149 karma · joined February 4, 2015
[0] www.damtp.cam.ac.uk/user/tong/talks/talk.pdf
See for example [0] (Swedish) and links within.
http://www.dn.se/nyheter/sverige/internationella-medier-sver...
However that is not quite the whole story. In Sweden, a life sentence is a sentence with no upper bound on the time, if you were immortal, you would be there forever. But, usually you are considered rehabilitated after, say, 10-16 years, if you indeed show signs that you have rehabilitated. Then there is no need to keep you locked up.
The "max X years" is meant as the number for which it took the longest time for someone to be considered rehabilitated. In the Swedish sense of it, it is not a "magic" number, but a case-by-case number.
EDIT: the user "nl" quotes the wikipedia article for Denmark in another reply which indicates it is more or less the same.
Then from LQG there is for example this [0], which portrays string theorists as a bit naive and ignorant.
I know that LQG is not purely focused on quantum gravity, there are some papers out there that discuss how to combine Yang-Mills theories to LQG, and it is suppose to be "easy" (see discussion around page 15 of [0] for example). But, as you might mean when you say that they are purely focused on QG, is that it is (or seems to be (to my very limited understanding of LQG)) to some degree considered a solved problem.
So is W^+, but it is charged, hence not its own antiparticle. W^- should in this case be considered the antiparticle.
For example with GR, it explained for example the precession of Mercury's elliptical orbit, and predicted time dilation (used now in GPS for example) and bending of light. It is true that gravity waves remains to be directly detected.
This is how physics have usually progressed in the past: Have an old theory, have some experiments not explained by that theory, invent new theory that can be reduced to the old theory and explains these new experiments and give new predictions. (The subject of string theory is somewhat different however.)
One is not allowed to add mass-terms to the Standard model (that is a term in the expression that explains the particle physics we know of), because they break symmetries that we know hold (gauge symmetry). So in order to add a mass-term it must be generated by a dynamical field -- the Higgs field -- such that those symmetries are still respected. Hence, the Higgs is able to give the mass-terms to the fermions.
However, the neutrinos are not like the other fermions. Fermions can have different chirality, but the neutrino only has one chirality. Due to the neutrinos being different, the Higgs field needs to be different in order to also generate mass-terms to the neutrinos (or another mechanism than the Higgs-mechanism must be used). Whatever that is, it is probable that it involves something that is beyond the Standard model.
Might be a bit technical, hopefully someone else can make it more understandable.
At one point I was using SymPy and I wanted to invert a symbolic matrix, a rather small one but it had some off-diagonal elements. This took a few seconds in mathematica, after a few hours in SymPy I had to halt the execution of that line. I never got around to look at the code to see what caused it, probably some simple bug, but that's another reason.
I have used Sage somewhat as well. It has more features than SymPy, for what I do professionally. Still some features are missing that I would need. But this might also just be a problem of the amount of experience I have with these tools.
The last problem is that these are much slower than mathematica. I would certainly not say that I'm a good programmer, so my code is probably very slow and badly written. In mathematica I have done some calculations that take days to complete, but they were quite heavy calculations. For these projects I could in principal have used SymPy, I know it has enough features, but with how much slower it is, it would be useless (unless I was able to improve my code to compensate).
With more experience I could give more specific concerns.
Since mathematica is so much faster and feature rich people use it and only very occasionally is it verified by some other software. I would prefer, and would make things easier and faster, if we had (verifiable code) + (one result), instead of (no code) + (one result) + (independent check of result), since only rarely one bothers/have the time to make the independent check. In some cases there is no option to make an independent check (e.g. "with enough effort" is usually too much effort).
I like open source, but I _have_ to use mathematica to be as productive as my peers in my field. The open source tools that exist are indeed inferior and that's why I cannot use them.
However, this is not a good argument, as my field is physics. I do believe that the use of mathematica for science is a inherently bad thing, and should not be considered an allowed part of doing science -- because it is closed source.
I consider the reductionistic part of science very important, so when I use some function in mathematica I do not know exactly how it is implemented hence I cannot reduce my result beyond the point of "Wolfram says it is ok.". But that is not ok.
