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Archive for the ‘paramathematics’ Category

How to Measure Intelligence?

Tuesday, September 20th, 2011

How should we measure intelligence? Or, in general, how should we measure a quality that doesn’t really have a good definition (the ability to apply knowledge to deal with new or trying situations?)? If the quality has the property that those that possess it are capable of judging who possesses it better than those who don’t, and if there is a lot of subjects in our environment, we could try an iterative algorithm.

Ask every subject to assess everyone they know in some way. Extract the first iteration of the measure of the quality for everyone. Then extract the second iteration by computing the weighed average of the assessments, weighed by the quality itself. Continue until convergence is achieved.

For example, we could ask everyone to provide the IQ of everyone else. No definition necessary — just provide a number. The resulting IQ of everyone would be, at first, the average of everyone’s rating of them. Now that we have the initial IQ, we use it to weigh the calculations of a more accurate IQ. We keep doing it until a subsequent iteration doesn’t alter the IQ calculations in a meaningful way.

It’s a wonderful way to come up with a tangible rating for something that’s undefinable, based simply on the easy to accept assumptions that a large number of people will together come up with the right answer, and that people who have been judged more highly should have more to say.

What’s more interesting, though, are the specifics around how exactly to do the assessment.

  • Asking everyone for a number suffers from the problem of unclear scale — one person’s 100 will not be the same as another person’s 100. A clever variation on the above is to ask people to compare others as opposed to rating them, because while we have a hard time quantifying things, we find it rather easy to compare options (an evolutionary ability?). In fact, if a measure doesn’t have any other meaning other than comparative, it probably should remain comparative only rather than quantitative (i.e. if a score of 100 doesn’t mean anything, why should we use scores). So, I will provide a ranked list of people, without much consideration for how much better the fifth person is from the sixth (they may even be just as good). We can then combine all such rankings into one global ranking with a simple rule: if person A is consistently above person B in individual rankings, person A should be above person B in the resulting ranking. In other words, for every pair of people, determine whether (A>B) occurs more often than (B>A) and place A above or below B, appropriately. There will no doubt be conflicts (e.g. A>B, B>C, C>A) which should be resolved in a way that violates the fewest individual inequalities. In such a case, the weighing can still be done by assigning some score to the resulting order, and maybe by taking into account how many conflicts I am contributing to (if many, my weight should be lower).
  • Asking everyone for one number suffers from the problem of confidence. I may be highly confident of one assessment and not at all confident of the other. Including a confidence rating (e.g. provide a score that you think is most likely to be true, but also scores on either side that you think are as likely as they are not to be true) may provide more information.

An Infinite Pinball Board

Friday, August 19th, 2011

Consider a ball balanced perfectly on one of the pegs in an infinite pinball board:

An infinite pinball board

A microscopic vibration sets the ball in motion. Can you place and size the pegs in such a way that the ball will fall directly on top of the peg below, bounce directly vertically up, and rest on the peg, waiting for yet another microscopic vibration to set it in motion, and so on, thus exemplifying one-dimensional Brownian motion.

Pi

Wednesday, December 29th, 2010

Why is pi equal to approximately 3.14?

Under what conditions would pi be less, or more than 3.14? What would the universe look like if pi was, say, 1? Is this question even meaningful?

It seems to me that this specific value of pi is a property of the Euclidean space which can be thought of as “flat” (the geometry of the plat piece of paper where angles in a triangle add up to 180 degrees), but that just prompts further questions. Why don’t we revisit the value of pi to account for the curvature of the geometry of our Universe? And is Euclidean geometry special at all? It comes about in a special way, with the introduction of the fifth postulate. But perhaps it’s no more special than some curved geometry and we should look for an explanation in how humans are constructed.

Before these questions can be answered (and some of them may have a decent explanation–here I am exposing my ignorance), I think an important thing to consider is what pi exactly measures and what relationships it plays a role in. For example, suppose that we can imagine a world where pi as given in some measure is equal to 1. Would that mean that every equation in that world that features pi can now safely substitute 1? Probably not — pi may happen to solve a lot of problems; both those that are based on some assumption that we can relax (such as the curvature of the geometry) and others that can’t be tweaked. Presumably, for example, all results that are non-geometric in nature that feature pi will not suddenly magically hold if we change the value of pi (in a way, pi would be no different than e, whose value is purely accidental).

