The shift in U.S. support for Ukraine in its
war with Russia, which enters its fourth year on Monday, has raised
alarms in Kyiv and in capitals across Europe. A new documentary finds
that those anxieties are especially high in some of Russia’s neighbors
on the Baltic Sea. John Yang speaks with NBC News producer Joel Seidman
and correspondent Kevin Tibbles for more about their film.
Notice: Transcripts are machine and human generated and lightly edited for accuracy. They may contain errors.
John Yang:
The shift in U.S. support for Ukraine and its war with
Russia, which enters its fourth year tomorrow, has raised alarms not
only in Kyiv but in capitals across Europe. A new documentary finds that
those anxieties are especially high in some of Russia's neighbors on
the Baltic Sea, Estonia, Finland and Sweden.
Man:
Every day we are working to get this message over to Russia that even if you try, we will make you pay.
Man:
Russia invaded one of their neighbors, so it was quite an
awakening for the whole Swedish society and of course, the Swedish
armed forces.
Man:
Yeah, at least in this part of the world, we would be ready to fight tomorrow.
John Yang:
The film is called "Putin's Endgame: The Stakes Beyond
Ukraine." It was produced in partnership with the Atlantic Council's
Eurasia Center. It's the work of two veterans of NBC News producer Joel
Seidman and correspondent Kevin Tibbles.
Kevin, I'd like to start
with you. In the film, we see you going traveling through these
countries, asking a lot of people the same question. What if Putin wins
in Ukraine? I want to play a little bit of you talking to two young men
about this in Estonia.
Man:
What happens to Estonia if Putin wins Ukraine?
Man:
We never thought about it, actually.
Man:
Why?
Man:
I don't know.
Man:
It's terrifying to think about this.
Man:
Yes. And the part of our brain is just blocking —
Man:
This scary thought about.
Man:
Yeah, because we don't know what this guy wants and what consequences this will bring.
John Yang:
How strong and how pervasive were those sentiments in what you found?
Kevin
Tibbles, Correspondent, "Putin's Endgame: The Stakes Beyond Ukraine":
They were very strong, very pervasive. You know what's interesting about
that is that those two young men, we're in the town of Narva, which is
just across the river, Narva river from Russia. Putin has already said
that he wants to retake Narva.
But what is also interesting here
is the fact that the Soviet Union took Estonia, Lithuania, Latvia, the
Baltic nations during the Second World War. They either murdered anyone
who was in any position, or they deported people to Siberia to perhaps
die in labor camps working for the Soviets.
So the memories of
that history are very strong. But you can also tell on the faces of
those two young boys that they're scared to death. They're scared to
death.
The question that I asked them, to be honest with you,
John, because they don't know what's going to happen, but what they do
know is that Putin is right across that river.
John Yang:
And they feel that Ukraine is fighting their war, preventing a future war with them. Is that right?
Kevin Tibbles:
Well, absolutely. And as a matter of fact, the Estonian
foreign minister said to us, listen, Ukraine is fighting our war for us.
We need to give them as much support as possible. And he's talking
about bringing up levels of GDP to support NATO. Of course, Article 5
says that if any member of NATO is attacked, everyone jumps in to assist
in that.
As we heard from one of the Estonian officials, they are
hoping that NATO is going to save the day. Well, of course, John, all
we're hearing now is that the whole question of Article 5 is now in
doubt because of what officials on this side of the Atlantic are saying.
John Yang:
Joel, I've heard this described as a passion project for you. What made you want to do this?
Joel
Seidman, Director, "Putin Endgame: The Stakes Beyond Ukraine": I've
been doing lots of films with Kevin over the years about the NATO
alliance, about Russia's aggression toward NATO. There are ships, many
of them with foreign flags, that have been dragging their anchors and
severing very important cables between the Baltic nations.
