Can you share a link to those claims from academia?
1,121 karma · joined May 16, 2015
Forbidding installing apps from non-official sources is obviously bad and I don't think most people want it.
Because access by password provides unique abilities to the person who knows the password.
Source?
That, and shell, sed and awk are standard tools which are easy to learn, every unix user should learn basics of (even a java developer), and this won't change anytime soon.
However, this can't be said of Perl - it is a powerful tool, but it became culturally obsolete and deprecated, and most unix users in the present and the future won't be bothered to learn it, when learning more modern languages like Python is a better investment.
And my answer to this is the same. Unsubstantiated assumption that universe started out, and that its entropy at this start was low. In addition, it is not at all clear how this assumption helps us to explain that an isolated system could not have higher entropy in the past long before we observed it.
Interesting, can you share some images, or a paper on this?
Btw I've tried some online image enhancers on a random painted image and it was not amazing, it did enhance some parts but not really by much. I'm sure specialized systems can do much better when the input image is made by the same source as the training set.
You certainly don't have to waste time convincing me of that, but it seems you should try to explain why this general asymmetry of concept pairs record-past, record-future is relevant to your original argument. We're at this for days and you did not write any coherent argument where this evidence (which I don't contest) would play obvious role.
When I talk about some statement as an assumption, this does not mean I contest its factual evidence or validity. I am interested in the structure of your argument, and all assumptions need to be illuminated, even if they are based in factual evidence.
> what is "the multiplicity argument"?
It's your original argument: given the system is evolving without external influences, and we know its macrostate and its entropy at some time, then most likely the future macrostates will be such that they do not have lower entropy, but higher or same, and this is so because there is immensely more microstates corresponding to macrostates of higher entropy (macrostates of high multiplicity) than there is microstates corresponding to macrostates with lower entropy (macrostates of low multiplicity).
I don't see how asymmetry of memories or records made plays role in this argument. I can see how they play role in my example with collecting data for 2years. But then my argument stands: the data becomes more irrelevant the farther into the past we retrodict, and for very distant past it can be discarded, and the multiplicity argument wins, and fails to be consistent with 2nd law.
To me, this is due to fact one cannot derive 2nd law in general, as probable behaviour for all processes. There is as many phase space trajectories increasing entropy as there is decreasing it. One has to select those macroprocesses that we consistently observe to have the same result (Jaynes ' states A -> B) and then one can derived 2nd law for those processes, only.
> Whether or not anyone actually bothered to make a record is irrelevant.
It is relevant in that it changes data based on which predictions (or retrodictions) are made. I'm sure in science, different data means possibly different predictions.
Try to formulate your whole argument (which I understand as being based on the multiplicity argument), including how "it is possible to remember the past" makes its application to distant past which nobody remembers invalid, while keeping its application to distant future valid.
Agreed. But it is true for your original argument applied to a non-equilibrium state at any single time instant, while not assuming any more on the past or the future states.
If we adopt further assumptions about the past states, but not about the future states, then we agree this problem of prediction/retrodiction is asymmetric between past and future and this may be the reason why the multiplicity argument does not have to result in past entropy being higher. In particular, there may be other facts on record about the past states and that would override/modify the multiplicity argument for the past.
> it is possible to change your scenario and collect data that allows reliable extrapolation into the past, for example, by looking at the coin before it is flipped and remembering (or writing down) what you saw. But for the future this is not possible. That is the essential asymmetry.
Yes, in any realistic scenario involving prediction and retrodiction at any time, we have some data on the past states (in some lucky cases, enough data for having certainty), but never data on the future states (we may have predictions, but those are not of the same quality as data). I agree.
But in addition, you seem to argue that this asymmetry of availability of data is an essential fact to derivations of the 2nd law.
Consider a scenario where we have an isolated system that is a mixture of miscible liquids that exists for ages but we have data on its state only for the last 2 years, and that data says its entropy was steadily rising the whole time.
Now, given this data, was entropy increasing before the collection of data started, or was it decreasing? For short enough times around the edges, we can extrapolate the entropy curve based on collected data, but for long enough times, we can't. Using the multiplicity argument, including the data, we get that entropy of very distant past states was much larger than entropy of the first recorded state. Which contradicts 2nd law.
