Duda Jarek

The version from wikipedia article is much weaker - the erasure is made randomly, while here we can control it - let us understand what's wrong here? There is also possible Mach-Zehnder version of this experiment, which seems to be clearer: Here is reported realization: http://singlephoton.wikidot.com/quantum-eraser There is a question of the coincident counter: is it required to get dependency of Ds1,Ds2 counts from rotation of the polarizer? We know about such dependency for coinciding photons - which entangled partner hit Dp. For photons pairs which hit Ds1 or Ds2 but not Dp, one would say that we should get interference - the readings shouldn't depend on the angle of polarizer(?) So without the coincidence counter, while we cannot distinguish which exactly photons were erasured, still the total number should be affected by polarizer rotation - the dependency would be probably weaker, but shouldn't it be still seen on statistical level? Physics from QFT to GRT is Lagrangian mechanics - finding optimizing action history of field configuration. I don't see why it contradict using constrains with causal loops, as long they are imperfect - leave physics a place to lie, breaking such loop. Hypothetical wormholes would allow to construct a perfect loop, like a cannon which shoots to itself if and only if in doesn't do it - it could be so large that thermodynamics couldn't prevent it ... it's why I don't believe in wormholes. But here everything from electronics to such hypothetical backtime channel is based on thermodynamics, statistics - degrees of freedom which seems random for us now, but physics could bend this randomness to optimize the action - e.g. if we could try to impose constrains with causal loop.

In quantum eraser experiments, getting information about one entangled photon decides if the second photon behaves classically or quantum (interfere). Optical lengths for these photons chooses time order of these events, so we can delay the "decision" to happen after what it decides about. But in "standard version" of such delayed choice quantum erasure this decision is made randomly by physics. I've just found much stronger version - in which we can control this decision affecting earlier events. Here is a decade old Phys. Rev. A paper about its successful realization and here is simple explanation: We produce two entangled photons - first spin up, second spin down or oppositely. Photon s comes through double slit on which there are installed two different quarter wave plates changing polarization to circular in two different ways. Finally there are two possibilities: u d R L d u L R where columns are: linear polarization of p, initial linear polarization of s, circular polarization of s after going through slit 1, circular polarization of s after going through slit 2. So if we know only the final circular polarization of s, we still don't know which slit was chosen, so we should get interference. But if we additionally know if p is up or down, we would know which slit was chosen and so interference pattern would disappear. So let us add polarizer on p path - depending on its rotation we can or cannot get required information - rotating it we choose between classical and interfering behavior of s ... but depending on optical lengths, this choice can be made later ... Why we cannot send information back in time this way? For example placing s detector in the first interference minimum - while brightness of laser is constant, rotating p polarizer should affect the average number of counts of s detector. What for? For example to construct computer with time loop using many such single bit channels - immediately solving NP hard problems like finding satisfying cryptokey (used to decrypt doesn't produce noise): Physics from QFT to GRT is Lagrangian mechanics - finds action optimizing history of field configuration - e.g. closing hypothetical causal time-loops, like solving the problem we gave it. Ok, the problem is when there is no satisfying input - time paradoxes, so physics would have to lie to break a weakest link of such reason-result loop. Could it lie? I think it could - there is plenty of thermodynamical degrees of freedom which seems random for us, but if we could create additional constrains like causal time loops, physics could use these degrees of freedom to break a weakest link of such loop. What is wrong with this picture?

We are used to stationary Schrödinger equation. Slowly varying potential makes it more complicated. Physics should smoothen rapidly varying potential ... but let us discuss what's happening while theoretical rapid change of potential (no adiabatic approximation). For example imagine that potential has one minimum before the switch moment and a different one after (e.g. capacitor charged in one way then in opposite one) - like in this picture: In minus infinity electron should be in the ground state of one potential and in plus infinity in ground state of the other - the question is how the transition of wavefunction would look like? The main problem is that quantum mechanics is time symmetric - such transition shouldn't be instant, so this symmetry suggests that the middle of this transition is the switch moment ... but it means that the wavefunction has started evolving before the switch??? I have to admit I don't understand the situation from perspective of quantum mechanics. The above picture used Maximal Entropy Random Walk instead (page 48 of http://arxiv.org/abs/1111.2253 ) - corrected Brownian motion to finally become thermodynamical model - not only approximate maximum uncertainty principle, but really maximizing entropy. Thanks of it, it doesn't longer disagree with thermodynamical predictions of quantum mechanics - the equilibrium dynamical state has probability density being exactly the squares of the lowest energy eigenfunction of Schrödinger's Hamiltonian. So this model agrees with the ground state in plus/minus infinities, but also naturally explains the transition - it indeed starts before the switch, but this time there is nothing strange about it: this model is thermodynamical - not fundamental but effective: we already know the history of potential and it allows us to estimate the best probability distribution of the particle. For example knowing that later it will be in another potential well allows us to tell that earlier it should be nearby. There is another strange thing about above picture - its Ehrenfest Newton's equation has opposite sign - the particle accelerates uphill then decelerates downhill ... but it's just required e.g. to transport density between these minimums ... But what's going on here in standard quantum mechanics? Would the wavefunction start transforming in the moment of change or before?

