## Posts

## Comments

**Marco Discendenti (marco-discendenti)**on Boltzmann brain's conditional probability · 2023-12-29T18:14:48.637Z · LW · GW

Your point is that in the case of the low entropy universe you have much possibilities for the time to consider for its random formation compared to the single brain?

**Marco Discendenti (marco-discendenti)**on Boltzmann brain's conditional probability · 2023-12-29T15:09:23.148Z · LW · GW

Can we estimate the probability of this 3rd hypothesis or even compare it with the probability of the other two?

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-29T14:42:43.356Z · LW · GW

Itt seems to me that it is actually easy to define a function $u'(...)>=0$ such that the preferences are represented by $E(u'^2)$ and not by $E(u')$: just take u'=sqrt(u), and you can do the same for any value of the exponent, so the expectation does not play a special role in the theorem, you can replace it with any $L^p$ norm.

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-29T04:11:52.577Z · LW · GW

There are infinitely many ways to find utility functions that represents preferences on outcomes, for example if outcomes are monetary than any increasing function is equivalent on outcomes but not when you try to extend it to distributions and lotteries with the expected value.

I wander if given a specific function u(...) on every outcome you can also chose "rational" preferences (as in the theorem) according to some other operator on the distributions that is not the average, for example what about the L^p norm or the sup of the distribution (if they are continuous)?

Or is the expected value the special unique operator that have the propety stated by the VN-M theorem?

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-27T20:28:43.768Z · LW · GW

You don't necessarily need to start from the preference and use the theorem to define the function, you can also start from the utility function and try to produce an intuitive explanation of why you should prefer to have the best expected value

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-27T20:11:47.327Z · LW · GW

Thank you for your insight. The problem with this view of utility "just as a language" is that sometimes I feel that the conclusion of utility maximization are not "rational" and I cannot figure out why they should be indeed rational if the language is not saying anything that is meaningful to my intuition.

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-27T11:23:49.702Z · LW · GW

Very interesting observations. I woudln't say the theorem is used to support his assumption because the assumptions don't speak about utils but only about preference over possible outcomes and lotteries, but I see your point.

Actually the assumptions are implicitly saying that you are not rational if you don't want to risk to get a 1'000'000'000'000$ debt with a small enough probability rather than losing 1 cent (this is strightforward from the archimedean property).

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-27T10:32:13.109Z · LW · GW

Ok we have a theorem that says that if we are not maximizing the expected value of some function "u" then our preference are apparently "irrational" (violating some of the axioms). But assume we already know our utility function before applying the theorem, is there an argument that shows how and why the preference of B over A (or maybe indifference) is irrational if E(U(A))>E(U(B))?

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-27T10:20:37.128Z · LW · GW

Apparently the axioms can be considered to talk about preferences, not necessarily about probabilistic expectations. Am I wrong in seeing them in this way?

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-26T16:07:51.736Z · LW · GW

**Marco Discendenti (marco-discendenti)**on Why does expected utility matter? · 2023-12-25T18:22:22.287Z · LW · GW

It seems indeed quite reasonable to maximize utility if you can choose an option that makes it possible, my point is why you should maximize *expected* utility when the choice is under uncertainty

**Marco Discendenti (marco-discendenti)**on How could humans dominate over a super intelligent AI? · 2023-01-28T09:52:15.826Z · LW · GW

Thank you for the reference

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-14T06:52:57.527Z · LW · GW

The ideal gas does have a mathematical definition of entropy, Boltzmann used it in the statistical derivation of the second law:

https://en.wikipedia.org/wiki/Entropy_(statistical_thermodynamics)

Here is an account of Boltzmann work and the first objections to his conclusions:

https://plato.stanford.edu/entries/statphys-Boltzmann/

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-14T06:40:54.278Z · LW · GW

I think you are not considering some relevant points:

1) the artificial system we are considering (an ideal gas in a box) (a) is often used as an example to illustrate and even to derive the second law of thermodynamics by means of mathematical reasoning (the Boltzmann's H-theorem) and (b) this is because it actually appears to be a prototype for the idea of the second law of thermodynamics so it is not just a random example, it is the root of out intuition of the second law

2) the post is talking about the *logic* behind the arguments which are used to justify the second law of thermodynamics

3) The core point of the post is this:

- in the simple case of the ideal gas in the box we end up thinking that it must evolve like the second law is prescribing, and we also have arguments to prove this that we find convincing
- yet the ideal gas model, as a toy universe, doesn't really behave like that, even if it is counterintuitive the decrease of entropy has the same frequency of the increase of entropy
- therefore our intuition about the second law and the argument supporting it seems to have some problem
- so maybe the second laws is true, but our way of thinking at it maybe is not, or maybe the second law is not true and our way of thinking the universe is flawed: in any case we have a problem

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-13T07:19:56.693Z · LW · GW

An ideal gas in a box is an egodic system. The Poincarè recurrence theorem states that a volume preserving dynamical system (i.e. any conservative system in classical physics) returns infinitely often in any neighbourhood (as small as you want) of any point of the phase space.

