Why can't anything travel faster than light?
The limit is not about light — it is the maximum speed at which any cause can reach any effect, and light simply happens to travel at it.
Simple intuition
The plain reason, in everyday words
The name is misleading. This is not a speed limit on light — it is the speed at which anything at all can carry an influence from one place to another, and light travels at it because light has no mass. Think of it as the exchange rate between space and time rather than a barrier. Everything is always moving through spacetime at the same total rate; sitting still means moving entirely through time, and speeding up means trading some of that for movement through space. You can trade more and more, but you can never trade all of it, because there is nothing left to give. That is why pushing harder does not eventually get you past the limit: the extra effort goes into the trade rather than into the speed, and the closer you get, the more it costs to gain anything at all.
It is a technological barrier we might one day beat with a better engine.
It is a property of the geometry of spacetime, not of any engine. The energy required rises without bound as the speed is approached, so no amount of thrust reaches it, and nothing about the limit depends on how the push is delivered.
Light is special and the limit is about light.
The limit is the invariant speed of spacetime itself. Light travels at it because photons are massless; anything massless must travel at exactly that speed, and gravitational waves do too.
Nothing at all can exceed the speed of light in any sense.
Several things can — the phase velocity of a wave in a medium, a spot of light swept across a distant surface, and the recession of distant galaxies from cosmic expansion. None of them carries information from one place to another, which is what the limit actually restricts.
Quantum entanglement sends information instantly and therefore breaks the rule.
Entanglement produces correlations that only become visible when the two results are compared through an ordinary channel, which travels no faster than c. No message can be sent this way.
It reframes a rule that sounds like an engineering obstacle as a statement about the structure of reality — and the reason it cannot be beaten is that beating it would mean effects preceding causes. It is also load-bearing in everyday technology: satellite navigation would be unusable within hours without relativistic corrections, and particle accelerators are designed around it. Understanding what does and does not count as exceeding it is also the fastest way to see through most claims that someone has.
Who worked it out
In the 1860s James Clerk Maxwell's equations for electricity and magnetism predicted waves travelling at a speed fixed by two measurable constants, with no mention of what they travelled relative to — an unexplained feature at the time.
What problem forced it
The Michelson–Morley experiment of 1887 failed to detect any variation in that speed with Earth's motion, undermining the idea of a stationary medium for light to move through.
How it changed since
Einstein's 1905 paper resolved the tension by taking the constancy of c as a postulate and letting space and time adjust instead. Hermann Minkowski recast the result geometrically in 1908, and general relativity extended it to gravity in 1915. Every subsequent test, from particle lifetimes to satellite clocks, has agreed.
Why satellite clocks need relativistic correction
The most everyday consequence, and the one that would break within hours if it were ignored.
What the expansion of the universe actually moves
Distant galaxies recede faster than light without breaking anything, and understanding why sharpens what the limit really restricts.
Written for Curio rather than collected from a forum — it is part of the curated corpus that ships with the platform. The references it draws on are listed under Sources.