Even if brain washing the whole society for referendum would be (not only possible, but even) cheaper than current bribing a few politicians (I really doubt), once again - I'm not talking about voting. I'm talking about discussion mainly - if someone want to give an argument there and want it to be highly judged (justified and in concrete categories) by other participants to be taken into consideration, he should deeply understand the whole situation, arguments of both sides, read many sources - such actively discussing person becomes much more resistant to influence of lobbyists. And of course such resistance is one of the main priorities while designing such discussion platform: http://www.scienceforums.net/topic/64446-how-to-design-a-place-for-massive-joint-work-like-creating-standards-legislations/

About your example, do you suggest that it would be easier for lobbyists to enforce their position by e.g. covering everything with posters (and it would work) than current e.g. talking to a buddy politician or a few bribes? And once again: not referendum, but mainly discussion - exchange and joint evaluation of arguments e.g. about this road.

From experience of Poland, people often vote for a person because of despair - they feel hopeless, they think ever worse about alternatives and so they choose what looks as the least evil. That's the major problem with representative democracy - you don't vote for ideas you believe in, but for a highly sponsored picture - who doesn't in fact have to share anything with your ideology ... I'm talking about shifting these decisions from prone to corruption unpredictable persons, to concrete problems, ideas ... and not about just voting about them, but discussing mainly. The same Tom Atlee above. For example first discuss given issue to find a consensus and eventually produce a few alternative compromises and then vote between them.

Here is great lecture of Tom Atlee with examples about direct democracy I'm talking about - mainly discussion of the people to find a consensus:

This thread is not directly about creating some law/standard, but to discuss about designing general computer platform for working on them - issues of Internet forums. I think it is enough of general comments - imagine millions of people fighting e.g. to make legislation in their way - how to design such place to make it won't turn into mob fight, but a civilized discussion ... ?

khaled, the problem/difference is that on such forum users would decide about extremely important things like legislation which affects them - casual citizens with their causes and billion dollars lobbyists between them. To make it work, it cannot be just a forum like this one, but really deeply well thought for this purpose - designed to handle massive serious discussions and by construction improve their level. Ben, the initial purpose for serious discussion platform was making a step toward direct democracy, so I've placed it there: http://www.scienceforums.net/topic/64141-national-discussion-forum-discuss-then-vote-direct-democracy-using-electronic-signature/ But the discussion was only general about direct democracy there, so I thought that: - it is much more universal tool, like for working on international computer standards, - unfortunately even looking very promising Free Internet Act initiative seems to have completely no interest because of current political apathy - I see that going with such initiative from the people has rather no chance now ... but giving politicians tool to improve working on international matters, then expanding it to the people might be more realistic (?), - and mainly because understanding nuances of designing (and maybe creating) such general tool for serious discussions of huge number of extremely interested persons is rather a task for computer scientists ...

Of course there are many involved issues like security, but I think the first step is to discuss how generally it should be designed - how should general rules of such place look like, the basics of its mechanics - to make it able to handle large amount of very interested persons and by the construction itself improving level of discussions. You can comment above brief description or propose alternatives.

Justin, I think internet has already greatly improved transparency of the government - especially because they lost monopoly on spreading information on national scale and made it much easier for people to organize. Such open discussion platform could be at first developed e.g. to massive joint work on international standards and if it would work, we could suggest politicians to use it to improve e.g. discussions/legislations on international scale ... and then natural next step would be allowing the citizens to look at it and then maybe give own perspectives as arguments in discussion... Panic, Fortunately internet has made that the age of people just blindly watching TV is slowly reaching its end - there appears huge amount of uncontrolled by government sources of information. But for society to be mature enough for e.g. frequent referendums there is still much needed - it's why I think we should now rather think of better way of serious discussions on national/world level - where what counts is not how loud is blind mob, but wise arguments.

