Ever since you were born the world is constantly changing, not just through big events but in smaller ways too.
The world you live in does not even exist. There might be one objective reality, but none of us where ever there. Everything you experience is filtered and distorted by your past experiences and current beliefs.
Not only that. You no longer exist. As you were at birth, that is. And after some amount of time every so often in your life, you will continue to be unrecognizable to the version of you from x years in the past. Your cells die off and new cells are created until you are literally composed of different matter than you once were. The closest thing to a constant thing tying you together would be the electrical signals in your brain. Memories. Like computer code sent from one PC to another. Also the DNA determining how your body is built.
It’s the classic Ship of Thesseus problem. If you replace a ship’s parts one piece at a time over many years until the old parts of the ship no longer remain, is it still the same ship? And in the same way, are you still the same you? Maybe our lives are full of many different people tied together only by our thoughts, memories, and genetic code.
The neurons you’re born with stay with you for the most part. Most of their complex organization is formed through a series of one time events early in development that can’t really be replicated and then stays with you for the rest of your life. You get shingles when you’re older because the same neurons were with you that got infected by chicken pox when you were younger are still there. There’s a few limited areas in the nervous system where new neurons might be formed, but in general neurons are life long cells so be nice to your nervous system. Most other cell types in your body are turning over as you said, including glia and other types of cells in your brain.
The phrase of something being a lifetime ago exists for a reason.
You’re changing mentally and physically all the time, especially when you’re younger and going through so many phases of growing up.
String enough of those changes together and at some point you will effectively become a new person, only connected to the previous iterations by memories that you share.
The death of one interation and the beginning of another is bound to be a blurry mess, but you can see it clearly over a large enough span of time.
The same is true with the environment around you, and even the wider world. It goes through iterations just the same as we do because nothing stands still, even if we want it to.
The world of a second ago no longer exists either.
There is no such thing as now. The line where the ‘now’ exists is between the future and the past. And that line has no thickness. Are we really alive if our entire perception is only of events that have happened in the past?
It’s the opposite: the past doesn’t exist anymore and the future is only imagined. All there is is the now.
But what is the now? It is a sliver of time that has no thickness. It is a point in time that well… has no length of time. 0 picoseconds. Thus does it even exist? Your entire perception is of things that only occurred in the past. When you say ‘right now’, immediately the now you are referring to is already the past. And like you say, the past doesn’t exist anymore either.
The person you were born as no longer exists, at some point “you” died and you didn’t notice.
Beat me to it
Sadly, the truth is, humanity is doomed. Within just 10 years, it will all look much much less welcoming. Much of the equator will become uninhabitable within a few decades. Horror scenario. Do not have kids. EVER.
