"Let's say time travel is possible. so what'll happen if someone goes back in time and kills their ancestors (old question)? could you explain it in layman's terms?"
Asked by: Prë Shānk
I really enjoy theoretical and quantum physics, and luckily, such a question has been explored in theory... AND in practice! I will stay clear of any complex ideas, words and explanations for this one... let me begin...
I'll use myself as the lab-rat here for this explanation. Let us state that in a moment of epiphany, I managed to build myself a fully-functional time-machine. I used this device to travel to World War 1, which my great-grandfather fought in (and survived) shortly before meeting my great grandmother. But, in a moment of homicidal madness, I decided it would be a hilarious prank to kill him.
The problem has arisen - if I kill my great grandfather, how can I exist in the current time-line? If he dies, he won't meet my great-grandma. They won't conceive my grandfather, which also means my father would never be born. Unless we are talking about immaculate conception (we're not), I wouldn't be born either. Thus, I will not be alive to build a time machine, or travel back in time... which PREVENTS me from traveling back in time to kill him. So he technically lives. Even though I killed him... and myself, in the process.
This sort of occurrence is a scientific enigma -- one that is generally thought to be impossible to resolve (much like traveling faster than the speed of light). This is known in theoretical physics as the 'Grandfather Paradox.' Luckily however, some rather smart quantum physicists dabbled with quantum mechanics, and discovered that it was possible to teleport a single photon along the time-line. Once this was discovered, they thought about how to address the issue of the grandfather paradox - the very issue that deemed time-travel impossible!
The quantum physicists isolated a single photon and fitted it with what they called a 'Quantum Gun'. When they sent it into the past, it would kill its earlier incarnation, thereby destroying itself (and potentially the entire universe too).
So what happened in the results? Well, when the photon was teleported back in time, the quantum gun would NOT function. Yet it WOULD function when it did not teleport back in time. This hinted one of two things - either time travel somehow damaged the quantum gun, OR, the more likely option (though it does sound very disconcerting), the universe has some kind of a defense mechanism in place that disabled the photon from destroying its earlier self.
This opens up a whole new level of thought - could humans travel back in time, but instead of it working out in the manner in which we previously thought, the universe would simply stop events that would prove fatal to the ancestor human from affecting the timeline? You could, in theory, travel back in time, swing an axe at your relative, yet instead of successfully killing him or her, the axe would fall out of your hands, or you would randomly fall down and die; preserving the integrity of the time-line, while destroying yourself and yourself only.
If you enjoyed this article, you might also like several other articles of ours that relate to time. Check them out: Time: Examining the Wibbly, Wobbly, Timey Wimey…Stuff, Does Time Exist, How We Can Hide Events From Time, If Time Were 2D, Is time Disappearing From the Universe & How Can We Travel Through Time?