0:00:01.087,0:00:05.272
There is something about physics

0:00:05.296,0:00:09.296
that has been really bothering me[br]since I was a little kid.

0:00:11.010,0:00:12.819
And it's related to a question

0:00:12.843,0:00:16.087
that scientists have been asking[br]for almost 100 years,

0:00:16.111,0:00:17.280
with no answer.

0:00:19.108,0:00:22.118
How do the smallest things in nature,

0:00:22.142,0:00:24.295
the particles of the quantum world,

0:00:24.319,0:00:27.350
match up with the largest[br]things in nature --

0:00:27.374,0:00:30.621
planets and stars and galaxies[br]held together by gravity?

0:00:31.250,0:00:34.023
As a kid, I would puzzle[br]over questions just like this.

0:00:34.047,0:00:36.939
I would fiddle around[br]with microscopes and electromagnets,

0:00:36.963,0:00:39.158
and I would read[br]about the forces of the small

0:00:39.182,0:00:40.516
and about quantum mechanics

0:00:40.540,0:00:44.104
and I would marvel at how well[br]that description matched up

0:00:44.128,0:00:45.298
to our observation.

0:00:46.220,0:00:47.803
Then I would look at the stars,

0:00:47.827,0:00:50.351
and I would read about how well[br]we understand gravity,

0:00:50.375,0:00:53.725
and I would think surely,[br]there must be some elegant way

0:00:53.749,0:00:56.394
that these two systems match up.

0:00:57.021,0:00:58.422
But there's not.

0:00:59.673,0:01:00.833
And the books would say,

0:01:00.857,0:01:04.040
yeah, we understand a lot[br]about these two realms separately,

0:01:04.064,0:01:06.674
but when we try to link[br]them mathematically,

0:01:06.698,0:01:08.028
everything breaks.

0:01:08.674,0:01:09.984
And for 100 years,

0:01:10.008,0:01:15.036
none of our ideas as to how to solve[br]this basically physics disaster,

0:01:15.060,0:01:16.874
has ever been supported by evidence.

0:01:18.271,0:01:19.925
And to little old me --

0:01:19.949,0:01:21.759
little, curious, skeptical James --

0:01:21.783,0:01:24.651
this was a supremely unsatisfying answer.

0:01:26.011,0:01:28.244
So, I'm still a skeptical little kid.

0:01:28.268,0:01:32.078
Flash-forward now[br]to December of 2015,

0:01:33.029,0:01:35.503
when I found myself smack in the middle

0:01:35.527,0:01:38.467
of the physics world[br]being flipped on its head.

0:01:39.999,0:01:43.319
It all started when we at CERN[br]saw something intriguing in our data:

0:01:43.343,0:01:45.617
a hint of a new particle,

0:01:45.641,0:01:49.857
an inkling of a possibly extraordinary[br]answer to this question.

0:01:51.777,0:01:53.904
So I'm still a skeptical[br]little kid, I think,

0:01:53.928,0:01:56.061
but I'm also now a particle hunter.

0:01:56.085,0:01:59.548
I am a physicist at CERN's[br]Large Hadron Collider,

0:01:59.572,0:02:03.043
the largest science[br]experiment ever mounted.

0:02:03.877,0:02:07.412
It's a 27-kilometer tunnel[br]on the border of France and Switzerland

0:02:07.436,0:02:09.286
buried 100 meters underground.

0:02:09.310,0:02:10.464
And in this tunnel,

0:02:10.488,0:02:14.441
we use superconducting magnets[br]colder than outer space

0:02:14.465,0:02:17.526
to accelerate protons[br]to almost the speed of light

0:02:17.550,0:02:21.427
and slam them into each other[br]millions of times per second,

0:02:21.451,0:02:24.277
collecting the debris of these collisions

0:02:24.301,0:02:28.272
to search for new, undiscovered[br]fundamental particles.

0:02:28.727,0:02:31.191
Its design and construction[br]took decades of work

0:02:31.215,0:02:34.247
by thousands of physicists[br]from around the globe,

0:02:34.271,0:02:36.812
and in the summer of 2015,

0:02:36.836,0:02:40.260
we had been working tirelessly[br]to switch on the LHC

0:02:40.284,0:02:44.751
at the highest energy that humans[br]have ever used in a collider experiment.

