I'm an engineering student and I read and watch a lot of books and documentaries about sciences like these; however, watching your videos makes me feel like I'm stupid 😂😂😂😂😂
+Ricky Hou +Ali elb Which sort of engineer (or job in general that create physical things) would HAVE to learn and fully understand this math and these concepts and their consequences in our perceived reality/our modern world for their field? I can imagine that maybe people who design computer chips with nanometers small transistors have to know quantum mechanics, which I guess would include learning and understanding this? Is that true? Any other jobs?
A good way to view these videos and understand is if at any point you are confused, restart the video from a little further back from a point you understand.
Taylor Bennett According to the biographists of Stephen Hawking, he does the same in his head since he can't write equations anymore. Nature is fantastic.
@@tarekwayne9193 not really some grammatical errors, it should say: This is crammed with a relentlessly incessant pounding of an asphyxiating, constrictive series of a bombardment of information. I love it.
@@stormixgaming8389 interesting, according to a prescriptive view of English grammar, you may indeed be right. However, as a descriptive linguist, his sentence reads more fluidly(predictive text wrote "fluidity" for me😒) to me and depicts what's going on in the speaker's delivery. It's not just one bombardment, it's multiple! It's a relentless, ongoing onslaught comprised of successive verbal machine gun attacks. Yours reads like an account of a singular fact. His puts in you in the mix, feeling each blast of knowledge whizz by, while others smack you squarely in the face. In addition, as I would wadger he's not a native English speaker, further kudos to him. I do agree that his sentence might have benefitted from commas at least. On the other hand, their absence again reflects the frenetic pace of the host.
@@tarekwayne9193 I can definitely see your point, there is a clear inherent mistake I missed while reading it to myself (as often happens with Individuals proof-reading their own work) , it should really say (IMO): "This is crammed with a relentlessly incessant pounding of an asphyxiating, constrictive series of bombardments of information. I love it." There definitely is a need to address the multitude of bombardments. Kudos to him again for being a non-native English speaker (Assuming from his name although we can never be sure)
PBS Space Time I have to say, I've been struggling to understand this whole spacetime thing for many years. I've not been able to grapple with the math, but your explanation in these videos have done wonders for me. This is really enlightening stuff, and I very much appreciate your ability to break it down. Thank you.
Steve Pittman Awesome! Unfortunately, I'm making a few graphical errors here and there. We'll try to correct them in a side video soon so that viewers have a clear reference going forward.
My head hurts. So you're saying that objects we interpret as 3d are actually 4d objects, and since we are unable to comprehend the "higher dimensions" our mind uses tricks like time, motion, velocity, acceleration, etc. to help us understand the "slices" that we see of the 4d loaf that is the universe? Kinda like how a flip book works, the entire flip book already exists, and none of the objects there in are moving, but when you take the book and flip it, you experience a single slice at a time. What I'm saying is that we view 3d flipbooks in a 2d way, the same way we view the 4d flipbook that is the universe, in 3d. Does any of that sound right?
That's right, but only in Newtonian physics. The purpose of this whole series is to explain how the thing you just described works with the addition of c as the universal speed limit.
That’s an impressive analogy. We use comparisons like yours to get a better sense of the 4D “reality” which our minds cannot truly grasp in any meaningful way. We are limited by and exist in our 3D understanding of reality, but by using math/physics (and even your analogy) as tools we can express those things we cannot see. Sadly for the stickman character within the 2D world, he is trapped in a single moment of spacetime...and as the page is turned each prior character fades into oblivion.
haha hes just taking a long way to say that... erhm... distance is a flexible concept if you don't define exact ways it should be measured, and that you can measure it relative to motions and simplify it with a hybrid So simple dude how can you miss it :P
Speaking of English, I have a weird question, why do Americans (like this guy) always say "voila" whereas I've never heard any British people saying that? I mean, why do they even say that? I don't really understand ^^' Could you explain it to me please?
Hi. I love your videos but there's a lot of things I don't get on this one. (I'm French, so I apologize in advance for my English mistakes.) 1. At 5:04, we see, with the white dot in the blue frame, that the photon traveled a certain distance in a certain amount of time. OK. During the same amout of time, Red Gabe sees the photon going at the same speed (c), but traveling less distance (since Red Gabe follows the photon). So, in order for the speed of light to remain constant, the time that went by for Red Gabe should be less than for Blue Gabe. All of this brings my question : Why isn't the white dot closer to the origin in the red frame than in the blue one ? 2. At 5:04 again. Can you explain the dots' positions ? I've been melting my mind for nearly one hour now. Sometimes I understand how to obtain the red frame starting from the blue one but not the opposite, and sometimes I'm just so confused that I forget everything, start again, and not understand it the way I just have done. My brain is a mess right now. 3. At 8:17. Is it usual to put time before space in vectors' coordinates ? That bothers me because it looks like (y;x) instead of (x;y) (although it's not y here but t). 4. At 8:27. I don't understand what spacetime interval lenght is and how you get thoses formulas for the vectors' lenghts. And how do you get -c² btw ? Some help would be really appreciated. :) Thanks to anyone who will explain. PS : I love the content of this channel and the fact that you stay close to us. It's awesome to have people who really want to teach such interesting stuff. Keep up the good work.
Piffrock Great comments, and thank you for the compliments. You also caught some errors in the video, so thank you for that, also! In order of your questions... (et a propos, je t'assure que ton anglais est parfait, contrairement a mon francais, en lequel j'ai beaucoup perdu -- see? I'm terrible!) 1 & 2) Tu as raison! The white dots and red dots are in the wrong place on the diagrams. This was my error -- the animator originally had it right, and I was rushing before we published, mixed myself up, and had him change it. It's my mistake. I added an annotation in the video indicating this. I'm sorry I wasted an hour of your life :( But you are completely correct. I made a mistake. 3) Yes, it is usual. I'd say the convention nowadays is to put time before space (I would say over 95% of modern textbooks and journal articles do it this way). 4) If you had a vector A in Euclidean space, and if you knew its components, how would you compute its length? Well, you would apply the Pythagorean theorem to its components -- (A_x)^2 + (A_y)^2. Technically, this is the length-squared, but let's just call this length for simplicity and because it will make the analogy to flat spacetime easier. Ok, in flat spacetime, you instead compute the *difference* of squares of the components. So, for the 4-velocity of the monkey as measured in any given frame, it is (Δx / Δτ)^2 - (c Δt / Δτ)^2. I called this the "spacetime interval length" because, in flat spacetime, the distance between points (i.e. between events) is computed as (Δx )^2 - (c Δt )^2. This is just how it works (see our earlier episode "Are Space and Time an Illusion?"). And you compute lengths of vectors analogously. This is not the technically correct term -- it is some pseudo-vocabulary I made up to try to minimize the amount of jargon in the episode. Anyway.... in the monkey's own frame, the monkey is always at the same location for all events at which he is present, so Δx between any two such events is 0. Also, in the monkey's frame, t = τ (τ denotes time on the monkey's clock, which is "grid time" in the monkey's own frame). Thus, in the monkey's frame, the "length" of its own 4-velocity vector is -(c^2). But the "length" of a vector cannot depend on the frame of reference used, just as the length of a vector in Euclidean space does not depend on how you orient your x and y axes. So it must come out to that value in ALL frames, because it is an intrinsic property of the 4-velocity vector, regardless of how one manages to compute it.
PBS Space Time 1. OK. 2. Yay !! I finally got it ! I must have spent another half an hour though. :D 3. OK. 4. Oh yeah, I re-watched (for the 5th ou 6th time) the video and that begins to make more sense to me. :) I forgot the fact about Minkowski. Thank you, I mean, REALLY, for these quick and complete answers. I really appreciate it ! This topic is difficult and the fact that you're here to teach it and answer the questions is beyond all hopes. PS : Your French is also perfect (except for the "a's" instead of "à's" but I assume it's not easy to type "à" with your keyboard). :)
PBS Space Time When viewed from a different frame of reference, are the dots supposed to "move" (of course not "move' but, YGTI) along the hyperbolas that you get when you graph (∆x)^2 - (c∆t)^2 = constant? In other words when you take slices of constant "space-time-interval", do you get these hyperbolas, and since those are the things that everyone can agree on, do the dots stay on those hyperbolas when viewed from a different frame of reference?
PBS Space Time I just graduated from High School, although I did take two semesters of college physics, and I'm going into college for Computer Science and Physics. Thanks for the reply! That clarifies a lot.
I watched all other videos in the spacetime series. This one seriously kicked my poor brain and sent it flying. Hoping to understand better on rewatch.
I just started watching space time this week to pass the time when I came down with Covid. It is so good I decided to go right back to the start and watch every one of the videos. Gabe is great. I have to watch each of his videos on curvature of space and time 3 times but I'm feeling a little less stupid each time😅.
