timo

What exactly is "dangerous"?

My guess is that Sensei thinks about dangers of SQL-injections or, more generally, the problem that a software may not be able to a) properly handle the input it gets and b) is also not able to handle problems that occur.

For example:

Assume your software takes a username USERNAME and issues the command to create that user in the database as

create_user("USERNAME")

Chosing the username dummy")delete_database()"create_user("youAreScrewed this would cause the following commands to be passed to the database

create_user("dummy")

delete_database()

create_user("youAreScrewed")

The forum software used by sfn is a commercial product used on many forums. I would be somewhat surprised if the developers of commercial software were unaware of how to develop software, though. I mean, there is even an xkcd comic about this (https://xkcd.com/327/). The question which characters to allow appears in all software development (and be it only for the documentation). So if unconventional characters are allowed I assume that this was on purpose.

EDIT: Guess I guessed correctly.

It is indeed common to consider the speed of light as the conversion factor between length and time. Then, Planck Length and Planck Time are in fact the same thing - by construction. And it is also common to say that in a sense almost everything moves at the speed of light, except with different amounts in time-direction and in space direction (fun fact: the only exceptions are things that move with the speed of light in the classical sense ). "Four-velocity" could be a term to look up if you want to do some Googling on this.

If I understand you correctly your method of calculating the proton mass is measuring a mix of protons and electrons and assuming that the electron mass is negligible in the mix?

Nevermind that statement. I did somehow assume Sensei wrote the first post in this thread (more precisely, I did not look at the names of the posters at all). I guess the point I wanted to make is the same as Sensei's.

If I understand you correctly your method of calculating the proton mass is measuring a mix of protons and electrons and assuming that the electron mass is negligible in the mix?

Is there anything you want to discuss about it?

A world-wide agreement of the individual governments would already suffice. The most well-known attempt to achieve that are the annual UN conferences on Climate Change (you may have heard about the famous "Kyoto protocol"). A potentially important step has been undertaken with the last conference in Paris, where limiting global warming to 2 Kelvin has been put into the final protocol (which still needs to be ratified by the member countries, though ... ). That sounds like little, and saying "we'd like to limit global warming" does not exclude "we missed our goals, what a pitty". But such agreements tend to tickle down in the form of population awareness, industry awareness, and blunt instruments like money for CO2-reduction measures from the governments (state, country, multi-country structures like the European Union).

Nope.

- The elementary particles in the Standard Model (i.e. all known / experimentally verified elementary particles) get their mass from the interaction with a constant background field.

- The Higgs Boson is an excitation of that background field around this constant value. The interactions of the Higgs Boson and the particles of the Standard Model do not contribute to the particles' masses

- Non-elementary particles also get some of their mass from the binding energy of their constituents

... and no one in the science community really calls the Higgs Boson "god particle".

I agree that trying to keep statements as simple and to-the-point as possible is a good idea in many cases. My reasons for this, however, may be a bit different than yours (also see my nitpicking below):

First, I am a firm believer in the theory that quality is the most important property of information (on a technical level - on a social level attention given to it may be even more relevant). Quantity is usually not an issue and arguably even a problem. Almost every Google (or Google Scholar) search comes up with more relevant results than I could ever handle in my whole life. And still I usually find a Google search insufficient to get relevant information for most things less trivial than the weather forecast.

Secondly, if I post something then I am usually a bit interested in the issue and want to understand it myself. And to do that want to get a clear picture in my mind that I understand and somewhat trust. Complexity introduces potential sources of errors and, well, makes the picture in my own mind less clear.

Remember that the simplest explanations are not only the ones that will carry the most weight with your opponent in debate, but will be the easiest for all to understand, and will leave the least doubt that you are attempting to use misinformation to influence the argument, or any other foul play.

Sorry for nitpicking on a single word, and maybe I put too much weight on it. But the term "opponent" really stuck out for me. I don't consider you my opponent. And I don't post with the attitude of having to battle someone or their opinion since confrontative arguing on the Internet is ... well, it's like arguing on the Internet.

