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imagine yourself at the edge of the
grand canyon in arizona
this is the epitome of natural beauty
calm serene and tranquil
it's a stunning view if you look over
the edge be careful
because a strong gust of wind or an
unintentional misstep
could blow you off the edge at any
moment having you fall
towards your doom this might be a morbid
thought but
danger can lie in many beautiful things
the universe for example
is beautiful but what if the existence
of the entire universe
was on the edge of a cliff where a
quantum fluctuation could result in
oblivion
where all life and everything we've come
to know could end in a split second
it turns out that the best current
understanding of fundamental physics
based on the standard model of particle
physics
seems to indicate exactly this
precarious situation
that our universe is actually near the
edge of a cliff in danger
of falling into the abyss at any moment
all of this is related to the higgs
boson
and the heaviest fundamental particle we
know of the top quark
to understand how we learn about this
looming threat
we need to take a deeper dive into the
quantum world and look more closely
at the list of usual suspects in this
case the central weird character of this
play
is quantum tunneling are we doomed or
not
and why that's coming up right now
to begin to understand the problem we
need to look at
energy potentials and consider a core
principle in physics
and that is that a system always wants
to minimize energy
we've discussed this before for example
it is the prime reason atoms combine to
form molecules
combinations of atoms can be more stable
by bonding together to form molecules
in physics minimizing the energy of a
system is key to understanding how
things work
just as in the case of atoms forming
molecules to lower overall energy of the
system
particles also have a propensity to
lower their potential energy
a very simple potential energy diagram
looks like a simple parabola
the y-axis is potential energy and the
x-axis represents a parameter by which
potential energy varies
such as position energy and field value
in this potential we have a minimum
or a lowest point at zero energy on the
x-axis
if we put a ball in this potential we
will find that it will fall towards the
minimum
of least potential energy this is a
classic example
of minimizing energy and since there's
only one minimum the situation is simple
and the ball will go towards this
minimum eventually coming to a rest at
the bottom
but what if there was more than one
minimum
and the diagram looked a bit more like
this
what if we had two minima where one
minimum
has a higher potential energy than the
other minimum now the situation
depends on what we do with the ball if
we place the ball very carefully
at the high energy minimum then the ball
will just be stuck there
we could also just put the ball in the
lower energy minimum
and it would also just stay there now
here's the interesting thing
if we place the ball near the high
energy minimum and it had some
additional kinetic energy
then if there was sufficient momentum
the ball could overcome the barrier
between the two minima and end up at the
lower minimum
so the ball could roll from the higher
minimum to the lower minimum
or from the higher energy state to the
lower energy state
a physical system trying to minimize
energy would always seek to fall
into its lowest possible minimum but the
key
is that in order to do this it has to
overcome
the barrier between the higher energy
and the lower energy minimum
so i hope you're with me so far the
particle either has
energy to go to the lowest minimum or it
doesn't and if it doesn't
then the particle will be stuck at the
higher energy minimum simple enough
now here's the shocker this is a
classical picture of how potential
energy works
but the world is fundamentally quantum
mechanical
not classical and it works a little bit
differently when quantum mechanics
enters the picture the heisenberg
uncertainty principle tells us
that in quantum mechanics the position
and momentum of a particle
is not something we can know exactly no
matter how hard we try
this changes the situation with our
potential because now we have to
consider
how a quantum particle would behave
instead of a classical ball
a quantum particle is not like a little
ball
it's wavy its position and momentum is
uncertain
if we look at the situation where the
particle is in the higher minimum
then because we don't know exactly the
position and momentum
we can no longer be certain whether the
particle will stay there or
overcome the barrier and drop down to
the lower minimum
because of this uncertainty the particle
is no longer
in a stable state but a meta-stable
state
where the phenomenon of quantum
tunneling could allow it to escape from
the higher minimum
to the lower minimum quantum tunneling
is a feature of the probabilistic nature
of quantum mechanics a simplistic way to
think of it is like this
in quantum mechanics a particle's
location is determined by a wave
function
defined by the schrodinger equation the
wave function squared gives us the
probability of finding this particle
at any location if we solve the equation
we will find that the probability of
finding the particle
at the lower energy state is non-zero in
other words
it has a finite probability of being
located beyond this barrier
and this probability increases if the
energy level is lower
beyond the barrier as in the example
here
it turns out that our universe could
also not be
in its lowest possible minimum meaning
that it may also be
how do we know this it all boils down to
one particle
the famous or infamous takes boson
this particle is the latest fundamental
particle having been discovered
relatively recently in only 2012.
