Big Think Interview With Lisa Randall

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Question: What do particle physicists do on a day-to-day\r\nbasis?

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Lisa Randall: So, particle physicists, we’re trying to\r\nunderstand the substructure of matter; what’s really out there, what’s at the\r\ncore of matter, how it interacts, what are the fundamental forces.  And as you go to deeper and deeper\r\nscales you learn different things. \r\nSo the sort of two-pronged approach, we have some very theoretical work\r\nthat goes on and some very experimentally oriented work.  We’re trying to see what we can find\r\nout at the collider that will turn on again next week, we hope.  The collider that will be running for\r\nthe next couple of years, the Large Hadron Collider, that will collide together\r\nprotons of high energy and tell us what’s out there.  We also try to combine it together with theoretical ideas\r\nwe’ve been working on.  Some of\r\nthem generated from more high energy theoretical ideas beyond what we can see\r\nwith experiment and we’re trying to put those together. 

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On a day-to-day basis, we could be thinking about many different\r\nthings.  We could be thinking about\r\nwhat the experiments will do.  We\r\ncould be thinking about the theoretical idea of how they fit together, doing\r\nthe calculations to see what the consequences of some ideas, which we call\r\nmodels, would be.  There might be\r\nsome speculations or hypotheses for what’s out there and we try to derive what\r\nthe consequences would be and test whether those ideas work, test these ideas\r\nthat might synthesize the various phenomena that we’ve observed, but we don’t\r\nyet understand.

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Question: What insights do you hope the LHC will yield?

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Lisa Randall: So, the LHC stands for Large Hadron\r\nCollider.  It’s large; it’s 27\r\nkilometers in circumference.  It’s\r\na big tunnel where two beams of protons will circulate around it and then collide\r\nat various points within the tunnel. \r\nWhen it collides, it will collide together at high energy, about seven\r\ntimes the energy of the highest energy collider we have yet had on earth.  And when it does that, the idea is for\r\nthe mass of the particles converts into energy.

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The energy that’s created in the collision can then convert\r\ninto new particles.  Those\r\nparticles can have heavier mass than anything that’s been created before, E=MC2,\r\nso having bigger energy means that we can create particles that have bigger\r\nmass.  It also will have what’s\r\ncalled high luminosity, which is to say, there’s a high collision rate.  So the hope is that by having these new\r\nparameters, this high rate of collision, these high energies, we’ll be able to\r\nstudy matter in ways we haven’t been able to study it before. 

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In the process, we want to understand the answers to\r\nquestions like; where do the masses of fundamental particle come from?  That might sound like an odd question\r\nsince mass seems like an intrinsic property to matter, but it turns out that in\r\nthe simplest versions of the theories you’ve ****, particles don’t have\r\nmass.  And we know that it’s\r\nactually only possible for particles to have mass because of something like a\r\nphase transition that happened **** universe, something called the Higgs\r\nMechanism, named after the physicist, Peter Higgs, who thought of it.  And the idea is that particles at high\r\nenergy might seem not to have mass, but at low energies they do.  And the question is; how did that come\r\nabout?  If it’s a simple Higgs\r\nMechanism implementation, we’ll spy something called the Higgs Boson.  It’s a particle that tells us that this\r\nis really what happens and really puts it all together.

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The standard model works to an incredibly high degree of\r\nprecision.  We believe that it’s\r\nright.  The standard model of\r\nparticle physics tells us what are the basic elements of matter?  What are the forces through which they\r\ninteract?  It’s been tested to a\r\nhigh degree of precision.  But it\r\ndoesn’t answer questions like; where do the particle masses come from, the\r\nelementary particle masses come from? \r\nAnd the other question it doesn’t answer is; why are those masses about\r\nthe scale that they are?  Why\r\naren’t those masses much bigger? \r\nThat has to do with something what we call the hierarchy problem of\r\nparticle physics, which is connected to the question of why gravity is so\r\nweak.  And those are the types of\r\nquestions we hope to answer at the LHC. 

