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# A Smolin: Realistic and anti-realistic interpretations of QM

#### A. Neumaier

I also don't think that relativistic QFT is "the final theory". It's not even mathematically completely consistent.
No inconsistency has been proved. It is simply unknown whether QED or the standard model are consistent or not. Settling this might have important consequences for the methods to squeeze out predictions from QFT, and hence is at least as important as finding a unified theory of the standard model plus gravity - which is unlikely to have any significant experimental consequences, as you say yourself:
So far, all observations concerning gravity are in accord with GR, but that's likely to be the case, because all we can observe concerning gravity is about its action on macroscopic systems, and there the classical theory is very accurate (in close analogy to our everyday experience that classical electrodynamics/optics is very accurate although here we know QED as the underlying quantum theory). So it's very hard to find specific phenomena where and how GR (or maybe some other classical field theory describing gravitation better, although I don't know of any clear empirical hint that this might be the case) has to be joined with QT.

#### Demystifier

2018 Award
Yes, sure, but that's not entirely just philosophy.
I'm glad that you think so. But I would like to stress that I arrived to those ideas by starting from philosophical questions. The point is that philosophy may lead to something that is more than philosophy, so one should not ignore ideas which at first look as just philosophy.

#### vanhees71

Gold Member
What is the nature of this indeterminacy you mention? Is it that the system is physically/ontologically smeared across its possible values, so the value exists in an unsharp way? Is it that the value sharply in an eigenstate, and we just can't say which until measurement? Or is the value truly non-existent until it is measured?
What do you mean by this question? If somebody starts the question with "what's the nature/mechanism...", usually he or she has a conceptual misunderstanding what the natural sciences are methodologically aiming at. First of all they are empirical sciences, i.e., a phenomenon of nature is investigated by making quantitative observations about it. If the phenomenon is reproducible and shows a clear regularity, one can compare it with the predictions of existing models/theories, as far as one is able to apply the formal, mathematical structure of the model/theory to it (and that's all you need to make a mathematical system a physical theory, and that's it concerning interpretation as far as natural science is concerned). If then the observation agrees, within the accuracy of the observation, you have found "an explanation" in the sense that you can understand the phenomenon in terms of the existing models/theories.

In some sense, that's the "boring" case, because then we haven't learnt something new about nature. So an experiment and theoretical analysis becomes interesting, if the observation deviates from what's expected from the existing theories. Then, usually a careful reaxamanation of the experimental setup starts, and one might figure out errors of this setup, or one tries to find variations of the measurement to see whether everything is reproducible with other methods. If the deviation with theory withstands all these careful testing, then a new model/theory is needed, and then some new model/theory is developed, with the caveat that the new theory has to work in all the cases the old theory worked before. If this is established, usually one can understand the success of the old theory as well as its failure in "explaining" the new phenomenon in the sense that the old theory can be understood as some approximation of the new theory, valid only in a certain realm and not applicable where the old theory failed.

This is of course a quite complicated mutual process, i.e., theories do not only "explain" in the above summarized sense a phenomenon or have to be modified due to a newly discovered phenomenon where it fails, but it also provides ideas for more experiments. E.g., quantum theory all of a sudden made it interesting to investigate how electrons behave when shot on a double slit. Before, when everybody thought electrons are just little classical particles, this experiment may never have been realized, because nobody would have thought that it might lead to interesting new phenomena. With de Broglie's hypothesis of "wave-particle duality" this became interesting, and indeed it's among the most interesting early experiments leading to the development of modern quantum mechanics, which finally made the quite inconstistent idea of "wave-particle duality" obsolete and lead to the probabilistic standard interpretation.

As any mathematical model, also physical theories start with some postulates, which cannot be reduced further to "more simple" postulates. Here, of course, simplicity is a subjective idea, but what theoretical physicists aim at is to find a minimal set of fundamental postulates for a theory, from which as many as possible phenomena can be "explained" in the above sense. The "fundamental postulates" themselves cannot be "explained" in this sense, but are just compact summaries of the results of, sometimes decade-long, efforts of experimentalists and theorists.

#### zonde

Gold Member
I don't think that there's anything wrong with QT in the realm where we really need it to describe the phenomena. It's not consistingly describing the gravitational interactions, and that's imho the only clear physical hint of failure of QT or rather its incompleteness.
I'm not sure I understand your point here. There are no gravitational interactions according to GR. Inertia just bends spacetime. GR describes that. It's predictions agree with observations. What else do you want? Any aesthetic considerations should not be relevant to physics, right?

#### vanhees71

Gold Member
No inconsistency has been proved. It is simply unknown whether QED or the standard model are consistent or not. Settling this might have important consequences for the methods to squeeze out predictions from QFT, and hence is at least as important as finding a unified theory of the standard model plus gravity - which is unlikely to have any significant experimental consequences, as you say yourself:
Well, I have some hope that solving the problem of a QT description of gravity might also solve the mathematical problems of QFT as a whole. E.g., some decades the (failed) hope was that string theory and its various relative might solve both the problem of quantum gravity and provide a mathematically consistent description of QFT, with the standard model as an approximation in the sense of an "effective theory", and as such it works pretty well, one could even say too well, because no clear contradicting observation has been made yet, despite its mathematical inconsistency.

#### vanhees71

Gold Member
This only covers states of microscopic systems in the lab.

Which preparatin nprocedure determines the quantum state of the solar system? How is the result of a measurement of some observables (say the mass of the Sun and the major planets) of this quantum state described from first principles (assuming Newonian gravity, which is fully adequate for this situation)?

The solar system is not coupled to an external measurement device as in the usual analysis of measurements.; the measurement is done from within. Without an explanation how this works, even ordinary quantum mechanics is an incompletely understood (and indeed incomplete) theory.
The preparation procedure of the solar system is not too well known, but the common idea is that stars and planets etc. around them form out of clouds of some material which is denser at some location than on average, and then gravity does its job. All this is of course well described by classical (even Newtonian) physics. A complete microscopic description is neither possible nor necessary.

A simpler example is the coffee in the cup on my desk, which has been prepared by me just some minutes ago. It's pretty well described as a system of local thermal equilibrium slowly equilibrating further to finally reach the temperature of my office which is also pretty well described to be in local thermal equilibrium, providing a "heat bath" within which the coffee sits and exchanges energy and water molecules, i.e., it cries to be described as a grand canonical ensemble close the thermal equilibrium and thus with classical physics like (viscous) hydro dynamics with heat conduction etc.

So preparation procedures need not be very "artificial" as, e.g., at a collider like the LHC, where proton bunches are accelerated and kept at high precision at a certain energy to get something accurately prepared to make experiments, where the much more microscopic detail is resolved. Already substituting the protons by Pb nuclei and performing heavy-ion collisions changes this completely, and again there's no better chance to understand what's going on than to use (semi-)classical methods like kinetic theory, relativistic viscous hydro, Langevin processes, etc. to describe the system. Even in p Pb and pp collisions one observes quite some "collectivity", at least in "high-multiplicity events".

It's a gift and a curse of nature at once that macroscopic, or even "mesoscopic" systems of some 1000 of particles, tend to behave according to classical or semi-classical models. It's a gift, because we have the chance to understand more by describing these system approximately with simpler models but also a curse, because we cannot so easily observe the (maybe) interesting quantum phenomena we are after.

#### A. Neumaier

The preparation procedure of the solar system is not too well known, but the common idea is that stars and planets etc. around them form out of clouds of some material which is denser at some location than on average, and then gravity does its job. All this is of course well described by classical (even Newtonian) physics. A complete microscopic description is neither possible nor necessary.
But to say that a complete microscopic description is not possible says that quantum theory does not apply for the solar system as a whole. A complete microscopic quantum description should therefore be possible in principle, even though we may never know the exact details. And such a microscopic quantum description would represent a single system only, which cannot be interpreted by a purely statistical interpretation. This is the reason why interpretation questions are still open, and why they may shed light on what is missing for a fundamental description of all of Nature.

