Professional, amateur, well learned, self taught scientist whatever. Mostly all of you folks on these postings I have found to have interesting knowledge that for me is enlightening and beneficial. Such is very conducive and a spur for my making up for misspent opportunities.
That was very well said. We all end up learning something on this site. Well moderated. no trolls.
Rod (post #34) quoted "Fred Hoyle thought this about abiogenesis (from a source I use). Fred Hoyle1 (an atheist) estimated the probability as one chance in 10^40,000." Helio rightly suggested some possible basis for this (imho) pure guess.
I am sorry, Fred, but 1 in 10 followed by 40,000 zeros is (imho) a totally ridiculous estimate. Descartes said "Cogito, ergo sum" (I think, therefore I am) and I think this is well applied to intelligent life (or even, by extension, just life).
The fact that we are here (not to forget intelligent creatures like dolphins) proves that it ain't that unlikely. In fact, judging from what we know about life, the probability is 1.0 i.e., certainty. I have to admit that the sample size is very small, but that does not stop us making assumptions about other matters associated with our planet.
The proposition, of course, is not life on all planets. But it would not be unreasonable (based on our scientific observations) to suggest a high likelihood of life developing on planets with similar atmospheres to ours and with surface water (defining temperature). Some might correctly find this too limiting - maybe Si based life instead of C perhaps and under vastly differing conditions - but this would only strengthen my point.
Cat
I am sorry, Fred, but 1 in 10 followed by 40,000 zeros is (imho) a totally ridiculous estimate. Descartes said "Cogito, ergo sum" (I think, therefore I am) and I think this is well applied to intelligent life (or even, by extension, just life).
The fact that we are here (not to forget intelligent creatures like dolphins) proves that it ain't that unlikely. In fact, judging from what we know about life, the probability is 1.0 i.e., certainty. I have to admit that the sample size is very small, but that does not stop us making assumptions about other matters associated with our planet.
The proposition, of course, is not life on all planets. But it would not be unreasonable (based on our scientific observations) to suggest a high likelihood of life developing on planets with similar atmospheres to ours and with surface water (defining temperature). Some might correctly find this too limiting - maybe Si based life instead of C perhaps and under vastly differing conditions - but this would only strengthen my point.
Cat
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On further reflection, whilst I am convinced that a cyclic theory is vastly more logical than a singularity based BB theory, there are some difficulties to be overcome. One is whether entropy can go into reverse in the contracting phase. According to cyclic theories, entropy must 'begin again' at the 'phase change'.
Cat
Given the reasonably strong evidence that the universe is accelerating in its expansion, how does this fit in a cyclical model?
Helio, in theory (all this is guesswork) expansion could be followed by contraction, and entropy might decrease. It is no more unbelievable than all that banging out of nothing; imho, much more likely. But that is just my imagining.
Cat
Cat
Nicely put. Assuming we can someday understand how DE operates, then we will, no doubt, have a lot more to say pro or con on any cyclical model. If we discover that a collapse process is at all possible, then science would be helpful to the cyclical supposition.
Though I hold a different t=0 cause, I too am outside the realm of science, and, worse, without much hope that science will ever offer anything more than logic arguments like fine tuning, etc.
Helio, I greatly respect your even handed approach.
On the subject of dark energy, I would suggest that we know virtually about it, except as a possible cause (ditto dark energy); I am particularly suspicious of two models with opposite consequences pertaining to "explain" > 95% of the Universe.
If we are not to gainsay reducing entropy, then why not changing dark matter? In fact, why not postulate exchanging dm and de? Who can prove otherwise.
OK, so it only means that we are back in the realms of imagination. No data - no proof - no reality.
Cat
On the subject of dark energy, I would suggest that we know virtually about it, except as a possible cause (ditto dark energy); I am particularly suspicious of two models with opposite consequences pertaining to "explain" > 95% of the Universe.
If we are not to gainsay reducing entropy, then why not changing dark matter? In fact, why not postulate exchanging dm and de? Who can prove otherwise.
