MigL

Had that discussion with AJB a few years back. The question was whether Gravity requires a field model or a geometric model. His reply ... in GR, geometry is the field. ( thanks AJB )

Thanking SFN is a little self-serving. SFN is the membership, and all the various opinions/knowledge contribute to the experience here; even the Mods are simply members who have taken on ( much ) more responsibilities. When you joined, followed the rules, and respectfully shared your opinions/knowledge with the rest of us, you made the Forum a richer experience for us all.

I don't think so. Gravitational fields don't propagate, they are simply there. What propagates are 'changes' to the gravitational field, such as the gravitational waves you mentioned. The gravitational field, as Geordief correctly stated, is simply a curvature at each point in space-time, as described by the metric. This geometry is the field, and 'measurements in space and time' are the definition of the metric. Newtonian gravity was not 'final', but neither is GR. And I doubt Quantum gravity will be 'final' either.

Keeping in mind I'm a lot younger than you old timers ( 😄😄 ), and was in Uni 40 to 44 years ago, my only experience was when one 'affluent' Arab guy, who drove a brand new Datsun 280z, wanted to buy my lecture notes for $500. He never showed up to lectures, and since the offer was $500 Canadian I had to decline. This was 2nd year; he wasn't there for the 3rd. Back in those days , if you wanted to plagiarize, you actually had to do research through periodicals and research papers, not just type search words into google.

Even after overcoming electron degeneracy, a neutron star is composed of ordinary matter, and there is no need for an 'event horizon', at least until the Tolman-Oppenhimer-Volkoff limit, and it becomes a Black Hole. The 'black hole' is the event horizon. As for the magnetic fields, other than the increase due to collapse and conservation of angular momentum ( figure skater effect ), I don't think we have a viable explanation yet. "The origins of the strong magnetic field are as yet unclear.[31] One hypothesis is that of "flux freezing", or conservation of the original magnetic flux during the formation of the neutron star.[31] If an object has a certain magnetic flux over its surface area, and that area shrinks to a smaller area, but the magnetic flux is conserved, then the magnetic field would correspondingly increase. Likewise, a collapsing star begins with a much larger surface area than the resulting neutron star, and conservation of magnetic flux would result in a far stronger magnetic field. However, this simple explanation does not fully explain magnetic field strengths of neutron stars.[31]" From Neutron star - Wikipedia

The angle of the 'v' on opposed cylinder engines contributes to the 'smoothness' of the engine. Flat 4 or flat 6 configurations are popular, as is 90o for V8s and 60o for V6s. This has to do with the equal distribution of firing pulses in the 720o cycle. Lately manufacturers have been using balance shafts to smooth out engine vibrations, and coming up with all sorts of weird angles, in order to make the engine more compact. "Since 1991, Volkswagen has produced narrow angle VR6 engines with V-angles of 10.5 and 15 degrees. These engines use a single cylinder head shared by both banks of cylinders, in a design similar to the 1922-1976 Lancia V4 engine. The VR6 engines were used in transverse engine front-wheel drive cars which were originally designed for inline-four engines. Due to the minimal extra length and width of the VR6 engine, it could be fitted to the engine compartments relatively easily, in order to provide a displacement increase of 50 percent." From V6 engine - Wikipedia

Hoping for clear skies in London ? Unless you mean London, Ontario ( in Canada ), I'm afraid you're gonna have to move.

I'm fairly certain that C Rovelli, a proponent of LQG also shows that BHs can only collapse to a certain point, and then must 'bounce, to something similar to a White Hole, but in the past, also preserving information. This is similar to the 'bounce' that LQG predicts as the initiator of the Big Bang, but I cannot recall where I read this. The problem is that both String theory and LQG are 'theories in search of a universe to describe'. They are both getting more and more elaborate, but there is no experimental verification of even their most basic presumptions.

Study something you enjoy learning about. ( as Genady mentioned )

I wasn't familiar with this version of Zeno's paradox, Studiot. The only one I'm familiar with involves the arrow travelling successive half-distances. Thanks for the info.

Substitute Karl Marx for Jesus and Communism for Christianity, and you have the same results, but much more recent. Every institution can be perverted by unscrupulous people for their own ends.

If it is true that a lot of American Republicans take the Bible literally, I would guess that it is also true of some members of this forum. Why would anyone take any of these stories literally, and not as a 'mirror' of the morality of our civilization at the time they were written ? To believe these stories you also have to believe in an omnipotent/omniscient white bearded man who created the universe, and killed His Son, just to resurrect him three days later. Sounds like a bit of a 'stretch' to me.