0:02:45.735,0:02:48.258
Now, higher energy is important

0:02:48.282,0:02:50.469
because for particles,[br]there is an equivalence

0:02:50.493,0:02:52.694
between energy and particle mass,

0:02:52.718,0:02:55.179
and mass is just a number[br]put there by nature.

0:02:56.068,0:02:57.386
To discover new particles,

0:02:57.410,0:02:59.532
we need to reach these bigger numbers.

0:02:59.556,0:03:02.810
And to do that, we have to build[br]a bigger, higher energy collider,

0:03:02.834,0:03:05.399
and the biggest, highest[br]energy collider in the world

0:03:05.423,0:03:06.889
is the Large Hadron Collider.

0:03:08.271,0:03:13.170
And then, we collide protons[br]quadrillions of times,

0:03:13.194,0:03:17.478
and we collect this data very slowly,[br]over months and months.

0:03:18.813,0:03:23.148
And then new particles might show up[br]in our data as bumps --

0:03:23.172,0:03:25.617
slight deviations from what you expect,

0:03:25.641,0:03:29.608
little clusters of data points[br]that make a smooth line not so smooth.

0:03:30.379,0:03:32.100
For example, this bump,

0:03:33.010,0:03:35.543
after months of data-taking in 2012,

0:03:35.567,0:03:37.696
led to the discovery[br]of the Higgs particle --

0:03:37.720,0:03:38.925
the Higgs boson --

0:03:38.949,0:03:42.314
and to a Nobel Prize[br]for the confirmation of its existence.

0:03:43.972,0:03:47.530
This jump up in energy in 2015

0:03:48.628,0:03:51.920
represented the best chance[br]that we as a species had ever had

0:03:51.944,0:03:53.421
of discovering new particles --

0:03:53.445,0:03:55.557
new answers to these[br]long-standing questions,

0:03:55.581,0:03:58.678
because it was almost[br]twice as much energy as we used

0:03:58.702,0:04:00.624
when we discovered the Higgs boson.

0:04:00.648,0:04:04.389
Many of my colleagues had been working[br]their entire careers for this moment,

0:04:04.413,0:04:06.489
and frankly, to little curious me,

0:04:06.513,0:04:09.423
this was the moment[br]I'd been waiting for my entire life.

0:04:09.447,0:04:11.178
So 2015 was go time.

0:04:12.654,0:04:14.864
So June 2015,

0:04:15.722,0:04:18.381
the LHC is switched back on.

0:04:19.040,0:04:21.917
My colleagues and I held our breath[br]and bit our fingernails,

0:04:21.941,0:04:24.452
and then finally we saw[br]the first proton collisions

0:04:24.476,0:04:26.432
at this highest energy ever.

0:04:26.456,0:04:28.532
Applause, champagne, celebration.

0:04:28.556,0:04:32.152
This was a milestone for science,

0:04:32.176,0:04:36.798
and we had no idea what we would find[br]in this brand-new data.

0:04:39.990,0:04:42.168
And then a few weeks later,[br]we found a bump.

0:04:44.192,0:04:45.868
It wasn't a very big bump,

0:04:46.952,0:04:49.464
but it was big enough to make[br]you raise your eyebrow.

0:04:49.488,0:04:51.739
But on a scale of one to 10[br]for eyebrow raises,

0:04:51.763,0:04:54.373
if 10 indicates that you've[br]discovered a new particle,

0:04:54.397,0:04:56.124
this eyebrow raise is about a four.

0:04:56.148,0:04:57.298
(Laughter)

0:04:58.432,0:05:03.643
I spent hours, days, weeks[br]in secret meetings,

0:05:03.667,0:05:06.027
arguing with my colleagues[br]over this little bump,

0:05:06.051,0:05:09.287
poking and prodding it with our most[br]ruthless experimental sticks

0:05:09.311,0:05:11.288
to see if it would withstand scrutiny.

0:05:11.988,0:05:15.449
But even after months[br]of working feverishly --

0:05:15.473,0:05:17.905
sleeping in our offices[br]and not going home,

0:05:17.929,0:05:20.006
candy bars for dinner,

0:05:20.030,0:05:21.600
coffee by the bucketful --

0:05:21.624,0:05:25.867
physicists are machines[br]for turning coffee into diagrams --

0:05:25.891,0:05:27.290
(Laughter)

0:05:27.314,0:05:29.850
This little bump would not go away.

