💡 GPS satellites must correct for relativistic time dilation — proving Einstein's predictions are practical, not theoretical
You don't need a DeLorean. You're already time-traveling — just very slowly. Einstein's theory of predicts that time passes more slowly for objects moving at high speed relative to a stationary observer. This isn't philosophy; it's engineering. GPS satellites, orbiting at 14,000 km/h, experience of approximately 7 per day. Without correction, GPS coordinates would drift by about 10 kilometers daily, rendering the entire system useless. General relativity adds another layer: clocks tick faster in weaker fields, so the satellites' higher altitude makes their clocks run slightly faster than ground-based ones. The net correction — roughly 38 per day — is built into every GPS chip in every phone on Earth.
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Philosophy Now5 words
The Bootstrap Paradox: Information from Nowhere
💡 Some time-travel paradoxes involve information or objects that exist without ever being created
A time traveler goes back to 1955 and gives Beethoven a book of Beethoven's complete symphonies. Beethoven copies them out and publishes them as his own. The symphonies become famous, get printed in a book, which the time traveler eventually buys and takes back to 1955. Who composed the music? The — named after the absurdity of pulling yourself up by your own bootstraps — describes a in which an effect is its own cause. Unlike the grandfather paradox, it doesn't involve logical contradiction; it involves mystery. The information exists, circulates, but was never created by anyone. Physicist Kip Thorne has argued that such loops are theoretically permissible under , provided they are — the universe allows time travel only when no paradox results.