## Gell-Mann and Hartle’s Decoherent Histories Quantum Mechanics

February 11, 2012

Is this only me feeling this way or the recent extension of Decoherent Histories Quantum Mechanics with One ‘Real’ Fine-Grained History due to Gell-Mann and Hartle makes a lot of sense? I was very much impressed to see that almost everything I was looking for naturally appears there! Apparently the major interest of the authors in their theory is the fact that it’s compatible with quantum  cosmology. But to me the use of the extended probabilities which could have negative values is what’s striking. Since the first day that I became  interested in Weak Measurements I was wondering if there could be a formulation of quantum mechanics in which the extended form of probabilities play a defining role! Here we go, there is this new formulation. Paraphrasing Aephraim Steinberg, if you look in the dark you’ll see negative probabilities! All the problems we were wondering about involving Weak Measurements and retrodiction, which gave negative probabilities could be viewed as history problems and now systematically appear in our formulation of quantum mechanics. This is so cool. I guess it’s now time to look at that particular application of quantum theory which has always shed light onto quantum foundations, namely quantum information, and see what can we do with the negative probabilities! Hopefully we’ll find some new stuff.

Nevertheless, there are some arguments that you shouldn’t interpret weak values as probabilities. Which in this case the whole debate goes back to the starting point! But since it looks like I’m the only reader of this blog now, I won’t go into the details.

## Video Lecture on Weak Measurements

December 11, 2011

I gave a talk on Weak Measurements as a part of ‘Random Walks on Physics’ at the University of Manchester. If anybody is interested, the video is linked below. The advantage of watching this one is that it’s targeted at undergraduate students. So one might find it easier to grasp than the more technical ones.

## Weak measurement and its implications in quantum foundations

November 13, 2011

I have uploaded a copy of my BSc dissertation for anyone who may possibly be interested. Unfortunately at Manchester you get only one month to work on your dissertation and I’ve chosen a topic which I’ve never had an experience on it before. So a word of warning that you probably shouldn’t expect to find anything profound in this work. Nonetheless, if you haven’t done weak measurements before and you’re interested in quantum foundations you might find this a compact review article about what’s going on!

Here is the link: Weak measurements and their implications in quantum foundations

## What a good BSc dissertation should *not* be!

October 27, 2011

One would expect a BSc dissertation to demonstrate an idea and give a clear, concise and complete grasp of its subject matter. Therefore, the first element that a dissertation relies upon is correct and sufficient information. It is not difficult to find sources of trustworthy information for science. Science students know how to use peer-reviewed journals and other sources to gather the required information. The second condition, which is again commonly satisfied by most of the reasonably done dissertations is coherence of the argument. An article in which the idea doesn’t flow easily is not normally acceptable. The third crucial requirement is conciseness. Extra information which is never used in the article makes it unreadable and indeed is not a good practice.

Almost everyone knows about these requirements and, rather unfortunately, a dissertation which satisfies the conditions above normally gets a first class grade. Nevertheless, I believe that the aforementioned conditions are far from being sufficient and in the educational system that I would be happy to be part of, it hardly gets a pass.

The author of a bachelor’s degree dissertation needs to have a good grasp of her writing and the material around the core facts which she includes in the article. This fluency cannot be measured solely by the observation of the coherence of an article that is only a concatenation of previously formulated facts. While I accept the premiss that a BSc dissertation does not have to contain original work, the student must demonstrate her knowledge of the subject by producing examples, in case of natural science, which have never appeared in print. This is certainly not too much to ask. It is quite simple to produce examples about the main theories, to give a clear picture of the arguments in a dissertation. Because while the length of the article supports, those examples are hardly used in the original papers, unless the papers contain very controversial and counter-intuitive arguments. In the same way author of a science textbook normally gives a problem set at the end of each chapter, independent examples could be formulated by a student to demonstrate the validity of the argument and also increase the coherence of the article. This is an element of originality which is very important, but normally absent in a dissertation.

Another factor which, alongside with the original examples, must be used to evaluate a dissertation is the section for open problems. One occasionally sees such sections in BSc dissertations. Nonetheless, the importance is almost universally ignored. Open problem section gives the student the chance to ask good questions. Asking good questions is almost as difficult as solving a problem, and it is as important as finding solutions. Clever questions lead off in different directions and are crucial points to start to look for inspirations. Having this section not only helps the students to find her future paths, but also helps the assessor to do the job more accurately. One who hasn’t grasped a theory would either ask simple-minded questions about that theory or just copy the well-known open problems one can find on the internet by spending only a few hours.

