Suppose you could possibly pace up Earth’s rotation so {that a} day was solely half as lengthy? What would occur? Properly, for starters we’d need to make new clocks that solely have hours 1 to six for am and pm. Should you had tickets to an 8 o’clock live performance, you’d be out of luck: 8 o’clock not exists.
However perhaps a extra germane query is, why do physicists ask nutty questions like this? It’s by no means going to occur—simply transfer on, proper? Properly, right here’s the deal. Fascinated about counterfactual situations provides us perception into how issues work right here in actuality. Plus, it’s enjoyable! Want I say extra? OK, it would even assist us construct a working area elevator.
Oh, you don’t know what an area elevator is? It’s a sci-fi staple, a tether from Earth as much as an orbiting area station in geosynchronous orbit. A cable-climbing automobile would trip up and down, identical to a daily elevator. Principally it’s a approach of getting out to area as simply and routinely as you trip an elevator to your workplace within the morning—no rockets required.
Let’s begin off with some primary questions and construct as much as some extra sophisticated physics.
What Is a Day?
You may’t get extra primary than that. However the reply isn’t easy. Should you stated a day is 24 hours, you’re proper—and incorrect. Should you’re standing exterior, the time at which the solar is at its highest level within the sky known as native midday. Should you stand there till the subsequent native midday, the quantity of elapsed time is outlined as 24 hours. So an hour is 1/twenty fourth of the time between two native noons.
However wait! This isn’t the identical as an entire revolution of the Earth. Should you measured the time of an entire revolution, you’d discover that it’s not precisely 24 hours. The reason being that the Earth is doing two issues directly: It is spinning on its axis, which causes the solar to seem to maneuver throughout the sky. Nevertheless it’s additionally orbiting the solar over the course of a 12 months, which suggests an entire rotation is not going to consequence within the solar being in the identical place within the sky.
There are literally two various kinds of days. The photo voltaic day is the one you’re pondering of, and it’s the one described above. The opposite kind known as a sidereal day. This is a completely not-to-scale diagram that can make it easier to perceive the distinction:
