There are some principles in entropy im having trouble understanding. If Entropy requires that the energy in the universe must always been constant, shouldnt in theory 'Heat Death' have occurred since forever ago even before the Big Bang? Why not?

Thank you!


Entropy and energy conservation are laws often used to predict the ultimately fate of the universe. Trough achieving thermal equilibrium and dissipation of mechanical energy the universe would become in a 'Heat Death' state where nothing would really occur.

The basic principles of this theory, as I understand, is that: (1) Energy cannot be created (nor it is infinite); and (2) the Universe is a closed system;

The problem I see is that there must be a hidden number (3) requisite: Time must be finite, for this to work properly. I cant aknowledge time as being finite because then nothing could have started 'time', (you would need to have a external process [and a external time] and acknowledge that the system is not closed).

If time is infinite, then there was an infinite time before the Big Bang, then, in my understanding, the Big Bang couldn't possibly exist and have formed. Because in infinite time 'Heat Death' would always be what there is.

This wouldn't suppose that one of the 2 basic principles is wrong (or energy can somehow be created or the Universe is not closed), and Entropy really doesnt apply to the universe at all? Another explanation I see is that if the principles are true, then in fully understandment of all Universe laws Entropy itself must be wrong (the system would never achieve thermal equilibrium or a 'final state').

Either way all propositions I see for the problem achieve that Entropy must be somehow flawed in some level. What are your toughts in this? Im not a physicist and if something Im stating is wrong please enlight me!


closed as unclear what you're asking by Dilaton, Dan, Waffle's Crazy Peanut, Emilio Pisanty, Jim Aug 20 '13 at 18:53

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    $\begingroup$ Entropy has always been a notoriously troublesome concept for introductory students. I'll leave the answering of your questions to someone more skilled, but I have two words of advice: 1) Any conjecture that implies a factual occurrence didn't occur is wrong. 2) If your understanding of a concept leads to concluding the Universe doesn't exist, your understanding is not correct. :) $\endgroup$ – David H Jul 23 '13 at 23:35
  • $\begingroup$ Or the concept, or the pressumptions, or anything else really. I think that those more 'inconservative theories' solve the problem in some way, like if the universe isnt closed.. but im sure there must be some work considering closed universe too $\endgroup$ – eJunior Jul 23 '13 at 23:39
  • $\begingroup$ Also telling that my conclusions are wrong without explaining is useless to me =/ $\endgroup$ – eJunior Jul 23 '13 at 23:46
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    $\begingroup$ What has the conservation of energy to do with entropy ...? And as I understand it "heat death" does not occure, it is note a process but the final equilibrium state of the universe, with the entropy maximized and therefore all irreversible processes have ceased. $\endgroup$ – Dilaton Aug 13 '13 at 10:45
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    $\begingroup$ @eJunior: No, in theory entropy is increasing but the energy in the universe isnt. So why is the word "entropy" in the sentence at all? You wrote: If Entropy states that the energy in the universe must always been constant Entropy isn't a statement, it's a number. $\endgroup$ – Ben Crowell Aug 13 '13 at 19:11

"Am I missing something?"

Yes and no. Alfred's answer shows how you are missing something. A more humorous take on Alfred's answer is Richard Feynman's recipe for doing physics that he gave in one of his lectures (reference: the audio version of the Feynman lectures on physics, I think he cracks this joke in one of the very first lectures): 1. First you guess a theory, and work out what experimental results it foretells, 2. Then you do the experiments, and see what the results are, 3. Lastly, if what you foretell doesn't match what is, then you're wrong and you go back to step 1. - repeat as needed! But I think you understand this.

But you are right to be mystified by the situation. The second law of thermodynamics is that entropy is always increasing. Why this is so when physical laws are just as valid with time running backwards is called "Loschmidt's Paradox". There has been a great deal of work to understand this and it's generally agreed that the answer has to do with the "boundary conditions" of the universe - roughly put, the universe was (observed fact) in an exquisitely low entropy state at the big bang, and so the overwhelmingly likeliest history is one where entropy rises with increasing time. But how and why that low entropy state arose is, as I understand it, one of the profound mysteries of modern physics. A good layperson's summary of why we have a second law of thermodynamics, how entropy is to some extent a subjective concept, and the discussion of this profound mystery is to be found in chapter 27 of Roger Penrose's "The Road to Reality". I would highly recommend you look at this reference.

As I understand it, Penrose does have a theory - Conformal Cyclic Cosmology wherein he explains that entropy is "destroyed" over extremely long timescales, but this is far from mainstream physics and highly speculative.

