as a sort of directional bias of which we are aware because - after all - we too are products of this same universe. Our sense of time is deeply affected by the movement of large astronomical bodies like the sun and moon etc..So it serves a handy way to measure the interval between various movements, and as we've evolved we use "time" to organise our lives in a more efficient manner.

There is no way to keep time unless there is a physical universe which contains things that are moving to which we can set our time.

 

[Chrisc]

I don't see much discussion following the original question.

Can any cosmological phenomenon be shown to obey an overall physical vector?

Yes, the cosmological phenomenon we call gravitation.
All mass gravitates and all mass gravitates in the same direction - toward mass.
If you are looking for a vector that is a universal physical constant, that would be it.
If you are looking for an absolute vector, there are none, as gravitation is a three
dimensional force.
The day any mass moves away from another without being persuaded to do so by some force other than gravity, will be the day the gravity vector reverses and time will be reversed.

 

[Phrak]

Yes, the cosmological phenomenon we call gravitation.
All mass gravitates and all mass gravitates in the same direction - toward mass.

Unfortunately, gravitation is time symmetric. Eliptical orbits are still eliptical orbits with t is replaced by -t. To make things easy, just think of running the film backwards. You still see the Earth orbiting the sun and nothing appears amiss.

Though, orbital decay is the result of friction. Friction is a thermodynamic process.

 

[john 8]

If time is not exist, how can it will be twin paradox phenomena? Gravity can changes times, so why shouldn't time is physical?

You bring up a valid question. So why don't you start by tell us in your own words what your idea of time is, I think this will help answer your question.

I say time is actually a consideration based on our perception of the movement of objects. There is a distance, there is a velocity of the objects travel, and that movement of that object or particle in relationship to its starting point and in relationship to its ending point is what gives us the idea of time. Time is a manifestation which has no existence beyond the idea of time brought about by the motion of objects, where an object may be either energy or matter. Time is not a thing that flows. Time does not move or cause things to move. It is this perception of motion which gives us the idea of time.


What do you think?

 

[john 8]

Going back to the OP:

I think time's apparent asymmetric nature was locked in at the moment of the big bang, and therefore; time is not reversible. To turn the clock back one would have to somehow overcome the force and direction to which symmetry broke at the BB. However i don't think time exists in any objective form other than it being a "sense" of our reality. To me it appears as a sort of directional bias of which we are aware because - after all - we too are products of this same universe. Our sense of time is deeply affected by the movement of large astronomical bodies like the sun and moon etc..So it serves a handy way to measure the interval between various movements, and as we've evolved we use "time" to organise our lives in a more efficient manner.

There is no way to keep time unless there is a physical universe which contains things that are moving to which we can set our time.

Hi Coldcall. After reading the above post I thought that I would see if you can sort out what you are trying to say about time. I will just take your statement and handle one section at a time.

I think time's apparent asymmetric nature was locked in at the moment of the big bang, and therefore; time is not reversible..

Here you seem to sugest that time was created by a supernatural explosion, the Big Bang.

However i don't think time exists in any objective form other than it being a "sense" of our reality.

Here you say time does not exist in any objective form. It is some sense. So what is it? Something created? Or some concept or sense?

I only ask you this so that I can understand what you are trying to say.

I will agree with your idea that our concept of time is due to the motion of things around us.


Time is actually a consideration based on our perception of the movement of objects. There is a distance, there is a velocity of the objects travel, and that movement of that object or particle in relationship to its starting point and in relationship to its ending point is what gives us the idea of time. Time is a manifestation which has no existence beyond the idea of time brought about by the motion of objects, where an object may be either energy or matter. Time is not a thing that flows. Time does not move or cause things to move. It is this perception of motion which gives us the idea of time.

 

[Dale]

Every measurement of time is based on what man decided that measurement to mean. Seconds, minutes, hours and so on are all man made. Time did not come pre-packaged in these units, man agreed on what to call these durations. Clocks measure how much of a pre-determined man made unit passed for a given motion. If something takes a minute of time, then that activity lasted for what man determined to be a minute. Time is the concept of man.

following this same train of thought:

"Every measurement of mass is based on what man decided that measurement to mean. Kilograms, slugs, tons and so on are all man made. Mass did not come pre-packaged in these units, man agreed on what to call these amounts. Balance scales measure how much of a pre-determined man made unit balances a given object. If something is a kilogram of mass, then that object balances what man determined to be a kilogram. Mass is the concept of man."

