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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.

There is a special happy feeling knowing one is not part of a garbage fire. Didn't walk from Springer Mtn to Mt Katahdin, but I walked some of it in Vermont and NH. It's all common sense stuff - pick your time (e.g. not winter in the north, not high summer in the South), bring a partner you don't mind having inspect you for tics, bring mosquito repellent, sturdy hiking boots, etc. Keep food in a bag and hang it from a high tree branch when you sleep, never in your tent. Take increasingly long walks before the trip, for several months, to build up muscles and spot any joint/tendon issues beforehand. Keep socks dry. Watch out for the protozoan fiend of Appalachia, Giardia lamblia. Do your homework on finding a high quality water filter that will strain out Giardia - pump filters are the best. Boiling water is a monumental PITA. Ditto cooking. Dried fruit, oat bars, pemmican, peanuts, trail mix, powdered milk or powdered non dairy drinks, are all handy sources that don't need fuel to prepare. Don't gather trail sources of food unless you know exactly what you're doing. Blackberries yes, mushrooms no. No sustained eye contact with bears. Etc.

Golden Plover chick

Unclear to me what "any background geometry" would be here. As @Genady pointed out, causation can be defined operationally, e.g. I push two distant planets together and local curvature increases in "response" to greater local mass. The stress-energy tensor includes mass, right? Energy density is the whole thing in GR context - rest mass, pressure, momentum etc? I agree with @Moontanman on how interesting this thread is. I wish I had spent more time in my youth on physics instead of counting cougar scat.

While these comments are certainly true, I think the relationship isn’t as trivial as it might appear; after all, a vanishing Einstein tensor doesn’t necessarily imply a flat spacetime, so these equations form only a local constraint on geometry, but they don’t uniquely determine it. Any background geometry is as much considered to be a ‘source’ as is local energy-momentum, when it comes to working out the particular form of a metric at a certain event. Furthermore you have the non-linearities of the constraint itself, which, in some sense, might also be considered a ‘source’. But those contributions of course don’t explicitly appear. Personally, I just think of spacetime as pure geometry - the only difference between vacuum and non-vacuum is how the Riemann tensor decomposes (Weyl and Ricci curvature), so I envision it purely geometrically all the way. In that way of thinking, no question of causation arises, you just have ever-shifting geometries. But maybe that’s just weird old me

Mechanical analog timer, such as: will be a PITA because you will have to rewind the wheel every time the previous cycle ends.... e.g. 48h The Arduino method will work as long as there is power (if there is no power, the plants also have no light anyway).

Buy a smart plug / wall receptacle. Connect it to Alexa similar home automation app. Setup schedule (the bulb and Alexa both do this simply, perhaps as a routine). Then just plug your lights into that junction with the new smart plug

That is f-ing hilarious!

Indeed. I --and others, you among them-- have said it before elsewhere on the forums, actually. It's the energy-momentum that sources the gravitational field. I also agree with the absence, of necessity, of any causal connection between the Einstein tensor and the energy-momentum tensor.

In spite of this, a 'causative relationship' exists operationally, i.e., we can, in principle, manipulate the source and this would affect geometry, but there is no way to manipulate geometry without manipulating the source. The 'symmetry' is broken.