contact_fusion

7 lat temudiscuss

My suspicion is that you are thinking of the tool VisIt ( https://wci.llnl.gov/simulation/computer-codes/visit/ ). VisIt vs yt has some tradeoffs, but by and large it is very useful for rapidly visualizing numerical simulations and supports a large variety of them. I use it daily.

contact_fusion

7 lat temudiscuss

It's already been said that, essentially, most PhD graduates are in a state of delusion - the truth is that nobody would make a rational decision to become an adjunct. This is very true. What I think still needs to be said that most PhD graduating institutions actively perpetuate these delusions. (In disclosure, I am associated with an academic institution doing academic research, but I am not an adjunct. Thankfully.)

There is really next to no value in taking on PhD work at an institution below a certain threshold. Nearly all tenure-track positions go to candidates with a very select background. They must have graduated from the top 30 (or so) institutions in their field. They usually have done a postdoc at another peer institution in that class. They need to have produced a large number of publications, which usually means having well connected collaborators, especially your PI/advisor. If you do not have this background, you stand little chance of even being considered for the tenure track.

That being said, the lower tier institutions are less capable of supporting their faculty, so they pad this with cheap labor in the form of PhD students. The selection hierarchy begins even before graduate school - whether you attend an elite institution in your field is a major academic accomplishment in itself. Many are tempted to take the consolation prize when they don't make it, and the faculty at the lower tier schools are all too happy to accommodate them.

The tenured faculty will never change this on their own. They are the winners, whose continuing success depends on a ready supply of people who are deceived into thinking that they actually have a shot. For some, this deceit is only a moderate one - if you are at an elite school you have maybe a 1 in 10 chance. For most, the rate is approximately zero. Very few people are willing to really give their students a realistic assessment, but in the end it doesn't matter whether they do anyway. Graduate school is like trying to get published as a novelist, or becoming a professional athlete. Everyone wants that kind of status. Heck, you can definitely support yourself, depending on what level of asceticism you can tolerate and how lucky, well connected, or (rarely) brilliant you are. It is just that the vast majority makes very little money/status, and a privileged few make a large amount. There will never be a shortage of people who try to make it anyway. Some would say the entire enterprise depends on it.

(edit - clarification)

contact_fusion

8 lat temudiscuss

No, graduate students in general have no leverage over their advisors. A single word from your advisor and you're out of the field.

There is little incentive to root out professors for any reason. The process of becoming a professor (grad school -> postdoc (N times) -> tenure track faculty -> tenured professor) is generally believed (by tenured professors, of course) to root out anyone unworthy of the position. You can believe what you want about the efficiency of such a process.

Public shame requires public understanding of scientific (mal)practice, so, good luck communicating that. Most of the time, the bad actors in question have already gotten papers past referees; what makes you think the public is capable of more thorough review?

Fraud is considered a serious allegation and as a result accusing someone of it requires going through a thorough process involving a host of university administrators, whose incentives are aligned with the profit motives of the university system.

Transferring graduate schools is essentially impossible, and even in the exceptionally rare circumstances that it happens, it always involves burnt bridges and often has to do with bigger fish (i.e. your advisor being offered a position elsewhere, and you're lucky enough they take you with them.) Without external funding to support you, you are usually replaceable. All graduate departments receive applications far in excess of the number of students they can support. They certainly will not consider taking on another from a school at which you've proven to be a problem. Academia has already established a quite successful leaky pipeline; the beginning (graduate school) is no different.

In academia, hierarchy is the rule, flat organizations the exception. You must purchase your influence, usually at significant cost (and luck is a significant component). As an undergraduate, the system is designed to cater to your interests; as a graduate student, you cater to the university's interests. Scientific integrity is a noble notion, and in some corners of academia, it survives, but it does so in spite of bad actors who thrive in a system designed to produce ten times the number of qualified applicants for each job, all of whom are judged according to easily gamed metrics. It would be nice if things weren't this way.

But the problem is, typically... if you decide to get a PhD in science, it is possible that you're already too obsessed with the subject to ever, truly, give it up, especially if it's "just" over working conditions. I can't speak for everyone, but most people leave because they were forced to.

contact_fusion

8 lat temudiscuss

Liquefaction has nothing to do with triboelectricity.