Effect of that "essential asymmetry" has a time span that is not universal, but limited to times where collection of data was happening. Outside it vanishes, and using only that data and the multiplicity argument, the distant past becomes as cloudy(highly entropic) as the distant future is.
This lack of skill is the same towards the future as towards the past, at least in the context of reversible theories of motion like classical mechanics or evolution governed purely by Schroedinger's equation.
Flip a coin, do not look at it, and make a short video of the coin from above when it is at the top position. This video provides us with details of state of the coin.
Assuming a fair coin and a strong enough flip, from this state of things we can't predict the resulting face, and also can't predict the starting face on the thumb. This problem is symmetric towards the future and towards the past.
The same argument holds for knowledge of one microstate of gas at single time instant. Past and future are equally undetermined, and all probabilities are the same towards the future as towards the past.
To get 2nd law, we need to assume the asymmetry in addition, and it's best if it is explicit. E.g a process connecting two equilibrium macrostates, where the two states aren't defined in a symmetric way. For example, as Jaynes does, we define B as the reliable result of autonomous evolution after manual intervention in A. This makes A,B asymmetric, because it is not stated in the assumptions (and usually not considered possible) that also A is the reliable result of autonomous evolution after intervention in B. This asymmetry is what allows us to derive 2nd law.
See e.g. this Jaynes' paper, Section IV The 2nd Law. https://github.com/lawrennd/jaynes/blob/main/gibbs-vs-boltzm...
It is interesting that this derives asymmetric 2nd law from symmetric (reversible) underlying microscopic model. The asymmetry comes in exclusively due to the assumption of B being the reliable result of intervention in A.
And that implies you lack information on the record, which is decisive for predicting successfully its playback.
> But under no circumstances can I ever accurately predict the outcome of flipping the coin again.
Because you lack the necessary information, because you assume those experiments are that way. If you set them up so that you don't look at the coin flip result, but in the next coin flip you measure the initial conditions and the flipping process accurately enough, the conclusion would be the opposite - you would accurately predict the new coin flip, and would not be able to predict the playback.
> Why? Because there is a fundamental asymmetry between the past and future.
Not at all. The asymmetry is due to how you defined constraints on the experiments.
> It is possible to make reliable records of the past, ... it is not possible to make reliable records of the future.
Record is, by definition, a pattern that has been created in the past, and this is likely to correlate more with the past states than with the future states. This is a property of the concept, not of some universal asymmetry between past and future. We may introduce analogous concept of a future record, which will be created in the future, and which will correlate with the future states.
We can talk instead about prediction and retrodiction. And then this is more of an easy/hard thing, not possible/impossible thing, and the distribution of success on this axis depends on details. Predicting Moon's position on sky 2 years into future is easier than retrodicting it 20 000 years into past.
None of this explains why your original argument does not apply to past macrostates.
Yes, knowledge of details of how the recorder works is indeed largely irrelevant, but that was obvious. The point was that being successful with predictions or retrodictions of some system is correlated with having enough information on its state and the laws it obeys. This difference of success for predicting playback vs predicting result of a future experiment sensitive to unknown conditions is due to sufficient information vs insufficient information. I don't see anything in your responses that shows some universal asymmetry between past and future that would explain why your original argument does not work for past macrostates, but does work for future ones.
No, this and other similar memory-induced asymmetries have much more prosaic reason. It is more successful to predict systems we have enough knowledge and control of (video playback) than those we don't (coin flip).
Predicting and retrodicting systems we understand and have memory of is successful, and predicting and retrodicting systems we don't understand and don't have memory of is not. This has nothing to do with universal asymmetry of past vs future.
Your memory of what has happened (e.g. some system had lower entropy in past) does not explain why your original argument does not apply now to retrodiction of past macrostates; the memory only contradicts the result of that argument.
> If I can reliably predict the outcome of any experiment, that means I know everything that is going to happen before it happens, including my own actions.
That would in no way prevent validity of 2nd law.
What you wrote after that is such an assumption. You can't derive asymmetry from nothing, logic or mechanics. The only way to have it, is to assume it in addition to those.