I think the best way is attending university lectures or picking up a textbook. Lecturers and textbook authors tend to put a lot of thought into how to teach relativity best and in which order (and there usually is evidence that they are actually qualified to talk about the subject they are teaching). I doubt that a list made up by some forum member on the fly or some anecdotes of forum members' own experiences can compete with that in terms of quality.

Yes, that is correct.

If you are used to re-formulating terms the identity is obvious. So it is a bit hard for me to guess what could be the blocker to your understanding. Perhaps this very simple statement helps:

The minus sign in front of your fraction "belongs" to the nominator, i.e.

[math] - \frac{bp}{cp - a} = \frac{-bp}{cp - a} [/math]

If that did not help yet (I recommend trying to go on from this first step by yourself before reading the 2nd hint):

Inelastic collisions mean that some of the kinetic energy that existed before the collision is converted to a different form of collision (e.g. into deformation of an object and ultimately heat). If kinetic energy is merely transferred from one of the colliding objects to the other the process is still called elastic. Hence, the part of a car accident where a car hits a pedestrian such that he or she is thrown through the air is an elastic collision. The part of the collision that causes the car and the person to take damage through deformation (except for the damage taken through landing after having flown through the air ) is the inelastic part. Collisions of things hitting the ground without bouncing back are obviously fully-inelastic.

I think it is safe to say that in the history of this forum there has not been a single incident of an extraordinary idea like the discovery of x-rays posted here having been stolen.

 

Pot meet kettle. We will see who has the agenda. Well, actually I will be banned because of an agenda here soon. Fine with me.

Fine with me, too.

I always dislike it when people generalize.

For what reason?

Not sure if that is obvious to everyone: The meaning of elastic in the context of particle physics is not to be understood in the sense of rubber balls bouncing off some wall (or another rubber ball). In particle physics the term "elastic scattering" refers to a process X -> Y where the particle content of Y is the same as X and no excited states are created in Y.

-> Some processes are elastic, e.g. {e-, e-} -> {e-, e-} (note that elementary particles cannot have excited states).

-> If new particles are created, the process is not elastic, e.g. {e+, e-} -> {2 photons}.

-> If input and output particles are identical but excited states are created, the process is explicitly called inelastic (e.g. deep inelastic proton scattering). The creation of an excited state usually is followed by a later decay step that will also create new particles.

-> Particle physics experiments tend to focus more on the inelastic processes, since that is the ones that create new particles or excited states that give insight into the objects' structures.

Depending on what you want to measure these ideas may or may not help/work:

1) Improve how the upper end of the spring is fixed. If if is just hanging from some rod glueing it to the rod may help

2) Reduce the forces involved by using smaller deviations from the equilibrium

3) Use a softer spring to achieve smaller forces with larger deviations

4) Maybe a small string between spring and mass can eliminate the spring's torsion to transfer to the mass. This may create new problems, tough

I remember having done a double-spring system as an undergrad. It was a lot of trial and error to get the system stable but we eventually a working combination of springs and masses that allowed data analysis. So a single-spring system should be feasible without too many headaches.

I don't see the problem with "a bunch of math [] that seems to work". From my perspective that is pretty much the holy grail of physics.

[math] \gamma = \left( 1 - \frac{v_{\rm normal}^2}{c^2} \right)^{-1/2} = \left( 1 - \frac{(c - v_{\rm new})^2}{c^2} \right)^{-1/2} = \left( 1 - \frac{c^2 -2 c v_{\rm new} + v_{\rm new}^2}{c^2} \right)^{-1/2} = \left( 2 \frac{v_{\rm new}}{c} - \frac{ v_{\rm new}^2}{c^2} \right)^{-1/2}[/math]

There is no real reason to do the conversion akin to Celsius->Kelvin, since the zero of our "normal" velocity measurement already correspond to "absolute zero". A more common conversion is to set the maximum to 1 (100%), i.e. [math]v_{\rm new} = v_{\rm normal}/c[/math]. Then, [math] \gamma = \left( 1 - v_{\rm new}^2 \right)^{-1/2}[/math], which in fact makes the time dilatation factor look simpler.