  • $\begingroup$ Have you read Penrose's "Cycles of Time"? Update: never mind. $\endgroup$ – Alfred Centauri Jul 24 '13 at 1:59
  • $\begingroup$ No I haven't. Scream Don't make comments like "Never Mind" to a physicist :) - you're bound to pique curiousity - is this psychological link[xkcd.com/356] nerd sniping? $\endgroup$ – WetSavannaAnimal Jul 24 '13 at 2:03
  • $\begingroup$ No, it's just that at the moment I added the comment, you edited your answer to include the final paragraph on CCC. The book is a perplexing read. Fascinating but leaving one with more questions than answers. $\endgroup$ – Alfred Centauri Jul 24 '13 at 2:06
  • $\begingroup$ Actually you have solved other problems that i had also. I was looking for this Loschmidt Paradox some days ago. So this Conformical Cyclic Cosmology is one possible explanation, there are another theories that you think they're worth reading? $\endgroup$ – eJunior Jul 24 '13 at 4:01
  • $\begingroup$ @eJunior Sorry I'm well out of my field of expertise, so I am no judge of the merits of such speculative cosmological theories. But I think Penrose full stop is well worth reading - he demands clarity and probes deeply. Hopefully a cosmologist will look at this question (I've added some tags to your question to try to flush one out). $\endgroup$ – WetSavannaAnimal Jul 24 '13 at 4:09

How is it possible for the universe to exist if entropy is at work?

Understood properly, the universe is, literally, all there is.

Am I missing something important?

Yes. It is necessarily the case that entropy does not exist independently of the all there is because there is literally no thing outside of existence.

Do you see? Entropy is not something that stands independently outside of all there is.

In other words, and this is crucial: the universe must exist if anything, anything at all, including entropy, exists.

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    $\begingroup$ I see that it must exist, what i wanna know is how. $\endgroup$ – eJunior Jul 24 '13 at 1:40
  • $\begingroup$ @eJunior, if you genuinely see that it must exist, what more is there to know? $\endgroup$ – Alfred Centauri Jul 24 '13 at 1:43
  • $\begingroup$ Because i want to understand. :) That is what learning is about. $\endgroup$ – eJunior Jul 24 '13 at 1:44
  • $\begingroup$ @eJunior, great, then I suggest that you learn what it means when I say that, if anything exists at all, the universe exists. Think about it, the existence of the universe cannot be contingent on anything that is contingent on the existence of the universe. $\endgroup$ – Alfred Centauri Jul 24 '13 at 1:47
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    $\begingroup$ @eJunior, the flaw has already been pointed out. You're conjecturing that the existence of the universe is ruled out by something that depends on the fact that the universe exists. It's a logical fallacy. Do you not see how hopeless this type of argument is? $\endgroup$ – Alfred Centauri Jul 24 '13 at 1:57

shouldnt in theory 'Heat Death' have occurred since forever ago even before the Big Bang?

This is in fact one of many examples of observations supporting the idea that time must not have existed before the big bang. Another good example is that in the present-day universe, stars use up deuterium nuclei, but there are no known processes that could replenish their supply. We therefore expect that the abundance of deuterium in the universe should decrease over time. If the universe had existed for an infinite time, we would expect that all its deuterium would have been lost, and yet we observe that deuterium does exist in stars and in the interstellar medium.

This is also required theoretically by general relativity. GR allows cosmological models of two types: (1) models in which time began at the big bang, and (2) models in which there was a "bounce" rather than a bang. Measurements of cosmological parameters such as the density of dark energy rule out type #2.

  • $\begingroup$ You might like to mention, from a science history standpoint, Olber's Paradox (but formulated rather before Olber, notably by Kepler and Halley) and solved by Kelvin in 1901 using an argument that had already been put forward in an 1848 essay "Eureka" by Romantic horror author Edgar Allan Poe. $\endgroup$ – WetSavannaAnimal Aug 13 '13 at 5:06
  • $\begingroup$ But 'sponteanous' creation of the universe is in itself also a violation of Entropy. Also i think its difficult to acknowledge that 'time began' (as a dimension) in the Big Bang with no explanation of why or how the process would take place, actually any process that would take place would have required time to occur. As of these deuterium nuclei, even with 'finite' time they would still require a process to form, otherwise it would be magic. $\endgroup$ – eJunior Aug 13 '13 at 14:58
  • $\begingroup$ @eJunior: But 'sponteanous' creation of the universe is in itself also a violation of Entropy. No, because there is no $t\le 0$, so there was no previous time with which we can compare entropies. i think its difficult to acknowledge that 'time began' (as a dimension) in the Big Bang with no explanation of why or how the process would take place This would be fine as a theological argument, but to make it a scientific argument you would have to deal with actual scientific theories. deuterium nuclei... would still require a process to form. Yes, big-bang nucleosynthesis. $\endgroup$ – Ben Crowell Aug 13 '13 at 19:10
  • $\begingroup$ Time is relative in the sense that any point in time can be t = 0, t = 0 as being the beginning of the Big Bang is a postulated concept not a physical fact, that doesnt imply that time wouldnt have existed before, T < 0 has never been refuted in even any theoretical sense. 'Spontaneous creation' violates action-reaction in the sense that any process would have to be fruit of a antecessor, and any process wich would have formed the Big Bang would need time to take place. $\endgroup$ – eJunior Aug 13 '13 at 19:57
  • $\begingroup$ One of the basic principles in Scientific Theory is that any theory needs to try to explain the phenomena in study, this one doesnt, I could propose spontaneous creation for every single phenomena that I see. I think 'spontaneous creation' is more of a conformation theory than an actual scientific one, one could also as easily say that there is no point in discussing t < 0. $\endgroup$ – eJunior Aug 13 '13 at 20:05

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