Israel,
very interesting posts. And you write so well! You give an excellent historical overview, and I fully agree with the 90% of your position. There are some things that I see differently. I address them in the same order as they appeared in your posts.
You write, "As we all know, Euclidean space is structureless, it is nothing but the mental abstraction of physical objects ... It is thought of as a background composed of no physical entities and no internal structure; simply because nothingness cannot have structure, no energy or no substance."
In my view, Euclidean space is the epitome of a perfect structure. Perfectly even, perfectly flat, perfectly regular. If it is 3D, that too is an aspect of its structure. It can be 4 or 7D, which would make it a different structure, with different properties. It appears to me that you are one of those people who take space for granted and cannot conceive an absence of space. Just like Hawking, in the video you suggested, started off making a universe with matter, then energy and, finally, space, lol. As if matter could exist without space. You super-smart PhDs view the world through the prism of abstract mathematics. Maybe that's why you overlook its most important thing, space.
You wrote re history, "In 1917 he introduced the cosmological constant in his equations to counter balance the force of gravity. He wanted to have a static universe for, without the constant, his universe will collapse."
See, to me this only means that Einstein, like everyone else, viewed matter as the primary... entity -? that affects space. I rather see space as primary and matter as the extension of its structure. Thus in my view this structure will sooner become empty than collapse because of matter in it.
You wrote re theory: "What expands is the space itself (the space of relativity)."
Again this view shows that space is taken for granted. The idea is untenable in an established universe (after the BB), since it implies that something --or someone-- is pouring energy at a constant rate into the universe and they do it evenly everywhere, except right where we are (why Sun is not getting any farther?) In a few hundred years the current period will be known as physics dark ages. Have you ever taken an inventory of your convictions trying to guess, which ones will be ridiculed by our descendants, just as we ridicule some of the most cherished notions of the past? I know, each generation, when we are still young, believe that people were ignorant in the past and that we are the ones to set things right, once and for all, for the benefit of humanity. It takes some living and a study of history to realize that we too will be laughed at hundreds of years from now. About some of our notions they will say, wow, already then they knew it! And about others... Have you ever tried to guess, which of our current believes will get into which category?
You say about the current theories, "We are talking about two different notions of "empty" space. In the former case, when we have no fields and matter we only have the energy of gravitational potentials (metric tensor), but in the case of QM we have the energy of the zero-point field. QM presupposes that there is some background whereas relativity denies it."
IMHO, both theories describe the same thing, at different scales. It's like digital music. At a sampling rate we hear it, it is continuous and the quality is better than when the technology was analogue. At another sampling rate, it is a collection of disjoint sounds. But it's the same music.
GR deals with the curvature of the surface. QM bumps into the micro-fluctuations in this surface. From the scale of GR, those fluctuations are unnoticeable, just like the digital nature of our music is unnoticeable to us, until we change the sampling rate.
You wrote, "This means that even if there were no matter-energy and fields in the universe we could still have the metric tensor (gravitational field). In this sense I say that the space of relativity is mere geometry, it is not a substantial entity as in the case of the quantum vacuum."
I don't understand how you could have metric tensor without matter-energy. -? Ah! I guess then the tensor would always predict flat space, ok. But the way you speak about geometry is as if nothing maintains its structure. It is the same structure as in QM, only at a different scale.
You say, "So, if you support the idea that space is the medium for light, you are implicitly saying that space is the absolute frame of reference because the speed of light is defined relative to the substantial space."
-?? My understanding of SR is that mathematically it is equivalent to LET. In either case, Lorentz transformation assures that c remains a constant for an observer. I thought that absolute reference frame made sense only in a stationary ether model, for then you could drive a thick nail into that station, lol, and label it O. In the model I propose, nothing is ever stationary in relation to the structure, because all movement is actually driven by it. I see the universe as the ultimate perpetuum mobile where space "wants" to be empty and so it expels all deformations introduced in it locally, and that's how everything moves.
Absolute reference frame with a dynamic structure? I completely don't get it. It's like the water in the ocean; it is totally real and tangible and you can even measure the rate with which it passes under the keel, but what use is it for navigation?
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