Lies in education [was Re: The "loop and a half"]

[Steve D'Aprano]

On Thu, 5 Oct 2017 02:14 pm, Stefan Ram wrote:

> Chris Angelico <rosuav at gmail.com> writes:
>>You can get through a lot of life believing that mass is conserved,
>>but technically it is not, as can be proven.
> 
>   Well, in fact, it is conserved.

It certainly is not. The whole point of Einstein's equation E = mc² is that
energy and mass are freely convertible. Neither energy nor mass alone are
conserved.


>   When an electron and a positron annihilate to give a gas of
>   two photons, this gas as a whole still has the same mass as
>   the electron before. And its center of gravity moves with
>   less than c.

That doesn't sound like any description of matter/anti-matter annihilation
I've every seen before.

I think you may be conflating the concepts of clouds of virtual
electron/positron particles with actual annihilation events between real
electron/positron particles.

In actual annihilation events, there is (as far as I know) generally a single
real photon produced, with momentum equal to the sum of the momentum vectors
of the original electron and positron. That moves away from the point of
production at the speed of light.



-- 
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.