The Biggest Ideas in the Universe | 5. Time

[@FigmentHF]

Thank you for all your time and effort. I left school with no real education, but I find all this stuff fascinating. It always felt academically impenetrable to me, and while I do occasionally get a bit lost, I can actually follow along with most of it. You’re a great communicator and teacher, you can convey complex ideas without being too esoteric, and yet you don’t tend to over simplify difficult concepts. It feels very genuine, honest and accessible. Thanks again!

[@wagfinpis]

I can not get enough of Sean's awesome consideration's. Great sense of humor, I love this guy every time I tune in! Only way to keep the appreciation short is to not even begin to mention it.

[@kostanchik10074]

Please, don’t stop these videos. This format is awesome!

[@James-fe7wd]

You sir have an incredible gift as an educator

[@brankooffice]

For some reason, I find you the most eloquent professor while also being the most informative in the whole field of science popularization. I watch all of your videos and read all of your books for years now and you always seem to give the most understandable definitions for science readers while not making a lot of compromises and avoiding bad analogies. Sometimes I wonder if science popularization would benefit more if you gave talks to your colleagues about how to explain things and how to structure talks then just educating the public directly. But please don't stop :) These are great.

[@curtthechameleon]

I feel the same, Brian Greene and Neil Tyson are also favorites.

[@mariapawlowski8078]

I agree with Goat boy. Carroll communicates for the edification of his audience.

[@mariapawlowski8078]

@@curtthechameleon Greene and Tyson are two of my favorites also. Brilliant communicators, something I'd enjoy seeing in more scientists.

[@Corvaire]

Ditto ;O)-

[@733eel]

I use to watch you back in the day i think it was the Universe or some series. You have always been able to talk to me as the years go on. I have no background in physics/maths but after a few years of watching your lectures and the many others like you it starts to make sense. Anyhows I guess all I wanted to say was thank you for being here all these years. Cheers

[@richardofoz2167]

Your description of psychological time at around 39-40 minutes is fascinating. Many years ago, when I was young and embarked on open-ended travel for the first time, I found that writing at intervals to my family at home was a weird experience for me. Reviewing my diary for news to send home, I found myself amazed that so much had happened in the previous week or fortnight. ("Was that just last week? It feels like 6 weeks ago!) Somehow, time had been "stretched" to a significant degree, and it struck me how differently time is experienced while traveling than while working. I attributed this to the fact that in a work routine, experiences are, to a high degree, predictable. Most people can anticipate reasonably well what they will be doing next Thursday morning or the Thursday morning after that. Consequently, little seems to happen. I frequently had the experience of talking to someone after a break of some weeks and finding I had no news to report to them. I think this is quite common. ("What's news?" "Oh, nothing.") When travelling, however, the reverse was true. Upon waking each morning, we generally had no idea where we would spend the night or who we might have met and what we might have done during the day. So looking back on my recent experiences, I would be amazed at how "full" life had been. For a long time I attributed this richer experience to travel itself, and work itself. But of course, it's due not to travelling or working as such, but to the lack or abundance of new memories, which is how we experience time. You have finally made clear to me - 50 years after the fact - what this experience of mine was all about.

[@cambriolage778]

Had to pause at 48:21 "the size of the macrostate is entropy" 𝖒𝖎𝖓𝖉 𝖇𝖑𝖔𝖜𝖓! A true moment of wow for me! Thank you, Sean for this work, it's a crucial part of my life!

[@alexpotts6520]

48:30 that equation (written S = k log W) is written on Boltzmann's gravestone

[@User-jr7vf]

And the grave in turn is featured at the top of Sean's blog.

[@pranaysheshak5931]

Watching this at 1.5x speed and thinking "I live life faster than 1 second/second"

[@SirThorp]

Quality content right here.

[@tanishqgandas2633]

you my friend deserve everything

[@jharris7]

🤣🤣🤣👏

[@bkbland1626]

Why? That serves no purpose.

[@positron5687]

Dito

[@mgenthbjpafa6413]

Sean has become, over the last decade, my most admired personality in terms of pedagogy inspiration on top of his explicit expertise on QM, we feel the joy of acquiring knew skills, confronting the edge of Human Knowledge. This may be a truism, but it must be acknowledged...Congrats, once more.

[@cmacmenow]

Just like to give a huge thanks to Sean for putting together these incredibly illuminating and engaging Y.T talks /presentations. Green screen,apps and real time iPad usage works beautifully.

