Space DOES NOT Expand Everywhere

[@Psychonaut165]

Out of all the physics channels I understand nothing about, this is my favorite

[@_PatrickO]

Other top channels for the average person are: Veritasium Sabine Hossenfelder The Science Asylum Fermilab

[@juezna]

@@_PatrickO Veritasium has had a couple of controversial videos, like the one with the self driving cars that was clearly a paid content to promote the technology. I think that type of content really compromises the integrity of a channel that sort of claims to be scientific. Still, it does have some good content but just take it with a grain of salt.

[@_PatrickO]

@@juezna You dislike him for a single non-science video he did? Grow up. I just searched it and saw debunking videos. It is unbelievably pathetic to get so worked up over a self admitted limited review of waymo that you think about it daily and make debunking videos. The people obsessed with hating self driving cars are disgusting luddites.

[@juezna]

@@_PatrickO wow Patrick, you seem to have me worked out because I do spend my days with a sense of consternation for the existence of the Veritasium waymo video, and even more so, developing a deep hatred for self driving cars. Thanks. You've saved my life. And of course, I promise not to make you so angry with observations about your so beloved youtube channels ever again.

[@mrspaceman2764]

WE'RE SHRINKING!!!! 😱😱😱😱😱😱

[@pixartist8190]

You always pick up on the "but why" questions that pop into my head when thinking about these things. I love it.

[@DrWhom]

there is no why, only how

[@aprilvereen3169]

@@DrWhom but why 😏

[@jacobsaintjames]

Happiness is being able to wrap my brain around an episode of PBS Space Time.

[@SSMLivingPictures]

So YOU'RE the one!

[@EduardoLauandeTeixeiradeSouza]

Every episode of PBS Spacetime is for me a physics or cosmology/astrophysics/astronomy class. the only difference is that it uses as little math as possible without sacrificing clarity and precision. Without demerit of other programs here in Brazil or abroad, PBS SpaceTime is my favorite channel. Thank you all a lot!!

[@Ormaaj]

The alien race simulating our universe had to do a memory upgrade duh. Last time they tried inserting new memory they got massive inflation. Solution: gradually interleave new bits amongst the old bits. The only side-effect is red-shifting of distant galaxies, but probably no one will notice.

[@_caracalla_]

it's not a bug! it's a feature of course!

[@ModernandVintageWatches]

Great 👍

[@sithlorddread8721]

Yeah it's actually explained by xyz, don't look into it

[@user0K]

It's Gmail. It will reach 15gb and stop

[@SamtheIrishexan]

The way humans are i find it likely that we are the equivalent of single cell infections on a single blood cell inside God.

[@spacedragon3478]

Actually, this video answeres some questions I've had since I was 16 or so. Never could this questions be answered by anyone I asked... Until now! I really love this channel for explaining phyiscs in an understandable way but at a level high enough for me to be satisfied. Thanks a lot Matt!

[@JamesJordanson]

It only took them more than 3 years to get to it, but at least they eventually did, unlike others who constantly skirt around it :)

[@uberfu]

If for nothing else - this kind of information corrects all the bullsh*t we were taugh in school. I have found for the many years I've been out of school that lower level education is mostly wrong and flawed.

[@ReapingTheHarvest]

​@@uberfu Higher level "education" is even worse.

[@thedarkercarter]

So the "pinched gravity" part is probably the thing that I've been missing in understanding the expanding universe. So I have to give a thanks for that. Like I knew that space was expanding more in the far reaches but nothing seemed to explain WHY it wasn't happening in the galaxy. So along with that and the Metric I now have a much better understanding!

[@Pseudothink]

Just don't watch Moonfall. Watching it has been shown to selective kill off brain cells used for understanding physics and cosmology, in the name of willing suspension of disbelief.

[@Mr.Nichan]

It's important to remember that time-like geodesics are the paths of objects affected only by gravity and momentum, i.e. orbits, or ballistic trajectories, or falling. The motion of most stars is mostly determined by gravity, with other forces having negligible effects on their paths through space-time, meaning that stars basically move along geodesics, as do planets, galaxies, and many other things. Thus, if you think of space as made up of points moving relative to each other along geodesics (I'm not actually sure how useful this is), space is orbiting and falling into galaxies, not just pinched together and stationary, with geodesics moving parallel to each other into the future like he said in the video. (I don't know if what he said makes more sense if you think of space in a slightly different or more specific way, or if he was just simplifying.) Now, to be clear, just because almost all stars are almost on geodesics, that obviously doesn't mean that all geodesics have stars on them. Every POSSIBLE ballistic trajectory (for an object of negligible mass) is a valid geodesic, not just the ones that actually have objects on them, so some geodesics are orbiting the galaxy the opposite way from most stars, some are falling into the galactic core and coming out the other side, before falling back in and repeating this (noting that the galaxy is not a point mass), a very few are obviously falling into black holes and never coming out, and some fly out of the galaxy and never return. (There are also light-like geodesics, which light moves along when it's moving through vacuum. As for space-like geodesics, I know tachyons would theoretically move along them. I don't think they're exactly analogous to physical objects, despite Einstein's talk of "measuring rods", since physical objects are usually held together by electromagnetic forces, which admittedly move slower than light, and also because it's not clear without calculation which instants of each point in the object you're assigning to the same space-time geodesic. I think maybe space-like geodesics could be thought of as faster-than-light paths between matching ticks of clocks in different locations, but that's a very problematic definition.)

[@paulembleton1733]

After listening to Roger Penrose talking about maximum entropy being the initial state of our universe, and its ultimate state which perhaps leads to another big bang, I imagined the universe as a zip file that can be infinitely unzipped, but the file size doesn’t grow it becomes more detailed, and this additional detail gives the impression of expansion for anything occupying it. From the universe’s perspective it isn’t expanding at all since it has no reference, either spatially or temporally. No new spacetime no stretching.

[@robertcairone3619]

Sounds exactly like those fractal zoom videos to me. Also, if the "unzipping" universe contains additional detail compared to the previous state, why would entropy have to increase in the positive time direction? Seems the created detail could be played against the entropic disorder so either factor could dominate locally.

[@Illiteratechimp]

I think of it more as the websites you try to hide on your browser history. Your wife or your mom (depending on your age and your living situation) accidentally finds one and they multiply as pop ups and pop unders, and expand in eternal shame and embarrassment

[@georgejones5019]

I don't believe it's expanding. The universe is massive and in constant movement, the movement is at such a large scale we cannot comprehend it. I think the expanded space we examine is just temporary and will later close. Think of asynchronus gears that are elipical shaped. So at certain points of time their edges can be farther or closer to one another, but the centers remain the same distance. It's just an illusionary effect.

[@paulembleton1733]

@@robertcairone3619 Maybe more like adding more detail to the current layer, opposed to zooming in on a fractal is seeing another layer of detail.

[@kennethferland5579]

An interesting informational perspective, though in this zip file analogy the shannon entropy never changes as the file size dosn't change, if information can never be created or destroyed then it fits quite well.

[@brutussmithicus]

This is the most accessible episode so far - I may recommend it to non-scientist friends. The concepts were more intuitive than most other episodes & the pacing meant that I didn't need to hit pause or rewind so often. Thank you so much for taking the time to create this awesome series, you have explained the concepts that eluded me during my late 80's quantum chemistry lectures :-)

[@Kj16V]

0:00 Finally, he says an explanation I understand.

[@Crackhonos]

Question: Lets imagine whole universe contains only two stellar mass stars. What the distance between them would need to be, in order for new space to be created between them ? Or how would we calculate distance between two objects in order for them to no longer be gravitationaly bound ?

[@Furrierity]

depends what ur universe is made up of

[@12MaNueL96]

It depends on their relative kinetic energy! If the gravitational energy is in absolute value greater than the kinetic energy, they are gravitationally bound, and the space in between does not expand. Viceversa if the relative kinetic energy is greater, they are not bound, and the space expands. By relative kinetic energy I mean 1/2mv^2 where v is the relative velocity. I'm sure you can find the distance as a function of the velocity and find out your answer with this :P

[@kaptenhiu5623]

@@davidbarroso1960 yes. How much is it?

[@Hansengineering]

@@kaptenhiu5623 4

[@kaptenhiu5623]

@@Hansengineering 4 what?

[@Sk1erDev]

If you had a cable that spanned the space between distant galaxies, would it experience tension?

[@angrymokyuu9475]

If you mean tension from the expansion of the universe, keep in mind that the electromagnetic force that holds molecules together is orders of magnitude more powerful than gravity, which is already more powerful than expansion at anything but intergalactic scales. Unless there's some fine detail with this particular setup I missed then there shouldn't be any detectable tension caused by expansion(this might change in a few billion years if Big Rip cosmology is true, but not in the here and now).

[@technicholy1299]

Yes, but not because the universe is expanding. The cable would bent and curved by dark matter along its entire length and this curvature would put tension on the cable. It would be pulled and distorted by dark matter all along its length.

[@deusexaethera]

If the cable were _anchored_ to solid objects in two galaxies on opposite ends of a large void, and those objects were somehow fixed in position relative to their host galaxies rather than orbiting the center, yes the cable would experience tension as the expansion of space in the void pushed the galaxies apart. But if the cable were free-floating, it would simply drift like any other free-floating object. In fact, given how little gravity is required to cancel the effect of "dark energy", it's quite possible that the gravity generated by the cable itself would prevent space from expanding in its immediate vicinity.

[@cristianosacchi]

@@deusexaethera Say that the cable hypothetically has no mass...

[@realmisteranderson]

No because it isn't anchored anywhere

[@aintaintaword666]

So if the empty space is stretching, but massive objects pinch space inwards, then there is some kind of a zero point in between, some small quantity of mass when space doesn't expand or contract?