And
that is what is called a hybrid war, that Russia has been testing the
alliance to see what to do. So we thought this is a good time to take
the temperature of the two newest NATO members, Sweden and Finland, and
also the NATO member that has its most eastern border with Russia, and
that's Estonia.
John Yang:
Hybrid warfare sounds high tech, but this isn't cyber-attacks. This isn't hacking. This is sabotage.
Joel Seidman:
Yes. And it's very difficult to point the finger onto
exactly who is behind it. And that's the beauty of hybrid warfare. The
officials that we spoke to and also the people in Helsinki that are
actually looking at this as institute, say these ships are basically
dragging their anchors, and they could drag their anchors up to 100
kilometers.
So therefore, that's not just an accident. They're
causing havoc, and they're breaking a lot of very important
communications lines.
John Yang:
Kevin, you mentioned NATO, and Joel just talked about
NATO. Is there a sense of what frightens people in this region more?
President Trump sort of pivot away from Ukraine or his talk about
perhaps leaving NATO?
Kevin Tibbles:
Well, I think they're both part and parcel of the same
thing. And the word that I would use is fear. What Joel was talking
about in terms of hybrid warfare, you know, it goes way beyond the
shipping. For example, the Estonians say that the Russians are jamming
their GPS signals and that sometimes planes can't land at their
airports.
It all seems to be a pattern of trying to destabilize
societies. We saw that in Ukraine prior to the invasion of Ukraine. In
the end, the Estonian foreign minister said to us that this is Donald
Trump's Churchill moment. Does Donald Trump want to be seen as someone
who perhaps stopped the Third World War, stop the invasion of the other
side?
If Vladimir Putin is really trying to recreate some imperial
slash Soviet style Russia, I mean, these people in the Baltic nations
know exactly what that's like because it's their relatives who were sent
to Siberian labor camps. So they are looking to the United States. And
the events of this past week, I think, have probably scared the living
daylights out of them.
John Yang:
Joel, what do you hope people will take away from this?
Joel Seidman:
I think that certainly our audience is the American
people. And I think this is an area of the world that's a little bit
alien to them. So we want to give them the opportunity to see what
normal citizens, border guards, heads of state, foreign ministers, think
about this region and understand that they are under threat and that
they do believe that they could be next.
John Yang:
Quickly, where can people see this?
Joel Seidman:
Certainly they could see it on the Atlantic Council's
YouTube channel. It is right there at the very top. And we encourage
Americans to take a peek.
John Yang:
Joel Seidman, Kevin Tibbles, thank you both very much.
Finland has confirmed that Russia is expanding its military presence
along Finland’s border, prompting the NATO ally to monitor the Russian
military’s movements and “prepare for the worst.”
According to
The Guardian, Maj. Gen. Sami Nurmi, who serves as the head of strategy
for the Finnish Defence Forces, recently warned that the Finnish
military is watching Russia’s movements “very closely” and noted that
Finland has to “prepare for the worst” as part of the country’s
responsibility to NATO.
The Guardian cited satellite images obtained by
The New York Times that allegedly show Russia’s expansion of military
infrastructure near the border of Finland. According to The Guardian,
the pictures show additional rows of Russian tents, military vehicles,
fighter jet shelter renovations, and construction on a helicopter base.
A picture of Russia’s expanded military forces near its border with Finland was shared Monday by Roman Sheremeta on X, formerly Twitter.
It looks like that Putin is preparing for war with NATO.
Russia
is building up military forces near the border with Finland –
constructing bases, bunkers, training grounds, and other military
infrastructure in the area.
— Roman Sheremeta đșđžđșđŠ (@rshereme) May 19, 2025
According to The Guardian, Nurmi addressed the recent reports of
Russia’s military expansion along the border of Finland, saying, “They
are changing structures and we are seeing moderate preparations when it
comes to building infrastructure close to our borders, meaning that they
will, once the war in Ukraine hopefully ends, start to bring back the
forces that have been fighting in Ukraine, especially land forces.”
