I broke my rule of not reading medium articles, but how exactly does this prevent the grandfather paradox? Once you're back in time you can still stop yourself in the future from entering the worm hole...
One proposal is the Novikov self-consistency principle.
Imagine a billiard table with a wormhole, which curves and goes three seconds backwards in time. It's set up so you can roll a ball into the wormhole, and it will emerge three seconds earlier and knock itself off the path, so it doesn't enter the wormhole. Paradox!
Except actually it emerges with a slightly altered path, and strikes itself only a glancing blow.
And why did it emerge with an altered path? Because it was struck a glancing blow.
The idea is that you can't do that because the conditions necessary for you to be at the entrance of the time travel working prevent you from being at the exit of the wormhole at the same time.
To get to the entrance, you must leave the Earth (with the entrance) at time X. After you've left, you can enter the wormhole and emerge from the Earth side at time X+e.
You leave Earth in 2020. You leave one end of the wormhole here, and take the other with you on a near-light-speed journey 40 light years away. One year goes by for you due to relativity, you pick up a burger from alien McDonald's, then step into your wormhole- which exits in 2021, not 2040.
Edit: no wait, I can't be understanding this right. You could just journey back home with your wormhole and give it to someone else.
Where's the paradox? Given that a person has already appeared out of nowhere - matter/energy has been created - I'd say that having someone with identical genetic make-up to them running around is minor stuff.
I exist in 2017. I go to 1978. I kill my other form before 2017 is reached. Therefore I cannot have traveled to 1978. What has occurred at each particualy moment is no longer consistent in a way that is clearly comprehensible by humans.
It's either perfectly consistent if you go minute by minute, or consistency goes out the window without any murder.
1978: Some matter and energy materializes. It appears to be a human being. Where did it come from? It's impossible to tell; it has no past as far as we're concerned.
1978: Oh my god, the mystery human has just killed another human. They look kind of alike, I guess.
1978: The mystery human is now in prison; its lack of citizenship or identity ("yeah, born in 1952 my ass, you're clearly at least 50 years old") does not prevent its incarceration.
2017: Nothing of note happens. Mystery human would be eligible for parole, if he hadn't died behind bars in 1996.
I think the last part is key: comprehensible to humans. I see the paradox but it’s a logical one not necessarily a physical one. I’m not even sure what time travel really means. Do you look at a river and think to capture it exactly as it was an hour ago? Would it really be the old river then? If you did capture it and add a few extra drops then set it in motion would there really be a problem? I’d posit that the past does not exist except as a mental construct to begin with. A “present moment” doesn’t even exist, how could you have a past moment to return to?
Actually, of interest Wikipedia seems to say that you wouldn't have to leave Earth at all (just bring the other half of the wormhole back), so I think you're right that it doesn't solve the grandfather paradox: https://en.wikipedia.org/wiki/Wormhole#Time_travel
But maybe when you go back you instantaneously become you? That would close the loop. The future you had essentially ceased to exist anyway so there's no reason to go back.
You'd need to physically catch up to yourself (your parents, in the case) which is impossible given they are traveling at the speed of light, in chase of the other end of the wormhole. At least that's what I could gather.
Why not send the wormhole on a circular journey? Accelerate out, decelerate, accelerate back, decelerate. Enjoy two relativistic trips, and end up parked side-by-side.
This is the mechanism Stephen Baxter used in his Xeelee sequence novels.
I like to think of it as a feedback loop stabilizing. I think it's the model used in Harry Potter. We won't be able to observe what happens during the stabilization. Paradoxes become impossoble then.
I consider their quality to be consistently low. This one is basically a weak summary of a Wikipedia article or two along with some overzealous assumptions.
Funny for me to read this, because I’d sworn off Medium articles too for the same reason, yet never heard other people talking about it.
I wouldn’t say it’s quality overall - many are well-written - rather that virtually none bring anything new to the table, have any insight into their subject. Something about the platform draws people whose goal is to write, not who have something to say.
For my part I think there is a kind of sophomoric "look at me" quality to most Medium articles that makes them mostly about promoting the author rather than pursuing any type of truth. This is why I stopped reading them, I get a twinge of annoyance every time I see medium, because I feel that I am about to read someone's sales pitch as to why they are the smartest, rather than read a genuine pursuit of truth.