[@bryanreed742]

Yeah, I wonder that myself. Also: does that expansive outer boundary condition slightly perturb the Schwartzchild-like solutions so that, strictly speaking, the effect is not zero but rather just too small to worry about, and in a way that's baked into the stable bound orbits such that there's no effect accumulating over time?

[@paulpeterson4216]

I had two questions, yours is one of them. The other is that, if you look to the distant past, those "parallel" lines do converge. At some point in the future do they diverge?

[@ThatCrazyKid0007]

@@paulpeterson4216 Yes, according to GR the geodesics converge into a singularity on one side and either diverge on the other side or converge again into a singularity. Given the way space is expanding, it seems the geodesics that started at the big bang are diverging out and why we think the universe is going to expand forever.

[@manoo422]

It applies anywhere that gravity is stronger than the expansion rate, so anywhere there is mass...

[@MichaelNiles]

Good question; If it's the flow of time increasing rather than space being created then I'd say no, we're just in a steady bubble of temporal flow, and that if we left our galaxy far away in the dust we'd simply experience time speeding up unregulated compared to our cozy home in our galaxy. No zero point of non-contraction/expansion found while on our journey.

[@jeff94577]

This video answers multiple questions that I've been wondering about for years and presents them in a way that shows how they are interconnected. (It even incorporates a discussion of Hawking radiation and sub-Planck-length phenomena.) Thank you for the clear presentation! I am amazed at how many of my questions actually had answers and even more amazed that they could be explained in language that I could understand.

[@michaelblair5146]

There isnt such a thing as sub planck length..

[@Andospar]

I revisited this presentation and found it as grand as the first viewing! Thank you again.

[@raurora]

This is one of your best videos. I think this is something that anyone who has tried to have a physical understanding of an expanding universe has thought about. Incredibly well explained.

[@snufkinmatt162]

If space doesn't expand inside a gravitational field, then what happens at the boundary between this and where space is expanding? Would the expanding space try to 'drag' neighbouring space with it and would you get a kind of tug-of-war between the two?

[@thedave1771]

Also gravitational fields are infinite in range, so we still need a cutoff point somewhere.

[@stefcep]

@@thedave1771 A gravitational field is just Gravitational force per unit mass. Gravitational field follows the inverse square rule, extending infinitely.

[@riccardoorlando2262]

@@hyperduality2838 You have no idea what a dual, in the mathematics sense, is.

[@Bellezzasolo]

I think the answer is that Matt has put too much reliance on the Schwarzchild metric, which assumes a cosmological constant of zero. Just like the ΛCDM model's FLRW metric neglects the fine structure of the universe, but works very well on the very large scales, so the Schwarzchild metric fails to consider the large scale, but is a very close approximation on the small scales. In the intermediate region neither metric will give you an accurate result, and you need to solve the Einstein Field Equations in full. Which is to say that expansion probably does have an effect on smaller scales, but it's so small as to be completely negligible.

[@lubricustheslippery5028]

Isn't space bending because of the gravity and that fix the difference in expanded and not expanded space?

[@mihiru]

"Gravitational field isn't something that lies on top of the fabric of spacetime, gravitational field IS the fabric of spacetime".....am gonna get a t-shirt made with that quote!

[@markrothenbuhler6232]

Here is PBS Space Time expanding our understanding and knowledge everywhere. Thanks, Matt!

[@osmosisjones4912]

Maybe the big bang started in a black spot before the previous universe ended

[@deanwalker6262]

@@osmosisjones4912 dude…

[@lucoot]

If a certain region of space has expanded more than the surrounding regions, will travelling in a straight line through the expanded region take longer than taking a detour around it?

[@osmosisjones4912]

What if the BigBang started in a black hole before the previous universe ended

[@innocentbystander3317]

Depends on the geometry for said region of space.. Is going around a tile of concrete faster than simply crossing the tile? How about a parking-lot sized tile of concrete vs a sidewalk tile? Also, what do you mean when you ask, "take longer"? What sort of masses will be affecting your travel? Time is relative, so one would need a frame of reference to answer your question.

[@terdragontra8900]

My guess is no, the universe can't expand in that way, but I'd love to hear a rigorous explanation from someone who knows what they are talking about

[@MADSK_LLZ]

Light follows the null geodesic, the straightest path connecting two points. Shine a beam of light and you'll have your answer.

[@clahey]

@@MADSK_LLZ except there can be multiple null geodesics. Think of gravitational lensing? There can be multiple paths light can take.

[@semigene]

This channel is ridiculously good. Thanks.

[@joymoding]

You guys must be mind readers up there, because this topic has been on my mind for a while now. The idea that the Planck length isn't an actual quantization of space, but rather a limit on energy-based measurement in an infinitely divisible spacetime is the only conclusion I've been able to come up with as well. But if it's true, it's immensely fascinating, because it implies there is some "existence" of space that is inaccessible by our current methods of measurement. But if this sub-planck space truly exists, then it must interact with the universe in some way (that's what it means to exist), which means there's some REAL thing out there that is capable of defining and describing space at smaller scales seemingly forever. Love all this stuff and the phenomenal videos that you produce. Keep it up!

[@CMVMic]

What makes spacetime infinitely divisible?

[@joymoding]

@@CMVMic Do you mean logically or mechanistically? Like do you mean "what makes you think spacetime is infinitely divisible?" or "what happens *physically* such that spacetime is infinitely divisible?"

[@jezmy2006]

@@CMVMic Because Matt said so ...

[@TheJackelantern]

I don't believe it is physically possible to infinitely divide a volume of space. Physically speaking. That would be arguing that there is an infinite amount of space in any given finite volume ... I do not believe that is actually possible and that the math is a fallacy on paper.. Meaning it doesn't mean it is physically possible just because you can mathematically write it down on a piece of paper. Hence just because I can write a story about magical unicorns doesn't mean they can physically exist here and do all the magical things I say they can. I think the answer will be more in the lines of space or energy is comming from somewhere else to expand the space or volume that is in question here. This whether be from out side this Universe, surrounding spacetime and energy, or from other dimensions etc.. Like how a river cannot increase its volume or flood a region without more water beeing introduced from some other source. Basically I would argue one cannot increase a volume of space without subracting from another, or without there being some sort of equal exhange or displacement. Just like energy, I do not believe it can be created nor destroyed... Here I believe it can only expand or contract where these two physical phenomenon are physically linked or bound as a part of a single over all volume.. This to where both phenomenon directly and physically affects or impacts the other. even if the volume itself were to be infinitely vast. I could be wrong, but I have a real hard time accepting math that argues we can get more physical space from literally nothing or just by just saying we can, on paper, add and subract more space.

[@joymoding]

@@TheJackelantern well, just because a region of space could be infinitely divided doesn't mean that it contains more space than it does. That would be impossible. I don't know whether or not space IS infinitely divisible, but there doesn't seem to be anything necessarily contradictory about the idea. You're correct, just because you can write down the idea doesn't make it correct, but I see nothing wrong with the idea though.

[@JubilantJerry]

Basically: the edges of objects that are gravitationally bound are "moving inward" relative to the grid that defines the expanding space, such that the object never changes size and the balance is never upset. This balance is lost if the dark energy density changes, which is why the big rip requires dark energy to become stronger over time.

[@Ethanthesharkganne]

"Basically" lol I love it. Thank you. Sounds great but the "basicall" makes it gold😁🤙

[@seijirou302]

@Michael Bishop I don't think he's mistaken as much as going directly to the conclusion for the sake of time. Remember all of these videos are high level overviews; even when they say "deep dive". Because of the negative pressure spacetime curvature from a massive body is eventually negated by distance; the reach of gravity is not infinite as Newtonian gravity would suggest. Bodies that do have a gravitational influence maintain it in balance with dark energy; so they don't experience expansion relative to each other, as long as dark energy remains constant. Dark energy is everywhere, but expansion is not. Only bodies with a gravitational interaction weaker than dark energy will recede from each other. On the rubber sheet analogy instead of a perfectly flat rubber sheet, it's like one that is inflated from beneath and would have the shape of a slight mound before any objects are placed on it.

[@JubilantJerry]

@Michael Bishop The video is not mistaken. There is no acceleration proportional to separation, only an average tendency for an outward velocity proportional to distance. The distance between objects only increases if they were moving away from each other in the first place. It is possible to calculate this: set up two test particles such that the velocity of one is parallel transported from the other. Calculate their geodesics. They will not diverge if the spatial geometry is flat (which is the generally accepted geometry of the universe). If dark energy worked the way you claimed, then gravitational attraction would have a maximum range and I think orbits become unstable well below that range too.

[@JubilantJerry]

Turns out my claim was not right: if the universe appears isotropic to an inertial object, and the edge of the object has 4-velocity equal to the parallel transport of the 4-velocity of the center of mass, then the edge of the object is not following a geodesic. If the edge were following a geodesic, there will be a tendency for the object to expand or contract, as if there was a force proportional to separation. This is not attributable to the expansion of space itself, instead it reflects the same acceleration that the space appears to undergo (the object may shrink even when space is expanding, as long as the expansion of space is slowing down). It is a gravitational effect of the matter and pressure of the universe contents, where dark energy is considered to have negative pressure which contributes to curvature in the opposite way as normal pressure.

[@lippytheoneguy8968]

Space is big and it keeps getting bigger.....thats because Matt O'Dowd is my...favorite physicist

[@i18nGuy]

I have trouble with the idea that there is no space expansion where there is mass. How far from a massive object do you have to get for expansion to begin? I could grapple better with competition between mass caused contraction and space expansion, but you seemed to say it just stops expansion. So where is the boundary?