The Guardian reported that while Russia’s expansion of military
forces on the border of Finland is not unexpected due to Finland joining
NATO in 2023 following the Russian invasion of Ukraine, Nurmi warned
that Finland is watching Russia’s movements “very closely.”
“They are doing it in phases. I would say it is still moderate
numbers. It’s not big construction, but in certain places building new
infrastructure and preparing, bringing new equipment in,” Nurmi said.
“You also have to evaluate whether they are preparing to send more
troops to Ukraine or preparing to build up their forces close to our
border. But I guess they are doing both.”
On Tuesday, President Donald Trump was asked
by reporters in the Oval Office whether he was concerned with the
reports of Russia’s “military build-up” along the borders of Finland and
Norway. In response, Trump said, “No. I don’t worry about that at all.
They’re going to be very safe. Those are two countries that are going to
be very safe.”
Reporter: “On Russia, are you worried about the reports of a military build-up along the borders towards Finland and Norway?”
Wikimedia CommonsThe HMS Terror survived oceanic warfare before she met her end on Sir John Franklin’s doomed expedition.
In 1845, seasoned naval commander Sir John Franklin set out to find the Northwest Passage aboard two ships, the HMS Terror and HMS Erebus. The Terror,
in particular, was quite an impressive ship. She was initially built as
a bomb vessel and participated in multiple skirmishes in the War of
1812.
When it came time to guide Sir Franklin on his venture north, both
ships were substantially reinforced with iron plating capable of
crushing through the Arctic ice. But despite their hardiness, both the Terror and Erebus disappeared with the crew of the Franklin expedition shortly after setting sail.
It would be another 170 years before anyone saw Erebus and Terror
again, but this time, they were at the bottom of an Arctic bay.
Historians have since attempted to piece together their final days — and
they include a grueling mixture of lead poisoning, starvation, and
cannibalization, before mysteriously becoming shipwrecked.
The Terror Embarks On The Franklin Expedition
Wikimedia CommonsBefore
embarking on the expedition that bore his name, Sir John Franklin was
knighted and selected to be the lieutenant governor of Tasmania.
In May 1845, accomplished Arctic explorer Sir John Franklin
was selected by the English Royal Navy to locate the lucrative
Northwest Passage. All the world’s major powers had long searched for
the trade route, which was a shortcut to Asia through the Arctic.
This would not be Terror‘s first Arctic expedition. She ventured to the Arctic first in 1836 and then to the Antarctic in 1843. Even before this, Terror had garnered an impressive resume. Launched in 1813, Terror
famously saw action in the War of 1812 and even participated in the
battle that inspired Francis Scott Key to write the poem that eventually
became “The Star-Spangled Banner.”
By all accounts, Terror was prepared to brave Franklin’s expedition and both she and her sister ship, Erebus,
were consequently equipped with robust, iron-layered hulls and steam
engines. These were among the most scientific equipment available at the
time.
Both ships were also stocked with three years’ worth of food.
Together they carried 134 men, though five were discharged within the
first three months of the venture. The Terror and Erebus together carried 32,000 pounds of preserved meat, 1,000 pounds of raisins, and 580 gallons of pickles.
The ships made two stops in Scotland’s Orkney Islands and then in Greenland before they set course for Arctic Canada.
The very last time anyone saw either the HMS Terror or its sister ship was in July 1845 when two whaling vessels spotted them cross from Greenland to Canada’s Baffin Island.
The next time the Terror was seen was at the bottom of an Arctic bay.
The Final Days Aboard Erebus And Terror
Wikimedia CommonsGraves of Franklin Expedition members on Beechey Island.
What happened after the HMS Terror set its course for Baffin
Island remains largely a mystery, but most researchers would agree that
both ships became trapped in the ice off King William Island on Sept.
12, 1846, and a desperate crew disembarked to find help.
According to an 1848 letter found under a cairn in Canada’s Victoria
Point in 1859, the ships had already been locked in ice for more than a
year and a half. The letter was written by a man named Francis Crozier
who had taken command of the Terror after Franklin perished.