#### A. Neumaier

I have some hope that solving the problem of a QT description of gravity might also solve the mathematical problems of QFT as a whole.
I have the opposite hope that solving the mathematical problems of QFT might also solve the problem of a QT description of gravity. Mathematical problems always point to lack of theoretical understanding, and progress comes through fixing these conceptual issues.

#### vanhees71

Gold Member
But to say that a complete microscopic description is not possible says that quantum theory does not apply for the solar system as a whole. A complete microscopic quantum description should therefore be possible in principle, even though we may never know the exact details. And such a microscopic quantum description would represent a single system only, which cannot be interpreted by a purely statistical interpretation. This is the reason why interpretation questions are still open, and why they may shed light on what is missing for a fundamental description of all of Nature.
Well, why do you say, it's not possible in principle? The single system then is described in terms of probabilities. The more I think about it, the less I see anything problematic in this. Even on the classical level, the many-body system is described in terms of statistical phsics and thus with probabilities, including fluctuations and all that, and that classical description can be derived, at least to some extent, from quantum many-body theory.

#### vanhees71

Gold Member
I'm glad that you think so. But I would like to stress that I arrived to those ideas by starting from philosophical questions. The point is that philosophy may lead to something that is more than philosophy, so one should not ignore ideas which at first look as just philosophy.
Well, yes. Theory building is an art, and you can be inspired by many non-scientific things ;-)).

#### A. Neumaier

The single system then is described in terms of probabilities.
What do probabilities mean for a single system? How does this show in the postulates of quantum mechanics?

#### vanhees71

Gold Member
I'm not sure I understand your point here. There are no gravitational interactions according to GR. Inertia just bends spacetime. GR describes that. It's predictions agree with observations. What else do you want? Any aesthetic considerations should not be relevant to physics, right?
Well, GR has built in its own failure, namely the unavoidable singularities of all physically relevant solutions. When it comes to the singularities of cosmology ("big bang") and black holes ("Schwarzschild, Kerr" of very compact objects), the physical laws of GR break down, and it's expected that an appropriate quantum treatment "cures" these deficiencies of the classical theory.

Further, there's nothing in GR that forbids to think about gravity as an interaction. The geometrization even can be derived from this ansatz (e.g., due to Weinberg; see also Feynman's book, "The Feynman lectures on gravitation", which is a brillant textbook on the subject).

#### vanhees71

Gold Member
What do probabilities mean for a single system? How does this show in the postulates of quantum mechanics?
I answered this question a zillion times. We don't need to go into this issue again (I know, I shouldn't have answered to this thread...).

#### cube137

I'm reading Smolin Einstein's Unfinished Revolutions and there is something that perflexed me. Quoting Smolin:

At the same time, there are several reasons pilot wave theory is not entirely convincing as a true theory of nature. One is the empty ghost branches, which are parts of the wave function which have flowed far (in the configuration space) from where the particle is and so likely will never again play a role in guiding the particle. These proliferate as a consequence of Rule 1, but play no role in explaining anything we’ve actually observed in nature. Because the wave function never collapses, we are stuck with a world full of ghost branches. There is one distinguished branch, which is the one guiding the particle, which we may call the occupied branch. Nonetheless, the unoccupied ghost branches are also real. The wave function of which they are branches is a beable.

The ghost branches of pilot wave theory are the same as the branches in the Many Worlds Interpretation. In both cases they are a consequence of having only Rule 1. Unlike the Many Worlds Interpretation, pilot wave theory requires no exotic ontology in terms of many universes, or a splitting of observers, because there is always a single occupied branch where the particle resides. So there is no problem of principle, nor is there a problem of defining what we mean by probabilities. But if one finds it inelegant to have every possible history of the world represented as an actuality, that sin is common to Many Worlds and pilot wave theory.
(Note: Rule 1 is simply "Given the quantum state of an isolated system at one time, there is a law that will predict the precise quantum state of that system at any other time." Smolin called this law Rule 1. "It is also sometimes called the Schrödinger equation. The principle that there is such a law is called unitarity."

Why didn't Demysitifer worry about the ghost branches? Are there many kinds of Bohmians with regards to how they treat the wave function? How does Demystifer and other Bohmians treat it compared to Smolin?

#### stevendaryl

Staff Emeritus
But the quote is obviously wrong, because we very well can use quantum theory to describe real-world experiments, and there's both the notion of the state, described by the statistical operator, its deterministic (!) time evolution, given the Hamiltonian of the system, and its probabilistic interpretation.
I think that what David Wallace was saying is obviously right. He didn't say that we can't use quantum theory. He was saying that in practice we treat macroscopic quantities different from microscopic in an ad-hoc way. That's true. It doesn't make quantum theory useless, but it makes it "softly inconsistent", to use my own phrase.

The state is determined by a preparation procedure, and it implies that not all observables of the system takes determined values, but a measurement of these observables give random results with probabilities given by the states. There's no contradiction in the sense of logic.
I think it is a contradiction. To me, the following two claims are just logically inconsistent (together with the rest of the quantum formalism)
1. A measurement always produces an eigenvalue of the quantity being measured.
2. Measurement devices and observers are themselves described by quantum mechanics.

#### zonde

Gold Member
Well, GR has built in its own failure, namely the unavoidable singularities of all physically relevant solutions. When it comes to the singularities of cosmology ("big bang") and black holes ("Schwarzschild, Kerr" of very compact objects), the physical laws of GR break down, and it's expected that an appropriate quantum treatment "cures" these deficiencies of the classical theory.
These hypothetical singularities can not be observed. Why should we care about them?

Further, there's nothing in GR that forbids to think about gravity as an interaction. The geometrization even can be derived from this ansatz (e.g., due to Weinberg; see also Feynman's book, "The Feynman lectures on gravitation", which is a brillant textbook on the subject).
Of course, just because there is one valid theory does not mean there can't be other theory describing the same phenomena. But we have a theory that correctly predicts observable phenomena. So why bother?

#### charters

What do you mean by this question? If somebody starts the question with "what's the nature/mechanism...", usually he or she has a conceptual misunderstanding what the natural sciences are methodologically aiming at
I am asking if you think the wavefunction of, say, an electron, describes 1) a new sort of spatially extended object, 2) a 0D classical point whose position is simply unknown, or 3) nothing but the probability of a classical detector click. I believe from you other comments your view is 3, in which case the measurement problem is akin to wondering: where did all these classical detectors come from in the first place? Why do we say they are made of electrons, if electrons on the quantum scale have no purchase as objectively existing objects?

My sense is your answer is going to be "who cares, the theory works." That's fine, but don't confuse not being interested in a problem with whether others are wrong to identify the problem as legitimate. Math works very well in practice, but Godel's incompleteness theorem is still an issue to contend with. The MP is similar in form.

#### vanhees71

Gold Member
I think that what David Wallace was saying is obviously right. He didn't say that we can't use quantum theory. He was saying that in practice we treat macroscopic quantities different from microscopic in an ad-hoc way. That's true. It doesn't make quantum theory useless, but it makes it "softly inconsistent", to use my own phrase.

I think it is a contradiction. To me, the following two claims are just logically inconsistent (together with the rest of the quantum formalism)
1. A measurement always produces an eigenvalue of the quantity being measured.
2. Measurement devices and observers are themselves described by quantum mechanics.
Why is there a contradiction? Is there any empirical evidence that 1. is wrong? If that were the case, there'd be a big crises of QT as a whole, and every theorist would struggle to find an alternative theory ;-).

Concerning 2. it's to some degree a matter of taste whether you except the standard quantum-statistical arguments as "description" of the measurement devices or not. So again, about this you can fight enternelly without coming to any conclusion either.

That there's any necessity to also describe us as quantum systems too to solve the "measurement problem" is somewhat exotic to me, because there's really no more direct interaction between us and the measured system (except in the case that you consider our own senses as measurement device of quantum systems, like the very interesting possibility to use our eyes directly as single-photon detectors which seems to be possible in principle according to new studies on the subject).

