How big is the ENTIRE UNIVERSE?
HTML-код
- Опубликовано: 5 июн 2024
- Visit brilliant.org/DrBecky/ to get started learning STEM for free, and the first 200 people will get 20% off their annual premium subscription.
Curtis-Lake et al. (2022; GS-z13 discovery in JWST data, no paywall) - arxiv.org/pdf/2212.04568.pdf
My video explaining the discovery of GS-z13 - • JWST confirms MOST DIS...
00:00 - Introduction
00:48 - 28 billion light years (the Observable Universe)
02:29 - 93 billion light years - correcting for expansion
03:48 - An example with JWST galaxy GS-z13
05:25 - Comoving distance vs lookback distance
05:53 - We can't say the Universe is infinite
07:23 - Brilliant
08:46 - Bloopers
Correction: 04:20 I wasn't very careful with my words or graphics here. For those familiar, I made the decision to skip over the idea of "proper distance" for simplicity in this video. This is the distance between us and the object (in this case GS-z13) when the light was emitted, which at the time was actually 2.34 billion light years. The Universe's expansion means that the light travel time is then the further "lookback distance" of 13.48 billion light years.
---
📚 My new book, "A Brief History of Black Holes", out NOW in hardback, e-book and audiobook (which I narrated myself!): hyperurl.co/DrBecky
---
📚 "The Year In Space" celebrating all things space in 2022 from me and the rest of the Supermassive Podcast team (use code XMAS22 for 20% off): store.headline.co.uk/products...
---
👕 My new merch, including JWST designs, are available here (with worldwide shipping!): dr-becky.teemill.com/
---
🎧 Royal Astronomical Society Podcast that I co-host: podfollow.com/supermassive
---
🔔 Don't forget to subscribe and click the little bell icon to be notified when I post a new video!
---
👩🏽💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don't know. If you've ever wondered about something in space and couldn't find an answer online - you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.
drbecky.uk.com
rebeccasmethurst.co.uk 
Наука
At 4:20 I wasn't very careful with my words or graphics. For those familiar, I made the decision to skip over the idea of "proper distance" for simplicity in this video. This is the distance between us and the object (in this case GS-z13) when the light was emitted, which at the time was actually 2.34 billion light years. The universe's expansion means that the light travel time is then the longer "lookback distance" of 13.48 billion light years.
Thanks! I was wondering if that would have a significant effect. And it certainly is more significant than I was expecting
Wikipedia only mentions JADES-GS-z13-0 having a present proper distance of 33.6 billion light years and a light-travel distance of 13.6 billion light years. The "proper distance" you mentioned (2.34 billion light years) is also very interesting, but is there a way to look this up for any given galaxy? Thanks!
So, where did all of this space come from that everything is stuffed into?
This is my personal understanding of it, so correct me if I'm wrong: I like to think in 4 dimensions or space time when it comes to those kind of distances. The further you look, the earlier, but also the closer things were when the light (or gravity wave etc) left. If we could observe the big bang, it would be the furthest thing we could observe now, that was also the closest thing when what we observe started on its journey towards us (not light, since that didn't exist yet). Basically the "edge" of the observable universe is a 0 dimenional point at the beginning of time that we are looking at when we look at any direction. And from there on the size of the observable universe is limited by the time from the big bang up to the point light started traveling towards us from any point in space. Anything that has happened since the light left that point in space has no influence on events here and can not be observed. In that respect it is completely irrelevant if it exists or not, sort of an event horizon of the observable universe in space time. Any flaws in my assumptions? (mind that I'm no astronomer or physicist)
420 makes a lot of people a bit sloppy, it's okay Becky!
" _Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space_ " -Douglas Adams
DMT contemplation about the limits of space and time do some real mind-boggling
Now I want some fairy cake.
Not as big as the Great White Handkerchief!
But if space isn’t sentient, how can it be aware of peanuts?
I'm so glad that you posted that - I lost my copy of HHGtTG....
Dr Becky, I think all of your regulars would agree…. We’re here for your hugely understandable scientific breakdown of the “universe” but equally important are the bloopers! ❤😂
I confess to skipping the bloopers entirely. I'm a cold insensitive bastard like that.