[@AeroCraftAviation]

I had the same question. Cannot even attempt an answer, but I'm here to corroborate the question.

[@Mosern1977]

Add to the fact that mass was apparently more concentrated back in the day if we are to believe this hogwash.

[@Barba_007]

maybe mass just slows the rate of expansion... I donno

[@i18nGuy]

Also, masses move through space. So in some sense there would be differences in space that had mass near them for a while without expansion, and then expansion continues/restarts when the mass moves on. That space wouldnt catch up its expansion. So space would not be uniformly expanded. I am not sure if the differences could be detected, or if there might be some latent effect due to the warping. (Crazy idea, perhaps even explaining what we think is due to dark energy but is warping of nonuniform space, for example where older galaxies rotate faster than expected.)

[@dimitrispapadimitriou5622]

Good question. Actually, there is no discontinuity between them. There is a smooth transition. An analogous case is a star that collapses to a black hole. The metric that describes the interior spacetime geometry of the collapsing star is different from the metric of the (approximately vacuum) exterior, but there is a smooth transition ( again) between the two that is described within the theory of General Relativity. Something similar happens between Galaxies and the intergalactic space, etc.

[@bxdanny]

So are there definite surfaces which form the boundaries of "gravitationally bound systems"? What happens at those boundary surfaces? Do we know how far from the Milky Way (or from our sun) the boundary is, outside of which space is expanding, and inside of which it isn't?

[@EconAtheist]

this is one of the few episodes i've ever watched (and i've watched all of matt's and many of matt's predecessor's) where i've ended up more confused - IN A GOOD WAY THOUGH - than before i watched. trippy stuff.

[@MrARock001]

Historians: This is a challenging and difficult time to be alive. Cosmologists: Actually, this is an extremely fortuitous time to be alive.

[@evilotis01]

both of those things can be (and are, imo) true

[@stdesy]

Any historian who would say that is a fool. We are constantly living in the best time in human existence. Even 100 years ago if you got a cut infected you could easily die from sepsis and premature babies pretty much were either left to die and only the lucky ones were given care and put on display for the public to gawk at. Not to mention everyone was horribly racist as a matter of course. As another person on educational KZbin is fond of saying “The past was the worst”

[@waynedarronwalls6468]

Cosmological Historians: This is a challenging and difficult but also extremely fortuitous time to be alive.

[@pierfrancescopeperoni]

Boltzmann brain: Actually, thi

[@gaslone79]

I don't think historians are the ones saying that. Click bate media on the other hand...

[@josephatthecoop]

I'm confused about what happens in the transition between the metrics. At 6:07 you said, "Space within any gravitationally-bound system is unaffected by the surrounding expansion." And at 6:45: "In fact, the space-time inside the Milky Way doesn't even know that the universe is expanding." So there is the vast amount of empty space-time between galaxies and clusters where the FLRW metric works, and there are gravity-bound blobs where it doesn't and where metrics akin to the Schwarzschild metric apply instead. But surely the boundary between the metrics isn't like, say, the boundary between Mexico and the US - a sharply drawn line where it's a kilometer-based metric on one side and mile-based metric on the other. Going from deep intergalactic space toward a galaxy, I would expect there's a gradual transition. Could we consider that there are degrees of gravity-boundedness? Gradations of isotropy and homogeneity? If 1 planck length grows to 10 way out there in the FLRW-metric space between galactic clusters, while 1 planck length stays exactly 1 planck length here in our cozy little gravity well, are there places in between where 1 planck length grows to 2, 3, 4, etc? And if that is correct, and the transition is continuous, can we rather say that the space-time inside the Milky Way knows so little about the expansion of the universe that for all meaningful purposes it's not happening there at all?

[@etone8662]

Expands yes.... and does it recontract or?

[@cristianosacchi]

Agreed - furthermore I wonder if in this sort of "boundary layer" between gravity and expansion there is some sort of "Lagrange Point" where an object is in equilibrium between the gravity well and the universe expansion

[@pasikeranen]

Fascinating, as always. My random thought from today's video was: "But if planck length is always constant, then doesn't that mean that the expansion of space has to happen by whole planck length(s) at a time?". It's probably meaningless trivia, but I've never thought that expansion of the universe might be quantised like that.

[@drunkbeaverproductions]

I may not have a doctoral understanding of physics so there may be a better answer... BUT... my understanding of Planck length is that it is the smallest measurable unit of time-space and that there is neither time nor space between the Planck lengths... so there is nothing there to expand. If you grid a section of spacetime ad infinitum, once you reach Planck length and have a grid made out of them there would be no further spacetime to evaluate in those boxes. If we took that box and expand it in scale, we have just added spacetime and can now grid it down again.... these layers of the smallest boxes having to 'get bigger' for us to keep going is what leads to expansion of the universe since/from the big bang... so in a way a Planck length is a type(minor edit) of singularity too maybe?? Interested in seeing others take on your thought and my answer as well... :)

[@pasikeranen]

@@drunkbeaverproductions You are touching upon the key to my thought experiment which is the "gridification" of spacetime using Planck length as the basis vectors. I'm thinking these Planck length grids as "pixels" (in 2D) or "voxels" in (3D). I'm pondering how to explain (without visuals) the questions that arise from this in my head. 1st is the "can spacetime only grow by 1 x Planck length". It would intuitively seem "yes" as there is no space measurable that is 0.5 x Planck. So if this is true, what happens when the spacetime expands by odd number of Plancks? If you grow a 3D voxel space by +1 (or +3, +5 etc.) around a point, that point will jiggle every expansion by +/-0.5 if only whole number coordinates are allowed. So does this mean that the Planck length (imaginary) grid around us jiggles by +/-0.5 whenever spacetime grows by odd number of Plancks? This is probably theoretical banter, but as (ex) 3D graphics programmer one can't help but wonder about this and might this have any implications... Then again I'm happy if someone here can disapprove me at the "Universe grows by whole Planck lengths only" assumption. :)

[@drunkbeaverproductions]

@@pasikeranen to not break 'Planck length' the universe could only expand by EVEN numbers of Planck lengths then... which is also interesting as a concept. if you are looking at 2D pixels or 3d voxels does that mean that we maybe need to evaluate the 11th dimensional "strixels" (String theory seems to want extra dimensions we don't usually consider)??

[@sebastienpaquin4586]

Question; on large scales, does the expansion of the universe deform stuff propagating trough it, like gravitational waves?

[@Dragonmastur24]

Yes! well, erm.. no! well.. um maybe? Definitely maybe! What perspective are you thinking things deform from? The perspective of the object? the perspective from that of the transmitter? or the perspective of that from the receiver? If you are of the perspective of the object/particle/wave/energy that is moving through space: then as @Strenkor En'Triel said: no. the object/wave does not get bigger nor longer than what it was when it was sent on its journey. If the perspective youre asking from is either side of receiving it or transmitting it, then yes it APPEARS as such that the universe is expanding it. a good example of this is as @Sander Bouma stated: CMB at least, thats the way ive heard why the cosmological constant matters in regards to the CMB. tl:dr no objects are stretched: but stuff moves away such that things look longer. its all about perspective. Edit: so as @Strenkor En'Triel Strenkor En'Triel suggested, my explanation was a little lackluster so i hope ive corrected the points.

[@KING-ll2mz]

Yep. That's what causes cosmological redshift.

[@nasunorahl]

more like, gravitational waves pushing everything apart. Much interfering waves inside galaxies and superclusters and whatnot preventing them from expanding apart. But everything else yes. No need for dark energy with this.

[@sabouma]

Yes and CMB is a great example of that

[@contentdeleted4978]

Why does google say light travels faster than space expands.

[@boringturtle]

Okay, so weird question, but... I've heard that it isn't "meaningful" to measure any distance less than half a planck distance, but is it meaningful to measure 1.5 planck distances? Does meaningful mean that that space doesn't exist? When new space is being "created" does it pop into being one unit at a time leaving infinitesimal gaps between planck cubes or is this simply a statement about the theoretical limits of observation/interaction?

[@Andromedon777]

Science doesn't say it doesn't exist below that. It just states our physics break down at that scale.

[@jimgraham6722]

Probably not cubes.

[@aw7049]

According to QM , is not a limitation of our understanding per se. Our currently understanding states it is just not posible. What can be wrong is our understanding.

[@Andromedon777]

@@aw7049 So QM says it is the absolute minimum?

[@aw7049]

My understanding is that the amount of energy needed to probe smaller and smaller becomes larger and larger. Plank introduced h to solve the black body radiation problem. But where it really comes to live is in the uncertainty principle. No measurement can be done more precise than h/2 because it would make the “paired” property too big.

[@goingballisticmotion5455]

This is the raisin loaf analogy. Bake a loaf of raisin bread. The bread expands and the raisins move apart, but each raisin keeps it size. So intergalactic space is the bread and galaxies are raisins.

[@AstroRamiEmad]

"Space," [the Hitchhiker's Guide] says, "is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen . . ."