0:05:30.704,0:05:32.842
So after a few months,

0:05:32.866,0:05:36.576
we presented our little bump to the world[br]with a very clear message:

0:05:37.457,0:05:40.168
this little bump is interesting[br]but it's not definitive,

0:05:40.192,0:05:43.521
so let's keep an eye on it[br]as we take more data.

0:05:43.872,0:05:46.163
So we were trying to be[br]extremely cool about it.

0:05:47.463,0:05:49.651
And the world ran with it anyway.

0:05:50.383,0:05:52.015
The news loved it.

0:05:52.735,0:05:55.290
People said it reminded[br]them of the little bump

0:05:55.314,0:05:58.737
that was shown on the way[br]toward the Higgs boson discovery.

0:05:58.761,0:06:01.889
Better than that,[br]my theorist colleagues --

0:06:02.548,0:06:04.865
I love my theorist colleagues --

0:06:04.889,0:06:08.501
my theorist colleagues wrote[br]500 papers about this little bump.

0:06:08.525,0:06:09.980
(Laughter)

0:06:10.574,0:06:14.540
The world of particle physics[br]had been flipped on its head.

0:06:15.745,0:06:19.987
But what was it about this particular bump

0:06:20.011,0:06:24.101
that caused thousands of physicists[br]to collectively lose their cool?

0:06:25.596,0:06:27.032
This little bump was unique.

0:06:28.198,0:06:29.567
This little bump indicated

0:06:29.591,0:06:32.613
that we were seeing an unexpectedly[br]large number of collisions

0:06:32.637,0:06:35.968
whose debris consisted[br]of only two photons,

0:06:35.992,0:06:37.236
two particles of light.

0:06:37.260,0:06:38.497
And that's rare.

0:06:39.069,0:06:41.689
Particle collisions are not[br]like automobile collisions.

0:06:41.713,0:06:43.232
They have different rules.

0:06:43.256,0:06:45.906
When two particles collide[br]at almost the speed of light,

0:06:45.930,0:06:47.351
the quantum world takes over.

0:06:47.375,0:06:48.635
And in the quantum world,

0:06:48.659,0:06:51.852
these two particles[br]can briefly create a new particle

0:06:51.876,0:06:54.656
that lives for a tiny fraction of a second

0:06:54.680,0:06:57.561
before splitting into other particles[br]that hit our detector.

0:06:57.585,0:07:00.990
Imagine a car collision[br]where the two cars vanish upon impact,

0:07:01.014,0:07:03.283
a bicycle appears in their place --

0:07:03.307,0:07:04.378
(Laughter)

0:07:04.402,0:07:06.863
And then that bicycle explodes[br]into two skateboards,

0:07:06.887,0:07:08.068
which hit our detector.

0:07:08.092,0:07:09.471
(Laughter)

0:07:09.495,0:07:11.448
Hopefully, not literally.

0:07:11.472,0:07:12.814
They're very expensive.

0:07:14.191,0:07:17.939
Events where only two photons[br]hit out detector are very rare.

0:07:17.963,0:07:21.685
And because of the special[br]quantum properties of photons,

0:07:21.709,0:07:25.497
there's a very small number[br]of possible new particles --

0:07:25.521,0:07:27.018
these mythical bicycles --

0:07:27.042,0:07:29.285
that can give birth to only two photons.

0:07:29.812,0:07:32.648
But one of these options is huge,

0:07:32.672,0:07:35.508
and it has to do with[br]that long-standing question

0:07:35.532,0:07:38.054
that bothered me as a tiny little kid,

0:07:38.078,0:07:39.438
about gravity.

0:07:41.946,0:07:44.618
Gravity may seem super strong to you,

0:07:44.642,0:07:48.742
but it's actually crazily weak[br]compared to the other forces of nature.

0:07:48.766,0:07:51.397
I can briefly beat gravity when I jump,

0:07:52.390,0:07:55.233
but I can't pick a proton out of my hand.

0:07:56.463,0:07:59.679
The strength of gravity compared[br]to the other forces of nature?

0:08:00.480,0:08:02.670
It's 10 to the minus 39.

0:08:02.694,0:08:05.231
That's a decimal with 39 zeros after it.

