Everything posted by swansont
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Climate Change Tipping Points:
All one can validly infer from this is that the max did not occur at 9AM or 3PM
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How does carnot efficiency limit manifest itself in solar cells?
It can't be at 0K Ideal is one thing but violating physical law is another.
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Is Gravity a Force?
One other aspect of the problems with thinking physics is telling us what reality is is that over its history we've found better and better descriptions of how nature behaves. So it's ludicrous to think that Newtonian physics described reality, when we know that it was supplanted by relativity and quantum mechanics, and we know that these models are incomplete, and it's likely we will have a better model at some point down the line.
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Is Gravity a Force?
Something with a certain behavior which we call the top quark was discovered. Generally, discussions about this do not split hairs about whether or not we are searching for reality, though there are some good discussions on the bad habit of reifying these things in physics. Mermin's "What's Bad About This Habit?" is a prominent one. Later on he quotes Bohr
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Is Gravity a Force?
This is different from One is asking about science, and the other is asking about scientists. Scientists are free to do things other than science, in this case metaphysics or some other philosophy, and some of them do. I am in no position to say they should or shouldn't. But people looking at the fundamental nature of the world are doing metaphysics, whether they explicitly admit it or not. (similar to the fact that some of what I do is engineering, even though I am a scientist. Disciplines blend together in many ways)
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Is Gravity a Force?
No, of course not. How do you get from what we said to this?
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How does carnot efficiency limit manifest itself in solar cells?
I have already mentioned reflection, recombination and creation of phonons.
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Is Gravity a Force?
I had thought that the difference between religious belief (belief despite there being no evidence) and other kinds (belief because of evidence) was apparent. The equivocation is why some people try to avoid using the word. The belief referenced in your quote is not religious belief, but the use with regard to creationism is. I apologize for overestimating the situation.
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Is Gravity a Force?
Believing a theory is not the normal description; in this case its because you have a non-scientific alternative that relies solely on belief. Notice that your quote does not actually cite belief. The theory works whether you believe in it or not, and it's a good theory because it works - it matches observation and because of its strong explanatory and predictive powers. If there was a competing theory one could objectively compare them. Lamarckism, for example, was discarded because it lacks a mechanism for it to work. Not working = bad Nothing about that lays claim to revealing realty. But the models and mechanisms of evolution aren't the examples that are most relevant. I argue that would be physics, and the reason that we know physics isn't trying to describe reality is because physics itself admits that it's making stuff up to make good models. Nobody claims that electric field lines physically exist. Phonons are quantized vibrational modes of a structure - not physical particles that exist independent of that structure. Electron holes are the absence of electrons, not some particle that exists on its own. These things aren't real, physical entities. They are calculational and conceptual aids to modeling behavior.
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Time dilation, electrons, and quantum mechanics
To expand on what I said earlier: some of these explanations are leaning a bit too hard on classical physics in quantum situations. What they are doing is trying to use a classical analogue, that a body in a circular orbit has a KE that is half the magnitude of the PE, so for an orbit close to the nucleus (i.e. using the Bohr theory, which we know isn't correct) an electron in hydrogen, which has an ionization energy of 13.6 eV, has a KE of 13.6 eV and a potential energy of -27.2 eV. Those numbers aren't actually true in the QM solution, but those are the most probable values. The improper extrapolation is to assign 1/2 mv^2 to the KE, since you can't assign a velocity to the electron. When you get to an atom with a large Z, some electrons have a high enough average KE that relativistic corrections are necessary. The incorrect explanation is to say you are correcting the speed, but this doesn't show up anywhere in the equations. You solve the relativistic version of the wave equation, which gives different results than the non-relativistic version (Schrödinger equation) so there is a difference in the energy eigenstates. A relativistic correction of energy, without ever invoking velocity. I recall some years ago reading a pop-sci article on this and they linked to the paper it was based on. The pop-sci article talked about the relativistic correction of the speed, and saying that the mass of the electron increased. When I read the journal paper, none of that was mentioned. It was only the energy that was corrected, as one might expect of a rigorous paper. The pop-sci article had tried to use this classical explanation to make the effect make sense, but it made for incorrect physics.
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How does carnot efficiency limit manifest itself in solar cells?