[@GodlessPhilosopher]

These lectures are incredible and Sean is a genius. Highly recommend his new book defending the many-worlds "interpretation" of QM.

[@qingyangzhang887]

"Something deeply hidden". I just read it. It's amazing.

[@avrenna]

It is amazing! And his book The Big Picture is a multidisciplinary masterpiece. I very, very highly recommend that one especially.

[@chrstfer2452]

How formal is it? Is there any exploration of the equations?

[@endrawes0]

@@chrstfer2452 informal for sure.

[@David-qv9yy]

how would dark matter affect quantum entanglement specifically near a black holes event horizon?

[@stewarthayne8304]

I did a masters degree in physics 25 years ago and then became a lawyer. All forgotten until now. This is so amazing to watch. So well presented. Thank you!

[@KamranRazvan]

You have a great course on "Great Courses" about the arrow of time. I "think" I finally grasped, in that course, what entropy is!

[@jcf20010]

I have that course too and have watched a couple of times. It's very good.

[@iruleandyoudont9]

you're a brilliant man Sean. thanks once again for making these vids. much respect.

[@kidzbop38isstraightfire92]

Your ability to comprehend complex ideas and explain it to us laypeople is, in my opinion, as good as Feynman's. Well done.

[@ibmor7674]

This guy is too dope, useful yet not boring.

[@CoreyChambersLA]

Sean Carroll is among the greatest teachers of all time.

[@deez9588]

Its amazing how he introduces such difficult topics without blantly providing facts. He asks questions, makes predictions, gives room to interpret. And all that comes with enthusiasm and general curiosity about the topic. Thank you Sean!

[@fatihokhider]

most near death experiance candidates agree that there is no time when we die ...this mean that entropy will stop with time and both are related to the process of living not the cosmose...Allah knows best.

[@jeannieh3661]

Clearly... He has the "Spherical Cow" Award. 🐄 ↔🔵 = 😇 Much love Sean

[@kenwalter3892]

Been waiting for this one.

[@bruinflight]

Sean Carroll is my favorite science guy (along with Dr Lincoln at Fermi Lab) and I just heard him utter what is now my favorite Sean Carroll quote (19:11), "That's crazy talk!" Love ya Sean!!! Thanks for all of your great, great internet chats, buddy! Be well!

[@rc5989]

I enjoy when Professor Carroll covers the bases in philosophy including the original Greek philosophers. I find that it enriches my understanding and familiarity with science.

[@tigertiger1699]

Man .. I really appreciate the effort you put in here…, I get to come n go on this.., but to look at it for an hour .. hurts the head

[@pizzacrusher4632]

These are so excellent! Thank you very much for doing this!!!! I wish everyone was as generous with their knowledge & expertise. Thanks again!

[@badron88]

These talks right here, and others like it, are the reason I'm planning to study physics. I'm coming up with some great ideas but don't know enough yet to answer them. Mr Carroll, thank you.

[@anm3037]

I just met this channel today 26/09/2023 and am already at part 5. It’s amazing how you explain these physics. Now I wonder if you are a university teacher …? If yes then your students are very lucky 🍀

[@NicleT]

Thank you for these video courses. They’re very important! I want also to share that I had myself a big accident when I was a teen that let me saw time slowing down significantly. This is what I felt while it was happening. My mind was “ultra aware” of each details that was unrolling from the accident but also I was struck to realize that at the same time, my perception of time was different. So I’m not saying time was running slower with my physical movements, but more that my perception of it let me feel it slower. It’s also important to say it was not a souvenir aftermath, but really while it was happening.

[@robbyjohnson6531]

Been looking for something like this for years. The equations in the last episode went way the hell over my head, and I got quite seriously lost. This one, though, I was able to follow the entire time. Blew my mind multiple times. Thanks for this.

[@jimwolfgang9433]

Thanks Sean, I've watched and listened to so many of your lectures and podcasts; but I think this format is the best yet imho. 👍

[@ag-bf3ty]

That part about novelty adjusting your perception of time makes sooooooo much sense. If I watch a movie for the first time, and then watch it again, it seems to always go by quicker the second time. Which is kind of odd and counterintuitive, since you'd think it would be more boring (and "time flies when you're having fun" as they say.) I think that maybe in the moment, it feels like it drags more slowly, but in retrospect you don't remember much and so it feels like it passed more quickly.

