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Cosmological time scale 1

Cosmological Time Scale 1. Created by Sal Khan.

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  • old spice man green style avatar for user Skywalker94
    How have scientists attempted to estimate the age of the universe? Where did 13.7 billion years come from in the estimates? (I mean off of what info was that estimate made?) I would be interested in doing some study on that.
    (72 votes)
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    • blobby green style avatar for user dave.mckee
      http://en.wikipedia.org/wiki/Age_of_the_universe#History has a good summary. In short, Edwin Hubble noticed that further away stars were moving away faster, as if everything had exploded from one point. This was measured by doppler shift, the phenomenon that police sirens coming towards you are higher pitched than those going away - the same phenomenon makes stars going away from you look redder than they should. Allan Sandage measured the redness, and therefore the speeds, and came up with a number of around 13 billion years. They didn't believe it at first.

      There have been other ways of confirming this result, but I don't know them to any more detail than the wikipedia article.
      (75 votes)
  • leafers seed style avatar for user Verosha Abeygoonewardena
    I've asked this question before too... but is it possible that the universe is possibly much older than 13.7 billion years? Maybe the radiation from some of the oldest objects haven't even reached us and therefore, haven't been detected yet?
    (8 votes)
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    • male robot hal style avatar for user Charles LaCour
      Yes, the universe could be infinitely old but there was an event 13.8 billions years ago that caused the universe to be opaque to electromagnetic radiation so any electromagnetic radiation that may have been traveling before the big bang would not be detectable after the big bang.
      (12 votes)
  • female robot grace style avatar for user Shivangi Bhatt
    How do we know that the Big Bang really happened? I know it has to do with the Doppler Red Shift that Hubble discovered, but what if it only happens in our part of the universe? How do we know if the Doppler Red Shift happens in other parts of the universe as well?
    (12 votes)
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    • male robot hal style avatar for user hemabillava
      The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by Big Bang nucleosynthesis. More recent evidence includes observations of galaxy formation and evolution, and the distribution of large-scale cosmic structures. These are sometimes called the "four pillars" of the Big Bang theory.
      Source: http://en.wikipedia.org/wiki/Big_Bang
      (3 votes)
  • piceratops ultimate style avatar for user Noah Major
    What is "Dark Energy Accelerated Expansion" and how does it work?
    (8 votes)
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  • old spice man green style avatar for user fat dan
    A question came to mind at the end of the video. Is one second in Time today the same as one second in Time 13.2 billion years ago, while maintaining the same space, or would it be variable and depend on the Point of Organ in the theater of Space maintained?
    (6 votes)
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    • blobby green style avatar for user Matthew Running
      A second is only an increment of time that we determine. So yes, it would be the same. I do not fully understand your question, but what I think you're asking is the dependence on your point in space and time. This is a very complex topic, but basically space is SPACETIME, which means they are woven together. One point in space differs from another in both space and time. To understand more, I suggest reading on relativity and time dilation theory.
      (3 votes)
  • male robot hal style avatar for user Neel
    What is a quantum fluctuation?
    (2 votes)
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    • male robot hal style avatar for user Reinhard Grünwald
      Energy can be converted into mass and vice versa (remember Einsteins formula: E=mc^2). If you provide enough energy, you can create a particle-antiparticle pair. In turn this pair can then "annihilate" each other to give back your initial energy.

      And now comes the magic trick: If you do that fast enough, you don't even need to have that energy in the first place! This is a consequence of the so called "uncertainty principle": the uncertainty in energy times the uncertainty in time will allways be larger than a constant (Planck's constant multiplied by some numbers).

