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 ...
- 4,286
82
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 ...
- 105k
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 \...
- 17.3k
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♦
- 94.2k
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. ...
- 105k
39
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."
...
- 235k
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 ...
- 52.2k
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 ...
- 363k
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 ...
- 235k
34
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 ...
- 1,281
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♦
- 17.1k
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 ...
- 105k
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 ...
- 105k
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^...
- 109k
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 ...
- 26.6k
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 – ...
- 235k
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 ...
- 363k
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 + ...
- 13k
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 ...
- 55.4k
28
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 ...
- 33.4k
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 ...
- 235k
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 ...
- 235k
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 ...
- 105k
26
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 ...
- 129k
24
votes
Gravity, matter vs antimatter
In addition to John's answer:
There is a subtlety in antimatter. In the standard model it is axiomatic that matter and antimatter have the same sign mass. But as long as gravity is not quantized in ...
- 235k
23
votes
If the protons in a nucleus were replaced by antiprotons and the electrons by positrons what fundamental change would be introduced into the universe?
If protons become antiprotons, but neutrons don't become antineutrons, then atomic nuclei will blow up, since antiprotons are made of antiquarks but neutrons are made of quarks.
- 13.4k
21
votes
Accepted
Observation of the effect of gravity on the motion of antimatter
Usually these error estimates are "one sigma" error bars, which is roughly the same thing as a 68% confidence limit. If you have an ensemble of data with $1\sigma$ error bars, you expect ...
rob♦
- 94.2k
20
votes
Accepted
Why do we not know whether or not neutrinos are their own antiparticles?
We know that neutrinos and antineutrinos exist, and it's possible to tell the difference between them. For example in a charged current detector electron neutrinos produce this reaction:
$$ \nu + n \...
- 363k
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