Will the Big Bang repeat?

[@SabineHossenfelder]

Completely coincidentally, Paul Tod put a new paper about Conformal Cyclic Cosmology on the arXiv just a few days ago. Among other things, he addresses the point I mentioned in the video about the eon-to-eon feedback, though the brief answer seems to be no one really knows: arxiv.org/abs/2202.10864

[@Benjamin_Gilbert-Lif]

Ohhhhh been waiting for this video!!!!!

[@smlanka4u]

The universe can start from 0. And then it can continue to the next 0.0 point and so on. The first universe started like this (+0-0)^6 and then (+0.0-0.0)^6. It makes all the elementary particles and interactions. It can continue making big bounces. There is a published research about it.

[@brothermine2292]

Why must feedback be positive (growing over time)? Negative feedback can cause regulation (settling down over time to a recurring pattern). Sequences can be either divergent or convergent, depending on the details.

[@hannybenny7632]

Maybe the cosmos repeats itself quantumphysically endless times and every conscious being lives his live again and again exactly the same ;)

[@brothermine2292]

@@hannybenny7632 : There's an old saying: "Stop the merry-go-round; I want to get off." I tried googling for a few minutes to try to find its origin, but failed, so I assume it originated during an earlier eon.

[@Lagrange_Point_6]

Excellent. I enjoyed that talk. Have to say, I rather like Penrose's CCC idea. It's a brave effort. He himself admits it is quite speculative and I am sure he'd have no problem with it being discussed in this informed and fairly detailed way.

[@johnsmith1474]

She was hardly detailed, she was dismissive. The elephant in the room is the 2cd Law, while everyone else ignores it, Penrose hunts it down and kills it.

[@victorblaer]

@@johnsmith1474 i agree. What intrigued me was the intensity vs frequency , graph which Penrose references in 'what happened before the big bang '. Specifically, per the 2nd law of thermodynamics, entropy increases, yet he makes an argument from empirical data that , apparently, entropy was maxed out at the big bang ...

[@NiteTrain345]

When Penrose speculates, I listen. One of the greatest minds of our Aeon, IMO.

[@Lagrange_Point_6]

@@victorblaer Yes. The entropy question is really quite fascinating. I've heard Penrose talk about this and, although it's a bit vague without the mathematics, he certainly throws up a number of deep philosophical issues I enjoy exploring.

[@DrVictorVasconcelos]

@@johnsmith1474 Of course she was dismissive, but that's because there are no praises to sing about. There is nothing there yet. It's speculation and Penrose himself knows this. The only actual test of his theory with real data to lend any credit to it is widely contested. And if you watch until the end, you'll see that she clearly states that the entropy issue is indeed a problem that receives less attention than it should.

[@TheoriesofEverything]

Yes. Looking forward to watching your comments on Penrose's ideas.

[@gangsterkami1]

My man Curt all over the internet. Listen here everyone. This man does the best interviews on physics, metaphysics, consciousness and God. You need to subscribe to this channel.

[@numbersix8919]

@@gangsterkami1 Is he part of the IDW?

[@iamlovingawareness2284]

@@numbersix8919 I don’t find that description particularly helpful. He’s intelligent, but his platform is open and easy to find. Why people call it “dark web” I haven’t quite understood. Maybe you could assist me with that?

[@numbersix8919]

@@iamlovingawareness2284 It's that place where AWMs flock to get their freeze peach. Dark! On occasion, someone who has something good to offer the world is also hosted.

[@angrymokyuu9475]

@@iamlovingawareness2284 "Intellectual dark web" was coined by some whiny researcher who didn't like what some people had to say. Since these people tended to have overlapping audiences, they're a "web". It's a "dark web" half because they're normally something you have to go somewhat out of your way to get to and and because that term has negative connotations. Some people gave that academic the ultimate middle finger by wearing it as a badge of honor, but I'm surprised anybody uses the term in either sense.

[@alisaiterkan]

I had been waiting for this episode! Penrose's contributions for the geometrification of the puzzle we have been trying to solve has been spectacular; and he seems to be such a gentleman that one can't help but root for him. Still, I don't see this video as a negative thing at all. When one gets on the podium and says "I claim X", the audience is supposed to ask how/why? Sabine is doing just that. I now hope for a response from Penrose.

[@RandyLunn]

Sabine, after every one of your videos, I have more appreciation for you and your ability to capture the essence of a topic in a concise and understandable manner. Thank you.

[@geraldvaughn8403]

I think Penrose has a point. Rescaling can be done when all matter has decayed. No matter means no time which means no distance.

[@LucianCanad]

So if I'm getting this right, rescaling would happen because, once the universe runs out of matter, it doesn't have a reference point anymore. That would enable a "system reset" to where the matter parameters (such as time and distance) made sense again?

[@Chance57]

Yes, that's the main conceit. In that reality, the figurative tree _doesn't_ make a sound if no one is around to hear it. I don't see why the actual fabric and spacetime decides to go "quick! No one's looking! Get really small again." I would like to know what it is exactly the universe is doing in those moments. Sure, the photons don't know what's going on because their perspective is whacked out, but what makes space-time contingent upon that? They don't all have the same energies and thus their wavelengths and with it, their frequency. You'd have to take inflation so far that energy levels got so low it wouldn't make sense to group electromagnetism together as one force anymore. By the time it would make sense to consider the photons alone, it wouldn't make sense to consider photons at all given such monolithic low energy fields.

[@Alexxf35]

@@LucianCanad The main question is what exactly would the Universe do once there is no matter left in it? Can it exist without any matter, or "reference points"? Interesting thought experiment.

[@bibekanandaghosh3625]

I'm very weak in physics but how would the heat increase? The end of aeon is cold but big bang as we know it is hot, what caused the increase in heat

[@rman229]

@@bibekanandaghosh3625Pressure

[@painless4785]

Without being able to imagine a 'beginning', Penrose's idea seems to be the most intuitive, which is why im drawn to it. I recognize that the universe is not always intuitive.

[@ProfShibe]

Same. I think current CCC is probably off, but something similar I think is very possible. Else what are the chances there’s only one universe (ever) and it just so happens to randomly have certain laws of physics allowing it to observe itself by pure chance? I really doubt that’s happening. Makes more sense it repeats and possibly has different laws for whatever reason too.

[@wordcel]

@@ProfShibeWhy should it have different laws on every cycle? The laws themselves are what make a cycle intuitive

[@johnholly7520]

I love getting notifications on Saturday morning letting me know that Sabine has dropped a new episode. I hope your back is doing better!

[@emalee8366]

I have the same experience. Always look forward to her videos.

[@cagrulucyildirimoglu771]

Even though there are many holes in this idea, it is incredibly creative. Thank you for the video!

