# Tag Info

107

The total amount of antimatter ever created on earth is not even sufficient to be visible by eye, so it is hard to answer. However, if a bunch of antimatter was available as stable solid or liquid material, there is no reason to think it would look different. Indeed, its interaction with visible light is pretty much exactly the same as usual matter, so it ...

76

Congratulations on finding a method for baryogenesis that works! Indeed, it's true that if you have a bunch of black holes, then by random chance you'll get an imbalance. And this imbalance will remain even after the black holes evaporate, because the result of the evaporation doesn't depend on the overall baryon number that went into the black hole. Black ...

46

This is a great question! It can be answered on many different levels. You are absolutely right that if we stick to the level of classical high school physics, something doesn't make sense here. However, we can get an approximately correct picture by "pasting" together a classical and a quantum description. To do this, let's think of when the classical ...

45

Antimatter looks just like matter. Experimentally, there is no difference between the spectral lines of antihydrogen and of ordinary hydrogen. Same emission spectrum. The photon is its own antiparticle. It interacts in the same way with matter as with antimatter. PS: Very recent Nature article by Ahmadi et al gives an upper bound of $2.10^{-10}$: http://...

44

So, what is antimatter? Even from the name it is obviously the "opposite" of ordinary matter, but what does that really mean? As it happens there are several equally valid ways to describe the difference. However, the one that I think is easiest to explain is that in antimatter, all of the electrical charges on all of the particles, at every level, have ...

39

To maintain lepton number as a conserved quantity. Consider, in detail, what's going on in a beta decay (well, I'm going to ignore the nuclear context). The reaction is then $$n \longrightarrow p^+ + e^- + \nu \,,$$ where you should take the symbol $\nu$ to mean some neutrino (without prejudice about matter-type or anti-matter-type for the moment). There ...

38

The original experiment was designed to find it as a proof of antimatter, not dark matter. the AMS is finally delivering on the promise of its original name when "AM" stood for "antimatter." When Ting sold NASA and DOE on the AMS, he said it might find runaway particles from oases of antimatter, helping solve a deep riddle. The big bang produced matter ...

38

Matter-antimatter annihilation, such as an electron annihilating with a positron to form two high-energy photons, can convert 100% of the mass into radiation. So fission and fusion are far from the most efficient ways to convert mass into other forms of energy. Unfortunately, the universe appears to contain almost no antimatter.

36

A sophisticated, yet easy way to see that this the answer must be "No." is to recall that velocity is relative — that there is no absolute notion of velocity. You said the matter was moving and the antimatter still, but that point of view (AKA frame of reference) is not privileged in any way. An observer at rest with respect to the matter has just as much ...

36

Research has created antihydrogen, and that is about it for the present as far as antimatter in bulk, which one would need for antiwater.. Scientists in the US produced a clutch of antihelium particles, the antimatter equivalents of the helium nucleus, after smashing gold ions together nearly 1bn times at close to the speed of light. They were gone ...

33

If by graviton you mean the spin 2 boson we get from attempting to describe gravity using quantum field theory, then the graviton is its own antiparticle just like the photon.

32

Antimatter has the same mass as normal matter, and its interaction with gravity should be the same according to GR and QM. That said, antimatter has only been created in tiny amounts so far and only few experiments have been performed to confirm there is no new physics involved. The gravitational interaction of antimatter with matter or antimatter has ...

32

The most efficient non-gravitational way of extracting energy from ordinary matter is indeed to convert it into elements in the $^{56}$Fe region. There is a fairly broad plateau of nuclides with binding energies of about $8.7$ MeV per nucleon, so it does not matter very much which of these you actually turn the source matter into. (However, $^{56}$Fe is ...

31

A particle isn't really a point particle; its position is best described by a wavefunction: the probability of finding it in any particular region in space. For annihilation to occur the wavefunctions of the two particles have to overlap - and to the extent that they overlap there will be a probability that annihilation can occur. The greater the overlap, ...