[@diamon999]

Well, I got plenty of time for this. Thanks

[@Ni999]

I wish this video was longer too.

[@TheHalothane]

In Forward's Dragon's Egg, a species lives on a neutron star. Gravity is so warped that time travels differently for them. They travel quicker through time than beings in another frame of reference. Granted, everyone in their frame of reference travels at the same time.

[@scowell]

Very much like the new background... much easier on the eyes. Thanks for listening! Love the content.

[@incoathwetrust4612]

Hey Sean, could you please explain how the spontaneous radio-active decay of an unstable nuclei does not actually violate time-reversal symmetry, contrary to what most people are inclined to believe? Thanks!

[@2ndAmendmentX]

I'd further want to understand why all of the four forces don't violate time-reversal symmetry. Gravity acts one way. If you reverse time, you have to reverse the force of gravity right?

[@dvoss7680]

Sean, I really enjoy your work and your lectures. I bought a few of your books and just wanted to say I really appreciate you. Thank you!

[@tonycotto8073]

This is simply the best explanation of time I've ever heard.

[@matthewrichmond4139]

I definitely recommend Carlo Reveli's lecture on the Physics and Phsychology of Time found on YT.

[@manlamb1]

I lent his book to someone before I was able to finish it but what I read was mind blowing.

[@ryrez4478]

awesome thank you Sean Carroll! btw i really appreciate that you know so much about philosophy as well. makes these videos even that much more interesting

[@d3vilm4ster]

OMG!!!!! I didn;t know you had a youtube channel!! I love how you explain things nad i hope you keep posting videos here. You are really brillant!

[@clayz1]

Nodded off, dreamed we were in conversation, I couldn’t break in because Sean just keeps talking. I try to break in, Sean keeps talking! Damn!

[@maddmann]

My brain hurts thanks keep this up I like it. Do not dumb it down

[@pedromalafayabaptista3655]

The strange thing is that time has a speed, being speed a derivative of length in order to time. The clocks beat is slowed down with the growth of velocity, so t=f(v) and v=dx/dt - too circular for my taste.

[@yeti9127]

Sean: Great lecture, as usual. The concept of time reminds me of something I read regarding the Mahabharata (Indian epic) story. This epic or the battlefield scenes were recited to a blind king by “time” itself. Interesting! So, the statement that “time travel” or “movement across time” has not been found to be imagined in any ancient culture may not be quite correct. In fact, the Bhagawat Geeta (ancient eastern -Indian- text) seems to have contained some of these time travel ideas. There are plenty of stories about sages moving across space. Schrodinger himself was quite fascinated by these Vedantic texts especially the All in One concept.

[@KungFuKeni]

Perhaps he meant popular stories, ones that were passed on from generation to generation

[@madderhat5852]

Question. 4:30 I thought given that everything in the universe is moving, that cancels out the idea of "choice" in moving through space. Wouldn't the only way not to move through space is not to move through time?

[@BitwiseMobile]

This guy reminds me of my Calculus professor. He makes complex things seem simple and easy to understand.

[@nuriagiralt617]

I'm so glad I don't have to worry about whether time is real anymore 🤓

[@philtrumcorp]

This is brilliant because i think it talks seriously about little metaphysical biscuits we all roll over in our heads in one way or another. Time seems more difficult to extract ones 'sentience' from (or something). We feel distinctly separate from other(inanimate) matter. But time seems like a force that we move along with in concert with the rest of the universe. You have to ask: What is the relationship between time and sentience? Is our perception of time twisted or limited/narrow or just wrong? ...Or is there some part of the experience of time that is emergent from sentience or self-awareness or consciousness. What is time to a rock? I think we'd all agree that time is nothing to a rock. It seems like that has implications for the realness of time?

[@chuckamok12]

best science communicator guy ever

[@JiminiCrikkit]

Thanks for another great episode ... this one reminds me of the old Greek god(S!) of time - Chronos and Kairos - where the former is how we think about time nowadays sequential (chronological), but equally back in the day there was Kairos - the god of timeliness, of situation... Love this idea.

[@llaauuddrruupp]

I love these videos, and this was maybe my favorite of them so far.