[@PrzemyslawSliwinski]

How does conformal scaling affects/is affected by the speed of light?

[@brothermine2292]

It takes genius to invent a theory that other genius skeptics haven't been able to falsify.

[@HarryNicNicholas]

@@PrzemyslawSliwinski how do you imagine? penrose may have modified his idea but last i heard at "the end of the universe" we only have photons, photons travel at lightspeed so in effect there is no "size" to the univese any more, their journey, in photon time, takes zero time, so there is A no time and B no distance = we have conditions for another big bang.

[@PrzemyslawSliwinski]

@@HarryNicNicholas Photons and 'gravitons' I suppose - since they predict a kind of inter-eon gravitational waves? I just struggle to reconcile the different size scales of eons with the same speed of light in each of them.

[@sanjursan]

Yes, incredible is the correct description.

[@gefginn3699]

I appreciate the education I receive here on this channel. Much love and care and blessings to you Sabine.

[@michaelsommers2356]

Penrose gave a talk at my university when I was an undergrad. In the Q&A I asked him about cyclic cosmologies. He said that they were only possible in perfectly uniform universes (at least that's how I remember his answer). I guess he's changed his mind.

[@thorium222]

Well, as far as I understand it he has concluded that the universe is perfectly uniform at the end of time.

[@spaceman081447]

@@thorium222 RE: "Well, as far as I understand it he has concluded that the universe is perfectly uniform at the end of time." Well, that would make sense. After trillions of trillions of trillions of years, when protons have decayed [?], black holes have evaporated through Hawking radiation, and, because of the continuing and extreme expansion of the universe, photons of all frequencies have been stretched into extremely low frequency (ELF) and low energy radio waves, entropy will have been maximized. That would seem to be "perfectly uniform at the end of time."

[@clocked0]

@@spaceman081447 And as far as relativity is concerned, the massless particles would also be bunched up into a singular point due to the inexistence of objects with mass and therefore the inability to measure any distance from the reference frame of the massless particles in question since without time nothing can evolve over... Well, time, and relative to a massless particle it gets absorbed at its destination the same moment it is emitted. So because of that, it physically cannot be anything but uniform in those conditions according to both Penrose and special/general relativity. There is literally zero room for anything but uniformity under those conditions.

[@spaceman081447]

@@clocked0 Well, that would obviously be true at the moment of the Big Bang, but we're talking about "the end of time."

[@clocked0]

@@spaceman081447 That's the point of CCC - The end of one universe is supposed to coincide with the big bang of another. The two are equivalent. That wasn't metaphor it's to be taken literally. Massless particles cannot measure time. It is literally the end of time according to GR.

[@Petrov3434]

Thank you, Sabine. One interesting detail you didn't mentioned is that close to "eons end" universe consists mostly of photons and photons are not "bored" with infinity -- they live in their NOW..... Altogether, I am happy you have addressed CCC hypothesis and -- I immensely value your efforts to popularize science. I am also grateful for your performance art and music !!

[@ollywright]

Thank you for covering my favourite crazy theory. It's fun trying to explain the conformal boundary to people, and the idea that the universe could become conformally invariant (and why).

[@MeppyMan]

My brain was in a superposition while watching this video. It both made complete sense and was simultaneously unintelligible.

[@CAThompson]

Me most Saturdays. 🙂 Mountain tops through the fog.

[@hughcaldwell1034]

I really like this idea from an aesthetic point of view. Though, as my father-in-law observed after I gave him a (very rough and ready) explanation of what CCC was, "Only a mathematician could think it worked that way." I.e. same as Sabine's question of what the conformal rescaling actually means in practice. Which is a fair objection, and one I leave to the actual physicists. The idea that reality might be so pure in its adherence to mathematical elegance is too good to be true - but this platonist lives in hope.

[@kfurgie999]

What made the philosophical aspect click was to consider the 'perspective' of a photon, which you shouldn't do since it's kind of meaningless, but if you do, you get that the photon travels 0 meters in 0 seconds. So, what I take from this is that space and time are only really meaningful if you have mass - or as Penrose puts it - if the universe can build a clock (and a ruler) No matter = no way for reality to define space and time, in fact, the whole of creation might as well be infinitely dense - without matter there is nothing to tell the difference between infinite density and total vacuum & no way to tell the difference between infinite time and no time at all

[@kfurgie999]

0 meters in 0 seconds applies when a photon travels one meter, or billions of miles between galaxies. For the last light of the universe, when there is nothing left for the light to reach - one wonders where it will go at the end of its existence - after 0 meters and 0 seconds - too

[@AlexanderGieg]

MetaBallStudios's "AGE of UNIVERSE" video has a nice easter egg at the very last frame of the video showing how it might work. It's just an artistic representation, but funny all the same to think about. Check it out and, if you don't catch it, just pause it at the very end and you'll see it: kzbin.info/www/bejne/kJOYooeal5t_mK8

[@DrVictorVasconcelos]

@@kfurgie999 I see that's the example that Penrose himself used in one of the videos about CCC. But that's not philosophical, that's scientific and physical. Neither photons nor any particle that travel at the speed of light "feel" time. Such particles, for example, do not decay; they don't "evolve". This is partially how you can tell that neutrinos travel slower than c from their evolution between neutrino types.

[@DrVictorVasconcelos]

You know, this is one of the biggest things to look out for with these theories. Theories that conform to our decidedly human ideas of aesthetics are more appealing but there's no reason to think that this leads anywhere. Unfortunately we select for this at many levels, such as when deciding what to think about, then deciding that an idea is worth writing, and then the editor and reviewers deciding which articles to publish, and then other people deciding on which theories to work on and eventually expand on. I think cosmology is the one field where you couldn't possibly make an argument for mathematical beauty (which many physicists do make in other areas).

[@bishopinskipp2113]

It may not be what really happens at the end of time/matter, but it is the most philosophically pleasing I've come across for a while. Rogers explanation of CCC helped form a model of all of space, time and infinity in my mind. However, nothing is really answered unless you know how the first in the chain starts.

[@BillyViBritannia]

Why should there even be a first?

[@IncompleteTheory]

At last, thanks for this Episode. I missed some more details about the fact, that CCC does not need an inflation part, because what we need for the inflation part of our past is naturally the expansion of the previous eon. I always found this an interesting part because the current inflation theory always seem a bit like a hat trick to me. Anyway, thanks for the episode and the much more polite than usual way to discuss/criticize a very decent man's theory indeed.

[@dewiz9596]

It seems to me that we have to deal with a lot of complications because of the “fact” that the expansion of the universe is accelerating. This acceleration, is, of course, based on our current “best efforts” at measuring cosmological distance. To me, distances beyond what are directly measurable by parallax methods are suspect. Given that the strong nuclear force is an (extremely) local phenomenon, why are we convinced that gravity and/or electromagnetism not also local, with a redefinition of what “local” means on these scales. . . As for inflation. . . I’m reminded of a cartoon, where a white-coated researcher standing in front of a blackboard full of equations says “and then a miracle happens”. Thanks, Sabine, as always, for making me think.

