time

is TIME passing by like a river, water under the bridge,? or
are WE moving through time, -like on a multi-lane, one way Hway at varying speeds?

 

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So you are having trouble defining what time actually is , true ?

 

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Time is about the understanding of the movement of things on the micro and macro scale and why .

Time is NOT an independent force , entity etc. , time has no efficacy

 

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river, yes, but I am immersed in time, I know that the 'now' has zero length, but an answer to my questions would go a long way to help me define it.
the rate movement through- or -in space is measured in time, duration. it is the x axis, so?

 

Your thinking of time in terms of mathematics , NOT in terms of WHY the mathematics is possible in the first place.

Understand what I'm saying ?

 

Newton thought of time as like an arrow...flying straight and true.
Einstein thought of time like a river...meandering along, backing up, creating whirlpools and eddies, slowing, speeding up etc.....
13.83 billion years of time separate us from the BB.
We look into the past everynight.

 

river, the question of "Why" --Math is possible, or --why there is movement, or a sequence of events, does not concern me here, but math matters.

paddoboy's illustration of a meandering, eddy-slowed river is intriguing, but what about me in that, do I stand on the bridge? or float along in the river? if I am slowing, caught in an eddy, I would be slowing in respect to what? the bank? If slower speed in my part of the time-river, which could be caused by my greater speed through space, (or weight gain), then the bank could not be space, right? so

I would have to go with James' opening sentence , that picture of time in modern physics leans more toward the concept of -'us moving through time'. so the follow up question is:

If my worldline that I trace is fixed (in the past), must not the 'paper", the medium that is time be fixed & stationary too? The place (in space) I am in, is of course not fixed, it is rotating, revolving, translating--- it would make my head spin to think about it.
Am right then to think that time could be thought of as fixed?
re: "memories", and their particular order:
Since the 'now' we live in has zero length, (the stilo that traces our timeline is really small), it must be the lag in our brains the smearing out of 'memory' that allows us to sense our existence. or
do we move through time in increments, like the movie films of old? each ratchet tooth a planck-length on the sprocket, --movement a planck-time duration per jump?
--us being on the film? the world is a [film] stage? actors and audience too?

 

James R in post 6 is 100% correct; but I want to note that "time's arrow" is statistical in nature, not fundamental. Things that naturally change do so to take a more probably state. Technically we say the entropy of a closed system always increases. For example, if your grocery store manager has made a tall pyramid of soup cans and your cart bumps into it, there are many more ways the cans can be in a jumbled pile on the floor. When you get down to only a few particles: To the quantum level time's arrow has lost its direction - If you are told everything about two states, A & B you can't tell if A changed into B or if B changed into A.

That is quite different in the "macro world." For example if state A is a pretty wine glass sitting on the edge of a table and state B is several hundred (many only tiny fragments) of glass lying on the floor you know A preceded B.

When there are only a few items you can't be so sure, even at the macro level. For example I show you a cigar box with state A (lid opened so you can see the 8 coins inside) and all are the same way up (either heads or tails) and state B is with half heads and half tails up (4 coins each way). You should bet that state A was before the lid was closed and the box was shaken to produce state B, if the odds on the bet are 1 to1 as State B has more ways to have happened; however, if the odds are you lose a dollar when wrong, but gain 10 dollars if correct, then bet state A followed state B as once in every 8 shakes that will happen. I. e. on a long run average of such bets you will win 10 dollars for every 7 you lose.

SUMMARY: "Entropy always increases" is only statically true. That is all the "arrow of time" is - just statics' "Law of large numbers." But I would not wait around for a pile of broken glass on the floor to leap up on the edge of the table and take the form of a beautiful wine glass - not impossible given the correct initial positions and momentum of each even tiny piece of glass - it just that you need to have those highly unique initial conditions.

Also I want to add, even though James said it, that time does not flow, does not even exist as an observable thing. What exists is change. In fact, as Mach did more than 100 years ago the variable or parameter "t" found in the equations of physic can be TOTALLY eliminated from them all.

That "t" is very convenient as with it you don't need to be specific as to which two changes you are comparing. I. e. you can describe one change as a function of parameter "t" but when pressed as to what this "t" is, you will need to admit that it is the number of swings of a grandfather clock's pendulum (or in the modern age, how many oscillation the crystal in your Timex watch made.) Etc.

