How we explore unanswered questions in physics | James Beacham

108,131 views ・ 2017-01-20

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Translator: Leslie Gauthier Reviewer: Camille Martínez
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There is something about physics
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that has been really bothering me since I was a little kid.
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And it's related to a question
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that scientists have been asking for almost 100 years,
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with no answer.
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How do the smallest things in nature,
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the particles of the quantum world,
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match up with the largest things in nature --
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planets and stars and galaxies held together by gravity?
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As a kid, I would puzzle over questions just like this.
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I would fiddle around with microscopes and electromagnets,
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and I would read about the forces of the small
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and about quantum mechanics
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and I would marvel at how well that description matched up
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to our observation.
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Then I would look at the stars,
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and I would read about how well we understand gravity,
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and I would think surely, there must be some elegant way
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that these two systems match up.
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But there's not.
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And the books would say,
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yeah, we understand a lot about these two realms separately,
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but when we try to link them mathematically,
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everything breaks.
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And for 100 years,
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none of our ideas as to how to solve this basically physics disaster,
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has ever been supported by evidence.
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And to little old me --
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little, curious, skeptical James --
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this was a supremely unsatisfying answer.
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So, I'm still a skeptical little kid.
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Flash-forward now to December of 2015,
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when I found myself smack in the middle
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of the physics world being flipped on its head.
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It all started when we at CERN saw something intriguing in our data:
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a hint of a new particle,
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an inkling of a possibly extraordinary answer to this question.
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So I'm still a skeptical little kid, I think,
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but I'm also now a particle hunter.
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I am a physicist at CERN's Large Hadron Collider,
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the largest science experiment ever mounted.
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It's a 27-kilometer tunnel on the border of France and Switzerland
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buried 100 meters underground.
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And in this tunnel,
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we use superconducting magnets colder than outer space
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to accelerate protons to almost the speed of light
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and slam them into each other millions of times per second,
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collecting the debris of these collisions
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to search for new, undiscovered fundamental particles.
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Its design and construction took decades of work
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by thousands of physicists from around the globe,
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and in the summer of 2015,
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we had been working tirelessly to switch on the LHC
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at the highest energy that humans have ever used in a collider experiment.
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Now, higher energy is important
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because for particles, there is an equivalence
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between energy and particle mass,
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and mass is just a number put there by nature.
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To discover new particles,
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we need to reach these bigger numbers.
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And to do that, we have to build a bigger, higher energy collider,
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and the biggest, highest energy collider in the world
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is the Large Hadron Collider.
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And then, we collide protons quadrillions of times,
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and we collect this data very slowly, over months and months.
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And then new particles might show up in our data as bumps --
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slight deviations from what you expect,
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little clusters of data points that make a smooth line not so smooth.
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For example, this bump,
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after months of data-taking in 2012,
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led to the discovery of the Higgs particle --
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the Higgs boson --
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and to a Nobel Prize for the confirmation of its existence.
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This jump up in energy in 2015
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represented the best chance that we as a species had ever had
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of discovering new particles --
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new answers to these long-standing questions,
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because it was almost twice as much energy as we used
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when we discovered the Higgs boson.
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Many of my colleagues had been working their entire careers for this moment,
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and frankly, to little curious me,
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this was the moment I'd been waiting for my entire life.
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So 2015 was go time.
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So June 2015,
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the LHC is switched back on.
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My colleagues and I held our breath and bit our fingernails,
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and then finally we saw the first proton collisions
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at this highest energy ever.
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Applause, champagne, celebration.
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This was a milestone for science,
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and we had no idea what we would find in this brand-new data.
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And then a few weeks later, we found a bump.
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It wasn't a very big bump,
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but it was big enough to make you raise your eyebrow.
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But on a scale of one to 10 for eyebrow raises,
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if 10 indicates that you've discovered a new particle,
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this eyebrow raise is about a four.
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(Laughter)
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I spent hours, days, weeks in secret meetings,
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arguing with my colleagues over this little bump,
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poking and prodding it with our most ruthless experimental sticks
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to see if it would withstand scrutiny.
