Sean Carroll

Blog

  • Visualizing Entanglement In Real Time

    Entanglement is one of the “spookier” aspects of quantum mechanics. In classical physics, the states of two distinct objects (their positions, velocities, spins, etc.) are specified completely separately from each other. Knowing what this tomato is doing gives you no information, in principle, about what that carrot is doing. But quantum mechanics says there is only one “state of the whole world,” which refers to absolutely everything in it. And, of course, the quantum state is specified as a superposition of possible measurement outcomes, rather than one definite possibility. So the quantum state of two vegetables might take the form “the tomato is in the refrigerator and the carrot is on the kitchen counter, or the carrot is in the refrigerator and the tomato is on the counter.” Although usually we talk about spins and polarizations of particles rather than locations of foodstuffs.

    Entanglement is by no means a mystery, in the same way that the measurement problem is a mystery. It’s just a straightforward prediction of quantum mechanics, repeatedly verified by experiments. But it bugs us, because it seems “nonlocal.” In the state described above, I can look at the tomato and instantly infer what the carrot is doing, without ever looking at it. This bothers people, although it doesn’t lead to anything dangerous or immoral, like communication faster than light. That’s because physical information still travels slower than light. Someone wondering about the carrot doesn’t gain any information just because you measured the location of the tomato; you still have to tell them what answer you got.

    Still, entanglement is pretty cool. And now Anton Zeilinger’s group in Vienna, one of the leading labs working on quantum experiments, has queried the Zeitgeist and responded in a way appropriate to our internet age: they made a YouTube video. (Since they are also old-fashioned scientists, they also wrote a paper.)

    Real-Time Imaging of Quantum Entanglement

    Let me try to explain this as I understand it, but I’ll confess up front this is a bit outside my comfort zone so real experts should chime in. Here we have two entangled photons, which can be polarized either H (horizontal) or V (vertical). The quantum state is of the form HV + VH, which means that we don’t know what either polarization is, but we know that the two polarizations must be opposite of each other. (If the state had been HH + VV, we still wouldn’t know either one, but we would know they were the same.) We send each photon through a merry path, observe one of them (that’s on the left), and see what happens to the other one (on the right). We’re looking at an image of where the individual photons land on a screen. You can see how the state of photon #2 is affected by what’s happening to photon #1.

    Doesn’t it seem like you could use this to send information faster than light, if photon #2 is instantly affected by what we do to photon #1? I believe the trick here is that we’re not taking an image of all of the #2 photons. We’re only taking images of #2 if photon #1 was registered in a certain state. That is, we send photon #1 through a filter that only lets horizontal polarizations through. If photon #1 gets through, we turn on the camera and image photon #2. If it doesn’t, the camera never triggers, and photon #2 hits the screen harmlessly. So no superluminal chitchat, you science-fiction fans out there.

    Nevertheless, pretty awesome. Quantum mechanics is sufficiently non-intuitive that we would only ever come up with it by having it forced on us by data. Even though experiments like this are completely explained by quantum mechanics as we currently know it, every little demonstration helps us appreciate it a bit more viscerally. As we strive toward a deeper understanding, that’s a crucially important part of the process.

  • The Universe on a Stratocaster

    There are those who believe that music brings meaning to an uncaring universe. It’s only natural, then, to try to capture the essence of reality on a musical instrument.

    Sadly, the true essence of reality remains unknown. But we are able to sum up the physics underlying the world of everyday experience in a single equation. So mathematician Nicholas Hoell did the obvious thing — or at least, what should be obvious — and painted that equation on his Stratocaster. (Click to embiggen.)

    Guitar_pic

    Note the depiction of a few complex arrangements of the underlying reductionistic constituents, providing a nod to the importance of emergent phenomena in encompassing a complete view of the world.

    I’m pretty sure that the perfect solo, played on this guitar, would reveal how to quantize gravity.

  • Morgan, Jon, and the Mystifying Balloons

    Morgan Freeman appears on the Daily Show to chat up his new movie, but Jon Stewart just wants to ask questions about physics and physicists. They are both fans! (Hat tip Megan Parlen.)

    Freeman doesn’t get all the details right, but his enthusiasm is genuine and infectious, and it’s clear that he’s picked some stuff up from hanging around with scientists (and making Through the Wormhole, of course). The poor man has clearly fallen prey to the dreaded balloon analogy for the expansion of the universe. More harm than good, that little bit of metaphorical imagery has done. It makes you think the universe is expanding into something, which it’s not (as far as we know). Much better to think about the real universe, with galaxies all around you and moving away.