Or a chance of hearing her singing :)
Yep
Some of the are just side splitting funny
We want LIVE bloopers!!
Yes, I mean we need Dr Becky live streams!!!
As a retired engineer, whose interest in physics was reignited when my son started studying theoretical physics, have to say your channel is one of the best at explaining these concepts. You have a real gift for this and deserve even more subscribers. Even my wife loves hearing you speak, even when she doesn’t understand 😁 Oh yes, and keep on adding the bloopers!
I would like to subscribe to Dr. Becky's channel but due to hearing problems on my part I find that her speech is hard for me to understand.
@@murp61 Try turning on the closed captions button, CC, in the upper right of the screen.
@@murp61 what can we do to help?
I don’t use the closed captions, so I’m not sure if that’s automatically generated for all videos.
I think there are some features (apps) that will take the speech and convert it to text.
Leave a note as to how we might be able to help…
Regards.
@@ark-astrophotography915 Yeah I'm going to try the closed captioning first and see how that goes, thanks!
What the substance called "space" is made of?
The speed limit of light is to prevent you from reaching the edge "membrane" of the universe. Because it knows you would poke at it until it goes pop. Of course you would poke at it. You know you would.
You know it 🤪
Would so poke it.
Oh, please, if they put an "End of the World Button...Do Not Press" on my desk, I'd press that puppy in ten seconds flat just to see what would happen.
the limit of the speed of light through what medium?
I would poke at it
I've never heard of co-moving distance before but it makes so much sense. Great video, one of my favorites!
What is the substance called "space" made of? They say space stretches but how do they know it is not being created?
There's something so pure and selfless about some scientists in their enthusiasm to share what they know or believe about the universe. I am very grateful to live in a time when I have access to this kind of information.
One reason I love this channel, Becky is so lively and shows true passion for the subject. Most of the other more popular channels on RUclips you can fall asleep to. Becky is genuinely entertaining!
Got the t-shirt, got the sweatshirt, love the show - at 83 I guess this makes me your oldest groupie.
Same hex tee & reflection hoody
And the book of coarse.
If you like something, support it
There was a guy a few posts ago who said he was 84, so you aren't the oldest.
I'm younger, but more decrepit.
The appreciation I feel towards Dr. Becky is indescribable. Thank you for being such a great role model for many, the great educational content and motivating me to pursue my dreams, studying astrophysics! I'm so thankful for this channel. 🖤
OMG. For so long I’ve had these questions about the distance to the most remote objects. Not only did your video explain it clearly, but it felt great to know the questions I was posing to myself were the right ones. I’ve always wondered how the distance to the farthest object could be the way it was if everything was continually moving. You explained that of course, that matters. And I suppose it also matters if we are moving toward that object or away from that object.
We are not moving away from distant galaxies but the distance between us is increasing. That's because the space in between is growing. Our actual movement barely even factors in, it makes a tiny difference.
Also, the speed of light is not about light, it's the speed of causality. That is the maximum speed of cause and effect and only things with no mass can cause an effect at the speed of light... that includes gravity waves.
So, not only can we not see beyond the event horizon of a black hole or the equivalent at the edge of the visible universe but nothing that happens there can affect anything here and visa versa. These places are beyond the reach of cause and effect.
We do know that the universe is a great many times bigger than we can observe and that is because it appears flat. The gravity from the mass in the universe curves spacetime. Measuring that curvature shoould enable us to calculate the size. We've tried and we can't detect the curvature.... it appears flat. That means all we can see is a tiny fraction of the total. How tiny, we have no idea yet.
The number 96, apparently, comes from the belief that there is enough space for some light emitting thing to travel in a direction opposite to the direction of the light we detect. But is it possible that such space exist if the speed of creation of space is not the speed of light or faster?
Thank you, Dr. Becky. This is one of the most straightforward explanations I've run across.
This piece is wonderful and enlightening. I've just discovered your channel recently and enjoy it. Keep it up!
