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Sean Carroll

theoretical physicist,

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LIVE TED Conversation: Join TED Speaker Sean Carroll

LIVE conversation with cosmologist Sean Carroll, TEDxCaltech Speaker and author of From Eternity to Here: The Quest for the Ultimate Theory of Time.

The conversation will open at 4pm (Eastern Standard Time), May 19, 2011. Sean is on vacation in Las Vagas, and will join us from his hotel room there to discuss the cosmos, the nature of time, and the science of poker.

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Topics: Cosmology Live Conversation physics time
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Closing Statement from Sean Carroll

Thanks for participating, everyone! I hope some light was shed. It's been a pleasure chatting with the TED community.

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    Paul van Zoggel

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    May 19 2011: Thank you very much for insights and clear language.

  • phil halper

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    May 19 2011: Thanks for answering question Sean really appreciate it. What do you think of the prospects of measuring the B mode are? Will Planck find it? or a ground based experiment?

  • Jean Millet

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    May 19 2011: Hello Sean, Thanks so much for your time. Probably too late for an answer, but I'll give it a try: if there are multiverses out there, what would "contain" them? absolute void, not even space?

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  • phil halper

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    May 19 2011: oh and by the way Baum Frampton model:
    http://arxiv.org/abs/astro-ph/0612243
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    Sebastien Zany

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    May 19 2011: Is the categorification of physics a worthwhile pursuit in your opinion?
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      Sean Carroll 50+

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      May 19 2011: That depends on what the results will be. It's pretty math, but physics is all about the results.

  • phil halper

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    May 19 2011: Hi Dr Caroll, what are your thoughts on the resolution of the Turok measurement problem of inflation via a matter bounce from loop quantum cosmology. Does such a bounce if real imply singualrities cant form and what does it mean for the validity of the Guth Borde Vilenkin theorem that says inflation must have a singularity at the beginning?
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      Sean Carroll 50+

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      May 19 2011: The Guth-Borde-Vilenkin theorem doesn't really say there must be singularities. They made some assumptions, and those assumptions might not apply to the real world. Most crucially, they are only talking about classical spacetimes, not quantum gravity. Everyone believes (or should believe) that singularities aren't "real" in quantum gravity; but we don't know what takes their place.

      I'm not very optimistic about loop quantum cosmology or loop quantum gravity more generally, but I'm happy to be proven wrong.
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    Oscar Pineda

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    May 19 2011: Dr. Carroll, can you recommend good books for laymen to learn about the newest developments in cosmology?

    Thanks!
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    Sebastien Zany

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    May 19 2011: Best introduction to theoretical cosmology for a mathematically inclined undergraduate?
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    Lindsay Newland Bowker 50+

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    May 19 2011: wonderful f you to do this..thanks.

    A second is an earth bound measurement..a solar system bound measurement. Why is it we think it is useful to understand cosmology..the age of the universe..its acceleration even the speed of light itself?
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      Sean Carroll 50+

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      May 19 2011: Because we hypothesize that the basic laws of physics are the same all over, and then we test that hypothesis -- and so far it's succeeded! The mass of the electron, the strength of gravity, etc. -- these are all things we can measure far away and long ago, and they seem to have the same values that they do nearby.

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  • phil halper

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    May 19 2011: What is the status of the Baum Frampton model, is that still on the table?
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      Sean Carroll 50+

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      May 19 2011: I don't know what that one is -- which probably means it's not very popular, if it's a cosmological model.
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    Sebastien Zany

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    May 19 2011: Do you believe physics will ever be able to account for consciousness?
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      Sean Carroll 50+

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      May 19 2011: I believe that consciousness, like every property of matter and energy, is ultimately compatible with the underlying laws of physics. That is, we don't need to violate the laws of physics to explain consciousness. On the other hand, it might not be helpful to think in terms of particles and forces if we want to create a theory of consciousness, just as we don't invoke particles and forces when we talk about hurricanes or the stock market. We'll have to see how the research goes.

      • Arhi Kuittinen

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        May 19 2011: If consciousness' "code" includes "logics" of 300 million years of evolution I think it would be impossible to gain artificially same level of deep process unity for the system of the individual consciousness. Emotions are needed for consciousness and there is no emotions without huge amount of cumulative evolutive processes in DNA based "biomatter".
        We can produce some kind of bastard copy versions of DNA-based programmed biomachines but they could not gain the independent consciousness to have self controlled and balanced emotions. 300 million year programming can not be copied. I think.