0:08:05.255,0:08:06.412
Worse than that,

0:08:06.436,0:08:09.463
all of the other known forces of nature[br]are perfectly described

0:08:09.487,0:08:11.524
by this thing we call the Standard Model,

0:08:11.548,0:08:14.983
which is our current best description[br]of nature at its smallest scales,

0:08:15.007,0:08:16.163
and quite frankly,

0:08:16.187,0:08:20.364
one of the most successful[br]achievements of humankind --

0:08:20.388,0:08:24.400
except for gravity, which is absent[br]from the Standard Model.

0:08:24.424,0:08:25.574
It's crazy.

0:08:26.046,0:08:29.146
It's almost as though most[br]of gravity has gone missing.

0:08:30.394,0:08:32.061
We feel a little bit of it,

0:08:32.085,0:08:33.761
but where's the rest of it?

0:08:33.785,0:08:35.067
No one knows.

0:08:36.003,0:08:40.406
But one theoretical explanation[br]proposes a wild solution.

0:08:42.120,0:08:43.459
You and I --

0:08:43.483,0:08:45.061
even you in the back --

0:08:45.085,0:08:47.230
we live in three dimensions of space.

0:08:47.254,0:08:49.811
I hope that's a[br]non-controversial statement.

0:08:49.835,0:08:51.664
(Laughter)

0:08:51.688,0:08:55.126
All of the known particles also live[br]in three dimensions of space.

0:08:55.150,0:08:57.340
In fact, a particle is just another name

0:08:57.364,0:09:00.373
for an excitation[br]in a three-dimensional field;

0:09:00.397,0:09:02.317
a localized wobbling in space.

0:09:03.288,0:09:06.817
More importantly, all the math[br]that we use to describe all this stuff

0:09:06.841,0:09:09.914
assumes that there are only[br]three dimensions of space.

0:09:09.938,0:09:13.319
But math is math, and we can play[br]around with our math however we want.

0:09:13.343,0:09:16.509
And people have been playing around[br]with extra dimensions of space

0:09:16.533,0:09:17.688
for a very long time,

0:09:17.712,0:09:20.297
but it's always been an abstract[br]mathematical concept.

0:09:20.321,0:09:23.493
I mean, just look around you --[br]you at the back, look around --

0:09:23.517,0:09:25.798
there's clearly only[br]three dimensions of space.

0:09:26.954,0:09:28.513
But what if that's not true?

0:09:30.109,0:09:36.364
What if the missing gravity is leaking[br]into an extra-spatial dimension

0:09:36.388,0:09:38.344
that's invisible to you and I?

0:09:39.355,0:09:42.449
What if gravity is just as strong[br]as the other forces

0:09:42.473,0:09:45.614
if you were to view it in this[br]extra-spatial dimension,

0:09:45.638,0:09:48.538
and what you and I experience[br]is a tiny slice of gravity

0:09:48.562,0:09:50.459
make it seem very weak?

0:09:52.158,0:09:53.333
If this were true,

0:09:53.357,0:09:56.105
we would have to expand[br]our Standard Model of particles

0:09:56.129,0:10:00.215
to include an extra particle,[br]a hyperdimensional particle of gravity,

0:10:00.239,0:10:03.234
a special graviton that lives[br]in extra-spatial dimensions.

0:10:03.258,0:10:04.723
I see the looks on your faces.

0:10:04.747,0:10:06.566
You should be asking me the question,

0:10:06.590,0:10:10.234
"How in the world are we going to test[br]this crazy, science fiction idea,

0:10:10.258,0:10:12.749
stuck as we are in three dimensions?"

0:10:12.773,0:10:14.055
The way we always do,

0:10:14.079,0:10:16.218
by slamming together two protons --

0:10:16.242,0:10:17.394
(Laughter)

0:10:17.418,0:10:19.982
Hard enough that[br]the collision reverberates

0:10:20.006,0:10:22.697
into any extra-spatial dimensions[br]that might be there,

0:10:22.721,0:10:25.320
momentarily creating[br]this hyperdimensional graviton

0:10:25.344,0:10:29.724
that then snaps back[br]into the three dimensions of the LHC

0:10:29.748,0:10:31.570
and spits off two photons,

0:10:32.278,0:10:33.616
two particles of light.