as the matter particles that make up our
universe interact with the higgs field
they obtain mass and become massive
without the higgs
there would be no massive fundamental
particles
keep in mind though that protons and
neutrons could still be massive without
the higgs boson
because their mass comes primarily from
the binding energy
created by the quark gluon plasma i made
a video about this if you want more
details
but without the higgs electrons would
not have any mass since they are a
fundamental particle
and without massive electrons atoms
would not be stable
this is because electrons wouldn't be
able to stick to atoms or more
simplistically
be able to orbit them since massless
objects move at the speed of light
electrons in our universe do have a mass
a very small
mass but this makes all the difference
because
without this slight mass atoms would not
exist
and of course if atoms did not exist it
would be a very different universe you
and i wouldn't be around watching
youtube videos
the higgs is also special because in the
standard model it comes with a
non-trivial potential
meaning that its lowest potential is not
at the center not at zero this leads to
the higgs mechanism
which in turn gives us the heavy
mediators of the weak force
in this mechanism the higgs field falls
into a minimum
away from the origin and in this way the
field obtains a non-zero expectation
value
this expectation value is what leads to
the mass of the higgs field
and other fundamental particles also
gain mass
through their interaction with the higgs
field i showed how this works in my
video on
electro weak theory if you want more
details
the behavior of the higgs potential is
determined experimentally
by the mass of the higgs boson and the
mass
of the top fork the heaviest fundamental
particle
the current best estimates of these
masses
puts the standard model in the
meta-stable region
in other words the latest research shows
that the higgs potential
could have another much lower energy
level
put another way the higgs field is not
currently
in its lowest minimum the higgs
potential appears to be in what's called
a false vacuum state
a true vacuum state is the lowest energy
and most stable state
it's like the valley at the bottom of a
mountain but a false vacuum is like a
divot on the wall of the mountain
if you're on the divot it can feel
stable because you're not
rolling towards the valley below but a
misstep can cause you to fall to the
valley below you
this false sense of stability is
analogous to the metastable state of the
universe
so why aren't we falling to the valley
there has to be some energy barrier
preventing us from doing so
but there are two big problems with
living in such a metastable universe
one is that if you create a high enough
energy event you can in theory overcome
the barrier
and push a tiny region of the universe
from the false vacuum to the true vacuum
creating a bubble of true vacuum that
will then expand in all directions
at the speed of light causing disaster
for the universe
the other problem is that because the
universe is fundamentally quantum
mechanical
even if you don't have enough energy to
overcome the barrier
a region of space can potentially tunnel
through the energy barrier between the
false vacuum
to the true vacuum this again would be
fatal for the universe
what we see of the universe today would
be destroyed
and all life would be gone if this were
to happen
what would we experience what would we
see
simulations show that the transition
would happen initially locally in a
small volume
nucleating a small bubble of the vacuum
in space
the bubble would then start to expand
reaching the speed of light very quickly
destroying everything in its way
the scary part is that we would not see
it coming because it would be
propagating at the speed of light
so any light from this nucleating region
would reach us
at the speed of light in other words we
would be incinerated at the very moment
we saw it
so why isn't everyone panicking there is
good reason to believe
that our physics is incomplete and there
is some new physics
that would save the universe why well
first of all close to the moment of the
big bang there probably was high enough
energy
to push our universe into the true
vacuum but we're still here
this suggests that either the energies
of the big bang were too low
or perhaps the universe is more stable
than our calculations show
the other reason not to panic is that
the metastable universe
likely has a very long lifespan in fact
in a 2018 paper published in the journal
physical review researchers calculated
that the lifespan of our metastable
universe is anywhere from 10 to the 88
to 10 to the 241 years this is compared
to roughly 10 to the 10
years that the universe has been around
already so
this is many many many orders of
magnitude longer
than the current age of the universe
however the same authors also suggest
that there's a chance
the universe has collapsed already in a
distant corner of the universe right now
and the death bubble is already speeding
in our direction
this is also a possibility but the good
news is
if you want to look at it that way is
we'll never see it coming
and it will be a quick and easy death at
the speed of light
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i'll see you in the next video my friend
[Music]
you