Dramatizations of novel future concepts are estimations of possibilities. Not all become realized within a brane and not all are tangible. However, enough predictions will undoubtedly lead to realized events. There is also philosophy involved with the statistics of multiverses. If a concept is created, it becomes probable, and therefore can generate a potential for divergence. This means that an unrealized portrayal in this brane may be real within another. This makes the proof of travelers difficult, at least I have found. A statement of "future" events that do not become true within this brane may be true in the brane the traveler is from. Therefore, their statements are both false and true, but only the false can be seen. This assumes that their premise is true that they actually traveled. This means that this community is tasked with deciphering false presented "predictions", under the models of false-false and false-true. Neither can be proven. This is part of why brane connections require such careful vetting of the population. A population must be willing to accept false-true statements as a potential for true in the connected brane.
For example: I state that I am a traveler from a different brane, and that travel is possible within this brane with minimal effort.
Models are- realization of event : acceptance of statements
False-false: Travel is not yet capable in this brane, and I am deemed not truthful in my statements. Concept is rejected. Travel is not explored, statement of false-false remains.
False-true: Travel is not yet capable in this brane, and I am deemed truthful in my statements. Concept is accepted. Travel is explored and realized, statement becomes true-true.
True-true/false (no intervention): Trickier. I state that in one month, weather patterns will violently change causing massive famine in currently habitable areas. Event becomes true. Did I estimate a possibility or did I know the outcome? This will divide a population into true-false and true-true. Doubt will now exist within the interested population. Since events true to my brane do not cause absolute truth in this brane, any future statements will now fall to the side of doubt. If I next say: in one year, energy consumption will prompt intervention by an extra-solar group, and this event does not occur, the population will retroactively apply false-false and true-false models.
So take, for example, cellular phones as an extension of prior estimations in science fiction. Were the initial estimations and timeline false-true or true-true? Did the initial concept come from the direct knowledge that the technology would exist, or did the creation of a false known concept cause the population to develop into a true event? The problem is, the development in this instance was under the assumption that the initial concept was false. What if my brane provided schematics to a travel device today? Would proof be reactive or inherent? Would the technology be assumed to be developed within this brane? Is your cellular phone the product of dreamed concepts or intervened technology? Is a large enough technology dangerous to a population unwilling to accept the origin?