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THE PARADOXES…
If you went back in time and visited your granny during her ninth birthday, don’t kill her! Because if you put a gun to her head and pull the trigger, she could not have given birth to your mum. YOU certainly were never born…
Therefore, you could not have killed anyone as you never existed. Now this means your granny couldn’t have been killed by you. She didn’t die at nine years old. This permits you to be born.
If you were born, could you go back and kill your granny? No, not your real granny. This general idea has been used in Back to the Future. Marty nearly stops himself from being born when he prevents his parents from falling in love.
Solving The Problem
- You simply can’t change history, meaning if you go back in time you have no free will (as shown in Twelve Monkeys, Crime Traveler, etc.). Events will get in your way if you try to kill your granny. YOU CAN’T DO IT.
- When you so-called change history, you’re actually moving up a different branch in time into another universe. The previous universe (where you were born) still exists. When you fire the gun, you’re really killing another version of your grandmother.
- Any actions you make in the so-called past have no effect on the present. It’s a different time-line universe. The laws of true solutions don’t present real time travel as you go into another world.
Conclusion
We can’t simply use the grandmother paradox to rule out time travel, claiming it causes logical inconsistencies. We need to look at all the possibilities.
How could we build a time machine?
The mathematics of general relativity suggest that under extreme conditions, space-time might become so warped it would be possible to travel back in time. There is also the possibility of tunnels in time created by negative mass.
- Very long rotating cylinders of matter – proposed by Frank Tipler
- Kerr’s spinning black holes – since most stars spin, this becomes worth looking into (proposed by Roy Kerr).
- Cosmic strings – as Richard Cott suggested
- Traveling faster than light – would take us back in time (as suggested by solutions to relativity).
- Wormholes might allow us to outpace light (if you walk through the shortcut quicker than light through conventional space).
- Tachyons – are sub-atomic particles which always travel faster than light and therefore move back in time constantly. They have not yet been found and remain hypothetical.
- Contracting Universe – Time might then be running backwards, but since everything else also would, it’s unsuitable.
- Macro-wormholes – Kip Thorne showed how we could use it as a time machine.