The Physics and Philosophy of Time - with Carlo Rovelli

From Boltzmann to quantum theory, from Einstein to loop quantum gravity, our understanding of time has been undergoing radical transformations. Carlo Rovelli brings together physics, philosophy and art to unravel the mystery of time.
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Carlo's book "The Order of Time" is available now - geni.us/JjwvO
Watch the Q&A: • Q&A The Physics and Ph...
Time is a mystery that does not cease to puzzle us. Philosophers, artists and poets have long explored its meaning while scientists have found that its structure is different from the simple intuition we have of it. Time flows at a different speed in different places, the past and the future differ far less than we might think, and the very notion of the present evaporates in the vast universe.
Carlo Rovelli is a theoretical physicist who has made significant contributions to the physics of space and time. He has worked in Italy and the US, and is currently directing the quantum gravity research group of the Centre de physique théorique in Marseille, France. His books 'Seven Brief Lessons on Physics' and 'Reality Is Not What It Seems' are international bestsellers translated into forty-one languages.
This talk and Q&A was filmed in the Ri on 30 April 2018.
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[@constantineefantis9158]

In the last three decades of the 20th century, and the first couple of decades of the 21st century, I constantly felt the need to remind scientists that all of the great scientists who gave us the foundations of modern science (Einstein, Curie, Darwin, Newton to name a few) considered themselves as philosophers more than scientists. After all, they were doctors of philosophy-not doctors of science. Somehow, in the last half of the twentieth century, and the beginnings of the 21st century, scientists seemed to have forgotten that, and as a result, philosophy seemed to stagnate, thus bogging science itself down. It is beyond refreshing to experience this lecture and other lectures of Dr. Rovelli, who is indeed a profound philosopher, besides being a great scientist. Refreshing is too light a description of Dr. Rovelli’s work, because great philosophers like him give me hope that we are perched on a new era of a golden age of discovery-where science and philosophy are once again united and not disparate entities.

[@Vooodooolicious]

I love your perspective. However, I did notice that during this talk he only referred to Einstein (the scientist) and not to Bergson (the philosopher of time.

[@michaelpisciarino5348]

1:51 Where are we in our understanding of time? 4:39 Order (The Time Line: Past, Present, Future, ) The Past is fixed. The Future has yet to come 9:36 Clocks 11:05 Your head is older than your feet. (Time is longer in the mountains) 14:35 The "Now." We see each other in the past. In Jupiter we see you 2 hours ago. 19:00 Now is only local. What makes something Real? 22:25 Thermodynamic distinction between past and future is *Entropy* 24:59 Order is in the eye of the observer 31:08 Cause and Effect, and Entropy 33:55 Clock Measurement. At the plank scale. Superposition of times at the quantum level. No Time Variable Needed. 36:00 Aristotle's definition. Time is the number/count of change. 39:52 Basic Conditions Granularity 42:12 Entropy 44:30 The Flow of Time. The Passing of Time 46:50 St. Augustine

[@qendrimgjata1525]

people like you should live forever

[@thomaspatel3423]

Thank you so much!

[@outsidethepyramid]

add this to your list: 15:06 nodded off. and i dont blame him

[@JamesHolben]

nice synopsis...

[@Bjowolf2]

They don't have time for that 😂

[@PeterStrider]

Such interesting ideas. Here is a personal attempt to understand it: Time is essentially change. I remember learning that a photon - which as we know travels (ie is in motion) at the speed of light, actually experiences no "time" during its own existence. It doesn't change at all. (Einstein's theorems explain time slows as objects approach the speeds of light. So for a photon time is stopped!). Imagine a particular photon, travelling from the edge of the cosmic microwave background - as far back as we can measure. The instant it collides with a digital sensor in the Hubble telescope is the exact same instant it was formed and released from the nuclear fusion reaction of hydrogen atoms - at the beginning of the earliest stars 300,000 years after the Big Bang. The "now" for that photon was a single "instant" of existence, during which a universe expanded for some 13.6 billion of our years. So it wasn't the motion that constituted time. It was the changes that went on all around it. Changes we see in the large scale universe are marked out or illuminated by countless gazillions of photons coming into and out of existence and illuminating changes between and within all the other countless non-instantaneous forms of being, such as atoms, molecules and so on. "Time" does not need a mind. It just is the process of physical change. Entropy is one metric for defining the actual process of passing time (the change of things toward greater disorder is a feature of time). Our brains perceive time in another, specifically biologically evolved way, to enable humans more successfully to survive and reproduce. Our perception of time is based on perceiving states of macroscopic being through our senses, and remembering them long enough to discern changes which we can hold in our memory (personally in our minds, or externalized with some technical or symbolic tools). These remembered changes are perceived and recalled relative to other regular cyclical patterns in our brain (our body clock and sense of time) or patterns of the sun each day, patterns of the seasons etc. Human time is very specific to our biological needs and evolution in space and time. It is not absolute. We cannot even conceive of absolute time because there is no privileged perspective in the cosmos. From the micro and quantum scale to the largest megascale of the universe, changes are just continually happening. Galaxy time is different to Planck time. And this means "Now" is not actually a time. It is simply the cognitive process of starting a mental stopwatch and deliberately comparing the sequences of changes. That is why we can only experience "now" when we deliberately think of it. It is not actually "part" of time, any more than the shooting of a starting gun is intrinsically part of the "time" taken to run the race. Another gun on the other side if the field can start another race whenever the officials decide. The reality of time (change) is the constantly varying flow of forces, energy and particles around and through us. "Past" is a name we give to the whole sequence of changes that led to this present state of existence. (But we tend only to think of "The Past" as those changes remembered as relevant to how we came to our current state of being). The "future" is everything and whatever this present state will become, as those forces, energies and particles continue changing according to their natural laws and processes. Our biological memory has a trick, allowing us to remember arrangements of things nd so compare them across a range of microscopic and macroscopic patterns. We call these patterns "time" and we imagine it has fundamental and independent existence. And it really does have fundamental importance for successful life as a biological creature. Not having an acute awareness of time, and of the types of befores and afters and causality that is biologically evolved into our bodies, would mean our time as a living being will be short. But this perceptive frame it is not universally relevant. Time for the cosmos in fact is irrelevant. It just is changing. The ancient Chinese philosophy of Dao, or the Way of Change , actually articulates this mystery profoundly. Paraphrasing it, we might say "the change that can be named is not the true change". The time that can be named, is not the true time. But it is the only time we have. So lets live within it well.

[@samh8829]

you have understood it very deeply

[@jameshoey303]

Thank you for sharing . Your comments are relevant and insightful..... Well above the average standard reply

[@JamesHolben]

Well put Sir.

[@kevintedder4202]

I'd agree. As he says, "the laws of physics work in both directions of time." I suspect that the universe does not care about time. Fundamental particles live in the 'Now' and do not remember where they came from or care where they are going to. So time becomes irrelevant. It is only observers that remember an event and, therefore, need to put this into a frame of reference, TIME.

[@samhill6590]

Apparently, you have too much time on your hands...

[@gokhanbayraktar2259]

I simply love Carlo's books. He has an authentic perspective and he does a great job in conveying his ideas. It takes me only a couple/few days to finish his books. I'm 15 mins through the video and my impression is that he can communicate his ideas much better when he writes. So if you find any part interesting for yourself, I highly recommend you to buy his book, the order of time.

[@miguelferreiramoutajunior2475]

So you didnt understand nothing, in fact.

[@jeffreyjernberg3650]

@@miguelferreiramoutajunior2475 Your statement is a double negative, conveying then that they understood everything.

[@DEATH0RI0N]

@@jeffreyjernberg3650 Mind blown.

[@jeffreyjernberg3650]

@@DEATH0RI0N Ditto, or etcetera, etcetera, as Thom Yorke would say, or What is relativity anyway, as Albert E. once said. Wow, now I understand reality, it's all relative. I can't hear myself think.......

[@wendysantamaria7441]

Same. I do think his books are so easy to understand and I love the way he explains everything in them.

[@cleitevieira]

Rovelli rescues the old (and great) tradition of Italian physicists with a strong Humanity cultural background. Great lecture!

[@jjt1881]

I came here looking for Quantum Gravity mainly because of Carlo Rovelli. Now I leave not only more interested in his work but also in the work of Dean Buonomano. I've never heard a better discussion on the topic of time in more than 28 years in the Academic world. I'm literally speechless and in awe. In all my years of studying philosophy of science, mathematics, cosmology, epistemology & metaphysics (even Neuroscience), I've never heard a more profound and insightful talk about the nature of time, as well as human & individual awareness of it. Simply, K U D O S!

[@abdulkaderjaleelmuhammad5259]

I think "CHANGE" is the 'tool' that makes us 'aware' of time. The change, may be the change of our 'shape' with 'age', or change of state of motion or change of state of energy or change of state of 'entropy', ...etc.. The change is always a change 'relative to time' (or with respect to time). If 'Laws of Physics' do not differentiate between past and future, it is because that these laws do not have a 'memory'; that is these laws do not keep a record for the 'past events and or past changes'! The talk is great in shining light upon these topics. Thanks for RI and for Prof. Carlo Rovelli.