The last two criteria are normally not considered to grant a first class grade (%70 in the British scaling system) to a dissertation. Even worse, the British educational system does not give the student sufficient amount of time to fulfil the requirement. An adequate educational system requires to provide enough support for the student to carry out the work needed to reach at that level and also needs to consider that as a measure to evaluate the quality of the dissertation. Any grade above %70 must only be awarded to the one who does excellencies in the article, for instance original problem solving, theorising or hypothesising.

## On the ethics of marriage

August 19, 2011

I would like to argue that any type of social contract and commitment of the form which appears in marriage, those that involve interactions of individuals’ personal lives are fundamentally unethical.

Given the subjectivity of value systems one particular action can be thought both justified and unjustifiable, in the same time, but with respect to different perspectives. (From now on, I shall refer to perspective as reference frame for the reasons of personal interest.) Nevertheless, marriage is an interaction which causes the personal aspect of people’s lives not to remain separable. On the other hand, while this entanglement is formed, marriage doesn’t give any mechanism to create a shared a reference frame, which is a source of catastrophe in these type of commitments, i.e. there is no way of having the same value system for two different people in all important aspects of their lives.

As a trivial idealised example consider a heavy smoker who knows all the consequences, but believes smoking is a vital action for him/her to maintain a happy life. So he/she chooses to do so… There is nothing here to argue, as he/she has chosen to perform an action consistent within his/her reference frame. Now imagine he/she loves someone who really hates smoking. In such a case at least one person should give up her/his attachment to the a priori value system.

What is more subtle is even given a shared reference frame, lack of a common threshold will make the relationship again unethical. As one may like something up to a threshold, not being bothered by it up to a second threshold, but as soon as that thing gets more, it’ll become intolerable for him/her. While the same intolerable could be pleasant for his/her partner!

More dramatically, by the entropy arguments, one can say the more socially sensitive the individuals are (the more stuff they have to care about) the deeper this conflict gets.

One might argue that by this reasoning almost all of the human activities are unethical, as most aspects of their lives are in one way or another entangled.  Nevertheless, this is irrelevant. Because most of the events in people’s lives had not much influenced at any time when their backward light cone had overlap. Of course those which did have any noticeable effect should be carefully considered, but there are surely very few of them.

One may still choose to act unethically for the benefits she/he gets from these accepted norms of the society. At the end of the day it’s the society which finds its ways.

One question remains: whether it is possible to arrive at a conflict free personal interaction, in the sense discussed above. I think the answer is not obvious. But I believe the least price would be departure from a minimal set of today’s accepted values, e.g. monogamy or accepted commitments in partnership (e.g. non-open relationships).

## Semantic anti-realism and quantum theory

June 30, 2011

I’ve recently given a talk in Open Minds VI: A Graduate Conference in Philosophy. Here is the video. I guess it should be acceptable as a blog post!

I never knew I’m that annoying when I speak! I really don’t like that!

## Quantum physics doesn’t add much to the problem of Freewill!

June 13, 2011

I obviously have enormous respect for Michio Kaku for his massive contribution to science. However, for some reason unknown when people become publicists, most of them tend to express their ideas about everything including the disciplines they don’t have any speciality in! And because of their big names the idea is normally taken too seriously! One example of that is this. Here Dr Kaku explains that according to Newtonian mechanics the state of physical systems is evolving deterministically and hence no room for freewill. But now we know that due to (standard) quantum mechanics the universe is in fact evolving non-deterministically and hence we have freewill!

No wait… What?!! How did we jump into the problem of freewill? Even if we assume Compatibilism is impossible, still I don’t see the connection from the non-determinism to freewill!

I guess what most of the people think of freewill, when they say it, is that a decision maker object has freewill if there are actually several choices (coming from non-determinism) and they could be chosen on the basis of something which is not external to the decision maker’s personal identity.  The problem of freewill mainly relies on the resolution of the latter, which is independent of the determinism of the underlying physics. So if you’re a non-compatibilist, you may claim that if the world evolves deterministically, no-one can have freewill. But the converse doesn’t hold, i.e. you can’t claim to have freewill just because the world is indeterministic.

Besides there are scientific problems with that claim as well. For instance according to the current state of cognitive neuroscience, decision making is a macroscopic process which is mainly based on the activity of orbitofrontal cortex and some other parts of your brain. Hence to be able to find someone guilty (in case of non-compatibilism) the *macroscopic* model of your physics has to be non-deterministic, not the microscopic one. Lets clear this up with an example: According to the International Football Association, “a goal is scored when the whole of the ball passes over the goal line, between the goalposts and under the cross bar.” So in a football match the referee checks whether the *macroscopic position state of the ball* has crossed the line or not! If you find a referee who doesn’t accept the goal, calming that according to quantum physics there is a non-zero probability of finding particles, belonging to the ball, outside the goal you’ll call him silly! I think the same should hold for the problem of freewill. Unless the neuroscientists tell us that our decisions are in fact based on the collapse of the wavefunction of a quantumly behaving objects!

