Note that this article is from The Guardian although it may appear that it is written by The Physics Times Editorial Board.

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This article titled “Carlo Rovelli: ‘Time travel is just what we do every day…’” was written by Carlo Rovelli, for The Observer on Sunday 31st March 2019 08.00 UTC

Theoretical physicists and mathematicians are fond of describing their theories and equations as beautiful but very few writers are able to bring this elegance to life for the general public. The Italian physicist Carlo Rovelli has proved himself to be one of those rare figures. His first attempt at writing a book for a mainstream audience, Seven Brief Lessons on Physics (2014), outsold Fifty Shades of Grey in his home country, has been translated into 41 languages and sold more than 1m copies. His second, The Order of Time, is an appreciation and lucid deconstruction of a quality we take for granted – “We inhabit time as fish live in water,” he writes.

Like other popular scientists such as Stephen Hawking, Carl Sagan and Brian Cox, Rovelli feeds our fascination with the fundamental forces that make our universe tick. Here, famous fans and Observer readers question him further.

Questions from famous fans

Ian McEwan

Novelist

Can you imagine a future in which relativity and quantum mechanics could be so well and generally understood that time, as mediated by relative motion and the strength of the local gravitational field, becomes part of our immediate and common sense appreciation of the world? Could we experience in the everyday space and time obviously and sensuously inseparable? Or are we bound by our very nature and our evolutionary past, and living between the very large and very small, to remain within the sensory limits we experience now?
I think that we will learn, and slowly counterintuitive ideas will become intuitive. It has happened with the fact that the Earth is a sphere (clarified two millennia ago) and the fact that it spins (clarified a few centuries ago). At first these were extremely counterintuitive ideas; nowadays we accept them as comprehensible. But it takes time. I think, for instance, that the day when we will have spaceships travelling very fast, and we experience directly things like meeting our children older than us on our return home… when we experience this, the elasticity of time will become obvious to us. Of course, all this is assuming our civilisation survives long enough and we do not destroy ourselves with conflicts and stupidity, which is something we humans seem to be very good at and not ready to move away from.

Es Devlin

Artist and designer known for her kinetic stage sculptures

The course of events often feels cyclical; in architecture, design and fashion, styles and tendencies seem to echo and recur. Could there be folds in the fabric of time that wrap around and touch one another, causing imprints and echoes?
Oh, Es! If your extraordinarily creative artist’s mind can make something out of these folds, wraps, imprints and echoes, I am the last one willing to tune this idea down! The fabric of time is multilayered, stratified; this is precisely the main idea of my last book. At some level, my answer would probably be negative, but at another level – the one woven by the memories and expectations of our brain – the answer is certainly yes; this is the level we actually mean, when we concretely think about what time is for us.

John Grant

Musician

How, if at all, has music helped you on your path of knowledge and understanding about the way things work?
I do not know. Like most people, I listen to a lot of music and in writing my book on time I have thought much about the relation between music and our sense of time flow. The fact that so much meaning is conveyed in such an apparently meaningless structure as a sequence of sounds has always mystified me.

Robin Ince

Comedian and co-host of The Infinite Monkey Cage

Does dealing with the reality of atomic and subatomic behaviour help take your mind off the surrealism of human political behaviour in these strange times?
I do not think that these times are particularly strange. Humans have massacred one another and had a hard time collaborating for ever. What changes is who the [short-term] winners are. As for me, no, dealing with physics does not help in taking my mind off humans’ continuous self-inflicted pain.

James Lovelock

Scientist best known for proposing the Gaia hypothesis

What is the best way to view time?
What we call time, and usually view as a very simple elementary notion, is actually a complex experience grounded on different levels. There is a basic physical level of “things happening”, but this is very far from our common notion of time, because it lacks all the rich features of what we call time. Then there are approximations due to our specific scale. There is the effect of the large number (myriads) of microscopic degrees of freedom we interact with. There is the very peculiar manner in which our brains interact with the world, based on memory and tentative anticipation of the future.