      In fact this is happening all the time: the empty space is not empty at all but it is buzzing of a multitude of (virtual) particle-antiparticle pairs that show up and disappear faster than the blink of an eye. This is called "quantum fluctuations" or sometimes "vacuum fluctuations".
      (4 votes)
  • blobby green style avatar for user Kurt Maxwell Weischadle
    Have we found any fossils that are in between the evolutionary process of ape and human? From my understanding we've only found humans and apes, nothing in between.
    (1 vote)
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    • purple pi purple style avatar for user venus.14scr
      humans did not evolve from apes;thats a pretty common misconception about evolution. the theory is actually that apes and humans share a common ancestor (i.e. they're both descendants of a different species that's neither human nor ape.) so it's like we're "cousins" of apes, not "children" of apes.
      i hope the way i explained that isn't too confusing.
      (5 votes)
  • male robot hal style avatar for user hemabillava
    Why does time move forwards, why not backwards?
    (2 votes)
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  • aqualine sapling style avatar for user Shoaib Salim
    If you throw a tennis ball from the space station into space, will the ball go on infinitely ?
    (1 vote)
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    • male robot hal style avatar for user Andrew M
      It depends how hard you throw it. Unless you throw it really, really hard, it's just going to stay in orbit around the earth. The space station is at an altitude where there is still a tiny, tiny bit of atmosphere that causes friction, so it needs a rocket boost periodically to stay in orbit. Without a rocket boost, the tennis ball will slowly lose altitude and then enter the atmosphere and burn up like meteors do.
      (5 votes)
  • leafers seed style avatar for user Nalin Venkat Sameera
    How can one asteroid destroy all the dinosaurs? Is that the only factor that caused the extinction of dinosaurs or did the climatic changes also play an important role?
    (2 votes)
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    • piceratops ultimate style avatar for user AegonTargaryen
      This asteroid was likely five miles in diameter. It hit the earth with such intensity that everything within maybe 500 miles was likely incinerated. Every bit of dirt within that radius and probably even farther was launched into the sky creating a massive dust cloud that obscured the Sun. A single asteroid could wipe out all life on Earth if it was big enough. Though some scientists are starting to think that a major series of volcanic eruptions were also occurring in present day Siberia and that this helped.

      For proof on how powerful asteroids are, there was one that in 1908 struck the area known as Tunguska Siberia. This particular asteroid was about the size of a 20 story apartment building but it exploded with the power of 1000 Hiroshima bombs knocking down an estimated 8 million trees. One eye witness who was 40 miles away said that the shock wave threw him a few meters. The asteroid didn't even hit the ground, it exploded 5 miles above the surface (about the altitude of airplanes).
      (3 votes)

Video transcript

What I've done here is I've copied and pasted a bunch of pictures that 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 it didn't have copyrights. This 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 the 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. 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 3 million years ago-- let me do this in a color that you can see-- about 3 million, so three million years ago, our ancestors look like this. This is Australopithecus afarensis. This is I think a depiction of-- this is Lucy. I believe the theory is that all of us have some DNA from her. But this was 3 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 200,000 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 with him getting on the jet liner. And I genuinely don't mean any offense to anyone. I just keep picking Jesus because frankly our calendar is kind of-- he's a good person that most people know about, 2,000 years ago. And so when we associate kind of a lot of modern history occurring after his birth. So this right here is obviously a painting of the birth of Jesus. And this is 2,000 years ago. And then this might be a little bit American-centric. But the Declaration of Independence, it was a major event. Actually even on a worldwide basis, it was the first secular democracy based on a kind of a constitutional democracy that showed up on the planet. They said we don't want the king of England anymore. And this was about 234 years ago. 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 events or periods of time 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 10 years ago. Because most of us, especially if you're over the age of 10, can kind of understand what 10 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 the 13.7 billion-- instead of saying the Big Bang occurred 13.7 billion years ago, let's pretend like it occurred 10 years ago. And if we pretend that it occurred 10 years ago, let's think about how many years, or minutes, or hours ago each of these events would have occurred. So if Big Bang, which is really 13.7 billion years, if it really had occurred 10 years ago, and we scaled everything down, if we had scaled everything down, then the Earth would have been created about 3.3 years ago. So this would have been 3.3 years ago. So there's nothing kind of amazing about this. This is a significant fraction of the age of the universe. So 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 give you an appreciation of the difference between million and billion-- if the universe was only 10 years old, then the dinosaurs would have been extinct 17 days ago. Not even a month ago, the dinosaurs would have been extinct. So if the universe was created when I was just graduated-- well, I'm in my '30s now, so when I was 24-- just last month, the dinosaurs would have gone extinct. And it 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, she would have been walking around on the planet. And modern humans wouldn't have shown up until 80 minutes ago, 80 minutes, a little over an hour. There wasn't even a modern human. Then the universe was 10 years, it didn't take until 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 10 years old instead of 13.7 billion-- and we scaled everything down-- then the birth of Jesus would have been 46 seconds ago. And then if we fast forward all the way to the Declaration of Independence, this would have occurred five seconds ago. So this isn't quite as mind blowing as the scale of the universe. But in my mind, this is still pretty amazing. I mean all that's happened since 1776 on a global basis could have been encapsulated in five seconds if the age of the universe was 10 years. So hopefully, that gives you a little bit of a perspective. In the next video, instead of condensing things in time, I'm going to compare this scale to kind of a distance scale. So we can kind of say, hey, if the universe was the number of pixels on my screen, how big would each of these things be?