[@orri93]

In R. Penrose favor I have heard him call CCC "outrageous" so he knows that it is a wild speculation. But if I remember correctly, he originally studied mathematics and they can do wild speculations and crazy generalizations. Also I have heard him explain that at the end of each cycle every particle would need to decay to photons. If only a single massive particle is left the whole thing doesn't work. Anyway thanks 💕 for a good video.

[@sagestrings869]

Black holes and Quantum tunneling would eventually turn all matter into massless particles

[@orri93]

@@sagestrings869 maybe 🤔 probably but we can't be sure (yet). Still no experimental result that demonstrated Hawkins radiation not proton decay.

[@sagestrings869]

True~ But I feel like protons not decaying make sense to explain the anti-matter paradix

[@orri93]

@@sagestrings869 how does proton not decaying explain the Baryon asymmetry mystery?

[@sagestrings869]

@@orri93 Well purelt speculatively if protons dont decay it very well maybe that when the big bang happens the number of Protons remain stable due to the equal creation of matter and anti-matter

[@greatPretender79]

Another one I had to watch twice and REALLY enjoyed. I like Penrose's theory, and trying to wrap my brain around the scaling, and the transferring of information from eon to eon!

[@JaleneR]

This is by far the simplest and clearest explanation of CCC I've seen to date, and I've watched many of Penrose's lectures on it. Thank you. :) That said, the theory still raises so many questions -- or perhaps I am simply unable to get my head around the (physical?) mechanism that begins a new eon.

[@DrVictorVasconcelos]

Absolutely. It also serves as a great introduction to PBS Space Time's "The Edge of an Infinite Universe" about conformal transformations and "What Happens After the Universe Ends" about CCC. Also related is PBS ST's "The Holographic Universe Explained" (which should be watched before Sabine's "Is The Universe REALLY a Hologram?")... but before the holographic principle you should learn about the "black hole information paradox"/"black hole information loss problem" for which both PBS ST and Sabine have videos and string theory basics which are on PBS ST as "What Are the Strings in String Theory?", "Why String Theory is RIGHT" and "Why String Theory is WRONG".

[@fteoOpty64]

I don't think any human can. They tend to just 'invent' stuff to fill-in the missing pieces. Yes, just to balance the equations. But the math is questionable from the start. Assumptions are several orders of magnitude too small. You would need 2k+ Einstein brains to solve it.

[@freefall9832]

It's all about time, fun to think about

[@unscrupulousyou]

Yeah same. I'd love someone to explain how new matter is formed in the new aeon. Anybody?!

[@PietroSperonidiFenizio]

You can see how much Sabine respects Penrose by the fact she practically made no joke for the whole video.

[@macysondheim]

Yea cuz Penrose the Big homie of the science community. Penrose been solid & he ain’t tryin to play games w/ these youngsters out here. He ain’t got time for no jokes like that..

[@johnvosarogo1785]

Some thoughts I've had regarding this topic: I think the best or most useful conceptualization of time is as a measurement of relative change. Anytime time is referenced change must always also be referenced. So change is fundamental to time and given a static closed system there can be no internal clock. An implication of this seems to be that once the universe evolves to it's final state of absolute heat death. Where any remaining undecayed particles are so isolated that they can never interact with each other and so for all intents and purposes there is no longer any relative change in the universe and all that's left is besides individual isolated particles is the quantum fluctuations of empty space. When the universe arrives at that state, time has essentially stopped since there are no longer any events by which to measure time. From that point on, anything that does happen could be said to happen instantly afterward. So, imagining an external clock, if it took a near infinite amount of time to elapse on that external clock for the quantum foam to produce a fluctuation that evolved into the next iteration of a material universe. From the internal perspective, lacking the concept of time following the heat death of the previous iteration, the emergence of the next could be said to have happened instantly following the end of time of the previous. Therefore it becomes easy to imagine that the near infinite amount of "time" required for the quantum foam to produce a fluctuation that will evolve into a material universe is actually no time at all. The ultimate implication of that being that not only is the emergence of a universe out of the quantum fluctuations of empty space probabilistically likely, it's inevitable, since whatever time is required is available and actually is relatively instantaneous from the perspective of a changeless universe. All of this however assumes eternally expanding space filled with quantum foam. How that originated, why there's even that as opposed to true nothingness? Probably has to do with probability and the uncertainty principle in a way thats difficult for me as a layperson to conceptualize or explain but I feel like I understand intuitively. True nothingness is a form of absolute certainty and the uncertainty principle is such that a state of absolute true nothingness must instantly and randomly evolve into a state with non zero energy. Or something like that. @sabinehossenfelder I'd love to know if you, or anyone else reading this, thinks any of it makes any sense lol 🙏🏽🙌🏽🌌

[@AugustinHadelichViolin]

I've been waiting for this video from you, ever since I watched a talk by Penrose about this. Also, did anyone notice the cyclic nature of the title screen at 0:52? That was a nice touch!

[@soultrick7474]

So happy that CCC gets more and more attention! Better later than..... Sir. Roger Penrose is our time genius, for the rest of us would be wise to listen more closely what ppl like him has in mind. Thanks Sabine :)) Word hypothesis kills me every time tho :D

[@BANKO007]

This is the first time I have half understood CCC and the most mind-boggling explanation of the universe I have heard, apart from all the other ones.

[@philochristos]

This was really good. I have a lot of reservations about Penrose's model, too, the biggest being the one you brought up about the physical meaning of the math and whether it really makes sense physically. But you brought up some others I hadn't thought of, and you explained them really well.

[@buddypvaz124]

Sabine, you are a rare source of enlightenment, entertainment, life affirming knowledge and I look forward to every opportunity I find to watch your lectures and discussions. I am improved every time I see another of your productions. Thank you for that.

[@jankadlcek608]

This kind of reminds me the hypothesis that the higs field might have more than one stable energy level - and it might be statistically possible for the universe to switch from one to another. Such a switch would reset everything in a really hardcore way and as it is about the higs field, it would comply with Sabine's request to deal with all the massive particles in the process. :)

[@howardandsuzie]

O

[@alakani]

For all we know vacuum decay might have already happened and this crappy universe is just one of the expanding death spheres :p

[@numbersix8919]

@@alakani That's why we need physicists.

