You make an interesting point. I believe (possibly wrongly) that you are saying that one should only consider mass that is within the local Hubble volume to compute the force on test galaxies, in which case we are at the gravitational center of the frame (because it truly is a finite sphere centered on us). One should not compute the force from the test galaxy's frame, since it is non-inertial to us. I think I can buy that argument. To me, it hinges on the finiteness of the Hubble volume and the speed of gravity. If the universe is infinite and if Newtonian gravity acted instantly, I think one could still argue that the test galaxy would feel no gravitational force, even in our inertial frame.

All inertial frames are correct in special relativity. Special relativity works well in this case.

Though we aren't perfectly inertial due to the acceleration of the sun and the galaxy, it's still close enough. Those accelerations are relatively small.

This is a nice Newtonian explanation, but I've always felt that there is more subtly than it acknowledges. It relies on Gauss' law applied to a frame centered on us, but why is that the correct frame? An argument can be made that gravity exerts no net force, just using Newton's law and symmetry.

It totally depends on the river and specific local conditions.

It is complicated because of how kinetic energy can manifest.

You can have an increase in velocity, an increase in mass, or a combination of both.

The exact combination is dependent on a massive amount of variables like LWD, Manning roughness coefficient, channel longitudinal profile, channel cross-section geometry, amount of precipitation, amount of time precipitation occurs over, antecedent soil conditions (saturation excess vs infiltration excess flow), aquifer and other groundwater dynamics, hyporheic exchange rates… the list goes on and on.

Yes light cannot escape them, which is because of the incredibly strong gravity well of a black hole.

The very recent articles on black holes and dark energy are very speculative.

You're welcome, glad I could help!

Very very slightly, yes. However, the quantity released is fairly minor. And it's diluted into quite a lot of water.

In addition, it is pertinent to note that the rifling marks present on both bullets are identical, yet one of the bullets does not rotate when discharged. Provided the assumption that the velocity of the bullets at the point of discharge is equivalent and that both are aerodynamically stable, it follows that the rotational force generated by the rifling in the first bullet consumes a portion of its kinetic energy. Consequently, there is an increase in the drag experienced by the rifled bullet as compared to its non-rifled counterpart. Moreover, it can be inferred that the absence of rotation on the second bullet results in a more laminar flow, causing less distortion of drag and leading to lower drag values

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It’s a myth! Our sense of smell just doesn’t get as much attention so doesn’t get trained like our vision does. https://www.theatlantic.com/science/archive/2017/05/alls-smell-that-ends-smell/526317/

Humans possess olfactory abilities akin to other animals. It is widely recognized that the scent of a newborn is distinctive and recognizable to most individuals. Although humans have evolved differently in this regard compared to other species, it is plausible that our sense of smell still serves a purpose that may not be consciously acknowledged.

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I had a brief reread of the articles discussing the theory. Bear in mind that my personal background is in Cosmic Inflation and so I'm not intimately familiar with this theory. From what I gleamed Einsteins Equations can predict an object that is essentially a concentrated bundle of Vacuum Energy, which is a commonly theorised candidate for Dark Energy. This object would look and act like a Black Hole to outside observers. Therefore, any Black Hole that we observe could in fact be a source of Dark Energy, and we wouldn't be able to tell with our current understanding of the model.

Essentially its a mathematical model that has been proposed, rather than any new observations.

> any object that crosses the event horizon is moving at or faster than the speed of light relative to an observer outside the black hole [..] In summary, while it is possible in theory to cross the event horizon of a black hole and orbit it

But hasn't the first bit just explained exactly why that's not possible, not even in theory?

Our reference frame is only locally inertial, where "local" means "close enough that the global geometry of spacetime can be ignored". In special relativity spacetime is flat everywhere and there is no such distinction, but in GR the same is not generally true.

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> My basic understanding of orbital mechanics would suggest that this should be possible right?

No, because it would require the velocity to exceed the speed of light when you're approaching the periapsis. This is where the "classic" calculations fail. In "regular" orbital mechanics problem the closer to periapsis you are, the faster you're moving, and this way you "climb up" from the gravity well. However in reality there is a limit of how fast you can move, and in your example you'd have to exceed the speed of light in order to climb up from the gravity well after crossing the event horizon, and this is not possible.

Correct me if i misunderstood. So in that article where they say black holes might be the source of dark energy they say so, because they measured/observed more dark energy impact around those black holes? Also fyi i am currently studying undergrad physics so the very basics(e.g. black holes are black because light cannot escape them) I think, I understand, so you can complicate more if you have the knowledge.

Dark energy and black holes are separate. Black holes are objects that are black because their gravity well is so strong that light cannot escape them. Dark energy is a force that pervades all of spacetime. We measure how much dark energy there is by the red shift of galaxies outside of our local group, and other standard candles like class 1a supernova and Cepheid variable stars. Is there a dark energy particle? Is it a fundamental force like the strong force in an atom? We don't know. So far we can just measure its impact on the expansion of the universe.

Would the release of CO2 in this reaction add to the acidification of the seawater?

No. Just...no.

You're completely ignoring the fact that once you cross the event horizon, you are effectively pulled to the "surface" of the "body". This is an effect which is inescapable, which is why a black hole is not a planet or star and should not and cannot be thought of as such.

No. The solutions to the relativistic version of the Kepler problem are different from the Newtonian ones:

You still have hyperbolic-like, parabolic-like and elliptic-like solutions. However, the parabolic ones can loop around the black hole a couple of times before going off to infinity, and the elliptic ones will have their perihelion precess around it. Additionally, you get solutions that cross the horizon and never come back out, eventually hitting the singularity, and trajectories that asymptotically approach a circular orbit.

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How come there is a large area of Mesozoic terrain that stretches across the Atlantic Rift on top of ground younger than it?