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If we’re really lucky, we might also get some insight into\r\ndark matter.  The matter that\r\ndoesn’t emit light that we know is out there in the universe.  So, there’s a number of questions that\r\nwe hope the LHC might help us answer. 

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Question: What is dark matter?

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Lisa Randall: As far as dark matter goes, we could be lucky\r\nin the sense that it seems that if you look at just the amount of dark matter\r\nthat’s out there in the universe, we can figure out what is called the relic\r\ndensity is given a sort of type of interaction.  That is to say, how much stuff should be left over now that\r\nthe universe is big and cool.  And\r\nit turns out that if particles had mass about the scale it’s going to be probed\r\nat the LHC, the Large Hadron Collider, that it turns out to have about the\r\nright relic density.  Now, this\r\nmight be just a coincidence, or it might be something deep and fundamental\r\ntelling us that the Large Hadron Collider might actually be able to produce the\r\ndark matter particle.  It might not\r\nproduce it directly, but it could produce something that decays into the dark\r\nmatter particles.  So there is some\r\nhope that by probing this energy, that the LHC will study, we can learn\r\nsomething about dark matter.

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Question: What is dark energy?

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Lisa Randall: There are various cosmological measurements,\r\nthat’s to say, by studying how things have evolved in looking out at what’s out\r\nthere in the sky, we can determine what type of matter it out there. It turns\r\nout that the kind of matter we see is only about 5% of the universe.  That is to say, stuff made up of protons\r\nand neutrons, the kinds of stuff we’re made of.  It seems only to be about 5% of the energy.  Then another 25% seems to be something\r\ncalled dark matter, which is matter that’s just like matter in the sense that\r\nit clumps together.  If we look at\r\ngalaxies, there’s lots of dark matter. \r\nBut it doesn’t interact with light in the same way that the matter we\r\nknow about does, which is why it’s dark and it’s hard to see, where I mean\r\nliterally mean see with light.  So,\r\nwe know it’s there because the gravitational effect.  And there’s various ways we’ve seen those gravitational\r\neffects, and there’s various ways we’ve seen those gravitational effects, but\r\nwe don’t yet know exactly what it is. 

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In addition to that, more recently we became aware of the\r\nfact that most of the energy density in the universe consists of something\r\nthat’s become known as dark energy. \r\nSo that is very different than dark matter.  Dark energy is just energy that permeates the universe, it’s\r\nnot associated with any particular type of particle, any type of matter, it’s\r\njust out there.  So if there was\r\nnothing, no particles around, there could still be this kind of energy.  And in addition to that, that energy\r\ndoesn’t clump and it doesn’t dilute as the universe expands.  So it’s a very special type of energy\r\nthat Einstein first thought could be around.  It turns out it was there in the amount that Einstein\r\nthought, but there seems to be this amount, this residual dark energy that’s\r\nleft that seems to dominate the energy density of the universe today.

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Question: How did the universe evolve to where it is today? 

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Lisa Randall: We have a pretty good idea of how the universe\r\nhas evolved to today and remarkably, in the last however many years, we’ve\r\nreally been able to test the evolution of the universe, the cosmology model we\r\nhave in much greater detail then we have ever had before.  So it’s really made cosmology into a\r\nprecision science in a way that it hadn’t been earlier on in this century. 

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We now have something which we call the Big Bang\r\nTheory.  Now the Big Bang Theory is\r\na little bit funny because it’s called the Big Bang Theory, but the Big Bang is\r\nthe one thing we don’t know about. \r\nWhat the Big Bang Theory tells us is really how things evolved at late\r\nstages.  How the universe given\r\nsome energy density which could consist of matter, radiation, dark energy.  Given those energies, how is the\r\nuniverse evolving, what’s happening? \r\nSo, Big Bang Theory tells us how it evolves and we have really nice experimental\r\nconfirmation.  We’ve seen that the\r\nuniverse is expanding, we’ve seen the Hubble expansion, we’ve see the relic\r\nradiation left over from the early time. \r\nIn the beginning, it was all hot and dense, but as the universe expanded\r\nthe radiation has cooled down significantly, so now we see this 3 degree\r\nmicrowave background in the sky.  And\r\nin addition to that, we even have detailed predictions for the abundance of\r\nvarious nuclei, which is very much connected with what happened as the universe\r\ncooled. 