#### vanhees71

Gold Member
These hypothetical singularities can not be observed. Why should we care about them?

Of course, just because there is one valid theory does not mean there can't be other theory describing the same phenomena. But we have a theory that correctly predicts observable phenomena. So why bother?
What other theory you are talking about. GR is GR, no matter whether you describe gravity as an interaction or insist on the quite common interpretation that it's entirely a kinematical effect of curved spacetime. For me the interpretation of gravity as an interaction as all the other fundamental interactions (i.e., electroweak and strong interactions) is of some attraction, because it's simplifying and unifying the picture, but that's again just a matter of personal taste of little importance in the sense of science.

#### vanhees71

Gold Member
I am asking if you think the wavefunction of, say, an electron, describes 1) a new sort of spatially extended object, 2) a 0D classical point whose position is simply unknown, or 3) nothing but the probability of a classical detector click. I believe from you other comments your view is 3, in which case the measurement problem is akin to wondering: where did all these classical detectors come from in the first place? Why do we say they are made of electrons, if electrons on the quantum scale have no purchase as objectively existing objects?

My sense is your answer is going to be "who cares, the theory works." That's fine, but don't confuse not being interested in a problem with whether others are wrong to identify the problem as legitimate. Math works very well in practice, but Godel's incompleteness theorem is still an issue to contend with. The MP is similar in form.
The wave function describes probabilities for measurement results no more no less. It's wrong to say an electron is the wave function (the more that at the most fundamental level wave functions do not make much sense but are quantized themselves). So indeed I think 3) describes my point of view best.

The classical detectors come from the physicists' curiosity to learn more about nature. That's why they build with some effort ever better ones (and that's often pretty expensive and we can be lucky to get them financed by tax-payers money).

That matter around us, and thus also measurement devices, are made of atomic nuclei and electrons is the conclusion that we very well understand their properties as many-body systems with atomic nuclei and electrons as the relevant degrees of freedom. That's also known as condensed-matter physics and a very successful application of quantum (field) theory. It's so successful that we have all the funny gadgets like the laptop I'm writing this text on and also to construct ever better measurement devices for all kinds of measurements on quantum systems down to the most fundamental building blocks, as far as we know them, and perhaps one day helping us to find even new ones.

#### charters

The wave function describes probabilities for measurement results no more no less. It's wrong to say an electron is the wave function (the more that at the most fundamental level wave functions do not make much sense but are quantized themselves). So indeed I think 3) describes my point of view best.
That matter around us, and thus also measurement devices, are made of atomic nuclei and electrons is the conclusion that we very well understand their properties as many-body systems with atomic nuclei and electrons as the relevant degrees of freedom.
So you claim free electrons do not exist - neither as an extended object nor as a classical point, as in options 1 and 2 in post # 42. But you also claim electrons suddenly do start to exist when composing macroscopic, many body systems.

#### stevendaryl

Staff Emeritus
Why is there a contradiction? Is there any empirical evidence that 1. is wrong? If that were the case, there'd be a big crises of QT as a whole, and every theorist would struggle to find an alternative theory ;-).
For a while, maybe. But if no satisfactory alternative theory was found, many of them would shift to pretending that the evidence doesn't REALLY show what it seems to show. In other words, many theorist would just live in denial about it. And that's exactly what we do have.

Concerning 2. it's to some degree a matter of taste whether you except the standard quantum-statistical arguments as "description" of the measurement devices or not. So again, about this you can fight enternelly without coming to any conclusion either.
The reason there is eternal fighting about it is because 1 & 2 are contradictory, and there is no agreement about how to fix it. On the other hand, there is a "rule of thumb" that allows us to get past the contradiction, which is that we have heuristics for when to treat a system as a measurement device obeying 1, and when to treat it as a quantum mechanical system. You can't consistently do both.

Let me sketch a scenario showing that rule 1 is contradictory with rule 2.

Suppose that you have a Stern-Gerlach type situation in which an electron that is spin-up in the z-direction is deflected left, and makes a black spot on the left side of a photographic plate. An electron that is spin-down makes a black spot on the right side.

Now suppose that we set up initial conditions that are precisely left-right symmetric. We send an electron through the Stern-Gerlach device that is spin-up in the x-direction.

According to rule 1, eventually the system evolves into a final state that is not left-right symmetric. Either the electron goes left and makes a spot on the left, or goes right and makes a spot on the right. So the final state does not satisfy the left-right symmetry of the initial state.

That is not possible, if everything obeys the laws of quantum mechanics. If the initial state is left-right symmetric, and the Hamilton is similarly left-right symmetric, then the final state will be left-right symmetric.

#### DennisN

I think, as with the question about a consistent QT of gravity, we'd need some empirical evidence clearly indicating that there's a real problem in describing an unanimously observed phenomenon which contradicts QT.
Your quote was specifically about QT of gravity (I think), but I'd like to say that in my opinion the best thing that could happen to quantum physics overall is empirical evidence that contradicts QT. If that would happen, things maybe would start to go in new, interesting directions.

#### vanhees71

Gold Member
So you claim free electrons do not exist - neither as an extended object nor as a classical point, as in options 1 and 2 in post # 42. But you also claim electrons suddenly do start to exist when composing macroscopic, many body systems.
I do not claim that free electrons do not exist. Where do you get this from? Of course free electrons exist. They are, of course, neither well described as a classical point particle (there's no consistent description of a classical point particle anyway) nor as a classical extended objects. That's why we use Q(F)T to describe them. According to the standard model they are described as the charged leptons (spin-1/2 Dirac fermions), thus carrying electric and WISO charges but no color charge.

Measurement devices are composed of atomic nuclei (protons and neutrons, which themselves are bound states of quarks and gluons) and electrons. That's what you have asked about not about the existence or non-existence of free electrons. Why should my statement above imply such obvious nonsense of non-existence of free electrons?

#### vanhees71

Gold Member
For a while, maybe. But if no satisfactory alternative theory was found, many of them would shift to pretending that the evidence doesn't REALLY show what it seems to show. In other words, many theorist would just live in denial about it. And that's exactly what we do have.

The reason there is eternal fighting about it is because 1 & 2 are contradictory, and there is no agreement about how to fix it. On the other hand, there is a "rule of thumb" that allows us to get past the contradiction, which is that we have heuristics for when to treat a system as a measurement device obeying 1, and when to treat it as a quantum mechanical system. You can't consistently do both.

Let me sketch a scenario showing that rule 1 is contradictory with rule 2.

Suppose that you have a Stern-Gerlach type situation in which an electron that is spin-up in the z-direction is deflected left, and makes a black spot on the left side of a photographic plate. An electron that is spin-down makes a black spot on the right side.

Now suppose that we set up initial conditions that are precisely left-right symmetric. We send an electron through the Stern-Gerlach device that is spin-up in the x-direction.

According to rule 1, eventually the system evolves into a final state that is not left-right symmetric. Either the electron goes left and makes a spot on the left, or goes right and makes a spot on the right. So the final state does not satisfy the left-right symmetry of the initial state.

