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The effectiveness of carbon sequestion via weathering of basalt etc. is ultimately limited by actual reaction rates. One only has to consider the rather slow disappearance of such basalt structures as eg the Giant's Causeway (and essentially the entire surface lithosphere of Northern Ireland), Fingal's Cave, Iceland to understand that these carbonation reactions are not lightning fast. Even in finely divided form, a visit to a basaltic black sand beach is scarcely seething with chemical activity. But that does not make it a factor to be ignored. It cannot be a solution to all our problems but it can help. EDIT: I see @studiot has just made the very same point (simulpost) I found quite a useful summary of its global relevance at https://www.degruyter.com/document/doi/10.2138/am-2019-6884/html?lang=en. I've wondered for a while whether weathering of the calcium silicate content of concrete had a similar effect, and found an interesting Caltech article at https://www.caltech.edu/about/news/weathering-cement-important-overlooked-sink-carbon-dioxide-53134 ... which I found quite interesting.1 point
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You need energy to extract the basalt. You need energy to transport it to a plant. You need energy to grind it up. You need energy to transport it to suitable farm land. And the farmer needs energy to spread it and plough it in. Nearly all of that at present is done using diesel. So at the moment, it's a big waste of time and effort, and probably adding more carbon than it's fixing. What it does do, is allow some big carbon-emitting companies to buy "carbon credits" and carry on emitting, while getting a tax break. Maybe in the future, when diesel, petrol and gas have genuinely been replaced with renewables or nuclear, the scheme might make a marginal difference.1 point
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It sounds like the question is only about gravitational time dilation, not about inertial frames or relativity of simultaneity. Bob and Alice agree that the local speed of light is c. They don't say "I can measure the speed of light in empty space using measurements I'm making locally in a gravitational well." Bob errs in doing so. Another way to say it is, "the coordinate speed of light isn't always c", however I don't know if "coordinate speed" (as in, measuring d and t using a distant observer's coordinates) is a standard term.1 point
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That's correct. They will not agree on the time the photon was emitted nor the distance, even taking into account the extra distance the photon traveled.1 point
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Some kind of a book,play or collection (?) about her later years coming out I think. They played this version of Pete Seeger's song whilst discussing her on the radio with the author.1 point
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Nah, it slowly gets time to think about the 'downward causation', you mentioned it already several times, and (nearly?) nobody reacted on that. My first assumption is that the universe is physically causally closed. That means that no momentum or energy somehow just leaks away, or arises from nowhere. E.g. the neutrino was proposed as a solution for missing energy in beta-decay. Only after 30 years (or so) it was confirmed that the neutrino really existed. My next assumption is that the brain is also physical, so we will never find physically causal holes in brain processes. That means that we will never find that a soul interacts with the brain: not as input (which would have been a nice gateway for proposing that we have libertarian free will), nor as output (which would have been a nice gateway for epiphenomalism). (And both together for interactionism.) Neither the neurologist, nor the physicist, studying the brain on their respective levels, will ever have to refer to some none-physical causes. So a 'cause' coming from 'elsewhere', (and wouldn't a downward causation be such a cause from 'elsewhere?) does not fit in this picture. So case closed. But to speak with PBS Spacetime's Matt O'Dowd: "not so fast". Take the following computer program: wait 10 minutes; shutdown computer; Such a kind of program can be written for every kind of computer system I know: Linux, Windows; and I am pretty sure Mac too, in short, all kinds of computer systems. Now imagine we give a computer running such a program to a physicist, and ask him to explain why this Linux computer stops after 10 minutes, but we allow him only to explain it on physical level. Theoretically, he can succeed (maybe 10 minutes is a bit short...). Using the physical architecture of the computer, and the laws of quantum mechanics he can causally explain why the computer shuts down. That means also, that his explanation is 'physically causally closed'. But now we give him another computer, running with Windows, and ask him again to explain why the computer turns off after 10 minutes. Now he must start all over again, because the hardware is different, and so are the changes because of the different operating systems. Assume he will just as well succeed. But let a programmer look, and she can tell in one glance why the computer stops. Would that count as 'downward causation'? Personally, I am inclined to say 'yes', because at least I have a better feeling of understanding why the computer stops by the programmer's explanation. Let's take a more complicated example: we organise a virtual tournament between two chess computer programs, A and B. A and B both have a red light, which signifies who has won the match. In about 70% of the cases, the light at A burns after a match. So we see the red light mostly flashing up on the A-side, but sometimes on the B-side. We ask the physicist for an explanation why sometimes the light at the A-side burns, and sometimes at the B-side, same conditions as above. Well, assume again he is able to understand what is happening, in a similar way as the simple program above. But did we learn something from his explanation? And do we now have a full understanding why in 70% of the cases the light at A-side flashes up? In the first place, we would understand much more if we knew, at a higher level, the lights depend on games of chess, and signify which program won the match. But in the second place, how correct the explanations of the physicist might be, can we say that he really understands why in 70% of the A wins? Let's ask the system administrator: "no, they are the same programs, both X-Chess". Are you sure? So she looks better, and suddenly she says "Wait! B is version 1.0, A is version 1.1. One moment, I'll look up the release notes". And there it is: Now we understand why the light on the A-side turns on more often! B just can't do certain moves, because they are not implemented in it. What would you say, @TheVat? Is this also an example of downward causation? At least, we need the knowledge that the hardware has implemented two chess programs, and by understanding chess, we understand what physically is happening: A's light burns, or B's. I'll make the arc to my compatibilist understanding of free will. Only on the level of persons mental phenomena, intentions, believes, observations, aesthetical and ethical values, and actions exist. So only on that level, free will can be meaningfully defined: as acting according my intentions, believes, observations, aesthetical and ethical values. Nevertheless, all the mental phenomena 'run on the physical wetware of the brain'. And therefore the physicist and the neurologist will simply not be able to find these on their respective level of explanation. Imprisoned on one side by their detailed view on reality, and mostly by using a meaningless, useless and theological concept of free will, they do not see the wood for the trees.1 point
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That surely is the Laplacian operator, which is nabla dot nabla. "dot" meaning the 3D "dot". 4D nabla dot 4D nabla is called the d'Alembertian, and it's a square (at least in physics). https://en.wikipedia.org/wiki/Laplace_operator https://en.wikipedia.org/wiki/D'Alembert_operator1 point
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Number 0, I am thinking of getting a psych eval. Seeing and talking to higher beings is something that would be worry me quite a bit. Especially combined with thinking of shooting as the first action.1 point
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Because it is based on the FLRW solution to the EFE, and therein only the spatial part of the metric is non-trivial and carries an expansion factor, there is no time dilation in this cosmological spacetime. Both GR in general and its particular solution for this case, the FLRW metric, predate Hubble’s observational findings. Metric expansion is a direct consequence of the laws of gravity, for any homogenous and isotropic distribution of energy-momentum that meets certain criteria; it’s not an independent, stand-alone idea. Accepted as the basis for a model in the context of cosmology, yes, but not invented or theorised - see above. Redshift was historically the first observational evidence that became available to us, but nowadays the Lambda-CDM model covers many other observations too, which were made after Hubble, eg the CMBR with its polarisation, the Ly-wavelength g-wave background, large-scale structure, acoustic baryonic oscillations, ratios of light/heavy elements etc. Among all proposed cosmological models, it is the one that fits the body of all available data the best - though it almost certainly won’t be the last word, I dare predict, because it also does have its problems. You are welcome to try and find a solution (that isn’t just a trivial diffeomorphism) to the EFE that leads to such a law. Remember that it should also be compatible with all other observations, in order to be a useful cosmological model.1 point