Archives de la catégorie: Débats

Je me suis engagé dans de longues discussions sur la physique et la philosophie par courrier électronique et à des forums Internet. Certains d'entre eux sont un peu méchant, mais la plupart ont été menées dans le bon goût. Ici, ils sont, à la fois pour votre plaisir de lecture et mes fins d'archivage.

Dieu — A Personal Story

I want to wrap up this series on atheism with a personal story about the point in time where I started diverging from the concept of God. I was very young then, about five years old. I had lost a pencil. It had just slipped out of my schoolbag, which was nothing more than a plastic basket with open weaves and a handle. When I realized that I had lost the pencil, I was quite upset. I think I was worried that I would get a scolding for my carelessness. Vous voyez, my family wasn’t rich. We were slightly better off than the households in our neighborhood, but quite poor by any global standards. The new pencil was, pour moi, a prized possession.

Continuer la lecture

The Origins of Gods

The atheist-theist debate boils down to a simple question — Did humans discover God? Ou, did we invent Him? The difference between discovering and inventing is the similar to the one between believing and knowing. Theist believe that there was a God to be discovered. Atheists “savoir” that we humans invented the concept of God. Belief and knowledge differ only slightly — knowledge is merely a very very strong belief. A belief is considered knowledge when it fits in nicely with a larger worldview, which is very much like how a hypothesis in physics becomes a theory. While a theory (such as Quantum Mechanics, par exemple) is considered to be knowledge (or the way the physical world really is), it is best not to forget the its lowly origin as a mere hypothesis. My focus in this post is the possible origin of the God hypothesis.

Continuer la lecture

Atheism and Unreal God

The only recourse an atheist can have against this argument based on personal experience is that the believer is either is misrepresenting his experience or is mistaken about it. I am not willing to pursue that line of argument. I know that I am undermining my own stance here, but I would like to give the theist camp some more ammunition for this particular argument, and make it more formal.

Continuer la lecture

Atheism vs. God Experience

I have a reason for delaying this post on the fifth and last argument for God by Dr. William Lane Craig. It holds more potency than immediately obvious. While it is easy to write it off because it is a subjective, experiential argument, the lack of credence we attribute to subjectivity is in itself a result of our similarly subjective acceptance of what we consider objective reason and rationality. I hope that this point will become clearer as you read this post and the next one.

Continuer la lecture

Atheism and the Morality of the Godless

In the previous post, we considered the cosmological argument (that the Big Bang theory is an affirmation of a God) and a teleological argument (that the highly improbable fine-tuning of the universe proves the existence of intelligent creation). We saw that the cosmological argument is nothing more than an admission of our ignorance, although it may be presented in any number of fancy forms (such as the cause of the universe is an uncaused cause, which is God, par exemple). The teleological argument comes from a potentially wilful distortion of the anthropic principle. The next one that Dr. Craig puts forward is the origin of morality, which has no grounding if you assume that atheism is true.

Continuer la lecture

Atheism – Christian God, or Lack Thereof

Prof. William Lane Craig is way more than a deist; he is certainly a theist. En fait, he is more than that; he believes that God is as described in the scriptures of his flavor of Christianity. I am not an expert in that field, so I don’t know exactly what that flavor is. But the arguments he gave do not go much farther than the deism. He gave five arguments to prove that God exists, and he invited Hitchens to refute them. Hitchens did not; au moins, not in an enumerated and sequential fashion I plan to do here.

Continuer la lecture

Risque – Wiley FinCAD Webinar

This post is an edited version of my responses in a Webinar panel-discussion organized by Wiley-Finance and FinCAD. The freely available Webcast is linked in the post, and contains responses from the other participants — Paul Wilmott and Espen Huag. An expanded version of this post may later appear as an article in the Wilmott Magazine.

What is Risk?

When we use the word Risk in normal conversation, it has a negative connotation — risk of getting hit by a car, par exemple; but not the risk of winning a lottery. In finance, risk is both positive and negative. De temps en temps, you want the exposure to a certain kind of risk to counterbalance some other exposure; de temps en temps, you are looking for the returns associated with a certain risk. Risque, in this context, is almost identical to the mathematical concept of probability.

But even in finance, you have one kind of risk that is always negative — it is Operational Risk. My professional interest right now is in minimizing the operational risk associated with trading and computational platforms.

How do you measure Risk?

Measuring risk ultimately boils down to estimating the probability of a loss as a function of something — typically the intensity of the loss and time. So it’s like asking — What’s the probability of losing a million dollars or two million dollars tomorrow or the day after?

The question whether we can measure risk is another way of asking whether we can figure out this probability function. In certain cases, we believe we can — in Market Risk, par exemple, we have very good models for this function. Credit Risk is different story — although we thought we could measure it, we learned the hard way that we probably could not.

