How long do you have to accelerate at G to reach the speed of light?

25 May 2013


Dear Dr Chris.

I have plucked up the courage to write to you with a question from a colleague of mine which I can't answer.

I have no idea why he wants to know this ( I think he reads too many science fiction comics or watches too much 'Star Treck' ) but here goes :-

If an object of negligible size & mass is launched from a standing start in a vacuum, and is subjected to an acceleration force of 1 G - how long will it take to reach the speed of light.

Hope you are able to provide an answer, or even a formula to calculate an approximate result when and if you have the time.

Best Regards

Jack Stott BSc(Hon) Elec Eng Science


Well, id say if you assume that you can reach the speed of light by normal means and can achieve exactly 1g throughout the trip (I will use 300,000,000 m/s and 10m/s per second as rough approximations for this and assume this is from not moving at all) it would take approximately 30,000,000 seconds (500,000 minutes, 8333.33333333 hours, 347.222222222 days, 49.6031746032 weeks or 0.9539072039 years).

Thanks for the suggested answer, but the original poster did ask for the formula / workings...

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