Problem is, rocket fuel has to have a certain efficiency. The thrust provided by the mass of propellant has to be able to acheive orbit.

Markus usually uses the analogy of "What is north of the North Pole ?" Myself, I would think geometry is needed for time and space. Without geometry, at 10-43, Planck scale/time, there is no geometry. This would be what J A Wheeler termed 'quantum foam'. As

It may be helpful to consider that, although the vacuum has energy, and therefore a masss equivalence, the vacuum, or space, does NOT have a velocity. So your definition of acceleration is not quite applicable. What we are considering is an accelerated rate of expansion.

Like the Event Horizon of a Black Hole, I like to think of space-time as a mathematical construct, which is'superimposed' on a volume evolving in time. This mathematical construct, or geometry, is the gravity field in GR, and is what is curving. I maintain that neither space nor time have any property that can be curved. And even if you could curve space like your Earth circumference/diameter analogy, we know that gravity is mostly a 'curvature' in time. How would you show that ?

Are those the voters, or the Government officials, Dim ?

The most populous species on the planet are insects, and a lsrge number of them are 'carnivores', subsisting on blood and innards of other species. Some of them even have 'herds' , like the 'farmer' ants with their aphid herds. ( you might wanna tell them aphid farming is bad for the environment )

Seems to be the response of most Governments, not just American. They make up for their incompetent response by throwing the people's money at the problem.

There is no question that, on a positively curved manifold, the circumference of a circle will be less than pi*D. Similarily, a triangle will have angles that add up to more than 180 deg. But this discussion originally started in another thread, where you claim the circumference of the Earth is less than pi times its diameter. Now we both know nobody has drilled a hole through the Earth's core to measure its diameter. The diameter is 'measured' against a co-ordinate system anchored on far-away points. This co-ordinate system will look like Janus' link from the other thread This co-ordinate system supplies us with x, y, z, and (-ict) co-ordinates which form the interval, S, that is the basis for the metric which determines the 'curvature' of this co-ordinate system we call space-time. It is also the model for gravity; and this model is what is curving. The surface of a sphere, like the Earth, is an actual physical thing, that can curve, and so, we can measure its curvature locally by comparing diameter to circumference. Space-time, on the other hand, is simply a volume evolving in time. It doesn't possess any property which can be curved, bent, warped, or twisted. Incidentally, the model which is GR, can be formulated in several ways, which are equivalent. It can be formulated in terms of varying distances and durations ( intervals ), or, in terms of the units themselves ( the rulers and clocks ) changing. ( this may be from Misner, Thorne, Wheeler Gravitation; but it's a big book, I can't find the reference right now )

For the orbits of Jupiter and Saturn, Newtonian gravity gives essentially the same results as GR. The only anomaly is the procession of the orbit of Mercury, which is much deeper in the Sun's gravitational well, and subject to much greater 'curvature' on the time axis. Since GR essentially reduces to Newtonian gravity at the lo mass/lo energy limit, only a fool would attemt to solve the set of EFEs for outer planetary orbits when Newtonian gravity will suffice. Even NASA uses Newtonian gravity models to land rovers on Mars and 'sling-shot' Voyager around outer planets. What does that have to do with comprehending GR ?

And is your measuring apparatus, rulers, clocks, etc. not also curved ? We use light to determine what is 'straight', yet light curves around massive objects. All we can do is measure the effects; we can't measure the underlying 'reality'. As members are fond of saying around here ... "The model is just the map, while 'reality' is the actual terrain"

The above members have explained things to you in the clearest possible manner, yet you are either unable, or unwilling, to comprehend. The model we have of gravity tells us that gravity's behaviour is exactly the same as if space-time, the co-ordinate system, was curved. It is not a 'description' of reality, but rather, a predictive model. And your incredulity ( or incomprehension ) notwithstanding, it does an excellent job at those predictions.

If we don't agree on the meaning, or even if we are, a 'civilization, how can we establish that we are in the 5-95% of the Gaussian distribution ? Intelligence, or lack thereof, also tends to alter the distribution curve, as our 'evolution' is not solely controlled by environmental forcings, once we have the ability to control our environment ( to an ever increasing degree ).

That seems rather ambiguous/inexact, as there are no other civilizations for comparison. One could argue that we are not fully 'civilized', and may be at the 0.01 % of our civilization lifespan. One could also make the argument that intelligence will have an effect on civilization lifespan, for better or for worse. It may mke our civilization last forever, even expanding to other star systems, or, it may lead to our early demise. You need a definition of 'civilization' and 'intelligence', for comparison purposes; and there are none for comparison to. Statistical analysis with too many unknowns, such as with the Fermi Paradox, usually lead to invalid conclusions.