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 4th January 2006, 04:06 AM #1 dogbite666 Thinker     Join Date: Jul 2004 Posts: 199 Is this statment true? According to the third law of thermodynamics any movment of mass must come from an energetic cause, Action and reaction are equal and act in opposite directions. If the Universe contains all matter, energy and time and no matter, energy or time can exist outside the universe then does the universe still obey the laws of thermodynamics as it's cause cannot be energetic?
 4th January 2006, 05:30 AM #2 Soapy Sam NLH   Join Date: Oct 2002 Posts: 25,885 The Universe is presumed to be a closed system. The conservation laws apply. Entropy applies. Eventually all matter / energy will be as evenly distributed as it's possible to be, with no spatial potential gradients - at which point everything stops. (A bit like an English seaside resort in January). Unless gravity pulls it all together again.
 4th January 2006, 06:16 AM #3 TonyL Scholar   Join Date: Aug 2004 Location: Virginia, USA Posts: 97 Originally Posted by dogbite666 According to the third law of thermodynamics any movment of mass must come from an energetic cause, . . . Well, the third law (aka. "you can't get a shut out") either says you can't get to absolute zero, or that the entropy of a system at a temperature of absolute zero is a constant that can be taken to be zero. I have trouble seeing how your statement applies. However, the first law (aka. "you can't win") states that you won't get more energy out than you put in, or more accurately $\Delta U=\Delta Q-\Delta W$, Where U is internal energy, Q is heat and W is work. The second law (aka. "you can't tie") states that in any thermodynamic process there will be some energy unavailable to do work. So, although these last two apply to the first part of your statement, your following question Quote: If the Universe contains all matter, energy and time and no matter, energy or time can exist outside the universe then does the universe still obey the laws of thermodynamics as it's cause cannot be energetic? doesn't quite follow. First, thermodynamics (heck, all of experimental physics) says nothing about what exist outside the universe, so we don't know that there are not other universes. Second, although It is possible that the laws of thermodynamics didn't hold prior to the creation of the universe (we don't really know the laws of physics outside our universe), that would not mean that the current universe does not obey the laws of thermodynamics. So, basically, to answer your question: 1) As far as we can tell, the universe obeys the laws of thermodynamics on all practical time and energy scales. 2) The creation of the universe may or may not have proceeded according to our laws of thermodynamics. I'm unaware of any current way of testing whether or not it did.
 4th January 2006, 06:22 AM #4 Xeriar Critical Thinker   Join Date: Nov 2004 Location: Twin Cities Posts: 253 Originally Posted by TonyL So, basically, to answer your question: 1) As far as we can tell, the universe obeys the laws of thermodynamics on all practical time and energy scales. 2) The creation of the universe may or may not have proceeded according to our laws of thermodynamics. I'm unaware of any current way of testing whether or not it did. Regarding 1) Fluctuation theorum does begin to take effect (reducing entropy) at meaningful time-size scales. __________________ Give fire to a man, and he will be warm for the day. Set him on fire, and he will be warm for life. Dumb quotes
 4th January 2006, 07:15 AM #5 hammegk Banned   Join Date: Jan 2002 Posts: 8,422 Black holes exhibit very very high entropy with gravity having overcome all pre-existing forces, result being maximal disorganization inside the event horizon. Somewhat paradoxically (at first glance) at t=0 big bang, the single entity that came into existence was at the lowest possible entropy and entropy has inceased ever since. That is, a single entity cannot be re-arranged. At t=0+ Gravitational clumping of "quantum-like" fluctuations would begin the increase in entropy.
 4th January 2006, 04:26 PM #6 Nancarrow Chelonian Overlord     Join Date: Dec 2005 Location: London, UK Posts: 468 Originally Posted by dogbite666 According to the third law of thermodynamics any movment of mass must come from an energetic cause The third law of thermo doesn't say anything like this, see one of the posters above, it's about the impossibility of getting to the absolute zero of temperature. Originally Posted by dogbite666 Action and reaction are equal and act in opposite directions Careful there! That's Newton's third law of motion, NOT the third law of thermo. Different laws from different parts of physics. Originally Posted by dogbite666 If the Universe contains all matter, energy and time and no matter, energy or time can exist outside the universe then does the universe still obey the laws of thermodynamics as it's cause cannot be energetic? I can't help you with that as I don't understand what you mean by a 'cause being energetic'. Can you elaborate?
 5th January 2006, 04:28 AM #7 dogbite666 Thinker     Join Date: Jul 2004 Posts: 199 Quote: Action and reaction are equal and act in opposite directions doh, thats Newtons third law!! I'll go stand in the corner with my dunse hat for the rest of the day!!!
 5th January 2006, 04:32 AM #8 dogbite666 Thinker     Join Date: Jul 2004 Posts: 199 OK, what I,m asking is that as the big bang was an energetic event must this mean that it must of had an energetic cause, which also must have been from something external to the Universe. However, how can this be if all matter, energy and time are encapsulated in the Universe itself? Dog.
 5th January 2006, 06:07 AM #9 Nancarrow Chelonian Overlord     Join Date: Dec 2005 Location: London, UK Posts: 468 So are you basically asking, "Where did the universe's energy come from?" If so then I'm afraid I've no idea, except I'm sure the latest models in cosmology, quantum field theory and superstring theory must have loads to say about it! One thing though: energy conservation simply means that the total energy in the universe is constant. It doesn't say anything about what the value of that constant is, and I guess we could take it to have any value we want as long as we stick to that value. And everybody's favourite value is, of course, zero.

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