# How does this confirm special relativity?

Tags:
1. Feb 11, 2017

### sander69

2. Feb 11, 2017

### mathman

From article:
Explaining exactly why special relativity requires antimatter to mirror matter involves a lot of math. But in a nutshell, if that mirror relationship were not exact, then the basic idea behind special relativity couldn’t be exactly right, Kostelecky says. Special relativity assumes that a single unified thing called spacetime splits differently into space and time for observers moving relative to each other. It posits that neither observer can say who is really moving and who is stationary. But, that can’t be exactly right if matter and antimatter don't mirror each other.

3. Feb 12, 2017

### Staff: Mentor

It looks like they are talking about CPT invariance (charge parity time). I don't know the mathematical derivation, but apparently if a theory is the same when you swap charge parity and time then it follows special relativity and vice versa.

That said, I am unclear how this experiment tests that. As far as I know antihydrogen is just a charge reversal compared to regular hydrogen. So this should be only a test of C invariance, not CPT.

4. Feb 12, 2017

### Mister T

Doesn't it go back to the Dirac equation? I don't understand the details, but isn't that a relativistic quantum theory that predicts the existence of antimatter.

5. Feb 12, 2017

### Staff: Mentor

Antiparticles are CPT conjugates of particles, so antihydrogen is the CPT conjugate of hydrogen. The charge reversal is the one that's obvious, but strictly speaking, if you look at the quantum wave functions, you have to take into account P and T reversal as well.

(The actual atoms and antiatoms are not states with definite parity either, which also complicates things in the detailed analysis.)

6. Feb 12, 2017

### Staff: Mentor

Oh, I didn't realize that. That makes sense.

7. Feb 14, 2017

### vanhees71

There's a famous theorem that any local relativistic QFT with a stable ground state, where relativistic means that the QFT leads to an S matrix that's invariant under special orthochronous Lorentz transformations must (a) for each particle also contain its antiparticle (where particle and antiparicle can be the same in the case of strictly neutral particles like the photon) and (b) the theory is also invariant under the combined CPT symmetry: If there's a process described by such a QFT there must be possible also a process, where all particles are interchanged with their antiparticle (C), space is reflected (P), and the time-reversal of the original process is (T) considered.

So, strictly speaking, ever more precise tests of this CPT theorem do not test just special relativity but also the restricting assumption that relativistic quantum theory is correctly described by a local relativistic QFT with a Hamiltonian bounded from below. So far CPT has been confirmed with all available experiments today.

8. Feb 14, 2017

### Ibix

...so CPT says a hydrogen emitting a photon in the +x direction should look like an anti-hydrogen absorbing a photon (which is the same as an anti-photon) coming from the -x side? Which implies that the absorbtion and emission frequencies of a hydrogen and an anti-hydrogen must be identical. So testing that they are identical tests CPT symmetry, which is an implication of quantum field theory, which requires relativity. So testing for identical frequencies is a test of relativity.

...right?

9. Feb 14, 2017

### vanhees71

It's a test of relativity under the additional assumption that the postulates underlying the Standard Model of elmentary particle physics hold true. Although I'm not aware of any consistent formulation of relativistic QT which is not a local relativistic QFT with a Hamiltonian bounded from below, in principle there could be such a theory, and then you could have a relativistic QT (i.e., a QT which is invariant under proper orthochronous Poincare transformations) but for which CPT is not a symmetry. As I said, that's however very speculative since against all efforts to find a violation of the predictions of the standard model (including tests of CPT symmetry) so far no such violations have been found. So far the Standard Model thus survived all tests ever done.

10. Feb 14, 2017

### Mister T

From the article in the current (February) edition of Physics Today, speaking about the transition between antihydrogen's 1s and 2s states ...

Would I be correct to conclude that orders of magnitude improvements will need to be made before we can even hope to see any differences between the spectra of hydrogen and antihydrogen?