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Old October 28th 16, 06:17 PM posted to sci.astro
Steve Willner
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Posts: 1,172
Default Link between dark matter and baryonic matter

In article ,
(Steve Willner) writes:
There's no such thing as "gravitational mass" in relativity unless
you want to define it redundantly as E/c^2. All energy contributes
to gravitation (or bends spacetime, if you prefer).


Maybe this is where you are going wrong... if you had a massless box
filled with photons, the box would behave as if it had rest mass.
That is to say, the box would gravitationally attract other objects,
and it would require a force to accelerate the box. From the
outside, you couldn't tell whether the box contained photons or
fishing weights (really small ones to match any reasonable amount of
electromagnetic energy). That's not at all the same as saying
photons have rest mass, though.

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