I know the term in this context has an entirely semantic origin, but actually those alternate universes are anything BUT “parallel” to ‘ours’, or we’d see them. The arrows of all of those others must all be perpendicular to ‘ours’ or we’d be encountering slightly different versions of ourselves over and over…

Oh, wait…

- riddle of the day

“Evolution can’t be because of entropy.”

I used to say that entropy only works in close systems, and that living things and earth aren’t close systems, but now i’m confused. If one becomes older because of entropy, then How could we evolve?

S = k*ln(W). Where is the disorder in entropy S? Increasing entropy is to increase the number of accessible microstates (~ the distribution of particles in 6-D phase space).

Have you tried to teach physics using this analogy? Because people who have have written papers and given presentations on how it engenders misunderstanding. The paper I cited above is one example, and I’ll cite another below.

Speaking of which, and I mean no offense, you seem to be under such a misapprehension yourself. What does the example of the messy room teach us about energy dispersal? You do not share your energy with the objects in the room. The objects in the room are not constantly colliding and sharing their energies with each other. Nothing about this scenario is similar to a system of microparticles. It’s not just an imperfect analogy; it’s no analogy.

Furthermore, low entropy systems aren’t even orderly to begin with! A 2008 presentation (PDF) from the American Institute of Physics conference explains this well:

The most basic example of the second law is neither difficult nor complex. Place a slightly warmer piece of iron on another piece of iron: the “heat energy” flows to the cooler iron until the two become exactly the same temperature. Technically, the “heat energy that flows” is actually the vibrational energy of atoms dancing in place in the metal that, on average, are moving faster in the warmer iron bar than in the cooler. At the surfaces of contact, the vibrations of the warmer bar interact with slightly slower vibrations in the cooler bar, whereupon over time the surplus energy of the warmer bar disperses. It spreads out so the vibrations of atoms held in place are at the same energy levels in both bars.

Quite clearly, no “disorder” or “order” is involved here! The atoms and molecules of all substances above absolute zero temperature are incomprehensibly disorderly, capable of being in any one of a truly gigantic number of different arrangements of their energy. The crucial point is that energy dispersal or spreading out is at the heart of any process involving thermodynamic entropy change-whether in iron bars or complex chemical reactions.

So it’s not even true that things tend to become less ordered as a result of entropy increase. Order, as pertains to this analogy, is a subjective aesthetic judgement. It doesn’t reliably tell us anything about energy dispersal. You see what a bad analogy this is?

Of course my room isn’t a proper thermodynamic system, but it’s essentially a microscopic system scaled up to a macroscopic size. If I bounce about the room, scattering objects about in a random way (as I do), I’m performing the same job as an energetic particle being sent into a small collection of gas particles. It’s not a perfect analogy for obvious reasons, but I think it’s a perfectly acceptable pedagogical aid – I don’t think there’s anything particularly profound to be found in taking certain analogies too seriously.

This implies that the physical matter and energy (and space also) in the universe are not conserved since any more amount can be created from the subtle source. Apart from the gross creation during the big bang, the space is continued to be created even now, at this observed accelerated rate. This is what we call as dark energy.

As our physical sciences know little about the creation during big bang, do they know little about this current accelerated rate of creation of space.

Comments are invited.

Look for papers by Tamara Davis and Charley Lineweaver. This question (which, as you note, is often not answered properly) is specifically addressed in one of them. I don’t want to track down the exact reference since all their joint papers are worth reading. Check them out.

The reason for these definitions is my conjecture that there is no dark energy and that the universe is infinite even though there is a finite distance between farthest existing matter. In my simple mind I visualize the universe to be a very large ball of transparent material. Somehow on top of this ball a rather large blob of something like mercury got dropped. This blob broke into many tiny drops that started rolling away from each other and accelerated as they went farther and farther away simply due to the curvature. Some drops collided to form bigger drops.

If we were on one of these drops, at the early stage, we would see a finite but expanding universe where the farthest blob was accelerating the fastest. We would not see the curvature since the very large ball is transparent. We would not even know that the very large ball exists. However, with the passage of time, as the drops roll over the surface of the ball, they would appear to be coming closer. This would be so because we would not be measuring along the surface. Instead, we would be looking along the chord. Of course, for my conjecture to be valid we are not there yet.

Also, with time, all drops would travel to the the other side of the ball and combine back into one large blob.

If expansion does not apply to bound systems, and
if large systems like galaxies are bound by gravity, and,
if gravity has no boundary, but weakens rapidly with distance, then

where is the boundary of a bound system like a galaxy or galaxy cluster? I know that it used to be set rather arbitrarily at the Holmberg radius, but we’ve known for decades that bound matter extends far beyond the visible mass of the galaxy.

IOW, how does space “know” precisely at which distance from a galaxy or galaxy cluster dark energy “should” appears, and where it “should” not? Also, does dark matter come into play in calculating the bound boundary?

James said: If “messy” were the macrostate of your room…

Entropy does not apply. From the article:

…a collection of ordinary macro things does not constitute a thermodynamic system as does a group of microparticles. The crucial difference is that such things are not ceaselessly colliding and exchanging energy under the thermal dominance of their environment as are microparticles.

James said: I think many physicists would say this is a bad use of the “order”, though it continues to be taught.

I’m not sure how many physicists would say this – many of them seem to be quite happy to explain entropy in this way – but it is indeed a bad use of “order,” or a bad explanation of entropy, because it’s false. Or maybe I’m wrong, but this explanation makes a lot more sense than any I’ve heard saying that order and entropy are the same thing.

There is no more widespread error in chemistry and physics texts than the identification of a thermodynamic entropy increase with a change in the pattern of a group of macro objects. The classic example is that of playing cards. Shuffling a new deck is widely said to result in an increase in entropy in the cards.

This erroneous impression is often extended to all kinds of things when they are changed from humanly designated order to what is commonly considered disorder: a group of marbles to scattered marbles, racked billiard balls to a broken rack, neat groups of papers on a desk to the more usual disarray. In fact, there is no thermodynamic entropy change in the objects in the “after” state compared to the “before”. Further, such alterations in arrangement have been used in at least one text to support a “law” that is stated, “things move spontaneously in the direction of maximum chaos or disorder”.

The foregoing examples and “law” seriously mislead the student by focusing on macro objects that are only a passive part of a system. They are deceptive in omitting the agent that actually is changed in entropy as it follows the second law — that is, whatever energy source is involved in the process of moving the static macro objects to more probable random locations. Entropy is increased in the shuffler’s and in the billiard cue holder’s muscles, in the tornado’s wind and the earthquake’s stress — not in the objects shifted. Chemically unchanged macro things do not spontaneously, by some innate tendency, leap or even slowly lurch toward visible disorder. Energy concentrated in the ATP of a person’s muscles or in wind or in earth-stress is ultimately responsible for moving objects and is partly degraded to diffuse thermal energy as a result.

I recommend just reading the whole paper. It’s short.

Essentially, it’s a case of understanding what “order” means in physics sense. The ice cube case, the system is considered to be ordered by virtue of confining some of the H2O molecules to a rigid subspace of the whole glass.
I think many physicists would say this is a bad use of the “order”, though it continues to be taught.