Nav Systems and Early Turns

Wednesday, December 1st, 2010

I used to own a nav system in my car and I noticed that as it gave me directions, it would strongly prefer turning early. Why is this? I settled on the following two reasons:

  • The characteristics of the search that is being employed — the search could branch out early because most often, when you ask for directions you have to change the general direction in which you’re heading
  • If you are going to miss the turns, it’s better to miss the earlier ones. It gives you greater flexibility in still getting to your destination. In other words, it’s better to have the option to turn early — turn if you can, because if you can’t, you can go straight and delay turning for later. If you prefer not turning early, you may end up not having an option to turn anymore, which will mean you’re likely to stop more frequently towards the end of the trip

The Theories of Time Travel

Friday, October 22nd, 2010

Let’s assume that what we all secretly hope for is true: that backwards time travel is possible (with a fast enough rocket you can travel forward in time already, thanks to Mr. Einstein). It’s unclear what such time travel would look like — there are many different theories and, consequently, interesting implications on the Universe, the existence of paradoxes, and the existence and the nature of time loops. Note that to help myself think through this, I have a human being travel in time; this may lead to inaccuracies and further questions — in most of the cases below, we can probably replace me with a photon, or even a quark, and get more precise results (“memory” becomes “momentum” or “spin”, etc.). But it’s more fun to think about people traveling in time.

  • Let’s first assume that there is only one version of the Universe.
    • If the links between causes and effects are not maintained, we have a consistent (paradox-free) time travel: moving backwards in time rewrites history and the previous version is lost. The I that travels back in time (call it I1) is not the same as the I that I1 meets in the past (I2). Whether I2 enters the time machine or not is irrelevant to I1. If I1 kills I2′s grandfather, I2 will not be born but I1 will not be affected in any way. It’s a very safe theory of time travel.
    • If the links between cause and effect are maintained (but their temporal relationship isn’t, necessarily), the Universe has to decide how to handle duplicates of matter/energy: it may choose to allow them, or not, or have an opinion somewhere in between.
      • If duplicates are allowed, I1 is identical to I2 but they are allowed to co-exist. If I1 prevents I2 from entering the time machine, I1 will cease to exist. What if I1 kill’s I2′s grandfather (who is also I1′s grandfather)?
        • It’s possible that I1 will simply not be able to do this — this is the theory where the Universe maintains its consistency (by making it prohibitively expensive — either by requiring you to put a lot of energy into your action or outright generating laws that locally forbid you to perform it), somewhat akin to what the writers of Lost did in the show. This energy-effect constrained time travel — the Universe not letting me kill my grandfather — is interesting. In order to maintain its consistency, the Universe would need to propagate all actions forward (“play them out”). If there is a sequence of actions that cause an inconsistency, the energy required to continue along this sequence would increase, proportionally to the probability of an inconsistency. It would be like an invisible magnetic field that steers actions in a particular direction. This could be implemented by a biased averaging out of quantum effects: let’s take light for example. We know that according to quantum theory, the movement of photons from A to B is realized through an infinite number of different paths which average out to a straight line. However, if the probabilities of the paths are different (due to the fact that some paths may cause an inconsistency in the future), the paths could actually average to something that’s not a straight line. To us it would seem that light travels in curved paths (without the presence of any “real” field, such a gravitational one)!

          Of course, these probabilities change gradually so no obviously apparent deviations from the norm would occur at first. For example, if I’m intending to kill my grandfather, the Universe will start steering me away from my intention through a small sequence of very likely events. If I persist in my intentions, the events increase in magnitude, but it’s possible (because there are just so many possible events that can influence me) that I will never realize my intention without even seeing anything strange with the Universe.

        • Otherwise, we have a phenomenon known as the Grandfather Paradox. I1 may create an unstable point in the spacetime: I1 (and thus I2, and the grandfather) will both exist and not exist at the same time, in a kind of macro-Shrödinger effect. What’s worse, anything that either was caused by I2 or the grandfather or would have been caused by I1 will also both exist and not exist. It’s unclear what effect this will have on the rest of the Universe — as these effects ripple through time, they expand their scope (the events that the grandfather caused themselves caused other events) but decrease their magnitude (think of it as a sound wave propagating through space, maybe bouncing off objects).
          • It’s possible that over time, as soon as they become small enough to be captured by quantum uncertainty, they stabilize so the ripple has a finite size (I can’t visualize what the ripple would actually look like, maybe a really fast-flashing grandfather).
          • Or the Universe could cease to exist.
      • If duplicates of matter/energy are not allowed, I1 would need to replace I2 (for this to work, the Universe would somehow need to have a unique identifier for everything in it). It’s difficult to think about replacing something complex like a human being because he or she is made of many building blocks, each having a different identifier, so let’s simplify and think of something that consists of a single block (say, a photon). The photon would replace its version from the past. Does this photon have “memory”, that is, its future state?
        • If so, the photon will likely change its course (behave differently than I1 did). This may mean that I2 may never end up traveling in time, but that’s fine because there is only version of it. This is equivalent to the theory of rewritten history.
        • If not, I1 simply merges into I2 — I2 enters a time loop which it will never be able to leave. It’s not aware of that, however, so to I1, the time travel ends its consciousness.