The question how effective the measure is, est, in my view, like asking ourselves, “What do we do with a probability number?” If I do a fancy calculation and tell you that you have 27.3% probability of losing one million tomorrow, what do you do with that piece of information? Probability has a reasonable meaning only a statistical sense, in high-frequency events or large ensembles. Risk events, presque par définition, are low-frequency events and a probability number may have only limited practical use. But as a pricing tool, accurate probability is great, especially when you price instruments with deep market liquidity.

Innovation in Risk Management.

Innovation in Risk comes in two flavors — one is on the risk taking side, which is in pricing, warehousing risk and so on. On this front, we do it well, or at least we think we are doing it well, and innovation in pricing and modeling is active. The flip side of it is, bien sûr, risk management. Ici, I think innovation lags actually behind catastrophic events. Once we have a financial crisis, par exemple, we do a post-mortem, figure out what went wrong and try to implement safety guards. But the next failure, bien sûr, is going to come from some other, totalement, unexpected angle.

What is the role of Risk Management in a bank?

Risk taking and risk management are two aspects of a bank’s day-to-day business. These two aspects seem in conflict with each other, but the conflict is no accident. It is through fine-tuning this conflict that a bank implements its risk appetite. It is like a dynamic equilibrium that can be tweaked as desired.

What is the role of vendors?

Dans mon expérience, vendors seem to influence the processes rather than the methodologies of risk management, and indeed of modeling. A vended system, however customizable it may be, comes with its own assumptions about the workflow, lifecycle management etc. The processes built around the system will have to adapt to these assumptions. This is not a bad thing. At the very least, popular vended systems serve to standardize risk management practices.

The Big Bang Theory – Partie II

Après avoir lu un papier en Ashtekar sur la gravité quantique et penser, Je ai réalisé ce que mon problème avec la théorie du Big Bang était. Il est plus sur les hypothèses fondamentales que les détails. Je pensais que je résumerais mes pensées ici, plus pour mon propre bénéfice que quiconque est.

Les théories classiques (y compris SR et QM) espace régal comme néant continue; d'où le terme continuum espace-temps. Dans ce point de vue, objets existent dans l'espace continu et interagissent les uns avec les autres en temps continu.

Bien que cette notion de continuum espace de temps est intuitivement attrayante, il est, au mieux, incomplet. Envisager, par exemple, un corps tourner dans le vide. On se attend à faire l'expérience de la force centrifuge. Imaginons maintenant que le corps est fixe et l'ensemble de l'espace est en rotation autour d'elle. Sera-ce l'expérience de toute la force centrifuge?

Il est difficile de voir pourquoi il y aurait une force centrifuge si l'espace est vide néant.

GR a introduit un changement de paradigme par gravité codant dans l'espace-temps rendant ainsi de nature dynamique, plutôt que le néant vide. Ainsi, masse se empêtré dans l'espace (et le temps), l'espace devient synonyme de l'univers, et la question du corps de filature devient facile de répondre. Oui, il connaîtra la force centrifuge si ce est l'univers qui tourne autour de lui, car il est équivalent à la rotation du corps. Et, needs a context, il ne sera pas, si elle est dans l'espace juste vide. Mais “vide” ne existe pas. En l'absence de masse, il n'y a pas géométrie de l'espace-temps.

Si, naturellement, avant le Big Bang (se il y avait une), il ne pouvait y avoir d'espace, ni d'ailleurs ne pouvait y avoir aucune “avant.” Remarque, cependant, que le papier Ashtekar ne indique pas clairement pourquoi il devait y avoir un big bang. Le plus proche qu'il obtient est que la nécessité de BB découle de l'encodage de gravité dans l'espace-temps dans GR. Malgré ce codage de gravité et rendant ainsi l'espace-temps dynamique, GR traite toujours l'espace-temps comme un continuum lisse — une faille, selon Ashtekar, QG qui rectifiera.

Maintenant, si nous acceptons que l'univers a commencé avec un big bang (et d'une petite région), nous devons tenir compte des effets quantiques. L'espace-temps doit être quantifié et la seule bonne façon de le faire serait par gravité quantique. Grâce QG, nous nous attendons à éviter la singularité du Big Bang GR, de la même façon QM résolu le problème de l'énergie sans limite de l'état fondamental de l'atome d'hydrogène.

Ce que je ai décrit ci-dessus est ce que je crois être les arguments physiques derrière la cosmologie moderne. Le reste est un édifice mathématique construit en haut de cette physique (voire philosophique) fondation. Si vous ne avez pas d'idées bien arrêtées sur le fondement philosophique (ou si vos points de vue soient compatibles avec elle), vous pouvez accepter BB sans difficulté. Malheureusement, Je ne ai vues divergentes.

Mon point de vue se articulent autour des questions suivantes.