Finally, there is a thick emotional layer, which is what gives us the sense of the “flow” of time. The problem of understanding time is the problem of disentangling this complex tangle of structures and effects. Your wonderful realisation of the notion of Gaia was based on viewing unity beyond apparent complexity. Understanding time is the opposite: viewing the complexity beyond apparent unity.

Nick Hornby

Novelist

I loved The Order of Time. It made my head spin, while your writing is clear and beautiful. However, I have decided to ignore you and I am going to think about time the old-fashioned way for the rest of my life – in a line, with a now, a yesterday and a next year. To think of it in terms of kisses and crowds of Italians jostling is too disorienting. What am I missing out on?
If you prefer to keep thinking about time in the old-fashioned way, what you are missing out on is a lot of fun and an opportunity to learn more in depth about how the universe really works. Not much more than this. I think one can happily keep living thinking that the Earth is flat or is at the centre of the universe; in daily life, it does not matter much, if at all. And of course I understand that crowds of Italians jostling is disorienting; but still, do you really feel that a world made of stone is more hospitable than a world made of kisses?

Hans Ulrich Obrist

Artistic director of the Serpentine Galleries, London

I am curious to know more about your unrealised projects. We know a lot about architects’ unrealised projects as they publish them, but we don’t know much about those of artists and scientists, which is why I’m mapping them. What is your dream?
I think most scientists have unrealised projects. My drawers are full of unfinished works. My dream project is between physics and biology. There is a common idea that a living organism is a sort of fight against entropy: it keeps entropy locally low. I think that this common idea is wrong and misleading. Rather, a living organism is a place where entropy grows particularly fast, like a burning fire. Life is a channel for entropy to grow, not a way to keep it low. My dream is to be able to articulate this properly and quantitatively. I do not know if I will ever be able to. I have to study.

Monica Grady

Space scientist

In The Order of Time, you write: “The characteristic features of time have proved to be approximations, mistakes determined by our perspective…” How does this affect your ability to read a bus timetable and get to an appointment on time?
Not at all, of course. Does knowing that in Sydney people live upside down make it harder for you to distinguish the floor from the ceiling? Realising that we use approximate concepts, and that it is a mistake to assume that they have universal validity, does not prevent us from using them. If anything, we understand them better, because we now know the limits of their validity.

Michael Pollan

Author and activist

I have three questions: do you think that quantum mechanics has any relevance for our understanding of consciousness? Do the quantum effects observed at the level of particles scale up to our experience of the world or do the effects wash out as you move up? Finally, you have said that your youthful experience of psychedelics opened you up to the nonintuitive ideas of theoretical physics. What specifically happened during those trips to change your mind?
I do not think that quantum theory plays any major role in our understanding of consciousness. However, I suspect that perhaps better understanding quantum theory could free us from some prejudices about the structure of reality, prejudices that obstruct us in [our] understanding of what consciousness is, whatever that word means. Quantum theory indicates that reality is more interdependent than it is in the picture classical physics paints.

The reason I think that quantum effects are more or less irrelevant for consciousness is precisely because they do not scale up to our experience of the world; they wash out as we move up in dimension. This is why the world looks so “non-quantum” to us, well described by classical mechanics.

Your question about my experience of psychedelics and its relation to the nonintuitive ideas of theoretical physics is delicate. Let me put it this way: I got so confused about the basic structure of reality that when, 10 years later, I had to dive into fundamental theoretical physics, I wasn’t scared of losing my bearings. You ask what specifically happened during those trips. The psychedelic experience is notoriously very strong and at the same time very hard to talk about. A drastic loss of the usual personal, emotional and intellectual coordinates. Overwhelming emotions, a sudden sense of seeing everything profoundly differently. The colourful visual theatre is nice and fun, but less important, at the end. In the days after my first experience, I wrote frenetically in a notebook about it. I filled an entire notebook. A few months later, my mother found the notebook and burned it.

