What Is a Frontier in Physics?

A frontier is a boundary between what scientists understand and what remains unknown.

Particle physics has developed an extremely successful theory called the Standard Model.

The Standard Model explains:

• quarks
• leptons
• photons
• gluons
• W and Z bosons
• the Higgs boson
• electromagnetic interactions
• weak interactions
• strong interactions

Yet important questions remain unanswered.

These questions define the frontiers of particle physics.

---

Why Look Beyond the Standard Model?

The Standard Model describes many experiments with extraordinary accuracy.

However, it does not explain everything we observe.

Important unresolved problems include:

• the nature of dark matter
• the origin of neutrino masses
• the matter-antimatter asymmetry
• how gravity fits with quantum physics
• the nature of dark energy
• why particle masses have their observed values
• whether additional particles or forces exist
• whether quarks and leptons are truly fundamental

Scientists therefore search for evidence that points to a deeper theory.

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An Important Scientific Principle

A successful theory does not become useless simply because it is incomplete.

For example:

Newtonian mechanics is still extremely useful even though relativity provides a deeper theory.

Likewise, any future theory of particle physics would have to reproduce the successful predictions of the Standard Model under conditions where the Standard Model already works.

Scientific progress often looks like:

successful model

↓

new observation

↓

unexplained result

↓

improved theory

↓

new predictions

↓

new experiments

---

Why Search for New Particles?

One major strategy is to search for particles that are not currently included in the Standard Model.

A new particle could help explain:

• dark matter
• neutrino mass
• matter-antimatter asymmetry
• additional forces
• Higgs physics
• force unification

New particles may be:

• very massive
• extremely short-lived
• electrically neutral
• weakly interacting
• produced only rarely

This makes them difficult to detect.

---

How Can a New Particle Be Found?

Scientists do not always observe a new particle directly.

Instead, they often reconstruct it from its effects.

The process may be:

high-energy collision

↓

new particle briefly produced

↓

particle decays

↓

detector measures decay products

↓

scientists reconstruct mass and other properties

This is how many short-lived particles are studied.

---

The Higgs Boson as an Example

For decades, the Higgs boson was predicted but had not been observed.

Scientists built increasingly powerful accelerators and sophisticated detectors to search for it.

At the Large Hadron Collider, experiments discovered a new particle in 2012 with properties consistent with the Higgs boson.

This shows how theoretical predictions can guide experimental searches.

It also shows why major discoveries can require:

• enormous machines
• decades of preparation
• huge datasets
• international collaborations

---

Dark Matter Searches

Dark matter is another major target.

Its gravitational effects are strongly supported by astronomical observations, but its particle identity remains unknown.

Scientists search for possible dark matter particles using several approaches:

Direct Detection

Look for dark matter interacting with detectors.

Indirect Detection

Look for products that might result from dark matter annihilation or decay.

Collider Searches

Try to produce invisible particles in high-energy collisions.

A possible clue could appear as:

missing energy or momentum

because an undetected particle carried energy away.

---

Neutrinos at the Frontier

Neutrinos are among the most mysterious known particles.

Scientists know that neutrinos oscillate between different flavour states.

This means neutrinos have nonzero mass differences.

However, several important questions remain:

• What are their absolute masses?
• What is the neutrino mass ordering?
• Are neutrinos their own antiparticles?
• Do neutrinos help explain the matter-antimatter asymmetry?

Neutrino experiments therefore form an important part of modern frontier physics.

---

Matter and Antimatter

The observable universe contains much more matter than antimatter.

The Standard Model includes some processes that distinguish matter from antimatter through CP violation.

However, the known effects appear insufficient to explain the large cosmic imbalance.

Scientists therefore search for additional sources of CP violation.

These could appear in:

• quark decays
• neutrino behaviour
• Higgs interactions
• undiscovered particles

---

The Higgs Frontier

Discovering the Higgs boson did not finish Higgs physics.

It began a new phase.

Scientists now want to measure the Higgs boson with far greater precision.

Important questions include:

• Does the Higgs interact exactly as predicted?
• How strongly does it interact with other particles?
• Does it interact with itself as expected?
• Are there additional Higgs bosons?
• Could the Higgs connect ordinary matter to dark matter?

Small deviations could reveal physics beyond the Standard Model.

---

Precision vs Energy

There are two major ways to search for new physics.