There are situations when huge amount of people has to jointly work on extremely important documents. For example HTML standards where a few large players like web browser producers discuss between each other and potentially millions of web designers around the world ... or thousands of politicians/lobbyist while working on compromises of legislations on scale of e.g. USA/EU/world. How such looking impossible tasks are conducted? Do they use some kind of e.g. TortoiseSVN? Are they transparent enough for interested sides? I don’t even want to imagine how it is made in politics, but for standards there are for example mailing lists, so to e.g. get to information you are interested in or would like to comment on, you would rather have to dig through huge list of multi-plot comments … Let us think about designing and maybe creating an open source tool for such serious discussions of potentially huge amount of people ... which then could be applied for different purposes of optimized and transparent work on important documents. How would a perfect situation look like? I imagine that from the page of the document we/they work on, I can click on paragraph/sentence to get to a page describing multiple related issues, summarized discussions which lead to its current form, links to these discussions I could participate in, proceeding votes between alternatives … So e.g. looking at the legislation, everyone could trace each sentence (e.g. to a lobbyist) and understand its evolution to the current form - thanks of this better understanding, interpretations could be closer to the expected result and generally people could better identify with e.g. the law. So how to design such a place? Here is a brief description how I would imagine it. First of all there shouldn't be anonymity there – for really serious discussions, the best would be if every action is digitally signed and this information and generally the whole history is available for all users. So statements there have legal status similar to signed article published by a journalist – think a few times before writing something there. All information about mechanisms used by this tool should be easily accessible (and also discussed and eventually modified). Digital signatures are usually equivalent to the real ones, so by the way this place could be used also e.g. for direct democracy. Secondly, statements should be relatively compact and rather focusing on a single issue – they should have one main link to what they refer to (and eventually additional links) – the discussion generally is a tree (with eventual less important transverse links), like on reddit but a bit more complicated. Thirdly, there is required well thought marking system – much more complicated than of reddit. To prevent pathologies, each mark should be signed and well justified … and marks also can be judged and so on. There would be rather required many different categories of marks - to not just give plus/minus, but also specify and well justify what for. Their direct purpose is to be able to freely customize the order of the list/subtree of related topics to display – from standard chronological through by some category of marks, up to different mixed custom criteria. Another purpose is using these marks in discussions or e.g. to nominate persons with high marks to take care of sites of some issue (his actions would be still fully traceable and evaluated). There is required some limit of points – for example 1/category/day and can accumulate up to 10/category. They can be spent (with justification) for pluses/minuses in selected categories (e.g. +1 patriotism, -1 realism). The weight of point depends e.g. on total marks of the author in this category. The "/category" is to motivate to look from perspectives of different values on others statements and so on one's own. Marks of marks influence their weight and generally the weights of marks of the author - there would be required some kind of page-rank to calculate final weights. Example of list of categories of marks (to discuss): - Morality / empathy (as external evaluation of situation) - Altruism/hard work (as own work/sacrifice, minus for selfishness, lazy distributing points) - Justice/objectiveness (e.g. unjustified marks, lack of objectivity) - Realism (awareness of the broader situation) - Patriotism (good for the nation) - Originality / innovativeness (minus for obviousness, plus for interesting idea) - Compactness (plus for good essence/form proportion, minus for leading nowhere comments) - ... ? Some may have subcategories - like realism in politics, economics, physics ... More controversial examples: - Coherence / consistency / transparency - minus for lies, frequent change of opinion (have to be distinguished from the legitimate evolution), plus for mature defense of an idea, the internal consistency, honesty in a difficult situations, - Openness / flexibility - minus for not adapting to changing realities, ignoring strong arguments, blind fanaticism ... plus for openness to different views, evolution of own thinking. Besides statements, there would be: - Profiles of persons/institutions/organizations/companies (with part edited by this subject and part everyone can discuss), - voting sites - secret (e.g. for final vote) or open (e.g. while choosing between alternatives), - sites for working on given petition, bill, referendum requests – with links to sites focusing on single sentences, planed deadline to stop working and start gathering signatures, - wiki-like pages on different subjects and specific topics for discussion, briefly introducing to the problem and results of discussions – with statistics and lots of links. Another important issue is changeability. I think people could change judges/marks. The main link of statements should be unchangeable, but additional links can be added/updated. Someone could comment on (a part of) the text, so there should be rather possible only adding succeeding updates. How would you imagine constructing a tool to improve working on important documents? A tool for serious discussions of potentially huge amount of sometimes extremely interested people? To increase their level by its construction? One of many applications could be some National Discussion Forum improving the work on legislations – by making it more transparent and easier for people to express their perspective on concerning them created law.