MobiusCoin Is just an acronym for "Fixed velocity geometrical description, in a 4 dimensional static spacetime, of the partial history of one object, in relation to another reference frame (the blue guy)". Is just a tool, witch combines many different concepts based on real-world things (like velocity, time, speed of light, reference points, relativity etc) in a visual representation of something usefull [for the next video].
Think of it this way. A 4-velocity vector always has "length" squared of minus c^2. This gives another way of seeing why nothing can travel through space faster than light. Like any other vector, a 4-velocity has components. The sum of the squares of these components add up to -c^2...
for anyone having a hard time trying to digest all of this I would suggest taking notes and drawing out these diagrams it really helped me understand this concept. looking back at the other videos is essential as well. at face value, this seemed really complicated but once I started taking notes I realized that I was overthinking all of this and that I was making it more complicated than it really was
same. I started my journey watching videos on quantum systems that came out this year, only to find my self rabbit holing down the years before i watch other videos so i can understand the context better. So i have a whole queue of videos that i was gonna watch, but ended up leaving for later lol. and little by little the pieces are starting to fit together, but i started just kind of watching the videos and not really understanding, to slowly fitting the puzzle, and the more i did the more i realized the less i knew, so even though i havn't been taking notes, which is a great idea, ive found that working through the problems even with my limited knowledge helped increase my understanding
The full version of this topic is extremely complicated. I don't know how anyone could ever break it down to where someone without physics or math training could understand it, but this is about as in depth as you can get in terms of the most simplest explanation there is that isn't just hand-waving.
This entire set of videos has been PHENOMENAL; both in the specific points and in clarifying it as part of a larger concept. Thank you so much and I'm buying some dang merch now!
This series is great! I (let's say) was present in some special relativity lectures and I know enough of the math to do my calculations but this makes me get the concept! Thank you for all the work that goes into this project.
What I love about Gabe.. yes, he speaks too fast for most of us and this content is too complex to understand it at that pace on first pass.. but it's a video. We can just watch it over and over. You might think this is a detriment, but I think it's perfect. I think people can learn effectively through repetition of content presented like this. It's awesome.
@@querywizard _"I think people can learn effectively through repetition!_ Exactly! With the next is to sit down and explain what you learned to someone else. (It need not be someone physically present. I often noticed I found the holes - where the "ice gets thin", so to speak - in my own knowledge when trying to explain it, even if its only a virtual dialogue within my own brain.)
I like how you try your best to stay on topic instead of, well for lack of a better term, going off on tangents. There would be so many things to branch off to but you keep it focused on the lesson at hand. Nice work!
I had an audit at work yesterday concerning my use and knowledge of N.D.T. (non- destructive testing) using a U.T. (ultra-sonic testing) device. Your awesome videos and conveyance of tangent vectors scored my brownie points. Thank you! Idea and Gameshow are also stellar PBS RUclips channels, but you take the cake. Keep em coming. "Nom nom nom".
PINKtheory Thanks! And I'm glad I helped. Mind if I ask how this exactly got you brownie points? (I assume you're an engineer from your description of the audit)
HI, your videos are awesome!!! I'm brazilian and I'm enjoying so much to watch your videos. And every time I re-watch a video I can comprehend more and more about it. Thank you so much and keep up with this!!! Congratulations !!
This hurts my brain. I just want to say how appreciative I am of people who tackle these incredibly difficult tasks of determining what our reality is and how it works. I enjoy learning whatever I can about it. Keep doing what you're doing.
Thanks so much for doing this series! I've always wanted to learn about four dimensional space time but didn't want to go through hours of lectures to first understand tensor calculus.
I've been trying so hard to understand these videos, but my mind is so simple lol. But still I can't stop watching them because I'm still so genuinely interested in them...
There's a massive difference in comprehensiveness between new and old PBS Space Time videos -- the new ones giving the viewer more space to think and time to grasp it.
--Apologies in advance if someone had already addressed what I am about to do so-- **This may be insignificant, but should both blue and white lines on Red Guy's graphic have opposite slope values @3:51? At the same time, should the monkey be parallel to Red Guy on the positive side of the graph? Definitions -to be on the same page- *An object: -Moving/being in the direction of one's anatomical LEFT is... POSITIVE on one's x-axis -Moving/being in the direction of one's anatomical RIGHT is NEGATIVE on one's x-axis *As seen @2:52 and @2:59 -Light moves to Blue Guy's anatomical left--graphed as positive. BLUE Line explanation: The reason is: @2:43, Red Guy approaches Blue Guy from Blue Guy's anatomical right (audience see's "from left"), relative to Blue Guy's frame of reference. We would expect to see Blue Guy do the same on Red Guy's perspective. However, when seen from Red Guy's frame of reference @3:51, Blue Guy is moving towards (not FROM) Red Guy's anatomical right-- audience sees "from the right". (If anatomical Left/Right is positive/negative respectively RELATIVE to Blue Guy, what is to say that is not the same for Red Guy?) Correction: Blue Guy should be moving from the anatomical right relative to Red Guy. In other words, TOWARDS the anatomical LEFT, not Right. (try simulating this, with toy soldiers on a table, and walking around it to see) Significance: Because Blue Guy was moving in the wrong direction on Red Guy's reference frame (but with the same speed), the graph (as it is in this video) shows the opposite slope of what really happened (aka, the slope of the Blue line should be positive--again TOWARDS the anatomical Left, which is positive) WHITE line explanation: @2:52, Light is being shot out towards Blue Guy's anatomical left (audience sees towards the right); therefore it's positive on his graph. However it is shown to be ALSO positive on Red Guy's graph, which isn't correct because anatomical left for Blue Guy is the reverse of Red Guy (aka Red Guy's anatomical right). Since it was reasoned that: anything moving in the direction of one's anatomical right is negative on the x-axis, it stands to reason that the WHITE slope is also opposite of what it should be. Correction: Light should have been going towards the Left of the screen (anatomical right of Red Guy) Significance: Since it was reasoned that: anything moving in the direction of one's anatomical right is negative on the x-axis---and that light was depicted as traveling towards Red Guy's anatomical Left, it stands to reason that the WHITE slope is also opposite of what it should be. MONKEY line explanation: Regarding Red Guy's reference frame: From the last two arguments, we can see that the direction of Blue Guy's movement is incorrect relative to Red Guy. However, compounded on that, the MONKEY's position, relative to Red Guy, is also incorrect. Notice that in both visualizations (at the right of the screen): @2:55 (Blue Reference) and @3:51(Red Reference), Blue Guy and Red Guy cross each other before Blue Guy crosses the Monkey. By doing this (while Blue Guy is moving in the wrong direction--relative to Red Guy), the monkey's position is also wrong. Another way to think about it is that anything at the anatomical left/right is positive/negative in value respectively. Since the monkey SHOULD be on the anatomical left of Red Guy, it should be on the POSITIVE side of Red Guy's graph. Correction: The monkey should be on the positive side, but of equal distance from Red Guy. Significance: The monkey isn't; therefore it's on the wrong side of the graph.
Yes finally a youtube channel that brings real topics in physics and explains them with very inviting editing and enthusiasm, we need more of this content and less of videos that relate to pointless things with a little science thrown in to keep people entertained. I could watch videos like this all day! KEEP THE VIDEOS COMING PBS SPACE TIME!!!!!!
Minor discrepancy: At 2:51, blue guy shoots the laser to his left. However, when the event is replayed at 3:54; blue guy shoots the laser to his right. Nonetheless, great video and thank you for posting!
Iwon't tellmyname You know what's funny? I ended up studying physics because I pretty much felt the same way about my physics courses in school. I almost quit the subject, but it bothered me immensely that I couldn't seem to follow what was going on. Years later, I'm still not sure I understand things as well as I'd like to, but I do know that I've managed to see a lot of the beauty in physics (and math) that I might never have been exposed to if I'd shied away from a subject that, in my early encounters with it, made me feel really dumb. Studying this subject despite the fact that I struggled so much just to understand what people were saying turned out to be one of the most rewarding decisions I ever made. Sometimes, you "never understand what's going on" because you're listening to gibberish. But sometimes, it's a signal that's there might be some really awesome mind-altering knowledge beneath the curtain if you can hang in there. The satisfaction of understanding something after 5 minutes just can't compare to the gratification of finally getting it after 5 weeks or 5 months. Just something to think about.
PBS Space Time That's the reason why I try to watch just about every video on this channel because even if right now I have no idea whats going on hopefully after watching the same video 3-4 times it starts to make sense and that's one of the most rewarding feelings in my opinion. I don't even expect to ever use any of this outside of school but I still love to learn things on this channel even if I'll never use them.