OK, so it only means that we are back in the realms of imagination. No data - no proof - no reality.
Cat
DE is indeed a term used for an imaginary force to explain acceleration of the expansion.Helio, I greatly respect your even handed approach.
On the subject of dark energy, I would suggest that we know virtually about it, except as a possible cause (ditto dark energy); I am particularly suspicious of two models with opposite consequences pertaining to "explain" > 95% of the Universe.
If we are not to gainsay reducing entropy, then why not changing dark matter? In fact, why not postulate exchanging dm and de? Who can prove otherwise.
OK, so it only means that we are back in the realms of imagination. No data - no proof - no reality.
Cat
DM, on the other hand, is less speculative. It was proposed and coined by Zwicky long ago to explain observed excess velocities for galaxies in clusters — more matter is the only good solution, in his view.
Then came Rubin’s discovery that galaxy’s rotations require more matter than can be observed.
More observations confirm DM, especially the observations of the Bullet cluster.
A theory/hypothesis becomes viable when its predictions are verified. Multiple lines of evidence are important to advance a theory/hypothesis, and DM has this, unlike DE.
Perhaps something better than MOND will come along and upset the apple cart but DM is very strong today in spite of the trouble we seem to have in finding the associate particle(s).
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Helio, the idea (imaginary assumption. like most in this area) is that from maximum entropy the cycle returns to minimum entropy at the start of the next phase (BH>BB). This is not so difficult as appears at first sight - contraction brings everything closer together and therefore more orderly.
Cat
Cat
Cat, entropy increases when you compress stuff. More collisions take place during compression vs. expansion. I’m doubtful a refreshed low entropy state would take place, but perhaps I’m missing something.
Second law of thermodynamics - Wikipedia
https://en.wikipedia.org › wiki › Second_law_of_therm...
The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. Entropy predicts the direction of ...
First law · Zeroth law · Third law of thermo · Thermodynamic system
You've visited this page 2 times. Last visit: 01/09/21
Second Law of Thermodynamics
https://www.grc.nasa.gov › www › airplane › thermo2
The second law states that there exists a useful state variable called entropy S. The change in entropy delta S is equal to the heat transfer delta Q divided by ...
Helio, I just put these here to remind me of the constraints, but also for others who may not be familiar with anything but "heat flows from hot to cold".
I am wondering whether the isolated system constraint might apply?
Anyway, the ideas of cyclic/open/closed etcetera have been around some time, so I will check further. Clearly a decrease in entropy might be necessary to achieve the BB situation. I thought the BB was minimum entropy, which then increased with expansion of the Universe? I can only see 'phases' starting low (BB) and increasing (BB) i.e., from start to finish of phase. Who knows whether an idea formulated on an obscure planet by intelligent ape offspring applies to the whole Universe?
Anyway, I find it an interesting question.
P.S. Just found these on Googling "decrease in entropy of universe with contraction"
Questions and answers
Quora
Question
Would nature itself break the laws of thermodynamics while the contraction of the universe by decreasing the entropy?
Answer · 1 vote
Nature does not care one hoot about any of the laws you mere mortals make. The laws of thermodynamics describe nature, but they are incomplete as far as the vastness of the universe is concerned. Nature is all about BALANCE…to the weight of a single electron. The laws of thermodynamics describe a one way universe because we believed the theory of one priest who came up with the Big Bang theory - a one way heat death universe. We know nature elegantly disobeys thermodynamics, as we see it balancing both the destructive forces and the constructive forces to the tee. We see an oak tree emerge from a tiny seed, produces fruit, dies, then goes back to seed again. We see a man produce a whole human being from his tiny seeds…this human grows into an adult, gets old, dies, is buried and his body is reconstituted into the soil, for the oak tree to use…. Nothing in nature is running down. Everything is in a state of rhythmic continuity. The piece of orange that has fallen on the ground, w…
More
ResearchGate
Question
In an accelerated expanding Universe entropy increases as temperature decreases. Doesn't it get in contradiction with 3rd law of Thermodynamics at 0K?