[@deshaunjackson8188]

No

[@shayneoneill1506]

I think as a general rule , if it could happen it probably has happened is a good metric, and the fact it hasnt suggests we're probably safe. There is one thing thats often missed though. Expansion of the universe means that since a vacuum collapse happens at the speed of light (or half light speed, theres a few lines of thinking on that) but no faster the universe might well be filled with collapsed vacuum, but it'll never reach us since we're moving away faster than it can expand

[@scottlypuff]

found your chanel the other day by grace of the algorithm and i am OBSESSED and have been bingeing for days maaany thanks!

[@phillupson8561]

My thought on this was if the universe continues to expand, eventually all matter would be separated out and simply not interact with any higgs fields, as time continues and less matter interacts with the higgs field the mass would appear to decrease, if E=MC2 (sorry no superscript) and E is fixed, then as M approaches 0 C would approach infinity, eventually the separated matter would accelerate to such speeds it would be almost everywhere at once, this would then mean collisions can happen and thus kick off a big bang. Ahh the joys of oversimplification.

[@Benjamin_Gilbert-Lif]

That’s what I figured as well but gravity may never be strong enough to break the strong nuclear force that would be nessesary for that, if it does or if matter decays than this seems plausible

[@gljames24]

here you go ²

[@LordAmerican]

Your idea about E=mc² doesn't work because that is for rest mass. The full equation is: E² = m²c⁴ + (pc)² ; where p is momentum. For massless particles this equation reduces to E=pc. You might think that it makes no sense for massless particles to have momentum because p=mv, but momentum doesn't actually require mass. In the case of massless particles the momentum is a function of their wavelength. So c remains constant no matter how low the mass gets. Also I fail to see how particles being spread out through space would stop interacting with the Higgs field. Being a quantum field the Higgs field would permeate all of space-time, just like any other.

[@woobilicious.]

@@LordAmerican I'm no physicist, but the Higgs field is scalar, which makes it "more interactive" than other fields, at least with say the EM field a particle that's red shifted outside of the causal horizon, then the field is effectively useless since it can't be used for any sort of interaction, but a lone proton can still get it's mass from the higgs. Pretty sure CCC requires a Higgs phase transition / decay, unlike the others.

[@khhnator]

wasn't VSL theories a big deal a few years ago? i surely remember more than one "joão magueijo changes the laws of physics!!" documentaries on discovery before the channel became mostly reality shows

[@katgirl3000]

Really interesting! Currently taking an introductory GR class right now and just a handful of pages from the Weyl Tensor description :). Been balking at getting through The Road to Reality so this was a terrific summary of Conformal Cyclic Cosmology! :). I Always get a lot out of your videos!

[@dj_laundry_list]

10:40 The fluctuations feed into each other recursively, but what is to say the gain is greater than 1 if they in fact amplify? Or what if there is some kind of destructive interference?

[@CAThompson]

And wouldn't that mean each new eon starts with more entropy?

[@brothermine2292]

I had the same question as your first question, about the possibility that the feedback might not be positive feedback, which I asked in a reply to Sabine's pinned comment.

[@SabineHossenfelder]

Yes, you are right, that could happen too. It's just that the way the thing with the Hawking points works out it looks to me like a positive feedback. In any case, I think no one really knows at the moment. It will be interesting to see how this develops. I really quite like Penrose's idea.

[@Achrononmaster]

You can sure say "more work needs to be done" but also there is a principle that can help CCC. You cannot get an exponential inflation unless there is a point in the far future aeon where a conformal rescaling actually does look (after you rescale your perspective) like a "big bang." So it is a self-consistency principle. Unless there is such a time that mass dilutes enough for the "gods-eye" observer outside the cosmos to say, "Oh look, that looks like a Big Bang if you telescope out a gazillion light years and rescale your clock and ruler". What might be the case though is that a universe gets stuck and never goes through such a state and then gets so dilute and smooth that it is basically nothingness, and so a conformal rescaling will be present but it would be a Big Bang with no oompphhh. If you reason this far, then you can probably tell how to rescue CCC from here: if the dilution is so thin, you still have quantum fluctuations, which can seed an inflation of another aeon, after-all, orthodox "standard cosmology" assumes as much. This all depends on what energy remnants are needed to undergo a successive inflation. (Also, it should be said, if QFT effects can excite enough energy to get an inflation then such effects can also de-excite enough by chance to seed an inflation too, if we wait long enough. You do not need (do not want) perfect conformal symmetry, that would be silly, perfect symmetry is a dead cosmos, so you would not want all rest mass to vanish for CCC, just most of it). But it might answer the question about the "fluctuation gain" factor ---- the answer being you cannot excite an exponential inflation event if there has been anything other than a gain = 1.00000... plus or minus a tiny amount. Now a random walk by a "tiny amount" can go infinitely far, but we are exciting a big bang here, so it's not the same, the effect is on how rapidly the next aeon expands, an exponential expansion is a pretty uncompromising thing, it wipes out so much structure and smooths spacetime so much, those fluctuations could turn out to be completely negligible for all future aeons.

[@AquarianSoulTimeTraveler]

@@SabineHossenfelder Very good... The most crucial takeaway here is that just because you can observe something and see it from your singular point in space and time it does not mean that you can accurately map it. I honestly believe that dark matter is rings or strings that have been folded over into hooks or been ripped and are hooks because once they are ripped the film that forms in between the ring is no longer visible to the rest of us who are comprised of strings all we can see is strings. There is a fundamental interaction and it is absorbing regular energies that pass through it and increasing its density. It is the cosmic glue holding all the singularity pieces together it is what ultimately allows for the recollapse of the universe everything that we see here from the singular point in space and time is a illusion caused by dark matter absorbing energies and exponentially growing the denser it gets the more can absorb making it denser making it absorb more making it get even more denser! Ultimately even if we map our entire galaxy perfectly and explore every single bit of it, it will still not be accurate... We are being fooled by an illusion of accelerating expansion of the universe past the speed of light... This is dark matter exponentially growing because it actually does interact with regular matter which is composed of strings it folds the strings over or rips them and makes it join into the dark matter converting regular matter into dark matter. It's like a big fluid holding everything together keeping all the singularity that is floating within the fluid from blasting out infinitely.

[@pnwjayro]

Hello from 2024 where we’ve discovered a concentric ring of galaxies in the universe - whether this helps prove his theory I’m not sure, I’m just learning about his theories now because of it. These are fascinating times!

[@jamoR72]

I am so glad this theory is being looked at seriously. Your one of the first people outside of Penrose himself I have seen discussing. It seems a mathematical model is not a conformal representation to what we observe in larger structures in reality. The conformal theory reminds me of fractals but I can't help but wonder if we make an error in science in seeing the laws as fixed or constant (and though he has his controversy Rupert Sheldrake comes to mind)...As such the problem with a conformal cyclical model would be that very assumption of constants ...Great problems to ponder.

