Thermodynamics

[Toby]

I was wondering if the 2nd law of thermodynamics still works in a vacuum?

I was always told that if there was no friction then something that started spinning would always spin but the 2nd law states that everything will eventually die out. Does this run true with this theory and if so how?

[SMF]

I don't think that the second law of thermodynamics says that everything will eventually die out. SM

[swansont]

Yes, it works in a vacuum. The second law says that entropy won't decrease spontaneously in a closed system. If the process is reversible, entropy doesn't increase.

[sacscale]

Yes, it works in a vacuum. The second law says that entropy won't decrease spontaneously in a closed system. If the process is reversible, entropy doesn't increase.

 

 

There are no perfectly reversible processes just as there isn't a perfect vacuum. Radioactive decay is spontaneous in a closed system while an object spinning in space is not a closed system and affected by other objects and energies.

[swansont]

There are no perfectly reversible processes just as there isn't a perfect vacuum. Radioactive decay is spontaneous in a closed system while an object spinning in space is not a closed system and affected by other objects and energies.

 

The lack of a perfect vacuum or closed system doesn't change the statement of the second law.

[farmboy]

The lack of a perfect vacuum or closed system doesn't change the statement of the second law.

 

Yeah exactly. You hear the second law (like many 'laws' these days) edited slightly to fit a specific topic or teaching method, and this is what leads to people asking questions like the OP's. To the OP, basically the second law just says that systems will move towards a state of increased entropy. This does mean that everything will die out, if you take die out to mean that all complexity will eventually be lost from the universe.

[sacscale]

The lack of a perfect vacuum or closed system doesn't change the statement of the second law.

 

 

A closed system is a required condition for the second law and the lack of a perfect vacuum would diffuse the energy of a spinning object.

[lemur]

Yeah exactly. You hear the second law (like many 'laws' these days) edited slightly to fit a specific topic or teaching method, and this is what leads to people asking questions like the OP's. To the OP, basically the second law just says that systems will move towards a state of increased entropy. This does mean that everything will die out, if you take die out to mean that all complexity will eventually be lost from the universe.

Wouldn't that only be the case if there were no forces that causes spontaneous organization (i.e. whatever the opposite of entropy is called)? Gravity seems to be such a force, imo, since it basically generates stratification within a gravity-well from greater to lesser density.

Edited March 20, 2011 by lemur

[swansont]

A closed system is a required condition for the second law and the lack of a perfect vacuum would diffuse the energy of a spinning object.

 

That doesn't change the statement of the second law, i.e. that entropy is unchanged in a reversible process.

 

Many statements in physics refers to an ideal case. That the ideal case is unattainable doesn't make the statement wrong.

 

Wouldn't that only be the case if there were no forces that causes spontaneous organization (i.e. whatever the opposite of entropy is called)? Gravity seems to be such a force, imo, since it basically generates stratification within a gravity-well from greater to lesser density.

 

The effects of gravity alone are reversible, at least at the Newtonian level. Stratification happens because of other interactions.

[farmboy]

Wouldn't that only be the case if there were no forces that causes spontaneous organization (i.e. whatever the opposite of entropy is called)? Gravity seems to be such a force, imo, since it basically generates stratification within a gravity-well from greater to lesser density.

 

Same as swansont's answer to the next question really dude, that doesn't contradict the second law in any way that I'm aware of. There are many examples of how a force can be applied locally to overcome the nature of entropy, it's just that the trend over the long term is for the system to move towards higher entropy. The human body, for example is an instance of a highly ordered (low entropy) system which makes use of chemical energy in the short term to prevent from naturally moving to a state of high entropy (decomposition).

 

I'm not a physicist, so forgive me if this is BS, but thermodynamics makes sense to me in statistical terms best. If you think about a random highly ordered system and then assume that you will make changes to it randomly. Now there is an entirely finite number of changes that can be made that will maintain the order of the system, but there are virtually an infinite number of changes that can be made which will add disorder to the system. So statistically any random change that is made will almost certainly introduce disorder to the system.

[lemur]

The effects of gravity alone are reversible, at least at the Newtonian level. Stratification happens because of other interactions.

I would say that stratification occurs when substances of different densities don't dissolve into each other uniformly but rather organize into layers of relatively homogeneous density. Then wouldn't mixing between the layers/strata require energy (stirring up) to increase entropy? E.g. if a star would supernova and absorb surrounding planets before re-condensing, it would gain new fuel but if it would condense into multiple gravity-wells, it would maintain fuel-reserves in the form of planets. So it seems like to the extent gravity can stratify matter into separate layers or gravity-wells, it can be an anti-entropic force, though it can also result in entropy, presumably, when for example heavier particles created by fusion sink into the higher-density layers of the star to undergo further fusion. Sorry, btw, if I am perverting astrophysics here since I'm just guessing about how this process could work based on assumptions about gravity, pressure, and fusion.

Edited March 20, 2011 by lemur

[sacscale]

Wouldn't that only be the case if there were no forces that causes spontaneous organization (i.e. whatever the opposite of entropy is called)? Gravity seems to be such a force, imo, since it basically generates stratification within a gravity-well from greater to lesser density.