[@mwm48]

I have always thought of expanding spacetime as actual time being created. Like a person walking on a treadmill. If the treadmill was moving at C, then you would have to move at C (against the treadmill) in order to seem like you are standing still - which is what we observe. Now imagine the treadmill is manifesting from all directions at once. If the universe stopped expanding, time would stop. 🤔

[@NotYourBusiness-bp2qn]

I find that analogy appealing as well. The problem is for some reason the universe is NOT expanding inside galaxies. But time passes everywhere, inside and outside galaxies so if the expansion is the physical form of time passing then galaxies should expand as well as time passes inside them too. Yet they don't and that is weird. Also I have a problem with the idea of "places where there is no gravity" as an explanation as to why some places experience "growth" while others don't. Gravity is everywhere, distant galaxies still tug on each other, the effect of gravity extends infinitely if given enough time. Gravitational waves have reached us from billions of light years away (as far as I understand) so clearly gravity is everywhere, even if very, very small in some places. I really think the astrophysics community is grasping at straws to explain these phenomena. Dark matter, dark energy, places where the universe expands but others where it doesn't for no apparent reason - it's all a big mess. We desperately need a new theory that explains these without placeholders like dark matter or dark energy or space that is created in some places but not in others for no discernible reason. Expansion started fast, then slowed down a lot, now it's accelerating again. Why? We need answers. Sadly human kind seems to have slowed down it's intellectual output by orders of magnitude compared to the last couple of centuries. Why? I don't know. But it sure seems so.

[@johnh539]

@@NotYourBusiness-bp2qn I have explained my theory( various comments ,different channels) based on M=E/C2 so I will not now.(I think it explains dark energy and relapses dark matter with dark mass, indeed it predicts/requires Quantum vacuums[ no gravity] ,I call them cavitations) I wanted to mention your comment about time. Whether you believe that gravity slows time or as I do, that time causes gravity ; what is beyond doubt is that where there is heavy gravity time moves slowly. In our space time the Earth was created 4.5 billion years ago but in the much greater gravitational pool/pit of the sun we might have only been created under a billion years ago or whatever the maths says. I wonder if within galaxies space is expanding but due to gravity time is happening exponentially faster in intergalactic space. You have to look through billions of light years of exponentially faster time to even notice the expansion of space. it just might be imposible to to detect in our infinitely slower time and smaller space for that matter . ‘The kettle may be coming to the boil but one half second observation it would be hard to tell.’

[@jerrybrown6169]

To me, this video is the best presentation, from PBS, on a scientific topic so far.

[@TheNidies]

Is there a known value / ratio where the bound gravity system 'loses' to the expansion? Could you have a very sparse galaxy where the phenomenon could be observed within, or does it effectively only happen far beyond in the space between galaxies? If you brought two small objects / particles (with their relatively weak gravitational field) into the space between galaxies, would you be able to observe the expansion between them? How far or large would two objects with mass need to be in order to observe the expansion between them? With the Milky Way and the Andromeda Galaxy heading towards each other, is there expansion between the two just being cancelled out by their velocity towards one another, or are they too close and instead form a bound gravity system? If they're a bound system, could one of the other galaxies that are red-shifted (ie 'heading towards us') have this phenomenon where they're far enough for expansion to take place, but the expansion is being negated by the object traveling towards us faster than the expansion? If yes - how close / fast do they need to be in order to actually catch up before the rate of expansion grows too large and they begin traveling away?

[@mvmlego1212]

@Seek Him with all your heart and you will find Him -- This sort of behavior doesn't help your cause; it only makes you and your cause look fanatical.

[@eVill420]

@Seek Him with all your heart and you will find Him like the other guy said, this just makes you sound like a lunatic

[@wynnschaible]

You have, it seems, exposed a weakness in this entire argument: for the whole Universe is, in one sense, a "gravitationally bound" system -- every part of it experiences the gravitational attraction of all the rest -- UNLESS there is the still undiscovered graviton, which, as a quantum particle, would presumably have (as with distance and time) a planck-related minimum: below this level the force does not exist, or at least "is not defined."

[@SergeiAndropov]

As I understand it, the Milky Way and the Andromeda galaxies don't have any velocity relative to each other except for that caused by the contraction of spacetime. To put it another way, there aren't rocket engines on each galaxy applying force to them so that they move towards one another. Instead, the distance between the galaxies is decreasing because the spacetime between them is contracting due to gravity. Gravity doesn't act on objects; it acts on spacetime, and the objects just come along for the ride. Gravity acts over unlimited distances, but it decreases with distance. After a certain distance, the amount that gravity contracts the spacetime between two objects will presumably be less than the amount by which empty space wants to expand. There probably is a way of calculating when that will happen, but I don't know what it is.

[@wynnschaible]

@@SergeiAndropov Sounds reasonable but this balance of forces model was explicitly denied in the video.

[@2013Arcturus]

Does time move faster in the void? If so, could that be why expansion seems to be speeding up, cause the baseline clock of the universe is ticking faster in the void? Basically, spacetime itself is older in the void.

[@t.c.bramblett617]

we do know that time travels faster and slower in various places. The only constant is the speed of light. So you are technically right, each point of spacetime is older or younger in reference to any other point. Note: As I understand it, anyway (as a layman). If I'm wrong and someone with more physics expertise can explain it better, let me know

[@markd7799]

We know things in the presence of gravity have a slower passage of time. This is a good question!

[@unslaadkrosis9435]

It feels like void should have a slower passage of time but it's the opposite apparently and it's annoying

[@katiebarber407]

i love this narrator. you seem to actually have genuine interest in the topic and understanding and most importantly, a desire to avoid sensationalism

[@johnyurkon5064]

What do you consider gravitational bound? We feel the gravitation effect of distant galaxies and all matter in the universe yet the space between galaxies expands, but not within the galaxy. At what point does gravitation stop expansion?

[@redthunder6295]

I believe "gravitational bound" refers to any chunk of matter that will not be separated despite dark energy on large scales. This would refer to local groups of galaxies which end up collapskng into a supergalaxies and get separated from all the other supergalaxies due to dark energy on large time scales

[@acarrillo8277]

This makes me wonder if there is an actual quantifiable gravitational threshold at which the universe can expand.

[@ferretappreciator]

42

[@osmosisjones4912]

Maybe the big bang started in a black spot before the previous universe ended

[@innocentbystander3317]

@@osmosisjones4912 Spam more, maybe you'll learn something if you could be slightly more annoying.

[@BongoBaggins]

Yes, the speed of light. But the speed of light is relative, so also no.

[@alwaysdisputin9930]

@@BongoBaggins Most galaxies are moving away from us faster than c

[@earlhunt8164]

Kudos! It's an art to make complicated concepts accessible. Well done.

[@monkeyrobotsinc.9875]

Says you.

[@ToxicallyMasculinelol]

If you already explained this and I just misunderstood, sorry: How does vacuum energy in an expanding spacetime not violate a conservation law? Is it being offset by some source of negative energy that's increasing at the same rate? I guess it's gravitational potential energy?

[@Illiteratechimp]

Conservation only applies locally

[@cnez1910]

pretty sure whatever law we invented to explain what we currently see would not apply anymore if we had a bigger picture

[@garethdean6382]

There are two ways to look at this. The first is that energy conservation, like all conservation laws, requires a symmetry. In this case, that space not expand or contract. If it DOES, then energy conservation as we know it breaks down. (So, for example the CMB goes from high to low energy photons.) Alternatively proponents of the 'zero energy universe' state that a higher conservation law applies. In the same way that conservation of mass is not a true law (Being broken by the interconversion of mass and energy) energy conservation is an approximation of a true conserved quantity, the energy momentum 4-vector.

[@andreja5521]

spacetime is not expanding, space does

[@wilderbeast9368]

Space-Time is made out of Frequency Zero Photons. Upon losing absolutely all energy, they hit the 0Hz range and obtain an infinite wavelength also. Though, similar to referenceless time, and because of a complete lack of oscillation, this infinite distance is travelled without actually going anywhere, as zero distance travelled would result in the same as infinite, a perfectly straight line. We experience gravity as longitudinal waves along these these 0Hz photon strings. What exactly are the longitudinal waves? Massive particles, or phenomena otherwise exhibiting the property of mass, cause stretch (Levity) and shrink (Gravity) in the Space-Time fabric. The current model we have of gravity, wherein objects under Earth's gravity makes a decline and incline when pushing against is thus spot on, as far as 2D representations. A longitudinal wave of gravity is a shrink, being tailed by a stretch.

[@JK-qv5wm]

I smile like an idiot each time hearing his iconic "spacetime" at the end.

[@dyeus4464]

This is that channel that I cannot stop watching even if it fills me with much dread and confusion, exponentially expands my unknowns and hit me with head and heart aches after.

[@TheoWerewolf]

Hold on.. there's a problem with the argument that Planck length chunks of space can be expanded infinitely. One of the basic properties of Planck length (or rather, volume) is that it is inherently impossible to get information about any inner structure from it (that would violate uncertainty), but if a Planck sized patch of space-time DID have some internal structure (even just being anisotropic in some way), expanding that region of space would expose that anisotropy. So either Planck volumes are inherently AND absolutely isotropic, or they can't be inflated this way. The problem with their being inherently and absolutely isotropic is that this suggests that they cannot be affected by any kind of gravity (which is a distortion of the tensor for spacetime in the gravitational field) as that would break the isotropy in some way (ie: the geometry on one 'side' of the Planck volume would be different from the other) and yet it would at the same time have to have no effect on the Planck volume, which seems to be a contradiction.

[@lomiification]

That property is defined for an unchanging space time, isn't it? In an expanding space time, that might not hold true

[@deusexaethera]

Planck-length units of space aren't quantized "pixels". They are arbitrary. You can measure two Planck-length units of space that overlap with each other if you want; the Planck length is merely the minimum size beyond which you can't conduct any measurements because the energy required to perform such an observation would spontaneously form a tiny black hole, erasing the data you attempted to collect.

[@kickinrocks6055]

"If you didn't vote for me, you ain't Blanck."

[@peceed]

There is no Planck length chunk of space, special relativity forbids it.

[@maxpavlovsky]

Let's just assume that the gravity is probabilistic. Problem solved.

[@kevinbishop724]

I am no mathematician - 1 year of college, but I love this stuff. A few years ago I read an article that made my brain shout. Some physicist had proposed the the ‘Big Bang” was the result of “a flaw in nothing.” I have yet to see or hear anything that makes more sense to me.

