KJW

Ok, I'll leave you to it. 🙂

Photosynthesis is made up of two sets of reactions: light reactions and dark reactions. The light reactions are associated with the absorption of light to drive the synthesis of two short-term energetic substances as well as the production of oxygen from water. The dark reactions use the two short-term energetic substances from the light reactions to produce sugars from carbon dioxide. The light reactions naturally require light, but the dark reactions do not occur in the dark even though light is not actually used in the dark reactions. Instead, light acts as a regulator of the dark reactions. What this means is that the synthesis of sugars (or at least those synthesised from carbon dioxide rather than from other sugars) does not occur in the dark. Thus, for growth to occur in the dark, it would seem that the sugars required would have to have already been synthesised during the daytime.

Actually, the reason I chose to read about photosynthesis was because of this thread. I wanted to find out if the dark reactions only occurred in the dark, as suggested by your post. But I found that instead of the dark reactions also occurring in the light, they actually only occur in the light.

No, you can't decouple translational from non-translational motion, but the point I'm making is that the energy that is in the non-translational motion doesn't contribute to either the pressure or the temperature of the (ideal) gas, except if you try to remove it.

Curvature is a two-dimensional notion. It requires a surface to be curved in both directions. So, a sphere is curved but a cylinder is not. In higher dimensions, curvature can also be considered in terms of sectional planes. However, in two dimensions, there is only one type of curvature; in three dimensions, there are two types of curvature; and in four or more dimensions, there are three types of curvature.

If pressure is independent of non-translational motion, and temperature is directly proportional to pressure, then temperature is independent of non-translational motion. One thing that was never made clear throughout this discussion is what temperature is. I felt that temperature was being conflated with energy. But I will agree that my view was somewhat perverse, and I'm not even sure how it arose. It is correct for gases, but questionable for solids and perhaps liquids as well. Each degree of freedom has an energy of ½kT. Therefore, temperature can be regarded in terms of the energy of a single degree of freedom. And the equipartition theorem ensures that the single degree of freedom can be any of the degrees of freedom, not just translation. This seems to be the argument against me. My argument was basically that it isn't all the degrees of freedom that contribute to temperature because it is only one degree of freedom whose energy specifies the temperature. But translations are quite ubiquitous, and the three translation modes always occur together. So instead of temperature being specified in terms of one degree of freedom with energy ½kT, temperature could be specified in terms of the three translational degrees of freedom with energy 3/2kT. And given that only translations contribute to pressure, it would seem that translations are quite special compared to the other degrees of freedom. However, I am also aware that temperature emerges as a Lagrange multiplier in statistical thermodynamics, so I'm not entirely wedded to the ideas I expressed in this thread.

I was reading about photosynthesis in Wikipedia earlier today, and it said that the "dark reactions" (the reactions that in effect reduce CO2 to simple sugars) do not occur in the absence of light.

No, that's not how gravity operates. The two wheels represent two clocks at different locations in space. The two wheels rotate at the same angular rate, representing simultaneity. But each wheel rolls different distances on the road, representing different proper times. The different proper times at different locations in space is the time dilation that causes the path to curve. The road represents a two-dimensional spacetime where width is space and length is time, and this spacetime need not be curved, for example in the case of an accelerated frame of reference in flat spacetime. In other words, the analogy doesn't only describe true gravity caused by matter, but also artificial gravity caused by an accelerated frame of reference. The equivalence principle ensures that the same analogy applies to both. The rubber sheet analogy is wrong because the curvature of the rubber sheet is not a correct representation of what causes gravity.

That's a standard argument, but my argument is that the familiar gravity we recognise as Newtonian gravity is caused by time dilation, whereas the trampoline analogy indicates spatial curvature as the cause of gravity. Thus, the trampoline analogy is misleading about what causes gravity. A correct analogy that I discovered recently is two wheels of unequal radius joined by an axle. As this rolls along a flat road, the trajectory will curve towards the smaller wheel, and the larger the difference between the radius of the two wheels, representing time dilation, the larger the curvature of the trajectory, representing the acceleration we feel as gravity.