[@Haraamcore13]

This man has such mad elegance and insight it’s unreal. Highly recommend the book (The Order of Time). His findings are simply astounding and his prose is impeccable.

[@helisoma]

yes the book is great also recommend it

[@nicolegraber6400]

Thank you for the recording of this lecture. What I really like about C. Rovelli's lectures, is that he often just talks, without showing dozens of slides. This is very convenient, because you can take your eyes off the screen; and it's very pleasant, because you can immerse yourself in your own imagination, while being guided by a clear and pleasant thread.

[@AmberExista]

I have had a drug induced experience where my brain could no longer properly produce a normal, subjective experience of time passage, and also the continuity effect was broken. A minute (as checked on the clock) felt more like an hour, and I would find myself in a moment, with 0 recollection of the events shortly before. This demonstrates his idea that what we understand of time is strongly regulated by some brain effects. If the brain couldn't bring together the musical notes already registered in a correct order, then there would be no talk of time at all. You'd only experience a snapshot of reality, and no experience of motion, since something requires at least two states in order to say it moved or changed. So then if the physical world has more than one state, the brain needs a way to work with these states. But then did the physical world and entropy determine the brain to develop this arrow of time perception of motion, in one direction, or is it just one possible way of 'making sense' of reality? Just like different eye designs in different species, perceive different wavelengths. Also, in one physics documentary, I have heard the idea that when you break a glass for instance, if you could reverse the velocities of the particles of that glass, you could reverse the whole thing. This example was brought up to demonstrate the idea that for the physical theories in themselves, a glass being unbroken is not forbidden. But for the velocities to change in the opposite direction, something has to change them, it doesn't happen spontaneously. And a realistic example of unbreaking a glass, or making order out of disorder, are all the biological mechanisms. How does this fit into the entropy idea? If you imagine the world at the beginning as a soup of chemicals, biological organisms are so much more 'ordered', and you could argue that in those examples, entropy decreased. I mean, I know I am complicating it all when I introduce biological, macro objects, but I find it relevant. In this video, I really like it how he points out that 'order' is defined by the system we choose, ordering balls by red and green for instance, so that's one problem addressed: what is order? But then the next problem would be, on what level does the observation that things go from order to disorder, apply? If you pour oil in water, in time, the water and oil will segregate in an orderly way. Organisms are clearly defined systems that produce order out of disorder. Because of these examples, I find it really hard to understand why entropy is considered the decisive factor in creating an arrow of time. Perhaps I need a more detailed explanation? The point where different disciplines like psychology, neuroscience and modern physics meet (in a sound, not a superstitious way), is incredibly fascinating.

[@Vooodooolicious]

It makes me think that life is a biological experiment that is chaotic and haphazard. Not something controlled. To me, it is an argument against God and at the same time evolution.

[@384384384384]

"In the beginning there was chaos. Out of chaos came order. Out of order came love." My ancestors came to the same conclusions thousand of years ago. My humble summary contribution to knowledge: " Love is the ink, wisdom is the message. Imagination is the way."

[@jaydawg7820]

yeah, i agree .. i dislike the use of 'entropy' as 'disorder', in my opinion its not 'disorder' but more like 'complexity' ... otherwise we're the most entropic disordered thing in the universe..(as far as we know)...

[@mohammadharisfahim6614]

Newton and Faraday used to stand here. And now Riovelli. This place is a legend.

[@josephhall2748]

Faraday used to stand here. This place is legend. It works with just one too lol

[@davidevans1818]

Umm - not Newton in the 17th century!

[@troyyoung1121]

Consciousness =having time to observe increments of activity

[@acefo4]

This presentation is extremely beneficial as an introduction to the conceptualized understanding of time. I am very much obsessed in the idea of "time", I wrote my perception of time roughly a year ago and now just watching this video, I have been pleased to find my understanding is well within reason. Here is what I wrote if anyone cares to read. And please I welcome criticism, constructive or not. Thanks... UNDERSTANDING “TIME” It's important to understand that the creation of the word and definition of “time” was created by man to give measurement of their passing moments in existence. As it's too common for people to just accept what has been oversimplified as the ultimate truth without questioning it. An example of this is the human notion of “time”, everyone accepts the premise of past, present, and future, some to the degree that they all exists simultaneously and or that they can be traversed, as if a highway, and it's accepted without further understanding the actuality that they are a man made virtual construct of reality and is no more realistic than (would insert God here, however to not offend) the boogeyman or Easter bunny. So I ask you for a moment to put aside these meaningless fabrications and try to come to the realization that what so many people refer to as “time”, more accurately fits the definition of Entropy. While this is loosely accurate to the true action that “time” measures, understanding Entropy helps the mind come to terms with what follows, “Matter Evolution”... the physical change of matter in the universe from one possible configuration to another, with the ultimate premise that all matter in existence within the known universe evolving from orderly to disorderly physical constructs (similar to if not exactly as with Entropy) so the notion of past, present, and future, no longer becomes valid if your interpretation of existence evolves into the idea that the entire known universe right now is in one possible configuration of existence that has infinite possible ways to exist from one moment to the next or from every little change of a property of matter within it. Now some configurations can be predicted accurately with an understanding of Causality, and Entropy, as some systems can and do create “partitions” of order from disorder, however this order is created with a fundamental principle to further disorder to the system as a whole. Moving on… The universal existence of “Matter Evolution” is not a concept that can be easily associated with having a past, present, or future, instead should be envisioned as that all of existence having different possible evolutionary outcomes in relation to any and all possible interactions that give change to any physicality of matter... (Still work in progress)

[@DSingh-ej3cu]

“Time is the substance I am made of. Time is a river which sweeps me along, but I am the river; it is a tiger which destroys me, but I am the tiger; it is a fire which consumes me, but I am the fire.” - Jorge Luis Borges

[@MN-sc9qs]

Slam dunk!

[@PaulSinghSelhi-VFX-TUTORIALS]

Sat Srl Akal. Akaal Moorat.

[@dontgetmadgetwise4271]

Yes? But this is physics.

[@dobbsmill3676]

Sounds like a perfume advert.

[@dannydetonator]

Do you understand this yourself well?

[@JoanneTenenbaum]

Deep and thrilling, like Rovelli's books. Rovelli has a gift for making abstract ideas understandable for all of us. I have always had the sense that time was a function of our limits of perception, so it was wonderful to hear Rovelli approach a similar conclusion. I was surprised to hear that this notion is considered new in quantum physics.

A general organization of chapters (thank you very much @michaelpisciarino5348 for sharing yours ☺🙏): 00:00 Introduction 04:27 The time we experience 07:15 What is "wrong" about our perception of time 08:57 Point #1: Time is relative (it´s not fixed) 13:58 Point #2: The meaning of "now" (it only makes sense within a certain "bubble") 20:43 Point #3: Past and future: does Physics really distinguish them? (Considerations on what entropy means) 32:54 Point #4: There is a minimum time interval (quantum gravity concept - work in progress) 39:05 "The journey back" (synthesis) Maybe it can help for future queries 😌🙌

[@slikclips2966]

The best talk on the concept of time I've ever heard. Truly mind opening. Great to hear the budding concept talked about by someone on the forefront of its discovery

[@troyyoung1121]

The past is interesting because we get to learn from the mistakes made Take heed Russia

[@amanous]

I was in the theatre that evening and this is one of the best lectures I have ever watched in the Ri (and I have been to so many since I have been a member for years and a huge fan!). I discovered him after someone mentioned 7 brief lesson on physics (on another Ri talk) which I had already read prior to the talk, so I was already pumped to be in this talk and seen him in person for the first time. Man, did he meet my expectations. His story telling ability is absolutely impeccable! Without a single slide on the screen and with the only visual stimulus being 2 clocks and a string, he captivated the audience for two hours while explaining some extremely complicated physics (and philosophy!). I would dare say we see in this man echoes of Feynman in the ability to communicate science!

[@schmetterling4477]

Of course he met your expectations. You don't know enough about physics to tell that he was bullshitting you. ;-)

[@pyb.5672]

I agree. Polymathic tendencies have always yielded the greatest strides forward. In an era of ultra-specialization, this line of thought is much needed. Absolutely stellar synthesis of time from a multi-disciplinary point of view. Its fantastic to see phenomenology being merged with modern physics.

[@voltydequa845]

@@schmetterling4477 But it's moderrrrrn physics, all time-is-what-is-not-what-it-seems-but-could-be-what-it-was-is-if-we-were-riding-a-counter-propagating-photon-coupled-with-two-bosons-and-one-virtual-higgs, and cosmology of white-holes-as-a-consequence-of-the-temporal-disatisfaction-of-black-holes-horizon-of-perpendicular-exhaustion-of-events. Then they talk with some of their friends and explain what is time, while the time cannot exist within a frame of time, how the white holes spit out Shroedinger's cats with meows silent if listened to.