        If somehow we can maintain this option at a macro scale, it’s possible that an individual may travel back in time and maintain his or her memory, provided that the interval of time travel is small (for example, if I1 travels back to before I2 was born, I1–an individual–would have to replace a bunch of particles which aren’t even part of a human being. That will very likely result either in the destruction of I2–I2 will not be possible given the new state that all of its particles will have assumed before they created it–or in the destruction of I1–the “memory” that each particle has will be insignificant and so I1′s consciousness will end as soon as he travels in time)

      • Another way not to allow duplicates would be for I1 and I2 to “swap” places: as soon as I1 travels backwards in time, it takes I2′s place and I2 takes I1′s place in the future. When I1 gets to the time when it first traveled in time, he ceases to exist. There is no paradox because time travel transfers both I1 and I2. It doesn’t matter whether I1 actually enters the time machine the second time around or not, because his existence ceases past that point anyway.
      • Finally, the Universe may choose some option in between, for example, I1 and I2 will be entangled in a way that doesn’t increase entropy. This may look like a kind of constrained time travel, where paradoxes are not possible because they are prevented by the entanglement of I1 and I2 (in other words, I1′s and I2′s actions will either make both of them survive the interval of their co-existence, or make them both self-destruct. At the event of time travel, I2 goes back and I1 is the only entity remaining.

        This brings me to an interesting idea: what if time travel and quantum theory are actually one and the same? What if the time interval where I1 exists in the past (and influences outcomes) is equivalent to the cat being both alive and dead: it cannot be inspected, and nothing can be said about what happened or what any of the outcome that I1 could have influenced was. The instant at which I1 entered the time machine would then correspond to the box being open — we find out what all those outcomes were.

  • Now let’s suppose there are many versions of the Universe. This is similar to the first case (rewriting history) but if the Universe bifurcates with every time travel, an awful lot of energy is needed to do time travel. Alternatively, the Universe may already exist in its virtually infinite forms, each form corresponding to a different possible unfolding of an event. We know from Newton that at a high level the world seems deterministic, but at a quantum level it’s not — this randomness I see as a basis for the different unfolding of the events (hence, once and for all answering the problem of free will: there is no free will, but there is also no determinism — what we perceive as “choosing” is just a particular folding up of all the quantum uncertainties). So every time we put a cat in a box, there are Universes in which the cat is dead and Universes in which it’s alive. We know which path we’re on as soon as we open the box. Time travel would then simply be an opportunity to follow a different path.

There is one problem with many of the sub-theories above, and that is a problem of the sudden injection of matter/energy. It couldn’t have been created from nothing. It’s possible that as this new matter/energy is injected, some other matter/energy is transferred into the future (where the travel originated). Possibly an arrangement such as one in Primer is needed where travel is only possible to a limited point in time, where all the prep work has been done, for example enough energy has been set aside to be “displaced” by the newly arriving energy. It may also be that the time travel portal has a standby energy consumption — it consumes energy at some rate, like a leaking pipe, all the time — this would allow energy of at most that rate to be transferred from the future.

Another way to solve the sudden injection problem is to borrow me for the duration of the time travel episode from the time chronologically after the event of time travel. That is, if in the year 2010 I go back to the year 2005, my extra existence for five years between 2005 and 2010 will be borrowed from what would have been my existence between 2010 and 2015. In other words, as soon as I reach the year 2010 the second time around, I jump to the year 2015. This is a kind of quantum entanglement, but not of I1 and I2, but rather of I1 and the future version of I1.

How to make sure you’re flying straight

Monday, October 11th, 2010

Consider birds flying in a V formation. Its purpose is to increase the aerodynamics of the birds. I wondered if it can also help maintain bearing.

Let’s make two simplifying assumptions. The birds are arranged in a symmetrical inverted V and are equally spaced. Moreover, each bird can fly by and large equally fast (which means that the choice of the bird in the front is seemingly arbitrary). Each bird, flying solo, may stray a little from its bearing, and if the birds simply ensured that they maintain a constant displacement from the bird in front of them, the formation would likely stray based on what the bird in the front does (and since that bird doesn’t see any other birds, it would very likely stray). However, in the V formation, if the bird in the front strays, the distance between it and the bird behind it decreases; the bird in the back noticed that and reshuffles itself to be in the front. This happens for any pair of birds next to one another in the formation. As a whole, the formation keeps itself in check and as a result the entire group flies straight.

The Pencil Curve

Sunday, September 26th, 2010

What is the shape of the curve traced by one tip of a pencil as you roll it up a cylinder (the pencil being tangent to the cylinder at all times)? The pencil starts just touching the cylinder. As the pencil moves closer to the cylinder, the tip first moves away, then quickly moves back, eventually to stop as the pencil becomes vertical.

Below is the diagram of the pencil’s start point, the end point, and an arbitrary point.



The pencil rolling on a cylinder. The tip tracing a curve is marked.

