I went to see the follow-up to Avatar (‘The Way of Water’). It took over 10 years to produce it. Indeed, how time flies: the first ‘Avatar’ was released in 2009 and was, apparently, the highest grossing film of all times (according to Wikipedia, at least). This installment is not doing badly either in terms of revenue and popularity but, frankly, I found it rather underwhelming. This may be because of the current international situation. Indeed, I wonder why American soldiers must always be the ‘true’ space explorers in such movies. Why not some friendly Chinese or Indian explorers? Fortunately, it will be a while before mankind will be able to build spaceships that can travel at speeds that would allow us to visit, say, the Gliese 667 Cc planet, which may well be the nearest planet that is inhabitable (practically speaking), but which is about 22 lightyears away, so that would be a few thousand years of travel with our current spacecraft. Mankind will have to find a way to keep our own planet inhabitable for some more time… Planets like Gliese 667 Cc and other exoplanets that may have life like we know it, will be safe from us for quite a while. 🙂
These are rather philosophical thoughts, but they came up as I was adding an annex to my one and only paper on cosmology, in which I argue there are no mysteries left: the question of ‘dark matter’ is solved when we think of it as anti-matter, and even the accelerating rate of expansion of the Universe could probably be explained by assuming our Universe is just a blob in a larger cluster of universes. These other universes are, obviously, beyond our horizon: that horizon is just the age of the Universe, which is currently estimated to be about 13.8 billion (109) years and which determines the limits of the observable Universe. Hence, not only can we not see or know the outer edges of our Universe (because those outer parts moved further out in the meanwhile, and at the rather astonishing speed of 2c/3, and so must assume the end-to-end distance across the Universe is of the order of 46 billion lightyears), but we would also never see the other universes that are tearing our own Universe apart, so to speak.
By the way, this thought is quite consistent with an earlier thought I had – much before I even knew about this acceleration in the expansion of our Universe when thinking about the Big Bang theory: I always wondered why the coming-into-being of our Universe should be such simple linear and unique process. Why not think of several Big Bangs at different places and times? So, if other universes would exist and tear ours apart, so to speak, then here you have the explanation !
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However, I am not writing this post to share some assumptions or observations. It is to share this thought: is it not strange to think we know all about how reality works (as mentioned, I think there are no real questions or mysteries left in the science of physics) but that, at the same time, we are quite alone with our science and technology here on Earth?
Indeed, other forms of intelligent life are likely (highly likely, in light of the rather incredible size of the Universe), but they are too far away to be relevant to us: probably hundreds or even thousands of lightyears away, rather than only 20 or 40 of lightyears, which is the distance to the nearest terrestrial exoplanets, such as the mentioned Gliese 667 Cc planet. So we know it all and we relish in such knowledge and then, one day, we just die?
It is a strange thought, isn’t it? 
Reading Feynman 
Jean:
You might like to read some of these articles: Gravity and cosmology articles – THE PHYSICS DETECTIVE https://physicsdetective.com/articles/articles-on-gravity-and-cosmology/
I view dark matter as inhomogeneous space. Einstein described a gravitational field as a place where space is “neither homogeneous nor isotropic”. He also https://einsteinpapers.press.princeton.edu/vol6-trans/197?highlightText=gravitatively&backToSearch=https%3A%2F%2Feinsteinpapers.press.princeton.edu%2F~searchResults%3FsearchMode%3Dapp%26searchParam-titles%3Dfull%26searchParam-versions%3Dall%26searchParam-years%3D%257B%2522operator%2522%253A%2522%2522%257D%26searchParam-sort%3Ddate%26searchParam-terms%3Dgravitatively%26searchParam-start%3D0%26searchParam-page%3D20 said “the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy”. Hence if the energy-density of space is not uniform, denser regions will have a gravitational effect. And it will not be uniform, because galaxies are gravitationally bound. Space expands between the galaxies but not within, and conservation of energy means the energy density of space is less between the galaxies than within the galaxies.
Regards
John Duffield
“The Physics Detective”
I still think spacetime itself has no other properties than its curvature. I feel some kind of ‘spherical’ geometry around objects – also taking into account that we cannot really imagine an infinite Cartesian space (in math, yes, but it is kinda hard when you think in terms of something physical, right?) – comes quite naturally. But txs for the references ! Kindest regards – good to hear from you and glad you’re still rocking and rolling ! 🙂 Jean Louis
Thanks. I don’t think spacetime has any properties at all! It’s an abstract mathematical thing that models space at all times, and hence it’s static. There is no motion in spacetime, and we live in a world of space and motion. The Earth is surrounded by space, not space time. I think that space has a variety of properties, because as Einstein said “a field is a state of space”. As for space being infinite, I think the expansion of the universe is proof that it isn’t. Imagining the edge of the universe is however, a little tricky…
Agreed. I do not have a problem imaging the ‘edge of the Universe’. Infinity and nothingness are mathematical concepts or – if you are spiritual – then they’re things you’d associate with the Heaven which priests and gurus promised us. In short, we should not try to imagine what’s beyond the edge, I think. Not when you’re doing science. 🙂