The article has a pretty good description of how liquefaction proceeds: higher pressure -> water present in material reduces contact between solid particles -> material friction reduced -> material behaves like a fluid. If you want more, find a book on basic rheology. I'm certain there are civil engineering textbooks that contain the material.

Further, it does not stand to reason that charged materials would suddenly acquire fluid properties. Solid materials are quite capable of sustaining charge without changing their bulk properties. Prior to significant change, local voltages would exceed the breakdown voltage and the charge would be neutralized.

contact_fusion

8 lat temudiscuss

Keep in mind that you are viewing the orbit in projection. The axes are simply the angular offset from the pointing.

Before I give away the punchline, try to imagine the orbit in a reference frame centered at the location of the black hole. Obviously, the motion should be elliptic; lets define a Cartesian coordinate system such that, say, the x-y plane coincides with the plane of the elliptic orbit. Now, we know that the black hole should reside at the focus of this orbit. But, as a far away observer, what are the chances that you would be seeing the orbit exactly face-on - i.e., you are sitting on the z axis, just really far away?

So, yes, the black hole is at the focus of the elliptic orbit, not the focus of the ellipse formed from the projection of the orbit onto your plane-of-sky, which geometry tells us is also an ellipse.

BTW, this isn't a problem for the astronomers. You can back out exactly what that inclination of the orbit is, provided you can measure the line-of-sight velocities of the star. (Actually, relative velocities will do; no absolute calibration necessary.) This is easily done by looking for some distinctive stellar spectral features and noting their relative shifts at different parts of the orbit. From this you can reconstruct the orbit completely. The key scientific results they derived was the even subtler redshift of these spectral features as the gravitational field grew stronger when the star approached the black hole.

edit: actually, you could do even better, and use the offset of the black hole from the elliptic focus, and use projective geometry to get the inclination angle!

contact_fusion

8 lat temudiscuss

The sound wave is not a "by-product." It is precisely the phenomenon you are describing. And while we are discussing equations and distribution functions, you might as well get the equation right: wave phenomena arise when the equations of motion are hyperbolic PDEs. Such systems involve the Laplacian, not just the gradient. Indeed, the physics of such systems are typically studied as a whole, in terms of... wave phenomena.

Further, not all waves require a medium. Light and gravitational waves are prominent examples. There is nothing to reduce these phenomena to, except for the fields themselves, whose form is dictated by... a wavelike solution.

While we are at it, let me disabuse you of your explanation of the sound speed. Turns out that the sound speed is a thermodynamic quantity; it is the speed at which small wavelike perturbations propagate. To properly derive the sound speed, one must linearize the Euler equations, and then adopt a thermodynamic equation of state, from which the sound speed is derived. It is, emphatically, not the speed at which molecules move.

Finally, it is obvious that you did not understand what I was driving at with respect to color. I agree wholeheartedly that we have no true color, within our minds, with which to perceive, say, soft x-rays. But this issue has to do with our own neurobiology, not fundamental physics. Comparing the two is what is problematic. There is little reason to suspect that our mental limitations have anything to do with anything but evolutionary necessity. Such limitations are categorically different than, say, the speed of light.

contact_fusion

8 lat temudiscuss

But a more complete notion of "object" isn't what solved the problem.

Much of what constituted physics prior to the advances by Galileo and Newton (and many others) was essentially what was developed by Aristotle. Within the Aristotelian framework, which is what most educated people knew at the time, the concept of a distinct "object" is perfectly well defined. My point is that the natural philosophers at the time were quite capable of asking the question, "do heavier objects fall faster?" without being led astray by an incomplete notion of "object." In other words, the problem is conceptual, not semantic. The Aristotelian - again, the dominant framework back then - was instead led astray by the notion that all objects had a "natural" tendency to move towards the center of the Earth, and that this tendency was stronger for heavier objects. This worldview had a very long history, and a fair amount of evidence (such as it was) to back it up.

In this context, what matters is not the distinct objects but instead what properties influence their dynamics. It should be clear then why it was necessary to demonstrate the empirical truth. Many plausible theories had emerged, including the prevailing Aristotelian one, which accounted for the differences in, say, a lead weight falling versus a feather. Or, to get back to your original example, the Aristotelian would have answered, probably confidently, that yes, your chain of cannonballs would fall faster than separate ones. Your (correct Newtonian) intuition is that the mere act of chaining them together should not alter them, given that the threads would not exert forces in free fall, and therefore mere mass should not alter the falling rate. But, those notions depend entirely on the Newtonian framework. "Force" and "free fall" are the undefined concepts, not "object."