  • kamal koubaa

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    May 19 2011: Hi professor,
    Is it possible to multiverse to be seen as many universes, each one includes another rather than separated ones, I think in such situation the accelerated expending can be explained by the impact of a bigger universe on the smaller one that is included in it?
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      Sean Carroll 50+

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      May 19 2011: When cosmologists talk about the "multiverse" these days, they are usually (not always) thinking of just a really big universe, in which different regions have different physical characteristics. It's a confusing terminology, but has become somewhat standard.
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    Oscar Pineda

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    May 19 2011: A friend asked me to post this question here, because he cannot connect right now...

    Dr. Carroll: I wanted to ask you about the famous "Drake equation" to calculate the number of intelligent civilizations in the Universe. The number that results from the equation is very arbitrary because it depends on many unknown factors (at least at the time Drake presented it and Carl Sagan mentioned it in Cosmos). Do you know if there is any new data that can help us fine-tune the values that we give each of the variables so that they can be more accurate with reality?

    Thanks!
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    Tim Colgan 50+

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    May 19 2011: How well considered is the many-worlds interpretation by academics?
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      Sean Carroll 50+

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      May 19 2011: I think it's the favorite possibility among most cosmologists and QM experts. But we admit that there are unanswered questions, such as the role of probabilities.
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        Tim Colgan 50+

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        May 19 2011: Do more lean towards a discrete set of universes or a continuum of universes?
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        Tim Colgan 50+

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        May 19 2011: In your view does the MWI remove the "need" for randomness as was traditionally formulated in quantum mechanics?
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          Sean Carroll 50+

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          May 19 2011: I think it changes it, without completely solving the problem. In MWI, the wave function of the universe evolves in a completely deterministic and reversible way. But "where we are" in the wave function seems to necessarily require a random component. Observations are irreducibly random, as far as we can tell.
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        Tim Colgan 50+

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        May 19 2011: Thanks. Impressive job answering so many questions in such a short time.

  • Sami Kosonen

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    May 19 2011: Hello! How you think physics helps you at the poker table? Does it help you to come up with the right strategy?

    Thanks!
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      Sean Carroll 50+

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      May 19 2011: See my reply to Ben elsewhere in the thread. I do think it helps -- but it's far from sufficient! This trip I've been doing well, but it's not always the case. Nerves of steel might be more important.

  • Andrew Cross

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    May 19 2011: Sean, you stated that: "...empty space essentially lasts forever (but) since empty space gives off radiation there's actually thermal fluctuations and it cycles around all the different possible combinations of the degrees of freedom that exists in empty space."

    Does this make life possible in the empty space era?
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      Sean Carroll 50+

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      May 19 2011: Yes, absolutely, at least in principle. Indeed, that's the big question: if a model like this is right, why aren't we random fluctuations in an otherwise empty space, rather than finding ourselves in a warm and inviting universe filled with stars and galaxies?

  • Craig Counterman

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    May 19 2011: How deeply do you believe in multiverses? Do you think about the other Sean Carrolls? If so, does it affect you? If not why not?
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      Sean Carroll 50+

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      May 19 2011: I'm open-minded, which I think is the right policy when there's so much we don't know. Right now my favorite approaches to explaining the arrow of time involve a multiverse, but maybe we just haven't thought of the right model yet.

      I think about other Sean Carroll's, but they don't bother me. I hope they're having fun. (Statistically, some are and some are not.)
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    Dana Shaw

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    May 19 2011: If a property of entropy is to expand over time, if there were a way to reverse linear time, would there also be a corresponding way to reverse entropy or would it continue to expand as it's not a property related to the progression of time?
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      Sean Carroll 50+

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      May 19 2011: The only real way to define "reversing time" is by "decreasing entropy." In the real world, you can set up a system of just a few atoms in which that happens (and people have done so), but once you get more than a few dozen particles it becomes infeasible.
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        Dana Shaw

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        May 19 2011: Since time is affected by a Black Hole, what effect would result from entropy encountering the event horizon of a black hole or the hole's powerful center?
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          Sean Carroll 50+

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          May 19 2011: Nothing special happens at the event horizon, actually; it's just a point of no return, past which you can't get back to the outside world. Black holes absorb new material and more entropy all the time -- the effect is just that you get a bigger black hole!

