Arrow of time

[Greg Boyles]

I don't understand how any theoretical physicist can credibly argue that the arrow of time is entirely a product of human perception and that it doesn't really exist when we have such things as the fossil record that clearly demonstrates that time has proceeded long before there were humans around to perceive it.

 

Just been watching the documentary Through the Wormhole - Does Time Really Exist?

[Iggy]

Is there something you can point to where a physicist says "the arrow of time is entirely a product of human perception"?

[IM Egdall]

The problem is the equations of physics are time-symmetric -- that is they work just as well going in both time directions. So it is hard for physicists to come up with a physics-based explanation for the arrow of time.

 

see for example: http://en.wikipedia....i/Arrow_of_time

 

The so-called second law of thermodynamics, however, does imply a direction of time -- but this is associated with a probability for a large number of constituents, and does not apply to just a few particles.

 

But I think you make a good point. Relics from the past are evidence for the arrow of time - aren't they?

Edited October 31, 2011 by IM Egdall

[swansont]

The problem is the equations of physics are time-symmetric -- that is they work just as well going in both time directions. So it is hard for physicists to come up with a physics-based explanation for the arrow of time.

 

Except for the second law of thermodynamics.

[Iggy]

Except for the second law of thermodynamics.

I've never understood this -- although I have frequently heard it repeated.

 

If you assume that heat moves from higher temp to lower temp then entropy increases over time. If you reverse time then entropy decreases. That, or so I assume, represents our arrow of time. Entropy increases in only one direction.

 

In classical mechanics (as an example)we can push a mass and it will accelerate. The application of a force on a mass makes it accelerate. Reversing time naturally means the mass decelerate.

 

When time advances one way the velocity increases and when time runs the other way velocity decreases.

 

But, the body from which the force is generated is switched around in the two cases. Just as thermodynamics assumes that heat moves one way so too does classical mechanics assume that force moves one way.

 

When this is taken into account I don't see exactly how thermodynamics represents the only arrow of time in physics -- or, indeed, an arrow of time at all.

 

More than that -- thermodynamic entropy is equivalent to statistical entropy. When thermodynamic entropy is a proven effect of statistical entropy (and that has been proven) the appropriate model of a gas or a solid is the kinetic theory of a gas or solid and they use classical mechanics.

 

In this light it would be literally impossible to say that thermodynamics represents our only example of an arrow of time. If it does have an arrow then by necessity something else does too.

 

That would be my point / question. I don't understand (though I have often heard) that physics doesn't have an arrow except for thermodynamics.

Edited November 1, 2011 by Iggy

[Greg Boyles]

Is there something you can point to where a physicist says "the arrow of time is entirely a product of human perception"?

 

 

In the afore mentioned documentary.

[Mystery111]

I don't understand how any theoretical physicist can credibly argue that the arrow of time is entirely a product of human perception and that it doesn't really exist when we have such things as the fossil record that clearly demonstrates that time has proceeded long before there were humans around to perceive it.

 

Just been watching the documentary Through the Wormhole - Does Time Really Exist?

 

Because the arguements against an arrow of time far outweigh any logical aruements suggesting such an abstraction even exists! Physics can easily demonstrate verbally at least that such a theory of an arrow is devoid of meaning. The only arrow which makes sense is a psychological arrow of time, which is directly linked to our sense of perception, the way events arise linearly in our perception.

 

I've never understood this -- although I have frequently heard it repeated.

 

If you assume that heat moves from higher temp to lower temp then entropy increases over time. If you reverse time then entropy decreases. That, or so I assume, represents our arrow of time. Entropy increases in only one direction.

 

In classical mechanics (as an example)we can push a mass and it will accelerate. The application of a force on a mass makes it accelerate. Reversing time naturally means the mass decelerate.

 

When time advances one way the velocity increases and when time runs the other way velocity decreases.

 

But, the body from which the force is generated is switched around in the two cases. Just as thermodynamics assumes that heat moves one way so too does classical mechanics assume that force moves one way.

 

When this is taken into account I don't see exactly how thermodynamics represents the only arrow of time in physics -- or, indeed, an arrow of time at all.

 

More than that -- thermodynamic entropy is equivalent to statistical entropy. When thermodynamic entropy is a proven effect of statistical entropy (and that has been proven) the appropriate model of a gas or a solid is the kinetic theory of a gas or solid and they use classical mechanics.

 

In this light it would be literally impossible to say that thermodynamics represents our only example of an arrow of time. If it does have an arrow then by necessity something else does too.

 

That would be my point / question. I don't understand (though I have often heard) that physics doesn't have an arrow except for thermodynamics.

 

Not even a thermodynamic arrow is true. That arrow still assumes that time is linear, which it is not.