[@ChristopherHartbooks]

I really liked the metaphor of the flow of time being experienced like a musical score - one note at a time. I read his recent book. I could not recommend it more highly.

[@noahgarcia1702]

Christopher Hart what’s the name of his newest book and what’s it about

[@frankeffenberger9698]

I don't know about a musical score, but the essence of music is in the playing and replaying of music both in our minds and in the anticipation of it in experiencing it.

[@xyz86457]

@@noahgarcia1702 The Order of Time

[@shaun906]

@Roger Loquitur people use metaphors to explain something simply via a shared experience.

[@kvaka009]

It isn't really a metaphor. Because when Beethoven composes his music, he is literally creating time-- ordering energy into most unlikely states, the possibility of which itself took nature to create all the billions of years of time, and then when you listen to that melody your brain too is arranged into highly ordered states that are resisting entropy by keeping Beethoven's music in existence, if only for a short time.

[@tarikdia5894]

I listened to this talk while falling asleep. Not sure when i dozed off but i had a dream where i knew i was dreaming and in the dream i was able to go back and forth between present and past and knowing i was in a dream i willingly went to certain points in my childhood and i enjoyed every second of it ... i woke up amazed and wondered what in the hell was i listening to in my sleep .... listened to it again and it was all clear now ... thank you for the talk and the dream.

[@JSB2500]

Lucid dream.

[@voltydequa845]

I dreamed I was riding a photon. But the riding was timeless and comfortless. A nightmare of eternity without progress. Then on top of that the image of Einstein torturing semantics. Double nightmare. Then I said, in the nightmare, "I do not believe in all this nonsense", and wakened me.

[@darwin5617]

A brilliant weaving of Newtonian, Quantum and our complex Biology....

[@HugoGuthrie]

Carlo Rovelli leads Physics by his clear consciousness of philosophy. He heralds his own momentum. Here I simply put together and so speak directly for his honour-- 'Time' is a human construct- Answer - What is discernible but not differentiable ? (Only relationship can answer..) His work reveals the human construct of perception and being and my hope is that he will reveal that computational intelligence is not possible; time has no part in computational analysis.

[@santanudutta2555]

It is interesting to speculate whether time would have the Same significance, or Any significance, in our lives if we were immortal. If we had infinite time to do everything what would be the urgency of doing anything by a certain time?

[@harishkd1]

Well said boss ..

[@neelroy2918]

In all seriousness, you dont have to be immortal, just retired to know the answer.

[@buddyrichable1]

Time takes on more significance because we age, we grow old. If we were immortal and stayed at age 40, for instance and still accumulated the wisdom of having lived many years, then it would depend on our situation. Immortality would be great if you were Hugh Hefner, but not so great if you were serving life in prison with no parole.

[@Leifler]

Before clocks and "standard time" people really didn't see the effect of time the same way. Meetings of "9 am" we're more like "morning meetings" and arrivals could vary by 30-60 minutes without and sense of it not being the "same time". Even early America, town by town clocks varied drastically before the train. Everyone's time really was "relative". Even how we identify ourselves greatly varies as some considerations for centuries old "Kings" was more likely their lineage. But the more you identify with a line or a people, "We" can be "my school class" or it can be "my heritage of thousands of years. So that "today" can be a literal 24 hours, or can be the last 20 years of technology or it can refer to 500 years of an ideal. Even your "immortality" is subjective when people used to value their families more, your children really were viewed as you living on. When you view that, you have far far more time to accomplish things as many in history have viewed that as their timeline for accomplishment. Especially like the mindset between kings "I have 40 years to work on this, then my son can keep working on it" vs say a president "I have to cram my ideas in 4 years, I MIGHT get 8, then I am done". It's a very different perception of life. And trickles throughout culture from your work time start (9 am meetings) to your concerns for your nation.

[@olivercox2565]

That’s such a mundane question. Firstly there is no time, only entropy. What you are really asking is what if entropy didn’t exist? If entropy didn’t exist there would be no universe.

[@SolaceEasy]

I love how his conclusion ties in the idea that the perception of time causes suffering. How does a Time Scientist release attachment to time?

[@garymills6702]

Death is the end of time for each of us as an individual. But in a way we've all already been dead before we were born!

[@mrMic9]

By studying and experiments with quantum physics, he knows firmly that the idea of time is only a product of our own mind, instead of subjectively existed. By realizing this fact, one's mind can begin to detach the concept of time, which leads to the reduction of the suffering caused by time.

[@richardmarker786]

Professor Rovelli, Thank you for your great presentation on 'time'. I very much appreciate that you presented this in English with such professional video and audio. I noticed that you had a full house except for one seat. I suspect the person belonging to that seat had heard all of this before. There are few people who so thoroughly and successfully combine philosophy with physics in forming their world views. I appreciate that you appear to view time as a sequencing of events. It can be challenging to think flexibly enough to adopt this view. You emphasize that one's experience strongly affects their perceptions. This runs much deeper than you may expect. Think of space as consisting of the fabric of space. All of physics and all of our life experiences occur as a result of how the fabric of space responds when we interact with it. There is a deeper level that falls outside of physics and outside of our experiences. The deeper level consists of the operation of the fabric of space itself. How can space be built and how can space be maintained? Since this falls outside of our experience we do not know a priori the metaphysical laws that prevail in the fabric of space. We only experience the laws of interacting with the fabric. It is possible to understand the operation of the fabric of space itself. In order to do this many of the philosophical things you mention must be considered. In the end, one must take their best guess and see where it leads. Most often it will lead down a path that conflicts with reality. In that case one must try a different thought path. Over four decades ago I started on a thought journey. Very early in the journey it seemed that Something and Nothing were a likely candidate for the starting point. Never in my wildest imagination did I guess where it would lead. The most direct result from this thought process was an understanding of gravity. I know it is presumptive to talk about gravity with someone so skilled in it as yourself. I mean no disrespect. Quite the contrary, it is your depth of understanding that appeals to me. My understanding of gravity runs contrary to deeply embedded concepts in physics. I know from your presentation that you give a great deal of consideration to embedded thoughts. First, General Relativity (GR) and space-time are only local approximations to reality. They are very good, but hide the true nature of space and time. There is no four dimensional space-time continuum. Time is continually slowing down, that is what prevents a space-time continuum as we understand it. What does it mean for time to continually slow down? Matter works as the brakes on time that is what creates time dilation. If we were able to separate a piece of space that contained no energy or matter, we could consider this to be a clock that does not slow down. Relative to that separated space we would find the clocks in our universe were slowing down. This is not a convergent series so readers should not be concerned. Time slows down at the same extremely low rate everywhere in the universe. This is why we have no perception of it locally. MOND gravity provides evidence of this slowdown at a distance, but we choose to ignore it and introduce Dark Matter. If we were allow ourselves to be objective, we might raise some questions about GR. It does not apply on the quantum level; nor, does it apply on the cosmological level. The cosmological failure is evidenced by Mordehai Milgrom's MOND work. Even black holes raise philosophical questions. If GR doesn't apply on the quantum level then how can we possibly deduce pure black holes from the continuous formula. At some point we get close enough to where time stands still that we are into the quantum area. I do understand that quantum effects are being considered, but the whole premise of time standing still should be rejected. In this view of gravity, space acts as a flywheel and matter acts as the brakes. This closely matches GR locally. There are many more philosophical conclusions that one gets from understanding Something and Nothing. Alas, nobody seems to believe such an understanding is possible. This is a difficult enough journey to make that it possibly would not happen again. Thank you for listening. Richard Marker

[@RashidMBey]

I'm commenting now to review this comment later. I value thoroughness, and this comment distinguishes itself from the rest of this section. Thanks, Richard.

[@voltydequa845]

«There are few people who so thoroughly and successfully combine philosophy with physics in forming their world views.» -- They are disjunctive and cannot be combined. ---- «If we were allow ourselves to be objective, we might raise some questions about GR. » -- Indro Montanelli, a great journalist fellow countrymen of Rovelli, used to say that it is not the freedom that is missing but free people. SR & GR are utter nonsense models built on top of semantic and cognitive confusion. The early critics (I do not remember the names now) were right - it went (physics) too theoretical, and substituted reality with math models. Though I fear that with these ones happened much worse -- they, together with the publicity given to this absurd & abstract & abstruse models, finished with shaping, towards cognitive anarchy, the minds of many people. Time ago a person wrote me something like "time exist since it is a part of the fabric of the universe". One can realize how this is detrimental only after trying to bring back to semantic sense this kind of persons - almost no hope. -- + The real physicists do not have time to question GR. The real book writers / sellers do not dare question GR. More confusion more they sell.

[@adsjar]

I listened to this twice. Not because it was hard to understand, but because it is so beautiful. Bought book. Shall read it in the fullness of time.

[@amaliaantonopoulou2644]

Carlo Rovelli is great. This is not only a conception of time, is a genuine philosophy of physics!

