Thermodynamics and solipsism

Durandal · Post by **Durandal** » 2006-05-07 03:32pm

I don't normally do this, but my thermodynamics and entropy understanding is quite rusty. Over at ArsTechnica, one of the writers posted a journal entry about how the second law of thermodynamics implies that all our observations are fictional, and scientists just pick and choose which observations they want to follow. Basically, he repackages solipsism in the same way that creationists repackage their bullshit into intelligent design.

The natural counter-argument is that, if this is the case, then we have no basis on which to even create a second law of thermodynamics. If our data were not reliable, we'd have no thermodynamics model at all. Without this model, there is no basis on which to say that our data are not reliable, according to his interpretation.

So I know the guy's wrong, and I know one reason why. But since he's wrong, there must be something about his interpretation of entropy that is also wrong. Some other posters have already called him on it, but there are people here I know to be credible, so I'm appealing to them.

Nephtys · Post by **Nephtys** » 2006-05-07 03:43pm

That's plain silly. If Entropy remained mostly constant, then dipped down... where did the energy input come from, to do work on the universe, which is by definition everything that is?

He's trying to use a hypothesis of how time works as a function of entropy to base this pitiful argument, by accepting it as fact because 'he took a class that mentioned it'. He of course, is saying a low entropy state is 'improbable', but um. Improbable does happen. And will happen, if given enough time.

Summing it up, this doofus is arguing that you cannot trust the past, but how can you not trust the past? Should we do everything, assuming Time Police from 2259 changed what Galileo discovered?

But those factors exist for many scientific explanations for the past. An excellent example is the existence of a past in which the arrangement of continents was different. There is no single piece of evidence that conclusively demonstrates that such a past occurred. Numerous pieces of evidence, however, suggests that this past certainly existed

"BUT THERE'S NO PROOF!!!1!!". Behold. He demands 'conclusive' evidence. Science doesn't prove, it only explains and disproves.

This is a huge article about apparently nothing.

Post by **Surlethe** » 2006-05-07 04:01pm

Just looking at the graphs of his predictions should tip off a bullshit detector: he assumes the second law of thermodynamics is true, and then he contradicts it!

In any case, as I understand thermodynamics, the reason lower-entropy states become exceedingly improbable is because of the second law; he simply makes a non-sequitur to the universe must have started in a high-entropy state, in essence putting the cart before the horse.

Post by **Darth Wong** » 2006-05-07 05:10pm

How exactly does this imbecile go from the second law, which states that entropy does not decrease in closed systems, to a statement that a past universal lower-entropy state is improbable?

He's engaging in a linguistic misinterpretation: the kind that happens when someone learns a physics concept in terms of words rather than equations.

The Second Law points out that it is extremely improbable for the entropy in a closed control volume A to decrease. In other words, if a control volume A has entropy S at point time=0, it will have entropy >= S at point time=1.

He misinterprets this to mean that the entropy of control volume A cannot be 0.5S at any point in time, even at time=-50. He concludes that this means cosmology is in violation of the Second Law of Thermodynamics.

He then goes on to essentially declare that the solution is to assume the Second Law is bunk, by assuming that entropy goes up and down at a whim. And then he uses this bizarre reasoning to conclude that there is no past.

Seriously, the biggest problem with this argument is figuring out which way to attack it, because it really makes no sense whatsoever; it's a giant non sequitur in which virtually every single step in logic is completely devoid of any comprehensible reasoning. It's like refuting the statement that the Earth must be flat because chocolate tastes delicious; your first reaction is to simply stare at the speaker in open-mouthed amazement.

Winston Blake · Post by **Winston Blake** » 2006-05-08 01:40am

Darth Wong wrote:It's like refuting the statement that the Earth must be flat because chocolate tastes delicious; your first reaction is to simply stare at the speaker in open-mouthed amazement.

It's funny, having read plenty of your hate mail and seen a lot of science-fictional rationalising, I can easily imagine how that argument could be made:

E.g. "Chocolate tastes delicious. God made the natural ingredients of the chocolate and made our brain feel pleasure in tasting it. You should be grateful for this. To question God's kindness on any other matter would be ungrateful, since he's given you so many nice things to experience. So don't question the Bible, and don't question me when i tell you that it says the Earth is flat. Thus, the Earth is flat, QED."

I'm sure there are many people who would see this rigorous proof as flawless.

Sriad · Post by **Sriad** » 2006-05-08 02:46am

Darth Wong wrote:Seriously, the biggest problem with this argument is figuring out which way to attack it, because it really makes no sense whatsoever; it's a giant non sequitur in which virtually every single step in logic is completely devoid of any comprehensible reasoning. It's like refuting the statement that the Earth must be flat because chocolate tastes delicious; your first reaction is to simply stare at the speaker in open-mouthed amazement.

In this particular case, the best place to start is at the beginning.

"For this to actually work, though, the past has to have been a low entropy state (such as the singularity prior to the big bang). And that is a problem, because low entropy states are overwhelmingly improbable."

Every argument in the rest of the entry (at least, that I could bring myself to read) moves forward from here; explaining how this base statement is wrong collapses the whole ill concieved structure. The starting axiom is staggeringly wrong in a way that is almost trivial to explain; there is no need to spread yourself thin on following points.

Ariphaos · Post by **Ariphaos** » 2006-05-08 06:16am

WTF? I normally expected much better from Ars :-(

Xon · Post by **Xon** » 2006-05-08 07:07am

Gah, Ars has a fundy rash.

