KJW

@grzegorzsz830402, what is your take on the delayed choice quantum eraser experiment?

Fair enough. But your proposed idea of applying just lime powder will not be fungicidal. You need the Cu for that which, as I say, is the key ingredient in Bx mixture for its intended application, in vineyards. Oh!! "Lime" as in calcium. I was thinking "lime" as in citrus (usually it's orange blossom in cleaners).

I believe that this violates the principle of general relativity. The principle of general relativity requires that clocks and rulers be allowed to behave naturally as clocks and rulers, whereas you are applying corrections to the clocks and rulers based on gravitation in violation of the principle. That the application of the corrections leads to flat spacetime means that the corrections are destroying information about the spacetime being measured. All the information about the measured spacetime is contained in the applied corrections and not at all in the flat spacetime. So, unless you somehow retain the information contained within the corrections and use that information in the description of the measured spacetime, the flat spacetime will not be a valid description of the measured spacetime. You appear to be constructing the following: [math]g_{\mu\nu} = \eta_{\mu\nu} + h_{\mu\nu}[/math] where: [math]g_{\mu\nu}[/math] is the measured metric tensor field using uncorrected clocks and rulers [math]\eta_{\mu\nu}[/math] is the flat spacetime metric tensor field [math]h_{\mu\nu}[/math] is the corrections field One difficulty of the above worth noting is that [math]\eta_{\mu\nu}[/math] and hence [math]h_{\mu\nu}[/math] can be mathematically chosen independently from [math]g_{\mu\nu}[/math], whereas given [math]g_{\mu\nu}[/math], there would seem to be a natural choice of [math]\eta_{\mu\nu}[/math] and hence [math]h_{\mu\nu}[/math]. In obtaining the curvature tensor fields, you would substitute the above expression for [math]g_{\mu\nu}[/math] into the expression of the curvature tensor fields in terms of [math]g_{\mu\nu}[/math] to obtain the expression of the curvature tensor fields in terms of [math]\eta_{\mu\nu}[/math] and [math]h_{\mu\nu}[/math].

Also no. It leverages that fact, but defines the meter in terms of the second and the numerical value of c That's actually an interesting point. Although defining c to have a particular numerical value does seem to be forcing the speed of light in a vacuum to be constant, in fact measuring out a metre of length involves creating the distance travelled by physical light in 1/c of a second. That is, the light will travel at whatever speed it wants to travel and isn't being forced to conform to a constant speed. But the use of physical light to define the metre does rely on the speed of light in a vacuum being able to fulfil the properties of a standard.

This forum is not a chain letter service.

Yes, we do have the right to complain. That is our right to free speech. Trump does have his right to free speech, but he doesn't have the right to break the law.

This fails to distinguish between a change caused by a change of the laws of physics and a change caused by some physical field. The problem with changing the laws of physics is that there needs to be a basis for that change. If the change is physically real, then that implies the existence of some field that gives rise to the measured change. And there also has to be underlying laws of physics that govern the basis for that change. So, the original set of changing laws of physics become replaced by a new set of constant laws of physics. In general relativity, this gives rise to covariance.

How can it not be about legal rights? In any society, it is inevitable that there will be disagreement, and therefore the need for some form of arbitration with the power of enforcement.

No, the religious people do have the right to express that they were offended by the performance, but do not have the right to have the performance banned.

Or as Rowan Atkinson has said: The freedom to be inoffensive is no freedom at all.

I don't agree with this because one also has to consider that the laws of physics determine the intrinsic size of the units that we define. The constancy of the fundamental constants is implied by the constancy of the laws of physics. For example, suppose you measure the length of some object. You use a steel ruler to measure the object in metres. But you could count the number of iron atoms along the edge of the ruler. Thus, instead of measuring the length of the object in metres, you have measured the object in terms of iron-to-iron interatomic distances. Any change in the laws of physics that alters the iron-to-iron interatomic distance would also alter the length of the object by the same amount, and therefore the length of the object in terms of iron-to-iron interatomic distances would be unchanged. But this invariance implies that the changes of the laws of physics cannot be measured, which justifies the assumption of the constancy of the laws of physics. When you express the fundamental constants in terms of their dimensions, the result is a system of equations. When this system of equations is inverted, you obtain a definition of the Planck units in terms of the fundamental constants. In principle, you could measure everything in terms of the Planck units. The laws of physics govern the intrinsic size of the Planck units, but you can't actually measure the Planck units because everything is measured relative to the Planck units, and therefore the laws of physics cannot be anything but constant. Also, because the Planck units are expressed in terms of the fundamental constants, the fundamental constants cannot be anything but constant. As I see it, the use of natural units is about making all the ostensibly different dimensions of measurement the same. So, whereas time and length appear to be different, multiplying time by c rescales time so that it is the same as length. And when this is done, c becomes 1 and dimensionless (but only because time and length now have the same dimensions).