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So there are really good tests of the Big Bang Theory and\r\nthis theory of expansion.  The\r\nthing is, it doesn’t tell us about the early stages.  And particularly, there was some mysterious features when we\r\nlooked at this background radiation, and I’m using “we” very loosely, the other\r\npeople when they looked out at the sky. \r\nAnd it was seen that radiation was very uniform and was homogeneous and\r\nisotropic, it looked the same in all different directions in the sky to a very,\r\nvery high degree of precision; like one out of ten thousand with very small\r\ntemperature deviations as you looked out at the sky.  Which was very surprising because there were pieces of the\r\nsky that didn’t even have enough time, according to the standard Big Bang\r\nTheory, to talk to each other. \r\nThey’re so far away that light could not travel between them in enough\r\ntime.  So, some how all these\r\ndifferent regions of the sky had to have originated in some common place.  And the theory of cosmological\r\ninflation combined together with Big Bang Theory seems to be what really\r\nworks. 

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So for cosmological inflation, the idea is that early on\r\nthere was actually an exponential expansion of the universe driven actually by\r\nsomething like dark energy except in a much greater energy density, and it\r\ndrove this exponential expansion of the universe.  Actually, later on in our evolution, we will also have an\r\nexponential expansion, but it’ll be a much slower exponential expansion.  But early on there was this very rapid\r\nphase of exponential expansion where the universe kept doubling its size, and\r\nduring that time, the universe grew an enormous amount, and then after it\r\nstopped that whatever it was that drove the expansion might have decayed, but\r\nsomehow the stuff that becomes our matter was created.  So, in some sense, that is really the\r\nbeginning that we can trace.  The\r\nfact that there was some expansion, some inflationary stage where it\r\nexponentially expanded, then afterward this more conventional Big Bang Theory\r\ntakes over. 

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And what’s really remarkable is that there’s sort of an\r\nimprint of this state of exponential expansion in the sky.  If you look at details at the cosmic\r\nmicrowave background, it’s very much in agreement with the predictions of\r\ncosmological prediction.  So it\r\nreally does seem like this happened and it explains some features; explains the\r\nflatness of the universe, the fact that the universe doesn’t – we can talk\r\nabout the geometry of it, even the three-dimensional spatial universe and it\r\nseems extremely flat.  And again,\r\nthat’s because if you think about a balloon, if you blow it up, if you blow it\r\nup enough even though we know over a large scale, it looks sort of round or\r\nspherical or oval, if you look at a small region, it looks very flat.  So, if you blow up a balloon enough at\r\nany given region, it looks flat, and the same way maybe we blew up the universe\r\nenough that it looks large and flat. \r\nSo, inflation seems to explain many features of the initial conditions\r\nof how things started before this Big Bang Theory took over.

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Question: What does this research into the universe’s early\r\nhistory tell us about its ultimate fate?

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Lisa Randall: Well, what really tells us about the ultimate\r\nfate of the universe is what we see today.  What we see today seems to be this dark energy that\r\ndominates.  And as I said earlier,\r\ndark energy doesn’t dilute as the universe expands.  Radiation dilutes, matter dilutes, so although we know right\r\nnow we have about 30% matter if we include dark matter and our matter.  That matter, as the universe grows,\r\nthat matter will become more and more dilute.  And dark energy is going to just take over at which point we\r\nwill again have exponential expansion of the universe.  At that point, we will cease to have\r\nmatter creation in the way we do today; star formation in the way we do.  Eventually we might have all the matter\r\nin black holes, but those black holes will radiate away.  So we will ultimately have, if this is\r\nright, a large essentially empty universe that will just keep growing.

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Question: When do you predict this will happen?

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Lisa Randall: This is not going to be the dominant thing\r\nthat affects any of our lives. \r\nThis is a projection based on what we observe today of what would happen\r\nbillions of years from now.