I have been lucky with all of my results, in the sense that one can check them by hand or by inferior products. But finding the result to begin with is why mathematica is almost necessary for a lot of calculations.
At first glance this sort of approach seems also to be applicable to some anxiety disorders, but from how I understand cognitive behavioural therapy, applying such a method might be a bad thing to do...
Some anxiety disorders makes you, such as mentioned in the article, "[...] procrastinate over all kinds of jobs from the most basic domestic tasks to the really important stuff [...]". One consequence can be that you rely on others to make you do them. For example if you have an anxiety disorder and you get anxious over planning a trip, you might tell a friend to help you do it. Now the anxiety could take another form, which makes you get anxious if you have not had your plan, as in this example, reviewed by a friend.
This could make it worse; You have task X that makes you anxious (planning trips, in the example), you invent task Y (seeking help from a friend, in the example) to relieve your anxiety for that task, but now when you try to perform task X, you get anxious if you have not done Y. Meaning to solve the underlying problem of breaking your behavioural pattern, you have to not only solve the behavioural pattern that makes you anxious over X, but also stop using Y, which was not there from the beginning (or might have been enhanced from applying this new behavioural pattern).
This is how I have come to understand a part of cognitive behavioural therapy, and I could definitely see how, if I were to use an app like this, I would start using it to relieve my anxiety by inventing a new behavioural pattern (i.e. using the app) that does not solve the problem, but instead induces anxiety over not using the app.
This article makes me then wonder, could a similar thing happen to someone with depression? (EDIT: Perhaps like p4wnc6 mentions in a comment below.)
It was pointed out to me that there might be a form of an app however that might be good in the realm of cognitive behavioural therapy in application to anxiety. One method of facing your problem is to get a realistic view of your expectations and realise your behavioural patterns to be able to break them. For example, one method is to have a thought-diary, where you record your thoughts on a regular basis so that, even without reviewing past entries, you at least start consciously thinking about what thoughts are, for example, inducing anxiety. So perhaps a tool that would help you recognize thought/behavioural patterns would be more safe (in the sense of the philosophy of cognitive behavioural therapy) to use.
Thanks for elaborating on this.
> There certainly are differential equations without solutions [---]
These statements are confusing, I think. Some DE:s might not have analytical solutions in terms of _elementary_functions_. For example, 'sin(x)' is considered an elementary function, and it is a certain curve that solves some differential equations.
Now lets say I give you a non-linear ODE that no-one can solve, but I say "'foo(x)' is the function which describes the solution to this ODE". It is a more or less pointless statement, but all it means is that 'foo(x)' gives the curve that solves the ODE. Just like 'sin(x)' for the DE that it solves, difference is we do not know any properties of 'foo(x)' -- but there is a cruve that we could call 'foo(x)'.
All I'm trying to say is: A DE "not having a solution" and "not having a solution in terms of elementary functions" are two very different things. "Not having a solution" means (or at least _should_ mean) you could not even numerically solve it in a small neighbourhood (e.g. the curve 'foo(x)' does not exists), "not in terms of elementary functions" means no analytical expression in terms of trigonometric, hyperbolic, exponentials, powers, and so on, can be written down.
edit: Reading others comments they seem to be saying the similar things. Sorry for unnecessarily reiterating this.
Nicaragua did: https://en.wikipedia.org/wiki/Nicaragua_v._United_States
It would however seem reasonable that, even if not expected at the time, people in charge could be held accountable after the fact as well. However this is perhaps way beyond what can be expected of international law.
Was this considered 'war crime', or was it a too modern way of conducting war so that it was not covered by the international laws at the time?
If against international law or not, has it ever been a case in an international court for the tactics used in Vietnam during this war? If not, is there a documented reason as to why not?
The 'Kepler' law for galaxies are modified to accommodate for a mass distribution. See e.g.: https://en.wikipedia.org/wiki/Galaxy_rotation_curve#Halo_den...