A key insight was needed, namely that you could separate out different causes in the motion; in this case, gravity and air resistance. (Though, of course, "cause" is itself a thorny concept...) Galileo's experiments demonstrated the point elegantly. More formally, this resulted in the development of the notions of inertial reference frames and linearity, which underpin much of classical physics.

I hope you don't think I'm belaboring the point. Newton's revolution was so total, so complete, that it changed everything about how we think about physical problems. Centuries of difficult philosophical and scientific work has been condensed down into a semester of freshman physics. To us, the problem is trivial, and it is easy to think that such experiments are so trivial as to be useless. To Galileo, this would not have been the case. A single thought experiment would not have been enough back then, even though it suffices now.

contact_fusion

8 lat temudiscuss

I wouldn't say that general relativity suggests that gravity is an "ambient side effect" of material presence. It means precisely that the geometry of spacetime is determined by the matter-energy content within that spacetime; and that matter moves on geodesics dictated by spacetime. I suppose that I am forced to accept that whether you think gravity is more like a shadow of matter than an active participant in dynamics is somewhat up to you, provided that you get the physics correct. If you don't, then your perspective is wrong.

Glancing at some of the other things you've said in the thread, you seem to be convinced that some waves, like sound waves, are somehow illusory. Let me assure you, there is nothing illusory about wave phenomena, both in general and with gravitational waves in particular. Anything that produces wave-like phenomena can be said to radiate emissions, to paraphrase, and in many cases, there is nothing really more "fundamental" than the wave.

As for the concept of color, I suppose it depends on what you mean by color. Color as defined by the wavelength/frequency of light is perfectly well defined outside of the visible spectrum. As a mental concept, I don't see why it is "irreducible." I suppose you are attempting to say that the universal speed of light is somehow fundamental... but in the same way that a "redder" red is impossible? This is a dubious analogy. It confuses the limitations of the mind with fundamental physics.

contact_fusion

8 lat temudiscuss

It may seem obvious to our modern eyes, but the notion that objects of different mass fall at the same rate is not at all obvious outside of the framework of physics that Galileo helped build.

Without proper notions of force, gravity, mass, density, and the form of the laws of gravity, surely you realize that the answer to your hypothetical is not trivial. This was kind of the whole point of Principia.

contact_fusion

8 lat temudiscuss

High energy density systems are quite hard to develop an intuition for.

While average kinetic energy is one way to think about temperature, think about it instead in terms of the Maxwellian particle distribution [1]. In this sense, the Maxwellian is a parameter of this distribution, and as it increases, the location of the distribution changes. A high temperature corresponds to, in this hypothetical system, more particles with higher velocities in the system. (This technically only applies to certain systems in which the assumptions hold. For example, in systems in which other degrees of freedom matter, such as vibration/rotation of molecules, the interpretation is harder. At high temperatures, these degrees of freedom are destroyed, though others, like ionization, can matter significantly.) Of course, these systems are highly collisional, in the sense that each particle will probably go only a short distance before Coulomb scattering off another particle. So the particles are not really vibrating; the energy is in translational motion, but in the mean, there is no real directionality to it, so the particles won't typically stream out of the plasma.

This can be readily understood in the context of achieving controlled fusion. Nuclei are positively charged, and therefore exert forces that tend to repel them away from other nuclei. The nuclear scale, at which nuclear reactions must occur, is very small, and the 1/r* Coulomb potential is quite large at those distances. As a result, it is to be expected that an individual fusion reaction should only occur when the kinetic energy of an incoming nucleus is sufficiently strong to overcome the Coulomb barrier. (Practically, quantum mechanics effectively reduces the barrier through tunneling, but nevertheless it is quite high.) As a result, you need a sufficiently large number of nuclei with high speed to have an appreciable fusion rate, i.e. your temperature must be high enough. (Hence, "thermonuclear" fusion.) This has to be contrasted with your confinement quality, in the sense that you have to keep your fuel at that temperature and at a sufficient density (so that your collision rate is high enough) long enough for fusion burn to consume an appreciable fraction of your fuel.