Neil Gaiman

Novelist

‘‘I’m haunted by the idea of Einstein telling a colleague that his dead wife was still alive and it is merely a failure in our perception to see all of time as existing at once. (I may have completely misunderstood what you and/or he were saying.) So are we flatlanders, failing to perceive a much richer universe around us, deluded by the idea of sequential time?
You haven’t misunderstood. We are flatlanders, failing to perceive a much richer universe around us, deluded by the idea of sequential time. But perhaps not in the simple-minded sense of our loved ones still being alive… The reason for the failure of our perception to see all of time as existing at once is deeply grounded in the physics of our environment and ourselves, but we still have the intelligence and imagination to allow us to see beyond those limits. And to imagine plural worlds, as you know well, I would say…

Helen Czerski

Physicist, broadcaster and writer

Time and gravity are grand concepts that can seem very remote from the practicalities of being human. What are the small things in life that bring you joy and what are your favourite ways to spend time with friends and family? Do you separate the small joys and the grand thoughts or are they all woven together?
I think that they are pretty much woven together, because I have difficulty compartmentalising my life. The small things that bring me joy are things like waking up in the morning and going out to watch the sea (I live near the sea) or just doing nothing with my companion. I like a lot hiking and travelling. I have a small, very old boat and as soon as I can, I just go out to sea, maybe even to eat bread and cheese while the sun sets.

Jim Al-Khalili

Theoretical physicist and host of Radio 4’s The Life Scientific

Despite all its success as a beautiful theory of the building blocks of the universe, quantum mechanics still leaves even those of us physicists who work with it daily both frustrated and bemused. Would you agree that maybe Einstein was right after all and that quantum mechanics is not yet complete?
Yes, I agree that maybe quantum theory is incomplete. Because how could we ever be sure that anything is “complete”? But only “maybe”, because I do not see compelling reasons to conclude that quantum theory can only be viewed as an incomplete theory. The reason is that any possible “completion” of quantum theory demands that we accept strangenesses that are even less plausible than those implied by quantum theory as it is. With the difference that the strangenesses of quantum theory as it is are empirically confirmed, while the strangenesses of its completion are arbitrary guesses. I think that quantum theory can make sense as it is: we just have to give up some cherished metaphysical prejudices and accept the deep relational aspect of nature that the success of the theory has revealed.

Questions from readers

I read recently that you take enormous pleasure in washing up piles of dishes. Why is this? And any tips for removing stubborn stains from pans? What other household chores do you enjoy?
Jane via email

I have no special tips. In fact, I do not think I am particularly good or effective at washing dishes. I just like doing it. The reason is that it is one of those (rare) human activities where you start with a disgusting mess, you immerse yourself in an easy task that relaxes your mind and you end up with everything nice and clean and shining and neat. Wouldn’t it be great if life was all like that? Usually, it is the opposite: you start with something so-so, you struggle and get nervous and at the end it is all a mess. My habit of cleaning dishes comes from my youth when I used to live with messy friends. Nobody ever wanted to do the dishes and cohabitation tended to raise tensions. I discovered that if I did the dishes for everybody then everybody loved me and living together became a pleasure. So I got a lot for a cheap price. In fact, in exchange, my room-mates routinely did the groceries and cooked wonderfully for me. Definitely worthwhile.

Do you believe in free will?
Celso Antonio via Twitter

Free will is an ambiguous expression. In the commonsense meaning of “being free to decide”, of course there is free will: we decide. If, instead, by free will you mean that in deciding we violate known laws of physics and their standard causal relations, then no, there is no free will in this sense; the evidence is now overwhelming. What happens in a “decision” is a very complex network of microevents in the brain, which is too complicated to predict. As clarified by Spinoza, free will is real: it is the name we give to our own inner complexity, which is too rich for us to disentangle or predict.

Is [Schrödinger’s] goddamn cat dead or not?
Afristotle via Twitter

I think the cat is never “dead and also alive”, as quantum theory is sometimes said to claim. The cat is either dead or alive. The subtle point, in my opinion, is that all contingent aspects of reality are relative to other physical systems and are realised in interactions. Therefore in principle a cat could be neither dead nor alive as long as it was not interacting with anything. But a macroscopic entity such as a cat is constantly interacting heavily with the rest of the world – therefore it is effectively always either alive or dead. Cats behave. The discussion on the interpretation of quantum theory is wide open, however. I think that different perspectives are possible. It may be a mistake to pretend to choose one. Maybe the different readings of quantum theory that are discussed are all interesting and the future will tell us better.

