
Why is it so hard to study anti-matter? - lubonay
http://www.askamathematician.com/2017/03/q-why-havent-we-been-able-to-see-the-spectra-of-anti-hydrogen-until-recently-why-is-it-so-hard-to-study-anti-matter/
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M_Grey
It's _much_ harder to come by then traditional "incredibly hard to come by"
substances like precious metals or coral snake venom; harder to store, harder
to study, and consequently _much_ more expensive. Keep in mind that something
like a coral snake's venom goes for more than $1000 a gram (Platinum being
~$30), but antimatter according to NASA estimates? $62.5 _trillion_ USD per
gram.

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Twisol
Gosh, I can only imagine how terrifying _a whole gram_ of antimatter would be.
It's kind of a good thing we can only generate it in such minuscule
quantities.

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ben_w
One gram would be about as bad as the Nagasaki nuke, so not that terrifying.

Sure, it's bad, but I only _sometimes_ lose sleep over all the nukes, so…

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eganist
> One gram would be about as bad as the Nagasaki nuke, so not that terrifying.

There's something fascinating about this sentence, but I can't quite put my
finger on what it is.

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eternalban
something to do with anti- ...

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eganist
Is it something material?

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eternalban
In a continental sense.

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itchyjunk
I always wonder why photon is its own anti matter. If it was not so, we
wouldn't be able to study anti matter with lasers for example.

Also, why is the anti particle pair of a charged particle the opposite charge,
but neutral particle/anti particle pair are both chargless? Though it does
make sense that in order to cancel each other out, it must be so..

I would say we live in a strange world but I don't know if a non strange world
would even exist.

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danbruc
_Also, why is the anti particle pair of a charged particle the opposite
charge, but neutral particle /anti particle pair are both chargless?_

That's just the definition of an antiparticle - same as the particle put
opposite charges.

 _Though it does make sense that in order to cancel each other out, it must be
so.._

That's right, this is required to maintain charge conservation in annihilation
processes.

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MereInterest
> That's just the definition of an antiparticle - same as the particle put
> opposite charges.

Well, a bit more is needed. If a particle has no charge, then it is possible
for it to be its own antiparticle, but it is not necessarily so. The photon is
neutral and is its own antiparticle. The neutron, on the other hand, is
neutral but is distinct from the antineutron. It is still an open question
whether the neutrino is its own antiparticle.

~~~
danbruc
_If a particle has no charge, then it is possible for it to be its own
antiparticle, but it is not necessarily so. [....] The neutron, on the other
hand, is neutral but is distinct from the antineutron._

The neutron is only electrically neutral, there are also weak isospin and
color charge. Antimatter is not only concerned with electrical charge but with
charges in general. In case of the neutron and antineutron this becomes
obvious if you compare the quark content of both.

~~~
hwillis
wikipedia:
[https://en.wikipedia.org/wiki/Charge_(physics)](https://en.wikipedia.org/wiki/Charge_\(physics\))

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mschuster91
Regarding that suspended frog... is being suspended in magnetic levitation
painful for the frog? Or could this, one day, be used to create artificial
gravity in space for humans?

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pythonistic
A very strong magnetic field has bad health (neurological and intracellular)
consequences. I can't find a good citation, but this blog post should help
explain the risks.

[https://gravityandlevity.wordpress.com/2015/01/12/how-
strong...](https://gravityandlevity.wordpress.com/2015/01/12/how-strong-would-
a-magnetic-field-have-to-be-to-kill-you/)

~~~
adrianN
The frog levitates at 16 tesla. That's a long way from the fields the article
talks about. Nevertheless, given that our brain reacts to magnetic
stimulation, I'd be wary of using it as artificial gravity.

~~~
M_Grey
...Plus anything metal on/in you would be violently ripped out. This would
make the fields used for a typical MRI look mild by comparison.

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hwillis
Inside a homogeneous magnetic field there is no force. It's kind of like being
under very high pressure- humans can survive many hundreds of psi as long as
the pressure is equal inside and outside the body.

The danger comes when there is a gradient to the field, as happens outside the
coil. Then ferromagnetic material wants to move from the low to high field,
like high pressure water will want to move to low pressure. As long as you're
inside the high field area, you're okay.

This is part of the reason why people can be MRI'd even with shrapnel in their
bodies. When the shrapnel is in the center of the volume being imaged, the
field is _relatively_ homogeneous except for the small induced gradient field.
The shrapnel is already "touching the magnet", so it doesn't feel much more
pull.

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M_Grey
We're talking about using this in the context of "artificial gravity"...
you're going to have a lot "outside of the coil" regions.

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hwillis
It would all occur inside the coil, as the field and therefor diamagnetic
force drops off cubically outside the field.

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M_Grey
Considering the original comment to which I'm ultimately referring, can you
actually imagine such as situation as it relates to _humans_ and "artificial
gravity"? Presumably we're talking about the scale of a space craft or
station...

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hwillis
Yeah, the entire station would be basically a giant solenoid. If you're
outside the coil the artificial gravity doesn't work. You can have metal
flying around without artificial gravity, but you can't get the artificial
gravity in an environment that metal will accelerate inside.

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Sir_Cmpwn
If antimatter has an indistinguishable spectrum from regular matter, maybe
there is more of it in the universe than we thought.

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danbruc
If there were regions of antimatter in the universe, then there would be
boundaries with regions of matter. And on those boundaries a lot of matter
antimatter annihilation would happen, we would see those boundaries glow in
energetic gamma light. We don't see something like that, therefore there are
probably no large region of antimatter in the universe.

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johnfn
Isn't space mostly empty? Aren't galaxies like millions of light years apart,
and don't they collide only incredibly rarely? If some galaxies were
antimatter and some matter, how would we know?

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hwillis
It is the most energetic reaction possible. We can see the background
radiation of the universe- hot objects give off heat, even when they are very,
very cold. The universe glows like it's 3 degrees above absolute zero, and we
can see it. Compared to that antimatter annihilation would look _very_ bright
indeed.

~~~
danbruc
The photons are much more energetic than the cosmic microwave background, the
intensity could still be low enough to escape detection.

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lutusp
Quote: "At the same time, atomic spectra is generated by ..."

s/is/are/

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erikb
Because it is anti and most scientists are pros.