[@richardschuerger3214]

Love this series - Ty for doing this. If we were to exist at an event horizon while time flows past us, we would be able to "see" one direction (the past) but not the other (future). Essentially time is flowing past us at the speed of causality and our perception of present time emerges from that

[@nathanisbored]

If I'm in a building, there's lots of air particles flying around. I would describe the room as a complex system with high entropy. But a giant standing next to the building would look at it and say it's a very simple system with low entropy: just a small collection of particles that can't get very far. It would take a lot of math to describe what's going on in the building from my perspective, but it would take very little math to describe what's going on in the box from the giant's perspective. It's a bit like studying the behavior of atoms in a system vs studying the behavior of molecules in the same system. It's mathematically more elegant to describe what the molecules are doing than what the atoms are doing. Another way to say that is: chemistry _emerges_ from thermodynamics and in the process, the mathematical theory jumps down in complexity. You could say this jump is also less fundamental and therefore is just an approximation, but then you could use the same argument to say that everything is just an approximation of something at a lower level. *Question:* Is there a sense in which entropy measures the zoom level required for a system to be mathematically elegant? A bit like how a Reynold's Number tell you what equation to use, entropy tells you whether you should be talking in terms of thermodynamics or in terms of chemistry, for example.

[@brunoprates862]

Adding one more question (this one is probably nonsense): Imagine our universe started with a very different initial condition, where all that exist are 2 particles perfectly orbiting one another. In this case, one cannot really distinguish past from future (we could play the movie of the particles backwards, and we couldn’t know that time is reversed). Would you still say our universe has an arrow of time in this case? If not, does that imply the arrow of time is also related to the content of the universe?

[@RMFpets]

About experiencing time fast as we get older it’s because when you are 10yo. one year is 1/10th as your life and when you are say 30 one year is 1/30th. So times seems faster because your have experienced more of it on reflection

[@detsistaaventyret]

Good work man! Best escapism ever :)

[@johntitorii6676]

Sean my new fav universe guy

[@derricksteed3466]

Perception of time: Cyprus 1974. I was, along with others along the street who were sat on their verandas, watching the Turkish jets paste the hell out of Nicosia airport from the comfort of my chair sat on the veranda of my house on the outskirts of that airport. Then one of those jets, unseen by me lets loose directly over the street. Naturally, I leaped off my chair to crouch down on the floor behind the wall surrounding the veranda. To my perception I seemed to be floating like a feather gently wafting its way as I drifted down to the floor - that seemed, at the time, to be far too long for comfort! And trust me please - what I experienced was in real time! Not retrospective at all! It was what I experienced in the moment.

[@852derek852]

Sean: “I’m not going to tell you which of these two is correct. I personally am a block universe person...” Me: “I too am a block universe person”

[@terryluxton774]

Dear Sean, I’ve loved all your KZbin content during this lockdown here in the uk, fantastic content I’ve really enjoyed it. There is a tv series that’s just aired in the uk called Devs, I won’t give to much away but it’s basically about a tech giant based in Silicon Valley who has developed a program that can see any given point in time. If you can get it in the US it’s worth a watch. Really well done and fun to watch during this lockdown. Once again fantastic work on all your KZbin content. Kind regards From the uk

[@kidzbop38isstraightfire92]

Where did you explain why things go from low entropy to high entropy? I get that microstates exist, but you didn't ever explain why those microstates tend to decrease in size/go to more disorder?

[@MartinWilson1]

Thanks. Hopefully the Tralfamadorians will get a mention in the Q and A. After all Sean, the goal is to be a master of multidisciplinary teaching.

[@clorofilaazul]

I think that often there is a missconcept between language and reality. The word "cup" isn't a cup, it's a linguistic/abstract representation of a cup. Likewise, the laws of physics are just language trying to explain the world and represent it in equations. Equations are a language with a special property like maths: they can predict, but they are still a language. If some equations seem to represent things that we haven't seen in the world, and now we can see them (like black holes), it doesn't mean they can represent other aspects of reality.

[@clorofilaazul]

@Vendicar Kahn It's not an hypothesis in the sense of a thesis. But I'll try my best. We discovered black holes in the theory. We didn't know they existed. So: theory was correct before we had evidence. But theory also brings us other conclusions (supositions) that aren't real, like "supersymmetry". We now know that there aren't enough particles like supersymmetry predicted. Another example is Shrodinger's cat. It can't be real. We have a living or a non living cat. We don't have what the theory implies. We can't take it literally. Some are real, in the sense that we discover empitric evidence, and some don't. I said in my comment "there is a missconcept between language and reality" because I see it as evidence. We do that mistake with words (language) and we also do it with some equations/scientific hypothesis. That's all I wanted to say. I love science, despite not being a scientist. I'm an artist. I mostly agree with what scientists say. I am just trying to help some people to keep in mind this mistake we often do: a missconcept between language and reality. Thank you for your question. I hope I have answered it.