But it does. It predicts extra dimensions and it predicts supersymmetry. However it might be that these are only visible beyond our achievable energy levels such that we cannot verify them. The goal would then be to find what other indirect (as in not actually observing the strings) feature string theory predicts, that is hopefully within our reach, and verify that.
> - Black hole information paradox
This is indeed a big question, but I would discard this in what I wrote since: What is the experiment here? There is theoretical evidence for the Black hole entropy, but even if we could create black holes, which has so far not been accomplished by the LHC, how would you measure it? It is a bit more difficult than a gas where you could deform it and measure temperature etc.
So this I would discard because I was considering discrepancies between theory and experiments.
> - Mechanism for...
some of these I would exclude in what I wrote because they might be explained by current theories, but it is just not known how exactly. Take ultra high energy cosmic rays, there are Shock-front acceleration mechanisms, Supernovae explosions etc that are candidates, and if I understand the formation of that unsolved problem correctly it is to among these candidates identify the correct one or the main one (or if the candidate is not among the ones we know now, find a new one and explain it).
> Well - relatively does. QFT is weirder. Part of it reduces to plain vanilla Maxwell, but it also includes forces [...]
Indeed. QFT is usually referred to as the more general framework, the actual models that explain our physics are usually called Electroweak theory (QED (Quantum electro dynamics) as a special case) and QCD (Quantum chromo dynamics). These are all QFTs with associated gauge groups (a.k.a. Gauge theories). QED reduces to Maxwell, more or less, in a classical limit.
> That doesn't mean the Newtonian model is just as good.
Oh, absolutely not. But for certain experiments it is preferable to use. The same goes with every theory so far, say GR or QFT, non of them are the final "theory of everything", but I wouldn't say that they are "wrong" or "misleading".
"There are some exceptions to these, but I will exclude these for now, since they are a bit technical."
Take for example the Anomalous magnetic dipole moment of the muon [1], it is a measurement that do not agree with theory, but it is far from being the centre of attention for physicists (certainly some people do have that as their main goal to explain, but in general).
So indeed, there are things that do not match up, as well as the need to find a new experiment that gives something new (in the sense: The anomalous magnetic dipole moment of the muon is not enough of a hint to find the "new theory" (it seems).)
[1] https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_p... The 11th point under that section of that article.
I suppose my use of the word "regime" is unconventional. What I mean is a "parameter regime", or "for a certain range of a parameter".
For example, for the range in which \hbar is much smaller than one (in some units), this is the "parameter regime" in which QM and Newtonian mechanics agree quite/indistinguishably well. And for the range in which \hbar is close to one, "Newtonian mechanics breaks down", in the sense that QM effects are large -- i.e. where Newtonian mechanics is no longer a good approximation to QM.
> Quantum mechanics is correct. Always, always, always[1] use Quantum mechanics!!! Newtonian mechanics is obsolete!
I would not agree with phrasing it like that, and it is indeed Special relativity (or a part of it).
If quantum mechanics makes Newtonian mechanics (NM) "obsolete", then what does that imply for Special relativity (SR)?
QM makes corrections to NM with the parameter \hbar. SR makes corrections to NM with v/c (velocities you make experiments at over speed of light). So say that we are doing a mechanics experiment on our desk (say dropping something on a spring, or whatever). And we go with your "always use QM", it would take a long time to write down what happens, the same (although a bit faster) if we were to go with "always use SR".
Before you start writing down what is going on for that experiment, you make an assumption/approximation of which range of parameters is relevant for you. An apple dropped on a spring bed would not have relevant corrections from QM nor SR.
> The reason that I am adding it as a comment is not to correct you -- you are already right -- but to maybe help other readers.
Absolutely! Thats is also my goal in discussing these things. I do not always know how to make them "popular"/less technical, so I'm very interested in hearing other ways of explaining it.
I believe we are saying the same thing.
Your "as Planck's constant approaces zero" is the same as me saying "in the regime where Planck's constant is irrelevant" (not quote from above, but those are the words I would use).
As you say, one can think of it as an expansion like:
QM = NM + \hbar C_1 + \hbar^2 C_2 + ...
