XPost: sci.physics.relativity
From: bill.sloman@ieee.org
On 13/02/2026 3:44 am, john larkin wrote:
> On 12 Feb 2026 16:23:57 GMT, ram@zedat.fu-berlin.de (Stefan Ram)
> wrote:
>
>> john larkin wrote or quoted:
>>> Do photons have the same gravitational effects as their mass
>>> equivalents?
>>
>> The electromagnetic stress-energy tensor bends spacetime. To see the
>> Hilbert stress-energy tensor T of a source-free electromagnetic field
>> F, please see the section "Electromagnetic stress-energy tensor" on
>> the Wikipedia page "Stress-energy tensor". (I think this also is
>> equation 4.2.27 in "General Relativity" (1984) - Robert M. Wald.)
>>
>> A single photon does not have mass, while a pair or gas of photons can
>> have mass.
You are confusing rest mass (which a photon lacks) with mass-energy.
The energy tied up in photon has mass, and that will have a
gravitational effect.
> That's what most sources say: m means mass as used by Newton and
> Einstein, and is what's in gravitational equations, and photons don't
> have any.
Einstein talks about mass-energy, not mass, and clearly didn't have the
same idea in mind as Newton had.
> So when two gammas collide and create a particle pair, mass appears
> where there was none.
>
> Right so far?
Wrong. The first LIGO observation was of two black holes merging
https://en.wikipedia.org/wiki/GW190521
"At 85 and 66 solar masses (M☉) respectively, the two black holes
comprising this merger are the largest progenitor masses observed to
date. The resulting black hole had a mass equivalent to 142 times that
of the Sun, making this the first clear detection of an
intermediate-mass black hole. The remaining 8 solar masses were radiated
away as energy in the form of gravitational waves."
Not only do photons have mass, but gravity waves do too.
--
Bill Sloman, Sydney
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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