[@DrVictorVasconcelos]

It's true that this isn't talked about much, but it's partly because there isn't much to talk about. There are a numerous of similar theories and the only reason this one is famous is that the author is Penrose. I'm not saying it's without merits, I agree with Penrose and Sabine that the entropy thing is very important and often overlooked. But that's not enough to make a theory stand on its own, especially because if you're allowed to just add things to cosmology like Penrose did (which is a problem because of Occam's razor), you could create any number of theories that also "solve" that problem (to the extent that you could say that this could even be called solving the problem, which is complicated). To be clear, it's basically a given that we have to add stuff to cosmology. Current theories fall short. The problem is that before you find any evidence of it, or at least theorize about ways to look for evidence using current or near-future techology, people aren't going to be paying much attention. Before that, any theory is as good as any other. People are tired of being led astray by mathematically beautiful theories (string theory, anyone?). Anyways, if you're searching for a different resource, PBS Space Time also has a video on it called "What Happens After the Universe Ends?". Closer to Truth also has interviews with him on CCC.

[@tim40gabby25]

I see.. why should constants remain so?

[@patinho5589]

3 mins in.. great exposition of the conformal re-scaling. Really loved that.

[@aquacruisedb]

So in layman's terms, CCC is the equivalent of "Turtles all the way down"?

[@CAThompson]

And up. Or is that elephants?

[@jorgepeterbarton]

Turtles that are infinitely smaller each step

[@foketesz]

It's great to see this level of respect and good disposition awarded to a proposition while opposing it.

[@thepom88]

I always see re-runs of The Big Bang Theory on TV!!

[@gm2407]

I would say you are living in the past, but from a space time perspective there is no now.

[@greendeane1]

The most attractive delivery of unimportant information on the internet. (The end of the universe doesn't affect my life much whereas Sabine makes my day.)

[@HarryNicNicholas]

personally my bias is that i hope penrose is right, i've held him close to my heart ever since the penrose tiles thing, people who understand, and solve, other people's problems without any great effort are my favourite people. i do hope that penrose is right cos i think CCC is a neat way to get around infinities, the way i've understood it is that if you are left with only photons then time has no real meaning and distance has no real meaning, so however "big" the universe has become it is just a speck once more, but the point you make about the higgs and scale does put a spanner in the works. whatever the explanation of how the universe began, what happened at the start, what happens at the end, and will there be an episode II of the universe, i hope we find out before i croak.

[@astee58]

Thanks for an extremely informative and really balanced presentation/ review.

[@TwentyNineJP]

If this cycle exists, could previous hyper-advanced civilizations hypothetically leave a message in the CMB?

[@SabineHossenfelder]

Yes... and indeed some people have looked for messages in the CMB. They didn't find any though.

[@TwentyNineJP]

@@SabineHossenfelder Thanks for the answer!

[@jorgepeterbarton]

@@SabineHossenfelder it seems like they would have to be damn advanced type III-IV alien, and just to write "ALIEN WOZ ERE" perhaps, by current detail of the CMB?

[@tim40gabby25]

The initials "SH" can clearly be seen. I'm not making this up. :)

[@blijebij]

@@SabineHossenfelder Does that not depend on how much time a universe gets to expand after such a message? As with enough time such a message would be totally redshifted? A reset of information signature to a lowest energy mode?

[@bartswitalski]

My favourite science explainer take on my favourite speculation in Physics/Cosmology? I'm sold

[@cmilkau]

The Higgs field is the only field with a positive vacuum energy (I hope I got that phrased right). Could that be a false vacuum? Maybe there's a lower energy state where the Higgs field is zero? Then as the universe expands, this false vacuum could decay into a true vacuum where all particles are massless. Such a state is also be assumed to have happened in the early universe, right?

[@shawn0fitz]

It's the only field that we know of. The inflaton is also taken to be a scalar field like the Higgs, but I believe the Higgs has been eliminated as the cause of inflation.

[@denysvlasenko9175]

Individual fields have no vacuum energy. The vacuum state is the such cumulative state of ALL fields which can't lose "a little bit of energy" and go to a state with a bit less energy (IOW: it is in a local minimum of energy).

[@MadDragon75]

Being that I have been an automotive mechanic for many years, His theory is very intriguing. I stumbled upon it on accident looking for answers myself. Just knowing how a diesel engine works with compression, It definitely has my attention.

[@DasIllu]

I always wondered what happens after the heat death. When all matter finally decayed. I thought if there really is no difference in energy throughout space anymore, aka maximum entropy, then spacetime becomes irrelevant. I read about different cyclic cosmology hypothesis in the 90's. And all i could think is that maximum entropy is also minimum entropy at the same time and a "new" cosmos would "condense" out of the evenly distributed radiation. Like fog on a window. So in my mind, the requirement for another big bang is is entropy crossing a threshold that causes spacetime itself to "decay". Alright, enough crackpotting for one day, i'm an electrician, after all.

[@Shagsteri]

hmm. maybe; maybe not. In an infinite universe; there will potentially be many universes created, expanding and interacting - all with different values and energy states. In an eternal universe/cold death view; it is considering linear progression. Maybe Universes collapse or change when they intersect another universe - and that could cause a phase change leading to cycling collapse ...

[@ricardosantos6721]

if there is only 1 universe and it has a beginning and an end, then it's beyond miraculous that it can support life. there are so many arbitrary physics constants need to align for that it's not even funny

[@dglebla]

Thank you for very good explanation of conformal remapping. That was very helpful!

[@ldbarthel]

Rather than rescaling, it seems to me that the "next" universe(s) could simply be the result of a fluctuation in the vacuum state left behind by the depleted prior iteration. I can't think of a test for this idea, but it's certainly simpler and requires fewer moving parts, as it were.

[@Achrononmaster]

There is a "test" or way to rule out that idea on just known theoretical grounds. Vacuum fluctuations are not suppressed by existing spacetime, (q.v. "Boltzmann brains") so it's just a matter of waiting some absurdly long time. However, you do not get a "new" universe this way, it will not inflate, because no matter how dilute, you are already _within_ a spacetime. Cosmic inflations are truly bubbles, they do not undergo exponential acceleration unless they _are_ the vacuum. But a small fluctuation in an existing universe is not the vacuum, it is a fluctuation in a vast vacuum and so has bugger-all influence (unless it takes the form of some fantastical Boltzmann brain thing, which is real magic, not physics). Plus, the whole idea of Boltzmann brains is pretty sketchy, no one can prove for sure they are "a thing."

[@Vastin]

@@Achrononmaster Boltzmann brains frankly seem pretty silly to me. Their proposed degree of order is so high that their odds of appearance should be uncountable orders of magnitude smaller than that of some kind of random vacuum fluctuation or almost any other hypothetical starting event. Thus you should have countless 'normal' universes for each Boltzmann brain, and you should certainly not expect to live in one.

