If you wanna make an omelet you gotta break
a few eggs. And by omelet I mean a theory of everything,
and by eggs I mean a billion billion subatomic particles obliterated in the next generation
of giant particle colliders. In June, the consortium of Europe’s top
particle physicists published their vision for the next several years of particle physics
experiments in the EU. A big part of that is the Future Circular
Collider, which, if it happens, will accelerate particles in a 100 kilometer circumference
underground ring encircling Geneva. It’ll be nearly 4 times the size of the
Large Hadron Collider, and it would be capable of colliding particle beams with 8 times the
current LHC energy. The hope is that this will open the window
to brand new physics - and perhaps break the current deadlock in our quest for a theory
of everything. But do the FCC or other upcoming collider
experiments really have a chance of succeeding? Today we’re going to discuss the incredibly
ambitious plans for future colliders, and try to honestly evaluate their prospects. But first, to get some perspective, we need
to take a step back and talk about how collider technology got to where it is today. Physicists have been building machines to
accelerate and subsequently obliterate particles since the 1920s. The first was the linear accelerator, or linac,
which uses oscillating electric fields to accelerate charged particles in a straight
line, while the beam is focused by magnetic fields. The cyclotron quickly followed - here the
particles are still accelerated by electric fields, but now a constant magnetic field
causes the beam to spiral outwards from its central source. Once accelerated, the particles were typically
slammed into a motionless target - often just a slab of metal. Some particles would collide with enough energy
to be destroyed, and their energy would be released in the form of new particles. In those first collision experiments, all
sorts of never-before-seen particles were observed allowing physicists to begin to map
out the subatomic realm. There’s a serious limit to the energy you
can muster by colliding particles into a stationary object. To be precise, collision energy with a fixed
target goes up with the square root of accelerator energy. Which means you’re wasting lots of energy. On the other hand, if you can collide two
beams moving in opposite directions WITH each other then you get the full oomph of the impact
- twice the energy in the individual beams. The key to doing this is to store the particle
beams in a ring so that they can be collided at your leisure. To that end, the particle storage ring was
invented by Gerard K. O’Neill in the mid 1950s. Within a few years, an Italian group built
the first particle beam collider - the AdA, or Anello di Accumuliazione. Apologies for my pronunciation. Its four meter ring collided electrons and
positrons. The Soviets quickly followed with their VEP-1,
which was smaller but collided electrons with one another to get a thousand times higher
luminosity than AdA. In collider-speak, luminosity is a measure
of the number of particle collisions across an area over a time period. More collisions means more chance of producing
weird particles. The Americans soon followed up with a 12 meter
electron-electron collider with a similar luminosity to VEP-1 but higher energies than
even the AdA. Finally we’d reached collision energies
needed to test predictions of the still relatively new quantum electrodynamics. This was huge in solidifying our understanding
of the quantum world. Graduating from electrons and positrons, in
1971 physicists started smashing protons together at CERN’s Intersecting Storage Rings facility. CERN does have a habit of extremely literal
naming. Since then, colliders have only grown in size
and energy. The Tevatron at Fermilab in Illinois was for
a while the largest collider at 6.3km around, operating from 1983 to 2011. It generated collisions energetic enough to
produce the very massive top quark, and so enabled the discovery of the final Fermion
- or matter particle - in the standard model. This entire effort reached its pinnacle with
the Large Hadron Collider at CERN in Switzerland. It propels twin proton beams in opposite di
rections around a 26.? km circumference ring beneath the Swiss and
French countrysides. The beams cross in four locations, where they
collide with energies of several terra-electron volts. Which is, for reference, a lot of energy. And the crowning achievement of the LHC was
the discovery of the Higgs boson in 2012. The existence of the Higgs confirms our explanation
of how the elementary particles acquire mass - which of course we’ve covered previously. In a sense this was the last missing piece
of the standard model - the one remaining particle that physicists thought MUST exist. LHC particle hunters expected that to be just
the beginning - that their giant collider would go on to discover many new particles
to take us beyond the standard model. The most highly anticipated were the particles
predicted by supersymmetry - or SUSY. This is an extension to the standard model
designed to solve several of its outstanding problems. Most notably the hierarchy problem - the fact
that there’s a huge difference between the strength of gravity and the other forces,
and a huge difference between the measured masses of the known particles and what we
expect their masses to be from quantum field theory calculations. The Higgs particle in particular should have
an enormous mass if our Standard Model understanding is the whole picture. The fact that the Higgs turns up at a “mere”
100 times the mass of the proton seemed to indicate that something beyond the standard
model was needed. SUSY solves the hierarchy problem by proposing
symmetric counterparts to the known particles. Among other things, those counterparts should
