Re: SPACE: New propulsion technologies

John Clark (
Mon, 16 Aug 1999 17:15:56 -0400

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Ron Kean <> Wrote:

>A photon reportedly has no rest mass, yet it behaves as if
>it has mass in the sense that it has momentum and is attracted by a
>gravitational field. I presume that if there were enough energy in the
>form of photons concentrated at one locality, a black hole could form,
>trapping the photons in their own gravity, just as a black hole can form
>if there is enough cold mass in one locality.

Yes and your intuition is excellent, bordering on the superb. As the wavelength of light gets smaller the energy gets larger, and so does the mass because E = MC^2 so M= E/c^2. Thus at some point the wavelength is so small and the mass is so great that a mini Black Hole is formed with a singularity at its center. The energy of the photon where this happens is the Plank Energy of 1.22 *10^28 electron volts. You can derive this from the formula E = [HC^5/G]^1/2 where H is the Plank constant divided by 2 PI, c is the speed of light, and G is the gravitational constant.

John K Clark

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