(QM = Quantum mechanics, NM = Newtonian Mechanics, \hbar = Planck's constant, and C_i are correction factors (your "insert super complicated formula here")). Take \hbar to zero and you are get what you just said. But if you go into a regime where \hbar is significant, "Newtonian Mechanics breaks down", e.g. corrections are of same size (or perhaps even larger).
It might be "unsatisfying" how I try to describe it, but I tried to say the same thing as you did (I think). :-)
This is interestingly put, and I would not completely agree with it. Let med give two examples:
1. Before Quantum mechanics we could measure the Photoelectric effect (that is, light that is energetic enough can shoot off electrons from metal plates). This is a Quantum phenomena, and we could measure it before the theory was discovered.
2. Before General relativity we could measure the precision of the elliptical orbit of Mercury. This could not be explained by Newtonian gravity, and is a relativistic effect. But could be measured before the theory was discovered.
And before these; Electric eels can shock you, and Magnetic rocks still attract each other, even before Maxwell, Ampere, or Coulomb were even born.
The problem now a days (for fundamental theoretical physics) is that we are mostly put in the categories: * There is no data we can't explain with theory. * Theory that is consistent with current data and only predicts new features at much higher energies than we can design experiments for.
There are some exceptions to these, but I will exclude these for now, since they are a bit technical. Example of the first one: There is no data directly implying a quantum nature of gravity [1]. Example of the second one: Supersymmetry might not be visible at LHC because LHC is too weak.
That second category is why people jump on new results directly, like the BICEP or the super-luminal neutrinos, and the hep-th/ section of arxiv.org is flooded with papers trying to explain it. However, for both these cases, the measurements turned out be be wrong.
> every day what you thought you knew is now obsolete.
This is what many people say, but I would not agree (in fundamental physics). For example:
* One can say Newtonian mechanics is wrong because we have Special relativity now. But one should say: There is a regime (high velocities) in which Newtonian mechanics breaks down. This regime is determined by the speed of light, c. Newtonian mechanics is still correct for velocities much smaller than c. * One can say that Quantum mechanics makes Newtonian mechanics wrong. But one should say: There is a regime where Newtonian mechanics breaks down and Quantum mechanics governs, which is determined by the Planck constant.
and so on. It is not "obsolete", or have not turned out to be wrong. One only needs to append new aspects in various regimes.
[1] See e.g. http://backreaction.blogspot.fr/2013/11/big-data-meets-eye.h... > Those of us working on the phenomenology of quantum gravity would be happy if we had data at all [...]
'Every year, the velocity of the distant quasars (going away relative us) is increased by 1 cm/s.'
"What’s more, there is an energy associated with any given volume of the universe. If that volume increases, the inescapable conclusion is that this energy must increase as well. And yet physicists generally think that energy creation is forbidden."
is regarding vacuum energy = dark energy = cosmological constant, etc, and continues to discuss it after that.
Another thing I find annoying is when they (this article and also others I have seen linked here on HN) paint the picture of that breaking energy conservation is some kind of magic going on -- it is far from it.
In General relativity (GR) you can construct conserved quantities from Killing vectors [1]. For example, if you have a time-independent metric (the GR tool for measuring lengths in space-time) you get a time-like Killing vector, which is associated to a certain conserved quantity; Energy. (Another example is when the metric has certain angular independences and you get conservation of angular momentum.)
Now in metrics that mimics cosmological evolution (that is, evolution in time), you have to break time-independence, hence your time-like Killing vector is gone and your energy conservation law is gone!
This is portrayed as some magic-like thing (at least that is how it sounds to me when I read these popular cosmology articles), but it is simply a consequence of the mathematics of GR. It might break some usual physics intuition, but I would not say that physicists (at least in this field) are surprised by it.
So it does not really "contradict basic physics", one just needs to know more about the details to get a good view of it. We do not need to figure out (or "conjure into existence") a way to break conservation of energy (as is the example here), it is already there in GR.
[1] https://en.wikipedia.org/wiki/Killing_vector_field#Geodesics The article on wikipedia is quite lacking on this point, but I link it here anyway.