[@Ssmiley612]

He does an incredible job breaking down each layer. He guides us through each fundamental concept with such ease

[@solomonlalani]

Thank you RI for the searching inquisitive souls like us to be able to learn from true legends of our times such as Carlo Rovelli, Jim Baggott, Andrew Pontzen, David Tong et al. Many other names: but thanks to all of these legends.

[@syed9576]

I'm one of those philosophers he talks about and so good to see this talk. I do disagree with certain points of his. But all that aside the thing that the best about this video? It's the fact that it has been viewed more than half a million times. In this world of anti-science, this is so good to see.

[@KillingDeadThings]

I wouldn't say the world is antiscience. We're more scientific now than at any point in human history. The middle ages was an antiscience time.

[@voltydequa845]

@@KillingDeadThings Not at all! IN the middle ages people used to have more common sense, and so distinguish between useful and hot air. It seems more primitive is more genuine is. Like monkeys - that you cannot trick them with packing, pay 2 take 3, or similar, because they do not fail when it comes to evaluating gain (in calories and/or necessary vitamins or else). Today's world, especially the western one, is metascientific.

[@davidcooke8825]

I loved Carlo’s book and this talk helped to consolidate that for me. Profound and provocative, with genuine consequences for living. Thank you

[@at19eden]

the way and the speed in which he s speaks is really hypnotic, his tone kept going harder and harder to hear

[@nathanokun8801]

The "thickness" of "now" can be considered the time it takes to do something for a reason and then get a response from your "target" on which to base your next action. Nearby, this is very short and "now" seems to be a thin slice of time. As the distance increases (or the response time of the target slows down), this interval gets larger and larger, but still forms the basic concept of "now" to humans. Thus, the concept of what is the separator of the past from the future -- what is "now" -- is usually based on our human perceptions, not on physics.

[@chickenduckquack]

'Now' is nothing to do with humans. Think of 'now' as being a snapshot of the 'State of the Universe'. Whatever is going on is frozen in that instant, so your thoughts or the movement of light, or Einstien whizzing past at any speed do not affect the 'now'. The now can only involve energy pushing masses around - a simple universe.

[@baddust]

Motion requires space but time requires motion and a brain to interpret relative motion. Therefore, time is a mental concept. Time also requires records of previous motion which we call the past. What we call the present is just a collection of recent memory's (records) and is therefore really a recollection of recent past events. The future is just a mental speculative guess about what events might happen that is based on past events. The real NOW is a constantly moving target with which we have no direct mental contact due to the delays inherent in our perception. We strive for certainty while adrift in sea of constant change and then we die.

[@jonathanjones770]

Perhaps

[@PeterStrider]

Interesting ideas. But time doesn't require motion. It requires change. I remember learning that a photon - which as we know travels (ie is in motion at the speed of light) actually experiences no time during its own existence. For a photon, travelling from the edge of the cosmic microwave background - as far back as we can measure - the instant it collides with a digital sensor in the Hubble telescope is the exact same instant it was formed - at the beginning of the earliest stars 300,000 years after the Big Bang. The now of that photon was a single instant of existence, during which a universe expanded 13.6 billion years. So it wasn't the motion that constituted time. It was the changes - marked out or illuminated by countless gazillions of photons coming into and out of existence and illuminating the changes within all the other countless non-instantaneous forms of being such as atoms, molecules and so on. Time does not need a mind. It just is the process of physical change. Entropy is one metric for defining the actual process of passing time (the change of things toward greater disorder is a feature of time). Our brains perceive time in a biologically evolved way, to enable humans more successfully to survive and reproduce. Our perception of time is based on larger scale changes which we can perceive through our senses and hold in our memory (personal or collective memory). These remembered changes are relative to other regular cyclical patterns in our brain (our body clock and sense of time) or patterns of the sun each day, patterns of the seasons etc. So "Now" is not actually a time. It is simply the cognitive process of starting a mental stopwatch and deliberately comparing the sequences of changes. That is why we can only experience "now" when we deliberately think of it. It is not actually "part" of time, any more than the shooting of a starting gun is intrinsically part of the "time" of the race. Another gun on the other side if the field can start another race whenever the officials decide. The reality of time (change) is the constantly varying flow of forces, energy and particles around and through us. Past is the whole sequence of changes that led to this present state of existence. The future is what this present state will become as those forces, energies and particles continue changing according to their natural laws and processes. Our biological memory has a trick, allowing us to remember arrangements of things nd so compare them across a range of microscopic and macroscopic patterns. We call these patterns "time" and we imagine it has fundamental and independent existence. And it really does have fundamental importance for successful life as a biological creature. But it is not universally relevant. Time for the cosmos in fact is irrelevant. It just is changing.

[@shnabo11]

Maybe I am misunderstanding what you are trying to say, but I disagree that time is a mental construct. "Time" in and of itself will continue with or without consciousness. The universal "now" does not need consciousness in order to move forward into the future and create a past, this has been occurring without consciousness for almost the entire evolution of the universe. When the first light emmited from the first stars hits the Hubble telescope it indeed would hit it at the instance it was created but only in the reference frame of that light, in a different reference frame such as our own it is happening at a different "now." Real things have happened after that first light, it has not/is not/will not all happen at once and therefore is separated by time. Also, because light has velocity (from a reference frame other than the light itself), it must have time. As I'm sure you're aware, velocity is the vectoral rate of change in the disposition, and in order for something to change a position it must traverse some amount of space and to do so a period of time, no matter how infinitesimally small or infinitely large, has to pass. I believe time dilation is also not a construct of the mind, it affects all matter. If you are curious enough, look up time dilation affects on the half life of muons moving at almost speed of light. Time is very real and sets the stage for all of physics. The explanation of "Now" is perhaps outside the realm of physics. But time itself is the stage that physics takes place. Maybe the meaning that we give time is a mental construct, but what we are referring to with that meaning is very real. I love talking about this stuff and love to hear different perspectives so please do let me know your thoughts! Cheers! :)

[@baddust]

@@shnabo11 Hello Shayne, You imply that time is a physical reality but can you point to any physics evidence. I find none. The universal "Now" moves forward because of the universes motion continuum. Motion is a real physical thing. The past is nothing but physical records that have been created by motion. It takes a thinking entity to observe these records and place them in a chronological order that represents the passing of time and therefore time is a mental construct developed by studying physical records. Physical records are not permanent. They get destroyed by motion. The oldest permanent records that I can think of is the Cosmic Microwave Background Radiation (CMBR) that is evidence of a "big bang". I do not accept the notion that there was nothing physical before the big bang but the evidence of it's existence has been destroyed and, I think, the CMBR will also be eventually destroyed. Space is also a physically real thing. and all physically real things are a form of energy. Light (electromagnetic energy) has a speed that is dependent upon the medium through which it moves. I try to observe mentally from outside local reference frames. Reference frames is a concept invented to help us understand why we perceive events differently when the location and speed of the event is different from the location and speed of the observer. Large amounts of space cannot be measured without motion and motion cannot exist without space. Small local amounts of space can be measured with a ruler. We typically use the speed off light to measure large amounts of space. All amounts of space are relative to other amounts of space. All amounts of motion are relative to other amounts of motion. Duration is a measure expressed in terms of relative motion. We use clocks to measure relative motion. A clock can be anything that has a reasonably constant repetition rate of motion and then we use that clock rate to measure other rates of motion. Indirectly, we use a clock to measure large distances of space and that clock is our planetary year, since we describe these distances in terms of light years. Anything that has an influence on the repetition rate of a clock affects it's measurements. One thing that affects a clock is gravity and another, by my way of thinking is the relative motion of the whole clock within the universe. In other words one motion can affect another and that is the basis of my opinion that the thing known as time dilation is not evidence that time is a physical thing. You say, "time itself is the stage that physics takes place". I say "measurement is the stage upon which physics takes place and our most significant tool of measurement is the clock which is dependent on a consistent repetition of motion". I too love talking about this stuff and I appreciate your response to my initial blurb. Regards Ed

[@baddust]