[@dxhelios7902]

@Sean what is the difference between entropy and time? Times defines entropy, entropy allows us to define time.

[@slash196]

Entropy does not allow us to define time. In a local system with decreasing entropy, clocks still run forward.

[@rikimitchell916]

re 5:55 the only way we can experience time is in the 'instant'=="now" we can never experience tomorrow...out of sequence (time travel)

[@jaschoudhury18]

Space and time definately affect Sean's left arm from time to time because it disappears from space on several occasions during this lecture!!

[@teghem6723]

@seancarroll. There are also plenty of mathematically explainable physical phenomena which are irreversible and which illustrate the AoT. Think about non-commutative operations or transformations and more fundamentally about surjections.

[@party-sy2tk]

Thankyou Sean. Very enjoyable and interesting talk. Glad I took the time to watch it!

[@byronwatkins2565]

I think the arrow of time is more generally due to complexity than to entropy. Chaotic systems are entirely reversible; yet, they are unpredictable. These are not entirely unrelated concepts, but systems that increase entropy are automatically chaotic. It is not entirely known whether the converse is true. A small perturbation in a chaotic system drastically affects its future; yet, playing it backwards seems entirely natural even with the perturbation. Playing backwards the same system without the perturbation also seems entirely natural and only a careful comparison between the two motions can reveal which system was perturbed... perhaps, the difference was infinitesimal initial conditions differences instead of a perturbation...

[@MeissnerEffect]

So, so good. One of the greatest scientists and communicators of our age. Or should that be ‘time’? Thank you Sean for your time, and energy, an amazing mind! 🎋🦋🌿

[@a.nunnikrishnan5492]

To understand why we experience different time-intervals for same experience depending on our state of awareness based on relativity principle and also the concepts of past, present and future pl refer the book SPACETIME AND THAT BEYOND By Unnikrishnan.

[@bramkivenko9912]

Sean, there is an arrow of time because the wave function only (apparently?) branches in one direction wrt time. If I'm mistaken you should do an advanced discussion on that specifically. The claim is always that we know the past but not the future. I do know the future. It must be an achievable state consistent with the current state. There are too many such future states to make useful predictions very far in the future. This is not specifically entropy. I think we need some second order definition of entropy that describes the complexity of achieving a state going forward vs backward in time.

[@charonme]

what is called "the arrow of time" in this video is just time asymmetry: while we know there is a difference between different times, we don't know the direction of time. The apparent "arrow" comes from the direction of our observation: we always observe time from lower to higher entropy

[@virajelix]

Sir Sean Carroll, you've mentioned in the beginning of this video that you are more on "Eternalism" than the other concepts. Has this something to do that everything is done; and that we move and experience things according to what have been already there? It's just like an algorithm within the eternal time that what we are doing has already got the consequence done... Just like a computer video game with algorithm programmed by the programmers; and that everything is already there; it needs only the interactions of the user. Please, let me know. Thank you so much with all these efforts you're doing. Best regards.

[@PavlosPapageorgiou]

Time is an adjacency relationship between points in phase space. Using time as an adjacency metric, phase space looks tapered at one end and wide at the other end for combinatorial reasons (entropy). We run through trajectories in phase space and fall towards the bigger macrostates because there are more paths leading there. There's no more mystery than this. The mathematical possibility of smaller macrostates reachable from now makes the past real. It's just the tapering of phase space that we interpret as a "past" with a "start". If you're asking why the "start" looks like a featureless singularity and not like some elaborate godly creation, that's a question of conservation of information. It seems empirically that the universe contains low or zero information, at the big bang or any other macrostate, and the 2nd law can be rephrased as keeping information constant while macrostates get bigger.

[@endrawes0]

Arguably, we don't choose to move through space either. That happens without intention. I'm on the earth. The earth moves.

[@konsamtambradhwaja3870]

Thank you Sean for this lecture.Very interesting and enjoyable talk.

[@1Hominid]

There is another time dilation phenomenon you didn’t mention. I noticed when driving down to the park trail to exercise that the BPM of music seemed faster than when I got back in the truck after a high intensity 45 minute bike ride. I did some research and this is called tachypsychia. Time appears to pass slower the higher your heart rate is and music is a good reference point. Listen to the same song with a resting heart rate then again after elevating it to 160+ for half an hour. The difference is pretty striking.