  • Padriac Fowler

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    May 19 2011: Conceptually, Dr. Carroll, that the universe is more likely to manifest an apple pie, rather than an orchard, some sugar, an oven, and then from these an apple pie, makes sense to me. This is an example of the random fluctuations of matter and energy in our universe - and furthermore that all possible "states" will one day be achieved. IF time is not circular but infinite, then do all of the finite configurations only happen once? I.e. If we detonate a bomb (one could substitute 'universe' here), which scatters its material far and wide, could a future configuration ever include the exact same bomb?
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      Sean Carroll 50+

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      May 19 2011: This is a very good questions that cosmologists are currently tackling, known as "the measure problem." In an infinite universe, it's very possible that everything that can happen actually does happen, infinitely many times. But if two things happen infinitely often, which is more likely? Of course we answer questions like this all the time, but in the case of an infinite universe the rules are just not clear right now. But we're trying. (And of course the universe might not be infinite after all.)
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    Oscar Pineda

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    May 19 2011: Hello again Dr. Carroll, this is a weird question and barely related, but I wanted to know what your thoughts on free will are. Is it possible to have some limited sort of free will given that we are entirely made of matter and matter has to obey the laws of physics? Some have posited quantum mechanics as a possible mechanism for free will, but do you think that makes any sense? These questions are commonly replied to by philosophers and I would love to hear the opinion of a physical scientist. :)

    Thanks!
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      Sean Carroll 50+

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      May 19 2011: I don't think quantum mechanics has anything to do with free will. Free will is a property of the way we think about macroscopic human beings, just like temperature is a property of the way we think about macroscopic collections of atoms. It is just as "real" as temperature is, even though it's completely absent in our microscopic particle-physics description of reality.
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        Oscar Pineda

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        May 19 2011: Thank you Dr. Carroll, that's what I thought. It always seemed strange to me that quantum mechanics was even proposed since its laws break down at our scale of the Universe. However, what are your general thoughts about free will? Do you think it exists or is it just an illusion? I know it's a weird question to ask, but it's something that philosophers talk about all the time, generally with complete disregard of what the actual sciences have discovered, and would love to hear the thoughts of a physicist.

        Thanks!
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          Sean Carroll 50+

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          May 19 2011: I think free will is an emergent property, and it exists just as much as all other emergent properties do. Whether you think that counts as "really" existing is up to you!

  • Enrique Zepeda

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    May 19 2011: Hi prof Carroll, I'm a futurist person, always thinking about the future and trying to imagine it, my question would be, humans will eventually live in other planets, how much time would it take and which planet would be chosen? I know biology is not your area, but will humans be genetically modified for the planet or the other way around?

    Thanks!
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      Sean Carroll 50+

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      May 19 2011: Too far outside my domain for me to give a reliable answer, I'm afraid. I do suspect that in the not-too-distant future we will experience great advances in biological engineering and modification, as well as human/mechanical interfaces. Unfortunately, planets outside our Solar System are so far away that getting to them is not a near-future prospect.

      • Enrique Zepeda

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        May 19 2011: So you think that even with biological modification, humans will never live in a planet inside the solar system?

        Thanks!
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          Sean Carroll 50+

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          May 19 2011: You mean "outside"? I don't say "never" about almost anything, as there's so much we don't currently know.
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    Nicholas Pauley

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    May 19 2011: is there any advise you would give to someone thinking about becoming a physicist?
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      Sean Carroll 50+

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      May 19 2011: Read a lot of books, take a lot of courses, and work really hard. And don't forget to have fun along the way, otherwise what's the point?

      Keep an open mind and always be learning new things.
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    Thomas Pisarchick 10+

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    May 19 2011: Kind of new this entropy idea, has me wondering. In a closed system is entropy a factor? I mean if something is in a state of rest then there is no entropy correct? Being that there are no forces either disruptive or orderly.
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      Sean Carroll 50+

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      May 19 2011: There can certainly be entropy in closed systems, or when things aren't changing. The gas in a box in a state of equilibrium has a very well-defined entropy.
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        Thomas Pisarchick 10+

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        May 19 2011: So entropy is just the possibility of change with the same outcome? No matter which atom is near which in the box it is still full of the gas. So with extremely high entropy is there instability in the form of atoms, being that the electron and other components can switch around?
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          Sean Carroll 50+

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          May 19 2011: Not necessarily; it depends on the physical conditions within the substance. Entropy likes to increase, but energy is conserved at the same time. If it costs energy for electrons to hop around, they will tend to stay put.
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        Thomas Pisarchick 10+

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        May 19 2011: Is it that entropy increases with energy then? If that box of gas were frozen then there would be less entropy? Or would the entropy be the same because there is the same amount of atoms? So does volume play a factor in entropy?