PBS Space Time I've been interested in physics for a long time, I read and watch videos on a huge array of subjects under its umbrella, and I've considered pursuing a degree in it. There are two things that put the brakes on such thoughts though. First, a lot of this stuff is seriously non-intuitive, and while I definitely appreciate the gratification of eventually understanding it, I'm afraid some or all of it will ultimately prove to be beyond me. Second, while I hate to drag out the old 'bad at math' cliche, I've never been able to get past college algebra, much less the really complicated stuff required for such a pursuit. And beyond that my brain just doesn't seem to be wired to translate math into understanding of physical reality. It's why, as I said above, I really value these videos.
Iwon't tellmyname I think 13-14 times is probably more realistic, but even then, our videos aren't enough. No videos are enough. You have to read books. I wish that weren't true, but I think it is. That said, use other videos and articles that we put IN THE DESCRIPTION as supplementary material. I can't emphasize enough how important it is to hear different people talk about this to help figure out what's "really" going on. Reason -- all of might make little mistakes here and there (including me), and hearing lots of perspectives helps you as a reader / viewer identify those errors. It's a time-investment, but it's worth it.
Oddly enough, this video actually helped me to understand one of the fundamental points of special relativity I was having difficulties understanding. Thank you!
I've had to re-watch this one the most out of the series to get a firm understanding of it Gabe. It's difficult to picture this one, and I had to watch this video a fourth time with my notes before I actually grasped the topics. I've only taken physics 101 and astronomy 101 at my college so sometimes this stuff feels over my head.
Jedidiah Young Hang in there. This was not mean to be absorbed in 10 minutes. See what I wrote to this other viewer: ruclips.net/video/P4rW_pPbD-U/видео.html&lc=z12ruzaiwqfgtzzkc22wi1z44xnpelp0m
Watching Spacetime would have helped me so much in high school. Which is why I will go to my old high school and tell several physics teachers about this series. It'll help clear up so much about the non mathematical part about relativity.
this is a pretty ambitious endeavor for this series. i'm still finding myself going back and rewatching all the episodes prior when i new one comes out.
I am so determined to understand this but I already realize I'm gonna have to rewatch this at least 3 or 4 more times to get a firm grasp of it. The first video in this series probably took me 5 rewatches over the course of 18 months before it fully sunk in but it's so worth it.
Thank you for the great channel and making complicated topics graspable for non-experts and giving them a starting point if they want to learn more. On a totally unrelated topic: At 6:28 - did you choose a Trabant 601 as representation of a car? :-)
when you try to explain something you don't have to rush keep the video simple and smooth bcoz there are many people like me who have problems in perceiving things
Wow. I'm wondering if we can get these spacetime videos on a separate playlist. This is one of those things that will need to be watched several times before finally clicking.
Wow, the earlier videos on this channel were deep! I got lost in the last few minutes. edit: I did some research and I understand now. Great video. Love everything on this channel!
As a sophomore engineer I was pompously thinking how difficult could this be. As I've been through the worst of math and physics.. but nope this stuff is too complicated to wrap my head around haha
Funny you say that. Students can do things like how to derive the Lorentz transformation and use it to get E=mc^2 and all that good stuff and still not have the slightest intuition about what is really going on, because they use math they learned as a sort of scaffolding to not have to really understand anything. This was a major hurdle for me. Anyone can follow an algorithm to derive a formula, but understanding what it really means is a lot more difficult. Like take a wave equation., like the heat equation (one spatial dimension): ∂u/∂t = k ∂^2u/∂x^2 Okay, I can follow the steps and use separation of variables to turn it into an ordinary differential equation, then I can solve it using the previous "cook book" methods I learned in differential equations 1. But wtf does that heat equation really mean? What does the constant mean? When I solve it, I get some sort of summation (or integral) of e raised to the imaginary number, but what does THAT mean? After my head explodes, I can go graph these type of equations and see what they do, but then translating that back through the heat equation and into the actual physical reality the math is describing? It's hard to do. And with this stuff, the actual physical reality the math is describing is completely, utterly NOT intuitive, because we simply live in a world where the classical approximation that relativity essentially replaced is "good enough." So, tl/dr, don't worry. This relativity stuff is inherently difficult because our brains have been trained for our entire lives to think in a way that is inconsistent with it, and that is even without looking at the difficult math (and it gets so much harder moving into curved spacetime).
@@EliteTeamKiller2.0 That's why you need to interleave the geometric analysis with the algebraic analysis. The heat equation is just a "spreading out function" that evens out a curve gradually into a flat line. Equations like e^iwt can be interpreted as a point that rotates around the origin in a circle through time. If you want to look at a wonderful way to do QM without doing any calculus or even algebra, look at Feynman's QED: The Strange Theory of Light and Matter. But yes, first you have to unlearn everything you thought you knew about the universe.
wish u wouldn't have left the show gage, I've always wanted to fly and be a person that explores the universe and not just the planet, your videos are wonderful and informational, while i understand science is a best either 100% accurate or a nice shot in the dark, that it is important to be focused on continual advancing our understanding and hopefully agility to travel to other parts of the universe. thank u for the great vids and i wish u the best.
A bit hard to undestand but on the second view it starts to make sense :P. Please dont dumb the videos down, youtube is full with easy to swallow videos. Thanks a lot, awesome work
The end part describing the vectors always gets fuzzy, but it's getting better with research. That Greek letter, tau is used for proper time, which is the monkey's time measured along it's own world line.
At 6:35 when you plotted the world line of the moving car (from your prospective) shouldn't it have been above the the 45 degree photon line (I.e. Inside your lightcone) otherwise your wouldn't 've been able to "see/observe" it? Love the series, keep up the good work...
Ahmed El-Hawary You can see events outside your light cone just fine. Just with a delay. For instance, if right now, a solar flare erupts, you'll find out about it 8 minutes from now. So it couldn't have influenced you casually (it was outside your light cone), but once its light reaches your eyes, you become aware of it and can reconstruct the historical fact that, according to your clocks, it occurred 8 minutes earlier, while you were reading this comment. The only events that you can't become aware of, even after the fact, are those that occur behind an event horizon (this will be discussed in a future episode). Now, part of the car's world line *could have been* inside my lightcone, sure -- I could have translated the whole curve vertically upward. That would simply mean that there some events at which the car was present that I could have influenced. I just opted not to draw it that way -- in other words, the car is pretty far away from me spatially at its point of closest approach.
This was clear to me because I already understand special relativity and knew a bit about Minkowski space, so I didn't have an distracting questions like "why."
The sound at 1:45 broke me, I was searching for about an hour for what game I heard that sound in a lot. Loaded up runescape, watched so many clips of games.... It was Borderlands!
I'm watching some older videos on the channel, and have come to the conclusion that it's seriously improved in terms of presenting complicated material to laymen. These old videos I have to playback at 75% speed for them to be even tolerable, but the metaphors and visual aids aren't as well chosen as well.
I think I'll have to re-watch all the videos a couple times to really absorb it. I think I get it..sort of. But not quite. It's super interesting though.
Man, I love your channel but I can't keep up with the speed you explain things. It would be great if you could increase the length of each episode a little and explained things a little bit slower. It's been a long time since I studied physics on the University and it's one of my favorite subjects. Keep up the good work.
On a real note tho: I'd be careful with reusing the term worldline between Steins;Gate and these videos. They mean different things based on how this guy has defined it. Steins;Gate Worldlines = basically time lines that they hop between (essentially their own universes) Space Time Worldlines = different perspectives of causal events within the same universe
Basically the coordinating axies represent metastable "solid" multi-phase resonance and fluid expansion-contraction, exponential transitions of temperature and perspective => distance timing, and the provided labels are for "world-view" perceptions of math-physics(?). Reaction "velocity" in Chemistry is more appropriate word use for QM.
Really a huge fan of the level of complexity of topics you're getting into. Its rare for a well made education youtube channel since most are aimed at beginners. Keep up the good work! Loving this series :)
Are you going to do an episode on the holographic principle in the future? I'd love to see that. You have a great way of explaining things, you don't assume I'm an idiot and don't overly simplify things like many other videos (and TV programs) do. So serious thanks for having the patience to explain all of this to us! New subscriber, you guys at PBS Digital Studios are some of my favorite channels to follow!! Keep up the amazing work!
vormov Maybe. We have to lay a lot of groundwork first, else such an episode would devolve into just stating buzzwords without deeper understanding, which I prefer to avoid.
PBS Space Time Some questions are popping right up in my mind while I'm watching. Firstly, which is true between "the straight-or-non-straight property of a spacetime line maintains when the reference frame changes" and "the inertial-or-non-inertial property of a reference frame depends on the (other) reference frame"? (Just to be clear with the first question). Secondly, is the new definition of inertial frame equivalent to "reference frame with constant 3D-space velocity"? If not, why?