[@stevenjones8575]

@@Vastin I agree they're silly (concluding they're real assumes the spontaneous brain would have an accurate portrayal of reality to conclude its own existence). But the idea behind them is the opposite of what you said: a brain spontaneously forming is unfathomably more likely than an entire universe spontaneously forming. So, the idea goes, as unlikely as a brain would be, you'll still see many, many more of them than you would fully realized universes. But again, yeah, they're silly.

[@Vastin]

​@@stevenjones8575 It's not the idea of a brain forming spontaneously that bothers me - it's the format of it that does. A perfectly ordered blob of high density matter - even one the size of the universe - doesn't have a lot of information in it initially. It could be described accurately in its entirety with a remarkably *small* amount of data and then develop complexity from that point on. The same is not true of a Boltzman Brain, which would require an enormous amount of specific data to describe in its initial state. It's not simply that both must appear spontaneously - but that they must appear spontaneously in a particular configuration, one of which is simply in an ultra-low entropy state, while the other must somehow appear in a perfectly balanced state of partial entropy. Frankly I'm pretty sure both premises are wrong. I'm much more in the camp of the cosmological evolution arguments where universes spawn each other actively, and the initial state of reality was much, much simpler than what we see today in our particular universe.

[@rafaelgusto9476]

Thank you. Ive been followig LQG for more than a decades now. The math is cleaner and poses less problem than the mulitverse so far. Loops are far more intuitive than multiplicity.

[@szkoclaw]

Just not next week, please, I have holidays booked.

[@wayneyadams]

I watched a video of an interview with Penrose and was struck by inconsistencies, contradictions actually, in his explanation of CCC. I admit that he had to dumb it down for the non-Physicists so that may have been the cause of the problems. Thanks for the link to the paper, it is nice to find research papers that don't cost $35 to $45 to read. Unfortunately, it has been over 40 years since I graduated so my math is rusty, and my cosmology is rusty and outdated, meaning it is going to take many hours of study before I actually have a good understanding of the paper. But what the heck, I'm retired so this is as good a way as any to spend my time. LOL Thanks for the video, link to the paper, and motivation.

[@Hy-jg8ow]

What would spark the need for the re-scaling? Is there a specific event that would trigger it?

[@sagestrings869]

When the last bit of mass is gone, time no longer means much because everything is massless and time dialates. Massless conscious observer would suddenly find all the light and energy Swarming back together until mass spontaneosly emerged from the colliding energy.

[@BlueFrenzy]

The core idea is that the rescaling is not actually a physical process but its a matter of perspective. Particles are point-sized, which means that they have no size. Because they have no size distance between them is just a matter of perspective. There's no clocks in the universe, but we create clocks. So imagine we have a particle orbiting around another one and we have a computer that ticks everytime the particle makes a full orbit. It doesn't matter if the particle's orbit is 1mm radius and takes 1 second to orbit the other particle or if the particle's orbit is 1 meter and takes 1.000 seconds to orbit. The computer will have exactly the same number of ticks, which makes it impossible to know the scale of spacetime. The only way to know the scale is if you have any non-conformal force or particle because then absolute distance creates a difference. If the universe manages to becomome conformal, it's not that there's a new rebirth. It just means that the particles that conforms our universe would look from the perspective of someone from the next eon like those particles were extremely concentrated (our current eon) and they kept expanding. In CCC actually all the eons runs at the same time, but each eon is within the first fraction of a second of the next eon.

[@Hy-jg8ow]

@@BlueFrenzy How can a purely physical reality be a "perspective"? Especially since right now a particle in the Andromeda galaxy is a measurable distance from a particle on Earth? Surely even in a universe which expanded further and even black holes evaporated, there will still be a distance a particle would have to travel to meet up with another..[which they could not, since the space between them could be accelerating them away from each other, with maybe even FTL relative speeds]. I may me completely dumb, but all of this sounds too metaphysical to me, too mathematical only, like a geometric speculation. The heat death of the universe makes more sense to me, or the big rip.

[@MrStevos]

That Guy again ! "Everything is relative" When there is no longer any mass there is no gravity, no space time, not time, no distance -"one man's ceiling is another man's floor" . How egotistical we humans are. Now that we admit that earth is not center of the universe, we have to believe "our Big Bang" is "The Big Bang". Time & the Universe are without beginning or end. Penrose may not be exactly correct. But he is one more step on our feeble quests at understanding..

[@magtovi]

@@Hy-jg8ow "The heat death of the universe makes more sense to me" That's the point of this theory, in this eon you see the infinite future as heath death, the only remnant thing is radiation (photons) in this infinitely large heath-dead universe, well that "looks" like a point-like big bang to the next eon when they look at their past. As BlueFrenzy commented, the conformal scaling is not a physical process that it's triggered at some point in time, is just a mathematical identification of what one eon sees as its future and what the next one sees as its past.

[@MaryAnnNytowl]

I was very interested to hear your opinions on this idea, so I'm glad you did finally get around to doing it. Thank you for this, and all you do. You are truly one of the bright spots in my otherwise dark world, and that means a lot to me. ❤❤

[@brothermine2292]

Seems implausible that a mathematical rescaling would reduce entropy. How does rescaling reduce the number of possible states?

[@OneCentChemist]

I guess by redefining the states, but that doesn't feel right. I agree it's implausible.

[@David-bh7hs]

It's like stretching a piece of paper out then crumpling it again and stretching it out.

[@danielduarte5073]

So well done I will have to watch this video several more times

[@leematthews6812]

Difficult to imagine someone of Penrose's stature would be concerned about criticism, goes with the territory, surely? I've attended a few of his lectures at the Royal Institution...still looking forward to the day when I can see Sabine doing a lecture at the same venue.

[@mg4361]

The Nobel prize does not make someone a stoic person or not petty. Great scientific minds can also be very petty and vindictive people.

[@brothermine2292]

The most recent RI lecture that I saw on KZbin was by a string theorist who claimed beauty is truth... that the mathematical beauty of a theory lets you know when you're on the right track. I think he said something like, you can judge a theory's correctness by the number of spinoff ideas it produces for pure mathematicians to research.

[@HarryNicNicholas]

there have been critics a lot less polite than sabine, i'm sure the two of them would enjoy a slugging out discussion with each other, they are both persuing the same goal - knowledge.

[@RubelliteFae]

Thanks for talking about CCC. Seems like not many people even consider it. Even if wrong, it's worth discussing if for no reason other than to develop a model closer to truth

[@dj_laundry_list]

Or if hipsters do it, it's non-conformal cycle cosmetology

[@CAThompson]

Maybe it's time for Grunge to make a come-back?