Thank you, Dr. Becky!! Bringing science to RUclips with expertise, sagacity, and humor. 😊
I know I probably say this on all of your videos, but I can listen to you talk for days. Thank you for providing content on you tube. I can not wait for what is in store for us in the future for what this telescope will provide for us. And of course your future news you will eventually provide us. Thank you so much!!
You're great! You filled in so many gaps in my knowledge when it comes to measuring light from the past. I had never heard the correction between WHEN the light left and WHERE that light is located in space currently named as the "comoving distance" until today. Thank you! I love your videos!
This is THE VERY first physics video (and I have seen dozens) that mentions this phrase "lookback size". I never heard that phrase before. THANK you for defining it + naming it, physicists! I've heard "comoving distance" before.
What is the substance called "space" made of?
I don't think humanity will be around long enough to comprehend and understand the universe.
I think it will, or at least our descendants
You need to look at the great filters series on Isaac Arthur. He shows how it’s impossible to make humanity extinct once it’s moved off earth
Great romp through the Universe. Waiting for the next chapter of this.
You're the first person I've ever seen label an ad section. That makes you awesome(as if being s science communicator didn't already) and I will comment, like, and subscribe just for this.
Fantastic video! Every since I was a wee child, I always wondered the size and possible "edge" of our universe. The notion of a possible end from where light originates from used to keep me up at night. Not to mention what could be beyond that but your absolutely right, cannot measure what is not yet observable. Great clip Becky!
I'm staggered that yours is the only comment I can see that mentions the surely related question of - if there is a limit to the size of the universe, if there is an edge - then what?
@@jonnylumberjack6223 If the universe is finite, it probably still doesn't have an edge. A finite universe would have some form of curved topology, so you could travel in one direction and never reach an actual stopping point, but rather eventually wind up back where your started (or at least you theoretically could if the universe wasn't expanding and you could somehow travel faster than the speed of light). We don't observe an overall curvature in spacetime, which could mean that the universe is flat and infinite, or if it is curved then it must be large enough that the spacetime within our sliver of the universe, the observable universe, simply appears to be flat.
Being able to detect a curvature or lack of curvature more accurately is probably the only way we could possibly determine a size estimate for the universe, but even then there could be too many unknowns to be certain. For instance, supposedly there are possible curved topologies for the universe that would still be infinite, so if we observe a curve that doesn't necessarily rule out an infinite universe.
Such a great description of an easily misunderstood topic! Thank you Doc!
The universe is definitely not infinite, I already asked it. I assumed they gave you all my posts. ‘I am not eternal’… there is another one. It also laughed. ahahaha
Love your bloopers. And along those lines, would love to see an episode about astronomical bloopers, basically concepts that turned out to be ridiculously wrong. I think that would be hilarious!
I've always wonder about this thanks for helping me understand how you do the correction factors when determining how far something really is.
Fascinating. I almost understood all that. Given I’m often as thick as a brick, for me, that’s an accomplishment. By the way I thoroughly enjoyed your book A Brief History of Black Holes. I listened to the audio version and like that you took the time to narrate it yourself. Your enthusiasm is felt in every chapter.
I doubt you are often as thick as a brick if you are curious to learn about the world around you.
Think of it this way , a friend who is say 10 feet away throws a ball at you , by the time you’ve caught it they have moved away from you by 20 feet , there now 30 feet away from you , in the same time It took for you to catch the ball .
Touche' on the book.
Petition to make "Univits" a common word to describe universal scale measurements!
Also Thank you Dr Becky for your book, admittedly I'm not much of a reader but I couldn't put your book down! Very informative and easy for an extremely non math person ( like myself) to follow! I hope you decide to publish more books like "A Brief History Of Black Holes" in the future!
That's just "units". All metric units are universal, just not in the way you're thinking of. Light years and parsecs are the only 2 units afaik that are used for intergalactic scales 🧐.
Awesome segue from the expansion of the universe to the expansion of the Christmas waistband. Proof undeniable you are the apex of brilliant astrophysicists.
Love you Dr. Becky! Thanks for the great content!
I always wonder if the time it took for those distant galaxies to travel to the point at which we observe the light from is also taken in consideration.
