The Horizon Problem | The Universe's biggest UNSOLVED mystery
Вставка
- Опубліковано 30 тра 2024
- If you’re struggling, consider therapy with BetterHelp #ad. Click betterhelp.com/drbecky for a 10% discount on your first month of therapy with a credentialed professional specific to your needs. | Ever wondered how the Universe looks roughly the same in all directions? Because, technically, it shouldn't. It doesn't make sense. So does that mean we're missing something in our physics? Something like inflation? Or is the universe cyclical, going through Big Bangs and Big Crunches? Or does the speed of light vary with time?
00:00 - Introduction
03:51 - What actually is the cosmic microwave background?
05:15 - What is the cosmic horizon?
06:21 - What is the "horizon problem"?
08:27 - Inflation - a solution to the horizon problem?
10:12 - Cyclical Universe - a solution to the horizon problem?
11:12 - Varying the speed of light - a solution to the horizon problem?
12:03 - But what about the "crisis is comoslogy"? Is it something else?
12:34 - Bloopers
Video filmed on a Sony ⍺7 IV
---
📚 My new book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): lnk.to/DrBecky
---
👕 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 та технологія
That joke about repeating cycles at 10:43 got me good
did she change anything in the matrix?
I think editing Becky was having a laugh at recording Becky. ❤
I was about to message Editing Dr. Becky (or is it Dr. Editing Becky?) about how she missed a blooper! Thanks for letting me in on the joke @PurajitMalalur!
Best Dad Joke of 2024...Well played, scientist.
I thougt it was a mistake in editing. Now I see it was a joke. Thanks.
Becky you're a legend. First year major in physics and loving it. Can't say for sure if I would have gone for it without your UA-cam videos. I'm serious, thanks.
Lovely to hear it! Glad my videos could be a help to you
Retired chemical engineer here. GO FOR IT! don't quit, dig deep, stand proud.
Just remember any issues, you can just say physics did something not seen now to fix the BS that doesn't fit. Like dark matter and energy, or cyclic universe. Or inflation.😂
Good luck finding a job
@@Flexible_photon Better than a gender studies degree.
My naïve assumption for the relative sameness of the observable universe has been that if the big bang happened everywhere all at once, it makes sense that it happened in the same way everywhere all at once, in which case it makes sense that everywhere looks roughly the same as everywhere else. I never considered that it was more complicated than that until this video, so thank you for quite literally expanding my horizon
You have a valid point though. You don't need to communicate any information from one side of the universe to the other if they just so happened to be the same. Not by chance, but because you're just experiencing the same conditions. The same kind of stuff experiencing the same sorts of conditions wouldn't need to communicate any information to its counterpart on the opposite side... as you would expect the same conditions to be affecting the same kinds of things existing at the same time in the same universe... in the same way.
All of the matter in our universe existed at the same point and at the same energy state, then expanded outward... If I had a pot of boiling water on the stove and then took two cups of the water out of that pot and walked one cup in one direction and the other cup in the other direction, I would still expect both cups of water to be the same temperature, despite them being no longer in contact (if in a vacuum). For anything else to occur, it would violate the conservation of energy... this video presents it backwards.
It looks the same everywhere all at once, because I ate the Everything Bagel...
@@davidlones365not to mention if you originate from a singularity the speed of light it pretty irrelevant
or just pointlessly confusing you, since that makes sense and their bs doenst.
Yes, if everything had causal contact at the big bang why would anything disconnect?
Dr. Becky... All science channels bring this up. I think the casual viewer needs an answer to the question - "why can't the temperature be the same"?
There was the big bang with lowest entropy everywhere. Why can't it be the same temperature everywhere? I know it's a problem, but why? Answer that, and you'll be the first of the UA-cam channels actually telling us why is it a problem :)
they dont know. they have fallen into the math hole where nothing is connected to reality anymore and the problem is they have been there so long they don't even realize they are no longer studying reality, but playing numbers with math.
For example, if you showed an astrophysicist a ballon full of air, had them measure it, then let out a little air, and had them measure it again, they would tell you that if you let out all the air, the ballon would collapse into an infinitely small singularity cuz thats what their math shows.
but we have all seen an empty ballon and its not that small...
and no I'm not anti science like some, ive just been into theoretical physics for so long that I've learned its all wrong. Every few years we rewrite what we thought and its never the same as a few years before. I guarantee you it will happen with the expansion rate of the universe in the next few years, then everything you learned about it before will be thrown out and laughed at.
Yet these people still dont get that they are not based in reality. they are based in imaginary numbers. and I don't mean e or pi.
Because temperature is directly related to matter and energy. When we're talking about matter distribution, we're directly talking about temperature. Temperature is a measure of the average movement of particles in a region of spacetime (I forgot the exact definition). Lots of movement = high temp, little movement = low temp. Lots of particles = higher temp, few particles = lower temp. An easy example: boiling water = water molecules flying in all direction: high temp, ice = water molecules stuck together: low temp. Septillions (10^24) of water molecules = lots: higher temperature than billions of water molecules = few (about the # of atoms/m^3 in interstellar space): few.
For the temperature to be the same everywhere, the distribution of matter would have to be the *exact same* everywhere.
Also the Big Bang had the lowest entropy. Entropy is a measure of chaos and a singularity is the most ordered thing that exists (in theory since nobody has ever proven that singularities physically exist, only mathematically).
@@louisrobitaille5810Again, I don't think that answered the question. We understand temperature and matter/energy distribution. The question is (in my estimation) why should we expect different regions to have different temperatures? After all, if the Big Bang singularity was everywhere all at once, wouldn't we expect that all expansion experienced essentially identical conditions? D shouldn't the default assumption be that everything is pretty much homogenous, and if we saw any major deviations then THAT would be cause for concern?
