Intergalactic scale Intergalactic Scale
- Where we left off in the last video, we were just kind of staring,
- amazed at this Earth's view of the Milky Way Galaxy,
- just making sure we understood how enormous and how many stars we were looking at
- and even this, even if each of these dots were stars this is a huge amount of stars
- but a lot of these dots are thousands of stars, are thousands of stars, so, so this
- our minds were already blown but what we're going to see in this video
- in some ways this is kind of just the beginning. And to some I am going to stop doing the particles of
- grain in the football field analogy, because at some point the particles of sand become so vast that our
- mind cannot even grasp it to begin with, but let's just start with our Milky Way
- and we saw in the last video the Milky Way right here - we're sitting here about 25,000 lightyears away from
- the center, it's roughly 100,000 light years in diameter, and then let's put it in perspective
- of its local neighborhood, so let's look at the local group,
- and when we talk about local group we're talking about the local group of galaxies
- of galaxies. so this right here is the Milky Way's local group, that's us right there
- sitting right over here about 25,000 light years from the center of the Milky Way
- you have some of these small, and I use the word "small" in quotation marks because these are also vast
- entities also unimaginable entities but we have these satellite galaxies
- around under the gravitational influence some of them, of the Milky Way, but the nearest large galaxy
- to us is Andromeda right over here, and this distance right over here and now were going to start talking
- in the millions of light years so this distance right here is 2.5 million, 2.5 millon light years just
- as a bit of reference if that's any reference at all 1 light year is roughly the radius of the Oort cloud
- and the Oort cloud was, or another way to think about it, the Oort cloud or one radius of the Oort cloud
- is about 50 or 60 thousand astronomical units and that's the distance from the Sun to the Earth, so you could view
- this as 2.5 million times 60,000 times the distance from the Sun to the Earth so this is an unbelievably
- large distance we're talking about here and that's to get to the next big galaxy over here
- but even these things are huge things with many, i mean just unfathomably many stars, but Andromeda in
- particular you, you know we said that the Milky Way 200-400 billion stars
- Andromeda people believe has on the order of 1 trillion stars, even these just start to become numbers
- its hard to grasp, but were not going to stop here so in this, over here this whole diagram over here
- its about 4 lightyears across if you go point to point if you go from one side to the other side
- this is about... not 4 light years, sorry, this is 4 million light years... 4 million...
- 4 light years is just the distance from us to the Alpha Centauri, so that's nothing,
- that would only take Voyager 1 80,000 years to get to.
- This is 4 million light years, so 4 million times the distance to the nearest star.
- But even this, even this is... I'm starting to stumble on my words, there are no words to describe this,
- even this is small on an intergalactic scale,
- because when you zoom out more, you can see our local group - it's right over here
- and this right over here is the Virgo Supercluster,
- and each dot here is at least one galaxy, but it might be more than one galaxy,
- and the diameter here is 150 million... 150 million light years.
- So what we so in the local group in the last diagram, the distance from the Milky Way to Andromeda,
- which was 2.5 million light years, which would be just this litte dot,
- just like that, that would be the distance between the Milky Way and the Andromeda.
- And now we're looking at the Virgo Supercluster, and that is 150 million light years
- but we're not done yet, we can zoom out even more! We can zoom out even more... and over here,
- so you had the Virgo Supercluster, 150 million light years, in the last diagram,
- this diagram here, I'd like to keep both of them on the screen if I can, this diagram
- right here, 150 million light years across, that would fit right about here, on this diagram.
- So this is all of the superclusters that are near us, and once again, near has to be used very loosely,
- here, this distance is about 150 million light years, a billion light years is 2... 3... 4... 5...
- a billion lightyears is about from here to there, so we start to talk on very massive... I guess we've
- always been talking on a massive scale, but now it's an even more massive scale. We're still not done!
- Because this whole diagram, these dots that you're seeing now, I wanna make it very clear,
- these aren'r stars, these aren' even clusters of stars, or clusters of millions or billions of stars,
- each of these dots are clusters of galaxies, each of those galaxies having
- hundreds of billions to trillions of stars, so we're just at an unbelievably massive scale at this point,
- but we're still not done, this is roughly about a billion light years across,
- right here is actually the best estimate of the visible universe, and in future videos
- we will talk a lot more about what the visible universe means,
- so if you zoom out enough, this entire diagram right here,
- about a billion light years, would fit right over... would fit just like that.