I’ve seen a lot of big names sitting down and thinking hardly about problems of philosophy and failing so badly. This one is a vivid example! You can hardly find bigger names than the participants of this panel discussion. But yet they’re discussing some philosophical problems that I would say they could ask any undergraduate philosopher! I mean, we should think about it once for ever. If philosophy is important for us we should do it properly, and if it’s not important we should leave it alone!

## Quantum philosophy: an anti-realist approach

February 18, 2011

I should apologise for the very incoherent post. However, I thought it’s better than nothing! I don’t think I can get a chance to write a serious post for a while. So here we go…

[update: Oh, I've chosen a fancy title, now I feel guilty for such an incoherence and unclear post! ]

Me, Howard Kelly and Joe Razavi were talking about truth-conditional semantics and justficationist theories of meaning† and in a big chunk of the discussion we were talking about the inadequacy of the principle of bivalence. The interesting thing is that we could see the principle of bivalence should not hold for general case in our philosophy, by the logical structure and by the fact that it was a necessary condition to get rid of the circularity of truth-conditional semantics. However, we couldn’t come up with a good example in natural language. No matter how complicated the situation was, we could always find a realist response to that. The only examples in which the realist could not say anything was examples from quantum mechanics. All other tries to come up with an example in natural languages were fail!

Independently, I raised this question: I think the claim should be easily verifiable if we could make a statement consisting of atomic facts. Basically because from the simplicity of our logical structure I had this feeling that if we could come up with examples of atomic facts it should be intrinsically different. However, we knew that we weren’t the first people who tried to find an example of atomic facts and failed. So we tried to, at least, make sense of what Wittgenstein and us were saying! Joe, whose fresh thoughts always open new perspectives to my mind suggested that if we think about it scientifically, atomic facts must be a set of bases which span the state space of our facts. However, the set is not unique (in the same way, intuitively, that the spanning bases for Euclidean 3-space isn’t unique). And since we don’t have the tools for it (as we do in sciences) it would be upsetting to look for such atomic facts.

I find the idea brilliant. It made me think if the same mysteries which exist on the boundaries of classical and quantum theories also exist on the boundaries of atomic facts and the large scale natural languages as well as thoughts! And whether there is chance to find something like the decoherence theory for philosophy of language!

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†chapter 4 and 5 of Thought and Reality by Michael Dummett (It’s actually a very important book in philosophy of language which I would recommend buying it.)

## No atheist posts…

January 30, 2011

OK, I’m planning to start blogging again! I haven’t written anything interesting yet, but just a quick announcement that you may have noticed that I’ve deleted all the atheist posts. That surely doesn’t mean I’m not an atheist any more. It’s just that I believe there are many nice and clever religious people for whom I have enormous respect and it’s stupid to talk in a rude and sarcastic language about the things they care for! I don’t think I can write in a way which is suitable for all of my target audience. If I have a point I’ll go to the person who I think I need to talk to, and make my point. I’m not planning to write anything about it any more…

## Yet Another Relativity Quiz

December 3, 2010

I designed a question a while ago and put a fallacy in it (I don’t know if it exists in any text book. I haven’t seen this before. I did it from the scratch). I asked a few undergrads in physics to spot the fallacy! To be honest I didn’t ask many people, but among those I did, surprisingly, no one could give me a correct answer!!! Here is the question. Have a look and PLEASE PLEASE tell me you can solve it!

Assume an observer is moving with a very high constant speed along the x axis (mass of the observer is negligible), relative to a mass distribution, $m_1 \mbox{ and } m_2$, symmetrical in the observer’s path as can be seen in figure 1. The force on $m_1$, in the centre of mass reference frame is $F_{12}=\frac{G m_1 m_2}{r^2}$ which gives the acceleration $a=\frac{G m_2}{r^2}$. However, in the observer’s reference frame the total mass of the system increases by a factor of $\gamma$ which gives the the acceleration $a=\frac{C G m_2}{r^2}$ where C is a constant. Because the length doesn’t contracts, since it is aligned along the y axis. What the hell?! This is clearly against our knowledge of physics! Surely acceleration should be reference frame independent! What about the gravitational potential? Is gravitational potential independent of the observer?

If you solved it, please don’t give your solution in the comments. I’m wondering to see how many people can work out basic relativity! Send it to my email address: salek [DOT] sina [AT] gmail [DOT] com.

Thank you

Figure 1