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Question: What might the LHC tell us about the existence of\r\nextra dimensions of space?

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Lisa Randall: The LHC will hopefully find the Higgs\r\nParticle; it hopefully will answer the question about the weakness of gravity\r\nand why there are different mass scales in the universe.  What the answer will be, we don’t know,\r\nalthough we’ve conjectured what it might be.  One of the possibilities that I and others have worked on is\r\nthe idea that there could be extra dimensions of space other than the ones we\r\nsee the forward, backward, left, right, up, down.  There could be other dimensions and they could be connected\r\nto explaining some of these features that we can’t otherwise understand.  We don’t know that that’s right.  Other people conjecture, in fact I’ve\r\nworked on it too, the idea that it might be something called supersymmetry,\r\nwhich have doubled the amount of particles in the universe, but again has some\r\nchance of explaining why there could be this huge hierarchy of mass\r\nscales. 

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So there could be various possibilities that we conjecture.  I don’t think anyone feels 100%\r\nconfident, probably there are some people that do, but we really don’t know\r\nwhat’s there.  That’s why we do\r\nexperiments.  All these theories\r\nhave good aspects and bad aspects and so until we actually see how the universe\r\nworks, sometimes the universe is far more clever than anything we think\r\nof.  So these were all\r\npossibilities, there’s some finer probability for all of them.  And we certainly want to make sure that\r\nthe machine will test these ideas that it is capable so we’ve made the right –\r\nwe tell them what the predictions are, what they should be looking for. 

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One thing to keep in mind is the experiments at the Large\r\nHadron Collider are very difficult because they are very messy.  There’s many billion events per second\r\nand you’ve got to narrow that down and be able to look at the small things that\r\nthe small predictions have a small probability of what could happen and be able\r\nto pull those out.  So, you have to\r\nhave a very clear idea of what it is that you are looking for.  And that’s why we want to make models\r\nand tell them what they should be looking for.  What are the unique features that will identify something\r\nthat’s new and can tell us what’s really going on at these energy scales?

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Question: What is supersymmetry?

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Lisa Randall: Well the term – to really understand\r\nsupersymmetry requires you to know something about quantum mechanics.  Supersymmetry connects together\r\ndifferent kinds of particles known as bosons and fermions.  Bosons are particles that like to be in\r\nthe same place, fermions are particles that don’t like to be in the same\r\nplace.  And the conjecture is,\r\nsupersymmetry is that for every particle that we know about is a partner that’s\r\nthe opposite in the sense that if the Higgs boson is a boson there will be a\r\nHiggs Zeno, a partner that’s a fermion. \r\nIf there are Gath Bosons there are Gath Genos, if there are fermions,\r\nthere are partnered bosons.  So it\r\nsort of doubles the number of particles which, if you think about it from the\r\npoint of view of what you’ve seen experimented, is quite dramatic.  If supersymmetry is right and explains\r\nwhat we call weak scale phenomena, this questions about masses and about the\r\nhierarchy problem, then we’d be able to see a whole school of new particles when\r\nthe LHC is running at full capacity.

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Question: What was the greatest “Eureka!” moment in your\r\ncareer?

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Lisa Randall: I mean, for any problem you work on there’s\r\nsome moment where there’s sort of maybe it’s a moment where no one else cares\r\nabout, where it all fits together and I found some simple way of doing\r\nsomething.  There are also the\r\nmodels that people have heard about such as the models about extra dimensions,\r\nsomething else that we did having to do with a different way of communicating\r\nsupersymmetry breaking.  There were\r\na lot of eureka moments in that and making it work out and the fact that we\r\ncould all tie it together.  So,\r\nit’s hard for me to pull those out because a lot of the time when you’re\r\nworking on something there’s that one thing that you get excited about.

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Question: Have you ever been completely surprised by the\r\nresult of an experiment?