Dear Dr Becky, this is the clearest explanation that I have heard and you make prefect sense - Thank you :) TIm
agreed. her explaining the lookback distance vs the co-moving distance really helped clear up some things in my mind.
I've been waiting so long for this video. Are the light years calculated for a exponential expansion?
Your Obsession has become infinitely more interesting since the James Webb Pictures. Great timing for you!!!!
The clearest explanation on the subject I’ve ever seen, thank you Dr. Becky!!
One question: why do we assume the expansion, hence the red shifting is uniform in all directions ? Couldn’t some parts of the universe be significantly denser than others hence expand at a different rate than others?
Becky: 5:01
@@DesmondKarani she does not address this at all, the different measured rates she is taking about are assumed isotopic - the same in every direction. It’s an assumption that on the largest scales everything is uniform but the latest info isn’t showing that is necessarily the case. I know of several researchers investigating exactly this topic and the related one of properly zeroing our absolute velocity - if space expansion is NOT uniform then the calculation that zeros out the cosmic background (half the sky is red shifted, the other blue shifted with motion respective of the CMB) is off as well. We should always question the assumptions and fail to show them false.
@@hugegamer5988 everyone knows that the cosmological principle is worth investigating further, especially due to discoveries such as the Great Arc. But, until now, none of these arguments have led to a conclusive evidence against the assumed isotropic universe.
What you're asking has been questioned several times before. There's even the "crisis in cosmology" issue that leads to further confusion. Until we have solid understanding of these issues, we'll have to continue using cosmological principle.
I'm certain you were aware of this if you've done your research 😉.
Yes, but the real answer is that it makes no difference at the scale of humans, which is effectively the only scale that really matters. The fact is the facts are always changing, and they have not really changed much over the last 100 years, so we are probably at 'peak human' right now and over the next 100 years humans will likely start knowing less not more, since as soon as the digital libraries crashes all the knowledge will crash with it.
Dr Becky, thank you for this video! I work in a planetarium and am frequently asked about the size of the Universe and am always doing my best to refine my answer - this video helped :)
What is the substance called "space" made of?
@@reasonerenlightened2456 1 part observation + 1 part speculation + 4 parts bullshit to validate their employment at the university = The answer to your question
Seriously i come for the knowledge, but stay for the Bloopers. Best part of my day. Thank you.
Great job Becky !!!!
Question: If there is a point at which expansion prevents us from seeing the farthest edge, what happens to the light beyond our observable horizon? Are those photons ultimately stuck in place at their maximum observable horizon, never to travel any further? That's how my untrained brain thinks about it...
As far as I know from videos over the years... outside of the visible universe, there is way way more universe we'll never be able to ever see since basically yes, the light will never arrive here due to expansion... so there will be parts of the universe, alot of the universe, we'll never know.
Thankfully the universe we can see is huge, but its still sad theres so much that will remain a mystery, unless we can somehow break physics.
@@NZBigfoot indeed, because space is not limited by the speed of light...
@@benegesserit9838 which almost begs the question: is space even a thing? does space in and of itself even exist without the context of matter/energy?
What boggles my mind more than the universe being infinitely large is the possibility it could have still been infinitely large (and dense!) at the Big Bang, and then rapidly expanded but remained infinitely large.
CCC hints at what you suggest. We are taught everything expanded from an single point according to CCC what made the Big Bang “special” was that everything was smooth and uniform with low entropy and not subject to the limits of size. So the initial surface could have been very large by our measurements.
big bangs are constantly happening
👍👍🚀🚀Good video. Very fun outtakes. Have your new book on order-looking forward to it!
amazingly explained! thanks
This is the kind of thing I used to think about when I was a student and relaxing while smoking something "funny" on Salisbury Plain. The other question that spaced me out was "if you drive a car at the speed of light and you looked in the rear view mirror......what would you see ?" Thanks Dr Becky .... do YOU have a belief as to how big the universe is ?
No material object can travel at the speed of light, so the question is invalid. If you travelled at just under the speed of light and looked back, whatever was back there would be so far redshifted that you couldn't see it.
