Physics predicts all of Cosmic Time. Here's how.

[@ScienceAsylum]

Watch this video ad-free on Nebula: nebula.tv/videos/scienceasylum-the-equations-that-proved-einstein-wrong Here's that bonus video I mentioned (Nebula Exclusive): nebula.tv/videos/scienceasylum-measuring-curvature-in-an-infinite-universe

[@aaronmicalowe]

I would watch the whole 2 hour conversation, with natural cuts for toilet breaks and the like.

[@ScienceAsylum]

@@aaronmicalowe I could just put in "intermission" screens like they used to do in super long movies 😆

[@aaronmicalowe]

@@ScienceAsylum Good idea. I actually remember those. And the lady who would sell ice cream from that flip down tray they'd carry around. And people could smoke in the cinema so the people on the top row couldn't barely see the movie through the fog.

[@aaronmicalowe]

@@jaycorrales5329 It's been stable for billions of years whereas climate change can kill us all within a few hundred years. But nobody cares. 🤷‍♂

[@quarkz26]

By far, my favorite format, I just love the banter between you two.

[@ghostagent3552]

and it's an actual conversation rather than a highly scripted question asking session

[@electeng6481]

They enjoy each other's company and we are learning ❤

[@kylethompson1379]

Personally, I find it time-wasting to have someone who (appears) to know little about physics interjecting for half of the video run-time, and e.g. jackknifing between thoughts with no real basis and offering no insight for me. I just prefer a quick and direct as possible answer to the topic posed in the title. Probably that sounds rude and unsupportive, but that's not my intent, and no offense intended to anyone, the content is good. I just often feel in a rush watching vids. And that's an opinion only. thanks!

[@EstamosDe]

​@@kylethompson1379for most humans, information cant be the 100% of the content, it wouldnt be so different than using an automated speech software into a book of physics, it can be done, but it wont engage or connect with most of us For me, sometimes I can lose my attention, her questions enforce the ideas of the video, and let me get attention back again if I lost it

[@adamuk73]

Thanks Nick. Excellent video. Look forward to the next one 👍

[@ScienceAsylum]

Thanks for the support!👍

[@thefalsehero]

Even though the math in these videos is far beyond me, the way you break it down makes it completely understandable. Great job, as always.

[@ScienceAsylum]

Thanks! It's always nice to hear this. If I'm going to show math, I want to do it right 👍

[@Cryowatt]

You should have mentioned what change in acceleration is called, because the terms are entertaining as hell. Velocity->Acceleration->Jerk->Snap->Crackle

[@hankseda]

One of his clones would have pointed this out, maybe my favorite the Nerd Clone 😅

[@alexpotts6520]

I do kind of appreciate that physicists have that trace of whimsy. Snap, crackle and pop are excellently named. (Also big shout-out to MACHOs and WIMPs.)

[@skilz8098]

You cannot forget pop

[@1224chrisng]

they better name the 6th 7th and 8th derivative Capt Crunch, Tony the Tiger and the Lucky Charms Leprechaun

[@wiseoldfool]

@@1224chrisng Now I'm getting confused between Tony the Tiger, and putting a tiger in your tank. I hope nobody ever thought it was a good idea to put breakfast cereal into a car's petrol tank.

[@Trainwreck1123]

It is understandable to be kind of confused by higher order derivatives because most people have very little context for something like that in normal life. Mathematically, you could go infinitely deep on that path but practically it's usually not useful to go beyond the 3rd order (position being 0, speed being 1, acceleration 2, jerk being 3) but the higher orders are loosely named up to the 6th. Wikipedia's "Fourth,_fifth,_and_sixth_derivatives_of_position" article gives some more information. These are used commonly in robotics and CNC manufacturing (my field) but I'm sure there are other places they are well known :)

[@ScienceAsylum]

Yeah, I almost never see a derivative higher than 2nd order. Higher orders are rare in the real universe.

[@skilz8098]

@@ScienceAsylum Well that depends on a few factors too. In some contexts, how many indeterminate forms did you come across, how many substitutions or transforms were applied... but yes even in them I think the average high for differentials or integrals is around 4 and some of the more extreme up to 7-11... Yet they all fail in comparison if one goes down the rabbit hole of studying various fractals especially in how they tend to appear in nature. Then again, this is going beyond "discrete, partitioned, math, spaces, and metrics" as this tends to be more fluid, continuous, analog like. It all depends on the eye of the beholder and what they make of it.

