# When the revolution of the earth on its axis accelerates

1. Jan 1, 2008

### ffrancis

Hi!

More than a decade ago, I used to listen to a so-called walking encyclopedia over the radio. One of the radio listeners verified the information that he had read somewhere:

That if the earth revolved on its axis at a much faster rate, then time would become faster.

However, this radio announcer used his common sense and he contradicted that idea. He said that if such were the case, then time would be much slower. I believe he said that because he was holding on to the idea that time is constant.

Is my question related to the theory of relativity? Do you agree with this so-called genius radio announcer?

Last edited: Jan 1, 2008
2. Jan 1, 2008

### yuiop

Hi and happy New year ;)
Before clocks were invented a year would be measured in days. If the Earth suddenly starting rotating twice as fast as normal, then a year would consist of 730 days instead of 365. By this crude definition of time then you could argue time has has speeded up. However this is a flawed arguement and is like saying a journey takes half the time at 60 mph than it would take at 30 mph because time speeds up. All that has really changed is the speed of the vehicle or the rotation rate of the earth. The modern definition of the second is "the time it takes for the magnetic field of a cesium atom to flip polarity 9,192,631,770 times, as measured by an atomic clock". By that definition the number of seconds in a year would be the same, even if the Earth rotated twice as fast. The length of a day is simply the pattern of light and shadow cast by the sun. At the North pole, night can last 6 months followed by a day lasting 6 months. Despite only having 2 days a year at the North pole a second at the North pole is pretty much the same as a second on the equator. (But see below)

However,there would be minuscule (in the order of nanoseconds) but measurable difference in in the rate of a clock on the equator of the speeded up Earth relative to a reference clock in space, due to relativistic effects. The radio announcer is partly right that time would be (relatively) slower if the Earth spun faster but he is far off the mark to say time would be "much slower". To give an idea of how small the difference would be, a cesium atom would flip polarity 9,192,631,769.96 times in an atomic clock on the speed doubled Earth, in the time a cesium atom flipped polarity 9,192,631,770 times in the space reference clock. To make a clock on the equator run 1% slower than a reference clock in space, the Earth's rotation speed would have to be about 100,000 times faster than it is now.

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