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Gian Giudice: Why our universe might exist on a knife-edge

May 3, 2013

The biggest surprise of discovering the Higgs boson? That there were no surprises. Gian Giudice talks us through a problem in theoretical physics: what if the Higgs field exists in an ultra-dense state that could mean the collapse of all atomic matter? With wit and charm, Giudice outlines a grim fate -- and why we shouldn't start worrying just yet.

Gian Giudice - Theoretical physicist
Gian Giudice is a theoretical physicist who has contributed greatly to our present understanding of particle physics and cosmology. Full bio

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So last year, on the Fourth of July,
00:12
experiments at the Large Hadron Collider
00:15
discovered the Higgs boson.
00:17
It was a historical day.
00:20
There's no doubt that from now on,
00:22
the Fourth of July will be remembered
00:24
not as the day of the Declaration of Independence,
00:26
but as the day of the discovery of the Higgs boson.
00:28
Well, at least, here at CERN.
00:32
But for me, the biggest surprise of that day
00:34
was that there was no big surprise.
00:39
In the eye of a theoretical physicist,
00:41
the Higgs boson is a clever explanation
00:44
of how some elementary particles gain mass,
00:46
but it seems a fairly unsatisfactory
00:49
and incomplete solution.
00:52
Too many questions are left unanswered.
00:54
The Higgs boson does not share the beauty,
00:57
the symmetry, the elegance,
01:00
of the rest of the elementary particle world.
01:02
For this reason, the majority of theoretical physicists
01:05
believe that the Higgs boson could not
01:08
be the full story.
01:11
We were expecting new particles and new phenomena
01:14
accompanying the Higgs boson.
01:17
Instead, so far, the measurements
01:19
coming from the LHC show no signs of new particles
01:21
or unexpected phenomena.
01:25
Of course, the verdict is not definitive.
01:27
In 2015, the LHC will almost double
01:31
the energy of the colliding protons,
01:35
and these more powerful collisions
01:38
will allow us to explore further the particle world,
01:40
and we will certainly learn much more.
01:44
But for the moment, since we have found
01:47
no evidence for new phenomena, let us suppose
01:50
that the particles that we know today,
01:54
including the Higgs boson,
01:57
are the only elementary particles in nature,
01:59
even at energies much larger
02:02
than what we have explored so far.
02:05
Let's see where this hypothesis is going to lead us.
02:07
We will find a surprising and intriguing result
02:12
about our universe, and to explain my point,
02:15
let me first tell you what the Higgs is about,
02:19
and to do so, we have to go back
02:23
to one tenth of a billionth of a second
02:26
after the Big Bang.
02:31
And according to the Higgs theory,
02:32
at that instant, a dramatic event took place
02:34
in the universe.
02:38
Space-time underwent a phase transition.
02:39
It was something very similar to the phase transition
02:44
that occurs when water turns into ice
02:47
below zero degrees.
02:51
But in our case, the phase transition
02:53
is not a change in the way the molecules
02:56
are arranged inside the material,
02:58
but is about a change
03:00
of the very fabric of space-time.
03:02
During this phase transition, empty space
03:06
became filled with a substance
03:08
that we now call Higgs field.
03:11
And this substance may seem invisible to us,
03:14
but it has a physical reality.
03:16
It surrounds us all the time,
03:19
just like the air we breathe in this room.
03:21
And some elementary particles interact
03:25
with this substance, gaining energy in the process.
03:27
And this intrinsic energy is what we call
03:31
the mass of a particle,
03:34
and by discovering the Higgs boson, the LHC
03:36
has conclusively proved that this substance is real,
03:40
because it is the stuff the Higgs bosons are made of.
03:44
And this, in a nutshell, is the essence of the Higgs story.
03:48
But this story is far more interesting than that.
03:51
By studying the Higgs theory,
03:56
theoretical physicists discovered,
03:58
not through an experiment
04:01
but with the power of mathematics,
04:03
that the Higgs field does not necessarily exist
04:05
only in the form that we observe today.
04:09
Just like matter can exist as liquid or solid,
04:12
so the Higgs field, the substance that fills all space-time,
04:17
could exist in two states.
04:22
Besides the known Higgs state,
04:25
there could be a second state in which the Higgs field
04:28
is billions and billions times denser
04:31
than what we observe today,
04:34