The Energy Frontier

Use higher collision energies to try to create heavier particles directly.

The Precision Frontier

Measure known particles and processes extremely accurately.

Even if a new particle is too massive to produce directly, it may slightly influence measurable quantities.

Therefore:

higher energy can reveal new particles directly

while:

higher precision can reveal new physics indirectly

---

Why Build More Powerful Accelerators?

A collider's energy determines what kinds of particles can potentially be produced.

Einstein's relation:

E = mc²

means that collision energy can be transformed into the rest mass of new particles.

Higher collision energy can therefore allow the creation of:

• heavier particles
• previously inaccessible states
• rare interactions

Higher energies also allow physicists to probe smaller distance scales.

---

Why More Collisions Matter

Energy is not the only important quantity.

Another key idea is luminosity.

Luminosity describes how many collision opportunities an accelerator produces.

Greater luminosity means:

more collisions

↓

more data

↓

more rare events

↓

greater measurement precision

This is the main goal of the High-Luminosity Large Hadron Collider.

---

The High-Luminosity LHC

The LHC completed its third major data-taking run in June 2026 and is now undergoing Long Shutdown 3.

During this shutdown, the accelerator and major experiments are being upgraded to become the High-Luminosity LHC, or HL-LHC. CERN plans for physics running to resume around 2030. The goal is not mainly to increase the maximum energy dramatically, but to produce far more collisions and therefore much larger datasets.

---

What Will the HL-LHC Study?

The increased collision rate will allow scientists to:

• measure Higgs properties more precisely
• study rare Higgs decays
• investigate top quarks
• test electroweak physics
• study strong interactions
• search for dark matter candidates
• search for new particles
• investigate rare processes

Even if no new particle is found directly, increasingly precise measurements can rule out or constrain many theories.

---

After the LHC

The LHC will not operate forever.

Scientists are therefore studying possible machines that could follow it.

No single future collider is guaranteed to be built.

Projects must be evaluated based on:

• scientific value
• technical feasibility
• cost
• energy use
• environmental impact
• construction time
• international support

---

Future Circular Collider

One major proposal is CERN's Future Circular Collider, or FCC.

The current FCC concept would begin with an electron-positron collider called:

FCC-ee

This would serve as a high-precision Higgs factory.

A later stage could potentially use the same large tunnel for a proton-proton collider capable of reaching much higher collision energies.

The feasibility study was completed in 2025. As of 2026, the project remains proposed rather than approved, with CERN indicating that a decision on whether to proceed is expected no earlier than 2028. If approved, operation would be aimed for around the mid-2040s.

---

Why Make the FCC So Large?

For a circular accelerator, bending high-momentum charged particles requires powerful magnetic fields.

A useful relationship is:

p = qBr

where:

• p = particle momentum
• q = charge
• B = magnetic field strength
• r = bending radius

For a given magnetic field:

greater momentum requires a larger radius

Therefore, a larger accelerator ring helps make higher-energy collisions possible.

---

A Higgs Factory

A Higgs factory is an accelerator designed to produce very large numbers of Higgs bosons under clean experimental conditions.

Electron-positron collisions are attractive for precision studies because electrons and positrons are fundamental particles.

Protons, in contrast, are composite particles containing quarks and gluons.

Electron-positron collisions can therefore provide especially clean conditions for measuring subtle Higgs properties.

---

CEPC

China is also developing the design for the Circular Electron Positron Collider, or CEPC.

The CEPC is proposed as a large circular electron-positron collider primarily intended for precision Higgs studies.

The project has completed major accelerator and reference-detector technical design work, but remains a proposed future facility rather than an operating or approved collider.

---

Linear Colliders

Not every future accelerator needs to be circular.

Another possibility is a linear collider.

Particles travel along straight accelerator sections and collide once rather than circulating around a ring.

This can be advantageous for high-energy electron-positron collisions because electrons lose significant energy as synchrotron radiation when forced to move in curved paths.

---

International Linear Collider

The International Linear Collider, or ILC, is a proposed electron-positron accelerator.

Its design is intended to allow high-precision studies of particles such as the Higgs boson.

The project has undergone extensive international technical development, but construction has not been approved. The concept remains under active international study.

---

Circular vs Linear Colliders

Both approaches have advantages and challenges.

---

Muon Colliders

Another idea is a muon collider.