[@BboyKeny]

I've never seen the present, since it takes time for the light that hit's the eye to be processed into your conscious perception.

[@bob-c702]

I'm glad I live in the particular world where this video got released..

[@brbuche]

At 9:10 minutes there is one idea about the space I'm in; it is that every object is always moving through space. No matter what coordinate system you use to describe space, it has to be relative to another object. And we' re always moving. There's no such thing as an object at rest in space. We have to artificially create space that's not related to time. So it is very similar to time, you can never go back to the same place in space, all the reference objects have moved.

[@marcop3049]

Dear Sean, look: I had this feeling that time is NOT really almost since I was a child. Then I become a physician, rational and or but neoplastic-oriented man... and well, here I should confess that even now after about 52 years of life, still I find intriguing, intellectually attractive the idea that time is just an illusion 🙂

[@marcop3049]

Plastic lol -> platonic!

[@anticaritz]

Thank you for the invaluable information

[@astee58]

Life surely exists. Maybe, as a growing life-entity with a mind, my perception just involves "time". And "matter", which gives me "space". Or "space-time". "Reality" is hard to separate from some kind of "experience". So a completely different kind of being probably could have another notion of space-time, like a fly for example. Different "personal", "macro-state" journeys through experiences of space-time? Thank you for these great lectures!

[@Docma8608]

according to Steven Hawkins, there are three types of times, thermodynamic time, cosmological time and psychological time so which one we are measuring

[@thederivationchannel4243]

Here's a question for Dr. Carroll and I haven't found an answer, or an audience interested enough to discuss it. In 1902 physicist Josiah Gibbs derived the probability distribution from Newtonian mechanics, but he needed the postulate of statistical equilibrium, or that dP/dt = 0. Why is this? How can we justify this postulate?

[@KamranRazvan]

Is time being created "new" as we move forward or does it already exist?

[@KamranRazvan]

@@X9523-z3v Not being a physicist, just a regular engineer having passed physics 101, I wonder about time when we discuss the expansion of universe and space being generated. If time & space are linked and are essentially connected, does it mean that when space is being created... time is also being created? Is there "new" time as we move forward or are we just moving along an existing time axis? Don't you hate it when engineers think physics?

[@KamranRazvan]

@@X9523-z3v Thank you for the reply - I understand the concept of change but my underlying philosophical problem (not understanding is less impressive than philosophical problem) is thinking of a stream .. if I watch a leaf floating and moving.. I can say the change of position of the leaf is what time is.. but it is the current, isn't it? I know that is not the right analogy .. but for something to move it has to have "something" to change with respect to.. the stream.. it hurts to my brain too.

[@Corvaire]

The only concept I would label time, is the difference between the expansion/colapse of our Universe in comparison to what is outside of it. The flow of our internal environment within the outside encompass is only relavent to it's reality of being actively enclosed. The action within our Universe is the flow of time. It won't happen again in the same way, nor will it ever do it in advance. As for the perception of time from a moving person to a stationairy one, it's the same. You're just in different spatial view points. If somebody in Africa says the mountain is brown, and somebody in Iceland says the mountain is green, they're both not wrong and both are viewing a mountain.

[@lixiaochen6]

Well, if time is the direction of the entropy increasing. And entropy increasing is the way the system as a whole can gain information (I don't know if this is true). It doesn't matter if the law of physics can go both ways, no system can gain information of itself going backwards, unless it is being observed by a greater outside system that has increasing entropy. In that sense, the eternalism is the better sale for me. I don't know how to reconcile this with the randomness nature of wave functions though.

[@leftblank6036]

Dr Carroll, why do we remember the past but not the future? why do memories form in the same direction as entropy? we could make predictions for entropy in the universe, for example an asteroid, we could predict it's whole life until it's destroyed based on it's passed information. So if this information can be predicted and is determined, why do we only have a memory of the past?

[@myothersoul1953]

That the laws of physics are reversible with respect to time seems more like an unconfirmed hypothesis than a fact. Yes we can use the laws of physics to retrodict the past but what if time itself were to reverse? Time always moves forward so we can't do any experiment to confirm that hypothese. We do have good reasons to believe it's the case but shouldn't we alway be a be skeptical?