[@rafaelgonzalez4175]

Mathematically you can formulate imagination.

[@justanotherguy469]

@@rafaelgonzalez4175 And that is so pulchritudinous. To be able to give form to no things.

[@rafaelgonzalez4175]

@justanotherguy469 I take it that comes from if things exist, then no things also exist. I would say that only applies to nothing. As each thing is defined individually. There can not be no things. There is nothing. That came from something. Not some things.

[@wiseoldfool]

Best ever description of heat death: "Stuff stops happening."

[@ScienceAsylum]

Doesn't sound very exciting... but that's because it isn't.

[@garros]

I think I might have experienced the heat death of my love life... lol

[@lionelmessisburner7393]

@@ScienceAsylumis it possible that if the heat death happens it wouldn’t truely be the end? Like couldn’t a quantum fluctuation start everything over again?

[@martifingers]

@@ScienceAsylum Unless Sir Roger Penrose is right and the whole thing starts again?

[@TheAnzamin]

The death of Action

[@SkylerLinux]

Heat Death really should be called the Gradient Death

[@ScienceAsylum]

That would definitely be clearer, since most people don't understand the nuances in the scientific definition of "heat."

[@SkylerLinux]

@@ScienceAsylum Also doesn't sound like the Universe will end in Fire

[@connormainwaring8866]

Yeah 'Heat Death' is kind of ambiguous as to whether heat is the subject or just an adverb. Heat Death, means the death of heat, which is a cold death. It sounds pretty cool though and gives an opportunity to flex your science knowledge in a single short sentence, so I think we should keep it.

[@alexpotts6520]

I've sometimes heard to heat death referred to as the "big freeze" (to mirror big rip and big crunch as the other end scenarios). I think big freeze is a much more intuitive name.

[@Broockle]

heat requires there to be cold. If heat is dead then so is any difference in temperature. If you think about it it kind of already means death of gradients. But yes, gradient death would be more clear 😆

[@zabs1671]

As a Bionerd I really love these conversations between a Physicist and Biologist. Physics simplified, but not all the way down! And I love your banter (as we say in the UK). ❤

[@ScienceAsylum]

Glad you enjoy it! This style creates a good balance, I think.

[@lordvader6678]

I am a big appreciator of you . Keep up the good work! 👍💪

[@amygirkin6599]

I absolutely love your explanations, and the two of you make such a great couple!!!! 😍

[@ninadgadre3934]

You both are entirely too adorable together, I absolutely love your chemistry. All the science learning is an added bonus! Thanks, please never stop doing this format!

[@darktower0603]

Always love your videos. Great information, entertaining and zero ego. By far my favorite science communicator! Thanks so much for the content!

[@johnrowson2253]

I am saving up for your book. Excellent video

[@ScienceAsylum]

Hope you enjoy it!

[@plat2716]

I love that you only spent a couple minutes explaining the foundations of calculus! "A-double-dot is the rate of change of A-dot which is the rate of change of A" It's the second derivative baby!

[@ScienceAsylum]

Haha! I explained only what _needed_ to be explained to understand what the equations say 🤷‍♂️

[@johnmckown1267]

"Universe carries on, doing nothing." That's me in retirement.

[@wiseoldfool]

Just sittin' on the dock of a bay....

[@alexpotts6520]

One detail it might have been nice to point out is that the cosmological constant really is a constant, unlike the matter desnity which decreases as the universe expands; that is, dark energy doesn't appear to be "stuff" which resides within space but a property of space itself. When space expands to create more space, that new space has dark energy, too. This explains why the universe was decelerating for the first 10 billion years or so, but then went through an inflection point and started accelerating again - the matter got thinner and thinner but the dark energy remained as dense as it ever was, and so it eventually won out.

[@lukedavis569]

Explaining with your wife is such a good format. It’s a really nice way to help the audience feel ok with not knowing some prerequisite knowledge and follow along in the narrative.

[@ScienceAsylum]

Yep, she calls me out when I assume unreasonable prerequisite knowledge. She's like "Whoa! Hold up! Expound on that a bit."

[@brianegendorf2023]

@@ScienceAsylum I wish I had time and/or a scientist had time to do that with me. Cause I learn more and more that at first blush, a lot of stuff scientists sat is pretty sketchy..until you realize that they are actually talking a language that they each understand are on the same page of.