In context, the temperature seems a simpler quantity to discuss rather than the pressure. It is easier to conceive of this pressure as a momentum flux, and in stars, gravitational confinement demands that the plasma pressure balance the crushing momentum flux of the weight of the star. Such static pressures are simply outside of our ability to intuit, and result in quite counterintuitive properties of matter.

[1] https://en.wikipedia.org/wiki/Maxwell-Boltzmann_distribution

*edit: inverse square is the force, the potential goes as 1/r... update for clarity.

contact_fusion

8 lat temudiscuss

Other replies have explained that the ions and electrons can be at different temperatures, and that is of course true. I can offer some more explanation why. While you have linked temperature to some average kinetic energy, this is not a strictly accurate notion of temperature. Temperature only means something in the context of thermodynamic equilibrium; for any system out of equilibrium, often a temperature cannot be defined, even as an average kinetic energy. The two concepts are linked to each other, in the sense that an average kinetic energy at the particle scale is a significant (and sometimes only, but not always) component of the internal energy of the system. But temperature is first and foremost an equilibrium concept.

A plasma is composed of both ions (partially ionized atoms, or if they are fully ionized, bare nuclei) and electrons. Together, they constitute two co-located but separate fluids, whose motions may be distinct; indeed, because electrons are so much lighter than ions, they respond to forces much more readily. In equilibrium, a single fluid must have sufficiently rapid interactions so that the particle distributions are driven to a Maxwellian. In that case, for a single fluid, a temperature is well defined. In the case of a two-fluid system, self-interactions (such as interactions between ions and themselves, and electrons and themselves) may be sufficient to establish two separate equilibria corresponding to each fluid; hence, the electron vs. ion temperature. Only in the case that ion-electron interactions are sufficiently rapid would those equilibria be driven together to a single-temperature fluid, in which case, Te = Ti.

This picture becomes rapidly more complicated at very high temperature (usually, around 0.1 keV or about a million K), at which point the photons being exchanged by hot charged particles become dynamically important, and a third temperature, the radiation temperature, may emerge. At this point, the plasma must be described using three temperatures - if, and only if, you are in a situation lucky enough for equilibrium to manifest. (Fortunately, equilibrium is not usually that hard to access.) In many cases, such as when the system undergoes a strong shock, the system may be driven very far from equilibrium, but only temporarily. In others, some underlying energetic process may continuously drive the system away from equilibrium, resulting in a metastable state; this is the case in stellar atmospheres, in which NLTE (non-local thermodynamic equilibrium) processes matter a great deal. Usually, physicists resort to kinetic theory to try to understand such situations.

contact_fusion

8 lat temudiscuss

It sounds like you have a particular viewpoint - atheistic ethical relativism. I'm sure you can appreciate that the existence of god and the existence of universal ethics are two separate questions. (Example: a universe with a god, just one that is morally ambiguous.)

Of course Taleb has condensed several different thoughts into a single aphorism. One might be that laws (civilizations, governments) tend to not last as long as broad ethical traditions. Another is the observation that what is legal is rarely what is right. Yet another is framing what should be a guide to your behavior: do what is most consistent with what you believe is right, not what is legal.

Some of what you are saying is related to the grand challenge of ethical philosophy. But your solution, relying on the law, will probably result in some pretty bad consequences, especially when you think about how laws are made - and that laws are sometimes used as a cover for bad behavior. Taleb is saying (among other things) that you should think about your ethical choices on the terms of your own ethics rather than appealing to some other authority (the law) as a guide for your actions. He is being a bit pretentious while making this point but the logic is sound, I think.

Personally I agree that Taleb's point about grandmotherly knowledge is a bit silly, but I think the underlying idea is well taken. Absent any fundamental understanding of how the world works, people still had to figure out how to survive in that world. Those that survived probably have made some choices that - perhaps in hindsight - aren't that dumb. That being said, the world is changing faster than ever before, so I think Taleb's analogy is very weak. I also find his point to be in contradiction with other things he has said before: notice that he has assigned some meaningless quantification of uncertainty ("90%") to the quality of this grandmotherly knowledge. Such a number has no basis in reality, and stinks of the type of probabilistic ignorance he rails against.

contact_fusion

8 lat temudiscuss

Feynman lectures are excellent for physical intuition but if someone doesn't have a few years of practice with physics it will be difficult to get much out of it. Feynman also doesn't have a lot in the way of problem solving, even with the companion problem solving book.