He stated that 24 men were already dead, including Franklin, and that
all the survivors planned to walk to a remote fur-trading outpost
hundreds of miles away. None of them completed the treacherous journey.
Brian SpenceleyThis
is the coffin of John Hartnell, one of three sailors found buried on
Beechey Island. His shipmates made fake handles for his coffin out of
tape.
Meanwhile, the British Royal Navy had dispatched dozens of search parties soon after the ships disappeared, but it would be another 170 years before anyone found the Terror and its sister ship.
But in 1850, American and British search parties were stunned to find
three unmarked graves on an uninhabited bit of land named Beechey
Island. They were dated 1846.
An even bigger discovery was made four years later when Scottish
explorer John Rae met a group of Inuits in Pelly Bay who had some of the
belongings of the Franklin crew.
Brian SpenceleyThe preserved body of John Torrington, now a mummified corpse still buried in the Canadian arctic.
The Inuits explained that there were piles of human bones scattered
around the area. Many of these skeletal remains were cracked in half
which suggested that Franklin’s men likely resorted to cannibalism
before they froze to death.
Then, in the 1980s and 1990s, researchers discovered knife marks on
additional skeletal remains that were found on King William Island. This
all but confirmed that after disembarking the Terror, a starving crew murdered and dismembered their peers before eating them and extracting their bone marrow.
In 1984, anthropologist Owen Beattie exhumed one of the bodies buried
on Beechey Island and found a pristinely preserved member of the
expedition named John Torrington. According to letters from the crew, the 20-year-old died on Jan. 1, 1846, and was buried in five feet of permafrost.
Brian SpenceleyPictured
is the frozen mummy of John Hartnell who was exhumed from Beechey
Island in 1986. He was the photographer, Brian Spencely’s, maternal
great-great uncle.
Torrington was lucky, nothing in his autopsy report suggested that he
was one of the crew members to fall victim to cannibalism. His
milky-blue eyes were still open when he was found. Experts also found
that his body was kept warm after he died, likely by a crew still
capable enough to conduct a proper burial.
Torrington’s 88-pound body suggested that he was malnourished before
he died and he contained deadly levels of lead. Because of this,
researchers began to believe that the crew’s food supply had been poorly
canned and likely poisoned all 129 of Franklin’s remaining men with lead on some level.
The three corpses found on Beechey Island remain buried there to this day.
Rediscovery And Continued Research
Parks Canada, Underwater Archaeology TeamThe Parks Canada team hosted seven dives, during which they inserted remotely-operated underwater drones into the ship.
In 2014, the HMS Erebus was discovered in 36 feet of water off King William Island. Two years later, the Terror
was located in a bay 45 miles away in 80 feet of water off the coast of
King William Island in Canada’s aptly-named Terror Bay.
In 2019, Parks Canada archaeologists sent underwater drones to explore the ship — and made a startling discovery.
“The ship is amazingly intact,” said lead archaeologist Ryan Harris.
“You look at it and find it hard to believe this is a 170-year-old
shipwreck. You just don’t see this kind of thing very often.
A guided tour of the HMS Terror by Parks Canada.
Why the ships separated and then sank remains a mystery today. “There’s no obvious reason for Terror
to have sunk,” said Harris. “It wasn’t crushed by ice, and there’s no
breach in the hull. Yet it appears to have sunk swiftly and suddenly and
settled gently to the bottom. What happened?”
With the help of local Inuits, the Parks Canada team was able to conduct seven dives in 2019 to create a 3D map of the Terror.
The crew sent remote-operated drones into the ship through the main
hatchway, the crew cabin skylights, the officers’ mess hall, and the
captain’s stateroom.
“We were able to explore 20 cabins and compartments, going from room
to room,” said Harris. “The doors were all eerily wide open.”
