In 2004 a whole layer of top CIA officials were forced out. Defense Secretary Colin Powell resigned. Dick Cheney purged the CIA of personnel who might have served as some counterbalancing force. Once the good and reasonable people were gone (fired, forced to resign etc.), the CIA ran amok. If we look honestly at what went wrong, it's pretty clear how to fix it. Fire all the people that lied to Congress and broke the law by employing prohibited techniques. Prosecute them to the fullest extent possible. Simultaneously, conduct an internal review of all the former CIA fired for political reasons and hire them back. These are the people America desperately needs to repair our broken system. The CIA is desperately in need of reform. The world is too dangerous and complicated a place to have the wrong people running our foreign policy. If they lied about torture, what else are they lying to Congress about? Clearly it isn't the solution to every problem but it would be the best possible, immediately actionable step. Bring back the good patriot Americans who were fired from their job with the intelligence agencies for political reasons. Get rid of and prosecute the bad apples.
Colin Powell was never Defense Secretary, he was Secretary of State. In any case, as the report notes, the CIA was already running amok before 2004, so any purge then was not a necessary prerequisite for the CIA to run amok, though it might have removed a constraint that would have reigned things in sooner.
Interesting how Peter Thiel who froze $45,000 of assets of Facebook competitor Diaspora* has taken a special interest in bad mouthing Twitter, call them "horribly mismanaged" etc. It's very clear he wants Twitter to fail. Peter Thiel influenced the debt downgrade with his comments. Knowing how the world works Thiel may very well have called up an analyst and played some dirty tricks as in the case of Diaspora*.
Minikanren is featured in a follow up to 'Seven Programming Languages in 7 Weeks' by Manning Pubs. 'Seven More Programming Languages in Seven Weeks'. I think Elixir and Julia are also going to be included in the book. Anyway, if anyone here is into Manning books there's a MiniKanren chapter to look forward to. Disclaimer?!: I do not work for Manning. Just a reader.
The most fruitful definition of a real number is as a limit of a Cauchy sequence. That way is much more useful in proving theorems.
Using infinitesimals is logically valid (alternative real analysis), useful for physics and other practical calculations but not at all helpful proving theorems.
Might I add that the concept of 'nearness' introduced by Riesz is the contrapositive of the usual limit definition and might be the way real analysis is taught 100 years from now.
Hyperreals are much more involved than mere epsilontics as they include all kinds of infinities. It's so mind blowing that I simply must defer to minds like Conway to play with such things.
There's a very subtle undertone of negativity in this article about physics. Before I get into, William Bardeen is not in the same league as 'Surfer Dude and his E8 Theory of Everything' which throws basic facts about representation theory out the window, coming up with 'todalay boogus' arguments which amazes auntie, mommie and magazine editors but a real physicist would instantly dismiss.
Bardeen is the real deal. His papers are very interesting and feel a bit like reading Sidney Coleman's papers. If you're interested...
Is nature scale invariant? So far the answer is absolutely NO but I strongly advise to wait and see. There are many topics that point to some breakdown in scale or reorganizing what we think of space and distance (dualities in string theory, conformal field theory).
OK, now the important thing I want everyone here to realize. You are living through a GOLDEN AGE of physics. You wouldn't think that based on what all the popular magazines tell you. Here's why...
1. Higgs particle - discovered!
2. Inflation - discovered! Denying this one is like denying the Big Bang itself. The evidence is overwhelming and in fact I would list this as the single greatest scientific discovery of all time. The concurrent discovery of gravity waves, quantum gravity and a real life example of a Hawking process only sweetens the deal.
3. Supersymmetry has basically already been discovered IMHO. They aren't announcing anything at CERN and won't until they have so many sigmas under their belt but trust me, it's coming and truth be told, it isn't really so surprising. SUSY physics has always been rock solid from the beginning. The situation is very similar to that before offical Higgs announcement and before someone went knocking on Andre Linde's front door. Many were extremely confident in the Higgs particle a least a year before the official announcement. The BICEP 2 results were even more glaringly apparent than the Higgs results. Many people were walking around the Earth with 'secret knowledge' that inflation theory was correct even 2 to 3 years before the official announcement.
So you are living through EXTREMELY interesting times but you wouldn't know it with all the big science bashing being thrown around.
