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21 votes
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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's user avatar
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16 votes

Do particle & anti-particle pairs belong to the same field?

Yes, that is correct. In fact, you don't even need quantum field theory for this. The Dirac equation was the original relativistic equations describing the quantum behavior of the electron, and it ...
Níckolas Alves's user avatar
15 votes
Accepted

Does antimatter have the same half-life as ordinary matter?

To say that scientists have created anti-helium-4 is a bit of an overstatement. Anti helium 4 nuclei (just the nucleus, no positrons orbiting it to make a neutral anti-atom) have been observed in LHC ...
AXensen's user avatar
  • 7,372
13 votes
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Would normal atoms and antimatter atoms be attracted to each other?

As far as we know, antimatter is affected by the same four fundamental forces as matter - the strong, weak, electromagnetic and gravitational forces. There is no mysterious fifth force that attracts ...
gandalf61's user avatar
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9 votes

Meaning of annihilate

As a naive person I thought annihilate meant destroy. Yes, that is what it means. Matter and antimatter destroy each other, cancel each other, nothing left over. No, not necessarily. First, you ...
hft's user avatar
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9 votes
Accepted

How can the Klein-Gordon equation have negative-energy solution if its Hamiltonian is positive-definite?

If you interpret the Klein-Gordon equation as describing a field theory (which is the modern way to look at it), then yes, the energy of the field is positive definite. The problem is if you try to ...
Andrew's user avatar
  • 49.7k
8 votes

If matter cannot be created or destroyed, how were scientists able to "create" matter out of light?

Matter can be created and destroyed. Matter is not a conserved quantity. Conserved quantities include energy, momentum, charge, angular momentum, etc. Those cannot be created or destroyed, at least ...
Dale's user avatar
  • 102k
8 votes

Do particle & anti-particle pairs belong to the same field?

Do particle & anti-particle pairs belong to the same field? Yes. For example, in Quantum Electrodynamics the Dirac field operator is usual written in terms of annihilation operators $a_{\vec p}^s$...
hft's user avatar
  • 20.7k
7 votes

Is the charge-conjugation symmetry in cond-mat physics different from that in QFT?

In condensed matter physics one can define holes as simple charge conjugation. E.g., if we define the ground state as $$ a_{\mathbf{k},\sigma}|0\rangle=0,\text{ if } k>k_F,\\ a^\dagger_{\mathbf{k},\...
Roger V.'s user avatar
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7 votes

Can bosons have anti-particles?

This is the answer to the bounty call "Can anyone give a proper source, does Higgs boson has an antiparticle or not, it is the own antiparticle itself. Both Wikipedia and ChatGPT are sure it does ...
OON's user avatar
  • 8,344
7 votes

Lagrangian for a free antimatter particle

My question is this: Is the Lagrangian of an antiparticle $$ L = +mc^2\sqrt{1-\frac{v^2}{c^2}}? $$ No. An antiparticle has the same mass as its particle partner. The antiparticle has the opposite ...
hft's user avatar
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6 votes
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Color vectors for antiquarks

From the above table, I can see that we need to have $F_3 \bar{r} = - \frac{1}{2} \bar{r}, \ \ F_3 \bar{g} = \frac{1}{2} \bar{g} \ \ F_3 \bar{b} = 0.$ ... What am I doing wrong? No. That's what you ...
Cosmas Zachos's user avatar
6 votes

How can the Klein-Gordon equation have negative-energy solution if its Hamiltonian is positive-definite?

Briefly speaking, there are at least two notions of energy $E$ and momentum ${\bf p}$: One notion stems from the Fourier-transform $({\bf x},t)\to ({\bf p},E)$ of spacetime, or equivalently, a plane-...
Qmechanic's user avatar
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6 votes
Accepted

Lagrangian for a free antimatter particle

The Lagrangian of a classical charged particle $\mathrm Q$ in an EM field is given by $$L_{\mathrm Q}(V,\mathbf A)=-mc^2\sqrt{1-\frac{v^2}{c^2}}+q\mathbf v \cdot \mathbf A -q V,$$ where $q$ is the ...
Mauricio's user avatar
  • 5,476
5 votes

How can the Klein-Gordon equation have negative-energy solution if its Hamiltonian is positive-definite?