Answer · 3 votes
Dear Arancha Ceada Following and quoting literally wikipedia, which I think has a good definition of the Nernst Theorem, see to compare for example the monograph: L. Landau and E. Lifshitz, Vol. 6, Statistical Physics, Pergamon 1980, Part I, pags 68-69 , it says: https://en.wikipedia.org/wiki/Third_law_of_thermodynamics 1. The Nernst heat theorem says that as absolute zero is approached, the entropy change ΔS for a chemical or physical transformation approaches 0. This can be expressed mathematically as follows: lim T → 0 Δ S = 0 {\displaystyle \lim _{T\to 0}\Delta S=0} 2. The Third law of thermodynamics is sometimes stated as follows, regarding the properties of closed systems in thermodynamic equilibrium: The entropy of a system approaches a constant value as its temperature approaches absolute zero. I think that the first question to ask is this one: Is the expanding universe a closed system in a thermodynamical equilibrium such that the third law of thermodynamics or Nernst theore…
More
ResearchGate
Question
It is commonly accepted that the Universe started in an ordered state with low entropy (S), which allowed its entropy to further increase - as observed - in line with the second principle of thermodynamics. What was then the most robust value of departure ? One could suppose that the entropy at the Big Bang was S=0 as the Universe was concentrated in one single micro-state (one single configuration). But this is a lot speculative as nobody knows what did the physics look like before Planck’s time (1.351 10-43 s). At this time, in an hot Big Bang scenario, one could use the values proposed by Planck to the Academy of Berlin in 1899 to compute the entropy : - Planck’s length : 4.051 10-33 m - Planck’s mass : 5.456 10-8 kg - Planck’s temperature : 3.551 1032 K These values are a combination of universal constants exclusively, thus without « human neutral ». One then finds an entropy : S = 1.381 10-23 J.s-1 , i.e. Planck’s constant, corresponding to (using Boltzmann’s equation : S = k.lnW) a number of micro-states : W = 2.718 (= natural number « e »). One could also use the formula of Bekenstein-Hawking for the entropy of a black hole, as the Universe was like a black hole at start (very hot, very dense). Using Planck’s length as diameter of the horizon circle of the black hole, we get an entropy : S = 1.652 10-23 J.s-1 , corresponding to W = 3.309 micro-states. We would thus have an entropy corresponding to 2-3 micro-states at Planck’s time. Another way would be to assess the entropy just after the presumed inflation stage (ending 10-33 s after the Big Bang). The entropy is then the area of the cosmological horizon in Planck's units, and would be about a million Planck’s lengths of radius, so probably a value of the order of ln W = 4.787 1012 which is still very low compared to the order of 10135 (maximum entropy one can squeeze in the modern cosmological horizon). Other proposals go in the direction of a very high entropy at the beginning of the Universe, which would itself start from a statistical fluctuation of low entropy : which would then be the order of magnitude of this low entropy ? In summary, could these evaluations be accepted and, whether yes or no, which would be the best value to have an idea of the entropy of the Universe shortly after the Big Bang ?
Answer · 0 votes
Please, read "human intervention" instread of "human neutral". With apologies !
More
Not saying I agree or not. Just posting to show maybe there is interesting content somewhere.
Cat
https://en.wikipedia.org › wiki › Second_law_of_therm...
The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. Entropy predicts the direction of ...
First law · Zeroth law · Third law of thermo · Thermodynamic system
You've visited this page 2 times. Last visit: 01/09/21
Second Law of Thermodynamics
https://www.grc.nasa.gov › www › airplane › thermo2
The second law states that there exists a useful state variable called entropy S. The change in entropy delta S is equal to the heat transfer delta Q divided by ...
Helio, I just put these here to remind me of the constraints, but also for others who may not be familiar with anything but "heat flows from hot to cold".