Muons are much heavier than electrons.

Because of their larger mass, they lose far less energy through synchrotron radiation when accelerated around a circular track.

This raises the possibility of producing extremely high-energy lepton collisions in a relatively compact ring.

---

Why Muons Are Challenging

Muons are unstable.

Their mean lifetime at rest is only about:

2.2 microseconds

Although relativistic time dilation extends their lifetime at high speeds, scientists must still:

• produce muons rapidly
• collect them
• cool the beam
• accelerate them quickly
• collide them before too many decay

Muon decay also creates challenging detector backgrounds and radiation issues.

Current international R&D aims to determine whether these challenges can be solved well enough for a future collider; present planning studies envisage development extending well into the 2030s before any possible construction decision.

---

Why Consider Muon Colliders?

A high-energy muon collider could combine some advantages of proton and electron colliders.

Muons are fundamental particles, so the collision energy is directly available in the interaction.

Yet because muons are much heavier than electrons, they can potentially circulate at very high energies with less synchrotron-radiation loss.

This could make them valuable for exploring extremely high-energy physics.

---

Future Accelerators Are Experiments Too

Before any future collider can be built, scientists must solve major engineering problems.

Research includes:

• stronger superconducting magnets
• more efficient radio-frequency cavities
• advanced cryogenics
• new detector materials
• higher-power targets
• improved beam control
• lower-energy accelerator technology
• more efficient computing

Accelerator development itself drives new technology.

---

Higher Energy Is Not the Only Frontier

Particle physics includes several other experimental frontiers.

These include:

Neutrino Frontier

Studying neutrino masses and oscillations.

Intensity Frontier

Producing enormous numbers of particles to study extremely rare processes.

Cosmic Frontier

Using astronomical observations to investigate dark matter, cosmic rays, and the early universe.

Precision Frontier

Testing known theories to extraordinary accuracy.

Non-Collider Experiments

Searching for new physics without relying on the highest-energy collisions.

CERN's current planning explicitly includes a broad non-collider research programme alongside collider development.

---

Rare Processes

Some new physics may reveal itself through extremely rare events.

Scientists therefore search for processes such as:

• unusual particle decays
• lepton-flavour violation
• neutrinoless double beta decay
• proton decay
• rare meson decays

If an event forbidden by the Standard Model were reliably detected, it would provide powerful evidence for new physics.

---

Searching for Tiny Differences

New discoveries may appear as very small deviations rather than dramatic new particles.

Suppose the Standard Model predicts:

measurement = 2.000000

but repeated experiments reliably obtain:

2.000150

Scientists would ask whether:

• the experiment contains an error
• the theoretical calculation is incomplete
• an unknown particle is influencing the process

Extremely precise measurements can therefore reveal physics at energy scales beyond the direct reach of current accelerators.

---

The Role of Better Detectors

Future discoveries depend not only on accelerators but also on detectors.

Modern detectors must measure:

• particle tracks
• energy
• momentum
• charge
• timing
• decay locations

Improved detectors may provide:

• finer spatial resolution
• faster timing
• better radiation resistance
• improved particle identification
• larger datasets

---

Computing at the Frontier

Particle physics also requires enormous computing resources.

Modern experiments can produce vast amounts of raw detector information.

Computing systems must:

• decide which events to record
• reconstruct particle tracks
• identify particles
• simulate collisions
• compare data with theory
• search huge datasets for rare signals

Machine learning is increasingly used to help recognize complex patterns.

---

International Collaboration

Modern particle physics experiments are often too large for one scientist, one university, or even one country.

Large collaborations bring together:

• physicists
• engineers
• computer scientists
• technicians
• mathematicians
• students

from many countries.

The CMS collaboration, for example, involves a very large international research community working on the same experiment.

---

Why International Collaboration Is Necessary

Large particle-physics projects require:

Financial Resources

Major accelerators are extremely expensive.

Technical Expertise

No single institution specializes in every technology.

Large Research Teams

Thousands of people may be needed to design, build, operate, and analyze an experiment.

Long-Term Commitment

Projects may take decades from initial design to final results.

Shared Infrastructure

Scientists from many countries can use the same accelerator and detectors.

---

Collaboration in Detector Construction

A single detector may contain millions of components.