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Lisa Randall: I think one thing that surprised us, Braman\r\nand I, when we were working together was this existence, or the possibility of\r\nthe existence, of an infinite extra dimension.  People had actually thought there were theorems that you\r\ncouldn’t have an infinite extra dimension, that gravity would just look wrong,\r\nthat there was no consistent way to do it.  And it was really interesting because we came across this by\r\nreally following the consequence of our equations to the end and there was just\r\nno mistaking that it was allowing the possibility of an infinite extra\r\ndimension.  And it was interesting\r\nto go back and see what assumptions have been made that made us think, or made\r\nother people think that it was impossible, and just to see how the theory was\r\nalmost smarter than we were and worked it out.  That was kind of fun.

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Question: What excites you most about your current research?

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Lisa Randall: Right now I’m enjoying thinking about what\r\nwe’ll see at the Large Hadron Collider. \r\nWhat is it that they could find that they’re not looking for yet?  Making sure that it’s what we have and\r\nmaking sure it does as much as we can. \r\nAlso thinking about what we can see in dark matter experiments.  Making sure, again, that we’ve\r\nconsidered all of the possibilities and we’ve looked for how to search and what\r\ncould be out there and to make sure that we can look for other candidates for\r\ndark matter, you know, what can it be? \r\nSo, right now I’m thinking really because we are in this era where these\r\nexperiments are turning on, so it’s important to really make sure that we use them\r\nfor all they’re worth.

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Question: Apart from science, what’s an area of intellectual\r\ninquiry that fascinates you?

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Lisa Randall: \r\nWell, right now, I’m interested in art and music.  I wrote a libretto for a small, what we\r\ncall a projective opera, which was kind of a different kind of way to communicate\r\nideas to the public.  It’s not a\r\nlinear story where we’re explaining things, but just to communicate why we care\r\nabout exploration discovery.  For\r\nme it was just an interesting experience to see what it’s like to do something\r\nthat is connected with performance. \r\nIt was performed at the Pompidou Center; it was performed at the Opera\r\nHouse in Barcelona, and that was a very exciting and interesting thing for\r\nme. 

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I think right now it’s also a little bit interesting to\r\nfollow what’s going on with the economy, what’s going on with various political\r\nthings and by fun -- kind of disturbing sometimes, but I think there are a lot\r\nof interesting questions that are lurking there that are fun to think about.

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Question: How can scientists reach out to the public more\r\neffectively?

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Lisa Randall: I think, I’ve obviously made the choice to\r\nspeak to the public at some level and it’s in part because I enjoy writing and\r\nI enjoy being able to think creatively in different ways.  I don’t think that any one particular\r\nscientist is obliged to do this, to speak to people.  But I do think that as a community, if we are expecting\r\nresources, it’s very difficult material and I think it’s important that the\r\ninformation is out there.

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When I wrote my book “Warped Passages,” I really had in mind\r\nan interested audience.  I think\r\nit’s very easy to try to pander to a large audience – not easy, but – or to\r\nwrite technical things for your audience, but there’s sort of this in-between\r\ncategory of people where they’re really smart and really interested, but they\r\njust don’t know the physics yet, and I think it’s important that if they wanted\r\nto know what we’re doing and why it’s important and what the full implications\r\nare, then that information is out there in a way that they can access.  And I just think, generally, it’s\r\nimportant to be able to communicate among different fields.  We live in an era where science is\r\nimportant to the decisions we make. \r\nIs what happens at the LHC going to determine our policy toward it?  Not necessarily, but being able to\r\nthink like a scientist on some level we’ll be able to think about predictions\r\nand risk and probabilities. \r\nThere’s some basic science training that might help people, but there’s\r\nalso just curiosity about the world which everyone has and understanding why we\r\ncare about these questions, what it is that we’re looking for and why it’s\r\ngoing to tell us these deep fundamental properties of the universe at both a\r\nsmall scale and the large scale. \r\nScales that we can directly access just by looking, that we need\r\ntechnology for and saying what is it that we’re after?  And I think those are – a lot of people\r\nwant to know that, and it’s important that they have access to that information.

Recorded on February 17, 2010
Interviewed by Austin \r\nAllen

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A conversation with the professor of theoretical physics at Harvard.

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