help cancel out the interactions of the known particles with the elementary quantum fields
on which those particles live, eliminating most of their mass in the process. But the supersymmetric counterparts do their
jobs most neatly if they have masses-slash-energies in a particular range: between 100 and 1000
GeV. The Large Hadron Collider reaches energy a
few times higher than the top of that range, so it should have seen such particles by now. But after a decade of searches at the LHC,
there’s still no sign of SUSY. So we find ourselves at an impasse. The Standard Model is complete, but there
is no compelling hint of the next direction to take. So what next? Well it’s clear that the Standard Model
is not the whole picture. Besides the hierarchy problem, the standard
model also doesn’t explain why neutrinos have mass. It doesn’t seem to give us a particle that
could explain dark matter. And there are other anomalies like the muon’s
magnetic moment. In general, to get closer to a theory that
unifies our understanding of the Standard Model’s motley zoo of particles and forces,
we probably need to achieve higher energies - energies even closer to the instant of the
Big Bang, when the forces of nature were literally unified, as we’ve talked about before. There are other clever ways to probe these
energies - for example using natural particle accelerators like the sun or supernovae or
quasars or galactic magnetic fields, which continuously spray the earth with particles
at higher energies than we can hope to replicate. But these ultra-high energy cosmic rays are rare, and to reliably detect a new particle we need to watch the result of billions of billions
of collisions - we need very high luminosities. Bigger and better colliders may be our best
shot. Let’s start with better before we move to
bigger. The LHC is currently in a long upgrade process,
with the final result being a factor of a couple increase in power - but more importantly
a factor of 5 increase in luminosity. This will be achieved by upgrading the existing
components with more cutting edge versions - for example better superconducting magnets
for more precise control of more energetic beams. We’ve been in the first off-line phase since
2018, with operations set to resume in 2021, and there’ll be another 2-year shutdown before
the new high-luminosity LHC comes online in 2027. The point of this upgrade isn’t primarily
to access higher energies where new particles might exist, but rather to make the LHC much
better at studying the current range. IF either SUSY or other very high-mass particles
do exist, then they may be actually a good way beyond the energy range of the LHC. And so for that we need a bigger collider. And so we come to the Future Circular Collider. If it goes ahead, it’ll hit energies of
100 TeV - 8 times the current LHC energy. Eventually the FCC will be smashing protons
like the LHC does, but to start with it’ll collide electrons and positrons with the express
intention of making as many Higgs particles as possible. Okay firstly, why electrons and positrons? Well remember that the first particle colliders worked with electron-positron beams, and for good reason: they are easier to work with
compared to protons. It’s easier to achieve the energies and
luminosities to produce, for example, large numbers of Higgs particles in relatively clean collisions. But why build a Higgs factory? Haven’t we already discovered the Higgs? Discovered, yes, but there’s still a lot
we don’t know. For example, at our current energies, we don’t
know how often it interacts with the superheavy top quark, a process that might contain hints
about new physics. The Higgs can also be used as a direct search
for new particles. The FCC will eventually graduate to proton-proton
collisions which will open up the discovery space further. The Future Circular Collider will cost 10s
of billions over its life. So is this a good investment? It’ll certainly tell us more about the Higgs,
and it may discover that elusive clue to take us beyond the standard model. However there’s no guarantee that any new
particles exist in the expanded energy range that the FCC will probe. That said, you can’t know if you don’t
look. The Future Circular Collider is the priority
defined by the European Strategy Group. But what about the US? Ever since Europe won the giant collider game
with the LHC, particle physicists in the US have focused on smaller experiments. FermiLab’s Tevatron was for a while the
largest collider in the world, but it was shut down in 2011 because it couldn’t compete
with the LHC. Since then the Chicago facility has reinvented
itself as leaders in, among other things, neutrino experiments - and when we visited
FermiLab earlier this year we saw the linear particle accelerator that is under development
to become DUNE’s neutrino source. But the next big-ish US collider will most
likely be the Electron-Ion Collider. It won’t be anywhere near the size of even
the LHC, but will have a more focused mission. It will smack electrons into protons and other
nucleons to probe the details structure and interactions between quarks. The EIC is the priority program endorsed by
the National Academy of Sciences, and while it doesn’t quite have final approval yet, if it
does happen it’ll be at Brookhaven National Labs on Long Island, starting in around 10
years. It’ll be an order of magnitude cheaper than
the Future Circular Collider at an estimated 1.6 to 2.6 billion. But that’s still a chunk of change. So is it worth it to do this sort of fundamental
science, even though the immediate returns to the nation and world are vague? Well, putting aside the fact that our modern
world is built on the technologies that came from this sort of fundamental physics research,
