Leaderboard

There is a shorter way to reply to only a part of a post. Select the part, a floating text appears offering to quote the selection (see below), click on it, the rest is the same minus a need to remove anything.

As fast as the electrons can get out of their way! 😊

Important cosmology update

just a very tiny insignificant correction: 2nd.

Yes. Hitler wasn't all bad. He made the trains run on time, built motorways and handy little air cooled cars, and kitted his troops out in some pretty snazzy uniforms. Unfortunately, he did have his little faults as well. So if someone had thrown him out with the bathwater when he was a baby, the world would be a bit nicer now. Religion is an obnoxious baby that grows bigger, takes over peoples minds, and becomes self-supporting by indoctrination, quite like Hitler. We can get the good bits of religion without the indoctrination of the next generation.

Think of a long railway train. A locomotive starts to pull one end. The far end starts moving almost instantly, even though the speed of the train is very slow. So a signal can be transmitted very fast, even though the medium transmitting it moves slowly.

Yes I can. As I have already pointed out, the kind of gravity we observe around us requires a very specific concept of time, which is the Einsteinian one. You can’t do away with it, or else the whole thing will no longer work. No, I’m not attached to anything (in fact, modified and alternative theories of gravity are a special interest of mine). I’m simply considering what works within a given domain of applicability, and what doesn’t. If you look at the classical low-energy regime, then clearly GR works very well in that it provides an excellent description of the phenomenology of gravity as we see and measure it, within its domain of applicability. The experimental evidence for this from the past 100+ years is incontrovertible and overwhelming. As I have said multiple times, this requires a specific notion of time - if you do away with that notion, or replace it with something different, then the model can no longer function. That’s all there is to it. Of course not. How could you think that? We already know that GR has a limited domain of applicability - at a minimum it cannot incorporate any quantum effects, and it is possible that even within the classical regime some phenomena might require modifications to ordinary GR. The jury is still out on that one. But that’s not the point here at all. This thread deals with your claim that time is not required for classical gravity to exist in the way we see it around us, and that’s manifestly false. MOND is only one example - there is in a fact a large number of alternative theories of gravity out there (none of which does away with time, btw!). The problem is that once you consider all available data (not just some isolated phenomenon), then none of the other models provide nearly as good a fit as GR does. We already know that it won’t be the final theory of gravity, but it really is the best one we have at present. It’s not - no one said such a thing. There are many different ways to define a concept of “time”, both in physics and in philosophy. The point we are making here is that classical gravity as we observe it around us requires a specific concept of time, being the Einsteinian one. Quantum field theory - which is the most fundamental theory we currently have - requires a Minkowski space-time background in order to work; the entirety of the Standard Model is formulated against this background, so Einsteinian time is as fundamental to QFT as it is to GR. To be precise, the Lorentz symmetry we find in local patches of Minkowski spacetime implies the CPT invariance of the Standard Model Lagrangian, and vice versa. One example of a model where a different notion of time is used is ordinary quantum mechanics - which is a low-energy, low-velocity, non-relativistic approximation to QFT that works only for systems where particle numbers are conserved. Here, time is simply a free parameter that is used to describe the evolution of a given system, it is not an observable of the theory, ie it can’t be consistently written as a Hermitian operator. GR and SR are models that describe aspects of the universe - as such they answer mostly only the how questions, but not the why ones, in the same manner as a map describes the topography of some territory without providing an explanation of the geological processes that gave rise to that territory. That doesn’t make the map any less useful, if you’re trying to find your way from A to B. The invariance of the speed of light is equivalent to saying that all inertial observers experience the same laws of physics; that’s an empirical finding about the world we find ourselves in. We don’t know yet why this is so, but if you really think about it, you’ll realise very quickly that the absence of this symmetry would immediately lead to physical and logical paradoxes that cannot be resolved, so at a minimum it is a matter of logical consistency. As for the gravity wells, the answer is in my signature. There is a well defined relationship between local sources of energy-momentum, and certain aspects of local spacetime geometry, as described by the Einstein equations. Thus, the relevant aspects of gravity in the interior of things like planets, stars etc are directly given by the distribution of energy-momentum there. But because spacetime as a manifold is everywhere smooth and continuous, the exterior vacuum geometry must match up with the interior geometry in a way that guarantees smoothness and continuity at the boundary. This provides a boundary condition that - along with the asymptotic behaviour far away from the central body - determines the exterior geometry. In most ordinary cases the embedding diagram belonging to this exterior geometry will look roughly like the “gravity well” you are referring to. This wasn’t the point. The issue is whether - given a geometric theory of gravity, be that GR or some of its viable alternatives - you can have gravitational radiation without there being time. The answer is clearly no. Thus, the presence of gravitational radiation implies some level of physical reality for time. Spacetime is not a physical medium, so there is nothing there that “vibrates” - that’s the kind of unfortunate misconception that is spread in pop-sci media. In reality, local geometry within some region of spacetime is determined not just by local energy-momentum, but also by distant sources. These do not appear explicitly in the field equations, but have to be provided in the form of initial and boundary conditions when solving them (they are differential equations after all). If it so happens that there is a distant source that has some form of non-vanishing quadrupole or higher multipole moment, then the local geometry will not be invariant under time translations, meaning you get tidal components that are explicitly time-dependent, even though all your local sources are stationary. This is how you get the characteristic effects of gravitational radiation.

