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Course: Cosmology and astronomy > Unit 1
Lesson 2: Time scale of the cosmosCosmological time scale 1
Cosmological Time Scale 1. Created by Sal Khan.
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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?(13 votes)
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(4 votes)
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?(9 votes)
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.(13 votes)
What is "Dark Energy Accelerated Expansion" and how does it work?(9 votes)
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?(7 votes)
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.(4 votes)
Is there any proof of the Big Bang?(6 votes)- Scientific theories are never proven.
The universe is expanding and from the observations we can make the universe has been expanding for the 13.5 billion years we can observe. Prior to 13.5 billion years ago the universe was opaque to light so we can't see it. With this observation as we go back in time everything within the observable universe was in a very small volume of space so this key part of the Big Bang theories which makes them highly likely.(3 votes)
Why does Sal keep referring to the meteor killing all the land dinosaurs? Weren't the ocean-dwelling dinosaurs also wiped out?(3 votes)- No. See if you can think of a reason why. Or google it.(3 votes)
Loving these time scales! :.) :.) However, I felt derailed at the1:54minute mark, where it discusses DNA. Not that Darwin is necessarily the last word on that topic, however if what is said here is based on Darwin's theory, then is it not more appropriate to describe humans and primates as sharing a common ancestor opposed to humans having a primate for an ancestor?
No tangential rant coming ^.^, however I am curious about the information source being stated as an example.
This is not to nitpick. It's more about past experiences with misinformation that have caused me to question authorities. A personal issue, I understand. Still, I wanted to mention the disparity, if indeed the comment is based on Darwin's theory, while acknowledging there are other theories I am unaware of.(2 votes)- Darwin had no knowledge of DNA also the primate is a name for taxonomic order of species that is defined by specific physical and genetic characteristics. Humans, gorillas and monkeys are a member of the order primate. These order primate is applicable to modern and ancient species as long as they match the characteristics for that order.(5 votes)
- Why do we define three spatial dimensions and time? The spatial dimentions aren't more related to each other than they are to time(2 votes)
- In everyday life we experience time and space differently. We have freedom to move in space but not in time so we have always treated them differently.(4 votes)
- What is a quantum fluctuation?(2 votes)
- 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)
Is there a standard for units of time? I've heard of epochs and eons and all those but I've never quite understood exactly how long the were.(2 votes)- The standard unit for time in the Metric or SI system is the second. Epoch and eon have differing definitions depending on the context so they are not really a good standard for defining time.(3 votes)
1:54Video 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?