[@jimmyzhao2673]

It's funny how even Einstein's 'biggest blunder' is worthy of a Nobel Prize.

[@pleappleappleap]

Yay! You're back!

[@araujo_88]

I could hear you two talking about physics for hours. I find it really entertaining that sort of Socratic conversation style.

[@Bildgesmythe]

Love you two! Great video.

[@ScienceAsylum]

Glad you enjoyed it!

[@joepeach997]

Could you please tell me if the characters in the middle background are arranged in a meaningful manner or just random? Also, I love how your wife gives me a way to understand your explanations somewhat better because she keeps me breathing at a normal pace. You both compliment each other very well. I thank you both for helping me and so many others to get the smallest grip on these magnificent concepts that are not intuitive. Always looking forward to your teachings.

[@ScienceAsylum]

The plushies are just arranged for maximum aesthetics.

[@joepeach997]

@@ScienceAsylum indeed!

[@Jack_Redview]

Good to see another video from you Nick

[@louisalfieri3187]

Really good one! I didn’t know how far we’ve come re: the expansion

[@TheXnev]

One of the cool things about Cosmology is that hopefully there will be a new wave of cosmological measurements from background gravitational waves! LIGO, VIRGO eLISA and LISA might be able to detect signals that can give us insights on possible Primordial Black Hole formation, or phase changes that drove inflation that could leave its traces in anisotropies in the background signal!

[@LendriMujina]

Einstein was human like everyone else. As brilliant as he was, he did still have biases. It was strong of him to eventually admit that.

[@cesarjom]

Yes in the case of the inclusion of this cosmological constant term to his EFEs, he was able to step back. However, we should not forget that Einstein would spend the rest of his research efforts and remaining days publishing material in opposition to the new quantum theory (soon to become QM) and spending time working on a unified field theory for EM and gravitation. Much of Einstein's efforts here were not at all seen as promising but it was his own personal beliefs in a deterministic solvable Universe that kept him on this futile course without any resolution in the end. I'm not taking anything away from the brilliance of Albert Einstein.

[@greg4367]

Who knew? A Physics presentation with great Chemistry. You two have it going on.

[@ScienceAsylum]

Thanks! Her and I feel pretty great about each other too 🙂

[@CliffSedge-nu5fv]

​@@ScienceAsylumQuick, trademark that slogan!

[@darkseraph2009]

I love this series. Keep 'em coming, Nick and Em!

[@IllIl]

Love these episode with the both of you

[@cesarjom]

Great job with the Friedmann equations. Very clear and insightful explanation of what its constituent parts represent in our physical Universe. Perhaps a follow up video that explain some intuitions for the derivations of the equations would be in order.

[@shelley-anneharrisberg7409]

This was such a fun video! Great explanations as always :)

[@ScienceAsylum]

Glad you enjoyed it! This style is working really well for me lately, especially for the topics I've been choosing.

[@Vidley1777]

1:25 Loving it how you didn‘t encircle the pi‘s, probably because they’re too common in physics and math equations to notice at this point right away that they aren’t latin. Also good job explaining what the terms mean, making me feel I have grasped a basic understanding of the structure of the equations.

[@ScienceAsylum]

Yeah, while the pi is a greek symbol, it feels more like a number (like 3 or 4) than a symbol (like rho and lambda) to me.

[@SteakPerfection]

Excellent vid - clear concise entertaining!!! Thank you ‼️🙏🏻😎

[@ScienceAsylum]

Glad you enjoyed it! 🤓🤓

[@sphakamisozondi]

I love this format. 🔥

[@christianmaxschafer8696]

Excellent Q&A - thumbs up!

[@ScienceAsylum]

Thanks! Glad you enjoyed it!

[@AlleyKatt]

Why watch this after I've already seen it on Nebula? Trad-itION! I love it when I (almost) immediately hear pretty much my thought in Amazing Em's voice. This is an enjoyable format, and probably more so for those of us who've been following you for some years. Enjoyed the Nebula bonus video, too, before I realised it was a bonus.

[@ScienceAsylum]

Glad you enjoyed it. The second video didn't feel right for here on YT, so I was grateful I had a place to put it. Also, I'm not sure if you know this or not, but you can tell if a Nebula video has bonus content in it by looking at the thumbnail. There will be a plus sign in the lower right corner. 👍 (Technically, that also includes extended versions of YT videos for some channels, but I'll probably never use "Nebula Plus" in that way.)