That is not possible, if everything obeys the laws of quantum mechanics. If the initial state is left-right symmetric, and the Hamilton is similarly left-right symmetric, then the final state will be left-right symmetric.
Obviously I'm to stupid to understand, why there's a contradiction between 1 and 2. Particularly your example of an apparent paradox is completely incomprehensible to me, because it contradicts the standard interpretation of QT. Of course, as Bohr has already analyzed, you cannot perform the SG expeirment with free electrons in practice. So let me put Ag atom instead of electron (because that was the atom Stern and Gerlach used at the time)

If you send an Ag atom with indetermined spin-z component through a Stern-Gerlach apparatus it is deflected with the probabilities given by the corresponding (pure or mixed) state either to the left or the right. That's the point, why Born introduced the probability interpretation of the quantum state in the first place: You cannot split a single Ag atom into pieces, because you never find a smeared classical-field like entity that's smeared according to the wave-function squared, but you always find a single spot on the screen after it run through the SG-magnet. It ends either "to the left" or "to the right" and thus either, through the entanglement between position and spin-z component through the running through the magnet we conclude that the spin component is either up or down, depending on where the electron landed. You can even prepare pure spin-z eigenstates by just looking at the corresponding partial beam (through filtering away all electrons running in the other region of space). I.e., here you have a paradigmatic example for a von Neumann filter measurement. Of course, for the single electron there's no way to predict, which value will be found. You can only say that with the probabilities given by the state the Ag atom is prepared in

In the case of the original experiment it was a beam of Ag atoms from an oven running through a little opening, so it's some mixed state of roughly given by (written as product of the spatial/momentum part and the spin part)
$$\hat{\rho} \propto \int_{\text{aperture}} \mathrm{d}^3 p \exp[-\vec{p}^2/(2m k T)] |\vec{p} \rangle \langle \vec{p}| \otimes \hat{1}_{\text{spin}}/2.$$
Of all Ag atoms the probability for either spin-z component up or down is 1/2, i.e., the symmetric situation you assume. Of course, each single atom will go either the one or the other direction, and for the single atom the situation is not symmetric. Only the probability distribution is symmetric, and that's what's also predicted by QM. This can be even calculated in good approximation analytically (I've still not found the time to write this up completely, but it's really not too complicated).

The final state of the Ag atom is a quantum state again and only describes probabilities, and this distribution obeys the left-right symmetry you rightly assume.

In experimental terms: What's symmetric is the distribution of many Ag atoms, all prepared in the same initial state, running through the setup. Each single atom "breaks" the symmetry of course, landing either "left" or "right" from the symmetry plane.

It's the same with any random experiment. Although a perfectly fair die is symmetric, any outcome is showing 1 of the six edges and thus breaks the cubic symmetry. Only "statistically", i.e., the "average" over many outcomes is symmetric, i.e., the probability for each outcome is the same, 1/6.

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# For all numbers x and y, the operation & is defined by x&y

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For all numbers x and y, the operation & is defined by x&y [#permalink]  27 Aug 2018, 09:32
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For all numbers x and y, the operation & is defined by $$x&y = \frac{x-y}{x-1}$$ . If $$(-3)&q=2$$, then q =

A. -11

B. -8

C. -5

D. 5

E. 11
[Reveal] Spoiler: OA

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Re: For all numbers x and y, the operation & is defined by x&y [#permalink]  28 Aug 2018, 06:54
(-3-q)/(-3-1) = 2

solve this and you get q = 5
Re: For all numbers x and y, the operation & is defined by x&y   [#permalink] 28 Aug 2018, 06:54
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# For all numbers x and y, the operation & is defined by x&y

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# Why use potential functions to solve Maxwell's equations?

I'm reading "Antennas and Wave Propagation" by Harish and Sachidananda. They introduce the phasor form of Maxwell's equations:

$$\nabla\times E=-j\omega\mu H$$ $$\nabla\times H = j\omega\epsilon E + J$$ $$\nabla\cdot D = \rho$$ $$\nabla\cdot B = 0$$

First of all they observe that by taking the curl of the first equation and rewriting the right hand side with the expression for $\nabla\times H$, we can show that $E$ satisfies a wave equation: $\nabla^2E+aE=bJ$, for some constants $a$ and $b$. They also note that in the same way we can show that $H$ satisfies the wave equation.

Then they introduce the notion of vector and scalar potential, and propose to find $V$, the scalar potential of $E$, and $A$, the vector potential of $H$. The motivation for doing this seems to be that finding $A$ and $V$ is easier because they both satisfy... the wave equation.

Why solve the wave equation to get the potentials, and then work out $E$ and $H$ from there? Why not just solve the wave equations for $E$ and $H$ directly?

• Related: physics.stackexchange.com/q/22747/2451 , physics.stackexchange.com/q/397633/2451 and links therein. – Qmechanic Jul 25 '18 at 15:00
• @Qmechanic The math is a little above my head there. In particular I've never heard the terms "degrees of freedom" and "gauge transformation". – Jack M Jul 25 '18 at 15:02
• Obviously having only (3+1) wave equations for the $\textbf{A},V$potentials is simpler than using the otherwise equally complicated (3+3) equations for the vectors $\textbf{E},\textbf{H}$. This simplification happens because the two vector Helmholtz equations are not really independent and the equivalent potential formulation proves that. – hyportnex Jul 25 '18 at 15:27
• @hyportnex Oh, so it's a matter of revealing the true nature of the problem? We're expressing the equations in terms of a minimal set of independent variables, rather than a set of bound variables? – Jack M Jul 25 '18 at 15:59
• I do not know what "true nature" might mean in this context but the vector Helmholtz equations are not independent because the solutions must also satisfy the Maxwell equations $curl\textbf{E}=-i\omega\mu_0 \textbf{H}$ and $curl\textbf{H}= i\omega\epsilon_0\textbf{E}$. The vector and scalar potentials are almost independent subject to a so-called gauge invariance, see en.wikipedia.org/wiki/Gauge_fixing. – hyportnex Jul 25 '18 at 16:10


text:
# Two different answers for an elastic strings question

I came across this question in a textbook and after a full day of going over it and consulting friends none of us can figure out why a particular approach to this question doesn't yield the correct answer.

The question

A light elastic string of natural length $$0.2m$$ has its ends attached to two fixed points $$A$$ and $$B$$ which are on the same horizontal level with $$AB = 0.2m$$. A particle of mass $$5$$kg is attached to the string at the point $$P$$ where $$AP = 0.15m$$. The system is released and P hangs in equilibrium below AB with $$\angle{APB} = 90^{\circ}$$. If $$\angle{BAP} = {\theta}$$, show that the ratio of the extension of $$AP$$ and $$BP$$ is $$\frac{4cos{\theta}-3}{4sin{\theta}-1}$$

The correct method

Let the extension of $$AP$$ be $$x_1$$ and the extension of $$BP$$ be $$x_2$$

$$x_1 = 0.2cos{\theta} - 0.15$$

$$x_2 = 0.2sin{\theta} - 0.05$$

$$\frac{x_1}{x_2} = \frac{0.2cos{\theta} - 0.15}{0.2sin{\theta} - 0.05}$$

$$\therefore \frac{4cos{\theta}-3}{4sin{\theta}-1}$$

Our method (seemingly incorrect)

With the same symbols for $$AP$$ and $$BP$$ and the tensions in $$AP$$ and $$BP$$ being $$T_1$$ and $$T_2$$ respectively.

Since the system is in equilibrium resolving horizontally gives:

$$T_1cos{\theta} = T_2sin{\theta}$$

$$\therefore \frac{T_1}{T_2} = tan{\theta}$$

Since for an elastic string $$T = \frac{{\lambda}x}{l}$$

$$T_1 = \frac{{\lambda}x_1}{0.15}$$

$$T_2 = \frac{{\lambda}x_2}{0.05}$$

$$\therefore \frac{x_1}{x_2} = 3\frac{T_1}{T_2}$$

$$\therefore \frac{x_1}{x_2} = 3tan{\theta}$$

The discrepancy here is not that I do not understand the first solution, but why the second method does not yield a correct result, the steps followed seem logical and correct to me.