There is a lot of talking about E-democracy, but I agree the society is not mature enough (yet?) - I'm talking 'only' about improving discussion level between the people and the government. The majority is not ready for too much power (what is conjugated with weakening identification with the system), but for being citizens and taxes they pay, they deserve for transparency and the feeling that they can show their perspective in discussions. There is a continuous spectrum of possibilities between current system and ochlocracy. There are required experts to make legislation, but what percent of country's experts on given topic really takes part in it? The legislation's role is not just to be pushed, but to solve some problem - full-time legislators may have their own agenda, confirmation biases, they are often theoreticians very distant from lower living people they decide about ... What I'm thinking about is a tool to allow all experts in the country (and e.g. people who knows the situation directly...) to participate in the discussions - show new arguments, missed perspectives, lacks of reasoning, weaknesses ... To combine the potential of all citizens to make better legislations. Sounds impossible? Many of what surrounds us today would sound impossible a few decades ago ...

'The people' are often short-sighted, egoistic etc. ... but the politicians are also not perfect, they make mistakes, there is corruption involved ... but most importantly they don't always understand well the perspective of people they decide about - the interface between the people and the government can be improve to give people more faith in the system and the government a better understanding. Another important issue is transparency required for preventing pathologies and so giving trust. Frequent referendums work well in Switzerland, but I completely agree that generally we should be very careful about it, it has a danger of turning into ochlocracy ... and for example can make life of minorities difficult. And so I'm emphasizing not voting, but rational democratic discussions - transparent exchange and evaluation of arguments of potentially all citizens. And democratic vote should be when discussion has lead to a few possible compromises. Discuss then vote - wisdom then equalizing. There are positive initiatives from the top, like televise proceedings of Supreme Court, but there are also needed for example ways for people to create legislation they believe is required and not trust politicians enough with it, like Free Internet Act to protect the net. Let me briefly write how I imagine such place for really serious discussions – shifting people’s energy from fb and rage in current political apathy age, toward organizing in social work for our better future. To join forces with the government, instead of fighting with each other. Created by the people to use direct democracy, but later maybe accepted and used by the government. A basic unit should be a ‘statement’, which - always has a text and one main link it refers to, - eventually ‘judge’ of what its main link points to and a few additional links. The link can refer to the whole/part of the site on given topic or a statement. If the purpose of the statement was to make judgment, the text should be only the justification. These judging statements can also be judged, for example because of poor justification. The marks of statements affect the mark of its author and weight of its judging. Finally, there is required some kind of page-rank algorithm to evaluate final marks of statements/persons and use them while sorting search results - in one of many ways, customized by the user. Everybody would get e.g. 10 points/day, which can be spent on marks in different categories, for example a statement could be “+1 patriotism, -1 realism” and explanation. Points in category given person has higher marks would have larger influence. Example of list of categories of marks (to discuss): - Morality / empathy (as external evaluation of situation) - Altruism/hard work (as own sacrifice/work, minus for selfishness, lazy distributing points) - Justice/objectiveness (e.g. unjustified marks) - Realism (awareness of the broader situation) - Patriotism (good for the nation) - Originality / innovativeness (minus for obviousness, plus for interesting idea) - ... ? Some may have subcategories - like realism in politics, economics, physics ... More controversial examples: - Coherence / consistency / transparency - minus for lies, frequent change of opinion (have to be distinguished from the legitimate evolution), plus for mature defense of an idea, the internal consistency, honesty in a difficult situations, - Openness / flexibility - minus for not adapting to changing realities, ignoring strong arguments, blind fanaticism ... plus for openness to different views, evolution of own thinking. Besides statements, there would be: - Profiles of persons/institutions/organizations/companies (with part edited by this subject and part everyone can discuss), - voting sites - secret (e.g. for final vote) or open (e.g. while choosing between alternatives), - sites for working on given petition, bill, referendum requests – with planed deadline to stop working and start gathering signatures, - wiki-like pages on different subjects (e.g. euthanasia, nuclear power ...) and different specific topics for discussion, briefly introducing to the problem and results of discussions – with statistics and lots of links. ?