  • Time, Born Again

    Lee Smolin has a new book out, Time Reborn: From the Crisis in Physics to the Future of the Universe. His previous subtitle lamented “the fall of a science,” while this one warns of a crisis in physics, so you know things must be pretty dire out there.

    I’m not going to do a full-fledged review of the book, which gives Lee’s argument for why “time” needs to be something more than just a label on spacetime or a parameter in an evolution equation, but a distinct fundamental piece of reality with respect to which the laws of physics and space of states can change. (Sabine Hossenfelder does offer a review.) There are also suggestions as to how this paradigm-changing viewpoint gives us new ways to talk about economics and social problems.

    Over at Edge, John Brockman has posted an interview with Lee, and is accumulating responses from various interested parties. I did contribute a few words to that, which I’m reproducing here.

    Time and the Universe

    Cosmology and fundamental physics find themselves in an unusual position. There are, as in any area of science, some looming issues of unquestioned importance: how to reconcile quantum mechanics and gravity, and the nature of dark matter and dark energy, to name two obvious ones. But the reality is that particle physicists, gravitational physicists, and cosmologists all have basic theories that work extraordinarily well in the regimes to which we have direct access. As a result, it is very hard to make progress; we know our theories are not absolutely final, but without direct experimental contradictions to them it’s hard to know how to do better.

    What we have, instead, are problems of naturalness and fine-tuning. Dark energy is no mystery at all, if we are simply willing to accept a cosmological constant that is 120 orders of magnitude smaller than its natural value. We take fine-tunings to be clues that something deeper is going on, and try to make progress on that basis. Sadly, these are subtle clues indeed.

    “Time” is something that physicists understand quite well. Quantum gravity remains mysterious, of course, so it’s possible that the true status of time in the fundamental ontology of the world is something that remains to be discovered. But as far as how time works at the level of observable reality, we’re in good shape. Relativity has taught us how to deal with time that is non-universal, and it turns out that’s not such a big deal. The arrow of time—the manifold differences between the past and future – is also well-understood, as long as one swallows one giant fine-tuning: the extreme low entropy of the early universe. Given that posit, we know of nothing in physics or cosmology or biology or psychology that doesn’t fit into our basic understanding of time.

    But the early universe is a real puzzle. Is it puzzling enough, as Smolin suggests, to demand a radical re-thinking of how we conceive of time? He summarizes his view by saying “time is real,” but by “time” he really means “the arrow of time” or “an intrinsic directedness of physical evolution,” and by “real” he really means “fundamental rather than emergent.” (Opposing “real” to “emergent” is an extremely unfortunate vocabulary choice, but so be it.)

    This is contrary to everything we think we understand about physics, everything we think we have learned about the operation of the universe, and every experiment and observation we have ever performed. But it could be true! It’s always a good idea to push against the boundaries, try something different, and see what happens.

    I have two worries. One is that Smolin seems to be pushing hard against a door that is standing wide open. With the (undeniably important) exceptions of the initial-conditions problem and quantum gravity, our understanding of time is quite good. But he doesn’t cast his work as an attempt to (merely) understand the early universe, but as a dramatic response to a crisis in physics. It comes across as a bit of overkill.

    The other worry is the frequent appearance of statements like “it seems to me a necessary hypothesis.” Smolin seems quite content to draw sweeping conclusions from essentially philosophical arguments, which is not how science traditionally works. There are no necessary hypotheses; there are only those that work, and those that fail. Maybe laws change with time, maybe they don’t. Maybe time is fundamental, maybe it’s emergent. Maybe the universe is eternal, maybe it had a beginning. We’ll make progress by considering all the hypotheses, and working hard to bring them into confrontation with the data. Use philosophical considerations all you want to inspire you to come up with new and better ideas; but it’s reality that ultimately judges them.

  • Sixty Symbols: The Arrow of Time

    Completing an action-packed trilogy that began with quantum mechanics and picked up speed with the Higgs boson, here I am talking with Brady Haran of Sixty Symbols about the arrow of time. If you’d like something more in-depth, I can recommend a good book.

    Arrow of Time – Sixty Symbols

    Will there be more? You never know! The Hitchhiker’s Guide to the Galaxy started out as a trilogy, and look what happened to that. (But I promise no prequels.)