> given a set of measurement values, the more states there are which produce those values, the more likely we are, all else being equal, to observe those values. And so a closed system will evolve by pure chance into a state where the entropy is maximized simply because you are more likely to observe values corresponding to greater numbers of underlying states.
This argument is that future macrostates of an isolated system passing through non-equilibrium states (due to some intervention to the system that was in an equilibrium state before) should be almost always of higher entropy, because those have immensely higher multiplicity than macrostates with lower entropy. There is hugely more microstates that are compatible with higher entropy macrostate, than microstates that are compatible with lower entropy macrostate.
However notice the word "future". We can formulate the same argument using "past": past macrostates of an isolated system passing through non-equilibrium states should be almost always of higher entropy, because those have immensely higher multiplicity than macrostates with lower entropy. There is hugely more microstates that are compatible with higher entropy macrostate, than microstates that are compatible with lower entropy macrostate.
Now, why does the argument give correct answer when applied to future macrostates but not when applied to past macrostates? We need additional assumption about the non-equilibrium process that makes the argument invalid for the past.
The problem with your handwavy argument about macrostates with higher multiplicity is not due to 2nd law being a probabilistic claim. The problem is that it is not clear from that argument alone why it applies to future states, but it does not apply to the past states. To address that, another assumption is needed, such as the asymmetric relation between my macrostates A,B.
In the formulation of 2nd law for adiabatically isolated systems, there is the initial equilibrium macrostate A, and the different equilibrium macrostate B that the system gets into eventually after the intervention, where either some constraint is released, or some macroscopic work is done. 2nd law states that if the same intervention in A results in B reliably, then S_B >= S_A.
This statement can be derived from mechanics and maximum entropy principle only under the assumption that B is a reliable result of intervention in A (always or with close to 1 probability). This is more than mechanics or logic can provide, and it means we have a restriction on the allowed set of microscopic processes considered.
It is not possible to derive 2nd law from mechanics or logic for all microscopic processes. Some microscopic processes bring the state B to state A, and those break 2nd law.
This is due to mixing in phase space, which is plausible for many particle systems. However, it works in both directions of the parameter t.
The only way to derive 2nd law including its time asymmetry (which is the major point of 2nd law) is to restrict considerations to those microscopic processes that are compatible with macroscopic processes that systematically lead to the same final state. This means we consider only subset of all microscopically possible processes. E.g. Jaynes selects those macroscopic processes that bring one macrostate A, via some irreversible evolution, to another macrostate B, repeatedly. Then, assuming this reliability of the resulting state, he derives non-decrease of entropy from maximum entropy principle and Hamiltonian statistical physics. If we didn't assume this restriction and allowed all mechanically possible processes, entropy could both increase and decrease.
> The reason entropy was lower in the past is that the universe started out in a low-entropy state. The reason for that is still a mystery.
This often repeated idea is in vein with Clausius' ostentatious statements on energy and entropy of the Universe, which have been out of place and plagued discussions of thermodynamics with needless mystical assumptions ever since he wrote them. There is no evidence for them, as there are no reliable measurements of entropy of the Universe. There is no need for them, as there are no good reasons to believe Universe has defined entropy at all. Thermodynamics, including 2nd law, is about finite sized systems free of strong gravity effects. It does not extrapolate easily beyond compact systems like planets/stars to ever bigger systems. There is no Universe in it anywhere.
2nd law that we see in daily life or a lab is not a statement about entropy of Universe being lower in the past, nor does it hang on such an assumption. It is (in one of its variants) the statement that a finite isolated system can change its macrostate to some other final macrostate, but this final macrostate is of higher or same entropy, so in real process entropy can't decrease.
This is an argument for observing high entropy macrostates at any time, assuming all microstates are equally probable. But not for evolution in time that makes entropy higher in the future, or at least non-smaller in the future. You assume the closed system evolves its microstate in time "by pure chance", i.e. any microstate is equally probable as the next microstate, which ignores many constraints there are due to physics laws like conservation of phase volume or energy. This probabilistic argument could be applied to past just as well as the future. But observations show entropy of an isolated system is lower in the past than in the present. So your argument does not really derive all aspects of 2nd law.