Different institutions may be responsible for:

• silicon trackers
• calorimeters
• magnets
• electronics
• software
• data analysis
• cooling systems
• mechanical structures

These components must eventually work together as one instrument.

This requires common technical standards and intense coordination.

---

Collaboration in Data Analysis

The data from a major experiment are studied by teams around the world.

A typical process is:

collision occurs

↓

detector records data

↓

data distributed to computing centres

↓

researchers analyze events

↓

different teams cross-check results

↓

collaboration approves publication

Independent checking reduces the risk of mistakes.

---

Why Replication Matters

Extraordinary discoveries require strong evidence.

A possible new-particle signal may initially be caused by:

• random statistical fluctuation
• detector malfunction
• misunderstood background
• incorrect calibration
• analysis error

Different experiments can test the same idea.

For example, the ATLAS and CMS experiments independently contributed to establishing the Higgs discovery.

Independent confirmation strengthens scientific confidence.

---

International Competition and Cooperation

Science can involve both competition and cooperation.

Different teams may compete to:

• make a discovery first
• develop better technology
• produce more precise measurements

At the same time, they cooperate by:

• sharing accelerator facilities
• developing common standards
• exchanging researchers
• publishing open scientific results
• building international projects

Competition can encourage innovation, while collaboration makes enormous projects possible.

---

Benefits of International Scientific Cooperation

International collaboration can:

• spread costs
• combine expertise
• train scientists and engineers
• encourage peaceful cooperation
• develop shared technology
• create international research networks
• improve scientific reliability

Particle physics therefore has scientific and societal effects beyond individual discoveries.

---

Challenges of International Collaboration

Large collaborations also face difficulties.

These can include:

• funding disagreements
• political changes
• different national priorities
• language and cultural differences
• complex management
• long decision-making processes
• deciding where facilities should be built

Future accelerators may require unprecedented levels of global cooperation.

---

Should We Build Bigger Colliders?

This is an important evaluation question.

Arguments in Favour

Future colliders could:

• study the Higgs in much greater detail
• explore previously unreachable energies
• search for new particles
• test fundamental theories
• develop advanced technologies
• train future scientists and engineers

Arguments Against or Concerns

They may involve:

• enormous construction costs
• high electricity use
• environmental impacts
• decades-long timelines
• uncertain probability of discovering new particles
• competition with other research priorities

A good scientific evaluation should consider both sides.

---

Science Without Guaranteed Discoveries

A future accelerator cannot guarantee the discovery of a new particle.

This may seem like a weakness, but it is part of experimental science.

Even finding nothing unexpected provides useful information.

A null result can:

• rule out theories
• place limits on particle masses
• constrain dark matter models
• test Standard Model predictions
• guide future research

Scientific progress includes eliminating incorrect possibilities.

---

Example: Searching for a Particle

Suppose a theory predicts a new particle with a mass below:

5 TeV/c²

Scientists search that region and find no evidence for it.

The experiment has still taught us something.

It may allow scientists to conclude:

the predicted particle does not exist in that mass range under the tested assumptions

The theory must then be changed or discarded.

---

Discovery Through Unexpected Results

Some major discoveries were not exactly what scientists originally expected.

Research can reveal:

• new particles
• unexpected decay patterns
• unexplained measurements
• entirely new phenomena

This is why experimental instruments capable of exploring unfamiliar territory are valuable.

---

Particle Physics and the Nature of Reality

Particle physics asks some of the deepest scientific questions possible.

For example:

• What is matter?
• What are the fundamental building blocks of nature?
• Why do particles interact?
• Why do particles have mass?
• Why does the universe contain matter?
• Are there more dimensions?
• Are the fundamental forces related?
• What is dark matter?

These questions go beyond simply cataloguing particles.

They concern the basic structure of reality.

---

From Atoms to Quarks

Our understanding has repeatedly changed.

Scientists once thought:

atoms were indivisible

Then:

atoms → electrons + nuclei

Then:

nuclei → protons + neutrons

Then:

protons and neutrons → quarks

Today, quarks and leptons are treated as fundamental.

But we do not know whether this is the final layer.

---

Could Quarks Have Structure?

Current experiments show no confirmed internal structure for quarks or leptons.

However, scientists continue testing whether they might be composite.

If internal structure were discovered, it would transform our understanding of matter.

The scientific approach is not to assume that today's model is final.

It is to keep testing it.