@@michaelsommers2356 the question is not invalid just because you think it is. You gate keeping troglodyte
@@michaelsommers2356 Yeah I like "what if" hypotheticals 🙂
@@uglybob7505 The hypothesis is invalid; you are not talking about this universe.
@@michaelsommers2356 I know mate, I was just letting my imagination run wild. If we didn't do that then look at all the awesome science fiction we would miss out on. Star Trek wouldn't be fun if we employed the rules of the universe to the letter 😆
It is one Mark Unit across. (A Mark unit is defined as the distance across the entire universe) , and I am sorry for my circular reasoning. Good perspective on the universe is offered by Dr. Becky. :)
I beg to differ. It's a Dragonlength. Are you going to argue with a dragon?
I like your reasoning, but only because I like your reasoning. Also think "Mark Unit" has a nice ring to it
What if the universe isn't spherical in shape but an oblate spheroid, like the earth? Does that change the nature of your reasoning to be oblately spherical rather than circular?
@@clickrick Livin La Vida Oblate
@Rick Martin thinking, I assume is inflating at all directions equally. Since there is no data to check against, it stands.
As a big computer nerd who's currently studying physics, I have the word Unix in my head a lot as well as universe and units. And Star Trek Voyager put unimatrix in my head as well. :)
Thanks Dr Becky for your very interesting lectures. Question - how are the great pressures found at the center stars and planets generated since gravity is zero at this point. Is there a tori of activity involved?
You're correct that we can't say that the universe is infinite, but it is useful to point out that the geometry of the universe indicates with a very high probability that it's infinite.
We only have one data point, which means we can't make any assessments about probabilities. The universe appears flat to us, but for all we know it's just so big that it seems flat, but actually isn't. On top of this, even if it is flat, that in no way guarantees it's infinite. We can't say that the universe is or is not infinite, and we also can't make any judgements about the likelihood that it is or isn't. Seeing as it's unfalsifiable either way, it's not even worth discussing from a scientific point of view.
Unfortunately it doesn't. There are topologies where even if the universe is flat out can be finite. What is more from our perspective we cannot infer this topology so we could never solve this conundrum.
@@Gremunky Hmm... Good point. We cannot see to infinity. I still believe our universe is infinite. It doesn't make sense that at some point it would just end. Our universe is expanding but what is it expanding into? The fact that it's expanding implies an end but how is that possible? We must be misinterpreting some data about it.
@@jerrylee8261 we may not be misinterpreting any data, it may just be that our current understanding of physics is so largely incomplete that the actual state of the universe is beyond our comprehension. It may even be that we cannot come to understand the universe through theoretical or experimental means. We just can't know, at least for now. I personally also believe the universe is infinite in all directions in both space and time; however, it is just that, a belief, no more valid or proveable than a belief in God or bigfoot
@@jerrylee8261 "the edge of the universe" could just be where there's no more matter, and the universe is expanding to occupy that free real estate. or we exist in a 4d object that in 3d loops around on itself in all directions (so if you fly far enough in 1 direction you'll return back to the same spot), and the expansion is like when you blow a balloon larger and larger (and again, there's no matter outside of our bubble). Or there could be some unknown physics that happens "on the edge", that we just don't know about due to our limited viewpoint. And any of them can make sense, 'cos you can't disprove them due to complete lack of data.
It's 42 you silly
IS THAT IN UNIVITS?
Awesome. I knew this intuitively but now I have a word for it. Comoving size!
We definitely need Dr. Becky’s face on a shirt with the words, “We cahhn’t know.”
Wouldn't it be funny if the observable universe would expand in our lifetimes to exactly the size we need to see the credits? I am personally curious about who wrote the storybook.
Wouldn't it be funnier if it read, "A Walt Disney Production"?
Sign at the end of the universe, by Duane Ackerson
dn puǝ sıɥʇ
Why do you think the credits would be in a script you could read, or in a language you could understand?
@@michaelsommers2356 because it would juxtapose the incomprehensible complexity and vastness of the Universe and our small, petty human life just perfectly.
