Is The Universe Finite?

Is The Universe Finite?


Thank you to Brilliant.org for sponsoring
PBS Digital Studios. Space is big. You just won’t believe how vastly, hugely,
mind-bogglingly big it is. Although according to a new paper, it may
literally be infinitely smaller than we previously thought. Every time you walk out the door, light from
the Big Bang strikes your face, enters your eyes. This is the cosmic microwave background radiation
– the left-over heat-glow from the very early universe. We can’t see this microwave light with our
eyes, but we can catch it with even a simple radio antenna. As soon as we became aware of its existence
we’ve been feverishly building better and better devices to collect it. Why? Because it encodes so many secrets. And within this light, a group of scientists
have just found evidence of the limits of space. A clue that our universe may be actually be
finite in size. Today on Space Time Journal Club we’ll delve
into the Nature Astronomy paper that just reported this: Planck evidence for a closed
Universe and a possible crisis for cosmology by Eleonora Di Valentino, Alessandro Melchiorri,
and Joe Silk. This is the map of the cosmic microwave background
– the CMB – made by the Planck satellite. We explored in a previous episode how that
speckled pattern is the frozen imprint of sound waves that reverberated through the
first few hundred thousand years after the big bang, only to be frozen in place as the
universe cooled. Analysis of the sizes of these speckles from
previous satellites, and the initial analysis from the Planck map, pointed to a universe that
is infinitely large and geometrically flat, and is dominated by the influences of dark
matter and a constant density of dark energy. For the most part this has agreed with our
observations of the modern universe. But more detailed study of the Planck data
has started to reveal tensions. We’ve talked about this so-called crisis
in cosmology – the Planck team calculate an expansion rate for the universe that does
not match the expansion rate observed today – particularly the modern expansion rate determined
from supernova measurements. And that’s even accounting for accelerating effect of
a constant dark energy. Despite this tension, the teams agree
on lots of things, including fact that the universe is, as close as we can tell, geometrically flat and infinite. But, I’ll come back to what exactly what I mean by that. But even this agreement seems to be fading. In the new study, astrophysicists claim to
have found clear evidence in the Planck data that the universe is NOT flat, but rather
curved inward on itself. If they’re right, the universe is not infinite
in extent. Before we get to the new study, let’s do
a super-quick review of geometry. Albert Einstein’s general theory of relativity
allows for three simple geometries for our universe. We have 1) a universe with positive curvature. The 2-D analogy for this is the surface of
a sphere, so a our 3-D space would be like the surface of a 4-dimensional sphere – also
known as a hypersphere. Just like with the 2-D spherical analog, lines
that start parallel in such a universe eventually come together. Such a universe has a finite volume, just
as a sphere has a finite surface area. If you travel far enough around you’ll get
back to where you started. Then there’s 2) the negatively curved universe,
analogous to a hyperbolic plane – an infinite saddle shape. All paths through space diverge from each
other. Such a universe is open – space goes on forever. And finally 3) the universe with zero curvature
– a geometrically flat universe. Parallel lines stay parallel, your high school
geometry still works, and again, space in such a universe goes on forever. The geometry of the universe is determined
by two things: 1) the mass and energy it contains. More stuff in the universe – a higher energy
density – means more gravity, which tends to pull a universe in on itself – it gives
positive curvature and closes the universe – making it finite. And 2) the rate of expansion. Rapid expansion tends to give negative curvature
and open the universe – make it infinite. The combination of these factors determine
the geometry. Like I said, previous studies were pointing
to a flat universe. For example, by looking at the geometry of
gigantic triangles defined by the largest of the speckles in the CMB. The curvature measured was consistent with
being zero – flat – but there’s always a degree of uncertainty due to the imperfect
nature of any measurement. The curvature COULD have been very slightly
positive or very slightly negative – just as the surface of the Earth appears flat if
you’re standing on the ground. It’s only when you get some elevation that
you see the curvature. But it turns out that evidence of very slight
curvature may have been hiding in the Planck data all along. The new study went much deeper into the Planck
data than just looking at triangles defined by the biggest blobs. The team analyzed ALL of the blobs. More accurately, they analyzed what we call
the power spectrum. That’s just the graph showing the distribution