TheN GroupTwo To answer your first question: the first statement is true (with a caveat I'll get to below),but the second is not. Let me elaborate... In special relativity, inertial frames correspond to the frames of observers whose world lines are geodesics. In an inertial frame, such a world line looks straight. But in a non-inertial frame (and I didn't draw any spacetime diagrams from a non-inertial perspective, for good reasons that will be clearer next week), such a line would not look straight. But it would still be a geodesic, since being or not being a geodesic is an intrinisic property that can be verified independent of any frame of reference. That's why the second statement in your first overall question is false -- inertial-ness is equivalent to geodesic-ness, and that property is inherent to curves in spacetime, even if we never throw down a frame of reference at all. Answer to your second question: yes, at least as measured with inertial frames of reference. Think about it -- in the spacetime diagram corresponding to how things look from inertial frame A, inertial frame B has to be a geodesic, i.e. straight. But straight on a spacetime diagram also has a kinematic meaning -- equal x-axis tick marks (and y and z) in equal ticks of frame A's clock. So yes, inertial observers will be seen *by other inertial observers* to have constant spatial velocity. Of course, a non-inertial observer would see an inertial observer accelerate, but all the diagrams we true show the point of view of some inertial observer. Excellent questions.
Your recent videos about general relativity have been excellent, thanks. I've been trying to wrap my head around what exactly spacetime could be, and it seems to behave like a fluid. Is the structure of spacetime like that of a zero viscosity fluid, and if so, then could the "liquid spacetime" be made of "molecules" like water?
Jayson Cody That's actually a pretty good way of thinking about it! Now spacetime isn't made of molecules, it's literally just space or emptiness with time, but that's a good way to visualize it. In fact, in cosmology when they model the universe, they use the assumption that the universe is similar to a perfect fluid. Good catch!
When we do this frame of reference anchoring, do we have to discard knowing that we're moving? On what basis do we say "from his perspective he's stationary"? When I'm moving, it doesn't seem to me that I'm stationary. I know this is pretty essential. You could say I'm assuming this based on my perceptual information which has a good success rate in daily life, but considering we take this to reflect the world's mechanics anyway, that perception is linked to these frames of reference, it seems we're assuming for physics that we can accurately relate ourselves to the world. I've read Einstein's book, and I'm following regardless, but I found this way of talking about frames of reference a bit funny or ad hoc.
Got into this in other videos. Just one problem, the universe is expanding. While light's speed can be constant in space, it has to be going faster in the Space-Time Continuum. On top of that, the CBM gives both a coordinate time and location for every event, even though it is viewed differently by every observer. Something has to give, my short hypothesis is that the angular momentum of the speed of light is always conserved. Yes, every particle's field is still traveling at the speed of light, this has been measured countless time with electromagnetism. Along with the twin paradox, there seems to be a major crisis with relativity. How does one absolutely rule one of the conflicting ideas out? As it just so happens the CMB gives a very clear direction that the earth is traveling through both the galaxy and the universe. Simply send two atomic clocks at the exact same speed relative to earth in opposite directions of the path of the earth through the universe and both clocks should give exactly the same time dilation relative to the universe, if not Simultaneity rules… we will see.
An object moving from left to right will apear contracted when it is on your left and expanded when on your right. This is because it is moving towards you on your left and moving away from you on your right.
This lecture actually reminds me a lot of the premise of the Prophets in Deep Space Nine. They have no concept of past/present/future and explain to Captain Sisko that they see him as simply existing at all points of his existence at the same time. This lesson almost explains to me how that can actually work. He's just a line on a graph to them.
(∆x/∆τ)^2-(c∆t/∆τ)^2=-c^2 Is it possible to use this equation to calculate the speed of *time* in meters per second relative to your internal reference?For an object moving at c: (c/∆τ)^2=(c∆t/∆τ)^2-c^2 (1/∆τ)^2=(∆t/∆τ)^2-1 1=∆t^2-∆τ^2
Donnie Darko is what came to mind while watching this video . The book he reads "the philosophy of time travel" deals with tangent vectors and world lines. its what the liquid streams that erupt from the characters chests are meant to represent
Whew! A video I understand (for the most part). I am still trapped on the event horizon, though. These darn Black Holes are making my brain dizzy. I can't stop thinking about them, because I don't quite get it. I though I did, until I watched the other video. Almost like an itch in my brain I can't quite scratch. I get what they are, but not what is really happening as far as events. Also, where does the hole lead? Is there an outside to the universe through here? Is it a hole or just extreme curvature?
This is not a bad introduction, tangent vectors are 4-velocity-vectors (considering the position and time of another reference frame relative to the time of one owns time relative to the time of the other reference frame) and the space time interval length is -c^2 in flat space time. Inertial observers are geodesic world lines or constant speed straight lines and non inertial observers like accelerating observers follow non geodesic or constant speed non-straight line because parallel vectors doesn't remain tangent vectors. And inertial observers moving with constant speed relative to other inertial observers on curved space time also correspond to non-straight lines due to the gravity- acceleration equivalence principle. One can always use Minkowski diagrams etc. to illustrate effects and events in relation towards each other with geometry.
Really awesome videos guys! :D I had a suggestion too.. At first I didn't understand why the ant on the basket ball could measure angles left and right but not up and down, but I wasn't thinking of the ant as being in a literally 2D universe. Video games are part of your channel so why not use Mario's 2D universe? (Maybe trying to figure out if hes actually on a small part of a basket ball or a plane) as a future example instead of an ant?
Neven Makowiecki The problem is that most people think of Mario as being 3D and just _displayed_ in 2D. Know what I mean? People have way more built-in assumptions about a video game that we would need to overcome than about ants on basketballs.
I was with you right up to the point you started talking
GW2
lol, good spot. 1st one to notice
🤣🤣🤣
😂😂😂😂😂😄😄😂😂😂👏👏👍👍
I'm an engineering student and I read and watch a lot of books and documentaries about sciences like these; however, watching your videos makes me feel like I'm stupid 😂😂😂😂😂
lmao
+Ricky Hou Same here bro :o
+Ricky Hou +Ali elb Which sort of engineer (or job in general that create physical things) would HAVE to learn and fully understand this math and these concepts and their consequences in our perceived reality/our modern world for their field? I can imagine that maybe people who design computer chips with nanometers small transistors have to know quantum mechanics, which I guess would include learning and understanding this? Is that true? Any other jobs?
Reading your comment makes me feel stupid.
GPS systems and satellites are examples of tech that need this field, I believe.
This series with Gabe was/is awesome! Still re-watching it after 4 years
too (:
As well
Same
yep I feel like I understand it more every time I watch it since I was like 12 when I first watched this
8 years!
A good way to view these videos and understand is if at any point you are confused, restart the video from a little further back from a point you understand.
+Kirrim Kerman Technical question: How do I set time before 00:00?
+Kirrim Kerman But on what vector do you suggest we observe it?
Instructions unclear. Stuck on an infinite time loop
Define "point"
Talking about truths of physics in terms of geometry alone. Pythagoras would be proud.
Taylor Bennett According to the biographists of Stephen Hawking, he does the same in his head since he can't write equations anymore. Nature is fantastic.
Taylor Bennett I think he would mainly just be glad that his work is still appreciated all these years later.
more like Euclid would be proud, he was more into geometry
Salman Memehood He would've been proud if we were using Euclidean spaces. :P
Graig Simmonette I would’ve liked your comment if you didn’t swear
I'm absolutely loving how in depth we're getting with space-time! Hard to find this kind of material anywhere. Thank you for not watering it down!!
this channel is an awesome step up after watching those watered down videos to get a basic grasp on it.
This is crammed with a relentlessly incessant pounding of asphyxiatingly constricted series of bombardments of information. I love it.
Haha... Well phrased!
@@tarekwayne9193 not really some grammatical errors, it should say: This is crammed with a relentlessly incessant pounding of an asphyxiating, constrictive series of a bombardment of information. I love it.
@@stormixgaming8389 interesting, according to a prescriptive view of English grammar, you may indeed be right. However, as a descriptive linguist, his sentence reads more fluidly(predictive text wrote "fluidity" for me😒) to me and depicts what's going on in the speaker's delivery.
It's not just one bombardment, it's multiple! It's a relentless, ongoing onslaught comprised of successive verbal machine gun attacks.
Yours reads like an account of a singular fact. His puts in you in the mix, feeling each blast of knowledge whizz by, while others smack you squarely in the face.
In addition, as I would wadger he's not a native English speaker, further kudos to him.
I do agree that his sentence might have benefitted from commas at least. On the other hand, their absence again reflects the frenetic pace of the host.
In retrospect, maybe there should indeed be an "an" before asphyxiatiingly......
As it is one series.....