---

Unification

Physicists have repeatedly discovered that apparently different phenomena can be connected.

For example:

electricity + magnetism → electromagnetism

and:

electromagnetism + weak interaction → electroweak theory

This raises an important question:

Could the strong interaction also be unified with the electroweak interaction?

And could gravity eventually be included?

A complete unified theory remains a major goal of fundamental physics.

---

Quantum Gravity

Gravity remains outside the Standard Model.

Scientists seek a framework combining:

general relativity

with:

quantum physics

Possible approaches include:

• string theory
• loop quantum gravity
• other quantum-gravity models

No experimentally confirmed theory has yet solved this problem.

Understanding quantum gravity could transform physics at:

• black holes
• the early universe
• extremely small scales

---

Future Physics May Look Very Different

It is possible that progress will come from:

• a larger accelerator
• a neutrino experiment
• a dark matter detector
• a precision measurement
• an astronomical observation
• gravitational-wave measurements
• an unexpected theoretical breakthrough

No one knows where the next major discovery will occur.

That uncertainty is what makes the subject a scientific frontier.

---

Example 1: Energy Frontier

Two colliders are compared.

Collider A:

5 TeV collision energy

Collider B:

50 TeV collision energy

Collider B may be capable of directly producing heavier particles because more collision energy is available for conversion into mass.

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Example 2: Luminosity Frontier

Two accelerators have the same collision energy.

Accelerator A produces:

1 million collisions

Accelerator B produces:

100 million collisions

Accelerator B gives scientists a better chance of observing an extremely rare process.

This is why increased luminosity is valuable.

---

Example 3: Precision Physics

Suppose a particle decays in a particular way:

1 time in every million decays

A new theory predicts:

1.2 times in every million

Scientists may need billions of events to distinguish between these possibilities reliably.

Large datasets allow extremely subtle effects to be tested.

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Example 4: Evaluating a Future Collider

Consider a proposed collider.

Potential benefits:

• more precise Higgs measurements
• access to new energy ranges
• new accelerator technology
• global scientific collaboration

Potential limitations:

• very high cost
• long construction period
• energy requirements
• uncertain discoveries

A strong evaluation should consider both scientific opportunity and practical constraints.

---

The Current Accelerator Landscape

As of 2026, the picture is broadly:

LHC

↓

currently undergoing major upgrade work

↓

High-Luminosity LHC

↓

planned return to physics around 2030

↓

possible post-LHC facilities

↓

FCC, CEPC, linear colliders, muon collider concepts and other proposals

The future has not yet been fully decided.

---

Different Machines Answer Different Questions

There may not be one perfect future accelerator.

For example:

electron-positron collider

→ extremely precise measurements

proton-proton collider

→ very high energy reach

muon collider

→ possible combination of high energy and clean lepton collisions

neutrino facility

→ neutrino properties

Different machines explore different parts of the frontier.

---

Why Scientific Strategy Matters

Building a major accelerator can take decades.

Scientists therefore need to decide what questions are most important long before construction begins.

Strategy requires considering:

• current experimental results
• theoretical questions
• available technologies
• funding
• international priorities
• environmental impact
• expected scientific return

The 2026 update of the European Strategy for Particle Physics is one example of how the research community sets long-term priorities.

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Scientific Research Is Global

No country has exclusive ownership of fundamental physical laws.

Researchers from around the world contribute to major experiments.

Knowledge gained through these projects becomes part of humanity's shared scientific understanding.

---

Did You Know?

The LHC itself is about 27 km in circumference, yet scientists are studying possible future circular colliders many times larger.

Making a collider larger is not simply about building something impressive.

For circular machines, a larger bending radius can help particles reach greater momentum without requiring impossibly strong magnets.

Future collider design therefore combines fundamental physics with:

• geology
• civil engineering
• superconductivity
• computing
• electrical engineering
• environmental science

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Another Frontier: Accelerator Technology

Future discoveries may depend on inventing completely new ways to accelerate particles.

Researchers investigate technologies such as:

• plasma wakefield acceleration
• advanced superconducting cavities
• stronger superconducting magnets
• novel beam-cooling techniques
• laser-driven acceleration

Traditional accelerators require long distances to reach high energies.

Future technologies may eventually allow much stronger accelerating fields over shorter distances.

---

Plasma Wakefield Acceleration

A charged particle or laser pulse travelling through plasma can create a powerful wave.