I am wondering whether the isolated system constraint might apply?
Anyway, the ideas of cyclic/open/closed etcetera have been around some time, so I will check further. Clearly a decrease in entropy might be necessary to achieve the BB situation. I thought the BB was minimum entropy, which then increased with expansion of the Universe? I can only see 'phases' starting low (BB) and increasing (BB) i.e., from start to finish of phase. Who knows whether an idea formulated on an obscure planet by intelligent ape offspring applies to the whole Universe?
Anyway, I find it an interesting question.
P.S. Just found these on Googling "decrease in entropy of universe with contraction"
Questions and answers
Quora
Question
Would nature itself break the laws of thermodynamics while the contraction of the universe by decreasing the entropy?
Answer · 1 vote
Nature does not care one hoot about any of the laws you mere mortals make. The laws of thermodynamics describe nature, but they are incomplete as far as the vastness of the universe is concerned. Nature is all about BALANCE…to the weight of a single electron. The laws of thermodynamics describe a one way universe because we believed the theory of one priest who came up with the Big Bang theory - a one way heat death universe. We know nature elegantly disobeys thermodynamics, as we see it balancing both the destructive forces and the constructive forces to the tee. We see an oak tree emerge from a tiny seed, produces fruit, dies, then goes back to seed again. We see a man produce a whole human being from his tiny seeds…this human grows into an adult, gets old, dies, is buried and his body is reconstituted into the soil, for the oak tree to use…. Nothing in nature is running down. Everything is in a state of rhythmic continuity. The piece of orange that has fallen on the ground, w…
More
ResearchGate
Question
In an accelerated expanding Universe entropy increases as temperature decreases. Doesn't it get in contradiction with 3rd law of Thermodynamics at 0K?
Answer · 3 votes
Dear Arancha Ceada Following and quoting literally wikipedia, which I think has a good definition of the Nernst Theorem, see to compare for example the monograph: L. Landau and E. Lifshitz, Vol. 6, Statistical Physics, Pergamon 1980, Part I, pags 68-69 , it says: https://en.wikipedia.org/wiki/Third_law_of_thermodynamics 1. The Nernst heat theorem says that as absolute zero is approached, the entropy change ΔS for a chemical or physical transformation approaches 0. This can be expressed mathematically as follows: lim T → 0 Δ S = 0 {\displaystyle \lim _{T\to 0}\Delta S=0} 2. The Third law of thermodynamics is sometimes stated as follows, regarding the properties of closed systems in thermodynamic equilibrium: The entropy of a system approaches a constant value as its temperature approaches absolute zero. I think that the first question to ask is this one: Is the expanding universe a closed system in a thermodynamical equilibrium such that the third law of thermodynamics or Nernst theore…
More
ResearchGate
Question
It is commonly accepted that the Universe started in an ordered state with low entropy (S), which allowed its entropy to further increase - as observed - in line with the second principle of thermodynamics. What was then the most robust value of departure ? One could suppose that the entropy at the Big Bang was S=0 as the Universe was concentrated in one single micro-state (one single configuration). But this is a lot speculative as nobody knows what did the physics look like before Planck’s time (1.351 10-43 s). At this time, in an hot Big Bang scenario, one could use the values proposed by Planck to the Academy of Berlin in 1899 to compute the entropy : - Planck’s length : 4.051 10-33 m - Planck’s mass : 5.456 10-8 kg - Planck’s temperature : 3.551 1032 K These values are a combination of universal constants exclusively, thus without « human neutral ». One then finds an entropy : S = 1.381 10-23 J.s-1 , i.e. Planck’s constant, corresponding to (using Boltzmann’s equation : S = k.lnW) a number of micro-states : W = 2.718 (= natural number « e »). One could also use the formula of Bekenstein-Hawking for the entropy of a black hole, as the Universe was like a black hole at start (very hot, very dense). Using Planck’s length as diameter of the horizon circle of the black hole, we get an entropy : S = 1.652 10-23 J.s-1 , corresponding to W = 3.309 micro-states. We would thus have an entropy corresponding to 2-3 micro-states at Planck’s time. Another way would be to assess the entropy just after the presumed inflation stage (ending 10-33 s after the Big Bang). The entropy is then the area of the cosmological horizon in Planck's units, and would be about a million Planck’s lengths of radius, so probably a value of the order of ln W = 4.787 1012 which is still very low compared to the order of 10135 (maximum entropy one can squeeze in the modern cosmological horizon). Other proposals go in the direction of a very high entropy at the beginning of the Universe, which would itself start from a statistical fluctuation of low entropy : which would then be the order of magnitude of this low entropy ? In summary, could these evaluations be accepted and, whether yes or no, which would be the best value to have an idea of the entropy of the Universe shortly after the Big Bang ?