I study astrophysics, so I won't be able to say much about SUSY or string theories or conformal field theories. I do agree that we're living in a golden age of physics! But your second and third points, inflation and SUSY-- those are definitely not confirmed. In fact, the primordial gravitational waves from BICEP2 are almost certainly dust contamination signal (e.g., http://arxiv.org/abs/1405.5857). The discovery of supersymmetric particles would also be extremely shocking to me, since my institution is heavily involved in CERN LHC experiments, and I haven't heard any hints of a discovery yet. Perhaps you know something that I don't!
> The discovery of supersymmetric particles would also be extremely shocking to me, since my institution is heavily involved in CERN LHC experiments, and I haven't heard any hints of a discovery yet.
Why does an absence of evidence imply that the arrival of evidence would be shocking? They're doing the experiment because they already believe things are this way and they're trying to get evidence to confirm it. If they disconfirmed it, that'd be surprising.
> They're doing the experiment because they already believe things are this way and they're trying to get evidence to confirm it.
That's not science, that's confirmation bias. In science, one would want to look for evidence that one's theory is false with as much vigor as a search for evidence that it's true. Science isn't law, and it's not religion.
> If they disconfirmed it, that'd be surprising.
If they falsified their theory while only seeking confirming evidence, yes, that would be surprising. This is why open-minded scientists try to avoid assuming what they should be proving (the real meaning of the expression "beg the question").
I'm not trying to start an argument here, but wouldn't "assuming what they should be proving" be the same as "hypothesizing?" That's a critical point of the scientific method. You don't really design experiments that can both confirm and refute a theory. When an "open-minded" scientist attempts to perform an experiment to test theory, they aren't personally responsible for subsequent theories and experiments that could disprove their results.
> wouldn't "assuming what they should be proving" be the same as "hypothesizing?"
No, the expression "assuming what you should be proving" has a special semantic meaning -- it refers to a thought process that uses its conclusion to support its investigation, or takes the preferred outcome as a given from the start, without seriously considering alternative explanations.
Hypothesizing means taking existing theory and extrapolating new untested properties, then presumably investigating whether there is any evidence for the hypothesis.
> You don't really design experiments that can both confirm and refute a theory.
On the contrary, the best experiments have the chance to either confirm or refute a hypothesis. The Michelson & Morley ether experiment is a classic of its kind -- its outcome would either confirm or refute the ether as it was imagined to be.
> When an "open-minded" scientist attempts to perform an experiment to test theory, they aren't personally responsible for subsequent theories and experiments that could disprove their results.
Not so. An open-minded scientist wouldn't pass up the chance to uncover any positive or negative evidence for or against his theory -- both kinds of evidence contribute to our understanding of nature. Remember the story about Bell Labs engineers Penzias and Wilson cleaning bird droppings from their microwave dish? They did that so someone else wouldn't scoop them by discovering that they had been fooling themselves about the source of the noise in their antenna (which ultimately was identified as the cosmic background radiation, now standing as evidence for the Big Bang).
The bottom line? Science isn't law, it's not adversarial, there aren't two competing sides, and a responsible scientist maintains an open mind with respect to evidence both for and against his theories.
No. One of the most commonly used definitions of faith is trust or confidence in a person or thing. Whether or not that trust or confidence is based on evidence or not is a separate matter that is not conveyed by the word.
Even in the case under discussion, that someone might have faith that something is a particular way, and are doing an experiment to confirm it (more likely disprove an alternative), that doesn't mean it's 'blind' as in without reason. People can have a lot of good reasons for believing something is a particular way without having measured it directly yet.
Not confirmed in the sense that many in the community are denying the result, which is as it should be. Even considering many models including dust a robust result remains. I think PRL and others are being unreasonably pessimistic but the only way to settle this is for there to be more experiments at different frequencies. Then they can move from the shock and denial phase onto the grieving process. BICEP scooped Planck, big time. It doesn't matter to me but it matters a whole lot to some people and the degree of sour grapes and poor sportsmanship is really stunning. Yes, I am saying a good deal of this is motivated by the tiny team beating the much bigger team though I absolutely disagree with their hypercompetitive interpretation of the whole enterprise of experimental physics. History will tell us that BICEP got lucky, very lucky and they got there first. The dust up is happening on Earth not in space and the latter is certainly much easier to explain away and still have at least a six sigma result. I've read the dust papers with an open mind and none of them add up.