and the mere existence of another state
04:36
of the Higgs field poses a potential problem.
04:40
This is because, according to the laws
04:44
of quantum mechanics, it is possible
04:47
to have transitions between two states,
04:50
even in the presence of an energy barrier
04:53
separating the two states,
04:56
and the phenomenon is called,
04:58
quite appropriately, quantum tunneling.
05:01
Because of quantum tunneling,
05:05
I could disappear from this room
05:07
and reappear in the next room,
05:09
practically penetrating the wall.
05:12
But don't expect me to actually perform the trick
05:16
in front of your eyes, because the probability
05:19
for me to penetrate the wall is ridiculously small.
05:21
You would have to wait a really long time
05:26
before it happens, but believe me,
05:28
quantum tunneling is a real phenomenon,
05:30
and it has been observed in many systems.
05:34
For instance, the tunnel diode,
05:37
a component used in electronics,
05:39
works thanks to the wonders
05:41
of quantum tunneling.
05:44
But let's go back to the Higgs field.
05:46
If the ultra-dense Higgs state existed,
05:49
then, because of quantum tunneling,
05:53
a bubble of this state could suddenly appear
05:55
in a certain place of the universe at a certain time,
05:59
and it is analogous to what happens when you boil water.
06:02
Bubbles of vapor form inside the water,
06:06
then they expand, turning liquid into gas.
06:09
In the same way, a bubble of the ultra-dense Higgs state
06:13
could come into existence because of quantum tunneling.
06:18
The bubble would then expand at the speed of light,
06:21
invading all space, and turning the Higgs field
06:24
from the familiar state into a new state.
06:28
Is this a problem? Yes, it's a big a problem.
06:31
We may not realize it in ordinary life,
06:35
but the intensity of the Higgs field is critical
06:38
for the structure of matter.
06:41
If the Higgs field were only a few times more intense,
06:44
we would see atoms shrinking, neutrons decaying
06:48
inside atomic nuclei, nuclei disintegrating,
06:51
and hydrogen would be
06:55
the only possible chemical element in the universe.
06:57
And the Higgs field, in the ultra-dense Higgs state,
07:01
is not just a few times more intense than today,
07:04
but billions of times,
07:08
and if space-time were filled by this Higgs state,
07:10
all atomic matter would collapse.
07:14
No molecular structures would be possible, no life.
07:17
So, I wonder, is it possible
07:21
that in the future, the Higgs field
07:25
will undergo a phase transition and,
07:27
through quantum tunneling, will be transformed
07:30
into this nasty, ultra-dense state?
07:33
In other words, I ask myself, what is the fate
07:38
of the Higgs field in our universe?
07:41
And the crucial ingredient necessary
07:44
to answer this question is the Higgs boson mass.
07:46
And experiments at the LHC found that the mass
07:51
of the Higgs boson is about 126 GeV.
07:55
This is tiny when expressed in familiar units,
07:59
because it's equal to something like
08:02
10 to the minus 22 grams,
08:04
but it is large in particle physics units,
08:06
because it is equal to the weight
08:10
of an entire molecule
08:12
of a DNA constituent.
08:14
So armed with this information from the LHC,
08:17
together with some colleagues here at CERN,
08:20
we computed the probability
08:22
that our universe could quantum tunnel
08:24
into the ultra-dense Higgs state,
08:27
and we found a very intriguing result.
08:30
Our calculations showed
08:34
that the measured value of the Higgs boson mass
08:36
is very special.
08:39
It has just the right value
08:41
to keep the universe hanging
08:44
in an unstable situation.
08:46
The Higgs field is in a wobbly configuration
08:49
that has lasted so far
08:52
but that will eventually collapse.
08:54
So according to these calculations,
08:57
we are like campers
09:00
who accidentally set their tent
09:03
at the edge of a cliff.
09:05
And eventually, the Higgs field
09:07
will undergo a phase transition
09:09
and matter will collapse into itself.
09:10
So is this how humanity is going to disappear?
09:14
I don't think so.
09:17
Our calculation shows that quantum tunneling
09:19
of the Higgs field is not likely to occur
09:22
in the next 10 to the 100 years,
09:26
and this is a very long time.
09:29
It's even longer than
09:32
the time it takes for Italy to form a stable government.
09:34
(Laughter)
09:38
Even so, we will be long gone by then.
09:40
In about five billion years,
09:44
our sun will become a red giant,
09:47
as large as the Earth's orbit,
09:49
and our Earth will be kaput,
09:52
and in a thousand billion years,
09:55