With that in mind, Landau/Lifshitz is an entirely different class. I'm a practicing astrophysical theorist and I would never claim to have grokked these volumes in anything nearing completeness. A serious post-PhD program of study can be undertaken to understand to the finer points of those books; this is a pursuit that would challenge any practitioner. (I place Physics of Shock Waves and High Temperature Hydrodynamic Phenomena by Zel'dovich and Razier in the same category of extremely information dense Soviet tracts on physics.) They are incredibly valuable, although I do think there is a bit of an element of "if you don't know L/L, you aren't a real theorist."

I think that recommending these texts is great for someone down the road, but if someone hasn't even had a full year of intro physics recommending these is not appropriate. Intro-level textbooks exist for a reason - not all of them are cheap, watered down versions of the "real stuff." (Some are, of course.) There are also some texts I've found (but don't remember, unfortunately) in the computer vision community that introduce some physics that would be great for someone with a computer science/engineering background.

edit: "cheap" as in "cheap feeling" not inexpensive, as most of those intro texts are more expensive than the graduate level

contact_fusion

8 lat temudiscuss

I know this may be perceived as nitpicking, but I am generally annoyed whenever the reproducibility/reliability crisis is referred to as a problem in science, writ large, rather than a specific problem in specific scientific subfields. This seems to be particularly common when the articles are written by practitioners within these subfields, such as neuroscience, biology, or psychology.

There is no reproducibility crisis in my field of science - astrophysics. To back this claim up, I searched at Retraction Watch for any mention of the top tier journals in astronomy & astrophysics - specifically, ApJ [1], MNRAS [2], A&A (none found), Icarus (none found), Nature Astronomy (none found) - and found exactly one correction and one retraction. Now certainly errata are published constantly, and I would be foolish to assume that just because Retraction Watch didn't catch many instances of scientific fraud or abuse within my field, that it practically doesn't exist. But no evidence for a "crisis" seems to exist, at least in my corner of science. Astrophysical research appears to be quite reliable and reproducible. For similar reasons, I haven't heard of a reproducibility crisis in analytical chemistry, or optical physics, or mathematics, to name a few - or, close to the interests of Hacker News, computer science. Feel free to correct me if I'm wrong.

I'm not saying this to bash non-astronomers, or non-physicists, or specifically life scientists. Biologists, neuroscientists, and psychologists are crucial participants in the greater scientific enterprise and their efforts lead more directly to alleviating human suffering than my work ever will. But when talking about reproducibility and reliability problems we cannot conflate different scientific disciplines with vastly different cultures, practices, and norms - a crisis in biology does not imply that physics has one too. Physics may have its own problems, but they aren't the same as the ones in biology.

Witness the rise of groups such as the Flat Earthers, who are rejecting basic scientific knowledge known for literal millenia.(Eratosthenes, anyone?) Or witness the anti-vaxxers, abandoning modern medicine for charlatanry. Pretending science is a monolithic enterprise and abandoning a fine-grained understanding of the validity and power of different types of scientific evidence just gives these movements strength, feeds their delusions, and weakens the prestige of scientists when we do need to stand together.

[1] http://retractionwatch.com/category/by-journal/astrophysical... [2] http://retractionwatch.com/category/by-journal/monthly-notic...

contact_fusion

9 lat temudiscuss

Your assumption is frankly incorrect.

Physics is generally expressed in terms of differential equations. This is not due to their analytical tractability - as anyone who has attempted to solve PDEs before will know, most (nearly all) differential equations do not yield to analytical solution. Perhaps you think that quantum mechanics demands a discretized view of reality. This would be a complete misunderstanding of quantum mechanics, and physics in general.

contact_fusion

9 lat temudiscuss

While I sympathize with your sentiment - indeed much research is done that is incremental, not groundbreaking - your comment does not accurately describe academic research.

Full-time scientist positions, whether in academia or elsewhere, are competitive in the extreme. Even with tenure protections, if your hypothetical researcher does not generate impactful research, he or she could expect to be out of a job in relatively short order. In other words, just publishing a paper is not enough anymore. Scientists are constantly evaluated by their peers, not just in the form of peer review. PIs, in particular, are judged harshly by the amount and quality ("impact") of their work, and the grant money they bring in. (Fun fact: usually about half of all grants just go to the university; the PI only gets to keep, and use, a fraction of it.)