[@AlleyKatt]

@@ScienceAsylum I did not know that. There you go teaching new stuff again!

[@ZomB1986]

9:21 here's a thought experiment: 0 dots = distance of your car. 1 dot = speed of car. 2 dots = acceleration = how far you're pushed back into your seat. 3 dots = speed at which you're pushed into your seat. 4 dots = acceleration at which you're pushed into your seat.

[@TheElectronicDilettante]

Going by the blue plot on the graph, it should be called the Universal Crack. Really cool channel. If I come away with more questions than when I started, you’re doing something right. Thanks for the video!!

[@ScienceAsylum]

Welcome to the channel! I'm glad you enjoy my work.

[@ShawnRavenfire]

I remember (or at least, I remember having remembered) when I was maybe five or six years old, and I left the front door open, and my father said, "I'm not going to heat the whole neighborhood." I immediately started picturing heat as expanding outward through the door, and knowing that there wasn't a barrier such as a closed door at the edge of the neighborhood, the heat would have to keep expanding to infinity, and from that, I imagined that there must be a coldest temperature possible, and everything must be moving gradually toward that temperature without ever reaching it. Then I thought, "I wonder if a long time ago, there was a beginning point when everything was really hot and squished together." Then I closed the door. It wasn't for another maybe twenty or thirty years or so, before it dawned on me what an profound thought that was!

[@martifingers]

Marvellous conversation. BTW what are the theories about why the rate of expansion varied?

[@Uaarkson]

I really like the idea that the preservation of relative angles between particles means that a fully expanded “heat dead” universe is equivalent to a singularity. It’s almost as if you can imagine a new Big Bang emerging out of that state at some grand inconceivable scale. And that maybe we’re all just experiencing a blip in a reality that truly is infinite in space and time, with no true beginning or end. I’m sure there’s some math somewhere that disproves this idea but it’s mine and I like it okay 😂

[@zebrastriber]

I am a bit late, but maybe Nick still gets to see it: Great video - as always. Thank you! I did an online course on Astrophysics few years ago and I noticed that I wanted to understand more about the "language" of physical formulas. What does a ² mean? Where does it come from and why is it used? I asked physics teachers for books on that matter, but their suggestions only helped so much. The way you have described the Friedmann equations reminded me of this. Is there any term that I could google for or any book that starts teaching formulas and how to really read them? I got your book already, but feel like it is a bit above me. Thank you advance! :-)

[@johntrentmusic]

Fascinating! I'd love to learn more about how the expansion has changed speed over time

[@TheSimTetuChannel]

Q: How much is the rate of change for ä ? A: Um, lots!

[@wiseoldfool]

I see what you did there!

[@ScienceAsylum]

😂 Good one!

[@DavidFlorence-n8c]

I love the new format!

[@thomziq]

Thanks for great content as usual :)

[@ScienceAsylum]

Glad you enjoyed it!

[@universemaps]

So well explained and many facts blow my mind 🤯

[@tim.martin]

Thanks

[@ScienceAsylum]

Thank you!

[@YeOldeBelmont]

I love these discussion videos!

[@Phych_uk]

EXCELLENT video. Nicely explained that someone with a good high school education can understand. Loved it! More please.

[@ScienceAsylum]

There will be more. I promise! 🤓

[@Mark_Williams.]

These talks with your wife are great. It brings us, the audience, along on the talk through her eyes and she can bounce things off you to help understand better. This felt a little short in some places, perhaps edited a bit too much down, but really enjoyable all the same! Don't be afraid to aim for 30min video times imo

[@ScienceAsylum]

I usually aim for 20 minutes, but this conversation was so (unusually) long and scattered that it became two decent 14-minute full videos and a 6-minute bonus video instead. At least now I know for sure how prepared I need to be going into these filming sessions. 😬 She really keeps me on my toes, which is a good thing.

[@SSMLivingPictures]

New Science Asylum! This literally made me prop up in my chair haha! Also odd timing for me, since I was reading Einsteins book on Special / General Relativity this morning😅

[@pouncingfoxes]

Thanks Nick! I bought your book, and this video is the perfect reminder to get started on it (as a summer project). Cheers!