of the different sizes of blobs in the CMB. Blob size is on the x-axis and number of blobs
of that size on the y. So we can see that we get a lot more blobs
at some sizes compared to others – with most blobs at around 1 degree on the sky. We talked about the power spectrum in enormous
detail in that earlier episode. One thing that we didn’t talk about is how
gravitational lensing influences the overall shape of the power spectrum. See, the light from the CMB doesn’t travel
straight to us. It passes through a universe full of galaxies
and galaxy clusters – all of which have enormous gravitational fields that act as lenses, slightly
deflecting the path of those rays of CMB light. The result is like looking at the universe
through a lumpy pane of glass. Everything is very slightly distorted. In the case of the CMB, this results in a
sort of smoothing or blurring out of the power spectrum- the peaks are less sharp than they
would be otherwise. Our brave scientists were able to determine
the amount of lensing present in the Planck CMB map – and they found way more than would
be expected for an open universe. See, gravitational lensing is caused by mass
– both dark matter and atoms. More lensing suggests the universe has a higher
energy density than previously thought. Remember that more energy density tends to
introduce positive curvature. The new study claims there’s enough extra
matter revealed by that lensing to actually close the universe into a finite hypersphere
surface rather than an infinite flat hyperplane. Obviously I’m glossing over a lot of details
here. These scientists didn’t just measure the
amount of lensing on its own. They created a model that included all of
the relevant parameters – the expansion rate, details of inflation, the amount and behavior
of all different types of mass and energy, etc. They found the range of models that fit the
shape of the power spectrum, and for the most part those pointed to positive curvature. That curvature was slight – meaning the universe
is still unthinkably vast, but if this is right then it’s not infinitely large. The researchers claim a greater than 99% statistical
confidence for positive curvature in this analysis. So, is the universe really closed and finite? Does that mean there’s enough matter to
cause it to re-collapse again? And can we find a faster route to India by
traveling all the way around the cosmos to get back to where we started? Well even if the universe is finite, it’s
still expanding and that expansion is accelerating. It will NEVER recollapse unless its physics
is very different to what we think. Also, beyond a certain distance from us that
expansion exceeds the speed of light, so there’s no lapping the universe regardless of its
geometry. There’s also a reason to be cautious before
we conclude that the universe is closed at all The researchers looked at a different indicator
of the amount of gravitational lensing: the so-called four-point correlation function. In short – lensing by a cluster of galaxies
tends to draw rays of light from different blobs together. A random distribution of blobs ends up with slight
clusterings. The four-point correlation function found
an amount of lensing consistent with the old result of less energy density and a flat universe. So why is there a conflict given that 99+%
confidence? It’s important to know that this percentage
is NOT the likelihood of the conclusion being correct. It’s the statistical confidence in the model
fit given the assumptions that went into the model. In other words, IF all of those assumptions
are correct then there’s less than 1% chance that a flat universe would look like
a positively curved universe just due to random uncertainties. So, there are three possibilities really:
one is that the universe really is positively curved and finite. Two is that the assumptions that went into
the model are wrong. We’ll come back to these. Three is that there’s a mistake – an issue
with the data. Let’s talk about that. Some very subtle systematic issue in the calibration
of the Planck data may have led to the unexpected results for both the geometry and the expansion
history of the universe. For example, the Planck CMB map required extremely
careful subtraction of all other sources of microwave radiation. If this step, or something like it, wasn’t
done perfectly it could lead to bad results. The “official” analysis of the Planck data
was extremely careful so any mistake would have to be very subtle. The authors of the new study redid part of
the Planck analysis to claim this evidence of positive curvature – which the Planck team
had themselves decided wasn’t significant. So did the new guys do a better job and prove
everyone else wrong? That would be surprising because most data
points to a flat universe. If this lensing signal is real then maybe
there’s curvature, or maybe its an indication of some unknown physics. In the case of the discrepancy in the expansion
rate, hidden physics is the great hope of many physicists. That “missing physics” could turn out to
