This is just another proof that spacetime as a real entity does not exist. If there are infinitely many spacetimes, spacetime cannot be the fabric of the universe but it can only be fodder for academic careers. There is one universe but an infinite number of spacetimes. So which spacetime is the true one? None of them. You pick and choose one and write a paper on your chosen spacetime and collect your academic points. Another physicist chooses another popular spacetime and she writes a paper on that spacetime. The whole thing is a joke.
Of course one picks a simplified spacetime and investigate how that works, extracting ways to relate the simple model to actually-observed astrophysical phenomena. Just like how quantum physicists 70 years ago were working with simple models of the weak interaction, comparing their models to tracks in cloud chambers, ticks of geiger counters, or ratios of radioactive elements found in spectral lines.
It turns out that one can knit together simplified models and build up a good description of a real complex system, but this has been known since at least the dawn of thermodynamics, if not since the time of Newton.
Indeed, Nasa and its counterparts have been working for decades with an approximation of the solar system: new bodies inside Neptune's orbit keep being found practically every year. It's not remotely likely that we know all the bodies of the solar system even out to Neptune (much less beyond), let alone their orbital parameters and how those evolve over mere millions of years <https://en.wikipedia.org/wiki/Stability_of_the_Solar_System>. Does that mean publishing the results of studies of long-running models of our solar system "can only be fodder for academic careers"? Even if it spots anomalies that lead to the actual discovery of very dim bodies?
> collect your academic points
The academic points mostly come from being cited by an author poking holes in your paper. Go investigate google scholar.
This is called the academic dialogue. And yes, a variety of scores are kept (e.g. the loathsome h-index).
But I guess you don't care, because you are happy writing obviously ignorant nonsense on hacker news for engagement and upvotes, right?
> There is one universe but an infinite number of spacetimes
There is possibly one unique spacetime that fully describes the universe, but guess what, we simply do not have enough computer power on the planet to validate such a model.
Here's the recent state of the art in computational cosmological simulation, n-body with n in the hundreds of billions:
There are more than a hundred billion stars in this galaxy; there are more than a hundred billion galaxies in our sky. And there are more than a hundred billion particles in a star. And there are lots of motes of dust and blobs of gas between stars. So we're quite a few orders of magnitude too small in n in our n-body simulating to be able to pick out our own universe, exactly described, from a large set of simulations.
We also obviously don't have an infinite number of observations, since neutrinos and gravitational waves are hard to detect at all (and we only see a small part of the frequency space of both), we've only just started having really good views in the near infrared (JWST), our views in X-Rays and gamma rays are fuzzy because of technological limits, and so on and so forth. We are just at the start of https://en.wikipedia.org/wiki/Multi-messenger_astronomy four centuries after Galileo used a telescope to find the four biggest moons of Jupiter. (Incidentally, three moons of Jupiter were just discovered two years ago, because hey telescopes are not all-powerful and all-seeing. Guess how they figured out where to point the Victor M. Blanco Telescope?).
> The whole thing is a joke
Honestly, it's amazing that you aren't embarrassed by how obvious your ignorant contrarianism is.
Write back if you're actually interested in expanding your knowledge rather than mocking people you don't know whose work you know very very very very little about.
This is just another proof that spacetime as a real entity does not exist. If there are infinitely many spacetimes, spacetime cannot be the fabric of the universe but it can only be fodder for academic careers. There is one universe but an infinite number of spacetimes. So which spacetime is the true one? None of them. You pick and choose one and write a paper on your chosen spacetime and collect your academic points. Another physicist chooses another popular spacetime and she writes a paper on that spacetime. The whole thing is a joke.