The World’s situation is far from being perfect and it doesn’t seem to have perspective to repair itself(?). So there are growing in strength on one side e.g. - idealistic utopian visions, like Zeitgeist movement/Venus project expecting that the system will itself transform into resource-based, or - rage movements on the other side, like occupy movements or Anonymous which doesn’t seem to have realistic alternatives to what they are against. Let us think here about reasonable constructive possibilities which are both achievable in this moment and giving hope for the real improvement for our future. The general feeling is that the main problem is that the power corrupts – not only the rich/politicians/lobbyists should decide about the future of our world, but the power should be somehow shifted toward the ones it directly applies to. On national level it is generally called direct democracy and is already included in constitution of many countries. However, in only a few of them it has some real influence, like in Switzerland or e.g. recent writing constitution of Iceland by its citizens . Fortunately we have Internet now, which could make direct democracy quite realistic. There remain conjugated questions: how should it look like and how to make it accepted on national/world level? Many countries accept electronic signatures as the real ones, making such signature perfect tool of direct democracy - to sign below initiatives and then use constitutional direct democracy. The problem is to organize these hundreds of thousands of willing people – create the place to gather them and find initiatives people would indeed agree to. The best would be if they could identify with it … believe in it – if they could take a part in its carving … Very promising example is recent initiative of creating Free Internet Act as counterattack on SOPA/PIPA/ACTA, which could wake people up from political apathy and make them believe that their action may indeed improve situation ... which literally translates into real organizing. But there is extremely important danger of direct democracy - it looks similar to ochlocracy ... it cannot be just mob shouting to e.g. lower taxes, but there is essential discussion phase before: on which there are considered realistic alternatives, basing on reasonable arguments. It should formulate a few possible compromises and then the people could choose one in pure democratic act. The main question is who should be involved in these discussions. I believe the priority is to shift this "discussion phase" of e.g. legislation toward the people. For this purpose, there would be extremely useful some specialized place designed for this purpose: National Discussion Forums – an open source project of forums for serious discussions of potentially millions of citizens, which could be then applied as the single additional discussion place on given level: state/country/union/world. For example to collectively work on legislations, then collect signatures there after finding the compromise. It should be discussion place without anonymity - in which all statements would be electronically signed and the whole history would be stored forever – everybody could express his opinion, but one should think a few times if he can indeed identify with what he is saying and want this information to be accessible. Alternatively he could ask someone braver to represent his point, for example by linking to the statement in an anonymous forum and commenting it. It would be a place where the politicians/government would be expected to express their transparency and discuss with citizens. In such a place new politicians would be born, by consequently building trust and support thanks of social work they have made and presented in this place. With time it could be officially accepted by government and among others became a place for referendums or even take some part of government’s role. It is extremely difficult to imagine discussions of millions of people on important for them matters, so it would require really well thought-out system of sorting/searching/(signed!)marks … also with required marks of marks and so on. It should be completely transparent, open source but still extremely safe. It shouldn't have some native moderators (to take care of e.g. legislation wiki-like pages), but some could acquire such status thanks of high marks from other citizens - but still all their actions would be traceable by everyone. Can a place for serious discussions of millions of interested people be realistic? How to design such a place to improve the level of discussion by the construction itself? If the system is not going to repair itself, is direct democracy a good direction for repairing it? If so, how should it look like and how to make the world to go in this direction?

Unless being in a singularity like a center of black hole or BB, general relativity says spacetime is semi-riemanian manifold: locally is Minkowski space (up to second order: curvature) - from microscopic QFT point of view (which CPT concerns), differences could appear on some hundreds decimals. GRT alone is both T and P symmetry. There indeed appears a problem with that CP symmetry is believed to be violated ... but I'm not entirely convinced that it is on fundamental level (equations) not symmetry breaking on solution level, like Higgs potential is symmetric while its solutions aren't? (...or fundamental physics is CPT symmetric, while its solution we live in has thermodynamical time arrow...). The question is how such T or P loop would transform particles? Ok, short living kaons could be transformed in long living ones - I would say they look the same in our description, but they are just different particles? But would transformed nucleons/electrons be different than ours? I don't think so - the eventual violation is on about tenth decimal, while we know there are no different stable field configurations (particles) so near ?

Big Bang in inflation theory could start with mathematical point which can be interpreted as having zero entropy ... but I thought Big Bounce would have rather some nonzero minimal radius and nonzero minimal entropy ... ? But even if it would be exactly zero, I don't understand why you think it should imply the first poll result? Heat death is not a well define state - it doesn't mean complete thermal equilibrium, but only approximate - like most of stars could not only became e.g. brown stars, but then they could still cool down to temperature near the surroundings (like current 2.7K) ... but thermodynamics should also make them evaporate to equilibrate the matter density - but gravity doesn't allow for that ... (gravity in opposite to electromagnetism is kind of opposing entropy growth - not spread uniformly, but rather gather everything in a single collapse ...) Heat death is not exactly slower transfer of energy as you write - in thermal equilibrium there is still a lot of energy transfer, but the same amount in both directions. Better description is that there are no gradients of different thermodynamical values, like average energy (temperature) or density of different substances (like osmotic pressure in our cells). ps. Penrose claims that there is even seen experimental evidence of something before Big Bang: http://physicsworld.com/cws/article/news/44388 This article supports what I have written about what I think I've heard on Penrose lecture - scenario 3) : "Central to Penrose's theory is the idea that in the very distant future the universe will in one sense become very similar to how it was at the Big Bang. He says that at these points the shape, or geometry, of the universe was and will be very smooth, in contrast to its current very jagged form. This continuity of shape, he maintains, will allow a transition from the end of the current aeon, when the universe will have expanded to become infinitely large, to the start of the next, when it once again becomes infinitesimally small and explodes outwards from the next big bang. Crucially, he says, the entropy at this transition stage will be extremely low, because black holes, which destroy all information that they suck in, evaporate as the universe expands and in so doing remove entropy from the universe. "