[@ScienceAsylum]

Good luck! I hope you enjoy it 🤓

[@pauljs75]

Alternately, c² is also the product of permeability and permittivity of a vacuum and not just the speed of light squared. So how would the electromagnetic properties of a vacuum play into this? It seems to be something that could describe the tension stored in spacetime itself. What happens if you make an allowance for direct substitution and use ε₀μ₀ in place of c²? That could also suggest that gravity doesn't always behave the same in conditions where it's interacting with electrical phenomena. There could be stuff with overlapping fields that has an effect similar to gyroscopic precession, and things will want to arc around a curve, spiral, or spin on their own axis instead of expressing kinetic energy in a linear fashion. And that adds some other variables to watch out for in physical interactions. It seems like an overlap of relativistic differential fields could be messy, since things like charges attract, act neutrally, or repel relative to each other. What challenges would a model like that present?

[@rtg_onefourtwoeightfiveseven]

You're right in that things look different in presence of an electric/magnetic field, and the Einstein Field Equations (which give rise to the Friedmann equations) can account for it. Not by replacing c^2 with epsilon_0 mu_0 - there's a much less roundabout way of doing it. Electromagnetic fields have energy density and pressure, which appear in the Einstein Field Equations and tell spacetime how to curve. In the specific situation of the universe being homogeneous (looks the same everywhere) and isotropic (looks the same in every direction), the Friedmann equations hold, and there are some circumstances in which this is the case with electric phemomena; for example, a uniform matter density which also has the same charge density everywhere. The equations end up looking the same, but the solution to the equations isn't the same; the big difference is the P term in the acceleration equation, because electromagnetic fields don't have the same pressure as ordinary matter. This means the acceleration history of the universe, and therefore its expansion history as a whole, ends up looking very different from that of uncharged matter. There are a great many reasons we don't believe this describes our universe, but it's definitely possible to see where the maths goes in this hypothetical scenario.

[@apollo-r5z]

In the initial moments after the big bang, the high rate of expansion may have generated a relativistic mass increase of the universe which may then have slowed down due to the formation of real mass locally, giving the impression that the far reaches of the universe are relativistic speeding up

[@johzek]

In 1915 the entire known universe was just our galaxy.

[@daverapp]

Dang, the last time I was here this early, "Last time I was this early" jokes were still in vogue.

[@ScienceAsylum]

😆

[@Big_Tex]

Whereas now they’re not 🤣

[@suomeaboo]

i always found it weird how "heat death" sounds like the opposite of what it actually is - death of heat instead of death by heat

[@maitlandbowen5969]

Thank you Nick. Haven’t watched you for a while. Same reaction - I like you, I like your explanations, very accessible (though I’m sure there are vast amounts I still don’t appreciate), 🍂🍃🌈

[@ScienceAsylum]

Welcome back! 🤓

[@DavidRavenMoon]

Em is sharp as a tack!

[@ScienceAsylum]

Always keeping me on my toes.

[@alczhou]

Great science, great couple. Am I the only one feeling this is Amy and Sheldon talking? Thank you.

[@Fizzbuzz994]

I apologize if this is a silly question, because I don't know what I'm talking about, but given my limited understanding we only say the universe is expanding when we try to mix general relativity with a classical view of a 3d space + time instead of modeling it as 4d spacetime. In other words, (unless I'm super confused) instead of expanding, we could say that the universe's space dimensions curve outward in the time dimension (at large scales -- and curve towards mass at smaller scales). It just seems more straight forward and intuitive way to think about it, but since everyone seems to stick with the expansion idea instead, I am probably not understanding it properly. I'd appreciate any clarification about why what I'm thinking is wrong. Or -- on the off chance I'm on the right track -- why is expansion the more popular model?

[@Mix1mum]

Hey Nick! Itd be rad to see you get theoretical on some newer meta/physics. Like, what are your thoughts on the universe in a black hole in a black hole in a black hole et al essentialy infintum factorial, and the speculations that the singularity presents from a higher dimension, so to us itll come 4th dimensional (as thats our highest level of waking consciousness). That means the singularity will be a point in time and that it hasnt necessarily happened yet and we are racing towards it. That could, interestingly, explain spaces expansion as well as the great attractor.

[@eritronc]

no sabia que tenias un libro, por supuesto lo compro, gracias por el video y tu trabajo para hacer mas entendible la fisica!!

