One big problem is when you notice a minor event resolves differently now, and you’re trying to figure out if it was somehow your fault, or if a hidden predatory time traveler wasn’t quite sneaky enough this time.
What did you try to fix now?
I just went to revisit my childhood dog. Again, nothing major…! Then I come back and the walls in the kitchen are a different color. I’m wondering if another time traveler has been messing with my house…
You might like Ray Bradbury’s short story “a sound of thunder.”
I’m quite familiar…! One of my dad’s favorite books!
It’s normal. Coders often forgot the little improvements done during the wee hours
Best regards from Italy,
One of my favourite videos…
…it’s a great channel if you haven’t seen it before. Lots of really good content.
The real problem is that the universe is nonlinear, so you don’t even need to make any sort of “butterfly effect” for everything to change. If you rewound time 20 years and played it back again, stuff would happen differently. We’re not on a great wheel turning.
The real problem is that conception is a very timing-critical event, so anything you change will result in the children born after that point being completely different people. Essentially, the people of the future will be unrecognisable a generation forwards from wherever you went (and forever different thereafter).
The only way to avoid it is to only deal with people who never causally interact with the broader population. Maybe you could talk to someone who is about to fall, unobserved, into a volcano, but pretty much anything else and you’ve screwed time completely.
If time travel transported you to a location over the cosmic horizon as well as through time, wouldn’t that solve any causal paradoxes? Because information travels at the speed of light, but the two locations are spreading apart far faster than the speed of light due to the expansion of the universe. Meaning that anything you did, up to and including collapsing a false vacuum state and dooming all existence in every direction at the speed of light, could never impact the other location.
The most common refutation to time travel is the violation of causality. Seems like this solves that issue. Maybe time travel is only impossible between two locations that are still causally linked. Wormholes only working when they exceed a certain distance?
But once you have connected two causally not connected spacetime coordinates with a wormhole they become causally connected, right? Therefore they would become susceptible to causal paradoxes.
In fiction the only plausible escape from wormhole paradoxes that I have read was in Greg Egan’s Diaspora.
I would argue that they do not act as two separate instances in time.
Action in one doesn’t occur in the other’s direct causal past or visa versa.
Basically, they exist, for all intents and purposes, contemporaneous of each other.
They act as two different places at the same point in time.
Only if you make more than one connection. If it’s just one connection, then you simply extend
casual causal space. Curse my autocorrect.
And if the Universe prevents the connection of two places already causally-linked (like Earth and Mars, for example), it’d probably prevent the opening of a second connection within the cosmic horizon of either existing node for similar reasons.
Basically, anything that allows the violation of causation would probably be impossible for all the reasons physicists go on and on about.
ETA: I’m going to try to reword this because I think I can do better job than my first attempt above (more for the understanding of others, not in response to those already involved in the conversation).
If two points in space were connected by a hypothetical wormhole, but these points were beyond their respective cosmic horizons (i.e., outside each other’s observable universes), they would not be causally linked in the conventional sense. Causality, as understood in classical physics, relies on events being linked by cause and effect relationships within the light cone of each other.
In this scenario, the locations are too distant for any information or influence to travel between them within the known laws of physics. As space is expanding, for the rest of time, no photon leaving one point will ever reach the other point. If a hypothetical wormhole connected these points across space and time, allowing instantaneous travel or communication, it wouldn’t violate causality in the traditional sense, because no causal relationship within the light cones of each location would be disrupted. It didn’t exist in the first place.
if we leave physics and enter metaphysics, we can quickly found a connection not causally-linked (that is, read-only) if we posit that the soul is immortal and trasmigrate between bodies. (yes, Joey, I’m talking about the years-long WIP you know…) but what happen when the same soul became causally linked ? as the OP know, I’m actively exploring the concept… one thing I’m sure, this leads to massive culture clash, but with what results and consequences ?
Let’s say that an ancient Semitic priest’s soul became for a brief time causally linked with a later incarnation, say, that of a modern astrophysicst, what can be the result ? well, “let’s the Light be”. and on the other side, perhaps the astrophysicst “see the light” beyond the creation vs. evolution diatribe…
and so on, hence my intention of, after the IFComp, of opening a debate on “speculative fantasy”…
Best regards from Italy,
Unfortunately only one wormhole is enough to make a causal paradox if the two spacetime coordinates are not beyond their respective observable universes with each other. It goes like this: We start from St1 -wormhole-> St2 -travel back in a ship that obeys the light speed limit-> St1. By choosing appropriate spacetime coordinates and ship speed(that does not violate light speed limit) there are possible scenarios where the ship arrives to St1 before we even started the journey.
If the two points are beyond their horizons with respect to each other, then we might need more then one wormhole to make a causal paradox, I believe.
Causally linked means the two spacetime coordinates are within their light cones of each other, as you pointed out. Even Earth and Moon has spacetime coordinates on them that are not causally linked to each other, if those two St points are less than 1.255 seconds apart. On the other hand, if the two space
time points are beyond their horizons, then there are no St coordinate pairs between them that are causally linked (in their future cones one might add, their past light cones might intersect due to the expansion of the universe).
This was literally the entire premise. Full stop. The two connected points DO NOT share each other’s observable universes. Period.
This is the exact idea I was trying to communicate earlier.
If both locations are beyond each other’s horizons, then a ship cannot travel from St2 to St1 without use of the wormhole. St1 and St2 are beyond the observable horizons with respect to each other. So:
EDIT: Sniped by @pinkunz lol
Line of sight light may not be causally linked on every coordinate pair between both bodies, but the two points are definitely still causally linked. Information propogates at the speed of light. So, for example, if you added or removed mass from Earth, the gravitational effects of that, however small, would propogate out to every point on the moon in less than 2 seconds.