Answer · 0 votes
Please, read "human intervention" instread of "human neutral". With apologies !
More
Not saying I agree or not. Just posting to show maybe there is interesting content somewhere.
Cat
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Can you two decide between yourselves who is right here. It will save me trouble investigating
This is a question a doubt any can answer. But we can favor one view over another.Can you two decide between yourselves who is right here. It will save me trouble investigating
Under normal circumstances, I'm confident entropy increases. So the question becomes more about the premise than the conclusion. If you compress the entire, unimaginably gigantic Universe back into an unimaginably small size then will things be "normal"? Nobody really knows because there is no guarantee some new phenomena that's never been considered, especially where our physics' equations shoot to infinity results, might emerge that may, or may not, suddenly produce such order that lowers entropy.
David, I hope Helio agrees, I don't think it is a question of right or wrong. We are in untrodden territory - pure conjecture and assumption. Frankly, I am more worried about the Universe contracting than I am about entropy decreasing. Which conjecture/model is right/wrong? I think it is just a matter of inclination, guesswork, or maybe what one had for breakfast?
Cat
Cat
Helio, in addition to #65, I think I have even more problem with the idea of a Universe expanding faster that the speed of light - OK just space expanding, but it seems to me that we are getting back to the old idea of aether? Space/time expanding ~~~ aether as an expandable medium?
Cat
P.S. space/time expanding but not the space occupied by mass?? Expansion of space/time checked by the presence of mass?? Mass inhibits space etc expansion??
So. IF the Universe contracts, does the increasing density correspondingly promote decrease in entropy??
The whole idea rests on the premise that the Universe can flip into contraction??
To me, the idea of beginning/end is anathema - anthropocentric delusion. We should not expect conclusions based on a system dependant on our limited sensory input to govern the workings of the Universe. In particular, consideration of semantics - vide Universe v. observable universe(s).
Cat
Cat
P.S. space/time expanding but not the space occupied by mass?? Expansion of space/time checked by the presence of mass?? Mass inhibits space etc expansion??
So. IF the Universe contracts, does the increasing density correspondingly promote decrease in entropy??
The whole idea rests on the premise that the Universe can flip into contraction??
To me, the idea of beginning/end is anathema - anthropocentric delusion. We should not expect conclusions based on a system dependant on our limited sensory input to govern the workings of the Universe. In particular, consideration of semantics - vide Universe v. observable universe(s).
Cat
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Yeah, the aether idea never completely vanished. People think it died when Einstein dismissed it but Einstein only said that no medium (ie aether) is necessary for light propagation; not that aether doesn't exist. [The Hubble Flow is particularly interesting as a possible springboard to work from.]
Given the BBT, space has done a great deal of expanding since that first moment, so more expanding, however that happens, seems easily justified. The hard part was determining if there was enough objective evidence for BBT because implications, like a continued expansion (and acceleration), have been tough pills to swallow for many. The brilliant Hoyle, though he supported the science that helped BBT, never accepted BBT as he always had hopes his, and other's, Steady State Theory, or modifications to it, would prove more favorable.