 

 

I believe synergy is the opposite of entropy and gravity does seem to be synergistic however such stratification (from less dense to more dense) is a localized phenomina and there are other forces. If such stratification continues a star is formed, energy is radiated, and most stars eventually explode but even carried to the extreme of a blackhole, mass is still lost to quantum evaporation.

 

Another example would be spontaneous crystal formation in a supersaturated solution but there would be the question of how the supersaturated solution was arrived at, kind of like the condensation of matter from the high energy of the "big bang".

 

The question in my mind is if our universe is a closed system or if the second law is a local approximation similar to an inertial frame of reference. A closed system would seem to preclude a "big bang" and where is the "dark energy" coming from?

[swansont]

I would say that stratification occurs when substances of different densities don't dissolve into each other uniformly but rather organize into layers of relatively homogeneous density. Then wouldn't mixing between the layers/strata require energy (stirring up) to increase entropy? E.g. if a star would supernova and absorb surrounding planets before re-condensing, it would gain new fuel but if it would condense into multiple gravity-wells, it would maintain fuel-reserves in the form of planets. So it seems like to the extent gravity can stratify matter into separate layers or gravity-wells, it can be an anti-entropic force, though it can also result in entropy, presumably, when for example heavier particles created by fusion sink into the higher-density layers of the star to undergo further fusion. Sorry, btw, if I am perverting astrophysics here since I'm just guessing about how this process could work based on assumptions about gravity, pressure, and fusion.

 

There would be no layers and strata if there was just Newtonian gravity involved. You need other interactions to dissipate the energy/increase the entropy.

[lemur]

The question in my mind is if our universe is a closed system or if the second law is a local approximation similar to an inertial frame of reference. A closed system would seem to preclude a "big bang" and where is the "dark energy" coming from?

That's why I brought up gravity. I wonder if gravity ultimately serves as a "containment force" that holds the universe together or if it can expand indefinitely (e.g. as radiation) without its emergent force-relations causing it to re-condense (and stratify).

 

There would be no layers and strata if there was just Newtonian gravity involved. You need other interactions to dissipate the energy/increase the entropy.

I don't understand what you mean with this. You're saying that the particles have to move to stratify? But isn't the force of gravity sufficient to induce the motion that mobilizes the particles to stratify?

[sacscale]

That's why I brought up gravity. I wonder if gravity ultimately serves as a "containment force" that holds the universe together or if it can expand indefinitely (e.g. as radiation) without its emergent force-relations causing it to re-condense (and stratify).

 

 

The evidence indicates the expansion is accelerating thus the need for "dark energy". Since gravitational force decreases with increasing distance it seems unlikely gravity will pull it back togeather.

Edited March 20, 2011 by swansont
fix quote tag

[swansont]

I don't understand what you mean with this. You're saying that the particles have to move to stratify? But isn't the force of gravity sufficient to induce the motion that mobilizes the particles to stratify?

Particles had to lose energy to become stratified in the first place, which they did not do via gravity.

 

 

(sacscale, please learn how to use the quote tag. You need to put at the end.)

[sacscale]

(sacscale, please learn how to use the quote tag. You need to put at the end.)

 

 

Please learn physics.

[farmboy]

Particles had to lose energy to become stratified in the first place, which they did not do via gravity.

 

 

(sacscale, please learn how to use the quote tag. You need to put

at the end.)

 

Would the process responsible for this be the same one that atoms say undergo when losing energy from a lazer or heating or something, giving rise to very specific spectral emissions (something I've learned from chemistry) or is it something completely new to me?

 

Apologies if that sounds silly lol.

[lemur]

The evidence indicates the expansion is accelerating thus the need for "dark energy". Since gravitational force decreases with increasing distance it seems unlikely gravity will pull it back togeather.

I understand your point, but my issue has to do with whether spacetime can actually continue extending indefinitely beyond a gravity-well. Or would it curve back around to itself or another gravity-well. It seems to me that people are always treating spacetime as something that mass exists within when imo it seems more logical that matter and gravitation are part of the same phenomenon and spacetime is basically just gravitation itself. So although we observe spacetime to extend indefinitely outward and to be expanding, I wonder if this isn't the effect of the dispersion of matter. Put another way, if you analogize "the fabric of spacetime" (i.e. gravitation) to an expanding balloon, the balloon could rupture and the remaining fragments would collapse because they were no longer being stretched by the rest of the balloon.

 

Particles had to lose energy to become stratified in the first place, which they did not do via gravity.

Do you mean potential energy getting expressed as kinetic energy as the settle deeper into the gravity well? I guess what I'm trying to say is that gravity pulls matter away other matter, which creates relative order and potential energy, which is somewhat insulated against entropy of friction by the vacuum that forms between the gravity-wells.

 

 

[sacscale]

I understand your point, but my issue has to do with whether spacetime can actually continue extending indefinitely beyond a gravity-well. Or would it curve back around to itself or another gravity-well. It seems to me that people are always treating spacetime as something that mass exists within when imo it seems more logical that matter and gravitation are part of the same phenomenon and spacetime is basically just gravitation itself. So although we observe spacetime to extend indefinitely outward and to be expanding, I wonder if this isn't the effect of the dispersion of matter. Put another way, if you analogize "the fabric of spacetime" (i.e. gravitation) to an expanding balloon, the balloon could rupture and the remaining fragments would collapse because they were no longer being stretched by the rest of the balloon.