0:10:35.417,0:10:38.327
And this hypothetical,[br]extra-dimensional graviton

0:10:38.351,0:10:42.058
is one of the only possible,[br]hypothetical new particles

0:10:42.082,0:10:44.217
that has the special quantum properties

0:10:44.241,0:10:48.477
that could give birth to our little,[br]two-photon bump.

0:10:50.000,0:10:55.820
So, the possibility of explaining[br]the mysteries of gravity

0:10:55.844,0:10:59.342
and of discovering extra[br]dimensions of space --

0:10:59.366,0:11:00.958
perhaps now you get a sense

0:11:00.982,0:11:05.106
as to why thousands of physics geeks[br]collectively lost their cool

0:11:05.130,0:11:07.012
over our little, two-photon bump.

0:11:07.036,0:11:09.936
A discovery of this type[br]would rewrite the textbooks.

0:11:10.739,0:11:11.891
But remember,

0:11:11.915,0:11:13.639
the message from us experimentalists

0:11:13.663,0:11:15.902
that actually were doing[br]this work at the time,

0:11:15.926,0:11:17.080
was very clear:

0:11:17.104,0:11:18.278
we need more data.

0:11:18.302,0:11:19.821
With more data,

0:11:19.845,0:11:23.869
the little bump will either turn into[br]a nice, crisp Nobel Prize --

0:11:23.893,0:11:25.653
(Laughter)

0:11:25.677,0:11:28.641
Or the extra data will fill in[br]the space around the bump

0:11:28.665,0:11:30.531
and turn it into a nice, smooth line.

0:11:31.515,0:11:32.733
So we took more data,

0:11:32.757,0:11:35.334
and with five times the data,[br]several months later,

0:11:35.358,0:11:37.048
our little bump

0:11:37.072,0:11:39.420
turned into a smooth line.

0:11:43.217,0:11:46.701
The news reported on a "huge[br]disappointment," on "faded hopes,"

0:11:46.725,0:11:49.235
and on particle physicists "being sad."

0:11:49.259,0:11:51.070
Given the tone of the coverage,

0:11:51.094,0:11:54.582
you'd think that we had decided[br]to shut down the LHC and go home.

0:11:54.606,0:11:55.756
(Laughter)

0:11:56.628,0:11:58.231
But that's not what we did.

0:12:01.057,0:12:03.071
But why not?

0:12:04.475,0:12:07.320
I mean, if I didn't discover[br]a particle -- and I didn't --

0:12:08.209,0:12:11.238
if I didn't discover a particle,[br]why am I here talking to you?

0:12:11.262,0:12:13.699
Why didn't I just hang my head in shame

0:12:13.723,0:12:14.947
and go home?

0:12:19.169,0:12:22.520
Particle physicists are explorers.

0:12:23.421,0:12:26.373
And very much of what we do[br]is cartography.

0:12:27.468,0:12:30.320
Let me put it this way: forget[br]about the LHC for a second.

0:12:30.344,0:12:33.726
Imagine you are a space explorer[br]arriving at a distant planet,

0:12:33.750,0:12:35.075
searching for aliens.

0:12:35.099,0:12:36.621
What is your first task?

0:12:37.931,0:12:41.007
To immediately orbit the planet,[br]land, take a quick look around

0:12:41.031,0:12:42.917
for any big, obvious signs of life,

0:12:42.941,0:12:44.760
and report back to home base.

0:12:44.784,0:12:46.408
That's the stage we're at now.

0:12:47.269,0:12:48.756
We took a first look at the LHC

0:12:48.780,0:12:51.064
for any new, big,[br]obvious-to-spot particles,

0:12:51.088,0:12:53.038
and we can report that there are none.

0:12:53.631,0:12:56.304
We saw a weird-looking alien bump[br]on a distant mountain,

0:12:56.328,0:12:58.498
but once we got closer,[br]we saw it was a rock.

0:12:58.816,0:13:01.456
But then what do we do?[br]Do we just give up and fly away?

0:13:01.480,0:13:02.767
Absolutely not;

0:13:02.791,0:13:05.096
we would be terrible scientists if we did.

0:13:05.120,0:13:08.733
No, we spend the next couple[br]of decades exploring,

0:13:08.757,0:13:10.237
mapping out the territory,

0:13:10.261,0:13:12.626
sifting through the sand[br]with a fine instrument,

0:13:12.650,0:13:14.108
peeking under every stone,

0:13:14.132,0:13:15.686
drilling under the surface.

