I think we're missing my point (from my first point).
Well, you wrote this in your first post:
Quote:
Just because no one has proven them wrong so far doesn't mean they won't be proven wrong in the future. They're just extensions of mathematics used to describe our environment, and as such I don't think they can ever be proven to be consistent.
They are physical observations that have been explained by mathematics. They have been consistent enough to take us to the moon and back a few times. I don't think we need any more proof of consistency than that. And just because the laws might be shown to be somewhat wrong, someday in the future has little, if any, bearing whatsoever on current events. Why do I belabor this? _________________ A Saudi saying, "My father rode a camel. I drive a car. My son flies a jet-plane. His son will ride a camel."
Live in Arizona? Check out: http://sustainablearizona.org and read my blog.
Joined: Nov 21, 2004 Posts: 579 Location: ~170ft/lbs@0rpm (on my bike)
Posted: Tue Dec 21, 2004 1:13 am Post subject:
MonteQuest wrote:
They are physical observations that have been explained by mathematics. They have been consistent enough to take us to the moon and back a few times. I don't think we need any more proof of consistency than that.
Your arbitrary definition of consistency isn't what I was refering to. Look at my first comment... I even linked the definition I was using. The implication was also that most general concepts like the second law are usually easier to disprove then prove, because to disprove them only requires one instance where they are violated, but proving them requires that you show they are true in every case. I never knew about the experiment you mentioned, but if correct, it disproves the second law. Of course you can restructure the language of the second law, or it's application...
but that's changing it after the fact.
Quote:
And just because the laws might be shown to be somewhat wrong, someday in the future has little, if any, bearing whatsoever on current events.
Of course it doesn't, but I'm not commenting on current events. I'm commenting on your statement that these laws aren't generalizations. They are mathematical generalizations...
and if most of our mathematical systems cannot be proven consistent, then how can our use of them to descibe our (most likely) more complex physical environment be anything more then a generalization, even if it's correct 99.99999999999999999% of the time in some arbitrary time interval, it's still a generalization.
Posted: Sat Dec 25, 2004 10:29 am Post subject: Keeping Chaos at Bay, 2nd Law; Part Four
Here's a little history and an explanation on the Second Law of Thermodynamics that I posted on another thread. I think it's worthy of a repeat here:
Sadi Carnot was a French theorist who studied the workings of the steam engine to abstract the essence of what an engine was all about. He discovered that heat energy at high temperature is capable of driving an engine and doing work. The same amount of energy at low temperature is not capable of doing useful work. The same amount of energy is still there, but something has changed. That something is what we call entropy. Carnot made an assumption that it is impossible to get something for nothing. This reasoning is what we call 2nd Law. He didn't discover the law or prove it, he just assumed it. It is an axiom whose verification lies in the fact that all predictions made on the basis of it always turn out to be true. Always, at least in the macro world that concerns us with regard to energy transfers..
2nd Law says you can't build a machine that will extract heat at low temperature and deposit that same amount of energy at higher temperature, without having any other effect. Take a refrigerator, for example. It removes heat from the food inside and dumps that energy at higher temperature into your kitchen. Here we can see entropy being decreased. But in order for your refrigerator to function, there must be another engine somewhere that is burning fuel to create heat at high temperature to create electricity to run your refrigerator. 2nd Law doesn't say heat can't be forced uphill or against a thermal gradient, but that the net effect of the power plant and your refrigerator running in tandem must always be to make heat run downhill or along the thermal gradient from high temperature to low. In other words, to run your refrigerator the power plant must always make more heat run downhill than the fridge makes run uphill. That principle is never violated. The result: an increase in overall entropy.
Gee, you say, if that is true, then you can't win! Yes, it is true, you can't. No free lunch. The principle that energy always runs from hot to cold is completely equivalent to saying entropy always increases. In an isolated system like the universe, this is a constant. In open and closed systems, like living organisms and the earth, entropy can be reversed or reduced at one point, but only with an even greater increase in entropy at another point. The rule of thumb used by engineers is that only about 1/3 of the energy in a heat source, such as a fossil fuel, can be used in another form such as electricity. Even more energy is lost when it is transmitted over power lines. So, while electric motors can be almost 100% efficient, the energy conversions required to turn a fossil fuel into electricity and transport it to power an electric motor results in only 1/3 of the energy in the fuel can be used. That is the inescapable consequence of the entropy imperative that rules the natural world. _________________ A Saudi saying, "My father rode a camel. I drive a car. My son flies a jet-plane. His son will ride a camel."
