Why is it so hard to study anti-matter? | Hacker News Reader

Why is it so hard to study anti-matter?

askamathematician.com

51 pointslubonay79 comments

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.

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.

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…

> 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.

something to do with anti- ...

Is it something material?

In a continental sense.

I just want to say how much I appreciate you leaving the ~50% of energy released as neutrinos out of your explosive yield estimate, you almost never see that.

Luck rather than skill, I'm afraid: I was just rounding and consider a factor of x2 to be close enough for things like this.

Well... credit for solid intuition then.

At least nuclear weapons only go off when the detonation explosives are triggered in exactly the right way. Anti-matter goes boom if anything goes wrong with the confinement system.

I do not recommend spending a large percentage of Gross World Product on antimatter weapons.

Or even a small percentage, if antimatter becomes cheaper.

In fact, I'd go as far as to suggest that — if you can figure out how to make and keep it — world peace is much better than having any military.

Of course this leads into the realistic aspect of science fiction... sufficiently advanced drive technology is indistinguishable from a weapon of mass destruction. We love to talk about fusion drives or antimatter reactions propelling us beyond Earth, but the truth is that such technology has a very dark side and one we're historically likely to exploit.

Little Boy was 0.7 gram mass equivalent, Fat Man was 1.0 gram. So you are looking at almost three times Hiroshima or two times Nagasaki.

Several militaries are looing into making it happen anyway:

http://cui.unige.ch/isi/sscr/phys/anti-BPP-3.html

https://arxiv.org/abs/physics/0507125

Note: The second one has very interesting implications for safety of citizens in countries possessing such devices. Especially given the number of accidents in nuclear transportation and command/control. ;)

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.

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.

> 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.

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.

wikipedia: https://en.wikipedia.org/wiki/Charge_(physics)

> I always wonder why photon is its own anti matter.

I speculate that that is because Photons are 'transcendent' (in some some sense).

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?

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...

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.

...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.

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.

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

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

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...

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.

Not necessarily be ripped out but it will heat up substantially.

Only in an oscillating field. In an MRI the gradient coils cycle on and off rapidly (rapid in human terms), which causes minor hysteresis heating. In a static field there would be no heating.

The human brain is almost completely unreactive to magnetic fields. The trick with TMS is that it creates an extremely short pulse- a time varying field, which induces a voltage at the focal point of the field. This voltage is on the order of 100 mV, which is well in excess of what is needed to trigger all of the nerves in an area to fire.

Static fields do not have the same effect unless you are moving through them at immense speed, eg passing from a region of 2 Tesla to 0 Tesla in a few milliseconds which would mean moving around the speed of sound through an MRI.

That article is a completely different kind of "very strong". Our "very strong" is a 1-2 Tesla, the strength of a high end neodymium magnet. Levitation is about 10x higher than that but in practical terms, it's not really that different from holding a big magnet to your face. It does not affect any significant chemical reactions.

This article is talking about fields so high that chemistry fundamentally breaks down and matter breaks into individual atoms. This only happens in neutron stars. It's 1,000x stronger than any field made by humans and 10,000x stronger than levitation fields. At these fields the atoms literally change shape.

Artificial gravity is easy to produce in space: just create a rotating frame of reference, such as a torus-shaped living quarters. Even if you set aside the other problems with very strong magnetic fields, generating one powerful enough to accelerate humans at roughly 9.8m/s is going to require a LOT of energy and some very bulky, finicky equipment (such as cooling for the superconductors). At that point why not just build a large motor and rotate the station?

Coriolis and associated vomiting for one

That can be solved by making the diameter of the torus large enough that the difference in acceleration between head and feet is not too high.

For 1g, the diameter of the spaceship would be a kilometer or more to seem normal. Possible, but it'll be beyond our means for quite a while.

Right. When I said "easy", I meant "easy relative to producing some ungodly strong magnetic field to do the job".

Not too hard at all if you tether two ships

No, the frog is not at all aware of what is happening. Basically to it, gravity has just shifted to higher up rather than always down.

This... would work for artificial gravity, you just need massive coils in the floor and ceiling. This field is 10-100x higher than the quench fields of superconductors[1], so there is no known technology that would be capable of making fields on such a large scale continuously. Even if there was the power requirements would be on a different scale. If we had that capability we would probably be way beyond having to worry about things like gravity.

[1]http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/scbc.html)

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

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.

Gotcha, makes sense. Are we sure the density of the intergalactic medium is high enough to make interactions between matter and antimatter produce light visible from long distances, though?

We have bounds on the density near such boundaries and their distance from Earth above which they would become visible. [1]

[1] https://en.wikipedia.org/wiki/Baryon_asymmetry#Regions_of_th...

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?

The space between galaxies is not completely empty, there is still about one atom per cubic meter. Boundaries in outer space would stretch across billions of square light years, enough space to generate noticeable signals even at such low densities.

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.

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

Watch this: https://www.ted.com/talks/david_deutsch_on_our_place_in_the_...

Any reason to suspect that these regions aren't just much larger than the observable universe?

That question is a nonstarter, essentially. Physics is interested and concerned with why the observable universe has almost no antimatter, so asking "what if all the antimatter is outside the observable universe" doesn't actually answer the question.

One could maybe argue that there has to be some fundamental asymmetry between matter and antimatter. If there were none, you have to find a good explanation why there was not the same amount of matter and antimatter right after the Big Bang and why therefore not all matter and antimatter just turned into photons leaving behind an empty universe. If on the other hand there is an asymmetry and matter is favored over antimatter, then the matter we see today would just be the difference left over after all the antimatter annihilated. In that case there seems to be no obvious reason why regions should form.

It's reasonable to suppose that if in one experiment you replace each particle by it's antiparticle you will get the same result. (Symmetry C) The problem is that this is not true in all experiments :(

It's reasonable to suppose that if in one experiment you make a mirror image of all the part of the experiments, with the mirrored version of all the velocities and spin, you will get the same result. (Symmetry P) The problem is that this is not true in all experiments :(

(I'll skip T symmetry.)

For some technical reason it's more easy to expect that if you combine both symmetries and change all particles by the antiparticle and make a mirrored version, you will get the same result. (Symmetry CP) This is almost almost almost true. Not completely true, but it's difficult to make an experiment where the result is different.

So, in some experiments the CP version is different from the original version. It is possible to measure this in a laboratory, and this is one possible explanation of the different of the amount of mater and antimatter around us, but no one is sure about the details. See https://en.wikipedia.org/wiki/CP_violation#CP_violation_and_...

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

s/is/are/

Because it is anti and most scientists are pros.

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