You should have seen that coming

You can rate the thread on the left above the first post. The feature is not used very often. So threads not showing a rating on the overview screen probably haven't been rated.

Two thoughts/comments (on the OP):

1) Costs of the raw material is not the only deciding factor. Almost everyone on the planet agrees that we have to cut down CO2 emissions. Legislation can drive the system towards a reduced use of non-renewable energy sources, say oil. A form currently employed is the sale of CO2 emission certificates. That means that to have the right to emit CO2 via burning fossil fuels you have to buy them. This is the system that is currently implemented in Europe. Doesn't work too well for reducing CO2 emissions because the market prices for emission certificates are much lower than what was originally expected. But it is a potential mechanism. Next, you could just directly impose a CO2 tax, which at the moment is often discussed in Germany. Lastly, legislation could simply forbid the use of fossil fuels for certain applications or at least partially do so (e.g. fuels sold in Germany have to have a certain share of bio-fuel mixed in). Personally, I would even go as far as to claim that the drop in fossil fuel prices is due to the Saudis knowing that no one will buy their oil in a few decades from now, so they put it on sale.

2) The expected path towards renewable energies is to make the electricity sector renewable first. This is already happening, with I think China and the US having been the countries that stocked up the most in renewable electricity generation last year. After that, the mobility and the heating sector are supposed to be included next. Partly by electrification (electric cars, electric heat pumps, possibly direct power-to-heat for high-temperature applications) and partly by synthetic fuels such as hydrogen, methane and liquid fuels generated from surplus renewable electricity. How this will look exactly in the future is a topic of current research. Currently, the research institutes researching on electric vehicles tend to see a future with more electricity in the mobility sector (because of the better efficiency) and research institutes researching on fuel-based mobility tend to see a future with more synthetic fuels (because they can be stored better). Also, for many countries (pretty much all European countries except Norway and maybe Switzerland) some kind of synthetic fuel will be required for the electricity sector once the renewable generation reaches around 80%.

As far as I see it there is a lot of research going on in synthetic fuels on different areas: efficient power-to-fuel technologies, future demand calculations, efficient engines, business models for synthetic fuels, ...

Is this ground state equal to the combined spins of the particles in the system. Is the kinetic energy only angular momentum?

Not necessarily. The prime example for a quantum mechanical system with non-zero energy of the ground state (and zero energy ground state for the corresponding non-QM systen) is the harmonic oscillator. This energy is a mix of potential energy and kinetic energy. The kinetic part is usually not attributed to an angular momentum, certainly not to a spin.

In principle, if you have an equation like x + x*y + y = 0 as one of your equations nothing stops you from calling x*y a variable P (x + P + y = 0) and applying the constraint that the value of this variable must equal x*y (which you could do in a second step after you already have a set of candidate solutions). (same for x + x² + y = 0, btw). Mathematically, it is valid. What is less clear is that you gain anything by doing so. The constraint cannot be formulated in matrix form, so you have a mixed form of (easy) matrix expressions and (potentially less easy) non-matrix expressions/constraints. And whether you have a square matrix or not depends on the number of parameters and equations (as always, but in this case it is less likely for them to be equal). If you are interested in this I suggest you just play around with a few very simple examples. This often gives the best insight.

The approach is correct: If certain values for the x² solve the equation then certain values of x² solve the equation (you don't even need to rename them to w for this statement to be true). And if the solving x² are all positive, then there indeed are values x that equate them when squared.

The reason you don't find any articles on systems of squares is that for the topic of solving the system of equation it is completely irrelevant if one of the variables is a square. As you found out yourself you could just re-name the x² to something else that looks less scary and solve for this value. And the 2nd part, the interpretation of the x²-solution for the underlying x, is not the topic of matrix calculations.