[@gaborbencsik468]

I'm not physicist, but my intuition says that if space remains the same density over time around gravitationally stable structures, then gravity itself is a mechanism that offsets the expansion. Often a gravitational field is pictured as warped spacetime, and sometimes it's pictured as a sort of vortex, where spacetime is actually moving, flowing inwards. I think the latter must be more closer to the underlying truth. But where does that space flow? To put it simply, I think mass eats up space over time, and when enough mass comes together to exactly offset the rate of expansion in a given region, then you have a.. galaxy? Objects are not pulled upon by a "force" of gravity, they merely drift with the current. I'm sure this would not work in any model of physics that are being taken seriously nowadays, but I think it might work with Steven Wolframs ideas, who I think is onto something.

[@JessicaBiros]

Question: would redshift in an infinitely divisible spacetime look different to a quantized spacetime in some specific edge cases, say diffraction patterns due to phasing in some specific arrangement of gravitational lensing events?

[@Tartersauce101]

Interesting. Or how about just cosmic dust and debris? The further light has to travel to reach us the more material it will have to pass through. Material slows light, lightspeed is only constant in a vacuum, this would create a red shift like effect. Also do all spectrums of light move equally between material? Could we be witnessing a filtering effect? Or most interestingly we could actually be at the center of the universe and all the light sources are doing exactly what they appear to be doing - flying outward away from us.

[@Unidentifying]

probably not since youre talking about quanta

[@JACKRAIDEN97]

@@hyperduality2838 your words are useless

[@andrewclimo5709]

Nice Matt, possibly the most enjoyable vid from my perspective. The intriguing corollary is that cosmic voids may be growing whilst galactic clusters remain bound. Speculation: Will filaments be the superhighways of the future, the only parts of the universe traversible to deep space, galaxy hopping, travellers ?

[@sammikinsderp]

This episode was INCREDIBLE! I thought I understood this topic in detail, but you really expanded upon it! Kudos, this was an incredible watch! I may even rewatch it!

[@bloodyorphan]

Another awesome video Matt. Entropic expansion versus Entropic collapse is a fundamental question. My solution is a photonium particle count per cubic of space, if the spacial photonium count is higher then we have entropic collapse, if the photonium count is lower then we have entropic expansion. Using this concept we can finally define the two tensors that allow atomic structure to exhibit temperature photons in direct opposition to the entropic collapse that is evident in the atomic structure. Another part of Skin theory B-)

[@ChillingSpartan]

7:30 - There is another explanation of the different rates of expansion. The 3D universe we are observing is in reality a 4D universe. We are moving through 4D space and are spiraling on a tilted 3D plane towards the center of a 4D sphere. The spiraling towards the center in 4D space is causing the expansion in 3D while the orbit and therefore the rate of change of distance to the center is causing the different rates of expansion.

[@imu2546]

Wait, does this mean that we could look at the expansion of the universe as everything in it shrinking to a more and more precise point, and space time remains constant? Like zooming in on a coordinate field.

[@externaldriver]

I'm only a dilettante but that sounds inconsistent with the idea of galaxies moving away from each other

[@tommat86]

@@externaldriver No, if everything shrinks in a fixed space, and the measuring units with it, it just seems like it's moving away. Or let's say, the distance gets bigger, but only relative to the measuring unit. @imu The point of view of shrinking objects feels also much more natural to me. In that case you also don't have to "create space", whatever that should mean...

[@jgraves3114]

I love this channel and many other pbs channels, some of the best content on the web and poignant work of a 21st century public broadcasting station.

[@winonafrog]

👍🏼

[@nct948]

genuine honest explanations, very impressive. Maybe I'll understand something of it one day lol. So I have subscribed ; thanks for this video

[@Flickvids100]

Question: Does this different expansion rates in spaces with/without matter explains the existence of huge voids in the universe? Are they just expanding faster and that's why they are noticeable and particular to us?

[@ThatCrazyKid0007]

Yep, pretty much. They represent patches in the early universe where gravity was overcome by the effect of dark energy due to a lower density of matter present in these regions and it created these spots where space can expand freely which compounded over several billion years resulted in these humongous voids.

[@Flickvids100]

@@ThatCrazyKid0007 Wow...that's amazing. Honestly, didn't think much about it until this video. Thanks for your answer.

[@DanHarkless_Halloween_YTPs_etc]

I normally come away from these episodes stoked that I've gained a better understanding of some incredibly weird and non-intuitive physics concepts. I'm afraid Matt's magical ability to make this stuff accessible to non-math-heads didn't really kick in for me this time, though. The revelation in a prior ep. that gravity "wins" over inflation at the galaxy scale was a big help to me. I don't feel like I've moved beyond that, though. For instance, I don't get why we would redefine what a meter and so on are, if expansion isn't going to stretch those units in our neck of the woods. It would seem to make more sense to just keep measuring receding galaxies as more of those meters away. And the stuff about infinitely divisible units of space emerging from within Planck lengths, but doing so one Planck-length quantum at a time, just sounds like pure contradiction. Is it just me, or was this an unusually hand-wavey episode...? 😐 ("These are not the Planck lengths you're looking for."…?)

[@Nuclearburrit0]

@Kleos what does any of this have to do with the comment you just replied to?

[@michaelbariso3192]

The communications delay between Earth and Mars is approximately 20 minutes. We're either viewing the light from Mars in the future, Einstein's past dimensions of space-time or in real time, which do you think is more logical? The speed of light according to Einstein's relativity is 186,000 miles per second, but according to physics if two mechanical watches were synchronized on earth and one traveled across the universe and back, there would be no difference in time between the mechanical watches proving the speed of light is instantaneous as the only way a mechanical watch will run slow is if you tighten the main spring :-). Big Bang, Einstein's relativity-time dilation and nearly all of science debunked. There are 7.7 billion people on planet Earth, yet I was the only one who knew I was viewing the light and images of the universe in real time, maybe I should be working for NASA or Elon Musk :-) Light waves can stretch, bend-curve and occupy a state of superposition, whereas the hypothetical Einstein projectile light particle (photon), a particle that has never been observed cannot be both a particle and wave. There are no space-time fantasy unions or gravity waves that can join a particle, wave and time together then bend, curve and stretch them like a rubber band. Neither time nor mass can create itself into nothing, reside in nothing or expand into nothing simply because nothing has no properties. Time and space are independent of each other, not material bodies or fantasy unions that magically stretch time like a rubber band into space-time dimensions. The James Webb Space Telescope is not a time machine, you can’t travel back in time to view the beginning of the universe with telescopes that were made in the future :-). Light and electromagnetic waves are independent of each other. If science uses Einstein's speed of light like an odometer to calculate past dimensions of distance and time, then using the same odometer to calculate forward dimensions of distance and time would mean the Big Bang was created in the future before time existed. The speed of light can be slowed from 186,000 miles per second down to 38 mph by shooting a laser through extremely cold sodium atoms acting as “optical molasses” If the universe were suddenly destroyed, collapsed or fell into a black hole do you honestly think slowing down the speed of light with sodium atoms would save the earth from being destroyed, giving people on earth time to find another planet to colonize and destroy :-). Using optical clocks, lasers and GPS to prove Einstein's time dilation-space-time curvature is like using a metal detector to find gold at Fort Knox. The closer you are to the electromagnetic fields, mass and gravity of the earth the more light bends aka gravitational lensing. Unlike the electron beam of a CRT-TV or high definition LED-LCD television the images we are viewing in the universe are in real time, not a series of frames that create the appearance of a moving image. There are no DCU digital convergence circuits in space :-). If black holes reside in a region of Einstein's theorized space-time where gravity and mass are so dense that nothing, neither mass-particles nor electromagnetic radiation such as light can escape then how could it be possible for the entire mass of our universe to escape the unimaginable density of the proposed Big Bang? According to general relativity sufficient compact mass-density will deform space-time to form a black hole which obviously debunks both Big Bang theory and relativity! Big Bang theorists rely on red shift to support the hypothesis that the universe is expanding, the very phenomena that supports the hypothesis of a (non-expanding static universe). You can duplicate the ion thruster jets of a black hole in a vacuum using a Tesla coil or build one using high voltage-an array of magnets-a CRT-TV yoke or inductor coil. Black holes are nothing but plasma driven vortex electromagnetic fields expanding electromagnetic waves in space. Since the vortex of black holes are thought to be at the center of all galaxies they might be the very force that created them. Gravitational lensing occurs in all wavelengths of light including (red shift-microwave background radiation). Gravity from huge celestial objects of galaxies bend, curve and expand light giving the appearance of what Einstein wrongly theorized as time dilation-space-time-debunking the big bang. Mass from galaxies, planets and black hole electromagnetic fields bend, curve and expand light giving the appearance of what Einstein wrongly theorized as time dilation-space-time dimensions. Light like all electromagnetic radiation and electricity is the result of moving electrons, as moving electrons of charged electromagnetic waves-light travel through the plasma of the universe each lump (or "quanta") of energy in the electromagnetic waves are charged then discharged to the next lump, eventually the energy dissipates causing the delay in radio communications giving the appearance of time dilation - the appearance of longer wavelengths in red shift. Light and electromagnetic waves are independent of each other. If space was curved-warped according to Albert Einstein's curved-warped gravity theory, like a boat in the ocean these same gravity waves would affect time and the perfect balance in solar system orbital mechanics throwing planets off course-out of orbit in a collision course towards the sun where a planets gravity and time would increase and decrease with different velocity rates as they ascend and descend the curves of gravity waves. Using optical clocks and lasers to prove Einstein's time dilation-space-time curvature is like using a metal detector to find gold at Fort Knox. The closer you are to the electromagnetic fields, mass and gravity of the earth the more light bends aka gravitational lensing. If gravity is the result of mass then before the universe came into being gravity couldn't have existed simply because mass was not yet created! Galaxies with massive gravity from the early Big Bang would have been gravitationally bound like the Andromeda galaxy is to the Milky Way galaxy, the sun, moon and planets in all solar systems in the universe yet these early galaxies were able to somehow escape these massive gravitational forces continuing to expand at an increasingly faster rate. Into what, nothing? Nothing has no properties! Neither the atom, universe nor time can be created or destroyed. Albert Einstein an autistic violinist patent clerk that had access to more papers than Suzanne Somers litter box yet creates theories with more bugs than Terminix. If the light from the universe travels from past dimensions of time then it's light is traveling into future dimensions of time (instantaneously). “And God said, Let there be light: and there was light.” a state of superposition where time, and gravity run inwardly, outwardly, in all directions in the same time frame, similar to the electromagnetic field having no beginning and no end. If space was curved-warped according to Albert Einstein's curved-warped gravity theory, like a boat in the ocean these same gravity waves would effect time and the perfect balance in solar system orbital mechanics throwing planets off course-out of orbit in a collision course towards the sun where a planets gravity and time would increase and decrease with different velocity rates as they ascend and descend the curves of gravity waves. Using optical clocks and lasers to prove Einstein's time dilation-space-time curvature is like using a metal detector to find gold at Fort Knox. The closer you are to the electromagnetic fields, mass and gravity of the earth the more light bends aka gravitational lensing. Neither time nor mass can create itself into nothing, reside in nothing or expand into nothing simply because nothing has no properties. Time and space are independent of each other, not material bodies or fantasy unions that magically stretch time like a rubber band into space-time dimensions. Einstein's disciples believe the light and moving images they see in the universe aren't really there, they're just recorded images of the past 13.8 billion years ago. You could lead a cult to water, but you can't make them think. Albert Einstein, an autistic violinist patent clerk that had access to more papers than Suzanne Somers litter box yet creates theories with more bugs than Terminix-Magnetron.