• I noticed that the classical-mechanics tag specifies it shouldn't be the only tag on a question, what other tags would be relevant here? – Tom Ryan Jun 19 at 18:05
• I'm adding the tag physics – user10354138 Jun 19 at 18:08
• If I understand correctly, you used the relationship between stress, strain and Young's modulus. $T$ is not the stress -- $T/A$ is, and there is no reason to assume the two sections of the rope have the same cross-section area after stretching – Shubham Johri Jun 19 at 18:10
• Are you sure it is $\angle APB=\theta$ not $\angle PAB=\theta$? You already have $\angle APB=90^\circ$ in the previous sentence. – user10354138 Jun 19 at 18:18
• @user10354138 oh yeah sorry I’ll fix that – Tom Ryan Jun 19 at 18:19

Both are correct, and the equality between the two identities will allow you to find $$\theta$$ and the other geometric parameters.
Your assumption that your second solution is incorrect is unwarranted. The "second solution" is an additional correct constraint as well, and serves to pin down $$\theta$$, which is, as a result, not arbitrary: As you increase the suspended weight from 0 to the critical value youo are considering, the angle $$\angle{APB}$$ decreases monotonically from $$\pi$$ to finally $$\pi/2$$.
Correspondingly, $$\theta$$ increases from 0 to crudely something like $$\pi/7.9$$, solving $$3\tan \theta =\frac{\cos\theta -3/4}{\sin\theta -1/4}.$$


text:
# Transcendental curve

A plane curve whose equation in rectangular Cartesian coordinates is not algebraic. In contrast to algebraic curves (cf. Algebraic curve), transcendental curves can have an infinite number of points of intersection with a straight line and an infinite number of points of inflection. On transcendental curves one encounters points of a special nature that do not exist on algebraic curves: points of termination, with the property that a circle of sufficiently small radius with centre at this point intersects the curve only at a single point; corner points (points of fracture) at which two branches of the curve come together, each of them having a tangent at this point; asymptotic points, which a branch of the curve approaches continuously, forming an infinite number of rotations around the point. Some transcendental curves have distinctive peculiarities of form (for example, they have a dotted branch consisting of an infinite set of isolated points).

One of the attempts to classify transcendental curves is based on the fact that in the overwhelming majority of known transcendental curves (as for all algebraic curves) the slope $y'$ of the tangent at each point of the curve is the root of an algebraic equation, the coefficients of which are polynomials in $x$ and $y$. In other words, the differential equation of the majority of known transcendental curves is a first-order equation of the form

$$\sum_{r=0}^nf_r(x,y)(y')^{n-r}=0,$$

where $f_0,\ldots,f_n$ are polynomials without common factors. This circumstance enables one to classify all algebraic curves, as well as almost-all transcendental curves (except, for example, the Cornu spiral), into groups of so-called pan-algebraic curves, which are distinguished by degree $n$ and rank $\nu$ — the maximal degree of the polynomials $f_0,\ldots,f_n$. For example, for curves of order three, $n=1$, $\nu=2$; for the Archimedean spiral, $n=2$, $\nu=4$. Pan-algebraic curves possess many of the properties inherent to algebraic curves. For example, the notions of the Hessian (algebraic curve) and the polar can be generalized to them. Concerning the attempts at further classifications of pan-algebraic curves, see [1].

Examples of transcendental curves are spirals, the catenary, the Dinostratus quadratrix, the cycloid, as well as the graphs of the transcendental functions: exponential, logarithmic, trigonometric, etc. (cf. Transcendental function).

#### References

 [1] A.A. Savelov, "Planar curves" , Moscow (1960) (In Russian)


text:
# Vertical Load Reactions On A Ramp

Hello,

I'm working on a small hardware project.

I have two load sensors located at distance $S_1$ ($x=0$) and $S_2$. Assuming we ignore the weight of the ramp ...

• What is the load on $S_1$ and $S_2$ as a function of $x$ where $x$ is an object's horizontal static position on the ramp?

Here's what I have so far:

• As the object moves horizontally away from $S_1$, the load on $S_1$ monotonically decreasing.
• As the object moves horizontally closer to $S_1$, the load on $S_1$ monotonically increasing.
• When the object is directly over $S_1$ ($x=0$), the load on $S_1 = w=mg$.
• When the object is directly over $S_2$ ($x = L = S_2$), the load on $S_1 = 0$.

I have feeling adding an incline does not change the vertical forces acting upon $S_1$ and $S_2$.

My question is, can this problem be reduced to a simply supported beam who's equations are:

$$S1 = (\frac{L - x}{L})w$$

and

$$S2 = (\frac{x}{L})w$$

Any other observations or insights would be great. Thanks!

-
A note: you may find our Robotics site useful :) –  Manishearth Jan 2 at 13:49
Oh nice! I didn't see that in the bottom of the page ;) –  Brian Chavez Jan 2 at 13:58
It's not there. It's a beta site -- on graduated sites, only other graduated sites are listed on the bottom. –  Manishearth Jan 2 at 14:03
It is called the lever rule and you are correct in splitting the weight across $S_1$ and $S_2$, but only for a static case. –  ja72 Jan 2 at 21:08
Take S1 as the origin. There is a torque about S1 due to the vertical force which is just $mg$ independent of the incline. This is the torque which the support S2 must counter to stop the ramp from rotating about S1. This gives you the force on S2, and the force on S1 is just $mg - F_{S2}$. So nothing essential in the problem depends on the incline and your simple beam equations should work.


text:
# Centering horizontally and vertically (simultaneously) using tabularx for multiline and width

Edit: (Partial solution given by This Question which was linked in comments and I've changed the code slightly; see EDIT at the bottom for the specific issue that remains)

I am trying to reproduce a specific layout of a csv file for a colleague. I've done so, but I had to do some really awful hacky things to get the spacing right on a table. The problem is that I need (more or less) specific width cells, which will force some of them to be multiple (vertical) lines, as well as needing some headers that will span multiple columns. Thus the content of the ensuing cells should ideally be centered within the (non merged) column/row intersections... but I can't seem to get it to work right without using some truly hideous \hspace* commands to force spacing eventually. Below is my MWE which is more or less the output I would like (the horizontal spacing still isn't quite right on the numbers, but I can't make it much better and it's honestly close enough) but there has to be a nice way to do this with \centering and/or the \tabularxcolumn and/or the \newcolumntype commands. Unfortunately after several hours of messing with it and reading documentation, I can't seem to figure out how to get it to work; I seem to not understand something about the syntax of these commands since all I get is errors whenever I change anything. (Side note: originally I used T for text column and wanted it to be twice the width of the S column, which would contain the numbers. I since abandoned that attempt since I can't figure out the syntax, but the commands remain).

So, to reiterate, the output is actually more-or-less fine (any improvement on the centering is great, but not really my question), but the way I get it in the code is truly hideous and I know there has to be a nice way to get this done. Google and tabularx documentation fails me (or, more accurately, I failed it) so I have to be missing some obvious bit of how the syntax is suppose to work because all I get is errors if I try to mess with it at all.

MWE:

\documentclass{article}
\usepackage[margin=2cm]{geometry}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{tabularx}
\usepackage{amssymb}

\renewcommand\tabularxcolumn[1]{>{\centering\arraybackslash}m{#1}}
\newcolumntype{T}{X}
\newcolumntype{S}{>{\centering\arraybackslash\hsize=.5\hsize}X}%

\begin{document}
\begin{center}
\Large \textbf{Teaching Assistant Classroom Observation Sheet}
\end{center}

\begin{tabularx}{\textwidth}{XXX}
Teaching Assistant: &&Course: \\
Evaluator: &&Date:
\end{tabularx}

\section{Preparation}
\begin{tabularx}{\textwidth}{| T | c | S S |S| S S |}\hline
Question & Not Observed & \multicolumn{2}{c |}{More Emphasis Needed} & &\multicolumn{2}{c |}{Fully Accomplished}\\ \hline
TA is well-prepared and able to work homework problems&& \hspace*{0.50cm}1\hspace*{0.50cm}& \hspace*{0.30cm}2\hspace*{0.30cm}& \hspace*{0.30cm}3\hspace*{0.30cm}& \hspace*{0.50cm}4\hspace*{0.50cm}& \hspace*{0.30cm}5\hspace*{0.30cm}\\ \hline
Knows material in text and lectures&& 1& 2& 3& 4& 5\\ \hline
Problem solving techniques are consistent with lecturer and text&& 1& 2& 3& 4& 5\\\hline
Promptly returns graded assignments&& 1& 2& 3& 4& 5\\ \hline
\end{tabularx}
\end{document}

PS: I tried to search for similar topics, but only seem to find requests to do either vertical or horizontal centering, and the couple I found that tried for both didn't handle the multi-line text blocks correctly... and since I couldn't decipher the syntax I couldn't seem to fix the examples I found in those threads to work for me.