  • Hither and Yon

    Best intentions (put nose to the grindstone, get these papers finished) notwithstanding, I do have a few more public lectures and whatnot coming up over the next few weeks. Would love to see you there! And if not, I recently did an episode of the Rationally Speaking podcast with Massimo Pigliucci and Julia Galef, where we talked about naturalism, science, philosophy, and other things I’m marginally qualified to speak on.

    Wednesday May 22: I’m giving a public talk on the arrow of time at UC Davis. This is in the midst of a conference on the early universe, which should also be fun.

    Wednesday May 29: I’ll be talking with Jim Holt, author of Why Does the World Exist?, at the LA Public Library. It’s possible this is will be sold out, but I think they’re going to tape it.

    Sunday June 2: I’m the keynote speaker at the American Humanist Society annual conference in San Diego. 10:30 a.m. on a Sunday, so this one might be easier to get into! In fact you can get in for free even if you didn’t register for the conference, by following these simple steps:

    1. Go to the website here: http://ahacon13.eventbrite.com/#
    2. Click the orange “Enter Promotional Code” link.
    3. Enter FREECON in the field that appears and click Apply.
    4. The list of items should then include the free “Free to the Public: Matt Harding & Sean Carroll” option.
    5. Choose that one (and any others) and then complete the registration.

    Thursday June 6: Opening night at the Seattle Science Festival features Brian Greene, Adam Frank, and me, under the stern but fair moderation of Jennifer Ouellette. Adam and I will give short talks, and Brian will show us the West Coast premiere of the multimedia performance Icarus at the Edge of Time.

    Wednesday June 12: I’m giving a public lecture at Fermilab on particles, fields, and the future of physics. It’s part of the Fermilab Users’s Meeting, as well as a workshop on the International Linear Collider. Not sure if I’ve ever given a public talk that will have so many people ready to correct my mistakes.

    After a couple more trips in July, my calendar actually does clear up, and I can look forward to uninterrupted vistas of productivity. Watch out!

  • Templeton Redux

    Not much more to say about the Templeton Foundation, but in the interest of open discussion it seems fair to point to a couple of alternative viewpoints. My original post was republished at Slate, where there are over 3300 comments thus far, so apparently people like to talk about this stuff?

    For a more pro-Templeton point of view, here’s Jason Wright, explaining why he didn’t think it was wrong to take money from JTF. While he is a self-described atheist, he thinks that “questions like the ultimate origin of the Universe and Natural Law may be beyond scientific inquiry,” and correspondingly in favor of dialogue between science and religion. To be as clear as possible, I have no objections at all to dialogue between scientists and religious believers, having participated in such and planning on continuing to do so. I just want to eliminate any possibility that my own contribution to such a dialogue will favor any position other than “religion is incorrect.” (Obviously that depends on one’s definition of “religion,” so if you want to indulge in a boring discussion of what the proper definition should be — be my guest.)

    From an anti-Templeton perspective, here’s Jerry Coyne, who doesn’t accept that it’s okay to draw a line between JTF itself and distinct organizations that take money from them. (Jerry’s post is perfectly reasonable, even if I disagree with it — but a short trip down to the comment section will give you a peer into the mind of the more fervently committed.) That’s fine — I admit from the start that this is a complicated issue, and people will draw the line in different places. But let’s admit that it is a complicated issue, and not pretend that there are any straightforward and easy answers.

    One thing that seems to bother some people is that I agreed to be on the Board of Advisors for Nautilus, a new science magazine that takes funding from Templeton. It’s instructive to have a look at the Board of Advisors for the World Science Festival, another organization that takes funding from Templeton. It’s a long and distinguished list, and here are some of the names included: Richard Dawkins, Daniel Dennett, Lawrence Krauss, Steven Pinker, Steven Weinberg. Are these folks insufficiently sincere in their atheistic worldview? Alternatively, would the world be a better place if they all resigned? I would argue not, for the simple reason that the WSF does enormous good for the world, and is an organization well worth supporting, even if I don’t agree with all of their decisions.

    Refusing to have anything to do with an organization that takes money from a foundation we don’t like is easier said than done. What about, say, the University of Chicago? Here they’re taking $3.7 million from Templeton for something called Expanding Spiritual Knowledge Through Science: Chicago Multidisciplinary Research Network. And here’s $5.6 million from Templeton for a program labeled New Frontiers in Astronomy and Cosmology, celebrating “a unique opportunity to honor the extraordinary vision of Sir John Templeton.” And here’s $2.2 million for a program on Understanding Human Nature to Harness Human Potential. Not to mention that the UofC has quite a prominent Divinity School (home of the best coffee shop on campus) and Seminary. (They also denied me tenure, which doubtless set the cause of reason and rationality back centuries.)