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-12T20:29:53.418Z · LW · GW

"What mechanism exists to cause the particles to vary in speed (given the magical non-deforming non-reactive box we are containing things in)?"

The system is a compact deterministc dynamical system and Poincarè recurrence applies: it will return infinitely many times close to any low entropic state it was before. Since the particles are only 3 the time needed for the return is small.

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-12T19:43:09.138Z · LW · GW

"conditional on any given (nonmaximal) level of entropy, the vast majority of states have increasing entropy"

I don't think this statement can be true in any sense that would produce a non-symmetric behavior over a long time, and indeed it has some problem if you try to express it in a more accurate way:

1) what does "non-maximal" mean? You don't really have a single maximum, you have a an average maximum and random oscillations around it

2) the "vast majority" of states are actually little oscillations around an average maximum value, and the downward oscillations are as frequent as the upward oscillations

3) any state of low entropy must have been reached in some way and the time needed to go from the maximum to the low entropy state should be almost equal to the time needed to go from the low entropy to the maximum: why shold it be different if the system has time symmetric laws?

In your graph you take very few time to reach low entropy states from high entropy - compared to the time needed to reach high entropy again, but would this make the high-low transition look more natural or more "probable"? Maybe it would look even more innatural and improbable!

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-12T11:56:40.044Z · LW · GW

Good point but gravity could be enough to keep the available positions in a bounded set

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-12T08:22:23.880Z · LW · GW

You do have spontatenous entropy decreases in very "small" environment. For gas in a box with 3 particles entropy is fluctuating in human-scale times.

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-12T07:22:37.133Z · LW · GW

In order to apply Poincarè recurrence it is the set of available points of the phase space that must be "compact" and this is likely the case if we assume that the total energy of the universe is finite.

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-11T07:04:43.037Z · LW · GW

Entropy "reversal" - i.e. decrease - must be equally frequent as entropy increases: you cannot have an increase if you didn't have a decrease before. My graph is not quantitatively accurate for sure but with a rescaling of times it should be ok.

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-11T06:37:26.229Z · LW · GW

Ok but even if I remove the idea of "entropy" from my argument the core problematic issue is still here: we have 50% probability that our universe is evolving in the opposite direction and an incredibly long chain of inbelievably improbable events is happening, and even if it is not happening right now it would happen with the same frequency of the standard "probable" evolution.

**Marco Discendenti (marco-discendenti)**on Unconvenient consequences of the logic behind the second law of thermodynamics · 2021-03-07T20:24:57.801Z · LW · GW

- If we want to "
*define*the direction of time by the increase in Entropy" then we have a problem in a universe where entropy is not monotonic, the definition doens't work - The "age of the universe" could be not really the age of the universe but the time after the last entropy minimum reached in a never-ending sequence of fluctuations

**Marco Discendenti (marco-discendenti)**on Forcing Anthropics: Boltzmann Brains · 2020-01-01T11:32:44.780Z · LW · GW

It's not enitrely clear what does t mean to create a number of "me": my consciuousness is only one and cannot be more than one and I only can feel sensations from one sigle body. If the idea is just to generate a certain number of physical copies of my body and embed my present consciousness into one of them at random then the problem is at least clear and determined from a mathematical point of view: it seems to be a simple probability problem about conditional probability. You are asking what is the probability that an event happened in the past given the condition of some a priori possible consequence, it can be easily solved by Bayes' formula and the probability is about one over 1 billion.

**Marco Discendenti (marco-discendenti)**on Two types of mathematician · 2019-12-31T08:45:54.939Z · LW · GW

There are two similar clusters/tensions in arts:

- visual art: on one hand you have to design the "big picture", with all its equilibia, balances and tensions, on the other hand you have to design the local and fine details, wich is something less imaginative and more formal and technical, with strict rules (for anatomy, shadows,...)
- creative writing: your story need to have emotional tensions on the scale of the general plot, but need also to be realistic and credible on the scale of more detailed single events and interactions, wich must respect some stricter constrains
- music composition: you need to design a general theme and mood and then you have to articulate the detailed development of the melodies and rithms which need to observe stricter rules in order to work appropriately

**Marco Discendenti (marco-discendenti)**on Expected utility and repeated choices · 2019-12-28T07:51:19.112Z · LW · GW

Thank you for your insights! You say: " Yes! You do have to think about the amount of games you play if your utility function is not linear"

Let's consider the case of rational agents acting in a temporal framework where they are faced with daily decisions. If they need to consider all their future possible choices in order to decide for a single present choice then it seems they are always completely unable to make any single decision (the computation to be made seems almost never ending) and this principle of expected utility maximization would turn out to be useless. How do we make rational decisions then?