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But even after months of working feverishly --
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sleeping in our offices and not going home,
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candy bars for dinner,
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coffee by the bucketful --
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physicists are machines for turning coffee into diagrams --
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(Laughter)
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This little bump would not go away.
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So after a few months,
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we presented our little bump to the world with a very clear message:
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this little bump is interesting but it's not definitive,
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so let's keep an eye on it as we take more data.
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So we were trying to be extremely cool about it.
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And the world ran with it anyway.
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The news loved it.
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People said it reminded them of the little bump
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that was shown on the way toward the Higgs boson discovery.
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Better than that, my theorist colleagues --
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I love my theorist colleagues --
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my theorist colleagues wrote 500 papers about this little bump.
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(Laughter)
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The world of particle physics had been flipped on its head.
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But what was it about this particular bump
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that caused thousands of physicists to collectively lose their cool?
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This little bump was unique.
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This little bump indicated
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that we were seeing an unexpectedly large number of collisions
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whose debris consisted of only two photons,
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two particles of light.
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And that's rare.
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Particle collisions are not like automobile collisions.
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They have different rules.
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When two particles collide at almost the speed of light,
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the quantum world takes over.
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And in the quantum world,
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these two particles can briefly create a new particle
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that lives for a tiny fraction of a second
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before splitting into other particles that hit our detector.
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Imagine a car collision where the two cars vanish upon impact,
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a bicycle appears in their place --
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(Laughter)
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And then that bicycle explodes into two skateboards,
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which hit our detector.
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(Laughter)
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Hopefully, not literally.
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They're very expensive.
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Events where only two photons hit out detector are very rare.
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And because of the special quantum properties of photons,
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there's a very small number of possible new particles --
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these mythical bicycles --
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that can give birth to only two photons.
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But one of these options is huge,
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and it has to do with that long-standing question
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that bothered me as a tiny little kid,
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about gravity.
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Gravity may seem super strong to you,
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but it's actually crazily weak compared to the other forces of nature.
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I can briefly beat gravity when I jump,
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but I can't pick a proton out of my hand.
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The strength of gravity compared to the other forces of nature?
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It's 10 to the minus 39.
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That's a decimal with 39 zeros after it.
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Worse than that,
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all of the other known forces of nature are perfectly described
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by this thing we call the Standard Model,
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which is our current best description of nature at its smallest scales,
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and quite frankly,
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one of the most successful achievements of humankind --
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except for gravity, which is absent from the Standard Model.
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It's crazy.
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It's almost as though most of gravity has gone missing.
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We feel a little bit of it,
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but where's the rest of it?
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No one knows.
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But one theoretical explanation proposes a wild solution.
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You and I --
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even you in the back --
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we live in three dimensions of space.
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I hope that's a non-controversial statement.
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(Laughter)
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All of the known particles also live in three dimensions of space.
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In fact, a particle is just another name
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for an excitation in a three-dimensional field;
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a localized wobbling in space.
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More importantly, all the math that we use to describe all this stuff
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assumes that there are only three dimensions of space.
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But math is math, and we can play around with our math however we want.
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And people have been playing around with extra dimensions of space
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for a very long time,
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but it's always been an abstract mathematical concept.
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I mean, just look around you -- you at the back, look around --
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there's clearly only three dimensions of space.
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But what if that's not true?
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What if the missing gravity is leaking into an extra-spatial dimension
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that's invisible to you and I?
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What if gravity is just as strong as the other forces
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if you were to view it in this extra-spatial dimension,
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and what you and I experience is a tiny slice of gravity
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make it seem very weak?
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If this were true,
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we would have to expand our Standard Model of particles
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to include an extra particle, a hyperdimensional particle of gravity,
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a special graviton that lives in extra-spatial dimensions.
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I see the looks on your faces.
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You should be asking me the question,
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"How in the world are we going to test this crazy, science fiction idea,
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stuck as we are in three dimensions?"
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The way we always do,
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by slamming together two protons --
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(Laughter)
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Hard enough that the collision reverberates
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into any extra-spatial dimensions that might be there,
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momentarily creating this hyperdimensional graviton
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that then snaps back into the three dimensions of the LHC
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and spits off two photons,
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two particles of light.