Regarding SUSY, strictly speaking no particles have been directly detected but anomalous currents abound and just about everything seen works perfectly with light SUSY and much better than with the standard model. The dilepton events alone are very compelling. http://www.science20.com/a_quantum_diaries_survivor/a_susy_e... SUSY is in plain view much the way the Higgs was in plain view for about a year before the official announcement. I have no special insider information, just a humble internet connection to download the important papers and a decent knowledge of particle physics. In hind sight, everyone will say 'of course' which always happens. From a theory point of view, SUSY is simply not an option unless there is some spectacularly new theory out there with novel concepts to replace QFT. The Coleman-Mandula theorem is extremely compelling. It basically tells us accept SUSY or find something to replace QFT. Since QFT works and there's no good reason to move on to something else (especially when something else doesn't exist presently and possibly never will), it's a safe bet SUSY must exist somewhere. It just so happens to be light SUSY and we're seeing it at the LHC right now. I think we're presently seeing the equivalent of a COBE picture of SUSY and next year it will sharpen up into a WMAP picture.
Are there any particular resources that you recommend for a high-level overview of this kind of stuff? I'm an engineer with a solid grasp of classical mechanics and strong math background, but very little exposure to modern physics (basically, anything discovered after 1905) and I would like to be able to read about and appreciate this type of work. Where to start?
Apologies for taking the conversation off on a tangent, but you seem passionate about this.
Do you have any rumors or specific knowledge (even if it's not something you'll share) regarding SUSY? They found missing energy? A new plethora of resonances? Higgsinos or sfermions? Something more exotic?
By the end of the last run, the people I talked to at CERN were fairly certain that there's no SUSY in the current dataset and that SUSY will likely not be found during the upcoming run. But perhaps the people I talked to are simply of a different persuasion.
Thanks for your post and link. I recently watched Particle Fever on Netflix and became extremely fascinated with the field. A lot of the information you posted is touched on in the documentary. It is mostly focused around CERN and the years leading up to the Higgs particle discovery. There are also great interviews with David Kaplan and Nima Arkani-Hamed.
You've likely seen it but if not you might enjoy it.
Surfer Dude and his E8 Theory of Everything ... 'todalay boogus' arguments which amazes auntie, mommie and magazine editors but a real physicist would instantly dismiss.
I suppose you're referring to Lisi? Neither he nor E8 were even mentioned in the article. You're both OT and unnecessarily unpleasant.
Well there is no way Lisi's E8 theory can fit gravity and the standard model at the same time. At first glance the group structure seems to allow it but the actual group representation (which are the actual particles allowed if one wishes to construct such a theory) don't allow it. I'm totally fine if someone wants to pursue this area of research the problem is the MAGAZINES have printed his theory as though it were a valid contender or alternative to string theory or some other theory. Lisi's theory isn't. If it were a plane, it never got off the ground, it blew up on the runway. A recent TIME magazine special issue features this broken 'theory'. It's deeply misleading and shows a lack of concern about misleading the public. Loop quantum gravity, simplicial quantum gravity, and causal sets etc. are all examples of broken theories that just don't work. Just so you know there ARE valid alternatives to superstring theory regarding unification or physics beyond the standard model. Alain Connes non-commutative gravity, superconformal field theories, Kac Moody algebras, twistor gravity, twistor string theory, plain old N=8 D=4 supergravity is a contender, SO(10), SU(5), MacDowell Mansouri gravity, matrix models,... I could list more. These theories aren't broken, they actually work. Those are the kinds of things the public deserves to hear and read in the magazines.
The road from theoretical physics to engineering is a very long one, so it's very hard to predict exactly what this would buy us. Relativity, for instance, spent a long time with no concrete engineering benefit, but now it allows GPS to be much more accurate by adjusting for the time dilation on GPS satellite clocks. As we get closer and closer to the mysteries at the heart of the universe, I think it's safe to say that the engineering benefit will be both more arcane and more powerful.
A lot of discoveries do not have immediate uses and some might indeed never have any applications. But discoveries can spurn others in unexpected ways. The most famous example of course if the WWW which came out of CERN, a pure physics research institution. Cryptography is another example that has had a profound impact on information security.
