Later in the show, when Dan is back in the late 1990s, he gets a call from this scientist...
Now, conceivably, the scientist's late 1990s self might have been calling Dan for some reason. But let's assume the scientist was in 2007 when he placed the call to Dan in 1998.
How might this have happened?
Greg Benford, a physicist at University of California-Irvine, and a science fiction writer (and a friend, so I know he's real), published an award-winning novel in 1980 entitled Timescape. In this novel, scientists from the future communicate with scientists in the past via tachyons.
Was that what was happening with Dan in Journeyman last night?
Well, in order for that to have occurred , here's would have been required in the telephone technology. Our telephones and cellphones and iPhones today work by encoding sound into electronic signals - electrons - and sending them through wires, or whatever carrier waves in the air, to receivers, which in turn decode the electronic patterns back into sounds that we can hear. Since electrons and the carrying signals travel at the speed of light, we can talk to anyone anywhere on the Earth just about instantly. Of course, if we try to do this with someone near the Moon, there will be a little delay (the Moon is 240,000 miles from Earth - light travels at 186,000 miles per second).
A tachyon telephone would work the same way - except, rather than the sound being encoded into electrons it would need to be encoded into tachyons (or, if it was encoded into electrons, those electrons would need to be hitched to a tachyon carrier wave).
Presumably our tachyon-knowledgeable scientist in Journeyman would understand this, and might have access to or even constructed a tachyon telephone.
But how about Dan? He would need to have a tachyon telephone in order to receive a call from a scientist in the future (the scientist in 2007, Dan in 1998) and have a conversation with him. Dan is seen using a late-1990s cell phone in last night's episode - his old phone, that he dug out in 2007 (hey, I have one just like it, buried somewhere in my desk!) - but there is no reason to think that it came tachyon enabled.
But Livia, Dan's former lover, also travels around in time, and she might have gotten to Dan's phone at some point, and given it a tachyon chip... a tachyon hack!
Interesting possibilities here, and I'm eager to see how Journeyman develops this.
In the meantime, you might enjoy the following:
Greg Benford's Timescape
my time-travel novel, The Plot to Save Socrates
20-minute podcast: Time Travel in Fact and Fiction
5 minute podcast of this tachyon analysis
The Plot to Save Socrates
"a Da Vinci-esque thriller" - New York Daily News
"Sierra Waters is sexy as hell" - curled up with a good book