Do you really think that mass is not physical? If not, then how is your logic plausible for time if it is so obviously not plausible for mass?

 

[Coldcall]

John8,

"Here you seem to sugest that time was created by a supernatural explosion, the Big Bang"

Supernatural? No I don't think i classed it as supernatural. But yes, as it stands at the moment, it appears the BB started off the universe. Or at least its the best theory that fits in with our current observations about the state of the universe.

"Here you say time does not exist in any objective form. It is some sense. So what is it? Something created? Or some concept or sense?"

No I don't think its been created as such; more like an emergent property or by-product of a universe in motion. I think Einstein's take on "time" is probably the most accurate we have at the moment in that space and time are sort of a combined property. Without "space" there cannot be "time", as there would be no measurable intervals in a universe with no space for movement to occur.

Basically without the properties of physical velocity and position there would be no "time". But "time" as we understand the phenomenom plays a vital role in biological complexity, and human ability to self-organise. So while "time" is a by-product of the physicality of the universe or our reality, we as intelligent animals have used that emergent property as a useful tool to organise.

 

[Phrak]

No I don't think its [time has] been created as such; more like an emergent property or by-product of a universe in motion. I think Einstein's take on "time" is probably the most accurate we have at the moment in that space and time are sort of a combined property. Without "space" there cannot be "time", as there would be no measurable intervals in a universe with no space for movement to occur.

While I understand you're efforts to understand, and I've gone over this same emergent idea as you have, you have to be careful.

How can time emerge? Was it absent at one time, to appear later after some previous cause? The argument doesn't really hang together well.

It's rather frustrating in the English language doesn't provide the verb structure required to made concise and definitive statements about these things, that don't sound meaningless.

 

[Coldcall]

Phrak,

Well I am of the school that believes "time" did not exist before the universe was created. Without any "space" for things to move around in there is unlikely to be "time".

So in essence "time" emerged with the birth of the universe.

It may not hang together all that well but it beats the idea that "time" existed before the birth of the universe.

 

[ThomasT]

A lot has been made of time's arrow not appearing in the equations of Newton, statistical mechanics, relativity and quantum mechanics - none preferring that past precedes the future or vice versa.

The physical processes that equations of motion are applied to are, for the most part, afaik, irreversible. Nature, afaik, isn't rewindable. An equation of motion is just a mathematical template that can be applied to the evolution of any physical system that it's appropriately associated with. And, insofar as it describes the evolution of a system, then it is, in that instance of use, describing an arrow of time.

Some very specific particle processes do seem to follow an asymmetry of time, but they are the far greater exception for interactions in general.

Afaik, all natural processes evolve asymmetrically. The arrow of time might be a bit easier to see in some than in others.

We ask if time as a universal property has a preferred direction.

Yes, there seem to be some good reasons to believe that the universe is expanding, that its contents are dispersing and dissipating, and that it is evolving toward equilibrium.

I ask if any cosmological phenomenon has been shown to obey an overall physical vector.

I think so, but you should ask the astronomy and cosmology people about this.

 

[Coldcall]

In my opinion, time is 100% irreversible. The reason why some people think it could be reversible is the fault of various scientific and mathematical interpretations which cause certain systems to "appear" as if they could be time reversible.

My argument for the irreversibility of time is based on the assumption that "time" got going when the universe broke into an asymmetric reality, in other words, at the BB, or at the inflationary period where space expanded exponentially.

So if "time's direction" was set at the BB then its quite unlikely we can now change its direction without having access to BB itself.

 

[Chrisc]

Unfortunately, gravitation is time symmetric. Eliptical orbits are still eliptical orbits with t is replaced by -t. To make things easy, just think of running the film backwards. You still see the Earth orbiting the sun and nothing appears amiss.

Though, orbital decay is the result of friction. Friction is a thermodynamic process.