[@Nuclearburrit0]

@@michaelbariso3192 none of that's true and most of what you just said makes no sense.

[@TreeDancingCloud]

@@Nuclearburrit0 I remember a similar event in "The Life of Brian." In response to the teacher saying "you are all different," one person said "I'm not."

[@duncanvantongeren4646]

Disregarding whether that insider is real and speaks truth: astrophysics is a masonic LIE.

[@TravisR1982]

Well played, Matt, well played. I kept anticipating your final utterance of "spacetime" over and over and over on your final sentence. Made me laugh heartily.

[@FrostCraftedMC]

what if the universe expanding is really just how gravity causes time and massive objects are just streching space time so it looks like things are getting father away in distance but really just father away in time... or both?

[@BiswarupRay]

Stretching space time means affecting the velocity of light. I have another idea, what if the universal constants are changing over time (say velocity of light is decreasing) so that the expansion of space is an effect of that?

[@wingnut2292]

So just like One can't tell the difference between Einstein's thought lab moving by rockets or a nearby gravity source, what if all mass is slowing somehow?

[@FrostCraftedMC]

@@BiswarupRay in another video he talks about time being a side effect of gravity due the the constant inward acceleration of space due to gravity. if youre far enough in space away from anything, no actions will ever interact with you so basically no time will happen. what im proposing is that all gravity sources are stretching out the light making it only look like the universe is expanding just like a box accelerating up and a room in earths gravity can be indistinguishable.

[@FrostCraftedMC]

@@wingnut2292 thats what im getting at! idk about slowing but wouldnt all light leaving earths gravity well be stretched by the gravity just like it can be bent by gravity? thus making it look like everythings expanding

[@captainzappbrannagan]

Still confused as to how empty space is scaling up in size, effectively adding new plank sized bits at an enormous rate without it affecting the zero point energy of the fabric of space. Does the energy to fill this come from the Time component of space?

[@JasonEllingsworth]

Nobody knows because as a species we are absolutely clueless due to not even being capable of exiting our own planets orbit and returning safely.

[@calinculianu]

it's not. The whole theory is bonkers and not even properly falsifiable. They base the entire theory on a single observation: red shift of light from distant objects. This observed phenomenon has potentially other explanations, perhaps some of which we haven't thought of yet. The whole theory is nuts. Yet this is the state of modern cosmology. It's crazy with a foundation of more crazy.

[@deusexaethera]

The laws of physics that apply within the universe don't necessarily apply to the universe itself. The new zero-point energy doesn't have to "come from" anywhere, just like the Big Bang didn't have to "come from" anywhere.

[@captainzappbrannagan]

@@deusexaethera billions of new plank lengths take energy to maintain a constant energy level no? Where does it get the energy from if not within our universe (all we know that exists for sure).

[@theorixlux]

question. it sounds like you're saying there is a negligible amount of stretching of gravitationally bound systems. is this correct? if so, then why say that there is no tug of war between celestial bodies, however small?

[@Aarorie]

Question: If you were travelling at relativistic speeds and the universe was contracting from your perspective, would your observable universe enlarge, to “fill in” the space left by the universes contraction?

[@Nilguiri]

What contraction are you talking about? If you're talking about length contraction, that occurs only in the direction of motion. The whole universe does not contract all around you!

[@ThomasJr]

this doesn;t make sense. If it contracts, the whole observable universe you can see at a high speed would be contracted right?

[@Nilguiri]

@@ThomasJr General Relativity is famous for not making sense! No, length contraction happens only in the direction of motion and increases to 100% as your speed approaches light speed. From the frame of reference of a photon crossing the entire universe, the distance it travels would be zero and it would not experience any time passing, and would would arrive instantly... again, from its perspective. That doesn't mean that the whole universe shrinks; there is no sideways contraction. Just as your light-speed spaceship will be contracted to zero length as you pass an observer at light speed but its width will remain unchanged. I've found a couple of videos which will explain it a lot better than I can: kzbin.info/www/bejne/Y4HSq5JvasRjiKM kzbin.info/www/bejne/iqm6Z5J7aNp_q9E Or search for others. Good luck.

[@Nilguiri]

@@coloradoing9172 That's not what he asked. And I think I answered his actual question above. Cheers.

[@coloradoing9172]

@@Nilguiri It's precisely what he asked, and you did not answer his question.

[@joseluisalcantarasanchez269]

Some time ago I asked myself the question: could there be something else happening to the universe that, from where we are, it looks like it is expanding? And yes, there is some other explanation about what is happening, and it looks the same: matter in the visible universe is conglomerating.

[@captainzappbrannagan]

Eventually all matter will fall into black holes as gravity and frame dragging slow everything down. Humans won't be around to see this though. Likely we will destroy ourselves long before that :(

[@joseluisalcantarasanchez269]

@@captainzappbrannagan All matter will not "fall" into black holes, but "pushed" into black holes.

[@captainzappbrannagan]

@@joseluisalcantarasanchez269 It will be pulled by gravity into the black hole, fall is appropriate. Where is the push coming from?

[@joseluisalcantarasanchez269]

@@captainzappbrannagan Space wants to be empty so it pushes matter together. Gravity is not attractive, it is the tension of space in the presence of matter and since all matter is moving, it all ends up conglomerating. Think of this: a particle in space, is it occupying a portion of space, or is it displacing space and replacing it with itself?

[@jmg5878]

The second you opened with “Space is big” all I could think of was “Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's long way down the road to the chemist's, but that's just peanuts to space” and now I want tea

[@ZenithWest169]

Hmm, so does that mean there's a specific distance between two massive objects (whether they be galaxies or electrons) where below that distance space doesn't expand and above it it does? If so quantum uncertainty would make that a pretty interesting analysis how space-time would expand given two neutrons separated at close to that distance.

[@mikip3242]

Rememeber that gravitational attraction doesn't depend on distance alone but also on the mass of both object. In short, the important thing is density. And yes, there's a critical density in cosmology that does just what you are saying.

[@ZenithWest169]

@@mikip3242 I was just more curious about the quantum uncertainty aspect. At the high school level you are taught two particles on opposite ends of the observable universe, would eventually come together due to gravity. Given an expanding universe that's not the case. But there seems to be a maximum distance (or density if you like) at which they still would. Since the position of particles are well kinda fuzzy, (for lack of better terms) it would be interesting to see how the distance/density would change if you included the statistical nature of quantum mechanics.

[@vivianriver6450]

@@mikip3242 What evidence is there that there is a critical density below which space doesn't expand and above it which it does. And furthermore, it seems like this notion is contradicted by the expansion of the denser universe that existed moments after the big bang.

[@ZenithWest169]

@@vivianriver6450 if you watched the video, Matt explained that space doesn't expand in galaxies but does expand in the space outside of galaxy (where gravity isn't strong). Logically if you were to keep reducing the "density" (matter) of a galaxy until it completely disappears, then there must exist some point in between the galaxy (no expanding space) and completely empty space (space would be expanding) where below/above it's either expanding or not expanding (you can't simply have partially expanding as that would just be considered expanding).

[@Smitsva]

I love PBS Space Time !

[@hihungryimcam]

Damn, this is one of the most helpful videos I've ever watched on this topic.

[@gabrielmontes1670]

What if the universe is not expanding but the light is slowing down? Are we entre able to tell the difference?

[@yury7595]

Interesting. Actually, the light changes its speed while traveling through different substances. What if the intergalactic space has more density? The speed of light there would be slower, and we have the sense that the distances are bigger.