The reason is gravity. The CMB era was 380 thousand years AFTER the Big Bang, and that's oodles of time for gravity to form clumpy regions, so the temperatures would be wildly non-uniform. The naive idea people have is wrong. The CMB did not come from the Big Bang, it came much later (380 thousand years later!!!) when the temperature was around 3300K, after the radiation opaque (plasma) era. Due to gravity there had to be very clumpy regions in this plasma, a consequence of this horizon being so "distant" from the Big Bang in time. But that clumpy model would not fit the data which is a perfect Planck black-body curve all around, with incredibly low angular deviation. I think you could say the angular deviations are "gaussian" too, so have no sign of any gravitational clumpiness. It is however correct to imagine prior to the CMB era there is a common cause linking the regions that at the CMB era were causally separated. That's the actual problem. The solution though cannot be "the big bang" because like I wrote, the gravity would clump stuff wildly, giving a highly non-gaussian angular spectrum to the CMB (probably a power distribution or something, I'm not sure).
Me looking at the night sky; so beautiful.
Astrophysicist looking at the night sky; so wrong.
Astrophysicists also find the universe beautiful. That's why they want to understand it.
L😂L
People: The night sky is dark because there is no Sun.
Astronomers: There are milions of suns. Why is it dark?
@@samuela-aegisdottir Optometrist: The absolute light threshold of the human eye is 1 photon per 100 average rod cells. This must be why the universe appears dark instead of infinitely bright.
@@user-fn1cd6mo9zit would be pretty cool to see the Hubble Deep Field haze with the naked eye tbh
It'd think the question should more be; why would things be _different?_ What would create a universe where different parts have different enough initial conditions to create large scale differences? Id' expect the structure of the universe to be basically uniform anywhere above the scale where causality could reach at the point where short range forces (e.g. within what became galactic clusters) started to dominate over longer range ones.
But that sort of pushes the question in the other direction: why isn't the universe *more* uniform? Is the problem more accurately stated as "Why isn't there more or less uniformity? Why *this* amount? "
Quantum fluctuations are random so we would expect one part of the universe to be different to another, but it does depend on how big the fluctuations were. If they were small everywhere that might explain it, but if they were large (and since they occurred in a tiny volume smaller than an atom) then you would expect huge differences in different locations.
@@tonywells6990 (Note, I'm not saying people are wrong, I'm say I think there must be something more interesting going on that was glossed over in the explanation.) My thought is that if those fluctuations are statically IID, then at any significant scale, you should expect them to average to the same result. It won't be exactly identical, but at anything larger than the causal scale there should be no reason to _expect_ things to be different. Even chaotic systems like turbulence only exhibit limited non uniformity and they are fully connected causally.
@@tonywells6990But the universe used to be smaller, I. e. the universe used to be so small that fluctuations *had* to cover the whole universe.
Then there’s the question of which field’s fluctuations we’re talking about. The gluon field? The weak field? The electromagnetic or gravitational field? The Higgs field?
When the universe was very small gluon forces could reach all the way “across” but not later when the weak field barely did.
I’m thinking of an analogy with the Casimir effect- the universe was effectively a cavity in which certain wavelengths/energy values of field bosons could exist but not others because there just wasn’t room for them. Nowadays ever longer values of photons and gravitons (if they’re real) can exist because they still have infinite range but gluin, W and Z particles and Higgs bosons can’t propagate beyond their confinement ranges any more.
@@markfergerson2145 Yes, somehow those fluctuations would still need enough time to travel across the universe.
@@markfergerson2145 The energy density was too high for any of those fields to have massive particles, you can think of it as the Higgs field being "unbroken". So all the particles were essentially force carriers and "photons" with infinite ranges.
I find it easier to think of the inflation field (whether or not you think of inflation as a field) at high potential energy that embedded the other forces, except gravity, into insignificance. When inflation ends that field phase changes and lose energy and the other fields starts to become significant, or at least that is my impression here. The quasi-stability energy range of the Higgs vacuum roughly overlap with inflation energy [LHC, Planck observations] so the unbroken, raw Higgs field can kick in.
I just learned why the weak force has to break electromagnetism symmetry at a higher range and then the strong force kicking in at QCD plasma energies: if the strong force had done it they would have produced nearly massless 'neutrinos', so no chemistry et cetera.
So there you have it, a series of phase transitions: inflation - Higgs field E/W - strong force QCD, And then the universe we know and love appeared. (It can be of interest to note that only inflation had a first order non-homogeneity (bubble) forming pjase transition, the two others seems to have been smooth second order ones - no potential energy release.)
I answered what fluctuations there seems to have been earlier, but I repeat here: fluctuations in inflation (most likely a quantum field, so quantum fluctuations).
And I love how you have fun with the uploads and add some of the bloopers and outtakes. You're a brilliant person who likes to have a great sense of humor. More people like you are needed and desired.
Always love the videos! It’d be really cool if you could do a video explaining the big magnetic monopoles
Hey Becky! A couple of weeks ago I've picked up your book at a local bookstore I often visit, and it's such a fun read! Your enthusiasm shines, and the tengants you go on are great. Keep being you, I love your videos!
I love your videos and would really like to be comfortable continuing to watch you, that said I'd really appreciate if you could do some more research on Better Help and their problematic practices. I both go to and support others going to therapy but please understand Better Help harms people.
It's sad but she's not going to stop advertising them. She's getting those sweet, sweet shill-checks. Dr. Becky's bank account doesn't give a shit as long as they keep coming in.
She knows, they pushed out a lot of long-term contracts with UA-camrs right before that info came out
That is an allegation not a proven fact. Although if you have in person reference system having a bad egg or two sneak onto your list near impossible to totally prevent. Example you go to a multi partner mental health practice one member might be bad or turned bad..
I found a mix of reviews it not an open and shut case against in this area of harming folk.
Privacy practices on the other hand there is an official US government complaint on.
@@chefRyan38 Still there is a long list of folk who claim to be helped as well this is not yet a clear one way or another issue in the area of care. Other areas are more problematic.
BetterHelp 👀REVIEWS - from none other than Trust Pilot - Reviews 7,022 • Excellent - Id say your beef is with the company. I would also go so far as to say it is awfully unsavory you to sit here like fat cat, and take down this fine ladies efforts to monetize an incredible show 🚧 If you have any respect for Dr Becky you would remove your comment altogether ✨Is this a way to treat someone whose teaching you selflessly?
I am having trouble believing I haven't come across your channel since you've been here since 2011. Your mind is brilliant and I love it. Space and Science have always gained my attention and thought. Keep the awesome information coming Dr. Becky and I'll keep watching.