[@paulcooper8818]

Thank you for the explanation. Many years ago I watched an interview with Mr. Penrose explaining this theory. It was my impression that as the universe aged, eventually all matter would cease to exist leaving only energy. Then there would be no scale to the universe and something like a phase change would occur presenting the new invocation of the universe. Not saying it makes any sense, just my interpretation.

[@BlueFrenzy]

If there's infinite universes behind us, wouldn't the infinite fluctuations cancel out?

[@magtovi]

Maybe the only strong enough "signal-noise ratio" fluctuations are of the immediate past eon.

[@peymanparsa1478]

Excellent Sabine. Clever analyses. Many physicists are proposing theories based on already established but problematic theories such as the Big Bang, Inflation, Singularity, Copenhagen interpretation of Quantum Physics, and with lack of understanding of the nature of Entanglement, double-slit experiments, dark matter, dark energy, apparent expansion of the space, gravity at large scales and finally time.

[@knarf_on_a_bike]

Seems like so much of CCC is untestable, it almost reminds one of a god hypothesis.

[@FromJunkToJanha]

the explanation of conformal is SO elegant! thank you for another great video!

[@robertschlesinger1342]

Interesting and worthwhile video.

[@youngtrout4950]

bing bang bong bwop

[@ronnieweather3175]

Yo this video is trippy asf shes pretty much explaining the same thing but in a way where theres no end or no beginning to the explanation

[@terrific804]

The cycle and creation of the universe repeating is far less likely than the creation of theories that can't be proven.

[@brothermine2292]

Theories that can't be disproved, however, are rare and require genius to produce.

[@johnstonewall917]

I am often reminded of the saying 'Not only is the universe stranger than we think, it is stranger than we can think.' I cannot add anything to these discussions but I have a feeling that great minds are approaching the answer, maybe not rapidly but certainly steadily. As for entropy, many years ago I was an engineering student and we learned that entropy was all to do with steam engines and measured in British Thermal Units per pound per degree Fahrenheit. Happy days!

[@dougmarkham]

I have a number of things I find fascinating about this theory. I'll start with the more mundane thing: 1) What I think of the idea of mass decay: So you have two things: A) Decay of the nucleus (needed to end frequency in Penrose's model) A) Ending of the higgs field (or at least all fermions which interact with it). My point here is that this sort of thing could happen and though it's maybe too difficult to measure,,the universe is under no obligation to make everything measurable to us. 2) What is causing the Conformal rescaling of space-time? So this is interesting and possibly understandable with high-school physics. Basically Penrose described atoms as having a frequency specific to the atomic number: the larger the atomic number, the greater the frequency. This being why atomic clocks use caesium. The nuclear strong force created by quarks interacting with gluons generates this frequency and this paradigm causes the interaction of matter with space-time. That's the important concept: if mass decays, warping of space-time will too. So when blackholes decay to nothing, massive warping of space-time unfurls. Now that's the first bit. The bridge to this song is how he relates frequency with rescaling. Penrose in his videos describes how two formulas are equivalent: E = Mc^2 [energy is equivalent to rest mass] E = hf [Energy is equivalent to frequency] *First thing to note: in CCC, the speed of light must remain constant. So this equivalence means Mass = Frequency. This makes sense, as we have already mentioned, atoms with larger atomic numbers have higher atomic frequency. So now we get to the chorus of this song: why the rescaling? Well, simple high-school physics tells you that: Speed = Distance / Time Or, in another form Speed = Distance / Frequency Here, the concept of time has to be appreciated as having two components: A) The sequence of time, eg., event A; event B; event C (basically, in classical physics, the sequence of time allows cause & effect). B) The scale of time The scale of time is basically like musical notation: A whole note lasts a bar, a half note lasts half a bar, a quarter note lasts a,quarter of a bar (so there are 4 of them equally spaced out per bar), etc. If you want to know how long it takes at light speed to get from the earth to a star in the Andromeda Galaxy, you need to be able to have some way of counting the scale of time eg using the frequency of an atomic clock. Thus, when you want to know the average speed you took for a journey, you divide the distance in kilometres by the number of hours. Similarly,,without the scale of time, distance has no meaning. So, we have to again recall that the speed of light in CCC must be constant. That means for bosonic radiation, if S = D/T, if time is decaying with mass, then distance has to decay too in order for the speed of light to remain constant. So what that means is that space-time conformable rescales. But wait, if the speed of light is a ratio, what happens if mass decays completely? Well, if T = D/S, then if D decays, T gers smaller and smaller tending towards zero. So as the scape of time and distance both decay, the ratio D/S (distance/ speed of light) gets lower and lower. Of course, as long as D doesn't reach 0, the speed of light can remain. At some point in space-time rescaling, photons will collide and photon pair collisions will regenerate matter. Whether that requires a complete singularity, or just the rescaling down to a very small size (to enable light speed to remain constant), was not mentioned by Penrose. However, it seems therefore that what transpires at the end of this space-time rescaling is a white hole~~the beginning of another Aeon. Now to discuss Sabina's main issue: that gravitational waves crossing through the white hole from one aeon to the next would non-linearly increase via positive feedback. Most of these gravitational waves are going to come from the expiring black holes. As blackholes arise from the collapse of matter as stars die (or if too much mass collapses in a given space), then one might expect that if each space-time rescaling produces roughly the same amount of mass at the beginning of each Aeon, then the number of 'popping' black holes at the end of an Aeon would be the same for each Aeon. Now here's where it gets difficult. Would each Aeon pass on the exact same gravitational wave pattern? Imagine if there was a beginning to all this. What would cause a symmetry break that would lead to a non-symmetrical distribution of gravitational waves through the Aeon boundary? Would different patterns of gravitational waves change the constants of each Aeon? If not,,then surely the conditions for life would arise in every Aeon? So the question is: how does the variance of gravitational waves impact the early universe? Also, gravity in our current universe state is non-linear according to GR, but with no mass and no spsce-time curvature ~~at the end of the Aeon going into the beginning of the next Aeon~~would that mean that temporarily, GR could be approximately linear until nuclear forces began to emerge? If so, the gravitational waves passing between Aeons might not lead to non-linear expansion of fluctuations between Aeons? Perhaps others better at physics will help explain why fluctuations would increase between Aeons non-linearly?

[@danielduarte5073]

Very well done I was asking some questions about Penrose And his ideas because of his notoriety

[@PaoloTreTreTre]

Sabine, you are amazing. it is a pleasure to listen to you. thank you

[@dj-kq4fz]

I definitely watched this too early in the morning. I'm going to rewatch after a bit of caffeine. Thanks! Dave J

[@KeithCooper-Albuquerque]

Thanks for another great video, Sabine. I so look forward to Saturdays and your wonderful videos!