You have a valid point. 'Negative energy solution' is a misnomer. Negative as well as positive frequency solutions have positive energy, as the Klein-Gordon hamiltonian correctly implies. As an ...
my2cts's user avatar
  • 24.5k
5 votes
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Average momentum of particle/anti-particle pairs

Your question hits on a lot of misconceptions, mostly derived from pop sci (YouTube) descriptions of virtual particles. There are at least two classes of virtual particles. Your favorite content ...
JEB's user avatar
  • 34.3k
5 votes

Do particle & anti-particle pairs belong to the same field?

That's ambiguous. Fermionic particles and anti-particles are most consisely discribed by a single field with multiple components. Its however always possible to decompose these and describe them as ...
Fictional's user avatar
  • 216
4 votes

Current bounds on the value of $g$ for antimatter

The ALPHA collaboration released their paper answering this today! The result is that the gravity experienced by antimatter (anti-hydrogen) is 0.75 ± 0.13 (statistical + systematic) ± 0.16 (simulation)...
Charles's user avatar
  • 756
4 votes

Are two oppositely charged black holes, matter & antimatter?

Antimatter of charged particles have the opposite charge. But this does not say that opposite charged matter is antimatter. just take not a black hole but a normal piece of matter you can charge two ...
trula's user avatar
  • 6,229
4 votes
Accepted

Are electrons and positrons part of a family of 4 (8? 16?) similar particles?

All charge-like quantum numbers flip upon a change of a particle to an anti-particle. In other words, charge-like quantum numbers are correlated. It is not like that one has a distinct particle with ...
Frederic Thomas's user avatar
4 votes

Lagrangian for a free antimatter particle

So, the kind of Lagrangian you are using from Landau describes a free particle as they understood within the context of the special theory of relativity. Now, particles like electrons and their anti-...
Albertus Magnus's user avatar
4 votes

Average momentum of particle/anti-particle pairs

In special relativity, we want to keep track of the four-momentum since it transforms as a Lorentz covariant object. Taking that into account you can find a Lorentz invariant quantity, namely $p_\mu p^...
Lucky Charms's user avatar
4 votes

Would normal atoms and antimatter atoms be attracted to each other?

Antimatter isn't attracted to normal matter by any extra special forces (as far as we currently know), it still obeys the four fundamental forces. The attraction would be the same as if they were both ...
Paolo Mancini's user avatar
4 votes

Has anyone measured the energy output of matter/antimatter annihilation?

I'm not sure if this answers your question, but Positron Emission Tomography (PET) is a standard type of medical imaging and uses a matter-antimatter annihilation process - namely electrons and ...
ad2004's user avatar
  • 1,106
3 votes
Accepted

Are two oppositely charged black holes, matter & antimatter?

Black holes are objects of the classical theory of General Relativity. There are no quantum particles or antiparticles in this theory. So there is no such a thing as an “anti-black-hole”. The No-Hair ...
safesphere's user avatar
  • 12.7k
3 votes

Why does the Matter Anti-Matter imbalance require breaking CP symmetry? Why can't it occur if time symmetry is broken?

Let's define our terms, just to make sure we are talking about the same thing. In a Lorentz-invariant model, where your system is unchanged under rotations and boosts, there are three discrete ...
rob's user avatar
  • 90.7k
3 votes

Are there any black holes made of antimatter?

According to theory, a black hole resulting from the collapse of antimatter is indistinguishable from one resulting from the collapse of matter. If a difference were found, that would invalidate the ...
John Doty's user avatar
  • 21.2k
3 votes
Accepted

Negative energy solutions not a problem for Klein-Gordon equation?

Both the Klein-Gordon and Dirac equations, if interpreted as RQM equations, have negative solutions. It is not that we are saying that Klein-Gordon gets a free pass. It is that nobody cared about the ...
naturallyInconsistent's user avatar
3 votes

If matter cannot be created or destroyed, how were scientists able to "create" matter out of light?

It is more accurate to think about conservation of mass as conservation of energy. That is, in an isolated$^1$ system, the total (mass + energy) will remain constant (as opposed to just the total mass ...
joseph h's user avatar
  • 29.6k
3 votes

If an electron is an elementary particle, where is charge "stored"?

The full information about all properties of (free) electrons and positrons is "stored" in the (quantum) field operator $$\psi(x) =\sum\limits_s \int d\mu(p) \left[ b(p,s) u(p,s) e^{-ip\cdot ...
Hyperon's user avatar
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