FUNDAMENATLLY: Any observed change is ALWAYS COMPARED TO other change(s) as time does not exist to be observed.

PS: I hope this thread is soon closed so it does not get filled with pages of ignorant garbage, like the other "time threads" have. Physics is facts, NOT opinions.

 

If you look at gravity, gravity causes material entropy to decrease, as matter loses its various degrees of freedom in favor of confinement. For example, at the temperature of the earth's core iron should be a high entropy gas. Instead gravitational pressure causes the iron to change phase into the lower entropy solid state. Gravity cause the arrow of time to slow, in the sense that space-time contracts. Time sort of sees a braking action, with the brake heat given off connected to the release of energy as entropy decreases.

This is considered an open system. However, if mass and energy was isolated in space and being acted upon by gravity in an integrated way; approximate a closed system, the entropy would still go down; time brake. One might infer that gravity has a connection to time potential, able to change the potential of time.

 

Good post, Wellwisher; but I think your "potential" is the lay, not the physicists' use of this term. Best example of fact a gravity dominated closed system lowers entropy is our highly ordered solar system. - It came from the chaos of a high entropy gas cloud. The fact that solar system has net angular momentum, is just that there are many more ways for the gas cloud to be in such a state than in a state with zero angular momentum.

 

Gravity does not lower entropy overall - it aids in increasing it! The solar system is not closed and a huge amount of entropy escapes in the form of solar radiation. What remains within the arbitrarily defined confine 'solar system'; in the form of sun + planets is more highly ordered than the initial cloud, but overall there has been a huge increase in entropy. Given your 'macro' vs 'micro' argument in #9, it's surprising you didn't immediately realize the statistical probability of net entropy decrease in a *truly closed* system the size of a proto-solar system gas cloud is fantastically small.

No, nothing to do with the cloud's entropy. It's because the initial cloud contained angular momentum in the first place, that's all. Pushing it back further in time, one could say the cloud's intial state as a turbulent fluctuation was a consequence of an entropic process I suppose.

 

Yes currently the sun is radiating energy into space and thus the solar system is not a closed system; however gravity did decrease the entropy of the chotic gas cloud when it was a closed system. If the mass that collected at the center of the solar system were less (and that often happens in space) there would not be enough release of gravitational energy to heat the central mass to fusion temperatures. I.e. a highly ordered system can and often does, arise from chaos. A lowering of entropy by mutual gravitational attraction with conservation of angular momentum (central mass rotating with planets going around it.). Probably even our solar system had a net decrease in entropy prior to the sun's core starting to release fusion energy, but that clearly is a "non-reversible" process so now that gravity is "far from dominate" entropy is increasing again. Note in post 11, I spoke of "gravity dominate" closed systems.

Matter streaming across the event horizon due to the Black Hole's gravity is an extreme case - it was a chaotic gas ripped apart by the gravity gradient that becomes condensed into a singularity. Also Wellwisher is correct: Gravity has made the Earth's core solid metallic crystals - Crystals are a very high state of order, low entropy) that gravity made from the Chaos of a gas cloud.

Even the inverse square electric field can make order out of chaos. Not easy to do as you must have very clean water to make a "super saturated" solution of Na+ and Cl- ions, but eventully there will be salt crystals on the bottom of the container. (That, however, may not be any reduction in entropy as the solution will be slightly warmer, just more ordered. The ions still in solution will still have a Maxwell/ Boltzmann distribution of velocities.)

 

A question arises, what if we evolved on Neptune where one part of it rotates faster than another part. Would we still have come up with the same way time is here on Earth or would we have found time being different and if so how so.

 

Not a very interesting question as once (before railroads) ever town had different time, based on its observation of "high noon." Lets try to stay on thread not lead thread astray. As Newton noted, his absolute mathematical time in his equations had nothing to due with Earth's rotation - not even with what we now call sidereal time, (Newton's "astronomical time"). Newton clearly states his time ("t" in his equations) is not "sensible" or we would say: "Not observable."

 

So then time is the same everywhere we would have evolved is that correct?

