I put this into these terms for simplicity: If (not saying it is so, but for the sake of perspective) a person (a consciousness, an atom, microbe, whatever) existed from the beginning, to modern day, say, for 15 billion years, it would "age" that 15 billion years. Yet, the beginning of those 15 billion, to use common terminology, was very fast years compared to the later, when compared to any one year within that expansion --for example when compared to the "size" or "rate" of 2018. No?
No. Everything that shares the same reference frame, regardless how it is moving, shares its
proper time. For everything in this frame, time is (obviously) unvarying. For observers in
other frames, the rate of time passing on Earth may be faster or slower relative to their own frame, according to their relative motion with respect to Earth.
To say that time runs faster or slower on Earth at some point in its history, you have to specify the frame relative to which Earth time is being measured.
... the average rate of 2018 is expanded considerably compared to year 6. Yet, from within that expansion, that person (consciousness, atom, whatever) sees no difference.
Time is what clocks measure. If a clock on Earth makes the same number of ticks for the duration of year 6 as it does for year 2018, the years last the same time. Observers moving relative to Earth may measure the duration of year 6 to be greater or less than the duration of year 2018.
If a massive rocket was used to accelerate the Earth through space, an external observer that did not accelerate would measure Earth's time to run more slowly than hers, and an observer on Earth would measure her clock to run slow relative to his; and if the Earth then turned around and returned to the unaccelerated observer, each would see the other's clock run fast on the return leg, but on Earth's return the unaccelerated observer would note that less time had elapsed overall on Earth (i.e. the twins paradox in reverse).
I see the same principle in the sci-fi stories about entering a black hole. They keep saying that as the space ship of whatever size approaches the event horizon of the black hole, the stresses would destroy the ship. I honestly do not see why. This is not a ship weathering a storm, but a ship becoming the black hole. I should think that the nose and the people inside the nose of the ship stretch (or compress, if you wish) with no awareness of distortion of size and shape, compared to the rear of the ship.
No; the stresses on a spaceship approaching a black hole are due to gravitational tidal forces, i.e. there is a significantly stronger gravitational force on the parts of a spaceship closest to the BH than the parts furthest away. This exerts a force tending to stretch the spaceship in the direction of the black hole. There is also a tidal compression force in addition to the stretching force. The combined effect results in what is whimsically called '
spaghettification'.
The effect of the event horizon on a spaceship crossing it depends on the size of the black hole. In General Relativity, spacetime at the event horizon is not special, and for very massive black holes such as those at the centre of galaxies, the gravitational gradient at the event horizon may be small enough that the spaceship can cross the event horizon without even noticing, and won't get spaghettified until closer to the singularity.