Of course nowadays most PIs do not write the papers themselves. Most of the writing falls on postdocs and graduate students. The PIs are full-time writing grant proposals to fund such work. (Of course anything else, including teaching classes or advising graduate students, goes on top of this full-time job.) As any practicing scientist can tell you, grant committees fall easily for fashion and fad, which in the scientific community are driven by citations.

The scientific process today is dominated by the grant mechanism, which is cyclic by design. A PI, when awarded a grant, funds grad students/postdocs/junior staff to produce research that is documented in the form of publications. These publications are used in turn as justification for a new grant, which will fund the next round of research. Citation-less papers are primarily useless in this regard, as the first evaluation a grant committee will make - often before even considering the scientific justification - is to examine the impact of the published work justifying it, which is usually measured algorithmically (citation number.) (Incidentally, the next step a grant committee will make is examining the reputation of the PI, which is a longer-term reflection of... citations.) It isn't hard to see why this incentivizes incremental work - groundbreaking work is risky and might not pay off; it takes time and resources, which are hard to obtain; and incremental work establishes a larger and more visible presence in the field, which is more likely to be noticed.

To put it simply, in nearly all realistic scenarios - excluding very prestigious (and rare) open-ended fellowships that ask no questions of the researcher - the reason that paper on the insulating properties of squirrel tails would exist is because a grant was awarded funding that research. In other words, because somebody gave a crap about it.

contact_fusion

9 lat temudiscuss

Nuclear fusion is nuclear power.

contact_fusion

9 lat temudiscuss

Lasers are still subject to the diffraction limit, regardless of the quality of focus.

We can examine this limit in the context of delivering energy to a remote object. This analysis will be simple - we assume that the optics are perfectly aligned (dubious - pointing is difficult); we assume nothing about the absorption properties of the object, which will necessarily need to be very high efficiency. The angular size T of a laser beam of wavelength L emitted by an aperture of diameter D_a is roughly L/D_a. Similarly, using the small angle approximation, this angular size T at the object itself will be the width of the beam, W, divided by the distance between the object and the aperture, D_o: T = W/D_o. Ultimately, this gives us the width: W = L*(D_o/D_a).

What does this tell us about the practicality of such a system? Visible light, wavelength roughly 500 nm, is perhaps a solid guess for a real system. Realistically the aperture size is probably limited to about 10 meters, but we can go even further and assume a synthesized aperture of a realistic system being 100 meters. You would want to get all of your beam for power transmission, so lets assume an upper limit for the beam width at the object to be 100 meters as well - probably unrealistic, but maybe solar sail/ultralight absorbers could get there. Throwing these numbers in gives a maximum range of... 2x10^10 meters. This is roughly a tenth of an AU. In comparison, this is about 50 Earth-Moon distances... and only a quarter of the distance between Earth and Mars at their closest approach. Coincidentally, this is also about one light-minute.

Any real power delivery system, using current tech and without assuming convenient fictions, will have a much more limited range. In short, lasers are not really perfect rays, even though they are approximately so over scales we typically encounter; at astronomical scale, diffraction always wins. This is why it is usually way better to bring the power with you - especially as you lose solar irradiance as you get further from the Sun. And for bringing power with you, nothing beats nuclear for energy density.

contact_fusion

9 lat temudiscuss

I think you're definitely right. Most programs out there are not worth paying anything for in the first place, much less $25,000 a year.

The problem, at least in my diagnosis, is that there is a huge disconnect between the "ideal education" and education in practice. Even at elite institutions known for the quality of their teaching, half or more of the work is done by screening their applicants and admitting only those who are equipped to succeed. In other words, the summa cum laude graduate from a state's flagship school would probably be a summa cum laude graduate anywhere. The same phenomenon is seen in charter schools, who pad their statistics by choosing only excellent students, and then claim that their better outcomes demonstrate the superiority of their management.

A useful concrete example is my academic department. We are well known for the quality of our teaching, and even provide graduate students with specific and well tested training in pedagogy, which is extremely rare in a STEM field. (This isn't to say we slack in research; this is a top school in the field. In other words, our graduates go to prestigious postdocs almost without exception, though in recent years its been getting harder and harder.) Nevertheless, we are ultimately limited by what we have to work with. If you have motivated students, you can teach excellent classes covering difficult material. If your students are unmotivated and without preparation, there is simply a limit to what you can teach them.