If one makes a movie of the gravitational kinematics of orbits(the periodicity of motion)
when gravity is an attractive force, observing the movie in reverse is not evidence of
the time symmetry of gravitation it is evidence of the time symmetry of kinematics when
gravity is still an attractive force. This can be seen in any periodic motion run in reverse.
Kinematics arise from dynamics and since the movie is a fixed record of the
periodicity of orbital kinematics arising from attractive dynamics of gravitation,
running the movie backward does not change that record it simply presents inverse kinematics.

If you hold to the idea that the kinematics observed in a movie running in reverse is evidence
of the dynamics giving rise to such inverse kinematics, then you would have
to admit a film of two masses moving together would produce evidence of
gravitational "repulsion" when that movie is run in reverse and the masses move apart.

Likewise, that the orbital kinematics of gravitation are unchanged with the change of the sign of t to -t,
is not evidence that gravitation remains attractive with the reversal of time. It is simply evidence
of the fact that we consider time the order of kinematic events. It is not evidence of the
time symmetry of the dynamics giving rise to these kinematical events unless you
are willing to allow the kinematics of gravitational attraction to reverse due to gravitational
repulsion.

 

[Phrak]

If one makes a movie of the gravitational kinematics of orbits(the periodicity of motion)
when gravity is an attractive force, observing the movie in reverse is not evidence of
the time symmetry of gravitation it is evidence of the time symmetry of kinematics when
gravity is still an attractive force. This can be seen in any periodic motion run in reverse.
Kinematics arise from dynamics and since the movie is a fixed record of the
periodicity of orbital kinematics arising from attractive dynamics of gravitation,
running the movie backward does not change that record it simply presents inverse kinematics.

If you hold to the idea that the kinematics observed in a movie running in reverse is evidence
of the dynamics giving rise to such inverse kinematics, then you would have
to admit a film of two masses moving together would produce evidence of
gravitational "repulsion" when that movie is run in reverse and the masses move apart.

Likewise, that the orbital kinematics of gravitation are unchanged with the change of the sign of t to -t,
is not evidence that gravitation remains attractive with the reversal of time. It is simply evidence
of the fact that we consider time the order of kinematic events. It is not evidence of the
time symmetry of the dynamics giving rise to these kinematical events unless you
are willing to allow the kinematics of gravitational attraction to reverse due to gravitational
repulsion.

That's a good argument that deserves more than the handwaving answer of 'running the movie backwards'. It gave me some pause for thought, not having looked at the details.

I think the question might be best stated as: "Is Newton's law of gravity
F = \frac{mMG}{r^2}
unchanged where t is replaced with -t?

F, is of course, directed inward, normally.

The force of gravity is not much different than any other force. We could think of the attractive force of gravity as a spring in extension connecting two masses. The spring just happens to have force that acts inversely proportional to r squared.

To make things simple, consider a circular orbit where we can replace the attractive force of gravity with the a connecting string in tension. The force of the string on the rotating mass is always directed inward, no matter if the orbiting mass is spinning in one direction or the other, which something like what we might see running the movie backward and if the force of gravity really is unchanged under time reversal.

So consider a mass in a circular orbit around a larger mass. The change in velocity is perpendicular to it's motion and directed inward. It may be maintained in it's circular orbit by a gravitational force, F_gravity = ma. F and the acceleration point in the same direction, inward. When it's trajectory x=x(t) is is replace with x=x(-t) the orbit is reversed in direction, but the change in velocity, the acceleration, is still directed inward.

Perhaps this is what we should have expected, since time doesn't appear in equation for gravitational force, but it's better to see why it doesn't appear.

Hope this helps.

 

[Chrisc]

That's a good argument that deserves more than the handwaving answer of 'running the movie backwards'. It gave me some pause for thought, not having looked at the details.

I think the question might be best stated as: "Is Newton's law of gravity
F = \frac{mMG}{r^2}
unchanged where t is replaced with -t?

F, is of course, directed inward, normally.

The force of gravity is not much different than any other force. We could think of the attractive force of gravity as a spring in extension connecting two masses. The spring just happens to have force that acts inversely proportional to r squared.

To make things simple, consider a circular orbit where we can replace the attractive force of gravity with the a connecting string in tension. The force of the string on the rotating mass is always directed inward, no matter if the orbiting mass is spinning in one direction or the other, which something like what we might see running the movie backward and if the force of gravity really is unchanged under time reversal.