    There’s no question that the University of Chicago has done much more to promote the cause of religion in the world than Nautilus has — which has been, to date, precisely nothing. One could say, with some justification, that some parts of the UofC have promoted religion, while other parts have not, and it’s okay to be involved with those other parts. But we begin to see how fuzzy the line is. Big grants like those above generally put a fraction of their funds toward “overhead,” which goes into general upkeep of the institution as a whole. Can we really be sure that, as we walk across the lawn, the groundskeeping was not partially paid for by the pernicious Templeton Foundation?

    But that doesn’t mean that self-respecting atheists employed by the UofC should instantly resign. I’m sure you could play the same game with most big universities. The world would not be improved by having thousands of atheist professors abandon their posts out of principle.

    It’s much more sensible to be a consequentialist rather than a deontologist when it comes to these ethical questions. I’m not going to stay away from Nautilus, or the World Science Festival, or the Foundational Questions Institute, out of some fruit-of-the-poisonous-tree doctrine according to which they have become forever tainted by accepting money from Templeton. Rather, I’m going to try to judge whether these organizations provide a net good for the world; I will complain when I think they are making a mistake; and if I think they’ve gone too far in a direction I don’t personally like, I will disengage. That’s the best I think I can do, according to my own conscience. Others will doubtless feel differently.

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  • You Kids, Knock Off That Horseplay

    And for a change of pace, here’s Bill Nye putting Neil deGrasse Tyson in a hold so Brian Greene can knock him around.

  • On Templeton

    A few recent events, including the launch of Nautilus and this interesting thread on Brian Leiter’s blog, have brought the John Templeton Foundation (JTF) back into the spotlight. As probably everybody knows, the JTF is a philanthropic organization that supports research into the “Big Questions of human purpose and ultimate reality,” encourages “dialogue among scientists, philosophers, and theologians,” and seeks to use science to acquire “new spiritual information.” They like to fund lots of things I find interesting — cosmology, physics, philosophy — but unfortunately they also like to promote the idea that science and religion are gradually reconciling. (As well as some projects that just seem silly.) They also have a huge amount of money, and they readily give it away.

    I don’t think that science and religion are reconciling or can be reconciled in any meaningful sense, and I believe that it does a great disservice to the world to suggest otherwise. Therefore, way back in the day, I declined an opportunity to speak at a Templeton-sponsored conference. Ever since then, people have given me grief whenever my anti-Templeton fervor seems insufficiently fervent, even though my position — remarkably! — has been pretty consistent over the years. Honestly I find talking about things like this pretty tiresome; politics is important, but substance is infinitely more interesting. And this topic in particular has become even more tiresome as people on various sides have become increasingly emotional and less reflective. But I thought it would be useful to put my thoughts in one place, so I can just link here the next time the subject arises.

    In brief: I don’t take money directly from the Templeton Foundation. You will never see me thanking them for support in the acknowledgments of one of my papers. But there are plenty of good organizations and causes who feel differently, and take the money without qualms, from the World Science Festival to the Foundational Questions Institute. As long as I think that those organizations are worthwhile in their own right, I am willing to work with them — attending their conferences, submitting articles, whatever. But I will try my best to convince them they should get money from somewhere else.

    I’ve had various opportunities to get money from Templeton, and I certainly don’t come running to blog about it every time the possibility arises. Once I even got a call from a corporate head-hunter who wanted to inquire about my interest in a job with JTF. (Someone had clearly not done their homework.) But it’s not, as many people argue, because I am worried that Templeton works in nefarious ways to influence the people it funds. That is pretty unclear; there are some dark murmurings to that effect, with this piece by John Horgan being perhaps the most explicit example, but little hard evidence. It wouldn’t be utterly shocking to find that a funding agency tried to nudge work that it supported in directions that it was favorable to; that’s the kind of thing that funding agencies do. But there are plenty of examples of people receiving money from JTF and swearing that they never felt any pressure to be religion-friendly. More importantly, I don’t see much evidence that the JTF is actively evil, in (say) the way the Discovery Institute is evil, deliberately lying in order to advance an anti-science agenda. The JTF is quite pro-science, in its own way; it’s just that I think their views on science are very wrong.

