Genady

Yes, but not only. Massless particles are affected by gravity too. They also produce gravity through pressure. Also, massive particles produce gravity not only by their mass but also by pressure and stress, if these are present. These gravity particles of course are not known currently, but if they are hypothesized, this issue might not exist: a proton you mentioned not only emits particles to interact with everything else, but also absorbs particles emitted by everything else which interacts with it.

I'd like to try before I give up. I'm sure I miss something because here, I pick numbers almost arbitrarily and get this: What is wrong with it?

The OP is about creating something out of nothing, and you equate zero with nothing, so discussing zero is not off topic. Aren't you looking for an excuse?

Equivalently, we know that not all humans speak Chinese and therefore speaking Chinese is an inborn ability. How are we humans imprinted at birth by neutrinos? Equivalently, I discovered the flatness of Earth before knowing anything about astronomy and therefore can't deny its accuracy. I disagree. Woo woo is not an accurate description of how this sounds.

Was it? Let's see... 0oC = 32oF, right? Then, 0oC+0oC = 64oF, right?

No, it was not a prediction. Homogeneity was an assumption long before the inflation idea. Inflation retrospectively explains it. It also retrospectively explains flatness, small non-uniformities, the absence of magnetic monopoles, and the power spectrum of CMB, IIRC. I am not aware of any experimentally confirmed predictions of it.

This is correct AFAIK. Alternatively, one could say that we have tons of different ideas, which is also a problem.

After the "singularity", a point on the time axis where the scale factor would be zero. There is only a low estimate for its duration. It could be as long as eternity as well. PS. If it was at all.

Preceded. The BB starts with an almost uniform, hot, dense, expanding state. Inflation is a brief "prequel" (how Alan Guth calls it) that dynamically creates the BB's initial conditions.

Not only helpful, but absolutely necessary. It is always done in science. This is impressed in scientists' mind endlessly in scientific education. It is rarely done in pop-sci media or youtube videos. E.g., I also stated here:

I do not.

Yes, I just don't see increasing as similar to expanding. But it is perhaps no more than unimportant semantics. One can, no problem. Friedmann–Lemaître–Robertson–Walker metric - Wikipedia

Took a picture of a resting hummingbird yesterday: Only after enlarging it at home and looking carefully, noticed a lizard resting nearby:

Why is it so?

If you shift the shape up, or the grid down as below, the shape does not intersect with the grid dots:

The expansion / contraction of space is clearly expressed in the Robertson-Walker metric. I am not familiar with a concept of expansion of/in time.

In case someone wants an explanation:

Are we? For what purpose? In what sense? Boundary between what and what? Between past and future, perhaps. But this is a temporal, not a spatial boundary. Every spatial point in the universe was a 'center' of expansion then, as it is now. PS. Remember, that we are talking here about an ideal homogeneous and isotropic universe. "Brooklyn is not expanding."

This style of writing from an intelligent person is painfully familiar to me.

No, of course it is not wrong. Every place in the universe you pick, was inside that hot dense stuff that was the universe content at the time of Big Bang.

Curious. I didn't know it needs explanation and more so, there is a way to explain it.

Is it this book? I have it for some time, but there always are other books in front of it somehow...

Thank you. I understand that xxx * 7xx = xxxxxx but I don't know what other information, if any, it gives me, because the Russian way of long division, which I did in school, was quite different: DIVIDE THE NUMBERS [RUSSIAN STYLE] - WITH REMAINDER explained by Photomath - YouTube (I assume that the x's are just placeholders.)

Sorry, but I still don't get it. Even the case of empty set is not "a complete absence of things", because there has to be a set for it to be empty, and this set is present rather than absent.