 

I think we would by now have gotten SR understood and some distant day even most will understand "time does not exist" I.e. is just one of the four coordinates that get mixed differently with SR's equations transforming from one inertial frame to another.

 

If time or ---movement through time can drop to zero in some conditions, so, -- in such cases does time disappear?
what is the difference between time and movement through time?

 

First para I disagree with almost entirely. Gravity is essential ingredient allowing pockets of lower entropy to form, but always at the expense of a raised overall entropy. May I suggest a good read through:
http://www.mathpages.com/home/kmath573/kmath573.htm
Highly unusual approach, but also highly instructive and last para there summarizes the situation well enough.

As for your 2nd para, it's general mainstream belief a BH represents the absolute maximum level of entropy achievable, vastly greater than any initial matter distribution from whence it came. Yes sure gravity is what allowed a crystalline phase in earth's inner core (best theoretical estimate), but again at the expense of a great increase in entropy radiated away during planetary formation. I'm not even confident the current earth's net entropy is less than the cold rocky fragments it formed from. That would need a detailed calculation taking into account the entropy locked up in the hot interior. And btw I should have made that same point wrt the sun in my #12.

As for the last para, similar deal. Low entropy crystals form at the expense of a greater rise in remaining fluid entropy. Non-equilibrium systems allow all such but without violating the second law.

 

Yes he asks the question we are discussing, but never (in quite a long article) answers it. (If you think he doee, please quote him.)

I think we agree that any dissipative (not reversible) process does increase entropy. Thus I need to discuss some about my assumptions on the "gas cloud"

First is it was mainly atomic hydrogen* with a little He and very very cold. Thus when two molecules collided they elastically scatter. - no dissipation. no entropy increase. The first excited level of H is 10.2ev above the ground state and that of He is much higher still. 300K is slightly less than 0.026ev so if the gas cloud was 30K, nearly 10 times hotter than space is now, The typical collision is about 4000 times too weak to excite hydrogen atom. Makes no radiation, no increase in entropy as is elastic - It can however changed their direction of travel, conserving momentum (as well as energy) of course.

Clearly the gas cloud did have net angular momentum like solar systeme to day has. Consider an atom with velocity significantly out of the current ecliptic plane. As it arcs either above or below that plane the gravitational attraction on it will tend to pull it back thru the plain and often it will elastically scatter with one atom more or less orbiting in the plain of the ecliptic. Then on average, both will in the future pass thru the plain but neither will get as far from it as the first considered atom did. This ELASTIC, non-entrophy creating process will repeat millions of times and then there will be rings of atoms going round the sun - not a chaotic gas cloud. Rings like still exist around some of the other planets. - Clearly a much more ordered / lower entropy state.

As this already proves my point, I'll stop here and not tell as much detail about the quite similar non-entropy producing process that takes place between particle pairs with in the ring (one traveling too fast hitting one traveling with less than orbital speed) That aggregate the particle into one orbiting mass, that gravity shapes into a sphere. I admit that in the process of becoming dense (no longer a gas) some inelastic processes do occur and the "proto-Earth" warms up, but the radiation lost is small as it goes as the fouth power absolute temperature.

Probably the lowering of entrop by formation of a well collected dense mass more than offsets the small loss of long wavelength IR - I won't try to prove that opinion, but simply admit, as I already have, at some point in the process of forming the solar system the net entropy started increasing again - certainly it is now with sun's irreversible fusion process and ~5000K surface radiation peaked in the visible.

But again, please note I spoke of gravity decreasing entropy only in a "closed system with gravity dominate process" Obviously, gravity is still very important, but it is reversibly being exchanged with kinetic energy - not an entropy increasing process, but a tiny amount of entropy is produced when a meteor, etc. hits a planet or asteroid, etc. I think solar fusion is now making much more entropy increase than that. I.e. the sun is the dominate entropy producer now, not gravity.

* Most of the universe's hydrogen is atomic, not H2. This is because there are processes (stellar UV the main one I think) even in "deep space" than can split H2 and once separated space is so big and empty, it is very rare for H + H --> H2 reaction to occur.

I should also note that just radiation escaping into space alone is not an entropy increasing process until the photon is inelastically absorbed. I bet more than half of the sun's radiation is still photons.