@@nilsp9426 Perhaps. If we lived inside a science fiction radio show.
The idea of an infinite universe is pretty interesting. Infinite would mean repetitive, which means if something happens once, it happens an infinite amount of times.
I realized an issue with this and why it prevents any “uncapped” FTL loopholes. Basically, if the universe is infinite, then anything can happen and will happen an infinite amount of times. So if someone creates a working FTL loophole (be it “warp drives” or something else we didn’t think of) and it is completely uncapped, and they decide to come here, then infinite people do the same thing and there would be infinite stuff everywhere because again, everything happens infinitely. Therefore if we figure out a way to travel at an uncapped speed then the universe cannot be infinite.
Conversely and far more likely, if the universe is infinite, then there must be a limit to every form of traversablilty.
Also please note that I am well aware of the whole “nothing travels faster than light” thing. I am simply arguing that if there are workarounds in any conceivable way, then either the universe is not infinite or there is a limit to that workaround too.
"infinite" could also just mean that you can always iterate another iteration
I don't think it's that easy. Alone because of dividing infinity by infinity, which can result in infinity, a finite number or 0.
If there would be an infinite universe and in every 10th galaxy a race that finds a way to travel faster than light, and they visit only one galaxy at a time, 80% of the galaxy wouldn't have visitors at any given time. If they visit places at random, despite infinite visitations there would probably be even galaxies that are never visited.
@@nightmareTomek I see where you’re coming from but my point is that in an infinite sequence, anything that can occur will occur infinitely. If we assume that the universe is, in fact, infinite, and that there is an uncapped FTL loophole, then distance, speed, and time are all variables which can be changed. Since everything is not equidistant, it would require travel over a greater distance to get from point A to B, but speed and time are also variables which can be changed, and in this case, the variables would be just right to correct for the difference of distances an infinite amount of times.
I just realized that my variable example may not have made much sense. Say you have to add 3 numbers to 10 and you want the last one to be a 5. You are also required to have one of the numbers be a 4. Therefore, one of your numbers also has to be a 1. Now, someone else also has to add three numbers to 10. This person also wants the last number to be a 5. However, he is required to have a 3 as one of his numbers, meaning his second number has to be a 2. You and the other person roll dice until you get the numbers you need (either 1 or 2)
If you and the other person roll the dice an infinite amount of times, then eventually you will both land on the numbers that you need.
@@jedislayer0719 Ooookay. I'm not that sure where you're coming from. What's your point exactly?
Anyway if the universe is infinite and FTL were possible doesn't mean we will be the ones that find it, nor that we will encounter any aliens who find, nor that there's time travel either.. Right?
@@nightmareTomek I’m just saying that if the universe is infinite and a form of FTL exists with uncapped capabilities (range, speed, or both depending on the type) then infinite “travelers” would be at any given point in the universe as soon as anyone could use FTL travel. Obviously this couldn’t happen so either the universe isn’t infinite or (more likely) it is and there is a limit to any method of traversing space. This whole rant was meant to be purely hypothetical
That almost made my head hurt, but I think I understand better now even though I'm not a scientist. Thanks Dr. Becky
i just ordered your book,cant wait to start reading it! :)
I had repetitive nightmares when I was young, the scary thing was a zoom effect alternating between tiny and astronomical scale. I often wonder what that was about and think sometimes that perhaps our whole universe is just some stuff in a petri dish.
Excellent explanation!
I have complete faith that Dr. Becky will have this all figured out by April.
You actually make this stuff make since..thanks
Y'all always be thankful for what you got y'all feel me and Tham feeling's.
Thank you for your honesty
Even knowing all the information in this video beforehand. I was still interesting to listening to. Your videos are very fun and interesting.
Thank you, Dr. Becky, for explaining how the universe can be 93 billion light years across when we can only see 28 billion light years across. I've seen other scientists on RUclips explain it but I was still confused. Your simple, direct explanation really clarified it for me.
I love your channel and have recommended in to my friends on Facebook.
I just found this channel from the Lateral Podcast Clips channel by Tom Scott. Loving this content!!
Welcome!