Thank you for actually explaining what that CMB photo shows! It's always presented as evidence that "everything looks the same no matter which direction you're facing", which causes me to wonder if we're looking at the same photo.
Part of that is because they show a projection onto a flat surface. Even when they show it in 3D, they show a sphere seen from the outside. The only way to properly look at the CMB would be in a planetarium so that we see it the way it was measured, i.e. from the inside.
Ok maybe that last bit is a bit unrealistically harsh as a kinematic dipole could make sense its just not the only way to explain the data and a mistake can lead to huge systemic bias if you are wrong. Not sure why I can't edit my posts anymore.
I am confused by this vidoe. At around 6:50 the video shows that there are MULTIPLE 380,000 light year horizons/ovals/patches when the Universe was 380.000 years old..so the ACTUAL FULL Universe was much larger than 380,000 light years at the age of 380,000 years? How do we know this? Then one of those patches expanded so rapidly it became the observable universe today? It's true that the observable universe at 380,000 years old was only about 380,000 light-years across. However, inflation suggests the e It's true that the OBSERVABLE e at 380,000 years old was only about 380,000 light-years across. However, inflation suggests the ENTIRE UNIVERSE was much larger, potentially infinitely larger, even at that young age was much larger, potentially infinitely larger, even at that young age.
@@aryangod2003the entire universe has always been larger than the observable universe, even now. We often talk about the observable universe because it’s the only stuff we can actually see, but the full universe is at least 250 times larger in diameter than that (based on universal curvature measurements)
It’s currently unknown whether then universe is finite or infinite… 250 is just the minimum we can prove through empirical data
it still blows my mind how much of the universe we simply can't see because we're embedded in a galaxy.
Sag A* is that giant who thought that the seat right in front of you at the theater looked really comfortable.
And just think how much easier astronomy would be if we could get rid of that pesky sun.
@@billcook4768 Or the atmosphere. Or the moon (which stabilizes the wobble of Earth).
Consider that a blessing. It'd xe much much harder to colonize space if ALL the ships and materials had to come from this solar system, had Sol been a wandering star thru intergalactic medium. ALL travels would take millions of years to the closest star, everything would be much riskier., with life extinguishing at Sun's red phase almost certainly. Being within a galaxy instead means we only suffer to get to nearest star, there we can gather resources and expand at exponential rate - in a few hundred thousands of years we'll get to the other side of the galaxy, once we learn to travel at just 5% light speed
Actually, it is amazing how much we can see because we are mostly in one of "arms" of galaxy.
Great video. Thanks for sharing, Dr Becky
You have the best questions and your answering is just as interesting thank You
I hear bad things about Better Help.
A big part of this problem can be ameliorated by, not adding, but removing something: the assumption that the universe needed to be in causal contact to look the way it does today, and by implication, the assumption that it started existing in a state of non-uniformity. Other assumptions would have to take their place, like 'the universe began existence in a state of least entropy, corresponding to maximum energy density in a flat distribution. Manifesting initiated the flow of time, which allowed quantum effects to break force symmetry, starting the expansion of space and giving room for quantum fluctuations to seed structure and cause minor regional differentiation'. Some version of Inflation would probably still be needed, to smooth out the fluctuations, but it could probably be more strictly constrained.
I believe it was Brian Green in his "Fabric of the Cosmos" book that wondered how it is possible that the universe today could be at its current state of relatively low entropy since it implies that the early universe was at an extremely low level of entropy. He didn't venture an answer to that problem as I recall (it's probably 20 years or so ago), but I would suggest that it may have existed in something like a Bose-Einstein state which has an entropy of zero since it acts as a single entity. As you've pointed out, we probably should be looking at this problem from the standpoint that the universe was very (if not absolutely) uniform at the earliest moments. If you assume that dimensions are actual fields, then it follows that they are causal, i.e., they are an effect resulting from a cause. That gives us the possibility of the universe existing before the "flow of time" as you say, actually began. While I'm a bit confused by the wording of "Manifesting initiated the flow of time", I tend to agree that the dimension of time was the latecomer to the party and that the 3 spatial dimensions holding this low entropy state of matter could have been around for an indeterminate period. It's difficult to express the idea of matter existing in the spatial dimensions without any time dimension for reference. But suffice it to say that it would not be constrained to the infinitesimally small core of the generally accepted Big Bang. It could have existed over a huge extent of space. Then, with the emergence of the 4th, time, dimension it would appear as if everything went from a point to the then actual extent of space in no elapsed time whatsoever. This would have the same effect as inflation in eliminating the horizon problem and it also starts at zero or near zero entropy from which we can evolve to the state of the universe today. With a few extensions, this model can also answer the question of the missing antimatter and perhaps provide some additional benefits such as additional conservation laws.
So more simple explanation , - big bang but there are plenty of questions , 1 - how from energy to matter formation, 2 - how was bubble for big bang formed 3- how inflation generated and from what assuming that space is immaterial 4 if universe 13.8 bln years why galaxies are almost same age 5 no explanations about accelerating expansion after big bang
The entropy problem is ill-conceived. Entropy is a statistical concept associated with not counting all degrees of freedom. If we count all degrees of freedom the entropy is constant for all time, never changing. If we do not count the Planck degrees of freedom (which we do not) then the statistics "takes over" so to speak, and so then there is no serious problem. The apparent "arrow of time" is nothing but a coordinate in the Block Universe, and you think entropy should be increasing only because you are failing to count everything, as well as failing to account for the "dynamical laws" which need not obey exact symmetries of the universal laws (by "dynamical laws" I include BV/ICs, so not just "The Laws"). Having noted that, nevertheless the apparent rise in entropy for time-evolving observers is a wonderful thing, things would be dead boring otherwise (no "life" most likely, but then no death either, hooray). Also a terrible thing (there'll be an end to life.)
10:44 One for the bloopers, Becky - either that, or you "wouldn't get excited for that" twice over? It's also a good thing when your re-delivery is so smooth you don't notice the doubling effect in post. 😁👍
Glitch in the Matrix
They changed something in the universe. Maybe it was the Hubble constant... @@iambiggus
I had to rewatch it just to confirm I'm not in the matrix...