I'm not sure what do you mean? - orientability is global property - if there is some small local loop reversing time directions, from some distant point we could go to this region, make the loop and then go back to the starting point ... also reversing our time directions. About "Everything is relative", it's not so simple. Our normal mugs objectively can break only toward our future. There are even substances with clearly defined time arrow - for example unstable isotopes (created thanks of supernovas in our past) decreases radioactivity while time passes ... while their time reversed versions would increase radioactivity instead. Very interesting would be mixing such two versions of the same isotope - our would decay and then recombine into the time reversed version ... and such substance would have no well defined time arrow. But there are also much simpler substances without objective time arrow - for example simple fluid in thermodynamical equilibrium - shouldn't its time reversed version look exactly the same? ... could we distinguish them? In other words: could the reversed astronaut from the thought experiment breath with our atmosphere?

sorcerer, Entropy can indeed relate to subjective information of an observer, but it also describes the ordering of system. For example imagine a box with two partly separated pars, in which there is some number of objects - we see that e.g. n of them are in left part, while m of them are in the right part - while shaking the box, natural entropy should increase: h(n/(n+m)) where h(p):=-p lg(p)-(1-p)lg(1-p) Entropy is indeed about probability - if there is only one objective scenario (probability is completely localized), entropy is zero ... but changing the picture into more effective one: from choosing which part given object chose, into choosing how many objects choose left part - makes that there appears entropy describing ordering of the system. While instead of dividing into two, we make a grid and finally take infinitesimal limit, we get phenomenological thermodynamics, like in diffusion equation. Even knowing the exact atom configuration, for each point we can calculate the number of atoms in a small ball around - getting density function - probability analogue allowing to define entropy. About entropy as our information, here is example showing that it can decrease with time (by attaching in the future): We know that given person just couldn't miss given meeting (almost certainly will be there in that moment) ... accordingly to our knowledge, 15 minutes before the meeting probability distribution of his possible positions will be more spread (larger entropy) and so on entropy will grow while going back in time... ... but after the meeting time, such entropy will grow again - this time in the proper direction. Big Bounce is kind of such a meeting - was well localized, so had relatively small entropy, so created entropy gradient and our natural reason-result chain ... About choosing scenario 1 ... but entropy is usually bounded from above: among probability distributions among N objects, maximal entropy is lg(N) ... so do you think the entropy would tend with succeeding BB to infinity, or maybe asymptotically tend to some finite value? michel, Not everything is relative, for example our mugs can break only toward our future ... but they were created in our past. The question is if e.g. your aliens could provide with mugs made in our future - they should also have tendency to increase entropy(break), but this time it could be made only toward our past.

Yes, I've mentioned that currently universe expansion seems to accelerate, but is there a reason to believe that it will be maintained forever? Gravity says that it should decelerate, but there is something pushing it away - so called dark energy ... but energy conservation says it should weakens with expansion - faster than gravity. Untrue? I completely agree that we observe only entropy growth ... but thermodynamics is effective theory, while more fundamental are time/CPT symmetric. The only solution to this conflict I can see, is that time arrow is not fundamental property of physics, but a property of the concrete solution we live in - in vicinity to low entropic Big Bang state - in which everything was well localized in small region and which has started our natural reason-result chains: star, earth creation, evolution, our lives... To see that 2nd law can work in both time directions, see e.g. thought experiment theoretically allowed by GRT: http://www.scienceforums.net/topic/62327-thermodynamical-thought-experiment-with-nonorientable-spacetime/