Ces postes peuvent sembler rêveries philosophiques inutiles, mais je ai du béton (et à mon avis, important) résultats, énumérés ci-dessous.

Il ya beaucoup plus de travail à faire sur ce front. Mais pour les deux prochaines années, avec mon nouveau contrat de livre et des pressions de ma carrière quant, Je ne aurai pas assez de temps pour étudier GR et de la cosmologie avec le sérieux qu'elles méritent. Je espère revenir à eux une fois la phase actuelle de propagation moi-même passe trop minces.

What is Space?

This sounds like a strange question. We all know what space is, it is all around us. When we open our eyes, we see it. Si voir c'est croire, then the question “Qu'est-ce que l'espace?” indeed is a strange one.

Pour être juste, we don’t actually see space. We see only objects which we assume are in space. Plutôt, we define space as whatever it is that holds or contains the objects. It is the arena where objects do their thing, the backdrop of our experience. En d'autres termes, experience presupposes space and time, and provides the basis for the worldview behind the currently popular interpretations of scientific theories.

Although not obvious, this definition (or assumption or understanding) of space comes with a philosophical baggage — that of realism. The realist’s view is predominant in the current understanding of Einstien’s theories as well. But Einstein himself may not have embraced realism blindly. Why else would he say:

In order to break away from the grip of realism, we have to approach the question tangentially. One way to do it is by studying the neuroscience and cognitive basis of sight, which after all provides the strongest evidence to the realness of space. Espace, dans l'ensemble, is the experience associated with sight. Another way is to examine experiential correlates of other senses: What is sound?

When we hear something, what we hear is, naturellement, son. We experience a tone, an intensity and a time variation that tell us a lot about who is talking, what is breaking and so on. But even after stripping off all the extra richness added to the experience by our brain, the most basic experience is still a “sound.” We all know what it is, but we cannot explain it in terms more basic than that.

Now let’s look at the sensory signal responsible for hearing. As we know, these are pressure waves in the air that are created by a vibrating body making compressions and depressions in the air around it. Much like the ripples in a pond, these pressure waves propagate in almost all directions. They are picked up by our ears. By a clever mechanism, the ears perform a spectral analysis and send electric signals, which roughly correspond to the frequency spectrum of the waves, to our brain. Noter que, so far, we have a vibrating body, bunching and spreading of air molecules, and an electric signal that contains information about the pattern of the air molecules. We do not have sound yet.

The experience of sound is the magic our brain performs. It translates the electrical signal encoding the air pressure wave patterns to a representation of tonality and richness of sound. Sound is not the intrinsic property of a vibrating body or a falling tree, it is the way our brain chooses to represent the vibrations or, more precisely, the electrical signal encoding the spectrum of the pressure waves.

Doesn’t it make sense to call sound an internal cognitive representation of our auditory sensory inputs? If you agree, then reality itself is our internal representation of our sensory inputs. This notion is actually much more profound that it first appears. If sound is representation, so is smell. So is space.

Figure: Illustration of the process of brain’s representation of sensory inputs. Odors are a representation of the chemical compositions and concentration levels our nose senses. Les sons sont une cartographie des ondes de pression d'air produites par un objet qui vibre. En vue, notre représentation de l'espace, et éventuellement le temps. Cependant, we do not know what it is the representation of.

We can examine it and fully understand sound because of one remarkable fact — we have a more powerful sense, namely our sight. Sight enables us to understand the sensory signals of hearing and compare them to our sensory experience. En vigueur, sight enables us to make a model describing what sound is.

Why is it that we do not know the physical cause behind space? Après tout, we know of the causes behind the experiences of smell, son, etc. The reason for our inability to see beyond the visual reality is in the hierarchy of senses, best illustrated using an example. Let’s consider a small explosion, like a firecracker going off. When we experience this explosion, we will see the flash, hear the report, smell the burning chemicals and feel the heat, if we are close enough.

The qualia of these experiences are attributed to the same physical event — the explosion, the physics of which is well understood. Maintenant, let’s see if we can fool the senses into having the same experiences, in the absence of a real explosion. The heat and the smell are fairly easy to reproduce. The experience of the sound can also be created using, par exemple, a high-end home theater system. How do we recreate the experience of the sight of the explosion? A home theater experience is a poor reproduction of the real thing.

In principle at least, we can think of futuristic scenarios such as the holideck in Star Trek, where the experience of the sight can be recreated. But at the point where sight is also recreated, is there a difference between the real experience of the explosion and the holideck simulation? The blurring of the sense of reality when the sight experience is simulated indicates that sight is our most powerful sense, and we have no access to causes beyond our visual reality.

Visual perception is the basis of our sense of reality. All other senses provide corroborating or complementing perceptions to the visual reality.

[This post has borrowed quite a bit from my book.]