Although at the time I said a pair of temperatures, perhaps it is more appropriate to say a range of temperatures between these two extremes. Then an object with an arbitrary absorption spectrum will equilibrate to some temperature within this range. The minimum and maximum temperatures define the thermodynamic efficiency of extracting work from the radiation. This thermodynamic efficiency would apply not only to an ideal heat engine, but also to other means of extracting work such as a photovoltaic cell. One thing I didn't mention is that the radiation being discussed is assumed to be isotropic.

Are you Are you aware that the thermal emission spectrum of an external surface (the thermal radiation inside a cavity is black-body) is equal the product of the absorption spectrum and the black-body distribution? That is, good absorbers of a given wavelength are also good emitters of that wavelength. Therefore, by arranging the absorption spectrum of an object to absorb at all wavelengths other than that of the radiation, emission will be maximised, absorption will be minimised, and the temperature will equilibrate to a minimum which becomes the cold sink of a heat engine; and by arranging the absorption spectrum of another object to absorb at only the wavelengths of the radiation, emission will be minimised, absorption will be maximised, and the temperature will equilibrate to a maximum which becomes the hot source of the heat engine.

A long time ago on a different forum, I made the claim that only perfect black-body radiation, both in terms of its relative frequency distribution and its intensity, can have a single temperature attributed to it. Every other distribution of radiation has a pair of temperatures attributable to it. The lower temperature is defined as the temperature achieved by an absorption spectrum that minimises absorption and maximises emission, while the higher temperature is defined as the temperature achieved by an absorption spectrum that maximises absorption and minimises emission. Then one can construct an ideal heat engine based on these two temperatures to extract work from the radiation. One can't do that if the radiation is perfect black-body as this has only a single temperature.

I can define the temperature of an atom (as of that any material object) in thermal equilibrium with its surrounding environment as being the same as that of the environment which can be measured by a thermometer. It occurred to me how one might do that. One could define the temperature of a single particle in thermal equilibrium with its surrounding environment in terms of the kinetic energy distribution over time of the particle. Applying the ergodic principle transforms this to an ensemble distribution for which the notion of temperature naturally applies.

One can't dismiss a causative relationship between two quantities simply because the mathematical relation between them is an equality. One really needs to examine the logical aspect of the relationship to establish whether there is a causative relationship and in which direction it occurs. In the case of the Einstein equation, what one really has is a connection between the mathematical realm and the physical realm. Without the Einstein equation, all one has is Ricci Calculus. It is the Einstein equation that transforms this to General Relativity. The Einstein equation does two things: 1, it establishes that it is the mathematical Einstein tensor that corresponds to the physical energy-momentum tensor; and 2, it establishes a proportionality relationship between them, including the use of physical constants to ensure dimensional homogeneity.

Why does the 5 pots have the same temperature as the 3 pots? Why does the 7 pots have the same temperature as the 3 pots and not the 5 pots? One other thing: In the ideal gas law, pressure, which is proportional to temperature, depends only on the translational motion of the gas molecules. Neither rotational motion, nor vibrational motion affects the pressure and therefore the temperature of an ideal gas.

Suppose you add thermal energy to a substance with 5 degrees of freedom. The equipartition theorem says that equal energy will be added to each degree of freedom. This means that 3/5 of the total added energy will be added to the 3 degrees of freedom corresponding to translation, leading to an increase in the temperature. The remaining 2/5 of the total added energy do not contribute to the increase in temperature, but because the increase in temperature due to the energy added to the 3 translational degrees of freedom is concomitant with the energy added to the 2 non-translational degrees of freedom, the energy of the 2 non-translational degrees of freedom will still depend on the temperature. There will be 3 units of energy in the object with 3 degrees of freedom and 5 units of energy in the object with 5 degrees of freedom. But the two objects are at the same temperature. Therefore, only 3 units of energy in the object with 5 units of energy are producing temperature, the same temperature as produced by the 3 units of energy in the object with 3 units of energy.

But this conflicts with the equipartition theorem. Each degree of freedom contributes an energy of ½kT. The more degrees of freedom, the more energy. But this requires that only the ever-present three translational degrees of freedom contribute to the temperature. Otherwise, the energy would not be proportional to number of degrees of freedom. The increase in heat capacity as the available degrees of freedom increases indicates that the energy is increasing faster than the temperature. Thus, the 5/2 R for the inclusion of rotations indicates that the increase of R from 3/2 R to 5/2 R is not causing an increase in temperature beyond the 3/2 R arising from translations. If all degrees of freedom contributed to the temperature equally, the heat capacity of all substances at all temperatures would be the same regardless of the number of available degrees of freedom.