30

Locality The random walk would be expected to create different (opposing) asymetries in different regions, including regions that are distant enough to not affect each other. If this would be the main cause of asymetry, then we'd expect it to cause a predominance of matter in some areas of the observable universe and a predominance of antimatter in other ...

29

Charged antimatter particles are stored using electric and magnetic fields in near vacuum conditions. (Near-vacuum conditions can be created on Earth) Anti-hydrogen is stored by exploiting its magnetic properties. (While neutral, it still has spin magnetic moment. The storage is done using strong superconducting magnets.) Antiparticles are easier to store ...

29

What does a proton look like? Due to the kaon having interacted with a proton in the hydrogen, the rightmost beam track produces a spray of 4 tracks. The longer highlighted track is clearly dark – it has produced a higher number of bubbles per centimetre than, say, the beam tracks; this tells us that it is moving more slowly. (For details, click here.) ...

28

Anti-matter is a lot less exciting than you probably think. If we could magically change all matter to anti-matter by waving a magic wand then it would make almost no difference. The anti-Dirk could drink an anti-glass of anti-water in exactly the same you drink a glass of water. The anti-water would have the same density, boiling point, ability to dissolve ...

28

Although pop sci sources often phrase it in terms of “converting” mass into energy, it is incorrect. $E=mc^2$ says that if you have a stationary mass $m$ then it already has an amount of energy $E=mc^2$. No conversion is necessary. The energy is already there otherwise energy would not be conserved. Also, an amount of stationary energy $E$ has a mass $m=E/c^... 27 Mesons are not elementary, they are composed of quarks. So take a look at their quark content. The charmed eta meson consists of a charm and an anti-charm quark, denoted$c\overline{c}$. An anti charmed eta meson would therefore be an anti-charm and an anti-anti-charm (which is just a charm) quark, i.e.$\overline{c}c$, which is obviously the same as$c\...

26

One cannot tell by the light spectra. Hydrogen and antihydrogen would give the same lines in the spectrum. The prevalence of matter over antimatter from other evidence indicates matter is predominant in the observable universe, and here is a nice review. How do we really know that the universe is not matter-antimatter symmetric? The Moon: Neil ...

26

Bananas are notorious for having high levels of potassium, though a quick Google will find plenty of other potassium rich foods. Anyhow, one of the common radioactive isotopes of potassium is potassium-40. This mostly decays by emission of an electron and anti-neutrino but rarely it can decay by emission of a positron i.e. anti-matter. So it is true that ...

25

There are other neutral particles with antiparticles, such as the neutron and the $K^0$ meson. In those cases we have a microscopic theory that says those particles are made of quarks: for instance, the $K^0$ is made of a down quark and an anti-strange quark, while its antiparticle the $\bar K^0$ is made of a strange quark and an anti-down. The neutrino is ...

24

The only experiment I know of was done by the ALPHA team at CERN. The results are published in this paper. The error bounds are huge - all the team were able to say is that the upper limit for the gravitational mass of antihydrogen is no greater than 75 times its inertial mass! However I believe an updated version of the experiment, ALPHA2, is in progress ...

24

Particle + antiparticle annihilation preserves quantum information. It is often said that annihilation creates a pair of photons, but that's a big simplification. It only applies to the electron + positron, and even in that case it may lead to more than 2 photons. If the electron's and positron's spins are parallel, an odd number of photons must be produced, ...

23

I would have guessed the answer John Rennie gives, but I actually suddenly realize I do not understand why, so I sought to fix this lack of knowledge by some reading. You should wait for upvotes / my deletion of the answer to tell whether to trust it. So, now, why is the postulated graviton its own antiparticle? My understanding is that antiparticles are ...

23

This is the chart of nuclides, i.e. the isotopes of all atoms. The green color shows that most nuclei have isotopes decaying with beta+ decay, i.e. positrons. If you go to the link there is interactive information. From this it is seen that everyday items which will always have a tiny percentage of the long lived isotopes will be decaying into positrons, ...

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