PETER STRIDER: Interesting ideas. But time doesn't require motion. It requires change. I remember learning that a photon - which as we know travels (ie is in motion at the speed of light) actually experiences no time during its own existence. ETM: BUT, How can you have change without first having motion? Change is a recognition of a result of motion by a thinking mind. Regarding the Photon, it actually experiences nothing because it has no mind. You have projected your mind onto the photon in an attempt to have a view or opinion from the perspective of the photon. PETER: For a photon, traveling from the edge of the cosmic microwave background - as far back as we can measure - the instant it collides with a digital sensor in the Hubble telescope is the exact same instant it was formed - at the beginning of the earliest stars 300,000 years after the Big Bang. ETM: To me, this is an absurd statement based upon your prior attempt to grant a photon a mind and claim that to it's mind it could see no differences between it's emission by a star and it's impingement on the Hubble telescopes digital sensor. This is also saying that this hypothetical photon mind would have no awareness of it's motion which would not be true if you also project your eyes onto the photon. PETER: The now of that photon was a single instant of existence, during which a universe expanded 13.6 billion years. So it wasn't the motion that constituted time. It was the changes - marked out or illuminated by countless gazillions of photons coming into and out of existence and illuminating the changes within all the other countless non-instantaneous forms of being such as atoms, molecules and so on. ETM: More nonsense based upon your wild idea that a photon has an existence of an immeasurable instance of duration. Physicists have measured the speed of light and know that it's travel from it's originating star and it's impingement on the Hubble telescopes digital sensor has a duration. PETER: Time does not need a mind. It just is the process of physical change. Entropy is one metric for defining the actual process of passing time (the change of things toward greater disorder is a feature of time). ETM: Again, change is always a product of motion and to perceive change requires a thinking mind. The idea of entropy is, like the idea of time, dependent upon the existence of motion and a thinking mind. PETER: Our brains perceive time in a biologically evolved way, to enable humans more successfully to survive and reproduce. Our perception of time is based on larger scale changes which we can perceive through our senses and hold in our memory (personal or collective memory). These remembered changes are relative to other regular cyclical patterns in our brain (our body clock and sense of time) or patterns of the sun each day, patterns of the seasons etc. So "Now" is not actually a time. It is simply the cognitive process of starting a mental stopwatch and deliberately comparing the sequences of changes. That is why we can only experience "now" when we deliberately think of it. It is not actually "part" of time, any more than the shooting of a starting gun is intrinsically part of the "time" of the race. Another gun on the other side if the field can start another race whenever the officials decide. ETM: The pieces of the universe are in constant motion relative to each other. The motion of these pieces cause them to combine, for some duration, to create a form different from the individual pieces. These forms are records of the event that was caused by the motion of the pieces in combination of their separate physical characteristics. It requires the thinking of our minds to recognize that this "combining event" happened prior to our "observation event" of the form that was created. From this our minds recognize the concept of past events versus current events which are both not possible without the motion of something. From this recognition the "concept of time" is created. Then we use the consistent relative motion of a clock (nature made or man made) to measure duration's of events and between events. I agree that "Now" is not a part of time. "Now" is an observation event that has been recorded in a thinking mind. An event cannot be created without motion. PETER: The reality of time (change) is the constantly varying flow of forces, energy and particles around and through us. Past is the whole sequence of changes that led to this present state of existence. ETM: In your own words "flow of forces" means motion. The past is the existence of records created by motion and their recognition by a thinking mind. PETER: The future is what this present state will become as those forces, energies and particles continue changing according to their natural laws and processes. Our biological memory has a trick, allowing us to remember arrangements of things and so compare them across a range of microscopic and macroscopic patterns. ETM: The "future" is a mental projection of what might or might not actually happen that is based upon thinking about records of previous events. The "patterns" you speak of are the records of previous events. PETER: We call these patterns "time" and we imagine it has fundamental and independent existence. And it really does have fundamental importance for successful life as a biological creature. But it is not universally relevant. Time for the cosmos in fact is irrelevant. It just is changing. ETM: You call your patterns time. but I call them records from which the concept of time is created from their observation by a thinking mind. I agree that the cosmos is in a state of constant relative motion by it's pieces and motion, by itself, is not time. Time is not a physical thing or a physical part of the universe.

[@ShardCollector]

Quantum physics and relativity are are somewhat hard to crasp, so when you spoke about time slowing down when the speed increases, this is what I thought: 1. What is the reference for "speed"? If we pass each other in the space at 10 000 m/s, neither of us could tell if we were both moving 5 000 m/s or if the other was moving at 15 000 m/s and the other 5 000 m/s in the same direction. Without reference, there is no speed. 2. When time slows down in speeds close to c, then if we launch a rocket at 5 000 000 m/s from our perspective but we were already moving at 0,5 c to the other direction, then is the rocket crew actually moving slower than us and thus aging faster? How do we know what speed we are moving, when things look relatively the same in every speed, because of the time dilation? 3. 1 meter is defined as a 1/299 792 458 of a second, but second doesn't exist by itself. Someone needs to measure it and the measurement is affected by both gravity and velocity. All we know is the "now" inside our little bubble, as was pointed out in the video. The bubble is our own reference point of time and space.

[@new-knowledge8040]

If you just discover special relativity on your own, you see its completeness rather than see it being presented in mere confusing fragments.

[@saxonhammer5511]

I believe you have grasped the most fundamental fact of the universe and that is 'spatial points' / 'particles' /objects have their own reference frames and none of those frames are fixed. Therefore all measurement is only accurate between the points measured and at the exact moment of measurement. From that point on that recorded measurement will become more inaccurate. The inaccuracy of the measurement maybe incredibly small but the universe still responds to the change nevertheless.

[@liammcguinness5465]

Time is now and has always been slowing down.We don't feel this because we live in this time frame,but if you view a distant object it is in a previous time frame. You will see what it was doing and that is always faster the further back you look

[@saxonhammer5511]

Liam Mc Guinness If we viewed a second earth 100 light years away but with all other aspects unchanged (relative speed, distance etc) a person walking on that distant earth would look normal (not slower or faster). However the event would have occured 100 years ago even though we would observe the motion live (in the now on this earth). If we view a black hole it does not matter how near/far away we are gravity at the black hole causes time to slow down so much that light becomes trapped. You see it is the time rate of the distant region that determines the speed of movement at that location. Things that affect our observations are relative speed and acceleration so if these factors are unchanging then we will observe a time delay but not a time dilation (slower/faster). As Carlo Rovelli says it is only in the last approx 100 years that we have known that space and time are intrinsically linked. As this has very little effect on earth we do not develop a true understanding of time instinctively during childhood and though adulthood because we live in a very tiny space within the universe. Most people in the world will be totally unconcerned and unaffected by this talk and its meaning because the human race has managed (until recently) perfectly well with the default "now bubble". The most major use for our newer understanding of time is the GPS network as the GPS satellites do experience time dilation.

[@liammcguinness5465]

Saxon Hammer If you did observe earth from a distance you would not only see things moving faster.you would also see the earth orbit mush faster.Dose this sound familiar.

[@TheFinalJudge]

Since there is a lot of discussion on presentation style, and since I could only find one reference to his book "The order of time" in some sub-response, I would like to advise reading that book as it covers the topic of his presentation in a clear, well-written, sufficiently high-level way. By referencing many authors throughout history and their insights, he manages to make an abstract topic into a coherent story and a pleasant read. Well done Carlo Rovelli!

[@amitanand7581]

Well after listing to your lecture I am really surprised that mathematics and physics is now being put into words and is being aligned with questions whose answers lie with in ourselves. That is our brain where emotions play a very strong part.

[@alexxela8956]

What a fitting way to end this. To use the word 'emotion' (for the first time i think in this lecture) to describe time. It's nothing more, nothing less. Never thought of that!

[@adonaiblackwood]

✨ Order is in the eye of the beholder. 🙏

[@dennisgalvin2521]

Just curious, are you a little bit OCD ?

[@adonaiblackwood]

@@dennisgalvin2521 having a lil OCD is good I suppose 😅 …otherwise I’d never clean or organize a thing in my life!

[@dennisgalvin2521]

@@adonaiblackwood Get that, I have the same thing only the opposite way around.

[@TheRealFranc]

At 44:08 is the most important breakthrough acknowledgement to be carried forward to make scientific progress in sorting out "time" which has been labelled a paradox recently by Lee Smolin.. In this video it's FINALLY refreshing to hear a physicist (Carlo Rovelli) that delves into time as a function of (the brain) memory and anticipation of the future. "we are the passage of time" "we are the time machine" aka "real" time. But, "There's something about time still missing" (and) "it's NOT in the quantum gravity, it's NOT in general Relativity, it's NOT in thermodynamics, it's in the speciic way our brain works". I myself have observed and declared that we are each a path of time, making us children of the greater and grander cycles of time of the Universe and our galaxy and solar system as it concerns us most immediately, locally and more personally.

[@ziggyfreud5357]

Thanks for your efforts in sharing your views of how some of us see time. For me, there is no time. And my now is a unique now as is everyones. We use the concept of time to measure change to help us interact with one another and make sense of our world. But the reality is that time doesn't exist. There is only my now for me :) Great lecture and thanks for sharing.

[@kvaka009]

Does your time for you exist? If yes, then time is as real as you. Are you real? Are you sure?

[@thuokagiri5550]

His simplicity,eloquence and pedagogical approach almost put him in league with Richard Feynman demystifying such counter-intuitive ideas for non physicist like me ....Simply elegant.

[@scottsaic]

I have watched several of Carlo Rovelli's youtube vids. I am not sure if it a language barrier or something, but he seams to allows stop short of giving a really detailed explanation of the point he is making. I tend to shrug my shoulders every time I would like just a little more detail of the current point because I almost got it and then yet he tappers off and on to the next point. I think great communicators have a good inner sense of knowing when a point, topic, argument has been explained (depending on the target audience). I am sure he has it all understood in his head, but IMO just doesn't have a real genius for explanation. I had to watch several videos to final get his message on what is time, piecing each of them together to get a coherent picture. Anyway I ended up buying his book "Reality Is Not What It Seems".