But the most compelling reason, at least to me, is we investigate because we can! That is just human nature.
Basic research is the foundation of all engineering. You can't design things without understanding how the universe works. If you need examples, look no further than to particle physics, which has had a huge influence on medical imagery since at least the fluoroscope.
All things hitherto designed have been designed without a complete and truthful understanding of the universe. If we go back in history, we find examples of useful inventions that were produced amid a rather poor understanding. Levers and inclined planes were produced without knowing anything about basic arithmetic, let alone physics.
We can only hope their new package system will contain something that allows the programmer to chose their own database. I want to use Couchbase and Elasticsearch. I can't see why any other document store couldn't do the same job as Mongo. Don't get me wrong, I'm ok with Mongo (but it's not for me) but can't we make at least some choice???
You can make your choice! The problem for a lot of people: you need to write a real-time adapter if you want it to be efficient and performant. We have implemented Redis adapter, for example: https://www.youtube.com/watch?v=-Vnb8tjnE3k
I was a bit turned off by the term 'isomorphic javascript' when I first read it mostly because of how it is so fundamental to mathematics and we can say the term isomorphic definitely earned its keep there. In programming I'm not so sure. The term does fit but it's a mouthful, almost as bad as XMLHttpRequest. Is there a cool word like AJAX to take the place of Isomorphic Javascript? Airbnb has a certain coolest factor and they've been using the term so it's most likely here to stay.
If we take relativity at face value, the speed of light is c = 2.997 x 10^8 <<<locally>>>. <<<Globally>>> the speed of light can be anything. Cosmologists talk about the universe expanding faster than light during the inflationary phase, which sounds confusing because we're told nothing can move faster than light. While it is true that the speed of light must propogate at only one velocity for all freely moving frames of reference, the speed at which space itself expands can be anything! Relativity does not restrict the speed at which space itself expands or contracts. TL;DR The maximum local speed of anything moving through space in a freely moving frame of reference is c. The speed at which space itself expands or contracts is not limited in any way by Einstein's theory and is consistent with observations of the the inflationary universe in which the universe expanded at faster than the speed of light.
I like to think of it as the speed of information. The quickest any information can move from point A to point B is c. (Even if those points are themselves moving.)
The universe can expand faster than c because there is not actually any information moving between the center and the perimeter.
I hope this clarifies the appartent contradiction. Light can't help but move at any other speed than c = 2.997 x 10^8 m/s. It can't go faster, nor slower. So how does the speed of light appear to slow down in certain circumstances? In a vacuum, the speed of light is always c. There is nothing to interfere with the propogation of the individual photons (little atoms of light) as they move through the vacuum. However, in a material such as glass the individual photons of light are absorbed and reemitted many trillions of times by the molecules making up the glass. The photons do a "stop over" and don't move at all, the velocity of these photons is zero (actually the photons temporarily don't exist except as energy absorbed by the atoms in the glass). Between lattice points or individual atoms the photons travel at velocity c. The combination of stop overs (absorbtion and reemission events) and free propogation gives the appearance light is travelling at a slower overall velocity than c.
This argument and explanation is constantly coming up on the subreddit askscience. I don't violently oppose it as much as some do, since I think it's somewhat helpful, but I would like to say that my preferred interpretation is that a `photon' isn't really a well defined object when inside strongly-coupled materials. For example, can you really sensibly talk about a freely propagating radio wave when its still within a quarter wavelength of an antenna? When atoms are spaced tenths of a nanometre apart and visible light has a wavelength of hundreds of nanometres it seems a bit silly to talk about it propagating freely in a material.
When you go through quantum field theory, photons are defined in terms of freely propagating particles, not interacting with other fields. When the disturbance in the EM field propagates into, e.g. a dielectric material, and strongly couples to various nuclear and electronic excitations, it is better described in terms of a massive quasiparticle, the polariton, which is a hybrid of the photon, phonon and electron fields and, being massive, propagates at less than c. You can, of course, describe it in terms of perturbations to the free photon corresponding to various types of virtual absorption and re-emission, but it's a bit misleading to think of it being physically absorbed and re-emitted with little stopovers. If anything, the classical model of a continuously interacting medium interacting with the EM wave creating a coherent response wave which interferes with and appears to slow down the EM wave is more instructive.