AFAIK you can get materials from essentially zero out to 4 eV. I don't know how closely you approximate a continuum, but from a purely hypothetical standpoint of an ideal case it's not IMO more outrageous than other assumptions one can make. But at some point the practicality has to kick in, since your material is infinitely thick. (edit: see e.g. https://en.wikipedia.org/wiki/Wide-bandgap_semiconductor https://en.wikipedia.org/wiki/Narrow-gap_semiconductor ) Even under the idealized case, though, the efficiency is not 100%, for reasons I've described.
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How does carnot efficiency limit manifest itself in solar cells?
You can get different bandgaps with different combinations of materials, and varying the doping/stoichiometery. GaAs. AlGaAs, AlGaxAs1-x etc. so there are potentially a quite large number of combinations But the proposal doesn't consider the possibility of e.g. a 2 eV photon being absorbed by a material with a 1 eV bandgap, or that the material has to be thick enough to absorb all the light if you want maximum efficiency
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Is Gravity a Force?
The professor is confirming the validity of general relativity. Any more is you reading something into it. How do you empirically determine the "best" explanation without invoking philosophy or other assumptions? "True" here means valid. i.e. we have confidence that the theory can be applied and give god answers. But it's still all about behavior and observation, and not about any underlying reality.
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Is Gravity a Force?
String theory has a model, but not much in the way of experimental confirmation thus far. It's physics, but not yet an actual theory in the scientific sense of the word - as beecee noted above, it's more properly termed an hypothesis.. It's a work in progress.
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Climate Change Tipping Points:
What's your point? I highlighted the information from your link, where they explained how they did the max and min temperature measurements and recordings. None of this, AFAICT, contradicts that. Pasting a couple of links doesn't clarify anything about your claims.
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How does carnot efficiency limit manifest itself in solar cells?
Two things. 1) I'm thinking of the case where, owing to thermal motion, that the electron needs a little more than 1.8 eV to reach the conduction band. 2) how does an electron with no KE contribute to a current? To your point about the electron thermalizing, sure - but this represents another loss mechanism you have to worry about I don't know how you would do that. Electrons dropping to a lower energy is a spontaneous reaction. The only way to prevent it is to somehow make the lower state unavailable
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Is Gravity a Force?
How do you test it? How do determine if that’s the “truth”? All you have are observations. If you don’t have that, all that’s left is philosophy (points at metaphysics)
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Time dilation, electrons, and quantum mechanics
Alternate viewpoints are fine, in general; there are many instances where you can explain a phenomenon by analyzing the energy, and also by analyzing the momentum.
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Question about length contraction and motion
Your map is only valid in one frame of reference
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Time dilation, electrons, and quantum mechanics
No, I made no mention of speed. There are relativistic corrections to the energy. Synchrotrons are classical and you can talk about the speed of the electrons. No, but you don’t know the speed. The explanations talking about this are making an invalid connection, using a classical equation/concept where it’s not valid https://en.wikipedia.org/wiki/Klein–Gordon_equation#Derivation
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Time dilation, electrons, and quantum mechanics
There are relativistic corrections to the energy, which do not explicitly require having motion. The explanation that it’s relativistic speeds is pop-sci/watered-down. QM uses things like energy and momentum operators, and you solve for energy eigenstates. Which differ when the energy gets to be an appreciable fraction of the rest energy.
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Existence is...the Absolute Singularity.
! Moderator Note You were the one who brought up functioning brain. Your original claim was “can you act, before you think?” This is moving the goalposts; both use of a fallacy and arguing in bad faith, both of which violate the rules
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Lorentz invariant gravity (split from Is Gravity a Force?)
! Moderator Note Critiques of GR and exploration of an alternative model is OT - split
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Is Gravity a Force?
Science cannot answer this. It’s a metaphysical question. One can’t affirm that GR is reality, only that it models observed behavior very well. In that model, gravity isn’t a force. In the Newtonian model, it is. You’re obviously quoting someone. What is the source of this quote?
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Climate Change Tipping Points:
“Recorded” is not the same thing as “measured” The image caption on the right says they use a max/min thermometer. It measures the high and low over some time period. It does not mean either one occurred at 9 AM. It means that’s when the numbers were recorded. This implies for a 9 AM recording, the high is for the previous day, just as your link says (Minimum temperature is recorded against the day of observation, and the maximum temperature against the previous day) https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100141761