[@gundropmusic]

Love Rovelli. His book The Order of Time is a revelation. Cutting edge physics and poetic lyrical writing. As people have said, he communicates better in writing so check out his books!

[@burnellking]

What Is Matter?-Never Mind. What Is Mind?-No Matter - b. russell

[@TJ-kk5zf]

very wise basketball player

[@sirknight4981]

His folks(parents if they weren't dead yet) rather, IIRC.

[@mkultra8640]

What a pleasure it was to listen to that talk. Next time this gentleman comes to the RI can we maybe give him some extra time, i could listen for hours. I really like his thoughts on how we perceive time through an emotional lens, I think his ideas about that are bang on. What a wonderful talk, excellent speaker!

[@hvbris_]

I liked that analogy of a "bubble" of now.

[@rodrigofl100]

you shouldn't, because if we can have two particles behaving the same, at the same time, and say these particles have no limit in the distance from one another, then you can clearly see this bubble popping from existence.

[@a-square4085]

The "bubble" now idea is one I've spent a lot of time thinking about. It's a fascinating concept.

[@a-square4085]

@@rodrigofl100 Maybe they are behaving the same, because they are the same particle. If you hold both ends of a hose facing you and rotate it, one end will rotate clockwise and the other will rotate counterclockwise. Just like two entangled subatomic particles. And distance & time have no meaning at the speed of light.

[@painstruck01]

do you still like it?

[@denverscott3423]

Brilliant lecture by Rovelli. Mind-expanding and thought-provoking. Time is relative to us all. Recommend this lecture for anyone who wants to understand life, the universe and everything!

[@chunchen3450]

Very insightful explanation of time. The beginning of the lecture was bit slow, but it immediately attracts me when he links time with micro states, entropy and what it means of order. This aspects as always been puzzeling for me. In the end, despite all physics rational property of time, I liked the last part that links how our biological brain works in terms of time, and most importantly the meaning of time to our understanding of life. Thanks for the video 👍

[@iam26]

This lecture opened a new perspective for me to observe my surroundings

[@amitanand7581]

Thanks once again. As I am overwhelmed by the concept of non existence of time in absolute terms. It is relative both at macro and micro level and is an instrument developed by our brain for our contin iued existence.

[@gowikipedia]

Despite his imperfect English diction, Rovelli does a stellar job of describing profoundly counterintuitive concepts. This is remarkable and very enjoyable to watch.

[@BreauxSegreto]

Thank you Dr. Rovelli ! Watching this and reading your most recent book, The Order Of Time... I’ve come up with a t-shirt idea 💡”Time is not a movement... it’s a perception.” ;)

[@ralpholiver2603]

I thought his discussion was going somewhere. The initial observations were right on. However, the conclusion was a dismissal of a number of scientific fields (quantum mechanics, general relativity, cognitive neuroscience, neuropsychology, social neuroscience, nanoneuroscience...etc.) Just saying there is "just stuff out there" & manufactured counting time in the brain is a return to Cartesian dualism. & please note: there is no science that concerns itself with "awareness." Closely linked with idea of a mental clock, awareness tells us who & where we are. We are left with "its all in your head" & as Dr. Freud said, "take a seltzer & sleep on it so U can tell me your dream in the morning !" Conclusion however: there is no real connection between brain & matter. Don't worry, sleep on it !

[@katttok]

Thanks

[@yazanshukair3813]

It is great lecture. Make us recognise how our brain 🧠 is limited and at the same time how we trying to go beyond our limitation

[@maksimiliankiefergregl]

Excellent explanation from Dr. Rovelli. His book "The Order of Time" is highly recommended. Now I need to get back to "Confessions" from St. Augustine.

[@derekdonahue5633]

He says the word "time" 278 times.

[@hamiltonjames2191]

279

[@notascoobyreally7520]

Pretty odd for a lecture about time....

[@dickhamilton3517]

you mean you weren't listening to what he said?

[@jameshoey303]

And this is important...why? Why did you waste your time counting this?

[@jameshoey303]

@@hamiltonjames2191 nurd!

[@maheshme89]

links to meditation and spirituality is: Time is mental counter of the number of changes. It is a tracker to track changes. If nothing is changing, there is no need for time. for humans change is seen only through our 5 senses. if we sit in a dark and silent cave without body movement and breathing, we cannot measure time. In that situation, the only movement is our thoughts, the most subtlest objects in our experience. If our thoughts and memories stop, we will be only left with pure awareness. This awareness is aware of the stillness and silence without labeling them. This awareness is pure subjectivity and when all senses come back online then all the objects and motion come back giving rise to time feeling again.

[@richardwhiteuk457]

Jeez.. I’m sure he’s a knowledgeable chap and everything, but I found this an unbelievably drab and laboured delivery of a lecture on what is normally a fascinating topic.

[@scottgreen3807]

Before we start I must add that the phrases the “past is coming back to us”, “the past is getting further away”, and “the future is coming”, and “the future becomes even more distant because of you” are all phases we use to use to manipulate the world as humans do with our minds, so how is the possible if time is what you think it is?

[@rossawilson01]

I'm one of those blurs in the top right! Great talk, fascinating and lovely guy who I got to speak about super determinism with afterwards, his book the order of time is a work of art as much science.

[@raquelfereres6396]

Beautiful talk and brilliant mind. Thank you. Time is a human experience

[@Syntax753]

Memory is what gives us the impression of the passing of time. Without memory, time doesn't exist. A rock has no concept of time. If I have bad memory, I have a different recollection of the passing of time than someone with a good memory. If time stopped, we would no longer have memories, and would have no opportunity to recall any memory. The fact we can remember at all, means the passing of time is infinitely memorable. Therefore, there is end of remembering, and therefore time. Therefore death is not an end and we will be alive once more seemingly the moment our time supposedly ends. Or perhaps time goes backwards, and we forget our past, and only remember our future. Which ends in birth rather than death. Time to watch the video

[@AlvaroALorite]

The way I see it: Memory is the property of a material system to react in a sufficiently similar manner when exposed to a sufficiently similar stimulus in different times t1 and t2. This material property is needed for the psychological property of "memory", in which one of the key distinctions is that with psychological memory, the original stimulation can be replicated, sufficiently similarly, endogenously.

[@funbox306]

Time is different for everyone. It comes with individual's consciousness. When one is conscious, there's time for him but when one is unconscious, there's no time . When we are awake or conscious.We perceive this world by five senses (sight, hearing,smell, touch, taste) and it creates time. On the other hand, when we are in dream , our brain is in subconscious state and as we know that again in dream we see the same world and there is also time but as soon as we wake up or be conscious that time vanishes. Similarly, when we are conscious, there's time created by individual's consciousness but when we die or be unconscious, again time vanishes. So time comes with consciousness !!!

[@pablocopello3592]

Good talk for science popularization and to open minds about a fundamental concept like time. Technically, TCP (Time, Charge, Parity) is a well established symmetry in QM, But CP symmetry is violated, so also T is not symmetric in QM (particle physics based in QM, to be precise). So, if you change time direction, you should also change all spacial directions as well as all charges (particles by their anti.particles to be more precise). That is Time is deeply ligated to space and matter and cannot be thought in a reverse direction without affecting also space and matter. Another part of physics that distinguish the direction of Time is the quantum measurements, that is not a time symmetric phenomena: of the many superposed histories, in each measurement instance only one (if histories follow the base of the measurement) has consequences , (in the Many Words for instance, words are created). In time reverse order you would see different superposed histories to appear, or in the MW interpretation, you would see Words being destructed. But the truth is that to "explain" quantum measurements we would need a theory without space-time. But it is true that to explain that our Psychological Time is unidirectional, it suffices with the 2nd. law of thermodynamics as Carlo explains. Finally, a good image of our Psychological Time comes from the aimaras. They think we are walking backwards, our future is at our back, and the past is in front, so we can see the past (with more or less detail depending on the distance), and we can guess the future, but we cannot really know. We cannot turn our head, we cannot change (much) our speed, we have to follow a path with many bifurcations, some of which we can choose, but we cannot change direction, and we know that all the paths end in a precipice. Of course that is emotional, and maybe that is so high a price to pay for our self consciousness.

[@maxyakov273]

The Universe does not know about time. We measure time by measuring motion with mechanical or chemical/atomic processes. So our notion of time is based on our measurement of physical processes. Maybe Einstein was correct about time's changing w/r speed and gravity, but maybe time changes because of change of motion or chemical/atomic processes. Time is a human interpretation of the feature of motion and chemical/atomic processes - these processes are not instantaneous, hence we have time. If motion or chemical/atomic processes were instantaneous, the Universe could not exist.

[@MrCobozco]

What a timeless presentation.

[@atkaaaaaaa]

incredibly well explained. Thank you so much for this inspirational talk !