Excellent presentation - many thanks!! 👏⭐🚀
So....its pretty big then? Another great video. Thanks Doc.
Fabulous video, thank you Dr Becky. The observable universe is though 93 billion light years across for the reason you gave for point 2 (as illustrated by the galaxy you mentioned which is now 33.3 billion light years away and is observable).
@Dr. Becky, any chance of doing a video of why potentially GS-z13 is as mature as we're seeing it although this breaks our understanding of how early galaxy's formed?
About as good a summary as I've ever encountered. Surely there must be intelligent beings trying to wrap their minds around all this 93 billion light years from here. I find this somehow comforting.
I found this to be a very clear treatment of the subject, better than Don Lincoln's presentation of a couple of years ago. And it illustrates the pedagogical value of terminology: defining a "lookback" distance and a "co-moving" distance doesn't just point to two distinct phenomena so that we can notice in the moment why they're different, the terms give us a handle on those phenomena that we can refer back to. They help us to anchor important ideas so that we can talk about them in meaningful shorthand, so that we can break the total picture down into manageable pieces.
But I think that I have to take issue, at least hypothetically, with the part of the video that addresses the question of whether the universe is infinite. The first issue is a lack of distinction between the size of the universe (in substance) and the size of spacetime (a metric) which leads to a real confusion about what is meant by the edge of the universe. This leads to a second issue of having an insufficient basis for discussing what is meant by the question of whether the "universe" (really, spacetime) is mathematically flat or closed or open.
A third issue seems to be a case of circular reasoning or begging the question, again arising from this ambiguity. It shows up in the video at around 6:15. You've tried to argue that it makes no sense to talk about something lying beyond the horizon of an expanding universe. But this needs clarification. If the universe has a finite age and expands at a finite rate from a finite-sized initial state, then it still has a finite size at any given point in time. If we take this universe to be distinct from spacetime, then what constrains spacetime to be likewise finite? It isn't a given, it's the very question that we're trying to answer.
Consider the universe at the moment it has expanded to be, say, N light years in radius. The center of that universe can't see anything more distant than N ly, fine. But in another year it will be able to see objects at N+1 light years. What's to stop a visible event from taking place during this intervening year, said event situated just beyond the radius N in (what we might be pleased to call) empty space? Nowhere has it been established that the universe is required to be all that there is, nor that spacetime is finite, so we can't just rule out this scenario on the basis of events constrained to take place within the universe in question.
This is a deliberately simple-minded objection, but I don't see that it can be answered on the basis of what's been given here. What's the missing piece, and how is it justified?
I was half expecting Dr. Becky to introduce "Wiibly-wobbly-timey-wimey" factors in the calculation of the size of the universe. Love how she broke it down for us plebes, though. Thanks, Doc!
Dr we love the Bloopers😎
I often wish I was a lot smarter so I could understand more as it is incredibly interesting and fun to think and talk about
Thanks a lot for sharing your knowledge and in a cool way, always appreciated. .
if we also considered a "return trip" distance, then there would be a case for saying "infinite."
So, is Space itself expanding as described in some other videos I have seen, or is it the way you beautifully describe it, neat, plain, and simple? I am a physicist myself, and I think now I will be sleeping a little better! Thank you!
Dr Becky... you have a major role in my daughter's emerging interest in the sciences. Your channel is hugely entertaining and educating, but for at least a few of us, it's a public service!
What is the substance called "space" made of?
@@reasonerenlightened2456 the same stuff as what's between trump's ears.
I love this stuff.🌠
Very good info
This is great!
We love you Dr Becky
Good content, 2 extra points:
1: the equivalence principle, and the idea that we are not in a special location in the universe, implies that an observer on the edge of our observable universe would see more of the same beyond what we can see. This is an important point because a lot of lay people think that there is something mysterious and unknowable beyond the observable horizon.
2: the accelerating expansion of the universe is shrinking the amount of stuff we can see. The expansion of space means that sufficiently distant objects are moving away from us faster than the speed of light, and the light from them can never reach us. In a few billion years from now only the local cluster will be visible, and the CMB will be so reshifted that it is not measurable.