[Speaking of Hoyle, I finished a book that included the author's suggestions why Hoyle -- arguably the Father of stellar nucleosynthesis -- never received the Nobel prize. Interested?
]Local space is expanding but it is an incredible tiny amount over only millennial scales, so that gravity is more than sufficient to reign-in any such spacetime expansion.
Perhaps, and maybe someone smarter will respond to this idea, we could simply note that as space expands it does add or subtract angular momentum from orbiting planets. So if the angular momentum is unchanged, so too will be its orbital distance, at least I think I'm right.
Is there an analogy you can use to help me see this? We both know gasses, when compressed, are essentially irreversible, so entropy increased, but a Universe?
Yes, this idea would be a bit bizarre if it weren't for the fact we really have no idea what DE is.
You're not alone.
When Lemaitre introduced his theory, a "beginning", matching the words of Genesis, had strong religious implications, of course, though some religions claim no beginning. Initially, Einstein refused to accept the idea that the universe wasn't always the same. But back then there were no galaxies, only nebulae, and there was little evidence for expansion, only a few dozen redshifts from Slipher. Eddington and deSitter, and others, seem to win Einstein over to Lemaitre's work once the problems with the Static Model failed.It's worth noting the BBT (Lemaitre) came mainly from Einstein's theory, GR, and not scientists trying to figure out some new discovery that had no explanation. This doesn't happen very often, and for it to be true of the biggest theory of all is remarkable to me.
I partially agree for the reason that no theory offers proof it is immutable. But when the abundance of objective evidence supports the claims made, and engineers are given the "laws" (e.g. GPS work) that do prove effective, it's hard to expect anything but respect for it.
Helio,
"But when the abundance of objective evidence supports the claims made, and engineers are given the "laws" (e.g. GPS work) that do prove effective, it's hard to expect anything but respect for it."
I respect what you are saying, but there is still the problem of t = 0 and "infinite" which means that there is an essential gap in the chain. There is a parallel with Newton. We did not know there was a "gap" until velocities became closer to c. Now we know that using "Newton" worked OK but that there was a flaw as v --> c. So that the fact that you say BBT works in practice is like saying Einstein is not needed because we use Newton.
I am saying v approaching c is like t approaching 0, as a simple analogy.
I am also saying that the sudden appearance of an infinitely small and infinitely hot bundle of everything with no back story is more than I can stomach - and I once supported it and "explained" it. I retract without an inquisition and support Galileo.
Cat
"But when the abundance of objective evidence supports the claims made, and engineers are given the "laws" (e.g. GPS work) that do prove effective, it's hard to expect anything but respect for it."
I respect what you are saying, but there is still the problem of t = 0 and "infinite" which means that there is an essential gap in the chain. There is a parallel with Newton. We did not know there was a "gap" until velocities became closer to c. Now we know that using "Newton" worked OK but that there was a flaw as v --> c. So that the fact that you say BBT works in practice is like saying Einstein is not needed because we use Newton.
I am saying v approaching c is like t approaching 0, as a simple analogy.
I am also saying that the sudden appearance of an infinitely small and infinitely hot bundle of everything with no back story is more than I can stomach - and I once supported it and "explained" it. I retract without an inquisition and support Galileo.
Cat
Agreed, but t=0 is outside the BBT itself. But, it would be wrong to suggest BBT doesn't imply it, so one gets stuck with it philosophically, which is like a bad after taste to what was nice-tasting wine.
But there is still no requirement for infinite anything. It could have started the size of a single string or something else less than the size of the Planck scale. This too is philosophical and only supposition, but it avoids some of the aftertaste even if the nice taste has faded away.
I don't see a gap because both BBT and Newton's equations have proven effective at addressing all phenomena within their limits. We now know Newton has limits as you noted, and we know t=0 is outside of BBT. The difference is Einstein has shown a better model over Newton, but there seems to be no improved model to BBT that can even approach t=0 as a physics model.
Just as Newton's model is still the primary science in engineering (vs. Relativity), so too is BBT over anything else.