[@FASTFASTmusic]

What if the gradient that looks exponential just be the beginning of a different, much much larger curve that eventually dips again?

[@chrisjust7445]

Some questions: 1 - Do the equations take time dilation into account? Gravity would slow time in different areas of the universe, which might alter when evidence of the early universe reaches us. 1a - If gravity slows time, does dark energy speed up time? 2 - Could the shape of higher dimensions (above the 4 space-time dimensions) be one cause for why the rate of expansion of space speeds up and slows down at different times?

[@rtg_onefourtwoeightfiveseven]

1: Yes. 1a: No. Dark energy isn't fundamentally an opposing force to gravity; it's something that sources gravity, like matter or light, although it sources gravity in a different way to matter (specifically because its pressure is different), which is why it speeds up the expansion instead of slowing it down. The rate of time dilation is determined by the energy density, not the pressure; both ordinary matter and dark energy have positive energy density, so in that sense they both "slow down time" in comparison to a hypothetical universe with nothing in it. 2: I don't know, maybe, but you don't need to resort to such overly elaborate explanations. Just the fact that there are different types of stuff in the universe - matter, light, dark energy - is enough to explain why it speeds up and slows down at different times.

[@MartinNolin-oo9kt]

9:06 In Swedish we have that letter. It sounds like "a" as in "scare" as opposed to "a" in "star".

[@EvilSandwich]

That was a cool beginner friendly explanation of derivatives. And I admit I probably would have not been able to resist the temptation to go on an entire tangent on explaining how calculus works. I do have to ask though. Friedmann used Newton's notation? That's pretty cool. I haven't seen that in a while

[@narfwhals7843]

I don't know what Friedmann used in the original paper, but the dot notation for time derivatives is used extensively all over physics.

[@EvilSandwich]

​@@narfwhals7843that makes a ton of sense in hindsight. I imagine leibniz notation would get really damn cumbersome after a while

[@narfwhals7843]

@@EvilSandwich You'll see it more in functions with multiple variables(though if one of them is time, the dot notation is often still used for that). But in that case the usual notation for partial derivatives is the "curly d".

[@ScienceAsylum]

@@EvilSandwich *"I imagine leibniz notation would get really damn cumbersome"* Yep, this is exactly it. Friedmann equations are already cluttered enough. Let's not make it worse.

[@EvilSandwich]

​@@ScienceAsylumSo if you see dot notation in physics, it's usually best to just assume it's acting on dt? That's actually really handy.

[@shawndeprey]

Your guy's relationship is so cute and I love it.

[@LendriMujina]

The Big Rip is a scenario I've had actual nightmares about. If you were around when it started happening, you would probably live long enough to see it coming. I can't imagine the kind of despair that would come with that. I am _so_ glad it's not considered plausible; the Big Freeze may be depressing, but it's preferable to _that._

[@Chris-hx3om]

Much like quantum vacuum decay, it would travel at light speed so no, you would not see it coming. You could predict it though. That's possibly even worse.

[@seekvapes9641]

What if the rip continues to sub-atomic scales and attempts to rip apark quarks, which create more matter when pulled apart, it would turn every atom into massive explosions of new matter until there was enough of it to slow the expansion down again, and thus indescribable ammount of new universes would be born.

[@LendriMujina]

@@Chris-hx3om Vacuum decay is an event with a point of origin, an epicenter. The Big Rip would be tied to a property of spacetime itself, the scale factor, which is *not* bound to the speed of light or any specific location. If it were to happen, it would happen *everywhere* simultaneously. How we'd see it coming is first the collapse of large-scale, loosely-bound structures, followed by smaller, tighter ones, then smaller, tighter ones, and...

[@LendriMujina]

@@seekvapes9641 Interesting proposal. But I'm not sure if any new matter resulting from that would stay close enough for it to make a difference. Even if new protons and neutrons form, what good would it do if they're flung away from each other too fast for any interactions to occur?

[@juliavixen176]

​@@seekvapes9641 A theory of quantum gravity is required to actually predict what would happen.

[@stefansauvageonwhat-a-twis1369]

So much info condensed wow

[@tim.martin]

Your partner has a great ability say my thoughts aloud. Especially the part about expansion rate being consistent (and surprise, it hasn't been consistent all the time).

[@lotusflowerrr]

I can't help but think that Entropy might be one of the most important theories mankind has ever come up with.