Fear + ignorance = religion = that thing zillions of people pray about daily for the last 5000 years with zero point zero results nor a single response ever and will continue like that.

I see.

Continuing from here for the orbiting Observer to Observer at CoM for simplicity. Once again will be using the Lewis Ryder reference in the previous post above. were going to set the orbital rotation along the z axis in cylindrical coordinates \[ds^2=-c^2dt^2+dr^2+rd\phi^2+dz^2\] \[\acute{t}=t, \acute{r}=r, \acute{\phi}=\phi-\omega t, \acute{z}=z\] \[\acute{ds}^2=-ct^2d\acute{t}^2+\acute{r}^2(d\acute{\phi}+\omega d\acute{t})^2+d\acute{z}^2\] \[=-(c-\omega^2\acute{r}^2)d\acute{t}^2+2\omega\acute{r}^2d\acute{\phi}^2 d\acute{t}^2+d\acute{r}^2+\acute{r}^2d\acute{\phi}^2+d\acute{z}2\] dropping the primes we have the invariant spacetime in a rotating frame \[ds^2=-(c^2\omega^2 r^2)dt^2+2\omega r^2d\phi^2 dt+dr^2+r^2d\phi^2+dz^2\] this becomes \[ds^2=g_{\mu\nu}dx^\mu d^\nu=g_{00}(dx^0)^2+g_{0i}dx^0dx^j+g_{ik}dx^i dx^k\] ijk sums over 1-3 where \[x^\mu=(x^0,x^1,x^2,x^3)=(ct,r,\phi,z)g_{\mu\nu}\] \[g_{\mu\nu}=\begin{pmatrix}-(1-\frac{\omega^2 r^2}{c^2}&0&\frac{\omega r^2}{c}&0\\0&1&0&0\\\frac{\omega r^2}{c}&0&r^2&0\\0&0&0&1\end{pmatrix}\] time interval between events \[ds^2=-c^2d\tau^2\] as world time not proper time relation between world time and proper time is given by \[d\tau^2\sqrt{-g_{00}}dt\] giving in the above case \[d\tau=\sqrt{1-\frac{\omega^2 r^2}{c^2}}dt\] lengthy process but hope that helps better understand the 3 clock scenario described by the OP... all the material as mentioned is from Lewis Ryder "Introductory to Relativity" Sagnac effect as shown above further detail here https://en.wikipedia.org/wiki/Sagnac_effect I'm also considering applying the Kerr metric to the rotating case to place observer at sea level instead of CoM have to think about that though

So what you have is a vague guess. It’s a far cry from that to having science to discuss. You lack a mathematical model, and thus can make no specific predictions.

As others mentioned, the conclusions are not logical. For example the incredulity that SARS-CoV-2 originated at one and not many wet markets rather makes sense. Jumping species is a fairly rare event so you would not expect it to happen frequently. If it did, tracing the origin would be rather impossible. To take an earlier pandemic as example, the 2009 H1N1 pandemic ("swine flu) were associated with a reassortment of viruses circulating in Eurasian and North American pigs. Genetic tracing indicates that the pandemic hat its origin in North America in swine herds. Pigs are bred everywhere, but obviously the pandemic started most likely with this event. There are also more epidemiological work on the Wuhan market that has been the epicenter of the largest (known) outbreak. https://doi.org/10.1126/science.abp8337 But what is perhaps more important is that OP still seems to think that genetic re-assortment, and associated development of new diseases requires some artificial intervention. In reality this is not so. There are many points of likely zoonotic spillover, which also includes our agricultural practices. There is a reason why we frequently hear of culls of thousands or even millions of livestock due to disease outbreaks. Due to immunization, treatment options and generally good access to healthcare, many countries are under the illusion that new diseases will only occur in exotic locations or, simply put, elsewhere. This, obviously a misconception. While we often have been lucky that many viruses e.g. in livestock do not simply jump to humans, the 2009 pandemic showed us that it does in fact happen. What we have is really a lottery and it can happen everywhere. Even if every single wet market is banned, there will be other sources. And since we are encroaching on natural habitats everywhere, we might increase the likelihood of genetic re-assortment of various as well as bacterial pathogens. While there are some legitimate concerns regarding pathogens escaping labs, I feel that the real issue why folks are so hung up on it, it because it seems like a much easier problem to address as the real one that were facing. These include zoonotic diseases, accelerated by habitat loss, but also the rise of antimicrobial resistances. Often times, the big challenges (not unlike global warming) just seem too big to tackle and instead we focus on the small stuff to make us feel that we are in charge. Then we get several warning shots (e.g. SARS, MERS, swine flu, etc) and even if something big happens that forces us to face it (COVID-19) we almost immediately go back into denial. I fear that the next pandemic will come as an utter surprise as all the ones before it.

Q. There were two cats on a roof. Which one slid off first? A. The one with the lower mew. for some reason (probably because I was studying coefficient of friction at the time), this joke cracked me up.

Please don't misrepresent my comments, Mordred. It's extremely rude. I wasn't focusing on language, unless you literally don't know the difference between charge and electromagnetic fields.