[@space-time-somdeep]

All i have understood is, we human have narrow spectrum to persive space and time. Beautiful ❤

[@sadovniksocratus1375]

''TIME'' - definitions == Can ''Time'' exist without matter ? No. Therefore, the right definition of ''time'' is to say: ''Gravity-time'' We have Earth ''gravity-time''. Another planets have their own ''gravity-time'' From ''gravity-time'' is possible to create another definitions of ''time'' ( atomic time-clock , biological-time, local-time, psychological-time . . . . ) =====

[@jimmy3546]

Sadovnik Socratus time exists without matter

[@eulexy3496]

@@jimmy3546 , how would you determine how much time has passed, without anything MOVING that tells ? Without matter there can be no time -- and there was actually no time before matter came to be in the universe!

[@ingabaronaitehammoud6495]

“Your brain is a time machine” Strong emotions ~energy ~dnr~ memory ~records of past~ time travel/dreams~ visions~ events~ strong emotions..this is a pathway back to the future..

[@priortokaraew7569]

It's painful being in a class with this gentleman

[@timmy18135]

👻👻👻👻👻👻👻playing chess with him?

[@theawantikamishra]

Why so?

[@vans2548]

The best version of this talk he has given. Something about the atmosphere at Ri i suspect. Good stuff.

[@cfworthy]

We are simply a living memory of the future. Time is relative to the observer, and cannot exist in its purest form as we perceive it. Question is... is our perception of Time governed by the gravitational field we generate? Ex. Does a fly observe time relative to its body mass?

[@petercorraini3459]

No.

[@amalekilawlor2922]

Just going to sum this up. Time is the rate of change between two points of reference you choose. It’s not a force, a field, and object, it is just a ratio/mental model we use to do calculations. As long as anything is changing in the universe that can be used as the measure for time. Before there was anything in the universe there was no such thing as time because nothing was changing. Why are people still “wondering” what time is? 🤷‍♂️

[@richardnicholas2957]

Because, what is change? Change means it is one way now and was a different way before. You can’t have change without having time. So change therefore cannot explain time.

[@amalekilawlor2922]

@@richardnicholas2957 exactly, change creates the measure of "time". You can't have change without time in the same way you can't have a line without two points.

[@aeomaster32]

It always amazes me how people discuss “time”, yet never bother to define it. Ideas can be no clearer than the clarity of the words used to covey them. Words need a clear definition to explain the concepts they stand for. Understanding suffers when using words that have nebulous meanings. Time is the measurement of motion - the rate at which events occur. If there were no time (so to speak), nothing would happen, even electrons would not move. The rate at which events happen at can be compared to other events, such as the rotation of the earth or sand through an hourglass or the motion (speed) of light. This comparison is called timing.

[@jeanetteyork2582]

...I agree..the definition is fundamental. Have you read The End Of Time by Julian Barbour?

[@aeomaster32]

No, I have not come across this book, but have read many other books aimed at the layman, including "A Brief History of Time" by Hawking. Not one of them has bothered to define the word, let alone explain the concept in understandable terms. Some seem to imply time as something independent of existence, a mystical property that came before matter. I once commented on this as follows: Well what about the question of WHEN the universe began? The question makes an assumption, that is the direct result of a misunderstanding of the word “time.” It assumes that time is independent of the universe, and that it was just ticking along, and at a certain point the universe occurred. Take a look at a definition of time. “An interval marked by similar events”. The problem is that events only take place among existents. After all, events could hardly take place prior to existence. Science regards time as motion (although businessmen equate it with money), and a part of existence (a fourth dimension), not separate from it. More accurately, time is the measurement of motion. One simply compares one motion to another. The sand through an hourglass, the revolution of a planet, the swing of a pendulum. These are the “similar events” referred to in the definition. We arrive at the conclusion that since time is a part of existence, there was no time before existence. Which leads us to the further conclusion, that there never was a time without existence, which leads to the final conclusion, that there could be no beginning.

[@joshuacarro]

straight aids out of your brain.

[@toddbeeman5933]

@@aeomaster32 The human mind can only reason within the limitations of its comprehension. Even grasping the concept of massive distances and the overall size of our observable universe can quickly become overwhelming for an average individual, because the knowledge of such vastness is foreign when regarding our lifetime's (and related generation's) survival. At least for how we perceive life and death. As the intelligence of mankind progresses, the frontiers of discovery, theories, and ideas grow. Such as the existence of higher dimensions, multiverse, gravitational waves, etc. However, we still don't have a definitive answer for details existing just moments before the Big Bang. Just because we can deduce from evidence our universe rapidly expanding from a much smaller ball of tremendous and dense energy, it doesn't mean nothing existed (energy, mass, and/or time) before. Humans are such tiny objects inside something gigantic. Currently, we can't even travel beyond a few surrounding planets, let alone our solar system, galaxy.. our lifetime is minute and nearly non-existent within the scale of the universe, referring to the part we know of due to inventing ways to see long distances. Existence could be far larger, even infinite. It's more likely for things to exist beyond our ever-so-limited capabilities of comprehension, than for us to be able to understand everything.. "Time" could simply be something requiring a more advanced intellect and different perspective than the reality of our capabilities. We're remarkably limited and have a evolved from the planet we still reside.. and so many people fight, even kill, because they're so close-minded to believe they know with certainty how existence began, and there's nothing more than just what's written in a book. That kind of enclosed selfish stupidity is ridiculous, disgusting, and senseless.

[@vytisagafonovas3887]

You impose that time has a property to have an effect on movement of objects. Tell me one example of such thing in nature. Also lets do an experiment. As Carlo from the video mentioned time slows down as gravity increases. So if we droped atomic clock, in perfect vacume, from ten meters on to the ground the time it would register would slow down more and more until it hit the ground. So if you are right, acceleration of clock itself should be less and less, proportional to time, until it hit the ground. The thing is we know that closer you are to the center of gravity, greater force will act upon an object. What would be your conclusions out of this experiment? Lets push it a little more, what about speed? If acceleration decreased than the speed of clock when it hit the ground should be less than that of what we would predict if we assume that time has no effect on motion. In that case would i be right to say that this would break law of conservation of energy?

[@MagdiNonDuality]

The sense of time, the emotional aspect of time is connected with the belief that I exist in time. Although we can ascertain that the world exist in time (via carbon dating for example) and that the human body exists in time (via the aging process of the body), it is a totally different matter to ascertain that I exist in time. We believe that I exist in time due to our confusion about I/consciousness and the world/body/mind. We mistake I/consciousness to be material, phenomenal.

[@ConnecttoSoul]

😇 Thank you for your amazing unique video, it is so much valued and I really value your hard work !👍

[@jamesbarlow6423]

Explains nothing. Unique?😂

[@voltydequa845]

@@jamesbarlow6423 They enjoy the scitainment. :)

[@nostalgia63]

Nice video. Philochrony is the theory that describes the nature of time and demonstrates its existence. Time is magnitive: objective, Imperceptible (intervals) and measurable.

[@FrankCoffman]

It's always "now." Things in "the now" change -- but the moment doesn't change. The past was simply a different arrangement of matter and energy, not a previous "now." There are no moments and no time, just a flow of things interacting and changing. "Now" isn't a thing. The misconception that so many people get hung up on is trying to define "now.' There's no "now." Forget it. There's just the state of things as it is.

[@SS-lp8fu]

yes you are absolutely correct in this. there is no past and future. There is no time. "Now" is also a moment we invented just like past and future. The state of things is as it is.

[@FrankCoffman]

There is a past and future in the sense that they are different configurations of matter and energy The past was a previous state of the world, not a previous time.

[@johnkechagais7096]

When on a mathematical line, i.e. a one dimensional space there is only those numbers before the point, the point itself and after the point on that line. Now take that axis ( the x axis to name it something) and move it in the direction of say the y axis. Still only the x axis exists, but its now moving in the direction of the y axis. The same thinking can be applied with time. only the passing of time exists not time in it self. This does not preclude a direction in time. I have heard Feynman, Susskind, Carol, an now Rovelli, try to put do put down the direction of time as a statistical consequence of the second law of thermodynamics, but all the laws of physics require a change in time and that change can have a direction.

[@FrankCoffman]

OK...but what is "a change in time"? How do you determine a change in time? By looking at a clock? Sorry, a clock isn't time -- it's a mechanical device. Instead of a clock, you could judge a change in time by using your pulse or just your perception of the passage of time. But in that case, you're relying on the rhythms and processes of your body to give you a sense of time. Again, you aren't measuring time. There is no way to measure time itself. When we think we're measuring time, we're actually comparing changes in the motions of different things (e.g. the moving parts of a clock compared to a car traveling on a road). If you disagree, please give me a way to directly measure time.

[@johnkechagais7096]

All units have the same problem what is a metre? a multiple of many atoms? That changes depending on the observer and relative velocities, this is also true of time it can be the based on the vibration of a caesium atom, and that also changes depending on the observer. The fact that quantum states, in the lowest energy level, are vibrating means that a change of time is happening locally for that quantum state. As soon as there is a Delta T involved in a function there is a direction of time and a previous event and so a direction of time. The increase in entropy is the consequence of time evolving rather than a sense of time being created by entropy. if there was no Delta T there would be no change of state and hence no evolution of a system, I can't think of any of the laws of nature that do not involve change in respect of time. I am not looking at it from my personal sense of passing of time. the only thing that I can think of that experiences no change of time is a light wave, as it travels at the speed of light and time has stopped for it.