 

 

A rupture of spacetime (i.e. gravitation) would cause it's predominance? According to General Relativity, gravitation is a warp of space/time by mass. The question of causes mass is, is currently being search for at CERN. The range of it's influence is theoretically infinite but as I said it's influence decreases with distance. However dispersion is a better way of conceptualizing increasing entropy rather than a tendency toward disorder, the universe tends toward uniformity.

[lemur]

A rupture of spacetime (i.e. gravitation) would cause it's predominance? According to General Relativity, gravitation is a warp of space/time by mass. The question of causes mass is, is currently being search for at CERN. The range of it's influence is theoretically infinite but as I said it's influence decreases with distance.

Can you think of any way to verify or falsify, on the basis of existing knowledge, whether spacetime can extend infinitely beyond gravity-wells or whether it must necessarily curve in on itself? If it were something that were universally present before the big bang, I would say that it could extend infinitely regardless of matter/gravity; but since it is supposedly expanding along with the matter and energy of the universe, that leads me to believe that it cannot extend infinitely beyond the gravity wells it emanates from.

 

 

However dispersion is a better way of conceptualizing increasing entropy rather than a tendency toward disorder, the universe tends toward uniformity.

But the universe was a relatively homogenous dispersion/cloud of matter, wouldn't it tend toward aggregation into increasingly distinct gravity-wells? I would not expect galaxies to gradually disperse into a more homogenous distribution. Even the EM wave-emission would keep tracing the curvature of spacetime as determined by gravitation, no?

 

 

[swansont]

 

Would the process responsible for this be the same one that atoms say undergo when losing energy from a lazer or heating or something, giving rise to very specific spectral emissions (something I've learned from chemistry) or is it something completely new to me?

 

Apologies if that sounds silly lol.

 

Not at all silly. Shining a laser on atoms increases the entropy of the photons (they can be emitted in almost any direction), and you can use this to slow and cool atoms.

 

Do you mean potential energy getting expressed as kinetic energy as the settle deeper into the gravity well? I guess what I'm trying to say is that gravity pulls matter away other matter, which creates relative order and potential energy, which is somewhat insulated against entropy of friction by the vacuum that forms between the gravity-wells.

 

If all you had was Newtonian gravity, you would trade kinetic energy for potential energy and back again. Masses wouldn't coalesce. You need other interactions for that.

[sacscale]

Can you think of any way to verify or falsify, on the basis of existing knowledge, whether spacetime can extend infinitely beyond gravity-wells or whether it must necessarily curve in on itself? If it were something that were universally present before the big bang, I would say that it could extend infinitely regardless of matter/gravity; but since it is supposedly expanding along with the matter and energy of the universe, that leads me to believe that it cannot extend infinitely beyond the gravity wells it emanates from.

 

 

 

But the universe was a relatively homogenous dispersion/cloud of matter, wouldn't it tend toward aggregation into increasingly distinct gravity-wells? I would not expect galaxies to gradually disperse into a more homogenous distribution. Even the EM wave-emission would keep tracing the curvature of spacetime as determined by gravitation, no?

 

 

 

 

Existing knowledge indicates space/time is flat and was created by the "big bang" from which it is expanding (along with matter and energy) but there is the question of what it is expanding into. However each particle of matter, star, and galaxy are being pull toward each other during this expansion, not toward a center of mass but away from it. A deceleration of the expansion might indicate a cyclic universe but an acceleration does not.

[lemur]

If all you had was Newtonian gravity, you would trade kinetic energy for potential energy and back again. Masses wouldn't coalesce. You need other interactions for that.

Why can't you view a coalescing cloud of matter as a collection of emerging centripetal concentrations. As they coalesce, their centers would be in motion relative to each other and they would be drawing matter away from their lagrangian point and thus creating an increasingly empty vacuum-space between them. The initial potential energy was in the dispersion of original matter. As the centripetal centers emerged, they would cause kinetic energy of the coalescing particles until a state of relative equilibrium was reached due to friction preventing further settling. How is this immune to Newtonian analysis?

[IM Egdall]

Existing knowledge indicates space/time is flat and was created by the "big bang" from which it is expanding (along with matter and energy) but there is the question of what it is expanding into. However each particle of matter, star, and galaxy are being pull toward each other during this expansion, not toward a center of mass but away from it. A deceleration of the expansion might indicate a cyclic universe but an acceleration does not.

 

Spacetime is flat for the visible universe; that is the part we can see. Objects so far away that their light has not reached us yet are part of the unobservable universe. What the spacetime curvature for the entire universe (observable plus unobservable) is unknown.

 

There is not a question of what the universe is expanding into. Per general relativity, the universe is expanding but it is not expanding into anything. There is nothing beyond the universe for it to expand into. Difficult to conprehend, I know, but this is the current understanding.

 

There is no center of the universe. It looks the same (on a grand scale) no matter where you are located in it.