@@tarekwayne9193 I can definitely see your point, there is a clear inherent mistake I missed while reading it to myself (as often happens with Individuals proof-reading their own work) , it should really say (IMO): "This is crammed with a relentlessly incessant pounding of an asphyxiating, constrictive series of bombardments of information. I love it." There definitely is a need to address the multitude of bombardments.
Kudos to him again for being a non-native English speaker (Assuming from his name although we can never be sure)
PBS Space Time I have to say, I've been struggling to understand this whole spacetime thing for many years. I've not been able to grapple with the math, but your explanation in these videos have done wonders for me. This is really enlightening stuff, and I very much appreciate your ability to break it down. Thank you.
Steve Pittman Awesome! Unfortunately, I'm making a few graphical errors here and there. We'll try to correct them in a side video soon so that viewers have a clear reference going forward.
My head hurts. So you're saying that objects we interpret as 3d are actually 4d objects, and since we are unable to comprehend the "higher dimensions" our mind uses tricks like time, motion, velocity, acceleration, etc. to help us understand the "slices" that we see of the 4d loaf that is the universe? Kinda like how a flip book works, the entire flip book already exists, and none of the objects there in are moving, but when you take the book and flip it, you experience a single slice at a time. What I'm saying is that we view 3d flipbooks in a 2d way, the same way we view the 4d flipbook that is the universe, in 3d. Does any of that sound right?
I have no idea what you're talking about...but it sounds pretty awesome
That's right, but only in Newtonian physics. The purpose of this whole series is to explain how the thing you just described works with the addition of c as the universal speed limit.
That’s an impressive analogy. We use comparisons like yours to get a better sense of the 4D “reality” which our minds cannot truly grasp in any meaningful way. We are limited by and exist in our 3D understanding of reality, but by using math/physics (and even your analogy) as tools we can express those things we cannot see. Sadly for the stickman character within the 2D world, he is trapped in a single moment of spacetime...and as the page is turned each prior character fades into oblivion.
This analogy you commented is straight from Brian Greene LOL
Yep.
I think I'm gonna have to rewatch this episode tomorrow XD
LazyMasterGamer [2]
LazyMasterGamer You and me both!!
LazyMasterGamer my thought exactly
LazyMasterGamer yeah... I hope we'll get it then :)
me 2
I've yet to see the English version
This made me laugh =D
Bandit Anansi : Turn on subtitles, it clarifies it all by saying uhhhhhhhhhhhhhhhhhhh
haha hes just taking a long way to say that... erhm... distance is a flexible concept if you don't define exact ways it should be measured, and that you can measure it relative to motions and simplify it with a hybrid
So simple dude how can you miss it :P
🤣
Speaking of English, I have a weird question, why do Americans
(like this guy) always say "voila" whereas I've never heard any British people saying that?
I mean, why do they even say that?
I don't really understand ^^'
Could you explain it to me please?
Hi. I love your videos but there's a lot of things I don't get on this one.
(I'm French, so I apologize in advance for my English mistakes.)
1. At 5:04, we see, with the white dot in the blue frame, that the photon traveled a certain distance in a certain amount of time. OK. During the same amout of time, Red Gabe sees the photon going at the same speed (c), but traveling less distance (since Red Gabe follows the photon). So, in order for the speed of light to remain constant, the time that went by for Red Gabe should be less than for Blue Gabe. All of this brings my question : Why isn't the white dot closer to the origin in the red frame than in the blue one ?
2. At 5:04 again. Can you explain the dots' positions ? I've been melting my mind for nearly one hour now. Sometimes I understand how to obtain the red frame starting from the blue one but not the opposite, and sometimes I'm just so confused that I forget everything, start again, and not understand it the way I just have done. My brain is a mess right now.
3. At 8:17. Is it usual to put time before space in vectors' coordinates ? That bothers me because it looks like (y;x) instead of (x;y) (although it's not y here but t).
4. At 8:27. I don't understand what spacetime interval lenght is and how you get thoses formulas for the vectors' lenghts.
And how do you get -c² btw ?
Some help would be really appreciated. :)
Thanks to anyone who will explain.
PS : I love the content of this channel and the fact that you stay close to us. It's awesome to have people who really want to teach such interesting stuff.
Keep up the good work.
Piffrock Great comments, and thank you for the compliments. You also caught some errors in the video, so thank you for that, also! In order of your questions... (et a propos, je t'assure que ton anglais est parfait, contrairement a mon francais, en lequel j'ai beaucoup perdu -- see? I'm terrible!)
1 & 2) Tu as raison! The white dots and red dots are in the wrong place on the diagrams. This was my error -- the animator originally had it right, and I was rushing before we published, mixed myself up, and had him change it. It's my mistake. I added an annotation in the video indicating this. I'm sorry I wasted an hour of your life :( But you are completely correct. I made a mistake.
3) Yes, it is usual. I'd say the convention nowadays is to put time before space (I would say over 95% of modern textbooks and journal articles do it this way).
4) If you had a vector A in Euclidean space, and if you knew its components, how would you compute its length? Well, you would apply the Pythagorean theorem to its components -- (A_x)^2 + (A_y)^2. Technically, this is the length-squared, but let's just call this length for simplicity and because it will make the analogy to flat spacetime easier. Ok, in flat spacetime, you instead compute the *difference* of squares of the components. So, for the 4-velocity of the monkey as measured in any given frame, it is (Δx / Δτ)^2 - (c Δt / Δτ)^2. I called this the "spacetime interval length" because, in flat spacetime, the distance between points (i.e. between events) is computed as (Δx )^2 - (c Δt )^2. This is just how it works (see our earlier episode "Are Space and Time an Illusion?"). And you compute lengths of vectors analogously. This is not the technically correct term -- it is some pseudo-vocabulary I made up to try to minimize the amount of jargon in the episode. Anyway.... in the monkey's own frame, the monkey is always at the same location for all events at which he is present, so Δx between any two such events is 0. Also, in the monkey's frame, t = τ (τ denotes time on the monkey's clock, which is "grid time" in the monkey's own frame). Thus, in the monkey's frame, the "length" of its own 4-velocity vector is -(c^2). But the "length" of a vector cannot depend on the frame of reference used, just as the length of a vector in Euclidean space does not depend on how you orient your x and y axes. So it must come out to that value in ALL frames, because it is an intrinsic property of the 4-velocity vector, regardless of how one manages to compute it.
PBS Space Time
1. OK.
2. Yay !! I finally got it ! I must have spent another half an hour though. :D
3. OK.
4. Oh yeah, I re-watched (for the 5th ou 6th time) the video and that begins to make more sense to me. :) I forgot the fact about Minkowski.
Thank you, I mean, REALLY, for these quick and complete answers. I really appreciate it ! This topic is difficult and the fact that you're here to teach it and answer the questions is beyond all hopes.
PS : Your French is also perfect (except for the "a's" instead of "à's" but I assume it's not easy to type "à" with your keyboard). :)
PBS Space Time
When viewed from a different frame of reference, are the dots supposed to "move" (of course not "move' but, YGTI) along the hyperbolas that you get when you graph (∆x)^2 - (c∆t)^2 = constant?
In other words when you take slices of constant "space-time-interval", do you get these hyperbolas, and since those are the things that everyone can agree on, do the dots stay on those hyperbolas when viewed from a different frame of reference?
Alex Knauth Yessir. You got it! Are you a physicist, or a physics student or something?
PBS Space Time I just graduated from High School, although I did take two semesters of college physics, and I'm going into college for Computer Science and Physics. Thanks for the reply! That clarifies a lot.
Literally the best series I've seen on the topic; I may start to understand it after another 30-40 views. Well done!
I watched all other videos in the spacetime series.
This one seriously kicked my poor brain and sent it flying.
Hoping to understand better on rewatch.
I just started watching space time this week to pass the time when I came down with Covid. It is so good I decided to go right back to the start and watch every one of the videos. Gabe is great. I have to watch each of his videos on curvature of space and time 3 times but I'm feeling a little less stupid each time😅.
Fuck, I was following this pretty well until the end. The 4-velocity stuff really messed me up.
MobiusCoin Is just an acronym for "Fixed velocity geometrical description, in a 4 dimensional static spacetime, of the partial history of one object, in relation to another reference frame (the blue guy)".
Is just a tool, witch combines many different concepts based on real-world things (like velocity, time, speed of light, reference points, relativity etc) in a visual representation of something usefull [for the next video].
Think of it this way. A 4-velocity vector always has "length" squared of minus c^2. This gives another way of seeing why nothing can travel through space faster than light. Like any other vector, a 4-velocity has components. The sum of the squares of these components add up to -c^2...