[@motorepoloh]

Tired light models were basically debunked: en.wikipedia.org/wiki/Tired_light

[@DrWhom]

@@yury7595 that's a different thing - the photons travel just as fast (c, always c) between different scattering events, but there are more of the latter in an optically dense material. Think relay race or pinball machine.

[@garethdean6382]

If light were slowing down across the universe it would be affecting things via good old E = mc^2, which would cause problems. If somehow it moved slower in intergalactic space we'd need an explanation WHY. Light generally moves faster in less dense media, not slower, and the rate seems to have been changing over time which would require a change in space itself or whatever filled it.

[@thealliedhacker]

We've seen analogies of gravity as the grid of space-time flowing into the gravity well, dragging everything else along with it. So if we have 2 massive gravity wells (e.g. galaxies), it would seem that space flows into them, but along the midpoint between those bodies there would have to be some kind of font of extra space being created, from which the space is flowing. Could this effect where 2 massive bodies essentially rip space between themselves apart be what we see as both the expansion of space and dark energy itself?

[@IvanVoras]

That would be conceptually elegant - the "new space" created by the expansion is "dark matter", whatever that might be. But that's probably too elegant to be true :D And besides, we have no idea how to test that...

[@MSpotatoes]

The comments on this channel are as fascinating as the videos, really good crowd.

[@pon1]

Isn't this expansion of space, actually stretching of space? Or is new space created where it expands? Could we at a large timescale expect a big rip or has that theory been abandoned for some reason? Also, doesn't the "thinning" of space explain why it is accelerating, since that would be equal to a anti-gravity "force".

[@douche8980]

Space doesn't actually exist as the entire spacetime is and always has been an infinitely dense point when compared to a bigger reality. Its just that objects made of quarks and atoms expand with in relation to their surrounding and this makes the distance between any two objects made of matter and energy increase.

[@InfiniteAnvil]

Question: Imagine an immense "ring" (or sphere, or hypersphere) of matter on an expanding spacetime, such that space on the inside of the ring is "empty", but is completely cut off from the rest of "empty" space by the ring of gravity-stabilized space. Would that inner area of spacetime expand?

[@Unidentifying]

Yes

[@contemporarilyancient]

Yesn't

[@filipsperl]

Hmm interesting thought

[@ketunky3056]

Why distance between sun and earth is not increasing

[@KerbalHub]

Yes, until the balloon of matter explodes from too much dark energy

[@JamesJordanson]

but how do we know that the planck constant or the gravitational constant do not change as a function of space or space density, e.g. how do we know that they are also the same in the galaxy of andromeda for example?

[@mtchtrnr]

Why don’t we say expansion is caused by a slightly negative gravitational “push” at all points? Would that look different from what we currently observe?

[@i_booba]

That’s basically what dark energy is. I’m just guessing here, but I think the reason we call it dark energy is because we can observe some sort of energy “spectrum” (probably the wrong term here) from the cosmic microwave background radiation, and it turns out that 68% of the current universe’s mass-energy is this weird “dark energy” stuff. And it also turns out that this dark energy is precisely linked to the accelerating expansion of the universe.

[@volbla]

I believe this is the proposal of Modified Newtonian Dynamics, a.k.a. MOND. Sabine Hossenfelder has a great talk on the Royal Society channel about the history of such theories.

[@thomasreedy4751]

@@i_booba I thought we called it dark energy because we can’t directly observe it. It is hypothesized to fix our mathematical models but we aren’t able to confirm it’s existence.

[@mtchtrnr]

Hmm. Thinking about this more, if every body of mass was surrounded by a gravitational "push", the bodies wouldn't be pushed away from each other. It would be more like they were all trapped in a matrix. I feel like gravity needs a differential to move things. I guess what I'm imagining is a reactive force at all points. Where any point of space doing the pushing would have to do equal pushing in the opposite direction. Our galaxies aren't getting squished though, afaik.

[@Faustobellissimo]

Why doesn't anybody seem to be bothered by the fact that our whole Standard Cosmological Model is based on a philosophical assumption that will never be able to be proven by experimental observations, namely the homogeneity of the universe?

[@itisinickt]

i bothers me. one day we will find out everything is wrong and based off one random guys thoughts 100 years ago

[@adlockhungry304]

Well, we do have a roughly homogeneous observable universe, based on observation.

[@Faustobellissimo]

@@adlockhungry304 No, observations are about isotropy, not homogeneity.

[@DrWhom]

@@Faustobellissimo nope. but if it bothers you, think about the negation of that assumption. if you are smart enough, that should bother you even _more_

[@Faustobellissimo]

@@DrWhom WHY?

[@nickisnyder3450]

I have a 9 year old grandson who was listening to a PBS SpaceTime on Space expanding and when it was over he told me: of course space is expanding grandma because space is spinning and that causes everything to go further out. If you had food on a plate and the plate was spinning it would fly off . I know the Earth is spinning around the Sun which is spinning around the black hole at the center of our universe but it didn't occur to me that even the galaxies are spinning, that the whole fabric of space could be spinning

[@OcrimIlle]

Question: galaxies far away are receding faster than near galaxies but galaxies far away are far also in time so we can only know for sure that they were receding fast in the past. How can we know that they are still receding away at that speed now? Is it possible that they slowed down in the meanwhile?

[@Roman8707]

A question I've been asking for a while as well but have never gotten an answer to.

[@wolfgangkranek376]

As far as I know actually it is speeding up, but ... Look up: "How Is The Universe Accelerating If The Expansion Rate Is Dropping?"

[@filipsperl]

I don't think there is a logical reason to believe they have slowed down since they emitted the light we recieve today. The farthest galaxies discovered are almost as old as the universe itself and if they behaved significantly differently than our closest neighbours, there would already be big headlines about it. Unless you're talking about galaxies slowing their recession over time being the reason we percieve the closer ones traveling slower. In that case, you can prove that galaxies are accelerating regardless of their distance from us based on at least 3 measurement at different times. That must have already been done.

[@OcrimIlle]

@@filipsperl I don’t quite get how this 3 measurements would prove that the expansion is accelerating

[@Yonasu]

Measuring the same galaxies over time?

[@michaldemjancuk3129]

Question: Well if fields strength decrease with square function (gravitational, electromagnetic...)f(x) = 1/X² ... Isn't there possibility, that light is just an field (which is basically true when it behaves like wave in some cases), so that would mean, that there's no redshift of distant galaxies moving away from us (because of the dark energy), there would be just weakening of the field (lowering the frequence - fake redshift), therefore there would be no expansion and it would explain the paradox with the thing that the spacetime is being created (Dark energy grows on behalf of nothing - like energy density etc...) and even not at the same rate everywhere, because of the gravitational pull in same places. What about that, is this possible, or what had I missed. Thanks a lot and sorry for not the best english... Love your show.

[@ThatCrazyKid0007]

I haven't done the math so it's just a guess, but I don't think the wavelength shift in the redshift matches a 1/r^2 function. If it did I think astronomers would've picked up on it immediately.

[@adlockhungry304]

Great question! And good answer! I’d love to see an episode that addresses this!

[@philphil3386]

Ok now, you get a big thumbs up from this nerd for one specific part. Not that I didn't enjoy the whole video, but the very end resonated with me. Like whoah dude. LOL What is space is flowing, not expanding? Then what? What if it's more like water in a river or ocean, than a self propagating expanding balloon.

[@Khorzho]

Wouldn't this mean there is an actual 'barrier' at the edge of the galaxy's influence, where external space time starts to stretch away?

[@sithlorddread8721]

Stretching away infinitely...

[@curtissharpe7084]

Yes and no. Time appears to be relatively static in it's scale outside of dilation as a result of extreme velocity, and resultant relativistic mass. If we assume that each object (read particle) in the universe is itself at rest (from it's own perspective, aside from any greater external masses exerting force), which they are, then the difference in the rate at which time 'moves' does not change, only apparent distance.

[@Lakoda26]

Question: What am I missing, if dark energy increases as empty space increases and energy cannot be created nor destroyed, where is the increased dark energy coming from?

[@narfwhals7843]

Energy can be created or destroyed in an expanding/contracting universe. Energy conservation applies to systems whose rules don't change over time. That isn't the case with expansion.

[@JasonEllingsworth]

You are missing about 99.9% of the information we need to even begin to make any kinds of assumptions on how our universe works. Every single statement being made is just a highly speculative theory.

[@seank7288]

I mean, I think he said space creates time, so dark energy being created by expansion doesn’t sound that crazy.

[@lrdrskillz1]

I have had this question for like 10 years... thank you for answering it

[@simonbrissenden5878]

This is a very clear explanation of a flawed theory. A general relativity expanding spacetime explanation for cosmic expansion requires dark energy to reconcile observation with theory, while a special relativity Doppler explanation for cosmic expansion does not (despite what Davis & Lineweaver inaccurately claimed in 2003). There is a paper in the April 2020 Journal of the Royal Astronomical Society of Canada "Matching Supernova Redshifts with Special Relativity and no Dark Energy" that documents this little known fact. What about doing a video on this?

[@aquaintsound]

Glad I stumbled onto this comment!

[@DrWhom]

he can do a video, explaining why it is a non-starter, and then you'd be less happy than you are right now

[@brucefoote540]

This is so simple it almost hurts me to think about it. Is it possible that all that out there, is not expanding Hubble style, but rather our measuring standards are contracting as we are falling "down" into the center of the black hole we are living within? They are not moving away, but rather we are falling at near the speed of light "down" into the center of our "black hole" and so "they" seem to be "moving away" that's why we can't see beyond the rim, the Swartz shield of our universe?

[@garethdean6382]

An issue would be that we'd be in the center of this hole, or near to it. That'd be quite a coincidence.

