[Still off-top] Physics [was Requests author discusses MentalHealthError exception]
Steven D'Aprano
steve at pearwood.info
Thu Mar 3 19:04:28 EST 2016
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)
>
> To be honest it is all over my head
It's good to be honest :-)
Yes, anti-matter has positive mass. There was still some tiny lingering
doubt up until (by memory) 20 years ago, at which time physicists actually
managed to make sufficient anti-matter that they could assemble it into
slow-moving atoms and observe the effect of gravity on it, and sure enough,
anti-matter falls due to gravity the same as regular matter.
(There wasn't really any serious doubt about this, since you can pull and
push anti-matter with electric and magnetic fields and it behaves exactly
the same way as regular matter. But if gravity had turned out to be
different, it would have been a truly paradigm-changing discovery.)
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.
--
Steven
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