Is there a layman’s way of explaining how gravity alters time, please? Sea-level and up-a-mountain kind of gravity…
HarvestingKarma via comment

The straight way of thinking is the opposite: it is not gravity that alters time, rather, it is the alteration of time that is responsible for gravity. The point is that a large mass like the Earth slows down time in its vicinity (please do not ask why, because I can only answer one question at a time). And the effect of this slowing down of time in the vicinity of the Earth is that things fall. A bit like when you run into the sea and your feet are slowed down by the water and your body is pulled downwards…

Is a new, more powerful linear [circular] collider than the LHC really worth it at the moment, given that the glory years of discovering new elementary particles appear to have ground to a halt?
bilyou via comment

This is a large and serious discussion, going on currently in the scientific community. There are good arguments on both sides. It is never easy to decide where best to allocate resources. Part of the scientific community is digesting the disappointment of not having found at LHC what they were convinced had to be there. For others, such a non-discovery has actually been a confirmation of expectations. It is good to stop and think sometimes.

How seriously should we be taking the recently mooted idea that the universe is a form of hologram? What difference would it make to doing science? To living life?
palfreyman via comment

I have never been convinced by this vague idea. If there is something to it, I have not yet seen it realised in a convincing way as a theory of our world. On the other hand, I have seen a lot of very free speculations in this direction, which I do not find very plausible. I might be wrong, of course. Others disagree.

Can time be said to exist if no observer/participant is there to experience it? How would one know? Could this not make consciousness a fundamental quality of the universe?
Gary W Kelly, Salinas, California

I definitely don’t think consciousness is a fundamental quality of the universe. Our subjective conscious experience is the product of the complexity of our brain: it is something very specific. The universe is not going to change whether we experience it or not. It is out there and it does what it does. This is what we learn when we are three years old and it’s true. What depends on our consciousness is the way we ourselves perceive time – our experiential time. Discovering that something we perceive depends on the way we are does not imply that the universe depends on us.

Do you think that Richard Feynman’s dictum “Shut up and calculate” has done a great disservice to physics? Isn’t physics about trying to understand the root causes behind physical phenomena, not just treating them as “black boxes” we can never hope to comprehend?
David Mitchell via comment

I think the dictum “Shut up and calculate” is misattributed to Feynman. Feynman was a deep thinker, asking subtle and fundamental questions and offering visual interpretation of his calculations: quite the opposite of “Shut up and calculate”. The expression “Shut up and calculate” has been used to characterise a certain excessive pragmatism in the physics of the 1950s. I believe we have moved out of it. Of course science is about understanding, not about predicting.

Is time travel a possibility? If so, is it limited in the direction one could travel, forward or back? And would it require a powerful engineered device or exist in nature?
Sagarmatha1953 via comment

Time travel is just what we do every day, isn’t it? Every single day we travel one day ahead in time… But this is not what you are asking… You are asking whether we can fast-jump into the future and whether we can go to the past. The answer to the first question is: certainly yes, it is just a question of money. The answer to the second is that it is improbable in a very technical sense. Let me explain: if you want to travel to the next millennium, it is sufficient to build a fast starship, travel fast enough back and forth, and in a few days (of yours) you can definitely be back here on Earth a millennium in the future. The science of this is completely uncontroversial and clear. The only problem is finding the money for such a starship. If instead you want to travel to a millennium ago, things are more complicated. The reason is that you have to beat the entropic arrow of time. This is not impossible, because the arrow of time is statistical, therefore it is just a matter of probability and improbability. But the improbability is overwhelming. So in a very technical sense, I think that going to the past is very improbable.

• The Order of Time by Carlo Rovelli is published by Penguin (£8.99). To order a copy go to guardianbookshop.com. Free UK p&p on all online orders over £15

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