I want to leave you with a quote by Fermilab’s first director, Robert Wilson, when questioned
by the Senate regarding the value of the Tevatron to the US - and in particular whether it helped
compete against the Russians: He said, “Only from a long-range point of view, of a developing technology. Otherwise, it has to do with: Are we good
painters, good sculptors, great poets? I mean all the things that we really venerate
and honor in our country and are patriotic about. In that sense, this new knowledge has all
to do with honor and country but it has nothing to do directly with defending our country
except to make it worth defending.” Dr. Wilson was addressing the US Senate, so
spoke of the nation - but the larger value of this sort of work is to elevate humanity. Whether it happens now or later - I for one
am patriotic about being part of a species capable of doing something like this. Of coordinating thousands of scientists over
many decades to build these crazy machines that can crack open the inner workings of
spacetime. Hey, so as you know - filming a youtube show
in space takes a lot of resources, and I just want to thank all our Patreon supporters for
making it so much more doable. Without you we’d probably have to film in,
like, low-earth orbit rather than deep space. Gross. And today a special thankyou to Alec S-L,
who’s supporting us at the quasar level. Alec, for complete transparency - we’re
using your contribution to purchase something like 10^30 protons to inject into the future
circular collider - assuming it actually gets built. We're currently piling them up as tanks of
hydrogen in Switzerland with a postit notes with your name. If any of those particular protons happens
to produce a previously undiscovered particle in the collider, we’ll be naming it the Alec S-L-ino. Hey, it’s a bit of a long shot, but you
deserve the chance at glory. Thank you for your help. Last time we talked about the most
destructive, parasitic, and generally unhealthy relationships between the stars - from novae
to black widow binaries. Let's get to your questions Jason Carter asks a tricky one: when two black
holes merge and share a single, warped event horizon, shouldn’t there be a thin sliver
of space in between that is not flowing towards either singularity? Actually not so much. The key point is that space doesn’t have
to flow directly towards the singularity. Think of the case of the rotating black hole
- the singularity is a ring, and relatively few geodesics - free-falling paths - hit the
singularity. Most pass through the ring. In the case of the merging black holes, you
can think of space as more flowing towards the center of mass - although it’s not quite
that simple. Numerical general relativity calculations
reveal an event horizon cross-section that’s called the pair-of-pants function - it looks
like cross-sections of a pair of pants moving upwards. They start separate, and the event horizons
move towards each other as they join, and at some point the event horizons touch and
then merge. At the instant after that touch what’s happening
at the seam? The flow of space anywhere on the event horizon
has to be exactly perpendicular to the face of the event horizon - so at the seam the
flow of space is straight down. In principle there should be a point right
at the center where there is no flow - if you were a point-like particle you could just
hang there. But everywhere else - including above and below that point the space is still flowing inwards. David Kosa asks how would we describe the
interaction of two merging stars of equal mass whose combined mass exceeds the Chandrashekar
limit? For those who don't know - the Chandrashekar
limit is 1.4 times the mass of the sun - it’s the maximum mass of a white dwarf before crushing
gravitational pressure causes electrons to be pounded into protons to form neutrons,
causing the thing to collapse into a neutron star. That happens in the cores of massive stars
when they die. But what about white dwarfs that gain
more mass after they form? Or that collide to have above that mass? Well, the limit still applies, but typically you
don’t get a neutron star. In order to get a neutron star, you need a
very symmetrical, clean application of pressure. If the white dwarf exceeds the limit by cannibalizing
a companion star, and also presumably if it collides with another star, then the process
is very assymetric and messy. Instead you’re most likely to just get an explosion as thermonuclear fusion rips through the white dwarfs carbon and oxygen
interior. That gives you a supernova and leaves nothing behind but a pretty cloud of gas Leandro asks how we manage to get such good
sound quality out here in space. Well space isn’t really empty - there’s
an average density of one atom per cubic meter, so technically sound is possible. Really it’s about engaging your diaphram
and projecting. Vocativecase say’s they will miss Bahar’s
painting. I miss it already - but with the power of
modern green screen technology - I mean, replicator technology out here in SPACE, why should we
deprive ourselves? *snaps fingers* .. nice
But until we can prove close to Planck levels of energy and size.... Isn't everything ripe for breaking?
I don't think it's worth the huge cost. It would be better to wait another 10 years and let other technology, such as magnets, improve. Given the cost, this will probably be the last particle accelerator built for decades. So its better to wait an extra 10+ years, let other technologies advance and get more out of this one.
Use the money for other physics experiments, ones that don't cost $20,000,000,000
When those who are directly impacted by particle accelerators seem dodgy about the benefits of a new 100km accelerator, that's not a good sign it's going to get built. Sounds like the Texas Supercollider all over again.