Einstein CentennialAnswer
Why does quantum physics seem so weird, even to physicists?
Why electrons can produce wave-like patterns, what two-slit experiments show, and why a physical measurement differs from a conscious observer.
THE QUESTION LIBRARY EINSTEIN CENTENNIAL
Has Einstein’s relativity ever failed a test?
What happened to OPERA's 2011 faster-than-light claim, how relativity is tested, and why successful measurements do not prove every possible prediction.
THE SHORT ANSWER
Relativity has survived the tests discussed here; an apparent failure is not automatically a confirmed failure. In 2011, OPERA reported neutrinos apparently arriving faster than light. Follow-up measurements and checks of its timing equipment resolved that anomaly. Other experiments continue testing Einstein's predictions within measured uncertainties. Those successes support relativity without proving that it is a complete description of every possible situation.
- OPERA's anomaly was resolved through timing checks and follow-up measurements.
- Different experiments test different predictions.
- A tested limit is supported by evidence, not universal observation.
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WHAT WE DON’T KNOW YET
These tests do not observe every event or establish that relativity is complete in all situations. Each result has a defined sensitivity and assumptions.
WHAT WOULD CHANGE THIS ANSWER
A reproducible discrepancy beyond stated uncertainties, independently checked after timing, equipment, and analysis alternatives are examined.
Relativity has survived the tests discussed here; an apparent failure is not automatically a confirmed failure. In 2011, OPERA reported neutrinos apparently arriving faster than light. Follow-up measurements and checks of its timing equipment resolved that anomaly. Other experiments continue testing Einstein's predictions within measured uncertainties. Those successes support relativity without proving that it is a complete description of every possible situation.
THE LONG ANSWER
Free long answer 1 of 3 this month.
Which relativity, and which prediction?
Special relativity describes relationships among space, time, and motion, including the vacuum light-speed limit. General relativity describes gravity through spacetime geometry. A test should identify a particular prediction and the precision of the comparison. NASA's explanatory archive stresses that there is no single experiment that proves relativity in every respect. Agreement across different experiments is the reason for confidence. NASA: relativity and its evidence.
What happened to OPERA in 2011?
OPERA timed neutrinos traveling from CERN to Italy's Gran Sasso laboratory. Its September 2011 result appeared to show a speed slightly above light's. The collaboration invited scrutiny rather than announcing an established new law. CERN's June 2012 update reported that four Gran Sasso experiments found travel times consistent with light speed. It attributed the original anomaly to a faulty element in OPERA's fiber-optic timing system. The case was a measurement problem, not a demonstrated violation of relativity. CERN's original report and subsequent updates.
The lesson is concrete: a flight-time result depends on more than detecting arrival. It also depends on determining departure, synchronizing clocks, and accounting for delays in the measuring apparatus. Checking that chain is part of evaluating a surprising result. Repeating an analysis while leaving an unnoticed equipment fault in place would not remove the fault.
What other tests support Einstein?
NASA's Gravity Probe B measured small changes in the orientation of orbiting gyroscopes. Its reported results agreed, within uncertainty, with predicted effects of curved spacetime and Earth's rotation. That is a test of gravitational predictions, distinct from OPERA's particle travel-time measurement. It adds evidence without making the two experiments interchangeable. Gravity Probe B results.
A July 2026 LIGO–Virgo–KAGRA preprint tested general relativity using gravitational-wave signals in GWTC-5.0. The collaboration reported overall consistency with the theory and no evidence for physics beyond it in those tests. It also discussed analysis limitations, including spurious high-frequency content in one event. A useful result includes such boundaries, not just a verdict that Einstein won. Original GWTC-5.0 analysis.
How do we know the speed limit has held?
We compare measurements with predicted behavior; we cannot observe every event in the universe. The limit concerns light in vacuum and the relativistic motion being tested. NASA explains why accelerating a massive object toward that speed requires increasing energy. A claim of a violation needs a precise definition, reliable timing, uncertainty estimates, and checks that eliminate ordinary alternatives.
Confidence is high in relativity's tested predictions. A repeatable discrepancy beyond the uncertainties, independently checked with suitable equipment, could change that confidence. Read how science corrects mistakes and why entanglement does not provide faster-than-light messaging.
THREE THINGS TO REMEMBER
- OPERA's anomaly was resolved through timing checks and follow-up measurements.
- Different experiments test different predictions.
- A tested limit is supported by evidence, not universal observation.
Keep asking
Why does quantum physics seem so weird, even to physicists?
Quantum physics seems weird because the rules that describe electrons and photons do not fit the familiar picture of tiny balls following definite paths.
New here?
God Plays Dice answers big questions in plain words, with sources and one of six honest labels.
Words worth knowing (3)
- special relativity
- Einstein's theory relating space, time, and motion.
- general relativity
- Einstein's theory of gravity as spacetime geometry.
- uncertainty
- The reported limits on a measurement or inferred result.
Sources & further reading
(4) · Checked Oct 5, 2026
- Ask an Astrophysicist: Relativity ↗NASA Goddard Space Flight CenterHistorical explanatory archive distinguishes special/general relativity, evidence from proof, and the energy required to accelerate a massive object.
- OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso ↗CERNSeptember 2011 report with February, March, and June 2012 updates; the final update resolves the anomaly through timing-system checks and four experimental comparisons.
- Results and Implications: Gravity Probe B ↗NASAOfficial account reports the 2011 gyroscope results and their measured uncertainties; supports two particular gravitational predictions.
- GWTC-5.0: Tests of General Relativity ↗LIGO Scientific, Virgo and KAGRA CollaborationsJuly 2026 research preprint; tested gravitational-wave signals were overall consistent with general relativity, with stated analysis limitations.
See a mistake? Report a problem. Corrections are made openly.
CONTINUE THE THREAD
Where this question leads.
Einstein CentennialAnswer
Can quantum entanglement send messages faster than light?
Einstein called it “spooky action at a distance,” and the matching is real, but here is why nobody can use it to send a message faster than light.
Einstein CentennialAnswer
Did Einstein lose his argument that God does not play dice?
A century after his famous letter to Max Born, experiments have ruled on part of Einstein’s hope, while the question of dice itself is still argued.