Indeed. In the CFL-phase of color superconductors the photon mixes with the diagonal gluon. One specific combination remains massless while the orthogonal combination gets a mass. My colleagues and I jokingly called them the phuon and the gluton when talking privately.
This is actually a very deep question. If you want a better answer than I'm about to give, read Feynman's QED lecture videos [1] or read the book [2].
The short answer is, they don't. They emit the photon in a random direction.
Fine, you say, but what about refraction and reflection, there the photons are emitted in another direction. What makes the atom "decide" what direction to emit a photon after it's absorbed?
They don't decide anything, they still just emit in a random direction. The mind fuck is that on the whole, statistically, almost all photons except for those travelling in the direction of refraction/reflection destructively interfere!
Very good question. Here's the gist of it, a rough way of thinking about it.
A time varying electromagnetic field is produced by moving charges (except for a minor distinction about steady currents). The direction of motion of the charges determines the polarization of the emitted field. Later on, when the field encounters matter it produces an identical motion of charges i.e; if originally an East-West charge motion produced a North-South field then a N-S field will induce an E-W motion among new charges which in turn re-emit N-S light. The original light and the re-emitted light interfere, the delay is what slows the light down, as noted by others. But you can see why the direction is the same.
Note: I suppose this picture is somehow tied to reciprocity of the Maxwell equations between sources and fields, I need to go look it up again.
They don't. A photon absorbed by an atom/molecule can be re-emitted in any direction. Imagine a thick piece of glass being traversed by a light beam: most of the photons will traverse it undisturbed (and thus maintain their original direction), but a few will be scattered all around (and that's the light you can see if you watch "inside" the glass from one of its sides).
On the other hand, depending on the light frequency and the crystalline structure of the material, photons can be scattered by the whole lattice itself, rather than by the single atoms/molecules. In this case, the direction follows the "rule of the mirror", which is dictated by quantum mechanics.
When you shine light through glass the maximum propagation speed, the speed at which you start getting photons out the other side, is about 2/3 the speed of light. This implies that the overwhelming majority of photons are adsorbed and re-emitted. So this explanation cannot be correct, as I can look through a pane of glass, but you're saying any photon adsorbed is re-emitted in any direction, and the overwhelming majority of photons must be adsorbed and re-emitted.
Sorry, my fault! We were talking about "absortion"/"stop over" as a way to describe in layman's term the interaction of photons with the glass atomic structure. In this sense, as others pointed out, we are talking about scattering and the final direction is indeed related to the original one. Anyway, light scattering is a quantum process and there is no way of observing the "moment" between "absorption" and "re-emission".
In my comment, I talked about actual absorption, which means that there is a finite time interval when the photon does not exist and the atom/molecule who absorbed it can be observed in a different state than usual (electron in a higher orbital for an atom, different vibrational modes for a molecule). Later, the atom/molecule will go back to its normal state emitting a photon with the same energy as the first one, or several lower energy photons. This actual re-emission will not have a favourite direction. Depending on the typical time scale of the re-emission, you may call this process fluorescence or phosphorescence (http://en.wikipedia.org/wiki/Phosphorescence).
On average it's a requirement of the conservation of momentum. But note that sometimes photons come out in a different direction (scattered), including to opposite direction (reflection). In these cases the momentum is absorbed by the medium.
You're either very confused, or you have a much deeper understanding of physics than me. I love that it could be either.
Does the conservation of momentum apply to things with no intrinsic mass?
Yes. You can define a special-relativistic momentum and it's a conserved quantity, and it does have a nonzero value even for things with zero rest mass (which necessarily move at the speed of light).
(It may help to observe that an object with nonzero mass moving at the speed of light would have infinite momentum, and then it maybe makes sense that "zero times infinity" becomes a finite number)
Indeed. That's the idea behind things like solar sails, for instance. Check out the article here- http://en.wikipedia.org/wiki/Radiation_pressure
and scroll down to "Radiation pressure by particle model: photons" if the top is confusing.
So the reason you have a coherent wavefront moving through a lens, as one example, is not because the photons are emitted in a particular direction, but at a particular time.