0:13:16.106,0:13:18.699
New particles can either[br]show up immediately

0:13:18.723,0:13:20.856
as big, obvious-to-spot bumps,

0:13:20.880,0:13:24.821
or they can only reveal themselves[br]after years of data taking.

0:13:26.103,0:13:30.513
Humanity has just begun its exploration[br]at the LHC at this big high energy,

0:13:30.537,0:13:32.328
and we have much searching to do.

0:13:32.352,0:13:38.177
But what if, even after 10 or 20 years,[br]we still find no new particles?

0:13:39.053,0:13:40.748
We build a bigger machine.

0:13:40.772,0:13:42.346
(Laughter)

0:13:42.370,0:13:44.060
We search at higher energies.

0:13:44.476,0:13:46.046
We search at higher energies.

0:13:46.946,0:13:49.999
Planning is already underway[br]for a 100-kilometer tunnel

0:13:50.612,0:13:53.588
that will collide particles[br]at 10 times the energy of the LHC.

0:13:53.612,0:13:55.949
We don't decide where[br]nature places new particles.

0:13:56.366,0:13:58.012
We only decide to keep exploring.

0:13:58.036,0:14:00.594
But what if, even after[br]a 100-kilometer tunnel

0:14:00.618,0:14:02.478
or a 500-kilometer tunnel

0:14:02.502,0:14:05.343
or a 10,000-kilometer[br]collider floating in space

0:14:05.367,0:14:06.945
between the Earth and the Moon,

0:14:06.969,0:14:10.031
we still find no new particles?

0:14:11.597,0:14:14.291
Then perhaps we're doing[br]particle physics wrong.

0:14:14.315,0:14:16.106
(Laughter)

0:14:16.130,0:14:18.087
Perhaps we need to rethink things.

0:14:19.127,0:14:22.389
Maybe we need more resources,[br]technology, expertise

0:14:22.413,0:14:23.921
than what we currently have.

0:14:24.610,0:14:27.951
We already use artificial intelligence[br]and machine learning techniques

0:14:27.975,0:14:29.128
in parts of the LHC,

0:14:29.152,0:14:31.558
but imagine designing[br]a particle physics experiment

0:14:31.582,0:14:33.251
using such sophisticated algorithms

0:14:33.275,0:14:36.443
that it could teach itself to discover[br]a hyperdimensional graviton.

0:14:36.467,0:14:37.624
But what if?

0:14:37.648,0:14:39.093
What if the ultimate question:

0:14:39.117,0:14:42.590
What if even artificial intelligence[br]can't help us answer our questions?

0:14:42.614,0:14:44.725
What if these open questions,[br]for centuries,

0:14:44.749,0:14:47.418
are destined to be unanswered[br]for the foreseeable future?

0:14:47.442,0:14:50.371
What if the stuff that's bothered me[br]since I was a little kid

0:14:50.395,0:14:52.918
is destined to be unanswered[br]in my lifetime?

0:14:54.395,0:14:55.551
Then that ...

0:14:56.282,0:14:58.376
will be even more fascinating.

0:15:00.144,0:15:03.369
We will be forced to think[br]in completely new ways.

0:15:04.361,0:15:06.419
We'll have to go back to our assumptions,

0:15:06.443,0:15:08.782
and determine if there was[br]a flaw somewhere.

0:15:09.401,0:15:12.796
And we'll need to encourage more people[br]to join us in studying science

0:15:12.820,0:15:15.882
since we need fresh eyes[br]on these century-old problems.

0:15:15.906,0:15:19.040
I don't have the answers,[br]and I'm still searching for them.

0:15:19.064,0:15:21.393
But someone -- maybe[br]she's in school right now,

0:15:21.417,0:15:23.101
maybe she's not even born yet --

0:15:23.783,0:15:26.916
could eventually guide us to see physics[br]in a completely new way,

0:15:26.940,0:15:31.208
and to point out that perhaps[br]we're just asking the wrong questions.

0:15:32.112,0:15:34.522
Which would not be the end of physics,

0:15:34.546,0:15:35.952
but a novel beginning.

0:15:37.204,0:15:38.354
Thank you.

0:15:38.378,0:15:40.919
(Applause)