Parks Canada, Underwater Archaeology TeamFound in the officers’ mess hall, these glass bottles have remained in pristine condition for 174 years.
The bowels of the HMS Terror appear frozen in time after
nearly two centuries in the dark depths of the Arctic archipelago.
Plates and glasses are still shelved. Beds and desks are in position.
Scientific instruments remain in their proper cases.
The team also found “blankets of sediment” on the ship and all its
contents. According to Harris, that sediment along with cold water and
darkness created “a near-perfect anaerobic environment that’s ideal for
preserving delicate organics such as textiles or paper.”
Indeed, the drones filmed countless journals, charts, and photographs that could all potentially be salvaged.
Parks CanadaCutlery, journals, and scientific instruments found inside the HMS Terror all seem to be perfectly intact after nearly two centuries underwater.
“There is a very high probability of finding clothing or documents,
some of them possibly even still legible. Rolled or folded charts in the
captain’s map cupboard, for example, could well have survived.”
As if peering into the mysterious wreck of the Terror wasn’t eerie enough, the team noticed that the only closed door on the whole ship was the captain’s room.
“I’d love to know what’s in there,” mused Harris. “One way or another, I feel confident we’ll get to the bottom of the story.”
After this look at the HMS Terror in its watery grave, check out five more intriguing shipwrecks. Then, take a look at 11 sunken ships found around the world.
A former staff writer for All That’s
Interesting, Marco Margaritoff holds dual Bachelor's degrees from Pace
University and a Master's in journalism from New York University. He has
published work at People, VICE, Complex, and serves as a staff reporter
at HuffPost.
Matt Crabtree is an assistant editor
at All That's Interesting. A writer and editor based in Salt Lake City,
Utah, Matt has a Bachelor's degree in journalism from Utah State
University and a passion for idiosyncratic news and stories that offer
unique perspectives on the world, film, politics, and more.
COPY
Cite This Article
Margaritoff, Marco. "The Eerie Story Behind The Shipwreck Of
The HMS Terror And The Expedition That Ended In Cannibalism."
AllThatsInteresting.com, August 28, 2019,
https://allthatsinteresting.com/hms-terror. Accessed May 6, 2025.
Nussaibah Younis grew up in a very
politically Islamic household in the UK. Both her parents had strong
views on what it should mean to practice the Muslim faith. Her mother
was a preacher and Nussaibah has developed the same ability to command a
room. She was giving school assemblies at the age of 11 - these turned
into persuasive speeches at Oxford university, and since then she's
convened diplomats in Washington and tribal leaders in Iraq. Along the
way Nussaibah has totally reassessed what her faith means to her.
Her job in policy took her to Iraq,
working on reconciliation projects in the wake of the Islamic State
group. There, tasked with designing a deradicalisation programme for
women who married fighters from the Islamic State group. When meeting
these IS brides, Nussaibah was surprised to find herself reflecting on
her teenage years. "It could have happened to me" she says, recounting
her admiration for a cleric who later joined al-Qaeda.
In Iraq Nussaibah developed an unlikely
coping mechanism, stand-up comedy. It eventually led her to write
Fundamentally, a satirical novel inspired by her past and now
shortlisted for the 2025 Women's Prize for Fiction. In this deeply
personal and often funny conversation, Nussaibah reflects on the
pressures of being a model Muslim woman, the terror of stepping away
from it, and the liberating power of fiction.
Presenter: Mobeen Azhar Producer: Helen Fitzhenry
Get in touch: outlook@bbc.com or WhatsApp +44 330 678 2707
(Photo: Nussaibah Younis at the Oxford Literary Festival. Credit: David Levenson/Getty Images)
Bal
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illusztrĂĄciĂłjĂĄn. Jobb oldalon: Szent LĂĄszlĂł ĂĄbrĂĄzolĂĄsa a
ThurĂłczi-krĂłnikĂĄban. IllusztrĂĄciĂł: Telex
Physicists have begun to explore the proton as if it were a
subatomic planet. Cutaway maps display newfound details of the
particle’s interior. The proton’s core features pressures more intense
than in any other known form of matter. Halfway to the surface, clashing
vortices of force push against each other. And the “planet” as a whole
is smaller than previous experiments had suggested.