[@jayakarjosephjohnson5662]

I think to describe ‘nature of time’ we may have to investigate ‘emergence of time’ determined by the dynamics of fundamental matter that we ascribe. Thus, string-matter atomic analogy is proposed, in that nature of fundamental matter is string like one-dimensional structure in segment with nodes on both sides, while such string-segments eigen-rotates time emerges that is Holarchical.

[@birendranag9662]

One of the insightful thing I have ever heard 🙂

[@surbhichauhan1438]

This was Sooooo Good. Thank you Royal Institution. Cheers !

[@jacobusopperman6502]

This is an amazing talk!

[@bobrolander4344]

Last month I was about to air my office and I noticed I had some loose papers and other small stuff lying around. Since it was pretty windy outside, I knew that everything would get blown away if I opened up both windows on opposite sides. But then I had an idea: If I stack all the papers and the small stuff around and on top of it, it would be one massive heap with enough inertia and friction _not_ to blow away with the wind. And now I hear of Rovelli's idea that time slows down near high mass densities. A stack of papers is more independent from outside interference than single papers are.

[@martineastburn3679]

Dr Rovelli, Some years ago, my father was flying his two super high precision atomic clocks to be calibrated and back. Both were always kept together and in use, only one was used but the other was used to verify they matched. If no match was attained, a human had to determine which was was to be the Master. Needless to say the project was not civilian but is in operation today. Concrete N.D. if you are interested.

[@GooogleGoglee]

This video occupied a lot of space/time :)

[@jameshoey303]

Not even funny

[@jaynarayan004]

i am a lay man. so far i have been in a very strong impression that time is the most fundamental and it is that which drives the rest. but the talk by prof carol proposed the idea of entropy to explain the time - this is what i could not understand (of course could not understand anything). the second point is that the concept of time being discrete object at the very very very fundamental level is some thing to meditate upon. I see the comment below by @Peter Strider explaining the concept of change in terms of time. I do have similar understanding. Powerful talk. need to read the book.

[@LarsUllits]

"Lucy : We've codified our existence to bring it down to human size, to make it comprehensible, we've created a scale so we can forget its unfathomable scale." - Luc Besson

[@amandayorke481]

Wow!!! These ideas are so hard to keep hold of ...

[@Sam_on_YouTube]

This was the subject of my college thesis. When I went through the physics in my thesis, I used decoherence and consistent histories to define the arrow of time rather than thermodynamics. Within any possible macroscopic timeline as experienced by any individual, that is any single path through spacetime, all events that are in the past, as seen relative to the reference frame of that path, can be derrived from the full set of quantum information that exists in the present, relative to that same frame. Whereas the future evolution of events along that path is statistical. Whether you have an Everett type view or not, there is no way to pick out either: 1. any arbitrary one of the many future branches as perceived along that branch: or 2. the one future that will occur out of the many possibilities, depending on which interpretation you prefer. So the future, relative to any particular path, either along an ever branching many worlds manifold or just through ordinary indeterministic spacetime, has a definite past and an uncertain future. That is the distinction.

[@marktaylor6052]

How does this tally with the Quantum Measurement Problem, as the observer and his apparatus do not have a wave function.

[@marktaylor6052]

You are basically assuming the Correspondence Principle is never violated. If a counterexample existed, or a counter-phenomena, then some substate of the universe would not correspond to a projection operator, and it would thus not be possible to represent the history of the universe as a product of such operators.

[@zohrebrown]

You sound so confused becausem as you say, you are always looking from the perspective of your own human position within time. There is no 'now' at all because time does not stop, it is a human construction to explain what they are experiencing, but even this is a continuity not a point. Your most important question is at 27:26 "Who put the universe in order, in a way that it looks in order to us?" But you don't go on to ask 'why'

[@Dyslexic-Artist-Theory-on-Time]

Time can be explained as a process of energy exchange formed by photon electron interactions. We have photon ∆E=hf electron couplings continuously transforming potential energy into the kinetic Eₖ=½mv² energy of matter, in the form of electrons as an uncertainty ∆×∆pᵪ≥h/4π probabilistic future comes into existence. All it takes for this to be logical is for the spontaneous absorption and emission of light waves to precedes absolutely everything that happens in our three-dimensional world.

[@loveisfreetobelikedisearne1920]

Tremendous talk, very enlightening, i never understood it better! Thank you

[@wipalo.the.artist]

Quantum gravity solution: Plot time as a vector like spacial dimensions, but to coincide with thermodynamics - a span of time is two points making a path, subtract energy consumption to balance thermodynamics. Double-slit experiment is showing a future fuzzy state (is/isn't) until it's observed. Thermodynamics says energy cannot be created nor destroyed, thus there is the same amount of energy in the universe at any given moment. To ensure that entropy and energy conservation is maintained, a future quantum state would be the most energy efficient ambient state until the future had become ∆t. The reason we can remember the past and not see the future is because ∆t is a temporal barrier like the light barrier. You can bend the rules with light travel, much like I assume temporal rules can be "bent" so long as ∆t in the future and past results in the maintaining the amount of energy at any given point of time. We picture us as a dot traveling down a timeline, but maybe we should visualize ∆t as the 0 point where x,y,z, & t intersect. Simply put, visualize a glass pipe with water flowing through. ∆t would be like a pinch in the pipeline, the flowing water is the future flowing to us in an unstructured fuzzy fluid state until the ∆t pinch forces the universe into a controlled and structured stream (Bringing order to entropy), facing the past and everything is beautifully organized based on the ∆t pitch, facing the future is an unrecognizable flow of energy that can't be processed until it passes ∆t.

[@chriscatignani8206]

How did it get so late so soon? It’s night before it’s afternoon. December is here before it’s June. My goodness how the time has flewn. How did it get so late so soon? ~ Dr. Seuss

[@vancouverterry9142]

"It gets late early now" -- Yogi Berra

[@u0000-u2x]

I do not understand the comments bashing his presentation. His English is very fluent and easy to grasp. What is hard to grasp is the topic, which is complex by nature...

[@prod.winterxphool6227]

That was an amazing lecture. I took lots of good notes on that, thanks.

Time is: A measure of change in the entire existing universe, caused by the motion of matter/energy/fabric of space expansion in relation to itself. Because time is an emerging property of change/motion, time is relative to speed. If ALL change in the existing universe were to stop completely, there would be NO time. And in order to go back in time, you would have to REVERSE ALL CHANGE/MOTION in the existing universe to a previous position, which is impossible because it would require all (mass/energy in the existing universe) +1. Which, by definition, rules out traveling back in time.

[@dogwithwigwamz.7320]

I can think of no better definition of time ( at the moment ) as a measure of the increasing entropy of the universe. Which is not without its problems. This is to say that what I think is not without its problems.

[@schmetterling4477]

Time is that which the clocks show. Why is everybody so confused about this trivial stuff? Have you never seen a clock?

[@phillipsmith4979]

So if time is about entropy and gravity slows down time. What is the relationship between gravity and entropy.

[@AlejandroLibreros]

I have the same question, his conclusion doesn't really fit well with general relativity

[@jwinburn]

You gave the answer in your question. :) Since gravity slows down time and entropy increases with time, as gravity increases entropy increases more slowly. At the event horizon in a black hole where time stops, entropy would stop increasing.

[@garyhalliday2140]

@@jwinburn I believe time stops at the singularity rather than at the event horizon, although I've never been there.

[@jwinburn]

@@garyhalliday2140 I disagree, but it's not important. The question involved entropy and gravity. Wherever time stops within a gravitational field, entropy would cease to increase. :)

[@garyhalliday2140]

@@jwinburn Yep, makes sense. I would love to be around to see what 'we' understand 200 years from now. :^)

[@XOPOIIIO]

Rather to say our brain exists rather than works, because it need's time to work, but if time is just how our brain works, it can work in reality, because it needs a real time to work 45:10

[@ghosh_a8716]

One of the most informative and thought proving talks on youtube. Thanks Ri.

[@dunkster0]

I'm new to this. What about age? How do we age without time. If time is only used as a measurement of change, I can understand a pendulum swing, because there is no idea or concept of progression, but with age there is. Can we age outside of time, hair turns gray, apple becoming rotten, plants grows, baby becomes adult. Is time causing the change or calculating it? I understand that outside of earth there are different concepts since there are different measurements of time

[@TedJ47]

things often age without any awareness of said process occurring (as in the case of a brain dead person on long term life support or of a person not being aware he or she has had cancer for a long time), which brings into doubt Rovelli’s tying emotional effect into the human perception of time. And yet time has passed, affecting the change but not causing it (biological processes cause the changes but the processes are triggered by the passage time).