We're running out of time!

We will have the collision with Andromeda Galaxy a few billion years before, so don't worry :)

Colliding with andromeda won’t do anything. Galaxies are almost all empty space.
- We'll see.
- Can't it mess up our nice solar system if other large objects come even remotely close?
- It could set if a wave of supernovas, though, which would be bad for anything living in either galaxy. AFAIK our understanding of the process isn't good enough to know.
- But it will be beautiful to watch!!
Neat there's even a video: https://en.wikipedia.org/wiki/Andromeda%E2%80%93MilkyWaycollision
5 is a few
Nah, we will build a stellar engine prior and move ourselves wherever we want. We will have colonized all the Milky Way and most of Andromeda. It'll be like a brother and sister finally meeting near the washer.
The sun is also slowly increasing in energy output. Earth will be too hot for complex life to exist in about 800 million years.
Space is so vast that the Earth and Solar System will survive.
Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today. Source

Have no fear, the sun will not explode. You need about 8 times the mass of the sun in order for a star to explode in a supernova. The sun will expand into a red giant when it finishes fusing hydrogen into helium. When this happens the earth might be swallowed up in the expansion. After the sun finishes burning helium and continues up the fusion chain to iron the fusion in the core will fail and the outer layers of the sun will puff off into a planetary nebula. This won't be a particularly violent event. The naked core leftover will be a white dwarf which is effectively just a molten ball of mostly carbon and oxygen gradually cooling off. It will take trillions of years to cool off.

Although, it's just a couple of hundreds of ~~thousands~~ millions of years before the sun ~~expansion~~ brightness makes Earth inhabitable. Not to make anyone freak out, but that's about 10 times less than 5 billions! Enjoy your life while you can!
Edit: sorry for writing mistakes at 2 am, see various sources below.
- No, the expansion will start in about 5 billion years. The subgiant expansion phase will last for about 1 billion years. The earth may or may not be engulfed during the expansion as the best guess is the sun will expand to somewhere between venus and earth's orbit. The planet will be uninhabitable but again, the expansion won't start for about 5 billion years.
  You're the second person in as many days that I've come across saying the red giant expansion phase will start in 500 million years. Where are you guys getting this info?
- It's a few hundred million years, not a few hundred thousand, before the photosynthetic cycle is disrupted by silicate weathering from increased brightness.

What's scary is that was already a few years ago, so it's a EVEN CLOSER now!

Tbh I think this shared experience kinda shows to me how we grow selfish as we grow up, we were quite aware that it will not affect us, but the thought of the world where we see so many people living ending one day like this haunted us, now we don’t care, we don’t care about anything that doesn’t affect us or people we know…

Maybe, when we are young, the world (and the universe at large) are part of our identity of self, but as we grow older we reduce our sense of "self" to just our own physical body and mind.
- I have seen some people having the inverse transition, blending with their environment and communities as they got older. Perhaps it's more like a cultural thing than a personal process. It's hard not to become selfish in our society model.
And that's the reason why we fuck our planet for profit. Climate change? Not our problem, the future generations can deal with it.
- Tbh climate change has started to affect all of us who don’t have the luxury to always remain in a climate controlled environment, i am not looking forward to coming home at 2pm when the (feels like) temperature is 50C, and god knows what we will hit this year
Personally I've always been into space exploration stories (I mean, Star Wars isn't always exploration (I read the books, and some are about uncharted stuff a bit, like Outbound flight, and I do like Star Trek too) and kinda hope we're at that tech by then. I also really enjoy stuff like Schlock Mercenary and videos like https://youtu.be/ulCdoCfw-bY which while showing a bomb, also talks about a way to use black holes to outlive Red and White Dwarves, which normally should be the last source of light and heat in the universe. A colony properly using the energy black holes would still contain could potentially last trillion of years longer than all stars.

There is a certain sort of ennui that comes with the realization that the heat death of the universe is inevitable, and no matter what you do, no matter how much you manage to make your mark on the world/solar system/galaxy/universe or how successful and prosperous your descendants may be, it will all eventually be lost to eternal entropic stasis.

Come join the last vibration
- Whoa what do you call this crazy noodle haha you guys know how to party
"As a child, I once considered such unknowns sinister. Now, though, I understand they bear no ill will. The universe is, and we are." - Solanum, Outer Wilds

too late. i hear the sun has already started exploding and that it’s allowing humanity to exist.

I read somewhere that the sun might expand a bit and become too hot for Earth in just 500 million years time, so it might be a shorter window than you'd think

You're missing a zero. The sun will expand into the red giant phase in about 5 billion years.
- Not if humans get their hands on it.
The sun will get brighter in 500 to 600 million years to the extent that many plants won't be able to survive due to disruption to the carbon cycle. Expansion comes later.
This is what I've heard, that basically if we were stomped back to single celled life today, evolution would not have time to bring back visible plants and animals before the earth became uninhabitable. So there's no starting over. I admit it kind of depresses me.

There is nothing we can do... Yet!

And there never will be. Then again, we won't stay around long enough to have to worry about it.
- Well, we might be able to siphon enough plasma from the sun and disperse it to make it so small it will not explode when it reaches its end of service period, but I guess a Type 3 civilization might have other priorities

Bad news captain, earth will have surface temperature of 100°C in 1 billion years already.

Not to worry. Before it explodes, our sun will expand into a red giant much larger than the orbit of the Earth.
No one on Earth will be around to witness the explosion. So we have that going for us, which is nice.

Humanity will either be long dead or colonizing other planets by then.

Star lifting. Mine the metals and shit out of that star and it'll potentially live trillions of years.

And no need to worry about political will. Thar's gold in that thar sun!

Gold only forms in a supernova
- Gold isn't formed in the sun but plenty exists there for the same reason it exists on earth. Ancient supernova that provided the material for our star system.
  But gold is just one thing they would mine there of course. My comment was referring to the value of the materials mined, not just the literal gold.

let's feed it more hydrogen!

That'll make it worse, unless we combine it with removing heavier elements. Basically if we figure out how to strip-mine the sun one day we'll make it last much longer
- it won't explode in 5 billion years if it already exploded in 4 billion years, so i definitely would call that a win