[Iggy]

In the afore mentioned documentary.

Do you know if it's available online? I'm looking for something to sink my teeth into -- this being a subject of which I've never seemed to be able to get enough.

 

You said something attributed to a physicist that surprised me, and I would love to hear their reasoning behind it. Anyone else who knows of a physicist saying and explaining the same -- I'd be eternally grateful.

 

EDIT:

 

At least... do you know who the physicist was?

Edited November 1, 2011 by Iggy

[swansont]

In the afore mentioned documentary.

 

Who said it? You don't mention anyone by name or provide a quote or a link.

 

I've never understood this -- although I have frequently heard it repeated.

 

If you assume that heat moves from higher temp to lower temp then entropy increases over time. If you reverse time then entropy decreases. That, or so I assume, represents our arrow of time. Entropy increases in only one direction.

 

In classical mechanics (as an example)we can push a mass and it will accelerate. The application of a force on a mass makes it accelerate. Reversing time naturally means the mass decelerate.

 

When time advances one way the velocity increases and when time runs the other way velocity decreases.

 

But, the body from which the force is generated is switched around in the two cases. Just as thermodynamics assumes that heat moves one way so too does classical mechanics assume that force moves one way.

 

When this is taken into account I don't see exactly how thermodynamics represents the only arrow of time in physics -- or, indeed, an arrow of time at all.

 

More than that -- thermodynamic entropy is equivalent to statistical entropy. When thermodynamic entropy is a proven effect of statistical entropy (and that has been proven) the appropriate model of a gas or a solid is the kinetic theory of a gas or solid and they use classical mechanics.

 

In this light it would be literally impossible to say that thermodynamics represents our only example of an arrow of time. If it does have an arrow then by necessity something else does too.

 

That would be my point / question. I don't understand (though I have often heard) that physics doesn't have an arrow except for thermodynamics.

 

Entropy in the second law is represented by an inequality. It is not symmetric. You have a situation where entropy can't decrease but when you do time reversal, it can.

[Iggy]

Entropy in the second law is represented by an inequality. It is not symmetric. You have a situation where entropy can't decrease but when you do time reversal, it can.

While I said that exactly in my last post and spoke about it extensively (indeed, used it as my one and only example), I will consider it further.

 

EDIT:

 

If anyone has something additional relevant, I welcome it.

Edited November 1, 2011 by Iggy

[Greg Boyles]

Because the arguements against an arrow of time far outweigh any logical aruements suggesting such an abstraction even exists! Physics can easily demonstrate verbally at least that such a theory of an arrow is devoid of meaning. The only arrow which makes sense is a psychological arrow of time, which is directly linked to our sense of perception, the way events arise linearly in our perception.

 

 

 

Not even a thermodynamic arrow is true. That arrow still assumes that time is linear, which it is not.

 

If it is not linear then what is it?

 

There has to me some significance to the fact that all creatures experience forward linear time identically to us in terms of aging and death etc.

 

There has to some signficance to the fact that ALL geological features progress in a manor that is consistent with our perception of forward linear time. I.E. We have never found a mountain range that has grown as a result of water flow and wind etc.

 

Although I agree that individuals' perception of the rate of flow of time can be subjective.

[Mystery111]

If it is not linear then what is it?

 

Non-linear and geometrical. Big Bang did not happen at one place either, it happened everywhere, so if you can use your imagination for a moment, what would that mean to any ''definate'' arrow of time?

 

The answer is you don't have one. If you want an arrow of time, a true phsical one, you connect all of spacetime to every other point of spacetime and draw arrows. You end up with an infinite amount of arrows of time, which is useless and bunk. You just don't have a defined past and space where you can say everything originated at.

 

There has to me some significance to the fact that all creatures experience forward linear time identically to us in terms of aging and death etc.

 

Do they experience it though? We know humans have the complex ability to catagorize the day into sets of hours and minutes, and while though all biological entities on Earth have internal clocks, such as sleep, eat ect, these other entities do not experience an objective time, that is applying our subjectivity on the holograph that we call perception. Time requires a very complex understanding of the world, which I doubt anything on Earth apart from a Human can appreciate.

 

It should be noted that the Suprachiasmatic Nucleus generates the ability to have the perception of a passing moment and it regulates our sense of time. This has been tested on fruitflies.

 

There has to some signficance to the fact that ALL geological features progress in a manor that is consistent with our perception of forward linear time. I.E. We have never found a mountain range that has grown as a result of water flow and wind etc.

 

Yes, the flow of time is due to our perception, and there is a name for it. It is called the Psychological Arrow of Time, which would be according to physics the only arrow that actually holds any meaning. It is the direct reason to why we ''think'' the world moves forward and our brain does this by doing something extraordinary: It creates the illusion that there really exists an objective known definate past and an expectant future. This ''boundary'' does not exist however in time according to quantum mechanics, which must mean one thing...