God damn it. I thought I found it first. And then I found your post. lol
Haha I left it in as a joke because I thought it was hilarious I was talking about the cyclical nature of the universe
I'm glad to see that in all the beauty you're observing out in the cosmos, you are finding time to enjoy the beauty of Yosemite too!
Currently reading “On the Origin of Time” and going this exact same description. You do a great job of describing it.
Thanks, dr. Becky! 😊
Stay safe there with your family! 🖖😊
Always enjoy your videos. Hope the back is good.
Brilliant as always!
awesome videos as always, thanks
Thanks for this week's video.
This episode is really good. Fascinating thank you
Glad you enjoyed it!
@@DrBecky I'm afraid I don't understand it. :(
If everything was clumped up in one tiny spot at the beginning, it must have had the same temperature everywhere, right? And when it expanded, should the temperature not fall in the same manner everywhere because it's all governed by the same laws of nature? Why do different regions have to interact with each other to keep the same temperature? Unless they expand at different rates - then it would make sense. But do we see that?
(If I put three identital glass beakers full of 100°C water in a room with the same temperature then it does not matter whether this is the same room or three different rooms with the same temperature; they will cool down with the same curve.)
Thank you. No one really understands their field or subject unless they can explain complex matters to the layman in everyday language. You have done so with aplomb. I just subscribed to your channel.
Thank you for sharing!! You just made me feel, oh it’s not just me! 👍
You explain things so well. 🎉
Ah, clever. Talking about cycles in the universe while in a yt loop cycle at 10:43. Kudos!
10:44
Hah, I thought it was a video editor blooper!
Dr Becky why haven’t I heard about this before? I’m really blown away. Horizon problem
Thank you, keep working.
Thanks doctor Becky for another great video. You are the best.
Love your videos. Thanks.
Thanks I enjoy listening to your thoughts.
I hope solve this problem some day . Working on it Dr Becky. But don't hold your breath.
6:57 confused about this part. You have three separate unconnected circles. But if the universe was still “small” and everything was bunched up together. Why wouldn’t the temperature have changed the same everywhere? How do we know enough time had passed to have enough random fluctuations to change the temperature in different places?
Knowing the speed of light, the age of the CMB, and the expansion rate of the universe, we can calculate how far away the places the CMB came from currently are from us, and also how far away they would have been when it was first emitted. So, we can know how far apart different points on the CMB would have been back then. Since information can travel at a maximum rate of the speed of light, if two points are far enough apart that light couldn't have traveled that distance since the universe began, they cannot have affected each other in any way: they cannot have any causal connection. While points on, say, opposite sides of the CMB would have been closer together when it was first emitted, the universe would also have been much younger, giving light much less time to travel, so the distance between things that could have any causal connection was also much smaller.
I don't know if I'm managing to explain this as clearly as I hope I am, but the simple version is that yes, the universe was smaller, but also so was the maximum distance between things that could have effects on each other. So fluctuations could not have transferred across the entire thing. So if there WERE any, they would be isolated. But the fluctuations are all so small that they're basically nonexistent. Kind of like measuring the temperature of the entire ocean and finding that every point is less than a fraction of a degree different from every other point in it.
Haven't made it all the way through yet, but I still don't understand how that invalidates the underlying idea of is it possible it just looked the same everywhere already?
but wasn't it a singularity at the beginning so couldn't thermal equilibrium have been there from the singularity time or are we saying that heat didn't exist until the universe had expanded to a certain size and then matter formed and at that time the distances were beyond light travel (causal contact)
@@kainotachi I think the problem is me not asking the question clearly. I’m assuming immediately after the Big Bang the universe was uniform in temperature and density. Then at some point different parts started to have different properties, a little hotter here, a lot cooler there, more matter clumped together over there, etc. No idea if this has a name so I’ll call it X. There is also a point where the universe became transparent and light could travel, call it Y. And another point where it became too big so that light from one point could not reach another point in 13 billion years, call it Z. CMDB happened after Y. How do we know Y came after X? If it came before X, then we don’t need to worry about Z. The CMDB is the same everywhere because so was the universe. Or have I completely missed something, which is probably more likely.
@@voraciousfred"but wasn't it a singularity at the beginning " - no. There is no upper limit to the size of the universe currently, and so there is no upper limit to how large the universe was pre-CMB emission. And there is no reason to believe that a mathematical singularity can indeed exist physically. This notion that the universe started as a singularity has been passed around the internet quite a bit, but it is hardly a well supported idea in physics.
Someone should do a supercut of Dr. Becky saying "nought". Her saying "nought" is like Carl Sagan saying "billions".
fr
"Chat about" Makes me feel like Beethoven hearing a melody in his head for the first time.
naughty
+1
Millions, billions, trillions is one of the funniest videos here.
nice explanation
I have faith you can solve it Dr. Becky.
You do a better job of explaining things on a cosmic scale than most! I appreciate ya :)
is that a taco-tortoise in your pic
I hope Dr. Becky gives her process of choosing her sponsors the same due diligence she would give to her own scientific work.
🙄🙄🙄
Great video topic. The CMB is always described to the public as the edge of the universe, but the observable universe is a different beast and relative. As a kid in the 80's I liked to draw cyclic big bang/big crunch posters. Then the accelerating expansion was popularized in the 90's which suggested a big rip cosmology. Penrose's cyclic big rip/big bang model seems to be the most likely of the theories out there, but these days I like to compare theories, mysteries and discoveries from a cyclic toroidal cosmology perspective where the universe is more of a rolling donut shape constantly turning itself inside out. Not a big bang as such but a big endless flow (white hole). Eventually, all matter completes an epic journey looping around and compressing into a universal black hole (the other side of the donut hole). Scientist like to say these days that the universe is flat, but there is still a substantial margin of error in their calculations. Enough to not rule out positive or negative curvature models.
PS: As a high school student in physics, I was kicked out of class for questioning the claim that the universe was infinite. Thanks education system.
I’m struggling to understand why the horizon problem is a problem at all. The fact that recombination occurs at a very specific temperature means that the first light of the universe will be emitted at a very specific frequency without needing to be in causal contact with anything far away. As long as space expands and cools off approximately uniformly in all regions of the Universe, recombination will happen simultaneously everywhere at the same temperature. What am I missing that makes causal contact a necessity?
I think the issue is that you assume that the universe started uniform, and inflation theory shows that you don't need to assume that, but you can explain it.