People who work in higher ed in less than prestigious institutions do not have the advantages we do. Their students are often (but not universally) less motivated and prepared than ours, so they have to work much harder to teach the same material. The problem is that everyone is already working as hard as they can, so in the end they are probably doomed to fail. They will retreat onto statements like "teaching how to learn." Yes, in theory, that is what the value of a liberal arts education is - you learn not only the curriculum but also acquire the attributes of an educated mind: how to think and reason; how to acquire more knowledge when needed; how to communicate both verbally and in writing. This is the "ideal education." Nevertheless you will simply never acquire this if you lack the tools necessary to do so - and if you have these tools, you will acquire them regardless of where you go.

The answer is that, frankly, college is pretty useless for most students. If you can make education work for you, you are very likely to succeed anyway. Personally, I cherish my education. I benefit tremendously from it, and at this point, my education colors my entire existence. Nevertheless, most of my high school classmates - even those who did relatively well in class - were woefully unprepared to take advantage of a college education. A corollary to this is that, no matter how much you value the academic lifestyle, it is extremely irrational to continue working in it unless you are a "winner."

contact_fusion

9 lat temudiscuss

The article referenced in that piece is available here, from the arxiv: https://arxiv.org/pdf/1603.07224.pdf The article has been up for some time, but has just now been published by Physical Review A; it is common practice for physicists to post a preprint on arxiv prior to publication, which happens after peer-review.

The momentum paradox you refer to is (possibly?) the Abraham-Minkowski controversy ( https://en.wikipedia.org/wiki/Abraham-Minkowski_controversy ) about electromagnetic momentum in dielectric media. I'm not an expert on this subject, but I would doubt that this new work definitively settles the controversy. Of course this is, no doubt, work towards settling the issue. My (limited) understanding is that the controversy is really about interpreting certain quantities that behave like momentum in certain contexts, and which contexts apply in certain experiments to measure them. I do not believe it constitutes a crisis in our understanding of light; this is a very technical detail.

Of course, using the mechanism of momentum transfer to the transmitting medium as an explanation of redshift - and by doing so, refuting the expansion of the universe - is just yet another "tired light" explanation. (This refers to the idea of explaining redshift through a path-dependent loss of energy for photons traveling from great distances.) This is not a new notion, dating at least to Zwicky in the fifties. This article ( https://arxiv.org/abs/astro-ph/0106566 ) details efforts to demonstrate the reality of this expansion. These efforts do not assume anything about the exact mechanism responsible for tired light, merely the notion that light loses energy as it travels. They refute this to better than 10 sigma.

>with our understanding of light physics in the mid 20th century. >If light behaves even slightly differently to how we currently believe, everything from galactic rotation to expansion goes out of the window.

I... suppose I have to admit that if the current theory of light is wrong, then there may be changes to how we interpret these results. You should know though that this would be extremely unlikely. Generally revolutions in physics tend to subsume the effective results of the theories that are replaced. Quantum mechanics provides a good example: if you take the limit h -> 0 (making Planck's constant zero), you recover classical mechanics. Relativity provides another: if you take the limit c -> infinity in relativity, you also recover classical mechanics. Our understanding of light is quite good.

Forgive me, but I'm detecting a little bit of an "international scientific conspiracy" vibe here. Unpopular work is published all the time, provided that it withstands scientific scrutiny. I know that sounds like I'm dodging the issue, but really, you can apply a cui bono here: what do scientists stand to gain by propping up "wrong" science? We don't get paid a lot, you know.

>Think of epicycles, which for millenia seemed obvious and correct, until heliocentricity (for all bodies, not just earth) became the dominant model due to improved theory - but no new observations.

I don't mean to pick nits, but it was improved observations (Kepler, Brahe, etc.) that drove the acceptance of the heliocentric model. Kepler was famous partly due to his unprecedentedly accurate measurements. Theory was not necessarily rigorous at the time, often referencing theological arguments; heliocentrism was hotly debated, but not novel. Later it was realized that epicycles form a basis set for any trajectory on the surface of a sphere; any trajectory can be reproduced using a sufficiently large number of them. This was a pitfall that astronomers of the time could never have known. Remember that they did not have Newton's insights yet.

On a final note, its great to hear that ATLAS has some good evidence for gamma-gamma interaction!

edit: fix link

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