if dark energy keeps on fueling
09:57
space expansion at the present rate,
09:59
you will not even be able to see as far as your toes,
10:02
because everything around you
10:06
expands at a rate faster than the speed of light.
10:08
So it is really unlikely
10:12
that we will be around to see the Higgs field collapse.
10:14
But the reason why I am interested
10:18
in the transition of the Higgs field
10:21
is because I want to address the question,
10:23
why is the Higgs boson mass so special?
10:27
Why is it just right to keep the universe
10:32
at the edge of a phase transition?
10:35
Theoretical physicists always ask "why" questions.
10:38
More than how a phenomenon works,
10:42
theoretical physicists are always interested in
10:45
why a phenomenon works in the way it works.
10:47
We think that this these "why" questions
10:50
can give us clues
10:54
about the fundamental principles of nature.
10:55
And indeed, a possible answer to my question
10:59
opens up new universes, literally.
11:03
It has been speculated that our universe
11:07
is only a bubble in a soapy multiverse
11:11
made out of a multitude of bubbles,
11:15
and each bubble is a different universe
11:17
with different fundamental constants
11:19
and different physical laws.
11:21
And in this context, you can only talk about
11:23
the probability of finding a certain value of the Higgs mass.
11:25
Then the key to the mystery
11:30
could lie in the statistical properties
11:32
of the multiverse.
11:36
It would be something like what happens
11:38
with sand dunes on a beach.
11:40
In principle, you could imagine to find sand dunes
11:42
of any slope angle in a beach,
11:45
and yet, the slope angles of sand dunes
11:48
are typically around 30, 35 degrees.
11:52
And the reason is simple:
11:55
because wind builds up the sand, gravity makes it fall.
11:57
As a result, the vast majority of sand dunes
12:01
have slope angles around the critical value,
12:04
near to collapse.
12:08
And something similar could happen
12:10
for the Higgs boson mass in the multiverse.
12:13
In the majority of bubble universes,
12:17
the Higgs mass could be around the critical value,
12:20
near to a cosmic collapse of the Higgs field,
12:23
because of two competing effects,
12:27
just as in the case of sand.
12:29
My story does not have an end,
12:32
because we still don't know the end of the story.
12:35
This is science in progress,
12:39
and to solve the mystery, we need more data,
12:42
and hopefully, the LHC will soon add new clues
12:46
to this story.
12:51
Just one number, the Higgs boson mass,
12:53
and yet, out of this number we learn so much.
12:57
I started from a hypothesis, that the known particles
13:02
are all there is in the universe,
13:06
even beyond the domain explored so far.
13:08
From this, we discovered that the Higgs field
13:10
that permeates space-time may be standing
13:14
on a knife edge, ready for cosmic collapse,
13:17
and we discovered that this may be a hint
13:22
that our universe is only a grain of sand
13:26
in a giant beach, the multiverse.
13:30
But I don't know if my hypothesis is right.
13:33
That's how physics works: A single measurement
13:37
can put us on the road to a new understanding
13:40
of the universe
13:43
or it can send us down a blind alley.
13:45
But whichever it turns out to be,
13:48
there is one thing I'm sure of:
13:50
The journey will be full of surprises.
13:53
Thank you.
13:57
(Applause)
13:58

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Gian Giudice - Theoretical physicist
Gian Giudice is a theoretical physicist who has contributed greatly to our present understanding of particle physics and cosmology.

Why you should listen

Gian Giudice is a permanent member of CERN's group for theoretical physics. He has researched topics like supersymmetry, extra dimensions and dark matter, and has formulated theories that describe the earliest stages of the universe and that apply our knowledge of the particle world to smaller distances.

As author of the popular book, A Zeptospace Odyssey, Giudice is active in communicating the complex work of the Large Hadron Collider to the public. Meant for the lay reader, the book shares both the innovations needed to build the LHC and the theories it was created to prove. After the Higgs boson discovery, Giudice found the surprising result that, if the Standard Model continues to hold up at very small distances, the universe must be in a critical state, near to a phase transition that could lead to the collapse of all atomic matter. Luckily, in his TED Talk, he shares that this would happen very, very, very far in the future.

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