  • sam ferris morris

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    May 19 2011: ok....so are there any growth patterns....that the universe seems to favor...because of the fundamental laws......?
    Is it possible to trace the fundamental asymmetries/symmetries all the way back....to the initial high entropy state.....and say ok....this particle(higgs boson for example) arose from this form...and then from then on....evolve all the emergent types of growth...into higher complexity forms.....
    i guess my question...if it makes sense....is did form or content come first.....or both together.....(I studied music...so I really dont have much technical knowledge)
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      Sean Carroll 50+

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      May 19 2011: I think you have to distinguish between entropy, which characterizes the particular configuration a system is in, and the underlying laws of physics, which give you the building blocks of different systems. In the current way we understand physics, the Higgs boson and so forth are really built into the fundamental structure of reality. It's just a matter of actually bringing it to life, which we're trying to do (for example) at the Large Hadron Collider.

      • sam ferris morris

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        May 19 2011: so does....symmetry/asymmetry and the compression of information....in the fundamental laws....play a role.....in those configurations.......so that say an anti proton / proton mixture.....such as those in a neutron star....might have less or more entropy....based on the fundamental laws...
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          Sean Carroll 50+

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          May 19 2011: It plays some role, yes. Entropy counts the number of configurations that look the same, and the number of configurations certainly depends on the fundamental laws of physics.

  • Yolanda Moreno

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    May 19 2011: hello Sean, It is very interesting this conversation and in the philosofical arena I hear about entropy as part of a process in time that goes like around a circle, like a cycle... Everything in the material world get involved in this entropic process but at certain point there is a phenomena that is called the neguentropic point. It can be like to start again another cycle of time... In some way the arrow of time you think its possible to go in circles???
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      Sean Carroll 50+

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      May 19 2011: It's possible, since there's not that much we're sure of yet in this game. But the challenge is to build a respectable model based on plausible physics, then to connect it to the observable universe so it can be tested. This isn't easy, but we're trying.
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    Thomas Pisarchick 10+

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    May 19 2011: Is the level of entropy is in direct relation to the state of sequence patterns occurring near the point of measure?
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      Sean Carroll 50+

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      May 19 2011: I'm not sure what that means, but I don't think so. The entropy of a state is (the logarithm of) the number of states that look macroscopically indistinguishable from it.
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        Thomas Pisarchick 10+

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        May 19 2011: This is hard for me to relate. It seems that there are sequences of occurrences in the universe. Some occurrences are that there are these three occurrences in a row, for example, some are that there are patterns of occurrences. Then there are different type of occurrences. So some spots of the universe would be riddled with occurrences and some spots with be empty of them. Is there a relation between the entropy and the occurrence factor. Something like a high entropy indicates the high rate of occurrences. I say near the point of measure because if the relationship exist then at another point in the universe where the occurrence rate is lower then so would the entropy be.

        Thank you for the responses

  • guy smyley

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    May 19 2011: sean, thanks for your time! just wondering... when two people watch a funny movie they laugh... when they watch a sad movie, they cry... would that count as a repeatable finding for a scientific experiment? would it prove that there is a dimension of emotions?
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      Sean Carroll 50+

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      May 19 2011: I think you would have to design a more careful scientific protocol than that. It might be possible to think of "emotions" as a dimension, but it's clearly not the same kind of dimension as time and space -- so one could argue that you're just abusing the terminology.

      But emotions are real, and hard to study. Human sciences in general are much more difficult than physics and astronomy.

      • guy smyley

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        May 19 2011: ah. thx for your response! when i was a little kid, one of my teachers had me read a book called flatland or something... and it said that to find the next dimension, you just had to go "inside yourself" or something like that lol. i guess that's what i've been imagining all these years!

  • Piotr Bulczak

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    May 19 2011: Hello Sean,

    Does that all mean that there is actually nothing like time? Is it just a our "feeling" of the changes around, states changes, fluctuations? Without any change around us would we be in present time time? Ok, just said there is no time in fact :-).
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      Sean Carroll 50+

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      May 19 2011: I'm someone who believe that time really exists. Otherwise how would we know when to participate in the TED chat?
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