@@kapsicosmic inflation is just that - an ad-hoc assumption. Remembers me on Paulis neutrino, which was proven to exist decades later.
I love her reaction to outside distractions, I can't hear any of it but it is still funny to watch
Same, I was wondering is maybe it was a pet. Does she have pets??
This is my first time hearing an explanation of the cosmic microwave background, I had not thought about the limited time frame for information to propagate, and the fact that it wouldn't be able to cover the distance from edge to edge. I would if the smoothness could be attributed to something mathematically modelled by a phase transition, as some phase transition models have shown the ability for many local influences to add up in a way that propagates long range or globally. Since we would really want to think of the information distance limit circles as many sets of overlapping circles that are 380,000 lightyears wide that have been expanding over time and how those interactions effect information propagation across the entire background.
interesting point of view
Inflation is often described as phase change event
You actually hit on many of the points that modern cosmology assumes to be true. The early universe went through a number of absolutely catastrophic events that operated like phase changes. The most significant would be the de-unification of the fundamental forces. These events caused the very laws of physics to change and presumably released incredible amounts of matter/energy. This is complicated by the fact that it's believed that at these events were largely triggered by decreasing concentrations of mass/energy as the universe expanded. Quantum fluctuations in the very early universe are going to be causing tiny timing variations in when these events occurred in different parts of the universe. The catastrophic mass/energy changes and literal different number of fundamental laws would then affect the timing of later events in a sort of butterfly effect that would amplify the timing disparities, causing neighboring parts of the universe to progressively get further out of sync. It's easy to imagine neighboring regions of space with mass/energy concentrations many orders of magnitude different with different numbers of physical forces ruling them even if the initial quantum fluctuations were tiny. The chaos at the borders between these regions would be unimaginable and would have scarred the present universe into a patchwork of wildly varying physical states.
The goal of inflation and competing theories is to somehow explain how the universe managed to stay in lockstep long enough so that either the most significant development phases occurred across the entire universe in lockstep or that the chaos of having out-of-step universe regions are somehow spread over so much universe today that they are far beyond the edges of the observable universe. Inflation does that by fiddling with the universe expansion rate. VSL theories fiddle with c, etc.
Later quantum fluctuations would have also affected the universe but these later ones would have progressively less effect on the present universe. And as you suggested, not only does it make sense that we'd see these overlapping information circles, we do see them. There's a whole portion of astrophysics where they examine the fine details of CMBR temperature variation. These are caused by quantum fluctuations or other perturbating events that happened much later than the sort of catastrophic fluctuations I mention above. These triggered gravitational waves that propagated across the pre-CMBR universe like it was a ringing bell. We can see these gravitational acoustic waves as tiny, very subtle variations in the angular granularity of the CMBR variations. In fact these sorts of fingerprints are what give us most of our knowledge of the pre-CMBR universe and are used to constrain inflation theories.
@@danheidel This was the explanation that many others in the other threads also ask - what prevents spacelike separated parts from going through the same evolution and end up in the same state. Do you have any reference to this explanation? Not doubting you but would be nice to read up a bit on it.
The thing I always like about the CMB is that when it was first emitted, before getting redshifted by crossing the expanding universe, it was visible light the approximate color of an orange creamsicle.
now im listening
Does this microwave background coincide with objects visible in the same area, or are the two reaching us at different time delays from when they were emitted?
@@snorman1911 The latter. The CMB is the oldest light in the universe, originating less than a half-million years after the Big Bang. Everything else we can see is closer and younger.
Thanks!
inflation explains a lot but it was "backed into." They basically said, here's the end result we want how do we get there. And many, many models were tried until we got one that worked. Fine, but that really isn't science. You can do that with math, whereas we know the result but until a "proof" is worked out to as "why," it fails. Also the biggest mystery of inflation is why did it start and why did it end so conveniently.
A little bit more than backed into as out of the 6 predictions, 4 have been confirmed and the multipole moment 'measuring the spectrum of the initial fluctuations' was a perfect match against the prediction. Now that is not to say I think it is right but it ddoes have far more weight than the other theories on the table..
10:44 did we just experience the shortest universal cycle? 😮
Glitch in the simulation ;)
@@chubert20yes simulation reset
😄😄😄
Love your videos! I think you missed a blooper at 10:50 I thought I was glitching 😅you start the same sentence at 10:43, miss a word or something and immediately do a retake I think the editor missed. Thank you for making me smarter with your vids!
I thought the same thing, but the comments section knows whats up, it was a joke from Becky, as she's talking about cycles.
@@kindlinso it kinda was my head glitching 😂 I just started reading the rest of the comments to see if I could find something but didn't realize I spaced out and clicked the rick & morty one at the end. Wasn't until I saw your reply that I realized I was looking under the wrong vid. Thank you for clearing that up for me though.e
Omgosh, at the very end, I KNEW IT ! You are from the South !! Absolutely perfect Southern Accent ! Kentucky, Carolinas, Georgia, about any of them! Southern Ohio !!
I'm still having trouble wrapping my head around the fact the C.B. is a sphere around us. Interesting video! Thank You !
I don't see a reason why there should be huge temperature fluctuations at the time the CMB was released. What will prompt such differences? It's not like there is some external force to stir the plasma and there are no seeds for nucleation either. Why cant the smoothness persist during normal expansion instead of inflation?
Because the universe can be brought back to the point, at such a small scale there are quantum fluctuations which play a major role. They should create more bumps in energy distribution than it is observed.
@@kriiistofel which paper is that in - I checked the Visual Horizons in world-models (W.Rindler) - that's just classification of the models based on horizon boundaries. I would like to look at the one showing that quantum fluctuations have a major role.
@@kriiistofel As far as I know, the fluctuations in the CMBR look _exactly_ like they were produced by quantum fluctuations. So no, there is no disagreement with observations here.