[@RyanMercer]

Hmmm

[@rexmundi2986]

I love so much when your wife is in your videos, cuz she's so clearly an educated scientist, but not a physicist, so her questions and observations are perfectly modulated for the casual observer to kind of make sense of what your talking about. It's awesome, keep having her ask questions!!!!

[@michaelsherwin4449]

You need to do an exercise in thought. What if gravity is a pushing force? What if dark energy is that pushing force? What if dark energy is there because a substance nearly undetectable is under internal pressure? What if that substance spirals into matter and is dissipated somehow? Then gravity becomes no more than a momentum impulse being imparted to matter. That substance spiraling into an atom is the electron cloud. When that substance gets pushed into the nucleus it is what is called a muon. Muons are seen to appear and then disappear thus they dissipate. Now imagine that the substance being forced along a wire results in electricity. When that substance flows into a magnet the substance is redirected by each layer of aligned atoms one way from the front side and the other way from the back side. There is much more to this exercise of thought but these are the basics.

[@williammorton8555]

I love the way she calls you out on things the are endemic in physics.. ".....four dots..... " Obfuscation by Redefinition!!!

[@narfwhals7843]

What exactly do you think is obfuscated or redefined in the dot notation? Four dots just means fourth time derivative. The dot notation was invented by newton. By convention, now it is basically exclusively used for time derivatives in physics.

[@njan5107]

Great video Nick, as always!

[@frodobolson213]

I've got a question. Is time infinite? Because if it is, even though the gradients no longer exists, in a long long long distant future something would starts happening again, right? Just because of probability and the weirdness of infinite things. Also, I remember you've got a video talking about it 🤔. Is it any method to predict if that's right or wrong? I'm still not understanding what time is...

[@straighttoyou]

4:49 It's still quite soon to come to assumptions. We don't know what's behind the wall of forever. There could be an outer boundary somewhere between that and the wall of forever. Everything could bounce back. Humanity may not be here to see it. Or to record data. Or, the Bright side of looking at it. We will, and then go, "remember when we thought that". 5:23 at the point when the entire universe goes down to zero, something weird happens with sub-atomic particles, kinda like a quantum computer. At that level things get interesting. Then as movement happens, particles that can compile do, causing matter to compile. When there is a grouping of matter, gravity follows. When more and more compiling happens, the density becomes greater. That's how everything you can and can't see, due to expansion. Can fit into the head of a pen. Then Big bang, also, time.... ( In this situation, even the matter that has escaped our view will not escape this reality)

[@KeithCooper-Albuquerque]

Great video, Nick!

[@ScienceAsylum]

Thanks!

[@pelimies1818]

Hey, how thermal death can occur (all will be photons and neutriinos), if the conservation laws try to conservate particle spins, electric charges, etc.?

[@davidcroft95]

For newbies and non-expert-in-the-field (altough it's an error even physicists do): the Friedmann equations describes how universe expand *given* certain assumptions (isotropy, homogeneity and other big words we all like). There is a difference between reality and the (mathematical) model we use to describe reality (which it's literally the first thing they mentioned at the start of the uni course, but strangely a lot of collegues tend to forget it)

[@ScienceAsylum]

The whole reason that the equations work is that those differences are negligible on that scale. That may have been an assumption back when the equations were first written, but now it's an _observation._ It's perfectly reasonable not to mention such things in an introduction to the topic.

[@wefinishthisnow3883]

New TSA video? I clicked like before even watching it. Edit: LOVED the original Zelda shirt!

[@stricklst]

Unrelated question Dr Lucid: i understand dark matter to be what keeps galaxies together, as the gracity of matter itself is not considered sucficient. Might not the gravitational waves created by the swirling of the matter itself be sufficient to keep it all together, as geese use air waves to fly easier in their V formation?

[@rtg_onefourtwoeightfiveseven]

Short answer is no. Long answer is: One can calculate the effect of the gravitational waves in general relativity, and it's nowhere near enough to hold everything together. You'd have to modify gravity an awful amount to make that work, and then that would break everything else. Moreover, even if it DID work, it wouldn't explain all the other things we need dark matter to explain. Like the 'lumpiness' (jargon: "power spectrum") of the cosmic microwave background, or the abundance of heavy hydrogen in the universe, or the way light gravitationally lenses around seemingly-empty space in the Bullet Cluster. You'd have to break gravity in different ways to explain each of them individually. But the same amount of dark matter explains them all, which is why it's the prevailing theory.