Your first point implies that the universe is far larger than we'd have from 13.8 billion years of expansion, but that is really dependent upon the geometry of space-time. An observer positioned at the horizon from my vantage point sees more of Earth's surface - not because the Earth is infinite, but because it is curved. With enough observers, eventually you'd have of for whom I was the observer on the horizon.
Also, I'd argue that despite the equivalence principle, we ARE at a special location. We are at the center of our observable universe. An observer at Proxima Centauri would have a slightly different perspective. We assume it's the same - that's the point of the equivalence principle, but we can't be 100% certain.
By the time the rest of the observable universe is beyond our observation horizon, it's probable that our local galaxy group will have merged into one. At that point, the old assumption that our galaxy was the whole universe would be a reasonable conclusion. If that future society did not have (or did not trust) the records from our era, I wouldn't be at all surprised if they came up with a far lower estimate of the universe's age as well...
Thanks Doc.
Another very clear explanation from Dr. Becky. We might call her the Empress of Explanation, the Grand Duchess of the Graspable, the Tsarina of Transpicuity. But she'd probably call that going overboard.
You're the only scientist I can understand. Everyone else speaks in riddles. Kudos to you, Dr. Becky.
"We can't say that the universe is infinite" - We also can't say that the universe is not infinite. We simply do not know.
Hi Dr. Becky.. what would happen if they did with JWST like they did with Hubble?? One spot in space for 48 hours?? (48 hours it was i think).. i could listen to your content all day.. love your content..
I just love stuff like this...
It’s from about here to over there, and frankly its more than we need.
Hello Dr.Bekcy alcance a leer con los subtítulos, que bien explicado, entendí muy bien, cuando traducirá al español? yo creo que tendría muchos seguidores acá en México. Tanks y bay bay 🙂🙂🙂
Maybe there is a "primordial" red dwarf somewhere out there shining since matter was possible in the universe and able to still shine when the universe is so huge and stretched that no photon it sends will ever reach another object of noticable size. Kind of romantic.
i love your explanation.
If it is ok, we can exchange emails.
I love the bloopers!!!🤟🤟🤪🤪
That's ahead of time
If JWST can see about 300 million years from the Big Bang will a future telescope have the capabilities to look directly at the Big Bang.
Just brilliant thank you, I always wanted to understand this. One question, when looking at proper distance , does it assume a constant expansion velocity of the universe or does it factor in the acceleration of the universe’s expansion? What rate do we use for that? Thank you
Dr. Becky mentions it in the crisis video, but figuring out the expansion ratio is an issue because we're getting different answers based on how far away the object were observing is
I have spent ages shouting at the screen, that was then what is now?? thank you for the explanation. cheers Neil
The best part is the last blooper. I had in my had when I heard it in the video, feeling silly :D
Wow you told the truth 👏 my belief is the expansion and elapsed time we can never see it however once we make a ftl we will start to observe more and more
I am not an astrophysicist, just a country boy in Texas. But I wonder about the universe and have found your videos enjoyable and sometimes I even learn something. One thought that stays in my head is 'does light ever end' and how light bends around objects. With the universe having so many "objects" in the path of light it must get bent many times before it reaches us earthlings. In the calculations you mentioned, does the bending of light play a considered factor? If it is bent then it is no longer a straight line and, therefore, must travel at a longer distance. I have so many questions about the universe and so do you, but you have more answers than I. Thanks for the videos and the bloopers.
Three questions:
1. Does that work for objects approaching us (M31)?
2. Is it realistic to think the 'big bang' conveniently took place 13.8 billion light years from us?
3. how do you measure the rate of expansion from a moving object?
The mark of a true scientist... the ability to say "we don't know" when that is the truth of the matter. It amazes me how many science channels and credentialed scientists these days talk about unproven theories and hypotheses as if they were known facts.
So the answer for now is, it's complicated we still have much work to do? As always, thank you for sharing your knowledge. 😃
Whats even more interesting is what exists outside of the non-infinite Universe. Is it just space waiting to be filled or could there be many other universes simultaneously expanding potentially having to interact at some point.