[Off-topic] Requests author discusses MentalHealthError exception

[Gregory Ewing]

alister wrote:
> On Thu, 03 Mar 2016 11:03:55 -0700, Ian Kelly wrote:
> 
>>On Thu, Mar 3, 2016 at 10:21 AM, alister <alister.ware at ntlworld.com>
>>wrote:
>>
>>Antimatter has positive mass.
> 
> Are you sure?
>  mix 1 atom of hydrogen + 1 of anti hydrogen & you end up with 0 mass

That's not because anti-hydrogen has negative mass, though.
It's just because photons happen to have zero mass. (You're
assuming here that photons are the only products, which is
not the only possible result, but it's one of the possibilities.)

Mass on its own is not a conserved quantity. The thing that's
conserved is total energy. Mass is just the energy something
has when it's standing still, so if the anti-hydrogen had
negative mass, it would also have negative energy when at
rest, and you would get a total of zero energy out of the
reaction. This is not what happens.

As far as I know, there are no negative masses anywhere in
any of our current theories of physics, nor have we observed
anything that would suggest the need for such a thing.

-- 
Greg