How the fuck did that get through quality control?

Post by **Darth Wong** » 2006-05-08 09:54pm

Xon wrote:Gah, Ars has a fundy rash.

How the fuck did that get through quality control?

Why should this surprise you? You don't seriously think that computer expertise somehow translates into scientific aptitude, do you?

brianeyci · Post by **brianeyci** » 2006-05-08 10:04pm

Darth Wong wrote:He's engaging in a linguistic misinterpretation: the kind that happens when someone learns a physics concept in terms of words rather than equations.

Lesson here, don't read science popularization books to try and learn science, trust me on this. Don't use the Internet. Don't use friends. The best bet are old textbooks you can get at a budget from used bookstores, or go to a university library with specialized textbooks (the public can access U of T although they can't take books out, if I knew this in high school I would have dove right into their libraries). Better yet sit in on lectures, you can just slip in and nobody would notice.

This of course takes more work and time than the average person wants to do.

Brian

Xon · Post by **Xon** » 2006-05-08 10:07pm

Darth Wong wrote:Why should this surprise you? You don't seriously think that computer expertise somehow translates into scientific aptitude, do you?

Ars technica normally has good/great scientific aptitude w.r.t. with thier articles. The OP is talking about a fairly fundamental misunderstanding of basic physics, which makes me wonder how the fuck that guy was allowed to post in the science blog of all things.

Post by **Darth Wong** » 2006-05-08 10:50pm

Xon wrote:
Darth Wong wrote:Why should this surprise you? You don't seriously think that computer expertise somehow translates into scientific aptitude, do you?
Ars technica normally has good/great scientific aptitude w.r.t. with thier articles. The OP is talking about a fairly fundamental misunderstanding of basic physics, which makes me wonder how the fuck that guy was allowed to post in the science blog of all things.

Technical aptitude and scientific aptitude are not the same thing at all. Ars Technica normally shows good technical aptitude. I have never seen any evidence that their staff is selected with any particular emphasis on scientific aptitude. A guy can know everything there is to know about pixel rendering pipelines and speculative branching, but that translates to precisely jack shit when it comes to scientific knowledge.

Ariphaos · Post by **Ariphaos** » 2006-05-09 05:06am

Darth Wong wrote: Technical aptitude and scientific aptitude are not the same thing at all. Ars Technica normally shows good technical aptitude. I have never seen any evidence that their staff is selected with any particular emphasis on scientific aptitude. A guy can know everything there is to know about pixel rendering pipelines and speculative branching, but that translates to precisely jack shit when it comes to scientific knowledge.

It doesn't prohibit such understanding either. I have every right to expect better from Ars, and as near as I can tell, the majority of people posting in the forums there share that view.

Turin · Post by **Turin** » 2006-05-09 10:00am

Darth Wong wrote:He's engaging in a linguistic misinterpretation: the kind that happens when someone learns a physics concept in terms of words rather than equations.

The Second Law points out that it is extremely improbable for the entropy in a closed control volume A to decrease. In other words, if a control volume A has entropy S at point time=0, it will have entropy >= S at point time=1.

Okay, recognizing that you may just feel like telling me "it's not my job to educate you, go do some more research, retard", where does the "extremely improbable" part come in to the Second Law? My understanding was that the entropy in a closed system never decreased?

(Now, I'm probably guilty of just what you're saying this guy is saying, a linguistist misinterpretation, except that I'm not stupid enough to try to make a serious technical argument based on only a handful of college-level science courses!)

Post by **Darth Wong** » 2006-05-09 01:24pm

Turin wrote:Okay, recognizing that you may just feel like telling me "it's not my job to educate you, go do some more research, retard", where does the "extremely improbable" part come in to the Second Law? My understanding was that the entropy in a closed system never decreased?

Not precisely. Take the analogy of a partitioned aquarium with red dye in one half and blue dye in the other half. Remove the partition and heat or otherwise agitate the water, and the two colours will run together, making purple water. However, if you ignore probability, it is entirely possible for these random molecular movements to separate the purple water into segregated blue and red halves again. It's just that it will never happen due to the extraordinarily low probability of such an event, which is why we consider diffusion to be a law.

Turin · Post by **Turin** » 2006-05-09 02:54pm

After reading that, I can't help but think that it was so simple (as long as you understand the basic principles involved) that I should have already realized it on my own. Sometimes I guess one gets a mental block on a concept.

But thank you!

Zero · Post by **Zero** » 2006-05-09 06:27pm

Darth Wong wrote:
Turin wrote:Okay, recognizing that you may just feel like telling me "it's not my job to educate you, go do some more research, retard", where does the "extremely improbable" part come in to the Second Law? My understanding was that the entropy in a closed system never decreased?
Not precisely. Take the analogy of a partitioned aquarium with red dye in one half and blue dye in the other half. Remove the partition and heat or otherwise agitate the water, and the two colours will run together, making purple water. However, if you ignore probability, it is entirely possible for these random molecular movements to separate the purple water into segregated blue and red halves again. It's just that it will never happen due to the extraordinarily low probability of such an event, which is why we consider diffusion to be a law.

What kind of odds are there that the solution would seperate out again? I had thought that entropy was thought of as a deviation from a specific preferred state, but aren't there an infinite number of alternative states to any preferred state? That's why I had thought entropy was never supposed to increase. If it's just extremely unlikely, that makes as much sense, since the odds of any specific preferred state existing out of a very very large number of possible states is very low, so it can be assumed that it won't ever happen.

Have I misunderstood thermodynamics?