Radius of observable universe | Scale of the universe | Cosmology & Astronomy | Khan Academy
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Radius of Observable Universe. Created by Sal Khan. Watch the next lesson: https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/big-bang-expansion-topic/v/correction-radius-of-observable-universe?utm_source=YT&utm_medium=Desc&utm_campaign=cosmologystronomy Missed the previous lesson? https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/big-bang-expansion-topic/v/big-bang-introduction?utm_source=YT&utm_medium=Desc&utm_campaign=cosmologystronomy Cosmology & Astronomy on Khan Academy: The Earth is huge, but it is tiny compared to the Sun (which is super huge). But the Sun is tiny compared to the solar system which is tiny compared to the distance to the next star. Oh, did we mention that there are over 100 billion stars in our galaxy (which is about 100,000 light years in diameter) which is one of hundreds of billions of galaxies in just the observable universe (which might be infinite for all we know). Don't feel small. We find it liberating. Your everyday human stresses are nothing compared to this enormity that we are a part of. Enjoy the fact that we get to be part of this vastness! About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content. For free. For everyone. Forever. #YouCanLearnAnything Subscribe to Khan Academy’s Cosmology & Astronomy channel: https://www.youtube.com/channel/UChNPnEkW8LYZ5Rwi8_A2-DA?sub_confirmation=1 Subscribe to Khan Academy: https://www.youtube.com/subscription_center?add_user=khanacademy
Comments
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So, surely this implies that the over the period of the example the universe expanded at a rate far greater than the speed of light. Is this possible?
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The coordinate in that space cannot be further than that factoring the expansion because the expansion of the universe at light speed or not would mean that the point is further than the initial point can you not see that.
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over time, then, the lights should become dimmer ... though not noticeable in our lifetimes
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I know you just give an arbitrary number, but the important thing is that the distance of those happy flying photons and the destination earth must be decreased, otherwise they will never reach us.
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I think there is something wrong with this type of thinking, but its probably me who is wrong. Anybody explain this to me please? Lets say it looks like the photon will cover a distance of about 1/3 the distance from its original point to the earth in a given time, and finally after the time has passed, it is still not in 1/3 of the way, but some smaller fraction (just like in the video). But, the speed of the universe expanding ahead of him is bigger than the speed of light. The distance between him and Earth will grow bigger and bigger and eventually, the photon will never reach us. In my opinion, this doeant correspond with what we observe, because we can see the edge of the observable universe - the black background, the microwave radiation. So there should be no place in our observable universe such that when a photon leaves it, it will never reach us.
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So by looking towards the direction earth, our solar system and the Milky Way is expanding towards, we would see further objects closer in time to reality than we would looking the opposite way?
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Photon: that's not too bad, I'm gonna get there in 30 MILLION YEARS. Very educational by the way. I've been interested in astronomy and am probably aiming for it as a college course and your videos offer a simple, informative way of learning the basic concepts. Thank you!
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Great job!
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13.72
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As space expands between two points, if the distance between the photon and an object continue to also expand relative to each other(space expanding faster than light), that photon will never reach the object. In the above example, I believe after 10 million years the distance to the end object(yellow dot) should be 29.999 Million years and not have expanded to 80 million(9:36-10:36).
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So light determined the " observable universe "?
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I don't like arbitrary numbers in my science.
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Good stuff.
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Thank you. I am no longer confused
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since universe is expanding faster and faster, 13 billion years ago this process should have been much slower than it is now and as long as any light still reach us from outer space we know that Universe expanding still slower than light. so I beleive that the light which was iluminated 13 billion years ago should have reached us or whatever ''mixture'' we where at that time way earlier than 13 billion years itself, since universe was expanding slower and probably distances between objects should have been shorter as Universe started from singularity.....
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If light is the fastest thing in the universe, and we can't see the entire universe, that must mean the universe is expanding faster than light. How can this be if light speed is the universal speed limit?
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you should do one where you have worked out the proper (scale) distances as the photon moves to us (and redshifts as 'its present' space stretches)...
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Just trying to bring up a point I don't hear that much; what if our idea of time is incorrect? That means all our theories are in a way disproved. Everything we talk about on the topic of astronomy and cosmology is based on the idea of time and numbers that could be incorrect. If anyone has any corrections to my assumptions please feel free to say, I am writing a research paper and it could really help
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This basically means that space is created at a speed faster than the speed of light if I understood correctly. If so how is that possible if speed of light is the ultimate barrier???
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OK so we have all this light coming towards us at the same time right? how do you observe the old light with all the new light coming into your field of view? Do you have a switch in your telescope that lets you see the old light?
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