be the subtle clue needed to push our understanding of the universe to the next level. For example, if the expansion rate of the
universe really has evolved it may mean that the behavior of dark energy is changing – and
that could reveal the true nature of dark energy. In fact, if the universe really is curved
and closed, the discrepancy between the early universe and modern expansion rates becomes
even stronger. That’s because the previous calculations
of that discrepancy assumed a flat universe. So, physicists get even more excited if this
result holds up. OK, lots of ifs and buts – and that is okay,
because that’s how science works. We are very careful about how we talk about
confidence and proof. The new result opens a tantalizing new possibility,
and also hones in on the real physics of our universe – even if that means honing in on
any errors we’ve made in our analysis. The tension between the Planck results and
other cosmological measurements seems to be growing. The good news is that future missions will
surely resolve it. Perhaps identifying any errors, perhaps discovering
the nature of dark energy, and perhaps verifying the positively curved, finite geometry of
space time. If you want to dive deeply into understanding
the building blocks of space time then you need to study quantum theory. Brillaint.org has a fun course called quantum
objects that include interactive challenges and problems to solve. Honestly, the best way to wrap your head around
quantum theory is to play with it. In this course you can explore the experiments
of quantum mechanics and use them to construct equations of motion, laws of physics, and
systems of measurement based on the algebra of quantum theory. Effective learning is about problem solving. To learn more about Brilliant, go to brilliant.org/spacetime. OK, so in the last episode we explored the
scientific and philosophical implications of the anthropic principle. But before we get to that, I want to invite
you to check out the Space Time discord, which you can access with the lowest $2 patreon
tier. There are loads of people over there talking
about all sorts of fascinating smart-person stuff 24-7, as well as making suggestions
for the show – some of which we’re definitely going to do. Here’s a discord question from Damagast: do
all PhD physicists casually talk about complex stuff like on Space Time videos, or do most
employed physicists just shut up and calculate? Well, actually, both. I know plenty of physicsts who LOVE talking
about the most complex, speculative, and philosophical stuff over a beer, and some who are laser
focused on their own field and don’t really think far beyond it. That’s ok too, but I prefer beers with the
former. So let’s see what you had to say about the the last episode. Scott Barnkow asks what are some testable
predictions of the refined anthropic principle? Well, I’m glad you asked Scott because next week we’re going to tell you about a very clear one: Stephen Weinberg’s prediction of the cosmological
constant years before dark energy was ever discovered. Speaking of next week, Vladimir postulates
that if there are to be trillions or quadrillions of humans in future space-faring civilizations,
isn’t it weird that we happen to be in the first 100 billion? Well, nice way to invent the doomsday argument Vladimir… like 35 years after Brandon Carter first proposed it. And we’ll be digging into that next week also. And we’ll answer your question P.S.Y – what
exactly DOES Nick Bostrum mean by “reference class” – as in, how do you choose the sample
of observers from which you consider yourself randomly selected. In order to save ourselves from imminent doom
we may have to hope future generations are NOT in our reference class. Tune in next week. Penny Lane notes that anyone believing in
a Goldilocks universe clearly never experienced English weather. Well, besides being a witty quip, this gets to an
important point: anthropic seletion only demands that our universe be able to produce observers
who think about the nature of the universe. There’s no reason they need to be in any way
happy about the universe they observe. In fact I feel like horrible English-style
weather may be strongly selected for. It encourages us to sit inside and think about
the nature of the reality. Regis Bodnar has a great point: while it may
be technically possible to observe a typical universe, it’s perhaps impossible to define
one. So, let’s see. How do we define a typical universe? Well it would be one whose particular configuration of fundamental constants gives you a universe similar in some respect to
lots of other configurations of constants. Honestly, that’s probably some massively exponentially
accelerating universe because the cosmological constant in most universes seems likely to
be a lot higher than ours. So a typical universe is mostly empty Singapore Breaking News likes to play space
time loudly so mom thinks they’re getting more brainy but in the background is playing
games on steam. Well, jokes on you Singapore Breaking News – that is
a brainy trick, so you got smarter despite yourself.