I respect it and understand why you and others don't agree with the "aftertaste", if you will.
However, if a cyclical model is more tasteful, would it, during the collapse phase, not also suffer with an "aftertaste". Any minimal blob size must be justified by physics.
I think the Pope is okay with your views.
IG2007
"Don't criticize what you can't understand..."
A cool conversation, finally.
Before joining the conversation, I want to say that, the BBT, as well as the Nexus theory, are conjectures and can never be proven because of the same reason. We cannot observe t = 0.
Now, let's look at the BBT before moving on to the Nexus theory, Correct me if I am wrong, the most common view of BBT is that the Universe started with basically an extremely hot and "infinitely dense" singularity and started to expand since then.
Now, let's take a look at the Nexus theory, it says that an "infinite" or an unknown number of Universes has preceded and shall follow the Universe we are in. To make it more accurate and more confusing, that basically means that everything that will happen has already happened and that everything that has already happened will happen again. And, each of those Universes started in a rather finitely dense and extremely hot temperatures.
Well, as I already said, both are conjectures to explain the Universe. Both have "infinities" and both have faults. The BBT's fault is that it assumes a singularity, and the Nexus theory's fault is that it assumes an "infinite" number of Universes after and before this one. And, also, for that to happen, the overall entropy of the Universe has to decrease, which fundamentally violates the 2nd Law of Thermodynamics. And also, for that to happen, Dark Energy needs to decrease.
Sure, no law is really a "law" if empirical observations don't match with the law, but well, Cat, unfortunately, I don't know of any empirical evidence which can outright dismiss the 2nd Law of Thermodynamics. And, coming to DE, I haven't really read an article yet that says that DE is decreasing. Moreover, we don't even know what DE is.
Well, to conclude, both have flaws of their own. I have my own theory about the Universe, but I think I will wait till I get a reply to this.
I think the Pope is okay with your views.
Before joining the conversation, I want to say that, the BBT, as well as the Nexus theory, are conjectures and can never be proven because of the same reason. We cannot observe t = 0.
Now, let's look at the BBT before moving on to the Nexus theory, Correct me if I am wrong, the most common view of BBT is that the Universe started with basically an extremely hot and "infinitely dense" singularity and started to expand since then.
Now, let's take a look at the Nexus theory, it says that an "infinite" or an unknown number of Universes has preceded and shall follow the Universe we are in. To make it more accurate and more confusing, that basically means that everything that will happen has already happened and that everything that has already happened will happen again. And, each of those Universes started in a rather finitely dense and extremely hot temperatures.
Well, as I already said, both are conjectures to explain the Universe. Both have "infinities" and both have faults. The BBT's fault is that it assumes a singularity, and the Nexus theory's fault is that it assumes an "infinite" number of Universes after and before this one. And, also, for that to happen, the overall entropy of the Universe has to decrease, which fundamentally violates the 2nd Law of Thermodynamics. And also, for that to happen, Dark Energy needs to decrease.
Sure, no law is really a "law" if empirical observations don't match with the law, but well, Cat, unfortunately, I don't know of any empirical evidence which can outright dismiss the 2nd Law of Thermodynamics. And, coming to DE, I haven't really read an article yet that says that DE is decreasing. Moreover, we don't even know what DE is.
Well, to conclude, both have flaws of their own. I have my own theory about the Universe, but I think I will wait till I get a reply to this.
That's the general idea for most perhaps, but formally, BBT doesn't go to a singularity for its start. It really has no hard start but it doesn't need one to be the theory that it is. It started when Lemaitre connected the idea of GR with his view of expansion, and he had some objective evidence to allow him to make a crude calculation of the expansion rate.
He then imagined what would happen if the clock were reversed, making the expansion a contraction. His model, the "Primeval Atom" never took it down to a singularity.
The question to ask when wanting to know how close to t=0 can we get is to see where the equations suddenly fall apart, which is very close to t=0.