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And this hypothetical, extra-dimensional graviton
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is one of the only possible, hypothetical new particles
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that has the special quantum properties
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that could give birth to our little, two-photon bump.
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So, the possibility of explaining the mysteries of gravity
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and of discovering extra dimensions of space --
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perhaps now you get a sense
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as to why thousands of physics geeks collectively lost their cool
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over our little, two-photon bump.
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A discovery of this type would rewrite the textbooks.
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But remember,
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the message from us experimentalists
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that actually were doing this work at the time,
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was very clear:
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we need more data.
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With more data,
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the little bump will either turn into a nice, crisp Nobel Prize --
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(Laughter)
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Or the extra data will fill in the space around the bump
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and turn it into a nice, smooth line.
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So we took more data,
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and with five times the data, several months later,
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our little bump
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turned into a smooth line.
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The news reported on a "huge disappointment," on "faded hopes,"
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and on particle physicists "being sad."
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Given the tone of the coverage,
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you'd think that we had decided to shut down the LHC and go home.
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(Laughter)
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But that's not what we did.
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But why not?
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I mean, if I didn't discover a particle -- and I didn't --
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if I didn't discover a particle, why am I here talking to you?
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Why didn't I just hang my head in shame
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and go home?
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Particle physicists are explorers.
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And very much of what we do is cartography.
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Let me put it this way: forget about the LHC for a second.
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Imagine you are a space explorer arriving at a distant planet,
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searching for aliens.
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What is your first task?
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To immediately orbit the planet, land, take a quick look around
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for any big, obvious signs of life,
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and report back to home base.
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That's the stage we're at now.
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We took a first look at the LHC
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for any new, big, obvious-to-spot particles,
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and we can report that there are none.
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We saw a weird-looking alien bump on a distant mountain,
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but once we got closer, we saw it was a rock.
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But then what do we do? Do we just give up and fly away?
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Absolutely not;
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we would be terrible scientists if we did.
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No, we spend the next couple of decades exploring,
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mapping out the territory,
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sifting through the sand with a fine instrument,
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peeking under every stone,
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drilling under the surface.
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New particles can either show up immediately
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as big, obvious-to-spot bumps,
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or they can only reveal themselves after years of data taking.
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Humanity has just begun its exploration at the LHC at this big high energy,
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and we have much searching to do.
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But what if, even after 10 or 20 years, we still find no new particles?
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We build a bigger machine.
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(Laughter)
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We search at higher energies.
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We search at higher energies.
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Planning is already underway for a 100-kilometer tunnel
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that will collide particles at 10 times the energy of the LHC.
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We don't decide where nature places new particles.
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We only decide to keep exploring.
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But what if, even after a 100-kilometer tunnel
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or a 500-kilometer tunnel
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or a 10,000-kilometer collider floating in space
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between the Earth and the Moon,
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we still find no new particles?
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Then perhaps we're doing particle physics wrong.
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(Laughter)
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Perhaps we need to rethink things.
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Maybe we need more resources, technology, expertise
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than what we currently have.
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We already use artificial intelligence and machine learning techniques
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in parts of the LHC,
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but imagine designing a particle physics experiment
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using such sophisticated algorithms
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that it could teach itself to discover a hyperdimensional graviton.
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But what if?
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What if the ultimate question:
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What if even artificial intelligence can't help us answer our questions?
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What if these open questions, for centuries,
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are destined to be unanswered for the foreseeable future?
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What if the stuff that's bothered me since I was a little kid
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is destined to be unanswered in my lifetime?
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Then that ...
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will be even more fascinating.
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We will be forced to think in completely new ways.
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We'll have to go back to our assumptions,
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and determine if there was a flaw somewhere.
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And we'll need to encourage more people to join us in studying science
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since we need fresh eyes on these century-old problems.
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I don't have the answers, and I'm still searching for them.
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But someone -- maybe she's in school right now,
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maybe she's not even born yet --
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could eventually guide us to see physics in a completely new way,
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and to point out that perhaps we're just asking the wrong questions.
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Which would not be the end of physics,
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but a novel beginning.
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Thank you.
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(Applause)
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About this website

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