Not everyone likes the idea of universe ​​created from a point singularity, so recently grows in popularity cyclic model - that our universe will finally collapse, use obtained momentum to bounce (so-called Big Bounce) and become the new Big Bang. One might criticize that we "know" that universe expansion is accelerating. But it is believed to be pushed away by "dark energy", so accordingly to energy conservation, this strength should decrease with R^3 ... while attracting gravity weakens like 1/R^2 and so should finally win - leading to collapse. But it seems there is a problem with the second law of thermodynamics here - on one hand entropy is said to be always increasing into the future, on the other Big Bangs should intuitively 'reset the situation' - start new entropy growth from minimum. I wanted to collect the possible approaches to this problem and discuss them - here is a schematic picture of the basic ones (to be expanded): The age of thermal death means that there are nearly no changes, because practically everything is in thermodynamical equilibrium, most of stars have extinguished. 1) The second law is sacred - succeeding Big Bangs have larger and larger entropy, 2) It is possible to break 2nd law, but only during the Great Bounce, 3) It is possible to break 2nd law in singularities like black holes - the universe may be already in thermal death, while the entropy slowly "evaporate" with black holes (I think I've heard such concept in Penrose lecture in Cracow), 4) The second law of thermodynamics is not fundamental, but effective one - physics is fundamentally time/CPT symmetric. So Big Bounce is not only single Big Bang, but from time/CPT symmetry perspective, there is also second BB-like beginning of universe reason-result chain in reverse time direction. The opposite evolutions would finally meet in the extremely long central thermal death age, which would probably destroy any low-entropic artifacts. Personally, I see 1) as a total nonsense - thermal death is near possible entropy maximum (like lg(N)). Also 3) doesn't seem reasonable - hypothetical Hawking radiation is kind of thermal radiation - definitely not ordering energy (decreasing entropy), but rather equilibrating degrees of freedom - leading to thermalization of universe. 2) sounds worth considering - physics doesn't like discontinuities, but Big Bounce is kind of special - crushes everything, resetting the system. And 4) is the most reasonable, but requires accepting that thermodynamical time arrow is not fundamental principle, but statistical effect of e.g. low entropic BB-like situation: where/when everything is localized in small region. To see that 2nd law can work in both time directions, there is nice thought experiment: http://www.scienceforums.net/topic/62327-thermodynamical-thought-experiment-with-nonorientable-spacetime/ Assuming our universe will eventually collapse, which thermodynamical scenario seems most reasonable? Why? Perhaps above list requires expansion? Did universe started in a point, or maybe something ends - something begins (like tonight)?

First of all, I totally agree that considering living things with fundamental physics is extremely inconvenient ... but it doesn't mean that there can be a contradiction between these totally different points of views. The problem you are talking about is mainly the conflict between: - looking time asymmetric 2nd law of (effective) thermodynamics and - CPT symmetric more fundamental physics. The main purpose of this thought experiment is to understand why there is no conflict here - that surprisingly 2nd law is also time-symmetric - depends only on reason-result chains ... which usually provide us with mugs from the past, so they can break only toward the future. Inside the rocket everything would be normal - but from our time perspective their mugs would break backward ... if they would provide such mug to the Earth, 2nd law would still give it tendency to increase entropy (break) - but this 'mug from future' could only break toward our past - in opposite direction to our 2nd law. If you don't like human origin mugs, you could e.g. crush a boulder or mix two different liquids - also a result of some reason-result chain (like liquid separation), what is the base of 2nd law. Simpler objects like a uniform liquid are thermodynamically time symmetric or reversible like many phase transitions. Secondly, it doesn't necessarily need to be a spacetime loop - ending points can be shifted in time, like in Hadley's peer-reviewed paper. I personally don't see it too realistic, only as thought experiment to understand thermodynamics, but you could get such loop for example by attaching mirror image to the left of black hole picture: Thirdly, why do you see here some exception of laws of physics?? It was intended to understand them, not contradict ... I completely agree that one couldn't go back and kill his grandfather - physics wouldn't allow him. The only natural for GRT point of view is the Einstein's block universe or eternalism ( http://en.wikipedia.org/wiki/Eternalism_%28philosophy_of_time%29 ) - that spacetime is already chosen - such that eventual time-loops would be already self-consistent. ps. The author of mentioned paper refers a few peer-reviewed ones, for example in Sorkin R D 1977 J. Physics A 10 717–725 there should be constructed a non-orientable wormhole (asymptotically flat), but it's not accessible electronically.