So consider a mass in a circular orbit around a larger mass. The change in velocity is perpendicular to it's motion and directed inward. It may be maintained in it's circular orbit by a gravitational force, F_gravity = ma. F and the acceleration point in the same direction, inward. When it's trajectory x=x(t) is is replace with x=x(-t) the orbit is reversed in direction, but the change in velocity, the acceleration, is still directed inward.

Perhaps this is what we should have expected, since time doesn't appear in equation for gravitational force, but it's better to see why it doesn't appear.

Hope this helps.

I am not sure I made my point clear since you have substituted the "hand waving" of springs and strings
in place of the "hand waving" of movies.
You have again predetermined the spring force (gravitation) will remain unchanged under a
translation in time "because" changing the sign of t leaves the direction of force unchanged.
You seem to have justified this by claiming t does not appear in the equation of gravitation,
so changing t will not change the direction of the force of gravitation.
Do you not see that you've used the kinematics to define the dynamics by pre-designating the
dynamics as unchanged? You've let the sign of t create a circular argument for the time
symmetry of the dynamics of gravitation, when in fact all the sign of t is affording you is
the ability to predict the reverse kinematics "IF" gravitation remains unchanged.
If gravitation remains unchanged through a translation in time, the second law of thermodynamics
would not exist.
That's a problem.

 

[Phrak]

I am not sure I made my point clear since you have substituted the "hand waving" of springs and strings
in place of the "hand waving" of movies.
You have again predetermined the spring force (gravitation) will remain unchanged under a
translation in time "because" changing the sign of t leaves the direction of force unchanged.
You seem to have justified this by claiming t does not appear in the equation of gravitation,
so changing t will not change the direction of the force of gravitation.
Do you not see that you've used the kinematics to define the dynamics by pre-designating the
dynamics as unchanged? You've let the sign of t create a circular argument for the time
symmetry of the dynamics of gravitation, when in fact all the sign of t is affording you is
the ability to predict the reverse kinematics "IF" gravitation remains unchanged.

No, no, it's not a circular argument. (BTW, that would be temperal 'inversion', rather than translation.)

You seem to think that all vectors such as acceleration and force should be inverted on inverting t. That depends on the equations of motion for any given physical arrangement.

Believe what you wish. I won't bother this further until you give a mathematical example.

If gravitation remains unchanged through a translation in time, the second law of thermodynamics
would not exist.
That's a problem.

This does not follow.
I have no idea what gives you this idea.

 

[john 8]

Originally Posted by john 8
Every measurement of time is based on what man decided that measurement to mean. Seconds, minutes, hours and so on are all man made. Time did not come pre-packaged in these units, man agreed on what to call these durations. Clocks measure how much of a pre-determined man made unit passed for a given motion. If something takes a minute of time, then that activity lasted for what man determined to be a minute. Time is the concept of man.

: following this same train of thought:

"Every measurement of mass is based on what man decided that measurement to mean. Kilograms, slugs, tons and so on are all man made. Mass did not come pre-packaged in these units, man agreed on what to call these amounts. Balance scales measure how much of a pre-determined man made unit balances a given object. If something is a kilogram of mass, then that object balances what man determined to be a kilogram. Mass is the concept of man."

Do you really think that mass is not physical? If not, then how is your logic plausible for time if it is so obviously not plausible for mass?

Holy crap! Do you really think that this is a logical argument in favor of your idea that time is a physical thing? I never said mass was not physical. Though your flawed logic makes it appear so.

Really? Did you even think this through? It sounds more like a knee jerk reaction.

Well you put this out here, so I will respond to it, but please think your thoughts through a bit better.

Here I go. I say that time is not a physical thing. You say time is a physical thing.

I say that there is no written or observational evidence that provides evidence that time is a physical thing.

You say time is a physical thing and yet have not given any scientific evidence to back up your claim. I am just supposed to take your word for it. Sorry, that is not science.



I said that every measurement of time is based on what man decided that measurement to be.

You wanted to use my example of time and replace time with mass and try to logically show that if mass is a real physical thing then time is a real physical thing. I like your ingenuity, yet it is severely flawed and I will show you how.