It’ll be easier to parameterize the curve: determine the coordinates of each point as a function of the distance of the bottom tip of the pencil to the bottom of the cylinder (where it is tangent with the table). Initially the pencil’s tip is just touching the cylinder and the distance t is equal to l, the length of the pencil. At the end, as the pencil is vertical, t=r, the radius of the cylinder.

We have, from the arbitrary point, \frac{y}{x+t}=tan 2\alpha = \frac{2tan \alpha}{1-tan^2\alpha} = \frac{2r/t}{1-r^2/t^2} = \frac{2rt}{t^2-r^2}.

\frac{x+t}{l}=\cos 2\alpha = 2\cos^2\alpha-1 = \frac{2t^2}{r^2+t^2}-1 = \frac{t^2-r^2}{t^2+r^2} so x = \frac{l(t^2-r^2)}{t^2+r^2}-t.
Similarly, y = \frac{2rt}{t^2-r^2}\cdot (x+t) = \frac{2rt}{t^2-r^2}\cdot\frac{l(t^2-r^2)}{t^2+r^2} = \frac{2rtl}{t^2+r^2}

We can plot the curve as a function of t:



Plotted pencil curve

One of my Favorite Proofs

Sunday, September 19th, 2010

Proof that \pi is irrational.

Assume \pi is rational, that is, assume it is of the form \frac{a}{b} where a and b are both positive integers. Let

f(x) = \frac{x^n (a-bx)^n}{n!}

F(x) = f(x) + \cdots + (-1)^j f^{[2j]}(x) + \cdots + (-1)^n f^{[2n]}(x)

where f^{[k]} denotes k-th derivative of f.

  1. f(x) has integer coefficients except \frac{1}{n!}
  2. f(x) = f(\pi - x)
  3. 0 \leq f(x) \leq \frac{\pi^n a^n}{n!} for 0 \leq x \leq \pi
  4. For 0 \leq j < n, the j-th derivative of f equals 0 at 0 and \pi
  5. For j \geq n, the j-th derivative of f is integer at 0 and \pi (from 1. above)
  6. F(0), F(\pi) is integer (from 4., 5. above)
  7. F(x) + F''(x) = f(x)
  8. (F'(x) \sin x - F(x) \cos x)' = f(x) \sin x (from 7. above)
  9.  \int_0^\pi f(x) \sin x is an integer
  10. For large n, this integral is between 0 and 1 (from 3. above)

Contradiction. So \pi is irrational.

How revolutionary change happens

Monday, June 14th, 2010

I think that there is a pattern to revolutions.

  • Revolutions reflect a zeitgeist, a mutual understanding between a large group of people, that change is necessary
  • Revolutions happen through individuals, but the specific individual is not instrumental to the revolution: the individual just happens to be the catalyst

I like to explain this process as a superposition of two probability functions: one is the intensity of the mutual understanding — over time it grows and declines. The other is the ability for the specific individuals to push the group over the boundary. Revolutions then happen with a probability that is a compounding of those two effects. If a particularly strong individual comes around, the revolution is simply more likely to happen.

Betting on the Timing of an Event

Sunday, June 13th, 2010

There are times when there is a disagreement over what time a particular event will happen and people want to turn the different in opinions into money. It is common to place “over-under” bets — if the event happens before time T, Andrew gets the money, otherwise Bob gets it. Usually the further the event is from T, the more money exchange hands.

I don’t like this style of betting because it’s simply not expressive enough. Instead, I prefer to bet by specifying my probability distribution of the timing of the event, and then using these distributions to determine payouts. My friend and I made this bet once and it was a fun activity, despite the math involved behind-the-scenes, not that frustrating and requiring very little mathematics to actually place the bet.

Essentially, each party draws a probability distribution of the timing of the event — a histogram with the time on the horizontal axis and the probability density function on the vertical axis. The latter can simply be intuited as “the relative probability that the event will happen around the time specified on the horizontal axis”. So if the histogram is twice as tall around 8pm than around 7pm, the event is twice as likely to happen around 8pm than around 7pm.

That’s all each person really needs to do. No need to worry about the area of the histogram summing up to 1 since the vertical axis can be scaled up appropriately. The two people should also agree on how money they are willing to bet — say k dollars each.

When the event actually occurs at time T, the two people compare the value of the probability density function (the height of the bar) at time T on their graphs (the height will be scaled appropriately so that the area adds up to 1–so of course you can’t cheat by making your graph taller) and pay up based on the difference in these values.

Executing such bets is a little difficult since it involves calculating areas under the graph which may be very irregular. Those who are mathematically masochistic can constrain themselves to piecewise linear functions, or, in the extremely, easily integrable functions; otherwise the graph can be scaned and a simple graphics editing application (like Photoshop) can be used to determine the area under the graph (using the flood fill and histogram tools).