 

... Time cannot be an objective factor of the world where time can be flowing. It cannot be part of the physical nature of the world in any form other than knowing that time is an eternal present moment, stuck frozen as though as preserved in Amber.

 

Although I agree that individuals' perception of the rate of flow of time can be subjective.

 

That is due to the Suprachiasmatic Nucleus. Time rate of flow is a subjective phenomenon caused by this Gene.

Edited November 2, 2011 by Mystery111

[Greg Boyles]

Non-linear and geometrical. Big Bang did not happen at one place either, it happened everywhere, so if you can use your imagination for a moment, what would that mean to any ''definate'' arrow of time?

 

The answer is you don't have one. If you want an arrow of time, a true phsical one, you connect all of spacetime to every other point of spacetime and draw arrows. You end up with an infinite amount of arrows of time, which is useless and bunk. You just don't have a defined past and space where you can say everything originated at.

 

 

 

Do they experience it though? We know humans have the complex ability to catagorize the day into sets of hours and minutes, and while though all biological entities on Earth have internal clocks, such as sleep, eat ect, these other entities do not experience an objective time, that is applying our subjectivity on the holograph that we call perception. Time requires a very complex understanding of the world, which I doubt anything on Earth apart from a Human can appreciate.

 

It should be noted that the Suprachiasmatic Nucleus generates the ability to have the perception of a passing moment and it regulates our sense of time. This has been tested on fruitflies.

 

 

 

Yes, the flow of time is due to our perception, and there is a name for it. It is called the Psychological Arrow of Time, which would be according to physics the only arrow that actually holds any meaning. It is the direct reason to why we ''think'' the world moves forward and our brain does this by doing something extraordinary: It creates the illusion that there really exists an objective known definate past and an expectant future. This ''boundary'' does not exist however in time according to quantum mechanics, which must mean one thing...

 

... Time cannot be an objective factor of the world where time can be flowing. It cannot be part of the physical nature of the world in any form other than knowing that time is an eternal present moment, stuck frozen as though as preserved in Amber.

Then you would be effectively saying that there is no possible way we can be sure about evolution, the fossil record, the geological record and plate tectonics because interpretation of these is dependant upon our subjective epxerience of and interpretation of chronology.

 

Sorry but I don't see how you can sustain such as argument.

 

I think I subscribe to the previous suggestion that the problem is not with the arrow of time but rather with our mathematics that currently describe it as undefined.

 

That is due to the Suprachiasmatic Nucleus. Time rate of flow is a subjective phenomenon caused by this Gene.

Yes but the direction of flow appears to be a widesspread local phenomenum, at least in our tiny corner of the universe. And since our perception cannot encompass more than our tiny corner of the universe.......

 

I would agree that the rate of flow of time, and possibly even the arrow, is probably not universal across the entire cosmos.

Edited November 2, 2011 by Greg Boyles

[Mystery111]

Then you would be effectively saying that there is no possible way we can be sure about evolution, the fossil record, the geological record and plate tectonics because interpretation of these is dependant upon our subjective epxerience of and interpretation of chronology.

 

Sorry but I don't see how you can sustain such as argument.

 

I think I subscribe to the previous suggestion that the problem is not with the arrow of time but rather with our mathematics that currently describe it as undefined.

 

Not at all. Of course we have a record, I never said that the distinction of a past or future was not real: it is real to the human mind. In all honesty, what good does it do to even imagine time outside of this experience? If physics already says that a past and future don't really exist, then we can be assured that the records we do keep is a reflection of our psychological makeup.

 

And the problem of not having an arrow has a broad range of reasons. Physics for one could not entertain this outdated Newtonian linear perspective of time.

 

Yes but the direction of flow appears to be a widesspread local phenomenum, at least in our tiny corner of the universe. And since our perception cannot encompass more than our tiny corner of the universe.......

 

I would agree that the rate of flow of time, and possibly even the arrow, is probably not universal across the entire cosmos.

 

It's not a widespead phenomena at all. What... just because every human mind is able to discern it's own reflection on reality does not make it a widespread phenomenon. Our perception is all there is in the idea of a past, present and future coexisting.

Edited November 2, 2011 by Mystery111

[Greg Boyles]

Not at all. Of course we have a record, I never said that the distinction of a past or future was not real: it is real to the human mind. In all honesty, what good does it do to even imagine time outside of this experience? If physics already says that a past and future don't really exist, then we can be assured that the records we do keep is a reflection of our psychological makeup.

 

And the problem of not having an arrow has a broad range of reasons. Physics for one could not entertain this outdated Newtonian linear perspective of time.