Thank you for making these excellent and challenging videos!
for anyone having a hard time trying to digest all of this I would suggest taking notes and drawing out these diagrams it really helped me understand this concept. looking back at the other videos is essential as well. at face value, this seemed really complicated but once I started taking notes I realized that I was overthinking all of this and that I was making it more complicated than it really was
same. I started my journey watching videos on quantum systems that came out this year, only to find my self rabbit holing down the years before i watch other videos so i can understand the context better. So i have a whole queue of videos that i was gonna watch, but ended up leaving for later lol. and little by little the pieces are starting to fit together, but i started just kind of watching the videos and not really understanding, to slowly fitting the puzzle, and the more i did the more i realized the less i knew, so even though i havn't been taking notes, which is a great idea, ive found that working through the problems even with my limited knowledge helped increase my understanding
Thank you for melting my brain with knowledge.
UnknownXV It is... HOT!
(better being melt than burnt)
That's what she said
The full version of this topic is extremely complicated. I don't know how anyone could ever break it down to where someone without physics or math training could understand it, but this is about as in depth as you can get in terms of the most simplest explanation there is that isn't just hand-waving.
Spacetime makes the Best videos on youtube
YES
This entire set of videos has been PHENOMENAL; both in the specific points and in clarifying it as part of a larger concept. Thank you so much and I'm buying some dang merch now!
This series is great! I (let's say) was present in some special relativity lectures and I know enough of the math to do my calculations but this makes me get the concept! Thank you for all the work that goes into this project.
What I love about Gabe.. yes, he speaks too fast for most of us and this content is too complex to understand it at that pace on first pass.. but it's a video. We can just watch it over and over. You might think this is a detriment, but I think it's perfect. I think people can learn effectively through repetition of content presented like this. It's awesome.
Just make sure you're appropriately caffeinated before trying to absorb information like this.
@@querywizard _"I think people can learn effectively through repetition!_
Exactly! With the next is to sit down and explain what you learned to someone else.
(It need not be someone physically present. I often noticed I found the holes - where the "ice gets thin", so to speak - in my own knowledge when trying to explain it, even if its only a virtual dialogue within my own brain.)
This is definitely one of the best channels i've ever found out in RUclips. Congratulations, man. Keep posting your awesome videos!
I like how you try your best to stay on topic instead of, well for lack of a better term, going off on tangents. There would be so many things to branch off to but you keep it focused on the lesson at hand. Nice work!
I had an audit at work yesterday concerning my use and knowledge of N.D.T. (non- destructive testing) using a U.T. (ultra-sonic testing) device.
Your awesome videos and conveyance of tangent vectors scored my brownie points. Thank you!
Idea and Gameshow are also stellar PBS RUclips channels, but you take the cake.
Keep em coming. "Nom nom nom".
PINKtheory Thanks! And I'm glad I helped. Mind if I ask how this exactly got you brownie points? (I assume you're an engineer from your description of the audit)
HI, your videos are awesome!!! I'm brazilian and I'm enjoying so much to watch your videos. And every time I re-watch a video I can comprehend more and more about it.
Thank you so much and keep up with this!!!
Congratulations !!
This hurts my brain. I just want to say how appreciative I am of people who tackle these incredibly difficult tasks of determining what our reality is and how it works. I enjoy learning whatever I can about it. Keep doing what you're doing.
So, what you’re saying is that my brain is a “punching bag”, and your words are a fist; Did I get this correct?
I totally feel you
😂😂😂😂😂😂😂😂😂😂
Thanks so much for doing this series! I've always wanted to learn about four dimensional space time but didn't want to go through hours of lectures to first understand tensor calculus.
I've been trying so hard to understand these videos, but my mind is so simple lol. But still I can't stop watching them because I'm still so genuinely interested in them...
There's a massive difference in comprehensiveness between new and old PBS Space Time videos -- the new ones giving the viewer more space to think and time to grasp it.
--Apologies in advance if someone had already addressed what I am about to do so--
**This may be insignificant, but should both blue and white lines on Red Guy's graphic have opposite slope values @3:51? At the same time, should the monkey be parallel to Red Guy on the positive side of the graph?
Definitions -to be on the same page-
*An object:
-Moving/being in the direction of one's anatomical LEFT is... POSITIVE on one's x-axis
-Moving/being in the direction of one's anatomical RIGHT is NEGATIVE on one's x-axis
*As seen @2:52 and @2:59
-Light moves to Blue Guy's anatomical left--graphed as positive.
BLUE Line explanation:
The reason is: @2:43, Red Guy approaches Blue Guy from Blue Guy's anatomical right (audience see's "from left"), relative to Blue Guy's frame of reference. We would expect to see Blue Guy do the same on Red Guy's perspective. However, when seen from Red Guy's frame of reference @3:51, Blue Guy is moving towards (not FROM) Red Guy's anatomical right-- audience sees "from the right". (If anatomical Left/Right is positive/negative respectively RELATIVE to Blue Guy, what is to say that is not the same for Red Guy?)
Correction: Blue Guy should be moving from the anatomical right relative to Red Guy.
In other words, TOWARDS the anatomical LEFT, not Right.
(try simulating this, with toy soldiers on a table, and walking around it
to see)
Significance: Because Blue Guy was moving in the wrong direction on Red Guy's
reference frame (but with the same speed), the graph (as it is in this
video) shows the opposite slope of what really happened (aka, the
slope of the Blue line should be positive--again TOWARDS the
anatomical Left, which is positive)
WHITE line explanation:
@2:52, Light is being shot out towards Blue Guy's anatomical left (audience sees towards the right); therefore it's positive on his graph. However it is shown to be ALSO positive on Red Guy's graph, which isn't correct because anatomical left for Blue Guy is the reverse of Red Guy (aka Red Guy's anatomical right). Since it was reasoned that: anything moving in the direction of one's anatomical right is negative on the x-axis, it stands to reason that the WHITE slope is also opposite of what it should be.
Correction: Light should have been going towards the Left of the screen (anatomical
right of Red Guy)
Significance: Since it was reasoned that: anything moving in the direction of one's
anatomical right is negative on the x-axis---and that light was depicted
as traveling towards Red Guy's anatomical Left, it stands to reason that
the WHITE slope is also opposite of what it should be.
MONKEY line explanation:
Regarding Red Guy's reference frame: From the last two arguments, we can see that the direction of Blue Guy's movement is incorrect relative to Red Guy. However, compounded on that, the MONKEY's position, relative to Red Guy, is also incorrect. Notice that in both visualizations (at the right of the screen): @2:55 (Blue Reference) and @3:51(Red Reference), Blue Guy and Red Guy cross each other before Blue Guy crosses the Monkey. By doing this (while Blue Guy is moving in the wrong direction--relative to Red Guy), the monkey's position is also wrong. Another way to think about it is that anything at the anatomical left/right is positive/negative in value respectively. Since the monkey SHOULD be on the anatomical left of Red Guy, it should be on the POSITIVE side of Red Guy's graph.
Correction: The monkey should be on the positive side, but of equal distance from
Red Guy.
Significance: The monkey isn't; therefore it's on the wrong side of the graph.
Brilliant !! The way you introduced the four velocity concept was really awesome.
This video made goosebumps!
Yes finally a youtube channel that brings real topics in physics and explains them with very inviting editing and enthusiasm, we need more of this content and less of videos that relate to pointless things with a little science thrown in to keep people entertained. I could watch videos like this all day! KEEP THE VIDEOS COMING PBS SPACE TIME!!!!!!
Minor discrepancy:
At 2:51, blue guy shoots the laser to his left. However, when the event is replayed at 3:54; blue guy shoots the laser to his right.
Nonetheless, great video and thank you for posting!
Gabe, you rock! I love the way you explain this subject (although my brain is feeling a bit muddled after watching two in a row!).
This is the one youtube channel that I pretty much never understand whats going on
Iwon't tellmyname You know what's funny? I ended up studying physics because I pretty much felt the same way about my physics courses in school. I almost quit the subject, but it bothered me immensely that I couldn't seem to follow what was going on. Years later, I'm still not sure I understand things as well as I'd like to, but I do know that I've managed to see a lot of the beauty in physics (and math) that I might never have been exposed to if I'd shied away from a subject that, in my early encounters with it, made me feel really dumb. Studying this subject despite the fact that I struggled so much just to understand what people were saying turned out to be one of the most rewarding decisions I ever made.
Sometimes, you "never understand what's going on" because you're listening to gibberish. But sometimes, it's a signal that's there might be some really awesome mind-altering knowledge beneath the curtain if you can hang in there. The satisfaction of understanding something after 5 minutes just can't compare to the gratification of finally getting it after 5 weeks or 5 months. Just something to think about.
PBS Space Time And then there are topics, like this, that are fascinating however long they take to learn. Well said.