[@rhaglen]

There are many languages in the world that do not have tense, i. e. the grammaticalisation of time in language. Simply put, tense means that for a given utterance the speaker has to relate any event talked about in that utterance grammatically to the moment of speaking, which we call 'now' . For example, if something happened before you talk about it, you use past tense tense. If someone happens after you talk about it, you use future tense. Of course, in many languages tense and aspect are linked in some way, but I won't go into that. There are, however, languages where events you talk about are bit grammatically related to 'now'. Instead, these languages mark an event as certain or uncertain (modality). Depending on the context, the certain event often gets interpreted as having already happened, while the uncertain event has not yet happened. This creates interesting translation problems when working on these types of languages. Now an interesting question is if speakers of languages without tense would be less likely to invent time travel movies than speakers of languages that do have tense. I leave this one up to the anthropological linguists.

[@sinebar]

Here's my definition of time: Time is the rate at which everything in the universe changes and the universe is always changing until the heat death of the universe.

[@ili626]

@39:00 - I don’t think it’s only “novelty”. I think it’s proportional to how long we’ve lived too. One year at five-years-old equals 20% of our life. At 50-years-old, one year is only 2% of our life. “Novelty” does have an effect , but it’s qualitative and depends on various contexts - a life in one town vs a life of constant travel, for example. Psychedelic experiences also provide novel experiences and augment time

[@reidelliot1972]

I am wondering about one of the earlier distinctions between time and space that Sean provides us. He clarifies that we largely believe time is always in motion and we cannot stop it. This is in contrast to space because we don’t HAVE to move in space. (I apologize for my elementary understanding of physics but couldn’t you equate these two definitions to vectors and scalars? Space has both direction and magnitude whereas time only has magnitude?) Even if you were to practically view space as “choosing” to move or walk around on the earth, isn’t there the underlying fact that the earth is still moving, as is the galaxy? This applies to the molecular-level of the universe and the quantum as well? It seems as though an object cannot exist in space unless it is in motion. What I’m trying to ask is, does redefining space as constant motion influence how we look at the relationship between space and time?

[@bharattak6284]

If space is so similar to time, why? 1. Can't their be more time dimensions, and that we are just stuck to one of these dimensions because other time dimensions are 'compactified' like we spoke about space? 2. Why is it so special that we move through time at 'fixed rate' whether we like it or not? How is it different from newtons first law that things keep moving in a straight line unless acted upon by a force? Maybe we just haven't discoved the 'force' that acts in time dimensions? Maybe our time 'mass' is too high so time 'accelerations' are too little? 3. This is a little unrelated and weird, but can you mathematically 'design' topologies that constrain you to move in a single direction? Thanks, really like these talks.

[@palfers1]

Let me recommend Alan Lightman's excellent little book on different models of time: "Einstein's Dreams"

[@costrio]

The difference not mentioned yet (still listening) between past present and future? Probability. The past is probability 1 - it has happened. The present is the point of observation (a la Shroedinger's idea) and when probabilities switch to 1 and all "spooky action at a distance collapses). The future is probability based upon present observations but until the present catches up to it, probabilities can reach very small numbers. Another question that I have wondered about the double slit experiment. Would it work with people? Blindfolded and sent to walk through a barrier with two slits. What pattern would they make on the display screen at the end? Also, I've noticed that the light source is always at 90 degrees to the partition with the slits in it. What if you turned the slit area to a 45 degree angle as relates to the light beam? What about the distance between the slots? What about having 3 or more slots? I like these kind of lectures but they always seem to discuss the basics and becomes very repetitious after viewing so many of them. I do like Sean's ideas but they are "preaching to the choir," so to speak, IMO. (No I'm not a scientist but just a curious guy with lots of questions. Feel free to ignore my ideas -- I'm used to it. ;)

[@frodo0111]

The idea that, at some level, the direction of time is irrelevant seems an overly simplistic paradigm for a toy model. It seems to selectively ignore real effects like gravity, acceleration, friction, multi-body interactions, etc. Can you explain why this level of coarse graining is useful? Thanks.

[@NGC-7635]

You know what’s awesome about video lectures? When you zone out for a second, or you don’t unserstwhat was said, you can just skip back 10-20 seconds and hear it again. Meanwhile in actual classrooms you zone out and it’s like “uhhh, guess I’ll never know what he said just then”

[@margaritahernandez7459]

Thanks. Very interesting.I am understanding more of the issues presented in your last book. I am not a physicist but I always was amazed about physics and got great grades in math and physics 👌 long time ago.