If I were to send information back in time to Albert Einstein, say in the form of his field equation, e.g.
G mn = - ½ g mn G= - 8 p T mn
And before he theorizes it himself, what would be the result? Well, that depends. If he were to publish it (which he did) and I go on to find it in a text book 100 years later - say Gravitation, by Charles W, Misner, Kip Thorne and John Wheeler - that would create an acausal anomaly. In other words, the information manifesting as the tensor field equation would have no true origin. The reason is that, according to all our current physics, that information would have to travel faster than light. But special relativity shows this isn't possible.
Now, however, new research by postdoctoral fellow Venkatesh Vilasini
See, e.g.:
Seems to show there can exist theoretical universes in which such causal loop anomalies are allowed. (It remains unclear whether such time loops are possible in our own universe. But, assuming they are, it ought to be possible for me to send information about the Kennedy assassination to my younger (17-year old) self in October, 1963, and enable him to act on it.
For her part. Vilasani modeled a set of theoretical universes in her doctoral thesis:
where all that is known is that there are people who exist who can discern on superluminally -delivered information and act on it - but who can't themselves communicate faster than light. Okay, let's return to my example about dispatching info (on the JFK assassination) superluminally back to my younger self in 1963,
I can assume my younger self - even at 17 - is bright enough to discern said information. After all he designed a science project entitled 'The Structure of the Universe'. So according to Vilasini's novel causal theory of time loops he (me as a younger self) ought to be able to act on the information. Note, there is no superluminal violation on my younger self's part since he isn't trying to communicate back to me over the decades and tell me "it worked" or even that the information was received.
Okay, let's say someone reading this objects and insists that just knowing what's about to happen in November, 1963, disturbs the timeline in some way. Two things: First, knowing that the future event will occur could be interpreted as simply a premonition. Second, even if that 17-year old me were to discern the reality of the message and fly directly to Love Field in Dallas to try and stop the event, there is absolutely no assurance he could succeed. What? Jump in front of JFK's limo on Elm Street and get shot by the Secret Service or run over?
Oh, oh, I get it. You mean phone the Dallas Morning News or Dallas cops and tell them what's about to happen? ("A team of hired assassins is about to kill Kennedy in his Dealey Plaza motorcade!") Yeah, right, just before being marched off to the funny farm. So the odds are that even sending a message back in time to my earlier self would not change history. It is what it is, alas.
Let me also quickly add here that Vilasini's team of researchers (at ETH Zurich) didn't require any of the theoretical universes to obey any specific physical laws, i.e. such as how gravity works. But they did determine that such causal loops could be mathematically possible assuming they didn't theorize them to be particularly exotic from the start. Also, it was found these anomalous causal loops could disturb reality by removing the source of some information sets - but they still seem to be possible in universes with one spatial dimension.
In statistics, especially regression analyses, we often say that "correlation does not imply causation." Meaning that just because I found in my published research, e.g.
that flares are correlated with large and complex sunspots, doesn't mean the latter caused them. But in Vilasini's hypothesis she is focused on the converse where "causation does not imply correlation." That is, the ability of two agents in these theoretical universes to send signals to each other.
Finally, the causal loops Vilasini et al examined don't necessarily lead to dramatic paradoxes but they do show past and future can be correlated in counter intuitive ways.
See Also:
And:
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