View source for Antimatter

==Properties==
There is no difference in the gravitational behavior of matter and antimatter. In other words, antimatter falls down when dropped, not up. This was confirmed with the thin, very cold gas of thousands of [[antihydrogen]] atoms that were confined in a vertical shaft surrounded by superconducting electromagnetic coils. These can create a [[Magnetic mirror|magnetic bottle]] to keep the antimatter from coming into contact with matter and annihilating. The researchers then gradually weakened the magnetic fields and detected the antiatoms using two sensors as they escaped and annihilated. Most of the anti-atoms came out of the bottom opening, and only one-quarter out of the top.<ref>
{{cite journal
 |last1=Castelvecchi |first1=D.
 |date= 5 October 2023
 |title=Antimatter falls down, not up
 |journal=Nature
 |volume=622
 |issue=7981
 |pages=14–15
 |doi=10.1038/d41586-023-03043-0
 |pmid=37759123
 |s2cid=263121330
 }}</ref>

There are compelling theoretical reasons to believe that, aside from the fact that antiparticles have different signs on all charges (such as electric and baryon charges), matter and antimatter have exactly the same properties.<ref>
{{Cite arXiv
 |last1=Dolgov |first1=A. D.
 |year=2002
 |title=Cosmological Matter-Antimatter Asymmetry and Antimatter in the Universe
 |eprint=hep-ph/0211260
}}</ref><ref>This is a consequence of the [[CPT theorem]]</ref> This means a particle and its corresponding antiparticle must have identical masses and decay lifetimes (if unstable). It also implies that, for example, a star made up of antimatter (an "antistar") will shine just like an ordinary star.<ref name="Dirac-1933b">As Dirac said in 1933 ''It is quite possible that for some of the stars it is the other way about, these stars being built up mainly of positrons and negative protons. In fact, there may be half the stars of each kind. The two kinds of stars would both show exactly the same spectra, and there would be no way of distinguishing them by present astronomical methods.'' {{harvnb|Dirac|1965|page=325}}</ref> This idea was tested experimentally in 2016 by the [[ALPHA experiment|ALPHA]] experiment, which measured the transition between the two lowest energy states of [[antihydrogen]]. The results, which are identical to that of hydrogen, confirmed the validity of quantum mechanics for antimatter.<ref>
{{cite journal
 |last1=Castelvecchi |first1=D.
 |date=19 December 2016
 |title=Ephemeral antimatter atoms pinned down in milestone laser test
 |journal=Nature
 |doi=10.1038/nature.2016.21193
 |s2cid=125464517
 }}</ref><ref>
{{cite journal
 |last=Ahmadi |first=M
 |display-authors=etal
 |date=19 December 2016
 |title=Observation of the 1S–2S transition in trapped antihydrogen
 |journal=Nature
 |volume=541 |issue=7638 |pages=506–510
 |bibcode=2017Natur.541..506A
 |doi=10.1038/nature21040
 |pmid=28005057
 |doi-access=free
 |hdl=1828/11655
 |hdl-access=free
 }}</ref>