[mkyc]

I get the feeling that you have no idea how science works, or what he's saying.

He's not saying that the 3rd law is faith, he's saying that you take it on faith. A statement of faith is one that rests on no proof or evidence. Someone who has either wouldn't be giving a dickish answer like "um, 3rd law" or "GTFO", they'd be busy explaining.

The most important part of science is questioning and attempting to falsify current theories. He has a legitimate question, answer it or be quiet.

[camccann]

You know, I sympathize with your argument, but... seriously, the second law of thermodynamics? If there's anything that qualifies as the cornerstone of sanity in physics, it's that.

Of course it's illuminating to analyze the question and figure out where, exactly it's gone wrong, much like it's fun to puzzle out subtly flawed mathematical proofs that 0 = 1.

But in the end an argument that concludes with something equivalent to "therefore, causality is broken" or "therefore, time is meaningless" doesn't really warrant serious consideration unless it's backed by some very serious evidence.

[jerf]

Contrary to modestly popular belief, "faith" is not best defined as "choosing to act as if you believe something you actually know is not true". That's a fun definition to smear someone with, but is not useful in understanding very many real phenomena. Faith is much better defined as something like "acting on the truth of a statement that you can not (effectively) 100% prove"; note it does not preclude having a Bayesian probability of greater than 0, it is simply what you act on. When I sit in a chair, I can not 100% prove it will not collapse on me (after all, I have sat in chairs that collapsed on me and my Bayesian probability that a generic chair will support me can not be 100%), but I have faith that it will not; that is, I act as if it will not collapse.

When presented with a perpetual motion device, I can have faith that it will not work. Thanks to the Second Law of Thermodynamics, my Bayesian confidence in that belief is quite high, so it is not as if my faith is stepping out on a limb. But I have not proved that the perpetual motion machine won't work by actually examining it and finding the flaw, I simply have very-well-founded faith that such a flaw exists. Faith is a perfectly appropriate word here.

(I parenthesized "effectively" up there to avoid a massive and irrelevant discussion of exactly what 100% means, though it still pokes through. But is interesting to note that since reaching 100% confidence is very difficult, "faith" comes up in virtually every decision you make.)

[camccann]

I don't really disagree with any of that as such, but it doesn't really mesh with the common usage of the word "faith", especially on something as utterly fundamental as the Second Law of Thermodynamics. From a standpoint of Bayesian confidence, even a cursory understanding of physics would probably lead one to assign the Second Law a likelihood of one minus epsilon, where epsilon is taken to mean roughly "the likelihood that I'm crazy and hallucinating this whole thing".

As an aside, if you're going to be talking about Bayesian probability, you should know better than to call "100%" confidence just "very difficult"...

[jerf]

There's a couple of things I'm willing to assign 100% probability to, in particular something along the lines of "for some reasonably recognizable definition of 'exist', something I can reasonably call 'myself' exists", on the grounds that if I do not in fact exist there's no "my Bayesian probability" to be arguing about in the first place. (It's not quite tautological in the strictest sense, for reasons too long to get into here, but it certainly is close.) So I can't quite go to "impossible". You can't very far on 100%, though; "impossible" is a reasonable approximation.

Oh, and part of my point is that common usage is wrong, on the grounds that the "common usage" is incoherent, meaningless, and information-free. (I basically take it as axiomatic that the worth of the definition of a word can be measured along those axes; I'm generally a descriptive grammarian but that doesn't mean I have to throw all standards out.) Use something more like my definition and you get meaning again.

[amix]

Assuming that you can break the laws of thermodynamics is like assuming you can divide by 0 when doing real number arithmetic. If you allow this you would end with a highly inconsistent system/world.

[RiderOfGiraffes]

Yes. So in which step are the laws broken?

[nazgulnarsil]

lol, it's called thermodynamics and if you didn't take it in college you can get a textbook pretty easily and check the math yourself. you can also do simple experiments at home to confirm the basic laws of thermodynamics. there is no "Science" that only men in important looking buildings wearing lab coats do. that's what distinguishes it from faith.

[pyre]

> lol, it's called thermodynamics

The point is that saying "Can't work because of X" is a cop-out to actually going through and proving where the loss of energy is. Thermodynamics just predicts that somewhere energy is lost from this system. Blindly saying "thermodynamics" and not critically thinking about how/where/why it applies is intellectually deficient. If people don't challenge assumptions, then progress is never made. Some day someone might be able to disprove thermodynamics in some really funky edge-case, but that knowledge will never be discovered if no one ever questions.

[klipt]

> Blindly saying "thermodynamics" and not critically thinking about how/where/why it applies is intellectually deficient.

Not necessarily. In some cases it's a more efficient use of time to place the burden of proof on the person challenging a widely held assumption. Especially if you're a physicist who regularly receives letters from cranks with no background experience claiming to have overthrown physics. If you analyzed all of them in detail you'd never have time to do any real work.

Should people challenge assumptions? Sure. Are you required to challenge every assumption at every conceivable opportunity? No, that's OCD behaviour.

Does my attitude stifle progress? I don't think so - if someone has a way around the second law they should be able to build a machine utilizing it, and empirical data beats thought experiments every time.

Incidentally, the second law as commonly phrased "entropy always increases" is only an approximation. Entropy can decrease at times with small probabilities as outlined by the Fluctuation Theorem.

[pyre]

> Should people challenge assumptions? Sure. Are you required to challenge every assumption at every conceivable opportunity? No, that's OCD behaviour.

Sorry that I was unclear. The parent post seemed to be implying that anyone that comes up with a perpetual motion thought experiment should just have the phrase "can't exist it would violate thermodynamics" tossed at it. I'm not advocating working out every thought experiment that anyone could come up with, but to workout none of them is just putting blind faith in the law of thermodynamics. And so far as I understand it, blind-faith is not supposed to be part of the scientific process.

[nazgulnarsil]

the laws of physics all hang together. you can't just have some phenomenon violate the laws of thermodynamics and not have that imply the universe works in a completely different way. thought experiments can't disprove reality. you need empiricism and theory.

[pyre]

So Newton's 'Laws' were never proven to be wrong. They are still consistent in all cases, right? And every theory in physics has been completely and 100% proven through lab tests and empirical evidence.

> thought experiments can't disprove reality

Reality is what it is. If thermodynamics is wrong, it doesn't change reality. It just changes our understanding of reality. Don't be so melodramatic. Once a law/theory is dis-proven there isn't some deja-vu-the-matrix-is-changing-something moment.

At the very least, figuring out where the energy loss is in the system will teach others something, and possibly yourself as well. Thought experiments are where theories come from. Unless you think that theories spring into existence without thought.

{edit} Please don't say, "but I already know about thermodynamics, so there is nothing more for me to learn!" because you would be entirely missing the point.

[camccann]

"The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

-- Sir Arthur Stanley Eddington

I suspect most physicists would sooner question their own sanity than question the Second Law, and with good reason.

[nazgulnarsil]

if you think science can be wrong you're the one who misunderstands it. science can not be wrong. science also can not be right. science provides us with more or less consistent interpretations of sensory data. Newton was not proven wrong. his predictions were subsumed by a more general case.

likewise if we discover a physical phenomenon that violates our current understanding of thermodynamics we don't throw that understanding out. anything that succeeds it needs to explain all the data that it explained + the new stuff.

[pyre]

I think that we're bickering over semantics here. I'm not saying that we jettison 100% of something when it doesn't explain a new phenomenon. When I say 'thermodynamics is proven wrong,' I mean that we find a case where it doesn't apply. As it stands now, the thermodynamics 'says' that it applies to everything. So when we find an exception it is 'wrong.'