All degrees of freedom do contribute to the entropy. But not all degrees of freedom contribute to the temperature. If it did, then given the equipartition theorem, all substances would have the same heat capacity, and the above equation you posted would not hold.

I was actually thinking the same question. The answer I came up with was that vibrational motion within crystals is translational motion of individual molecules. The modes that do not correspond to temperature are rotations of individual molecules, vibrations within individual molecules, which are distinct from the vibrations between molecules within a crystal, and electronic states. The way I see it is if one were to place a quantity of helium, which has only translational modes, within a sample of a given substance that has an arbitrary number of modes, then how much energy is transferred from the sample to the helium or visa versa? At thermal equilibrium, the two temperatures must be equal, but what is the distribution of energy? I think the virial theorem is involved. I seem to recall that vibrational motion within crystals is not just translational motion but also potential energy. That is, two modes but only one corresponding to temperature.

Option 2 is saying that general relativity is not the most fundamental theory of physics. The dimension of mass is not only associated with gravitation, but is everywhere in physics. The current definition of a unit of mass is not even based on being a gravitational source, but rather specifies a numeric value of Planck's constant. However, if mass is quantum mechanically producing spacetime curvature, then that spacetime curvature must also be consistent with general relativity. There was a time that I believed in option 1 but in more recent times I have felt that spacetime curvature is too ethereal to provide us with anything other than gravitation. On the other hand, I find it difficult to accept that there may be some physics that isn't entirely based on the properties of spacetime.

Well, chromium(VI) compounds can cause organic material to burst into flames.

One thing should be mentioned: Only the translational modes of molecular motion contribute to the temperature. Different substances have different heat capacities because they absorb energy in all their modes, but only the translational modes increase the temperature, thus the more modes that are available to the molecule, the more energy that is absorbed for a given increase in temperature.

I think the image of Nikola Tesla on the first video should be considered a big red flag as far as pseudoscience is concerned.

Yes, the SMT-VSL and the expanding universe theory are equivalent. This means that there are no observational or experimental differences between these two points of view. If you are seeking to observe differences, then you are really saying that the SMT-VSL and the expanding universe theory are not equivalent because any observable difference is a non-equivalence. If you are abandoning equivalence, then why would matter shrink in preference to an expanding universe? The size of atoms is governed by laws of physics, whereas the size of the universe is not, so one would not expect there to be a constraint on the size of the universe similar to the constraint on the size of atoms. Also, if you are abandoning equivalence, then where specifically is the non-equivalence? That is, what specific observation or experiment distinguishes these two theories? This actually requires you to look beyond the apparent equivalences to something not deducible by a mere change in the point of view.

Let [math]M[/math] be the mass of the non-rotating spherical mass (neutron star but assumed to be non-rotating), [math]R[/math] be the radius of the spherical mass, and [math]h[/math] be the height above the ground at radius [math]R[/math] from which the object of mass [math]m[/math] (measured at height [math]h[/math]) is dropped. Assuming that the collision with the ground is completely non-elastic, the energy [math]E[/math] (also measured at height [math]h[/math]) released is: [math]E = \left(1 - \sqrt{\dfrac{g_{tt}(R)}{g_{tt}(R+h)}}\right) m c^2[/math] where [math]g_{tt}(R)[/math] and [math]g_{tt}(R+h)[/math] are the [math]tt[/math]-components of the Schwarzschild metric at [math]R[/math] and [math]R+h[/math] respectively. Thus: [math]E = \left(1 - \sqrt{\dfrac{1 - \dfrac{2 G M}{c^2 R}}{1 - \dfrac{2 G M}{c^2 (R+h)}}}\right) m c^2[/math] Note that [math]\sqrt{\dfrac{g_{tt}(R)}{g_{tt}(R+h)}} = \sqrt{\dfrac{1 - \dfrac{2 G M}{c^2 R}}{1 - \dfrac{2 G M}{c^2 (R+h)}}}[/math] is the ratio of the mass of an object at [math]R[/math] to the mass of the same object at [math]R+h[/math], the object being at rest at both heights.