Most are comfortable with the supposition it came from a singularity because it's such a short step to where physics is and t-0. It also sounds cool and it gets associated with BHs, which are cool, etc. But BBT limits itself to the physics that can define it, not the metaphysics that can't.
Is there any means to test this "theory"? If not, it's supposition, not theory.
This is why it's important to understand where science draws the line and requires objective-based ideas. BBT has been tested over and over and does extremely well, though another could replace it. Any other model, however, must address all the same questions, especially the CMBR.
It's unclear if even the conservation laws hold true for the entire Universe. So there may be some wiggle room.
IG, the cyclic models require a contraction after the known expansion. Since it is a model of the future course of the Universe (imho) and since there is no evidence from before the BB, there can be no traces or properties to be found as yet. These remain part of the supposition.
Likewise, there is no way of knowing whether decrease in entropy can follow with contraction. I cannot produce any evidence for decrease in entropy. All I can do, is to point out that (local) entropy decreases as steam condenses to water and freezes to ice (in terms of order). This is just a vague suggested analogy. We cannot know whether the 2ndLoT might be reversed during contraction.
I heartily agree that my suggestions are only "thought models" without any way of proving one way or the other. BUT, I would suggest, no worse that "infinite" anything, including singularities.
Cat
Likewise, there is no way of knowing whether decrease in entropy can follow with contraction. I cannot produce any evidence for decrease in entropy. All I can do, is to point out that (local) entropy decreases as steam condenses to water and freezes to ice (in terms of order). This is just a vague suggested analogy. We cannot know whether the 2ndLoT might be reversed during contraction.
I heartily agree that my suggestions are only "thought models" without any way of proving one way or the other. BUT, I would suggest, no worse that "infinite" anything, including singularities.
Cat
Yes. And this is only accomplished as the heat is removed and ejected into an external heat sink. We use the universe as the great heat sink, but in reality, we are using our atmosphere.
In the early 70's, one of my thermo profs. predicted that we could struggle with too much heating of our atmosphere as a result of all that waste heat. Waste heat is not something than can be put to use but how to get it out into space is an issue. I would assume the climate models include all the waste heat we generate, though solar radiation through increasing amounts of greenhouse gases is the bigger issue since direct sunlight is over 1300 watts per sq. meter (1000 watts at the surface).
Helio,
"Yes. And this is only accomplished as the heat is removed and ejected into an external heat sink. We use the universe as the great heat sink, but in reality, we are using our atmosphere."
But, this ties in with my post #72. We are looking at hypothetical contraction / entropy decrease.
And in #72, I did say this:
"All I can do, is to point out that (local) entropy decreases as steam condenses to water and freezes to ice (in terms of order). This is just a vague suggested analogy. We cannot know whether the 2ndLoT might be reversed during contraction."
Cat
"Yes. And this is only accomplished as the heat is removed and ejected into an external heat sink. We use the universe as the great heat sink, but in reality, we are using our atmosphere."
But, this ties in with my post #72. We are looking at hypothetical contraction / entropy decrease.
And in #72, I did say this:
"All I can do, is to point out that (local) entropy decreases as steam condenses to water and freezes to ice (in terms of order). This is just a vague suggested analogy. We cannot know whether the 2ndLoT might be reversed during contraction."
Cat
Nature hates perfect lawns. Ruthlessly relentlessly, with not the slightest sensitivity, feeling, or compassion for domesticated inbred weakness, it does all it can to eat them. It would be the same with the Utopian perfect baby looking for life eternal (for life into perpetuity) in the womb. And, the same with the attempt at the environmentally perfectly balanced Utopia on the Earth. Nature apparently likes the wild, the frontier, and wants life pitting itself against it in it(!), in order to grow strong in genius, in prosperity, and in survivability, into it. Nature is very, very, good at one thing, relentlessly ruthlessly outlasting, overpowering, and destroying mankind's eternal stupidity in pushes for in-turning, inbreeding, scientifically perfect Utopias in place.
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