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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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00:12:00,706 --> 00:12:01,856
(Laughter)

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00:12:02,728 --> 00:12:04,331
But that's not what we did.

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But why not?

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00:12:10,575 --> 00:12:13,420
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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00:12:25,269 --> 00:12:28,620
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)