PBS Space Time That's the reason why I try to watch just about every video on this channel because even if right now I have no idea whats going on hopefully after watching the same video 3-4 times it starts to make sense and that's one of the most rewarding feelings in my opinion. I don't even expect to ever use any of this outside of school but I still love to learn things on this channel even if I'll never use them.
PBS Space Time I've been interested in physics for a long time, I read and watch videos on a huge array of subjects under its umbrella, and I've considered pursuing a degree in it. There are two things that put the brakes on such thoughts though.
First, a lot of this stuff is seriously non-intuitive, and while I definitely appreciate the gratification of eventually understanding it, I'm afraid some or all of it will ultimately prove to be beyond me. Second, while I hate to drag out the old 'bad at math' cliche, I've never been able to get past college algebra, much less the really complicated stuff required for such a pursuit. And beyond that my brain just doesn't seem to be wired to translate math into understanding of physical reality. It's why, as I said above, I really value these videos.
Iwon't tellmyname I think 13-14 times is probably more realistic, but even then, our videos aren't enough. No videos are enough. You have to read books. I wish that weren't true, but I think it is. That said, use other videos and articles that we put IN THE DESCRIPTION as supplementary material. I can't emphasize enough how important it is to hear different people talk about this to help figure out what's "really" going on. Reason -- all of might make little mistakes here and there (including me), and hearing lots of perspectives helps you as a reader / viewer identify those errors. It's a time-investment, but it's worth it.
Oddly enough, this video actually helped me to understand one of the fundamental points of special relativity I was having difficulties understanding. Thank you!
I've had to re-watch this one the most out of the series to get a firm understanding of it Gabe. It's difficult to picture this one, and I had to watch this video a fourth time with my notes before I actually grasped the topics. I've only taken physics 101 and astronomy 101 at my college so sometimes this stuff feels over my head.
Jedidiah Young Hang in there. This was not mean to be absorbed in 10 minutes. See what I wrote to this other viewer: ruclips.net/video/P4rW_pPbD-U/видео.html&lc=z12ruzaiwqfgtzzkc22wi1z44xnpelp0m
Watching Spacetime would have helped me so much in high school. Which is why I will go to my old high school and tell several physics teachers about this series. It'll help clear up so much about the non mathematical part about relativity.
this is a pretty ambitious endeavor for this series. i'm still finding myself going back and rewatching all the episodes prior when i new one comes out.
I am so determined to understand this but I already realize I'm gonna have to rewatch this at least 3 or 4 more times to get a firm grasp of it. The first video in this series probably took me 5 rewatches over the course of 18 months before it fully sunk in but it's so worth it.
Taking notes may also be beneficial.
Thank you for the great channel and making complicated topics graspable for non-experts and giving them a starting point if they want to learn more. On a totally unrelated topic: At 6:28 - did you choose a Trabant 601 as representation of a car? :-)
Either this shit is ramping up faster and faster.. or i'm getting dumber and dumber >.>
Yes, it's too fast to follow. Looks more like MTV or a commercial.
I'd have to watch this video and close my eyes from time to time so I can better imagine the concepts in my head. Love the video, huge fan (y)
when you try to explain something you don't have to rush keep the video simple and smooth bcoz there are many people like me who have problems in perceiving things
Oh look. The best channel on youtube has released another video. And just from the title alone i can tell its gonna be great :)
I don't care for the other PBS channels, but the content on THIS particular channel is solid! Subscribed!
Wow. I'm wondering if we can get these spacetime videos on a separate playlist. This is one of those things that will need to be watched several times before finally clicking.
Thanks Gabe, I gained a brief flicker of insight from this. Will rewatch.
Wow, the earlier videos on this channel were deep! I got lost in the last few minutes.
edit: I did some research and I understand now. Great video. Love everything on this channel!
Holy hell this certainly engenders a newfound level of respect for all physicist of the past and of present.
I really appreciate the deep dive. I feel like most of the math/physics/science channels out there just graze the surface. Good Job.
As a sophomore engineer I was pompously thinking how difficult could this be. As I've been through the worst of math and physics.. but nope this stuff is too complicated to wrap my head around haha
Funny you say that. Students can do things like how to derive the Lorentz transformation and use it to get E=mc^2 and all that good stuff and still not have the slightest intuition about what is really going on, because they use math they learned as a sort of scaffolding to not have to really understand anything. This was a major hurdle for me. Anyone can follow an algorithm to derive a formula, but understanding what it really means is a lot more difficult.
Like take a wave equation., like the heat equation (one spatial dimension):
∂u/∂t = k ∂^2u/∂x^2
Okay, I can follow the steps and use separation of variables to turn it into an ordinary differential equation, then I can solve it using the previous "cook book" methods I learned in differential equations 1. But wtf does that heat equation really mean? What does the constant mean? When I solve it, I get some sort of summation (or integral) of e raised to the imaginary number, but what does THAT mean? After my head explodes, I can go graph these type of equations and see what they do, but then translating that back through the heat equation and into the actual physical reality the math is describing? It's hard to do.
And with this stuff, the actual physical reality the math is describing is completely, utterly NOT intuitive, because we simply live in a world where the classical approximation that relativity essentially replaced is "good enough."
So, tl/dr, don't worry. This relativity stuff is inherently difficult because our brains have been trained for our entire lives to think in a way that is inconsistent with it, and that is even without looking at the difficult math (and it gets so much harder moving into curved spacetime).
@@EliteTeamKiller2.0 That's why you need to interleave the geometric analysis with the algebraic analysis. The heat equation is just a "spreading out function" that evens out a curve gradually into a flat line. Equations like e^iwt can be interpreted as a point that rotates around the origin in a circle through time. If you want to look at a wonderful way to do QM without doing any calculus or even algebra, look at Feynman's QED: The Strange Theory of Light and Matter. But yes, first you have to unlearn everything you thought you knew about the universe.
wish u wouldn't have left the show gage, I've always wanted to fly and be a person that explores the universe and not just the planet, your videos are wonderful and informational, while i understand science is a best either 100% accurate or a nice shot in the dark, that it is important to be focused on continual advancing our understanding and hopefully agility to travel to other parts of the universe. thank u for the great vids and i wish u the best.
5:15 Well that diagram just got 20% cooler.
Okay, I'm gonna go get my noose, I shouldn't have made an mlp joke.
keep making these vids! The world (and me) need them!
A bit hard to undestand but on the second view it starts to make sense :P. Please dont dumb the videos down, youtube is full with easy to swallow videos. Thanks a lot, awesome work
Props on the very usability-aware correction on the diagram!
The end part describing the vectors always gets fuzzy, but it's getting better with research. That Greek letter, tau is used for proper time, which is the monkey's time measured along it's own world line.
At 6:35 when you plotted the world line of the moving car (from your prospective) shouldn't it have been above the the 45 degree photon line (I.e. Inside your lightcone) otherwise your wouldn't 've been able to "see/observe" it?
Love the series, keep up the good work...
Ahmed El-Hawary You can see events outside your light cone just fine. Just with a delay. For instance, if right now, a solar flare erupts, you'll find out about it 8 minutes from now. So it couldn't have influenced you casually (it was outside your light cone), but once its light reaches your eyes, you become aware of it and can reconstruct the historical fact that, according to your clocks, it occurred 8 minutes earlier, while you were reading this comment. The only events that you can't become aware of, even after the fact, are those that occur behind an event horizon (this will be discussed in a future episode).
Now, part of the car's world line *could have been* inside my lightcone, sure -- I could have translated the whole curve vertically upward. That would simply mean that there some events at which the car was present that I could have influenced. I just opted not to draw it that way -- in other words, the car is pretty far away from me spatially at its point of closest approach.
This was clear to me because I already understand special relativity and knew a bit about Minkowski space, so I didn't have an distracting questions like "why."
The sound at 1:45 broke me, I was searching for about an hour for what game I heard that sound in a lot. Loaded up runescape, watched so many clips of games.... It was Borderlands!
Love how fun really scientific topics like this are getting lots of views now! Totally awesome!
I'm watching some older videos on the channel, and have come to the conclusion that it's seriously improved in terms of presenting complicated material to laymen.
These old videos I have to playback at 75% speed for them to be even tolerable, but the metaphors and visual aids aren't as well chosen as well.
Everything makes sense till 4-Velocity. That justification that there wasn't time for would help a lot!
best among the lot...Such a lucid explanation....Even a medical graduate like me understood the topic quite perfectly...
Wow that will take one or two rewatches to fully get a hand on... thanks for the thinking material^^
yeah, I need to start this series over again before I move on. One more go would help it soak in
I think I'll have to re-watch all the videos a couple times to really absorb it. I think I get it..sort of. But not quite. It's super interesting though.
Man, I love your channel but I can't keep up with the speed you explain things. It would be great if you could increase the length of each episode a little and explained things a little bit slower.