[@12jswilson]

"I've seen equations with 4 dots." Mathematicians: "pffff. Amateurs. Try looking at a Taylor Series expansion."

[@dariomiric2958]

I assume to go back completely, we can't use GR anymore as quantum effects are super important in the Universe that small. We need quantum description of gravity.

[@ThiagoFer93]

You said the speed of expension has sped up and slowed down a couple times. But has it ever been lower than the energy density of the universe, that it contracted a bit before expanding faster again? Also, excellent video as always!

[@ScienceAsylum]

No. As far as we can tell, it has been consistently an expansion. It's just the rate of that expansion that changes.

[@marksteers3424]

So in the heat death the universe is uniform (or it asymptotically approaches this uniform state). Totally uniform is totally ordered and therefore zero entropy. Does that mean this is the same as the instant of the big bang?

[@narfwhals7843]

Totally uniform is not the same as zero entropy. It is the same as zero _complexity_ . That is a significant difference that is topic of much modern research. Totally uniform means you have no information about which particle is where. It is the macrostate with the highest number of indistinguishable microstates. It is maximum entropy. However, in Roger Penrose's Conformal Cyclic Cosmology, there is a way to transform this infinite future highest entropy of this "aeon" into the low entropy past of a next "aeon" by something called "conformal scaling".

[@marksteers3424]

@@narfwhals7843 Thanks - I am aware of Roger Penrose's CCC - I suppose I wondered if that is the most accepted theory.

[@narfwhals7843]

@@marksteers3424 It certainly isn't the most accepted. It is a fringe hypothesis. But really all models of the very distant future are. The heat death is our best idea based on observations and accepted models of standard cosmology.

[@damirmogut4038]

We do really want the whole conversation...i.e. a uncut podcast??? We want it all...

[@Mehdi_Hammar]

God bless both of you 🙌❤

[@wiseoldfool]

You guys are totally crazy. With you I feel like I've found my home.

[@A-Milkdromeda-Laniakea-Hominid]

What about conformal cyclical cosmology? Couldn't we yet still get the good graph of "bumps" ?

[@ScienceAsylum]

While conformal cyclical cosmology is _technically_ "cyclical," it's not cyclical in the same way that bumpy curve is cyclical.

[@A-Milkdromeda-Laniakea-Hominid]

@@ScienceAsylum Gotcha. Thanks.

[@theburntginger]

I didn't realize the expansion of the universe wasn't constant. The fact that it has sped up and slowed down breaks my brain. My face = 9:17

[@Lucky10279]

9:29 Oh, what physics equations involve 4th derivatives? I'd heard before that 3rd derivatives are typically the highest we need in physics.

[@ScienceAsylum]

Off the top of my head, I've seen them in bending stress models.

[@lygaret]

Ive always wondered, when we falk about "1 picosecond from the big bang", how does relativity translate that period of time to what we'd perceive? If most energy in the universe was photons before things cooled moving at C, does "1 picosecond" actually mean "fast?"

[@rtg_onefourtwoeightfiveseven]

When we're talking about an expanding universe, there is a specific reference frame in which the expansion looks the same in all directions. (That's why it makes sense to say things like "the Milky Way Galaxy is moving through the universe at X km per second"; there's an implicit "with respect to the reference frame in which the expansion looks the same in all directions"). It's in this reference frame that we talk about the time interval being 1 picosecond - and yes, it does actually mean 'fast'.

[@iamborg3of9]

@scienceasylum, would love to see a video about Roger Penrose Conformal cyclic cosmology and your thoughts. if the universe is expanding to nothing. then perhaps when it reaches that state, that is when something starts to happen again, as per CCC

[@X3MgamePlays]

I have seen several video's of gravity being described as if the space-time is being pulled into the matter. Could it be that this, pulling in, is just the same as the expansion of space? The only question remaining would be, if this is caused by gravity. Or if gravity is caused by the space expansion.

[@amygirkin6599]

One more comment: Have you done a video explanation of what it is when you're looking at the picture of the Cosmic Background Radiation? I understand that it exists, but I really can't resolve what I am actually looking at. THANK YOU FOR ALL THAT YOU DO!!

[@ScienceAsylum]

The oval shape is just a Mollweide projection of the inside surface of a sphere. We do it with Earth maps all the time.