Speed of Light to Foot per Hour

No object with mass can reach or exceed c — it would require infinite energy. However, there are phenomena that appear to exceed c without violating physics: the expansion of the universe (space itself stretches), quantum entanglement (no information is transmitted), and phase velocity in certain media. Tachyons — hypothetical faster-than-light particles — have never been detected and would violate causality if they existed.

It is exactly that value by definition — in 1983, the meter was redefined as the distance light travels in 1/299,792,458 of a second. The specific number came from fixing c as exact and inheriting the historical length of the meter from the earlier platinum-iridium prototype. If the meter had been defined differently, c would have been a different exact integer.

About 8 minutes and 20 seconds on average (Earth's orbit is elliptical, so the range is 8m 10s to 8m 27s). Light from the Moon takes 1.3 seconds. From Jupiter at closest approach, about 35 minutes. From the nearest star (Proxima Centauri), 4.24 years. The observable universe is about 46 billion light-years in radius — meaning the light we see from its edge left over 13 billion years ago.

According to special relativity, time dilates for an object moving near c relative to an observer. At 99% of c, time passes about 7 times slower for the traveller compared to a stationary observer. At 99.9999% of c, the factor is about 707. GPS satellites need relativistic corrections (both special and general relativity) applied constantly — without them, GPS would accumulate errors of roughly 10 km per day.

Special relativity predicts several bizarre visual effects. Stars ahead of you would blueshift into ultraviolet and eventually X-rays, while stars behind would redshift into radio invisibility. Aberration would compress the entire sky into a bright ring ahead of you — a phenomenon called relativistic beaming. Time dilation means a trip to Proxima Centauri (4.24 light-years) would feel instantaneous to you at exactly c, though 4.24 years would pass on Earth. Of course, only massless particles can actually reach c — anything with mass would need infinite energy to get there.

Tectonic plates move at 2–15 cm/year on average — far below even 1 ft/h. However, during episodic "slow-slip events" on faults (a kind of slow-motion earthquake), the fault face can creep at detectable rates closer to mm/day. True ft/h movement would be catastrophic — the San Andreas Fault creeping at 1 ft/h would translate to 2.4 miles/day, far exceeding any measured geological rate.

Metal extrusion (forming rods or tubes by forcing material through a die) often runs at 1–100 ft/h depending on the alloy and die profile. Some ceramic and glass fiber drawing processes operate in this range. Paper mill wet-end press sections can be as slow as 10–50 ft/h during startup. These speeds are slow enough that workers can safely observe and adjust the process manually.

Icebergs drift with ocean currents at roughly 0.5–1 km/day, equivalent to about 55–110 ft/h. Calving glaciers can lurch forward at thousands of ft/h during surge events. The famous 2017 calving of iceberg A-68 from the Larsen C ice shelf happened over a period of days — so its "speed" of separation was only a few ft/h at most.

It depends on the magnitude. 1 ft/h = 24 ft/day = 288 in/day — for something moving a few feet per hour, inches per day becomes a large awkward number. Conversely, for very slow movement (0.01 ft/h = 2.88 in/day), in/day gives a cleaner number. Engineers choose whichever unit gives a value between roughly 1 and 1,000 to minimize leading zeros.

Sea stars (starfish) move at roughly 0.06 m/min, which is about 11.8 ft/h — surprisingly fast. Coral polyps and sea anemones are essentially sessile but can contract at a few mm/min. Some fungi extend their hyphal tips at 1–4 mm/h — about 0.003–0.013 ft/h. Slime molds (Physarum polycephalum), often used in computing research, can advance at up to 4 cm/h (about 1.3 ft/h).