Why can't we use the laser based methods for creating anti-matter as a fuel? A few years ago scientists were able to form positrons using gold from a laser. Why can't we just use a sort of positrion plasma as a kind of fuel? I presume it would be too hard to contain them all because of the enormous positive electric feild but I am unsure.
 A: The methods we currently have to create it require very, very expensive equipment, are very, very energy inefficient, and can't create a lot of it which together make it almost unimaginably expensive. The most expensive material on Earth. Those two things make other disadvantages, being really dangerous and energy intensive to store, irrelevant.
NASA says that 1g of anti-matter costs 62 trillion dollars to make.
https://science.nasa.gov/science-news/science-at-nasa/1999/prop12apr99_1
And the energy required to produce it given by this link:
https://www.symmetrymagazine.org/article/april-2015/ten-things-you-might-not-know-about-antimatter
equates to ~500 million times more energy to produce than the energy you would get out of it, which is just a little under 3 Hiroshima bombs.
For 62 trillion dollars, you could fund the Manhattan project then build a lot of Hiroshima bombs AND build a lot of nuclear power plants, AND build the uranium mine, AND build the uranium refinery, AND pay the staff to run them all.