 

 

 

It's not a widespead phenomena at all. What... just because every human mind is able to discern it's own reflection on reality does not make it a widespread phenomenon. Our perception is all there is in the idea of a past, present and future coexisting.

 

I think we are arguing around semantics here. Of course the past and present don't litterally exist for us in the present, at least not in a way that we can perceive them. Although einstein's theory states that time is a physical dimension and therefore the past, present and future literally exist simultaneously some where in space-time.

 

Science is supposed to eliminate human subjectivity and does a god job on the whole. Therefore our enquiries into geology, plate tectonics and evolution objectively prove that there is an arrow of time, not withstanding the specifics about how humans subjectively mark the passing of time individually.

[swansont]

So are you going to name the physicist(s) who claim this, or continue to ignore the request?

[Greg Boyles]

So are you going to name the physicist(s) who claim this, or continue to ignore the request?

 

 

I don't remember his name but he was featured in the documentary mentioned in my original post. The documentary is available on youtube if you are interested.

[imatfaal]

Through the Wormhole .... with Morgan Freeman

 

I didn't realise that Morgan Freeman was an actor AND a physicist

 

 

There is a list of experts - one of whom made the claim I would guess

http://science.discovery.com/tv/through-the-wormhole/ask-the-experts/

[IM Egdall]

Except for the second law of thermodynamics.

 

 

Yes, the second law of thermodynamics gives a forward arrow of time -- but it is a statistical law. It applies only to a large number of things. When we look at the behavior of a small number of particles, they show time symmetry. No arrow of time is revealed.

Edited November 3, 2011 by IM Egdall

[michel123456]

IMHO if you want to study time symmetry, you have to involve all physical processes including the ones that made up the particle itself. Maybe under time reversal a particle is not a (same)particle anymore.

IOW if you take the movie of a particle and turn it backward, it is not a correct time reversal (IMHO). Time symmetry should use a reversed particle (elcitrap) moving in negative time through negative distance under maybe negative energy & negative gravity. Turning only time upside-down gives only laughable results.

[swansont]

Yes, the second law of thermodynamics gives a forward arrow of time -- but it is a statistical law. It applies only to a large number of things. When we look at the behavior of a small number of particles, they show time symmetry. No arrow of time is revealed.

 

Yes, the amount of entropy is statistical, but the probability of interaction that give rise to the statistics show an asymmetry. The asymmetry tends to show up as soon as you have three particles and/or internal states.

 

e.g. It's physically possible for three particles to come together, stick to each other and be at rest, in the reversal of a simple explosion. But it's more likely that they don't. If we run a number of trials we would see that it does happen — in, say, one case out of a million, the particles would do that, and entropy would decrease. But the probability shows the asymmetry.

 

I don't remember his name but he was featured in the documentary mentioned in my original post. The documentary is available on youtube if you are interested.

If you can't remember his name, how do I know you accurately remembered what he said? This is your thread — you have some responsibility here.

[michel123456]

(...)e.g. It's physically possible for three particles to come together, stick to each other and be at rest, in the reversal of a simple explosion. But it's more likely that they don't. If we run a number of trials we would see that it does happen — in, say, one case out of a million, the particles would do that, and entropy would decrease. But the probability shows the asymmetry.

(...)

 

I guess you mean: without gravity. Because with gravity the 3 particles would stick together unavoidably.

[Mystery111]

Antiparticles have a negative vacuum energy and would be a particle moving backwards in time. But we don't see these effects so it is unlikely you can model proper particles moving backwards or even forwards in time. They might even be allowed to move at superluminal speeds and still not oscillate in time; they might even have a negative energy (though this actually is a frame-dependant assertion).

 

I think we are arguing around semantics here. Of course the past and present don't litterally exist for us in the present, at least not in a way that we can perceive them. Although einstein's theory states that time is a physical dimension and therefore the past, present and future literally exist simultaneously some where in space-time.

 

 

 

No, you arguing that an arrow of time exists from entropy. There is no such thing, as I have explained, past, present and future coexist side-by-side because we can discern a past and a present and a future to allow events to be recorded as though it were moving in some forward directionality.

[swansont]

I guess you mean: without gravity. Because with gravity the 3 particles would stick together unavoidably.

 

Gravity doesn't make the problem go away. You still need three particles colliding at the same instant, with momentum that adds to zero to get a time-reversed event. Gravitational collapse requires inelastic collisions, which is another example of this.

[michel123456]

Gravity doesn't make the problem go away. You still need three particles colliding at the same instant, (...)

yes.

with momentum that adds to zero to get a time-reversed event.(...)

Why? if you expect zero momentum, then the reverse explosion would never occur. What would be the cause of the separation of the 3 particles? Certainly not a zero state.