108 votes

What does antimatter look like?

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 ...
fffred's user avatar
  • 4,266
81 votes

Why is matter-antimatter asymmetry surprising, if asymmetry can be generated by a random walk in which particles go into black holes?

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 ...
knzhou's user avatar
  • 102k
56 votes

If electrons can be created and destroyed, then why can't charges be created or destroyed?

Electrons can only be created and destroyed in processes that keep electric charge constant. There are three Standard Model interactions involving the electron: $\rm W^-\to e^-\bar{\nu}_e$ and $\rm \...
Chris's user avatar
  • 17.2k
52 votes

What kind of matter is positronium?

You should consider positronium as evidence that your partition of the universe into matter and antimatter is overly simplistic. You write that Matter is made up of electron, proton, and neutron. ...
rob's user avatar
  • 89.9k
47 votes
Accepted

Why don't electron-positron collisions release infinite energy?

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. ...
knzhou's user avatar
  • 102k
41 votes
Accepted

Why was the first discovered neutrino an anti-neutrino?

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^+ + ...
dmckee --- ex-moderator kitten's user avatar
38 votes
Accepted

Why is Anti-helium so important in the search for dark matter?

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." ...
anna v's user avatar
  • 234k
38 votes

Is fission/fusion to iron the most efficient way to convert mass to energy?

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 ...
G. Smith's user avatar
  • 51.6k
37 votes
Accepted

Gravity, matter vs antimatter

This is a perfectly good argument and one of the reasons that all the physicists I know believe that antimatter behaves just like matter in a gravitational field. It is important to distinguish ...
John Rennie's user avatar
36 votes
Accepted

Is it possible to obtain antiwater from antihydrogen and antioxygen atoms? And how is its property w.r.t. the ordinary water?

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 ...
anna v's user avatar
  • 234k
35 votes

Is there a possibility for discovery of anti-graviton, i.e. the graviton antiparticle?

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.
John Rennie's user avatar
33 votes

Is fission/fusion to iron the most efficient way to convert mass to energy?

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 ...
Buzz's user avatar
  • 16.1k
33 votes

Why is matter-antimatter asymmetry surprising, if asymmetry can be generated by a random walk in which particles go into black holes?

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 ...
Peteris's user avatar
  • 1,271
33 votes
Accepted

Regarding matter-antimatter asymmetry

Well, suppose that you're in the office and you go to the coffee machine. You notice that there is an incredibly tiny puddle of coffee left in the pot. The pot is almost completely empty, but it's not ...
knzhou's user avatar
  • 102k
33 votes

Do extremely high-voltage power lines emit positrons?

Your analysis doesn't make sense because the units don't match up. $1100 \, \text{kV}$ is not more than twice $510 \, \text{keV}/c^2$, because the two quantities can't be compared at all. It's like ...
knzhou's user avatar
  • 102k
32 votes

Conversion of mass into energy with 100% efficiency

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^...
Dale's user avatar
  • 100k
31 votes

Can positrons attract electrons?

They attract each other and form a system completely analogous to a hydrogen atom, called positronium. This will then annihilate into at least two photons. The half-life time depends on whether the ...
my2cts's user avatar
  • 24.3k
29 votes
Accepted

What does antimatter look like?

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 – ...
anna v's user avatar
  • 234k
29 votes

Is it possible to obtain antiwater from antihydrogen and antioxygen atoms? And how is its property w.r.t. the ordinary water?

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 ...
John Rennie's user avatar
29 votes

What happens to the quantum information of a particle and an antiparticle when they annihilate?

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 + ...
PM 2Ring's user avatar
  • 12.2k
29 votes

If electrons were just positrons moving backwards in time, then shouldn't we see them coming out of black holes?

The short answer to your question is that positrons are not really electrons moving backward in time, and the premise of your argument doesn't work. However, something like what you are saying, is ...
Andrew's user avatar
  • 48.8k
27 votes
Accepted

If the protons in a nucleus were replaced by antiprotons and the electrons by positrons what fundamental change would be introduced into the universe?

Changing all particles into antiparticles and vice versa is known as a charge symmetry operation (C) and for a long time it was believed this would leave everything totally unchanged. Similarly ...
Anders Sandberg's user avatar
26 votes
Accepted

Why is the charmed eta meson its own antiparticle, but the neutral kaon is not?

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 ...
lemon's user avatar
  • 13.2k
26 votes

Is there a known isotope that generates anti-matter?

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 ...
John Rennie's user avatar
26 votes
Accepted

Is it possible that antimatter has positive inertial mass but negative gravitational mass?

A long comment: AEGIS is a collaboration of physicists from all over Europe. In the first phase of the experiment, the AEGIS team is using antiprotons from the Antiproton Decelerator to make a beam ...
anna v's user avatar
  • 234k
26 votes
Accepted

Are the properties of anti-hydrogen opposite to those of hydrogen?

In particle physics, every type of particle is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge) Bold mine. Note physical charges. There ...
anna v's user avatar
  • 234k
26 votes
Accepted

Do laws of physics prohibit direct conversion of particles to antiparticles?

It depends on the particular kind of particle. Assuming the Standard Model holds, then: Electrons can't convert to positrons because that would violate conservation of charge. Neutrons can't convert ...
knzhou's user avatar
  • 102k
25 votes

Why didn't the Klein-Gordon equation suggest antimatter like the Dirac equation did?

In the beginnings of quantum theory, people were looking at the K-G and the Dirac equation as equations for wave functions (or at least something similar that would give them a probability density ...
ACuriousMind's user avatar
  • 125k
24 votes

Is there a possibility for discovery of anti-graviton, i.e. the graviton antiparticle?

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 ...
Selene Routley's user avatar

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