EDIT I have edited the newcolumntype and \tabularxcolumn lines in my MWE to the following:

\renewcommand\tabularxcolumn[1]{>{\centering\arraybackslash}m{#1}}
\newcolumntype{T}{X}
\newcolumntype{S}{>{\centering\arraybackslash\hsize=.5\hsize}X}%

Now I have the issue that the \multicolumn command doesn't play nicely with the X column type, leaving some awkward overhang on the \hline command. I'd like a way to make the right hand side look a bit nicer.

• in what your question differ from tex.stackexchange.com/questions/316923/…. it seems to be duplicate to it – Zarko Sep 27 '18 at 16:55
• Well, my Google-Fu has failed as I didn't find that one. It is almost perfect! The issue I have (which I had with other 'solutions' I found) is that the X column doesn't play nicely with the \multicolumn command, which I need for a couple of the headers. It makes the lines not match up quite right on the right hand side... can't seem to find a particularly good solution aside from injecting some hspace to force the line over a bit. – Jason Sep 27 '18 at 17:10

your question is actually duplicate to this question, however since you have other issues in your table code, i will propose some improvements (see code, main changes are indicated by % <---):

\documentclass{article}
\usepackage[margin=2cm]{geometry}
\usepackage{cellspace, tabularx}      % <---
\setlength\cellspacetoplimit{4pt}     % <---
\setlength\cellspacebottomlimit{4pt}  % <---

\renewcommand\tabularxcolumn[1]{m{#1}}
\newcolumntype{C}{>{\centering\arraybackslash}X}
\newcommand\mcx[1]{\multicolumn{2}{>{\hsize=\dimexpr2\hsize+2\tabcolsep\centering}X|}{#1}} % <---

\begin{document}
\begin{table}[!ht]%
\setlength\tabcolsep{4pt}
\begin{tabularx}{\linewidth}{|>{\hsize=3\hsize}S{C} | c | CC | C | CC |}
\hline
Question
&   Not Observed
&   \mcx{More Emphasis Needed}
&   &   \mcx{Fully Accomplished}         \\
\hline
TA is well-prepared and able to work homework problems
&   & 1 & 2 & 3 & 4 & 5                                             \\
\hline
Knows material in text and lectures
&   & 1 & 2 & 3 & 4 & 5                                             \\
\hline
Problem solving techniques are consistent with lecturer and text
&   & 1 & 2 & 3 & 4 & 5                                             \\
\hline
&   & 1 & 2 & 3 & 4 & 5                                             \\
\hline
\end{tabularx}
\end{table}
\end{document}

which gives

• the cellspace package is used for adding some vertical space to cells' contents. this is dan with adding S specifier to selected column (in your case the firs one is appropriate)
• to preserve C cell features in preamble is added command \addparagraphcolumntypes{C}
• width of multicolumn cells is used macro \dimexpr. in calculation is consider width of two eidth of C cells and two \tabcolsep. with this its width is the same as width of two standard X, i.e. C cells.
• the table in put in float table environment that it is centered in text and that the settings inside table are limited only to this table. instead table you also can use center environment:

\begin{center}
\setlength\tabcolsep{4pt}
\begin{tabularx} ....

\end{tabularx}
\end{center}

• Ah, this is beautiful, thanks! Do you mind explaining the cellspace option and commands, and why you enclosed the tabular environment inside a table environment? I thought the point of using tabular (among others) is that it essentially already is a table environment? – Jason Sep 27 '18 at 18:01
• @Jason, see short explanation added to answer. – Zarko Sep 27 '18 at 18:16


text: Many people make the mistake of only developing a trading strategy – i.e., a strategy that determines the type of asset they want to trade and the level of risk they want to be exposed to. Little thought is given to the money management strategy. That is a mistake because a money management strategy will help you manage your balance so you can get through bad patches and maximize winning streaks.


text:
# MSP430 Pin Variables

I am trying to program an MSP430FR5969 for the first time. I successfully executed and modified a program to blink one of the LEDs connected to P1.0. The relevant predefined variable is P1OUT.

The other LED is connected to P4.6 but I do not know which variable corresponds to it. P4OUT doesn't seem to work, and I am not sure it is the right one because there are several pins: P4.4, P4.5, P4.6 and the variable P4OUT doesn't seem to differentiate between them.

What is the variable naming scheme? More importantly, what reference document would answer similar questions?

• If you're blinking P1OUT then you're blinking all the pins on port 1, not just the zeroth pin. – Samuel Jul 13 '14 at 7:13
• yes, thanks, i've learned that! the original sample program from TI had the line P1OUT ^= 0x01; // Toggle P1.0 using exclusive-OR which has a lot more nuance in it than i could appreciate at first sight :) – necromancer Jul 13 '14 at 7:22

the . means a particular bit of a multi-bit output. P4 is not really one pin but a bank of pins! :)

    P4DIR |= BIT6;  /* set P4.6 to output */
P4OUT |= BIT6;  /* set P4.6 to 1 */
P4OUT &= ~BIT6; /* set P4.6 to 0 */

The MSP430 does not technically have individual pin control. Instead, you have to control the entire register at once. P1OUT is the name of the register, not the pin.

In order to turn on, let's say, P1.0 and P1.6 (both are in the P1OUT register), you would first have to set them to output (P1DIR = 0b01000001; //or 0x41) and then set the value of the register (P1OUT = 0b01000001; /or 0x41). Notice that the value you are assigning to the port is 8 bits, which corresponds to the 8 pins connected to the P1OUT register.

If you want to, for example, toggle just one of the pins without changing the rest of the port, you can either set the value manually, or you can always use bitwise operations, like P1OUT ^= 0b00000001;. This toggles bit 0 without affecting any of the other pins. Besides exclusive OR (^), you have bitwise AND (&), bitwise OR (|), etc. You use these to change the individual pins without changing the entire port value. If you look in the header file, you may also find defines, such as:

#define BIT0                   (0x0001)
#define BIT1                   (0x0002)
#define BIT2                   (0x0004)

So you can say P1OUT ^= BIT0; to toggle bit 0.

If you would like to have the illusion that you're controlling one pin at a time, you can use the following functions:

#include <stdint.h>

typedef enum {
LED_GREEN = BIT6,
LED_RED = BIT0
} PIN_Def;

static inline void set_pin(uint8_t volatile * const port, PIN_Def pin) {
*port |= pin;
}
static inline void clear_pin(uint8_t volatile * const port, PIN_Def pin) {
*port &= ~pin;
}
static inline uint8_t test_pin(uint8_t volatile * const port, PIN_Def pin) {
return *port & pin;
}
static inline void toggle_pin(uint8_t volatile * const port, PIN_Def pin) {
*port ^= pin;
}

Then, to toggle BIT0, all you would need to do is call the following from inside main:

toggle_pin(P1OUT, LED_RED);

You can use the functions to set, clear, check, and toggle pin states.

Source: TI Forums


text:
# Introduction to SGX¶

Graphene project uses SGX to securely run software. SGX is a complicated topic, which may be hard to learn, because the documentation is scattered through official/reference documentation, blogposts and academic papers. This page is an attempt to curate a dossier of available reading material.

SGX is an umbrella name of technology that comprises several parts:

• CPU/platform hardware features: the new instruction set, new microarchitecture with the PRM (EPC) memory region and some new MSRs and some new logic in the MMU and so on;
• the SGX Remote Attestation infrastructure, online services provided by Intel and/or third parties (see DCAP);
• SDK and assorted software.

SGX is still being developed. The current (March 2020) version of CPU features is referred to as “SGX1” or simply “SGX” and is more or less finalized. All new/changed instructions from original SGX are informally referred to as “SGX2”.

Features which might be considered part of SGX2:

• EDMM (Enclave Dynamic Memory Management) is part of SGX2
• FLC (Flexible Launch Control), not strictly part of SGX2, but was not part of original SGX hardware either

As of now there is hardware support (on a limited set of CPUs) for FLC and (on an even more limited set of CPUs) SGX2/EDMM. Most of the literature available (especially introduction-level) concerns original SGX1 only.