I will totally agree with you 100% that when you replace the term time with the term mass what you said is true about mass.

Here is where your logic falls flat:

Balance scales measure how much of a pre-determined man made unit of a given object is .

Balance scales require that you put a real physical object on it in order for that scale to give a man made unit. The important point here is, mass is a real physical thing and does not need to be measured in order for it to be a physical thing. Mass was a physical thing before it was measured. Mass is a physical thing even if it is not measured. Mass is defined in scientific reference books as something that is a real physical thing. Time is not.

You see, we already know that mass is a physical thing, measuring this thing does not change it. You are already applying a known physical thing to a scale and getting a man made unit of that measurement. The mass is an outside influence that is added to the scale and the scale then reacts to this influence (mass) and gives a man made measurement. The scale is provided a real physical thing, that thing was physical before it was measured.

Now time on the other hand is not a known physical thing that is defined as such in any scientific reference book. Clocks do not measure time. Time is not an outside influence that effects the movement of the clock.

In order for a clock to measure a thing called time then a clock would have to be constructed to measure this outside influence you call time. Time would have to be made in such a way as to have the ability to effect other physical objects. In order for any thing to have the ability to influence other physical objects that thing would have to be physical in some way, either a particle or a wave. So this rules out time as being a physical thing since it is neither a particle or a wave.

Your logic is faulty because mass is already known to be a real physical thing so your example does not prove that mass is a real physical thing because it can be measured. Mass was already a thing.



Clocks are a man made device operating as man designed it, counting off man made increments that man gave a numeric significance to, that results in a man made concept called time. Clocks are designed to give numbers, to which man assigns a significance or importance to. A clock could be considered to be a device or machine that generates a number or numbers in a regulated manner that was pre-determined by man. A clock is akin to a regulated number generator that converts mechanical, electrical, or the motion of an object to a number through a pre-determined engineering of the device, and these numbers are delivered at a rate that follows the set standards that man has agreed to be universal in all such machines.


Please share with me your definition of a clock and time that shows that clocks actually measure anything outside of its immediate construction. What outside influence is a clock measuring?


In order for your logic to be correct you will have to show that time is a physical thing before it is measured.

If time is physical it will be either a particle or a wave. Which is it?

 

[Chrisc]

No, no, it's not a circular argument. (BTW, that would be temperal 'inversion', rather than translation.)

It is circular. You've claimed that changing the sign of time "results" in inverted kinematics with no regard for the dynamics that gave rise to those kinematics in
the first place. Then you claim your inverted kinematics prove the dynamics are unchanged.
All you've done is shown the kinematical symmetry between left and right hand orbits.

You seem to think that all vectors such as acceleration and force should be inverted on inverting t. That depends on the equations of motion for any given physical arrangement.

Of course it depends on the equations of motion, but it depends on more than the kinematics of those equations.

Believe what you wish.

It is not belief, it is reason.

I won't bother this further until you give a mathematical example.

The mathematical example is your own, "When it's trajectory x=x(t) is is replace with x=x(-t) the orbit is reversed in direction, but the change in velocity, the acceleration, is still directed inward."

Why is the acceleration still directed inward? Is this something you've discovered or are you aware that all you've done is changed the orbit from left to right or right to left?

If I flip the spring in my clock, the hands will run backward. But the spring is still losing tension just as it was when the hands ran forward. This flip of the spring is what you are defining as time. It is not. It is the dynamics of the spring force that determines the kinematics of the hands or which way time runs. It is not the kinematics of the hands that determine which way time runs.

This does not follow.

It does, but you won't see it if you insist time is nothing more than kinematics.

I have no idea what gives you this idea.

It will make sense when you realize kinematics arise from dynamics. The second law of thermo"dynamics" expresses the indisputable empirical evidence of the order of events observed in the kinematics arising from . . . dynamics.

 

[Office_Shredder]

No, no, it's not a circular argument. (BTW, that would be temperal 'inversion', rather than translation.)

It's not very convincing considering all you've done is pick a periodic process and act shocked that it's periodic. Most people don't think of gravity as orbiting bodies, but as things falling or coming together. Is that process time reversible?