The experimental investigations mark the next stage in the quest to
understand the particle that anchors every atom and makes up the bulk of
our world.
“We really see it as opening up a completely new direction that will
change our way of looking at the fundamental structure of matter,” said Latifa Elouadrhiri (opens a new tab), a physicist at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia, who is involved in the effort.
The
experiments literally shine a new light on the proton. Over decades,
researchers have meticulously mapped out the electromagnetic influence
of the positively charged particle. But in the new research, the
Jefferson Lab physicists are instead mapping the proton’s gravitational
influence — namely, the distribution of energies, pressures and shear
stresses throughout, which bend the space-time fabric in and around the
particle. The researchers do so by exploiting a peculiar way in which
pairs of photons, particles of light, can imitate a graviton, the
hypothesized particle that conveys the force of gravity. By pinging the
proton with photons, they indirectly infer how gravity would interact
with it, realizing a decades-old dream of interrogating the proton in
this alternative way.
Physicists have learned a tremendous amount about the proton over the
last 70 years by repeatedly hitting it with electrons. They know that
its electric charge extends roughly 0.8 femtometers, or quadrillionths
of a meter, from its center. They know that incoming electrons tend to
glance off one of three quarks — elementary particles with fractions of
charge — that buzz about inside it. They have also observed the deeply
strange consequence of quantum theory where, in more forceful
collisions, electrons appear to encounter a frothy sea made up of far more quarks as well as gluons, the carriers of the so-called strong force, which glues the quarks together.
All this information comes from a single setup: You fire an electron
at a proton, and the particles exchange a single photon — the carrier of
the electromagnetic force — and push each other away. This
electromagnetic interaction tells physicists how quarks, as charged
objects, tend to arrange themselves. But there is a lot more to the
proton than its electric charge.
Latifa Elouadrhiri, a senior staff scientist at
Jefferson Laboratory, led the collecting of data from which she and her
collaborators are now calculating mechanical properties of the proton.
Courtesy of Latifa Elouadrhiri
“How are matter and energy distributed?” asked Peter Schweitzer (opens a new tab), a theoretical physicist at the University of Connecticut. “We don’t know.”
Schweitzer has spent most of his career thinking about the
gravitational side of the proton. Specifically, he’s interested in a
matrix of properties of the proton called the energy-momentum tensor.
“The energy-momentum tensor knows everything there is to be known about
the particle,” he said.
In Albert Einstein’s theory of general relativity, which casts
gravitational attraction as objects following curves in space-time, the
energy-momentum tensor tells space-time how to bend. It describes, for
instance, the arrangement of energy (or, equivalently, mass) — the
source of the lion’s share of space-time twisting. It also tracks
information about how momentum is distributed, as well as where there
will be compression or expansion, which can also lightly curve
space-time.
If we could learn the shape of space-time surrounding a proton, Russian (opens a new tab) and American (opens a new tab)
physicists independently worked out in the 1960s, we could infer all
the properties indexed in its energy-momentum tensor. Those include the
proton’s mass and spin, which are already known, along with the
arrangement of the proton’s pressures and forces, a collective property
physicists refer to as the “Druck term,” after the word for pressure in
German. This term is “as important as mass and spin, and nobody knows
what it is,” Schweitzer said — though that’s starting to change.
In the ’60s, it seemed as if measuring the energy-momentum tensor and
calculating the Druck term would require a gravitational version of the
usual scattering experiment: You fire a massive particle at a proton
and let the two exchange a graviton — the hypothetical particle that
makes up gravitational waves — rather than a photon. But due to the
extreme weakness of gravity, physicists expect graviton scattering to
occur 39 orders of magnitude more rarely than photon scattering.
