When our sun burns out and goes red giant (if that's what it does), and incinerates Earth... From the time that Earth is habitable, like now, till it melts. How long would this process take? Would living beings start feeling the heat (like we did this summer) and would it happen within the lifetime of a human? Gosh, it's really something to worry about... feeling sorry for those descendants of ours.

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"I am happy to report that once again the universe is doing just great, thank you, purring with perfection, ever-changing same as always. Light is still cruising along at 186,000 miles per second, and the expanding universe shows no signs of contracting. At this rate, it won't be long before they'll have to let the photon belt out another notch."
Swami Beyondananda's 2007 State of the Universe address

No. You can stop concerning your self about the sun going super nova. It will never do that.
BUT

Our sun is of the type and size that with current knowledge of this subject which is considerable. That it is about half way through its life span of 10 billion years. That suggests it is 4.5 billion years until it will slowly grow in size as it completes the phase of burning (converting ) all of its hydrogen into helium. Only then will sol grow and engulf the inner planets, including Earth. So the answer is . . .relax . You have another 3.5 billion years of much more like we have now.

If the star at the center of the system was one of those shorter life span super massive blue giants then, you might have reason to be concerned.
It is not. So do not.

Greenfeather. Astromark is correct, the sun will not go supernova. Neither is it likely to go nova. The process of a main sequence star turning to a red giant is hundreds of millions of years..so, although we expect it eventually, it will not be in a hurry.
Your local weather is much more attuned to the ocean temperatures which affect the jet stream lattitudes (steering currents). that can change a lot faster...in decades. If the North Atlantic conveyor shuts down due to melting polar ice diluting the density of the Gulf Stream as it approaches Iceland, the climate could shift in your lifetime. That's the real concern. Pete.

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A third rate theory forbids.
A second rate theory explains after the fact.
A first rate theory predicts.
A. Lomonosov

On the other hand, I've read that Earth is expected to get hot
enough to be completey uninhabitable long before the Sun even
begins to turn into a red giant. Like, within a billion years.

-- Jeff, in Minneapolis

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http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

I've read it will "only" take a 100 million years before the Earth is uninhabitable. It seems we got ourselves quite a scale...

Hi greenfeather. You may find this link interesting. It follows the evolution of the Sun from birth to death and all the stages in between.

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"A mystic is a person who is puzzled before the obvious but who understands the nonexistent." -- Elbert Hubbard

Oh, I'm concerned. Believe me. But I feel pretty helpless to change it, so I try not to think about it too much. (other than not driving an SUV, and not voting for idiots).

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"I am happy to report that once again the universe is doing just great, thank you, purring with perfection, ever-changing same as always. Light is still cruising along at 186,000 miles per second, and the expanding universe shows no signs of contracting. At this rate, it won't be long before they'll have to let the photon belt out another notch."
Swami Beyondananda's 2007 State of the Universe address

Kinda puts us in our place, doesn't it - the Earth, as a planet, may very well survive the Sun going red giant, but multi-cellular life on Earth may well be way more than half-way through its tenure here.

(I suspect that many thousand species of bacteria will continue to find the Earth a very comfortable place, long, long after us eukaryotes have gone - after all, what could a thriving colony, 20 km down in basalt, care about what's happening on the surface? Their ancestors, many trillion times removed, survived the Late Heavy Bombardment epoch - a red giant Sun is surely a mere hiccough in comparison).

No, Greenfeather please keep voting. Then we can blame you.
and you do not need to worry about driving a SUV. In just 50 years from now nobody will be driving cars for anything other than essential services. The dramatic shortage of petroleum will push them to extinction. ( the SUV )go out and take photo's. It does not get any better than it is now. I predict the shortages of petroleum will be a very big issue for the next generation.
The death of our sun is not even in the envelope of consideration for another two billion years.

I heard another theory that when the Sun loses its mass, which it's going to do, that it'll push the planets orbits further away from it. Mercury is too close and hence will be engulf, but Earth and Venus would not be engulf cause their orbits would be further away from the Sun than it is now.

It doesn't matter though cause once the Sun becomes a white dwarf, the temperature on Earth would be 0 degrees Kelvin and no life could survive in that. Extinction of all life forms on this planet is inevitable.
l
Of course, if our technology becomes advnace enough, we could travel to other Earth-like planets around habitable stars and keep doing that.... Or, we'll just turn the Earth into a spaceship or just make stars and planets. Who knows. It'll be a few billion years from now and I believe all life on Earth would be extinct by then anyway.

Thanks for the link; it gives a plausible summary. As the universe continues to age over the trillions of years in an environment "rich" in water and hydrogen, one would expect the gravitational attraction of the cold dark remnant of the sun and each of the surviving planets to grow in mass especially since they will no doubt pass through several molecular clouds several times as they continue orbiting the center of the MW. Is it possible that the sun could light up again or the terrestrial planets to grow to brown dwarfs? Trillions of years is quite a spell. Having a luminous Jupiter orbiting at 10 or 20 AU about the dark center of mass of the system should offer a challenge for understanding cosmology by any emerging sentients of the period. Maybe we should leave them a note or two.

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

I hate to be that way, but nearly every post shows over confidence or a likely error. Some experts think the sun was much hotter as a proto star, reached a minimum energy output about 4.2 billion years ago, and has increased it's energy output perhaps 1% each billion years since then, and will continue on this slope for the next 4 billion years, when the core runs out of hydrogen. The fossil record poorly supports that increase the past 4 billion years, so there is resonable probability the sun will have about the same energy output over the 8.2 billion year period.
With the hydrogen gone in the core, fusion stops (or perhaps is much reduced for a few hours, or perhaps minutes) The collapse progesses at perhaps 2000 kilometers per hour toward the center of the core and toward the surface of the sun which is about 600,000 kilometers from the starting point of the collapse.
About 300 hours later (some think much longer) the collapse would reach the surface; except long before that, fresh hydrogen that was outside the core is now inside the core. The temperature and pressure of the core is much higher and both hydrogen and helium are being fused. The collapse is overwelmed by more energy than before and the sun may gain 1% in energy output and diameter per year until, it has a radius of about 100 million kilometers, after which it will shink perhaps 1% per million years until it is about the size of Earth.The surface temperature will increase as it shrinks partially offsetting the decreasing surface area. This is called a white dwarf and it has a very hot surface which may only cool 1 degree c per million years according to some experts. The surface area is reduced about 10,000 times, so everywhere more than a million kilometers from the white dwarf will be very cold, but not 0 degrees k, perhaps more like 30 degrees k, and cooling almost as slowly as the white dwarf due to the thick thermal insulating layers of snow like volitiles on the surface of Earth, assuming Earth did not vaporize completely when the red giant sun was near maximum radius. Yes I think the planets that remain will slowly grow in mass after the red dwarf stage shrinks considerably, but not nearly enough to become brown dwarfs. Neil

Well let's just hope we're out of the way when that time comes, be a 100 millon or 4 billion years what ever. Not that it will make much difference for us in the here and now.