- So we're talking about a super small amount of this part right here...
- and this is just the visible universe, I wanna make it clear, this is not
- the entire universe, and we say the visible universe, 'cause think about what's happening,
- think about a point out here, and we're observing it, let's say, it's 13 billion light years away,
- we're gonna talk more about this in future videos, 13 billion light years,
- and I feel it's almost a sacrilage to be writing on this,
- because this complexity that we're seeing here is just mindboggling,
- but this 13 billion lightyear away object, we're observing... the light's just getting to us....
- the light left at some point, 13 billion lightyears ago, so we're actually observing this object
- close to the beginning of the actual universe, and the reason why it's the visible universe
- is there might have been something a little bit further out, maybe it's light hasn't reached us yet,
- or maybe the universe itself, we'll talk more about this, is expanding so fast
- that the light will never ever reach us, so it's actually a huge question mark,
- on how big the actual universe is, and then some people might say
- well, does it even matter? - because this by itself is a huge, huge distance,
- and I wanna make it clear, you might say, OK, if this light over here
- this is coming from 13 billion light years away, or this is 13 billion light years away,
- then you could say, hey, so everything that we could observe, that we can observe the past of,
- is about 26 billion light years, but even there we have to be careful,
- 'cause remember, the universe is expanding: when this light was emitted,
- and I'll do a whole video on this, because the geometry of it is kind of hard to visualize,
- when this light was emitted, where we are, in the Virgo Supercluster,
- inside of the Milky Way galaxy, where we are was much closer to that point,
- it was on the order of, and I wanna make sure I get this right,
- 36 million light years, so we were super close by, you know, astronomical scales,
- we were super close only 36 million light years to this object when that light was released,
- but that light was coming to us and the whole time the universe expanding, so we were
- also moving away from it, if you just think about it, all the space, everything
- is expanding away from each other, and only 13 billion years later
- did it finally catch up with us. But the whole time it was happening,
- this object has also been moving away from us, so our best estimate of where this object is now
- based on how space is expanding, is on the order of 40 or 45 billon light years away.
- We are just observing where that light was emitted 13 billion years ago. I wanna be very clear,
- what we are observing, this light is coming from something very primitive,
- that object, that area of space where that light was emitted from,
- has now condensed into way more mature astronomical structures,
- if you take it from the other point of view, people sitting in this point of space now
- and now they've moved 46 billion light years out, when they observe our region of space,
- they're not going to see us, they are not gonna see Earth as it is now,
- they're gonna see the region of space where Earth is, at a super primitive stage,
- shortly after the Big Bang - when I use words like 'shortly', I use that also loosely,
- we're talking about hundreds of thousands or even millions of years,
- so I'll talk more about that in a future video, but the whole point of this video is
- you know, it's beyond mind numbing, you know, I would say the last video about the Milky Way
- that alone was mind numbing, but now we are in a reality where
- just the Milky Way becomes something that's almost unbelievably insignificant
- when you think about this picture right here. And the really mind numbing thing is,
- if someone told me that this is the entire universe, this by itself would certainly
- put things in perspective, but it is unknown what's beyond it! There are some estimates
- that this might be only one times 10th on the 23rd of the entire universe
- and it might even turn out that the entire universe is smaller than this
- and that's an interesting thing to think about, but I'll leave you there,
- because I think no matter how you think about it, it's just, I don't know,
- actually before doing this video I stared at some of these photos for like half an hour,
- this is my least productive day, just because it's so awe-inspiring to think about
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
Have something that's not a question about this content?
This discussion area is not meant for answering homework questions.
Share a tip
When naming a variable, it is okay to use most letters, but some are reserved, like 'e', which represents the value 2.7831...
Thank the author
This is great, I finally understand quadratic functions!
Have something that's not a tip or thanks about this content?
This discussion area is not meant for answering homework questions.
At 2:33, Sal said "single bonds" but meant "covalent bonds."
For general discussions about Khan Academy, visit our Reddit discussion page.
Here are posts to avoid making. If you do encounter them, flag them for attention from our Guardians.
- disrespectful or offensive
- an advertisement
- low quality
- not about the video topic
- soliciting votes or seeking badges
- a homework question
- a duplicate answer
- repeatedly making the same post
- a tip or thanks in Questions
- a question in Tips & Thanks
- an answer that should be its own question