Experiments can’t possibly detect such a weak effect.
“I remember reading about this when I was a student,” said Volker Burkert (opens a new tab),
a member of the Jefferson Lab team. The takeaway was that “we probably
will never be able to learn anything about mechanical properties of
particles.”
Gravity Without Gravity
Gravitational experiments are still unimaginable today. But research
in the late 1990s and early 2000s by the physicists Xiangdong Ji and,
working separately, the late Maxim Polyakov revealed (opens a new tab) a workaround (opens a new tab).
The general scheme is the following. When you fire an electron
lightly at a proton, it usually delivers a photon to one of the quarks
and glances off. But in fewer than one in a billion events, something
special happens. The incoming electron sends in a photon. A quark
absorbs it and then emits another photon a heartbeat later. The key
difference is that this rare event involves two photons instead of one —
both incoming and outgoing photons. Ji’s and Polyakov’s calculations
showed that if experimentalists could collect the resulting electron,
proton and photon, they could infer from the energies and momentums of
these particles what happened with the two photons. And that two-photon
experiment would be essentially as informative as the impossible
graviton-scattering experiment.
Merrill Sherman/Quanta Magazine
How could two photons know anything about gravity? The answer
involves gnarly mathematics. But physicists offer two ways of thinking
about why the trick works.
Photons are ripples in the electromagnetic field, which can be
described by a single arrow, or vector, at each location in space
indicating the field’s value and direction. Gravitons would be ripples
in the geometry of space-time, a more complicated field represented by a
combination of two vectors at every point. Capturing a graviton would
give physicists two vectors of information. Short of that, two photons
can stand in for a graviton, since they also collectively carry two
vectors of information.
An alternative interpretation of the math goes as follows. During the
moment that elapses between when a quark absorbs the first photon and
when it emits the second, the quark follows a path through space. By
probing this path, we can learn about properties like the pressures and
forces that surround the path.
The Jefferson Lab physicists scraped together a few two-photon
scattering events in 2000. That proof of concept motivated them to build
a new experiment, and in 2007, they smashed electrons into protons
enough times to amass roughly 500,000 graviton-mimicking collisions.
Analyzing the experimental data took another decade.
From their index of space-time-bending properties, the team extracted the elusive Druck term, publishing their estimate (opens a new tab) of the proton’s internal pressures in Nature in 2018.
They found that in the heart of the proton, the strong force
generates pressures of unimaginable intensity — 100 billion trillion
trillion pascals, or about 10 times the pressure at the heart of a
neutron star. Farther out from the center, the pressure falls and
eventually turns inward, as it must for the proton not to blow itself
apart. “This comes out of the experiment,” Burkert said. “Yes, a proton
is actually stable.” (This finding has no bearing on whether protons decay, however, which involves a different type of instability predicted by some speculative theories.)
Merrill Sherman/Quanta Magazine
The Jefferson Lab group continued to analyze the Druck term. They
released an estimate of the shear forces — internal forces pushing
parallel to the proton’s surface — as part of a review published in December (opens a new tab).
The physicists found that close to its core, the proton experiences a
twisting force that gets neutralized by a twisting in the other
direction nearer the surface. These measurements also underscore the
particle’s stability. The twists had been expected based on theoretical
work from Schweitzer and Polyakov. “Nonetheless, witnessing it emerging
from the experiment for the first time is truly astounding,” Elouadrhiri
said.
Now they’re using these tools to calculate the proton’s size in a new
way. In traditional scattering experiments, physicists had observed
that the particle’s electric charge extends about 0.8 femtometers from
its center (that is, its constituent quarks buzz about in that region).
But that “charge radius” has some quirks. In the case of the neutron,
for instance — the proton’s neutral counterpart, in which two negatively
charged quarks tend to hang out deep inside the particle while one
positively charged quark spends more time near the surface — the charge
radius comes out as a negative number. “It doesn’t mean the size is
negative; it’s just not a faithful measure,” Schweitzer said.
