The jumps manifest themselves with a small blue flash and a ripple as Dan appears to vanish from the present, and appear instantly in the past. He is missing from the present for a period of time unrelated to the period he spends in the past. His disappearances and reappearances are rarely witnessed by anyone else. Dan does not arrive in the same location he departed, but instead arrives near the person who he is supposed to help. His jumps are typically restricted to the area he leaves from, usually keeping him in the San Francisco area. Originally, when Dan arrives to the past, he is unconscious. But as the series goes on, Dan somehow gets a hold on the jumps. It becomes evident when Dan feels the jumps coming on and as the jump occurs, he is seen walking with the ripples being shown behind him. Dan is also trying to figure out the mechanics of his travels. He has questioned a physicist who seems to have known his father in the past, and has discussed the possibility of tachyon particles being able to cause time jumps. It is now clear that the scientist is aware of Dan's travels, as well as those of others like him. It has also been discovered that those born around the time of a rare passing comet (the fictional "Joseph-Lee" comet) have this ability.