Particles can "surf" this wave and gain energy.

This idea is called:

plasma wakefield acceleration

It may eventually provide extremely high accelerating gradients.

However, major engineering and beam-quality challenges remain before it could replace conventional large colliders.

---

What Does Success Look Like?

A future experiment does not need to discover a spectacular new particle to succeed.

It can advance science by:

• measuring known particles more accurately
• excluding proposed theories
• discovering unexpected patterns
• improving technology
• producing new datasets
• revealing which questions should be asked next

Science advances through both discoveries and constraints.

---

How Particle Physics Advances Knowledge

Particle physics has changed our understanding from:

matter as continuous substance

to:

atoms

to:

subatomic particles

to:

quarks and leptons

to:

quantum fields and fundamental interactions

Future research may reveal another deeper level.

---

Connecting the Ideas

The frontier of particle physics can be summarized as:

Standard Model

↓

successful but incomplete

↓

unanswered questions

↓

new theories

↓

new experiments

↓

better accelerators and detectors

↓

international collaboration

↓

new evidence

↓

deeper understanding of nature

---

Major Questions at the Frontier

Scientists continue to investigate:

• What is dark matter?
• Why do neutrinos have mass?
• Are neutrinos their own antiparticles?
• Why is matter more abundant than antimatter?
• Are there undiscovered particles?
• Are there additional forces?
• Does the Higgs behave exactly as predicted?
• Are quarks and leptons truly fundamental?
• Can the fundamental forces be unified?
• How can gravity be described quantum mechanically?
• Are there additional dimensions?
• What happened at the highest energies of the early universe?

These questions are not signs that physics has failed.

They are signs that there is still more physics to discover.

---

Key Terms

Frontier physics – Research investigating the limits of current scientific understanding.

Beyond the Standard Model – Physics not fully explained by the Standard Model.

Luminosity – A measure related to the rate at which particle collisions can occur.

High-Luminosity LHC – An upgraded version of the LHC designed to produce much larger collision datasets.

Higgs factory – A collider optimized for producing large numbers of Higgs bosons for precision study.

Future Circular Collider (FCC) – A proposed future collider programme being studied at CERN.

CEPC – The proposed Circular Electron Positron Collider studied in China.

ILC – The proposed International Linear Collider.

Muon collider – A proposed accelerator that would collide positive and negative muons.

Energy frontier – Research using increasingly high particle energies.

Precision frontier – Research seeking very small differences between measurements and theoretical predictions.

Intensity frontier – Research using extremely large numbers of particles or events to study rare phenomena.

Plasma wakefield acceleration – An experimental accelerator method using waves in plasma to accelerate charged particles.

International collaboration – Scientific cooperation between researchers and institutions from different countries.

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Key Takeaways

• The Standard Model is extremely successful, but important questions remain unanswered.
• Scientists search for new particles because they may explain dark matter, neutrino masses, matter-antimatter asymmetry, or other unexplained phenomena.
• New physics can be found through both direct particle searches and high-precision measurements.
• Higher collision energies allow scientists to search for heavier particles and probe smaller scales.
• Higher luminosity provides more collisions and improves sensitivity to rare processes.
• The LHC entered a major upgrade phase in 2026 and is being transformed into the High-Luminosity LHC, with physics running planned to resume around 2030.
• Proposed future accelerators include the FCC, CEPC, ILC, and possible muon colliders, but their future construction is not guaranteed.
• The FCC remains under study, with a decision on whether to proceed expected no earlier than 2028.
• Different future colliders would serve different purposes: precision measurements, higher energies, or specialized particle studies.
• Future accelerator research also explores technologies such as plasma wakefield acceleration and advanced superconducting systems.
• Particle physics is not limited to colliders; neutrino experiments, dark matter searches, precision measurements, and astrophysical observations are also major frontiers.
• Large experiments require extensive international scientific collaboration because of their cost, complexity, and scale.
• International collaboration combines expertise, shares resources, improves reliability, and trains new generations of scientists and engineers.
• A null result can still be scientifically valuable because it rules out theories and narrows the range of possible explanations.
• Particle physics advances our understanding by repeatedly testing whether our current description of nature is complete.
• The next major breakthrough may come from a new collider, a precision experiment, an astronomical observation, or something researchers have not yet anticipated.