100 Replies to “Is The Universe Finite?

  1. Honestly the idea of the universe being flat is ridiculous, explosions don't go in one or two directions, you can see stars in every direction of the planet.
    Sure it could be that it's relatively flat, but then you need to explain what is limiting it from expanding in all directions mostly evenly.
    It's kinda preposterous that scientists would think the universe is flat.

  2. Is this meant to be news? As far as I knew we've known that the universe was finite for quite some time.

    Finite, but unbounded.

  3. Hey you 👆 Yeah you! Close YouTube, put your phone on your dresser and go to sleep. This video will not help you sleep, it's 3AM…

  4. Somebody needs to surpass this simple scenario, universe is round or flat or have a negative curvature, what about a complexity shaped universe and dinamic, not like a silent lake surface but more like a stormy sea full of wawe of different sizes.

  5. How can wormholes help in reaching your destination faster than light could if the universe has zero curvature? The shortest distance between any two points is always a straight line and in a geometrically flat universe nothing's preventing you from travelling in a straight line except for any obstacles in your path. Making it impossible to take a shortcut because you are already taking the shortest path, right??

  6. Does flat necessarily mean infinite? I've read that a 4D torus would also appear flat, but is finite as going in any direction leads you eventually back around

  7. Physics is always different than what we think. Scientists can be so short sighted sometimes… oo! We found an extra solar planet! Now we know there are other planets out there! (Duh) they really need to rely on common sense a bit more.

  8. BTW it's proven now the universe is round and finite also we live in a 4 demontional sphere but the additional diamontions are still unknown 🙁

  9. I started learning about space with John Michael Gordier but after discovering PBS Spacetime my quantum physics soon surpassed JMGs channel. Recently I've been looking at a lot a quantum physics dank memes and I'm nearly beyond PBS Spacetime aswell.

  10. Well after listening to the explanation that's some really misleading name.

    Anyway it seems like the whole issue is proving whether the expanding universe means only that galaxies on average scatter apart from each other at some speed, or if the spacetime itself stretches as that would change the mentioned geometry from flat to something else.

  11. A hypersphere in Minkowsky space? Would this imply into space not being spacelike somewhere? I can't wrap my head around a timelike tangential direction and the degenerate metric at the boundary.

  12. Question:
    Let's say you fall into a supermassive black hole, and an outside observer would see you approach it but never quite make it there. And then they wait until Hawking radiation eventually evaporates the black hole. What happens from your perspective then? Will the Hawking radiation catch up to you as you fall in?

  13. guys… i am sorry as i am very interested in these topics, but, come on… the observatory tools are so laughably small compared to what we will have once we live in several solar systems, that… come on. Leave that question be. It doesnt matter for now what "answer" we might get.

    measure this stuff with a telescope that has an apperture of 4 light years, then i will take these speculations serious…

  14. Does this contradict eternal inflation? It seems to me that an inflating universe would have to be hyperbolic, given the massive expansion.

  15. nothing wrong with english weather. rain is wonderful. wind is wonderful and the coldest it gets here is two degree celsius in winter. just put a coat on and you are fine. i dont even ever have to put the heating on. typically being an island, the maritime climate makes winters milder and summers milder. only in recent years climate change has affected the summer making it really really hot and the winters have been more mild than before. when i was a kid they went down to minus eight. but that was great as it meant snow fights. consider northern finland-they embrace the climate by having winter sports and sledging with dogs. rain means no drought. whereas lots of peoples live in places where its too hot and hardly any rain. so britain is a perfect goldlilocks climate and only idiots complain about it. i cant understand why people, especially paler skinned causasians who are physically adapted to live in colder climates of northern europes, want hot weather. in hot weather humans sweat more, because its too hot so the body is having to cool itself down. and we need to drink more fluids as we are losing fluid in the heat. there is risk of dehydration, heat exhaustion and sun stroke, as well as skin cancer. so only idiots want hot weather. the most optimal temperature for humans actually is room temperature-with is about fifteen-to seventeen degrees celsisu. loads of places in america are like hot and dont get enough rain. look at california at the moment ravished by bush fires. . and as a brit im perfectly adapted to colder weather and plenty of rain. rainy overcast days , hail and snow make me very happy, and thunderstorms too.