There is some thought experiment constructed to help finding intuitions about the 'conflict' between CPT conservation and 2nd law of thermodynamics. Like for wormhole loops, I see it completely unrealistic - I only think it is inspiring mind exercise and may lead to some better understanding of thermodynamics (and temporal logic). General Relativity Theory determines shape and rotation of light cones in each point of spacetime (like near black hole), but it is time (and CPT) symmetric - doesn't directly distinguish between past and future of such light cones. Without any additional reasons like entropy gradient, we could time-flip the light cones. Another from 2nd law of thermodynamics way to distinguish past and future of such light cones is by continuity ... but let us imagine there is some loop on which GRT makes that light cones have configuration like that: Where the start and the beginning have the same position, but may be shifted in time. Of course it would require some really nasty singularity inside such loop - even more than in the center of black hole where spacetime is no longer a manifold. There are rather completely no reasonable scenarios to obtain such singularity, maybe mathematics could forbid such global solution. Here is some 2002 paper from Classical and Quantum Gravity Journal about nonorientable specitime (precisely not time-orientable), here is its arxiv version. They are probably completely unrealistic, but only for this thought experiment let us assume for a moment that there exists such time reversing loop - and a rocket flied through it and returned back to Earth orbit. If someone really doesn't like such loop concept, one can imagine that this rocket was transformed by CPT symmetry - it would be made of antimatter, but it would be enough for thermodynamical considerations. Ok, let's get to the main subject - thermodynamics. Inside this rocket, the astronaut shouldn't feel a difference - he could e.g. just break a mug ... but from our perspective it would be time reversed: pieces would get together into the mug. Everything (like mugs) have tendency to get into higher entropic state (broken), but our things (mugs) came from past reason-result chains, so such state change (breaking) can only have e.g.: unbroken state toward past time direction and broken toward future. In contrast, reason-result chain of mugs from the rocket came from our future time direction, so it can increase entropy only while breaking toward our past. So it seems that 2nd law doesn't only emphasize just e.g. entropy gradient direction, but can work in both - depending only on reason-result chains ... ? This thought experiment becomes real mind feast if we allow the astronaut to land (not antimatter case) Time reversed molecules are nearly the same, temperature is average energy so it also shouldn't depend on time direction - he should be able to just breath in our atmosphere (??) His body should be in thermal equilibrium with environment - heat exchange should work normally, so I don't see a reason his time-reversed metabolism should work improperly (??) So it would seem that he could also eat our food ... but there appears a problem - from his time perspective, it could need turning e.g. back into a chicken The situation is really really strange - great mind exercise - I would gladly hear your comments, expansions ... I think the only reasonable causality understanding here is Einstein's block universe - that like in GRT, the spacetime is already created and 'we only travel to our future there'. So eventual time-loops are already made self-consistent, like in good SF movies (e.g. Twelve monkeys) - if one would like to kill his grandfather in the past, there would happen something that he couldn't do it. If you disagree, how do you understand the conflict between CPT conservation and 2nd law? How would look such contact of time-opposite natural reason-result chains? (theoretically allowed by CPT conservation) For example some believe in cyclic universe model - that our universe will finally collapse into nearly a point. From the perspective of CPT conservation, such Big Collapse point would be Big Bang it reversed time - low entropy state (spatially localized) creates entropy gradient (2nd law), starts reason-result chains ... and so evolution of universe in reversed time direction ... which should finally meet with ours in some far far future. Why against current acceleration growth, it should finally start collapsing? Because of energy conservation - gravity pulls together (1/r^2), while some 'dark energy' push it out, but its density (and so strength) should decrease with the volume (1/r^3) ...

If someone is interested, I have just finished large paper about MERW and its connections to quantum mechanics (e.g. to show these results on congress on emergent quantum mechanics this weekend) - a preliminary version of my current PhD: "Surprisingly the looking natural random walk leading to Brownian occurs to be often biased in a very subtle way: usually refers to only approximate fulfillment of thermodynamical principles like maximizing uncertainty. Recently, a new philosophy of stochastic modeling was introduced, which by being mathematically similar to euclidean path integrals, finally fulfills these principles exactly. Its local behavior is usually similar, but may lead to drastically different global properties. In contrast to having practically no localization properties Brownian motion, this recent approach turns out in agreement with thermodynamical predictions of quantum mechanics, like thermalizing to the quantum ground state probability density: squares of coordinates of the lowest energy eigenvector of the Bose-Hubbard Hamiltonian for single particle in discrete case or of the standard Schrodinger operator while including potential and making infinitesimal limit. It also provides a natural intuition of the amplitudes' squares relating to probabilities. The present paper gathers and formalizes these results. There are also introduced and discussed some new expansions, like considering multiple particles with thermodynamical analogue of Pauli exclusion principle or time dependent cases, which allowed to introduce thermodynamical analogues of momentum operator, Ehrenfest equation and Heisenberg uncertainty principle." It should appear on arxiv soon, now it can be download here: http://dl.dropbox.com/u/12405967/phd2.pdf I would really gladly discuss about it and would be grateful for any comments

There is extremely interesting yesterday's NASA announcement: http://www.nasa.gov/mission_pages/voyager/heliosphere-surprise.html Voyager has found bubble-like foam of magnetic field lines (flux ropes/vortex lines?) coming from our Sun: "(...) "The sun's magnetic field extends all the way to the edge of the solar system," explains Opher. "Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are now, the folds of the skirt bunch up." When a magnetic field gets severely folded like this, interesting things can happen. Lines of magnetic force criss-cross, and "reconnect". (Magnetic reconnection is the same energetic process underlying solar flares.) The crowded folds of the skirt reorganize themselves, sometimes explosively, into foamy magnetic bubbles. (...)" ps. Here is recent PRL article about laboratory experiments of magnetic flux ropes: http://prl.aps.org/abstract/PRL/v105/i7/e075005