## Installation Instructions¶

Todo

TBD

### Linux kernel drivers¶

For historical reasons, there are three SGX drivers currently (January 2021):

• https://github.com/intel/linux-sgx-driver – old one, does not support DCAP, deprecated

• https://github.com/intel/SGXDataCenterAttestationPrimitives/tree/master/driver – new one, out-of-tree, supports both non-DCAP software infrastructure (with old EPID remote-attestation technique) and the new DCAP (with new ECDSA and more “normal” PKI infrastructure).

• SGX support was upstreamed to the Linux mainline starting from 5.11. It currently supports only DCAP attestation. The driver is accessible through /dev/sgx_enclave and /dev/sgx_provision.

The following udev rules are recommended for users to access the SGX node:

groupadd -r sgx
cat > /etc/udev/rules.d/65-graphene-sgx.rules << EOF
SUBSYSTEM=="misc",KERNEL=="sgx_enclave",MODE="0660",GROUP="sgx"
SUBSYSTEM=="misc",KERNEL=="sgx_provision",MODE="0660",GROUP="sgx_prv"
EOF

Also it will not require IAS and kernel maintainers consider non-writable FLC MSRs as non-functional SGX: https://lore.kernel.org/lkml/20191223094614.GB16710@zn.tnic/

The chronicle of kernel patchset:

v1 (2016-04-25)
https://lore.kernel.org/lkml/1461605698-12385-1-git-send-email-jarkko.sakkinen@linux.intel.com/
v2
?
v3
?
v4 (2017-10-16)
https://lore.kernel.org/lkml/20171016191855.16964-1-jarkko.sakkinen@linux.intel.com/
v5 (2017-11-13)
https://lore.kernel.org/lkml/20171113194528.28557-1-jarkko.sakkinen@linux.intel.com/
v6 (2017-11-25)
https://lore.kernel.org/lkml/20171125193132.24321-1-jarkko.sakkinen@linux.intel.com/
v7 (2017-12-07)
https://lore.kernel.org/lkml/20171207015614.7914-1-jarkko.sakkinen@linux.intel.com/
v8 (2017-12-15)
https://lore.kernel.org/lkml/20171215202936.28226-1-jarkko.sakkinen@linux.intel.com/
v9 (2017-12-16)
https://lore.kernel.org/lkml/20171216162200.20243-1-jarkko.sakkinen@linux.intel.com/
v10 (2017-12-24)
https://lore.kernel.org/lkml/20171224195854.2291-1-jarkko.sakkinen@linux.intel.com/
v11 (2018-06-08)
https://lore.kernel.org/lkml/20180608171216.26521-1-jarkko.sakkinen@linux.intel.com/
v12 (2018-07-03)
https://lore.kernel.org/lkml/20180703182118.15024-1-jarkko.sakkinen@linux.intel.com/
v13 (2018-08-27)
https://lore.kernel.org/lkml/20180827185507.17087-1-jarkko.sakkinen@linux.intel.com/
v14 (2018-09-25)
https://lore.kernel.org/lkml/20180925130845.9962-1-jarkko.sakkinen@linux.intel.com/
v15 (2018-11-03)
https://lore.kernel.org/lkml/20181102231320.29164-1-jarkko.sakkinen@linux.intel.com/
v16 (2018-11-06)
https://lore.kernel.org/lkml/20181106134758.10572-1-jarkko.sakkinen@linux.intel.com/
v17 (2018-11-16)
https://lore.kernel.org/lkml/20181116010412.23967-2-jarkko.sakkinen@linux.intel.com/
v18 (2018-12-22)
https://lore.kernel.org/linux-sgx/20181221231134.6011-1-jarkko.sakkinen@linux.intel.com/
v19 (2019-03-20)
https://lore.kernel.org/lkml/20190320162119.4469-1-jarkko.sakkinen@linux.intel.com/
v20 (2019-04-17)
https://lore.kernel.org/lkml/20190417103938.7762-1-jarkko.sakkinen@linux.intel.com/
v21 (2019-07-13)
https://lore.kernel.org/lkml/20190713170804.2340-1-jarkko.sakkinen@linux.intel.com/
v22 (2019-09-03)
https://lore.kernel.org/lkml/20190903142655.21943-1-jarkko.sakkinen@linux.intel.com/
v23 (2019-10-28)
https://lore.kernel.org/lkml/20191028210324.12475-1-jarkko.sakkinen@linux.intel.com/
v24 (2019-11-30)
https://lore.kernel.org/lkml/20191129231326.18076-1-jarkko.sakkinen@linux.intel.com/
v25 (2020-02-04)
https://lore.kernel.org/lkml/20200204060545.31729-1-jarkko.sakkinen@linux.intel.com/
v26 (2020-02-09)
https://lore.kernel.org/lkml/20200209212609.7928-1-jarkko.sakkinen@linux.intel.com/
v27 (2020-02-23)
https://lore.kernel.org/lkml/20200223172559.6912-1-jarkko.sakkinen@linux.intel.com/
v28 (2020-04-04)
https://lore.kernel.org/lkml/20200303233609.713348-1-jarkko.sakkinen@linux.intel.com/
v29 (2020-04-22)
https://lore.kernel.org/lkml/20200421215316.56503-1-jarkko.sakkinen@linux.intel.com/
v30 (2020-05-15)
https://lore.kernel.org/lkml/20200515004410.723949-1-jarkko.sakkinen@linux.intel.com/

## SGX terminology¶

Architectural Enclaves
AE

Architectural Enclaves (AEs) are a set of “system” enclaves concerned with starting and attesting other enclaves. Intel provides reference implementations of these enclaves, though other companies may write their own implementations.

AEP

Todo

TBD

AEX

Todo

TBD

Attestation

Attestation is a mechanism to prove the trustworthiness of the SGX enclave to a local or remote party. More specifically, SGX attestation proves that the enclave runs on a real hardware in an up-to-date TEE with the expected initial state. There are two types of the attestation: Local Attestation and Remote Attestation. For local attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Report using the EREPORT hardware instruction. For remote attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Quote using the Quoting Enclave (and the Provisioning Enclave if required). The enclave then may send the collected attestation evidence to the local or remote party, which will verify the evidence and confirm the correctness of the attesting enclave. After this, the local or remote party trusts the enclave and may establish a secure channel with the enclave and send secrets to it.

Data Center Attestation Primitives
DCAP

A software infrastructure provided by Intel as a reference implementation for the new ECDSA/PCS-based remote attestation. Relies on the Flexible Launch Control hardware feature. In principle this is a special version of SDK/PSW that has a reference launch enclave and is backed by the DCAP-enabled SGX driver.

This allows for launching enclaves without Intel’s remote infrastructure. But this requires deployment of own infrastructure, so is operationally more complicated. Therefore it is intended for server environments (where you control all the machines).

Orientation Guide
EPID
A way to launch enclaves with Intel’s infrastructure, intended for client machines.
Enclave

Todo

TBD

Enclave Dynamic Memory Management
EDMM
A hardware feature of SGX2, allows dynamic memory allocation, which in turn allows dynamic thread creation.
Enclave Page Cache
EPC

Todo

TBD

Enclave Page Cache Map
EPCM

Todo

TBD

Enhanced Privacy Identification
Enhanced Privacy Identifier
EPID

Todo

short description

Contrary to DCAP, EPID may be understood as “opinionated”, with most moving parts fixed and tied to services provided by Intel. This is intended for client enclaves and deprecated for server environments.

DCAP
A way to launch enclaves without relying on the Intel’s infrastructure.
Flexible Launch Control
FLC

Hardware (CPU) feature that allows substituting Launch Enclave for one not signed by Intel. A change in SGX’s EINIT logic to not require the EINITTOKEN from the Intel-based Launch Enclave. An MSR, which can be locked at boot time, keeps the hash of the public key of the “launching” entity.