  16. 0:20 … The Milky-way is already mindboggeling big. Heck, most people can't even wrap their heads around the size of our solar system.

  17. I think we realy need a better map of the cmb and some other crucial data plus a better theoretical understanding of the universe to draw any more conclusions into this topic

  18. So spacetime is an infinitely long 4d cilinder with 3 dimensions curling up (spatial) and 1 extending forerver (time)?

  19. What if the scale at which we're looking at the universe can't see the curvature of the universe because the Delta is statistically indistinguishable from errors in measurement.

  20. Question: Doesn't dark energy show that the universe is open/negative curvature? If two galaxies move parallel to each other, but are too distance for their mass to be attractive over dark energy, then the two galaxies will diverge. This is exactly in line with the definition of a universe with negative curvature.

  21. But how can a finite universe expand, it is finite remember. If it expands, it is technically infinite because new space appears all the time

  22. Supposedly the idea of multiple universes is not applicable for bubbled infinite universes. Because infinite universes do not have boundaries, so where does the next universe begin?

  23. Question: in the calculations where the negative curvature of dark energy is calculated against the positive curvature of gravity, there seems to be a base assumption that if the universe lacked both, then it would have 0 curvature and be flat 'by default'. Is there justification for this assumption? Is a flat universe somehow more 'natural' then one where space has an intrinsic positive or negative curvature, before gravity or dark energy are introduced?

  24. So for the universe to be flat and infinite it must contain exactly the correct amount of mass? If that were the case then surely we can't be in a flat universe. We're either in a very slightly curved closed universe or a very slight curved open universe, but we can't possibly be exactly balanced to infinitely many decimal places. What am I missing? It seems like the only way for the universe to be truly flat is if the balance of matter and dark energy is determined by some deeper principle to be exact, it can't just be an emergent property. Again, I clearly don't understand something.

  25. I was interested to see that the diagram at 6:10 showed the energy paths shifting from blue to red.
    Was this merely artistic licence or, perhaps, a Freudian desire to indicate an alternative cause of red shift?

  26. I've always pictured the universe as a growing faster than light 4 dimensional sphere… a flat universe never made sense to me, this is fascinating.

  27. Is the universe infinite? Please explain how it could stop with nothing (not even empty space) past the observable universe. Until you can literally explain that your thoughts are meaningless.

  28. What a stupid video… Scientists and astrologists agreed that the change in star formations is caused from the universes expansion decades ago… In short yes the universe, in our eyes currently, is infinite because we don't even know where or when the universe begins and ends.

    You know!… Back before Pluto was no longer considered a planet…

  29. The universe is supposed to be all that exists, does that not mean therefore that it must be infinite and cosmology is studying only a domain within it. If it curves, what is a the centre of curvature? If it’s flat, what lays above and below? Is that not part of the universe too.

  30. 0:22 Wait? Why only every time I walk out the door? Why is the universe ambushing me like a bad teenage prankster with light that I can't even see?

  31. Why is it so hard to comprehend that the universe can both be a perfect sphere, and because it’s expanding infinitely it is also flat. I.e. from any point in existence where an observer could view its own position relative to the infinite sphere it would appear to be infinitely flat. That is the nature of infinity. Therefore existence is both infinite sphere and infinitely flat.

    Existence is a bead of light, relative in size, as tiny as it is infinite, and we are all inside. Careening through an endless bulk, in everything at all, falling in a perfect circle yet the straightest line of all.

    My poem, found here

    https://www.poems-and-quotes.com/poets/33552

  32. Have we ever successfully used the gravitational lensing to resolve an image of our own galaxy? Would this be virtually improbable to capture and know with high confidence that the image is of our own galaxy?