[@edcunion]

Penrose has the math chops to construct that framework for his theory and is understately sincere about it, infinity is a tough nut to crack with our skull bound finite grey matter CPUs. The persistent gravity wave and/or Hawking point ideas mixed with binary cyclicity through eternity perhaps is as reasonable an idea as anything we're able to compute, given how long we've been walking upright on our planet's surface, looking around at things while soaking in our sun's generally beneficial rays!

[@aristotlespupil136]

Rescaling infinity to a finite point is a neat trick I have to admit, but it only seems to be there to solve a fundamental problem in the model that shouldn't exist in the first place. It reminds me of the epicycles that were used to make circular orbits work...

[@dria7387]

Awesome, Sabine

[@EarlWallaceNYC]

The intro. was very kind. But, scientific debate isn't (shouldn't be) personal. And, your analysis was respectful and intriguing, as usual.

[@modgeosys]

I remember watching a self-deprecating Penrose describe CCC (at a conference in the Canary Islands) using an old overhead projector that he quipped he had to borrow from a museum. Whether the hypothesis holds any water or not, it was incredibly entertaining. :-)

[@odenwalt]

Imagine the timeline of the universe, like a slinky connected end to end, so it looks like a torus. Each loop in the torus is an Eon. With enough loops you would encounter Poincaré recurrence. Causality repeats and the universe is eternal.

[@taylankammer]

I've understood maybe about half of this but I was still enthralled the whole time. :D

[@emmanuelweinman9673]

I already watched this video in the previous universe. Nice to see you again 😉

[@stevealston201]

Sabine your awesome thank you so much for your hard work in opening and broadening mine and other people's minds. Your videos are always so well made and full of knowledge. Thank you again for all you do.

[@ChayComas]

I am obsessed with Conformal Cyclic Cosmology

[@CeresKLee]

Who are you to criticize a Nobel Prize winner? You are Dr. Sabine Hossenfelder and there no other I would have rather listen to criticizing anyone! I watching and listen to lot about CCC and this the first time I hear of the Weyl curvature hypothesis and the Erebon field. THANK YOU1 Being mathematical-challenged, I take a lot on faith. My faith was shaken in modern physics in the raise of the Inflationary Theory and then the untestable String Theories. I was looking for cosmology to be redeemed by CCC but seems the question of the half-life of electrons is a issue. CCC seems to gain epi-cycles, so to speak.

[@superdog797]

Thanks for making this video Dr. Hossenfelder

[@rjsmith2007]

I gotta say CCC is one of my favorite theories I've heard so far

[@LuisAlbright]

Fascinating. I’m not a physicist … though I grew up with them, and I like to keep up (as best I am able with my brain-of-small-bear) with these concepts. Your channel is a fascinating, and entertaining help in that effort. I do like … to a degree … Penrose’s CCC, and am also drawn to Smolen’s “evolutionary” universe (though with serious reservations). Please keep this up. Endlessly entertaining and informative (plus I’ve developed a mild crush, but no matter).

[@jman8128]

this is foundamental question too. I d love to hear.

[@armandos.rodriguez6608]

As always excellent info video.Thank You Kindly.

[@brothermine2292]

One obvious approach to the question about whether the number of past eons is finite is to postulate a loop: the end of some eon is the beginning of an earlier eon. In its simplest form there would be only one eon, whose mouth eats its tail.

[@Shagsteri]

This raises the interesting question of "daughter universes". Isn't a black hole guarded by a horizon? That singularity could be another universe.

[@HarryNicNicholas]

this is another point i like about this idea, that as time ceases to have meaning the "next big bang" is actually the first and only big bang. it is the first universe every time......

[@Shagsteri]

@@HarryNicNicholas I am not sure on your concept. Doesn't matter if cyclic or initial or daughter universe; the same Outcome remains. *but* in an infinite universe, there will be other univiserses; and at some point they will intersect ... Some say cosmic strings are those intersections.

[@sinisterminister3322]

While I don’t really understand CCC, I am still attracted to it for aesthetic reasons and also because it solves the problem of what existed before the big bang. One way I have of understanding CCC is that from the perspective of a massless particle moving at the speed of light, there is no space and time. If there are only massless particles left at the end of an eon, the universe effectively reverts back into being a single point becoming the Cosmic Egg for the next universe. Hossenfelder has, of course, every right to criticize it.

[@PhysicsNative]

Excellent, as usual. We need healthy skepticism and debate to address the multitude of sensational but unphysical ideas and there are so many. Penrose is a wonderful cartoonist, popular mathematician and science fiction author. He doesn’t care much about the physics.

[@EnglishMike]

What a ridiculous take.

[@ultrametric9317]

Although not directly related, an absolutely fascinating study is the so-called chronometric cosmology of Irving Segal. He wrote a book on it, "Mathematical Cosmology and Extragalactic Astronomy" (1975). The conformal group plays an essential role in this work. It is fairly dense reading. Penrose's main idea comes from a little appreciated invariance of Maxwell's equations in vacuo. It was shown in the early part of the last century that these were not just Lorentz, but conformally invariant. If the expansion of the universe goes on indefinitely, then eventually all that will be left is free radiation running around with essentially no sources to interact with. Without a fixed scale for time, eons are as long or short as microseconds. In this world a vacuum fluctuation would be a big event - a new Big Bang.

[@gangsterkami1]

Great job Sabine, this is a fantastic review of Penrose's CCC. I will be using this video to send to everyone that requires an introduction to CCC. You covered every significant point of CCC in simple yet informative manner, extremely impressed. I don't agree with your final thoughts on the matter. You propose good questions at the end. However, it seems that essentially your questions stem from your assumption that all processes in metaphysics/physics follow the same rules we know for spacetime. You must recognise this is an assumption. Edit: I am happy to respond to all your thoughts you provide in the video if you give this comment a heart. It will let me know you are actually interested in my observations on your final thoughts.

[@ricardoabh3242]

I am a big fan of ccc :) I like that Sabine underlines the issues, but when a few argument are “why”. Then I don’t agree, most theories have a ton of “why”, like “why expansion”…”why the fine tuning “…”why multiverse “

[@jaybingham3711]

The story of an inexorable march toward maximal entropy and it, at the exact moment it comes about, also being indistinguishable from a highly ordered "singularity" is certainly elegant. Guess we'll just have to wait and see.

[@c_b5060]

12:19 This deserves a little more attention.

[@danielleriley2796]

2:30 ish the sphere projection. Imagine a globe inside a cone, project lines, unroll the cone = Lambert conformal conic projection = aviation maps = curved flight paths around a globe in real life give you straight lines on your map.

[@ifeelaway]

I am a big believer in "consider the source." I 💚 Roger and while he might not be 100% right, I believe he is onto something. Only "time" will tell.