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宇宙的时间尺度(一). Sal Khan 创建




what I've done here is I've copied and pasted a bunch of pictures that uh signify events in our history when you think about history on a grander scale that most of us have some relation to or we kind of have heard it talked about a little bit and the whole point of this is to try to understand or try to begin to understand how long 13.7 billion years is so just to start off I have here this is the best depiction I could find where I didn't have copyrights is from NASA of the Big Bang and I've talked about it several times the Big Bang occurred 13.7 billion years ago and then if we go a little bit forward actually a lot forward we get to the formation of our actual solar system and the earth this is kind of a protoplanetary disk or a depiction of a protoplanetary disk forming around our young Sun and so this right here is 4.5 billion years ago now this over here once again these aren't pictures of them these are just depictions because no one was there with a camera this is what we think the asteroid that killed the dinosaurs looked like when it was impacting earth and it killed the dinosaurs 65 million years ago 65 million 65 million years ago years ago so until then we had land dinosaurs and then this as far as the current theories go got rid of them now we'll fast forward a little bit more at about three million years ago three million let me do this in a color that you can see about three million so three million years ago years ago our ancestors look like this this is Australopithecus afarensis this she's this is I think a depiction this is Lucy this is one of our probably many of us share I believe the the theory is that all of us have some of some DNA from her but this was three million years ago and you fast-forward some more and you actually have the first modern humans appearing on the planet people that looked and thought like you and me this is two hundred two hundred thousand years ago that's right over here obviously this drawing was done much later but this is a depiction of a modern human so 200,000 years ago and then you fast forward even more and I don't want to keep picking on Jesus I did that when him getting on the jetliner and I generally don't mean any offense to anyone I just keep picking Jesus because frankly our calendars is kind of he's a good person that most people most people know about 2,000 years ago and so when we associate you know kind of a lot of modern history occurring after his birth so I'll put this right here is obviously a painting of the birth of Jesus and this is 2,000 years ago 2,000 years and then this might be a little bit a little bit American centric but you know the Declaration of Independence it was a major event actually even on a worldwide basis it was the first secular democracy that based on a kind of a constitutional democracy that that showed up on the planet they had gotten rid of they said we don't want the kid the King of England anymore and this was about 234 years ago 234 and I always remembered because I was born almost on the 200th anniversary so you just have to add my age to 200 so this is 234 years ago so these are all these are all events or periods of time that that we've heard about and we've talked about and people throw around these type of years but what I want to do in this video is relate it to time scales that we can comprehend so instead of the Big Bang occurring 13.7 billion years ago let's pretend like it occurred ten years ago because we can most of us especially if you're over the age of ten can kind of understand what ten years is it's a very very long period of time but something that's well within our lifetimes well within our experience so let's say let's say the 13.7 billion instead of saying the Big Bang occurred 13.7 billion years ago let's pretend like it occurred ten years ago ten years ago and if we pretend that it occurred ten years ago let's think about how many years or minutes or hours ago each of these events would have occurred so if the Big Bang which is really 13.7 billion years if it really ten years ago and we scaled everything down if we had scaled everything down then the earth the earth would have been created about 3.3 years ago so this would have been 3.3 years ago so still nothing you know nothing kind of amazing about this this is a significant fraction of the age of the universe so not that not that mind-blowing just yet but if we go all the way to when the dinosaurs were extinct the last land dinosaurs now the 65 million years and this will wake give you an appreciation of the difference between million and billion if the universe was only ten years old this then the dinosaurs would have been extinct 17 days ago not even a month ago the dinosaurs would have been extinct so the if the universe was created when I was you know uh you know just graduated well I'm in my 30s now so when I was 24 just last month the dinosaurs would have gone extinct and he gets even crazier 17 days ago the dinosaurs would have extinct Australopithecus afarensis would have walked on the earth 19 hours ago yesterday 19 hours ago 19 hours ago she would have been walking around on the planet and modern humans modern humans wouldn't have shown up until 80 minutes ago 80 80 minutes a little over hour there wasn't even a modern human then did you know the universe was ten years it didn't take it till just very recently the last hour for us to see someone that looks something like us looks and thinks something like us fast forward even more the birth of Jesus if the universe was ten years old instead of 13.7 and billion and we scaled everything down then the birth of Jesus would have been 46 seconds ago 46 seconds ago and then if we fast-forward all the way to the Declaration of Independence this would have occurred this would occurred five seconds ago five seconds ago so this isn't quite quite as mind as mind-blowing as the scale of the universe but in my mind this is pretty still pretty amazing I mean all that's half and since 1776 on a global basis could have been encapsulated in five seconds if the universe was if the age of the universe was ten years so hopefully that gives you a little bit of a perspective in the next video I'm going to compare instead of instead of condensing things in time I'm gonna compare this scale to kind of a distant scale so we can kind of say hey if the age if the universe was the the number of pixels on my screen how big would each of these things be