I'm probably going to show my ignorance with this question, but why do we even think a horizon problem exists at all? Assuming the same starting state for the entire universe, and assuming that the same processes (rules of physics) happen in every portion of the expanding universe, we should expect similar results in every portion of the universe today. A relatable analogy might be having two people with the same make and model of kettles and stovetops on opposite sides of earth, and having them start heating the water at the same time. Assuming the same starting conditions and the same rules of physics, we would expect that both people will observe the water in both kettles to look very similar as they boil at nearly identical times. We would expect this to be the result, not be surprised by it. We wouldn't feel a need to figure out how one pot knew what the other pot was doing so that it could do the same thing. Those two pots of water didn't need to communicate with each other for them to end up looking the same. They just followed the same rules of physics from the same starting conditions and undergoing the same processes. What am I missing that requires us to worry about a horizon "problem"?
It's not a dumb question and you're not missing anything. If there is no mechanism like inflation to bring the entire observable universe into causal contact, then the uniformity of the CMB means that the inital conditions of the universe were (almost) the same everywhere. Setting the initial conditions everywhere the same is a perfectly fine solution to the horizon problem and would have belonged definitely in this video in my opinion. It's just too boring for most physicists to accept it seems that there is no mechanism to explain such initial conditions. If the universe had the same energy density and elementary particle composition everywhere from the start, even while it was not in thermal equilibrium yet, it would have thermalised everywhere to the same temperature. In your analogy, the kettles on opposite sides of Earth do the same thing because they both heat water at normal ambient pressure starting at (roughly) the same temperature. But imagine it's the beginning of the universe, and there has not been any possibility for the two experimentalists to talk to each other about the kettles and the local atmospheres are completely different. The ambient pressures and temperatures may be completely different, and the particle compositions are different, i.e. one kettle is filled with oil. Then of course the kettles do completely different things. To solve the horizon "problem", you either need to put in the same initial conditions everywhere by hand into the model of the universe, or you need a mechanism like inflation to make them the same, no matter what the actual initial conditions before inflation where. Since inflation solves other so-called "problems" like the flatness problem, and would dilute away abundances of some expected particles like magnetic monopoles that are predicted for example by string theory, a lot of people like inflationary scenarios for different reasons. But again, you could also just set the curvature to zero as an initial condition, and think that string theory is wrong and magnetic monopoles do not exist in the first place. Inflation is in some way predictive as it solves several "problems" with one explanation, but how fundamental these problems are is very debatable and the theory can also be formed every way you like by picking all sorts of different inflaton potentials, so it's not really predictive in some other sense. I think a lot of physicists are not skeptical enough and consider inflation as a very likely scenario, but it's still one of the more reasonable speculations I'd say. In the end, we just don't understand the beginning of the universe very well, and one should be honest with that.
I think the problem here is (using your analogy) is that there's a bunch of people all over Earth wanting to boil kettles and are too far apart to communicate with each other, yet somehow, everyone on Earth managed to get their kettle boiling at the same time as everyone else. You would think all the times would be different, and therein lies the problem, because they aren't (as evident by the tiny differences in the CMB).
You just warmed my heart ❤️ keep doing what you do, perfect❤
That makes sense, thank you.^
Seeing you struggle to find "contraction" actually made me feel better. If someone much smarter than me can lose words, then maybe I'm not going senile.
if it makes u feel an better, if ur still questioning it then u should be good. if ur ever certain that your not crazy, thats probably when you should be worried
disappointing to see better help as an advertising partner
seriously
Thanks 🙏
Great video as always ! Thanks a lot ! I don't completely understand the issue of the horizon problem. I think of an analogy : water boil at 100°C everywhere (at constant pressure, etc.) because it is an intrinsic property of water : why couldn't that kind of reasoning explain the horizon problem? I guess I suck at thermostatistics and that's the issue, but...
I still don't 'get' what the problem is. If the distribution of the stuff in the nascent universe was virtually uniform, then no matter how fast it expanded (whether different part were within sight of each other or not) why wouldn't we expect different parts to develop in the same way preserving that uniformity, anyway?
I am thinking exactly the same as you. Maybe I havent't understood but it looks so obvious to me, that if everything, at time "0" was in "contact" with everything, then at time "380000" years, when light began to exist, everything would have been similar to everything else, including the temperature. So why do we need to bother with inflation? But there must be something I'm missing perhaps.
The problem is that the homogeneity of causally disconnected regions of space would imply that the speed of light was not constant which seemingly violates our laws of relativity.
@@mikotagayuna8494 Why should they be causally disconnected if they were a singularity at time 0? In addition to that, while they were expanding as a plasma, before year 380000, haven't they had time to comfortably exchange information at the speed of light? EDIT: Maybe I am beginning to understand. You are referring to parts in the universe that are so far away from each other that light emitted by one had no time yet to reach the other, meaning that one is beyond the observable universe of the other. But then isn't the background cosmic radiation that we are observing, the one of the universe observable to us anyway? Becoause otherwise it wouldn't be observable to us, would it?
I also have the same question, however I suspect that the answer is that actually there is a misconception in the size of the universe at time zero. There is a lower limit to how small the universe can get, and this limit is always bigger than that of speed of light times age considered. It is supposed that before that limit, inflation happened.
Not sure, but my best guess is maybe cosmologists just ran a simulation and found it was "too clumpy" without inflation. It does seem rather intuitive to me that if things are evolving according to the same laws of physics everywhere, they would look roughly the same everywhere. But my best guess as to what the video means is that there would still be a lot of deviations over time leading to something that is on average still the same but with very large variations ("clumpiness") and that the variations we see are too small and aren't compatible with simulations. But I don't actually know.
glitch in the Matrix at 11 minutes
Or just the variation in the local speed of light
So, @Dr. Becky, one question I have had about the CMB is, given that it was light occurring and traveling outwards, why are we even seeing it from inside the bubble? Shouldn't it *_only_* be visible to a hypothetical observer located on the other side of it? For example, if you take a flashlight and shine it away from yourself, you cannot see the light being sent outward. If there was absolutely nothing for that light to reflect off of, there should be no perception of light. Why is the CMB any different than that?
Also, why does any part of the CMB (or anything else, for that matter) have to have interacted with any other particular part for both to be the same as each other? Everything came from a central source (i.e. the object that was the thing that expanded into what we call the "universe").
We're experiencing more problems than answers in astrophysics and in general physics nowadays , ah? Things that we took for granted aren't anymore. This makes me feel that there's a lot of BS going on in physics.
Can't have "wishy washy" Dr Becky 😄 Great explaination.
