Antimatter is the opposite of normal matter & has the same mass of normal matter but the charge carried by it is opposite. When matter and antimatter meet, they annihilate each other producing pure energy.
It is believed that equal amounts of matter & antimatter were formed after the Big Bang. Today, there is a negligible amount of antimatter in the universe. Normal matter dominates antimatter.
But, what would've happened if our universe was made of antimatter? What would the planets, stars & galaxies made of antimatter look like? Antimatter can be made in the laboratories. But handling & storing it offers many challenges which makes it the costliest thing in the universe.
Considering the level of technology we have today, physicists have been able to make antihydrogen and study its properties. It's been experimentally proven that anti-hydrogen produces exactly the same light as regular hydrogen. So, an antimatter Sun would be exactly the same as our Sun. People living in an antimatter universe would witness the universe exactly as we do.
So, does that mean galaxies made of antimatter might be existing somewhere in the universe? Although, theoretically possible, if antimatter galaxies were out there, we would see them interacting with regular matter in their vicinity. These galaxies would thus be blasting out radiation and would be annihilated completely after some time which is not what we observe in space.
The mystery of antimatter is still an unsolved mystery in Physics. Nobody knows where all the antimatter went.
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