# Question: Does Gravity Increase With Speed?

by on April 13, 2004

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In principle, the answer is yes, but it depends crucially on exactly how you accelerated the spacecraft to such a ridiculous speed. Consider a 100 metre sized spacecraft, for example. To collapse into a black hole, it would need a mass 35 times larger than Jupiter. How much energy would you need to apply to the spacecraft to accelerate it enough to acquire this mass? This is easily computed using E=mc2 – ie. multiply the mass (in kilograms) by the speed of light (in metres per second) squared. The answer is 6 times 10 to the power 45 Joules, which is roughly the combined energy output of all the hundred billion stars in the Milky Way since the Big Bang.

So – if you could focus all this energy in some way on one little spacecraft, you could accelerate it up to fast enough to become a black hole. But if you focussed all this energy on anything small, it would probably become a black hole, whether or not it were moving! If, for example, you zapped a stationary peanut with this sort of energy, it would collapse to form a black hole!

Dr. Paul Francis received his PhD in astrophysics at the University of Cambridge, and worked at Steward Observatory, with NASA and at the University of Melbourne before getting tenure at Mt Stromlo Observatory (part of the Australian National University).