How about Timey Wimey Dr. Becky. 😁
We can observe inside a 13.8 billion light years radius sphere. The universe could be many times that, say 500 billion light years. A spec in a big pond, using a two dimensional reference.
Your enthusiasm is contagious.
Currently it's believed to be 93 billion light years across
As mentioned above, with expansion taken into account, the observable horizon is actually currently about 46.5 Bly away (93Bly diameter). Given the current limits of measurement of space-time curvature, which show it to be at or nearly "flat", the non-observable universe beyond the horizon must continue on at least another 250x further than that.
The channel SEA put out a great two-part video: _Journey to the Edge of the Universe_ and _Beyond the Observable Universe_ . The second in particular goes into detail about how theory expects it to look at the largest scales.
I have always wanted to get this theory of mine to the ears of a real science person, and you are by far the best one. I think, (with absolutely no scientific background or understanding of physics) that the other side of any blackhole ought to be a "big bang" and that we should not view the "big bang" as an instantaneous event, rather something continuous. Essentially the blackhole at one end is creating the ever expanding horizon of the universe in it.
@dr. Becky
I do like the "NB: NOT TO SCALE" notice on the CBM image
Minor correction for 5:53
The distance to the horizon is about 46 billion light years since the universe expanded in the 13.8 billion years since the light was sent in our direction.
she knows that. rewatch it. there's a diagram about it.
Such a bad mistake for an astrophysicist!
I decided to leave out the distinction between lookback distance and co-moving distance (i.e. corrected for expansion) in this video for brevity's sake. I have made a video on this before though if you want to know more: ua-cam.com/video/6kJ0I7SyJsU/v-deo.html
*The universe’s second biggest mystery. #1 is still “Is a hot dog a sandwich?”
Solved! Yes, yes it is.
Is tomato a fruit or vegetable? 🍅 🍅
No. See, no mystery. Always a fun question though! Amazing how dividing it can be as well. And I really have no opinion on it honestly.
No it's a baguette
Are socks shoes?
Very good explanation of Inflation, tops!
What if the origin of the source is next to being unity?
The inflation idea is basically logical due to the fact is that time is dependent on the energy intensity exists where things are interacting. So a period where local speeds were at the light's speed limit. That is to say the speed of one point compared to its immediate neighbor can only be at light speed;; yet two opposite neighbors could be twice the speed of light and that keeps increasing as one notes more neighbors to neighbors, etc..
The only thing that would disrupt this flow would be if it ran into a bit of former universe material not up to speed. Though it would likely be soon blown away after it introduced some measure of slowing in the flow. And of course, as the energy intensity reduced due to the expansion, time would tick by quicker and the apparent effect that is called inflation would fade away, as we note times passing now.
Sad to see you’re still promoting better help. Not a good company at all.
WHat are they guilty of?
@@JeanPierreWhite I'm not op, but.. Betterhelp don't always get you the help that you're depending on them for. Many people have reported being completely ignored by the therapists they're connected to.
Betterhelp also automatically opt you in to having your conversations recorded (you have to choose to opt out), and they sell that information on.
I look forward to a number of youtubers (including Dr Becky) eventually posting videos saying "sorry, I'd signed contract before the issues came to light, and had to keep promoting them, I won't sign another one".
@@JeanPierreWhiteThey use entirely unqualified people. It's beyond bad management, they are actively harmful.
They apparently sold patients data to advertisers and insurance companies... Without consent from those patients.
@@dancooperishit's been almost a year since the FTC fined them... How long do such contracts run?
If the universe doesn't conform to our assumptions then there's something wrong with our assumptions. So...
Why should we assume that there would have been large variances in temperature across the early universe in the first place? It would seem to me that even when the effects of an event are spread out that they still evolve along the same general lines as each other because they evolve from the same starting conditions, regardless of how widely separated they may become.
I guess that there is some mathematical physics behind this assumption, but I've never heard that particular assumption defended in detail before. How robust is that assumption at all?
Because that implies that the speed of light may not be constant and that is central to our understanding of relativity.
@@mikotagayuna8494 I don't see why it would necessarily imply anything of the sort.
I'm asking why isn't it conceivable that different areas of the universe are the same temperature, _not_ because they are trading photons between each other, but rather because they simply inherited the same starting conditions?
@@HermanVonPetri There is only one scenario where the starting conditions could make this happen and that is a scenario with an absolutely homogenous start and that would end up with a universe with only a homogenous gas and nothing else.
Shortly, your hypothesis is contradicted by observations and our understanding of physics.
@@KarelGut-rs8mq But the whole problem in the first place is that observations show that the universe _was_ a highly homogeneous gas for many thousands of years after the big bang -- and yet we still exist.
So nice to see someone think and not try to use big fancy words to prove how smart they are. But I found it such a pity that you assumed their vision of expansion was correct. A McG
I read your credentials after listening. Quite shocked at your brilliant credentials! 😅Thank you for these explainer videos and for being unafraid to be regular rather than pompous. 🙂
May I offer a hypothesis: the universe is infinite and forever, no start and no big bang. The horizon is just the limitation of our telescopes and the decay of photon energy over vast distances and most importantly, this observable horizon we see is moving through that infinite universe at different speeds at different times. Perhaps going through cycles. This would explain why we see the universe expansion speeding up. It's not, it's simply oscillating as this observable sphere completes a cycle and the arc of this cycle has slow points and quick points.
Stopped watching at BetterHelp. That business needs to end, and I struggle to respect anyone who profits from the anguish and pain of others. You deserve better, Dr. Smethurst. Your followers also deserve better. You are selling vulnerable people who trust you to a predatory company.
This has been mentioned in the comments multiple times now and they still pop up as sponsored.
all advertising & sponsorship on yt is disgusting. prey on people's weaknessses, or force feed people something long enough until they give in. marketing is one of the main reasons we have insane levels of consumerism which leads directly to environmental issues. it's a backbone of capitalism. recommed you use one or more adblockers, watching yt with no ads is fantastic.
@@daos3300sure, but tricking me into subscribing to a VPN that sells my private data is less serious than tricking me into paying for unlicensed therapy from people paid by the word.
