Editing Interstellar travel (section)

==== Antimatter rockets ====
{{Main|Antimatter rocket}}
{{more citations needed section|date=August 2015}}
An [[antimatter rocket]] would have a far higher energy density and specific impulse than any other proposed class of rocket.<ref name="crawist" /> If energy resources and efficient production methods are found to make [[antimatter]] in the quantities required and store<ref>{{cite web|url=http://home.web.cern.ch/about/engineering/storing-antimatter|title=Storing antimatter - CERN|website=home.web.cern.ch|access-date=5 August 2015|archive-date=28 August 2015|archive-url=https://web.archive.org/web/20150828182849/http://home.web.cern.ch/about/engineering/storing-antimatter|url-status=live}}</ref><ref>{{cite web|url=https://newscenter.lbl.gov/2011/06/05/alpha-quarter-hour/|title=ALPHA Stores Antimatter Atoms Over a Quarter of an Hour – and Still Counting - Berkeley Lab|date=5 June 2011|access-date=5 August 2015|archive-date=6 September 2015|archive-url=https://web.archive.org/web/20150906020619/https://newscenter.lbl.gov/2011/06/05/alpha-quarter-hour/|url-status=live}}</ref> it safely, it would be theoretically possible to reach speeds of several tens of percent that of light.<ref name="crawist" /> Whether antimatter propulsion could lead to the higher speeds (>90% that of light) at which relativistic [[time dilation]] would become more noticeable, thus making time pass at a slower rate for the travelers as perceived by an outside observer, is doubtful owing to the large quantity of antimatter that would be required.<ref name="crawist" /><ref>{{Cite book|last=Rouaud|first=Mathieu|date=2020|title=Interstellar travel and antimatter|publisher=Mathieu Rouaud |url=http://www.voyagepourproxima.fr/SR.pdf|isbn=9782954930930|access-date=10 September 2021|archive-date=10 September 2021|archive-url=https://web.archive.org/web/20210910152837/http://www.voyagepourproxima.fr/SR.pdf|url-status=live}}</ref>

Speculating that production and storage of antimatter should become feasible, two further issues need to be considered. First, in the annihilation of antimatter, much of the energy is lost as high-energy [[gamma radiation]], and especially also as [[neutrino]]s, so that only about 40% of ''mc''<sup>2</sup> would actually be available if the antimatter were simply allowed to annihilate into radiations thermally.<ref name="crawist" /> Even so, the energy available for propulsion would be substantially higher than the ~1% of ''mc''<sup>2</sup> yield of nuclear fusion, the next-best rival candidate.

Second, heat transfer from the exhaust to the vehicle seems likely to transfer enormous wasted energy into the ship (e.g. for 0.1''g'' ship acceleration, approaching 0.3 trillion watts per ton of ship mass), considering the large fraction of the energy that goes into penetrating gamma rays. Even assuming shielding was provided to protect the payload (and passengers on a crewed vehicle), some of the energy would inevitably heat the vehicle, and may thereby prove a limiting factor if useful accelerations are to be achieved.

More recently, [[Friedwardt Winterberg]] proposed that a matter-antimatter GeV gamma ray laser photon rocket is possible by a relativistic proton-antiproton pinch discharge, where the recoil from the laser beam is transmitted by the [[Mössbauer effect]] to the spacecraft.<ref>{{cite journal |last=Winterberg |first=F. |title=Matter–antimatter gigaelectron volt gamma ray laser rocket propulsion |date=21 August 2012 |journal=[[Acta Astronautica]] |volume=81 |issue=1 |pages=34–39 |bibcode = 2012AcAau..81...34W |doi = 10.1016/j.actaastro.2012.07.001 }}</ref>