With FLC, Launch Enclave can be written by other companies (other than Intel) and must be signed with the key corresponding to the one locked in the MSR (a reference Launch Enclave simply allows all enclaves to run). The MSR can also stay unlocked and then it can be modified at run-time by the VMM or the OS kernel.

Support for FLC can be detected using CPUID instruction, as CPUID.07H:ECX.SGX_LC[bit 30] == 1 (SDM vol. 2A calls this “SGX Launch Control”).

Launch Enclave
LE

Todo

TBD

Local Attestation

In local attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Report using the EREPORT hardware instruction. This form of attestation is used to send the attestation evidence to a local party (on the same physical machine).

Intel Attestation Service
IAS

Internet service provided by Intel for “old” EPID-based remote attestation. Enclaves send SGX quotes to the client/verifier who will forward them to IAS to check their validity.

PCS
Provisioning Certification Service, another Internet service provided by Intel.
Memory Encryption Engine
MEE

Todo

TBD

OCALL

Todo

TBD

SGX Platform Software
PSW
Software infrastructure provided by Intel with all special Architectural Enclaves (Provisioning Enclave, Quoting Enclave, Launch Enclave). This mainly refers to the “old” EPID/IAS-based remote attestation.
Processor Reserved Memory
PRM

Todo

TBD

Provisioning Enclave
PE

One of the Architectural Enclaves of the Intel SGX software infrastructure. It is part of the SGX Platform Software. The Provisioning Enclave is used in EPID based remote attestation. This enclave communicates with the Intel Provisioning Service (IPS) to perform EPID provisioning. The result of this provisioning procedure is the private EPID key securely accessed by the Provisioning Enclave. This procedure happens only during the first deployment of the SGX machine (or, in rare cases, to provision a new EPID key after TCB upgrade). The main user of the Provisioning Enclave is the Quoting Enclave.

Provisioning Certification Enclave
PCE

One of the Architectural Enclaves of the Intel SGX software infrastructure. It is part of the SGX Platform Software and DCAP. The Provisioning Certification Enclave is used in DCAP based remote attestation. This enclave communicates with the Intel Provisioning Certification Service (PCS) to perform DCAP provisioning. The result of this provisioning procedure is the DCAP/ECDSA attestation collateral (mainly the X.509 certificate chains rooted in a well-known Intel certificate and Certificate Revocation Lists). This procedure happens during the first deployment of the SGX machine and then periodically to refresh the cached attestation collateral. Typically, to reduce the dependency on PCS, a cloud service provider introduces an intermediate caching service (Provisioning Certification Caching Service, or PCCS) that stores all the attestation collateral obtained from Intel. The main user of the Provisioning Certification Enclave is the Quoting Enclave.

Intel Provisioning Service
IPS
Internet service provided by Intel for EPID-based remote attestation. This service provides the corresponding EPID key to the Provisioning Enclave on a remote SGX machine.
Intel Provisioning Certification Service
PCS

New internet service provided by Intel for new ECDSA-based remote attestation. Enclave provider creates its own internal Attestation Service where it caches PKI collateral from Intel’s PCS, and the verifier gets the certificate chain from the enclave provider to check validity.

IAS
Intel Attestation Service, another Internet service.
Quoting Enclave
QE

One of the Architectural Enclaves of the Intel SGX software infrastructure. It is part of the SGX Platform Software. The Quoting Enclave receives an SGX Report and produces a corresponding SGX Quote. The identity of the Quoting Enclave is publicly known (it signer, its measurement and its attributes) and is vetted by public companies such as Intel (in the form of the certificate chain ending in a publicly known root certificate of the company).

Remote Attestation

In remote attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Quote using the Quoting Enclave (and the Provisioning Enclave if required). This form of attestation is used to send the attestation evidence to a remote party (not on the same physical machine).

Intel SGX Software Development Kit
Intel SGX SDK
SGX SDK
SDK
In the context of SGX, this means a specific piece of software supplied by Intel which helps people write enclaves packed into .so files to be accessible like normal libraries (at least on Linux). Available together with a kernel module and documentation.
SGX Enclave Control Structure
SECS

Todo

TBD

SGX Quote
The SGX quote is the proof of trustworthiness of the enclave and is used during Remote Attestation. The attesting enclave generates the enclave-specific SGX Report, sends the request to the Quoting Enclave using Local Attestation, and the Quoting Enclave returns back the SGX quote with the SGX report embedded in it. The resulting SGX quote contains the enclave’s measurement, attributes and other security-relevant fields, and is tied to the identity of the Quoting Enclave to prove its authenticity. The obtained SGX quote may be later sent to the verifying remote party, which examines the SGX quote and gains trust in the remote enclave.
SGX Report
The SGX report is a data structure that contains the enclave’s measurement, signer identity, attributes and a user-defined 64B string. The SGX report is generated using the EREPORT hardware instruction. It is used during Local Attestation. The SGX report is embedded into the SGX Quote.
SGX2

This refers to all new SGX instructions and other hardware features that were introduced after the release of the original SGX1.

Encompasses at least EDMM, but is still work in progress.

State Save Area
SSA

Todo

TBD

Security Version Number
SVN

Todo

TBD

Trusted Execution Environment
TEE
A Trusted Execution Environment (TEE) is an environment where the code executed and the data accessed are isolated and protected in terms of confidentiality (no one has access to the data except the code running inside the TEE) and integrity (no one can change the code and its behavior).
Trusted Computing Base
TCB

In context of SGX this has the usual meaning: the set of all components that are critical to security. Any vulnerability in TCB compromises security. Any problem outside TCB is not a vulnerability, i.e. should not compromise security.

In context of Graphene there is also a different meaning (Thread Control Block). Those two should not be confused.


text:
## LaTeX forum ⇒ MiKTeX and proTeXt ⇒ Configuration of TeXnicCenter with MiKTeX

Information and discussion about MikTeX distribution for Windows and the related proTeXt: Installing, updating, configuring
scootie49
Posts: 1
Joined: Mon Jun 04, 2007 6:51 pm

### Configuration of TeXnicCenter with MiKTeX

I just installed TeXnicCenter on a different computer. I don't know how to answer:

"Enter the full path of the directory, where the executables, (latex, tex, etc) of your TEX distribution are located"

I have MiKTeX installed on my computer, so I just don't know the path to type in. I seem to remember it being something about a "bin".

Any help would be appreciated. Thanks.

localghost
Site Moderator
Posts: 9204
Joined: Fri Feb 02, 2007 12:06 pm
Just look into the (standard) installation folder of your system partition. It depends a little bit on the MiKTeX system installed. Here is an example for MikTeX 2.6 in the standard folder.
`C:\Program Files\MiKTeX 2.6\MiKTeX\bin`

You have to add the name of the binary that is to be executed to give TeXnicCenter the full path.
`C:\Program Files\MiKTeX 2.6\MiKTeX\bin\latex.exeC:\Program Files\MiKTeX 2.6\MiKTeX\bin\latex.exeC:\Program Files\MiKTeX 2.6\MiKTeX\bin\pdflatex.exeC:\Program Files\MiKTeX 2.6\MiKTeX\bin\bibtex.exeC:\Program Files\MiKTeX 2.6\MiKTeX\bin\makeindex.exe`

Just to mention a few. Note that there are more binaries required like dvips. You can find them in the same path.
LaTeX Community Moderator

¹ System: openSUSE 42.2 (Linux 4.4.52), TeX Live 2016 (vanilla), TeXworks 0.6.1

tolee
Posts: 1
Joined: Fri Dec 20, 2019 6:08 pm
pliss sir..i want it


text:
# Critical temperature for carbon dioxide and methane are 31.1 °C and –81.9 °C respectively.

Question:

Critical temperature for carbon dioxide and methane are 31.1 °C and –81.9 °C respectively. Which of these has stronger intermolecular forces and why?

Solution:

Higher is the critical temperature of a gas, easier is its liquefaction. This means that the intermolecular forces of attraction between the molecules of a gas are directly proportional to its critical temperature. Hence, intermolecular forces of attraction are stronger in the case of CO2.