When the Sun will grow to the size of a red giant, as astronomers tend to believe will happen after 5 billion years, then planet Earth will NOT be swallowed by the red giant, contrary to what astronomers believe.
Gravity is NOT a constant originating from the center of a star or of a planet. They are hollow anyway, i.e. have no core whatsoever. It is a bi-directional force originating from near the surface. Therefore, if the distance between the surface of the Earth and the surface of the Sun is roughly 140 million (rounded figure) miles, then gravity will make sure it stays that way, no matter how large or small either the Sun or planet Earth will be resized.
In other words, if the Sun expands by 300 million miles in diameter, then planet Earth’s orbit, and of all the other planets in our solar system, will be 150 million miles out too. We must not forget that gravity is both pull and push, i.e. bidirectional force, therefore a constant factor. Simple as that.
The red giant Sun will not swallow planet Earth.
Besides, a red giant is a star that generally has a cooler surface temperature than smaller stars more near the blue part of the light spectrum. In other words, planet Earth will not get burnt dry because of the bigger star. Bigger does not mean hotter.
Planet Earth will turn a little cooler, but not as much as we might think. The Earth’s surface temperature has much to do with the atmospheric workings. Yes, they will change, gradually, but largely self adapting to the ever changing surface of the Sun. It has happened up to today, and it will still happen after billions of years too.
Scientists should also stop thinking of the Sun as being a self-sustaining furnace. Every star is fed through a grid of stars with an interstellar configuration of energies that conventional scientists have no clue of. And the Sun does not give heat to planet Earth like a charcoal fire would do. Heat is just the conversion of the infra-red part.
The terms “hot star” and “cold star” are therefore incorrect. The energy conversion is up to the planetary conditions. Besides, the Sun is not that hot. What it truly emanates is composite radiation that our dear scientists have no understanding of. How little do we know how that complete radiation spectrum gets converted in life sustaining miracles.
Well, we still have 4.999 billion years to find out.