[@Morilore]

10:51 wouldn't the distance btwn any two points be a linear combination of 0,1,2,...,n-1,n,n+1,... Planck lengths? Any measurement would only return an integer but the expected average value (which is only a mathematical abstraction, after all) could be any real number and could grow continuously as space expands.

[@danielmihalik2785]

This might have an obvious answer I didn't think about but how do we know that it's the distance increasing instead of the speed of light decreasing? If the speed of light suddenly dropped in half, wouldnt that seem like the distance of everything doubling?

[@wingracer1614]

Yes. Just one problem, can you show any way for light to go twice as fast? Because everything we know so far says that is impossible and there has never been any observation showing such a thing.

[@RobertWF42]

Good question - I recall from college physics class that Maxwell's equations can be used to solve for the exact speed of light based on some other constants. I suppose those constants could be slowly changing. I think the red-shifting of light emitted by galaxies billions of light years away is evidence space is expanding rather than light slowing down.

[@CMVMic]

@@RobertWF42 isn't the red shifting observer dependent. It has to do with the location of the observer.

[@kylelochlann5053]

No that wouldn't work as so much of fundamental physics is dependent on the speed of light, for example the fine-structure constant would then be time dependent and this would show up in spectra of the early universe. That said, however, you could have a shrinking matter universe under rescaling of dimensionless constants which in every way reproduces the observed expansion. There is no way to tell the difference between shrinking matter and expanding cosmologies.

[@danielmihalik2785]

@@wingracer1614 Yeah, but light going twice as fast would still be OK, since it wouldn't be "faster than light" The speed limit is not 3*10^9m/s, it's the speed of light

[@sthomas6369]

I'm not wrapping my head around how you can reconcile "map any point in the early Universe to the future Universe" with the notion that you can "add Plank lengths". Perhaps I'm over simplifying but if you had a volume of Plank length cubed in the early Universe, the vertices could be defined as "points in the early Universe" and then as the Universe expands, you add more Plank lengths, don't you now have more points in the future Universe than in the early Universe, and you break geodesic conservation?

[@deltakurshiva]

As I understand it, it's just that a "point" in the geodesic sense does not refer to "a vertex in the planck length grid". The former is infinitely densely packed (you just pick your "point"), while the latter is finite per volume of space. The grid stays constant, but the coordinate system in which the grid is defined is infinitely finely scalable , and a "point" is an arbitrary coordinate. Remember that the planck length is a distance and not an absolute position.

[@luvcherry]

I think because the plank length is just a relative distance for us to measure not an actual "thing" that would get bigger or not, I think if a random quark (I'm no scientist) was hanging out alone in empty space the expansion wouldn't get so big around it that it suddenly loses meaning in how we understand physics which is what the length is for if that makes sense (?)

[@DJThermite]

At 8:48, is that basically just gravitational inertia through time? Meaning the force of expansion is insufficient to overcome a certain amount of local gravity?

[@TrimutiusToo]

But question still remains... Does dark energy affect the size of galaxies?

[@ThatCrazyKid0007]

I don't think so, the mass inside the galaxy curves the metric so it's static around it and thus no expansion. What deternines the size is probably the amount of matter that got clumped together during the early universe period before the dark energy whisked away the more diffuse matter that didn't get as strongly gravitationally bound to the rest of the matter that would later form the galaxy.

[@TrimutiusToo]

@@ThatCrazyKid0007 question is, what is the density of dark energy inside galaxies, because if it is significant enough it will still have some effect

[@kylelochlann5053]

Yes, but the effect is small as galaxies are relatively small and have relativity high energy density.

[@masterofdoctory]

Nonphysicist Question: What is the difference between universal expansion, and us "shrinking"? If many worlds is correct, and Sean Carroll is correct that it doesn't cause the creation of energy/mass, then is it possible that the expansion of the universe is just an affect of our many worlds "separating" causing our instantiation to have a lower energy density which just appears as us shrinking / our universe expanding? Well I hope that doesn't come across as ridiculous as it reads... Either way, please answer. I can't find anything on the internets that answers my question.

[@deusexaethera]

Matter doesn't just lose energy while sitting around like that. If it did, we would see particles getting lighter as time goes on, evidenced by an increased acceleration within electromagnetic fields in lab experiments. We don't see that.

[@jpt3640]

To me your thinking makes absolute sense. It means: does our meter shrink or does the paper expand? We just cannot know. But well, the second is more likely. ;)

[@masterofdoctory]

@@deusexaethera Thanks for the response :) How would you know mass was dropping? You'd need to compare to something right? I don't know how to ask this properly, but imagine the four fundamental forces are devided out amongst the "many worlds" scaling down measurable forces proportionally... Hope that makes sense.

[@masterofdoctory]

@@jpt3640 lol. I'm pretty sure I'm wrong. Just trying to understand why. I mean no offense, but do you have reason to suspect I'm right? Other than it seems possible at a first glance?

[@masterofdoctory]

Also, I'm not saying, "just lose mass / matter while sitting around." I'm asking if the creation of "many worlds" causes expansion (or shrinkage) within our instance of ST while maintaining a sort of cosmological energy density across the many worlds... Christ, that reads crazy. Please know I'm not crazy, just stupid :)

[@Chance57]

Frankly, I'm afraid this is my limit of understanding. I've heard this idea explained 10s of times and it never clicks. I'll probably have to take a real deal physics course to go beyond. Hopefully the amazing work you guys have put out, alongside other creators, will have been a benefit to me when I do.

[@karlkarlsson9126]

I think 09:00 sums it up, we don't have a theory for what space is actually made of.

[@aigarius]

Is there a consideration on the possibility of the expansion of the time dimension as well? Wouldn't the plank length expansion actually explain or cause the creation of the phantom particles in vaccum?

[@Rayalot72]

@Kleos Weird Schizo sales scheme.

[@The.Renovator]

So, if space can expand infinitely and contract infinitely, wouldn't this give even more merit to the idea that inside of a blackhole is another universe? Maybe time begins flowing backwards at the singularity and gives rise to a universe that expands infinitely instead of contracting infinitely?

[@CMVMic]

Infinity is paradoxical

[@osmosisjones4912]

Maybe the big bang started in a black spot before the previous universe ended

[@titian5298]

nice conjecture

[@osmosisjones4912]

Maybe the speed of light is the speed it is because of 2 opposing forces pulling on space Time in the speed of light is how it balances out

[@sonicgravitypodcast4436]

great show--love it; happy to support it on Patreon too. I think black holes actually blow out spacetime, and the gravity of the black hole is constantly pulling in the accretion disk and the rest of the galaxy together--inward, but spacetime blowing out of the black hole continually gives the accretion disk and the matter in the galaxy room to continuously circle the drain. I can't help but think that space is moving through us the same way time moves through us, and that's why there's no noticeable expansion within our galaxy. the universe is expanding the further you look out because there are more black holes between us and that spot (the further you look out), and it's possible that the pressure pushing the universe apart is the space those black holes are ejecting elbowing for room. I wrote it down--and a theory of quantum gravity here. I know it's kind of woo, but I learned it all mostly from you, so blame yourself for getting me excited about quantum physics. And, I hope you read far enough to the part about how bumblebees flap their wings at 600x per second and hummingbirds at 200x per second (not because they have fast muscles, but) because they have slow time. Anyway, love the show--nourishes the brain and the imagination. Here's the proof. www.sonic-gravity.us/blog/sonic-gravity-draft-gravitational-research-foundation-essay-contest/

[@supersmily5811]

That leads to the obvious question: If space isn't expanding here where we are but IS expanding in space with less matter in it: What effects would expanding space have on a human or their spaceship travelling between galaxies? That could be an additional limiting factor on space travel beyond breaking the speed of light.

[@nenmaster5218]

Want some scientifc watch-suggess, i ask around, for no deeper reason but to share science-fun?

[@xBris]

Hm. If new spacetime has non-zero energy density, then doesn't that mean new energy is created? Doesn't that violate some fundamental laws?

[@debray-kingbomatthieu5579]

Violate the conventional law, the law which rules our measurement.

[@TheA13000]

Really an Interesting question. Maybe dark energy got properties that eludes traditional physics. Well, could it be some kind of inertial momentum of the big bang expansion, and by so, infinite, but not very strong for some reason? If the universe is infinite, of course. I'm not really sold by my own idea, maybe I miss some notions.

[@DIGtotheIT]

The fabric itself probably has zero energy

[@debray-kingbomatthieu5579]

@@DIGtotheIT Yes, zero energy zero density in our values, not in the real value. It's probably energy which span instead energy localized. This means : negative, growing energy, growing empty volume. That's true because theorically a particle beyond light speed see its kinetic energy increase in every direction, its vibrations stretches, in the best case in turns more massive. You could use this particle, in a lot of alike, and use it to perform light speed propulsion, why not go faster than light in a light speed frame.

[@ExaltedDuck]

I'm always amazed at the local expansion of space around my midsection. It's not that noticeable month to month or year to year but on time span veyond that, it's absolutely undeniable.

[@happygood18]

How Big is Observable Universe? Light Speed × Universe's Age Right? 🙂

[@247tubefan]

I think space itself expands faster than lightspeed.

[@RevolutionAdvanced1]

Significantly larger due to inflation. Something like 90 billion light years across if I remember right.

[@happygood18]

First, I want clear out that I am just an average person on science. Secondly, this is a idea of mine about the *OBSERVABLE* Universe. Nothing serious here. *Finally, Isn't observable universe as big as far light reaches, otherwise how will we observe it? Note that I am talking about observable one. Oh and, I don't know if light also expand with universe or not.*

[@happygood18]

@@RevolutionAdvanced1 Check my latest comment.

[@happygood18]

@@247tubefan Check my last comment