Yt is tracking blockers and restricts access to those that block ads “it’s how we make our money “
@@daos3300correct but remember this entire UA-cam with servers, and billions of storage cost is possible because of same ads, nothing comes for free
Hi Dr Becky, Could the reason for the cosmic background radiation being so even be down to the pressure that the plasma was experiencing up until a point then it allowed the association of subatomic particles? Testable with plasma physics equipment and might explain the issue simply.
Hi Dr Becky. I follow many science channels, but yours is one of my all-time favorites. I have a question. I’ve reached the end of my brain’s capacity to figure this one out, so maybe you can help.
My understanding is that the Cosmic Microwave Background is the oldest light in the universe… which we have the capacity to perceive. And yet, there still exists a cosmic horizon, beyond which exists light (younger light) that’s too far away for us to detect, due to inflation.
I’m having trouble reconciling these two things. We can see the oldest light in the universe and yet there are potentially younger galaxies too far away for us to see. I THINK I’ve worked it out in my brain, but a concise explanation would be amazing.
I’m sure the answer is simple… My brain is just fumbling a bit with this one.
Thanks!
Another incredibly interesting video!!! Love those bloopers too!
Hello Dr. Becky, could you provide resources that would explore why entropy may or may not be related to the cosmic background radiation issue? I'm wondering if what we see is just like a hot cup of coffee in a cold room if that makes sense. I'm just a layman with limited understanding of physics and my question may be spurious. Please feel free to just say that. :)
It's hilarious to hear physicists talk about cosmology while we're living through all of our models getting trashed by recent observations. And the theories just keep getting weirder and weirder, and less and less coherent, and nobody seems to mind. They never just throw up their hands and say "We don't know. Nobody knows. And our theories are ridiculous."
Instead of proposing that the speed of light changes, does the application of time dilation cause the same problems? For instance, in the young universe, depending on regional density time may have been slower relative to what we experience now. What effect would this have on our observations? Does the speed of light remain constant based upon the dilated time in which light would appear to move slower, or remain constant based on our perception of time that would actually make it appear to move faster (if a second is 10% longer relative to us, does c appear 10% faster or 10% slower for that region)?
As a Californian by birth, nice shirt. ;)
Also, nice video. I’m curious: at a hunch level, do you suspect inflation is (at least partially) wrong? What do you guess that future research might turn up?
Hi, Dr. Becky! On the one hand, we learn that the CMB was released when the universe reached a certain temperature. On the other hand, we question how the whole CMB is all the same temperature. Given the first fact, why is the second fact surprising? I guess there could be some variation in the collision speed it takes to ionize a neutral atom, for example from quantum mechanics or the effectively randomized characteristics of each impact. But what if you average that out over about the same number of atoms as the Laniakea supercluster? (I think that's the approximate mass that was in each pixel in the CMB, but it's extremely large regardless.) Would we really expect to see anything but the tiniest variation? What am I missing?
About the horizon distance. Wouldn´t gravity waves have an influence on the distance the light needs to travel? I assume that the light (or anything else) than has to travel up and down the ripples instead of the otherwise flat space-time which is a longer distance, like going along a sine-wave instead of the x-axis. I have no idea what the amplitude of those waves is or if that is even detectable, but might that not give a different result?
Giordano Bruno nailed it: it's infinite expansion and infinite contraction at the same time. The finite point of the big bang is analogous to the finite point of super-massive black holes at the center of galaxies. Dark matter is perhaps more mere novel matter, forged in a potentially unobservable process (aside from side effects) between the interplay of universe-scale extremes. We could potentially see this in data by either observing a loss of energy apparent in the system if we can ever see a graviton (that energy could potentially be going towards the closest, biggest "bucket"). We could potentially see this in data by continuing to observe dark matter clusters (as they become light). Or, perhaps this generative structure could be mathed-out right now by projecting if the milky way itself sufficiently recreates our own observable universe given some odd 13.78 billion years (though that age may have to be rethought).
Im not anywhere close to a physiscist but I have a question. Is it possible that at the start of the universe the amount of energy present (say photons) that had no mass was more, so the gravitational pull on what is the edge of the universe is less allowing for a greater amount of inflation, but then because of all the high energy photons around that more turned into mass which then produces more space time curvature which then slows the expansion.... and then i realise that doesnt slow the speed of lighy
"-So, how big is your anxiety, Becky?
-Well, doctor, on a cosmic scale..."😁
Thanks for keeping the 'bloopers' in :-). And: when shown the images around 0:35, it almost seems like mirror images? Like we're living in a donut universe, where we can look at that distant object from both sides while light is bended traveling towards us in the donut universe.
Cyclical Universe segment repeating cyclically ...... well played, Dr. Becky.
No. It doesn't matter that the distance between parts of the Universe are not in causal contact with each other. The factors that created the conditions in one part vs another all came from the same initial situation. Light Speed limit plays no part in the uniformity of the overall warp & woof of the fabric of existence. Ms Becky keeps talking about "the parts were/are too far from each other for Light to inform..." and all I keep saying back to the screen is "It Doesn't Matter"...
All the stars in the nite sky, and none of them hold a candle to you my dear Dr Becky...
Do you have to vary the speed of light, or could it be accounted for by varying the expansion rate of the universe?
There is another perfectly good explanation for the so-called “horizon problem:” that WE are observing from the CENTER of the expansion… ergo what we observe in any direction in a symmetrical expansion will be the same. Materialists of course reject this because it would indicate an intentional and directed creation.
10:43 -- Perfect timing, I was just starting to get distracted.
10:49 -- Perfect timing, I was just starting to get distracted. What? Oh. Circumlocution cycles predict more of the same.
Upper window mounted ERVs are going to be real game changers. So long as they can be networked to individual room sensors and set to work together you can mimic a ducted system pretty closely.
I know ionization isn't great because of ozone production, but what's wrong with hydroxl? Panasonic seems pretty convinced it's a better way to deal with ultrasmall particulates and odors than high pressure loss HEPA filters and expensive carbon capture.
Becky, I'm not a physicist at all, but I sometimes wonder... in all these years, CMB always measured the same, rendering identical maps of temperature? Or (even tiny) deviations were found?
Dr Becky, more and more you are convincing me of simulation theory.
So Dr. Becky managed to earn a Doctorate and not have anxiety? That alone is an accomplishment.