    And that’s the real reason why I don’t want to be involved directly with Templeton. It’s not a matter of ethical compromise; it’s simply a matter of sending the wrong message. Any time respectable scientists take money from Templeton, they lend their respectability — even if only implicitly — to the idea that science and religion are just different paths to the same ultimate truth. That’s not something I want to do. If other people feel differently, that’s for them and their consciences, not something that is going to cause me to shun them.

    But I will try to explain to them why it’s important. Think of it this way. The kinds of questions I think about — origin of the universe, fundamental laws of physics, that kind of thing — for the most part have no direct impact on how ordinary people live their lives. No jet packs are forthcoming, as the saying goes. But there is one exception to this, so obvious that it goes unnoticed: belief in God. Due to the efforts of many smart people over the course of many years, scholars who are experts in the fundamental nature of reality have by a wide majority concluded that God does not exist. We have better explanations for how things work. The shift in perspective from theism to atheism is arguably the single most important bit of progress in fundamental ontology over the last five hundred years. And it matters to people … a lot.

    Or at least, it would matter, if we made it more widely known. It’s the one piece of scientific/philosophical knowledge that could really change people’s lives. So in my view, we have a responsibility to get the word out — to not be wishy-washy on the question of religion as a way of knowing, but to be clear and direct and loud about how reality really works. And when we blur the lines between science and religion, or seem to contribute to their blurring or even just not minding very much when other people blur them, we do the world a grave disservice. Religious belief exerts a significant influence over how the world is currently run — not just through extremists, but through the well-meaning liberal believers who very naturally think of religion as a source of wisdom and moral guidance, and who define the middle ground for sociopolitical discourse in our society. Understanding the fundamental nature of reality is a necessary starting point for productive conversations about morality, justice, and meaning. If we think we know something about that fundamental nature — something that disagrees profoundly with the conventional wisdom — we need to share it as widely and unambiguously as possible. And collaborating with organizations like Templeton inevitably dilutes that message.

    There’s no question that Templeton has been actively preventing the above message from getting across. By funding projects like the AAAS Dialogue on Science, Ethics, and Religion, the JTF has done its best to spread the impression that science and religion get along just fine. This impression is false. And it has consequences.

    So I won’t directly work with or take money from the JTF, although I will work with people who do take money from them — money that is appropriately laundered, if you will — if I think those people themselves are worth supporting or collaborating with in their own right. This means that approximately nobody agrees with me; the Templeton-friendly folks think I’m too uptight and priggish, while the anti-Templeton faction finds me sadly lacking in conviction. So be it. These are issues without easy answers, and I don’t mind taking a judicious middle ground. It’s even possible that I’ll change my mind one way or another down the road, in response to new arguments or actions on the part of the parties involved.

    And if anyone is tempted to award me the Templeton Prize, I will totally accept it! And use the funds to loudly evangelize for naturalism and atheism. (After I pay off the mortgage.)

  • Snowmass Young Physicists Survey

    Modern experimental particle physics is a high-budget, long-time-scale operation, which requires a great deal of planning. Fortunately there is a process in place, dubbed Snowmass after the scenic location in Colorado where meetings were traditionally held. (Funding agencies subsequently decided that it was unseemly for scientists to hold meetings in places that sound like vacation resorts, so this year “Snowmass” is in Minneapolis.)

    Any field depends on the engagement and interest of its younger members, so it’s great to know there is a Snowmass Young Physicist Movement. And if you’re a young high-energy physicist, they would like your input. Below is the message from organizer Marcelle Soares-Santos, but the short version is that they’re asking people to complete this brief survey. Every bit of information helps.

    Dear all,

    The Snowmass process which is ongoing through this summer encompasses a series of studies carried out by the high energy physics community with the goal to establish a coherent long term plan for the field in all of its Frontiers — Cosmic, Energy and Intensity.

    The young scientists forum at Snowmass is organizing a survey to obtain a snapshot of views, concerns and aspirations of our scientists, specially those at the early stage of their careers. We are reaching out to students, postdocs and faculty asking that you contribute by completing the survey and forwarding this message to your colleagues.

    The link to the survey is: http://tinyurl.com/snowmassyoung

    The estimated time to complete the survey is 5 to 10 minutes. You will note that the survey also includes questions for those who left academia, so if you can help us reach more people from that demographic group, that will be much appreciated too.

    Thank you very much for your participation!

    Cheers,
    Marcelle Soares-Santos
    On behalf of the Snowmass Young group.