So we've made it all the way to the 20th century with the history of astronomy. Plenty had to happen to get us to that point, but the most amazing stuff is yet to come! Shortly after Einstein did his best work, a guy named Edwin Hubble demonstrated that what we thought was the entire universe was actually just one little island of stars out of billions of other galaxies. And that's just the tip of the iceberg! The universe is also expanding! What does all this mean for cosmology? Let's find out.
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- Burn My Uncle: Murali Kumar we really don’t know much outside of earth say for example maybe mars is just a projection of what we think is mars, maybe the rovers human sent are hacked before they arrive and touch down, maybe the specimen that they retrieved are placed by aliens, because mars is was like earth before, maybe there are even more intelligent life in mars that we’ll be shot down when we arrive in the future
- stan1027: The balloon analogy would be valid if everything was moving away from one central point, the point of the big bang. There is also the idea that everything in motion must be moving in some direction. So if a distant galaxy is moving away from the Milky Way, and an observer somewhere in that galaxy looked back toward the milky way and saw that it was accelerating away from their galaxy at an accelerated rate, that would have to mean they were moving in opposite directions. Bit it cannot be that every galaxy is moving in the opposite direction from every other galaxy. That's the part I cannot understand. Can you explain that?
- Murali Kumar: Burn My Uncle Right! Also Speculation brought us all the way from none to this much advancement in Science..
- Professor Dave Explains: the observable universe doesn't have any physical significance other than to us, it's just how far we can see from here. there are no actual edges to the universe, nor a central region.
- Murali Kumar: Thanks for the quick response Professor.....
- Murali Kumar: Hello Professor. This Lecture was Great and your explanation is too good.... I want to know, How is this Universe Expanding and where it is Expanding? Just like you showed an example of balloon expansion, I can say it expands on the White Space around it. In that view, what is outside Universe?
- Saulius Savelis: not only moving to and away can redshift or blueshift, distance itself is a factor together with space dispersion
- Robert Zanatta: We can only see objects that are about just over 13 billion light years away; as far as we can tell there is no light coming to us from farther than that which will ever reach us. That would make is seem like the universe is about 26 billion or so light years across, but the the currently accepted theory is that the universe is actually around 92 billion light years across (and growing). As to how that the 26 and 92 billion light year values came to be, perhaps Professor Dave will explain... :-) So the truth is that no one really knows what's past the observable universe, or what it is growing into.
- Murali Kumar: NASA has announced that their mission Opportunity is Completed as they couldn't regain connection with their Rover craft. Professor, what's your view about Moon-landing Hoax?
- Tomi Soetan: Thanks so much for this professor Dave! In all honesty I was avoiding this video because I saw it in my recommendations and I thought it would be complex and hard to understand. You explained it all brilliantly and make me excited to learn more about this! I’ll surely be checking out the rest of this series and be doing some reading on this. Have a great day and keep doing what you’re doing please!
- Professor Dave Explains: The reason it's stronger between us and Andromeda is the distance. Gravitational attraction drops off by the square of the distance, so only galaxies very close to each other will be able to attract one another over the force of the expansion. As for an accelerating expansion, there is no fundamental difference between an attraction and a repulsion, here we have a repulsion (dark energy) that is increasing in magnitude over time, due to the expansion of spacetime, and as a force increases, acceleration increases. That's Newton's second law of motion. For all the galaxies moving away, the dots on the balloon analogy is about as effective as it gets, feel free to recreate this one in real life for a better sense of it. As for dark energy not ripping galaxies apart, it will one day. Right now the gravitational attraction amongst the stars in a galaxy is much too strong, but dark energy will grow and grow up galaxies are ripped apart, then systems, and on a long enough timeline even individual atoms will be torn apart. I cover all of this in upcoming tutorials in this series regarding dark matter/energy and the end of the universe, so all will be clearer!
- stan1027: I just cannot wrap my head around the ideas that: 1. Gravitational attraction between the Milky Way and Andromeda can be greater than the "force" (for lack of a better word) that is supposedly causing all other galaxies to move away from each other. 2. The idea that any object (i.e. a Galaxy) can be accelerating at an exponential rate AWAY from anything else. I am admittedly uneducated in these matters, but as far as I know, there is no phenomena here on earth that is comparable to that, and the only way something can accelerate at an exponential rate is when it's being drawn TOWARD something else. 3. The idea that no matter which galaxy you might be looking out from, every other galaxy would still appear to be moving away from you at an exponential rate. That just doesn't make sense to me. 4. Why isn't this "force" that is causing galaxies to move away from each other so rapidly also causing galaxies themselves to be ripped apart? Can you possibly explain these things in a way I might understand? Thanks!
- Professor Dave Explains: Well no one can visualize four spatial dimensions. But we understand all of this because of the math. It's not some flight of fancy, nor is it dogma in the slightest, the math tells us how things are. Math that is unfortunately way too complicated for me to describe, but maybe one day!
- Professor Dave Explains: Imagine the universe as being only the surface of the balloon. The surface has no center. All the dots are moving away from each other in the same way. It's difficult to imagine because it requires envisioning three spatial dimensions curving around a fourth, that's why these lower-dimension analogies are the best we can do.
- Wardell Lindsay: Hubble did not believe the Universe is expanding based on counting galaxies. He believes redshift is an " hither to unknown principle of nature". The Universe is stationary, the Gravity Energy is stationary @ v=c. Age=15.84Gy, R=150GPm.
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- Professor Dave Explains: Hubble gathered the data. The astrophysics community collectively interpreted the data to conclude that the universe is expanding, and observation which has been corroborated in countless years over the past century. Also, I would highly dought that he believed redshift was an unknown principle, it must have been observed on earth with sound waves already.
- stan1027: Ok, this, I guess, is the part I will never understand, trying to imagine three spatial dimensions curving around a fourth. My little brain simply cannot grasp that concept. And because of that circumstance, I cannot imagine that anyone else can, either. This kind of thing is what I think of as being "scientific dogma", where those who claim to be able to imagine this say it, and anyone who wants to be a part of the scientific "in crowd" will say it makes sense to them too, even when it really doesn't. No need to reply again, but I do thank you for your time in trying to explain this to someone like me.
- $ Varun.J $: Hey hi professor! Can it be that the universe just like other elements has a tendency to become stable. And its expanding in order to make itself stable relative to all the integrated particles present in it? BTW UR VIDEOS ARE ASWM!
- Sergusy: Professor Dave Explains May be you are right, but if the universe is expanding then doesn’t it mean the amount of matter near the edges of the observable universe has to be considerably smaller comparing to the central region?
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- harsh mars: Can't wait for upcoming episodes.. I kinda like space....
- Sergusy: Hi. It would be the greatest explanation ever if there was no extra “if”. If the universe were expanding, than those dots on a air balloon were getting not only apart, but bigger also. Therefore all the galaxies on the “edges” of the observable universe also were bigger.
- Professor Dave Explains: You're taking the analogy a little too far, the dots on the balloon are not equivalent to galaxies, it's just a visual tool to help people understand how all the galaxies can be receding from each other simultaneously. Galaxies are not getting bigger.
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Edwin Hubble, Doppler Shift, and the Expanding Universe | |
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