Also, G has a time unit component, so if you reversed time you have no reason to believe G will be unchanged

 

[Phrak]

Either of you two can use all the rhetoric you wish, but unit you put up with a concrete, mathematically backed example, I'm done with this parade. In either case you will fail to provide a valid argument, so it is moot.

 

[Dale]

Do you really think that this is a logical argument in favor of your idea that time is a physical thing?

Certainly not. It is a "reductio ad absurdum" rebuttal of your argument, not an a affirmative argument in favor of my position.

If time is physical it will be either a particle or a wave. Which is it?

I notice that you have dropped your "physics is about either matter or energy" in the other thread for this "physics is about either particles or waves". You are making the same argument with different categories so I will give you the same response as I gave https://www.physicsforums.com/showpost.php?p=1972713&postcount=53":

I wouldn't categorize physics like that, nor have I ever seen anyone else do so. Since you are making up this categorization, which category do you think distance belongs in? You should put time in the same category.

Also, what is your time-free definition of a wave?

 

[gendou2]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

 

[ZapperZ]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

But there are many phenomena that have a broken time reversal symmetry[1,2]. In fact, the CP violating events in kaon decays indirectly implies a broken T symmetry in such decays.

Zz.

[1] Covington et al. PRL 79, 277 (1997).
[2] Kaminski et al. Nature, 416, 610 (2002).

 

[Chrisc]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

I certainly do.
That's what my posts refuting Phrak's comments are about.
What's missing is the Principle of General Relativity applied to our "qualification" of fundamental
dimension instead of as it is now, just a quantification of measure. This is the reason the constant
debate over as you put it, the "categorization" of time continues.
It is also why such dimensional equivalences expressed by E=mc^2 are falsifiable and incredibly accurate "quantitatively".
If you're interested, I have submitted a model of time that predicts the second law of thermodynamics
in the FQXI.org contest.
"The Heuristic Significance of the Principle of General Relativity on the Nature of Time"
It is probably too absurd for most to appreciate, but might help you understand the dilemma.

As for your question of the time symmetry of the laws of physics, you will find all the laws are
and always will be time symmetric as long as the operational definition of time remains the accepted
definition of time in physics.
Any argument against such a kinematical-mathematical operation is futile as it amounts to disputing
the axioms of mathematics. Without any concern for the identities, kinematic and dynamic the math
represents, this operational definition of time cannot fail. This is the gist of Phrak's argument above.

So as long as we ignore the evidence of the second law (the most pervasive empirical evidence in
the history of the universe) and as long as we do not care about the few exceptions such as ZapperZ
pointed out, we can keep our heads in the sand and look for more comfortable solutions.

 

[Dale]

All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).

No, as mentioned above not all known laws are time-symmetric. The "boringness" of the broken egg experiment is governed by the time asymmetric 2nd law of thermo: dS/dt >= 0.

 

[ThomasT]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

The second law of thermodynamics is the thermodynamic arrow of time.

The basic equations of motion are time-independent.

The arrow of time does appear in experiments.

The universe is expanding. Since this is the source of all motion, maybe it can be used as the basis for some new fundamental law of physics.

The source of the expansion is an unsolvable problem.

 

[DB Katzin]

That's what some people think, but I really don't believe it at all. Time is something humans invented, just like any measurement system.

I think there is a distinction between a "measuring system" and the object the system is measuring. When one is describing the physical characteristic of an object the system: meters vs. yards, pounds vs. Kg is certainly arbitrary and invented but the object and quality being measured is something we all sense more or less in common: how big it is, how heavy it is, etc. Time it seems is different. When describing something when we ask how old is it we are not talking about an intrinsic quality you can rub up against like size or weight, even color or smell. Yet we all know what is being asked even if our measuring system differs: hours, days vs. moons since the great fire, etc. But I think you mean something different when you say "time is invented." Don't you mean something like this. We live in a world where we are aware of change. We change, the seasons change, the weather changes, the world changes. But not at the same rate. We need things like 2 o'clock so we can coordinate activities--something we do a lot of in complex society. So we count up a bunch of changes--sunrises, quartz crystal vibrations, etc and we standardize it so we know when to do stuff in relation to other stuff. But you don't find time anywhere. Even though you can spend time, you can't buy much with it, and even though you can save time, you can't put it in the back and get interest.