@Killtech, I think you are on the verge of realising that c (and the other fundamental constants) must be constant because when we measure something, it is relative to the definition of the units that have been used, and therefore, in order to obtain a definite value for a measurement, the units of measurement have to be assumed to be intrinsically constant.

When I first saw this a few days ago, I thought it might be a joke. It reminds me of the Scunthorpe problem.

The deflection of light by the Sun is twice that predicted by Newtonian gravity. Half of this value (equal to the value predicted by Newtonian gravity) satisfies the equivalence principle and is the result of the gravitational time dilation. The remaining half is due to the curvature of the three-dimensional space. I believe that these two halves are equal because the spacetime trajectory is lightlike.

Perhaps it would help if you read the Wikipedia article on the history of atomic theory: https://en.wikipedia.org/wiki/History_of_atomic_theory Knowing the history of atomic theory provides an understanding of how the knowledge of atoms developed over time.

Another example is a chemical synthesis, the product of a particular chemical reaction on a starting material whose structure is known by whatever means. It may be that the substance produced has never been produced before. In this case, there is no known sample with which to compare our substance produced. But the substance produced is not entirely unknown, either. It is likely to be the substance that was intended to be produced on the basis of what is known about the chemical reaction. And if it is not the substance that was intended to be produced, then it is likely to be in some way related to the starting material or the substance that was intended to be produced. In either case, it becomes much easier to analyse the spectra of the substance than if the substance is truly unknown. Proton nuclear magnetic resonance spectroscopy is especially useful in this regard.

There is a force acting on the wires due to the magnetic field. Magnetic field??? Where did THAT come from???

The solubility of Ca(OH)2 decreases with temperature. However, heat may speed up the equilibration. The solubility of CaCO3 is actually not very low (0.013 g/L @ 25 °C, although it will be lower in Na2CO3 solution), so the problem I mentioned above may not be as much of a problem as I had suggested. I think heating the mixture with stirring will eventually complete the reaction. In a laboratory setting, one could use a Soxhlet extractor to extract Ca(OH)2 into the flask containing the Na2CO3 solution, though this is probably overkill.

I think it's like eye of newt. Welcome to the alchemy forum. The problem with trying to react undissolved calcium hydroxide is that the solid particles tend to become coated with insoluble calcium carbonate, preventing further access of the calcium hydroxide to the carbonate solution.

https://en.wikipedia.org/wiki/Formose_reaction

Broadly speaking, you are asking how a chemist knows what a given substance is. In the modern day, we have several instruments that provide spectroscopic data that helps identify the structure of a substance. It should be noted that this depends on the purpose of the investigation. For example, if we simply wish to check that the substance is what it is claimed to be, then one can simply compare a spectrum of the unknown with a spectrum of a known sample. The spectrum itself need not provide much information about the structure because all one needs is that the two spectra be the same, like comparing fingerprints. By contrast, if the substance is truly unknown, then one would choose spectroscopic data that provides useful information about the structure. And different instruments provide different information about different aspects of the structure. For example, a low-resolution mass spectrum tells one the molecular mass of the substance. A high-resolution mass spectrum tells one the molecular formula of the substance. A proton nuclear magnetic resonance spectrum provides information about the environment of each hydrogen atom in the molecule, including couplings to adjacent hydrogen atoms. X-ray crystallography provides what is more or less an actual picture of the molecule, including precise bond lengths and bond angles (though this does require a good quality single crystal of the substance, and substantial computer processing of the diffraction data, and may not provide a complete picture). There is of course a lot more that could be said, but I think the above provides a glimpse into the world of the working chemist.

Unless you can produce a metric that describes what you are saying, it violates General Relativity. And unless this metric agrees with measured data, it violates reality. Although we don't currently know what dark energy is, any hypothesis needs align with General Relativity, by which I mean that it needs to use the same language as General Relativity.

As I see it, the band gap is the minimum energy difference between the bands, whereas the width of the bands themselves can increase the energy difference that is accessible. A 1 eV band gap corresponds to an infrared photon of wavelength 1240 nm, whereas a 4 eV band gap considered to be an insulator corresponds to an ultraviolet photon of wavelength 310 nm. Thus, the band gap of a semiconductor is thermally accessible, whereas the band gap of an insulator is not visibly accessible. I was unable to locate data on band widths, so I can't at present say that the energy difference between the bands admits visible photons. I'm guessing that there is an immediate absorption and lossless reemission that is due to the continuum of energy differences between the bands. This is different to refraction and different to absorption by non-metallic materials. However, I must say that the details are getting somewhat beyond me. Have you ever seen rhodamine B? It forms shiny dark green crystals and a violet solution (and violet smears in trace amounts on a white benchtop). I find this intriguing.

I don't know if thermal excitation is necessary for a metallic lustre. The energy of visible photons may be sufficient to bridge the band gap. And because of the almost continuum of energy levels, reflections would occur over a broad spectrum, appearing as an opaque metallic lustre.

It's my understanding that's how semiconductors work. It's why the conductivity of semiconductors increases with temperature instead of decreases like normal conductors.