  33. Question: If the overall curvature of the universe is determined by the amount of gravity generated by the energy, matter, antimatter, and dark matter within the universe (a constant), and the effect of Dark Energy in causing the expansion of space, how does the period of Inflation play into this? Surely during Inflation as Dark Energy was (briefly) so much more powerful then it is now, that should have caused far more negative curvature to spacetime then it did afterward. Thus if the values are perfectly balanced NOW, surely the universe overall must have had negative curvature during inflation.

    This would seem to be an even greater problem if the theory proposed in this video's paper is true and the universe just barely has positive curvature, as the far greater negative curvature from inflation would probably have caused the universe to INITIALLY have negative curvature, and then when inflation ended somehow that curvature needs to snap into positive curvature, turning an infinite spacetime into a finite one.

  34. One very important conclusion from the observational data of the cosmic microwave background (CMB) is that the CMB defines a cosmological frame of reference called the CMB rest frame. The home galaxy (Milky Way) is moving at a speed of around 552 km/s with respect to this rest frame and this has been measured from the anisotropy of the CMB radiation. From the velocity of the Milky Way galaxy we can identify a CMB rest point using Hubble's law and find that the Milky Way galaxy is located at a distance of approximately 26 million light years from the CMB rest point.

    Now when we consider the density of matter in the universe, then it is possible to show that this is consistent with there being an event horizon at a Schwarzschild radius of 8.77 billion light years at a time 13.8 billion years ago. The CMB is not an echo of a Big Bang but instead is radiation generated within the universe and turned back at this event horizon. All reasonable estimates of matter density lead to the predicted existence of this event horizon which should be detectable.

    With this explanation in place the age of the universe is much greater than 13.8 billion years and the first galaxy formed an estimated 126 billion years ago.

    https://www.academia.edu/5009126/The_evolution_of_the_universe
    Richard

  35. It's all an illusion: The apparent change in the size of the universe in 4D (y) is a function of the real change in size in 5D (x) using the space-time density ratio equation y=1/x^3. This is based on the spacetime density change ratio of the volume of a sphere using compressible space-time where real distance between objects is measured from a 5 dimensional space-time perspective while apparent distance between objects is measured from 4 dimensional space-time perspective. Thus, the universe is shrinking while it appears to be expanding and dark energy is an artifact of incomplete perception.

  36. To me, the closed geometry supports the M-theory description of "bubble universes" that can connect through branes to fabricate a multiverse.

    Our universe might be closed/finite, but that doesn't put a limit on the number of alternate closed/finite universes according to multiverse theory. Of course, if you consider black holes to be "inside-out" universes themselves, they could be reflections of alternate universes and therefore indicate a limit to the number of alternate universes outside the cosmological event horizon.

  37. I think the more logical theory about how the universe we live in is is the one I read on a 1990s book named Star Maker which says we live on the 3D "surface" (or projection) of a 4D "sphere".

  38. The universe is built by allah swt, so it is measurable…. The size is how much Allah swt wants and he said in Quran that it is be created bigger than it was….

  39. If the universe is finite would light eventually be bent back from the edge to the center and in that massive collection of energy recreate the original singularity once all reflected light had reach the center thus causing another slightly smaller big bang without consuming the existing matter already in existence.

  40. Understanding simplified: So, when a question will get an answer, this answer will became a new question. Therefore, this goes on forever. Shit… 😂 Brainfuck at it’s most beautiful form.

  41. Using equations to map the refraction of sound to get an origin point to measure how far the sound emitting object location was is what I used to do. Those measurements are always considered estimates even though we had equations for them and their distances were very small compared to space. I'm not sure how accurate their lensing diagram is.

  42. Is the amount of matter created at the Big bang finite? If so, there must be an edge of the matter sphere, there is no more matter if you travel further form that edge.

  43. If the certainty of the universe beeing finite is 99% and 1% of it beeing infinite, when a Person looks at the universe, the Chance of it beeing infinite would still be infinetly higher than the Chance of a finite universe, because there are infinetly more persons existing in an infinete universe than in a finite universe.