It's been a long time since I studied physics on the University and it's one of my favorite subjects.
Keep up the good work.
Juliano Fernandes Schroeder Me, too, but we're under constraints (budget, time, etc etc)
Thanks for the awesome videos!
I wish that I would have seen this video earlier. Great job in helping me understand physics!
This video kicked my ass, maybe if i watch it 7 more times....
i love the way he feeds it out to us. you have no time to run off on tangents and lose connection with his explanations.
but the real question is" where is the Steins;Gate worldline??!!
This must be the will of Steins Gate
El Psy Kongroo
EL PSY KONGROO
On a real note tho: I'd be careful with reusing the term worldline between Steins;Gate and these videos. They mean different things based on how this guy has defined it.
Steins;Gate Worldlines = basically time lines that they hop between (essentially their own universes)
Space Time Worldlines = different perspectives of causal events within the same universe
Basically the coordinating axies represent metastable "solid" multi-phase resonance and fluid expansion-contraction, exponential transitions of temperature and perspective => distance timing, and the provided labels are for "world-view" perceptions of math-physics(?).
Reaction "velocity" in Chemistry is more appropriate word use for QM.
In high school I used to hate physics. Now I'm 30 and you guys made me love it.
Marse Petrarse Best compliment ever. Thank you!
Really a huge fan of the level of complexity of topics you're getting into. Its rare for a well made education youtube channel since most are aimed at beginners. Keep up the good work! Loving this series :)
Are you going to do an episode on the holographic principle in the future? I'd love to see that. You have a great way of explaining things, you don't assume I'm an idiot and don't overly simplify things like many other videos (and TV programs) do. So serious thanks for having the patience to explain all of this to us!
New subscriber, you guys at PBS Digital Studios are some of my favorite channels to follow!! Keep up the amazing work!
vormov Maybe. We have to lay a lot of groundwork first, else such an episode would devolve into just stating buzzwords without deeper understanding, which I prefer to avoid.
PBS Space Time Some questions are popping right up in my mind while I'm watching. Firstly, which is true between "the straight-or-non-straight property of a spacetime line maintains when the reference frame changes" and "the inertial-or-non-inertial property of a reference frame depends on the (other) reference frame"? (Just to be clear with the first question). Secondly, is the new definition of inertial frame equivalent to "reference frame with constant 3D-space velocity"? If not, why?
TheN GroupTwo To answer your first question: the first statement is true (with a caveat I'll get to below),but the second is not. Let me elaborate... In special relativity, inertial frames correspond to the frames of observers whose world lines are geodesics. In an inertial frame, such a world line looks straight. But in a non-inertial frame (and I didn't draw any spacetime diagrams from a non-inertial perspective, for good reasons that will be clearer next week), such a line would not look straight. But it would still be a geodesic, since being or not being a geodesic is an intrinisic property that can be verified independent of any frame of reference. That's why the second statement in your first overall question is false -- inertial-ness is equivalent to geodesic-ness, and that property is inherent to curves in spacetime, even if we never throw down a frame of reference at all.
Answer to your second question: yes, at least as measured with inertial frames of reference. Think about it -- in the spacetime diagram corresponding to how things look from inertial frame A, inertial frame B has to be a geodesic, i.e. straight. But straight on a spacetime diagram also has a kinematic meaning -- equal x-axis tick marks (and y and z) in equal ticks of frame A's clock. So yes, inertial observers will be seen *by other inertial observers* to have constant spatial velocity. Of course, a non-inertial observer would see an inertial observer accelerate, but all the diagrams we true show the point of view of some inertial observer.
Excellent questions.
Your recent videos about general relativity have been excellent, thanks. I've been trying to wrap my head around what exactly spacetime could be, and it seems to behave like a fluid. Is the structure of spacetime like that of a zero viscosity fluid, and if so, then could the "liquid spacetime" be made of "molecules" like water?
Jayson Cody That's actually a pretty good way of thinking about it! Now spacetime isn't made of molecules, it's literally just space or emptiness with time, but that's a good way to visualize it. In fact, in cosmology when they model the universe, they use the assumption that the universe is similar to a perfect fluid. Good catch!
That hearts and blows my mind at the same time!
When we do this frame of reference anchoring, do we have to discard knowing that we're moving? On what basis do we say "from his perspective he's stationary"? When I'm moving, it doesn't seem to me that I'm stationary.
I know this is pretty essential. You could say I'm assuming this based on my perceptual information which has a good success rate in daily life, but considering we take this to reflect the world's mechanics anyway, that perception is linked to these frames of reference, it seems we're assuming for physics that we can accurately relate ourselves to the world. I've read Einstein's book, and I'm following regardless, but I found this way of talking about frames of reference a bit funny or ad hoc.
This amount of complexity makes my tummy tickle with excitement (and apparently also makes me talk like a 5-year-old)
Got into this in other videos. Just one problem, the universe is expanding. While light's speed can be constant in space, it has to be going faster in the Space-Time Continuum. On top of that, the CBM gives both a coordinate time and location for every event, even though it is viewed differently by every observer. Something has to give, my short hypothesis is that the angular momentum of the speed of light is always conserved. Yes, every particle's field is still traveling at the speed of light, this has been measured countless time with electromagnetism. Along with the twin paradox, there seems to be a major crisis with relativity.
How does one absolutely rule one of the conflicting ideas out? As it just so happens the CMB gives a very clear direction that the earth is traveling through both the galaxy and the universe. Simply send two atomic clocks at the exact same speed relative to earth in opposite directions of the path of the earth through the universe and both clocks should give exactly the same time dilation relative to the universe, if not Simultaneity rules… we will see.
I am f*cking bliiiind.
I had to watch it three times to understand it
Yarib Suárez Yep, me too.
Enlightenment I'm still picking pieces of my brain off the wall....
***** thank God I'm not the only one!
An object moving from left to right will apear contracted when it is on your left and expanded when on your right. This is because it is moving towards you on your left and moving away from you on your right.
So, world-lines in Flat Spacetime all have the same 4-Velocity of -c^2?
This lecture actually reminds me a lot of the premise of the Prophets in Deep Space Nine. They have no concept of past/present/future and explain to Captain Sisko that they see him as simply existing at all points of his existence at the same time. This lesson almost explains to me how that can actually work. He's just a line on a graph to them.
(∆x/∆τ)^2-(c∆t/∆τ)^2=-c^2
Is it possible to use this equation to calculate the speed of *time* in meters per second relative to your internal reference?For an object moving at c:
(c/∆τ)^2=(c∆t/∆τ)^2-c^2
(1/∆τ)^2=(∆t/∆τ)^2-1
1=∆t^2-∆τ^2
I don’t actually understand what you said but it seems like a legitimate question which is why I liked it
Donnie Darko is what came to mind while watching this video . The book he reads "the philosophy of time travel" deals with tangent vectors and world lines. its what the liquid streams that erupt from the characters chests are meant to represent
yeah!!!!!
Glad someone else agrees! im not crazy!
+Brian Lung and in Stains Gate.
Repeated watching really does help.
Whew! A video I understand (for the most part). I am still trapped on the event horizon, though. These darn Black Holes are making my brain dizzy. I can't stop thinking about them, because I don't quite get it. I though I did, until I watched the other video. Almost like an itch in my brain I can't quite scratch. I get what they are, but not what is really happening as far as events. Also, where does the hole lead? Is there an outside to the universe through here? Is it a hole or just extreme curvature?
This is not a bad introduction, tangent vectors are 4-velocity-vectors (considering the position and time of another reference frame relative to the time of one owns time relative to the time of the other reference frame) and the space time interval length is -c^2 in flat space time.
Inertial observers are geodesic world lines or constant speed straight lines and non inertial observers like accelerating observers follow non geodesic or constant speed non-straight line because parallel vectors doesn't remain tangent vectors.
And inertial observers moving with constant speed relative to other inertial observers on curved space time also correspond to non-straight lines due to the gravity- acceleration equivalence principle.
One can always use Minkowski diagrams etc. to illustrate effects and events in relation towards each other with geometry.
nadjim73 Yep. And that's where we're going in Part 3.
Really awesome videos guys! :D I had a suggestion too.. At first I didn't understand why the ant on the basket ball could measure angles left and right but not up and down, but I wasn't thinking of the ant as being in a literally 2D universe. Video games are part of your channel so why not use Mario's 2D universe? (Maybe trying to figure out if hes actually on a small part of a basket ball or a plane) as a future example instead of an ant?
Neven Makowiecki The problem is that most people think of Mario as being 3D and just _displayed_ in 2D. Know what I mean? People have way more built-in assumptions about a video game that we would need to overcome than about ants on basketballs.
How come we don't see much of this guy? awesome video love PBS-ST