[Still off-top] Physics [was Requests author discusses MentalHealthError exception]

[Oscar Benjamin]

On 4 March 2016 at 00:04, Steven D'Aprano <steve at pearwood.info> wrote:
> On Fri, 4 Mar 2016 07:20 am, alister wrote:
>
>> On Thu, 03 Mar 2016 11:03:55 -0700, Ian Kelly wrote:
>
>>> Antimatter has positive mass.
>>
>> Are you sure?
>>  mix 1 atom of hydrogen + 1 of anti hydrogen & you end up with 0 mass (+
>> LOTTS of energy)

This is incorrect. Mass and energy are both conserved. In a
particle/antiparticle annihilation new particles are created. See
here:
https://en.wikipedia.org/wiki/Annihilation

The mass is carried by the new particles. The new particles may have a
total *rest mass* which differs from the total rest mass of the
previous particles. However the total mass is the rest mass plus the
mass associated with the "kinetic energy" of the particles.

> As far as the reaction of matter and anti-matter, we've known for about a
> century that mass and energy are related and freely convertible from one to
> the other. That's the famous equation by Einstein: E = m*c**2. Even tiny
> amounts of energy (say, the light and heat released from a burning match)
> involve a correspondingly tiny reduction in mass.

This is also incorrect and suffers from the same misinterpretation as
above. Mass and energy are not interchangeable in the sense that you
can exchange one for the other with e=mc^2 giving the exchange rate.
Rather mass and energy are *the same thing*. Although they are
different concepts defined in different ways and having different
dimensions and units they are inseparable: e=mc^2 gives us the
proportion in which the two appear together.

--
Oscar