  44. Many/most recent cosmological hypotheses are based on CMB observation but can you explain how is the CMB source data interpreted, how are EM measurements turned into "the" Mercator projection of the early Universe (geometrically)? What assumptions and simplifications are used to create "the map"?
    I mean CMB photons reaching an observer at a point in time arrive from a spherical (barring gravitational lensing) surface which expands at light speed. Which way are detection from this receding spherical "slice" interpreted as the map of the early Universe?
    Does our CMB map (es viewed from Earth) change over time as the CMB "source sphere" recedes or are temporal changes insignificant / can be ignored?
    Is movement of our observation point (Sun, Milky Way, Virgo, etc.) relative to CMB compensated (how?) or again insignificant?
    How are non CMB sources filtered? How are CMB photons separated from closer, lower frequency sources at right distance to be red shifted into CMB frequencies?
    What is the scale of the CMB map? How far was CMB from "Earth" at the time of recombination, what size of sphere does the map depict?
    (etc. :))

  45. Aparently the rest of Youtube doesn't like me anymore because I'm honest and to be Honest I'll Speak using Math Symbols

    U + r / ((M^ i) + H ^ e + a) – d == (U+r) + A * 2Me^i == Brighter than me…
    You are Over my Head = You are A Star to me and the Limits of my Eye

    Wau^e + (tau *L) = wau ^ -e + pi * i == Beach Time & the Tao of Wau "The limits .. b^i*t*c/h spit Pi in my i"

    Not a Mathemetician, so probably doesn't work in that sense,
    just thought it was clever and funny..
    One day someone might appreciate effort.. Too bad Feynman's not around anymore..

  46. A couple of heuristics that i've found to useful with analyses in the past are (1) it's not constant and (2) it's not linear. I do wonder sometimes whether something similar would apply to exactly flat universes…. it's a rather fascinating and lovely one whatever it turns out to be.

  47. 8:06 But new paper presents finding (again?) that the expansion is not accelerating. Earlier conclusion would be result of limited and biased (directionally clustered) observations. There would be no need for dark energy to explain observations.
    https://www.aanda.org/articles/aa/abs/2019/11/aa36373-19/aa36373-19.html
    https://arxiv.org/abs/1808.04597

  48. One of the least recommendable video on universe. Something about the way the guy is explaining make it sound SO boring. PBS please do a better job at explaining. This is not very good.

  49. Aren‘t there any quantum mechanisms that disturb (or redirect) the photons from the CMB on their immense long journey? Fluctuations, spontaneous collisions, etc. And wouldn’t that cause the CMB, as we see it, to be “false”?

  50. All science seems to follow a pattern where people make ridiculously complex and detailed analysis of the "currently accepted" without challenging the status quo, until the status quo somehow breaks on it's own, and then someone makes another breakthrough that defines our progress for then next 300 years and everyone laughs at all the detailed papers about the previously accepted truth.

    I don't know where I was going with this… I mean I build automation, so the whole purpose of my job is to literally do the exact same thing.

  51. I'll fully admit that I too have Space Time in the background while gaming or writing code. I do the same thing with a lot of sciency channels.

  52. In my opinion the big bang was just a collision of two particles that got accelerated in a very large version of a large hadron collider in an outer verse and our verse is still located somewhere in the particle accelerator as leftover from the actual particle collision, what at least would explain why the universe is expanding. Any collisions we perform in physical experiments just spawns new tiny verses. Due to the mass difference between the outer verse and created verse, one second in the outer verse is probably our hole lifetime in new verse. Sounds like inception?! The main issue is, we still do not really know what caused the big bang, which we are almost certain of having happened somewhere 14-18 billion years ago, and what was before the big bang.

  53. In summary: all evidences show that we, human beings, don't know nothing about the universe (or multiverse).

  54. My personal take on this even if there is a finite scatterering of matter there is zero wall at the end of the matter. Also do not believe that the big bang was the beginning of everything. I am just an enthusiast but not convinced that everything came out of nowhere, maybe everything is expanding from a previous universal collapse. Time I'm sure existed always. Just my opinion.

  55. Assuming one could keep up and overcome the speed of the expansion of a positively curved universe, would it be theoretically possible to travel away from a certain point and end up "looping over" and reach it from the opposite side?

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