Live in Arizona? Check out: http://sustainablearizona.org and read my blog.
Last edited by MonteQuest on Sun Aug 14, 2005 10:14 pm; edited 1 time in total
Posted: Tue Jan 10, 2006 5:52 am Post subject: Re: The Three Laws of Thermodynamics
I oftentimes refer to "art" as work of instinct. When things become unclear, as they do particularly on a forum like this (heck how much more extreme can one go in the approach to understand near future events) then it is a clear relief when the right piece of artwork has been found.
I do post a lot of graphics, oftentimes seemingly out of context but that is superficially misleading.
Posted: Tue Jan 10, 2006 10:38 am Post subject: Re: The Three Laws of Thermodynamics
Quote:
And they don't apply in isolated and open systems? You are saying that in space( an isolated system) and in living systems(open) you can create and destroy energy and transfer energy without a loss? Care to explain yourself.
They aren't really as important in open systems. Sure according to classical theory the first law still holds, but the second law is meaningless since theres allways a heat sink with lower temperature that heat is trying to migrate to, and for the third law theres an infinite number of steps you take in an open system to get closer to zero. Then factor in quantum effects of very large systems and you do get strange behavior, such as negative pressure from vacuum energy.
Technically you never get heat death in a flat spacetime thats expanding. However if you have a nonzero cosmological constant (which seems to be the case now) then eventually you do get heat death do to unrah radiation effects that turn your open system into behaving like a closed system.
Quote:
Closed, an exchange of energy but not matter. The earth is a closed system.
This is irrelevant for discussions about thermodynamics. As long as you have a heat sink you dont run into heat death and the game goes on.
Joined: Aug 17, 2005 Posts: 580 Location: Portugal
Posted: Tue Jan 10, 2006 3:34 pm Post subject: Re: Question
MonteQuest wrote:
Isolated! The Earth is NOT an isolated system.
No, it is a closed system: exchanges energy but not matter. Still subject to the Laws.
Monte
Actually, it's open. Some molecules from the atmosphere escape the gravitational field, while others get trapped in it. Not that this makes much of a difference in practical terms.
Still, I don't see what the problem with the laws of thermodynamics. Any textbook on statistical mechanics does a good job explaining it. But I'll agree it's not that straightforward to understand (as most students can tell you, lol ).
Basically in an expanding universe with a cosmological constant you have unruh radiation as a global background due to uniform acceleration. At todays estimates it would be at around 10^-29 K or so. Small, but nonzero so you run out of heat sink unless you manage to get a black hole bigger than the current size of the universe.
Posted: Thu Sep 07, 2006 7:54 pm Post subject: The first rule of Thermodynamics is...
...we don't talk about Thermodynamics.
The second rule of Thermodynamics is, we don't talk about Thermodynamics.
I look around the forum & I see allot of new members.
That means allot of you have been breaking the first two rules of Thermodynamics.
<|sweet|>
Lou...
You don't know where I've been Lou!
You don't know where I've been.
-------------------------
I'd like to hear some explainations of thermodynamics for laymen.
Sort of a cliff-notes version... _________________ "When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours." - Stephen F Roberts.
Praise HawkMan
Last edited by Aaron on Thu Sep 07, 2006 7:57 pm; edited 1 time in total
Joined: Sep 06, 2004 Posts: 5315 Location: Smalltown New Zealand
Posted: Thu Sep 07, 2006 8:03 pm Post subject: Re: The first rule of Thermodynamics is...
Aaron wrote:
I'd like to hear some explainations of thermodynamics for laymen.
Law 1. If you put coffee in a thermos it keeps it hot.
Law 2. If you put chilled orange in it keeps it cool.
Law 3. If you drop it, it breaks.
That's all the thermos-dynamics you need to know. _________________ "Complex problems have simple, easy to understand, wrong answers." - Henry Louis Mencken
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