The new approach measures the region of space-time that’s
significantly curved by the proton. In a preprint that has not yet been
peer reviewed, the Jefferson Lab team calculated that this radius may be
about 25% smaller (opens a new tab) than the charge radius, just 0.6 femtometers.
Planet Proton’s Limits
Conceptually, this kind of analysis smooths out the blurry dance of
quarks into a solid, planetlike object, with pressures and forces acting
on each speck of volume. That frozen planet does not fully reflect the
raucous proton in all its quantum glory, but it’s a useful model. “It’s
an interpretation,” Schweitzer said.
And physicists stress that the initial maps are rough, for a few reasons.
First, precisely measuring the energy-momentum tensor would require
much higher collision energies than Jefferson Lab can produce. The team
has worked hard to carefully extrapolate trends from the relatively low
energies they can access, but physicists remain unsure how accurate
these extrapolations are.
As a student, Volker Burkert read that directly
measuring the gravitational properties of the proton was impossible.
Today he participates in a collaboration at Jefferson Laboratory that’s
in the process of teasing out those same properties indirectly.
Thomas Jefferson National Accelerator Facility
Moreover, the proton is more than its quarks; it also contains
gluons, which slosh around with their own pressures and forces. The
two-photon trick cannot detect gluons’ effects. A separate team at
Jefferson Lab used an analogous trick (involving a double-gluon
interaction) to publish a preliminary gravitational map of these gluon
effects in Nature last year (opens a new tab), but it too was based on limited, low-energy data.
“It’s a first step,” said Yoshitaka Hatta, a physicist at Brookhaven
National Laboratory who was inspired to start studying the gravitational
proton after the Jefferson Lab group’s 2018 work.
Sharper gravitational maps of both the proton’s quarks and its gluons
may come in the 2030s when the Electron-Ion Collider, an experiment
currently under construction at Brookhaven, will begin operations.
In the meantime, physicists are pushing ahead with digital experiments. Phiala Shanahan (opens a new tab),
a nuclear and particle physicist at the Massachusetts Institute of
Technology, leads a team that computes the behavior of quarks and gluons
starting from the equations of the strong force. In 2019, she and her
collaborators estimated the pressures (opens a new tab) and shear forces, and in October, they estimated the radius (opens a new tab),
among other properties. So far, their digital findings have broadly
aligned with Jefferson Lab’s physical ones. “I am certainly quite
excited by the consistency between recent experimental results and our
data,” Shanahan said.
Even the blurry glimpses of the proton attained so far have gently reshaped researchers’ understanding of the particle.
Some consequences are practical. At CERN, the European organization
that runs the Large Hadron Collider, the world’s largest proton smasher,
physicists had previously assumed that in certain rare collisions,
quarks could be anywhere within the colliding protons. But the
gravitationally inspired maps suggest that quarks tend to hang out near
the center in such cases.
“Already the models they use at CERN have been updated,” said
Francois-Xavier Girod, a Jefferson Lab physicist who worked on the
experiments.
The new maps may also offer guidance toward resolving one of the
deepest mysteries of the proton: why quarks bind themselves into protons
at all. There’s an intuitive argument that because the strong force
between each pair of quarks intensifies as they get further apart, like
an elastic band, quarks can never escape from their comrades.
But protons are made from the lightest members of the quark family.
And lightweight quarks can also be thought of as lengthy waves extending
beyond the proton’s surface. This picture suggests that the binding of
the proton may come about not through the internal pulling of elastic
bands but through some external interaction between these wavy,
drawn-out quarks. The pressure map shows the attraction of the strong
force extending all the way out to 1.4 femtometers and beyond,
bolstering the argument for such alternative theories.
“It’s not a definite answer,” Girod said, “but it points toward the
fact that these simple images with elastic bands are not relevant for
light quarks.”
